International Journal of Antennas and Propagation The latest articles from Hindawi Publishing Corporation © 2014 , Hindawi Publishing Corporation . All rights reserved. Enhancement of Cross-Borehole Pulse Radar Signature on a Partially Water-Filled Tunnel Tue, 16 Dec 2014 07:23:44 +0000 Cross-borehole pulse radar has been employed to detect a deeply located empty tunnel. In this paper, effects of underground water collected in the bottom of an empty tunnel on cross-borehole pulse radar signatures are analyzed numerically. B-scan images, stacks of received pulses, are calculated by applying the finite-difference time-domain (FDTD) method for 6 different heights of water from the bottom to the half height inside an empty tunnel. The most important features of an empty tunnel, the fastest time of peak (TOP) and time of arrival (TOA) extracted from the B-scan images, are slowed considerably depending on the increased height of water inside the tunnel. To compensate the weak TOP like that of an empty tunnel, a relation curve is formulated only utilizing measurable parameters of the fastest TOP and the fastest TOA. Then, a unified curve including the effects of two granites with the low and high dielectric properties is derived to cover widely varied dielectric properties of underground rocks. Based on the fastest TOP of an empty tunnel, the average difference between the fastest TOP of an empty tunnel and that of a partially water-filled tunnel decreases from 22.92% to 2.59% after enhancement. Ji-Hyun Jung and Se-Yun Kim Copyright © 2014 Ji-Hyun Jung and Se-Yun Kim. All rights reserved. Subarrayed Antenna Array Synthesis Using Ternary Adjusting Method Mon, 15 Dec 2014 09:11:13 +0000 Ternary adjusting method is proposed and combined with particle swarm optimization (PSO) algorithm for subarrayed antenna array synthesis. Ternary variables are introduced to represent element adjustments between adjacent subarrays. Compared to previous methods, rounding-off operations are not required any longer, and the equation constraint of the fixed total element number is also removed, which effectively reduces the complexity of implementation while obtaining improved topology exploration capability simultaneously. Guolong He, Yafeng Zhan, Yukui Pei, and Bin Wu Copyright © 2014 Guolong He et al. All rights reserved. A Novel Performance Analysis of the Microstrip Antenna Printed on a Cylindrical Body Thu, 11 Dec 2014 06:14:29 +0000 Performance of a circular patch microstrip antenna is highly affected by the effective dielectric constant of a used substrate material. When the circular patch is conformed on a cylindrical body, the effective dielectric constant is changing with curvature due to the changing in the fringing field. Consequently, some of antenna parameters such as resonance frequency, input impedance, voltage standing wave ratio, return loss, quality factor, and antenna bandwidth are functions of curvature. In this work, we study the effect of curvature on the performance of circular patch microstrip antenna. A mathematical model for the antenna parameters as functions of curvature is also introduced. The model is applied in case of using two substrates of different refractive index values. By extension, the antenna performance was studied through simulation by using method of moments (MoM) which is reliable in solving Maxwell’s integral equations in the frequency domain. The results from simulation compare very favorably with the described analytical results. Amr M. Mahros, Marwa M. Tharwat, and Ali Elrashidi Copyright © 2014 Amr M. Mahros et al. All rights reserved. Genetic Algorithms in Antennas and Smart Antennas Design Overview: Two Novel Antenna Systems for Triband GNSS Applications and a Circular Switched Parasitic Array for WiMax Applications Developments with the Use of Genetic Algorithms Thu, 11 Dec 2014 00:10:42 +0000 Genetic algorithms belong to a stochastic class of evolutionary techniques, whose robustness and global search of the solutions space have made them extremely popular among researchers. They have been successfully applied to electromagnetic optimization, including antenna design as well as smart antennas design. In this paper, extensive reference to literature related antenna design efforts employing genetic algorithms is taking place and subsequently, three novel antenna systems are designed in order to provide realistic implementations of a genetic algorithm. Two novel antenna systems are presented to cover the new GPS/Galileo band, namely, L5 (1176 MHz), together with the L1 GPS/Galileo and L2 GPS bands (1575 and 1227 MHz). The first system is a modified PIFA and the second one is a helical antenna above a ground plane. Both systems exhibit enhanced performance characteristics, such as sufficient front gain, input impedance matching, and increased front-to-back ratio. The last antenna system is a five-element switched parasitic array with a directional beam with sufficient beamwidth to a predetermined direction and an adequate impedance bandwidth which can be used as receiver for WiMax signals. Stylianos C. Panagiotou, Stelios C. A. Thomopoulos, and Christos N. Capsalis Copyright © 2014 Stylianos C. Panagiotou et al. All rights reserved. Performance Investigations of Quasi-Yagi Loop and Dipole Antennas on Silicon Substrate for 94 GHz Applications Mon, 08 Dec 2014 08:25:45 +0000 This paper introduces the design and implementation of two high gain Quasi-Yagi printed antennas developed on silicon substrate for 94 GHz imaging applications. The proposed antennas are based on either driven loop or dipole antennas fed by a coplanar waveguide (CPW) feeding structure. For better matching with the driven antennas, a matching section has been added between the CPW feedline and the driven antenna element. To improve the gain of either loop or dipole antennas, a ground reflector and parasitic director elements have been added. Two Quasi-Yagi antenna prototypes based on loop and dipole antenna elements have been fabricated and experimentally tested using W-band probing station (75–110 GHz). The measured results show good agreement with simulated results and confirm that the proposed antennas are working. In addition, a feed and matching configuration is proposed to enable coupling a microbolometer element to the proposed Quasi-Yagi antenna designs for performing radiation pattern measurements. Osama M. Haraz, Mohamed Abdel-Rahman, Najeeb Al-Khalli, Saleh Alshebeili, and Abdel Razik Sebak Copyright © 2014 Osama M. Haraz et al. All rights reserved. Near-Field Spherical Scanning Antenna Measurements: Probe Deconvolution and Sensitivity Thu, 04 Dec 2014 11:49:57 +0000 We define and calculate sensitivity for several actual and simulated probes. Probe sensitivity can have a significant impact on the measurement uncertainty associated with probe deconvolution in near-field spherical-scanning, antenna measurements. Ronald C. Wittmann and Michael H. Francis Copyright © 2014 Ronald C. Wittmann and Michael H. Francis. All rights reserved. Comparison of Semidefinite Relaxation Detectors for High-Order Modulation MIMO Systems Thu, 27 Nov 2014 11:59:57 +0000 Multiple-input multiple-output (MIMO) system is considered to be one of the key technologies of LTE since it achieves requirements of high throughput and spectral efficiency. The semidefinite relaxation (SDR) detection for MIMO systems is an attractive alternative to the optimum maximum likelihood (ML) decoding because it is very computationally efficient. We propose a new SDR detector for 256-QAM MIMO system and compare its performance with two other SDR detectors, namely, BC-SDR detector and VA-SDR detector. The tightness and complexity of these three SDR detectors are analyzed. Both theoretical analysis and simulation results demonstrate that the proposed SDR can provide the best BLER performance among the three detectors, while the BC-SDR detector and the VA-SDR detector provide identical BLER performance. Moreover, the BC-SDR has the lowest computational complexity and the VA-SDR has the highest computational complexity, while the proposed SDR is in between. Z. Y. Shao, S. W. Cheung, and T. I. Yuk Copyright © 2014 Z. Y. Shao et al. All rights reserved. Study on Zero-Doppler Centroid Control for GEO SAR Ground Observation Wed, 26 Nov 2014 13:41:19 +0000 In geosynchronous Earth orbit SAR (GEO SAR), Doppler centroid compensation is a key step for imaging process, which could be performed by the attitude steering of a satellite platform. However, this zero-Doppler centroid control method does not work well when the look angle of radar is out of an expected range. This paper primarily analyzes the Doppler properties of GEO SAR in the Earth rectangular coordinate. Then, according to the actual conditions of the GEO SAR ground observation, the effective range is presented by the minimum and maximum possible look angles which are directly related to the orbital parameters. Based on the vector analysis, a new approach for zero-Doppler centroid control in GEO SAR, performing the attitude steering by a combination of pitch and roll rotation, is put forward. This approach, considering the Earth’s rotation and elliptical orbit effects, can accurately reduce the residual Doppler centroid. All the simulation results verify the correctness of the range of look angle and the proposed steering method. Yicheng Jiang, Bin Hu, Yun Zhang, Meng Lian, and Zhuoqun Wang Copyright © 2014 Yicheng Jiang et al. All rights reserved. Dual-Polarized Crossed Bowtie Dipole Array for Wireless Communication Applications Wed, 26 Nov 2014 11:45:14 +0000 A dual-polarized array with downtilted radiation patterns is proposed for wireless communication applications. The proposed dual-polarized antenna element achieves an enhanced impedance bandwidth and compact dimensions by introducing a parasitic circular patch and vertical metal cylinders, which is a good candidate for radiating elements in base station antennas. By optimizing the amplitude and phase distribution along the feed, a radiation pattern with a downtilted angle is obtained. The dual-polarized array antenna achieves an impedance bandwidth for VSWR 1.5, covering the frequency bands for 3G/LTE systems. Moreover, the proposed array achieves high port isolation, the stable antenna gain over the entire operating band. Therefore, the proposed array antenna is very suitable for potential wireless communication applications. A prototype has been manufactured and measured. The measurements, that match the design objectives, are also presented. Zhi-Ya Zhang, Shuang Li, Shao-Li Zuo, Jia-Yue Zhao, Xiao-dong Yang, and Guang Fu Copyright © 2014 Zhi-Ya Zhang et al. All rights reserved. A Broadband and High Gain Tapered Slot Antenna for W-Band Imaging Array Applications Sun, 23 Nov 2014 09:25:42 +0000 A broadband and high gain tapered slot antenna (TSA) by utilizing a broadband microstrip- (MS-) to-coplanar stripline (CPS) balun has been developed for millimeter-wave imaging systems and sensors. This antenna exhibits ultrawideband performance for frequency ranges from 70 to over 110 GHz with the high antenna gain, low sidelobe levels, and narrow beamwidth. The validity of this antenna as imaging arrays is also demonstrated by analyzing mutual couplings and 4-element linear array. This antenna can be applied to mm-wave phased array, imaging array for plasma diagnostics applications. Dong Sik Woo, Kang Wook Kim, and Hyun-Chul Choi Copyright © 2014 Dong Sik Woo et al. All rights reserved. A Flexible Monopole Antenna with Dual-Notched Band Function for Ultrawideband Applications Thu, 20 Nov 2014 11:45:42 +0000 We present a flexible ultrawideband (UWB) planar monopole antenna with dual-notched band characteristic printed on a polyimide substrate. The antenna is fed by a step coplanar waveguide (CPW) that provides smooth transitional impedance for improved matching. It operates from 2.76 to 10.6 GHz with return loss greater than 10 dB except for the notch band to reduce the interference with existing 3.5 GHz WiMAX band and 5.5 GHz WLAN band. With a combination of rectangular and circle patches in which the U-shaped slot is carved, the overall size of antenna is 30 mm × 20 mm. Moreover, a pair of arc-shaped stubs located at both sides of the feed line is utilized to create the notch band for WiMAX band. The results also show that the antenna has omnidirectional radiation pattern and smooth gain over the entire operational band. Xiaoyan Zhang and Guohao Wang Copyright © 2014 Xiaoyan Zhang and Guohao Wang. All rights reserved. Design of Highly Isolated Compact Antenna Array for MIMO Applications Thu, 20 Nov 2014 06:00:26 +0000 In order to achieve very high data rates in both the uplink and downlink channels, the multiple antenna systems are used within the mobile terminal as well as the base station of the future generation of mobile networks. When implemented in a size limited platform, the multiple antenna arrays suffer from strong mutual coupling between closely spaced array elements. In this paper, a rigorous procedure for the design of a 4-port compact planar antenna array with high port isolation is presented. The proposed design involves a decoupling network consisting of reactive elements, whose values can be obtained by the method of eigenmode analysis. Numerical results show the effectiveness of the proposed design approach in improving the port isolation of a compact four-element planar array. Tiancong Huang, Yantao Yu, and Lijun Yi Copyright © 2014 Tiancong Huang et al. All rights reserved. Development of Ultra-Broadband Base Station Antenna for All Mainstream LTE 700/800/900 MHz Frequency Bands Thu, 20 Nov 2014 00:00:00 +0000 LTE deployment is being accelerated due to its improved radio access structure meeting the requirements of current and next generation of wireless networks. Its low band application presents useful aspects such as low density of base station while providing good in-building penetration. In this work, we design and develop a dual-polarized base station antenna supporting 698 MHz to 960 MHz with an azimuth-plan half-power beam width of 90° covering all mainstream LTE 700/800/900 MHz frequency bands representing the widest low frequency range being actively used in the current mobile communication industry. In the design process, rigorous algorithm based on swarm method is developed to tune the electrical performances under strict base station antenna requirements. Experimental results from pattern tests demonstrate the design analysis and the significant advantages of using swarm method in the antenna development process. Doudou Samb, Zhonglin Wu, Mulin Liu, and Hu Bin Jie Copyright © 2014 Doudou Samb et al. All rights reserved. Monte Carlo Simulation of the Echo Signals from Low-Flying Targets for Airborne Radar Mon, 17 Nov 2014 11:38:19 +0000 A demonstrated hybrid method based on the combination of half-space physical optics method (PO), graphical-electromagnetic computing (GRECO), and Monte Carlo method on echo signals from low-flying targets based on actual environment for airborne radar is presented in this paper. The half-space physical optics method , combined with the graphical-electromagnetic computing (GRECO) method to eliminate the shadow regions quickly and rebuild the target automatically, is employed to calculate the radar cross section (RCS) of the conductive targets in half space fast and accurately. The direct echo is computed based on the radar equation. The reflected paths from sea or ground surface cause multipath effects. In order to accurately obtain the echo signals, the phase factors are modified for fluctuations in multipath, and the statistical average value of the echo signals is obtained using the Monte Carlo method. A typical simulation is performed, and the numerical results show the accuracy of the proposed method. Mingyuan Man, Zhenya Lei, Yongjun Xie, Botao Chen, and Qing Wang Copyright © 2014 Mingyuan Man et al. All rights reserved. Compact Shorted Stacked-Patch Antenna Integrated with Chip-Package Based on LTCC Technology Sun, 16 Nov 2014 00:00:00 +0000 A low profile chip-package stacked-patch antenna is proposed by using low temperature cofired ceramic (LTCC) technology. The proposed antenna employs a stacked-patch to achieve two operating frequency bands and enhance the bandwidth. The height of the antenna is decreased to 4.09 mm (about /25 at 2.45 GHz) due to the shorted pin. The package is mounted on a 44 × 44 mm2 ground plane to miniaturize the volume of the system. The design parameters of the antenna and the effect of the antenna on chip-package cavity are carefully analyzed. The designed antenna operates at a center frequency of 2.45 GHz and its impedance bandwidth is 200 MHz, resulting from two neighboring resonant frequencies at 2.41 and 2.51 GHz, respectively. The average gain across the frequency band is about 5.28 dBi. Yongjiu Li, Long Li, Xiwang Dai, Cheng Zhu, Feifei Huo, and Gang Dong Copyright © 2014 Yongjiu Li et al. All rights reserved. Rectangular Ring Antenna Excited by Circular Disc Monopole for WiMAX System Thu, 13 Nov 2014 11:35:39 +0000 This research presents a rectangular ring antenna excited by a circular disc monopole (CDM) mounted in front of a square reflector. The proposed antenna is designed to cover a frequency range of 2.300–5.825 GHz and thereby is suitable for WiMAX applications. Multiple parametric studies were carried out using the CST Microwave Studio simulation program. A prototype antenna was fabricated and experimented. The measurements were taken and compared with the simulation results, which indicates good agreement between both results. The prototype antenna produces an impedance bandwidth ( < −10 dB) that covers the WiMAX frequency range and a constant unidirectional radiation pattern ( and ). The minimum and maximum gains are 3.7 and 8.7 dBi, respectively. The proposed antenna is of compact size and has good unidirectional radiation performance. Thus, it is very suitable for a multitude of WiMAX applications. Souphanna Vongsack, Chuwong Phongcharoenpanich, Sompol Kosulvit, Kazuhiko Hamamoto, and Toshio Wakabayashi Copyright © 2014 Souphanna Vongsack et al. All rights reserved. Deployment Challenges for Large-Scale MIMO Communications Sun, 09 Nov 2014 12:42:49 +0000 Ahmed Iyanda Sulyman, Joonhyuk Kang, and Shahram Yousefi Copyright © 2014 Ahmed Iyanda Sulyman et al. All rights reserved. On the Accuracy of Asymptotic Solutions for TM Waves Diffracting on an Impedance Wedge Sun, 09 Nov 2014 12:29:08 +0000 The contribution focuses on the accuracy of two asymptotic solutions aimed at representing the electromagnetic field scattered by penetrable wedges. One is a heuristic manipulation of the solution for the perfect electrical conductor, and the other one is a more rigorous coefficient based on approximate boundary conditions. The results presented here extend those proposed by other authors by illustrating the accuracy of such solutions at the edge of validity of the uniform theory of diffraction. In particular, they show that the heuristic formulation can be freely applied in similar conditions, while the other might not always lead to accurate predictions. Sonia Fu, Pierre Jacolot, Tommaso Balercia, Christian Rom, Jørgen B. Andersen, and Gert F. Pedersen Copyright © 2014 Sonia Fu et al. All rights reserved. A Novel CPW-Fed UWB Antenna with Band-Stop Function Sun, 09 Nov 2014 09:55:47 +0000 A novel coplanar waveguide-fed (CPW) ultrawideband (UWB) antenna with band-stop function is presented in this paper. The proposed antenna comprises a CPW-fed slot rectangular patch with an open stub ground plane, and two inverted L-shaped strip conductors are fabricated on the back plane. The overall size of the antenna is 25 × 25 × 1.6 mm2, and it achieves good impedance matching and radiation gain. Simulated and measured results show that the designed antenna operates at 2.9 GHz–13.08 GHz with band rejection in the frequency band of 7.7 GHz–9.05 GHz for satellite applications, and the proposed antenna is suitable for UWB wireless communication applications. Huaming Chen, Zhengrong Li, Baiyu Li, and Guangfu Sun Copyright © 2014 Huaming Chen et al. All rights reserved. Design of a Small Modified Minkowski Fractal Antenna for Passive Deep Brain Stimulation Implants Tue, 04 Nov 2014 00:00:00 +0000 A small planar modified Minkowski fractal antenna is designed and simulated in dual frequency bands (2.4 and 5.8 GHz) for wireless energy harvesting by deep brain stimulation (DBS) devices. The designed antenna, physically being confined inside a miniaturized structure, can efficiently convert the wireless signals in dual ISM frequency bands to the energy source to recharge the DBS battery or power the pulse generator directly. The performance metrics such as the return loss, the specific absorption rate (SAR), and the radiation pattern within skin and muscle-fat-skin tissues are evaluated for the designed antenna. The gain of the proposed antenna is 3.2 dBi at 2.4 GHz and 4.7 dBi at 5.8 GHz; also the averaged SAR of the antenna in human body tissue is found to be well below the legally allowed limit at both frequency bands. The link budget shows the received power at the distance of 25 cm at 2.4 GHz and 5.8 GHz are around 0.4 mW and 0.04 mW, which can empower the DBS implant. The large operational bandwidth, the physical compactness, and the efficiency in wireless signal reception make this antenna suitable in being used in implanted biomedical devices such as DBS pulse generators. Sara Manafi and Hai Deng Copyright © 2014 Sara Manafi and Hai Deng. All rights reserved. Bistatic Scattering due to Hydrometeors on Cochannel Intersystem Communication Links over a Subtropical Path Thu, 30 Oct 2014 08:09:46 +0000 The performance of fixed satellite systems in the shared frequency band depends on the tolerance level of interference between them. Interference disturbs the functionality of the ground station and causes signal degradation. The knowledge of interference level must therefore be known for an optimal satellite design. In this work, we evaluate interference due to hydrometeors for a situation in which a satellite downlink signal is affected by the signal from a terrestrial microwave network operating at the same frequency as the satellite system in a subtropical station: Durban, South Africa. The evaluation of the transmission loss is based on the modified 3D bistatic radar equation and the exponential rain cell model for the scattering. The results of intersystem interference for different station separation over frequencies variation, terrestrial antenna gains, and exceedance probabilities are presented. The effect of the additional rain attenuation on the satellite signals is also examined. The results point out to some remarkable attenuation differences between the effective transmission loss and the transmission loss statistics for small time unavailability at the frequencies considered in this work. This could be detrimental in link budget design if overlooked. P. A. Owolawi and T. Wallingo Copyright © 2014 P. A. Owolawi and T. Wallingo. All rights reserved. Reduction of the In-Band RCS of Microstrip Patch Antenna by Using Offset Feeding Technique Wed, 29 Oct 2014 12:17:58 +0000 This paper presents a method for implementing a low in-band scattering design for microstrip patch antennas based on the analysis of structural mode scattering and radiation characteristics. The antenna structure is first designed to have the lowest structural mode scattering in a desired frequency band. The operating frequency band of the antenna is then changed to coincide with that of the lowest structural mode scattering by adjusting the feed position on the antenna (offset feeding) to achieve an antenna with low in-band radar cross section (RCS). In order to reduce the level of cross polarization of the antenna caused by offset feeding, symmetry feeding structures for both single patch antennas and two-patch arrays are proposed. Examples that show the efficiency of the method are given, and the results illustrate that the in-band RCS of the proposed antennas can be reduced by as much as 17 dBsm for plane waves impinging from the normal direction compared to patch antennas fed by conventional methods. Weiwei Xu, Junhong Wang, Meie Chen, Zhan Zhang, and Zheng Li Copyright © 2014 Weiwei Xu et al. All rights reserved. Erratum to “Joint Delay Doppler Probability Density Functions for Air-to-Air Channels” Tue, 28 Oct 2014 14:23:50 +0000 Michael Walter, Dmitriy Shutin, and Uwe-Carsten Fiebig Copyright © 2014 Michael Walter et al. All rights reserved. Analysis of a Compact and Superdirective Metamaterial-Inspired Monopole Antenna Tue, 28 Oct 2014 00:00:00 +0000 The directivity of a metamaterial-inspired compact (0.145λ0) monopole antenna was investigated. The proposed structure is composed of a split-ring resonator (SRR) parasitic element placed in the vicinity of a monopole antenna. Two configurations denoted by A1 and A2 were considered depending on the position of the slot in the SRR element. By analyzing simulated and measured results, the superdirectivity (7.5 dBi for A1 and 9 dBi for A2) of the structure was discussed. It is found that the monopole-SRR and/or ground plane-SRR coupling effects may be responsible for the superdirectivity of the structure. Saber Dakhli, Hatem Rmili, Kourosh Mahdjoubi, Jean-Marie Floc’h, and Fethi Choubani Copyright © 2014 Saber Dakhli et al. All rights reserved. Outage Probability of Dual-Hop Multiple Antenna Relay Systems with Interference at the Relay and Destination Mon, 27 Oct 2014 00:00:00 +0000 This paper analyzes the outage performance of a dual-hop relaying system in which the relay is equipped with multiple antennas, while the source and destination have a single antenna. New exact closed-form expressions for the outage probability of both the amplify-and-forward (AF) and the decode-and-forward (DF) relaying systems are derived, assuming that the relay and destination are impaired by cochannel interferers and additive white Gaussian noise (AWGN). Numerical results are presented to verify the theoretical analysis. Mengmeng Liu, Jianhua Zhang, and Ping Zhang Copyright © 2014 Mengmeng Liu et al. All rights reserved. Synthesis of Phase-Only Reconfigurable Linear Arrays Using Multiobjective Invasive Weed Optimization Based on Decomposition Mon, 20 Oct 2014 06:22:53 +0000 Synthesis of phase-only reconfigurable array aims at finding a common amplitude distribution and different phase distributions for the array to form different patterns. In this paper, the synthesis problem is formulated as a multiobjective optimization problem and solved by a new proposed algorithm MOEA/D-IWO. First, novel strategies are introduced in invasive weed optimization (IWO) to make original IWO fit for solving multiobjective optimization problems; then, the modified IWO is integrated into the framework of the recently well proved competitive multiobjective optimization algorithm MOEA/D to form a new competitive MOEA/D-IWO algorithm. At last, two sets of experiments are carried out to illustrate the effectiveness of MOEA/D-IWO. In addition, MOEA/D-IWO is compared with MOEA/D-DE, a new version of MOEA/D. The comparing results show the superiority of MOEA/D-IWO and indicate its potential for solving the antenna array synthesis problems. Yan Liu, Yong-Chang Jiao, Ya-Ming Zhang, and Yan-Yan Tan Copyright © 2014 Yan Liu et al. All rights reserved. A Generalized Approach for Computation of Near Field Radiation Pattern of an Antenna Sun, 19 Oct 2014 09:44:39 +0000 A generalized procedure in the form of an analytical formulation for the determination of radiation pattern of an antenna at any arbitrary distance which covers the near field as well as far field is presented in this paper. With the prior knowledge of either the current or field distribution on the radiating aperture, the proposed near field analysis is generic and can be applied for wide variety of antenna elements. The underlying principle of the generalized procedure is tantamount to considering the radiating aperture as an array of point electric and magnetic dipoles. The validity and novelty of the proposed new approach have been substantiated considering an open ended circular cylindrical waveguide and a conical horn as case studies and treating the far field as a special case of near field with pertinent distance criterion. The effect of change in the distance of observation ranging from reactive near field to far field on the radiation patterns of these antennas has also been discussed. The simulation studies reveal that the depicted normalized phase patterns of both the circular waveguide and conical horn follow the changes in the profile of the corresponding amplitude patterns. Preetham Shankpal, Varun Arur, Govind Kadambi, and James Shuttleworth Copyright © 2014 Preetham Shankpal et al. All rights reserved. An Improved Chaos Genetic Algorithm for T-Shaped MIMO Radar Antenna Array Optimization Tue, 14 Oct 2014 10:49:48 +0000 In view of the fact that the traditional genetic algorithm easily falls into local optimum in the late iterations, an improved chaos genetic algorithm employed chaos theory and genetic algorithm is presented to optimize the low side-lobe for T-shaped MIMO radar antenna array. The novel two-dimension Cat chaotic map has been put forward to produce its initial population, improving the diversity of individuals. The improved Tent map is presented for groups of individuals of a generation with chaos disturbance. Improved chaotic genetic algorithm optimization model is established. The algorithm presented in this paper not only improved the search precision, but also avoids effectively the problem of local convergence and prematurity. For MIMO radar, the improved chaos genetic algorithm proposed in this paper obtains lower side-lobe level through optimizing the exciting current amplitude. Simulation results show that the algorithm is feasible and effective. Its performance is superior to the traditional genetic algorithm. Xin Fu, Xianzhong Chen, Qingwen Hou, Zhengpeng Wang, and Yixin Yin Copyright © 2014 Xin Fu et al. All rights reserved. Radiation Characteristic Improvement of X-Band Slot Antenna Using New Multiband Frequency-Selective Surface Tue, 14 Oct 2014 08:18:23 +0000 A new configuration of frequency-selective surfaces (FSSs) is designed and presented with multiresonance characteristics which covers all of the frequency domain of X-band from 8 to 12 GHz. The proposed FSS comprises three conductor-based split ring resonators, connected together. In this design, two unit cells of the FSS with different lengths are employed side by side to design the FSS. The FSS is used to enhance the gain of the new designed triangle slot antenna at X-band. The proposed FSS is analyzed by using reflected-wave unit-cell box method. The single, double, and array of the FSS cells are studied. Next, the designed FSS along with the antenna is analyzed. The measurement and simulated results of the impedance and radiation characteristics, especially the increment of the gain, are presented. Elham Moharamzadeh Copyright © 2014 Elham Moharamzadeh. All rights reserved. Optimized Wideband Impedance Matching Balun for Conducting Two-Arm Antennas Tue, 14 Oct 2014 07:45:10 +0000 A split coaxial balun with a step transition of the inner conductor diameter is introduced to satisfy impedance matching between unbalanced feeder and balanced antennas. The location of the step transition along the axis of the balun and the diameter change are two dimensional parameters that are not present in the conventional split coaxial balun. These additional parameters, together with the double slot width, provide more flexibility to design the balun for better impedance matching. The effects of the three dimensional parameters on the input impedance seen at the (unbalanced) coaxial line side of the balun are investigated when it is terminated with specific lumped impedance at its (balanced) split side. An optimization procedure is introduced to arrive at the balun dimensional parameters to give the best matching with specific load impedance. The proposed balun is designed to feed (balanced) two-arm antennas such as the dipole and the bowtie antenna from 50 Ω-coaxial line. The electromagnetic simulation shows that the proposed balun results in a perfect impedance matching. A comparison with the performance of the conventional split balun used to feed a dipole antenna shows that the balun proposed in the present paper gives a much lower value of the return loss at the design frequency and a wider bandwidth for VSWR ≤ 1.5. The simulation results obtained using the MoM are compared with experimental measurements showing good agreement. Khalid F. A. Hussein Copyright © 2014 Khalid F. A. Hussein. All rights reserved.