International Journal of Antennas and Propagation The latest articles from Hindawi Publishing Corporation © 2016 , Hindawi Publishing Corporation . All rights reserved. Improved OAM-Based Radar Targets Detection Using Uniform Concentric Circular Arrays Tue, 24 May 2016 07:11:56 +0000 Without any relative moves or beam scanning, the novel Orbital-Angular-Momentum- (OAM-) based radar targets detection technique using uniform concentric circular arrays (UCCAs) shows the azimuthal estimation ability, which provides new perspective for radar system design. However, the main estimation method, that is, Fast Fourier Transform (FFT), under this scheme suffers from low resolution. As a solution, this paper rebuilds the OAM-based radar targets detection model and introduces the multiple signal classification (MUSIC) algorithm to improve the resolution for detecting targets within the main lobes. The spatial smoothing technique is proposed to tackle the coherent problem brought by the proposed model. Analytical study and simulation demonstrate the superresolution estimation capacity the MUSIC algorithm can achieve for detecting targets within the main lobes. The performance of the MUSIC algorithm to detect targets not illuminated by the main lobes is further evaluated. Despite the fact that MUSIC algorithm loses the resolution advantage under this case, its estimation is more robust than that of the FFT method. Overall, the proposed MUSIC algorithm for the OAM-based radar system demonstrates the superresolution ability for detecting targets within the main lobes and good robustness for targets out of the main lobes. Mingtuan Lin, Yue Gao, Peiguo Liu, and Jibin Liu Copyright © 2016 Mingtuan Lin et al. All rights reserved. A Miniaturized Meandered Dipole UHF RFID Tag Antenna for Flexible Application Mon, 23 May 2016 11:38:35 +0000 A miniaturized meandered dipole antenna for UHF RFID tag is proposed. Different resonance frequencies and impedance can be achieved by adjusting the number of the meanders, which can help to reduce the size of the antenna. Due to the radiation patches, the input impedance of the antenna can be flexibly tuned in a large scale. The proposed antenna is printed on polyethylene (PET) substrate with a total volume of 48 mm × 13.7 mm × 0.5 mm. Modeling and simulation results show that the reflection coefficient of the antenna is less than −15 dB at 860–960 MHz. Experimental studies demonstrate that the minimum threshold power of the antenna is between 23 and 26 dBm and the measured read range is 3-4 m. Xiuwei Xuan, Lianrong Lv, and Kun Li Copyright © 2016 Xiuwei Xuan et al. All rights reserved. Ray-Based Statistical Propagation Modeling for Indoor Corridor Scenarios at 15 GHz Thu, 19 May 2016 12:03:30 +0000 According to the demands for fifth-generation (5G) communication systems, high frequency bands (above 6 GHz) need to be adopted to provide additional spectrum. This paper investigates the characteristics of indoor corridor channels at 15 GHz. Channel measurements with a vector network analyzer in two corridors were conducted. Based on a ray-optical approach, a deterministic channel model covering both antenna and propagation characteristic is presented. The channel model is evaluated by comparing simulated results of received power and root mean square delay spread with the corresponding measurements. By removing the impact of directional antennas from the transmitter and receiver, a path loss model as well as small-scale fading properties for typical corridors is presented based on the generated samples from the deterministic model. Results show that the standard deviation of path loss variation is related to the Tx height, and placing the Tx closer to the ceiling leads to a smaller fluctuation of path loss. Qi Wang, Bo Ai, Ke Guan, David W. Matolak, Ruisi He, and Xin Zhou Copyright © 2016 Qi Wang et al. All rights reserved. A Novel Adaptive Algorithm Addresses Potential Problems of Blind Algorithm Wed, 18 May 2016 14:25:32 +0000 A hybrid algorithm called constant modulus least mean square (CMLMS) algorithm is proposed in order to address the potential problems existing with constant modulus algorithm (CMA) about its convergence. It is a two-stage adaptive filtering algorithm and based on least mean square (LMS) algorithm followed by CMA. A hybrid algorithm is theoretically developed and the same is verified through MatLab Software. Theoretical model is verified through simulation and its performance is evaluated in smart antenna in presence of a cochannel interfering signal and additive white Gaussian noise (AWGN) of zero mean. This is also tested in Rayleigh fading channel using digital modulation technique for Bit Error Rate (BER). Finally, a few computer simulations are presented in order to substantiate the theoretical findings with respect to proposed model. Corresponding results obtained with the use of only CMA and LMS algorithms are also presented for further comparison. Muhammad Yasin and Muhammad Junaid Hussain Copyright © 2016 Muhammad Yasin and Muhammad Junaid Hussain. All rights reserved. Cavity-Backed Angled-Dipole Antennas for Millimeter-Wave Wireless Applications Tue, 17 May 2016 09:11:21 +0000 A cavity-backed angled-dipole antenna is proposed for millimeter-wave wireless applications. The angled-dipole radiator is built on both sides of an RT/Duroid 5880 substrate () and fed by a parallel-plate transmission line. The cavity-backed reflector is utilized to improve the radiation characteristics of the angled dipole, such as gain, back-radiation, symmetric pattern, and similar 3 dB beamwidth in the - and -planes. The design, with a cavity aperture of , results in a dB bandwidth of 26.7–30.6 GHz, a gain of 6.6–8.0 dB, and a similar 3 dB beamwidth of approximately 70° for both the - and -planes. Eight-element linear arrays with the proposed antenna having a center-to-center spacing of 5.6 mm are characterized, fabricated, and measured. By applying nonuniform power distribution across excitations, the array achieves a scan angle up to 40° and a sidelobe level below −15 dB. Son Xuat Ta and Ikmo Park Copyright © 2016 Son Xuat Ta and Ikmo Park. All rights reserved. Miniaturized Coupling Structures for Decoupling PIFAs on Handheld Devices Mon, 16 May 2016 11:16:19 +0000 One efficient approach is introduced in this paper to reduce mutual coupling and correlation coefficient for two closely placed PIFAs in a handheld device. The approach is based on one miniaturized structure which consists of two metallic layers, printed on either side of one thin dielectric layer. Due to the small spacing between two conducting patches, high electromagnetic field is induced within the dielectric layer. The geometry and position of this structure have been modified to decouple the PIFA array at 1.9 GHz and produce maximum miniaturization thereby occupying less space on a handheld device ground plane. By employing the proposed structures, a 20 dB reduction in mutual coupling is achieved. The correlation coefficient also reduces to 0.007278. The performance of the structure is validated by both simulated results and measured data obtained from several fabricated prototypes. Qian Li and Yaxin Yu Copyright © 2016 Qian Li and Yaxin Yu. All rights reserved. One-Step Leapfrog LOD-BOR-FDTD Algorithm with CPML Implementation Mon, 16 May 2016 10:44:46 +0000 An unconditionally stable one-step leapfrog locally one-dimensional finite-difference time-domain (LOD-FDTD) algorithm towards body of revolution (BOR) is presented. The equations of the proposed algorithm are obtained by the algebraic manipulation of those used in the conventional LOD-BOR-FDTD algorithm. The equations for -direction electric and magnetic fields in the proposed algorithm should be treated specially. The new algorithm obtains a higher computational efficiency while preserving the properties of the conventional LOD-BOR-FDTD algorithm. Moreover, the convolutional perfectly matched layer (CPML) is introduced into the one-step leapfrog LOD-BOR-FDTD algorithm. The equation of the one-step leapfrog CPML is concise. Numerical results show that its reflection error is small. It can be concluded that the similar CPML scheme can also be easily applied to the one-step leapfrog LOD-FDTD algorithm in the Cartesian coordinate system. Yi-Gang Wang, Yun Yi, Bin Chen, Hai-Lin Chen, Kang Luo, and Run Xiong Copyright © 2016 Yi-Gang Wang et al. All rights reserved. Pilot Design for Sparse Channel Estimation in Large-Scale MIMO-OFDM System Thu, 12 May 2016 14:59:49 +0000 The pilot design problem in large-scale multi-input-multioutput orthogonal frequency division multiplexing (MIMO-OFDM) system is investigated from the perspective of compressed sensing (CS). According to the CS theory, the success probability of estimation is dependent on the mutual coherence of the reconstruction matrix. Specifically, the smaller the mutual coherence is, the higher the success probability is. Based on this conclusion, this paper proposes a pilot design algorithm based on alternating projection and obtains a nonorthogonal pilot pattern. Simulation results show that applying the proposed pattern gives the better performance compared to applying conventional orthogonal one in terms of normalized mean square error (NMSE) of the channel estimate. Moreover, the bit error rate (BER) performance of the large-scale MIMO-OFDM system is improved. Chao Xu, Jianhua Zhang, Mengmeng Liu, and Changchuan Yin Copyright © 2016 Chao Xu et al. All rights reserved. Brush-Painting and Photonic Sintering of Copper Oxide and Silver Inks on Wood and Cardboard Substrates to Form Antennas for UHF RFID Tags Thu, 12 May 2016 14:54:38 +0000 Additive deposition of inks with metallic inclusions provides compelling means to embed electronics into versatile structures. The need to integrate electronics into environmentally friendly components and structures increases dramatically together with the increasing popularity of the Internet of Things. We demonstrate a novel brush-painting method for depositing copper oxide and silver inks directly on wood and cardboard substrates and discuss the optimization of the photonic sintering process parameters for both materials. The optimized parameters were utilized to manufacture passive ultra high frequency (UHF) radio frequency identification (RFID) tag antennas. The results from wireless testing show that the RFID tags based on the copper oxide and silver ink antennas on wood substrate are readable from ranges of 8.5 and 11 meters, respectively, and on cardboard substrate from read ranges of 8.5 and 12 meters, respectively. These results are well sufficient for many future wireless applications requiring remote identification with RFID. Erja Sipilä, Johanna Virkki, Jianhua Wang, Lauri Sydänheimo, and Leena Ukkonen Copyright © 2016 Erja Sipilä et al. All rights reserved. Cell Curvature and Far-Field Superconvergence in Numerical Solutions of Electromagnetic Integral Equations Thu, 12 May 2016 11:47:07 +0000 Two curved targets are used to explore far-field superconvergence effects arising in numerical solutions of the electric-field and magnetic-field integral equations. Three different orders of basis and testing functions are used to discretize these equations, and three different types of target models (flat facets, quadratic-curved facets, and cubic-curved facets) are employed. Ideal far-field convergence rates are only observed when the model curvature is one degree higher than the basis order. Andrew F. Peterson Copyright © 2016 Andrew F. Peterson. All rights reserved. Beam Performance Optimization of Multibeam Imaging Sonar Based on the Hybrid Algorithm of Binary Particle Swarm Optimization and Convex Optimization Thu, 12 May 2016 08:14:52 +0000 It should be noted that the peak sidelobe level (PSLL) significantly influences the performance of the multibeam imaging sonar. Although a great amount of work has been done to suppress the PSLL of the array, one can verify that these methods do not provide optimal results when applied to the case of multiple patterns. In order to suppress the PSLL for multibeam imaging sonar array, a hybrid algorithm of binary particle swarm optimization (BPSO) and convex optimization is proposed in this paper. In this algorithm, the PSLL of multiple patterns is taken as the optimization objective. BPSO is considered as a global optimization algorithm to determine best common elements’ positions and convex optimization is considered as a local optimization algorithm to optimize elements’ weights, which guarantees the complete match of the two factors. At last, simulations are carried out to illustrate the effectiveness of the proposed algorithm in this paper. Results show that, for a sparse semicircular array with multiple patterns, the hybrid algorithm can obtain a lower PSLL compared with existing methods and it consumes less calculation time in comparison with other hybrid algorithms. Weijie Xia, Xue Jin, and Fawang Dou Copyright © 2016 Weijie Xia et al. All rights reserved. Location Optimization for Square Array Antennas Using Differential Evolution Algorithm Tue, 10 May 2016 14:04:13 +0000 In recent works thinned arrays giving minimum peak sidelobe levels for planar square antenna arrays are obtained using Hadamard difference sets. In the current work thinned array configurations giving lower peak sidelobe levels than those given in the literature are obtained for square arrays of , , , and elements. Differential evolution algorithm is used in the determination of the antenna locations. Erkan Afacan Copyright © 2016 Erkan Afacan. All rights reserved. Implementation of Associated Hermite FDTD Method in Handling INBCs for Shielding Analysis Tue, 10 May 2016 13:39:10 +0000 For modeling of electrically thin conductive shields, the unconditionally stable Associated Hermite (AH) FDTD scheme is combined with the impedance network boundary conditions (INBCs) in this paper. The two-port network equations of INBCs in frequency domain are transformed into AH domain to represent the relationship of tangential components of the electric and magnetic fields at faces of the shield. The established AH-INBCs shielding boundaries are incorporated into a set of implicit equations to calculate the expansion coefficients vectors of electromagnetic fields in the computational domain. The method is free of CFL condition and no convolution integral operation for solving the conventional INBCs-FDTD is involved. Numerical example shows that, compared with analytical solutions and conventional FDTD method, the proposed algorithm is efficient and accurate. Lihua Shi, Zhengyu Huang, Qing Si, and Yinghui Zhou Copyright © 2016 Lihua Shi et al. All rights reserved. Design of Symmetrical Beam Triple-Aperture Waveguide Antenna for Primary Feed of Reflector Tue, 10 May 2016 12:57:05 +0000 This research presents a triple-aperture waveguide antenna as the primary feed of parabolic reflectors. The proposed antenna is able to rectify the asymmetry and also achieve a symmetrical unidirectional beam through the application of two parasitic coupling apertures. The design of the antenna is that of a rectangular waveguide (radiating aperture) vertically jointed to the two coupling apertures of the same measurement widthwise (i.e., one stacked on top and the other underneath) to achieve the symmetrical beam. The rectangular waveguide is 97.60 mm and 46.80 mm in width () and height (), respectively, to propagate the WLAN frequency band of 2.412–2.484 GHz. Simulations were carried out to determine the optimal antenna parameters and an antenna prototype was subsequently fabricated and tested. The simulated beamwidths in the - and -planes at  dB were equally 67° (i.e., 67° for both the - and -planes) and at  dB also equally 137°, while the measured results at  dB were equally 65° and at  dB equally 135°. The simulation and measured results are thus in good agreement. The simulated and measured antenna gains are, respectively, 8.25 dBi and 9.17 dBi. The findings validate the applicability of the antenna as the prime feed for rotationally symmetric parabolic reflectors. Kanawat Nuangwongsa and Chuwong Phongcharoenpanich Copyright © 2016 Kanawat Nuangwongsa and Chuwong Phongcharoenpanich. All rights reserved. Millimeter Wave Fabry-Perot Resonator Antenna Fed by CPW with High Gain and Broadband Tue, 10 May 2016 11:57:31 +0000 A novel millimeter wave coplanar waveguide (CPW) fed Fabry-Perot (F-P) antenna with high gain, broad bandwidth, and low profile is reported. The partially reflective surface (PRS) and the ground form the F-P resonator cavity, which is filled with the same dielectric substrate. A dual rhombic slot loop on the ground acts as the primary feeding antenna, which is fed by the CPW and has broad bandwidth. In order to improve the antenna gain, metal vias are inserted surrounding the F-P cavity. A CPW-to-microstrip transition is designed to measure the performances of the antenna and extend the applications. The measured impedance bandwidth of less than −10 dB is from 34 to 37.7 GHz (10.5%), and the gain is 15.4 dBi at the center frequency of 35 GHz with a 3 dB gain bandwidth of 7.1%. This performance of the antenna shows a tradeoff among gain, bandwidth, and profile. Xue-Xia Yang, Guan-Nan Tan, Bing Han, and Hai-Gao Xue Copyright © 2016 Xue-Xia Yang et al. All rights reserved. Design of an L-Band Cross-Dipole Phased Array Feed for FAST Mon, 09 May 2016 14:10:23 +0000 The Five-Hundred-Meter Aperture Spherical Telescope (FAST) is a Chinese megascience project that aims to build the largest single dish radio telescope in the world. Given its multiple simultaneous beam formation, phased array feed (PAF) is widely used to extend the field of view and enhance the survey speed of the radio telescope. In this study, a broadband and low cost PAF element using cross-dipole antenna at L-band is designed based on the requirement of the FAST. The antenna is fed by two microstrip baluns which have high performance and is easy to manufacture compared to the traditional coaxial balun. A simple system model is also introduced to evaluate the PAF performance. The measured results of the fabricated element and the simulations of the system performance validate the effectiveness of element design. Yubing Han and Luoqing Zhong Copyright © 2016 Yubing Han and Luoqing Zhong. All rights reserved. An Optimal Electric Dipole Antenna Model and Its Field Propagation Mon, 09 May 2016 13:47:22 +0000 An optimal electric dipole antennas model is presented and analyzed, based on the hemispherical grounding equivalent model and the superposition principle. The paper also presents a full-wave electromagnetic simulation for the electromagnetic field propagation in layered conducting medium, which is excited by the horizontal electric dipole antennas. Optimum frequency for field transmission in different depth is carried out and verified by the experimental results in comparison with previously reported simulation over a digital wireless Through-The-Earth communication system. The experimental results demonstrate that the dipole antenna grounding impedance and the output power can be efficiently reduced by using the optimal electric dipole antenna model and operating at the optimum frequency in a vertical transmission depth up to 300 m beneath the surface of the earth. Yidong Xu, Lili Guo, Wei Xue, Korochentsev Vladimir, and Junwei Qi Copyright © 2016 Yidong Xu et al. All rights reserved. A Small Planar Antenna for 4G Mobile Phone Application Mon, 09 May 2016 06:09:11 +0000 The analysis and design of a small planar multiband antenna operating in the 4G frequency bands are presented. The numerical and experimental results demonstrated that the proposed antenna satisfies the requirement of 6 dB return loss for the impedance bandwidth of the LTE700/LTE2300/LTE2500 and WiMAX3500 bands. The gains at 750 MHz/2.3 GHz/2.6 GHz/3.5 GHz are 2.1 dBi/4.9 dBi/4.7 dBi/4.3 dBi, respectively. The measured radiation patterns verify the suitability of the antenna to be employed in mobile phones. The dimensions of the radiant patch are 49 × 10 mm2. The proposed antenna can be easily fabricated and customized to various 4G mobile phones as a compact internal antenna. Hu Jian-rong, Li Jiu-sheng, and Wu Di Copyright © 2016 Hu Jian-rong et al. All rights reserved. Effect of Antenna Parameters on the Field Coverage in Tunnel Environments Thu, 05 May 2016 07:46:01 +0000 Radio wave propagation in confined spaces is consequent upon the reflections of boundaries; thus, the radiation characteristics of the antenna have significant influence on the field coverage in the confined space. This paper investigates the effects of antenna parameters on field coverage characteristics in a tunnel environment. A modified modal method is proposed to analyse the wave propagation properties along the tunnel. The relationships between the amplitudes of modes and the antenna parameters, including the beam width, beam direction, and antenna location, are analysed. The results indicate that by properly selecting the antenna parameters, optimum field coverage in tunnel environments can be realized. Dawei Li and Junhong Wang Copyright © 2016 Dawei Li and Junhong Wang. All rights reserved. Radar Coincidence Imaging for Off-Grid Target Using Frequency-Hopping Waveforms Thu, 05 May 2016 06:47:41 +0000 Radar coincidence imaging (RCI) is a high-resolution staring imaging technique without the limitation of the target relative motion. To achieve better imaging performance, sparse reconstruction is commonly used. While its performance is based on the assumption that the scatterers are located at the prediscretized grid-cell centers, otherwise, off-grid emerges and the performance of RCI degrades significantly. In this paper, RCI using frequency-hopping (FH) waveforms is considered. The off-grid effects are analyzed, and the corresponding constrained Cramér-Rao bound (CCRB) is derived based on the mean square error (MSE) of the “oracle” estimator. For off-grid RCI, the process is composed of two stages: grid matching and off-grid error (OGE) calibration, where two-dimension (2D) band-excluded locally optimized orthogonal matching pursuit (BLOOMP) and alternating iteration minimization (AIM) algorithms are proposed, respectively. Unlike traditional sparse recovery methods, BLOOMP realizes the recovery in the refinement grids by overwhelming the shortages of coherent dictionary and is robust to noise and OGE. AIM calibration algorithm adaptively adjusts the OGE and, meanwhile, seeks the optimal target reconstruction result. Xiaoli Zhou, Hongqiang Wang, Yongqiang Cheng, Yuliang Qin, and Haowen Chen Copyright © 2016 Xiaoli Zhou et al. All rights reserved. A Review of Computational Electromagnetic Methods for Graphene Modeling Sat, 30 Apr 2016 11:28:35 +0000 Graphene is a very promising optoelectronic material and has gained more and more attention. To analyze its electromagnetic properties, several numerical methods have been developed for graphene simulation. In this paper, a review of application of graphene in electronic and photonic device is provided, as well as some widely used computational electromagnetic algorithms for graphene modeling. The advantages and drawbacks of each method are discussed and numerical examples of these methods are given to illustrate their performance and application. Yu Shao, Jing Jing Yang, and Ming Huang Copyright © 2016 Yu Shao et al. All rights reserved. Through-Wall Detection with LS-SVM under Unknown Wall Characteristics Thu, 28 Apr 2016 11:44:24 +0000 One of the main challenges in through-wall imaging (TWI) is the presence of the walls, whose returns tend to obscure the target behind the walls and must be considered and computed in the imaging procedure. In this paper, a two-step procedure for the through-wall detection is proposed. Firstly, an effective clutter mitigation method based on singular value decomposition (SVD) is used. It does not require knowledge of the background scene or rely on accurate modeling and estimation of wall parameters. Then, TWI problem is cast as a regression one and solved by means of least-squares support vector machine (LS-SVM). The complex scattering process due to the presence of the walls is automatically included in the nonlinear relationship between the feature vector extracted from the target scattered fields and the position of the target. The relationship is obtained through a training phase using LS-SVM. Simulated results show that the proposed approach is effective. We also analyze the impacts of training samples and signal-to-noise ratio (SNR) on test detection accuracy. Simulated results reveal that the proposed LS-SVM based approach can provide comparative performances in terms of accuracy, convergence, robustness, and generalization in comparison with the support vector machine (SVM) based approach. Fangfang Wang, Yerong Zhang, and Huamei Zhang Copyright © 2016 Fangfang Wang et al. All rights reserved. A Novel Dual-Band Circularly Polarized Rectangular Slot Antenna Thu, 28 Apr 2016 09:44:51 +0000 A coplanar waveguide fed dual-band circularly polarized rectangular slot antenna is presented. The proposed antenna consists of a rectangular metal frame acting as a ground and an S-shaped monopole as a radiator. The spatial distribution of the surface current density is employed to demonstrate that the circular polarization is generated by the S-shaped monopole which controls the path of the surface currents. An antenna prototype, having overall dimension 37 × 37 × 1 mm3, has been fabricated on FR4 substrate with dielectric constant 4.4. The proposed antenna achieves 10 dB return loss bandwidths and 3 dB axial ratio (AR) in the frequency bands 2.39–2.81 GHz and 5.42–5.92 GHz, respectively. Both these characteristics are suitable for WLAN and WiMAX applications. Biao Li, Yang Ding, and Ying-Zeng Yin Copyright © 2016 Biao Li et al. All rights reserved. Optically Controlled Reconfigurable Filtenna Tue, 19 Apr 2016 14:14:16 +0000 This work is regarding the development of a novel antenna called optically controlled reconfigurable filtenna, which is based on the integration of a broadband printed antenna with a bandpass reconfigurable RF filter. The filter is designed by applying defected microstrip structure (DMS) technique and positioned in printed antenna feeding line in order to keep the same size of the original antenna. The filtenna bandwidth is optically reconfigurable by using two photoconductive silicon switches excited by CW laser at 808 nm. Numerical results rely on independent and switchable operational modes through the 2.4 and 5.1 GHz ISM bands, whereas measurements demonstrate two reconfigurable modes based on single-band/dual-band operation over the same frequency bands. The proposed device is validated by theoretical, numerical, and experimental results. L. G. Silva, A. A. C. Alves, and Arismar Cerqueira Sodré Jr. Copyright © 2016 L. G. Silva et al. All rights reserved. A Moving Source Localization Method for Distributed Passive Sensor Using TDOA and FDOA Measurements Mon, 18 Apr 2016 13:56:07 +0000 The conventional moving source localization methods are based on centralized sensors. This paper presents a moving source localization method for distributed passive sensors using TDOA and FDOA measurements. The novel method firstly uses the steepest descent algorithm to obtain a proper initial value of source position and velocity. Then, the coarse location estimation is obtained by maximum likelihood estimation (MLE). Finally, more accurate location estimation is achieved by subtracting theoretical bias, which is approximated by the actual bias using the estimated source location and noisy data measurement. Both theoretical analysis and simulations show that the theoretical bias always meets the actual bias when the noise level is small, and the proposed method can reduce the bias effectively while keeping the same root mean square error (RMSE) with the original MLE and Taylor-series method. Meanwhile, it is less sensitive to the initial guess and attains the CRLB under Gaussian TDOA and FDOA noise at a moderate noise level before the thresholding effect occurs. Zhixin Liu, Yongjun Zhao, Dexiu Hu, and Chengcheng Liu Copyright © 2016 Zhixin Liu et al. All rights reserved. Tracking of Range and Azimuth for Continuous Imaging of Marine Target in Monopulse ISAR with Wideband Echoes Mon, 18 Apr 2016 13:38:50 +0000 Real-time tracking of maneuvering targets is the prerequisite for continuous imaging of moving targets in inverse synthetic aperture radar (ISAR). In this paper, the range and azimuth tracking (RAT) method with wideband radar echoes is first presented for a mechanical scanning monopulse ISAR, which is regarded as the simplest phased array unit due to the two antenna feeds. To relieve the estimation fluctuation and poor robustness of the RAT method with a single snapshot, a modified range and azimuth tracking approach based on centroid algorithm (RATCA) with forgotten factor and multiple echoes is then proposed. The performances of different forgotten factors are investigated. Both theoretical analysis and experimental results demonstrate that RATCA is superior to RAT method. Particularly, when target echo is missing occasionally, RAT method fails while RATCA still keeps good performance. The potential of continuous imaging with shipborne ISAR is verified by experimental results. With minor modification, the method proposed in this paper can be potentially applied in the phased array radar. Junhao Xie, Wei Zhou, Gongjian Zhou, Yeshu Yuan, and Shaobin Li Copyright © 2016 Junhao Xie et al. All rights reserved. Investigation on the Inversion of the Atmospheric Duct Using the Artificial Bee Colony Algorithm Based on Opposition-Based Learning Mon, 18 Apr 2016 12:09:55 +0000 The artificial bee colony (ABC) algorithm is a recently introduced optimization method in the research field of swarm intelligence. This paper presents an improved ABC algorithm named as OGABC based on opposition-based learning (OBL) and global best search equation to overcome the shortcomings of the slow convergence rate and sinking into local optima in the process of inversion of atmospheric duct. Taking the inversion of the surface duct using refractivity from clutter (RFC) technique as an example to validate the performance of the proposed OGABC, the inversion results are compared with those of the modified invasive weed optimization (MIWO) and ABC. The radar sea clutter power calculated by parabolic equation method using the simulated and measured refractivity profile is utilized to carry out the inversion of the surface duct, respectively. The comparative investigation results indicate that the performance of OGABC is superior to that of MIWO and ABC in terms of stability, accuracy, and convergence rate during the process of inversion. Chao Yang, Jian-Ke Zhang, and Li-Xin Guo Copyright © 2016 Chao Yang et al. All rights reserved. Optimal Pattern Synthesis of Linear Antenna Array Using Grey Wolf Optimization Algorithm Sun, 17 Apr 2016 13:20:21 +0000 The aim of this paper is to introduce the grey wolf optimization (GWO) algorithm to the electromagnetics and antenna community. GWO is a new nature-inspired metaheuristic algorithm inspired by the social hierarchy and hunting behavior of grey wolves. It has potential to exhibit high performance in solving not only unconstrained but also constrained optimization problems. In this work, GWO has been applied to linear antenna arrays for optimal pattern synthesis in the following ways: by optimizing the antenna positions while assuming uniform excitation and by optimizing the antenna current amplitudes while assuming spacing and phase as that of uniform array. GWO is used to achieve an array pattern with minimum side lobe level (SLL) along with null placement in the specified directions. GWO is also applied for the minimization of the first side lobe nearest to the main beam (near side lobe). Various examples are presented that illustrate the application of GWO for linear array optimization and, subsequently, the results are validated by benchmarking with results obtained using other state-of-the-art nature-inspired evolutionary algorithms. The results suggest that optimization of linear antenna arrays using GWO provides considerable enhancements compared to the uniform array and the synthesis obtained from other optimization techniques. Prerna Saxena and Ashwin Kothari Copyright © 2016 Prerna Saxena and Ashwin Kothari. All rights reserved. Design of Asymmetrical Relay Resonators for Maximum Efficiency of Wireless Power Transfer Sun, 17 Apr 2016 08:53:29 +0000 This paper presents a new design method of asymmetrical relay resonators for maximum wireless power transfer. A new design method for relay resonators is demanded because maximum power transfer efficiency (PTE) is not obtained at the resonant frequency of unit resonator. The maximum PTE for relay resonators is obtained at the different resonances of unit resonator. The optimum design of asymmetrical relay is conducted by both the optimum placement and the optimum capacitance of resonators. The optimum placement is found by scanning the positions of the relays and optimum capacitance can be found by using genetic algorithm (GA). The PTEs are enhanced when capacitance is optimally designed by GA according to the position of relays, respectively, and then maximum efficiency is obtained at the optimum placement of relays. The capacitance of the second resonator to th resonator and the load resistance should be determined for maximum efficiency while the capacitance of the first resonator and the source resistance are obtained for the impedance matching. The simulated and measured results are in good agreement. Bo-Hee Choi and Jeong-Hae Lee Copyright © 2016 Bo-Hee Choi and Jeong-Hae Lee. All rights reserved. Efficient Design of the Microstrip Reflectarray Antenna by Optimizing the Reflection Phase Curve Sun, 10 Apr 2016 11:25:18 +0000 The microstrip reflectarray antenna is an attractive directional antenna combining advantages of both the reflector and the microstrip array antenna. For the design of this kind of antenna, the conventional method, which is based on the reflection phase curve, may not be effective because of the approximations made in the design procedure. The common optimization method that employs an optimization algorithm in conjunction with the full-wave simulation to optimize the antennas’ structural parameters is able to achieve better performances in comparison with the conventional method; but it is impractical for large-scale microstrip reflectarray antennas due to too many structural parameters from variable reflection elements. To tackle the design problem of the microstrip reflectarray antenna, a new method is proposed for the first time. It optimizes the reflection phase curve rather than the structural parameters and then utilizes the optimized reflection phase curve to design the antenna. A microstrip reflectarray antenna working at 5.8 GHz and with a fixed size of 300 mm × 300 mm is designed for high gain as a sample design. The results show that the proposed method has greatly improved the antenna’s gain over 2.2 dB (from 19.7 dBi to 21.9 dBi) in comparison with the conventional design method, and it only needs to optimize 6 structural parameters, in contrast to 22 for the common optimization method. Xing Chen, Qiang Chen, Pan Feng, and Kama Huang Copyright © 2016 Xing Chen et al. All rights reserved.