International Journal of Antennas and Propagation http://www.hindawi.com The latest articles from Hindawi Publishing Corporation © 2014 , Hindawi Publishing Corporation . All rights reserved. Low-Power Optically Controlled Patch Antenna of Reconfigurable Beams Thu, 28 Aug 2014 09:45:41 +0000 http://www.hindawi.com/journals/ijap/2014/978258/ A novel compact beam-reconfigurable patch antenna based on light control of no more than 30 mW optical powers is successfully demonstrated. It consists of one T-shape driven patch and one slot-etched parasitic patch. A silicon dice is employed as the photoconductive switch that is bridged across the slot center for optical control of reconfigurable beams. The antenna greatly reduces the total optical powers required for reconfigurable beams. Such design is based on the fact that the current phase change of the parasitic patch is sensitive to the conductivity of the silicon dice. A few conductivity changes of the silicon dice induced by the optical light can lead to a big phase change of the parasitic patch currents, eventually resulting in reconfigurable beams with low optical power requirement. Deshuang Zhao, Yifei Han, Feng Liang, Qiaoli Zhang, and Bing-Zhong Wang Copyright © 2014 Deshuang Zhao et al. All rights reserved. Probing Electric Field in an Enclosed Field Mapper for Characterizing Metamaterials Wed, 27 Aug 2014 11:50:56 +0000 http://www.hindawi.com/journals/ijap/2014/728756/ Spatially mapping electromagnetic fields in the quasi-two-dimensional field mapper (a parallel plate waveguiding system; Justice et al. (2006)) for characterizing metamaterial devices, especially those integrating the metal boundary, may encounter troubles including electromagnetic leakage caused by the air gap and energy guiding along finitely high metal walls. To eradicate them, a moving contact approach is proposed. The physical air gap between the mobile metal walls and the stationary upper plate of the mapper is closed, while their relative movement is still allowed during the field mapping. We demonstrate the method of closing the gap by mapping the E-field distribution in a rectangular waveguide. Sucheng Li, Chendong Gu, Yadong Xu, Shahzad Anwar, Weixin Lu, Zhi Hong Hang, Bo Hou, and Huanyang Chen Copyright © 2014 Sucheng Li et al. All rights reserved. Low SAR, Simple Printed Compact Multiband Antenna for Mobile and Wireless Communication Applications Wed, 27 Aug 2014 11:26:23 +0000 http://www.hindawi.com/journals/ijap/2014/946781/ Simple multiband planar antenna for wireless communication applications is presented. The proposed antenna performs four resonant modes covering multibands of wireless standards, including LTE 700, GSM, DCS, PCS, UMTS, and LTE 2300/2500. Furthermore, it covers the ISM, WiMAX, and the WLAN bands. The geometry of the proposed antenna consists of a single FR4 substrate where an open cavity fed by a coplanar U-shaped monopole is etched on one side and a short-circuited meander line in the opposite side. The cavity by its nature supports a wide range of higher frequencies, while its boundary that consists of a thin monopole resonates at 900 MHz. The meander line in the opposite side supports the LTE 700 band. The operating bands ranges are (680–748 MHz), (870–960 MHZ), (1.36–1.59 GHz), and (1.71–2.56 GHz). The antenna size is 30 × 18 × 0.8 mm3. The antenna not only has a compact size but also supports a low SAR radiation at all the operating frequencies. The proposed antenna is tested using the four recommended test positions of the CTIA association where the proposed antenna reveals good performance in all test cases in the presence of handset (keypad, battery, speaker camera, RF circuit, and LCD) in talking position, and in standby position. K. S. Sultan, H. H. Abdullah, and E. A. Abdallah Copyright © 2014 K. S. Sultan et al. All rights reserved. Dual-Feed Small-Size Penta-Band PIFA for LTE/WWAN Mobile Handset Applications Wed, 27 Aug 2014 05:43:51 +0000 http://www.hindawi.com/journals/ijap/2014/104614/ A dual-feed small-size penta-band PIFA for LTE/WWAN mobile handset applications is presented. The proposed PIFA is composed of a simple U-shaped patch with dual-shorting pins connected to the ground plane. The patch, having a low profile of 5 mm, has dimensions of about 10 × 35 mm2. The antenna is excited at one arm of the U-shaped radiating patch to cover the higher band of GSM1800/1900/UMTS2100/LTE2300/2500, while it is excited at the other arm to realize the GSM900. In this way, the proposed PIFA achieves enhanced bandwidth coverage with no increased dimensions and additional active switches. In addition, the matching networks, employed on both feeds, ensure a high electrical insulation between the low and the high frequency bands, covered by the antenna. The measured antenna efficiency is 45%~50% and over 60% for the lower band and the higher band, respectively. A prototype of the proposed PIFA with dual-feed and dual-shorting pins was fabricated. The measured results including reflection coefficients and radiation characteristics are presented. Mingyang Liu and Bin Zhao Copyright © 2014 Mingyang Liu and Bin Zhao. All rights reserved. Novel Cross-Type Network for Wide-Tuning-Range Reconfigurable Multiband Antennas Tue, 26 Aug 2014 13:02:53 +0000 http://www.hindawi.com/journals/ijap/2014/741960/ This paper presents a cross-type network design with a novel reconfigurable functionality to realize a tunable multiband antenna. By attaching a reconfigurable network at the feeding port of a broadband antenna, multi-input impedance adjustment enables the production of multimatching operating bands. Each band can be independently controlled by a single component with a considerably wide tuning range and high selectivity. The experiments in this study involved using an ultra-wideband (UWB) antenna connected to the proposed cross-type network. The tunable antenna operates in a dual band of (1.39 to 2.34 GHz) and (2.1 to 3.6 GHz) with tunable frequency ratios of 168% and 132%, respectively. The average bandwidths at and are approximately 50 MHz and 148 MHz, respectively, implying narrowband operation. The measured radiation pattern revealed that the tunable antenna exhibits a nearly omnidirectional radiation pattern at both 1.8 and 3.5 GHz. The network circuit architecture can be extended to the multiband function type by adopting this matching approach. The amount of shunt matches determines the number of operation bands. Chieh-Sen Lee, Chi-Lin Tsai, and Chin-Lung Yang Copyright © 2014 Chieh-Sen Lee et al. All rights reserved. Antenna Miniaturization with MEMS Tunable Capacitors: Techniques and Trade-Offs Wed, 20 Aug 2014 06:54:39 +0000 http://www.hindawi.com/journals/ijap/2014/709580/ In today’s mobile device market, there is a strong need for efficient antenna miniaturization. Tunable antennas are a very promising way to reduce antenna volume while enlarging its operating bandwidth. MEMS tunable capacitors are state-of-the-art in terms of insertion loss. Their characteristics are used in this investigation. This paper uses field simulations to highlight the trade-offs between the design of the tuner and the design of the antenna, especially the impact of the location of the tuner and the degree of miniaturization. Codesigning the tuner and the antenna is essential to optimize radiated performance. Samantha Caporal Del Barrio, Art Morris, and Gert F. Pedersen Copyright © 2014 Samantha Caporal Del Barrio et al. All rights reserved. On the Bivariate Nakagami-Lognormal Distribution and Its Correlation Properties Mon, 18 Aug 2014 06:59:00 +0000 http://www.hindawi.com/journals/ijap/2014/328732/ The bivariate Nakagami-lognormal distribution used to model the composite fast fading and shadowing has been examined exhaustively. In particular, we have derived the joint probability density function, the cross-moments, and the correlation coefficient in power terms. Also, two procedures to generate two correlated Nakagami-lognormal random variables are described. These procedures can be used to evaluate the robustness of the sample correlation coefficient distribution in both macro- and microdiversity scenarios. It is shown that the bias and the standard deviation of this sample correlation coefficient are substantially high for large shadowing standard deviations found in wireless communication measurements, even if the number of observations is considerable. Juan Reig, Lorenzo Rubio, and Vicent M. Rodrigo-Peñarrocha Copyright © 2014 Juan Reig et al. All rights reserved. Measurement-Based LoS/NLoS Channel Modeling for Hot-Spot Urban Scenarios in UMTS Networks Sun, 17 Aug 2014 12:21:59 +0000 http://www.hindawi.com/journals/ijap/2014/454976/ A measurement campaign is introduced for modeling radio channels with either line-of-sight (LoS) or non-line-of-sight (NLoS) connection between user equipment (UE) and NodeB (NB) in an operating universal mobile telecommunications system. A space-alternating generalized expectation-maximization (SAGE) algorithm is applied to estimate the delays and the complex attenuations of multipath components from the obtained channel impulse responses. Based on a novel LoS detection method of multipath parameter estimates, channels are classified into LoS and NLoS categories. Deterministic models which are named “channel maps” and fading statistical models have been constructed for LoS and NLoS, respectively. In addition, statistics of new parameters, such as the distance between the NB and the UE in LoS/NLoS scenarios, the life-distance of LoS channel, the LoS existence probability per location and per NB, the power variation at LoS to NLoS transition and vice versa, and the transition duration, are extracted. These models are applicable for designing and performance evaluation of transmission techniques or systems used by distinguishing the LoS and NLoS channels. Jiajing Chen, Xuefeng Yin, Li Tian, Nan Zhang, Yongyu He, Xiang Cheng, Weiming Duan, and Silvia Ruiz Boqué Copyright © 2014 Jiajing Chen et al. All rights reserved. Application of Hybrid Finite Element-Boundary Integral Algorithm for Solving Electromagnetic Scattering from Multiple Objects over Rough Sea Surface Wed, 13 Aug 2014 11:39:25 +0000 http://www.hindawi.com/journals/ijap/2014/301934/ A hybrid algorithm of the finite element method (FEM) is presented to solve two-dimensional (2D) scattering from multiple dielectric objects above the rough sea surface. Compared with traditional FEM based on approximate absorbing boundaries, FEM based on the boundary integral method (BIM) can reduce the calculational region and solution time of the scattering problem. In the hybrid method, the whole computational region is divided into the sea surface and multiple isolate interior regions for the dielectric objects. FEM is only used to simulate the scattering from multiple interior regions enclosing the objects, whereas the large sea is considered exactly by BIM. The coupled interaction among the isolate interior regions and the sea can be taken into account by BIM. The hybrid technique presented here is efficient and versatile for addressing scattering from multiple arbitrary targets above rough sea surfaces. Scattering properties of multiple dielectric objects above the sea surface under different conditions are discussed in detail. Run-Wen Xu and Li-Xin Guo Copyright © 2014 Run-Wen Xu and Li-Xin Guo. All rights reserved. Advanced MIMO Techniques in the Heterogeneous Networks Tue, 12 Aug 2014 13:08:35 +0000 http://www.hindawi.com/journals/ijap/2014/193954/ Xiang Zhang, Lin Zhang, Guangyue Lu, Xiaoli Chu, and Yulong Zou Copyright © 2014 Xiang Zhang et al. All rights reserved. Knowledge-Aided STAP Using Low Rank and Geometry Properties Tue, 12 Aug 2014 12:40:55 +0000 http://www.hindawi.com/journals/ijap/2014/196507/ This paper presents knowledge-aided space-time adaptive processing (KA-STAP) algorithms that exploit the low-rank dominant clutter and the array geometry properties (LRGP) for airborne radar applications. The core idea is to exploit the clutter subspace that is only determined by the space-time steering vectors, by employing the Gram-Schmidt orthogonalization approach to compute the clutter subspace. Simulation results illustrate the effectiveness of our proposed algorithms. Zhaocheng Yang, Rodrigo C. de Lamare, Xiang Li, and Hongqiang Wang Copyright © 2014 Zhaocheng Yang et al. All rights reserved. Graph-Based Resource Allocation for D2D Communications Underlying Cellular Networks in Multiuser Scenario Tue, 12 Aug 2014 11:41:20 +0000 http://www.hindawi.com/journals/ijap/2014/783631/ With the characteristics of considerable user equipment, massive traffic and numerous local services, but limited frequency resources, the mobile communications in the future require efficient use of frequency resources. Device-to-device (D2D) communications underlying cellular networks have been considered as a promising solution to improve the resources utilization in local scenario. In this paper, we investigated the resources allocation problem in multiuser scenario and proposed a graph-based resources allocation scheme which can achieve suboptimal performance but with low computational complexity and less feedback information. Bin Guo, Shaohui Sun, and Qiubin Gao Copyright © 2014 Bin Guo et al. All rights reserved. Joint Two-Dimensional Ambiguity Resolving Based on Space-Time Filtering for MIMO-SAR Tue, 12 Aug 2014 10:54:54 +0000 http://www.hindawi.com/journals/ijap/2014/452141/ In order to resolve the range and azimuth ambiguity in MIMO-SAR imaging, this paper proposed a joint two-dimensional ambiguity resolving method based on space-time filtering, which according to the ambiguity in different subscene is relative to different nearest echo range, and different azimuth time is relative to different instantaneous incidence angle, to make two-dimensional space-time steering vector for resolving ambiguity of the echo, which also can finish the imaging processing at the same time. Simulation results validate the proposed processing approach for the MIMO-SAR system. Ping-ping Huang, Hua-sheng Li, Sheng Zhang, and Guang-Cai Sun Copyright © 2014 Ping-ping Huang et al. All rights reserved. The Radiation Problem from a Vertical Hertzian Dipole Antenna above Flat and Lossy Ground: Novel Formulation in the Spectral Domain with Closed-Form Analytical Solution in the High Frequency Regime Tue, 12 Aug 2014 09:45:22 +0000 http://www.hindawi.com/journals/ijap/2014/989348/ We consider the problem of radiation from a vertical short (Hertzian) dipole above flat lossy ground, which represents the well-known “Sommerfeld radiation problem” in the literature. The problem is formulated in a novel spectral domain approach, and by inverse three-dimensional Fourier transformation the expressions for the received electric and magnetic (EM) field in the physical space are derived as one-dimensional integrals over the radial component of wavevector, in cylindrical coordinates. This formulation appears to have inherent advantages over the classical formulation by Sommerfeld, performed in the spatial domain, since it avoids the use of the so-called Hertz potential and its subsequent differentiation for the calculation of the received EM field. Subsequent use of the stationary phase method in the high frequency regime yields closed-form analytical solutions for the received EM field vectors, which coincide with the corresponding reflected EM field originating from the image point. In this way, we conclude that the so-called “space wave” in the literature represents the total solution of the Sommerfeld problem in the high frequency regime, in which case the surface wave can be ignored. Finally, numerical results are presented, in comparison with corresponding numerical results based on Norton’s solution of the problem. K. Ioannidi, Ch. Christakis, S. Sautbekov, P. Frangos, and S. K. Atanov Copyright © 2014 K. Ioannidi et al. All rights reserved. Network-Coded Relaying in Multiuser Multicast D2D Network Tue, 12 Aug 2014 08:58:27 +0000 http://www.hindawi.com/journals/ijap/2014/589794/ D2D communication trades short-range communication for achieving high communication rate and short communication latency. Relay aided D2D communication can further tackle the problem of intermediate obstacles blocking the communication. In this work, multidevice multicast communication via a layer of parallel relay nodes is considered. Two relaying strategies, respectively, called the conventional relaying (CR) and network-coded relaying (NCR), are proposed. The throughput of these two schemes is analytically derived and evaluated through numerical study. Theoretically, NCR shows advantage over CR in twofold: one is higher throughput and the other is requiring less relay nodes and, hence, consuming less aggregate power. Numerical studies verify the analysis and show that the throughput performance gap between the two schemes increases significantly, actually exponentially with the number of devices. Mingjun Dai, Shengli Zhang, Hui Wang, Bin Chen, Xiaohui Lin, Hongwei Liu, and Li Zhang Copyright © 2014 Mingjun Dai et al. All rights reserved. Near-Field to Far-Field Transformation Techniques with Spiral Scannings: A Comprehensive Review Sun, 10 Aug 2014 00:00:00 +0000 http://www.hindawi.com/journals/ijap/2014/143084/ An overview of the near-field-far-field (NF-FF) transformation techniques with innovative spiral scannings, useful to derive the radiation patterns of the antennas commonly employed in the modern wireless communication systems, is provided in this paper. The theoretical background and the development of a unified theory of the spiral scannings for quasi-spherical and nonspherical antennas are described, and an optimal sampling interpolation expansion to evaluate the probe response on a quite arbitrary rotational surface from a nonredundant number of its samples, collected along a proper spiral wrapping it, is presented. This unified theory can be applied to spirals wrapping the conventional scanning surfaces and makes it possible to accurately reconstruct the NF data required by the NF-FF transformation employing the corresponding classical scanning. A remarkable reduction of the measurement time is so achieved, due to the use of continuous and synchronized movements of the positioning systems and to the reduced number of needed NF measurements. Some numerical and experimental results relevant to the spherical spiral scanning case when dealing with quasi-planar and electrically long antennas are shown. Renato Cicchetti, Francesco D’Agostino, Flaminio Ferrara, Claudio Gennarelli, Rocco Guerriero, and Massimo Migliozzi Copyright © 2014 Renato Cicchetti et al. All rights reserved. Fading Evaluation in the 60 GHz Band in Line-of-Sight Conditions Thu, 07 Aug 2014 10:55:03 +0000 http://www.hindawi.com/journals/ijap/2014/984102/ An exhaustive analysis of the small-scale fading amplitude in the 60 GHz band is addressed for line-of-sight conditions (LOS). From a measurement campaign carried out in a laboratory, we have estimated the distribution of the small-scale fading amplitude over a bandwidth of 9 GHz. From the measured data, we have estimated the parameters of the Rayleigh, Rice, Nakagami-m, Weibull, and - distributions for the small-scale amplitudes. The test of Kolmogorov-Smirnov (K-S) for each frequency bin is used to evaluate the performance of such statistical distributions. Moreover, the distributions of the main estimated parameters for such distributions are calculated and approximated for lognormal statistics in some cases. The matching of the above distributions to the experimental distribution has also been analyzed for the lower tail of the cumulative distribution function (CDF). These parameters offer information about the narrowband channel behavior that is useful for a better knowledge of the propagation characteristics at 60 GHz. J. Reig, M.-T. Martínez-Inglés, L. Rubio, V.-M. Rodrigo-Peñarrocha, and J.-M. Molina-García-Pardo Copyright © 2014 J. Reig et al. All rights reserved. Rigorous 2D Model for Study of Pulsed and Monochromatic Waves Propagation Near the Earth’s Surface Thu, 07 Aug 2014 00:00:00 +0000 http://www.hindawi.com/journals/ijap/2014/158297/ A model problem considered in the paper allows solving rather complex 2D problems of the electromagnetic wave propagation with a required accuracy using conventional personal computers. The problems are of great importance for the theory and practical applications. The association of FDTD schemes with exact absorbing conditions makes up the basis for constructing models of the kind. This approach reduces the original open initial boundary value problems to the equivalent closed problems which can be solved numerically using the standard grid methods. Seil S. Sautbekov, Yuriy K. Sirenko, Nataliya P. Yashina, and Aleksey A. Vertiy Copyright © 2014 Seil S. Sautbekov et al. All rights reserved. Low-Complexity Transmit Antenna Selection and Beamforming for Large-Scale MIMO Communications Wed, 06 Aug 2014 07:45:20 +0000 http://www.hindawi.com/journals/ijap/2014/159375/ Transmit antenna selection plays an important role in large-scale multiple-input multiple-output (MIMO) communications, but optimal large-scale MIMO antenna selection is a technical challenge. Exhaustive search is often employed in antenna selection, but it cannot be efficiently implemented in large-scale MIMO communication systems due to its prohibitive high computation complexity. This paper proposes a low-complexity interactive multiple-parameter optimization method for joint transmit antenna selection and beamforming in large-scale MIMO communication systems. The objective is to jointly maximize the channel outrage capacity and signal-to-noise (SNR) performance and minimize the mean square error in transmit antenna selection and minimum variance distortionless response (MVDR) beamforming without exhaustive search. The effectiveness of all the proposed methods is verified by extensive simulation results. It is shown that the required antenna selection processing time of the proposed method does not increase along with the increase of selected antennas, but the computation complexity of conventional exhaustive search method will significantly increase when large-scale antennas are employed in the system. This is particularly useful in antenna selection for large-scale MIMO communication systems. Kun Qian, Wen-Qin Wang, and Huaizong Shao Copyright © 2014 Kun Qian et al. All rights reserved. Indoor Massive MIMO Channel Modelling Using Ray-Launching Simulation Wed, 06 Aug 2014 07:42:58 +0000 http://www.hindawi.com/journals/ijap/2014/279380/ Massive multi-input multioutput (MIMO) is a promising technique for the next generation of wireless communication networks. In this paper, we focus on using the ray-launching based channel simulation to model massive MIMO channels. We propose one deterministic model and one statistical model for indoor massive MIMO channels, both based on ray-launching simulation. We further propose a simplified version for each model to improve computational efficiency. We simulate the models in indoor wireless network deployment environments and compare the simulation results with measurements. Analysis and comparison show that these ray-launching based simulation models are efficient and accurate for massive MIMO channel modelling, especially with application to indoor network planning and optimisation. Jialai Weng, Xiaoming Tu, Zhihua Lai, Sana Salous, and Jie Zhang Copyright © 2014 Jialai Weng et al. All rights reserved. A Fully Reconfigurable Polarimetric Phased Array Antenna Testbed Wed, 06 Aug 2014 05:50:08 +0000 http://www.hindawi.com/journals/ijap/2014/439606/ The configurable phased array demonstrator (CPAD) is a low-cost, reconfigurable, small-scale testbed for the dual-polarized array antenna and radar prototype. It is based on the concept that individual transmit and receive (TR) modules and radiating elements can be configured in different ways to study the impact of various array manifolds on radiation pattern performance. For example, CPAD is configured as (a) a 4 × 4 planar array, (b) a planar array with mirror configuration, and (c) a circular array to support the multifunctional phased array radar (MPAR) system risk reduction studies. System descriptions are given in detail, and measurements are made and results are analyzed. Sudantha Perera, Yu Pan, Yan Zhang, Xining Yu, Dusan Zrnic, and Richard Doviak Copyright © 2014 Sudantha Perera et al. All rights reserved. Rateless Space Time Block Code for Massive MIMO Systems Sun, 03 Aug 2014 06:33:36 +0000 http://www.hindawi.com/journals/ijap/2014/154261/ This paper presents a rateless space time block code (RSTBC) for massive MIMO systems. The paper illustrates the basis of rateless space time codes deployments in massive MIMO transmissions over wireless erasure channels. In such channels, data may be lost or is not decodable at the receiver due to a variety of factors such as channel fading, interference, or antenna element failure. We show that RSTBC guarantees the reliability of the system in such cases, even when the data loss rate is 25% or more. In such a highly lossy channel, the conventional fixed-rate codes fail to perform well, particularly when channel state information is not available at the transmitter. Simulation results are provided to demonstrate the BER performance and the spectral efficiency of the proposed scheme. Ali H. Alqahtani, Ahmed Iyanda Sulyman, and Abdulhameed Alsanie Copyright © 2014 Ali H. Alqahtani et al. All rights reserved. Capacity of κ-μ Shadowed Fading Channels Thu, 24 Jul 2014 12:07:05 +0000 http://www.hindawi.com/journals/ijap/2014/975109/ The ergodic capacity of fading channels modeled with a κ-μ shadowed distribution is investigated to derive closed-form expressions. The κ-μ shadowed distribution is of particular interest because it contains, as special cases, other classical ones like one-side Gaussian, Rayleigh, Rician, Nakagami-m, κ-μ, and Rician shadowed distributions. The paper discusses the physical meaning of the distribution parameter variations and also their impact on the channel capacity. These results can be used to study the behavior of different channels like the ones in underwater acoustic communications, land mobile satellite systems, body centric communications, and other wireless communication applications. The analytical closed-form expression results are validated with numerical simulations. Celia García-Corrales, Francisco J. Cañete, and José F. Paris Copyright © 2014 Celia García-Corrales et al. All rights reserved. Technique of Coaxial Frame in Reflection for the Characterization of Single and Multilayer Materials with Correction of Air Gap Thu, 24 Jul 2014 09:22:08 +0000 http://www.hindawi.com/journals/ijap/2014/324727/ Techniques based on fixture probes in reflection are used in microwave reflectometry as a novel diagnostic tool for detection of skin cancers, for complex permittivity measurements on liquid samples and oil shale, and for complex dielectric permittivity of animals’ organs and tissues measurements in microwave band for the needs of modern veterinary medicine. In this work, we have developed a technique to characterize multilayer materials in a broadband frequency range. A coaxial probe in reflection has been specially developed for microelectronic substrate. Using SMA connector, loss tangent of 10−4 and relative permittivity have been measured with an error of 0.145%. The extension of the coaxial probe in reflection technique to multilayer substrates such as Delrin and Teflon permitted to measure bilayer material provided the good knowledge of electrical parameters and dimensions of one layer. In the coaxial transmission line method, a factor that greatly influences the accuracy of the results is the air gaps between the material under test and the coaxial test fixture. In this paper, we have discussed the influence of the air gaps (using samples of 0.5 mm air gaps) and the measures that can be taken to minimize that influence when material is measured. The intrinsic values thus determined have been experimentally verified. We have described the structure of the test fixture, its calibration issues, and the experimental results. Finally, electromagnetism simulations showed that the best results can be obtained. Zarral Lamia, Djahli Farid, and Ndagijimana Fabien Copyright © 2014 Zarral Lamia et al. All rights reserved. A Passive Harmonic Tag for Humidity Sensing Wed, 23 Jul 2014 11:01:02 +0000 http://www.hindawi.com/journals/ijap/2014/670345/ This paper describes a passive harmonic tag for radio frequency identification (RFID) and wireless sensor applications. The tag uses a dual polarized UHF patch antenna as an input antenna. One of the outputs is connected to a frequency doubler, which consists of a Schottky diode with its output connected to a patch tuned at twice the input frequency. The other output of the input antenna feeds a DC power harvested converter that drives an oscillator which modulates its output signal by controlling the bias point of the Schottky diode. The antenna’s output is also used as a humidity sensor. To achieve this, the antenna is loaded with an interdigital capacitor with humidity-dependent capacitance. The antenna is consequently detuned when humidity varies, and therefore the second harmonic power is received. The tag is manufactured using standard fiberglass substrate. The basic theory of harmonic tag operation is described and compared with the standard backscattering approach. Experimental results with a proof of concept using commercial components are presented. Antonio Lazaro, Ramon Villarino, and David Girbau Copyright © 2014 Antonio Lazaro et al. All rights reserved. Capacity Estimation of the Very Short-Range Electromagnetic Underwater Channel Based on Measurements Tue, 22 Jul 2014 14:08:28 +0000 http://www.hindawi.com/journals/ijap/2014/318421/ The significant attenuation experienced by electromagnetic waves in sea water is the main reason why acoustic waves are generally preferred in underwater communication. Nevertheless, acoustic waves have various drawbacks. For example, they are negatively affected by factors such as mechanical noise, slow propagation speed, and, particularly, low bandwidth, which leads to digital links at a lower bit rate. However, in short-range links, these problems can be overcome by reconsidering the use of electric current communications. For instance, data collected by remote-control vehicles in offshore oil and gas and renewable energy plants can be transmitted at distances of even 1 m or less. This study uses previous frequency response measurements taken in deep water to explore the capacity of a short-range electromagnetic underwater channel. Because of water movement, the nonstatic position of the vehicle when the transmission occurs means that the channel is regarded as randomly time-variant. A statistical model is proposed and the ergodic capacity is calculated for a 7 MHz bandwidth channel at distances ranging from 0.5 m to 5 m as well as for different values of transmitter power. The results of this study reflect capacity values of tens of kbps at distances of approximately 5 m to several Mbps at distances of less than 1.5 m. Jesús López-Fernández, Unai Fernández-Plazaola, and Jose F. Paris Copyright © 2014 Jesús López-Fernández et al. All rights reserved. Path Loss Model with Antenna Height Dependency under Indoor Stair Environment Tue, 22 Jul 2014 11:22:55 +0000 http://www.hindawi.com/journals/ijap/2014/482615/ A novel, receiving antenna-height-dependent path loss model under indoor stair environment is presented. The effect of a cross-beam in the stairs is also considered. The proposed model can be applied to describe both of the line-of-sight (LOS) and the non-LOS (NLOS) cases. By using least square criterion, the parameters of proposed model are extracted. Finally, using the maximum likelihood estimation, the precision of the proposed model is evaluated by the standard deviation of shadowing. Yu Yu, Yang Liu, Wen-Jun Lu, and Hong-Bo Zhu Copyright © 2014 Yu Yu et al. All rights reserved. Yagi Array of Microstrip Quarter-Wave Patch Antennas with Microstrip Lines Coupling Tue, 22 Jul 2014 11:18:05 +0000 http://www.hindawi.com/journals/ijap/2014/102362/ A new kind of Yagi array of quarter-wave patch antennas is presented. The Yagi array has a low profile, a wide bandwidth, and a high gain. A main beam close to endfire is produced, with a vertical polarization in the horizontal plane. A set of microstrip lines are introduced between the driven element and the first director element to enhance the coupling between them, and therefore the bandwidth could be increased and the back lobes could be suppressed. Measured results show that the Yagi array with 4 elements generates a peak gain of about 9.7 dBi, a front-to-back ratio higher than 10 dB, and a 10 dB return loss band from 4.68 GHz to 5.24 GHz, with a profile of 1.5 mm and an overall size of 80 × 100 mm2. An increase of the number of director elements would enhance the gain and have the main beam pointing closer to endfire. Juhua Liu, Yue Kang, Jie Chen, and Yunliang Long Copyright © 2014 Juhua Liu et al. All rights reserved. Beamforming Techniques for Wireless MIMO Relay Networks Tue, 22 Jul 2014 09:07:58 +0000 http://www.hindawi.com/journals/ijap/2014/354714/ Athanasios G. Kanatas, Demosthenes Vouyioukas, Gan Zheng, and Laurent Clavier Copyright © 2014 Athanasios G. Kanatas et al. All rights reserved. A Single RF MIMO Loading Network for High-Order Modulation Schemes Tue, 22 Jul 2014 00:00:00 +0000 http://www.hindawi.com/journals/ijap/2014/879127/ Recently, a novel MIMO transmitter architecture has been introduced that requires only a single radio-frequency (RF) chain and is built on parasitic antenna arrays. MIMO transmission in this case is achieved by shaping directly the radiation pattern with the aid of analog tunable loads attached to the parasitics. As it has been shown, such a single RF MIMO system can support all PSK modulation formats with purely imaginary loading values. This paper extends its capabilities and proposes a novel architecture for parasitic antennas that is able to provide complex loading values, even with a negative real part. Definitely, this will extend the flexibility of parasitic antennas to multiplex successfully over the air more complex signaling formats, for example, QAM signals. The bit error rate evaluation shows that the proposed architecture could be very promising in emerging devices and also illustrates its robustness under possible loading perturbations that might have been raised due to nonidealities in the design. Bo Han, Vlasis I. Barousis, Antonis Kalis, Constantinos B. Papadias, Athanasios G. Kanatas, and Ramjee Prasad Copyright © 2014 Bo Han et al. All rights reserved.