International Journal of Antennas and Propagation http://www.hindawi.com The latest articles from Hindawi Publishing Corporation © 2016 , Hindawi Publishing Corporation . All rights reserved. Transient Electromagnetic Field Coupling to Buried Thin Wire Configurations: Antenna Model versus Transmission Line Approach in the Time Domain Thu, 11 Feb 2016 17:18:08 +0000 http://www.hindawi.com/journals/ijap/2016/3943754/ The paper examines the antenna model for the transient analysis of electromagnetic field coupling to straight wire configurations buried in a lossy half-space. The wire antenna theory (AT) model is implemented directly in the time domain and it is based on the corresponding space-time Pocklington integrodifferential equation. The solution of the Pocklington equation is carried out analytically. The obtained results are compared against the results calculated via the transmission line (TL) approach. The TL approach is based on the telegrapher’s equations, which are solved using the modified transmission line method (MTLM) and Finite Difference Time Domain (FDTD) technique, respectively. Some illustrative computational examples for buried straight wire scatterer and horizontal grounding electrode are given throughout this work. Dragan Poljak, Silvestar Šesnić, Khalil El-Khamlichi Drissi, Kamal Kerroum, and Sergey Tkachenko Copyright © 2016 Dragan Poljak et al. All rights reserved. Blind Direction-of-Arrival Estimation with Uniform Circular Array in Presence of Mutual Coupling Sun, 07 Feb 2016 13:56:38 +0000 http://www.hindawi.com/journals/ijap/2016/8109013/ A blind direction-of-arrival (DOA) estimation algorithm based on the estimation of signal parameters via rotational invariance techniques (ESPRIT) is proposed for a uniform circular array (UCA) when strong electromagnetic mutual coupling is present. First, an updated UCA model with mutual coupling in a discrete Fourier transform (DFT) beam space is deduced, and the new manifold matrix is equal to the product of a centrosymmetric diagonal matrix and a Vandermonde-structure matrix. Then we carry out blind DOA estimation through a modified ESPRIT method, thus avoiding the need for spatial angular searching. In addition, two mutual coupling parameter estimation methods are presented after the DOAs have been estimated. Simulation results show that the new algorithm is reliable and effective especially for closely spaced signals. Song Liu, Lisheng Yang, Shizhong Yang, Qingping Jiang, and Haowei Wu Copyright © 2016 Song Liu et al. All rights reserved. Composite GPS Patch Antenna for the AR Bandwidth Enhancement Sun, 07 Feb 2016 13:39:32 +0000 http://www.hindawi.com/journals/ijap/2016/3250920/ A composite Global Positioning System (GPS) patch antenna with a quadrature 3 dB hybrid coupler was designed and implemented for working RHCP and had a broadband axial ratio (AR) bandwidth. We designed two patches as a FR-4 patch and 1.5 mm thickness thin ceramic patch with a quadrature 3 dB hybrid coupler. A CP radiation pattern was achieved, and the AR bandwidth improved by incorporating a quadrature 3 dB hybrid coupler feed structure in a micro-strip patch antenna. SMD by chip elements was applied to the quadrature 3 dB hybrid coupler. For the composite FR-4 and ceramic patch antennas, the VSWR measurement showed a 2 : 1 ratio over the entire design band, and the 3 dB AR bandwidth was 295 and 580 MHz for the FR-4 patch and ceramic patch antennas, respectively. The antenna gains for the composite FR-4 and ceramic patch antennas were measured as 1.36–2.75 and 1.47–2.71 dBi with 15.11–25.3% and 19.25–28.45% efficiency, respectively. Minkil Park, Wonhee Lee, and Taeho Son Copyright © 2016 Minkil Park et al. All rights reserved. Coordinated Semidirectional Distributed Antenna System with Capacity and Energy Efficiency Analyses for Cloud Cellular Network Thu, 04 Feb 2016 13:33:55 +0000 http://www.hindawi.com/journals/ijap/2016/8042871/ In order to further explore the coordination gain from the cloud cellular network, the Coordinated Semidirectional Distributed Antenna System (CS-DAS) is proposed with deploying 180-degree sector antennas. Based on the CS-DAS, the coordinated cellular deployment structure is established with corresponding communication procedure designs. The handover process for CS-DAS is designed with less handover rate and signaling overheads. The system performances of ergodic capacity and Energy Efficiency are derived, with a strong focus on the downlink performances, and analyzed with comparisons of current cellular structure. The numerical expressions of ergodic capacity are obtained with improvements of coordinated gain. The Energy Efficiency with different transmission modes is also investigated. The simulation results verify the performance improvements. Xiaodong Xu, Chengjin Luo, Ya Liu, Xiaofeng Tao, and Ping Zhang Copyright © 2016 Xiaodong Xu et al. All rights reserved. A Liquid Metal Conical Helical Antenna for Circular Polarization-Reconfigurable Antenna Tue, 02 Feb 2016 08:39:06 +0000 http://www.hindawi.com/journals/ijap/2016/3782373/ A novel polarization-reconfigurable conical helical antenna based on the liquid metal is presented. The antenna is implemented by using truncated structure, variable pitch angle, a matching stub, and a mechanical autorotation device. The experimental results show that a good agreement between simulations and measurements is obtained. The gain of the antenna achieves higher than 8 dBi in the work band (1525–1660.5 MHz), and the 3 dB axial ratio (AR) bandwidth reaches 410 MHz. The polarization mode of the antenna can be switched between right-hand and left-hand circular polarization. Yun Zhou, Shaojun Fang, Hongmei Liu, and Shiqiang Fu Copyright © 2016 Yun Zhou et al. All rights reserved. Low-Profile Repeater Antenna with Parasitic Elements for On-On-Off WBAN Applications Tue, 02 Feb 2016 06:39:53 +0000 http://www.hindawi.com/journals/ijap/2016/4743207/ A low-profile repeater antenna with parasitic elements for on-on-off WBAN applications is proposed. The proposed antenna consists of a planar inverted-F antenna (PIFA), two parasitic elements, and a ground plane with a slot. Due to the slot, the impedance matching of the resonance formed by the PIFA is improved, which makes the proposed antenna operate in the 5.8 GHz industrial, scientific, and medical (ISM) band. To cover the 5.2 GHz wireless local area network (WLAN) band, a dual resonance characteristic is realized by the slot and the two parasitic elements. The first coupling between the PIFA and the slot not only makes the slot operate as a resonator, but also forms secondary coupling between the slot and the two parasitic elements. The two parasitic elements operate as an additional resonator due to secondary coupling. The antenna has the enhanced near surface radiation in the 5.8 GHz ISM band due to addition of the slot and radiation toward off-body direction in the 5.2 GHz WLAN band. In order to evaluate antenna performance considering the human body effect, the antenna characteristics on a human equivalent phantom are analyzed. Do-Gu Kang, Jinpil Tak, and Jaehoon Choi Copyright © 2016 Do-Gu Kang et al. All rights reserved. Spatial Stationarity of Ultrawideband and Millimeter Wave Radio Channels Sun, 31 Jan 2016 12:44:20 +0000 http://www.hindawi.com/journals/ijap/2016/3212864/ For radio channels with broad bandwidth resource, such as those often used for ultrawideband (UWB) and millimeter wave (mmwave) systems, the Wide-Sense Stationary Uncorrelated Scattering (WSSUS) and spatial stationary assumptions are more critical than typical cellular channels with very limited bandwidth resource. This paper studies spatial stationarity and bandwidth dependency of the Multipath Component (MPC) parameters, and the concept of local region of stationarity (LRS) is used as the measure of the physical stationarity region. LRS calculation results based on channel measurements show that the size of LRS is bandwidth dependent in all measured bands, 2–4 GHz, 14–16 GHz, and 28–30 GHz. The results in this paper point out that an inappropriate choice of bandwidth in channel parameter estimation could violate spatial stationary assumptions. The paper indicates LRS sizes for different bandwidths in the three bands. Yi Tan, Jesper Ødum Nielsen, and Gert Frølund Pedersen Copyright © 2016 Yi Tan et al. All rights reserved. RF Performance of Layer-Structured Broadband Passive Millimeter-Wave Imaging System Thu, 28 Jan 2016 13:41:32 +0000 http://www.hindawi.com/journals/ijap/2016/6894676/ Low profile and simple configuration are advantageous for RF module in passive millimeter-wave imaging system. High sensitivity over broad operation bandwidth is also necessary to detect right information from weak signal. We propose a broadband layer-structured module with low profile, simple structure, and ease of manufacture. This module is composed of a lens antenna and a detector module that consists of a detector circuit and a broadband microstrip-to-waveguide transition. The module forms a layer structure as a printed substrate with detector circuit is fixed between two metal plates with horn antennas and back-short waveguides. We developed a broadband passive millimeter-wave imaging module composed of a lens antenna and a detector module in this work. The gain and the antenna efficiency were measured, and the broadband operation was observed for the lens antenna. For the detector module, peak sensitivity was 8100 V/W. Furthermore, the detector module recognized a difference in the absorber’s temperature. The designs of the lens antenna and the detector module are presented and the RF performances of these components are reported. Finally, passive millimeter-wave imaging of a car, a human, and a metal plate in clothes is demonstrated in this paper. Kunio Sakakibara, Kunihiko Ohkawa, Yutaka Aoki, and Nobuyoshi Kikuma Copyright © 2016 Kunio Sakakibara et al. All rights reserved. Transmit/Receive Spatial Smoothing with Improved Effective Array Aperture for Angle and Mutual Coupling Estimation in Bistatic MIMO Radar Wed, 27 Jan 2016 08:12:48 +0000 http://www.hindawi.com/journals/ijap/2016/6271648/ We proposed a transmit/receive spatial smoothing with improved effective aperture approach for angle and mutual coupling estimation in bistatic MIMO radar. Firstly, the noise in each channel is restrained, by exploiting its independency, in both the spatial domain and temporal domain. Then the augmented transmit and receive spatial smoothing matrices with improved effective aperture are obtained, by exploiting the Vandermonde structure of steering vector with uniform linear array. The DOD and DOA can be estimated by utilizing the unitary ESPRIT algorithm. Finally, the mutual coupling coefficients of both the transmitter and the receiver can be figured out with the estimated angles of DOD and DOA. Numerical examples are presented to verify the effectiveness of the proposed method. Haomiao Liu, Xiaojun Yang, Rong Wang, Wei Jin, and Weimin Jia Copyright © 2016 Haomiao Liu et al. All rights reserved. Design of a Broadband Inverted Conical Quadrifilar Helix Antenna Tue, 26 Jan 2016 11:45:16 +0000 http://www.hindawi.com/journals/ijap/2016/5109875/ This paper introduces the design of a broadband inverted conical circularly polarized quadrifilar helix antenna (QHA). The antenna has many good characteristics, including wide beam and broad bandwidth, which are achieved by utilizing inverted conical geometry and adjusting the dimensions of the inverted conical support. The antenna is fed by a wideband network to provide 90° phase difference between the four arms with constant amplitude. The antenna impedance and axial ratio bandwidth values are more than 39% and 31.5%, respectively. The measured results coincide well with the simulated ones, which verified the effectiveness of the proposed design. Jingyan Mo, Wei Liu, Weidong Fang, Haigao Xue, and Zhongchao Lin Copyright © 2016 Jingyan Mo et al. All rights reserved. Advances in New Signal Processing Techniques for 5G Tue, 26 Jan 2016 08:12:42 +0000 http://www.hindawi.com/journals/ijap/2016/4345762/ Kan Zheng, Xianbin Wang, Periklis Chatzimisios, and Wei Xiang Copyright © 2016 Kan Zheng et al. All rights reserved. A W-Band Radiometer with the Offset Parabolic Antenna for Radiometric Measurements Thu, 21 Jan 2016 12:18:45 +0000 http://www.hindawi.com/journals/ijap/2016/4705072/ This paper deals with the development of a W-band noise-adding radiometer which combines the millimeter-wave (MMW) radiometric measurements with a high-resolution imager. The offset parabolic antenna is presented to achieve an accurate measurement and a high resolution. To reduce the cross-polarization level of the antenna, a multimode feed horn with a multistep structure is proposed to match the focal region fields of the reflector. It has advantages over the corrugated horns in lower mass and easier manufacturing. In addition, due to an unavoidable settling time for the noise-adding radiometer output signal passing through the low-pass filter, a theoretical criterion for the optimum duty cycle determination to reject extraneous contributions from the transient is proposed in this paper. The appropriate duty cycle threshold is 0.33 for the developed W-band radiometer. Also, a geometric correction method is presented to correct the obtained passive image suffering from a distortion for a better image interpretation. Preliminary experimental results are given to illustrate and verify the presented techniques. Li Wu, Shu-sheng Peng, Jian-zhong Xu, and Ze-long Xiao Copyright © 2016 Li Wu et al. All rights reserved. A SIW Antipodal Vivaldi Array Antenna Design Thu, 21 Jan 2016 07:11:23 +0000 http://www.hindawi.com/journals/ijap/2016/9280234/ A kind of compact SIW (substrate integrated waveguide) Vivaldi array antenna is proposed and analyzed. The antenna consisted of 4 Vivaldi structure radiation elements fed by an equal power divider with SIW technology. The radiation element is composed of antipodal index gradient microstrip lines on both sides of the substrate. The measured reflection coefficient of the array antenna is less than −10 dB from 8.88 GHz to 10.02 GHz. The measured gain of the array antenna is 13.3 dB on 9.5 GHz. Ying Suo, Wei Li, and Jianzhong Chen Copyright © 2016 Ying Suo et al. All rights reserved. Dual-Band Operation of a Circularly Polarized Four-Arm Curl Antenna with Asymmetric Arm Length Tue, 19 Jan 2016 12:35:47 +0000 http://www.hindawi.com/journals/ijap/2016/3531089/ This paper presents dual-band operation of a single-feed composite cavity-backed four-arm curl antenna. Dual-band operation is achieved with the presence of the asymmetrical arm structure. A pair of vacant-quarter printed rings is used in the feed structure to produce a good circular polarization (CP) at both bands. The cavity-backed reflector is employed to improve the CP radiation characteristics in terms of the 3-dB axial ratio beamwidth and broadside gain. The proposed antenna is widely applicable in dual-band communication systems that have a small frequency ratio. Examples of such a system are global positioning systems. Son Xuat Ta and Ikmo Park Copyright © 2016 Son Xuat Ta and Ikmo Park. All rights reserved. Polarimetric Scattering from Two-Dimensional Dielectric Rough Sea Surface with a Ship-Induced Kelvin Wake Tue, 19 Jan 2016 09:13:25 +0000 http://www.hindawi.com/journals/ijap/2016/2474708/ Based on the polarimetric scattering model of second-order small-slope approximation (SSA-II) with tapered wave incidence for reducing the edge effect caused by limited surface size, monostatic and bistatic polarimetric scattering signatures of two-dimensional dielectric rough sea surface with a ship-induced Kelvin wake is investigated in detail by comparison with those of sea surface without ship wake. The emphasis of this paper is on an investigation of depolarized scattering and enhanced backscattering of sea surface with a ship wake that changes the sea surface geometric structure especially for low wind conditions. Numerical simulations show that in the plane of incidence rough sea surface scattering is dominated by copolarized scattering rather than cross-polarized scattering and that under low wind conditions a larger ship speed gives rise to stronger enhanced backscattering and enhanced depolarized scattering. For both monostatic and bistatic configuration, simulation results indicate that electromagnetic scattering signatures in the presence of a ship wake dramatically differ from those without ship wake, which may serve as a basis for the detection of ships in marine environment. Pengju Yang and Lixin Guo Copyright © 2016 Pengju Yang and Lixin Guo. All rights reserved. Experimental Study on Brush-Painted Passive RFID-Based Humidity Sensors Embedded into Plywood Structures Mon, 18 Jan 2016 08:24:07 +0000 http://www.hindawi.com/journals/ijap/2016/1203673/ The integration of electronics and wood is an interesting research area due to the increasing interest to add functionality into various wooden products. The passive RFID-based humidity sensor tag prototype, presented in this paper, is fabricated directly on plywood substrate to be embedded into wooden structures, by using brush-painting and photonic sintering of cost-effective silver ink. To the best of our knowledge, this is the first demonstration of brush-painted antennas as sensor elements. The developed sensor tag is fully passive and small in size, meaning it can be permanently enclosed into wooden structures. In addition, the sensor tag has all the functionalities of an ordinary passive UHF RFID tag, and a peak read range of about 10 meters. The sensor performance was evaluated in normal room conditions, after two 100% relative humidity tests, and after drying in normal room conditions for 9 days. According to the results, the fabricated UHF RFID-based humidity sensor tags have a great potential to be utilized in humidity sensing applications, and also in normal automatic identification and supply chain control of various wooden products. In addition, the first results of more cost-effective brush-painted copper UHF RFID tags on plywood substrate are presented. Erja Sipilä, Johanna Virkki, Lauri Sydänheimo, and Leena Ukkonen Copyright © 2016 Erja Sipilä et al. All rights reserved. A Single-Point-Fed Wideband Circularly Polarized Rectangular Dielectric Resonator Antenna Sun, 17 Jan 2016 11:44:14 +0000 http://www.hindawi.com/journals/ijap/2016/8210781/ A single-point-fed circularly polarized (CP) rectangular dielectric resonator antenna (DRA) with wide CP bandwidth is presented. By using and modes of the rectangular DRA, a wideband CP performance is achieved. The coupling slot of the antenna contains a resistor loaded monofilar-spiral-slot and four linear slots. Design concept of the proposed antenna is demonstrated by simulations, and parameter studies are carried out. Prototype of the proposed antenna was fabricated and measured. Good agreement between the simulation and measurement is obtained. The measured impedance bandwidth ( dB) and 3 dB axial-ratio (AR) bandwidth are 51.4% (1.91–3.23 GHz) and 33.0% (2.15–3.00 GHz), respectively. Deqiang Yang, Meng Zou, and Jin Pan Copyright © 2016 Deqiang Yang et al. All rights reserved. Antenna Array Design in MIMO Radar Using NSK Polynomial Factorization Algorithm Sun, 17 Jan 2016 06:21:26 +0000 http://www.hindawi.com/journals/ijap/2016/4580479/ The work presented here is concerned with the antenna array design in collocated multiple-input multiple-output (MIMO) radars. After knowing the system requirements, the antenna array design problem is formulated as a standard polynomial factorization. In addition, an algorithm based on Newton-Schubert-Kronecker (NSK) polynomial factorization is proposed. The algorithm contains three steps. First, linear factors are extracted by extended Vieta theorem. Then, undermined high-order factors are confirmed with Newton interpolation and certain high-order factors should be searched for within the undermined ones. Finally, the antenna array configurations are determined according to the result of polynomial factorization. Simulations confirm the wide use of the proposed algorithm in MIMO radar antenna array design. Shuainan Gu, Ke Li, Xiukun Ren, and Na-e Zheng Copyright © 2016 Shuainan Gu et al. All rights reserved. A Novel Technology for Measurements of Dielectric Properties of Extremely Small Volumes of Liquids Wed, 13 Jan 2016 14:12:35 +0000 http://www.hindawi.com/journals/ijap/2016/1436798/ A high sensitivity sensor for measurement radio frequency (RF) dielectric permittivity of liquids is described. Interference is used and parasitic effects are cancellation, which makes the sensor can catch weak signals caused by liquids with extremely small volumes. In addition, we present the relationship between transmission coefficient and permittivity of liquids under test (LUT). Using this sensor, quantitative measurements of the dielectric properties at 5.8 GHz are demonstrated of LUTs. Experiments show that the proposed method only requires the volume of 160 nanoliters for liquids. Therefore, the technology can be used for RF spectroscopic analysis of biological samples and extremely precious liquids. Wei-Na Liu Copyright © 2016 Wei-Na Liu. All rights reserved. The Analysis of a Wideband Strip-Helical Antenna with 1.1 Turns Mon, 11 Jan 2016 09:39:52 +0000 http://www.hindawi.com/journals/ijap/2016/5950472/ A wideband strip-helical antenna with 1.1 turns is analyzed numerically and experimentally. By replacing the traditional wire helix with wide metallic strip, the forward traveling current on the strip helix with about one turn smoothly decays to the minimum value at the open end of the helix. Therefore, the strip helix can excite a wideband circular polarization (CP) wave with 50-ohm impedance matching. The proposed antenna is printed on a hollow-cylinder with a substrate relative permittivity of and a thickness of  mm. A 50 Ω coaxial cable is directly connected to excite the strip-helical antenna without any additional impedance matching section. The ground plane is placed below the antenna in order to provide a directional radiation pattern. To demonstrate this method, a prototype of 1.1-turn strip-helical antenna is tested. The test shows that the proposed antenna can reach an overlapped bandwidth of 46% with height of 0.52, where is the wavelength in free space at the center operation frequency. Xihui Tang, Botao Feng, and Yunliang Long Copyright © 2016 Xihui Tang et al. All rights reserved. Study on Horizontally Polarized Omnidirectional Microstrip Antenna Sun, 10 Jan 2016 10:30:57 +0000 http://www.hindawi.com/journals/ijap/2016/8214153/ A horizontally polarized omnidirectional microstrip antenna is proposed in this paper. The structure of designed antenna is with two back-to-back horizontally polarized microstrip antenna elements. Gain variation on main radiation plane of this new antenna is analyzed and radiation theory is deduced; formula of directivity on main radiation plane is given. Better omnidirectional characteristic of this antenna can be obtained by decreasing patch physical length. Both simulated and measured results verify the omnidirectional radiation patterns and input impedance characteristics. Good omnidirectional radiation patterns (gain variation in -plane less than ±0.4 dBi) and input impedance characteristics are obtained; moreover, cross polarization less than −20 dBi is achieved. Kun Wei, Jian-ying Li, Ling Wang, Zi-jian Xing, and Rui Xu Copyright © 2016 Kun Wei et al. All rights reserved. FPGA Implementation of Real-Time Compressive Sensing with Partial Fourier Dictionary Wed, 06 Jan 2016 08:34:35 +0000 http://www.hindawi.com/journals/ijap/2016/1671687/ This paper presents a novel real-time compressive sensing (CS) reconstruction which employs high density field-programmable gate array (FPGA) for hardware acceleration. Traditionally, CS can be implemented using a high-level computer language in a personal computer (PC) or multicore platforms, such as graphics processing units (GPUs) and Digital Signal Processors (DSPs). However, reconstruction algorithms are computing demanding and software implementation of these algorithms is extremely slow and power consuming. In this paper, the orthogonal matching pursuit (OMP) algorithm is refined to solve the sparse decomposition optimization for partial Fourier dictionary, which is always adopted in radar imaging and detection application. OMP reconstruction can be divided into two main stages: optimization which finds the closely correlated vectors and least square problem. For large scale dictionary, the implementation of correlation is time consuming since it often requires a large number of matrix multiplications. Also solving the least square problem always needs a scalable matrix decomposition operation. To solve these problems efficiently, the correlation optimization is implemented by fast Fourier transform (FFT) and the large scale least square problem is implemented by Conjugate Gradient (CG) technique, respectively. The proposed method is verified by FPGA (Xilinx Virtex-7 XC7VX690T) realization, revealing its effectiveness in real-time applications. Yinghui Quan, Yachao Li, Xiaoxiao Gao, and Mengdao Xing Copyright © 2016 Yinghui Quan et al. All rights reserved. A Computational Model for Real-Time Calculation of Electric Field due to Transcranial Magnetic Stimulation in Clinics Thu, 31 Dec 2015 15:28:10 +0000 http://www.hindawi.com/journals/ijap/2015/976854/ The aim of this paper is to propose an approach for an accurate and fast (real-time) computation of the electric field induced inside the whole brain volume during a transcranial magnetic stimulation (TMS) procedure. The numerical solution implements the admittance method for a discretized realistic brain model derived from Magnetic Resonance Imaging (MRI). Results are in a good agreement with those obtained using commercial codes and require much less computational time. An integration of the developed code with neuronavigation tools will permit real-time evaluation of the stimulated brain regions during the TMS delivery, thus improving the efficacy of clinical applications. Alessandra Paffi, Francesca Camera, Filippo Carducci, Gianluigi Rubino, Paolo Tampieri, Micaela Liberti, and Francesca Apollonio Copyright © 2015 Alessandra Paffi et al. All rights reserved. Two-Dimensional Direction-of-Arrivals Estimation Based on One-Dimensional Search Using Rank Deficiency Principle Thu, 31 Dec 2015 06:26:02 +0000 http://www.hindawi.com/journals/ijap/2015/127621/ A novel efficient method for two-dimensional (2D) direction-of-arrivals (DOAs) estimation is proposed to reduce the computational complexity of conventional 2D multiple signal classification (2D-MUSIC) algorithm with uniform rectangular arrays (URAs). By introducing two electrical DOAs, the formula of 2D-MUSIC is transformed into a new one-dimensional (1D) quadratic optimal problem. This 1D quadratic optimal problem is further proved equivalent to finding the conditions of noise subspace rank deficiency (NSRD), which can be solved by an efficient 1D spectral search, leading to a novel NSRD-MUSIC estimator accordingly. Unlike 2D-MUSIC with exhaustive 2D search, the proposed technique requires only an efficient 1D one. Compared with the estimation of signal parameter via rotation invariance techniques (ESPRIT), NSRD-MUSIC has a significantly improved accuracy. Moreover, the new algorithm requires no pair matching. Numerical simulations are conducted to verify the efficiency of the new estimator. Feng-Gang Yan, Zhi-Kun Chen, Ming-Jian Sun, Yi Shen, and Ming Jin Copyright © 2015 Feng-Gang Yan et al. All rights reserved. Fitting Green’s Function FFT Acceleration Applied to Anisotropic Dielectric Scattering Problems Thu, 31 Dec 2015 06:07:06 +0000 http://www.hindawi.com/journals/ijap/2015/123739/ A volume integral equation based fast algorithm using the Fast Fourier Transform of fitting Green’s function (FG-FFT) is proposed in this paper for analysis of electromagnetic scattering from 3D anisotropic dielectric objects. For the anisotropic VIE model, geometric discretization is still implemented by tetrahedron cells and the Schaubert-Wilton-Glisson (SWG) basis functions are also used to represent the electric flux density vectors. Compared with other Fast Fourier Transform based fast methods, using fitting Green’s function technique has higher accuracy and can be applied to a relatively coarse grid, so the Fast Fourier Transform of fitting Green’s function is selected to accelerate anisotropic dielectric model of volume integral equation for solving electromagnetic scattering problems. Besides, the near-field matrix elements in this method are used to construct preconditioner, which has been proved to be effective. At last, several representative numerical experiments proved the validity and efficiency of the proposed method. Shu-Wen Chen, Feng Lu, and Yao Ma Copyright © 2015 Shu-Wen Chen et al. All rights reserved. Compact Planar Sparse Array Antenna with Optimum Element Dimensions for SATCOM Ground Terminals Wed, 30 Dec 2015 08:12:55 +0000 http://www.hindawi.com/journals/ijap/2015/806981/ A novel antenna array architecture for low-cost and compact SATCOM mobile terminal is presented. Based on equal-amplitude aperiodic phased array with fewer active chain numbers, it possesses advantages including lower weight, less cost, and higher power efficiency compared to conventional periodic phased arrays. It is implemented with printed patch antenna so that it guarantees compactness. The elements position and dimensions are jointly designed, with an effective sparse array synthesis strategy that takes actual patch antenna design constraint into consideration, to obtain a maximum array aperture efficiency. Executable and practical approach for variable dimension patch antenna designing, including defect substrate element and small scale array, is introduced and utilized to implement proposed sparse array. Full-wave simulation results demonstrate the advantages of proposed array antenna as well as the effectiveness of corresponding design approach. Junqi Lu and Yongxin Guo Copyright © 2015 Junqi Lu and Yongxin Guo. All rights reserved. Compressed Measurements Based Spectrum Sensing for Wideband Cognitive Radio Systems Wed, 30 Dec 2015 08:01:01 +0000 http://www.hindawi.com/journals/ijap/2015/654958/ Spectrum sensing is the most important component in the cognitive radio (CR) technology. Spectrum sensing has considerable technical challenges, especially in wideband systems where higher sampling rates are required which increases the complexity and the power consumption of the hardware circuits. Compressive sensing (CS) is successfully deployed to solve this problem. Although CS solves the higher sampling rate problem, it does not reduce complexity to a large extent. Spectrum sensing via CS technique is performed in three steps: sensing compressed measurements, reconstructing the Nyquist rate signal, and performing spectrum sensing on the reconstructed signal. Compressed detectors perform spectrum sensing from the compressed measurements skipping the reconstruction step which is the most complex step in CS. In this paper, we propose a novel compressed detector using energy detection technique on compressed measurements sensed by the discrete cosine transform (DCT) matrix. The proposed algorithm not only reduces the computational complexity but also provides a better performance than the traditional energy detector and the traditional compressed detector in terms of the receiver operating characteristics. We also derive closed form expressions for the false alarm and detection probabilities. Numerical results show that the analytical expressions coincide with the exact probabilities obtained from simulations. Taha A. Khalaf, Mohammed Y. Abdelsadek, and Mohammed Farrag Copyright © 2015 Taha A. Khalaf et al. All rights reserved. Estimation of the Reception Angle Distribution Based on the Power Delay Spectrum or Profile Tue, 29 Dec 2015 13:03:49 +0000 http://www.hindawi.com/journals/ijap/2015/936406/ The paper presents an estimation of the reception angle distribution based on temporal characteristics such as the power delay spectrum (PDS) or power delay profile (PDP). Here, we focus on such wireless environment, where the propagation phenomenon predominates in azimuth plane. As a basis to determine probability density function (PDF) of the angle of arrival (AOA), a geometrical channel model (GCM) in form of the multielliptical model for delayed scattering components and the von Mises’ PDF for local scattering components are used. Therefore, this estimator is called the distribution based on multielliptical model (DBMM). The parameters of GCM are defined on the basis of the PDS or PDP and the relative position of the transmitter and the receiver. In contrast to the previously known statistical models, DBMM ensures the estimation PDF of AOA by using the temporal characteristics of the channel for differing propagation conditions. Based on the results of measurements taken from the literature, DBMM verification, assessment of accuracy, and comparison with other models are shown. The results of comparison show that DBMM is the only model that provides the smallest least-squares error for different environments. Cezary Ziółkowski and Jan M. Kelner Copyright © 2015 Cezary Ziółkowski and Jan M. Kelner. All rights reserved. Optimization and Design of Wideband Antenna Based on Factor Tue, 29 Dec 2015 09:30:45 +0000 http://www.hindawi.com/journals/ijap/2015/971646/ A wideband antenna is designed based on factor in this paper. Firstly, the volume-surface integral equations (VSIEs) and self-adaptive differential evolution algorithm (DEA) are introduced as the basic theories to optimize antennas. Secondly, we study the computation of of arbitrary shaped structures, aiming at designing an antenna with maximum bandwidth by minimizing the of the antenna. This method is much more efficient for only values at specific frequency points that are computed, which avoids optimizing bandwidth directly. Thirdly, an integrated method combining the above method with VSIEs and self-adaptive DEA is employed to optimize the wideband antenna, extending its bandwidth from 11.5~16.5 GHz to 7~20 GHz. Lastly, the optimized antenna is fabricated and measured. The measured results are consistent with the simulated results, demonstrating the feasibility and effectiveness of the proposed method. Han Liu, Chengyou Yin, Weidong Gao, and Yulong Sun Copyright © 2015 Han Liu et al. All rights reserved. Efficient DoA Tracking of Variable Number of Moving Stochastic EM Sources in Far-Field Using PNN-MLP Model Tue, 29 Dec 2015 06:19:20 +0000 http://www.hindawi.com/journals/ijap/2015/542614/ An efficient neural network-based approach for tracking of variable number of moving electromagnetic (EM) sources in far-field is proposed in the paper. Electromagnetic sources considered here are of stochastic radiation nature, mutually uncorrelated, and at arbitrary angular distance. The neural network model is based on combination of probabilistic neural network (PNN) and the Multilayer Perceptron (MLP) networks and it performs real-time calculations in two stages, determining at first the number of moving sources present in an observed space sector in specific moments in time and then calculating their angular positions in azimuth plane. Once successfully trained, the neural network model is capable of performing an accurate and efficient direction of arrival (DoA) estimation within the training boundaries which is illustrated on the appropriate example. Zoran Stanković, Nebojša Dončov, Bratislav Milovanović, and Ivan Milovanović Copyright © 2015 Zoran Stanković et al. All rights reserved.