International Journal of Antennas and Propagation http://www.hindawi.com The latest articles from Hindawi Publishing Corporation © 2015 , Hindawi Publishing Corporation . All rights reserved. A Printed Monopole Antenna for Triple-Band WLAN/WiMAX Applications Thu, 29 Jan 2015 06:14:55 +0000 http://www.hindawi.com/journals/ijap/2015/254268/ A new compact design of monopole antenna for triple-band WLAN/WiMAX applications with two band-notches based on broadband antenna is presented. By introducing a stub loaded ground and two new paper clip structures etched on radiation patch, a compact overall dimension 31 mm 33 mm 1 mm and three separated operating bands effectively covering 2.4/5.2/5.8 GHz WLAN bands and 2.5/3.5/5.5 GHz WiMAX bands can be achieved. Compared with familiar U type slot, the introduced compact paper clip structure can save about 37% of dimension regions, which could effectively improve efficiency of band-notch formation. Simulated and measured results demonstrate that the proposed antenna has good dipole-like radiation characteristics with appreciable gain across the operating bands. Besides, main parameters of the two etched paper clip structures are investigated to control the positions and bandwidths of the two stop-bands, respectively, on basis of which the three working bands can be adjusted independently. Huiqing Zhai, Lu Liu, Zhihui Ma, and Changhong Liang Copyright © 2015 Huiqing Zhai et al. All rights reserved. Robust Adaptive Beamforming Based on Worst-Case and Norm Constraint Wed, 28 Jan 2015 14:22:35 +0000 http://www.hindawi.com/journals/ijap/2015/765385/ A novel robust adaptive beamforming based on worst-case and norm constraint (RAB-WC-NC) is presented. The proposed beamforming possesses superior robustness against array steering vector (ASV) error with finite snapshots by using the norm constraint and worst-case performance optimization (WCPO) techniques. Simulation results demonstrate the validity and superiority of the proposed algorithm. Hongtao Li, Ke Wang, Chaoyu Wang, Yapeng He, and Xiaohua Zhu Copyright © 2015 Hongtao Li et al. All rights reserved. Low-Profile Magnetic Loop Monopole Antenna Based on a Square Substrate-Integrated Cavity Mon, 26 Jan 2015 06:48:21 +0000 http://www.hindawi.com/journals/ijap/2015/694385/ A low-profile monopole antenna with height below is proposed. The antenna is based on a square substrate-integrated cavity radiating through apertures in its four side walls. This effectively creates a small square loop of magnetic currents, which radiates omnidirectionally as an electric monopole. The antenna cavity has a side length of less than and thus resonates in the monomode region, in a fundamental mode. This means that the structure is robust in terms of feeding and manufacturing tolerances, as no parasitic modes can be excited. The designs of the cavity and the feed are introduced in detail. The measurement results from a manufactured prototype operating at 5.9 GHz show good agreement with simulations and validate the proposed approach. Thomas Kaufmann and Christophe Fumeaux Copyright © 2015 Thomas Kaufmann and Christophe Fumeaux. All rights reserved. Nonuniform Overlapping Method in Designing Microstrip Patch Antennas Using Genetic Algorithm Optimization Tue, 13 Jan 2015 06:41:38 +0000 http://www.hindawi.com/journals/ijap/2015/805820/ Genetic algorithm (GA) has been a popular optimization technique used for performance improvement of microstrip patch antennas (MPAs). When using GA, the patch geometry is optimized by dividing the patch area into small rectangular cells. This has an inherent problem of adjacent cells being connected to each other with infinitesimal connections, which may not be achievable in practice due to fabrication tolerances in chemical etching. As a solution, this paper presents a novel method of dividing the patch area into cells with nonuniform overlaps. The optimized design, which is obtained by using fixed overlap sizes, shows a quad-band performance covering GSM1800, GSM1900, LTE2300, and Bluetooth bands. In contrast, use of nonuniform overlap sizes leads to obtaining a pentaband design covering GSM1800, GSM1900, UMTS, LTE2300, and Bluetooth bandswith fractional bands with of 38% due to the extra design flexibility. J. M. Jeevani W. Jayasinghe, Jaume Anguera, Disala N. Uduwawala, and Aurora Andújar Copyright © 2015 J. M. Jeevani W. Jayasinghe et al. All rights reserved. MIMO Antennas in Radar Applications Sun, 11 Jan 2015 13:35:36 +0000 http://www.hindawi.com/journals/ijap/2015/696790/ Wen-Qin Wang, Mathini Sellathurai, Frankie Kit Wing Chan, Wei Xu, and Shengqi Zhu Copyright © 2015 Wen-Qin Wang et al. All rights reserved. Joint Multichannel Motion Compensation Method for MIMO SAR 3D Imaging Sun, 11 Jan 2015 10:00:13 +0000 http://www.hindawi.com/journals/ijap/2015/852520/ The multiple-input-multiple-output (MIMO) synthetic aperture radar (SAR) system with a linear antenna array can obtain 3D resolution. In practice, it suffers from both the translational motion errors and the rotational motion errors. Conventional single-channel motion compensation methods could be used to compensate the motion errors channel by channel. However, this method might not be accurate enough for all the channels. What is more, the single-channel compensation may break the coherence among channels, which would cause defocusing and false targets. In this paper, both the translational motion errors and the rotational motion errors are discussed, and a joint multichannel motion compensation method is proposed for MIMO SAR 3D imaging. It is demonstrated through simulations that the proposed method exceeds the conventional methods in accuracy. And the final MIMO SAR 3D imaging simulation confirms the validity of the proposed algorithm. Ze-min Yang, Meng-dao Xing, Guang-cai Sun, and Zheng Bao Copyright © 2015 Ze-min Yang et al. All rights reserved. A New Kind of Circular Polarization Leaky-Wave Antenna Based on Substrate Integrated Waveguide Thu, 08 Jan 2015 10:17:43 +0000 http://www.hindawi.com/journals/ijap/2015/397960/ A new kind of circular polarization leaky-wave antenna with N-shaped slots cut in the upper side of substrate integrated waveguide (SIW) is investigated and presented. The radiation pattern and polarization axial ratio of the leaky-wave antenna are studied. The results show that the width of N-shaped slots has significant effect on the circular polarization property of the antenna. By properly choosing structural parameters, the SIW based leaky-wave antenna can realize circular polarization with excellent axial ratio in 8 GHz satellite band. Chong Zhang, Junhong Wang, Meie Chen, Zhan Zhang, and Zheng Li Copyright © 2015 Chong Zhang et al. All rights reserved. Target Localization with a Single Antenna via Directional Multipath Exploitation Tue, 06 Jan 2015 07:58:28 +0000 http://www.hindawi.com/journals/ijap/2015/510720/ Target localization in urban sensing can benefit from angle dependency of the pulse shape at a radar receiver antenna. We propose a localization approach that utilizes the embedded directivity in ultra-wideband (UWB) antennas to estimate target positions. A single radar unit sensing operation of indoor targets surrounded by interior walls is considered, where interior wall multipaths are exploited to provide target cross-range. This exploitation assumes resolvability of the multipath components, which is made possible by the virtue of using UWB radar signals. The proposed approach is most attractive when only few multipaths are detectable due to propagation obstructions or owing to low signal-to-noise ratios. Both simulated and experimental data are used to demonstrate the effectiveness of the proposed approach. Ali H. Muqaibel, Moeness G. Amin, and Fauzia Ahmad Copyright © 2015 Ali H. Muqaibel et al. All rights reserved. Beam Tilt-Angle Estimation for Monopole End-Fire Array Mounted on a Finite Ground Plane Tue, 06 Jan 2015 06:55:17 +0000 http://www.hindawi.com/journals/ijap/2015/351439/ A modified method for the beam tilt-angle estimation of monopole end-fire array mounted on finite ground plane is proposed. In the simplified model, the monopole array and ground plane are approximated to two line sources of transverse and longitudinal electric current, respectively. It is deduced that the beam tilt angle is a function about the length of ground plane in front of array , the length of monopole array , and the phase constant . After verifying the optimizing principle of monopole end-fire array, a 10-element monopole Yagi-Uda antenna satisfying Hansen-Woodyard condition is designed and measured for the analysis. By comparison and analysis, the value of is demonstrated to be the key point of the proposed method. And a slow wave monopole array is proved to be able to achieve a low beam tilt angle from end-fire with only a short-length ground plane. Jia Cao, Zhenghui Xue, and Meng Cao Copyright © 2015 Jia Cao et al. All rights reserved. Application of Synthetic Storm Technique for Diurnal and Seasonal Variation of Slant Path Ka-Band Rain Attenuation Time Series over a Subtropical Location in South Africa Mon, 05 Jan 2015 12:17:16 +0000 http://www.hindawi.com/journals/ijap/2015/474397/ As technology advances and more demands are on satellite services, rain-induced attenuation still creates one of the most damaging effects of the atmosphere on the quality of radio communication signals, especially those operating above 10 GHz. System designers therefore require statistical information on rain-induced attenuation over the coverage area in order to determine the appropriate transmitter and receiver characteristics to be adopted. This paper presents results on the time-varying rain characterization and diurnal variation of slant path rain attenuation in the Ka-band frequency simulated with synthetic storm techniques over a subtropical location in South Africa using 10-year rain rate time-series data. The analysis is based on the CDF of one-minute rain rate; time-series seasonal variation of rain rate observed over four time intervals: 00:00–06:00, 06:00–12:00, 12:00–18:00, and 18:00–24:00; diurnal fades margin; and diurnal variation of rain attenuation. Comparison was also made between the synthesized values and measured attenuation data. The predicted statistics are in good agreement with those obtained from the propagation beacon measurement in the area. The overall results will be needed for an acceptable planning that can effectively reduce the fade margin to a very low value for an optimum data communication over this area. J. S. Ojo and P. A. Owolawi Copyright © 2015 J. S. Ojo and P. A. Owolawi. All rights reserved. A High-Isolation Dual-Polarization Substrate-Integrated Fabry-Pérot Cavity Antenna Mon, 05 Jan 2015 06:52:02 +0000 http://www.hindawi.com/journals/ijap/2015/265962/ A dual-polarization substrate-integrated Fabry-Pérot cavity (SI-FPC) antenna is presented in this paper. The patch embedded in SI-FPC is excited with a near-field coupled feeding structure for V-polarization and with a slot-coupled feeding structure for H-polarization. The feeding structures are separated by a ground plane to improve the isolation between the ports. As a design example, an antenna operating at 10.0 GHz is fabricated and measured. A high degree of port isolation (<−40 dB) over the whole operating bandwidth (9.5–10.2 GHz) and good cross-polarization level (>25 dB) can be achieved. Chang Chen, Bo-Liang Liu, Ling Ji, and Wei-Dong Chen Copyright © 2015 Chang Chen et al. All rights reserved. Guaranteed Stability of Sparse Recovery in Distributed Compressive Sensing MIMO Radar Thu, 01 Jan 2015 09:49:36 +0000 http://www.hindawi.com/journals/ijap/2015/421740/ Low SNR condition has been a big challenge in the face of distributed compressive sensing MIMO radar (DCS-MIMO radar) and noise in measurements would decrease performance of radar system. In this paper, we first devise the scheme of DCS-MIMO radar including the joint sparse basis and the joint measurement matrix. Joint orthogonal matching pursuit (JOMP) algorithm is proposed to recover sparse targets scene. We then derive a recovery stability guarantee by employing the average coherence of the sensing matrix, further reducing the least amount of measurements which are necessary for stable recovery of the sparse scene in the presence of noise. Numerical results show that this scheme of DCS-MIMO radar could estimate targets’ parameters accurately and demonstrate that the proposed stability guarantee could further reduce the amount of data to be transferred and processed. We also show the phase transitions diagram of the DCS-MIMO radar system in simulations, pointing out the problem to be further solved in our future work. Yu Tao, Gong Zhang, and Jindong Zhang Copyright © 2015 Yu Tao et al. All rights reserved. Compact Wideband Antiparallel Diode Frequency Triplers Utilizing Planar Transitions Thu, 01 Jan 2015 09:33:37 +0000 http://www.hindawi.com/journals/ijap/2015/373179/ Two designs of frequency triplers, which use planar transitions as baluns and an antiparallel diode pair to achieve wide bandwidth, are presented. The ultrawideband transitions are utilized for input and output impedance matching of the frequency triplers. The design process and operation principles are described in this paper. The implemented frequency triplers exhibit flat response over wide frequency range of 3 to 9 GHz. The proposed Type A frequency tripler shows conversion loss of ~18 dB with above 30 dB even harmonics suppression. With Type B frequency tripler, conversion loss of ~17 dB and above 25 dB even harmonic suppression are achieved. Wahab Mohyuddin, Kang Wook Kim, and Hyun Chul Choi Copyright © 2015 Wahab Mohyuddin et al. All rights reserved. A Novel 3D Imaging Method for Airborne Downward-Looking Sparse Array SAR Based on Special Squint Model Wed, 31 Dec 2014 13:00:59 +0000 http://www.hindawi.com/journals/ijap/2014/982014/ Three-dimensional (3D) imaging technology based on antenna array is one of the most important 3D synthetic aperture radar (SAR) high resolution imaging modes. In this paper, a novel 3D imaging method is proposed for airborne down-looking sparse array SAR based on the imaging geometry and the characteristic of echo signal. The key point of the proposed algorithm is the introduction of a special squint model in cross track processing to obtain accurate focusing. In this special squint model, point targets with different cross track positions have different squint angles at the same range resolution cell, which is different from the conventional squint SAR. However, after theory analysis and formulation deduction, the imaging procedure can be processed with the uniform reference function, and the phase compensation factors and algorithm realization procedure are demonstrated in detail. As the method requires only Fourier transform and multiplications and thus avoids interpolations, it is computationally efficient. Simulations with point scatterers are used to validate the method. Xiaozhen Ren, Yao Qin, and Lihong Qiao Copyright © 2014 Xiaozhen Ren et al. All rights reserved. Small Antennas: Miniaturization Techniques and Applications Tue, 30 Dec 2014 08:53:54 +0000 http://www.hindawi.com/journals/ijap/2014/134103/ Wenhua Yu, Wenxing Li, Dau-Chyrh Chang, and Yingsong Li Copyright © 2014 Wenhua Yu et al. All rights reserved. An Effective Technique for Enhancing Direction Finding Performance of Virtual Arrays Tue, 30 Dec 2014 06:51:40 +0000 http://www.hindawi.com/journals/ijap/2014/728463/ The array interpolation technology that is used to establish a virtual array from a real antenna array is widely used in direction finding. The traditional interpolation transformation technology causes significant bias in the directional-of-arrival (DOA) estimation due to its transform errors. In this paper, we proposed a modified interpolation method that significantly reduces bias in the DOA estimation of a virtual antenna array and improves the resolution capability. Using the projection concept, this paper projects the transformation matrix into the real array data covariance matrix; the operation not only enhances the signal subspace but also improves the orthogonality between the signal and noise subspace. Numerical results demonstrate the effectiveness of the proposed method. The proposed method can achieve better DOA estimation accuracy of virtual arrays and has a high resolution performance compared to the traditional interpolation method. Wenxing Li, Xiaojun Mao, Wenhua Yu, and Chongyi Yue Copyright © 2014 Wenxing Li et al. All rights reserved. Singularity Processing Method of Microstrip Line Edge Based on LOD-FDTD Thu, 25 Dec 2014 12:39:03 +0000 http://www.hindawi.com/journals/ijap/2014/980967/ In order to improve the performance of the accuracy and efficiency for analyzing the microstrip structure, a singularity processing method is proposed theoretically and experimentally based on the fundamental locally one-dimensional finite difference time domain (LOD-FDTD) with second-order temporal accuracy (denoted as FLOD2-FDTD). The proposed method can highly improve the performance of the FLOD2-FDTD even when the conductor is embedded into more than half of the cell by the coordinate transformation. The experimental results showed that the proposed method can achieve higher accuracy when the time step size is less than or equal to 5 times of that the Courant-Friedrich-Levy (CFL) condition allowed. In comparison with the previously reported methods, the proposed method for calculating electromagnetic field near microstrip line edge not only improves the efficiency, but also can provide a higher accuracy. Lei Li, Xin Zhang, and Yingsong Li Copyright © 2014 Lei Li et al. All rights reserved. Recognition and Parameter Extraction of One-Dimensional Electronic Scanning for 3D Radar Thu, 25 Dec 2014 00:10:24 +0000 http://www.hindawi.com/journals/ijap/2014/567954/ Most of the existing antenna scan type (AST) identification techniques focus on only mechanical scanning (MS) and rarely research electronic scanning (ES), especially one-dimensional (1D) ES. This paper proposes a recognition and parameter extraction method of 1D ES for 3D radar, which employs both MS and ES. An ES pattern simulator is designed to synthesize pulse amplitude (PA) data first. Then 1D ES is distinguished from MS and two-dimensional (2D) ES based on the features extracted from the difference sequences of beam sequence, such as resemblance coefficient (RC) and variance. Subsequently, two vital parameters for 1D ES are extracted, namely, beam position number in elevation and pulse number in a beam position. Finally, some simulation results are shown to validate the proposed algorithm. Cheng Li, Wei Wang, Longfei Shi, and Xuesong Wang Copyright © 2014 Cheng Li et al. All rights reserved. VIE-FG-FFT for Analyzing EM Scattering from Inhomogeneous Nonmagnetic Dielectric Objects Wed, 24 Dec 2014 08:51:31 +0000 http://www.hindawi.com/journals/ijap/2014/720947/ A new realization of the volume integral equation (VIE) in combination with the fast Fourier transform (FFT) is established by fitting Green’s function (FG) onto the nodes of a uniform Cartesian grid for analyzing EM scattering from inhomogeneous nonmagnetic dielectric objects. The accuracy of the proposed method is the same as that of the P-FFT and higher than that of the AIM and the IE-FFT especially when increasing the grid spacing size. Besides, the preprocessing time of the proposed method is obviously less than that of the P-FFT for inhomogeneous nonmagnetic dielectric objects. Numerical examples are provided to demonstrate the accuracy and efficiency of the proposed method. Shu-Wen Chen, Hou-Xing Zhou, Wei Hong, and Jia-Ye Xie Copyright © 2014 Shu-Wen Chen et al. All rights reserved. Validation of the - Model of the Power Spectral Density of GPS Ionospheric Amplitude Scintillation Tue, 23 Dec 2014 09:22:55 +0000 http://www.hindawi.com/journals/ijap/2014/573615/ The - model has become widely used in statistical analyses of radio channels, due to the flexibility provided by its two degrees of freedom. Among several applications, it has been used in the characterization of low-latitude amplitude scintillation, which frequently occurs during the nighttime of particular seasons of high solar flux years, affecting radio signals that propagate through the ionosphere. Depending on temporal and spatial distributions, ionospheric scintillation may cause availability and precision problems to users of global navigation satellite systems. The present work initially stresses the importance of the flexibility provided by - model in comparison with the limitations of a single-parameter distribution for the representation of first-order statistics of amplitude scintillation. Next, it focuses on the statistical evaluation of the power spectral density of ionospheric amplitude scintillation. The formulation based on the - model is developed and validated using experimental data obtained in São José dos Campos (23.1°S; 45.8°W; dip latitude 17.3°S), Brazil, located near the southern crest of the ionospheric equatorial ionization anomaly. These data were collected between December 2001 and January 2002, a period of high solar flux conditions. The results show that the proposed model fits power spectral densities estimated from field data quite well. Kelias Oliveira, Alison de Oliveira Moraes, Emanoel Costa, Marcio Tadeu de Assis Honorato Muella, Eurico Rodrigues de Paula, and Waldecir Perrella Copyright © 2014 Kelias Oliveira et al. All rights reserved. Advances in Massive MIMO Antenna Design, Channel Modeling, and System Technologies Mon, 22 Dec 2014 12:05:02 +0000 http://www.hindawi.com/journals/ijap/2014/160431/ Kan Zheng, Xuefeng Yin, Periklis Chatzimisios, and Yan Xin Copyright © 2014 Kan Zheng et al. All rights reserved. Enhancement of Cross-Borehole Pulse Radar Signature on a Partially Water-Filled Tunnel Tue, 16 Dec 2014 07:23:44 +0000 http://www.hindawi.com/journals/ijap/2014/396835/ Cross-borehole pulse radar has been employed to detect a deeply located empty tunnel. In this paper, effects of underground water collected in the bottom of an empty tunnel on cross-borehole pulse radar signatures are analyzed numerically. B-scan images, stacks of received pulses, are calculated by applying the finite-difference time-domain (FDTD) method for 6 different heights of water from the bottom to the half height inside an empty tunnel. The most important features of an empty tunnel, the fastest time of peak (TOP) and time of arrival (TOA) extracted from the B-scan images, are slowed considerably depending on the increased height of water inside the tunnel. To compensate the weak TOP like that of an empty tunnel, a relation curve is formulated only utilizing measurable parameters of the fastest TOP and the fastest TOA. Then, a unified curve including the effects of two granites with the low and high dielectric properties is derived to cover widely varied dielectric properties of underground rocks. Based on the fastest TOP of an empty tunnel, the average difference between the fastest TOP of an empty tunnel and that of a partially water-filled tunnel decreases from 22.92% to 2.59% after enhancement. Ji-Hyun Jung and Se-Yun Kim Copyright © 2014 Ji-Hyun Jung and Se-Yun Kim. All rights reserved. Subarrayed Antenna Array Synthesis Using Ternary Adjusting Method Mon, 15 Dec 2014 09:11:13 +0000 http://www.hindawi.com/journals/ijap/2014/898717/ Ternary adjusting method is proposed and combined with particle swarm optimization (PSO) algorithm for subarrayed antenna array synthesis. Ternary variables are introduced to represent element adjustments between adjacent subarrays. Compared to previous methods, rounding-off operations are not required any longer, and the equation constraint of the fixed total element number is also removed, which effectively reduces the complexity of implementation while obtaining improved topology exploration capability simultaneously. Guolong He, Yafeng Zhan, Yukui Pei, and Bin Wu Copyright © 2014 Guolong He et al. All rights reserved. A Novel Performance Analysis of the Microstrip Antenna Printed on a Cylindrical Body Thu, 11 Dec 2014 06:14:29 +0000 http://www.hindawi.com/journals/ijap/2014/613245/ Performance of a circular patch microstrip antenna is highly affected by the effective dielectric constant of a used substrate material. When the circular patch is conformed on a cylindrical body, the effective dielectric constant is changing with curvature due to the changing in the fringing field. Consequently, some of antenna parameters such as resonance frequency, input impedance, voltage standing wave ratio, return loss, quality factor, and antenna bandwidth are functions of curvature. In this work, we study the effect of curvature on the performance of circular patch microstrip antenna. A mathematical model for the antenna parameters as functions of curvature is also introduced. The model is applied in case of using two substrates of different refractive index values. By extension, the antenna performance was studied through simulation by using method of moments (MoM) which is reliable in solving Maxwell’s integral equations in the frequency domain. The results from simulation compare very favorably with the described analytical results. Amr M. Mahros, Marwa M. Tharwat, and Ali Elrashidi Copyright © 2014 Amr M. Mahros et al. All rights reserved. Genetic Algorithms in Antennas and Smart Antennas Design Overview: Two Novel Antenna Systems for Triband GNSS Applications and a Circular Switched Parasitic Array for WiMax Applications Developments with the Use of Genetic Algorithms Thu, 11 Dec 2014 00:10:42 +0000 http://www.hindawi.com/journals/ijap/2014/729208/ Genetic algorithms belong to a stochastic class of evolutionary techniques, whose robustness and global search of the solutions space have made them extremely popular among researchers. They have been successfully applied to electromagnetic optimization, including antenna design as well as smart antennas design. In this paper, extensive reference to literature related antenna design efforts employing genetic algorithms is taking place and subsequently, three novel antenna systems are designed in order to provide realistic implementations of a genetic algorithm. Two novel antenna systems are presented to cover the new GPS/Galileo band, namely, L5 (1176 MHz), together with the L1 GPS/Galileo and L2 GPS bands (1575 and 1227 MHz). The first system is a modified PIFA and the second one is a helical antenna above a ground plane. Both systems exhibit enhanced performance characteristics, such as sufficient front gain, input impedance matching, and increased front-to-back ratio. The last antenna system is a five-element switched parasitic array with a directional beam with sufficient beamwidth to a predetermined direction and an adequate impedance bandwidth which can be used as receiver for WiMax signals. Stylianos C. Panagiotou, Stelios C. A. Thomopoulos, and Christos N. Capsalis Copyright © 2014 Stylianos C. Panagiotou et al. All rights reserved. Performance Investigations of Quasi-Yagi Loop and Dipole Antennas on Silicon Substrate for 94 GHz Applications Mon, 08 Dec 2014 08:25:45 +0000 http://www.hindawi.com/journals/ijap/2014/105625/ This paper introduces the design and implementation of two high gain Quasi-Yagi printed antennas developed on silicon substrate for 94 GHz imaging applications. The proposed antennas are based on either driven loop or dipole antennas fed by a coplanar waveguide (CPW) feeding structure. For better matching with the driven antennas, a matching section has been added between the CPW feedline and the driven antenna element. To improve the gain of either loop or dipole antennas, a ground reflector and parasitic director elements have been added. Two Quasi-Yagi antenna prototypes based on loop and dipole antenna elements have been fabricated and experimentally tested using W-band probing station (75–110 GHz). The measured results show good agreement with simulated results and confirm that the proposed antennas are working. In addition, a feed and matching configuration is proposed to enable coupling a microbolometer element to the proposed Quasi-Yagi antenna designs for performing radiation pattern measurements. Osama M. Haraz, Mohamed Abdel-Rahman, Najeeb Al-Khalli, Saleh Alshebeili, and Abdel Razik Sebak Copyright © 2014 Osama M. Haraz et al. All rights reserved. Near-Field Spherical Scanning Antenna Measurements: Probe Deconvolution and Sensitivity Thu, 04 Dec 2014 11:49:57 +0000 http://www.hindawi.com/journals/ijap/2014/587874/ We define and calculate sensitivity for several actual and simulated probes. Probe sensitivity can have a significant impact on the measurement uncertainty associated with probe deconvolution in near-field spherical-scanning, antenna measurements. Ronald C. Wittmann and Michael H. Francis Copyright © 2014 Ronald C. Wittmann and Michael H. Francis. All rights reserved. Comparison of Semidefinite Relaxation Detectors for High-Order Modulation MIMO Systems Thu, 27 Nov 2014 11:59:57 +0000 http://www.hindawi.com/journals/ijap/2014/614876/ Multiple-input multiple-output (MIMO) system is considered to be one of the key technologies of LTE since it achieves requirements of high throughput and spectral efficiency. The semidefinite relaxation (SDR) detection for MIMO systems is an attractive alternative to the optimum maximum likelihood (ML) decoding because it is very computationally efficient. We propose a new SDR detector for 256-QAM MIMO system and compare its performance with two other SDR detectors, namely, BC-SDR detector and VA-SDR detector. The tightness and complexity of these three SDR detectors are analyzed. Both theoretical analysis and simulation results demonstrate that the proposed SDR can provide the best BLER performance among the three detectors, while the BC-SDR detector and the VA-SDR detector provide identical BLER performance. Moreover, the BC-SDR has the lowest computational complexity and the VA-SDR has the highest computational complexity, while the proposed SDR is in between. Z. Y. Shao, S. W. Cheung, and T. I. Yuk Copyright © 2014 Z. Y. Shao et al. All rights reserved. Study on Zero-Doppler Centroid Control for GEO SAR Ground Observation Wed, 26 Nov 2014 13:41:19 +0000 http://www.hindawi.com/journals/ijap/2014/549269/ In geosynchronous Earth orbit SAR (GEO SAR), Doppler centroid compensation is a key step for imaging process, which could be performed by the attitude steering of a satellite platform. However, this zero-Doppler centroid control method does not work well when the look angle of radar is out of an expected range. This paper primarily analyzes the Doppler properties of GEO SAR in the Earth rectangular coordinate. Then, according to the actual conditions of the GEO SAR ground observation, the effective range is presented by the minimum and maximum possible look angles which are directly related to the orbital parameters. Based on the vector analysis, a new approach for zero-Doppler centroid control in GEO SAR, performing the attitude steering by a combination of pitch and roll rotation, is put forward. This approach, considering the Earth’s rotation and elliptical orbit effects, can accurately reduce the residual Doppler centroid. All the simulation results verify the correctness of the range of look angle and the proposed steering method. Yicheng Jiang, Bin Hu, Yun Zhang, Meng Lian, and Zhuoqun Wang Copyright © 2014 Yicheng Jiang et al. All rights reserved. Dual-Polarized Crossed Bowtie Dipole Array for Wireless Communication Applications Wed, 26 Nov 2014 11:45:14 +0000 http://www.hindawi.com/journals/ijap/2014/349516/ A dual-polarized array with downtilted radiation patterns is proposed for wireless communication applications. The proposed dual-polarized antenna element achieves an enhanced impedance bandwidth and compact dimensions by introducing a parasitic circular patch and vertical metal cylinders, which is a good candidate for radiating elements in base station antennas. By optimizing the amplitude and phase distribution along the feed, a radiation pattern with a downtilted angle is obtained. The dual-polarized array antenna achieves an impedance bandwidth for VSWR 1.5, covering the frequency bands for 3G/LTE systems. Moreover, the proposed array achieves high port isolation, the stable antenna gain over the entire operating band. Therefore, the proposed array antenna is very suitable for potential wireless communication applications. A prototype has been manufactured and measured. The measurements, that match the design objectives, are also presented. Zhi-Ya Zhang, Shuang Li, Shao-Li Zuo, Jia-Yue Zhao, Xiao-dong Yang, and Guang Fu Copyright © 2014 Zhi-Ya Zhang et al. All rights reserved.