International Journal of Antennas and Propagation http://www.hindawi.com The latest articles from Hindawi Publishing Corporation © 2016 , Hindawi Publishing Corporation . All rights reserved. Minimum Lens Size Supporting the Leaky-Wave Nature of Slit Dipole Antenna at Terahertz Frequency Wed, 28 Sep 2016 07:51:16 +0000 http://www.hindawi.com/journals/ijap/2016/5826957/ We designed a slit dipole antenna backed by an extended hemispherical silicon lens and investigated the minimum lens size in which the slit dipole antenna works as a leaky-wave antenna. The slit dipole antenna consists of a planar feeding structure, which is a center-fed and open-ended slot line. A slit dipole antenna backed by an extended hemispherical silicon lens is investigated over a frequency range from 0.2 to 0.4 THz with the center frequency at 0.3 THz. The numerical results show that the antenna gain responses exhibited an increased level of sensitivity to the lens size and increased linearly with increasing lens radius. The lens with the radius of 1.2 is found to be the best possible minimum lens size for a slit dipole antenna on an extended hemispherical silicon lens. Niamat Hussain, Truong Khang Nguyen, Haewook Han, and Ikmo Park Copyright © 2016 Niamat Hussain et al. All rights reserved. Hierarchical Precoding in a Realistic Ultradense Heterogeneous Environment Exceeding the Degrees of Freedom Tue, 27 Sep 2016 08:36:33 +0000 http://www.hindawi.com/journals/ijap/2016/4796474/ Cell densification is a widely used approach to increase the spectral efficiency per area of cellular networks. Such Ultradense Networks (UDNs) consisting of small cells are often coordinated by macro base stations (BSs). With universal frequency reuse interference from the macro BS limits the system spectral efficiency. In this work we exploit the degrees of freedom at the macro BS to apply interference coordination. We propose a hierarchical precoding strategy in the spatial domain in order to project interference from the macro BS into the subspace of small cell users enabling linear cancellation. The macro BS interference towards small cell users is aligned within the joint null space of users served by the macro BS. Compared to classical interference alignment, our scheme does not require coordination between macrocells and small cells. We present three algorithms: in the first the interference is minimized by iterative alignment, in the second the uncoordinated interference from the small cells is considered, and in the third iterative Minimum Mean Square Error (MMSE) technique is used. We provide numerical evaluation, complexity analysis, and robustness analysis of these algorithms based on a realistic channel model showing the benefit of hierarchical precoding compared to the uncoordinated case. Mohamed Shehata, Martin Kurras, Khaled Hassan, and Lars Thiele Copyright © 2016 Mohamed Shehata et al. All rights reserved. Compressive Detection Using Sub-Nyquist Radars for Sparse Signals Mon, 26 Sep 2016 13:36:10 +0000 http://www.hindawi.com/journals/ijap/2016/3512617/ This paper investigates the compression detection problem using sub-Nyquist radars, which is well suited to the scenario of high bandwidths in real-time processing because it would significantly reduce the computational burden and save power consumption and computation time. A compressive generalized likelihood ratio test (GLRT) detector for sparse signals is proposed for sub-Nyquist radars without ever reconstructing the signal involved. The performance of the compressive GLRT detector is analyzed and the theoretical bounds are presented. The compressive GLRT detection performance of sub-Nyquist radars is also compared to the traditional GLRT detection performance of conventional radars, which employ traditional analog-to-digital conversion (ADC) at Nyquist sampling rates. Simulation results demonstrate that the former can perform almost as well as the latter with a very small fraction of the number of measurements required by traditional detection in relatively high signal-to-noise ratio (SNR) cases. Ying Sun, Jianjun Huang, Jingxiong Huang, Li Kang, Li Lei, and Yi Tang Copyright © 2016 Ying Sun et al. All rights reserved. A Hybrid 3DMLUV-FIA Method for Scattering from a 3D Dielectric Object above a 2D Dielectric Rough Surface Thu, 22 Sep 2016 16:19:36 +0000 http://www.hindawi.com/journals/ijap/2016/1563782/ The electromagnetic scattering from the composite model of a three-dimensional (3D) dielectric object located above a two-dimensional (2D) dielectric rough surface is analyzed in this work. Poggio, Miller, Chang, Harrington, Wu, and Tsai (PMCHWT) integral equations are discretized by the method of moments (MoM) into a matrix which is solved by Biconjugate Gradients Stabilized (BICGSTAB) method. Method of 3DMLUV was used for PEC object located above rough surface. Comparing to the case when object and rough surface are both PEC, the memory requirement and computational complexity for dielectric models are increased due to doubled unknown number. Moreover, compared to dielectric object in free space, the coupling between dielectric object and dielectric rough surface will result in complicated numerical simulation. To solve this problem, the updated rank based 3D Multilevel UV (3DMLUV) method is employed to reduce memory consumption and CPU time overhead. The 3DMLUV has been successfully applied in the scattering of PEC targets; however, when the object or rough surface becomes dielectric, the coupling between dielectric object and dielectric rough surface will lead to slow constriction. Therefore, the Fast Iterative Approach (FIA) is applied to further speed up the constricted speed of the matrix required in 3DMLUV. The efficiency, stability, and accuracy of the proposed method are demonstrated in a variety of scattering problems. Wu Xuezhi and Wenping Yu Copyright © 2016 Wu Xuezhi and Wenping Yu. All rights reserved. Small Antennas: Miniaturization Techniques and Applications 2016 Thu, 22 Sep 2016 13:47:06 +0000 http://www.hindawi.com/journals/ijap/2016/9410108/ Wenhua Yu, Yingsong Li, and Manos M. Tentzeris Copyright © 2016 Wenhua Yu et al. All rights reserved. Geolocation of a Known Altitude Target Using TDOA and GROA in the Presence of Receiver Location Uncertainty Tue, 20 Sep 2016 11:25:40 +0000 http://www.hindawi.com/journals/ijap/2016/3293418/ This paper considers the problem of geolocating a target on the Earth surface using the target signal time difference of arrival (TDOA) and gain ratio of arrival (GROA) measurements when the receiver positions are subject to random errors. The geolocation Cramer-Rao lower bound (CRLB) is derived and the performance improvement due to the use of target altitude information is quantified. An algebraic geolocation solution is developed and its approximate efficiency under small Gaussian noise is established analytically. Its sensitivity to the target altitude error is also studied. Simulations justify the validity of the theoretical developments and illustrate the good performance of the proposed geolocation method. Bing Deng, Le Yang, Zheng Bo Sun, and Hua Feng Peng Copyright © 2016 Bing Deng et al. All rights reserved. Evolutionary Algorithms Applied to Antennas and Propagation: Emerging Trends and Applications Thu, 15 Sep 2016 08:54:32 +0000 http://www.hindawi.com/journals/ijap/2016/5279647/ Sotirios K. Goudos, Dimitris E. Anagnostou, Christos Kalialakis, Pandian Vasant, and Symeon Nikolaou Copyright © 2016 Sotirios K. Goudos et al. All rights reserved. Broadband Circular Polarizer Based on Multilayer Gradual Frequency Selective Surfaces Wed, 07 Sep 2016 16:44:17 +0000 http://www.hindawi.com/journals/ijap/2016/4928109/ This paper presents a broadband circular polarizer based on multilayer gradual frequency selective surfaces. The unit cell includes two identical circles and a bar, whose dimensions decrease layer by layer with a reduction factor. This design can provide a good phase difference that is close to 90°. The bandwidth of the polarizer reaches 66.7%, from 7.9 to 15.8 GHz, which can convert the incident linear polarization waves into circular polarization waves. A sample polarizer is fabricated and measured. The results show that the operation frequency ranges from 7.75 to 15.2 GHz, coinciding with the simulation. Meanwhile, the working frequency band covers the range of 8.2–14.5 GHz when the incident angle increases to 25°. Wei Zhang, Jian-ying Li, and Ling Wang Copyright © 2016 Wei Zhang et al. All rights reserved. A Compact High-Pass Filter Using Hybrid Microstrip/Nonuniform CPW with Dual-Mode Resonant Response Wed, 07 Sep 2016 16:40:29 +0000 http://www.hindawi.com/journals/ijap/2016/1940850/ A novel and miniature high-pass filter (HPF) based on a hybrid-coupled microstrip/nonuniform coplanar waveguide (CPW) resonator is proposed in this article, in which the designed CPW has exhibited a wideband dual-mode characteristic within the desired high-pass frequency range. The implemented filter consists of the top microstrip coupled patches and the bottom modified nonuniformly short-circuited CPW resonator. Simulated results from the electromagnetic (EM) analysis software and measured results from a vector network analyzer (VNA) show a good agreement. A designed and fabricated prototype filter having a 3 dB cutoff frequency () of 5.78 GHz has shown an ultrawide high-pass behavior, which exhibits the highest passband frequency exceeding 4. under the minimum insertion loss (IL) 0.75 dB. The printed circuit board (PCB) area of the filter is approximately , where is the guided wavelength at . Hui Chen, Di Jiang, Ke-Song Chen, and Hong-Fei Zhao Copyright © 2016 Hui Chen et al. All rights reserved. State-of-the-Art Developments of Acoustic Energy Transfer Tue, 06 Sep 2016 17:25:40 +0000 http://www.hindawi.com/journals/ijap/2016/3072528/ Acoustic energy transfer (AET) technology has drawn significant industrial attention recently. This paper presents the reviews of the existing AETs sequentially, preferably, from the early stage. From the review, it is evident that, among all the classes of wireless energy transfer, AET is the safest technology to adopt. Thus, it is highly recommended for sensitive area and devices, especially implantable devices. Though, the efficiency for relatively long distances (i.e., >30 mm) is less than that of inductive or capacitive power transfer; however, the trade-off between safety considerations and performances is highly suitable and better than others. From the presented statistics, it is evident that AET is capable of transmitting 1.068 kW and 5.4 W of energy through wall and in-body medium (implants), respectively. Progressively, the AET efficiency can reach up to 88% in extension to 8.6 m separation distance which is even superior to that of inductive and capacitive power transfer. Md Rabiul Awal, Muzammil Jusoh, Thennarasan Sabapathy, Muhammad Ramlee Kamarudin, and Rosemizi Abd Rahim Copyright © 2016 Md Rabiul Awal et al. All rights reserved. Design of Large Thinned Arrays Using Different Biogeography-Based Optimization Migration Models Tue, 06 Sep 2016 15:40:12 +0000 http://www.hindawi.com/journals/ijap/2016/5359298/ Array thinning is a common discrete-valued combinatorial optimization problem. Evolutionary algorithms are suitable techniques for above-mentioned problem. Biogeography-Based Optimization (BBO), which is inspired by the science of biogeography, is a stochastic population-based evolutionary algorithm (EA). The original BBO uses a linear migration model to describe how species migrate from one island to another. Other nonlinear migration models have been proposed in the literature. In this paper, we apply BBO with four different migration models to five different large array design cases. Additionally we compare results with five other popular algorithms. The problems dimensions range from 150 to 300. The results show that BBO with sinusoidal migration model generally performs better than the other algorithms. However, these results are considered to be indicative and do not generally apply to all optimization problems in antenna design. Sotirios K. Goudos and John N. Sahalos Copyright © 2016 Sotirios K. Goudos and John N. Sahalos. All rights reserved. Scalable Frequency Selective Surface with Stable Angles of Incidence on a Thin Flexible Substrate Tue, 06 Sep 2016 14:02:53 +0000 http://www.hindawi.com/journals/ijap/2016/6891065/ A band-stop scalable frequency selective surface (FSS) structure that provides stability for an angle of incidence and polarization is designed using the repetitive arrangement of a unit structure miniaturized on a thin dielectric substrate. The designed miniaturized FSS has a hexagonal unit cell of a minimum size of 0.081 λ at 2.5 GHz in which a triangular loop is repeated. In addition to the frequency stability, the proposed structure reduces the design complexity that is the biggest shortcoming of the miniaturization techniques studied previously. A scalable FSS structure possessing stable frequency response characteristics over a wide band ranging from 2 to 8 GHz, which is achieved by the control of a single design variable, can be designed. For verification of the proposed structure, FSS structures that operate in the bands of 2.5 GHz, 5 GHz, and 8.2 GHz have been designed and fabricated on a very thin substrate. It has been confirmed that the results of the measurement and simulation correspond well with each other. The designed structures also demonstrate high stability for both the polarized wave and the incidence angle of the incident wave. In-Gon Lee and Ic-Pyo Hong Copyright © 2016 In-Gon Lee and Ic-Pyo Hong. All rights reserved. Planar Dual-Band Monopole Antenna with an Extended Ground Plane for WLAN Applications Mon, 05 Sep 2016 13:09:07 +0000 http://www.hindawi.com/journals/ijap/2016/6798960/ A compact planar microstrip-fed monopole antenna designed for dual-band operation is proposed for WLAN applications. The antenna is composed of a rectangular strip monopole in addition to an inverted-L parasitic element that is connected to the truncated ground plane of the microstrip feed. Besides exciting an additional band of operation, the parasitic element also improves the bandwidth of the band excited by the strip monopole. Several simulated parametric studies are conducted to investigate the effects of each geometrical parameter on the behavior of the antenna. Experimental and simulation results demonstrate that the proposed antenna covers the 2.4 and 5.8 GHz bands utilized in WLAN. In both bands, the proposed antenna exhibits good impedance match, moderate gain (approximately 2 dBi), and sustainable omnidirectional-like radiation patterns in both principal planes. An equivalent circuit model of the antenna is also developed. Ayman S. Al-Zayed and V. A. Shameena Copyright © 2016 Ayman S. Al-Zayed and V. A. Shameena. All rights reserved. Wind Speed Inversion in High Frequency Radar Based on Neural Network Tue, 30 Aug 2016 16:31:17 +0000 http://www.hindawi.com/journals/ijap/2016/2706521/ Wind speed is an important sea surface dynamic parameter which influences a wide variety of oceanic applications. Wave height and wind direction can be extracted from high frequency radar echo spectra with a relatively high accuracy, while the estimation of wind speed is still a challenge. This paper describes an artificial neural network based method to estimate the wind speed in HF radar which can be trained to store the specific but unknown wind-wave relationship by the historical buoy data sets. The method is validated by one-month-long data of SeaSonde radar, the correlation coefficient between the radar estimates and the buoy records is 0.68, and the root mean square error is 1.7 m/s. This method also performs well in a rather wide range of time and space (2 years around and 360 km away). This result shows that the ANN is an efficient tool to help make the wind speed an operational product of the HF radar. Yuming Zeng, Hao Zhou, Hugh Roarty, and Biyang Wen Copyright © 2016 Yuming Zeng et al. All rights reserved. A Wideband and Polarization-Independent Metasurface Based on Phase Optimization for Monostatic and Bistatic Radar Cross Section Reduction Tue, 30 Aug 2016 13:54:19 +0000 http://www.hindawi.com/journals/ijap/2016/7595921/ A broadband and polarization-independent metasurface is analyzed and designed for both monostatic and bistatic radar cross section (RCS) reduction in this paper. Metasurfaces are composed of two types of electromagnetic band-gap (EBG) lattice, which is a subarray with “0” or “π” phase responses, arranged in periodic and aperiodic fashions. A new mechanism is proposed for manipulating electromagnetic (EM) scattering and realizing the best reduction of monostatic and bistatic RCS by redirecting EM energy to more directions through controlling the wavefront of EM wave reflected from the metasurface. Scattering characteristics of two kinds of metasurfaces, periodic arrangement and optimized phase layout, are studied in detail. Optimizing phase layout through particle swarm optimization (PSO) together with far field pattern prediction can produce a lot of scattering lobes, leading to a great reduction of bistatic RCS. For the designed metasurface based on optimal phase layout, a bandwidth of more than 80% is achieved at the normal incidence for the −9.5 dB RCS reduction for both monostatic and bistatic. Bistatic RCS reduction at frequency points with exactly 180° phase difference reaches 17.6 dB. Both TE and TM polarizations for oblique incidence are considered. The measured results are in good agreement with the corresponding simulations. Jianxun Su, Yao Lu, Zengrui Li, Rongrong Zhang, and Yaoqing (Lamar) Yang Copyright © 2016 Jianxun Su et al. All rights reserved. Design of UAVs-Based 3D Antenna Arrays for a Maximum Performance in Terms of Directivity and SLL Tue, 30 Aug 2016 11:33:05 +0000 http://www.hindawi.com/journals/ijap/2016/2621862/ This paper presents a design of UAVs-based 3D antenna arrays for a maximum performance in terms of directivity and side lobe level (SLL). This paper illustrates how to model the UAVs formation flight using 3D nonuniform antenna arrays. This design of 3D antenna arrays considers the optimization of the positions of the antenna elements to model the UAVs formation flight. In this case, a disk patch antenna is chosen to be used as element in each UAV. The disk patch antenna is formulated by the well-known cavity model. The synthesis process is carried out by the method of Differential Evolution for Multiobjective Optimization (DEMO). Furthermore, a comparison of the performance of 3D nonuniform antenna arrays is provided with respect to the most conventional arrays (circular, planar, linear, and the cubic) for UAVs formation flight. Jesus Garza, Marco A. Panduro, Alberto Reyna, Gerardo Romero, and Carlos del Rio Copyright © 2016 Jesus Garza et al. All rights reserved. High Gain Slot Array with Fabry-Perot Cavity Feeding Circuit Mon, 29 Aug 2016 11:04:54 +0000 http://www.hindawi.com/journals/ijap/2016/9674742/ A new approach for designing slot arrays using a Fabry-Perot cavity for the feeding circuit is presented. The proposed array has simpler and smaller feeding circuit compared to conventional feeding networks that have multiple dividers or combiners. The dividers and combiners are usually sources of losses. In addition, the profile of the proposed array is not limited by the half-wavelength resonance condition that exists for Fabry-Perot resonator antennas based on partially reflecting surfaces. The operating frequency is not sensitive to the profile of the antenna. A small profile can be achieved without the utilization of an artificial magnetic conductor or a substrate with high dielectric constant. To validate the proposed approach, full-wave numerical results are presented at 5.8 GHz showing good impedance matching, a high gain of about 22 dB, and an efficiency of 76%. Halim Boutayeb and Mourad Nedil Copyright © 2016 Halim Boutayeb and Mourad Nedil. All rights reserved. Thinning and Weighting of Planar/Conformal Arrays Considering Mutual Coupling Effects Mon, 29 Aug 2016 10:19:34 +0000 http://www.hindawi.com/journals/ijap/2016/7521723/ Based on an improved active element pattern (AEP) technique, a novel effective method for sidelobe suppression considering mutual coupling (MC) in planar and conformal sparse arrays is proposed in this paper. A thinning and weighting process that includes the thinning module, optimization module, and far-field calculation module is presented, and three key points, namely, the modified AEP modeling, far-field calculation of planar and conformal thinned arrays, and modified thinning strategy, are highlighted. As an effective optimization algorithm, the differential evolution algorithm (DEA) is adopted in order to achieve low sidelobe. Several numerical examples are shown to validate the consistency and effectiveness of the proposed synthesis approach. With the first use of the AEP technique for the synthesis of sparse arrays, the planar and conformal microstrip arrays with the desired array filling factor are studied to obtain the expected sidelobe level (SLL). You-Feng Cheng, Wei Shao, Ran Zhang, Xiao Ding, and Meng-Xia Yu Copyright © 2016 You-Feng Cheng et al. All rights reserved. Optimization of a Conical Corrugated Antenna Using Multiobjective Heuristics for Radio-Astronomy Applications Mon, 29 Aug 2016 06:14:01 +0000 http://www.hindawi.com/journals/ijap/2016/7024704/ This paper presents the design of a tree sections corrugated horn antenna with a modified linear profile, using NURBS, suitable for radio-astronomy applications. The operating band ranges from 4.5 to 8.8 GHz. The aperture efficiency is higher than 84% and the return losses are greater than 20 dB in the whole bandwidth. The antenna optimization has been carried out with multiobjective versions of an evolutionary algorithm (EA) and a particle swarm optimization (PSO) algorithm. We show that both techniques provide good antenna design, but the experience carried out shows that the results of the evolutionary algorithm outperform the particle swarm results. S. López-Ruiz, R. Sánchez Montero, F. Tercero-Martínez, P. L. López-Espí, and J. A. López-Fernandez Copyright © 2016 S. López-Ruiz et al. All rights reserved. A New Method of Wave Mapping with HF Radar Thu, 25 Aug 2016 13:13:57 +0000 http://www.hindawi.com/journals/ijap/2016/4135404/ Study of wave height inversion with High-Frequency Surface Wave Radars (HFSWRs) has been going on for more than 40 years. Various wave inversion methods have been proposed, and HFSWRs have achieved great success in local wave measurements. However, the method of wave mapping is still under development, especially for the broad-beam HF radars. Existing methods of wave mapping are based on narrow-beam radar with beamforming. This paper introduces a way of wave height inversion, using the ratio of the second-harmonic peak (SHP) to the Bragg peak (RSB). A new wave mapping method is proposed, which can be used in both narrow and broad-beam radars, according to the way of wave inversion based on the RSB. In addition, radar wave measurements at the buoy position are compared with the in situ buoy, which show a good agreement. At last, the results of wave mapping on the two-hour timescale are given. Lijie Jin, Biyang Wen, and Hao Zhou Copyright © 2016 Lijie Jin et al. All rights reserved. Evolutionary Algorithms Applied to Antennas and Propagation: A Review of State of the Art Thu, 25 Aug 2016 10:04:51 +0000 http://www.hindawi.com/journals/ijap/2016/1010459/ A review of evolutionary algorithms (EAs) with applications to antenna and propagation problems is presented. EAs have emerged as viable candidates for global optimization problems and have been attracting the attention of the research community interested in solving real-world engineering problems, as evidenced by the fact that very large number of antenna design problems have been addressed in the literature in recent years by using EAs. In this paper, our primary focus is on Genetic Algorithms (GAs), Particle Swarm Optimization (PSO), and Differential Evolution (DE), though we also briefly review other recently introduced nature-inspired algorithms. An overview of case examples optimized by each family of algorithms is included in the paper. Sotirios K. Goudos, Christos Kalialakis, and Raj Mittra Copyright © 2016 Sotirios K. Goudos et al. All rights reserved. Computationally Efficient Angle and Polarization Estimation in the Presence of Multipath Propagation Using Dual-Polarization Vector Sensor Array Thu, 25 Aug 2016 09:44:54 +0000 http://www.hindawi.com/journals/ijap/2016/7537160/ This paper presents a computationally efficient angle and polarization estimation method for a mixture of uncorrelated and coherent sources using a dual-polarization vector sensor array. The uncorrelated sources are separated from the coherent sources on the basis of the modulus property of eigenvalues. The angles of the uncorrelated sources are estimated by employing rotational invariance and the associated polarization is obtained from the estimate of the uncorrelated array response matrix through elementwise division. For the distinguished coherent sources, two Hankel matrices are constructed from the elements of the estimated coherent array response matrix of each coherent group, from which two rotational-invariant submatrix pairs are extracted for estimating the coherent angles with a high precision. The least-square solution to the coherent polarization equation is derived for estimating the coherent polarization parameters. For each uncorrelated source and coherent group, the proposed method estimates the associated angle and polarization parameters separately, which avoids the need of 3D spectral search. In comparison with the existing methods, the simulation results show that the proposed method yields favorable performance in terms of computational efficiency and estimation accuracy. Weijian Si, Pinjiao Zhao, Zhiyu Qu, and Liwei Wang Copyright © 2016 Weijian Si et al. All rights reserved. Separate DOD and DOA Estimation for Bistatic MIMO Radar Thu, 25 Aug 2016 09:22:10 +0000 http://www.hindawi.com/journals/ijap/2016/9170403/ A novel MUSIC-type algorithm is derived in this paper for the direction of departure (DOD) and direction of arrival (DOA) estimation in a bistatic MIMO radar. Through rearranging the received signal matrix, we illustrate that the DOD and the DOA can be separately estimated. Compared with conventional MUSIC-type algorithms, the proposed separate MUSIC algorithm can avoid the interference between DOD and DOA estimations effectively. Therefore, it is expected to give a better angle estimation performance and have a much lower computational complexity. Meanwhile, we demonstrate that our method is also effective for coherent targets in MIMO radar. Simulation results verify the efficiency of the proposed method, particularly when the signal-to-noise ratio (SNR) is low and/or the number of snapshots is small. Lin Li, Fangfang Chen, and Jisheng Dai Copyright © 2016 Lin Li et al. All rights reserved. A Novel SIW H-Plane Horn Antenna Based on Parabolic Reflector Thu, 25 Aug 2016 09:21:41 +0000 http://www.hindawi.com/journals/ijap/2016/3659230/ A new type of H-plane horn antenna based on the parabolic reflector principle is proposed in this paper. The parabolic reflector is constructed with the substrate integrated waveguide technology and is used for generating large radiation aperture and uniform phase distribution at the aperture, yielding a fan beam with very narrow beamwidth in H-plane. A feeding source composed of a probe and an inductive-post reflector is designed as the feed, which can transmit a unidirectional incident wave toward the parabolic reflector. Two metallic strips with post arrays are designed as a transition for the matching between the horn aperture and the free space and also work as a director to realize unidirectional radiation and reduce the front-to-back ratio. The antenna has the advantages of narrow beam, compact size, and easy integration, and the operation bandwidth is from 27 GHz to 35.5 GHz. The experimental results show good agreement with the simulated results. Shiqiao Zhang, Zheng Li, and Junhong Wang Copyright © 2016 Shiqiao Zhang et al. All rights reserved. On-Body Characterization of Planar Differential Antennas for Multiple, Wide, and Narrow Bands Thu, 25 Aug 2016 09:21:12 +0000 http://www.hindawi.com/journals/ijap/2016/7439403/ This paper reports the results of the on-body experimental tests of a set of four planar differential antennas, originated by design variations of radiating elements with the same shape and characterized by the potential for covering wide and narrow bands. All the antenna designs have been implemented on low-cost FR4 substrate and characterized experimentally through on-body measurements. The results show the impact of the proximity to the human body on antenna performance and the opportunities in terms of potential coverage of wide and narrow bands for future ad hoc designs and implementations through wearable substrates targeting on-body and off-body communication and sensing applications. Luigi Vallozzi, Domenico Pepe, Thijs Castel, Hendrik Rogier, and Domenico Zito Copyright © 2016 Luigi Vallozzi et al. All rights reserved. A Wideband End-Fire Conformal Vivaldi Antenna Array Mounted on a Dielectric Cone Tue, 23 Aug 2016 11:11:24 +0000 http://www.hindawi.com/journals/ijap/2016/9812642/ The characteristics of a novel antipodal Vivaldi antenna array mounted on a dielectric cone are presented. By employing antipodal Vivaldi antenna element, the antenna array shows ultrawide bandwidth and end-fire radiation characteristics. Our simulations show that the cone curvature has an obvious influence on the performance of the conformal antenna, in terms of both the bandwidth and the radiation patterns. The thickness and permittivity of the dielectric cone have an effect on the bandwidth of the conformal antenna. Measurement results of both single antenna and conformal antenna array show a good agreement with the simulated results. The measured conformal antenna can achieve a −10 dB with bandwidth of 2.2–12 GHz and demonstrate a typical end-fire radiation beam. These findings provide useful guidelines and insights for the design of wideband end-fire antennas mounted on a dielectric cone. Zengrui Li, Xiaole Kang, Jianxun Su, Qingxin Guo, Yaoqing (Lamar) Yang, and Junhong Wang Copyright © 2016 Zengrui Li et al. All rights reserved. Simple and Efficient Preconditioner for Surface Integral Solution of Scattering from Multilayer Dielectric Bodies Mon, 22 Aug 2016 11:36:46 +0000 http://www.hindawi.com/journals/ijap/2016/4134327/ The computation of scattering from multilayer dielectric bodies is studied by using the combined tangential formulation (CTF) of surface integral solution. A simple and efficient preconditioner is designed for the surface integral solution of multilayer dielectric bodies and validated by numerical experiments. Compared with the traditional near field preconditioner, the proposed preconditioner significantly reduce CPU time and memory requirement. Furthermore, the multilevel fast multipole algorithm (MLFMA) is employed to improve the capability of the solutions. The trick of efficiently implementing MLFMA is presented for multilayer dielectric bodies. Numerical examples are presented to verify the accuracy and efficiency of the approach for computing scattering from multilayer dielectric problems. B. B. Kong and X. Q. Sheng Copyright © 2016 B. B. Kong and X. Q. Sheng. All rights reserved. Experimental Study on Inkjet-Printed Passive UHF RFID Tags on Versatile Paper-Based Substrates Thu, 18 Aug 2016 06:27:58 +0000 http://www.hindawi.com/journals/ijap/2016/9265159/ We present the possibilities and challenges of passive UHF RFID tag antennas manufactured by inkjet printing silver nanoparticle ink on versatile paper-based substrates. The most efficient manufacturing parameters, such as the pattern resolution, were determined and the optimal number of printed layers was evaluated for each substrate material. Next, inkjet-printed passive UHF RFID tags were fabricated on each substrate with the optimized parameters and number of layers. According to our measurements, the tags on different paper substrates showed peak read ranges of 4–6.5 meters and the tags on different cardboard substrates exhibited peak read ranges of 2–6 meters. Based on their wireless performance, these inkjet-printed paper-based passive UHF RFID tags are sufficient for many future wireless applications and comparable to tags fabricated on more traditional substrates, such as polyimide. Han He, Lauri Sydänheimo, Johanna Virkki, and Leena Ukkonen Copyright © 2016 Han He et al. All rights reserved. Study on the Accuracy Improvement of the Second-Kind Fredholm Integral Equations by Using the Buffa-Christiansen Functions with MLFMA Wed, 17 Aug 2016 12:04:13 +0000 http://www.hindawi.com/journals/ijap/2016/2417402/ Former works show that the accuracy of the second-kind integral equations can be improved dramatically by using the rotated Buffa-Christiansen (BC) functions as the testing functions, and sometimes their accuracy can be even better than the first-kind integral equations. When the rotated BC functions are used as the testing functions, the discretization error of the identity operators involved in the second-kind integral equations can be suppressed significantly. However, the sizes of spherical objects which were analyzed are relatively small. Numerical capability of the method of moments (MoM) for solving integral equations with the rotated BC functions is severely limited. Hence, the performance of BC functions for accuracy improvement of electrically large objects is not studied. In this paper, the multilevel fast multipole algorithm (MLFMA) is employed to accelerate iterative solution of the magnetic-field integral equation (MFIE). Then a series of numerical experiments are performed to study accuracy improvement of MFIE in perfect electric conductor (PEC) cases with the rotated BC as testing functions. Numerical results show that the effect of accuracy improvement by using the rotated BC as the testing functions is greatly different with curvilinear or plane triangular elements but falls off when the size of the object is large. Yue-Qian Wu, Xin-Qing Sheng, Xing-Yue Guo, and Hai-Jing Zhou Copyright © 2016 Yue-Qian Wu et al. All rights reserved. Two-Dimensional DOA Estimation for Monostatic MIMO Radar with Electromagnetic Vector Received Sensors Wed, 17 Aug 2016 08:40:39 +0000 http://www.hindawi.com/journals/ijap/2016/2952539/ We study two-dimensional direction of arrival (2D-DOA) estimation problem of monostatic MIMO radar with the receiving array which consists of electromagnetic vector sensors (EMVSs). The proposed angle estimation algorithm can be applied to the arbitrary and unknown array configuration, which can be summarized as follows. Firstly, EMVSs in the receiver of a monostatic MIMO radar are used to measure all six electromagnetic-field components of an incident wavefield. The vector sensor array with the six unknown electromagnetic-field components is divided into six spatially identical subarrays. Secondly, ESPRIT is utilized to estimate the rotational invariant factors (RIFs). Parts of the RIFs are picked up to restore the source’s electromagnetic-field vector. Last, a vector cross product operation is performed between electric field and magnetic field to obtain the Pointing vector, which can offer the 2D-DOA estimation. Prior knowledge of array elements’ positions and angle searching procedure are not necessary for the proposed 2D-DOA estimation method. Simulation results prove the validity of the proposed method. Guimei Zheng and Jun Tang Copyright © 2016 Guimei Zheng and Jun Tang. All rights reserved.