http://www.hindawi.com The latest articles from Hindawi Publishing Corporation © 2013 , Hindawi Publishing Corporation . All rights reserved. Wed, 19 Jun 2013 09:20:30 +0000 http://www.hindawi.com/journals/ijap/2013/853746/ We derive the probability of false alarm and detection threshold under employment of the generalized detector (GD) in cognitive radio (CR) systems for two scenarios: firstly, the independent antenna array elements; the secondly, the correlated antenna array elements. The energy detector (ED) and GD spectrum sensing performances are compared under the same initial conditions. The simulation results show that implementation of the GD improves the spectrum sensing performance in CR systems both for independent and correlated antenna array elements. Modar Safir Shbat and Vyacheslav Tuzlukov Copyright © 2013 Modar Safir Shbat and Vyacheslav Tuzlukov. All rights reserved. Tue, 18 Jun 2013 14:43:27 +0000 http://www.hindawi.com/journals/ijap/2013/596278/ A detailed study on Goos-Hänchen (GH) lateral displacements of the reflected and transmitted waves propagating at the interface between an isotropic medium and a gyroelectric medium in Voigt configuration is presented. After the reflection coefficient and transmission coefficient are derived, based on the stationary phase approach, GH lateral displacements are obtained analytically. The numerical results for a specific gyroelectric medium are also given. It shows that with the existence of an applied magnetic field, the GH effect occurs not only during total reflection but also during nontotal reflection, which is not true for isotropic media. Moreover, due to the nonreciprocal property of the gyroelectric medium, the sign of the incident angle also influences the displacements. Finite-element method simulations have verified the theoretical results. Jinbao Wang, Hui Huang, Cheng Chen, Hanfeng He, Yuanyuan Dong, and Huan Qi Copyright © 2013 Jinbao Wang et al. All rights reserved. Sun, 16 Jun 2013 13:30:52 +0000 http://www.hindawi.com/journals/ijap/2013/657653/ By exploiting favorable characteristics of a uniform cross-array, a passive localization algorithm of narrowband cyclostationary sources in the spherical coordinates (azimuth, elevation, and range) is proposed. Firstly, we construct a parallel factor (PARAFAC) analysis model by computing the third-order cyclic moment matrices of the properly chosen sensor outputs. Then, we analyze the uniqueness of the constructed model and obtain three-dimensional (3D) near-field parameters via trilinear alternating least squares regression (TALS). The investigated algorithm is well suitable for the localization of the near-field cyclostationary sources. In addition, it avoids the multidimensional search and pairing parameters. Results of computer simulations are carried out to confirm the satisfactory performance of the proposed method. Jian Chen, Guohong Liu, and Xiaoying Sun Copyright © 2013 Jian Chen et al. All rights reserved. Sun, 16 Jun 2013 11:56:59 +0000 http://www.hindawi.com/journals/ijap/2013/761278/ We briefly review different synthesis techniques for the design of passive microwave components with arbitrary frequency response, developed by our group during the last decade. We provide the theoretical foundations based on inverse scattering and coupled-mode theory as well as several applications where the devices designed following those techniques have been successfully tested. The main characteristics of these synthesis methods are as follows. (a) They are direct, because it is not necessary to use lumped-element circuit models; just the target frequency response is the starting point. (b) They are exact, as there is neither spurious bands nor degradation in the frequency response; hence, there is no bandwidth limitation. (c) They are flexible, because they are valid for any causal, stable, and passive transfer function; only inviolable physical principles must be guaranteed. A myriad of examples has been presented by our group in many different technologies for very relevant applications such as harmonic control of amplifiers, directional coupler with enhanced directivity and coupling, transmission-type dispersive delay lines for phase engineering, compact design of high-power spurious free low-pass waveguide filters for satellite payloads, pulse shapers for advanced UWB radar and communications and for novel breast cancer detection systems, transmission-type th-order differentiators for tunable pulse generation, and a robust filter design tool. Israel Arnedo, Iván Arregui, Magdalena Chudzik, Fernando Teberio, Aintzane Lujambio, David Benito, Txema Lopetegi, and Miguel A. G. Laso Copyright © 2013 Israel Arnedo et al. All rights reserved. Sun, 16 Jun 2013 11:49:02 +0000 http://www.hindawi.com/journals/ijap/2013/528347/ Radio-frequency tomography was originally proposed to image underground cavities. Its flexible forward model can be used in free-space by choosing an appropriate dyadic Green's function and can be translated in the microwave domain. Experimental data are used to validate a novel inversion scheme, based on the algebraic reconstruction technique. The proposed method is improved by introducing physical bounds on the solution returned. As a result, the images of the dielectric permittivity profiles obtained are superior in quality to the ones obtained using classical regularization approaches such as the truncated singular value decomposition. The results from three experimental case studies are presented and discussed. V. Picco, T. Negishi, S. Nishikata, D. Spitzer, and D. Erricolo Copyright © 2013 V. Picco et al. All rights reserved. Sat, 15 Jun 2013 15:57:54 +0000 http://www.hindawi.com/journals/ijap/2013/575062/ A high gain omnidirectional antenna with low profile is proposed and is investigated numerically and experimentally. Based on the conventional center-fed circular epsilon-negative (ENG) zeroth-order resonator (ZOR) antenna, dendritic structure negative permeability metamaterial (NPM) is used as the substrate to enhance the gain of the omnidirectional antenna. The experimental results show that the gain of a center-fed circular ENG ZOR antenna with NPM substrate is enhanced about 2.2 dB, and the efficiency is enhanced about 38%, in the whole broad operating bandwidth as compared to that of the antenna without NPM substrate, which can be used to improve the reliability of wireless communications. Hangfei Tang, Quanwen Hou, Yahong Liu, and Xiaopeng Zhao Copyright © 2013 Hangfei Tang et al. All rights reserved. Sat, 15 Jun 2013 15:57:21 +0000 http://www.hindawi.com/journals/ijap/2013/694819/ A compact multiband printed monopole antenna is presented. The proposed antenna, composed of a modified broadband T-shaped monopole antenna integrating some band-notch structures in the metallic patch, is excited by means of a microstrip line. To calculate the bandwidth starting frequency (BSF) of the T-shaped broadband antenna, an improved formula is proposed and discussed. The multiband operation is achieved by etching three inverted U-shaped slots on the radiant patch. By changing the length of the notch slots, operation bands of the multiband antenna can be adjusted conveniently. The antenna is simulated in Ansoft HFSS and then fabricated and measured. The measurement results show that the proposed antenna operates at 2.25–2.7 GHz, 3.25–3.6 Hz, 4.95–6.2 GHz, and 7-8 GHz, covering the operation bands of Bluetooth, WiMAX, WLAN, and downlink of X-band satellite communication system and thus making it a proper candidate for the multiband devices. Junjun Wang and Xudong He Copyright © 2013 Junjun Wang and Xudong He. All rights reserved. Thu, 13 Jun 2013 17:59:40 +0000 http://www.hindawi.com/journals/ijap/2013/934509/ The concept of virtual aperture and the point spread function for designing and characterizing ultra-wideband near-field multiple-input multiple-output active imaging array are investigated. Combining the approach of virtual aperture desynthesis with the monostatic-to-bistatic equivalence theorem, a kind of linear UWB MIMO array, the split transmit virtual aperture (STVA) array, was designed for through-the-wall imaging. Given the virtual aperture, the STVA array is the shortest in physical aperture length. The imaging performance of the designed STVA array in the near field is fully analyzed through both numerical and measured data. The designed STVA array has been successfully applied to imaging moving targets inside buildings. Biying Lu, Yang Zhao, Xin Sun, and Zhimin Zhou Copyright © 2013 Biying Lu et al. All rights reserved. Thu, 13 Jun 2013 14:27:54 +0000 http://www.hindawi.com/journals/ijap/2013/596347/ Distributed MIMO (D-MIMO) system is one of the candidates for future wireless access networks. In this study, the spatial correlation and capacity in indoor D-MIMO system are presented. All results are from the actual channel measurements in typical indoor scenarios, including office and corridor. Based on measured data, spatial correlation coefficients between distributed transmitting antennas are analyzed. Although the literature about D-MIMO system assumes the small scale fading between distributed antennas is independent, we find that spatial correlation may still exist in specific propagation scenario. This correlation can also degrade the performance of D-MIMO system. To mitigate the impact of spatial correlation, one efficient method is to use transmitting antenna selection technique. Yan Zhang, Limin Xiao, Shidong Zhou, and Jing Wang Copyright © 2013 Yan Zhang et al. All rights reserved. Wed, 12 Jun 2013 15:16:53 +0000 http://www.hindawi.com/journals/ijap/2013/935609/ Next generation wireless communication networks intend to take advantage of the integration of terrestrial and aerospace infrastructures. Besides, multiple-input multiple-output (MIMO) architecture is the key technology, which has brought the wireless gigabit vision closer to reality. In this direction, high-altitude platforms (HAPs) could act as relay stations in the stratosphere transferring information from an uplink to a downlink MIMO channel. This paper investigates the performance of a novel transmission scheme for the delivery of mobile-to-mobile (M-to-M) services via a stratospheric relay. It is assumed that the source, relay, and destination nodes are equipped with multiple antennas and that amplify-and-forward (AF) relaying is adopted. The performance is analyzed through rigorous simulations in terms of the bit-error rate (BER) by using a recently proposed 3D geometry-based reference model in spatially correlated flat-fading MIMO channels, employing a hierarchical broadcast technique and minimum mean square error (MMSE) receivers. Nikolaos Nomikos, Emmanouel T. Michailidis, Demosthenes Vouyioukas, and Athanasios G. Kanatas Copyright © 2013 Nikolaos Nomikos et al. All rights reserved. Wed, 12 Jun 2013 12:09:53 +0000 http://www.hindawi.com/journals/ijap/2013/472645/ A printed reconfigurable ultra-wideband (UWB) monopole antenna with triple narrow band-notched characteristics is proposed for cognitive radio applications in this paper. The triple narrow band-notched frequencies are obtained using a defected microstrip structure (DMS) band stop filter (BSF) embedded in the microstrip feed line and an inverted π-shaped slot etched in the rectangular radiation patch, respectively. Reconfigurable characteristics of the proposed cognitive radio antenna (CRA) are achieved by means of four ideal switches integrated on the DMS-BSF and the inverted π-shaped slot. The proposed UWB CRA can work at eight modes by controlling switches ON and OFF. Moreover, impedance bandwidth, design procedures, and radiation patterns are presented for analysis and explanation of this antenna. The designed antenna operates over the frequency band between 3.1 GHz and 14 GHz (bandwidth of 127.5%), with three notched bands from 4.2 GHz to 6.2 GHz (38.5%), 6.6 GHz to 7.0 GHz (6%), and 12.2 GHz to 14 GHz (13.7%). The antenna is successfully simulated, fabricated, and measured. The results show that it has wide impedance bandwidth, multimodes characteristics, stable gain, and omnidirectional radiation patterns. Yingsong Li, Wenxing Li, and Qiubo Ye Copyright © 2013 Yingsong Li et al. All rights reserved. Mon, 10 Jun 2013 09:49:10 +0000 http://www.hindawi.com/journals/ijap/2013/917676/ An effective design procedure, based on the Elliot synthesis method, is proposed to investigate the properties of waveguide slot arrays with multilayer dielectric cover. Then, the features of the designed arrays are analyzed by means of a FEM commercial software, namely, Ansys HFSS 13. We show how a proper choice of the dielectric cover configuration allows increasing the array gain and aperture efficiency, while taking advantage of the properties of the radome structure, in terms of insulation, protection, and pressurization of the radiating waveguides. Therefore, a significant outcome of the optimal choice of the multilayer dielectric cover is the reduction of the number of slots with respect to an array radiating into free space with the same gain and efficiency, with a consequent reduction of the production cost. Giorgio Montisci, Zusheng Jin, Mingchao Li, Hu Yang, Giovanni Andrea Casula, Giuseppe Mazzarella, and Alessandro Fanti Copyright © 2013 Giorgio Montisci et al. All rights reserved. Tue, 04 Jun 2013 16:39:35 +0000 http://www.hindawi.com/journals/ijap/2013/415607/ A new flexible microwave tag system using a frequency-scanning type RFID is proposed with multiple resonators based on defected ground structures (DGSs). The proposed system achieves fully passive tag systems using multiple resonators with a spiral-shaped DGS over a wide frequency range. The resonator implemented on the rear side of a transmission line has the advantages of excellent band notch characteristics as well as bit-error avoidance from the frequency selective reflection. In addition, the tag system is designed on a thin flexible substrate in order to be applicable for amorphous surfaces. The proposed microwave tags have been implemented with wideband antennas at 3–7 GHz on thick and thin flexible substrates. The flexibility of the thin substrate has been evaluated in terms of cognitive capability for various radiuses of curvatures. From the experimental results in an anechoic chamber, the excellent recognition of various multibits identification codes in a wireless transmission environment has been verified. Seok-Jae Lee, Jongsik Lim, Dal Ahn, and Sang-Min Han Copyright © 2013 Seok-Jae Lee et al. All rights reserved. Tue, 04 Jun 2013 16:01:24 +0000 http://www.hindawi.com/journals/ijap/2013/640514/ This paper is focused on magnetic-LC (MLC) resonators, namely, slotted resonators that can be considered the complementary counterparts of the so-called electric-LC (ELC) resonators. Both resonators exhibit two symmetry planes (i.e., they are bisymmetric), one of them being an electric wall and the other a magnetic wall at the fundamental resonance. Therefore, compared to other electrically small resonators such as folded stepped impedance resonators (SIRs), split ring resonators (SRRs), and their complementary counterparts, MLC and ELC resonators exhibit a very rich phenomenology. In this paper, single-ended microstrip lines and differential microstrip lines loaded with MLC resonators are studied, and potential applications are highlighted. J. Naqui, M. Durán-Sindreu, and F. Martín Copyright © 2013 J. Naqui et al. All rights reserved. Thu, 30 May 2013 18:32:25 +0000 http://www.hindawi.com/journals/ijap/2013/827904/ The statistical model plays an important role in BAN radio propagation characterization. However, a traditional least-square statistical model is not necessarily the best choice when only limited samples can be collected. This paper proposes the method for improving the density model in BAN radio propagation characterization; the final PDF result validates the correctness of the method. Xiaodong Yang, Zhiya Zhang, Shuyuan Yang, Qammer Hussain Abbasi, and Wei Zhao Copyright © 2013 Xiaodong Yang et al. All rights reserved. Thu, 30 May 2013 14:14:34 +0000 http://www.hindawi.com/journals/ijap/2013/670154/ Usually, multiple-input-multiple-output (MIMO) testbeds are combined with channel emulators for testing devices and algorithms under controlled channel conditions. In this work, we propose a simple methodology that allows over-the-air (OTA) MIMO testing using a MIMO testbed solely, avoiding the use of channel emulators. The MIMO channel is emulated by linearly combining the signals at the testbed transmitter. The method is fully flexible, so it is able to emulate any equivalent baseband narrowband MIMO channel by adequately selecting the weights of the linear combination. We derive closed-form expressions for the computation of such weights. To prove its feasibility, the method has been implemented and tested over a commercial MIMO testbed. Jesús Gutiérrez, Jesús Ibáñez, and Jesús Pérez Copyright © 2013 Jesús Gutiérrez et al. All rights reserved. Thu, 30 May 2013 14:10:35 +0000 http://www.hindawi.com/journals/ijap/2013/285304/ Propagation prediction models based on ray tracing in coverage estimation for digital broadcasting systems are compared. Geometrical Theory of Diffraction (GTD), Slope Uniform Theory of Diffraction (S-UTD), and Slope UTD with Convex Hull (S-UTD-CH) models are compared for computation time and propagation path loss. S-UTD-CH model is optimum model with respect to computation time and relative path loss. Mehmet Baris Tabakcioglu and Ahmet Cansiz Copyright © 2013 Mehmet Baris Tabakcioglu and Ahmet Cansiz. All rights reserved. Wed, 29 May 2013 18:57:08 +0000 http://www.hindawi.com/journals/ijap/2013/593247/ An easy and efficient approach, based on artificial intelligence technique, is proposed to jointly estimate the amplitude, elevation, and azimuth angles of far field sources impinging on 2-L-shape array. In these proposed artificial intelligence techniques, the metaheuristics based on genetic algorithm and simulated annealing are used as global optimizers assisted with rapid local version of pattern search for optimization of the adaptive parameters. The performance metric is employed on a fitness evaluation function depending on mean square error which is optimum and requires single snapshot to converge. The proposed approaches are easy to understand, and simple to implement; the genetic algorithm specifically hybridized with pattern search generates fairly good results. The comparison of the given schemes is carried out with 1-L-shape array, as well as, with parallel-shape array and is found to be in good agreement in terms of accuracy, convergence rate, computational complexity, and mean square error. The effectiveness and efficiency of the given schemes are examined through Monte Carlo simulations and their inclusive statistical analysis. Fawad Zaman, Ijaz Mansoor Qureshi, Junaid Ali Khan, and Zafar Ullah Khan Copyright © 2013 Fawad Zaman et al. All rights reserved. Mon, 27 May 2013 09:46:52 +0000 http://www.hindawi.com/journals/ijap/2013/270845/ The analysis, design, and realization of a modified Vivaldi antenna optimized for time domain fidelity factor in the half-space located in the direction of the antenna main beam are presented. The proposed antenna shows improved angular-dependent fidelity property, with respect to the signal transmitted in the main beam direction. A substantial increase in the fidelity factor is achieved by utilizing spatial filter effect introduced by adding two dielectric slabs parallel to the antenna substrate. By choosing optimal dimensions and location of the slabs, the signal waveforms in the mentioned half-space are equalized so as to improve the quality of the radiated signal waveform in the main beam direction. As a result, the fidelity property in the half-space is improved greatly. The simulated and measured fidelity factor in the angular operational region is studied and compared with experimental measurements. The ranges with the fidelity factor better than the value of 0.9 are improved by 95% in H-plane and by 14% in E-plane, respectively. Zhi Zeng, Ke Xu, Zhaohui Song, and Qinyu Zhang Copyright © 2013 Zhi Zeng et al. All rights reserved. Sun, 26 May 2013 14:26:06 +0000 http://www.hindawi.com/journals/ijap/2013/715046/ A miniaturized planar electromagnetic bandgap (EBG) structure with embedded meander line as bridge is proposed in this paper. The dimensions of the unit cell of the proposed EBG structure are 15 mm × 15 mm × 0.36 mm. Simulation and measurement of the noise transmission coefficient () have been performed for the structure, and good agreement can be seen. According to the measured results, the −30 dB noise suppression bandwidth ranges from 0.97 to 21.54 GHz, which cover almost the whole noise band in ultrawideband applications. Moreover, its effects on signal integrity and electromagnetic emission are also analyzed. Zhaowen Yan and Yansheng Wang Copyright © 2013 Zhaowen Yan and Yansheng Wang. All rights reserved. Wed, 22 May 2013 13:19:47 +0000 http://www.hindawi.com/journals/ijap/2013/516946/ The current focus in defense arena is towards the stealth technology with an emphasis to control the radar cross-section (RCS). The scattering from the antennas mounted over the platform is of prime importance especially for a low-observable aerospace vehicle. This paper presents the analysis of the scattering cross section of a uniformly spaced linear dipole array. Two types of feed networks, that is, series and parallel feed networks, are considered. The total RCS of phased array with either kind of feed network is obtained by following the signal as it enters through the aperture and travels through the feed network. The RCS estimation of array is done including the mutual coupling effect between the dipole elements in three configurations, that is, side-by-side, collinear, and parallel-in-echelon. The results presented can be useful while designing a phased array with optimum performance towards low observability. H. L. Sneha, Hema Singh, and R. M. Jha Copyright © 2013 H. L. Sneha et al. All rights reserved. Wed, 22 May 2013 10:23:50 +0000 http://www.hindawi.com/journals/ijap/2013/785675/ In order to better assess the behaviours of the propagation channel in a confined environment such as a railway tunnel for subway application, we present an optimization method for a deterministic channel simulator based on 3D ray tracing associated to the geometrical optics laws and the uniform theory of diffraction. This tool requires a detailed description of the environment. Thus, the complexity of this model is directly bound to the complexity of the environment and specifically to the number of facets that compose it. In this paper, we propose an algorithm to identify facets that have no significant impact on the wave propagation. This allows us to simplify the description of the geometry of the modelled environment by removing them and by this way, to reduce the complexity of our model and therefore its computation time. A comparative study between full and simplified environment is led and shows the impact of this proposed method on the characteristic parameters of the propagation channel. Thus computation time obtained from the simplified environment is 6 times lower than the one of the full model without significant degradation of simulation accuracy. Siham Hairoud, Pierre Combeau, Yannis Pousset, Yann Cocheril, Marion Berbineau, and Rodolphe Vauzelle Copyright © 2013 Siham Hairoud et al. All rights reserved. Mon, 20 May 2013 19:00:57 +0000 http://www.hindawi.com/journals/ijap/2013/649049/ Ultra wideband (UWB) systems are the most appropriate for high data rate wireless transmission with low power consumption. However, the antenna design for UWB has been a challenging task. Moreover, it is always desirable to have more freedom by designing different shape antennas with identical characteristics so that they can be used in either transmitter or receiver depending on other physical constraints such as area. To tackle these issues, in this paper, we have investigated a joint optimization of three different shape-printed monopole antennas, namely, printed square monopole antenna, printed circular monopole antenna and printed hexagonal monopole antenna, for UWB applications. More specifically, we have obtained the optimized geometrical parameters of these antennas by minimizing the mean-square-error for desired lower band edge frequency, quality factor, and bandwidth. The objective of joint optimization is to have identical frequency characteristics for the aforementioned three types of PMA which will give a freedom to interchangeably use them at either side, transmitting or receiving. Moreover, we employ particle swarm optimization (PSO) algorithm for our problem as it is well known in the literature that PSO performs well in electromagnetic and antenna applications. Simulation results are presented to show the performance of the proposed design. Muhammad Zubair and Muhammad Moinuddin Copyright © 2013 Muhammad Zubair and Muhammad Moinuddin. All rights reserved. Sun, 19 May 2013 13:29:30 +0000 http://www.hindawi.com/journals/ijap/2013/279070/ A new modeling method of cabin path loss prediction based on support vector machine (SVM) is proposed in this paper. The method is trained with the path loss values of measured points inside the cabin and can be used to predict the path loss values of the unmeasured points. The experimental results demonstrate that our modeling method is more accurate than the curve fitting method. This SVM-based path loss prediction method makes the prediction much easier and more accurate, which covers performance traditional methods in the channel propagation modeling. Xiaonan Zhao, Chunping Hou, and Qing Wang Copyright © 2013 Xiaonan Zhao et al. All rights reserved. Thu, 16 May 2013 14:42:02 +0000 http://www.hindawi.com/journals/ijap/2013/405943/ A novel reconfigurable compact patch array antenna for directional and broadside application is proposed. The presented antenna has successfully been able to function for directional beam at 320° or 35° and divisive broadside beam at 43° and 330°. This is realized in the unique form of aperture coupled spiral feeding technique and positioning of the radiating elements at 0°, 90,° and 180°. The switchable feature is effectively performed by the configuration of three PIN diodes. All PIN diodes are positioned at the specific location of the aperture coupled structure. It is discovered in simulation that the switches can be represented with a copper strip line or touchstone (TS) block . The proposed antenna design operates at 2.37 GHz to 2.41 GHz and has a maximum gain of 6.4 dB and efficiency of 85.97%. Such antenna produces a broadside HPBW with a wider bandwidth covering from −90° to 90° compared to the normal microstrip antenna which could only provide HPBW of −50° to 50°. Moreover, the proposed antenna has small physical dimension of 100 mm by 100 mm. The simulation and measurement results have successfully exhibited the idea of the presented antenna performance. Therefore, the antenna is sufficiently competent in the smart WiMAX antenna application. M. Jusoh, M. F. Jamlos, M. R. Kamarudin, and T. Sabapathy Copyright © 2013 M. Jusoh et al. All rights reserved. Thu, 16 May 2013 08:36:37 +0000 http://www.hindawi.com/journals/ijap/2013/649602/ A time domain channel prediction method exploiting features of sparse channel is proposed for orthogonal frequency division multiplexing (OFDM) systems. The proposed predictor operates in the time domain on each channel tap and separates the negligible taps from significant channel taps before performing prediction. We also compare the proposed prediction method with the classical frequency domain method realized at each OFDM subcarrier and demonstrate that our method increases the prediction accuracy and reduces the computational complexity. Simulations on the physical channel model verify the performance of the proposed method. Changwei Lv, Shujuan Hou, and Wenbo Mei Copyright © 2013 Changwei Lv et al. All rights reserved. Tue, 14 May 2013 14:29:44 +0000 http://www.hindawi.com/journals/ijap/2013/194145/ In many RFID practical applications, it is required that reader can effectively read tags which are placed in radiation covering area randomly. In this paper, a passive UHF dual-dipole tag antenna with quasi-isotropic patterns is designed, which can reduce the sensibility of tag read-orientation in a long distance. Two dipoles with four-axis reflection symmetric structure are used, and the two arms of the dipole are bent to fill the space of the antenna. In this way, a quasi-isotropic tag is easier to be obtained. The test results show that the gain deviation of the proposed antenna was less than 3.25 dB, and the maximum reading range in different directions was from 6.9 m to 10.0 m, with better quasi-isotropic performance and reading range than other commercial tags. Chunfang Qin, Lingfei Mo, Hongliang Zhou, and Hongjian Zhang Copyright © 2013 Chunfang Qin et al. All rights reserved. Mon, 13 May 2013 19:25:34 +0000 http://www.hindawi.com/journals/ijap/2013/738659/ This paper presents impact of layout sizes of Al0.27Ga0.73N/AlN/Al0.04Ga0.96N/GaN HEMT heterostructure high-mobility transistors (HEMTs) on SiC substrate on its characteristics that include the threshold voltage, the maximum transconductance, characteristic frequency, and the maximum oscillation frequency. The changing parameters include the gate finger number, the gate width per finger. The measurement results based on common-source devices demonstrate that the above parameters have different effects on the threshold voltage, maximum transconductance, and frequency characteristics. Liwei Jin, Zhiqun Cheng, and Qingna Wang Copyright © 2013 Liwei Jin et al. All rights reserved. Mon, 13 May 2013 18:15:56 +0000 http://www.hindawi.com/journals/ijap/2013/179296/ Passive radar (or Passive Coherent Localisation) is an advancing technology for covert operation. The signal transmitted from sources of opportunity such as radio or TV stations is used as illumination for a certain area of interest. Part of the transmitted signal is reflected by radar targets, for example, moving objects such as vehicles or aircraft. Typical radar parameters are derived from the comparison between the direct line-of-sight from the transmitter and the signal scattered from the target object. Such systems are an attractive addition to existing active radar stations because they have the potential to discover low-flying and low-observable targets and no active radar transmitter is required. Printed dipole antennas are very attractive antenna elements for such systems because of their easy fabrication, low-cost, polarisation purity, and low-profile properties. The present paper describes the design of an antenna array using printed dipole elements with flared arms for a passive radar system operating in the GSM900 frequency range. Isolated antenna elements and a small uniform linear antenna array were designed and optimised using computational electromagnetic methods. Several prototypes have been fabricated on conventional microwave PCB substrate material. Preliminary measurement results for antenna matching and far-field radiation patterns are shown. Peter Knott Copyright © 2013 Peter Knott. All rights reserved. Sun, 12 May 2013 07:58:54 +0000 http://www.hindawi.com/journals/ijap/2013/850489/ A compact handset multiple-input multiple-output (MIMO) antenna for long-term evolution (LTE) 700 band (746~787 MHz) applications is proposed. The proposed antenna consists of two symmetrical PIFAs. Without the usage of any additional coupling elements between closely mounted antennas, a high isolation (>15 dB) and a low enveloped correlation coefficient () are achieved by the optimum location and arrangement of MIMO antenna elements. Byeonggwi Mun, Frances J. Harackiewicz, Byeongkwan Kim, Hyunho Wi, Jonghyun Lee, Myun-Joo Park, Changwon Jung, and Byungje Lee Copyright © 2013 Byeonggwi Mun et al. All rights reserved.