Search

An intelligent antenna synthesis method is proposed to automatically select suitable antenna type and provide optimal geometric parameters according to the requirement of antenna performance. The performance characteristics of different antennas are analyzed, and a smart antenna selection model is established to recommend the appropriate antenna by using support vector machine (SVM). Then, the stacking ensemble model is built by combining five primary learners to give full play to the advantages of each type of learners and, finally, the geometric parameters of the antenna are provided. Microstrip patch antenna, spiral antenna, and horn antenna are used to demonstrate the accuracy and efficiency of the model. The system shows a great ability of antenna classification with accuracy over 99% and parameter prediction with a mean absolute percentage error (MAPE) of less than 6%. Moreover, the results are compared with the traditional data-driven model, and the key parameters of the model are comprehensively discussed. The proposed method could be widely used in intelligent antenna design in practice. [ABSTRACT FROM AUTHOR]

This communication presents a concept of a sub-6 GHz antenna-on-display (AoD) that can eventually be integrated into the transparent area of a display panel of various wireless devices for the first time in the literature. The transparency of the proposed microwave AoD is realized using metal mesh conductive film and features optical transparency, which is compatible with high-resolution liquid crystal display (LCD)/organic light-emitting diode (OLED) display panel requirements. To maximize the radiation efficiency despite the extremely thin substrate ($0.0048\lambda _{0}$), a traveling-wave antenna topology is inspired and further modified to incorporate the inherent structural limitations of modern-day high-resolution display panels. Eventually designed to operate in a leaky-wave mode, a novella dedicated feeding mechanism is introduced to minimize undesired coupling between the antenna structure and the display panel. The composite right-/left-handed (CRLH) unit cell employs a single shunt inductor topology to maximize the radiation efficiency. The measured 6 dB impedance bandwidth of the proposed microwave AoD is from 2.36 to 6.17 GHz, which is consistent with the fast wave region of the proposed unit cell. The measured realized gain of the microwave AoD consisting of 13 unit cells is 2.68 dBi at 5.5 GHz with a radiation efficiency of 62.5%. This is the first demonstration to ascertain that an AoD topology can be applicable at microwave applications while reducing the antenna-to-ground distance by approximately a factor of 20 compared to previous studies. [ABSTRACT FROM AUTHOR]

In this article, we propose using new machine learning (ML)-based optimization methods as an alternative to traditional optimization methods, for complex antenna designs. This is an efficient methodology to tackle computational challenges, as it is capable of handling a large number of design parameters and is more efficient as well as informative. The proposed technique is applied for modeling the gain performance in the principal plane of a monopole antenna when its radiation properties are modified by placing spatially dependent dielectric material around it. Using the proposed methodology, the dielectric constant values are mapped to the gain pattern of the design. We use two ML techniques for this purpose, namely Gaussian process (GP) regression and artificial neural network (ANN). Once each of these models is obtained, they are further used for estimating the dielectric constant values that can suggest optimal directions to modify gain patterns for single-beam and multiple-beam patterns rather than the conventional omnidirectional pattern of a monopole antenna. The performance of this technique is compared with heuristic optimization techniques, such as genetic algorithms (GAs). The proposed method proves to be quite accurate in spite of being a high-dimensional nonlinear problem. A prototype of a monopole design with three-beam gain pattern is fabricated and tested. The measurement results agree well with the simulation results. The proposed methodology can provide useful and scalable optimization tools for computationally intensive antenna design problems. [ABSTRACT FROM AUTHOR]

In this communication, two composite right-/left-handed transmission line (CRLH-TL)-based reconfigurable antennas with multiple-parameter reconfiguration capability have been presented. In antenna I, the polarization is switched between circular polarization and linear polarization. In antenna II, a split-ring resonator (SRR) is introduced that is connected with the ground through another p-i-n diode D2. In the D2 OFF-state, the metamaterial behavior of the SRR establishes. Due to negative permeability at the frequency of operation, it produces magnetic coupling with the antenna and the antenna starts radiating at a new band (5.2 GHz), forming dual-band characteristics with circular polarization. Antenna II is capable of providing band/frequency and polarization/band, frequency, and polarization reconfiguration using different ON/OFF combination states of diodes D1 and D2. The antennas are suitable for 2.4/5.2 GHz WLAN and 3.5/3.6 GHz WiMAX applications. [ABSTRACT FROM AUTHOR]

A dual-circular polarization (CP) textile antenna is investigated for wearable applications at 3.5 GHz WiMAX and 5.8 GHz industrial, scientific, and medical bands. The proposed antenna is composed of a dual-band monopole antenna and a polarization rotation artificial magnetic conductor (PRAMC). Through the PRAMC, the dual-CP radiation is enabled and the backward radiation is alleviated, in which the left-handed CP is generated in the lower band and the right-handed CP is realized in the upper band. Notably, dyadic reflection coefficient analysis is employed to understand the operating mechanism. Both monopole and PRAMC are printed on textile substrate, achieving conformability and comfortability. In addition, numerical results indicate that the performance of the antenna is robust to lossy human body and structural deformations. For verification, the prototype of the antenna was fabricated by two types of manufacturing process (i.e., laser cutting and screen printing), and the advantages and drawbacks of each fabricating approach are discussed for referring. The antenna made by laser cutting was tested on the phantom with the −10 dB impedance bandwidths of 11.7% and 9.1%, the 3 dB axial ratio bandwidths of 2.0% and 8.2%, and the peak gains of 6.6 and 7.2 dBic, in dual bands, respectively. [ABSTRACT FROM AUTHOR]

In this study, a novel single-fed low-profile circularly polarized (CP) antenna with a bandpass filtering response is proposed. It is based on a planar substrate integrated waveguide (SIW) dual-mode (TE102/TE201) cavity. When the vias on the edge become sparse, the electromagnetic wave leaks out while maintaining a good dual-mode filtering response. The antenna is folded in order to reduce the aperture size to form an un-splitted radiation beam with small side lobes. Owing to a rotated dual-mode operation, the fields escaping from four sets of sparse vias are approximately of equal amplitude with a progressive phase difference of 90° in sequence. CP radiation is thus achieved when the four orthogonal half-mode radiation patches are excited by the leaking field. By adopting a single feeding with two pairs of asymmetrical shorting pins, the peak gain is improved significantly and a 3 dB axial ratio (AR) response with two minima is obtained simultaneously. Long metal walls and rectangular slots are introduced to fold the current flow and change the wave direction. Consequently, sidelobe level is significantly reduced and the antenna directivity is enhanced. To verify this novel design idea, an antenna prototype with a height of 0.036 λ0 has been fabricated using the multilayer PCB process and measured in a near-field microwave chamber. Measured results are well consistent with the simulation, demonstrating CP radiation with a flat/high gain and good filtering performance. [ABSTRACT FROM AUTHOR]

Compact high-gain wideband antenna systems for through-the-wall imaging and wireless communications, featuring 160% fractional bandwidth, are presented. Each radiating system, consisting of two orthogonal Vivaldi antennas forming a cross-shaped configuration so as to excite linear (horizontal/vertical) and circular polarization (CP), is equipped with a top-mount spherical–axicon dielectric lens. The optimized shaping of the lens and of the outer edge Vivaldi arms allow achieving gain levels exceeding 15 dBi with good front-to-back-ratio. The proposed antenna features a broadside gain diagram with stable radiation pattern and wideband impedance matching in the frequency range between 650 MHz and 6 GHz. CST Microwave Studio, implementing a full-wave locally conformal finite integration technique (FIT), was employed to design and characterize the antenna and to guide its physical realization. Two-port equivalent circuits were developed to characterize parasitic coupling effects between the Vivaldi antennas ports, while a full-wave analysis allowed characterizing their frequency- and time-domain behaviors. The numerical results concerning the antennas parameters, illustrating the suitability of the proposed antennas to support narrow and ultra-wideband signal waveforms, are found to be in good agreement with the experimental measurements performed on an antenna prototype. [ABSTRACT FROM AUTHOR]

A wideband high-power dual-branch helical reflectarray antenna (RAA) is presented. The reflecting element consists of two metal helical branches, and the variable rotation angles enable full 360° phase adjustment. An X-band RAA prototype with $9 \times 9$ rectangular grid is simulated and measured. Full-wave simulations show that the maximum gain of 23.7 dB is achieved with the beam focused at ($\theta = 20{{^{\circ }}}$ , $\varphi = 0{{^{\circ }}}$) direction at center frequency of 9.3 GHz and the 1 dB gain bandwidth is over 24.2%. The measured reflection coefficient is lower than −16.3 dB in the whole band. From 8.4 to 10.8 GHz, the tested axial ratio is less than 2.3 dB. At center frequency, the tested gain is 23.4 dB and the corresponding aperture efficiency is 50.6%. The beam-scanning performance of the RAA is tested within 30° angular in two orthogonal planes with the scan loss of less than 1.5 dB and the axial ratios of lower than 1.4 dB. Taking the flat-topped beam as an example, the beam-forming capability of the RAA is verified. The measured results demonstrate the feasibility of the proposed design. The simulated results show that the power-handling capacity of the RAA is about 358 MW under vacuum condition. [ABSTRACT FROM AUTHOR]

The issue of asset tracking in dense environments where the performance of the global positioning system (GPS) becomes unavailable or unreliable is addressed. The proposed solution uses a low-profile array of antenna elements (sensors) mounted on a finite conducting ground. A compact-size sensor array of six electrically small dual-band omnidirectional spiral antenna elements was designed as a front end of a tracker to operate in the 402 and 837 MHz spectrum bands. For the lower band, a three-element superposition method is applied to support estimation of the angle of arrival (AOA), whereas all six sensors are employed for the higher band. A low complexity and accurate AOA determination algorithm is proposed, the projection vector (PV), and this is combined with the array mentioned. Orthogonal frequency division multiplexing (OFDM) is integrated with the PV technique to increase the estimation resolution. The system was found to be suitable for installation on the roof of vehicles to localize the position of assets. The proposed system was tested for the tracking of nonstationary sources, and then two scenarios were investigated using propagation modeling software: outdoor to outdoor and outdoor to indoor. The results confirm that the proposed tracking system works efficiently with a single snapshot. [ABSTRACT FROM AUTHOR]

A concurrently dual-polarized, simultaneous transmit and receive (STAR) antenna system with high transmit (TX)-receive (RX) isolation is presented. The STAR antenna consists of four dual-polarized patches, two for TX and two for RX. The radiators are fed using a network consisting of four 90° hybrids and four 180° hybrids. The input ports of the feed network constitute the inputs/outputs of the STAR antenna system. The system supports concurrent transmission and reception of waves with both right- and left-hand circular polarization. Due to the phase cancellation and geometrical symmetry of the antenna, the TX/RX coupling between ports with the same polarization is canceled using the feed network. In addition, four right-angle slots are inserted in the ground plane and a cross-shaped, high-impedance surface is inserted between the radiating patches to further suppress the coupling between the differently polarized TX and RX ports. Simulation and measurement results of a fabricated prototype show good agreement and demonstrate TX/RX isolation levels greater than 38 dB for all polarization combinations over a 6.5% bandwidth (6.0–6.4 GHz). Moreover, the fabricated prototype provides broadside axial ratios below 2.5 dB and realized gains above 7.8 dBic for all TX and RX modes, demonstrating good, concurrent-dual-polarization performance. [ABSTRACT FROM AUTHOR]

A simple conformal ultrawideband (UWB) antenna with monopole-like radiation patterns is proposed in this communication. To achieve the wide bandwidth, two rings are arranged concentrically around the main annular-ring circular patch antenna, in which two rectangular slots are added. The antenna has monopole-like radiation patterns generated by combining four propagation modes of TM01, TM02, TM03, and TM04 throughout the operating bands. To enhance the flexibility and robustness, the proposed antenna is fabricated using conductive fabric embedded into polydimethylsiloxane (PDMS) polymer. To our knowledge, this is the first flexible UWB antenna with monopole-like radiation patterns reported in the open literature. The measured results show that the antenna achieves a 10 dB return loss bandwidth from 2.85 to 8.6 GHz. Monopole-like radiation patterns are maintained throughout the frequency band, agreeing well with simulated results. This has been validated through the measured mean realized gain (MRG) pattern from 2.85 to 8.6 GHz. The fabricated antenna was bent and tested at various curvatures to verify its conformability. To evaluate suitability for UWB communications, the system-fidelity factors of the antenna are investigated using full-wave analysis in CST Microwave Studio, in both flat and bent conditions, validating its potential for UWB pulse transmission. [ABSTRACT FROM AUTHOR]

This article presents a novel dual-polarized millimeter-wave (mm-Wave) patch antenna with bandpass filtering response. The proposed antenna consists of a differential-fed cross-shaped driven patch and four stacked parasitic patches. The combination of the stacked patches and the driven patch can be equivalent to a bandstop filtering circuit for generating a radiation null at the upper band edge. Besides, four additional shorted patches are added beside the cross-shaped driven patch to introduce another radiation null at the lower band edge. Moreover, by embedding a cross-shaped strip between these four stacked patches, the third radiation null is generated to further suppress the upper stopband. As a result, a quasi-elliptic bandpass response is realized without requiring extra filtering circuit. For demonstration, a prototype was fabricated with standard PCB process and measured. The prototype operates in the 5G band (24.25–29.5 GHz) and it has an impedance bandwidth of 20%. The out-of-band gain drops over 15 dB at 23 and 32.5 GHz, respectively, which exhibits high selectivity. These merits make the proposed antenna a good element candidate for the 5G mm-Wave massive MIMO applications to reduce the requirements of the filters in the mm-Wave RF front ends. [ABSTRACT FROM AUTHOR]

This article presents an efficient analysis method for a novel continuous transverse stub (CTS) antenna. As opposed to state-of-the-art CTS antenna designs, the proposed architecture achieves circular polarization using a single CTS array and without any polarization converter. The structure consists of long radiating slots/stubs fed by over-moded parallel-plate waveguides. More precisely, the transverse electromagnetic (TEM) mode and the first transverse electric (TE1) mode of the feeding waveguides are used to generate a circularly polarized field. The array is analyzed using a spectral mode-matching method. First, the active reflection coefficient of the infinite array is derived in closed form. A windowing approach is then adopted to compute the radiation patterns of finite-size arrays. Numerical results obtained with this method are in excellent agreement with full-wave simulations, carried out with a commercial software. The performance of this class of CTS antennas has been investigated using the developed model. It is theoretically demonstrated that the proposed array can be designed to attain an axial ratio (AR) lower than 3 dB over a 52.9% relative bandwidth at broadside. Furthermore, the active input reflection coefficient is lower than −10 dB over a 40.8% relative bandwidth, when the array steers its main beam at $\theta _{0}=45^\circ $. This solution is an attractive candidate for next generation satellite communication terminals. [ABSTRACT FROM AUTHOR]

A multistage collaborative machine learning (MS-CoML) method that can be applied to efficient multiobjective antenna modeling and optimization is proposed. Machine learning methods, including single-output Gaussian process regression (SOGPR) and symmetric and asymmetric multioutput GPR (MOGPR) methods, are introduced to collaboratively build highly accurate multitask surrogate models for antennas. Variable-fidelity electromagnetic (EM) models are simulated, with their responses utilized to build separate MOGPR surrogate models. By combining the three machine-learning methods in a multistage framework, mappings between the same and different responses of the EM models with variable fidelity are learned, therein helping to substantially reduce the computational effort under a negligible loss of predictive power. Three antenna designs aiming at single-band, broadband, and multiband applications are selected as examples. And, for illustrating the applicability and superiority of the proposed MS-CoML method, a reference point-based multiobjective antenna optimization algorithm is used to optimize these three antennas. Simulation results show that using the MS-CoML method can significantly reduce the total optimization time without compromising modeling accuracy and optimized performance. [ABSTRACT FROM AUTHOR]

One of the greatest challenges in applying compressive sensing (CS) signal processing techniques to electromagnetic imaging applications is designing a sensing matrix that has good reconstruction capabilities. Compressive reflector antennas (CRAs) are a class of antennas that have been shown to provide enhanced image reconstruction performance over traditional reflector antennas (TRAs) when CS techniques are employed. In this article, we present a unified CRA design method, which considers both the sensing capacity and efficiency of the antenna and can be used for both compressive imaging and multiple-input multiple-output (MIMO) communication applications. The unified design method is assessed for a CRA configuration in which dielectric scatterers are added to the surface of a TRA. The design results demonstrate the ability of the unified design method to enhance the CS reconstruction capabilities of the CRA. [ABSTRACT FROM AUTHOR]

This article presents a graphene-based, dynamically reconfigurable antenna with a voltage-controlled, far-field radiation pattern in the microwave frequency band. The proposed antenna consists of two radiating patches and a planar feed network mainly composed of a graphene-based attenuator and a power divider with a hybrid graphene–metal phase shifter. The output phase of the phase shifter changes by a bias voltage on the graphene. The antenna has two operating states with different beam directions when the bias voltage is between 0.7 and 5 V. The equivalent circuit model is employed to analyze the phase shift characteristic of the graphene–metal phase shifter. Then the prototype of the reconfigurable antenna is fabricated and tested. The experimental results are in good agreement with the simulated ones. This article demonstrates that in the microwave frequency band, by proper design, the graphene–metal structure can be used to realize the new type of the reconfigurable antenna, in which this kind of graphene-based tuning structure can be easily stacked with other circuits by a simple pasting technique than soldering. This feature has potential applications in flexible radio frequency system in future. [ABSTRACT FROM AUTHOR]

In this work, a novel miniaturized meandered slot-line-based quad-band multiple-input-multiple-output (MIMO) antenna system is presented. The proposed design consists of two-antenna elements meandered in an H-shaped configurations. The miniaturization techniques of meandered slot-line and reactive loading are implemented to operate the antenna in sub-1 GHz bands with compact structure which results in an antenna size of $0.08\lambda _{o}$ corresponding to its lowest operating band. The frequency reconfigurability in the design is achieved by reactively loading the slots using varactor diodes. Covering most of the modern communication standards, the antenna operates in 0.665–1.13 GHz, 1.415–2.005 GHz, 2.42–3.09 GHz, and 3.18–3.89 GHz bands. Furthermore, complete analysis of frequency reconfigurability and design procedure is provided as a guideline for designing such an antenna system for any desired band of operation. The proposed two-element design is realized on a board dimensions of $60\times 120\times0.76$ mm3 using an RO4350 substrate. The proposed design is well-suited for wireless terminals with second generation cognitive radio (CR) capabilities for radio-frequency (RF) front-end applications. [ABSTRACT FROM AUTHOR]

In this article, a compact low-profile antenna for octa-band unbroken metal-rimmed smartphone applications is proposed. The antenna consists of a capacitive coupling rectangular vertical plate and two new-type extended ground branches. For lower frequency, the LTE700, GSM850, and GSM900 bands are provided by the bezel mode which is generated through capacitive coupling excitation of a rectangular vertical plate to the bezel. For upper frequency, the DCS, PCS, UMTS, LTE2300 and LTE2500 bands are covered by the multiple modes of two ground branches. With the proposed structure, the operating bands can be expanded and optimized simply. All the mentioned bands are achieved in the size of ($70 \times 7 + 20 \times 2$) $\times $ (1.5 + 0.8) mm3 on the 130 mm $\times \,\, 70$ mm system board. The antenna is fabricated and measured to verify this proposal. The tested results include reflection coefficient, radiation patterns, efficiency, and gain. [ABSTRACT FROM AUTHOR]

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]

An arm-implantable rectenna, supported by a compact planar inverted F-antenna (PIFA) and a rectifier, is proposed for wireless data telemetry and power transfer in the Medical Device Radiocommunications Service (401–406 MHz) and industrial, scientific, and medical (ISM) (902.8–928 MHz) bands. The rectifier is integrated into the system by using the antenna’s ground plane delivering, thus, a robust solution for the implanted devices. Each development stage is theoretically analyzed first and then experimentally tested. The antenna size is $16 \times 14 \times 1.27$ mm3. The slit/slot loading techniques applied onto the radiator offer the antenna size reduction and the dual-band operation. PIFA’s resonance stability is shown and its radiation and safety responses are addressed. Further, an arm-attached matching layer (ML) is proposed to enhance the wireless power link. Then, an analysis of rectifier circuits is conducted in order to obtain optimum conversion efficiency at low input powers. By following an attentive design process, the final system (rectenna) is built and tested in whole; the measurements verify our approach. [ABSTRACT FROM AUTHOR]

In medical microwave imaging (MMWI), the antennas usually operate at close distance from the body and are required to pick up weak echoes from the inside that are masked by high skin reflection. The near-field antenna behavior strongly determines how the received signals affect the effectiveness of the imaging algorithms. However, these usually simply assume the usual antenna far-field radiation characteristics. Here, we discuss three antenna effects that can deteriorate the overall imaging performance but are rarely addressed in the literature: antenna internal reflections, angular dispersion of the “near-field phase center,” and antenna frequency dispersive electric length. We propose dedicated methods to characterize these factors and present mitigation strategies to be integrated into the inversion algorithms. We demonstrate these effects for three frequently used broadband antennas, using signals from an experimental breast imaging lab setup. In fact, the antenna study and design cannot ignore that it operates in the near field of breast and interacts with its boundary. The methods and conclusions can be extended to other MMWI applications. To the best of our knowledge, this is the first systematic study of the above antenna factors in the context of MMWI. [ABSTRACT FROM AUTHOR]

A compact, frequency-reconfigurable filtenna with sharp out-of-band rejection in both its wideband and continuously tunable narrowband states is presented. It is intended for use in cognitive radio applications. The wideband state is the sensing state and operationally covers 2.35–4.98 GHz. The narrowband states are intended to cover communications within the 3.05–4.39 GHz range, which completely covers the Worldwide Interoperability for Microwave Access (WiMAX) band and the satellite communications C-band. A p-i-n diode is employed to switch between these wide and narrowband operational states. Two varactor diodes are used to shift the operational frequencies continuously among the narrowband states. The filtenna consists of a funnel-shaped monopole augmented with a reconfigurable filter; it has a compact electrical size: 0.235\lambda \textrm {L} \times 0.392\lambda \textrm {L} , where the wavelength \lambda \textrm {L} corresponds to the lower bound of its operational frequencies. The measured reflection coefficients, radiation patterns, and realized gains for both operational states are in good agreement with their simulated values. [ABSTRACT FROM AUTHOR]

A novel compact multi-ultrawideband (multi-UWB) and multi-dual-band frequency reconfigurable annular sector slot antenna (FR-ASSA) is presented for wireless applications. Three measured UWB states (3.48–5.5, 5.18–7.35, and 6.06–8.05 GHz) are achieved using six p-i-n diodes employed across a moderately wide slot inserted in a 32 \times 35 mm2 ground plane. Furthermore, 18 dual-band states with independent tuning ability of each band are provided. In dual-band states, the measured frequency tuning ranges are from 2.5 to 3.22 GHz (1.29:1) for the first resonance ( f_{1}) and from 4.36 to 6.58 GHz (1.51:1) for the second resonance ( f_{2})$ . The proposed FR-ASSA can support the standards such as WiMAX lower and middle bands (2.5–28 and 5.2–5.8 GHz), 4G LTE 2500 (2500–2690 MHz), WLAN IEEE 802.11a (5.15–5.825 GHz), and UWB groups #1 (3.4–5 GHz), #2 (5–6.6 GHz), and #3 (6.6–8 GHz) spectrums. [ABSTRACT FROM PUBLISHER]

This communication presents a small, low-profile planar triple-band microstrip antenna for WLAN/WiMAX applications. The goal of this communication is to combine WLAN and WiMAX communication standards simultaneously into a single device by designing a single antenna that can excite triple-band operation. The designed antenna has a compact size of 19 \times 25\;\textmm^2 (0.152 \lambda0\;\times 0.2 \lambda0). The proposed antenna consists of F-shaped slot radiators and a defected ground plane. Since only two F-shaped slots are etched on either sides of the radiator for triple-band operation, the radiator is very compact in size and simple in structure. The antenna shows three distinct bands I from 2.0 to 2.76, II from 3.04 to 4.0, and III from 5.2 to 6.0 GHz, which covers entire WLAN (2.4/5.2/5.8 GHz) and WiMAX (2.5/3.5/5.5) bands. To validate the proposed design, an experimental prototype has been fabricated and tested. Thus, the simulation results along with the measurements show that the antenna can simultaneously operate over WLAN (2.4/5.2/5.8 GHz) and WiMAX (2.5/3.5/5.5 GHz) frequency bands. [ABSTRACT FROM PUBLISHER]

A compact unidirectional ring dielectric resonator (DR) antenna (DRA) with lateral radiation patterns is investigated for the first time. The unidirectional patterns are obtained by combining an equivalent horizontal magnetic dipole of the DR \textHEM{11\delta + {1}} mode and a vertical electric dipole located at the center of the DR. A wideband version of the design is also investigated, in which the higher-order DR \text HEM{11\delta + {2}} mode is excited and merged with a slot mode to give a wideband magnetic dipole. The wideband electric dipole is obtained by making use of the parasitic effect of the DR. To demonstrate the idea, the original and wideband DRAs were designed in WLAN (2.40–2.48 GHz) and WiMax (3.4–3.7 GHz) bands, respectively. Their prototypes were fabricated and measured, and reasonable agreement between the measured and simulated results was obtained. In each design, the measured and simulated front-to-back radiation ratios are both over 15 dB, with measured and simulated 3-dB beamwidths of at least 117°. [ABSTRACT FROM PUBLISHER]

A very small coplanar waveguide (CPW)-fed rectangular slot antenna with dual band-notched characteristics for super ultrawideband (UWB) applications is proposed. This antenna consists of a rectangular slot, a beveled rectangular patch, two S-shaped slits cut in the ground plane and an elliptical ring slot (ERS) etched in the patch. The corners of a simple rectangular patch are beveled to improve the impedance bandwidth, especially at the middle frequencies of the band. In addition, a pair of semicircle slots is etched in the ground plane to enhance the bandwidth to more than 23 GHz. A pair of S-shaped slits connected to the rectangular slot, and an ERS cut in the beveled rectangular patch, is employed to create band-notched performances in WiMAX and WLAN spectrum, respectively. The proposed antenna has a very small size of 15 \times 15 \textmm^2, and therefore, it is one of the smallest UWB slot antennas that have been reported until now, and provide a very wide impedance bandwidth from 2.6 to more than 23 GHz for \textVSWR < 2 with dual band-notched properties. [ABSTRACT FROM PUBLISHER]

A wideband printed dipole with V-shaped ground branches is proposed, which is designed for multiple-input multiple-output (MIMO) antennas. It is based on a dipole with an integrated balun, and V-shaped ground branches are introduced to improve the impedance matching. The bandwidth of this element reaches 62.3% (2.30–4.40 GHz), which covers all three WiMAX bands (2.30, 2.50, and 3.30 GHz) and the 2.40 GHz WLAN band. Based on this element, a quad-element MIMO antenna is designed and fabricated. By reusing the V-shaped ground structure between adjacent elements, the size of this quad-element antenna is only $0.31 \lambda \times 0.31\lambda \times 0.01\lambda $. Meanwhile, a bandwidth of 60.6% (2.30–4.30 GHz) is achieved, in which the ${{\rm{S}}_{11}} < - 10\;{\rm{dB}}$, ${{\rm{S}}_{12}} < - 10\;{\rm{dB}}$, and ${{\rm{S}}_{13}} < - 13\;{\rm{dB}}$. Directional radiation patterns with 2.1 dBi average gain are attained, which are very stable throughout this band. This antenna system can be suitable for multielement MIMO devices such as wireless routers and adapters. [ABSTRACT FROM PUBLISHER]

The design of a four-band slot antenna for the global positioning system (GPS), worldwide interoperability for microwave access (WiMAX), and wireless area network (WLAN) is presented. The antenna consists of a rectangular slot with an area of \mathbf0.\mathbf37\lambda _g \times \mathbf0.\mathbf14\lambda _g = \mathbf48 \times \mathbf18\;\bf m\bf m^\mathbf2 (where \lambda _g is the guide wavelength), a $T$-shaped feed patch, an inverted $T$-shaped stub, and two $E$-shaped stubs to generate four frequency bands. The radiating portion and total size of the antenna are less than those of the tri-band antennas studied in literature. Parametric study on the parameters for setting the four frequency bands is presented and hence the methodology of using the design for other frequency bands is proposed. The multiband slot antenna is studied and designed using computer simulation. For verification of simulation results, the antenna is fabricated and measured. The simulated and measured return losses, radiation patterns, realized peak gains, and efficiencies of the antenna are presented. Measured results show that the antenna can be designed to cover the frequency bands from 1.575 to 1.665 GHz for the GPS system, 2.4–2.545 GHz for the IEEE 802.11b&g WLAN systems, 3.27–3.97 GHz for the WiMAX system, and 5.17–5.93 GHz for the IEEE 802.11a WLAN system. The effects of the feeding cable used in measurement and of the cover are also investigated. [ABSTRACT FROM PUBLISHER]

A novel multi-band design of planar slot antenna with compact operation for IEEE 802.16m WiMAX system is proposed. With the use of C- and inverted L-shaped slots, multi resonant modes close to 2.6/3.5/5.5 GHz bands can be excited to meet the specifications of WiMAX system (IEEE 802.16m). The obtained impedance bandwidth across these operating bands can reach about 525/743/813 MHz for the 2.6/3.5/5.5 GHz bands, respectively. We derive more than 10% reduction in antenna size and gain compact operation only from 32\,\times\,14\,\times\,0.8 mm^3 antenna dimension. The measured peak gains and total radiation efficiencies are about 3.0/4.3/5.2 dBi and 88/95/97% for the 2.6/3.5/5.5 GHz bands, respectively, with nearly omni-directional pattern in the XY-plane. [ABSTRACT FROM PUBLISHER]

AeroMACS is a system currently under development for airport surface communications. It is based on the IEEE802.16-2009 standard, and is developed in cooperation with the WiMAX forum. The frequency band allocated to AeroMACS is 5091–5150 MHz. When specifying the AeroMACS system, knowledge of typical propagation conditions at airports is of importance. Typically, path loss models are used to estimate the range of a transmitter within different zones of the airport, and typically fading characteristics are used to estimate the performance of, e.g., the selected coding and modulation schemes. Propagation measurements have been performed at the Barajas airport in Madrid, Spain. The measurements includes Non-Line-Of-Sight (NLOS) as well as Line-Of-Sight (LOS) conditions. Based on these measurements, path loss parameters and path loss models are developed for different zones of large airports. [ABSTRACT FROM PUBLISHER]

The effects of carrier frequency, antenna height and season on a broadband wireless access (BWA) system deployed in a rural area at 825 MHz and 3535 MHz are studied in this paper. With the aid of digital terrain information, both large scale and small scale fading effects present in the rural channel are discussed. Our investigation found that the frequency dependence of a wireless channel varies strongly with the environment. Also, the effects of the antenna height in rural areas of irregular terrains vary with the available clearance above the clutters in the regions. This paper uses extensive measurement campaigns to quantify these effects in winter and spring using a BWA system (IEEE 802.16e) deployed in Hetzwege/Abbendorf, Germany. In the study of small scale fading, the variations of the fading distributions of the wireless channel due to season changes are derived and the corresponding multipath propagations are discussed in this paper. [ABSTRACT FROM PUBLISHER]

A novel Koch-like fractal curve is proposed to transform ultra-wideband (UWB) bow-tie into so called Koch-like sided fractal bow-tie dipole. A small isosceles triangle is cut off from center of each side of the initial isosceles triangle, then the procedure iterates along the sides like Koch curve does, forming the Koch-like fractal bow-tie geometry. The fractal bow-tie of each iterative is investigated without feedline in free space for fractal trait unveiling first, followed by detailed expansion upon the four-iterated pragmatic fractal bow-tie dipole fed by 50-\Omega coaxial SMA connector through coplanar stripline (CPS) and comparison with Sierpinski gasket. The fractal bow-tie dipole can operate in multiband with moderate gain (3.5–7 dBi) and high efficiency (60%-80%), which is corresponding to certain shape parameters, such as notch ratio \alpha, notch angle \varphi, and base angles \theta of the isosceles triangle. Compared with conventional bow-tie dipole and Sierpinski gasket with the same size, this fractal-like antenna has almost the same operating properties in low frequency and better radiation pattern in high frequency in multi-band operation, which makes it a better candidate for applications of PCS, WLAN, WiFi, WiMAX, and other communication systems. [ABSTRACT FROM PUBLISHER]

A coplanar waveguide (CPW)-fed, multi-band, trapezoidal monopole antenna with linear and circular polarization realized in a single substrate layer is presented. It is demonstrated that, polarization of the antenna originate from resultant surface currents controlled by the physical aspects of the trapezoid. A prototype fabricated on Rogers RO4350B® substrate with dielectric constant 3.48 occupies an overall dimension of 55\,\times\,50\,\times\, 0.762 mm^3. The antenna provides a 2:1 VSWR bandwidth of 80% (from 1.55 GHz to 3.60 GHz) and 8% (from 5.13 GHz to 5.55 GHz) in the first and second band respectively. It also exhibits a 3 dB axial ratio bandwidth of 8% (from 2.21 GHz to 2.40 GHz) in the IEEE 802.16e WiMAX band. In addition, the antenna facilitates quasi omnidirectional coverage along with moderate gain and efficiency. A parametric study of the key parameters is also performed and the mechanism of polarization is described through surface current analysis. [ABSTRACT FROM PUBLISHER]

A novel printed diversity monopole antenna is presented for WiFi/WiMAX applications. The antenna comprises two crescent shaped radiators placed symmetrically with respect to a defected ground plane and a neutralization lines is connected between them to achieve good impedance matching and low mutual coupling. Theoretical and experimental characteristics are illustrated for this antenna, which achieves an impedance bandwidth of 54.5% (over 2.4–4.2 GHz), with a reflection coefficient < -10 dB and mutual coupling < -17 dB. An acceptable agreement is obtained for the computed and measured gain, radiation patterns, envelope correlation coefficient, and channel capacity loss. These characteristics demonstrate that the proposed antenna is an attractive candidate for multiple-input multiple-output portable or mobile devices. [ABSTRACT FROM AUTHOR]

An efficient technique is introduced to reduce mutual coupling between two closely spaced PIFAs for MIMO mobile terminals. The proposed mutual coupling reduction method is based on a T-shape slot impedance transformer and can be applied to both single-band and dual-band PIFAs. For the proposed single-band dual PIFAs, the 10 dB impedance bandwidth covers the 2.4 GHz WLAN band (2.4–2.48 GHz), and within the WLAN band an isolation of over 20 dB is achieved. Moreover, the dual-band version covers both the WLAN band and the WiMAX band of 3.4–3.6 GHz, with isolations of over 19.2 dB and 22.8 dB, respectively. The efficiency, gain and radiation patterns of the two-PIFA prototypes are verified in measurements. Due to very low pattern correlation and very good matching and isolation characteristics, the capacity performances are mainly limited by radiation efficiency. The single-band and dual-band PIFAs are also studied with respect to their locations on the ground plane. An eight-fold increase in the bandwidth of one PIFA is achieved, when the single-band PIFAs are positioned at one corner of the ground plane, with the bandwidth of the other PIFA and the good isolation unchanged. [ABSTRACT FROM PUBLISHER]

A novel triple-frequency microstrip-fed planar monopole antenna for multiband operation is proposed and investigated. Defected ground structure (DGS) is used in this antenna, which has a rectangular patch with dual inverted L-shaped strips and is fed by a cross-shaped stripline, for achieving additional resonances and bandwidth enhancements. The designed antenna has a small overall size of 20\,\times\,30 mm^2, and operates over the frequency ranges, 2.14–2.52 GHz, 2.82–3.74 GHz, and 5.15–6.02 GHz suitable for WLAN 2.4/5.2/5.8 GHz and WiMAX 3.5/5.5 GHz applications. There is good agreement between the measured and simulated results. Experimental results show that the antenna gives monopole-like radiation patterns and good antenna gains over the operating bands. In addition, effects of both the length of the protrudent strips and the dimensions of the DGS for this design on the electromagnetic performance are examined and discussed in detail. [ABSTRACT FROM PUBLISHER]

This paper reports the modeling of foliage attenuation for a broadband wireless access system deployed over mixed terrains in rural areas at 3.5 GHz. The foliage is composed of leaves and leafstalks, and are the dominant scatterers along the transmission paths. The foliage attenuation is determined using the Torrico-Lang model combined with digital topography information. In this model, leaves are modeled as thin lossy circular dielectric discs whereas leafstalks (petioles) are modeled as thin lossy dielectric cylinders. Three measurement campaigns were performed using the mobile WiMAX system (IEEE 802.16 e) deployed in Hetzwege/Abbendorf during winter, spring and mid-summer. Using the winter data as a baseline, the foliage loss due to different degrees of foliation in spring and in winter is studied. The derived foliage loss is then verified and compared with an empirical exponential decay model. [ABSTRACT FROM PUBLISHER]

In order to prevent interference problem due to existing nearby communication systems within the UWB operating frequency, a compact triple band-notch UWB antenna is presented in this communication. This antenna, designed for the rejection of interference with Worldwide Interoperability for Microwave Access (WiMAX), lower and upper wireless local area networks (WLANs) covering 3.3–3.6 GHz, 5.15–5.35 GHz and 5.725–5.825 GHz, provides three notched bands by only one structure with simple design. Based on simulation and measurement, it shows that the proposed antenna can guarantee a wide bandwidth from 3.03 to 11.4 GHz with triple unwanted band-notches successfully. [ABSTRACT FROM AUTHOR]

A new wideband compact slot antenna array for indoor WLAN access points (AP) is described, covering several wireless communication services from 2.4 to 4.8 GHz, that is especially designed to enhance MIMO system capacity. The array topology provides both spatial and polarization diversity. Despite very close packing of the array elements, these exhibit very low mutual coupling and low cross-polarization, greatly favoring MIMO diversity gain. A detailed MIMO performance comparison is conducted against a common array of patches in indoor environment, based both on simulation and indoor measurements: the new antenna shows a clear improvement in terms of channel capacity. [ABSTRACT FROM AUTHOR]

A novel printed multiband inverted-F antenna (IFA) for laptop computers is presented. The antenna has a simple structure and it is sufficiently narrow to easily fit on each side of the housing of the display unit of the laptop. The antenna is designed to operate in all the allocated Wi-Fi and WiMAX frequency bands while providing near omnidirectional coverage in the horizontal plane. The multiband performance of the proposed antenna and its omnidirectionality are validated by measurements. [ABSTRACT FROM AUTHOR]

Two compact ultrawideband (UWB) slot antennas with band-rejected characteristics are proposed for UWB communication applications. The entire size of both antennas is as small as 15\ mm\times 22\ mm\times 0.8\ mm, which is smaller than most of the proposed UWB antennas. The radiator is a stepped slot excited by a 50 \Omega feed line. By etching a half-wavelength and a quarter-wavelength slot from the ground plane of UWB slot antennas, respectively, two UWB antennas with band-notched characteristics can be obtained. The potential interference between UWB and WLAN/WiMAX can be reduced. Omnidirectional radiation patterns and constant gain can be observed in the pass bands. Time-domain characteristics of both proposed antennas are analyzed under different conditions. It demonstrates that the time-domain characteristics of the antennas are good enough for UWB applications. The results show that proposed antennas are very suitable for various portable UWB systems. [ABSTRACT FROM AUTHOR]

An inverted-FL antenna is proposal with a self-complementary structure. This unique design is realized by integrating an inverted-F antenna with a self-complementary structure and an inverted-L element. The proposed antenna with a volume of 10 x 10 x 45mm3 achieves a constant impedance of 188 Ω without attaching a matching load required since a self-complementary antenna of an axially symmetric type has constant impedance. This antenna acquired broadband and multiband characteristics covering the GSM850/GSM900/DCS/ PCS/UMTS2100/UMTS2600 bands and the 2.5G/3.5G bands for Mobile-WiMAX by simulation and measurement. [ABSTRACT FROM AUTHOR]

In this paper, a printed microstrip-line-fed rhombus slot antenna with a pair of parasitic strips is presented. With the use of these parasitic elements along the microstrip feed line, bandwidth enhancement for wideband operation can be obtained. From experimental results, the measured impedance bandwidth, with a 10 dB return loss, can operate from 1.80 to 6.09 GHz which is wider than a conventional microstrip-line-fed printed rhombus slot antenna without parasitic elements. By selecting proper dimensions of parasitic strips, the proposed antenna can provide PCS, IMT-2000, and WiMAX multiband operations for various wireless communication services Details of the proposed antenna are described, and experimental results are presented and discussed. [ABSTRACT FROM AUTHOR]

A small-size uniplanar printed antenna suitable for 2.4/5.2/5.8 GHz WLAN and 2.5/3.5/5.5 GHz WiMAX operations is presented. The antenna is a coupled-fed PIFA and shows a height of 9 mm and a width of 13 mm only, when mounted at the top edge of the display panel in the laptop computer. The multiband operation is achieved by using the coupling feed and further embedding a band-notching slit in the radiating arm of the PIFA. With the coupling feed, two wide operating bands can be generated at about 2.5 and 5.5 GHz for the PIFA. By further embedding the slit of length about a quarter-wavelength at about 4 GHz, a band notching characteristic at about 4 GHz is obtained, which leads to an additional resonance at about 3.5 GHz and shows very small effects on the desired 2.5 and 5.5 GHz bands. This behavior results in successful excitation of an additional resonant mode for 3.5 GHz WiMAX operation. Hence, with no increase in the antenna size, three wide operating bands for covering all the desired operating bands of WLAN/WiMAX systems are achieved for the proposed PIFA. Details of the design considerations are presented, and results of the fabricated prototype are discussed. [ABSTRACT FROM AUTHOR]

A dielectric resonator (DR) antenna with a well is proposed, of which the beamwidth is increased to more than 120 ° by bending the ground plane. This DR antenna has its 10-dB return-loss band in 3.4-3.8 GHz, thus can be used as a sectorial antenna in WiMAX (3.4-3.7 GHz) base station. [ABSTRACT FROM AUTHOR]

An empirical propagation prediction model is described for mobile communications from high altitude platforms (HAPs) in different types of built-up areas. The model introduced here is defined as a function of the angle of elevation. The target frequencies are selected from the 2 to 6 GHz frequency band prospective for 3G and 4G mobile systems, namely at 2.0, 3.5, and 5.5 GHz. This new HAP model recognizes two cases-line of sight (LOS) and non-line of sight (NLOS) between a HAP and a user at street level. The simulation of the urban environment is based on a statistical approach. Additional shadowing path loss is calculated using the uniform theory of diffraction for NLOS conditions. Normal distribution of the additional shadowing path loss was distinguishable from the simulation results. The shadowing path loss is defined as a function of the elevation angle. The results of the empirical model developed for idealized conditions are verified by measurements taken from a remote-controlled airship in different types of urban environment. Close correlation was achieved between the theoretical model and the experimental data. The HAP elevation dependent shadowing model is easy to implement and can be used for realistic planning and simulations of mobile networks provided via HAPs in built-up areas. [ABSTRACT FROM AUTHOR]

The band-rejected designs of the printed open slot antenna for wireless local area network (WLAN)/worldwide interoperability for microwave access (WiMAX) applications are investigated. First, the broadband characteristic (2.3 ∼ 6↑ GHz) of open slot antenna design with small size is implemented and measured. Then, inserted a single strip on the broadband antenna is studied and investigated. By inserting a strip on the printed open slot of the broadband antenna, to reject frequency from 3.56 to 4.58 GHz, a dual-broadband design of the open slot antenna with small size is obtained for WLAN applications in the 2.4 GHz (2400-2484 MHz) and 5 GHz (5150-5825 MHz) bands. Furthermore, by inserting two strips of different length on the open slot antenna, a three-band antenna is achieved. By adjusting the dimension of two strips on open slot antenna, a three operating modal frequencies at 2.37 ∼ 2.72, 3.31∼ 3.78, and 4.5 ∼ 5.97 GHz for WiMAX application have been obtained. Detailed design steps and experimental results for the designs are studied and investigated in this paper. [ABSTRACT FROM AUTHOR]

This paper proposes a novel type of ultrawide-band (UWB) antenna, which has a low voltage standing wave ratio (VSWR) while excepting from interference with existing wireless system with band notched characteristics. The bandwidth and central frequency of the notched band can be adjusted with ease by proper selection of antenna parameters. Simulation results well justify the design methods presented in the paper. As an important example, a band-notched antenna that yields an impedance bandwidth of 3.1-10.6 GHz with VSWR < 2, except the bandwidth of 5.15-5.825 Gift for IEEE802.11, is proposed and evaluated. [ABSTRACT FROM AUTHOR]