International Journal of Antennas and Propagation http://www.hindawi.com The latest articles from Hindawi Publishing Corporation © 2015 , Hindawi Publishing Corporation . All rights reserved. MIMO Antenna Design and Channel Modeling 2014 Thu, 30 Jul 2015 07:52:27 +0000 http://www.hindawi.com/journals/ijap/2015/675650/ Wenhua Chen, Manos M. Tentzeris, Neil Trappe, Yuan Yao, Yan Zhang, and Xinyi Tang Copyright © 2015 Wenhua Chen et al. All rights reserved. Compressive Sensing for High-Resolution Direction-of-Arrival Estimation via Iterative Optimization on Sensing Matrix Wed, 29 Jul 2015 13:31:09 +0000 http://www.hindawi.com/journals/ijap/2015/713930/ A novel compressive sensing- (CS-) based direction-of-arrival (DOA) estimation algorithm is proposed to solve the performance degradation of the CS-based DOA estimation in the presence of sensing matrix mismatching. Firstly, a DOA sparse sensing model is set up in the presence of sensing matrix mismatching. Secondly, combining the Dantzig selector (DS) algorithm and least-absolute shrinkage and selection operator (LASSO) algorithm, a CS-based DOA estimation algorithm which performs iterative optimization alternatively on target angle information vector and sensing matrix mismatching error vector is proposed. The simulation result indicates that the proposed algorithm possesses higher angle resolution and estimation accuracy compared with conventional CS-based DOA estimation algorithms. Hongtao Li, Chaoyu Wang, and Xiaohua Zhu Copyright © 2015 Hongtao Li et al. All rights reserved. A Novel Miniaturized Dual Slant-Polarized UWB Antenna Array with Excellent Pattern Symmetry Property for MIMO Applications Wed, 29 Jul 2015 07:54:07 +0000 http://www.hindawi.com/journals/ijap/2015/801638/ A novel miniaturized 1 × 10 uniform linear dual slant-polarized UWB antenna array for MIMO base station is presented. The antenna array operates in the frequency band from 1710 to 2690 MHz with a 17.3–18.7 dBi gain in a size of 105 × 1100 × 37 mm. The array element is composed of two single-polarized dipoles evolved from bow-tie antenna with slots on them, which miniaturize the size of the antenna. The 10 array elements are fed through an air dielectric strip-line power splitter. Two parameters, the beam tracking and the beam squint, are presented to quantitatively describe the pattern symmetry property of the antenna. The simulated and measured radiation performances are studied and compared. The results show that the pattern symmetry property of the single antenna element has been improved about 24% compared with the former study, and the antenna array also provides excellent pattern symmetry property. Zhi Zeng, Jianjun Huang, Zhaohui Song, and Qinyu Zhang Copyright © 2015 Zhi Zeng et al. All rights reserved. Design of a Minimized Complementary Illusion Cloak with Arbitrary Position Tue, 28 Jul 2015 11:24:53 +0000 http://www.hindawi.com/journals/ijap/2015/932495/ This paper has developed a complementary illusion cloak to hide the objects with arbitrary shapes and sizes. In the proposed cloak, a complementary cloak is first introduced by using the trapezoid coordinate transformation. Then an illusion device in terms of another trapezoid coordinate transformation is designed to cloak the object. With two coordinate transformations, the complementary illusion cloak device can be arbitrarily placed to hide the target object, and the sizes of the antiobject used to cloak the object are obviously compressed. Numerical results including target objects with different shapes are given to verify correctness and effectiveness of the proposed cloak. Yan Shi, Lin Zhang, Wei Tang, Long Li, and Chang-Hong Liang Copyright © 2015 Yan Shi et al. All rights reserved. LTE Technology: Antenna, RF Front-Ends, and Channel Modeling Tue, 28 Jul 2015 07:57:25 +0000 http://www.hindawi.com/journals/ijap/2015/764178/ Qingfeng Zhang, Sai Wai Wong, Cheng Jin, Xiu Yin Zhang, Yifan Chen, Dimitrios Sounas, and Nima Chamanara Copyright © 2015 Qingfeng Zhang et al. All rights reserved. DOA Estimation for Mixed Uncorrelated and Coherent Sources in Multipath Environment Mon, 27 Jul 2015 13:20:14 +0000 http://www.hindawi.com/journals/ijap/2015/636545/ A novel direction-of-arrival (DOA) estimation method is proposed to cope with the scenario where a number of uncorrelated and coherent narrowband sources simultaneously impinge on the far-field of a uniform linear array (ULA). In the proposed method, the DOAs of uncorrelated sources are firstly estimated by utilizing the property of the moduli of eigenvalues of the DOA matrix. Afterwards, the contributions of uncorrelated sources and the interference of noise are eliminated completely by exploiting the improved spatial differencing technique and only the coherent components remain in the spatial differencing matrix. Finally, the remaining coherent sources can be resolved by performing the improved spatial smoothing scheme on the spatial differencing matrix. The presented method can resolve more number of sources than that of the array elements and distinguish the uncorrelated and coherent sources that come from the same direction as well as improving the estimation performance. Simulation results demonstrate the effectiveness and efficiency of the proposed method. Heping Shi, Wen Leng, Anguo Wang, and Tongfeng Guo Copyright © 2015 Heping Shi et al. All rights reserved. Compact Unequal Power Divider with Filtering Response Mon, 27 Jul 2015 13:14:33 +0000 http://www.hindawi.com/journals/ijap/2015/658102/ We present a novel unequal power divider with bandpass responses. The proposed power divider consists of five resonators and a resistor. The power division ratio is controlled by altering the coupling strength among the resonators. The output ports have the characteristic impedance of 50 Ω and impedance transformers in classical Wilkinson power dividers are not required in this design. Use of resonators enables the filtering function of the power divider. Two transmission zeros are generated near the passband edges, resulting in quasielliptic bandpass responses. For validation, a 2 : 1 filtering power divider is implemented. The fabricated circuit size is 0.22 λg  0.08 λg, featuring compact size for unequal filtering power dividers, which is suitable for the feeding networks of antenna arrays. Wei-Qiang Pan, Jin-Xu Xu, Kai Xu Wang, and Xiao Lan Zhao Copyright © 2015 Wei-Qiang Pan et al. All rights reserved. Dual-Frequency Two-Element Antenna Array with Suppressed Mutual Coupling Mon, 27 Jul 2015 12:50:05 +0000 http://www.hindawi.com/journals/ijap/2015/912934/ An efficient technique utilizing the defected ground structure (DGS) to suppress the mutual coupling effect of a dual-frequency microstrip antenna array is studied. The proposed dual-frequency DGS beneath two patches includes two circular split ring slots, each of which corresponds to one resonant frequency of the patches. The characteristic of the compact DGS is theoretically and experimentally investigated. The prototypes of the patches arrays with and without the proposed DGS are fabricated. Both the simulated and measured results show that the mutual coupling between array elements has been obviously reduced at the two operating frequency bands with the implementation of the proposed DGS structure. Yantao Yu, Lijun Yi, Xiaoya Liu, Zhaokai Gu, and Nadia Media Rizka Copyright © 2015 Yantao Yu et al. All rights reserved. MIMO Antenna with High Isolation for WBAN Applications Mon, 27 Jul 2015 12:49:40 +0000 http://www.hindawi.com/journals/ijap/2015/370763/ A multi-input multi-output (MIMO) antenna with high isolation is proposed for 2.4 GHz ISM band (2.4–2.485 GHz) WBAN applications. The proposed MIMO antenna consists of two PIFA elements and utilizes an isolator composed of a shorted strip and two slits in the ground plane. Although the separation between the two PIFAs is minimized to 8 mm (0.06 ), isolation performance is improved by virtue of an isolator. To analyze the antenna’s performance on a human body, the proposed antenna is placed on a human muscle-equivalent flat phantom and is investigated through simulations. The measured −10 dB reflection coefficient bandwidth of the antenna ranges from 2.11 GHz to 2.6 GHz, and the isolation is lower than −38 dB over the 2.4 GHz ISM band. Do-Gu Kang, Jinpil Tak, and Jaehoon Choi Copyright © 2015 Do-Gu Kang et al. All rights reserved. A Novel Metamaterial MIMO Antenna with High Isolation for WLAN Applications Mon, 27 Jul 2015 12:24:56 +0000 http://www.hindawi.com/journals/ijap/2015/851904/ A compact metamaterial-MIMO antenna for WLAN applications is presented in this paper. The MIMO antenna is designed by placing side by side two single metamaterial antennas which are constructed based on the modified composite right/left-handed (CRLH) model. By adding another left-handed inductor, the total left-handed inductor of the modified CRLH model is increased remarkably in comparison with that of conventional CRLH model. As a result, the proposed metamaterial antenna achieves 60% size reduction in comparison with the unloaded antenna. The MIMO antenna is electrically small (30 mm × 44 mm) with an edge-to-edge separation between two antennas of at 2.4 GHz. In order to reduce the mutual coupling of the antenna, a defected ground structure (DGS) is inserted to suppress the effect of surface current between elements of the proposed antenna. The final design of the MIMO antenna satisfies the return loss requirement of less than −10 dB in a bandwidth ranging from 2.38 GHz to 2.5 GHz, which entirely covers WLAN frequency band allocated from 2.4 GHz to 2.48 GHz. The antenna also shows a high isolation coefficient which is less than −35 dB over the operating frequency band. A good agreement between simulation and measurement is shown in this context. Nguyen Khac Kiem, Huynh Nguyen Bao Phuong, Quang Ngoc Hieu, and Dao Ngoc Chien Copyright © 2015 Nguyen Khac Kiem et al. All rights reserved. Linear Array Design with Switched Beams for Wireless Communications Systems Mon, 27 Jul 2015 12:08:11 +0000 http://www.hindawi.com/journals/ijap/2015/278160/ This paper presents an analysis for optimal design of switched beamforming applied to a linear array for wireless communication systems. The beam switching scheme provides coverage of a given sector in azimuth and controls the sidelobe level simultaneously. The analysis was developed considering arrays composed of Quasi-Yagi elements. The model assumes a user moving in the azimuthal direction under a constant velocity and with an estimation of the signal-to-noise ratio (SNR) at the mobile user (MU). The radio base station applies the beam that yields the best performance during transmission. The decision is based on the feedback information received from the MU. The goal of the analysis is to determine the best trade-off between the array size and number of feedback bits necessary to maximize the SNR at the receiver. The results show that a compromise between the number of beam-pointing directions and the array size should be taken into consideration for a wireless communication system design. Vinícius Ludwig-Barbosa, Edson Schlosser, Renato Machado, Filipe Guterres Ferreira, Sabrina Müller Tolfo, and Marcos Vinício Thomas Heckler Copyright © 2015 Vinícius Ludwig-Barbosa et al. All rights reserved. 2D Active Antenna Array Design for FD-MIMO System and Antenna Virtualization Techniques Mon, 27 Jul 2015 12:05:49 +0000 http://www.hindawi.com/journals/ijap/2015/873530/ Full dimension MIMO (FD-MIMO) is one of the key technologies presently studied in the 3GPP for the next generation long-term evolution advanced (LTE-A) systems. By incorporating FD-MIMO into LTE/LTE-A systems, it is expected that system throughput will be drastically improved beyond what is possible in conventional LTE systems. This paper presets details on the 2D active antenna array design for FD-MIMO systems supporting 32 antenna elements. The FD-MIMO system allows for dynamic and adaptive precoding to be performed jointly across all antennas thus achieving more directional transmissions in the azimuth and elevation domains simultaneously, to a larger number of users. Finally, we discuss 2D antenna array port virtualization techniques for creating beams with wide coverage, necessary for broadcasting signals to all users within a sector, such as the CRS (Common Reference Signal). Ioannis Tzanidis, Yang Li, Gary Xu, Ji-Yun Seol, and JianZhong (Charlie) Zhang Copyright © 2015 Ioannis Tzanidis et al. All rights reserved. A CPW-Fed Quasi-PIFA Antenna Using Quasi-Lumped Resonators for Mobile Phones Mon, 27 Jul 2015 11:58:33 +0000 http://www.hindawi.com/journals/ijap/2015/715958/ A novel single CPW-fed Quasi-Planar Inverted-F Antenna (PIFA) using quasi-lumped elements is developed for mobile communication handheld terminals operating at 2.6 GHz. The antenna is composed of an inductor covered by a set of interdigital and parasitic capacitors. The proposed antenna achieves a measured bandwidth of 11% for return loss with the antenna gain of about 4 dBi. The antenna is designed in single layer (zero height) which is appropriate to be used in thin devices where a small room is considered for the antenna. The proposed antenna is suitable for use in Long Term Evolution band 7. The operating frequency of introduced antenna depends on the number of interdigital fingers and inductor length rather than the total resonator patch only, so that the operating frequency can be altered while the total patch size remains unchanged. The calculated operating frequency is confirmed by simulation and measurement. Also the dipole-like simulated radiation pattern is confirmed by measurement. Majid Rafiee, Mohd Fadzil bin Ain, and Aftanasar Md. Shahar Copyright © 2015 Majid Rafiee et al. All rights reserved. On the Cross Correlation Properties of MIMO Wideband Channels under Nonisotropic Propagation Conditions Mon, 27 Jul 2015 11:45:30 +0000 http://www.hindawi.com/journals/ijap/2015/904153/ Wideband (WB) and ultrawideband (UWB) systems combined with multiple-input multiple-output (MIMO) technology increase both the systems performances and the complexity of the channel models required to evaluate their capabilities. Because in real scenarios waves propagate nonisotropically, the accuracy of the channel model is increased if nonisotropic propagation is considered. The channel bandwidth is the key term in the evaluation process of these systems because large bandwidths introduce frequency selectivity, a unique phenomenon of WB and UWB systems with more complexity in the latter case. This is due to the fact that, unlike WB technology in which the propagating signal is the only affected parameter by the frequency selectivity, in the UWB case, this phenomenon also affects the antenna propagation pattern (APP). In this paper, we developed a novel channel model based on the statistical analysis of two-dimensional cross correlation functions (CCFs) of WB/UWB MIMO nonisotropic channels. A mathematical solution to assess the frequency selective behavior of the UWB APP is also presented. The CCF reveals how the power spectral density (PSD) of the channel is influenced by bandwidth, nonisotropic propagation, and APP. Ana Maria Pistea and Hamidreza Saligheh Rad Copyright © 2015 Ana Maria Pistea and Hamidreza Saligheh Rad. All rights reserved. High Selectivity Dual-Band Bandpass Filter with Tunable Lower Passband Mon, 27 Jul 2015 11:41:40 +0000 http://www.hindawi.com/journals/ijap/2015/762504/ This paper presents a novel method to design dual-band bandpass filters with tunable lower passband and fixed upper passband. It utilizes a trimode resonator with three controllable resonant modes. Discriminating coupling is used to suppress the unwanted mode to avoid the interference. Varactors are utilized to realize tunable responses. The bandwidth of the two bands can be controlled individually. Transmission zeros are generated near the passband edges, resulting in high selectivity. For demonstration, a tunable bandpass filter is implemented. Good agreement between the prediction and measurement validates the proposed method. Wei-Qiang Pan, Xiao-Lan Zhao, Yao Zhang, and Jin-Xu Xu Copyright © 2015 Wei-Qiang Pan et al. All rights reserved. Power Allocation Optimization: Linear Precoding Adapted to NB-LDPC Coded MIMO Transmission Mon, 27 Jul 2015 11:35:46 +0000 http://www.hindawi.com/journals/ijap/2015/975139/ In multiple-input multiple-output (MIMO) transmission systems, the channel state information (CSI) at the transmitter can be used to add linear precoding to the transmitted signals in order to improve the performance and the reliability of the transmission system. This paper investigates how to properly join precoded closed-loop MIMO systems and nonbinary low density parity check (NB-LDPC). The elements in the Galois field, GF(), are directly mapped to transmit symbol vectors. This allows NB-LDPC codes to perfectly fit with a MIMO precoding scheme, unlike binary LDPC codes. The new transmission model is detailed and studied for several linear precoders and various designed LDPC codes. We show that NB-LDPC codes are particularly well suited to be jointly used with precoding schemes based on the maximization of the minimum Euclidean distance (max-) criterion. These results are theoretically supported by extrinsic information transfer (EXIT) analysis and are confirmed by numerical simulations. Tarek Chehade, Ludovic Collin, Philippe Rostaing, Emanuel Radoi, and Oussama Bazzi Copyright © 2015 Tarek Chehade et al. All rights reserved. Map-Based Channel Model for Urban Macrocell Propagation Scenarios Mon, 27 Jul 2015 11:17:15 +0000 http://www.hindawi.com/journals/ijap/2015/172501/ The evolution of LTE towards 5G has started and different research projects and institutions are in the process of verifying new technology components through simulations. Coordination between groups is strongly recommended and, in this sense, a common definition of test cases and simulation models is needed. The scope of this paper is to present a realistic channel model for urban macrocell scenarios. This model is map-based and takes into account the layout of buildings situated in the area under study. A detailed description of the model is given together with a comparison with other widely used channel models. The benchmark includes a measurement campaign in which the proposed model is shown to be much closer to the actual behavior of a cellular system. Particular attention is given to the outdoor component of the model, since it is here where the proposed approach is showing main difference with other previous models. Jose F. Monserrat, Saúl Inca, Jordi Calabuig, and David Martín-Sacristán Copyright © 2015 Jose F. Monserrat et al. All rights reserved. Dual Zeroth-Order Resonant USB Dongle Antennas for 4G MIMO Wireless Communications Mon, 27 Jul 2015 11:05:03 +0000 http://www.hindawi.com/journals/ijap/2015/816051/ A multiband multiple-input multiple-output (MIMO) antenna system consisting of two antenna elements has been proposed for 4G USB dongle application. The designed MIMO antenna system with a compact volume of 25 mm × 30 mm × 3.5 mm operates in two zeroth-order resonance (ZOR) modes to cover the LTE band 13 (746–787 MHz), GSM850/900 (824–960 MHz), and LTE band 7 (2500–2690 MHz) simultaneously. A pair of L-shaped parasitic strips and an etching slot on the ground are employed to achieve good isolation between two elements. Measurement results show that proposed MIMO antenna system has total efficiency over 40% across the operation band and isolation less than −8 dB at the lower band and −16 dB at the upper band, respectively. Yan Shi, Lu Zhang, and Chang-Hong Liang Copyright © 2015 Yan Shi et al. All rights reserved. The Communication Solution for LTE System under Radar Interference Circumstance Mon, 27 Jul 2015 10:03:00 +0000 http://www.hindawi.com/journals/ijap/2015/849695/ The interferences of radar and communication system coexistent environment are analyzed in this paper, and an attractive detection mechanism of the radar video signal and proportional fair scheduling algorithm based on channel sensing are proposed to realize the communication by using radar radiant intermissions. And the simulation is designed based on the proposed model to test this plan. The simulated results show that the packet scheduling algorithm is an excellent candidate for the communication solution for LTE system under radar radiant intermissions. Hang Zheng, Yunjie Li, and Yunpeng Zhu Copyright © 2015 Hang Zheng et al. All rights reserved. Energy-Efficient User Association Strategy for Hyperdense Heterogeneous Networking in the Fifth Generation Systems Mon, 27 Jul 2015 06:30:28 +0000 http://www.hindawi.com/journals/ijap/2015/686783/ Redesigning user association strategies to improve energy efficiency (EE) has been viewed as one of the promising shifting paradigms for the fifth generation (5G) cellular networks. In this paper, we investigate how to optimize users’ association to enhance EE for hyper dense heterogeneous networking in the 5G cellular networks, where the low-power node (LPN) much outnumbers the high-power node (HPN). To characterize that densely deployed LPNs would undertake a majority of high-rate services, while HPNs mainly support coverage; the EE metric is defined as average weighted EE of access nodes with the unit of bit per joule. Then, the EE optimization objective function is formulated and proved to be nonconvex. Two mathematical transformation techniques are presented to solve the nonconvex problem. In the first case, the original problem is reformulated as an equivalent problem involving the maximization of a biconcave function. In the second case, it is equivalent to a concave minimization problem. We focus on the solution of the biconcave framework, and, by exploiting the biconcave structure, a novel iterative algorithm based on dual theory is proposed, where a partially optimal solution can be achieved. Simulation results have verified the effectiveness of the proposed algorithm. Lei Li, Hao Jin, Zhipeng Yan, Changqing Yang, and Yong Wu Copyright © 2015 Lei Li et al. All rights reserved. Adaptable Bandwidth for Harmonic Step-Frequency Radar Mon, 27 Jul 2015 06:23:15 +0000 http://www.hindawi.com/journals/ijap/2015/808093/ A spectrum sensing technique is described which is used to enhance the performance of harmonic step-frequency radar in the presence of harmful radio frequency (RF) interference (RFI). This technique passively monitors the RF spectrum for subbands of high signal-to-interference-plus-noise ratio (SINR) within a constrained bandwidth of interest. An optimal subband is selected for the harmonic radar that maximizes SINR and minimizes the range resolution cell size, two conflicting objectives. The approach is tested using an experimental setup that injects high power RFI into a harmonic step-frequency radar, which significantly degrades radar performance. It is shown that the proposed spectrum sensing technique significantly improves the SINR and the peak-to-average sidelobe power level of the harmonic radar at the sacrifice of range resolution. Anthony F. Martone, Kyle A. Gallagher, Kelly D. Sherbondy, Kenneth I. Ranney, Traian V. Dogaru, Gregory J. Mazzaro, and Ram M. Narayanan Copyright © 2015 Anthony F. Martone et al. All rights reserved. Design of a Substrate-Integrated Fabry-Pérot Cavity Antenna for K-Band Applications Mon, 27 Jul 2015 06:09:56 +0000 http://www.hindawi.com/journals/ijap/2015/373801/ This paper presents the design of a planar, low-profile, high-gain, substrate-integrated Fabry-Pérot cavity antenna for K-band applications. The antenna consists of a frequency selective surface (FSS) and a planar feeding structure, which are both lithographically patterned on a high-permittivity substrate. The FSS is made of a circular hole array that acts as a partially reflecting mirror. The planar feeding structure is a wideband leaky-wave slit dipole fed by a coplanar waveguide whose ground plane acts as a perfect reflective mirror. The measured results show that the proposed antenna has an impedance bandwidth of more than 8% (VSWR ≤ 2), a maximum gain of 13.1 dBi, and a 3 dB gain bandwidth of approximately 1.3% at a resonance frequency of around 21.6 GHz. The proposed antenna features low-profile, easy integration into circuit boards, mechanical robustness, and excellent cost-effective mass production suitability. Truong Khang Nguyen and Ikmo Park Copyright © 2015 Truong Khang Nguyen and Ikmo Park. All rights reserved. The Applications of Metamaterials Tue, 21 Jul 2015 09:58:06 +0000 http://www.hindawi.com/journals/ijap/2015/729617/ Hui Feng Ma, Sanming Hu, Yun Gui Ma, Yun Lai, and Karu Esselle Copyright © 2015 Hui Feng Ma et al. All rights reserved. Advances in Antenna Array Processing for Radar 2014 Tue, 21 Jul 2015 09:56:09 +0000 http://www.hindawi.com/journals/ijap/2015/196910/ Hang Hu, Haiming Qi, Michelangelo Villano, and Ahmed Shaharyar Khwaja Copyright © 2015 Hang Hu et al. All rights reserved. Comparison Analysis of Single Loop Resonator Based Miniaturized Triple-Band Planar Monopole Antennas Thu, 16 Jul 2015 13:17:26 +0000 http://www.hindawi.com/journals/ijap/2015/495353/ We systemically analyze and discuss a group of miniaturized triple-band planar monopole antennas by integrating with a single loop resonator (SLR) as part of the radiation patch. Two configurations (rectangular and circular shaped radiation patches) are presented and the corresponding SLRs are integrated in the patches to contribute additional operating frequencies. Two feed techniques (coplanar waveguide and microstrip feeds) are performed to couple the electromagnetic waves. The conventional planar monopole antennas without the SLRs are also analyzed comparatively. Numerical and experimental methods are performed to demonstrate and discuss the proposed designs. Kaimin Wu, Yongjun Huang, Ruiming Wen, Jian Li, and Guangjun Wen Copyright © 2015 Kaimin Wu et al. All rights reserved. Aligned Space Time Block Codes for the 2-User X Channel with Secrecy Constraints Thu, 16 Jul 2015 11:45:28 +0000 http://www.hindawi.com/journals/ijap/2015/594791/ Interference alignment (IA) is a technique used to reduce the dimension of the interference, where consequently the multiplexing rate is increased. In the 2-user X channel, combining IA with space-time block codes increases the diversity gain. These gains are achieved with the cost of leaked information at unintended receivers, where this leaked information can be used to decode other receiver’s signals. In this paper, we consider each of the two two-antenna receivers as an eavesdropper with 1 or 2 additional eavesdropping antennas. As such, we suggest receiver structures to answer the question: “Is the leaked information sufficient to properly decode the unintended signals?” besides quantifying the leaked information in terms of secrecy sum rates (SSR). Interestingly, we show that the SSR is negative, indicating that the quality of the eavesdropped signals is superior to that of the intended signals. To assure confidentiality, we propose an interleaved multiple rotation-based transformation scheme that neutralizes any a priori knowledge about the structure of the eavesdropped information and rotates the transmitted symbols using orthogonal matrices, preserving both the power and the distance between symbols. Manar Mohaisen Copyright © 2015 Manar Mohaisen. All rights reserved. A Tutorial on Optical Feeding of Millimeter-Wave Phased Array Antennas for Communication Applications Wed, 15 Jul 2015 12:44:11 +0000 http://www.hindawi.com/journals/ijap/2015/264812/ Given the interference avoidance capacity, high gain, and dynamical reconfigurability, phased array antennas (PAAs) have emerged as a key enabling technology for future broadband mobile applications. This is especially important at millimeter-wave (mm-wave) frequencies, where the high power consumption and significant path loss impose serious range constraints. However, at mm-wave frequencies the phase and amplitude control of the feeding currents of the PAA elements is not a trivial issue because electrical beamforming requires bulky devices and exhibits relatively narrow bandwidth. In order to overcome these limitations, different optical beamforming architectures have been presented. In this paper we review the basic principles of phased arrays and identify the main challenges, that is, integration of high-speed photodetectors with antenna elements and the efficient optical control of both amplitude and phase of the feeding current. After presenting the most important solutions found in the literature, we analyze the impact of the different noise sources on the PAA performance, giving some guidelines for the design of optically fed PAAs. Ivan Aldaya, Gabriel Campuzano, Gerardo Castañón, and Alejandro Aragón-Zavala Copyright © 2015 Ivan Aldaya et al. All rights reserved. Synthesis of Thinned Concentric Circular Antenna Arrays Using Modified TLBO Algorithm Mon, 13 Jul 2015 12:41:56 +0000 http://www.hindawi.com/journals/ijap/2015/586345/ Teaching-learning-based optimization (TLBO) algorithm is a new kind of stochastic metaheuristic algorithm which has been proven effective and powerful in many engineering optimization problems. This paper describes the application of a modified version of TLBO algorithm, MTLBO, for synthesis of thinned concentric circular antenna arrays (CCAAs). The MTLBO is adjusted for CCAA design according to the geometry arrangement of antenna elements. CCAAs with uniform interelement spacing fixed at half wavelength have been considered for thinning using MTLBO algorithm. For practical purpose, this paper demonstrated SLL reduction of thinned CCAAs in the whole regular and extended space other than the phi = 0° plane alone. The uniformly and nonuniformly excited CCAAs have been discussed, respectively, during the simulation process. The proposed MTLBO is very easy to be implemented and requires fewer algorithm specified parameters, which is suitable for concentric circular antenna array synthesis. Numerical results clearly show the superiority of MTLBO algorithm in finding optimum solutions compared to particle swarm optimization algorithm and firefly algorithm. Zailei Luo, Xueming He, Xuedong Chen, Xin Luo, and Xiaoqing Li Copyright © 2015 Zailei Luo et al. All rights reserved. A Multiple Beamforming Network for Unequally Spaced Linear Array Based on CORPS Sun, 12 Jul 2015 08:28:04 +0000 http://www.hindawi.com/journals/ijap/2015/757989/ This paper proposes an alternative and innovative way to design a simpler beamforming network (BFN) based on balancing alternated power combiners and dividers, to feed a nonuniformly spaced linear array with Gaussian amplitude and coherent (in-phase) signals. Thus, a two-beam design configuration of the feeding network for a nonuniform array with beam steering capability is proposed and analyzed. The nonuniform aperture and the complex inputs of the feeding network are optimized by means of a differential evolution algorithm. In addition, a comparative analysis between a uniform and nonuniform linear array with the proposed feeding network is performed. Simulation results show the advantages and effectiveness of the proposed feeding network exploiting the nonuniformity of the antenna elements, in terms of side lobe level and directivity. Furthermore, research results show an inherent reduction in hardware complexity of the network. Armando Arce, Marco Cardenas-Juarez, Ulises Pineda-Rico, David H. Covarrubias, and Enrique Stevens-Navarro Copyright © 2015 Armando Arce et al. All rights reserved. Aspects of the Subarrayed Array Processing for the Phased Array Radar Sun, 12 Jul 2015 08:16:07 +0000 http://www.hindawi.com/journals/ijap/2015/797352/ This paper gives an overview on the research status, developments, and achievements of subarrayed array processing for the multifunction phased array radar. We address some issues concerning subarrayed adaptive beamforming, subarrayed fast-time space-time adaptive processing, subarray-based sidelobe reduction of sum and difference beam, subarrayed adapted monopulse, subarrayed superresolution direction finding, subarray configuration optimization in ECCM (electronic counter-countermeasure), and subarrayed array processing for MIMO-PAR. In this review, several viewpoints relevant to subarrayed array processing are pointed out and the achieved results are demonstrated by numerical examples. Hang Hu Copyright © 2015 Hang Hu. All rights reserved.