International Journal of Antennas and Propagation The latest articles from Hindawi © 2017 , Hindawi Limited . All rights reserved. Cross Spectral Analysis of CODAR-SeaSonde Echoes from Sea Surface and Ionosphere at Taiwan Thu, 23 Feb 2017 08:08:41 +0000 It is well known that the primary targets responsible for first-order sea echoes observed by a High-Frequency (HF) radar are the advancing and receding ocean waves with the wavelengths at Bragg scales. However, in light of the fact that the ionospheric sporadic E (Es) and F layers may be present in the viewing range of the HF radar for ocean wave detection, the radar returns reflected from the F and Es layers may significantly contaminate the ocean wave power spectrum. The characteristics of the first-order sea echoes and ionospheric interferences measured by the CODAR-SeaSonde in Taiwan area are analyzed and presented in this article. The coherences and phases of the normalized cross spectra of the sea and ionospheric echoes between different pairs of the receiving channels are calculated, respectively. One of the striking features presented in this report is that the ionospheric echo heights scaled from the ionogram observed by the Chung-Li ionosonde are about 30 km lower than those observed by the DATAN CODAR-SeaSonde. It is also found that the coherences of the sea echoes are generally smaller than those of the ionospheric echoes by about 15% on average, and the phase fluctuations (standard deviations) of the sea echoes are substantially larger than those of the ionospheric layer reflection echoes. In addition, statistics show that the sum of the mean phases of the ionospheric echoes between the three receiving channel pairs is approximately zero, while it is not for the sea echoes. These results seem to suggest that the use of the discrepancies in the characteristics of the coherences and phases between the sea and ionospheric echoes may provide a potential means to be helpful to distinguish the sea and ionospheric echoes in the CODAR-SeaSonde observed cross power spectrum. Chien-Ya Wang, Ching-Lun Su, Kang-Hung Wu, and Yen-Hsyang Chu Copyright © 2017 Chien-Ya Wang et al. All rights reserved. Integrated Filtering Microstrip Duplex Antenna Array with High Isolation Wed, 22 Feb 2017 09:55:15 +0000 This paper presents a 2 × 1 integrated filtering microstrip duplex antenna array with high isolation and same polarization. The antenna consists of two radiating patches fed by two T-shaped probes and a power distributing duplex network (PDDN). The PDDN is composed of two bandstop filters and a 180-degree phase shift power divider. And the PDDN is designed to achieve the functions of power division, frequency selectivity, and port isolation. A Transmission Line (TL) model is adopted to design the PDDN, and the detailed synthesis procedure is presented. For demonstration, the proposed antenna is designed and fabricated. The implemented antenna achieves an average gain of 10 dBi, a cross-polarization ratio of 20 dB, and an isolation of 35 dB within the operation band. Xian-Jing Lin, Ze-Ming Xie, and Pei-Sheng Zhang Copyright © 2017 Xian-Jing Lin et al. All rights reserved. A Model to Determine the Propagation Losses Based on the Integration of Hata-Okumura and Wavelet Neural Models Wed, 22 Feb 2017 06:30:08 +0000 Radioelectric spectrum occupancy forecast has proven useful for the design of wireless systems able to harness spectrum opportunities like cognitive radio. This paper proposes the development of a model that identifies propagation losses and spectrum opportunities in a channel of a mobile cellular network for an urban environment using received signal power forecast. The proposed model integrates the Hata-Okumura (H-O) large-scale propagation model with a wavelet neural model. The model results, obtained through simulations, show that the wavelet neural model forecasts with a high degree of precision, which is consistent with the observed behavior in experiments carried out in wireless systems of this type. Luis F. Pedraza, Cesar A. Hernández, and Danilo A. López Copyright © 2017 Luis F. Pedraza et al. All rights reserved. Outage Analysis of Multihop Wireless Backhaul Using Millimeter Wave under Blockage Effects Tue, 21 Feb 2017 09:24:38 +0000 We consider multihop millimeter-wave (mm-Wave) wireless backhaul communications, by which small cell base station (SBS) clusters can connect to a macrocell base station (MBS). Assuming the mm-Wave wireless backhaul links suffer from outage caused by obstacles that block the line-of-sight (LoS) paths, we derive the statistics of a perhop distance based on the blockage model using stochastic geometry and random shape theory and analyze the multihop outage probability using the statistics of a perhop distance. We also provide an optimal number of hops to minimize the end-to-end outage performance between the MBS and the destination SBS cluster when the end-to-end distance is given. Haejoon Jung and In-Ho Lee Copyright © 2017 Haejoon Jung and In-Ho Lee. All rights reserved. Maximum Likelihood Time Delay Estimation Based on Monte Carlo Importance Sampling in Multipath Environment Mon, 20 Feb 2017 08:20:10 +0000 In multipath environment, the computation complexity of single snapshot maximum likelihood for time delay estimation is huge. In particular, the computational complexity of grid search method increases exponentially with the increase of dimension. For this reason, this paper presents a maximum likelihood estimation algorithm based on Monte Carlo importance sampling technique. Firstly, the algorithm takes advantage of the channel frequency response in order to build the likelihood function of time delay in multipath environment. The pseudoprobability density function is constructed by using exponential likelihood function. Then, it is crucial to choose the importance function. According to the characteristic of the Vandermonde matrix in likelihood function, the product of the conjugate transpose Vandermonde matrix and itself is approximated by the product of a constant and an identity matrix. The pseudoprobability density function can be decomposed into product of many probability density functions of single path time delay. The importance function is constructed. Finally, according to probability density function of multipath time delay decomposed by importance function, the time delay of the multipath is sampled by Monte Carlo method. The time delay is estimated via calculating weighted mean of sample. Simulation results show that the performance of proposed algorithm approaches the Cramér-Rao bound with reduced complexity. Bin Ba, Weijia Cui, Daming Wang, and Jianhui Wang Copyright © 2017 Bin Ba et al. All rights reserved. Pattern Synthesis of Linear Antenna Arrays Using Enhanced Flower Pollination Algorithm Mon, 20 Feb 2017 00:00:00 +0000 In this paper, a new variant of flower pollination algorithm (FPA), namely, enhanced flower pollination algorithm (EFPA), has been proposed for the pattern synthesis of nonuniform linear antenna arrays (LAA). The proposed algorithm uses the concept of Cauchy mutation in global pollination and enhanced local search to improve the exploration and exploitation tendencies of FPA. It also uses dynamic switching to control the rate of exploration and exploitation. The algorithm is tested on standard benchmark problems and has been compared statistically with state of the art to prove its worthiness. LAA design is a tricky and difficult electromagnetic problem. Hence to check the efficacy of the proposed algorithm it has been used for synthesis of four different LAA with different sizes. Experimental results show that EFPA algorithm provides enhanced performance in terms of side lobe suppression and null control compared to FPA and other popular algorithms. Urvinder Singh and Rohit Salgotra Copyright © 2017 Urvinder Singh and Rohit Salgotra. All rights reserved. Wideband and UWB Antennas for Wireless Applications: A Comprehensive Review Mon, 20 Feb 2017 00:00:00 +0000 A comprehensive review concerning the geometry, the manufacturing technologies, the materials, and the numerical techniques, adopted for the analysis and design of wideband and ultrawideband (UWB) antennas for wireless applications, is presented. Planar, printed, dielectric, and wearable antennas, achievable on laminate (rigid and flexible), and textile dielectric substrates are taken into account. The performances of small, low-profile, and dielectric resonator antennas are illustrated paying particular attention to the application areas concerning portable devices (mobile phones, tablets, glasses, laptops, wearable computers, etc.) and radio base stations. This information provides a guidance to the selection of the different antenna geometries in terms of bandwidth, gain, field polarization, time-domain response, dimensions, and materials useful for their realization and integration in modern communication systems. Renato Cicchetti, Emanuela Miozzi, and Orlandino Testa Copyright © 2017 Renato Cicchetti et al. All rights reserved. THz-SAR Vibrating Target Imaging via the Bayesian Method Sun, 19 Feb 2017 00:00:00 +0000 Target vibration bears important information for target recognition, and terahertz, due to significant micro-Doppler effects, has strong advantages for remotely sensing vibrations. In this paper, the imaging characteristics of vibrating targets with THz-SAR are at first analyzed. An improved algorithm based on an excellent Bayesian approach, that is, the expansion-compression variance-component (ExCoV) method, has been proposed for reconstructing scattering coefficients of vibrating targets, which provides more robust and efficient initialization and overcomes the deficiencies of sidelobes as well as artifacts arising from the traditional correlation method. A real vibration measurement experiment of idle cars was performed to validate the range model. Simulated SAR data of vibrating targets and a tank model in a real background in 220 GHz show good performance at low SNR. Rapidly evolving high-power terahertz devices will offer viable THz-SAR application at a distance of several kilometers. Bin Deng, Xin-yun Wang, Cheng-guang Wu, Yu-liang Qin, and Hong-qiang Wang Copyright © 2017 Bin Deng et al. All rights reserved. Compact Liquid Crystal Based Tunable Band-Stop Filter with an Ultra-Wide Stopband by Using Wave Interference Technique Sun, 19 Feb 2017 00:00:00 +0000 A wave interference filtering section that consists of three stubs of different lengths, each with an individual stopband of its own central frequency, is reported here for the design of band-stop filters (BSFs) with ultra-wide and sharp stopbands as well as large attenuation characteristics. The superposition of the individual stopbands provides the coverage over an ultra-wide frequency range. Equations and guidelines are presented for the application of a new wave interference technique to adjust the rejection level and width of its stopband. Based on that, an electrically tunable ultra-wide stopband BSF using a liquid crystal (LC) material for ultra-wideband (UWB) applications is designed. Careful treatment of the bent stubs, including impedance matching of the main microstrip line and bent stubs together with that of the SMA connectors and impedance adaptors, was carried out for the compactness and minimum insertion and reflection losses. The experimental results of the fabricated device agree very well with that of the simulation. The centre rejection frequency as measured can be tuned between 4.434 and 4.814 GHz when a biased voltage of 0–20 Vrms is used. The 3 dB and 25 dB stopband bandwidths were 4.86 GHz and 2.51 GHz, respectively, which are larger than that of other recently reported LC based tunable BSFs. Longzhu Cai, Huan Xu, and Daping Chu Copyright © 2017 Longzhu Cai et al. All rights reserved. Direction-of-Arrival Estimation for Coprime Array Using Compressive Sensing Based Array Interpolation Thu, 16 Feb 2017 07:03:23 +0000 A method of direction-of-arrival (DOA) estimation using array interpolation is proposed in this paper to increase the number of resolvable sources and improve the DOA estimation performance for coprime array configuration with holes in its virtual array. The virtual symmetric nonuniform linear array (VSNLA) of coprime array signal model is introduced, with the conventional MUSIC with spatial smoothing algorithm (SS-MUSIC) applied on the continuous lags in the VSNLA; the degrees of freedom (DoFs) for DOA estimation are obviously not fully exploited. To effectively utilize the extent of DoFs offered by the coarray configuration, a compressing sensing based array interpolation algorithm is proposed. The compressing sensing technique is used to obtain the coarse initial DOA estimation, and a modified iterative initial DOA estimation based interpolation algorithm (IMCA-AI) is then utilized to obtain the final DOA estimation, which maps the sample covariance matrix of the VSNLA to the covariance matrix of a filled virtual symmetric uniform linear array (VSULA) with the same aperture size. The proposed DOA estimation method can efficiently improve the DOA estimation performance. The numerical simulations are provided to demonstrate the effectiveness of the proposed method. Aihua Liu, Qiang Yang, Xin Zhang, and Weibo Deng Copyright © 2017 Aihua Liu et al. All rights reserved. Precision Imaging of Frequency Stepped SAR with Frequency Domain Extracted HRRP and Fast Factorized Back Projection Algorithm Thu, 16 Feb 2017 00:00:00 +0000 Novel frequency domain extracted method (FDEM) to obtain high range resolution profile (HRRP) for frequency stepped synthetic aperture radar (SAR) is proposed in this paper, and the mathematical principle and formulas of this new HRRP obtaining idea combined with classical fast Fourier transform (FFT), chirp transform (CZT), and single point Fourier transform (SPFT) are deduced, analyzed, and compared in detail. Based on the HRRP data, precision imaging processing is completed using a data block partition based fast factorized back projection algorithm. Imaging validations are executed and all results proved that the FDEM has a great capability of antijamming. It is more effective than conventional time domain IFFT method (TDM) and shows a great promise in frequency stepped radar imaging and applications. Can-bin Yin and Da Ran Copyright © 2017 Can-bin Yin and Da Ran. All rights reserved. A Time Modulated Printed Dipole Antenna Array for Beam Steering Application Thu, 16 Feb 2017 00:00:00 +0000 This paper presents time modulated beam steered antenna array without phase shifters. The beam steering is analyzed considering a two-element time modulated antenna array (TMAA) of printed dipoles with microstrip via-hole balun. The proposed array resonates at the Industrial, Scientific, and Medical (ISM) radio bands, 2.45 GHz and 5.8 GHz, and offers wide bandwidth inherited due to modified structure of ground plane. Array elements are excited by complex exponential excitation signal through broadband power divider and radio frequency (RF) switches to achieve amplitude and phase variation without phase shifters. Differential Evolution algorithm is used to modify the time sequences of the RF switches connected to the antennas to generate radiation pattern with optimum dynamic efficiency by suppressing sideband radiations. Also switch-on time instant of RF switch connected to the subsequent element is modulated to steer the beam towards different directions. The proposed prototype is fabricated followed by parametric optimization. The fabrication results agree significantly well with simulated results. Ruchi Gahley and Banani Basu Copyright © 2017 Ruchi Gahley and Banani Basu. All rights reserved. Tensor-Based Methods for Blind Spatial Signature Estimation in Multidimensional Sensor Arrays Wed, 15 Feb 2017 06:39:24 +0000 The estimation of spatial signatures and spatial frequencies is crucial for several practical applications such as radar, sonar, and wireless communications. In this paper, we propose two generalized iterative estimation algorithms to the case in which a multidimensional (-D) sensor array is used at the receiver. The first tensor-based algorithm is an -D blind spatial signature estimator that operates in scenarios where the source’s covariance matrix is nondiagonal and unknown. The second tensor-based algorithm is formulated for the case in which the sources are uncorrelated and exploits the dual-symmetry of the covariance tensor. Additionally, a new tensor-based formulation is proposed for an -shaped array configuration. Simulation results show that our proposed schemes outperform the state-of-the-art matrix-based and tensor-based techniques. Paulo R. B. Gomes, André L. F. de Almeida, João Paulo C. L. da Costa, João C. M. Mota, Daniel Valle de Lima, and Giovanni Del Galdo Copyright © 2017 Paulo R. B. Gomes et al. All rights reserved. Wearable Passive E-Textile UHF RFID Tag Based on a Slotted Patch Antenna with Sewn Ground and Microchip Interconnections Mon, 13 Feb 2017 00:00:00 +0000 We present a wearable passive UHF RFID tag based on a slotted patch antenna comprising only textile materials (e-textile, textile substrate, and conductive yearn). As a novel manufacturing approach, we realize the patch-to-ground and antenna-to-IC interfaces using only conductive thread and a sewing machine. We outline the electromagnetic optimization of the antenna for body-worn operation through simulations and present a performance comparison between the e-textile tag and a tag produced using regular electronics materials and methods. The measured results show that the textile tag achieves the electrical performance required in practical applications and that the slotted patch type antenna provides stable electromagnetic performance in different body-worn configurations. Johanna Virkki, Zhigang Wei, Aruhan Liu, Leena Ukkonen, and Toni Björninen Copyright © 2017 Johanna Virkki et al. All rights reserved. Suppressed Band Characteristics of an UWB Conical Monopole Antenna with Split Loops Based on the Equivalent Circuit Sun, 12 Feb 2017 00:00:00 +0000 In this study, the principle of band suppressing an UWB antenna by attaching a small resonator is explained by developing its equivalent circuit. The realized UWB antenna is a conical monopole antenna that contains a split loop for band suppression. The conical monopole antenna corresponds to a transmission line terminated with load impedance, and the split loop is an LC resonator. The coupling between the conical monopole antenna and the split loop is represented as mutual inductance. Equivalent circuits for the UWB antenna suppressing single band [WLAN] and dual band [WLAN, WiMAX] have been suggested, and these equivalent circuits provide insight into the performance characteristics of the developed band suppressed UWB antenna to which a small sized resonator is installed. Simulation and measurement results on the input impedance and VSWR of the proposed equivalent circuit are closely matched. Thus, the validity of the equivalent circuit is confirmed. The measurement results demonstrate that the proposed antenna exhibits a gain of over 3 dBi in the working band and has an omnidirectional radiation pattern. Band rejection has been also implemented by split loops. Eun-Seok Jang, Che-Young Kim, Dae-Geun Yang, and Sung-Su Hong Copyright © 2017 Eun-Seok Jang et al. All rights reserved. Performance Analysis of Two-Dimensional Maximum Likelihood Direction-of-Arrival Estimation Algorithm Using the UCA Thu, 09 Feb 2017 06:38:28 +0000 We address the performance analysis of the maximum likelihood (ML) direction-of-arrival (DOA) estimation algorithm in the case of azimuth/elevation estimation of two incident signals using the uniform circular array (UCA). Based on the Taylor series expansion and approximation, we get explicit expressions of the root mean square errors (RMSEs) of the azimuths and elevations. The validity of the derived expressions is shown by comparing the analytic results with the simulation results. The derivation in this paper is further verified by illustrating the consistency of the analytic results with the Cramer-Rao lower bound (CRLB). Yun-Seong Cho, Jeong-Min Seo, and Joon-Ho Lee Copyright © 2017 Yun-Seong Cho et al. All rights reserved. Smart Cylindrical Dome Antenna Based on Active Frequency Selective Surface Tue, 07 Feb 2017 06:59:50 +0000 In this paper, we proposed a beamforming antenna, which is realized using an omnidirectional antenna in the center surrounded by a cylindrical smart dome. The smart dome is made of 16 active frequency selective surface columns of which the amplitude and phase response can be continuously tuned by varying the bias voltages of the employed varactors. Thus, the performance of the proposed antenna could achieve higher gain, better nulling level, and more agility than many switch methods-based cylindrical reconfigurable antennas. Moreover, in order to overcome the unavailable analytical synthesis caused by complex mutual coupling between columns, we develop a genetic algorithm based optimization system and conducted a serial of experiments to evaluate the high-gain, nulling, continuously steering, and frequency-invariant ability. The results show that, during the frequency tunable range of the AFSS (2.0 GHz to 2.7 GHz), the antenna can offer an additional gain of up to 6.57 dB and nulling level of −56.41 dBi. For the high-gain modes, the −3 dB beam widths are 26°–34°, which offers enhanced angular resolution compared with other reported beam-sweeping work. Furthermore, the radiation pattern is continuously steerable. Tongyu Ding, Shaoqing Zhang, Liang Zhang, and Yanhui Liu Copyright © 2017 Tongyu Ding et al. All rights reserved. Modelling of Electromagnetic Scattering by a Hypersonic Cone-Like Body in Near Space Tue, 07 Feb 2017 00:00:00 +0000 A numerical procedure for analysis of electromagnetic scattering by a hypersonic cone-like body flying in the near space is presented. First, the fluid dynamics equation is numerically solved to obtain the electron density, colliding frequency, and the air temperature around the body. They are used to calculate the complex relative dielectric constants of the plasma sheath. Then the volume-surface integral equation method is adopted to analyze the scattering properties of the body plus the plasma sheath. The Backscattering Radar Cross-Sections (BRCS) for the body flying at different speeds, attack angles, and elevations are examined. Numerical results show that the BRCS at a frequency higher than 300 MHz is only slightly affected if the speed is smaller than 7 Mach. The BRCS at 1 GHz would be significantly reduced if the speed is greater than 7 Mach and is continuously increased, which can be attributed to the absorption by the lossy plasma sheath. Typically, the BRCS is influenced by 5~10 dBm for a change of attack angle within 0~15 degrees, or for a change of elevation within 30~70 km above the ground. Ji-Wei Qian, Hai-Li Zhang, and Ming-Yao Xia Copyright © 2017 Ji-Wei Qian et al. All rights reserved. KBNN Based on Coarse Mesh to Optimize the EBG Structures Thu, 02 Feb 2017 07:30:40 +0000 The microwave devices are usually optimized by combining the precise model with global optimization algorithm. However, this method is time-consuming. In order to optimize the microwave devices rapidly, the knowledge-based neural network (KBNN) is used in this paper. Usually, the a priori knowledge of KBNN is obtained by the empirical formulas. Unfortunately, it is difficult to derive the corresponding formulas for the most electromagnetic problems, especially for complex electromagnetic problems; the formula derivation is almost impossible. We use precise mesh model of EM analysis as teaching signal and coarse mesh model as a priori knowledge to train the neural network (NN) by particle swarm optimization (PSO). The NN constructed by this method is simpler than traditional NN in structure which can replace precise model in optimization and reduce the computing time. The results of electromagnetic band-gap (EBG) structures optimally designed by this kind of KBNN achieve increase in the bandwidth and attenuation of the stopband and small passband ripple level which shows the advantages of the proposed KBNN method. Yi Chen, Yu-bo Tian, and Fei-yan Sun Copyright © 2017 Yi Chen et al. All rights reserved. Defected Ground Structure: Fundamentals, Analysis, and Applications in Modern Wireless Trends Wed, 01 Feb 2017 00:00:00 +0000 Slots or defects integrated on the ground plane of microwave planar circuits are referred to as Defected Ground Structure. DGS is adopted as an emerging technique for improving the various parameters of microwave circuits, that is, narrow bandwidth, cross-polarization, low gain, and so forth. This paper presents an introduction and evolution of DGS and how DGS is different from former technologies: PBG and EBG. A basic concept behind the DGS technology and several theoretical techniques for analysing the Defected Ground Structure are discussed. Several applications of DGS in the field of filters, planar waveguides, amplifiers, and antennas are presented. Mukesh Kumar Khandelwal, Binod Kumar Kanaujia, and Sachin Kumar Copyright © 2017 Mukesh Kumar Khandelwal et al. All rights reserved. SAR Reduction Using Integration of PIFA and AMC Structure for Pentaband Mobile Terminals Tue, 31 Jan 2017 09:07:57 +0000 In this paper, a capacitive grating artificial magnetic conductor (AMC) is presented to reduce the specific absorption rate (SAR) in pentaband mobile terminals. The AMC structure is implemented using a dielectric film with the printed arrays of the metal strips placed at the top and the bottom of the dielectric. It is difficult to design the AMC structure to operate at low (824~960 MHz) and high bands (1710~2170 MHz) simultaneously, because of the limited space available for the antenna. Hence, we have designed the capacitive grating AMC to operate at a high band. Then, we attached a PIFA to the AMC structure to cover low and high bands. As the AMC structure is operated as a perfect electric conductor (PEC) in low band, the radiating branches of the PIFA for the low and high bands should be located on the non-AMC and the AMC structures, respectively. Even though the AMC structure is operated at a high band, the effect against the head could be reduced in the pentaband due to the spreading effect of the electromagnetic (EM) field at lower bands. From measured results, the 1 g SAR in the case of the AMC antenna is significantly lower than that in the case where only the PIFA is present in the pentaband. Jae-Gon Lee and Jeong-Hae Lee Copyright © 2017 Jae-Gon Lee and Jeong-Hae Lee. All rights reserved. Cascaded Multitype Interferences Suppression Method Using Sparse Representation and Array Processing for GNSS Receiver Mon, 30 Jan 2017 00:00:00 +0000 Interference suppression techniques have been intensively studied in nearly two decades due to their importance for maintaining the integrity and functionality of global navigation satellite system (GNSS). However, the interference suppression method applicable for the complex receiving environment in which there are multitype interfering signals has not been considered in most of the researches. To deal with this problem better, a cascaded multitype interferences suppression method using sparse representation and array processing is proposed. In the first stage, according to the sparsity of the narrowband and modulated wideband interference signals, a novel parallel multichannel signal interference suppression method based on matching pursuit (MP) algorithm and a design strategy for the overcomplete dictionary are proposed to mitigate the interferences with sparse features. Then, the minimum power distortionless response (MPDR) beamformer is employed in the second stage to suppress the residuary interferences (such as Gaussian noise interferences). Compared with existing algorithms, the proposed method can not only effectively suppress the interference arriving from the same direction with the desired signal and increase the Degree of Freedom (DoF) of the array antenna, but also introduce no distortion into the navigation signal. The effectiveness of the proposed method is illustrated by theoretical analysis and several simulation results. Qiang Guo and Liangang Qi Copyright © 2017 Qiang Guo and Liangang Qi. All rights reserved. Propagation Analysis for Wireless Sensor Networks Applied to Viticulture Mon, 30 Jan 2017 00:00:00 +0000 Wireless sensor networks have been proposed as a solution to obtain soil and environment information in large distributed areas. The main economic activity of the São Francisco Valley region in the Northeast of Brazil is the irrigated fruit production. The region is one of the major agricultural regions of the country. Grape plantations receive large investments and provide good financial return. However, the region still lacks electronic sensing systems to extract adequate information from plantations. Considering these facts, this paper presents a study of path loss in grape plantations for a 2.4 GHz operating frequency. In order to determine the position of the sensor nodes, the research dealt with various environmental factors that influence the intensity of the received signal. It has been noticed that main plantation aisles favor the guided propagation, and the vegetation along the secondary plantation aisles compromises the propagation. Diffraction over the grape trees is the main propagation mechanism in the diagonal propagation path. Transmission carried out above the vineyard showed that reflection on the top of the trees is the main mechanism. Felipe Pinheiro Correia, Marcelo Sampaio de Alencar, Waslon Terllizzie Araújo Lopes, Mauro Soares de Assis, and Brauliro Gonçalves Leal Copyright © 2017 Felipe Pinheiro Correia et al. All rights reserved. A Frequency-Tracking and Impedance-Matching Combined System for Robust Wireless Power Transfer Sun, 29 Jan 2017 00:00:00 +0000 One of the greatest challenges to power embedded devices using magnetically coupled resonant wireless power transfer (WPT) system is that the amount of power delivered to the load is very sensitive to load impedance variations. Previous adaptive impedance-matching (IM) technologies have drawbacks because adding IM networks, relay coils, or other compensating components in the receiver-side will significantly increase the receiver size. In this paper, a novel frequency-tracking and impedance-matching combined system is proposed to improve the robustness of wireless power transfer for embedded devices. The characteristics of the improved WPT system are investigated theoretically based on the two-port network model. Simulation and experimental studies are carried out to validate the proposed system. The results suggest that the frequency-tracking and impedance-matching combined WPT system can quickly find the best matching points and maintain high power transmission efficiency and output power when the load impedance changes. Yanting Luo, Yongmin Yang, Suiyu Chen, and Xisen Wen Copyright © 2017 Yanting Luo et al. All rights reserved. Design of a Microstrip Series Power Divider for Sequentially Rotated Nonuniform Antenna Array Thu, 26 Jan 2017 07:07:20 +0000 This paper deals with the design of a microstrip series power divider for circularly polarized sequential rotational antenna array. The theoretical description of the design is firstly proposed, comprising the cases of nonuniform weighted antenna arrays. A more flexible open octagon shape instead of the classical open ring is suggested, highlighting benefits in the case of nonuniform power distribution. A design example of an ultra-high frequency (UHF) band sequentially rotated Tschebischeff antenna array finally demonstrates the effectiveness of the proposed implementation. Daniele Inserra, Wei Hu, and Guangjun Wen Copyright © 2017 Daniele Inserra et al. All rights reserved. Compact Dual-Band Coupler for Vehicular Beam-Forming Array Wed, 18 Jan 2017 07:50:53 +0000 A novel kind of compact dual-band quadrature patch coupler for vehicular beam-forming array is proposed for the first time in this paper. To keep the performance of the first operating frequency 2.4 GHz (for Bluetooth Low Energy (BLE)) and generate the second operating frequency 5.9 GHz (for Dedicated Short Range Communications (DSRC)) simultaneously, complementary triangular split resonant rings (CTSRRs) and splitting gaps are employed to improve the performance of this new coupler; final size of the proposed coupler is (for 2.4 GHz). To validate the performance and design method of the coupler this paper proposed, a 3D model is constructed and optimized with ANSOFT HFSS firstly and then a coupler prototype is fabricated and measured. The measured results show that the amplitude unbalance (AU) is 0.54 dB and 0.44 dB for 2.4 GHz and 5.9 GHz, respectively, and the corresponding phase unbalance (PU) is 93.5 and 92 degrees, respectively. Dakui Wu and Guoxin Zheng Copyright © 2017 Dakui Wu and Guoxin Zheng. All rights reserved. Two-Dimensional AOA Estimation Based on a Constant Modulus Algorithm Wed, 18 Jan 2017 00:00:00 +0000 We propose a two-dimensional (2D) angle of arrival (AOA) estimator using the algebraic constant modulus algorithm (ACMA). This algorithm was originally introduced to estimate the one-dimensional (1D) AOA. An extension to estimate and automatically pair the elevation and azimuth angles for different sources is derived and proved in this paper. The ACMA method factorises a matrix into two different matrices; one is of constant modulus and contains the azimuth AOA information; however the second was previously ignored. In this paper we will prove that this second matrix contains the elevation AOA information. Thus, 2D AOA estimation is proved possible using the ACMA method. Simulation results are presented to illustrate the proposed method’s performances under different conditions. Saleh O. Al-Jazzar, Zoubir Hamici, and Sami Aldalahmeh Copyright © 2017 Saleh O. Al-Jazzar et al. All rights reserved. Path Loss Channel Model for Inland River Radio Propagation at 1.4 GHz Mon, 16 Jan 2017 08:04:40 +0000 In this paper, a propagation path loss model for inland river is proposed by three improvements compared with the Round Earth Loss (REL) model for open-sea environment. Specifically, parameters optimization uses Okumura-Hata model in dB scale to replace the equation transformed from the free space loss in REL model; secondly, diffraction loss caused by the obstacles (e.g., large buildings, bridges, or some other facilities near the river bank) is also taken into account; mixed-path methodology as another improvement is used for Inland River (IR) model because the actual propagation environment between transmitter (TX) antenna and receiver (RX) antenna contains both land part and water part. The paper presents a set of 1.4 GHz measurements conducted along the Yangtze River in Wuhan. According to the comparison between path loss models and experimental results, IR model shows a good matching degree. After that, Root Mean Square Error (RMSE), Grey Relation Grade and Mean Absolute Percentage Error (GRG-MAPE), Pearson Correlation Coefficient, and Mean Absolute Percentage Error (PCC-MAPE) are employed to implement quantitative analysis. The results prove that IR model with consideration of mixed path and deterministic information is more accurate than other classic empirical propagation models for these scenarios. Junyi Yu, Wei Chen, Kun Yang, Changzhen Li, Fang Li, and Yishui Shui Copyright © 2017 Junyi Yu et al. All rights reserved. Improved QRD-M Detection Algorithm for Generalized Spatial Modulation Scheme Mon, 16 Jan 2017 00:00:00 +0000 Generalized spatial modulation (GSM) is a spectral and energy efficient multiple-input multiple-output (MIMO) transmission scheme. It will lead to imperfect detection performance with relatively high computational complexity by directly applying the original QR-decomposition with M algorithm (QRD-M) to the GSM scheme. In this paper an improved QRD-M algorithm is proposed for GSM signal detection, which achieves near-optimal performance but with relatively low complexity. Based on the QRD, the improved algorithm firstly transforms the maximum likelihood (ML) detection of the GSM signals into searching an inverted tree structure. Then, in the searching process of the branches, the branches corresponding to the illegitimate transmit antenna combinations (TACs) and related to invalid number of active antennas are cut in order to improve the validity of the resultant branches at each level by taking advantage of characteristics of GSM signals. Simulation results show that the improved QRD-M detection algorithm provides similar performance to maximum likelihood (ML) with the reduced computational complexity compared to the original QRD-M algorithm, and the optimal value of parameter of the improved QRD-M algorithm for detection of the GSM scheme is equal to modulation order plus one. Xiaorong Jing, Mingyue Wang, Wei Zhou, and Hongqing Liu Copyright © 2017 Xiaorong Jing et al. All rights reserved. Miniature Coplanar Implantable Antenna on Thin and Flexible Platform for Fully Wireless Intracranial Pressure Monitoring System Tue, 10 Jan 2017 10:35:25 +0000 Minimally invasive approach to intracranial pressure monitoring is desired for long-term diagnostics. The monitored pressure is transmitted outside the skull through an implant antenna. We present a new miniature (6 mm × 5 mm) coplanar implant antenna and its integration on a sensor platform to establish a far-field data link for the sensor readout at distances of 0.5 to 1 meter. The implant antenna was developed using full-wave electromagnetic simulator and measured in a liquid phantom mimicking the dielectric properties of the human head. It achieved impedance reflection coefficient better than −10 dB from 2.38 GHz to 2.54 GHz which covers the targeted industrial, scientific, and medical band. Experiments resulted in an acceptable peak gain of approximately −23 dBi. The implant antenna was submerged in the liquid phantom and interfaced to a 0.5 mW voltage controlled oscillator. To verify the implant antenna performance as a part of the ICP monitoring system, we recorded the radiated signal strength using a spectrum analyzer. Using a half-wavelength dipole as the receiving antenna, we captured approximately −58.7 dBm signal at a distance of 1 m from the implant antenna which is well above for the reader with sensitivity of −80 dBm. M. Waqas A. Khan, Elham Moradi, Lauri Sydänheimo, Toni Björninen, Yahya Rahmat-Samii, and Leena Ukkonen Copyright © 2017 M. Waqas A. Khan et al. All rights reserved.