International Journal of Antennas and Propagation http://www.hindawi.com The latest articles from Hindawi Publishing Corporation © 2015 , Hindawi Publishing Corporation . All rights reserved. Stepped Cylindrical Antenna with a Higher-Order Mode Ring Patch for Wideband Conical Radiation Pattern Thu, 21 May 2015 14:19:39 +0000 http://www.hindawi.com/journals/ijap/2015/394621/ A stepped cylindrical antenna with a higher-order mode ring patch for wideband conical radiation pattern is proposed. To accomplish a low profile with wideband conical radiation characteristics, a stepped cylindrical monopole and a TM41 higher-order mode ring patch with four shorting pins are utilized. The proposed antenna has a monopole-like radiation pattern with a wide 10-dB return loss bandwidth of 11 GHz (2 GHz–13 GHz). It can cover various wireless services, such as wireless broadband (WiBro; 2.3 GHz–2.39 GHz), wireless local area networks (WLAN; 2.4 GHz–2.484 GHz, 5.15 GHz–5.35 GHz, and 5.725 GHz–5.875 GHz), digital multimedia broadcasting (DMB; 2.63 GHz–2.655 GHz), and ultra wideband (UWB; 3.1 GHz–10.6 GHz). The antenna has a height of only 0.12λ0 at 2 GHz. Jinpil Tak, Do-Gu Kang, and Jaehoon Choi Copyright © 2015 Jinpil Tak et al. All rights reserved. Research on Polarization Cancellation of Nonstationary Ionosphere Clutter in HF Radar System Thu, 21 May 2015 13:02:23 +0000 http://www.hindawi.com/journals/ijap/2015/631217/ Oblique projection polarization filter (OPPF) can be applied as an effective approach for interference cancellation in high-frequency surface wave radar (HFSWR) and other systems. In order to suppress the nonstationary ionosphere clutter further, a novel OPPF based clutter suppressing scheme is proposed in this paper. The polarization and nonstationary characteristic of the clutter are taken into account in the algorithms referred to as range-Doppler domain polarization suppression (RDDPS) and the range-time domain polarization suppression (RTDPS) method, respectively. The RDDPS is designed for weak ionosphere clutter and implemented in the range-Doppler domain directly, whereas the RTDPS algorithm is designed to suppress the powerful ionosphere clutter with a multisegment estimation and suppression scheme. About 15–23 dB signal to interference ratio (SIR) improvement can be excepted when using the proposed method, whereas the targets can be more easily detected in the range-Doppler map. Experimental results demonstrate that the scheme proposed is effective for nonstationary ionosphere clutter and is proven to be a practical interference cancellation technique for HFSWR. Xingpeng Mao, Hong Hong, Weibo Deng, and Yongtan Liu Copyright © 2015 Xingpeng Mao et al. All rights reserved. A Butterfly-Shaped Wideband Microstrip Patch Antenna for Wireless Communication Thu, 21 May 2015 12:58:42 +0000 http://www.hindawi.com/journals/ijap/2015/328208/ A novel butterfly-shaped patch antenna for wireless communication is introduced in this paper. The antenna is designed for wideband wireless communications and radio-frequency identification (RFID) systems. Two symmetrical quasi-circular arms and two symmetrical round holes are incorporated into the patch of a microstrip antenna to expand its bandwidth. The diameter and position of the circular slots are optimized to achieve a wide bandwidth. The validity of the design concept is demonstrated by means of a prototype having a bandwidth of about 40.1%. The return loss of the butterfly-shaped antenna is greater than 10 dB between 4.15 and 6.36 GHz. The antenna can serve simultaneously most of the modern wireless communication standards. Liling Sun, Maowei He, Jingtao Hu, Yunlong Zhu, and Hanning Chen Copyright © 2015 Liling Sun et al. All rights reserved. The Application of JDL to Suppress Sea Clutter for Shipborne HFSWR Wed, 20 May 2015 09:03:28 +0000 http://www.hindawi.com/journals/ijap/2015/825350/ This paper deals with the problem of sea clutter suppression for shipborne high frequency surface wave radar (HFSWR) based on the joint domain localized (JDL) adaptive processing algorithm. The performance of the novel method is compared with 2D FFT plus digital beamforming (FFT-DBF) and orthogonal weight in different azimuths. The results based on simulated and real data show that the novel method provides higher detection performance than others. Zhenyuan Ji, Chunlei Yi, Junhao Xie, and Yang Li Copyright © 2015 Zhenyuan Ji et al. All rights reserved. Statistical Angular Resolution Limit for Ultrawideband MIMO Noise Radar Wed, 20 May 2015 08:40:59 +0000 http://www.hindawi.com/journals/ijap/2015/906313/ The two-dimensional angular resolution limit (ARL) of elevation and azimuth for MIMO radar with ultrawideband (UWB) noise waveforms is investigated using statistical resolution theory. First, the signal model of monostatic UWB MIMO noise radar is established in a 3D reference frame. Then, the statistical angular resolution limits (SARLs) of two closely spaced targets are derived using the detection-theoretic and estimation-theoretic approaches, respectively. The detection-theoretic approach is based on the generalized likelihood ratio test (GLRT) with given probabilities of false alarm and detection, while the estimation-theoretic approach is based on Smith’s criterion which involves the Cramér-Rao lower bound (CRLB). Furthermore, the relationship between the two approaches is presented, and the factors affecting the SARL, that is, detection parameters, transmit waveforms, array geometry, signal-to-noise ratio (SNR), and parameters of target (i.e., radar cross section (RCS) and direction), are analyzed. Compared with the conventional radar resolution theory defined by the ambiguity function, the SARL reflects the practical resolution ability of radar and can provide an optimization criterion for radar system design. Xiaoli Zhou, Hongqiang Wang, Yongqiang Cheng, Yuliang Qin, and Haowen Chen Copyright © 2015 Xiaoli Zhou et al. All rights reserved. Ship-Borne Phased Array Radar Using GA Based Adaptive α-β-γ Filter for Beamforming Compensation and Air Target Tracking Wed, 20 May 2015 06:49:47 +0000 http://www.hindawi.com/journals/ijap/2015/563726/ Beam pointing error caused by ship motion over the ocean affects the tracking performance of the ship-borne phased array radar. Due to the dynamic nature of the sea environments, the ship-borne phased array radar must be able to compensate for the ship’s motion adaptively. In this paper, the adaptive α-β-γ filter is proposed for the ship-borne phased array radar to compensate for the beam pointing error and to track the air target. The genetic algorithm (GA) and the particle swarm optimization (PSO) methods are applied to estimate the gain parameters of adaptive α-β-γ filters, while achieving the optimum objective of minimum root mean square error (RMSE). The roll and pitch data measured from a gyroscope of the sea vehicle and generated from ship motion mathematical model are used in the experiments. The tracking accuracy of adaptive α-β-γ filter using the GA method is compared with PSO method under different ship motion conditions. The convergent time and tracking accuracy of ship-borne phased array radar using the proposed GA based adaptive α-β-γ filter are also compared with the adaptive extended Kalman filter (AEKF). Finally, it is proved that the proposed GA based adaptive α-β-γ filter is a real time applicable algorithm for ship-borne phased array radar. J. Mar, Chen-Chih Liu, and M. B. Basnet Copyright © 2015 J. Mar et al. All rights reserved. Joint Phased-MIMO and Nested-Array Beamforming for Increased Degrees-of-Freedom Wed, 20 May 2015 06:34:53 +0000 http://www.hindawi.com/journals/ijap/2015/989517/ Phased-multiple-input multiple-output (phased-MIMO) enjoys the advantages of MIMO virtual array and phased-array directional gain, but it gets the directional gain at a cost of reduced degrees-of-freedom (DOFs). To compensate the DOF loss, this paper proposes a joint phased-array and nested-array beamforming based on the difference coarray processing and spatial smoothing. The essence is to use a nested-array in the receiver and then fully exploit the second order statistic of the received data. In doing so, the array system offers more DOFs which means more sources can be resolved. The direction-of-arrival (DOA) estimation performance of the proposed method is evaluated by examining the root-mean-square error. Simulation results show the proposed method has significant superiorities to the existing phased-MIMO. Chenglong Zhu, Hui Chen, and Huaizong Shao Copyright © 2015 Chenglong Zhu et al. All rights reserved. Bandwidth Enhancement Technique of the Meandered Monopole Antenna Wed, 20 May 2015 06:34:23 +0000 http://www.hindawi.com/journals/ijap/2015/904741/ A small dual-band monopole antenna with coplanar waveguide (CPW) feeding structure is presented in this paper. The antenna is composed of a meandered monopole, an extended conductor tail, and an asymmetrical ground plane. Tuning geometrical structure of the ground plane excites an additional resonant frequency band and thus enhances the impedance bandwidth of the meandered monopole antenna. Unlike the conventional monopole antenna, the new resonant mode is excited by a slot trace of the CPW transmission line. The radiation performance of the slot mode is as similar as that of the monopole. The parametrical effect of the size of the one-side ground plane on impedance matching condition has been derived by the simulation. The measured impedance bandwidths, which are defined by the reflection coefficient of −6 dB, are 186 MHz (863–1049 MHz, 19.4%) at the lower resonant band and 1320 MHz (1490–2810 MHz, 61.3%) at the upper band. From the results of the reflection coefficients of the proposed monopole antenna, the operated bandwidths of the commercial wireless communication systems, such as GSM 900, DCS, IMT-2000, UMTS, WLAN, LTE 2300, and LTE 2500, are covered for uses. Chien-Jen Wang and Dai-Heng Hsieh Copyright © 2015 Chien-Jen Wang and Dai-Heng Hsieh. All rights reserved. Beamspace Unitary ESPRIT Algorithm for Angle Estimation in Bistatic MIMO Radar Wed, 20 May 2015 06:28:31 +0000 http://www.hindawi.com/journals/ijap/2015/621358/ The beamspace unitary ESPRIT (B-UESPRIT) algorithm for estimating the joint direction of arrival (DOA) and the direction of departure (DOD) in bistatic multiple-input multiple-output (MIMO) radar is proposed. The conjugate centrosymmetrized DFT matrix is utilized to retain the rotational invariance structure in the beamspace transformation for both the receiving array and the transmitting array. Then the real-valued unitary ESPRIT algorithm is used to estimate DODs and DOAs which have been paired automatically. The proposed algorithm does not require peak searching, presents low complexity, and provides a significant better performance compared to some existing methods, such as the element-space ESPRIT (E-ESPRIT) algorithm and the beamspace ESPRIT (B-ESPRIT) algorithm for bistatic MIMO radar. Simulation results are conducted to show these conclusions. Dang Xiaofang, Chen Baixiao, Yang Minglei, and Zheng Guimei Copyright © 2015 Dang Xiaofang et al. All rights reserved. Design of a Circularly Polarized Galileo E6-Band Textile Antenna by Dedicated Multiobjective Constrained Pareto Optimization Wed, 20 May 2015 06:13:06 +0000 http://www.hindawi.com/journals/ijap/2015/895963/ Designing textile antennas for real-life applications requires a design strategy that is able to produce antennas that are optimized over a wide bandwidth for often conflicting characteristics, such as impedance matching, axial ratio, efficiency, and gain, and, moreover, that is able to account for the variations that apply for the characteristics of the unconventional materials used in smart textile systems. In this paper, such a strategy, incorporating a multiobjective constrained Pareto optimization, is presented and applied to the design of a Galileo E6-band antenna with optimal return loss and wide-band axial ratio characteristics. Subsequently, different prototypes of the optimized antenna are fabricated and measured to validate the proposed design strategy. Arnaut Dierck, Frederick Declercq, Thomas Vervust, and Hendrik Rogier Copyright © 2015 Arnaut Dierck et al. All rights reserved. Multitarget Direct Localization Using Block Sparse Bayesian Learning in Distributed MIMO Radar Tue, 19 May 2015 14:35:27 +0000 http://www.hindawi.com/journals/ijap/2015/903902/ The target localization in distributed multiple-input multiple-output (MIMO) radar is a problem of great interest. This problem becomes more complicated for the case of multitarget where the measurement should be associated with the correct target. Sparse representation has been demonstrated to be a powerful framework for direct position determination (DPD) algorithms which avoid the association process. In this paper, we explore a novel sparsity-based DPD method to locate multiple targets using distributed MIMO radar. Since the sparse representation coefficients exhibit block sparsity, we use a block sparse Bayesian learning (BSBL) method to estimate the locations of multitarget, which has many advantages over existing block sparse model based algorithms. Experimental results illustrate that DPD using BSBL can achieve better localization accuracy and higher robustness against block coherence and compressed sensing (CS) than popular algorithms in most cases especially for dense targets case. Bin Sun, Haowen Chen, Xizhang Wei, and Xiang Li Copyright © 2015 Bin Sun et al. All rights reserved. Direct Data Domain Sparsity-Based STAP Utilizing Subaperture Smoothing Techniques Tue, 19 May 2015 13:51:32 +0000 http://www.hindawi.com/journals/ijap/2015/171808/ We propose a novel direct data domain (D3) sparsity-based space-time adaptive processing (STAP) algorithm utilizing subaperture smoothing techniques for airborne radar applications. Different from either normal sparsity-based STAP or D3 sparsity-based STAP, the proposed algorithm firstly uses only the snapshot in the cell under test (CUT) to generate multiple subsnapshots by exploiting the space-time structure of the steering vector and the uncorrelated nature of the components of the interference covariance matrix. Since the interference spectrum is sparse in the whole angle-Doppler plane, by employing a sparse regularization, the generated multiple subsnapshots are jointly used to recover the interference spectrum. The interference covariance matrix is then estimated from the interference spectrum, followed by the space-time filtering and the target detection. Simulation results illustrate that the proposed algorithm outperforms the generalized forward/backward method, the conventional D3 least squares STAP algorithm, and the existing D3 sparsity-based STAP algorithm. Furthermore, compared with the normal sparsity-based STAP algorithm using multiple snapshots, the proposed algorithm can also avoid the performance degradation caused by discrete interferers merely appearing in the CUT. Zhaocheng Yang, Rui Fa, Yuliang Qin, Xiang Li, and Hongqiang Wang Copyright © 2015 Zhaocheng Yang et al. All rights reserved. A Compact Wideband Dual-Polarized Antenna with Harmonic Suppression Using Nonuniform Defected Ground Structure Tue, 19 May 2015 13:45:56 +0000 http://www.hindawi.com/journals/ijap/2015/505123/ A wideband dual-polarized coplanar waveguide (CPW) fed antenna integrating a wide stop-band filter is presented. The designed filter is based on a nonuniform defected ground structure (DGS) in order to obtain a wide stop-band and a compact size. This filter is used to reject harmonics and spurious radiation arising from the RF front end. The complete structure (antenna and filter) has been optimized to have a compact size of ( being the free-space wavelength at the lowest operating frequency). The realized antenna operates in the frequency range between 2.7 GHz and 5.9 GHz (bandwidth of about 74%). The isolation between feeding ports is more than 18 dB. The complete structure has a wide stop-band characteristic (103%) for harmonic rejection. The simulated numerical results have been confirmed with measurements. Lana Damaj, Anne-Claire Lepage, and Xavier Begaud Copyright © 2015 Lana Damaj et al. All rights reserved. An Improved Antenna Array Pattern Synthesis Method Using Fast Fourier Transforms Tue, 19 May 2015 13:09:06 +0000 http://www.hindawi.com/journals/ijap/2015/316962/ An improved antenna array pattern synthesis method using fast Fourier transform is proposed, which can be effectively applied to the synthesis of large planar arrays with periodic structure. Theoretical and simulative analyses show that the original FFT method has a low convergence rate and the converged solution can hardly fully meet the requirements of the desired pattern. A scaling factor is introduced to the original method. By choosing a proper value for the scaling factor, the convergence rate can be greatly improved and the final solution is able to fully meet the expectations. Simulation results are given to demonstrate the effectiveness of the proposed algorithm. Xucun Wang, Yiguo Zhou, and Yanfei Wang Copyright © 2015 Xucun Wang et al. All rights reserved. Two-Dimensional Direction of Arrival (DOA) Estimation for Rectangular Array via Compressive Sensing Trilinear Model Tue, 19 May 2015 13:03:24 +0000 http://www.hindawi.com/journals/ijap/2015/297572/ We investigate the topic of two-dimensional direction of arrival (2D-DOA) estimation for rectangular array. This paper links angle estimation problem to compressive sensing trilinear model and derives a compressive sensing trilinear model-based angle estimation algorithm which can obtain the paired 2D-DOA estimation. The proposed algorithm not only requires no spectral peak searching but also has better angle estimation performance than estimation of signal parameters via rotational invariance techniques (ESPRIT) algorithm. Furthermore, the proposed algorithm has close angle estimation performance to trilinear decomposition. The proposed algorithm can be regarded as a combination of trilinear model and compressive sensing theory, and it brings much lower computational complexity and much smaller demand for storage capacity. Numerical simulations present the effectiveness of our approach. Huaxin Yu, Xiaofeng Qiu, Xiaofei Zhang, Chenghua Wang, and Gang Yang Copyright © 2015 Huaxin Yu et al. All rights reserved. A Generalized Oblique Projection Filter with Flexible Parameter for Interference Suppression Tue, 19 May 2015 13:00:05 +0000 http://www.hindawi.com/journals/ijap/2015/320769/ A generalized oblique projection (GOP) with an adjustable parameter defined as interference suppression cost (ISC) is proposed. Therefore, an optional optimized signal to interference-plus-noise ratio (SINR) and user controlled actions on the interference filtering are presented in this GOP framework. Theoretical analysis and numerical simulation demonstrate that when the ISC is derived from minimum variance distortionless response (MVDR) algorithm, the SINR performance of GOP filter is better than both MVDR and oblique projection (OP) filters. Further, an application of GOP filter in ionospheric clutter cancellation in a high frequency surface wave radar (HFSWR) system is given. The ISC is designed specifically to introduce an extra coherent loss to the clutters and a satisfying clutter suppression result is achieved. Besides the examples given, more designs of GOP filter can be inspired by the flexibility of ISC. As a generalized form of OP filter, GOP filter expands the connotation of oblique projection based technique and could be used in spatial filtering, polarization filtering, and other array signal processing applications. Yi-ming Wang, Xing-peng Mao, Hong Hong, Jie Zhang, and Yu-mei Cui Copyright © 2015 Yi-ming Wang et al. All rights reserved. Novel Multiband Metal-Rimmed Antenna for Wearable Applications Tue, 19 May 2015 11:41:28 +0000 http://www.hindawi.com/journals/ijap/2015/319894/ A novel multiband antenna with an unbroken metal rim for wearable applications is presented. In order to achieve a wideband behavior, minimizing at the same time the size of the clearance area on the antenna ground plane, a novel feeding structure is proposed. This is achieved by connecting the metal rim to the ground plane thus allowing generating one lower-frequency resonance without occupying a large area. An additional resonance is then obtained using a suitable shorting patch. In this way, the proposed antenna presents a broadband behavior, while the width of the clearance area on the ground plane is of only 2 mm. The antenna performances in free-space and on a human phantom simulating a human body are analyzed by means of numerical simulations. Finally, the specific absorption rate (SAR) is analyzed to establish the antenna reliability in wearable applications. The experimental results demonstrate superior and stable performances of the metal-rimmed antenna when it is employed in wearable applications. Bin Liu, Jianghong Han, Songhua Hu, and Li Zhang Copyright © 2015 Bin Liu et al. All rights reserved. Design of a Smart Antenna for Mobile Ad Hoc Network Applications Tue, 19 May 2015 11:40:43 +0000 http://www.hindawi.com/journals/ijap/2015/273047/ Among the mobile ad hoc networks appealing characteristics there are network reconfigurability and flexibility. In this context a smart antenna capable of self-configuring multiple high-directivity beams provides a major advantage in terms of power saving, increased range, and spatial reuse of channels. In this paper a smart antenna made of a cylindrical array of patches suitable for MANETs is presented. Marco Di Filippo, Leonardo Lucci, Dania Marabissi, and Stefano Selleri Copyright © 2015 Marco Di Filippo et al. All rights reserved. Beam Scanning Properties of a Ferrite Loaded Microstrip Patch Antenna Tue, 19 May 2015 11:35:51 +0000 http://www.hindawi.com/journals/ijap/2015/697409/ Axially magnetized ferrite loaded microstrip patch antenna (MPA) with tunable beam scanning properties is presented. Ferrite cylinders are optimally positioned within the near field region of the patch to introduce phase tapers needed for beam scanning. The interaction between the radiated EM wave and the gyrotropic properties of ferrites is controlled by varying the magnetizing fields. A beam scan of ° is achieved for a DC biasing range of 0–0.19 T. Simulated antenna properties are verified using experimental results. Recent LTCC technology allows the biasing coils to be embedded within the ferrite material to considerably reduce the required external magnetizing field. Sheikh Sharif Iqbal Mitu and Farooq Sultan Copyright © 2015 Sheikh Sharif Iqbal Mitu and Farooq Sultan. All rights reserved. Design of Compact Trapezoidal Bow-Tie Chipless RFID Tag Tue, 19 May 2015 11:35:49 +0000 http://www.hindawi.com/journals/ijap/2015/502938/ This paper presents a novel compact design of a low cost fully printable slot-loaded bowtie chipless RFID tag. The tag consists of two trapezoidal metallic patches loaded with multiple slot resonators. Slots with similar size or adjacent frequencies are loaded alternately on two bow-tie patches to double the number of data bits within the UWB frequency band without increasing the mutual coupling between slots. A coding capacity of 12 bits is obtained with 12 slots within a reasonable size of 35 mm 33 mm. RCS of the tag has been given by simulation. Measurements have been done using a bistatic radar configuration in the frequency domain and transmission coefficient is measured. The agreement between the simulation and measurement validates this new concept of design. This tag has high data capacity and low cost and can be directly printed on product such as personal ID, credit cards, paper, and textile because it needs only one conductive layer. Lei Xu and Kama Huang Copyright © 2015 Lei Xu and Kama Huang. All rights reserved. Culture Medium Geometry: The Dominant Factor Affecting In Vitro RF Exposure Dosimetry Tue, 19 May 2015 11:25:52 +0000 http://www.hindawi.com/journals/ijap/2015/438962/ Biological experiments that expose living cells or tissues to RF energy must have an aqueous medium to provide essential water, ions, nutrients, and growth factors. However, as we show here, the medium inherently functions as a receiving antenna that conveys RF energy to the biological entity in a manner entirely determined by exposure vessel geometry, orientation to the incident RF flux, frequency, and dielectric properties of the medium. We show for two common experimental arrangements that basic antenna theory can predict electromagnetic energy patterns that agree well with those otherwise obtained by computationally intensive methods that require specialized resources. Alessandra Paffi, Francesca Apollonio, Micaela Liberti, Asher Sheppard, Giorgi Bit-Babik, and Quirino Balzano Copyright © 2015 Alessandra Paffi et al. All rights reserved. Metamaterial Inspired Microstrip Antenna Investigations Using Metascreens Tue, 19 May 2015 09:46:29 +0000 http://www.hindawi.com/journals/ijap/2015/236136/ A dual layer periodically patterned metamaterial inspired antenna on a low cost FR4 substrate is designed, simulated, fabricated, and tested. The eigenmode dispersion simulations are performed indicating the left handed metamaterial characteristics and are tunable with substrate permittivity. The same metamaterial unit cell structure is utilized to fabricate a metascreen. This metascreen is applied below the proposed metamaterial antenna and next used as superstrate above a simple patch to study the effects on impedance bandwidth, gain, and radiation patterns. The experimental results of these antennas are very good and closely match with the simulations. More importantly, the resonance for the proposed metamaterial antenna with metascreen occurs at the left handed (LH) eigenfrequency of the metamaterial unit cell structure. The measured −10 dB bandwidths are 14.56% and 22.86% for the metamaterial antenna with single and double metascreens, respectively. The metascreens over the simple patch show adjacent dual band response. The first and second bands have measured −10 dB bandwidths of 9.6% and 16.66%. The simulated peak gain and radiation efficiency are 1.83 dBi and 74%, respectively. The radiation patterns are also very good and could be useful in the UWB wireless applications. Muhammad Tauseef Asim and Mushtaq Ahmed Copyright © 2015 Muhammad Tauseef Asim and Mushtaq Ahmed. All rights reserved. High-Efficiency Electromagnetic Wave Controlling with All-Dielectric Huygens’ Metasurfaces Tue, 19 May 2015 09:16:00 +0000 http://www.hindawi.com/journals/ijap/2015/432095/ Subwavelength dielectric blocks with varying thicknesses are introduced to realize 0∼2 phase change. A Huygens’ metasurface composed of such nonuniform building blocks is shown to efficiently refract normally incident waves in a broadband. According to the same physical mechanism, we fabricate an electrically thin lens with concentric subwavelength dielectric blocks and integrate it with a patch antenna to form a three-dimensional (3D) ultra-low-profile lens antenna system. Full-wave simulation demonstrates the lens antenna’s excellent performances in high directivity, broadband, low loss, and low side-lobe levels. Zheng-bin Wang, Jin Shi, and Jin-chang Chen Copyright © 2015 Zheng-bin Wang et al. All rights reserved. Polarized Uniform Linear Array System: Beam Radiation Pattern, Beamforming Diversity Order, and Channel Capacity Tue, 19 May 2015 09:10:08 +0000 http://www.hindawi.com/journals/ijap/2015/371236/ There have been many studies regarding antenna polarization; however, there have been few publications on the analysis of the channel capacity for polarized antenna systems using the beamforming technique. According to Chung et al., the channel capacity is determined by the density of scatterers and the transmission power, which is obtained based on the assumption that scatterers are uniformly distributed on a 3D spherical scattering model. However, it contradicts the practical scenario, where scatterers may not be uniformly distributed under outdoor environment, and lacks the consideration of fading channel gain. In this study, we derive the channel capacity of polarized uniform linear array (PULA) systems using the beamforming technique in a practical scattering environment. The results show that, for PULA systems, the channel capacity, which is boosted by beamforming diversity, can be determined using the channel gain, beam radiation pattern, and beamforming diversity order (BDO), where the BDO is dependent on the antenna characteristics and array configurations. Xin Su and KyungHi Chang Copyright © 2015 Xin Su and KyungHi Chang. All rights reserved. Design Variations on Planar Differential Antenna with Potential for Multiple, Wide, and Narrow Band Coverage Tue, 19 May 2015 08:43:50 +0000 http://www.hindawi.com/journals/ijap/2015/478453/ This paper presents three practical antenna implementations based on variations of one general planar differential antenna topology originally proposed for ultrawideband (UWB) applications. All designs were implemented on a low-cost FR4 substrate and experimentally characterized in an anechoic chamber. The results show how the proposed design variations lead to the required antenna performances and how they give rise to new opportunities in terms of coverage of wide, narrow, and multiple frequency bands for communication and sensing applications below 5 GHz. In particular, the results show how a significant enhancement in bandwidth performance is achieved by folding the differential radiating elements. Moreover, they show how an agile design strategy enables adaption of the antenna design to different requirements for covering wide, narrow, and multiple bands, making the proposed class of antennas suitable for different wireless applications. In detail, the proposed class of antennas covers multiple frequency bands, ranging from the 868 MHz and 915 MHz bands to 2.4 GHz industrial scientific and medical (ISM) bands, including the 1.2 GHz L band for Global Positioning and Navigation Satellite Systems (GNSS) and the lower portion of the UWB band. Domenico Pepe, Luigi Vallozzi, Hendrik Rogier, and Domenico Zito Copyright © 2015 Domenico Pepe et al. All rights reserved. Control of the Radiation Patterns Using Homogeneous and Isotropic Impedance Metasurface Tue, 19 May 2015 08:35:19 +0000 http://www.hindawi.com/journals/ijap/2015/917829/ We propose to control the radiation patterns of a two-dimensional (2D) point source by using impedance metasurfaces. We show that the radiation patterns can be manipulated by altering the surface impedance of the metasurface. Full-wave simulation results are provided to validate the theoretical derivations. The proposed design enjoys novel properties of isotropy, homogeneity, low profile, and high selectivity of frequency, making it potentially applicable in many applications. We also point out that this design can be implemented with active metasurfaces and the surface impedance can be tuned by modulating the value of loaded elements, like resistors, inductors, and capacitors. Fan Yang, Zhong Lei Mei, and Tie Jun Cui Copyright © 2015 Fan Yang et al. All rights reserved. Suppression of Specular Reflections by Metasurface with Engineered Nonuniform Distribution of Reflection Phase Mon, 18 May 2015 13:21:58 +0000 http://www.hindawi.com/journals/ijap/2015/560403/ We make preliminary investigations on a new approach to reducing radar cross section (RCS) of conducting objects. This approach employs novel planar metasurfaces characterizing nonuniform distribution of reflection phase. The operation principle of this approach and the design rule of the associated metasurfaces are explained using a simplified theoretical model. We then present a design example of such metasurfaces, in which three-layer stacked square patches with variable sizes are utilized as the reflecting elements. The proposed RCS-reduction approach is verified by both numerical simulations and measurements on the example, under the assumption of normal plane wave incidence. It is observed that, in a fairly wide frequency band (from 3.6 to 5.5 GHz), the presented example is capable of suppressing the specular reflections of conducting plates significantly (by more than 7 dB) for two orthogonal incident polarizations. Xin Mi Yang, Ge Lan Jiang, Xue Guan Liu, and Cheng Xiang Weng Copyright © 2015 Xin Mi Yang et al. All rights reserved. Design of a Compact and High Sensitivity Temperature Sensor Using Metamaterial Mon, 18 May 2015 12:29:05 +0000 http://www.hindawi.com/journals/ijap/2015/301358/ The present paper aims at sensing the temperature. A sensor metamaterial consisting of two concentric metallic rings and a thin metallic wire deposited on the surface of BaTiO3 substrate is reported. The use of BaTiO3 makes the resonant frequency of the structure shift as the temperature varies and makes the sensor applicable in many fields of applications. Numerical simulations and theoretical results are presented and compared to each other; there was a good agreement between them. This sensor is smaller, easier to fabricate, and very sensitive to the changes in temperatures. Sabah Zemouli, Abdelhafid Chaabi, and Houcine Sofiane Talbi Copyright © 2015 Sabah Zemouli et al. All rights reserved. Modified Luneburg Lens Based on Metamaterials Mon, 18 May 2015 12:26:19 +0000 http://www.hindawi.com/journals/ijap/2015/902634/ We present the design, fabrication, and experimental characterization of a modified two-dimensional Luneburg lens based on bulk metamaterials. The lens is composed by a number of concentric layers. By varying the geometric dimensions of unit cells in each layer, the gradient refractive index profile required for the modified Luneburg lens can be achieved. The cylindrical waves generated from a point source at the focus point of the lens could be transformed into plane waves as desired in the microwave frequency. The proposed modified Luneburg lens can realize wide-angle beam scanning when the source moves along the circumferential direction inside the lens. Numerical and experimental results validate the performance of the modified Luneberg lens. Haibing Chen, Qiang Cheng, Aihua Huang, Junyan Dai, Huiying Lu, Jie Zhao, Huifeng Ma, Weixiang Jiang, and Tiejun Cui Copyright © 2015 Haibing Chen et al. All rights reserved. Compact Two-Section Half-Wave Balun Based on Planar Artificial Transmission Lines Mon, 18 May 2015 11:41:44 +0000 http://www.hindawi.com/journals/ijap/2015/256536/ Artificial transmission lines are realized by a series of meandered-line inductors, parallel-plate capacitors, and interdigital capacitors, which belong to metamaterial transmission lines. An ameliorated artificial transmission line is proposed to realize a low characteristic impedance transmission line. A two-section half-wave balun at 900 MHz is designed, fabricated, and measured in this paper. The compact balun is based on conventional and ameliorated planar artificial transmission lines instead of microstrip transmission lines. The main advantage of the proposed balun is its size reduction, which occupies only about 10% of a conventional one. Measured results match well with theory and simulation. The balun features excellent amplitude and phase balance in microwave power combining and a reasonable bandwidth of the return loss as well. Changjun Liu, Zhenyu Yin, Yilan Yang, and Wen Huang Copyright © 2015 Changjun Liu et al. All rights reserved.