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The Piergiorgio L. E. Uslenghi Letters Prize Paper Award was established in 2009 to recognize the best contribution published in the IEEE Antennas and Wireless Propagation Letters during the previous year. [ABSTRACT FROM AUTHOR]

The article presents the winners in the Harold A. Wheeler Applications Prize Paper Award for 2017. It highlight the significance of the award which recognizes authors of the best applications paper published in the Institute of Electrical and Electronics Engineers (IEEE) Transactions on Antennas and Propagation. The winners include Dia'aaldin J. Bisharat, Shaowei Liao and Quan Xue.

We give an overview of recent developments in the modeling of radiowave propagation, based on machine learning (ML) algorithms. We identify the input and output specification and the architecture of the model as the main challenges associated with ML-driven propagation models. Relevant papers are discussed and categorized based on their approach to each of these challenges. Emphasis is given on presenting the prospects and open problems in this promising and rapidly evolving area. [ABSTRACT FROM AUTHOR]

This paper provides a survey of various experimental data available on the value of the propagation path loss of radio waves in a cellular wireless environment. It is shown starting with the Okumuraet al.’s paper on propagation measurements and other available published experimental data that they all exhibit that the electric field varies as $\rho ^{-1.5}$ within a cellular radius of a few kilometers, where $\rho $ is the radial distance of the receiving antenna from the transmitting one. This decay in the fields is equivalent to a propagation loss of −9 dB/octave or −30 dB for a decade of the distance. This value is independent of the nature of the ground, whether it be composed of rural, urban, suburban, or water. This is the first time it is stated that the propagation path loss due to the presence of ground generates a path loss of 90 dB when the signals travel a distance of 1 km. This value is rather large when compared to a loss of 30–50 dB produced by buildings, trees, and similar artifacts. Therefore, the experimental data indicate that the effect of trees and buildings have a secondary influence on the decay of the electric field with distance, the dominant one is the propagation loss over an imperfect ground. Contemporary propagation models do not acknowledge this fact. Outside the cellular radius of a few kilometers, the path loss appears to be 12 dB/octave or 40 dB/decade of distance. In a companion paper, it will be demonstrated that the values for the path loss can be explained from an analytical standpoint without taking recourse to statistics which involves a lot of assumptions on the functional variation of the variables of interest. [ABSTRACT FROM AUTHOR]

Three main characteristics of massive multiple-input-multiple-output (MIMO) are studied. The widespread use of these characteristics and their lack of validation motivates this paper based in measurements. First, we study the channel hardening when the number of antennas in the base station (BS) increases. Second, we focus on the channel vector orthogonality between two users. Third, we investigate the rank of the spatial covariance matrix. The data used for this paper have been obtained in two measurement campaigns with all real antennas (i.e., neither virtual arrays nor virtual users). The first one has 64 BS elements arranged in 3 configurations, and it serves 8 users with 2 antennas each. The second campaign has 128 BS elements, serving 2 users with 2 antennas each. Both campaigns include line-of-sight and nonline-of-sight scenarios, designed according to the future 5G deployment scenarios. We show the rate of channel hardening when the number of BS elements increases. We evaluate the sum rate of two users at specific distances between them. We observe the large angular spread occupied by the user. [ABSTRACT FROM AUTHOR]

This paper presents a simple, compact, and low-power method for generating extremely low-frequency radio signals below ~500 Hz. This paper is motivated by the prohibitively large size and low efficiency of conventional antennas operating in this frequency range. The successful generation of time-varying magnetic fields produced by the physical rotation of a 3 cm3 permanent magnet is demonstrated. Ground plane and receiver orientation effects are analyzed both theoretically and experimentally. Observations as a function of distance from the source indicate that the fields are dominated by the static component, rather than by the radiation component, of the generated field. Based on these observations, the electromagnetic radiation emitted by a spinning magnet source is predicted to be weak. Nevertheless, static magnetic signaling using this technique is proven to be both possible and practical at frequencies below ~500 Hz and at distances in excess of 100 m. [ABSTRACT FROM AUTHOR]

The conventional time-modulated arrays (TMAs) have a low radiation efficiency, since each antenna turns off at specific time slots. In this paper, first, the efficiency of TMA is investigated analytically. Next, the optimized switching sequences are proposed to enhance the radiation efficiency of a specific sideband, while preserving the level of the other sidebands. The practical hardware limitations are considered in the switching sequence design. Moreover, a low-cost flexible eight-element printed dipole array operating at 1.2–1.4 GHz is implemented to verify the proposed algorithms. The measured radiation patterns indicate that by applying the proposed sequences, the TMA efficiency improves by 8.3 dB for the fundamental frequency. The efficiency enhancement for the first and second sidebands is 2.9 and 2.95 dB, respectively. In addition, a fast and low-cost setup for TMA measurement using the commercial software defined radio dongle is implemented in this paper. [ABSTRACT FROM AUTHOR]

The emerging applications for wearable electronics have experienced enormous growth over the last decade. Antennas, being one of the critical components in modern wireless devices, thus need to be specifically designed to function while being worn and bent. In this paper, we present a systematic investigation of the effects of bending applied on wearable patch antennas over cylindrical surfaces. The resonant frequency variations and radiation pattern variations have been studied by simulating and measuring patch antennas that are bent by different angles. A frequency shift plot with respect to bending radius has been generated to target antennas for various wearable applications. An analytical approach has been presented to study the effect of resonant frequency shifting for both E- and H-planes bending. A lumped element circuit model is used to interpret the E-plane bending from different perspectives. One of the main objectives of this paper is to develop useful design-oriented charts and provide a better understanding of the effects of antenna bending to assist wearable antenna designers. [ABSTRACT FROM PUBLISHER]

A compact and wideband folded dipole antenna with multi-resonant modes is presented in this paper. Three resonant modes are obtained by using a modified planar folded dipole and its coupled feeding structure. Incorporating the shorting pins and parasitic patches, multiple resonant modes in the antenna are manipulated, shifted, and then combined to increase the impedance bandwidth. Using this concept, a prototype of a multi-mode folded dipole is designed, fabricated, and measured. The experimental results show that the proposed antenna achieves a bandwidth of 80% from 1.57 to 3.68 GHz, while occupying a compact size of $0.3\lambda _{0}\times 0.15\lambda _{0}\times 0.05\lambda _{0}$ ($\lambda _{0}$ is the wavelength in free space at the lowest operating frequency). Furthermore, a simple and effective design to achieve good omnidirectional radiation performance is developed by placing two proposed folded dipoles back to back. The antenna exhibits a flat gain variation of less than 1.27 dB over a broad bandwidth (82%) in the horizontal plane. Such a compact, wideband, planar antenna is a promising candidate for indoor signal coverage, wireless access points, and micro base stations in 2G/3G/4G/5G and WLAN/WiMAX wireless communication systems. [ABSTRACT FROM AUTHOR]

Tunnels represent strong multipath environments for communications, where wireless propagation differs from regular indoor or outdoor scenarios. Moreover, with an adequate operating frequency choice, a tunnel behaves as an oversized waveguide, extending the communication range but affecting the signal with strong fadings. These fadings have been closely studied in the literature in the longitudinal dimension (tunnel length). Nevertheless, they also occur in the cross section, where they have only been analyzed statistically and on a small scale. In this paper, we present the results from an extensive measuring campaign carried out at the Somport tunnel, in Spain. We have adopted the modal theory approach to analyze the large-scale fadings (also known as slow fadings) in the longitudinal, transversal, and vertical dimensions. More specifically, the modes’ geometry allowed for the adequate placement of transmitters to create different periodic fading structures and to virtually divide the tunnel cross section into sectors, where the fadings presented a phase shift of 180°. This study enabled the development of large-scale spatial diversity schemes and navigation techniques to improve communication and localization inside these scenarios. [ABSTRACT FROM AUTHOR]

We present the Bio-Matched Horn antenna: a novel 1.773 cm3 on-body antenna for very low-loss communication with wireless implants across the 1–9 GHz bandwidth. To achieve this unique performance, the Bio-Matched Horn is composed of water-filled holes used to mimic the frequency-dependent permittivity of the underlying tissue over its entire bandwidth. The horn shape further allows the proposed antenna to communicate efficiently through the biological tissue for both subcutaneous and deep-tissue wireless implants. Measurement results at 2.4 GHz are in good agreement with simulations and show a transmission loss of 8.01 dB to a 4 mm-deep implant and 19.21 dB to a 2 cm-deep implant. Compared to the previous designs, this is a remarkable improvement by 14.5 and 10.8 dB for subcutaneous and deep-tissue communication, respectively. In this paper, we discuss the operation principle and design of the Bio-Matched Horn, its performance for subcutaneous and deep-tissue implant telemetry, sensitivity to rotational and positional misalignments, and specific absorption rate performance. [ABSTRACT FROM AUTHOR]

In certain radar and wireless communication applications, omnidirectional circularly polarized (CP) antennas are desired but existing solutions have complex 3-D structures and are large in size. In this paper, a compact and low profile CP antenna having omnidirectional pattern on azimuthal plane is demonstrated. The CP waveform is synthesized by combining two linearly polarized and omnidirectional antennas with 90° phase difference on their terminals. The most challenging part of the design is the realization of the horizontally polarized antenna with omnidirectional radiation pattern. This antenna is designed using a novel two-faced slot antenna structure capable of emitting in-phase radiation of equal magnitude on both sides of the antenna. The two faces of the low-profile slot antenna are connected by a thin meander parallel plate waveguide to provide antiparallel field distributions over the two faces of the slot radiators. This special design removes radiation nulls on E-plane that exists on conventional slot antennas, the mechanism of which has been carefully discussed in this paper. The other antenna is a compatible pair of planar inverted-F antennas constructed on the sides of the finite-ground plane two-faced slot antenna for the provision of vertically polarized omnidirectional radiation. A feed network with power splitter and phase shifter is also accommodated on the compact CP antenna. The antenna is designed and fabricated, and its performance is measured against numerical simulations. It is shown that the fabricated antenna at 2.4 GHz can provide measured axial ratio of lower than 1.8 and gain variations of less than ±1.5 dB over all azimuth angles. [ABSTRACT FROM PUBLISHER]

The objective of this special issue is to publish papers related to the basic physics of Electromagnetism in thecontext of radio wave propagation, see editorial of Part I. [ABSTRACT FROM AUTHOR]

This paper summarizes the lessons learned using a physics-based macromodel in studying electromagnetic wave propagation over an imperfectly conducting ground in cellular wireless communication. First, it has been observed that the path loss exponent is independent of the nature of the ground parameters inside the cell of interest. Second, the electrical parameters of the environment have little effect on the path loss exponent in the cellular band. Third, it is observed that lowering the base station antenna toward the ground provides a stronger signal in the near field within the cell of interest. Furthermore, tilting the transmitting antenna toward the sky enhances the signal strength. Tilting the antenna toward the ground increases the signal strength but, in addition, enhances the interference pattern and, hence, is not a good solution. A typical path loss inside the cell is 30 dB per decade of distance, and outside the cell, it increases to 40 dB per decade. By bringing the antenna closer to the ground and then tilting it toward the sky, a good nonintuitive solution is provided. In such scenarios, a path loss of 20 dB per decade for some components of the field, the lowest possible, can be achieved for certain orientations and deployment of the base station antenna. In addition, it is shown that operating an antenna inside a metallic box eliminates its radiation capabilities and, hence, has no physical meaning even though it is claimed in the contemporary literature that it simulates a rich multipath environment. Finally, a note on the proper interpretation of the term channel capacity and its implications is delineated. [ABSTRACT FROM AUTHOR]

This paper presents a $2 \times 2$ multibeam array employing a novel wideband linearly polarized cavity-backed patch antenna for fifth-generation (5G) wireless communication technology. The antenna array comprises four layers stacked on top of one another. The proposed antenna element is composed of three substrate layers and excited using a substrate-integrated waveguide aperture-coupled feed. The antenna element exhibits −10 dB impedance bandwidth of 36.2% from 53 to 76.4 GHz with very flat gain and excellent radiation characteristics. A prototype is fabricated and tested. The compact 2-D scanning multibeam $2 \times 2$ antenna array is demonstrated at 60 GHz, where the proposed antenna element is utilized as a radiating element. By employing a novel compact beamforming network (BFN) in the design, the proposed array achieves a size reduction of more than 28% compared to an array fed with the conventional BFN, without degradation in the array performance. A wide bandwidth larger than 27% for $\vert \text{S}_{\mathbf {11}}\vert < -10$ dB and a peak gain of 12.4 dBi is achieved. The array shows a good symmetrical radiation pattern in the two perpendicular planes. Verified by prototype measurements, the proposed antenna element and multibeam array with features of a compact structure, low cost, wide bandwidth, and superior radiation performance would be practically attractive for 5G applications. [ABSTRACT FROM AUTHOR]

This paper addresses the question of how much information can be transmitted reliably over a wireless channel. It is shown that the limit of this mode of transmission is dictated by the amount of information that an electromagnetic field is capable of carrying. The methodology for the analysis of this problem is along the theory developed by Kolmogorov. This allows one to quantify the amount of information that can be transmitted by a wireless communication system taking into account the physical limitations governed by the laws of electromagnetism. Starting from the results related to the amount of information carried by an electromagnetic field, a novel antenna synthesis technique that simultaneously takes into account the requirements of information and antenna theory is introduced and applied to the synthesis of multiantenna systems. [ABSTRACT FROM AUTHOR]

This paper combines a study of human body morphology with physical layer characteristics to introduce a novel biometric identity feature for security in wearable communication applications. The physical layer characteristics of close fitting wearable devices are shown to vary in a unique manner through electromagnetic interactions between the tissue morphology and the antenna. Experimental measurement results demonstrate the new biometric concept using return loss characteristics to identify individuals on multiple body parts. An optimized directional coupler design is implemented with the antenna to optimize the characteristic feature detection range for human identification. Experiments conducted on human subjects using a prototype standalone test-bed and sensing circuitry at 2.45 GHz show that classification accuracies of over 98% are achieved for stationary subjects and 93% for mobile subjects. The new physical layer biometric has the potential to be used for authentication and authorization by using return loss as an indicator for secure user applications, using circuitry already implemented in wireless wearable communication systems. [ABSTRACT FROM AUTHOR]

This paper presents a planar omnidirectional multiple-input multiple-output (MIMO) antenna with pattern phase diversity. The profiles of conventional dual-polarized omnidirectional MIMO antennas are too high to be planar integrated due to the limited bandwidth of vertical-polarized element. Therefore, a dual-channel horizontal-polarized MIMO antenna is proposed for the planar integration of omnidirectional MIMO antenna. The antenna is formed with four-element folded dipole array, and a compact feed network with two sets of 90° progressive phases is employed to feed the two channels with shared elements, thus the antenna can be integrated into a sheet of substrate with an ultralow profile of 0.8 mm. Although the polarization and radiation pattern (amplitude) of the two colocated channels are the same with each other, a high isolation is still achieved as a result of the orthogonal pattern phase. A prototype was fabricated to validate the performance. The measured highest isolation between two channels is 31.7 dB, and −10 dB isolated bandwidth is 2.29–2.57 GHz (11.7%) with S11 < −14 dB and envelope correlation coefficient less than 0.05, which shows a good diversity performance. Therefore, the proposed dual-channel antenna gives a feasible solution for the planar integration of the omnidirectional MIMO system. [ABSTRACT FROM AUTHOR]

This paper describes the design and testing of a multiple-in multiple-out (MIMO) antenna for metal-frame smartwatch applications. The antenna operates from 2.4 to 2.49 GHz, which can cover Bluetooth/WiFi band. The design procedure is based on the theory of characteristic modes and it is discussed thoroughly. By employing a pair of degenerated modes to design the MIMO antenna, a high port-to-port isolation can be achieved over the operating frequency band. Simulated and measured results are presented to verify the antenna design. Furthermore, the antenna has a low envelope correlation coefficient and a high effective diversity gain even when it is mounted on the human phantom. Hence, the proposed antenna proves to be a good candidate for smartwatch applications. [ABSTRACT FROM AUTHOR]

This paper proposes a method to represent and predict received signal instantaneous polarization states as a function of arbitrary transmit polarization states for time-dispersive channels. The model incorporates frequency-dependent characterizations to represent the polarization dispersion behavior of a received signal across its bandwidth in a multipath channel. The representation takes advantage of signal dispersion features typical of depolarized signals, and employs subbanded characterizations to achieve polarization representations exhibiting high degrees of polarization in each subband. Experiments are conducted that demonstrate the utility of the modeling approach to predict polarization dispersion responses for arbitrary transmit polarizations based on measurements from two orthogonal transmit polarizations. [ABSTRACT FROM AUTHOR]

In this paper, multiband antennas based on a single ring slot are proposed for 4G/5G smartphone applications. The basic structure of the antenna is consisted of a large metal ground and an unbroken metal rim, in which a single 2 mm-wide ring slots is realized between the metal ground and rim. Here, a reconfigurable 4G antenna (820–960 and 1710–2690 MHz) is initially devised by loading multiple grounded stubs and a simple dc controlling circuit with varactor diode into the upper section of the ring slot. To further cover the sub-6 GHz spectrum (3400–3600 MHz) for future 5G communications, a four-element multi-input multi-output (MIMO) slot antennas configuration is designed by utilizing the lower section of the ring slot. A prototype antenna was fabricated, and good agreement is shown between the measured and simulated results. Due to the advantages such as multiband operation, MIMO configuration for 5G communications, high isolation, and compact structure, the proposed antenna design is attractive for 4G/5G smartphones. [ABSTRACT FROM AUTHOR]

In this paper, two different patch antenna geometries are proposed for wireless sensor applications involving electromagnetic propagation from inside the jet engine to our designed relaying antenna at the rim of the inlet. First, an enhanced modified version of our earlier proposed two-element circular patch antenna array is proposed. We follow with a fresh new design based on two-element array of hybrid rectangular circular patch antenna geometry. Both antenna designs are discussed in light of basic governing equations enabling initial design calculations, intuitions behind selecting the design elements based on desired propagation characteristics, simulation results, as well as fabrication and experimental measurements. Because of the environmental constraints, the proposed antennas need to be an extremely low profile and ultrathin. The proposed relaying antennas are designed to have a dual-beam pattern, one of which is directed toward the inside of the jet engine. The antennas are simulated using HFSS as well as fabricated and measured inside an anechoic chamber. Experimental results, which sufficiently agree well with the simulation results, demonstrate the achievement of the desired characteristics by fabricated antennas for deployment on jet engines. [ABSTRACT FROM AUTHOR]

A novel study on monitoring and analysis of the debilitating condition of patients suffering from the neurological disorder is presented. Parkinson’s disease is characterized by limited motor ability of a patient. Freezing of gait is a major nonmotor condition among aging patients and its evaluation can reduce the chances of any secondary disorders. In this paper, amplitude and phase information of the radio signals observed for a fixed period of time are used to differentiate the motor and nonmotor symptoms. The amplitude information is classified using a support vector machine, while the linear transformation is applied to obtain sanitized phase information for detection. The proposed method is very handy with the minimum deployment overhead. The analysis shows that this method also offers a high-accuracy level of around 99% based on the observation of a number of patients. These features make it an attractive solution for real-time patient monitoring systems. [ABSTRACT FROM AUTHOR]

Wide-angle coverage, fine angular resolution, and low-power consumption are the key characteristics of millimeter-wave short-range wireless systems, such as access points in fifth-generation cellular networks and automotive radars. In this paper, we present a 60 GHz switched-beam antenna system addressing all these requirements. It consists of two identical parallel-fed arrays of eight slots, each fed by a passive pillbox beamformer. A switch network comprising four single-pole-multiple-throw switches excites one of the two arrays at a time and selects the radiated beam. The whole system is fully integrated into a multilayer low-temperature cofired ceramic module. The antenna covers a scan range of about ±39° in one plane using 11 beams between 57 and 66 GHz. The proposed architecture enables the simultaneous achievement of continuous coverage (beam crossover levels of about −3 dB) and of low sidelobe levels. Dedicated numerical tools are used for a preliminary design of the antenna. The design procedure, the technological development, and the experimental results are discussed in detail. [ABSTRACT FROM AUTHOR]

This paper presents a physics-based macro model that can predict with a high degree of accuracy various experimental data available for the propagation path loss of radio waves in a cellular wireless environment. A theoretical macro model based on the classical Sommerfeld formulation can duplicate various experimental data including that of Okumuraet al.carried out in 1968. It is important to point out that there are also many statistical models but they do not conform to the results of the available experimental data. Specifically, there are separate path loss propagation models available in the literature for waves traveling in urban, suburban, rural environments, and the like. However, no such distinction is made in the results obtained from the theoretical analysis and measured experimental data. Based on the analysis using the macro model developed after Sommerfeld’s classic century-old analytical formulation, one can also explain the origin of slow fading which is due to the interference between the direct wave from the base station antenna and the ground wave emanating from the reflections of the direct wave and occurs only in the near field of the transmitting antenna. The so-called height gain occurs in the far field of a base station antenna deployment which falls generally outside the cell of interest, while in the near field, within the cell, there is a height loss of the field strength for observation points near the ground. A physical realization of the propagation mechanism is illustrated through Vander Pol’s exact transformation of the Sommerfeld integrals for the potential to a spatial semiinfinite volume integral and thus illustrates why buildings, trees, and the like have little effects on the propagation mechanism. [ABSTRACT FROM AUTHOR]

Complex scattering targets are often made by structures constituted of wedges that may interact at near field. In this paper, we examine the scattering of a plane electromagnetic wave by two separated arbitrarily oriented perfectly electrically conducting wedges with parallel axes. The procedure to obtain the solution is based on the recently developed semianalytical method known as generalized Wiener–Hopf technique that allows a comprehensive mathematical model of the problem in the spectral domain avoiding multiple steps of interaction among separated objects. The numerical results are presented to validate the procedure in terms of spectral quantities, GTD/uniform theory of diffraction coefficients and total far fields for engineering applications. The structure is of interest in electromagnetic applications, in particular, to accurately predict path loss in propagation with diffraction phenomena. [ABSTRACT FROM AUTHOR]

Wireless communications are expected to take place in increasingly complicated scenarios, such as dense urban, forest, tunnel, and other cluttered environments. A key emerging challenge is to understand the physics and characteristics of wave propagation in these environments, which is critical for the analysis, design, and application of advanced mobile and wireless communication systems. In this paper, we present a full-wave field-based computational methodology for radio wave propagation in complex urban environments. Both transmitting/receiving antennas and propagation environments are modeled by first-principles calculations. A system-level, large scene analysis is enabled by the scalable, ultraparallel algorithms on the emerging high-performance computing platforms. The proposed computational framework is verified and validated with semianalytical models and representative measurements. [ABSTRACT FROM AUTHOR]

This paper describes and evaluates a new test facility able to generate different wireless multipath radiocommunication channels. It is used to recreate various electromagnetic (EM) environments, such as those inside vehicles. This test facility, in the form of a moderate volume metallic chamber, contains apertures, left opened or obstructed as required, and a variable quantity of salt water. Both are used to adjust the EM losses and to control smoothly and accurately the delay spread of the communication channel inside the test facility. A frequency range between 2 and 3 GHz is studied. As a first step, the root-mean-square (rms) delay spread is measured inside a vehicle for several locations of the receiving antenna and for different scenarios including different line-of-sight and non-line-of-sight paths. Then, the test facility is introduced, dimensioned, and evaluated, trying to reproduce the rms delay spread of each previous in-vehicle radiocommunication configuration. A comparison between the measurement data performed both in the vehicle and in the configured test facility is presented. This comparison shows a good agreement between these two sets of measurements. It demonstrates that different static wireless in-vehicle multipath channels, corresponding to various transmitting and receiving antenna configurations, can be reproduced inside the proposed prototype test facility. [ABSTRACT FROM AUTHOR]

Crossed-dipole (CD) antennas have been widely employed for dual polarization in wireless communication systems in recent years. In this paper, a novel design concept of dual-polarized shared-dipole (DPSD) antenna is presented. Different from the traditional CD antennas, the arms of the DPSD antenna are shared for two orthogonal polarizations. This design technique leads to significant size reduction and high isolation compared to the traditional CD antennas. The operation principle of the proposed antenna is theoretically analyzed. To validate the presented design concept, two novel DPSD antennas are designed, fabricated, and measured. The first design is a four-port DPSD antenna, which is a straightforward demonstration of the operation principle of the DPSD antenna. The second design is a highly integrated DPSD antenna, which avoids the use of a feed network and provides a simple configuration to design the dual-polarized antenna. Both of the DPSD antennas are designed to operate at 1.7–2.7 GHz for base station applications. The simulated and measured results confirm that the two DPSD antennas have wide bandwidth with VSWR < 1.5 and isolation > 35 dB dB. In addition, stable gain and half-power beamwidth are obtained with the variance less than ±0.55 dB and ±3.5°, respectively. [ABSTRACT FROM AUTHOR]

A circular patch antenna loading symmetrically with some conductive shorting vias can radiate monopolelike pattern in its fundamental mode as well as the higher order modes. As a result, this antenna can be considered as a candidate to replace the conventional large profile monopole antenna in many communication systems. However, no comprehensive analytical study has been presented for it. In this paper, an analytical method based on cavity model and the generalized multipole technique is intended to investigate the antenna. A sample of the antenna is designed and analyzed using the proposed theory. The electromagnetic fields, radiation pattern, input impedance, and return loss of the antenna are analytically expressed. The designed antenna is implemented and measured. The measurement results are compared with the analytical results to justify the analysis. [ABSTRACT FROM AUTHOR]

This paper presents a low-profile coplanar dual-polarized dual-band base station antenna array. A slotted patch antenna operating from 0.82 to 0.99 GHz with four shorting strips is proposed and analyzed. The four shorting strips are employed not only to improve the impedance matching in the lower band but also to remove the center part of the patch, thus making room for higher band dipoles operating from 1.68 to 2.86 GHz. The height of the proposed array is nearly half of the conventional base station array while other performances are guaranteed. The measured results show that the proposed antenna array has wide impedance bandwidths of 18.7% (0.82–0.99 GHz) and 57.9% (1.68–2.86 GHz) (VSWR < 2) with a low profile ($0.109\lambda _{0}$ at 820 MHz). The measured gains are 13.8±0.5 dB and 16.7 ± 1 dB in lower and upper bands. Large front-to-back ratio (>24.6 dB) and high isolations (>30 and >25 dB in lower and upper bands, respectively) are achieved. The proposed antenna can be easily built with printed circuit board fabrication technique and applied in low profile multiband base stations for 2G/3G/4G and the next-generation systems. [ABSTRACT FROM AUTHOR]

In this paper, low-profile broadband planar folded transmitarray antennas (FTAs) are proposed and studied based on a novel Fabry–Perot polarizer. A novel element is proposed to carry out high-efficiency transmission, the phase compensation and the 90° polarization rotation at the same time. The element consists of two identical dielectric slabs, sandwiched by three metal layers, and has a thickness of only about $0.1\lambda $. To verify this element, a transmitarray antenna is first designed and its highly efficient radiation performance is demonstrated by both simulations and the experiments. Low-profile FTAs are then designed and studied. The results show that the advantages of broad bandwidth, high gain, lower profile, planar geometry, and ease of integration can be achieved. The experiments of the FTA antenna demonstrate a 3 dB gain bandwidths of 18% and a peak gain of 25.2 dBi. [ABSTRACT FROM AUTHOR]

This paper presents a broadband dual-polarized filtering dipole antenna for base-station application, which has a compact size of 50 $\text {mm} \times 50\,\,\text {mm} \times 31.8$ mm. The antenna consists of four parts: main radiator, feeding baluns, reflector, and two parasitic loops. Without using complex filtering circuits, the dual-polarized dipole antenna realizes satisfactory filtering performance and enhanced bandwidth by employing only two parasitic loops. Two specific radiation nulls are thus generated and individually controlled by the two parasitic loops. To further improve the upper stopband selectivity and bandwidth, a simple open-ended stub is added to the arms of the dipole. As a result, the bandwidth can be tuned from 7.4% to 47.6%, and the realized gain is decreased dramatically from 8.6 dBi at 2.7 GHz (in-band) to −10 dBi at 2.9 GHz (out-of-band). For demonstration, a broadband dual-polarized dipole antenna is implemented. Measured results show that the proposed antenna has more than 34 dB port isolation over 48.7% (1.66–2.73 GHz) impendence bandwidth (VSWR < 1.5). The measured in-band gain is about 8.15 dBi with stable 3 dB beamwidth 65.4°±2.4° in the horizontal plane, whereas the out-of-band radiation suppression is more than 17 dB. [ABSTRACT FROM AUTHOR]

Electrically small antennas (ESAs) can be passively matched only over very narrow bandwidths and the resulting antennas have low gains. These are the major limiting factors for ESAs used in transmit applications, especially at high-frequency (HF) and lower Very HF frequency bands. This paper discusses the challenges of transmit ESA matching circuit design and the design process of a new non-Foster transmit matching architecture for electrically small monopole antennas that achieves wide bandwidth, high transmission efficiency (transducer power gain), and stability at the same time. The proposed circuit is composed of a current buffer (for high isolation), a transformer (for real-part matching), and a negative impedance converter (for imaginary-part matching). The measured −6 dB (−10 dB) $|S_{11}|$ fractional bandwidth of the proposed non-Foster transmitting system is 110% (39%), while the maximum bandwidth that can be achieved is 0.076% (0.047%) when matched with the conventional passive matching. The transmission efficiency of the system is improved by as much as 34.4 dB compared to the same antenna without the proposed non-Foster matching circuit, and it retains an enhanced efficiency over the entire frequency band of operation (26–89 MHz). The system remains stable within this frequency band. The measurement results of the compact and broadband transmitting antenna prototype verify the design concept. [ABSTRACT FROM AUTHOR]

In this paper, the use of a dispersive prism with a triangular shape is proposed to reduce the dispersive radiation nature of a leaky-wave antenna (LWA) in groove-gap waveguide technology. The operation of gap waveguide technology is based on the use of metallic pins that act as an artificial magnetic conductor, so the electromagnetic fields are confined and guided in the desired directions. To control a leaky-wave radiation of these confined fields is possible by tailoring the height of the pins, its periodicity, and the waveguide width. This radiation, as in any conventional LWA, is dispersive, leading to beam squint as the frequency is varied. Here, we mitigate this beam squint by using a prism made of dispersive pins and choosing appropriately their periodicity and height. With this prism, the leaky-wave radiation is focused into one single direction in a wide frequency band. This concept is demonstrated with a prototype designed to radiate at $\varphi =41^\circ $ with a central frequency of 12 GHz and the high gain of 16.5 dBi. A 22% frequency bandwidth for the 3 dB realized gain at $\varphi =41^\circ $ is achieved, and the main radiating direction, with half-power beamwidth of 5°, steers only ±0.5° from 11.4 to 13.4 GHz. [ABSTRACT FROM AUTHOR]

This paper presents the design of dual-port subarray modularization integrating a three-port circulator, realized by using substrate integrated waveguide (SIW) technology, and a subarray of antenna elements for dual uplink and downlink beamforming. In particular, a $2\times2$ element module is implemented and fabricated on a standard printed circuit board substrate to demonstrate its radiation characteristics and operational mechanism. In this design, the SIW structure is used to reduce the radiation from microstrip lines at millimeter-wave frequencies and avoid contaminating the radiation patterns of subarrays. Greater than 5 dBi suppression has been achieved for good compatibility with the integration of radio frequency devices. The measured results show that the subarray modularization improves the insertion loss and results in an excellent isolation for independent transmitting and receiving beamforming network implementation. Numerical and experimental results are shown to verify the performance of these designs. [ABSTRACT FROM AUTHOR]

This paper presents a dual-polarized conformal loop antenna for capsule endoscopy systems. The antenna is designed on the capsule shell, with two orthogonal counterparts to generate dual-polarized radiation. This design exhibits broad impedance bandwidths of 271 and 247 MHz for each port, covering the entire Medical Device Radiocommunications Service band as well as the 433.05–434.79 MHz Industrial Scientific Medical band. Due to the highly orthogonal current distributions of the proposed structure, an isolation of higher than 33 dB is achieved among the operating frequency bands in measurement. The dual-polarized antenna also shows an omnidirectional radiation property and a low cross-polarization level of around −40 dB, which helps to enhance communication quality, regardless of position and orientation. Whether other electronics and biocompatible coatings are included or an electromagnetic interference shielding is considered, the antenna still presents a robust performance. The cubic tissue phantom model is utilized for the initial design and optimization of the antenna structure. Moreover, the CST voxel human model is applied to study the conformal antenna in a realistic environment. Measurements are implemented using a solid tissue-mimicking phantom, and performances consistent with theoretical predictions are achieved. Finally, the wireless biotelemetry property is evaluated via the calculation of the communication link budget with an external antenna. [ABSTRACT FROM AUTHOR]

In this paper, a novel wideband and low-profile discrete dielectric lens (DDL) antenna is presented. The proposed unit cells of DDL with the square-pyramid structure can realize wideband antireflection at an air–dielectric interface. By increasing the phase compensation range, the DDL antenna with very large gain bandwidth but large DDL thickness would be achieved. Furthermore, based on the large gain bandwidth technology, a novel multifolded lens structure is proposed to realize the low-profile design, in which a broadband polarization rotation reflection surface is proposed, while a polarized grid is used appropriately. Finally, the proposed multifolded DDL antenna can achieve a very large gain bandwidth, while the thicknesses of the DDL unit cell and the total antenna can be greatly reduced. For demonstration, the proposed multifolded DDL antenna is fabricated and measured. The fabrication was implemented by using a simple and low-cost 3-D printing technology. The results show that the proposed lens antenna can realize a 1 dB gain drop bandwidth of 43%, thickness of less than 1/3 focal-length-to-diameter ratio, and maximum aperture efficiency of 32%. Good agreement can be observed between the measurement and simulation. [ABSTRACT FROM AUTHOR]

Radiated testing of massive multiple-input-multiple-output devices in fading radio-channel conditions is expected to be essential in the development of the fifth-generation (5G) base stations and user equipment (UE) operating at or close to the millimeter-wave (mm-wave) frequencies. In this paper, we present a setup upgrading the multiprobe anechoic chamber-based system designed originally for 4G UE. We describe methods for mapping radio-channel models onto the probe configuration and discuss the differences to the former 4G case. We also propose metrics to assess the accuracy of the test setup and find key design parameters by simulations. The results with the utilized channel models indicate that at 28 GHz, up to $16 \times 16$ planar arrays can be tested with a range length of 1 m and with at minimum eight active dual polarized probes. [ABSTRACT FROM AUTHOR]

In this paper, a novel decoupling method without adding any decoupling structure is investigated, and it is able to apply to multiple-input and multiple-output (MIMO) antenna designs with dual and multiple elements. The decoupling mechanism applied in here is to change the electrical length of the radiators to manipulate the radiation pattern for obtaining pattern diversity and good isolation simultaneously. The design mechanism and procedures for realizing pattern diversity are presented. To validate the proposed method, a two-element monopole antenna array with inverted-L elements is initially studied with the isolation better than 20 dB. Next, a four-element MIMO antenna utilizing two different types of monopole elements is proposed to further verify the feasibility of the proposed decoupling method. Finally, an eight-element MIMO antenna operating at 3.5 GHz is implemented with a compact total size of $40\times 100$ mm2, and the measured isolations between two elements are better than 15 dB. Envelope correlation coefficient and channel capacity are calculated to evaluate the MIMO performance, and good results are obtained. The target application of the proposed design is for laptop, small cell base station, or WiFi box with multiple elements. [ABSTRACT FROM AUTHOR]

This paper presents the details and results of double-directional propagation measurements carried out in two indoor office environments: a semi-open, cubicle-type office space and a more traditional work environment with closed offices. The measurements cover seven frequency bands from 2.4 to 61 GHz, permitting the propagation characteristics to be compared over a wide range of candidate radio frequencies for next-generation mobile wireless systems, including ultra high frequency and millimeter-wave bands. A novel processing algorithm is introduced for the expansion of multiband measurement data into sets of discrete multipath components. Based on the resulting multipath parameter estimates, models are presented for frequency-dependent path loss, shadow fading, copolarization ratio, delay spread, and angular spreads, along with their interfrequency correlations. Our results indicate a remarkably strong consistency in multipath structure over the entire frequency range considered. [ABSTRACT FROM AUTHOR]

Multipolarized antenna systems are able to reduce equipment size while maintaining low interantenna correlation and are thus attractive for mobile-to-mobile (M2M) wireless communications. In this paper, a polarized multiple-input multiple-output (MIMO) channel model is proposed by using a geometrical theory based on a two-cylinder M2M reference model. A geometrical approach is used to model channel depolarization, where the MIMO signal contributions of the scatterers are determined from a greatly simplified ray-tracing method. The modeling method provides a mechanism for computing MIMO-polarized channel impulse responses analytically, and the cross-polarization discrimination (XPD) and MIMO time–frequency function are further derived. The proposed model shows good agreement with measurements and simulation results from the literature and provides insights on the MIMO channel depolarization behavior. In addition, numerical simulations with appropriate modeling parameters are conducted. The XPD is shown to depend on the distribution of scatterers and MIMO subchannel index. Moreover, the co-polar channel is shown to have a higher time–frequency correlation than the cross-polar channel. This should be carefully considered in a multipolarized antenna system design. [ABSTRACT FROM AUTHOR]

Conventional wireless power transfer systems consist of a microwave power generator and a microwave power receiver separated by some distance. To realize efficient power transfer, the system is typically brought to resonance, and the coupled-antenna mode is optimized to reduce radiation into the surrounding space. In this scheme, any modification of the receiver position or its electromagnetic properties results in the necessity of dynamically tuning the whole system to restore the resonant matching condition. It implies poor robustness to the receiver location and load impedance, as well as additional energy consumption in the control network. In this paper, we introduce a new paradigm for wireless power delivery based on which the whole system, including transmitter and receiver and the space in between, forms a unified microwave power generator. In our proposed scenario, the load itself becomes a part of the generator. Microwave oscillations are created directly at the receiver location, eliminating the need for dynamical tuning of the system within the range of the self-oscillation regime. As a proof-of-concept demonstration, we experimentally show that, such self-oscillating wireless power delivery systems can provide robust operation against changes in the environment or in the location of the load. The proposed concept has relevant connections with the recent interest in parity-time symmetric systems, in which balanced loss and gain distributions enable unusual electromagnetic responses. [ABSTRACT FROM AUTHOR]

Magnetic induction (MI) communication technique has shown great potentials in complex and RF-challenging environments, such as underground and underwater, due to its advantage over EM wave-based techniques in penetrating lossy medium. However, the transmission distance of MI techniques is limited since magnetic field attenuates very fast in the near field. To this end, this paper proposes metamaterial-enhanced magnetic induction (\textM^2\textI) communication mechanism, where an MI coil antenna is enclosed by a metamaterial shell that can enhance the magnetic fields around the MI transceivers. As a result, the \textM^2\textI communication system can achieve tens of meters communication range by using pocket-sized antennas. In this paper, an analytical channel model is developed to explore the fundamentals of the \textM^2\textI mechanism, in the aspects of communication range and channel capacity, and the susceptibility to various hostile and complex environments. The theoretical model is validated through the finite element simulation software, Comsol Multiphysics. Proof-of-concept experiments are also conducted to validate the feasibility of \textM^2\textI. [ABSTRACT FROM PUBLISHER]

The objective of this presentation is to illustrate the accuracy of the Schelkunoff formulation over the Sommerfeld solution for a vertical electric dipole radiating over an imperfect ground. In an earlier paper, the alternate form of the Sommerfeld Green's function developed by Schelkunoff was presented (Schelkunoff, 1943 and Dyab, 2013). Here we demonstrate the application of this new methodology for two classes of problems. First, the problem of predicting the propagation path loss in a wireless communication environment is illustrated. The second application problem described in this paper deals with the verification of experimental data related to propagation over an Aluminum sheet at THz frequencies. It is seen that the main contribution of the reflected field is due to a specular image point as expected for a metal and the presence of surface waves in the total reflected field is absent, even though the permittivity of the metal is negative at these frequencies. Both theoretical predictions and experimental data demonstrate that there is little contribution to the reflected field due to a surface wave. Also, a clear definition is made to characterize surface waves as there is confusion as to what a surface wave really is. [ABSTRACT FROM PUBLISHER]

While conventional antenna array synthesis determines the beamforming weights that create a specified antenna radiation pattern, secure array synthesis formulates the beamforming weights that enhance security for wireless transmission of sensitive data. This paper focuses on creating beamformers that improve the generation of secret encryption keys based on bidirectional estimation of the reciprocal electromagnetic propagation channel between two radios. The technique uses semidefinite programming to determine the array weights that maximize the average secure key rate under a constraint on the total transmit power. The numerical implementation of the technique incorporates array mutual coupling, and the results demonstrate that the technique outperforms a conventional beamforming solution, with the improvement becoming significant for certain channel correlation conditions. [ABSTRACT FROM AUTHOR]

Combining a reflectarray and a transmitarray together, a novel array antenna with bidirectional high-gain beams is proposed in this paper. A novel single-layer metal-only defected square-ring slot element, which has a near-zero thickness, is introduced as the phasing element. Full 360° phase shift range is achieved by utilizing the cross-polarized field of the phasing element. As a bidirectional high-gain antenna (bi-HGA), a transmit-reflect-array using the proposed elements is then designed, fabricated, and measured. It is only composed of a thin metallic sheet with 420 mm side length, spatially fed by a corrugated horn. Well-defined pencil beams are formed in broadside directions on both sides. The measured gains of the transmitted and reflected beams at 10 GHz are 25.5 dBi with 15% 1 dB gain bandwidth and 25 dBi with 14% 1 dB gain bandwidth, respectively. The proposed bi-HGA exhibits distinctive advantages of being ultrathin $(0.0067\lambda _{0})$ , lightweight, and low cost without using dielectric substrates, and is a promising candidate for bidirectional wireless communication applications. [ABSTRACT FROM AUTHOR]

This paper presents a low-profile planar dipole antenna with omnidirectional radiation pattern and filtering response. The proposed antenna consists of a microstrip-to-slotline transition structure as the feeding network and a planar dipole as the radiator. Filtering response is obtained by adding nonradiative elements, including a coupled U-shaped microstrip line and two I-shaped slots, to the feeding network. Within the operating passband, the added nonradiative elements do not work, and thus the in-band radiation performance of the dipole antenna is nearly not affected. However, at the side stopbands, the added elements resonate and prevent the signal passing through the feeding network to the dipole antenna, suppressing the out-of-band radiation significantly. As a result, both satisfactory filtering and radiation performances are obtained. For demonstration, an omnidirectional filtering dipole antenna is implemented. Single-band bandpass filtering responses in both the reflection coefficient and realized gain are obtained. The measured in-band gain is ~2.5 dBi, whereas the out-of-band radiation suppression is more than 15 dB. [ABSTRACT FROM PUBLISHER]

The coexistence of microwave and millimeter-wave technologies becomes the inexorable trend of future wireless communication systems. The corresponding components of the system are required to cover these two frequency bands simultaneously. However, it is difficult for the existing dual-band antenna configurations to achieve a frequency ratio larger than 3. In this paper, a novel topology is proposed to solve this problem. For the desired dual-band operation, a signal routing approach is proposed to guide the microwave/millimeter signals to the specific elements, respectively. The classical aperture coupling mechanism is deliberately utilized to block the millimeter-wave signal from feeding to the microwave antenna element and route the millimeter-wave signal into the millimeter-wave antenna element. Meanwhile, the substrate- integrated waveguide (SIW)-based millimeter-wave antenna element has the high-pass nature to reject the microwave signal. Therefore, the antenna elements for microwave and millimeter-wave bands can be designed separately with a high flexibility. First, a dual-band antenna was implemented to support 5.8 and 30 GHz simultaneously by integrating an annular-ring antenna element and an SIW slot antenna element. Furthermore, different radiation properties at the two bands can be easily realized owing to the high flexibility of the proposed approach. For validation, these two antennas were fabricated and measured. [ABSTRACT FROM PUBLISHER]