Search

Global Positioning System (GPS) is an essential part of modern life but is susceptible to same frequency jamming. GPS jamming can add excessive noise to a received low power signal and have the capability to change or completely distort information being sent through the GPS signal. Adaptive antenna arrays have long since been a solution to mitigating GPS jamming via beamnulling algorithms. However, there is little research on the effectiveness of these beamnulling algorithms under varying element positioning. In this work, an adaptive antenna array, consisting of Right-Hand Circularly Polarized (RHCP) nearly square GPS antenna elements, was constructed and tested for beamnulling applications. Two beamnulling algorithms (LCMV and MVDR) and two orientations (Orientation 1, an optimal 2x2 λ/2 spacing orientation, and Orientation 2, a less common “+” shaped array with 0.55λ spacing) are simulated, tested, and compared with each other.

Design and additive manufacturing of four different antennas that operate at microwave frequency is proposed. The designs were prototyped on flexible FR4 substrates to make them suitable for wearable sensors and biomedical applications. Contact and non-contact printing methods for antenna fabrication using screen printing and aerosol jet printing (AJP), respectively, were extensively studied as part of this research. Ansys High Frequency Structural Simulator (HFSS) was used to design and simulate the antenna characteristics. Nanoparticle silver ink, of ~10nm size, was used to fabricate antennas under AJP method. In addition, a screen-printing approach using copper paste was used to fabricate antennas. A vector network analyzer (VNA) was used to experimentally verify the nature of fabricated samples. The reflection coefficient (S11) and radiation patterns for the simulated design and fabricated samples were found to align closely. A return loss of -10 dB was achieved for the wide range of operating frequency. This demonstrates the effectiveness of the proposed antennas. Compact sizing, simplicity of manufacturing, a larger impedance spectrum, simple design, and high performance are some of the major advantages of the proposed additive manufacturing method.

Abstract: The amount of mobile data handled by wireless broadband cellular networks is increasing explosively. Multiple-input multiple-output (MIMO) systems have gained a significant importance in modern wireless communication systems. MIMO offers many dimensional advantages that can be utilized to boost capacity and coverage without utilizing more bandwidth or transmit power. The introduction of MIMO systems with large antenna arrays (also known as massive MIMO) and the use of millimeter wave (mmWave) frequency bands are considered some of the key enabling technologies in the 5th generation of cellular systems to satisfy high data rate demands. However, when it comes to hardware implementation, massive MIMO systems with a large number of antennas face some challenges. Each antenna element is driven by a dedicated RF-chain; therefore, the RF-cost increases with the number of antennas. Each RF chain in a MIMO transmitter includes a power amplifier (PA), a mixer and a digital-to-analog converter (DAC). These components are expensive and power-consuming. Consequently, the cost will increase if the number of antennas grows. Reduced-cost MIMO systems have been drawing attention lately. In this dissertation, the hardware of a reduced-complexity and cost MIMO transmitter utilizing a single RF chain is presented. The RF chain includes a linear, low-cost, and energy-efficient PA and without the need for a mixer or DAC. This MIMO transmitter can convert digital signals in the baseband to the RF domain. In this MIMO transmitter, antennas are fed by two-port networks called load modulators. Load modulators are diode-based RF circuits that generate the desired outputs. The MIMO transmitter is designed at 3 GHz. The MIMO transmitter is capable of generating 64-QAM constellations at its output ports. This MIMO transmitter is perfectly suitable to operate with current MIMO receivers.

The antenna pattern is an essential part of the design of RF systems and affects the performance and capabilities for many applications in communications, radar, and sensing. There are many applications which require specified antenna patterns with specific directivity, beamwidth, and sidelobe level (SLL). Single-element antennas usually have simple and specific patterns which are difficult to be shaped to meet more complicated pattern requirements. For instance, the popular parabolic reflector antenna uses a reflector which can be shaped to produce a desired radiation pattern with high directivity. However, it has a large structure and can only produce single fixed-beam patterns. On the other hand, array antennas consist of multiple antenna elements which together can be used to synthesize antenna patterns with narrower beams and lower sidelobes as compared to single-element antennas. More specifically, many applications which require high directivity, narrow beam patterns with low sidelobes include: (1) radars, which often use a narrow beam to detect targets for achieving a better angular resolution, higher signal-to-noise ratio (SNR), and low sidelobes to avoid ambiguity coming from signal returns from other directions; (2) modern cellular phone base stations which employ specially shaped beam patterns to provide uniform signal strength with the coverage area while minimizing radiation into the sky; (3) newest satellite communications/broadcasting systems which adopt spotlight beams to cover specific zones while reducing interference into neighboring areas for enhanced security and SNR. The first array antennas for producing shaped directive beam patterns were introduced during World War II for early radar systems using an array of dipole elements. The disadvantages of such a dipole array were that the dipole elements were large 3D objects requiring manual labor to produce and the design was difficult to use for higher frequency such as for X band or higher. The Yagi-Uda antenna, an end-fired dipole array, uses parasitic dipoles to produce high gain and have also been widely used for receiving broadcast and communication signals in the VHF and UHF frequency range. The later generation of radar systems used slotted waveguides, with the arrays of slots cut into the sides of waveguide walls. These slots are sequentially excited with proper phase and magnitude as the electromagnetic waves propagate along the waveguide, constituting a type of series-fed array. The main disadvantage of the slotted-waveguide antenna lies in their 3D structure, which is not easy to fabricate accurately, especially at frequencies above 18 GHz.In modern applications, printed circuit board (PCB) antennas using microstrip patch elements are preferred since they can provide small, lightweight, low-profile planar designs which are easily manufactured using modern PCB fabrication. PCB antennas are also favored for their ease in interfacing the antennas with modern monolithic microwave integrated circuit (MMIC) devices used in RF systems. Phased array antennas are used in many modern applications which require actively scanning the beam to different angles. In earlier phased array systems, a single high-power source such as a Klystron or Traveling Wave Tube (TWT) produced an RF signal with MW or GW of total power distributed over all array elements. This approach requires careful management of the high-voltage and thermal issues. With the advances in small high-power solid-state amplifiers, modern phased arrays replace the single high-power source and distribution architecture with a small individual transmit/receive (T/R) module behind every array element. This makes PCB-based array antennas even more desirable for its ease in interface between array elements and T/R modules.While phased arrays using T/R modules are mainly used for military and defense high power radar applications, many commercial communication systems applications need small, lightweight, low-profile, and low-cost high-gain antennas with specified radiation patterns with narrow fixed beams and low sidelobes. Some of these examples include (1) automobile radar systems which require broad elevation beamwidth and narrow azimuth beamwidth, with low sidelobe patterns for detecting people and objects, (2) base station antennas on cellular towers which require a special shaped pattern for providing uniform signal strength over the coverage area at different distances from the tower, and (3) the user-segment of the satellite communications systems which requires specific antenna gain levels and patterns that meet certain FCC gain-pattern envelope masks for avoiding interference to neighboring satellites. For these applications, the antenna array must be designed to produce a specific radiation pattern by controlling the amplitude and phase distribution across the array aperture which is related to the far-field pattern via the Fourier transform relationship. Without using T/R modules on each array element as in the more expensive military and defense phased arrays, a sophisticated feeding network would be required to properly distribute power and phase to all array elements according to the desired aperture distribution. Most conventional feeding networks adopt corporate feeds which split the signal from the source using a network of power dividers to distribute power to the array elements. Corporate and parallel feeds are favored for straight-forward implementation of the approximate aperture amplitude distribution by using unequal power dividers and mismatch lines. However, such power dividers cannot realize the aperture amplitude distribution with a high accuracy, and thus cannot achieve accurate patterns and very low sidelobe level (SLL). Furthermore, the corporate feed network approach; (1) requires a large number of power dividers for a large number of elements, (2) suffers from increased ohmic and dielectric losses from long feed transmission lines, and (3) produces undesired spurious radiation due to mismatches accumulated from all power dividers and final mismatch lines. Alternatively, the series-fed architecture which uses a common feedline running through elements to distribute power sequentially minimizes feed line length and eliminates power dividers, thus minimizing power loss and spurious radiation. Therefore, the series-fed array design approach is very popular at very high frequency ranges such as for 68-82 GHz mm-wave radars for vehicles. In the conventional series-fed array designs, the aperture amplitude distribution for a desired pattern is implemented by varying the width of the patch array elements, which varies the amount of power radiated from each element. The drawback to this conventional design method is that the bandwidth and pattern of individual elements also change with the patch width, which causes the final array pattern to deviate from the designed array pattern predicted from array factor multiplication. Another conventional series-fed design method is to vary the widths of the feedlines interconnecting patch elements. However, when using this method, the phase velocity along the series-fed array varies which then requires the patch elements to be adjusted to maintain resonance and for element spacings to be adjusted for all elements to be in phase. Furthermore, there is a limit to both the available range of coupling coefficients and accuracy in implementing the amplitude distribution due to limits in the line width and tolerance in manufacturing. Therefore, it remains a major challenge to design a series-fed array for specified patterns due to the lack of a systematic design methodology that can achieve streamlined and accurate implementation of specified amplitude distributions in a way that is simple and practical without requiring multiple design iterations.This dissertation introduces a novel series-fed array design process for systematically implementing a desired aperture amplitude distribution for series-fed microstrip antenna arrays. In contrast to the conventional series-fed arrays which vary amplitude coupling by tapering the width of patch elements or feedlines, the different amount of coupling at each array element is achieved by varying the gap between the main feedline and a novel T-coupler which can achieve a wide range of coupling coefficients from -5 dB to less than -20 dB. The coupling coefficients from the normalized aperture amplitude distribution are then used to obtain the corresponding coupling gap for each array element. The proposed streamlined series-fed array taper design process allows effective control of the shape of the far-field pattern within only one design iteration. Since the taper amplitude distribution is controlled only by the coupler between the main transmission line and array element, all elements in the array can be identical and there is extreme flexibility in the choice of element types. The dissertation includes several design examples to demonstrate the efficiency, effectiveness, and versatility of the proposed design methodology. So far, a design example was completed for an X-band dual-channel array with a customer-specified Taylor aperture taper in the azimuth plane for use in Synthetic-Aperture Radar (SAR) and Ground Moving Target Indication (GMTI) in an airborne radar system. The novel design method presented here will significantly advance the state-of-the-art in designing series-fed array antennas and enable new capabilities of series-fed array antennas. For instance, the phase between elements on the feedline are fixed in conventional series-fed arrays and so they are rarely used for beam scanning. Using the proposed novel design method, it will be possible to place phase shifters between the couplers and elements to produce a beam-scanning series-fed array. Series-fed arrays also suffer from what is known as beam squint, which is the deviation of the main beam direction with change in frequency. This limits the operational bandwidth of series-fed arrays intended for patterns that are constant over frequency. A dispersive transmission line can be used to compensate the change in phase between elements over frequency and eliminate beam squint. This can also help to ensure a constant array pattern over frequency. Using the novel design method presented here and with the added capabilities of beam-scanning and wider operational bandwidth by eliminating beam squint, future series-fed array designs can be used for a wider range of applications. The novel design method presented here lays the foundation for new series-fed array designs that improve upon the current conventional designs and can add new capabilities for more applications in the future.

With the advent of mmwave 5G, and future G technologies, there is a path paved for multitude of applications in the cellular, augmented and virtual reality (AR/VR), internet-of-things (IoT) etc. domains. There is a need for compact, highly directional and low-loss antennas for reduced size, greater coverage, low power consumption. Partially reflective surfaces as superstrates are well known for enhancing antenna radiation. However, in the past, electrically large surfaces were used with little regards to the size and aperture efficiency of the antennas. In this dissertation, compact source antennas are used with smaller 2D metamaterial superstrates acting as partially reflective surfaces (PRS) to form metamaterial antenna (MMA) block. The dissertation is divided into three segments. After going over the theoretical framework for infinite periodic surfaces and development of equivalent circuits in chapter 2, finite PRS surfaces with source antennas are analyzed in chapters 3 and 4. Different types of PRS surfaces and source antennas are changed one at a time to explain the design methodology and arrive at highly aperture efficient MMA blocks. In chapter 5, single MMA block is used to create virtual arrays using beam-splitting PRS designs and analyze its performance with conventional arrays. The single MMA blocks are also showcased in array element reduction applications to reduce feedline complexities associated with conventional arrays. Chapter 6 focuses on formation of passive phased arrays using near field phase manipulation properties of the PRS. This property is used to create dual beam antennas. Next, designs that focus on creating polarization splitters using yet another variation of PRS, called beam and polarization splitting PRS (BPS-PRS) are proposed. The dual beam antennas and polarization splitters can be applied to emerging multiple-input multiple-output (MIMO) communication applications. MMAs are also useful as GNSS positional sensors as seen by their low phase center variation properties which are also showcased. Finally, chapter 7 focuses on near-field applications of the MMA by proposing free space vertical interconnects and power dividers that are useful for high frequency printed circuit board (PCB) integrated chip-to-chip intra-connects and interconnects. Additional loss reduction technologies that are useful for on-chip silicon implementations are also demonstrated by using Copper nanowires on coplanar waveguide transmission lines for frequency ranges up to 180 GHz. Chapter 8 concludes the work and gives directions for the future work.

A common assumption made by antenna engineers is to consider a system to be linear and time-invariant (LTI). This assumption is incredibly powerful and has enabled a century of advancements, but consequently has perhaps made electrical engineering too reliant upon it. There are multiple cases of fundamental limits being circumvented by including non-LTI devices and analysis. Additionally, there are limitations of some systems that are not well understood or avoided as a subject due to their non-LTI nature. Exotic antennas are attractive to complex, modern communication systems, but they are effectively useless if they cannot be deployed in practical settings after design sequences - as is sometimes the case in the presence of potentially nonlinear devices. Therefore, this work provides insight into the limitations of non-LTI analysis for antenna engineering and the trade-offs of some antennas that are erroneously capable of nonlinear behavior. Doing so will help shed light on the ramifications of casually making the LTI assumption and methods to better understand such antennas.

In recent years, metasurfaces have shown promising abilities to control and manipulate electromagnetic (EM) waves through modified surface boundary conditions. These surfaces are electrically thin and comprise an array of spatially varying sub-wavelength scattering elements (or meta-atoms). Metasurfaces can transform an incident EM wave into an arbitrarily tailored transmitted or reflected wavefront through carefully engineering each meta-atom. Recent developments in metasurfaces have opened exciting new opportunities in antenna design, sensing, and communications systems. In particular, reconfigurable metasurfaces - wherein meta-atoms are embedded with active components - lead to the development of low-cost, lightweight, and compact systems capable of producing programmable radiation patterns and jointly performing multi-function communications, and enable advanced sensors for next-generation platforms. This research introduces reconfigurable metasurfaces and their various applications in designing simplified communications systems, wherein the RF aperture and transceiver are integrated within the metasurface. Finally, we will present our recent work on reconfigurable metasurfaces control, metasurface-enabled direct signal modulation, and deep learning-based metasurface design.

The millimeter-wave radar is one of the key sensor technologies utilized in the automotive industry for advanced driver assistance systems and autonomous vehicles. Its ability to leverage phenomena such as the Doppler effect and the polarization of electromagnetic waves make it an extremely versatile sensor, capable of detecting position and velocity of potential roadway obstacles, as well as distinguishing between obstacles of different types (pedestrians, other vehicles, etc.) based on their polarization responses. Additionally, its relative insensitivity to precipitation and fog allows for all-weather operation, even in conditions that severely inhibit visibility. However, radar is not a perfect all-encompassing sensing solution; in particular, its most significant drawback is imaging resolution inferior to that of optical sensors like cameras and lidar. A radar’s resolution is closely linked to its antenna system. Angular resolution is improved with a narrow antenna beam, which translates to a large effective aperture. Similarly, fine range resolution is achieved using the frequency-modulated continuous-wave technique, which requires high transmit-to-receive antenna isolation. Typically, this isolation is accomplished with spatial separation between elements. Limited available mounting space on most vehicles prohibits the large antenna system size mandated by these requirements. The focus of this dissertation is the development of an antenna system architecture which provides a very narrow beam and high isolation, while supporting dual-polarized transmit and receive capability for polarimetry applications. The use of a common transmit/receive aperture makes the antenna system relatively compact while eliminating parallax. The shared aperture is a single dielectric lens, which focuses at both the transmit and receive feeds by means of a novel polarization-independent spatial power divider. This device was designed using concepts from the flourishing field of electromagnetic metamaterials and metasurfaces, and can be constructed using standard semiconductor fabrication techniques. While modern automotive radars operate at the 79 GHz band, there is a strong interest in exploring higher millimeter-wave frequencies (particularly the 230 GHz band) for future systems. The shift to a shorter wavelength will result in improved angular and range resolution while reducing antenna size. Therefore, separate versions of the common-aperture dual-polarized transceiver antenna system have been designed for operation at the two bands. One of the challenges of moving to higher frequency is the availability and performance of millimeter-wave electronics and waveguide components. In support of high frequency dual-polarized radar antennas, an orthomode transducer with a simple structure has been designed for reduced fabrication complexity at the 230 GHz band. Additionally, there is currently a lack of data on the backscattering properties of many target classes at 230 GHz. The antenna and orthomode transducer designs of this work have been incorporated as part of the front ends of radar systems operating at this band. As a demonstration of the utility of 230 GHz radar, as well as the antenna system itself, a set of polarimetric backscattering measurements of several road surfaces is presented. Such data can be used to inform algorithms for discrimination between different surfaces, and assessment of road conditions. Another topic in this dissertation is the design of a low-profile passive reflector, which can enable radar sensors to detect and identify road markings, a task currently handled only by cameras. As an appendix, a planar antenna system with high isolation for wireless communication and radar applications at 6 GHz is presented.

Size-reduced antennas and compact antennas are desirable for many applications due to the sleek designs and the ability to fit within many possible shells. However, when an antenna’s size is decreased, the Q value increases. This high Q causes many problems with the antenna system, including narrow bandwidth. In this thesis, two different types of array antennas with high Q values will be investigated. This narrow bandwidth is increased through the use of frequency tuning to make frequency agile systems. With two different types of tuning, continuous and discrete through the use of varactors and PIN diodes, the overall frequency tunable bandwidth of these high Q antennas is boosted. Propagation modelling through Georgia Southern University’s campus is also investigated to determine ideal transmitter locations for full coverage as well as excellent coverage throughout the campus.

Ingestible and implantable electronics are devices designed for applications that are utilised to improve patients’ health outcomes by helping in prevention, diagnosis and monitoring of disorders. In their operation, ingestible and implantable devices produce large amounts of data that should be collected continuously and exchanged via radio communication. A major challenge for this communication is the mitigation of data loss. This PhD research addresses different aspects of this challenge by exploring a) the feasibility of Bluetooth in ingestible devices, b) improving the design of 433 MHz antennas for ingestible devices, and c) also on a relevant topic about ingestible and implantable sensors, studying the sensing of multiple gases with temperature modulated single-element gas sensors. The feasibility of Bluetooth is explored through developing a custom Bluetooth device for assessing the signal attenuation of transmissions from standard Bluetooth devices which was tested for a variety of human tissue analogues to imitate their dielectric properties and measure propagation losses. It was revealed that the signal attenuation through the tissues could be tolerated up to around 85 mm and that Bluetooth devices are deemed to be viable for such communications. In the next stage of this PhD thesis, a 433 MHz meandering pattern antenna was designed that could be placed into standard ingestible capsules. This work involved the simulations and measurements of different designs and focused on analysing the antenna return losses and gain patterns under different ambient dielectric conditions. The effect of battery location relative to the antenna patterns was also explored. The acquired data suggested that an optimal design could be obtained that could tolerate the very large shift in dielectric conditions present in different segments of the gut. The data provides a broad perspective regarding the design of meandering antennas for ingestible and implantable devices. In the final stage of this PhD thesis, a temperature modulated single-element gas sensing system was developed to study how the technique of temperature modulation could be implemented for measuring and differentiating multiple gases simultaneously. Using single-element gas sensors reduces the footprint of the sensor electronics, providing more space for communications electronics in ingestible devices. The system was tested for H2 and H2S sensing. The outcomes demonstrated that the technique was feasible and showed the practicality of using signal processing techniques in gas sensing systems. The work presented in this PhD research added to the body of knowledge in the fields of ingestible and implantable sensing devices.

Real-life communications applications necessitate the development of antennas with different patterns and radiation characteristics. Antennas that can produce the beam scanning in a conical sweep can be advantageous for applications such as spaceborne wind scatterometers weather radars. This work presents the synthesis, prototyping and measurements of threeantennas that can produce the conical beam scanning: The 3D-printed shaped and materialoptimized lenses, the flat-layered meta-lenses, and the transmitarray antennas. The synthesis of the 3D-printed lens and meta-lens inhomogeneity requires the use of a software package hybridizing the computational electromagnetics method of Geometrical optics (GO) with the optimization strategy of Particle Swarm Optimization (PSO). Additionally, a new synthesis algorithm is presented for the design of transmitarrays that can produce the conical beam sweep based on the optimization of the feed location and a modified transmitarray phase compensation. Novel implementation and fabrication methods based on additive manufacturing and metamaterial structures are presented for the realization of the proposed antennas. In the last part of this work, Orbital Angular Momentum (OAM) beams for antenna applications are investigated. The theory and mathematical formulations of the far-field properties of OAM beams using the antenna aperture field method are presented in a systematic and comprehensive manner. Transmitarray antennas are proposed to generate circularly-polarized (CP) OAM beams with cone-shaped radiation patterns. Antennas with cone-shaped patterns can be advantageous for applications such as geosynchronous satellite based navigation and guidance systems that serve moving vehicles and ceiling-mounted indoor wireless systems. An ultra-thin “S-ring” transmitarray unit cell is introduced to support CP that can provide arbitrary CP phase compensation by proper rotation of the elements. The synthesis, prototyping and measurement validation of a proof-of-concept transmitarray prototype are presented and demonstrate that the proposed transmitarray antenna can be a unique apparatus that generates CP OAM cone-shaped patterns.

Telecommunication has rapidly evolved in the past decades, quickly becoming one of the most expansive industries, especially with the presence of new attractive eras like 5Gnetworks, automotive radars, and CubeSats. The use of miniaturized satellites such as CubeSats for cheaper and wider communication coverage has opened the possibilities for cluster satellite communication. These units exist in a continuously varying environment as much physical as electromagnetic. Hence, the establishment of a successful communication link among the space units but also ground stations becomes challenging. This new situation can be confronted with the installation of new reconfigurable antennas. These are emitting units performing diverse radiating characteristics on demand. In other words, one reconfigurable antenna can take the role of multiple antennas of different properties. This fact also troubleshoots the real estate limitations on CubeSats. Greater benefits for modern wireless systems that outcome from such an antenna type, are the improved spectrum efficiency by enabling more than one operation, the enhanced carrier (signal) power, the reduction of the interference, the mitigation of multipath and Faraday rotation phenomena, and many more. This dissertation aims to provide a series of novel reconfigurable antennas with frequency, pattern-space, and polarization agility. The antennas employ reconfigurable networks for meeting the diversity properties while concluding the system to a single RF port. The antennas are formed by planar structures with a PCB fabrication process to reduce size and cost, but also to ease their assemble on CubeSat units or any device that requires switchable radiating properties.

Abstract: Multipath interference is an error generating issue in high-accuracy global navigation satellite system (GNSS) applications. Since the propagation of surface waves along the surface of antenna structure is the root cause for reception of multipath signals in GNSS antennas, surface wave suppressing ground structures are needed for GNSS antennas that are employed in high-precision GNSS applications. Two-dimensional (2D) corrugated structures, also known as choke rings, are commonly used as the ground structure for high-accuracy GNSS antennas. Despite their superior performance, choke rings suffer from large size, heaviness, costly fabrication, and inability to integrate with printed circuit board (PCB) structures. The objective of this thesis has been to design low-profile substitutions for these bulky structures. First, a review of literature is conducted on the multipath signals, surface waves, and surface wave suppressing ground structures to acquire a deep understanding of the problem and techniques to analyze it. Then, a compact dual-band substrate integrated choke ring (SICR) ground structure has been designed by engineering the location of via holes and partial copper cladding of the substrates in a multilayer structure. Next, a novel technique for miniaturization of corrugated structures is presented and folded corrugations are introduced. The miniaturization is achieved by implementing a fold or slit inside each corrugation. The proposed miniaturization technique is modeled using the modal expansion method and an equivalent circuit is extracted which precisely models the surface impedance of the proposed folded corrugation. A time-efficient deign procedure is presented based on the equivalent circuit model and a Folded SICR (FSICR) structure is designed. Finally, the idea of folded corrugations is expanded to multi-folded corrugations (MFCs) to achieve further miniaturization. The design procedure is adjusted as well to design dual-band multi-folded corrugated structures. A dual-band Double-Folded SICR (DFSICR) structure is designed to suppress the propagation of surface waves over the main GNSS frequency bands, L1 (1573-1587 MHz) and L2 (1215-1240 MHz). The performance of the proposed structures has been investigated by mounting a right-handed circularly polarized (RHCP) GNSS antenna on it. The introduced designs demonstrate significant multipath mitigation capabilities, close to that of a classic choke ring, while they eliminate the drawbacks of a conventional one. An example design of DFSICR shows miniaturization of 85% in height and 38% in diameter compared to the conventional choke rings. It also demonstrates weight reduction of more than 90%, thanks to its substrate integrated design. It worth noting that although the motivation behind the introduced miniaturization technique has been to address a problem in GNSS antennas, the approach looks promising for miniaturization of other corrugated structures such as spoof surface plasmon polariton (SPP) waveguides and components.

Size reduction is necessary to fit the recent demand for small sized communication systems in consumer electronics. Wireless communication systems rely on antennas for long range transmission of signals, so size reduced antennas have been sought after in recent years. Also, not many antennas are designed for use in bidirectional scenarios like subways, tunnels, bridges, etc. Three sized reduced antennas with circular polarization are presented for use in bidirectional communication systems. An electrically small pattern reconfigurable array, an electrically small two-sided printed cross dipole, and a size reduced printed wideband antenna are introduced within this thesis. All antennas’ results are obtained from simulation, with two of the antenna designs being measured to verify their results.

Photonic topological insulators (PTIs) represent an area of emerging research into a new class of materials and devices with exciting electromagnetic properties. These materials are capable of supporting directional conducting modes along their surface or edge at frequencies that lie in the material bandgap. The presence of the bandgap ensures that the bulk of the material behaves as an insulator, which allows for a very high degree of energy confinement at the surface. This work briefly details a few variations on PTIs and then proceeds to focus on the creation of interface modes for 3D dielectric structures using only a 1D integration technique to obtain the geometric phase that is required for a material to be classified as topological. This 1D Zak phase allows for a simpler method to create topological waveguides with propagation path bends in fixed directions, along with a directional dependence based on the rotational nature of the fields. A shift towards more traditional forms of PTIs in the latter half of the thesis focuses on the application aspects of topological insulators. The use of metallic spin PTI metasurfaces as antennas been demonstrated with device operation broken down into (1) confined and (2) leaky wave propagation. While the confined mode is best known for its use as energy guiding structures, abrupt truncations can allow for radiation at the aperture with a `self-matched' property, allowing for immunity to the reflection caused due to the aperture impedance mismatch. Operation of the same PTI structure above the light cone in its leaky region enables the use of the PTI metasurface as a leaky wave antenna having an azimuth phase variation, with energy wrapped around in a closed loop propagation path. These waves possess an inherent orbital angular momentum (OAM), and control of the OAM beam charge can be achieved by the manipulating the physical and electrical path lengths. This control is invaluable to switching and multiplexing of different beam orders, which has a pivotal role to play in affecting the channel capacity and increasing data transmission rates for communication systems, among other important applications.

Reactive and resonant loads have been used from the very beginning of antenna design to improve impedance matching, bandwidth, and current distributions on antennas, and to create multiband and reconfigurable antennas.Trap loaded dipoles are one of the simplest resonator-loaded antennas and are traditionally loaded with either an inductor-capacitor pair or a quarter wavelength stub integrated into a dipole or monopole to create a second operating frequency at the trap resonant frequency. Adding resonant loads to antennas will only increase in popularity and practicality as filtennas are more often used for their SWaP improvements, better noise performance, and potential for additional degrees of reconfigurability. In this dissertation, I demonstrate that resonant loads can introduce lossy modes, and I significantly revise and expand the theory of the basic trap dipole antenna, which is a valuable aid in designing resonator loaded antennas with higher degrees of complexity. Based on the new analysis, I demonstrate novel series LC trap dipoles, dual-band inductor loaded trap dipoles, and parallel and series LC trap slots. The newly developed design process also allows for the integration of any kind of resonator or reactive load to be used to create trap style antennas. A reconfigurable load is also used to demonstrate novel tunable trap antennas. The design procedure is ultimately adaptable to any resonators that can be practically fabricated and physically incorporated into the antenna structure.

An analytical model is proposed to characterize and quantify the effects that diffracted fields have on the performance of phased array antennas. The work involves the combination of diffraction theory techniques and how each can be used to analyze this phenomena with the use of antenna elements as sources. As these antenna elements are placed along a ground plane of relatively large size in terms of λ diffracted fields can perturb the expected cross-polarization radiation performance of the element. As the element is moved along the ground plane and at different relative distances from the edges, depending on the electromagnetic radiation nature of the antenna structure, these edges produce diffracted fields that can affect the performance of the co- as well as the cross-polarized fields of the antenna. This is of great importance when working with highly pure polarized elements for applications that require low cross-polarization. The expansion of an equivalent current model is proposed where the antenna element can be expressed at a distance from the edges and the diffracted fields generated from such edges are calculated from these equivalent currents. Every element position over the ground plane will generate a theoretical equivalent current that would radiate the diffracted fields, which then contribute to the overall array pattern. This work shows a successful implementation of the proposed technique and how this can be combines with finite element method (FEM) analysis in order to predict the radiated fields from different element positions providing an advantage over resource hungry simulations. This proves to be an effective tool by reducing the calculation time substantially for scalable applications where the phased array can be over thousands of elements and extremely difficult to gather resources to produce a predicted pattern.

With an increasing demand for high-speed wireless communication, current wire- less infrastructure cannot provide the bandwidth required for high-speed data transfer for multiple users. The next generation of millimeter-wave (mmW) communication systems operate in the frequency range of 30–300 GHz and can provide orders of magnitude greater bandwidth. In addition, these systems rely on adaptive strategies to achieve high data-rate communication which requires reconfigurable elements. In our research, we introduce a new class of reconfigurable radio frequency (RF) microsystems using paraffin phase-change material (PCM) that enables low-loss recon- figuration for mmW components. Paraffin (alkane) is a low-loss nonpolar dielectric that undergoes a 15% reversible volume change through its solid to liquid phase transition. Using this unique combination of loss characteristics and mechanical properties, we have developed continuously variable capacitors. These electro-thermally actuated variable capacitors are low loss with series resistance of less than 0.7 Ω at the mmW band and can be monolithically integrated with antennas and RF components to introduce reconfiguration.In this work, we present a frequency reconfigurable slot antenna which covers the 94 GHz–102 GHz band. In order to achieve reconfiguration, the slot antenna is loaded with two paraffin PCM capacitors. The capacitors are actuated using joule heaters and with the increase in temperature, paraffin goes through a solid to liquid transition. As the volume of the paraffin increases, the capacitance decreases continuously by approximately 15%, which results in increasing the resonance frequency. The realized gain of the antenna at 100 GHz is 3 dBi and it is approximately constant over the reconfiguration range. The Efficiency of the antenna is >72% for the entire reconfiguration range thanks to the low dielectric loss of the paraffin.To evaluate the performance gains of the reconfigurable antennas, new payoff metrics are defined for each of pattern, polarization and frequency reconfiguration schemes. These figures-of-merit, capture both the increased diversity due to the reconfiguration states and the associated losses. In addition, a paraffin PCM based, continuously-tunable true-time delay phase shifter is designed and optimized. By periodically loading a coplanar waveguide transmission line with paraffin PCM variable capacitors, propagation constant along the line is varied and phase shift is achieved. A figure-of-merit of 74.8◦/dB is obtained while maintaining a return loss more than 15 dB. Designed phase shifter has a maximum insertion loss of 4.8 dB for a 360◦ phase shift at 100 GHz.To evaluate the actuation performance of the PCM device, a fully-coupled multiphysics simulation is developed. To simulate the electro-thermo-mechanical actuation, four physics modules including, electric currents, heat transfer, laminar flow and solid mechanics are coupled.To characterize the dielectric properties of paraffin at the mmW band, a model- based characterization scheme using time-domain spectroscopy is proposed. Using this method, the relative dielectric constant of paraffin is measured to be 2.55 which is approximately constant over the frequency range of 26 GHz–1.2 THz. Loss tangent of paraffin is monotonically increasing with respect to frequency and it is estimated as 6.6 × 10−4 at 110 GHz.A six-layer photolithography process is used to realize mmW antennas and phase shifters, where all the components, including heater, antenna and capacitor are monolithically fabricated. Moreover, to deposit paraffin films, a new spin coating process is developed and characterized.Mechanical displacement of the paraffin PCM capacitors are measured using optical profilometer and maximum displacement of 1.4 µm is achieved. Reconfiguration capability of the antenna is measured using on-wafer probing and frequency shift in the range of 94–101 GHz is obtained.This work is the first demonstration of the paraffin-based reconfigurable mmW capacitor that is capable of continuous tuning.

With the development of wireless communications and its growing importance in all aspects of everyday life, the demand for developing robust and versatile wireless devices that support higher data rates is increasing. Antennas play a central and critical role in this endeavor. For RF and antenna engineers, next-generation antenna designs involve new materials and fabrication processes for emerging wireless applications. In the first part of this work, reconfigurable antennas based on liquid metal and 3D printed microfluidics are proposed. With the development of a robust liquid handling process on printed circuit board (PCB), two reconfigurable patch antenna implementations are introduced and characterized for the use of wide-band frequency reconfigurable or polarization reconfigurable antennas. An organ-tuned monopole antenna for microwave induced thermal ablation is also proposed based on liquid metal reconfiguration. The studies aim to explore novel reconfiguration technique enabled by new materials and manufacturing technologies with the potential of providing more functionalities and reduced cost. In the second part of the work, conformal antennas based on electro-textile for wireless body-area network (WBANs) are investigated. Electro-textile is playing a key role in the current and future smart garments implementations. We start with the detailed design and modeling strategies for embroidery-based electro-textile antennas. The patch antenna bending effects are then carefully investigated both numerically and experimentally. Nature-inspired global optimizations (e.g. particle swarm optimization and brain-storm optimization) are implemented in these designs and analyses.

The advent of VLSI and microelectronics has made it possible to reduce the size of electronic devices by several orders of magnitude while increasing their functional capabilities and reducing production costs. This massive scaling has enabled the development of satellites that can be as small as a cube of volume 10 cm x 10 cm x 10 cm. Such satellites, called ‘CubeSats’, have revolutionized the satellite industry today. This reduced volume makes launching CubeSats economically affordable, fostering the participation of small scale establishments and universities in space programs. Owing to their small size, it is now possible to conceive launching of multiple instances of the same CubeSat for advanced missions, which was not economically viable with conventional satellites. Even though numerous CubeSats have been launched, most of the current CubeSat missions operate at low data rates and low spatial resolution. One of the major reasons for this is the absence of compact high gain antennas that can integrate with the small CubeSat form factor while providing the required data rates for deep space missions or spatial resolution for remote sensing. This work addresses this very challenge by developing tools that can aid the integration of high gain antennas with the small CubeSat form factor. In particular, we include the following: (a) an in-depth understanding of umbrella reflector antennas with an emphasis on lower number of ribs to aid stowage, (b) analysis of complex knit mesh surfaces to understand the tradeoff between mesh density and RF transmission loss, (c) innovative feed designs that are optimized for efficient illumination of reflector antennas and minimum volume, (d) characterization of chassis interaction with the antenna system, and (e) development of a metal-only, low-profile, stepped parabolic reflector that can be 3D printed and readily integrated with the CubeSat chassis, simplifying deployment. As a part of this dissertation, we describe the development of one of the largest apertures at Ka-band: a 1m mesh-deployable offset reflector that can be stowed in a volume of 10 cm x 10 cm x 30 cm. The success of this endeavor marks a major milestone in the field of CubeSats, which allows advanced space missions at lower costs to become a reality.

Historically, antennas for airborne applications have been a separate class unto themselves. They have unique requirements for conformality, structural integrity, and long-range communication. Furthermore, the must successfully meet these criteria in a metallic environment. The antennas designed for Small Unmanned Aerial Systems (SUAS) have more stringent requirements than their predecessors due to the inherent Size Weight and Power (SWaP) restrictions and the increased importance of consistent communication for remote operation. Previous work has proven the utility of conformal antennas with a quasi-isotropic radiation pattern in the enhancement of SUAS communication for non-metallic structures. These structures however are not suited for performance on a metallic SUAS or in a metallic environment. For metallic SUAS, a new antenna will be devised using the Method of Moments (MoM). The following antenna synthesis procedure optimizes performance by taking into account the modality of the deformed ground structure the antenna is placed upon. The performance of this antenna will be assessed.

This dissertation presents millimeter-wave transmit/receive phased-arrays at 60 GHz, which are used to demonstrate long-range and high data-rate communication links. A 32-element one-dimensional (1-D) phased-array is built with 2$\times$2 beamformer chips flipped on a low-cost printed circuit board. Series-fed microstrip antennas are used, which limits the bandwidth to around 2 GHz at 64 GHz center frequency. The phased-array scans only in the azimuth plane with a 3$^o$ beamwidth and has a wide beam of 12$^o$ in elevation. The phased-array's high effective isotropic radiated power (EIRP) of around 42 dBm and low noise figure of 6.5 dB enable long-range communication at 500 Mbps over 800 m.A two-dimensional (2-D) scanning phased-array is also built using the same beamformer chips on a more complex multilayer board. The 2-D phased-array has an EIRP of 45 dBm in saturation and scans up to +/- 15$^o$ in the elevation plane and +/-50$^o$ in the azimuth. Stacked microstrip antennas are used, enabling a wide bandwidth of $\sim$8 GHz for the phased-array. Data-rates of up to 30 Gbps are achieved with 64-QAM modulation using the full bandwidth of the phased-array.An analysis of intermodulation effects in receive-mode phased-arrays is presented and verified through experimental results from a Ka-band 5G phased-array. The intermodulation products are shown to peak at scan angles which do not correspond to the interferer directions.Experimental evidence is presented to show that the adjacent channel power ratio (ACPR) of transmit phased-arrays improves with larger number of elements at a given backoff from the compression point. This implies better transmit efficiency in larger phased-arrays. Finally, techniques are presented for reducing the number of phase-shifters in a 2-D phased-array while maintaining a limited scan range in the vertical and horizontal planes. It is shown that the number of phase-shifters can be reduced by 75\%, while maintaining a scan range of +/-15$^o$ in the elevation and +/-40$^o$ in the azimuth.

For many RF and microwave applications, a balun is imperative to ensure the proper performance of a balanced structure that is connected to an unbalanced structure. Sleeve baluns are a common type of balun that are relatively cheap and basic, but they are also large, heavy, and time consuming to assemble. This works presents several novel methods of using additive manufacturing techniques to mitigate all of these issues. First, a methods of 3D printing basic designs to reduce weight and improve ease of assembly is presented. This method is then used to construct balun with up to two folds, which reduces the overall size of the balun with each consecutive fold. Next, a castable silicone is used to also reduce the overall size of a balun by reducing the effective wavelength on the balun’s interior, which is first tested with traditional unfolded baluns. This method was then combined with the folded balun design to compound the size reduction from both methods. A final method of printing a dielectric core and applying metal to the core is then presented. The performance of all of the baluns is presented and discussed and future improvements are addressed. Ultimately, this work establishes a method of drastically reducing the size of sleeve baluns to a point where they can be used as in line components, while still maintaining performance levels comparable to a standard, bulky sleeve balun.

Today's warfighter relies on extensive wireless technology to stay connected to allied forces and the battle theater. Communication equipment, IFF (identification friend-or-foe) identifiers, global positioning systems, jammers, and targeting systems are only a few of these applications. Often, each member of a unit will be required to carry many of these systems on their body during dismounted operations. As the number of required systems increases, so does their overall weight. One of the largest parts of these pieces of equipment is the antenna. SINCGARS, the workhorse of the US military's dismounted long distance communications, operates in 25 kHz channels in the VHF band (30-87.975 Mhz). This corresponds to wavelengths of roughly 3.5 - 10 meters. Common antennas operate with at least one dimension which is roughly half a wavelength. These dimensions can be reduced with various tradeoffs. A form factor of this size adds unnecessary weight and strain to the warfighter. While patch antenna are commonly used conformal antennas, their dimensions are roughly half a guided wavelength in width and length. Along with their bulky size, patch antennas are susceptible to their nearby environments and have constraints on surfaces upon which they can be placed. An electrically small, placement-insensitive antenna is introduced in this work. Proper feeding of this antenna requires a sizable RF choke be placed in-line orthogonally to the antenna's plane. This feeding method compromises the conformality of the antenna, as well as significantly increasing the weight and dimensions of the package. This work will present two novel feeding methods for this antenna in order to reduce package size, weight, and to ensure it remains conformal.

This dissertation focuses on designing, fabricating and testing antennas that are suitable for operation within the V/W bands. In particular, this work focuses on the design of slotted rectangular waveguide antenna arrays and cross slotted waveguide fed horn antennas. These structures are known for their high efficiency and high circularly polarized gain that can be implemented in satellite and terrestrial communication links. In addition, such designs can be implemented in radar applications that operate infrequency bands around 72 GHz or 84 GHz bands. Such antenna structures are inexpensive to fabricate since they can simply be machined using high precision conventional methods (like milling) and laser cutting when suitable. In particular, this dissertation discusses two designs involving cross-slotted waveguides. The first one consists of an array of cross slotted rectangular waveguide antennas exhibiting radiation beams with Left Hand or Right Hand circular polarization. The array is composed of 8x16 elements and generates a circularly polarized gain of 25 dB over the frequency range 84.2 – 85.7 GHz. The array also exhibits a cross polarization discrimination of more than 20 dB and an isolation of more than 20 dB between the feeding ports. A new type of z-arm shaped cross slots is introduced that fits on the broad-wall of a conventional rectangular waveguide. The feeding network is also optimized to regulate the power and the phase of each rectangular waveguide element in order to increase the gain of the antenna array. This dissertation also presents the theoretical analysis of the second design which is a cross slotted waveguide polarizer. The polarizer achieves a RHCP or LHCP by altering the feeding ports. The polarizer feeds different conical horns or pyramidal horns without affecting their characteristics. The efficiency of the polarizer is improved by combining the power of different crossed slots using square waveguide combiners. Other modes of operation of the cross slot polarizer are investigated for multiband operation and an antenna system operating at 72 GHz and 84 GHz simultaneously is designed.

Communication systems for aircraft are often implemented through antennas that protrude from the airframe and contain radiation nulls - which have detrimental effects on the aerodynamics of the craft and its ability to maintain a strong data link with a ground station through maneuvers, respectively. Small Unmanned Aircraft Systems (SUAS) in particular would greatly benefit from the use of quasi-isotropic and conformal antennas due to the increased impact of aerodynamics and communication links on their performance. Previous work has pursued antennas that either produce an approximately uniform power distribution or function favorably under significant conformation. This work provides an investigation of antennas that exhibit traits of conformality or quasi-isotropic radiation when conformed to a SUAS airframe. A specific variant of a dipole structure is explored and shown to have a highly quasi-isotropic radiation pattern within a size constrained form factor and conformal to the surface of typical SUAS. Considerations are made for the practical challenges of conformal attachment to SUAS and the tangible improvement on the communication system is assessed.

Abstract: The Quadruple Loop (QL) antenna was designed and investigated to deliver a robust body-worn antenna for bio-medical applications. The QL antenna is a very thin single-layer groundless structure which allows for the installation of neighboring electronics and sensors on biomedical device. The initial research objective was achieved after measurement results confirmed the superior performance of the QL antenna to the standard square loop. This was evident in gain and bandwidth improvement after the inclusion of the four circular patches to the original loop. In the second research stage, different fabrication tools and materials were used to make a number of QL antennas. The different antennas were intended to operate as GSM-900, GSM-1800, and BLE epidermal antennas. Radiation pattern measurements were conducted to compare their results with their simulation counterparts. Later, data communication tests showed that the acquired BER readings could qualify the BLE and GSM-900 antennas to work as part of 4-QAM wireless links. Moreover, a stretchable QL epidermal antenna made of novel silver ink had its measured results agree with simulations. Besides these hands-on endeavors, numerical analysis was used to explain the low values of gain of epidermal antennas. This is added to finding an equivalent and more efficient mathematical model of biological tissues which make up the human arm. The equivalent model was tested in software and has the practical potential to be realized in physical phantom making.

In modern RF systems, tunable devices are increasingly necessary to provide agility in crowded spectral environments. The antenna, as an integral part of any wireless system, must be capable of operating well at multiple frequencies and in a variety of environments where space and spectrum are at a premium. This work presents a novel method of magnetic reconfiguration through actuation of a ferrofluid load with a permanent magnetic field. When compared with previously published methods utilizing DC voltage, ferrofluid actuation has the benefit of providing electrical isolation between the tuning mechanism and the tunable element. Furthermore, we show in this work that magnetic actuation of ferrofluid allows for continuous tuning across frequency with a permanent magnet bias, as opposed to conventional magnetic tuning methods which normally require application of a variable magnetic field to a stationary load. Magnetic actuation of ferrofluid can be accomplished at a distance with a combination of magnets, and the system remains configured by the local bias magnet even after removal of the positioning field. Thus, magnetic tuning at a distance with ferrofluid offers a way to compensate for antenna package loading effects in situ. This work shows that magnetic tuning with a repositionable ferrofluid load has a broad range of applications in reconfigurable filter and antenna design.

Guided wave structures can perform as broadband antenna elements through the use of a gradual impedance transformation. The impedance match is typically created through gradual structural changes to match the impedance of the guide to that of free space. For parallel plate waveguide, it has been shown that serrating the edge of one of the conductors at the truncation between the waveguide and freespace can minimize reflection at that plane and present a broad impedance match between the waveguide and freespace. This method, however, is most effective when the parallel plate and serration are an appreciable size of a wavelength. This work presents potential alternative edge treatment designs other than the triangular serration for better impedance matching and radiation performance, particularly at small electrical sizes. This study extends the insights gathered from the edge treatment investigation to their potential in inducing ground plane currents when included in an antenna design that is placed over a large ground plane. With the ability to excite ground plane currents on metallic structures, the investigated antenna can improve the performance of electrically small antennas through strategic placement. This antenna is what is used as the feeding mechanism for the proposed edge treatments so their behavior is accurately characterized.

This thesis presents a new approach to extend and reduce the transmission range in wireless systems. Conditioning is defined as purposeful electromagnetic interference that affects a wireless signal as it propagates through the air. This interference can be used constructively to enhance a signal and increase its energy, or destructively to reduce energy. The constraints and limitations of the technology are described as a system model, and a flow chart is used to describe the circuit process. Remaining theoretical in nature, practical circuit implementations are foregone in the interest of elementary simulations depicting the interactions of modulated signals as they experience phase mismatch. Amplitude modulation and frequency modulation are explored with using both positive and negative conditioning, and conclusions to whether one is more suitable than the other are made.

Characteristic Mode Theory is one of the very few numerical methodsthat provide a great deal of physical insight because it allows us to determine thenatural modes of the radiating structure. The key feature of these modes is that thetotal induced antenna current, input impedance/admittance and radiation patterncan be expressed as a linear weighted combination of individual modes. Using thisdecomposition method, it is possible to study the behavior of the individual modes,understand them and therefore control the antennas behavior; in other words, controlthe currents induced on the antenna structure.This dissertation advances the topic of antenna design by carefully controlling theantenna currents over the desired frequency band to achieve the desired performancespecifications for a set of constraints. Here, a systematic method based on the Theory of Characteristic Modes (CM) and lumped reactive loading to achieve the goalof current control is developed. The lumped reactive loads are determined based onthe desired behavior of the antenna currents. This technique can also be used toimpedance match the antenna to the source/generator connected to it. The technique is much more general than the traditional impedance matching. Generally, thereactive loads that properly control the currents exhibit a combination of Foster andnon-Foster behavior. The former can be implemented with lumped passive reactive components, while the latter can be implemented with lumped non-Foster circuits(NFC).The concept of current control is applied to design antennas with a wide band(impedance/pattern) behavior using reactive loads. We successfully applied this noveltechnique to design multi band and wide band antennas for wireless applications. Thetechnique was developed to match the antenna to resistive and/or complex sourceimpedance and control the radiation pattern at these frequency bands, considering size and volume constraints. A wide band patch antenna was achieved usingthe developed technique. In addition, the technique was applied to multi band wireless Universal Serial Bus (USB) dongle antenna that serves for WLAN IEEE 802.11a/b/g/n band applications and Radio Frequency Identification (RFID) tag antennafor 915MHz band applications with superior performance compared to previous published results.This dissertation also discusses the total Q of an antenna from the CM standpoint.A new expression as well as additional physical information about each mode'sindividual contribution to the total antenna Q are provided.Finally, the theory is used to an analyze the antenna in both radiation and/orscattering modes. In the antenna scattering mode, the field scattered by an antennacontains a component that is the short circuit scattered field, and a second componentthat is proportional to the radiation field. In this dissertation, an analytical studyof this phenomena from the CM standpoint is performed aiming to shed some lighton antenna scattering phenomenon where additional physical insight is obtained andthus used to reach desire results.

The demand for miniaturized, broadband communication systems has created a need for electrically small, broadband antennas. However, all passive electrically small antennas have a fundamental gain-bandwidth limitation related to their electrical size, as first described by Wheeler and Chu. This limitation can be overcome using active non-Foster circuits (negative inductors and/or negative capacitors), which can deliver a broadband input match with active matching techniques, or can help reduce phase dispersion using negative delay effects. This thesis will illustrate the advantages of non-Foster circuits in obtaining broadband small antennas, in addition to examining their practical limitations due to noise in receive applications, and nonlinearity in transmit applications.

The accelerating increase in information traffic demands the expansion of optical access network systems that require high-performance optical and photonic components. In short-range communication links, optical interconnects have been widely accepted as a viable approach to solve the problems that copper based electrical interconnects have encountered in keeping up with the surge in the data rate demand over the last decades. Low cost, ease of fabrication, and integration capabilities of low optical-loss polymers make them attractive for integrated photonic applications to support futuristic data communication networks. In addition to passive wave-guiding components, electro-optic (EO) polymers consisting of a polymeric matrix doped with organic nonlinear chromophores have enabled wide-RF-bandwidth and low-power active photonic devices. Beside board level passive and active optical components, on-chip micro- or nano-photonic devices have been made possible by the hybrid integration of EO polymers onto the silicon platform. In recent years, silicon photonics have attracted a significant amount of attentions, because it offers compact device size and the potential of complementary metal–oxide–semiconductor (CMOS) compatible photonic integrated circuits. The combination of silicon photonics and EO polymers can enable miniaturized and high-performance hybrid integrated photonic devices, such as electro-optic modulators, optical interconnects, and microwave photonic sensors. Silicon photonic crystal waveguides (PCWs) exhibit slow-light effects which are beneficial for device miniaturization. Especially, EO polymer filled silicon slotted PCWs further reduce the device size and enhance the device performance by combining the best of these two systems. The potential applications of these silicon-polymer hybrid integrated devices include not only optical interconnects, but also optical sensing and microwave photonics. In this dissertation, the design, fabrication, and characterization of several types of silicon-polymer hybrid photonic devices will be presented, including EO polymer filled silicon PCW modulators for on-chip optical interconnects, antenna-coupled optical modulators for electromagnetic wave detections, and low-loss strip-to-slot PCW mode converters. In addition, some polymer-based devices and silicon-based photonic devices will also be presented, such as traveling wave electro-optic polymer modulators based on domain-inversion directional couplers, and silicon thermo-optic switches based on coupled photonic crystal microcavities. Furthermore, some microwave (or RF) components such as integrated broadband bowtie antennas for microwave photonic applications will be covered. Some on-going work or suggested future work will also be introduced, including in-device pyroelectric poling for EO polymer filled silicon slot PCWs, millimeter- or Terahertz-wave sensors based on EO polymer filled plasmonic slot waveguide, low-loss silicon-polymer hybrid slot photonic crystal waveguides fabricated by CMOS foundry, logic devices based on EO polymer microring resonators, and so on.

The physical size and material properties of antennas are major limiting factors of the antennas performance. These limitations are usually manifested through parameters such as bandwidth, quality factor and efficiency. The presented research examines these fundamental limitations with specific focus on electrically small antennas, and a new bound for antenna efficiency is developed.

Sustaining current increases in wireless data rates has driven engineers of all related backgrounds to seek fresh and innovative approaches in wireless system design. With the advancement of RF switching technology, transceiver architectures, and digital signal processing capabilities, the pressure now falls on the antenna designs for future broadband and adaptive wireless services. The first part of the work focuses on enhancing the bandwidth of low-profile patch antennas for circularly-polarized (CP) wireless systems. We start with an in-depth examination of the CP patch antenna cavity model and reveal that traditional circularly polarized (CP) patch antennas are not being utilized to their full potential for bandwidth. Some new modifications to enable broader bandwidths are proposed. A high-performance antenna for future Mars Rover missions is also discussed, and a novel CP Half E-shaped patch antenna subarray was developed and prototyped to demonstrate its use. Another concept uses composite right/left-handed (CRLH) transmission lines towards creating wideband CP arrays. Our resulting array prototype using a CRLH transmission line feed network showed an overall bandwidth of 60%, which is a formidable increase compared to designs using conventional quarter-wavelength transmission lines.In the second part of this work, reconfigurable antenna functionalities for software and cognitive radios are pursued. With the development of practical reconfigurable antenna simulation models in conjunction with nature-inspired optimization techniques, two reconfigurable E-shaped patch antenna implementations are evaluated for potential use as frequency or polarization reconfigurable antennas. This is particularly useful for systems wanting to achieve unidirectional patterns with a low-profile antenna. Both the frequency and polarization reconfigurable designs were optimized, fabricated, and characterized through measurement. Our frequency reconfigurable E-shaped patch antenna design is able to support an overall bandwidth of 50% by incorporating MEMS switches. The CP reconfigurable version design provided CP bandwidths of 17% and 20% for an element and array concept, respectively. Lastly, a rejection reconfigurable array element is developed. The design uses a reconfigurable frequency rejection slot within a wideband monopole antenna, and some simulation and experimental measurement studies are undertaken. By integrating another reconfigurable filter, a higher-order filter capability is achieved, leading to stronger rejection levels from strong blockers.

Reflectarray antennas uniquely combine the advantages of parabolic reflectors and phased array antennas. Comprised of planar structures similar to phased arrays and utilizing quasi-optical excitation similar to parabolic reflectors, reflectarray antennas provide beam steering without the need of complex and lossy feed networks. Chapter 1 discusses the basic theory of reflectarray and its design. A brief summary of previous work and current research status is also presented. The inherent advantages and drawbacks of the reflectarray are discussed. In chapter 2, a novel theoretical approach to extract the reflection coefficient of reflectarray unit cells is developed. The approach is applied to single-resonance unit cell elements under normal and waveguide incidences. The developed theory is also utilized to understand the difference between the TEM and TE10 mode of excitation. Using this theory, effects of different physical parameters on reflection properties of unit cells are studied without the need of full-wave simulations. Detailed analysis is performed for Ka-band reflectarray unit cells and verified by full-wave simulations. In addition, an approach to extract the Q factors using full-wave simulations is also presented. Lastly, a detailed study on the effects of inter-element spacing is discussed. Q factor theory discussed in chapter 2 is extended to account for the varying incidence angles and polarizations in chapter 3 utilizing Floquet modes. Emphasis is laid on elements located on planes where extremities in performance tend to occur. The antenna element properties are assessed in terms of maximum reflection loss and slope of the reflection phase. A thorough analysis is performed at Ka band and the results obtained are verified using full-wave simulations. Reflection coefficients over a 749-element reflectarray aperture for a broadside radiation pattern are presented for a couple of cases and the effects of coupling conditions in conjunction with incidence angles are demonstrated. The presented theory provides explicit physical intuition and guidelines for efficient and accurate reflectarray design. In chapter 4, tunable reflectarray elements capacitively loaded with Barium Strontium Titanate (BST) thin film are shown. The effects of substrate thickness, operating frequency and deposition pressure are shown utilizing coupling conditions and the performance is optimized. To ensure minimum affects from biasing, optimized biasing schemes are discussed. The proposed unit cells are fabricated and measured, demonstrating the reconfigurability by varying the applied E-field. To demonstrate the concept, a 45 element array is also designed and fabricated. Using anechoic chamber measurements, far-field patterns are obtained and a beam scan up to 25o is shown on the E-plane. Overall, novel theoretical approaches to analyze the reflection properties of the reflectarray elements using Q factors are developed. The proposed theoretical models provide valuable physical insight utilizing coupling conditions and aid in efficient reflectarray design. In addition, for the first time a continuously tunable reflectarray operating at Ka-band is presented using BST technology. Due to monolithic integration, the technique can be extended to higher frequencies such as V-band and above.

After being theorized by Veselago in 1967, recent developments in metamaterials over the last two decades have allowed scientists and researchers to physically demonstrate that artificial composite media can be engineered to exhibit exotic material properties, such as negative refractive index, by exploiting features in arrays of sub-wavelength unit inclusions. These unconventional electromagnetic properties are realized through the coupling of the microscopic unit inclusions, which govern the macroscopic properties of the structure. After demonstrating that a periodic array of capacitively-loaded loop (CLL) inclusions paired with continuous wire results in negative refraction, this study performs numerical simulations to characterize random metamaterial structures. These structures consist of CLLs that are randomized in both position and orientation. In addition, this thesis introduces an innovative antenna enhancing structure consisting of capacitively-loaded loop (CLL) metamaterial elements loaded radially around a standard dipole antenna at an electrically small distance. As a result of this innovative arrangement, the dipole antenna is easily transformed into a directive mechanically scanned antenna with high realized gain. The desired directivity and gain can be tuned based on the number of radial CLL fins placed around the dipole. Interactions between the antenna and metamaterial elements result in significant enhancement of the maximum radiated field amplitude and front-to-back ratio. This innovative CLL-loaded dipole antenna is compared to the conventional Yagi-Uda antenna. The structures presented in this thesis are modeled using full-wave simulation, and one antenna structure is experimentally verified as a proof-of-concept.

This dissertation focuses on the development of next generation wireless communications at millimeter-wave and sub-terahertz frequencies. As wireless providers experience a bandwidth shortage and cellular subscribers demand faster data rates and more reliable service, a push towards unused carriers fre- quencies such as 28 GHz, 60 GHz, and 180 GHz will alleviate network conges- tion while simultaneously providing massive bandwidths to consumers. This dissertation summarizes research in understanding millimeter-wave wireless propagation, the design and fabrication of millimeter-wave and sub-terahertz on-chip antenna arrays on an integrated circuit semiconductor process, and the accurate measurement of on-chip antenna radiation patterns in a wafer probe station environment.

Phased array systems present desirable antenna features like beam steering and high gain. However, due to their high cost, civilian applications cannot generally afford them, restricting their usage to military. Hardware involved in phased array systems is expensive and the number of devices is high, since there is usually one device of each kind (filter, amplifier, shifter..) for each individual antenna. Alternative techniques, mainly based on TDMA, have been developed looking for lowering the number of elements in the system. However, these approaches increase the system bandwidth, multiplying it by a factor of $N$ (Number of antennas), as they use redundant information. In this thesis, a novel phased receiver, based on an economic sampling scheme is proposed. All the elements in an array receive a common information (signal amplitude) and a unique information (relative delay between elements). The idea is to sample only the information required to reconstruct the transmitted signal and discard the redundant one. This idea is achieved by sampling just one antenna during each RF cycle and then gathering all the information taking in account the relative delay between different antenna elements. The proposed technique is mathematically proved and validated by simulation. As a first approach, the equation for the received signal in the frequency domain is derived for a linear array. The radiation pattern and the received signals are simulated for equally spaced planar and linear arrays. Bandwidth signal transmission is demonstrated and tapering effects are shown. After that, the proposed technique is expanded for arbitrary structures and the resulting system bandwidth is enhanced by using different sampling order sequences.

Advanced wireless communication and sensing systems have created a growing need for high performance, compact antennas. Low-profile wideband phased arrays are of particular interest, and have recently been shown to be capable of extremely large bandwidths. However, the size, weight, and cost of phased arrays still makes them impractical for many applications. The development of thinner, lightweight, and inexpensive wideband arrays is critical to improving the capabilities of small platforms such as small unmanned aerial vehicles.Like all antennas, phased arrays are limited by a fundamental compromise between size and performance. Although the theoretical limitations of electrically small antennas have been well known for over 60 years, similarly general limits have not yet been developed for periodic antenna arrays. In the first part of this thesis, we derive a new fundamental bandwidth limit for any periodic array that is backed by a conducting ground plane and constructed from passive and reciprocal materials. This limit is related to several critical design factors, including the array's thickness, polarization, scan angle, materials used, as well as the overall complexity of the array design. We also consider the common case when all radiating currents are confined to a thin planar sheet placed above the ground plane. We show here that such planar phased arrays have a fundamental impedance bandwidth limit of 8.3:1 (with VSWR ≤ 2:1), in the absence of material loading. This bandwidth may be further improved by adding dielectric superstrate or magnetic substrate material layers.Knowledge of such fundamental bandwidth limits is extremely useful in the design of practical wideband arrays, which is the focus of the second part of this thesis. A key challenge with many wideband arrays is developing a feed circuit that supports extremely wide bandwidths without significantly adding to the size, weight, and cost of the design. Here, we demonstrate a novel approach that overcomes this problem by exploiting the natural reactance of the feed circuit as a simple impedance matching network for the array. The result is a simultaneous reduction in size and weight and improvement in bandwidth compared to other feeding techniques. We refer to our design as the Tightly Coupled Dipole Array with Integrated Balun (TCDA-IB), and it achieves 7.35:1 bandwidth while maintaining a low VSWR of ≤ 2.65:1 while scanning to ± 45° in all planes. A prototype 8×8 array was constructed and demonstrated excellent performance relative to simulation. We also demonstrate that by adding reconfigurable components to the TCDA-IB, its maximum scan angle may by increased to as much as ± 70° while maintaining a 5:1 impedance bandwidth.Our fundamental bandwidth limits reveal for the first time the extent of the realizable design space for wideband low-profile arrays, and suggest there are significant opportunities for further improvement. Several practical techniques are also presented for increasing bandwidth and scanning performance while reducing the total size, weight and cost of the array. In summary, the ongoing development of high-performance wideband low-profile arrays will likely remain an important and fertile area of research for the foreseeable future.

Single-dish reflector antennas are often used for their ability to produce a highly directive (narrow beam) radiation pattern which increases in directivity as the diameter of the reflector increases. However, as reflectors grow larger in the pursuit of more directivity, they become more expensive and unwieldy to construct, maintain, and operate. A more practical solution is to employ an array of elements which are smaller individually, but which can yield similar or better gains when arrayed together.However, one trade-off associated with this approach is that antenna arrays are subject to losses introduced by atmospheric turbulence. Inhomogeneous cells of water vapor in the troposphere change the refractivity of the air along the path of the propagating wave, distorting the wavefront and introducing a phase error between the elements of the array. These losses are stochastic and site-dependent.Techniques have been developed over the past several decades to compensate for such losses on the receiving end, but uplink arraying remains challenging as it requires prediction of atmospheric conditions to effectively compensate the signal before transmitting. This is especially true at higher frequencies such as Ka-band given that atmospheric phase noise increases with frequency. Thus, a critical first step in system planning is to determine the losses a particular array configuration will experience based on the phase statistics of a given site. To this end, NASA Glenn Research Center has deployed site test interferometers to three ground-station sites with the intent to characterize their phase instability ahead of upgrades to Ka-Band operation. The sites to be studied are Goldstone, California; White Sands, New Mexico; and the island of Guam.Using three years of data collected from these campaigns, the primary goal of this thesis is to develop a thorough characterization of the phase statistics of each site which may then be used to determine the sites’ suitability for uplink arraying. In addition, a secondary goal is the development of the data analysis software suite that was used to process the data, which it is hoped will facilitate easy analysis of future sites for system designers.

Generation and detection of microwave radiation is done with electronic systemswhere the underyling processes involve oscillating free charges (such as on an an-tenna or within a transistor or diode). On the higher energy side of the spectrum,generation and detection of near infrared and visible radiation is achieved viaquantum transitions with emission wavelengths that are dictated by the material.Solutions moving up towards the THz regime using microwave based solutions arelimited by carrier transit time and RC time-constant limitations. Techniques andsolutions moving down toward the THz regime using photonic techniques haveemission wavelengths naturally limited by the band gap of the material. However,THz quantum-cascade (QC) lasers, which are an extension of photonic conceptsto lower energies, have artificially engineered energy levels and hence emissionwavelengths. THz QC-lasers have been demonstrated to operate at frequenciesbetween 1.2 and 5.0 THz and the best high-temperature operation is based uponthe metal-metal (MM) waveguide configuration, in which the multiple-quantum-well active region is sandwiched between two metal cladding layers, typically sep-arated by 2-10 μm. Soon after the demonstration of MM waveguide QC-lasers,it was recognized that the beam pattern from a conventional cleaved-facet Fabry-Pérot (FP) ridge cavity produced a highly divergent beam pattern, characterizedby concentric rings in the far field.This thesis presents work on a new approach to tailor the beam pattern of THzMM waveguide QC-devices. Namely, dispersion engineering using metamaterialsbased on the composite right/left-handed (CRLH) transmission line formalism isadapted to the MM waveguide configuration to realize an entirely new class ofdevices. Dispersion, radiative loss, and radiation patterns are presented for manynewly designed 1-D and 2-D THz QC transmission line metamaterial designs. Thefirst ever active 1-D THz QC transmisison line metamaterial is experimentallycharacterized and its radiation pattern and polarization closely match theoreticaland full-wave finite element method (FEM) simulated predictions.Proven microwave techniques such as circuit, antenna cavity modeling andarray factor theory are used to understand the radiative properties of conventionalTHz QC-lasers. We predict far-field beam patterns and polarizations, approximatecavity quality factors, and associate these properties with individual surfaces orstructures of the device. The analysis technique is also applied to the project's 1-Dand 2-D THz CRLH QC-devices yielding qualitative agreement with experiments.The first THz design, analysis and experimental verification of a metasur-face comprised of an array of passive THz QC transmission lines is presented.By using the cavity model, array factor, circuit and electromagnetic theory asurface impedance model is developed to characterize the metasurface. The sur-face impedance model reveals waveguide mode dependent radiative coupling withthe light line and capacitve/inductive surface impedance. Polarization dependentangle-resolved Fourier transform infrared reflection spectroscopy measurementsmatch the model and full-wave FEM predictions, further assisting the under-standing of such devices.To address the broader goal of a directive and scalable THz QC-device, thefeasibility of a 2-D metamaterial inspired QC-laser and an active reflectarray isconsidered. Finally, preliminary work on a technology enabling active metasurfacereflector for a QC vertical external cavity surface emitting laser is discussed.

Using wireless transmitters to create an ocean of radio frequency (RF) energy and to power remote devices have been a dream since Nikola Tesla invented wireless communications. Recently, wireless power technology has been embedded into a plethora of consumer electronics to improve device reliability and extend battery life. Soon enough, miniature wireless sensors adapting microwave energy harvesting modules for power will be located at spots where it would be otherwise inconvenient, such as, to change their batteries. These spots include locations inside human body, within the steel or concrete of buildings, and in the dangerous innards of chemical plants. However today, even the most robust nodes can be counted on to last only a few years due to the existence of a battery. Ideally, engineers need a sensor that can last forever without external power sources or battery changes. According to research presented in this dissertation that dream is now within reach. While solar energy harvesting has been widely used for years to power remote devices, several other types of energy-harvesting approaches have also emerged for micropower applications including vibration, thermal, mechanical, and RF. Of these technologies, RF energy is the only one that can provide either intentional or ambient power source for batteryless applications. Thanks to mobile and Wi-Fi networks, ambient RF energy is ubiquitous. Note that more than a million smartphones phones are activated every day, representing a large source of transmitters for RF energy harvesting. Moreover, when more power or more predictable energy is needed than what is available from ambient sources, RF energy can be broadcasted in unlicensed frequency bands.Of particular interest is the efficient harvesting of low power RF signals, which would possibly mean range improvements for dedicated microwave power transmission and considerably more DC power from ambient RF energy harvesting. Hence, in this dissertation, we propose a new class of microwave energy harvesting system which exhibits substantially improved conversion efficiency than the ones available off-the-shelf or in literature. The enhancement is due to novel rectifier circuits that can approach theoretical efficiency bounds by handling the best components on the market.Although the developed energy harvester offers game-changing efficiency performance, maximum power supplied by a single module is usually not enough to energize most consumer electronics. Accordingly, a mathematical tool is presented to predict the optimal way of interconnecting multiple microwave energy harvesters. Subsequently, an energy harvesting array with nine elements is designed to power up a commercial thermometer and its LCD display using nothing more than ambient Wi-Fi signals in an office environment. In the end, the operational bandwidth of the designed ambient energy harvester is widened to include all cell phone bands and Wi-Fi to harvest more RF power from the environment.

This thesis describes the origins, improvements, and variations of a broadband microwave antenna that can be beam-steered by a micro-electromechanical system (MEMS). The steerable MEMS antenna of this work was comprised of a planar antenna on top of a Silicon membrane. The membrane is etched to create a gimbal hinge structure and a platform which supported the antenna and gave it one or two degrees of freedom of rotation. The antennas presented were broadband and fed by a coplanar waveguide (CPW) transmission line which traversed the hinge structure. The antenna's orientation in space was designed to be changed through electrostatic actuation of the antenna platform's hinges. The goal of this thesis was to improve on the initial design and performance of the prototypic antenna. The best variation of the prototype antenna could rotate ±4.0° in two degrees of freedom under 800 VDC of actuation voltage and had a bandwidth of 1.55. The mechanical and electrical aspects of the device were studied and analyzed concurrently. Three variations of the MEMS antenna platform were design and modeled; Generations 1 - 3 (G1 - G3). The G1 platform was an optimized version of the prototypic MEMS platform. The G2 platform could rotate in two dimensions but had much thinner hinges and a more robust antenna platform. The G3 platform was a one degree of freedom version of the G2 platform. A new antenna shape was selected and optimized for integration with the three generations of antenna platforms; the planar inverted cone antenna (PICA). The G3 platform had the best overall electrical and mechanical performance. Two additional antennas were simulated on the G3 platform; a cylindrical dielectric resonator antenna (C-DRA) and a teardrop dielectric resonator antenna (Td-DRA). The three best antenna variations on the G3 platform were simulated to have maximum actuation angles ranging from 10 - 13° and have bandwidths of 3.62 (PICA), 1.70 (C-DRA), and 1.78 (Td-DRA).

We are interested in measuring the in situ antenna performance in analog land mobile radio (LMR) FM systems. The gain (efficiency and directivity) and self-impedance of an antenna sufficiently characterize its performance and a number of traditional methods exist to measure these quantities. However it is hard to do antenna gain measurements using these methods. Furthermore, it turns out that volumetric antenna gain measurements are not quite relevant for understanding in situ performance. In this thesis, we present a novel approach for directly measuring the in situ performance of antennas in analog LMR systems. The procedure involves receiving an FM signal simultaneously using the antenna under test (AUT) and a reference antenna. Both received signals are demodulated to audio using separate but identical receivers. Then a convenient method for characterizing the audio signal quality is to analyze the private line (PL) tone. The PL tone signal-to-noise ratio (SNR) is calculated by measuring the power of the tone relative to the sub-audio noise power. The PL tone SNR for both antenna systems is compared as it provides a ``bottom line'' evaluation of the antenna performance. The audio SNR can also be mapped to RF SNR using a theoretical method. From simulation and experimental studies, we conclude that the RF SNR estimated using this technique is within 0.5 dB of the actual value for RF SNR values between +3 and +36 dB. Finally, we demonstrate this procedure in actual in situ LMR antenna measurements.

Electrically small, low profile antennas have become the new frontier in wireless communication research. With the pressure to miniaturize wireless communication devices, engineers are turning to small low profile antennas as a way to reduce their antennas and hence their devices. Ideally, one would also like to at least maintain antenna bandwidth and efficiency while reducing size. However, in theory, antenna performance degrades when it is miniaturized—impedance bandwidth decreases with the reduction in antenna size. This thesis investigates the possibility of increasing the input impedance bandwidth without enlarging the volume of the antenna. This thesis attempts to break the fundamental tradeoff between antenna size and bandwidth by loading it with a nonlinear element. First, a brief summary of antenna background definitions is presented. Next, the analytical framework of the thesis is presented using a model of a narrowband antenna. A literature review of various narrowband electrically small antennas is studied, including the pros and cons of the Inverted-F antenna (IFA), Inverted-L antenna (ILA), and the Planar Inverted-F antenna (PIFA).Next, the analysis and the methodology leading to results are discussed and simulated results are presented. Simulated results show that the PIFA is able to achieve a higher bandwidth with a loaded nonlinear element. However, it is difficult to sustain the efficiency of the antenna due to harmonics generated by nonlinearity in the antenna. Results indicate that an increase in nonlinearity tends to generate harmonics which leads to losses in the antenna.

Miniaturized microwave components have drawn increased attention due to the size shrinking of the modern communication systems. This dissertation proposes two approaches to address this problem by reducing the size of the RF components and the antennas. First, miniaturized substrate integrated waveguide components are introduced and developed by using the metamaterial concept. Traditional waveguide components have excellent performance but with a bulky size due to the above-cutoff frequency operation. We demonstrate that by loading the metamaterial elements, the rectangular waveguide can be operated well below the cutoff frequency while maintaining good performance. Based on the substrate integrated waveguide technology, their wave propagation characteristics are studied and their practical applications for guided and radiated RF/microwave components, including transmission lines, filters, couplers, diplexers, oscillators, and leaky-wave antennas, are proposed and implemented. These devices are substantially miniaturized with superior performance achieved.Second, various miniaturized planar antennas are developed to meet the industry application requirements. Different techniques, such as the metamaterial resonators, meta-surfaces, multi-layer folded structures, and the shared radiator approach, are adopted to design different antennas which are suitable to be applied in many wireless systems, including the WLAN links, cellular phone systems and ultra-wideband communication systems. Some special antennas, such as dually or circularly polarized antennas, diversity antennas, are also designed for specified applications. These antennas exhibit good radiation performance with a smaller size compared with the conventional planar antennas. Some of them are going to be used in commercial WLAN communication systems.

This thesis focuses on the design of efficient, highly integrated antennas for millimeter- wave systems. Two gaps in the exisiting literature are addressed. First, the sinuous antenna on silicon dielectric lenses is explored. The antenna is demonstrated to be an excellent option for integrated systems requiring high-gain, dual-linear polarization, and a multi- octave bandwidth. A design with cross-pol below -17 dB, polarization variations less than ±5◦, and stable impedance properties over a 4:1 bandwidth is demonstrated.Second, silicon RFIC antennas are studied, with the goal of achieving a high level of integration and a design scalable to frequencies beyond 100 GHz. A novel solution is proposed, which uses a dielectric superstrate layer to enhance the efficiency and gain of standard patch and elliptical slot antennas. Compared to a stand-alone W-band patch in a standard CMOS process, the proposed solution yields a 7 dB improvement in antenna efficiency. Because all of the metal layers are integrated on chip and the required dielectric layer is not electrically thin, the superstrate-loaded antennas are an excellent candidate for high-efficiency on-chip antennas beyond 100 GHz.

Complex multiple antenna systems are emerging today as market pressures to improve link capacity and reliability on complex integrated platforms. Complexity is therefore inherent in both the analysis and design of such systems. Modal analysis of various types has been used in a variety of fields to manage this inherent complexity. For single antenna systems, the Theory of Characteristic Modes (CM) has been used to great success in designing single antennas. In this dissertation, four interconnected topics are discussed, which are crucial to the proper extension of Characteristic Modes to complex antenna systems, especially multiple antenna systems. First, existing characteristic mode systems are reviewed and their common properties examined. A software architecture is then discussed which enables the computation of characteristic modes in general, requiring only that the particular system definition satisfies those common properties. The software is used to perform all computations, analyses, and designs in this dissertation.Second, a general, high-performance, wideband mode tracking system is proposed. It is shown to be efficient and robust through several challenging examples. It is the first robust tracker proposed in connection with Characteristic Modes. Third, a procedure is proposed to compute the number, location, and even voltages of ports on a given antenna or antennas using a CM description of the problem. Its mathematical construction is inspired by results from the emerging field of Compressed Sensing. Its generality is demonstrated through a number of simulated designs.Lastly, two new modal systems related to CM are proposed. One modal system, Subsystem Classical Characteristic Modes, produces modes which successively optimize the ratio of stored power to radiated power for an antenna embedded in a multistructure system. The other modal system, Target Coupling Characteristic Modes, produces modes which successively optimize the ratio of induced current intensity on a target structure to the current intensity on a source antenna. The modal systems are related through a projection matrix, which demonstrates the tradeoff between mutual coupling and radiation properties for a given multiple antenna system. The two modal systems are applied to several examples to validate their properties. Then, they are used in a new design procedure to systematically reduce the mutual coupling between two parallel dipoles. It is found that through loading an intermediate structure suggested by the proposed modal systems, the mutual coupling may be reduced, also predicted by the modal coupling analysis. The resulting designs generally improve upon designs available in the literature.The dissertation concludes with a summary and discussion of future work. The appendices discusses various definitions, including a novel derivation of Classical Characteristic Modes from the starting point of orthogonal eigenpatterns.