International Journal of Antennas and Propagation The latest articles from Hindawi Publishing Corporation © 2014 , Hindawi Publishing Corporation . All rights reserved. Baseband Transceiver Design of a High Definition Radio FM System Using Joint Theoretical Analysis and FPGA Implementation Wed, 16 Apr 2014 12:47:52 +0000 Advances in wireless communications have enabled various technologies for wireless digital communication. In the field of digital radio broadcasting, several specifications have been proposed, such as Eureka-147 and digital radio mondiale (DRM). These systems require a new spectrum assignment, which incurs heavy cost due to the depletion of the available spectrum. Therefore, the in-band on-channel (IBOC) system has been developed to work in the same band with the conventional analog radio and to provide digital broadcasting services. This paper discusses the function and algorithm of the high definition (HD) radio frequency modulation (FM) digital radio broadcasting system. Content includes data format allocation, constellation mapping, orthogonal frequency division multiplexing (OFDM) modulation of the transmitter, timing synchronization, OFDM demodulation, integer and fraction carrier frequency (integer carrier frequency offset (ICFO) and fractional CFO (FCFO)) estimation, and channel estimation of the receiver. When we implement this system to the field programmable gate array (FPGA) based on a hardware platform, both theoretical and practical aspects have been considered to accommodate the available hardware resources. Chien-Sheng Chen, Chyuan-Der Lu, Ho-Nien Shou, and Le-Wei Lin Copyright © 2014 Chien-Sheng Chen et al. All rights reserved. Measurement-Based Delay and Doppler Characterizations for High-Speed Railway Hilly Scenario Tue, 15 Apr 2014 16:41:28 +0000 This paper presents results for delay and Doppler spread characterization in high-speed railway (HSR) hilly scenario. To investigate the propagation characteristics in this specific terrain, a measurement campaign is conducted along the “Guangzhou-Shenzhen” HSR in China. A wideband channel sounder with 40 MHz bandwidth is used to collect raw data at 2.4 GHz band. The delay spread and Doppler frequency features are analyzed based on measured data. It is found that there are abundant multipath components (MPCs) in this scenario. We present the relationship between the delay spreads and the transceiver distances. The measured route can be divided into four areas with different delay and Doppler characteristics. Finally, a tapped delay line (TDL) model is proposed to parameterize the channel responses in the HSR hilly environment, which is supposed to provide criterions for evaluations of the radio interface and development of wireless communication system. Yan Zhang, Zunwen He, Wancheng Zhang, Limin Xiao, and Shidong Zhou Copyright © 2014 Yan Zhang et al. All rights reserved. Compact Multiband Slot Antenna for WLAN/WiMAX Operations Tue, 15 Apr 2014 16:36:56 +0000 A novel compact triple-band slot antenna is proposed for WLAN/WiMAX applications. With the use of three L-shaped slots and an open-ended slot on the ground plane, three resonant modes centered at 2.4/3.5/5.8 GHz are excited. These modes cover the standards of 3.5 GHz WiMAX and 2.4/5.8 GHz WLAN, three useful frequency bands for present wireless communication systems. The proposed antenna fed by L-shaped microstrip line has a small overall dimension of  mm2. The numerical and experimental results show that acceptable radiation characteristic is obtained over the operating bands. Jianhui Bao, Qiulin Huang, Xinhuai Wang, and Xiaowei Shi Copyright © 2014 Jianhui Bao et al. All rights reserved. Far-Field Pattern Reconstruction from Near-Field Data Collected via a Nonconventional Plane-Rectangular Scanning: Experimental Testing Tue, 15 Apr 2014 13:27:02 +0000 This paper deals with the experimental validation of an efficient near-field-far-field (NF-FF) transformation using the planar wide-mesh scanning (PWMS). Such a nonconventional plane-rectangular scanning technique is so named, since the sample grid is characterized by meshes wider and wider when going away from the center, and makes it possible to lower the number of needed measurements, as well as the time required for the data acquisition when dealing with quasi-planar antennas. It relies on the use of the nonredundant sampling representations of electromagnetic fields which employ an oblate ellipsoid or a surface formed by two circular “bowls” with the same aperture diameter but eventually different bending radii to shape a quasi-planar antenna. A two-dimensional optimal sampling interpolation formula allows the reconstruction of the NF data at any point on the measurement plane and, in particular, at those required by the classical NF-FF transformation with the conventional plane-rectangular scanning. The measurements, performed at the planar NF facility of the antenna characterization laboratories of Selex ES, have confirmed the effectiveness of this innovative scanning also from the experimental viewpoint. Francesco D’Agostino, Ilaria De Colibus, Flaminio Ferrara, Claudio Gennarelli, Rocco Guerriero, and Massimo Migliozzi Copyright © 2014 Francesco D’Agostino et al. All rights reserved. Compact Microstrip Antenna Structures with Multiband, Broadband, and Band-Notched Properties, for Portable Devices Mon, 14 Apr 2014 13:45:14 +0000 Alistair P. Duffy, Mohammad Naser-Moghadasi, Jalil Rashed-Mohassel, and Bal Singh Virdee Copyright © 2014 Alistair P. Duffy et al. All rights reserved. New Approach for Unambiguous High-Resolution Wide-Swath SAR Imaging Mon, 14 Apr 2014 11:10:09 +0000 The high-resolution wide-swath (HRWS) SAR system uses a small antenna for transmitting waveform and multiple antennas both in elevation and azimuth for receiving echoes. It has the potential to achieve wide spatial coverage and fine azimuth resolution, while it suffers from elevation pattern loss caused by the presence of topographic height and impaired azimuth resolution caused by nonuniform sampling. A new approach for HRWS SAR imaging based on compressed sensing (CS) is introduced. The data after range compression of multiple elevation apertures are used to estimate direction of arrival (DOA) of targets via CS, and the adaptive digital beamforming in elevation is achieved accordingly, which avoids the pattern loss of scan-on-receive (SCORE) algorithm when topographic height exists. The effective phase centers of the system are nonuniformly distributed when displaced phase center antenna (DPCA) technology is adopted, which causes Doppler ambiguities under traditional SAR imaging algorithms. Azimuth reconstruction based on CS can resolve this problem via precisely modeling the nonuniform sampling. Validation with simulations and experiment in an anechoic chamber are presented. Yueguan Lin, Yida Fan, Hai Jiang, and Wei Wang Copyright © 2014 Yueguan Lin et al. All rights reserved. Broadband Loop Antenna on Soft Contact Lens for Wireless Ocular Physiological Monitoring Sun, 13 Apr 2014 13:21:38 +0000 This paper presents a novel loop antenna with broadband for wireless ocular physiological monitoring (WOPM). The antenna is fabricated on a thin-film poly-para-xylylene C (parylene C) substrate with a small thickness of 11 μm and dimension of  mm2. With the advantage of small size, the proposed antenna is suitable to apply to the soft contact lens and transmit the signal in microelectromechanical Systems (MEMS). Because the pig's eye and human's eye have similar parameters of conductivity and permittivity, the experimental results are obtained by applying the proposed antenna on the pig's eye and cover from 1.54 to 6 GHz for ISM band (2.4 and 5.8 GHz) applications. The measured antenna radiation patterns, antenna gains, and radiation efficiency will be demonstrated in this paper, which are suitable for application of wireless ocular physiological monitoring. Ssu-Han Ting, Bo-Ming Jeng, Wen-Shan Chen, Jin-Chern Chiou, and Ching-Hsing Luo Copyright © 2014 Ssu-Han Ting et al. All rights reserved. Effect of Parasitic Element on 408 MHz Antenna for Radio Astronomy Application Thu, 10 Apr 2014 17:45:23 +0000 Antenna is one of the important subsystem components in a radio telescope system. In this paper, analysis on the effect of parasitic element on 408 MHz antenna in a radio telescope system is presented. Higher gain up to 10.24 dBi with reduction on beamwidth size has been achieved by optimizing the position of parasitic element relative to the driven element. The proposed antenna is suitable to be utilized in a transient radio telescope array. Radial Anwar, Mohammad Tariqul Islam, Norbahiah Misran, Geri Gopir, Baharudin Yatim, and Mhd Fairos Asillam Copyright © 2014 Radial Anwar et al. All rights reserved. Switchable Electromagnetic Bandgap Surface Wave Antenna Thu, 10 Apr 2014 12:26:23 +0000 This paper presents a novel switchable electromagnetic bandgap surface wave antenna that can support both a surface wave and normal mode radiation for communications at 2.45 GHz. In the surface wave mode, the antenna has a monopole-like radiation pattern with a measured gain of 4.4 dBi at ±49° and a null on boresight. In the normal mode, the antenna operates like a back-fed microstrip patch antenna. Qiang Bai, Kenneth L. Ford, and Richard J. Langley Copyright © 2014 Qiang Bai et al. All rights reserved. Simple and Efficient Computational Method to Analyze Cylindrical Plasmonic Nanoantennas Thu, 10 Apr 2014 09:01:04 +0000 We present in this work a simple and efficient technique to analyze cylindrical plasmonic nanoantennas. In this method, we take into account only longitudinal current inside cylindrical structures and use 1D integral equation for the electric field with a given surface impedance of metal. The solution of this integral equation is obtained by the Method of Moments with sinusoidal basis functions. Some examples of calculations of nanoantennas with different geometries and sources are presented and compared with the commercial software Comsol 3D simulations. The results show that the proposed technique provides a good precision in the near-infrared and lower optical frequencies 100–400 THz. Karlo Costa and Victor Dmitriev Copyright © 2014 Karlo Costa and Victor Dmitriev. All rights reserved. “Three Crossings” Compensations of the High Speed Moving MIMO Radar Thu, 10 Apr 2014 08:58:28 +0000 The problems of the “Three Crossings” motions and compensations for the moving target of the high speed moving MIMO radar are studied. Firstly, the space model is established to describe the problems by educing the equations of delay and transmitting pattern, which are changing with time. The echo characteristics are analyzed and the formulas of the “Three Crossings” are given. Secondly, a compensation method, which uses the fractional Fourier transform (FrFT) to compensate the crossing Doppler-cell and the preprocess to compensate the crossing range-cell and crossing-beam, is proposed. This method could compensate the “Three Crossings” simultaneously with little complexity of calculation because the preprocess deals only with the transmitting signals. Lastly, the phantom antenna array is employed in the simulations, the working model of “sparse transmitting dense receiving” is applied to the simulation of crossing-beam, and the results of simulations demonstrate the validity and the practicability of the method of combining the preprocess and the FrFT to compensate “Three Crossings.” Cheng Luo and Zishu He Copyright © 2014 Cheng Luo and Zishu He. All rights reserved. Wideband Circularly Polarized SIW Antenna Array That Uses Sequential Rotation Feeding Thu, 10 Apr 2014 08:54:49 +0000 A wideband right-handed circularly polarized (CP) substrate integrated waveguide- (SIW-) based diamond ring-slot antenna array at the X-band is presented in this study. The array consists of four elements that exhibit wideband impedance matching characteristics and good radiation performance. The array also employs a sequential rotation feeding method to achieve the wideband axial ratio (AR) bandwidth. The feeding network is based on the SIW power divider with a delay line related to sequential rotation feeding. To validate our design, an antenna array is fabricated and measured. The measured impedance and AR bandwidths are 19.2% () and 14.1% ( dB), respectively. Moreover, the antenna has a stable CP peak gain of more than 12 dBic from 10.1 GHz to 10.7 GHz. Fang-Fang Fan, Ze-Hong Yan, and Wei Wang Copyright © 2014 Fang-Fang Fan et al. All rights reserved. Small-Size Wearable High-Efficiency TAG Antenna for UHF RFID of People Thu, 10 Apr 2014 08:49:37 +0000 This paper introduces a small-size, low-profile wearable radiator based on the coupled patches and vertically folded patches techniques for application as a tag antenna for identification of people in the European UHF RFID band. The electric field distribution comes out dominantly from the central coupling slot, and thus the electric properties of the radiator are almost unaffected by the human body to which the antenna is intended to be attached. Accordingly, with the relative size   at 866 MHz  mm3), the antenna exhibits total efficiency better than 50%, even if it is attached directly to a person. Milan Svanda and Milan Polivka Copyright © 2014 Milan Svanda and Milan Polivka. All rights reserved. RFID Presenter: A New Way to Feel a Talk Thu, 10 Apr 2014 08:22:13 +0000 RFID is a key which enables technology for the Internet of Things paradigm, allowing the virtualization of the physical objects into the Internet. There are uncountable applications whereby these connected objects can be a breakthrough for new business models, and this work shows a good example of that. We present the RFID Presenter as the evolution of a classical consumer electronic product to a novel connected Internet product with the addition of the RFID technology. It supposes a new way to manage the conference talks in a personalization way, improving the end-user interaction and providing services that were impossible before. The design, implementation, and validation of a real gadget are well explained in order to give a real example of how the Internet of Things can be integrated into daily objects and enhance the end-user experiences. Jonathan Ruiz-de-Garibay, Jon Legarda, Szilárd A. Kados, and Xabier Eguiluz Copyright © 2014 Jonathan Ruiz-de-Garibay et al. All rights reserved. Analysis of a Compact Wideband Slotted Antenna for Ku Band Applications Thu, 10 Apr 2014 00:00:00 +0000 The design procedure and physical module of a compact wideband patch antenna for Ku band application are presented in this paper. Finite element method based on 3D electromagnetic field solver has been utilized for the designing and analyzing process of proposed microstrip line fed modified - shaped electrically small patch antenna. After successful completion of the design process through various simulations, the proposed antenna has been fabricated on printed circuit board (PCB) and its characteristics have been studied. The parameters of the proposed antenna prototype have been measured in standard far-field rectangular shape anechoic measurement compartment. It is apparent from the measured antenna parameters that the proposed antenna achieved almost stable variation of radiation pattern over the entire operational band with 1380 MHz of 10 dB return loss bandwidth. The maximum gain of 7.8 dBi and 89.97% average efficiency within the operating band from 17.15 GHz to 18.53 GHz ensure the suitability of the proposed antenna for Ku band applications. M. R. Ahsan, M. Habib Ullah, F. Mansor, N. Misran, and T. Islam Copyright © 2014 M. R. Ahsan et al. All rights reserved. Development of a Semielliptical Partial Ground Plane Antenna for RFID and GSM-900 Wed, 09 Apr 2014 13:17:32 +0000 A novel compact broadband patch antenna for UHF (ultrahigh frequency), RFID (radio frequency identification), and GSM-900 (global system for mobile communications) band is shown in this paper. The antenna is composed of an ellipse shape annular ring at the patch. The ground plane of the planar antenna is modified with a semiellipse shape slot. The structure can generate substantial amount of current at the feed-line. The geometry of the antenna is evaluated by using HFSS simulation software and deliberated across the paper. Parametric study is exhibited to delineate the response change of the antenna. The antenna has a physical width of 0.24 λ and length of 0.3 λ. It covers a frequency starting from 0.9 GHz to 1.08 GHz. A fractional bandwidth of 18.2% has been achieved from 0.9 GHz till 1.08 GHz. An average gain of 5.5 dBi is achieved at the resonance frequency. The simulated and measured results have good agreement. M. R. Zaman, R. Azim, N. Misran, M. F. Asillam, and T. Islam Copyright © 2014 M. R. Zaman et al. All rights reserved. Novel Applicators for Local Microwave Hyperthermia Based on Zeroth-Order Mode Resonator Metamaterial Wed, 09 Apr 2014 07:34:42 +0000 It is demonstrated that a theory of zero-order mode resonator (ZOR) metamaterial (MTM) structure can be used for the development of a novel class of applicators for microwave thermotherapy, for example, for hyperthermia in cancer treatment or for physiotherapy. The main idea of creating such an applicator is to generate and radiate a plane electromagnetic (EM) wave into the treated biological tissue, at least in a certain extent. The main aim of this paper is to investigate whether an EM wave generated by ZOR MTM structure and emitted into the biological tissue can produce a homogeneous SAR distribution in the planes parallel to the applicator aperture and achieve a penetration depth approaching the theoretical limit represented by SAR distribution and penetration depth of an ideal EM plane wave. EM field distribution inside a virtual phantom of the treated region generated by the applicator that is based on the proposed ZOR MTM principle is investigated using a well-proven full-wave commercial simulation tool. The proposed applicator type shows both a low unwanted leaked electromagnetic field and a fairly homogeneous electric field in its aperture as well as in the virtual phantom of the treated region. David Vrba and Jan Vrba Copyright © 2014 David Vrba and Jan Vrba. All rights reserved. Realization of Negative Group Delay Network Using Defected Microstrip Structure Tue, 08 Apr 2014 07:43:16 +0000 A design of negative group delay (NGD) networks using a U-shaped defected microstrip structure (DMS) and lumped elements is presented in this paper. The signal attenuation characteristics of DMS were utilized to get NGD time. The group delay (GD) time and signal attenuation of the proposed networks are controlled by an external resistor connected across the DMS slot. For experimental validation, a single-stage and cascaded two-stage NGD networks were designed and fabricated. From experimental results, the GD of  ns with the maximum insertion loss of 37.84 dB was obtained over bandwidth of 40 MHz. Girdhari Chaudhary, Yongchae Jeong, and Jongsik Lim Copyright © 2014 Girdhari Chaudhary et al. All rights reserved. Frequency Diverse Array Radar Cramér-Rao Lower Bounds for Estimating Direction, Range, and Velocity Tue, 08 Apr 2014 06:43:49 +0000 Different from phased-array radar, frequency diverse array (FDA) radar offers range-dependent beampattern and thus provides new application potentials. But there is a fundamental question: what estimation performance can achieve for an FDA radar? In this paper, we derive FDA radar Cramér-Rao lower bounds (CRLBs) for estimating direction, range (time delay), and velocity (Doppler shift). Two different data models including pre- and postmatched filtering are investigated separately. As the FDA radar has range-angle coupling, we use a simple transmit subaperturing strategy which divides the whole array into two subarrays, each uses a distinct frequency increment. Assuming temporally white Gaussian noise and linear frequency modulated transmit signal, extensive simulation examples are performed. When compared to conventional phased-array radar, FDA can yield better CRLBs for estimating the direction, range, and velocity. Moreover, the impacts of the element number and frequency increment are also analyzed. Simulation results show that the CRLBs decrease with the increase of the elements number and frequency increment. Yongbing Wang, Wen-Qin Wang, and Huaizong Shao Copyright © 2014 Yongbing Wang et al. All rights reserved. Enhanced Loop Structure of NFC Antenna for Mobile Handset Applications Tue, 08 Apr 2014 06:13:50 +0000 A new structure of an NFC loop antenna for mobile handset applications is proposed. The proposed antenna consists of conventional loop elements and a parasitic loop embedded capacitor to enhance its performance. Although the sintered ferrite sheets with higher relative permeability have been used to reduce the performance deterioration due to the eddy current on the battery pack of a mobile handset, their costs are high, and they are considerably breakable. In this paper, with the proposed structure, we effectively enhance the performance of an NFC loop antenna by employing the ferrite-polymer composite with lower relative permeability . Byungje Lee, Byeongkwan Kim, and Sunghyun Yang Copyright © 2014 Byungje Lee et al. All rights reserved. A Low-Profile WLAN Antenna with Inductor and Tuning Stub for Broadband Impedance Matching Tue, 08 Apr 2014 00:00:00 +0000 This paper presents a low-profile multiband antenna suitable for wireless local area networks (WLANs), using a chip inductor and tuning stub for broadband impedance matching. The proposed antenna is compact and covers three bands: 2.4-GHz (2.400–2.484 GHz), 5.2-GHz (5.150–5.350 GHz), and 5.8-GHz (5.725–5.825 GHz). The measured 10-dB bandwidths are 12.0% (2.28–2.57 GHz) in the lower band for 2.4-GHz WLANs and 39.1% (4.81–7.15 GHz) in the upper band for 5 GHz-WLANs. The measured peak gain of the antenna is between 2.7 and 4.39 dBi and the radiation patterns are omnidirectional. Woo-Su Kim, Sunho Choi, and Gye-Taek Jeong Copyright © 2014 Woo-Su Kim et al. All rights reserved. A Temporal Millimeter Wave Propagation Model for Tunnels Using Ray Frustum Techniques and FFT Mon, 07 Apr 2014 16:35:26 +0000 A temporal millimeter wave propagation model for tunnels is presented using ray frustum techniques and fast Fourier transform (FFT). To directly estimate or simulate effects of millimeter wave channel properties on the performance of communication services, time domain impulse responses of demodulated signals should be obtained, which needs rather large computation time. To mitigate the computational burden, ray frustum techniques are used to obtain frequency domain transfer function of millimeter wave propagation environment and FFT of equivalent low pass signals are used to retrieve demodulated waveforms. This approach is numerically efficient and helps to directly estimate impact of tunnel structures and surfaces roughness on the performance of millimeter wave communication services. Choonghyen Kwon, Hayeon Kim, Haengseon Lee, Hyo Hyun Choi, Woo-jin Byun, and Kwangseon Kim Copyright © 2014 Choonghyen Kwon et al. All rights reserved. Tunable Plasmonic and Hyperbolic Metamaterials Based on Enhanced Nonlinear Response Sun, 06 Apr 2014 11:44:49 +0000 We present here tunable and reconfigurable designs of linear and nonlinear plasmonic and hyperbolic metamaterials. Rich scattering features of multilayered composite nanoparticles are demonstrated, which include complex and exotic scattering signatures combining multiple dipolar Fano resonances and electromagnetic induced transparency (EIT) features. These dipole-dipole multi-Fano scattering responses can be further tuned through altering the plasmonic properties of the concentric layers or the permittivity of the core, for instance, by the presence of nonlinearities. Strong third-order nonlinear effects, such as optical bistability, may also be induced in the scattering response of nonlinear nanoparticles due to the highly enhanced and confined fields inside their core. Nonlinear hyperbolic metamaterial designs are also explored, which can realize tunable positive-to-negative refraction at the same frequency, as a function of the input intensity. Negative Goos-Hänchen shift is demonstrated based only on the hyperbolic dispersion properties of these layered metamaterials without the usual need of negative index metamaterials. The Goos-Hänchen shift may be tuned from positive-to-negative values, when the structure is illuminated with different frequencies. A plethora of applications are envisioned based on the proposed tunable metamaterials, such as ultrafast reconfigurable imaging devices, tunable sensors, novel nanotag designs, and efficient all-optical switches and memories. Christos Argyropoulos, Francesco Monticone, Nasim Mohammadi Estakhri, and Andrea Alù Copyright © 2014 Christos Argyropoulos et al. All rights reserved. Low Complexity Direction and Doppler Frequency Estimation for Bistatic MIMO Radar in Spatial Colored Noise Sun, 06 Apr 2014 06:27:14 +0000 We investigate the algorithm of direction and Doppler frequency estimation for bistatic multiple-input multiple-output (MIMO) radar in spatial colored noise. A novel method of joint estimation of direction and Doppler frequency in spatial colored noise based on propagator method (PM) for bistatic MIMO radar is discussed. Utilizing the cross-correlation matrix which is formed by the adjacent outputs of match filter in the time domain, the special matrix is constructed to eliminate the influence of spatial colored noise. The proposed algorithm provides lower computational complexity and has very close parameters estimation compared to estimation of signal parameters via rotational invariance technique (ESPRIT) algorithm in high signal-to-noise ratio (SNR). It is applicable even if the transmitted waveforms are not orthogonal. The estimated parameters can be paired automatically and the Cramér-Rao Bound (CRB) is given in spatial colored noise. Simulation results confirm the effectiveness of the proposed method. Lingyun Xu, Guangbin Zhang, Xiaofei Zhang, and Zongze Xu Copyright © 2014 Lingyun Xu et al. All rights reserved. Microstrip Antenna Design for Femtocell Coverage Optimization Thu, 03 Apr 2014 11:48:07 +0000 A mircostrip antenna is designed for multielement antenna coverage optimization in femtocell network. Interference is the foremost concern for the cellular operator in vast commercial deployments of femtocell. Many techniques in physical, data link and network-layer are analysed and developed to settle down the interference issues. A multielement technique with self-configuration features is analyzed here for coverage optimization of femtocell. It also focuses on the execution of microstrip antenna for multielement configuration. The antenna is designed for LTE Band 7 by using standard FR4 dielectric substrate. The performance of the proposed antenna in the femtocell application is discussed along with results. Afaz Uddin Ahmed, M. T. Islam, Rezaul Azim, Mahamod Ismail, and Mohd Fais Mansor Copyright © 2014 Afaz Uddin Ahmed et al. All rights reserved. Radiation Efficiency Improvement Method for Multifeed Circular Polarization Antenna Array with Mutual Coupling Effect Thu, 03 Apr 2014 11:47:18 +0000 In the circular polarization antenna array, the input impedance, axial ratio, and radiation pattern of antenna patch will be changed. Compared with the performances of single antenna, the mutual coupling also led to the low efficiency of all antennas. A novel radiation efficiency elevation method of multifeed circular polarization (CP) antenna array is demonstrated in this paper, in order to solve the problem. To prove the concept of novel method, dual-feed antenna with stubs is developed and fabricated. According to the measured results, each antenna would increase in efficiency by approximate 1dB by applying this novel design method. Therefore, this paper provides dramatically useful results of lessening the negative effect resulting in mutual coupling. Zijian Xing, Ling Wang, Jianying Li, and Kun Wei Copyright © 2014 Zijian Xing et al. All rights reserved. Correction of Channel Imbalance for MIMO SAR Using Stepped-Frequency Chirps Thu, 03 Apr 2014 11:00:57 +0000 To simultaneously achieve two-dimensional high resolution and wide swath in synthetic aperture radar (SAR), azimuth MIMO structure combined with stepped-frequency chirp signals was developed via splitting the antenna into subapertures. During transmitting each subaperture transmits a chirp pulse at a different carrier frequency, while during receiving every subaperture receives the scattered pulses at the same time. Separating the scattered pulses received by each subaperture and downlinking them to the ground yield different signal paths. Due to the dedicated network in the SAR system, the channel imbalance is inevitable. To correct the channel imbalance, this paper presents an external calibration method, where the channel characteristics are estimated from the peak value of a strong point target for each channel. Simulation and real raw data experiments are performed to validate the proposed method. Xiulian Luo, Yunkai Deng, Robert Wang, Lei Guo, and Mingjiang Wang Copyright © 2014 Xiulian Luo et al. All rights reserved. Joint Delay Doppler Probability Density Functions for Air-to-Air Channels Thu, 03 Apr 2014 06:37:54 +0000 Recent channel measurements indicate that the wide sense stationary uncorrelated scattering assumption is not valid for air-to-air channels. Therefore, purely stochastic channel models cannot be used. In order to cope with the nonstationarity a geometric component is included. In this paper we extend a previously presented two-dimensional geometric stochastic model originally developed for vehicle-to-vehicle communication to a three-dimensional air-to-air channel model. Novel joint time-variant delay Doppler probability density functions are presented. The probability density functions are derived by using vector calculus and parametric equations of the delay ellipses. This allows us to obtain closed form mathematical expressions for the probability density functions, which can then be calculated for any delay and Doppler frequency at arbitrary times numerically. Michael Walter, Dmitriy Shutin, and Uwe-Carsten Fiebig Copyright © 2014 Michael Walter et al. All rights reserved. Application of the Characteristic Basis Function Method Using CUDA Thu, 03 Apr 2014 06:34:08 +0000 The characteristic basis function method (CBFM) is a popular technique for efficiently solving the method of moments (MoM) matrix equations. In this work, we address the adaptation of this method to a relatively new computing infrastructure provided by NVIDIA, the Compute Unified Device Architecture (CUDA), and take into account some of the limitations which appear when the geometry under analysis becomes too big to fit into the Graphics Processing Unit’s (GPU’s) memory. Juan Ignacio Pérez, Eliseo García, José A. de Frutos, and Felipe Cátedra Copyright © 2014 Juan Ignacio Pérez et al. All rights reserved. Suppression of Cross-Polarization of the Microstrip Integrated Balun-Fed Printed Dipole Antenna Tue, 01 Apr 2014 07:52:02 +0000 The high cross-polarization of the microstrip integrated balun-fed printed dipole antenna cannot meet the demands of many engineering applications. This kind of antennas has high cross-polarization levels (about −20 dB). And we find that the high cross-polarization radiation is mainly produced by the microstrip integrated balun rather than the dipole itself. The very limited method to lower the cross-polarization level of this kind of antennas is to reduce the substrate thickness. In this paper, to improve the low cross-polarized performance, firstly, an equivalent model is presented to analyze the cross-polarization radiation. Secondly, a novel structure with low cross-polarization is proposed. The microstrip integrated balun is enclosed by a center slotted cavity. The E-field of the microstrip integrated balun is transformed parallel to the dipole arms by the slot, so the radiation of the cross-polarized component is suppressed. Measured results show that this structure can achieve a bandwidth wider than 40% while reducing the cross-polarization level to less than −35 dB within the frequency band. Huang Jingjian, Zhang Xiaofa, Xie Shaoyi, Wu Weiwei, and Yuan Naichang Copyright © 2014 Huang Jingjian et al. All rights reserved.