International Journal of Antennas and Propagation http://www.hindawi.com The latest articles from Hindawi Publishing Corporation © 2015 , Hindawi Publishing Corporation . All rights reserved. Analog Beamforming and Digital Beamforming on Receive for Range Ambiguity Suppression in Spaceborne SAR Thu, 26 Feb 2015 08:21:47 +0000 http://www.hindawi.com/journals/ijap/2015/182080/ For future spaceborne synthetic aperture radar (SAR) missions, digital beamforming (DBF) on receive in elevation to form a sharp high receive beam will be adopted to improve the signal to noise ratio (SNR) level and suppress range ambiguities. However, in some special cases, range ambiguities may be received by grating lobes with the high receive beam gain, and range ambiguities would not be well suppressed and even may be increased. In this paper, a new receiving approach based on analog beamforming (ABF) and DBF is proposed. According to the spaceborne SAR imaging geometry and the selected pulse repetition frequency (PRF), the antenna patterns of all subapertures of the whole receive antenna in elevation are adjusted by ABF at first. Afterwards, signals from all subapertures in elevation are combined by a real time DBF processor onboard. Since grating lobes could be suppressed by the antenna pattern of the subapertures via ABF, range ambiguities would be well suppressed even if ambiguities are received by grating lobes. Simulation results validate the proposed approach. Pingping Huang and Wei Xu Copyright © 2015 Pingping Huang and Wei Xu. All rights reserved. Circularly Polarized Triband Printed Quasi-Yagi Antenna for Millimeter-Wave Applications Wed, 25 Feb 2015 14:04:09 +0000 http://www.hindawi.com/journals/ijap/2015/329453/ This paper describes the design and development of a triband with circularly polarized quasi-Yagi antenna for ka-band and short range wireless communications applications. The proposed antenna consists of an integrated balun-fed printed dipole, parasitic folded dipole and a short strip, and a modified ground plane. The antenna structure, together with the parasitic elements, is designed to achieve circular polarization and triband operating at resonant frequencies of 13.5 GHz, 30 GHz, and 60 GHz. Antenna design was first simulated using HFSS ver.14, and the obtained results were compared with experimental measurements on a prototype developed on a single printed circuit board. Achieved characteristics include −10 dB impedance bandwidth at the desired bands, circular polarization axial ratio  dB, front to back ratio of 6 dB, gain value of about 4 dBi, and average radiation efficiency of 60%. The paper includes comparison between simulation and experimental results. Dalia M. Elsheakh and Magdy F. Iskander Copyright © 2015 Dalia M. Elsheakh and Magdy F. Iskander. All rights reserved. A Novel CP Horn Antenna with Switchable Polarization by Single Port Feeding Tue, 24 Feb 2015 16:31:44 +0000 http://www.hindawi.com/journals/ijap/2015/562521/ A novel CP horn antenna with switchable polarization by single port feeding is presented. The antenna is composed of a coaxial-waveguide converter and a balance-cavity, a horn, a square-to-circular waveguide transition, and a stepped-septum polarizer, which simplify the feeding and can work on the left-hand or right-hand circular polarizations by manual exchanging the mounting position of the coaxial-waveguide converter and the balance-cavity. The antenna achieves an impedance bandwidth (3.88~5.12 GHz) of 27.5% and a 3 dB-AR (Axial Ratio) bandwidth of 18.6%, with the 3 dB-AR beamwidth of about 149°, and the antenna gain is over 13.3 dB in the available band. Yangzhen Huang, Junping Geng, Xianling Liang, Ronghong Jin, and Xudong Bai Copyright © 2015 Yangzhen Huang et al. All rights reserved. Effects of Metamaterial Slabs Applied to Wireless Power Transfer at 13.56 MHz Tue, 24 Feb 2015 13:45:23 +0000 http://www.hindawi.com/journals/ijap/2015/840135/ This paper analyzes the effects of a metamaterial slab (or a practical “perfect lens”) with negative permeability applied to a two loop magnetically coupled wireless power transfer (WPT) system at 13.56 MHz, based on theory, full-wave electromagnetic- (EM-) simulations, and measurements. When using lossless slabs with ideal negative permeability in EM-simulations, the WPT efficiencies have been found to be enhanced close to 100% due to the magnetic field focusing. For the case of using a realistic slab made of ring resonators (RR) with (s: slab width, d: distance between the transmitting and receiving loops), the WPT efficiency has been found to significantly decrease to about 20%, even lower than that of a free space case (32%) due to the heavy power absorption in the slab. However, some efficiency enhancement can be achieved when is optimized between 0.1 and 0.3. Overall, the significant enhancement of efficiencies when using a lossless slab becomes moderate or only marginal when employing a realistic slab. Gunyoung Kim, Taek-Kyu Oh, and Bomson Lee Copyright © 2015 Gunyoung Kim et al. All rights reserved. A Bandpass Filter Based on Half Mode Substrate Integrated Waveguide-to-Defected Ground Structure Cells Mon, 23 Feb 2015 07:22:49 +0000 http://www.hindawi.com/journals/ijap/2015/969035/ A half mode substrate integrated waveguide-to-defected ground structure (HMSIW-DGS) cell and its embedded form are proposed to miniaturize a bandpass filter. Both cells can purchase wideband frequency response and low insertion loss, as well as simple and easy fabrication. By cascading two of them according to design requirement, an X-band bandpass filter is designed and measured to meet compact size, low insertion loss, good return loss, second harmonic suppression, and linear phase. Yong Mao Huang, Zhenhai Shao, Zhaosheng He, Chang Jiang You, and Di Jiang Copyright © 2015 Yong Mao Huang et al. All rights reserved. Fabrication and Characterization of a W-Band Cylindrical Dielectric Resonator Antenna-Coupled Niobium Microbolometer Mon, 23 Feb 2015 07:09:23 +0000 http://www.hindawi.com/journals/ijap/2015/736291/ We report on the fabrication and characterization of a novel antenna-coupled detector configuration for detection at 94 GHz, a coplanar waveguide- (CPW-) fed, slot-excited twin dielectric resonator antenna- (DRA-) coupled niobium (Nb) microbolometer. The antenna is based on two low permittivity cylindrical dielectric resonators (CDRs) excited by rectangular slots placed below the CDRs. The antenna resonant currents are fed to an Nb microbolometer by the means of a CPW feed. The ceramic DRA structure is manufactured using a novel fabrication process that enables patterning an SU-8–Alumina (Al2O3) nanopowder composite using conventional photolithography. The detector measured a voltage responsivity of 0.181 V/W at a modulation frequency of 150 Hz. The detector measured a time constant of 1.94 μs. The antenna radiation pattern of the developed detector configuration was measured and shows a good agreement with the simulation. M. Abdel-Rahman, M. Kamran Saleem, Najeeb Al-Khalli, Nacer Debbar, Majeed A. S. Alkanhal, and Abdelrazik Sebak Copyright © 2015 M. Abdel-Rahman et al. All rights reserved. A Compact Dual-Band RFID Tag Antenna Mountable on Metallic Objects Mon, 23 Feb 2015 07:03:41 +0000 http://www.hindawi.com/journals/ijap/2015/131908/ A compact (50 × 50 × 4 mm3) dual-band radio frequency identification (RFID) tag antenna mountable on metallic objects is proposed for the ultra-high frequency (UHF) band (917∼923.5 MHz) and the microwave (MW) band (2.4∼2.45 GHz). With the proximity-coupled feed loop, the proposed antenna consists of two symmetric planar inverted-F antenna (PIFA) elements for the UHF band passive tag and a meander microstrip patch antenna for the MW band active tag. The performance of the proposed antenna is verified by mounting it on the different sizes of the metallic object. Furthermore, the passive tag antenna in the UHF band furthermore may be used for energy harvesting techniques to improve the lifetime of the active tag in the MW band. The measured maximum read range is 5.50 m in the UHF band and 14.15 m in the MW band when the proposed tag antenna is mounted on the metallic objects. The total efficiency for all operating frequency bands is higher than 50%. High isolation (>12 dB) between tag antennas in the UHF band and the MW band is achieved. Byeonggwi Mun, Yonghyun Yoon, Hyunwoo Lee, Hark-Yong Lee, and Byungje Lee Copyright © 2015 Byeonggwi Mun et al. All rights reserved. Study the Effect of Using Low-Cost Dielectric Lenses with Printed Log-Periodic Dipole Antennas for Millimeter-Wave Applications Sun, 22 Feb 2015 13:59:44 +0000 http://www.hindawi.com/journals/ijap/2015/209430/ Design of V-band high-gain printed log periodic dipole array (PLPDA) antenna loaded with a low-cost spherical dielectric lens is introduced. The proposed antenna consists of microstrip-line-fed log-periodic dipole antenna designed to operate in the V-band with a peak gain of 12.64 dBi at 60 GHz. To enhance the antenna gain, a dielectric lens is installed. The antenna prototype is fabricated and then tested experimentally using Agilent E8364B PNA Network Analyzer. Experimental results agree well with the simulated ones. The simulated results show that the proposed antenna can work from 42 GHz up to 82 GHz with a fractional impedance bandwidth of 64.5% covering the whole V-band (50–75 GHz). At 60 GHz, the proposed antenna has peak gain of 26.79 dBi with a gain variation of 3.5 dBi across the whole V-band with stable radiation patterns over the operating band. The proposed PLPDA antenna achieves good side-lobe suppression, excellent front-to-back ratio in both E- and H-planes, and low cross-polarization levels over the entire frequency range. These unique features will make this antenna suitable for different interesting applications such as millimeter-wave radar and imaging applications. Osama M. Haraz, Abdel Razik Sebak, and Saleh Alshebeili Copyright © 2015 Osama M. Haraz et al. All rights reserved. Wearable Fabric Reconfigurable Beam-Steering Antenna for On/Off-Body Communication System Sun, 22 Feb 2015 13:52:08 +0000 http://www.hindawi.com/journals/ijap/2015/539843/ This paper presents a comparison of on-body performances between omnidirectional (loop antenna) and reconfigurable beam-steering antennas. Both omnidirectional and reconfigurable antennas were manufactured on the same fabric substrate and operated at the frequency band of the WLAN 802.11a (5.725–5.85 GHz). The reconfigurable antenna was designed to steer the beam directions. In order to implement the beam-steering capability, the antenna used two PIN diodes. The maximum beam directions of three states (states 0, 1, and 2) were steerable in the -plane (°, 28°, and 326°, resp.). The measured peak gains were 5.9–6.6 dBi and the overall half power beam width (HPBW) was 102°. The measured results of total radiated power (TRP) and total isotropic sensitivity (TIS) indicated that the communication efficiency of the reconfigurable beam steering antenna was better than that of the loop antenna. When the input power was 0.04 W (16 dBm), the simulated specific absorption rate (SAR) values of the reconfigurable beam steering antenna on the body were less than 0.979 W/kg (1 g tissue) in all states, satisfying the SAR criteria of the US. Seonghun Kang and Chang Won Jung Copyright © 2015 Seonghun Kang and Chang Won Jung. All rights reserved. A New Jammer Suppression Method in MIMO Radar Using Matrix Pencil Method and Generalized Likelihood Ratio Test Sun, 22 Feb 2015 12:18:12 +0000 http://www.hindawi.com/journals/ijap/2015/802471/ We propose a new algorithm to suppress the jammer signals and estimate the direction of arrival (DOA) of the signal of interest (SOI) for collocated MIMO radar by using the matrix pencil method (MPM) and the generalized likelihood ratio test (GLRT). The conventional GLRT divides the visible region into small angle samples, suppresses the jammer signals at each angle sample, and then estimates the DOA of the SOI. In the proposed algorithm, we extract the eigenvalues of received signals regardless of the SOI and jammer by using the MPM, which contain the information of the DOA of SOIs or jammers. Then, in order to suppress the jammers, we apply the GLRT to the extracted DOAs instead of to the entire visible region. By applying the MPM again to the received signals in which the jammer signals are suppressed, we can estimate the DOAs of the SOI. Since the proposed algorithm does not depend on the number of angle samples, it shows fast and accurate results regardless of the angle resolution. In order to verify the proposed algorithm, we compared the results with the results of the conventional GLRT and show the computing time. Kang-in Lee, Wonjune Kang, Young-Seek Chung, Hoon-Gee Yang, and Jong Mann Kim Copyright © 2015 Kang-in Lee et al. All rights reserved. A Novel Inversion Method of Manufacturing Flaws in the Packaging of Conformal Load-Bearing Antenna Structure Sun, 22 Feb 2015 11:33:03 +0000 http://www.hindawi.com/journals/ijap/2015/795323/ Composite material is widely used in the conformal load-bearing antenna structure (CLAS), and the manufacturing flaws in the packaging process of the CLAS will lead to the degradation of its wave-transparent property. For this problem, a novel inverse method of the flaw’s dimension by antenna-radome system’s far field data has been proposed. Two steps are included in the inversion: the first one is the inversion from the far filed data to the transmission coefficient of the CLAS’s radome; the second one is the inversion from the transmission coefficient to the flaw’s dimension. The inversion also has a good potential for the separable multilayer composite material radome. A 12.5 GHz CLAS with microstrip antenna array is used in the simulation, which indicates the effectiveness of the novel inversion method. Finally, the error analysis of the inversion method is presented by numerical simulation; the results is that the inversed error could be less than 10%, if the measurement error of far field data is less than 0.45 dB in amplitude and ±5° in phase. P. Li, W. Y. Xu, L. W. Song, and Y. Y. Qiu Copyright © 2015 P. Li et al. All rights reserved. Generation of OAM Radio Waves with Three Polarizations Using Circular Horn Antenna Array Sun, 22 Feb 2015 11:09:16 +0000 http://www.hindawi.com/journals/ijap/2015/132549/ This paper provides an effective solution of generating OAM-carrying radio beams with all three polarizations: the linear, the left-hand circular, and the right-hand circular polarizations. Through reasonable configuration of phased antenna array using elements with three polarizations, the OAM radio waves with three polarizations for different states can be generated. The vectors of electric fields with different OAM states for all three polarizations are presented and analyzed in detail. The superposition of two coaxial OAM states is also carried out, and the general conclusion is provided. Xudong Bai, Ronghong Jin, Liang Liu, Junping Geng, and Xianling Liang Copyright © 2015 Xudong Bai et al. All rights reserved. A Suspended Stripline Frequency Tripler Using a Left-Handed Nonlinear Transmission Line Sun, 22 Feb 2015 11:05:16 +0000 http://www.hindawi.com/journals/ijap/2015/247537/ A suspended stripline frequency tripler using a left-handed nonlinear transmission line (LH NLTL) is presented. The proposed tripler using the LH NLTL is composed of a series of varactor diodes, shunt inductances, and a high-pass filter implemented with suspended stripline (SSL). An ultrawideband microstrip-to-suspended stripline transition is also utilized. The fabricated LH NLTL provides the minimum insertion loss of 1.7 dB and the maximum insertion loss of 4.7 dB for a wide frequency band from 2.6 to 18 GHz. As a tripler, the measured minimum third harmonic conversion loss is 15.3 dB at an input frequency of 2.4 GHz and typically 17 dB from 2 to 3.1 GHz. In Bok Kim, Hongjoon Kim, Hyun Chul Choi, and Kang Wook Kim Copyright © 2015 In Bok Kim et al. All rights reserved. Seasonal Variations of Polarization Diversity Gain in a Vegetated Area considering High Elevation Angles and a Nomadic User Sun, 22 Feb 2015 09:06:13 +0000 http://www.hindawi.com/journals/ijap/2015/194626/ Seasonal variations of the polarization diversity gain are addressed for a nomadic user in a vegetated area taking high elevation angles and nongeostationary satellites into consideration. Corresponding experimental data were obtained at a frequency of 2.0 GHz at Stromovka Park in Prague, the Czech Republic, within the full in-leaf and out-of-leaf periods of 2013 and 2014, respectively. By detecting copolarized and cross-polarized components of the transmitted left- and right-handed circularly polarized signals, the corresponding diversity gain was obtained for multiple-input single-output (MISO), single-input multiple-output (SIMO), and combined MISO/SIMO cases. It was found that tree defoliation results in a significant decrease of the polarization diversity gain achieved for low time percentages in particular scenarios. Milan Kvicera and Pavel Pechac Copyright © 2015 Milan Kvicera and Pavel Pechac. All rights reserved. Dual Band-Notched Microstrip-Fed Vivaldi Antenna Utilizing Compact EBG Structures Thu, 19 Feb 2015 13:53:08 +0000 http://www.hindawi.com/journals/ijap/2015/439832/ We propose an ultra-wideband (UWB) antipodal Vivaldi antenna (AVA) with high-Q stopband characteristics based on compact electromagnetic bandgap (EBG) structures. First, an AVA is designed and optimized to operate over an UWB spectrum. Then, two pairs of EBG cells are introduced along the antenna feed line to suppress the frequency components at 3.6–3.9 and 5.6–5.8 GHz (i.e., WiMAX and ISM bands, resp.). Simulated and measured results show a voltage standing wave ratio (VSWR) below 2 for the entire 3.1–10.6 GHz band with high attenuation at the two selected subbands. This simple yet effective approach eliminates the need to deform the antenna radiators with slots/parasitic elements or comprise multilayer substrates. Furthermore, the flexibility it offers in terms of controlling both the number and locations of the band-reject frequencies is advantageous for antennas with nonuniform flares as in the AVA. K. A. Alshamaileh, M. J. Almalkawi, and V. K. Devabhaktuni Copyright © 2015 K. A. Alshamaileh et al. All rights reserved. An Open Slot Antenna with Bandwidth Extension for WLAN/UWB Applications Wed, 18 Feb 2015 13:51:52 +0000 http://www.hindawi.com/journals/ijap/2015/341080/ An open slot antenna with extended bandwidth for WLAN and UWB applications is proposed. The radiating structure is composed of a rectangular microstrip patch antenna exciting an L-shaped slot etched on the ground plane. The feed position is optimized to get better impedance match for the higher range of the UWB spectrum, while a step in the slot, realized in the ground plane, is employed to extend the lower limit of the bandwidth so as to cover the 2.4 GHz WLAN frequency band. Using these design solutions the antenna bandwidth is successfully extended to 140% so as to cover both the WLAN and the UWB spectrum. Jing-Ya Deng, Tian-Qi Fan, Yan Zhang, Xiang Wen, Guo-Qiang Liu, and Li-Xin Guo Copyright © 2015 Jing-Ya Deng et al. All rights reserved. NLOS Path Loss Model for Low-Height Antenna Links in High-Rise Urban Street Grid Environments Wed, 18 Feb 2015 13:26:22 +0000 http://www.hindawi.com/journals/ijap/2015/651438/ This paper presents a NLOS (non-line-of-sight) path loss model for low-height antenna links in rectangular street grids to account for typical D2D (device-to-device) communication link situations in high-rise urban outdoor environments. From wideband propagation channel measurements collected in Seoul City at 3.7 GHz, we observed distinctive power delay profile behaviors between 1-Turn and 2-Turn NLOS links: the 2-Turn NLOS has a wider delay spread. This can be explained by employing the idea that the 2-Turn NLOS has multiple propagation paths along the various street roads from TX to RX, whereas the 1-Turn NLOS has a single dominant propagation path from TX to RX. Considering this, we develop a path loss model encompassing 1-Turn and 2-Turn NLOS links with separate scattering and diffraction parameters for the first and the second corners, based on the Uniform Geometrical Theory of Diffraction. In addition, we consider the effect of building heights on path loss by incorporating an adjustable “waveguide effect” parameter; that is, higher building alleys provide better propagation environments. When compared with field measurements, the predictions are in agreement. Juyul Lee, Myung-Don Kim, Hyun Kyu Chung, and Jinup Kim Copyright © 2015 Juyul Lee et al. All rights reserved. Analysis and Design of Leaky-Wave Antenna with Low SLL Based on Half-Mode SIW Structure Wed, 18 Feb 2015 06:42:21 +0000 http://www.hindawi.com/journals/ijap/2015/570693/ This paper presents a novel leaky-wave antenna based on the Half-Mode Substrate Integrated Waveguide (HMSIW) structure with low side lobe level. The effect of the structural parameters of the LWAs on the radiation performances is studied. Using beam-forming technique, the leakage loss factor α along the radiation aperture is designed in a tapered way by controlling the aperture depth along the structure. This controls the radiated power along the antenna aperture and finally achieves the radiation pattern with low SLL. Furthermore, the antenna structure is optimized to get an even lower SLL. Jiaying Guo, Zheng Li, Junhong Wang, Meie Chen, and Zhan Zhang Copyright © 2015 Jiaying Guo et al. All rights reserved. Improved Vlasov Antenna with Curved Cuts and Optimized Reflector Position and Shape Tue, 17 Feb 2015 08:32:29 +0000 http://www.hindawi.com/journals/ijap/2015/193630/ This paper presents a Vlasov antenna with curved cut shape and improved reflector position and geometry suitable for high power microwave applications. The curved shape of the proposed cut totally eliminates the sharp edges and angles present in Vlasov antennas with step and bevel cuts. Furthermore, with the proposed reflector configuration, the wave is radiated in the direction of the axis of the waveguide. A Vlasov antenna, designed for operation at 3 GHz, is used to compare the three cut types. An additional comparison is conducted to validate the concept of the enhanced reflector position, using the bevel-cut antenna and the improved cut. The proposed antenna results in increased antenna gain and in good performance in terms of sidelobe level and half-power beamwidth, with maximum radiation directed toward the axis of the waveguide center. H. M. El Misilmani, M. Al-Husseini, and K. Y. Kabalan Copyright © 2015 H. M. El Misilmani et al. All rights reserved. Antenna Polarization Optimization for Target Detection in Non-Gaussian Clutter Thu, 12 Feb 2015 07:17:55 +0000 http://www.hindawi.com/journals/ijap/2015/640730/ Adaptive polarization design of radar antenna has recently become the focus of attention in radar polarization community. A polarimetric detector against non-Gaussian clutter with transmitter polarization optimization has been proposed in this paper. First, the radar data model including the realistic dependence of the clutter on the transmitted polarization is introduced. Then the polarimetric detector with transmitter polarization optimization is developed. By employing the simulation, we demonstrate that the polarization waveform optimization can bring the significant performance gain on target detection as compared to the conventional full-polarization approach. Besides, jointly optimizing transmitter and receiver polarization to form a scalar measurement is confirmed not to achieve a better detection performance than vector measurement with only transmitter polarization optimization. Xu Cheng, Yong-zhen Li, and Xue-song Wang Copyright © 2015 Xu Cheng et al. All rights reserved. Joint DOA and Polarization Estimation for Unequal Power Sources Tue, 10 Feb 2015 07:01:26 +0000 http://www.hindawi.com/journals/ijap/2015/471374/ For most joint direction of arrival (DOA) and polarization estimation methods, the performances of proposed methods in dealing with unequal power sources are not discussed. However, sources with unequal powers apparently exist widely in actual applications. In this study, we propose a joint DOA and polarization estimation method for unequal power sources by utilizing the invariance property of noise subspace (IPNS) to the power of sources. This work extends the IPNS method to the dual polarized antenna array for joint DOA and polarization estimation. Moreover, we theoretically prove that the IPNS remains valid even when the sources are correlated. The computer simulations illustrate that the proposed method can effectively estimate the DOA and polarization parameters as the power difference between sources increases, as opposed to the polarimetric multiple signal classification (MUSIC) algorithm, which suffers from degradation in resolution probability. In addition, the performances of the proposed method are provided, as well the Cramer Rao Bound (CRB), which show approximate performance as the polarimetric MUSIC algorithm. Qingyuan Fang, Yong Han, Ming Jin, and Wenyi Dong Copyright © 2015 Qingyuan Fang et al. All rights reserved. An Optimal Transmission Strategy for Joint Wireless Information and Energy Transfer in MIMO Relay Channels Thu, 05 Feb 2015 09:31:36 +0000 http://www.hindawi.com/journals/ijap/2015/109818/ An optimal resource allocation strategy for MIMO relay system is considered in simultaneous wireless information and energy transfer network, where two users with multiple antennas communicate with each other assisted by an energy harvesting MIMO relay that gathers energy from the received signal by applying time switching scheme and forwards the received signal by using the harvesting energy. It is focused on the precoder design and resource allocation strategies for the system to allocate the resources among the nodes in decode-and-forward (DF) mode. Specifically, optimal precoder design and energy transfer strategy in MIMO relay channel are firstly proposed. Then, we formulate the resource allocation optimization problem. The closed-form solutions for the time and power allocation are derived. It is revealed that the solution can flexibly allocate the resource for the MIMO relay channel to maximize the sum rate of the system. Simulation results demonstrated that the performance of the proposed algorithm outperforms the traditional fixed method. Dingcheng Yang, Xiaoxiao Zhou, and Lin Xiao Copyright © 2015 Dingcheng Yang et al. All rights reserved. A Novel Execution Mode Selection Scheme for Wireless Computing Tue, 03 Feb 2015 11:28:11 +0000 http://www.hindawi.com/journals/ijap/2015/106053/ Computation offloading is an effective way to alleviate the resource limited problem of mobile devices. However, the offloading is not an always advantageous strategy for under some circumstances the overhead in time and energy may turn out to be greater than the offloading savings. Therefore, an offloading decision scheme is in demand for mobile devices to decide whether to offload a computation task to the server or to execute it in a local processor. In this paper, the offloading decision problem is translated into a dynamic execution mode selection problem, the objective of which is to minimize the task execution delay and reduce the energy consumption of mobile devices. A novel execution mode adjustment mechanism is introduced to make the execution process more flexible for real-time environment variation. Numerical results indicate that the proposed scheme can significantly reduce the task execution delay in an energy-efficient way. Jiadi Chen and Wenbo Wang Copyright © 2015 Jiadi Chen and Wenbo Wang. All rights reserved. An MPI-OpenMP Hybrid Parallel -LU Direct Solver for Electromagnetic Integral Equations Sun, 01 Feb 2015 11:48:12 +0000 http://www.hindawi.com/journals/ijap/2015/615743/ In this paper we propose a high performance parallel strategy/technique to implement the fast direct solver based on hierarchical matrices method. Our goal is to directly solve electromagnetic integral equations involving electric-large and geometrical-complex targets, which are traditionally difficult to be solved by iterative methods. The parallel method of our direct solver features both OpenMP shared memory programming and MPl message passing for running on a computer cluster. With modifications to the core direct-solving algorithm of hierarchical LU factorization, the new fast solver is scalable for parallelized implementation despite of its sequential nature. The numerical experiments demonstrate the accuracy and efficiency of the proposed parallel direct solver for analyzing electromagnetic scattering problems of complex 3D objects with nearly 4 million unknowns. Han Guo, Jun Hu, and Zaiping Nie Copyright © 2015 Han Guo et al. All rights reserved. A Printed Monopole Antenna for Triple-Band WLAN/WiMAX Applications Thu, 29 Jan 2015 06:14:55 +0000 http://www.hindawi.com/journals/ijap/2015/254268/ A new compact design of monopole antenna for triple-band WLAN/WiMAX applications with two band-notches based on broadband antenna is presented. By introducing a stub loaded ground and two new paper clip structures etched on radiation patch, a compact overall dimension 31 mm 33 mm 1 mm and three separated operating bands effectively covering 2.4/5.2/5.8 GHz WLAN bands and 2.5/3.5/5.5 GHz WiMAX bands can be achieved. Compared with familiar U type slot, the introduced compact paper clip structure can save about 37% of dimension regions, which could effectively improve efficiency of band-notch formation. Simulated and measured results demonstrate that the proposed antenna has good dipole-like radiation characteristics with appreciable gain across the operating bands. Besides, main parameters of the two etched paper clip structures are investigated to control the positions and bandwidths of the two stop-bands, respectively, on basis of which the three working bands can be adjusted independently. Huiqing Zhai, Lu Liu, Zhihui Ma, and Changhong Liang Copyright © 2015 Huiqing Zhai et al. All rights reserved. Robust Adaptive Beamforming Based on Worst-Case and Norm Constraint Wed, 28 Jan 2015 14:22:35 +0000 http://www.hindawi.com/journals/ijap/2015/765385/ A novel robust adaptive beamforming based on worst-case and norm constraint (RAB-WC-NC) is presented. The proposed beamforming possesses superior robustness against array steering vector (ASV) error with finite snapshots by using the norm constraint and worst-case performance optimization (WCPO) techniques. Simulation results demonstrate the validity and superiority of the proposed algorithm. Hongtao Li, Ke Wang, Chaoyu Wang, Yapeng He, and Xiaohua Zhu Copyright © 2015 Hongtao Li et al. All rights reserved. Low-Profile Magnetic Loop Monopole Antenna Based on a Square Substrate-Integrated Cavity Mon, 26 Jan 2015 06:48:21 +0000 http://www.hindawi.com/journals/ijap/2015/694385/ A low-profile monopole antenna with height below is proposed. The antenna is based on a square substrate-integrated cavity radiating through apertures in its four side walls. This effectively creates a small square loop of magnetic currents, which radiates omnidirectionally as an electric monopole. The antenna cavity has a side length of less than and thus resonates in the monomode region, in a fundamental mode. This means that the structure is robust in terms of feeding and manufacturing tolerances, as no parasitic modes can be excited. The designs of the cavity and the feed are introduced in detail. The measurement results from a manufactured prototype operating at 5.9 GHz show good agreement with simulations and validate the proposed approach. Thomas Kaufmann and Christophe Fumeaux Copyright © 2015 Thomas Kaufmann and Christophe Fumeaux. All rights reserved. Nonuniform Overlapping Method in Designing Microstrip Patch Antennas Using Genetic Algorithm Optimization Tue, 13 Jan 2015 06:41:38 +0000 http://www.hindawi.com/journals/ijap/2015/805820/ Genetic algorithm (GA) has been a popular optimization technique used for performance improvement of microstrip patch antennas (MPAs). When using GA, the patch geometry is optimized by dividing the patch area into small rectangular cells. This has an inherent problem of adjacent cells being connected to each other with infinitesimal connections, which may not be achievable in practice due to fabrication tolerances in chemical etching. As a solution, this paper presents a novel method of dividing the patch area into cells with nonuniform overlaps. The optimized design, which is obtained by using fixed overlap sizes, shows a quad-band performance covering GSM1800, GSM1900, LTE2300, and Bluetooth bands. In contrast, use of nonuniform overlap sizes leads to obtaining a pentaband design covering GSM1800, GSM1900, UMTS, LTE2300, and Bluetooth bandswith fractional bands with of 38% due to the extra design flexibility. J. M. Jeevani W. Jayasinghe, Jaume Anguera, Disala N. Uduwawala, and Aurora Andújar Copyright © 2015 J. M. Jeevani W. Jayasinghe et al. All rights reserved. MIMO Antennas in Radar Applications Sun, 11 Jan 2015 13:35:36 +0000 http://www.hindawi.com/journals/ijap/2015/696790/ Wen-Qin Wang, Mathini Sellathurai, Frankie Kit Wing Chan, Wei Xu, and Shengqi Zhu Copyright © 2015 Wen-Qin Wang et al. All rights reserved. Joint Multichannel Motion Compensation Method for MIMO SAR 3D Imaging Sun, 11 Jan 2015 10:00:13 +0000 http://www.hindawi.com/journals/ijap/2015/852520/ The multiple-input-multiple-output (MIMO) synthetic aperture radar (SAR) system with a linear antenna array can obtain 3D resolution. In practice, it suffers from both the translational motion errors and the rotational motion errors. Conventional single-channel motion compensation methods could be used to compensate the motion errors channel by channel. However, this method might not be accurate enough for all the channels. What is more, the single-channel compensation may break the coherence among channels, which would cause defocusing and false targets. In this paper, both the translational motion errors and the rotational motion errors are discussed, and a joint multichannel motion compensation method is proposed for MIMO SAR 3D imaging. It is demonstrated through simulations that the proposed method exceeds the conventional methods in accuracy. And the final MIMO SAR 3D imaging simulation confirms the validity of the proposed algorithm. Ze-min Yang, Meng-dao Xing, Guang-cai Sun, and Zheng Bao Copyright © 2015 Ze-min Yang et al. All rights reserved.