International Journal of Antennas and Propagation The latest articles from Hindawi Publishing Corporation © 2015 , Hindawi Publishing Corporation . All rights reserved. Evolution of Satellite Communication Antennas on Mobile Ground Terminals Sun, 04 Oct 2015 13:07:10 +0000 Getting connected whenever and wherever you travel is not kind of luxury any more. Satellite communication researchers are making it a reality to bring you data, video, and voice services when you are away from home, out of office, or on a long journey. Satellite communication antenna mounted on mobile ground terminals is an essential prerequisite of successful connectivity. In this paper, we review the evolution of this kind of antenna in its historical context and outline the major research achievements on ground mobile terminals. Many striking demonstrations and prototypes are revisited to understand the emerging technologies and assess their potential towards practical implementations. The future trends and challenges are also discussed. Haifeng Zhou, Mingchinq Jong, and Guoqiang Lo Copyright © 2015 Haifeng Zhou et al. All rights reserved. Taming the Electromagnetic Boundaries via Metasurfaces: From Theory and Fabrication to Functional Devices Sun, 04 Oct 2015 13:04:02 +0000 As two-dimensional metamaterials, metasurfaces have received rapidly increasing attention from researchers all over the world. Unlike three-dimensional metamaterials, metasurfaces can be utilized to control the electromagnetic waves within one infinitely thin layer, permitting substantial advantages, such as easy fabrication, low cost, and high degree of integration. This paper reviews the history and recent development of metasurfaces, with particular emphasis on the theory and applications relating to the frequency response, phase shift, and polarization state control. Based on the current status of various applications, the challenges and future trends of metasurfaces are discussed. Xiangang Luo, Mingbo Pu, Xiaoliang Ma, and Xiong Li Copyright © 2015 Xiangang Luo et al. All rights reserved. A Through-the-Wall Radar Imaging Method Based on a Realistic Model Sun, 04 Oct 2015 12:53:07 +0000 An image focusing method based on a realistic model for a wall is proposed for through-the-wall radar imaging using a multiple-input multiple-output array. A technique to estimate the wall parameters (i.e., position, thickness, and permittivity) from the radar returns is developed and tested. The estimated wall properties are used in the developed penetrating image formation to form images. The penetrating image formation developed is computationally efficient to realize real-time imaging, which does not depend on refraction points. The through-the-wall imaging method is validated on simulated and real data. It is shown that the proposed method provides high localization accuracy of targets concealed behind walls. Tian Jin and Alexander Yarovoy Copyright © 2015 Tian Jin and Alexander Yarovoy. All rights reserved. A Two-Stage Procedure for Microwave Imaging of a Buried Dielectric along with the Randomly Rough Surface above It Sun, 04 Oct 2015 11:53:38 +0000 A two-stage microwave imaging procedure based on the contrast source inversion (CSI) is proposed for the determination of a buried dielectric along with the rough surface above it. It was previously shown that, the CSI, is very effective for the determination of a dielectric buried under a known rough surface. However, for an unknown surface, the application of the CSI to the entire region containing both the object and the roughness will yield significantly inaccurate dielectric property values and, thus, determination of objects will be almost impossible especially when they are small in size or low in contrast. Thus, we propose to construct a reference model for the background without the object by preimaging the entire region in a frequency-hopping scheme and imposing the a priori known property values to the approximately determined morphology of the background. In the second stage, the CSI is performed at single frequency, assuming the constructed reference model as the background. In this case, by taking the advantage of nonlinear inversion and without a restrictive assumption about the characteristics of the rough surface, the proposed approach yields qualitatively satisfactory results even for multiple objects buried under a surface having a high frequency or large roughness. Tolga Ulaş Gürbüz and Birol Aslanyürek Copyright © 2015 Tolga Ulaş Gürbüz and Birol Aslanyürek. All rights reserved. A Subspace Preconditioned LSQR Gauss-Newton Method with a Constrained Line Search Path Applied to 3D Biomedical Microwave Imaging Sun, 04 Oct 2015 11:51:40 +0000 Three contributions that can improve the performance of a Newton-type iterative quantitative microwave imaging algorithm in a biomedical context are proposed. (i) To speed up the iterative forward problem solution, we extrapolate the initial guess of the field from a few field solutions corresponding to previous source positions for the same complex permittivity (i.e., “marching on in source position”) as well as from a Born-type approximation that is computed from a field solution corresponding to one previous complex permittivity profile for the same source position. (ii) The regularized Gauss-Newton update system can be ill-conditioned; hence we propose to employ a two-level preconditioned iterative solution method. We apply the subspace preconditioned LSQR algorithm from Jacobsen et al. (2003) and we employ a 3D cosine basis. (iii) We propose a new constrained line search path in the Gauss-Newton optimization, which incorporates in a smooth manner lower and upper bounds on the object permittivity, such that these bounds never can be violated along the search path. Single-frequency reconstructions from bipolarized synthetic data are shown for various three-dimensional numerical biological phantoms, including a realistic breast phantom from the University of Wisconsin-Madison (UWCEM) online repository. Jürgen De Zaeytijd and Ann Franchois Copyright © 2015 Jürgen De Zaeytijd and Ann Franchois. All rights reserved. Photonic Wannier-Stark Ladder from Coupled Electromagnetic Cavities Sun, 04 Oct 2015 11:29:20 +0000 We have investigated the photonic Wannier-Stark ladder in the system of coupled electromagnetic cavities, which consists of a stack of metallic plates structured with subwavelength apertures and where the tilted potential effect is mimicked by imposing the gradient variation of refractive index. Making an analogy to its quantum counterpart and assuming the translational property of its solutions, we have shown the photonic ladder has the eigenenergies, that is, frequencies, in a geometrical series. Within the approximation of small gradient, the ladder states manifest the equidistant frequency spacing in the spectrum. By both analytical derivation and numerical simulation, we have illustrated the geometrically progressed energies of the photonic Wannier-Stark ladder. Shahzad Anwar, Sucheng Li, Weixin Lu, and Bo Hou Copyright © 2015 Shahzad Anwar et al. All rights reserved. Recent Advances in the Modeling of Transmission Lines Loaded with Split Ring Resonators Sun, 04 Oct 2015 11:29:06 +0000 This paper reviews the recent advances in the modeling of transmission lines loaded with split ring resonators (SRRs). It is well known that these artificial lines can exhibit a negative effective permeability in a narrow band above the SRR fundamental resonance, providing stopband functionality. By introducing shunt inductive elements to the line, the stopband can be switched to a pass band with left-handed (LH) wave propagation. For the design of microwave circuits based on these artificial lines, accurate circuit models are necessary. The former circuit model of SRR-loaded lines was presented more than one decade ago and is valid under restrictive conditions. This paper presents the progress achieved in the modeling of these artificial lines during the last years. The analysis, restricted to coplanar waveguide (CPW) transmission lines loaded only with SRRs (negative permeability transmission lines), includes the effects of SRR orientation, the coupling between adjacent resonators, and the coupling between the two SRRs constituting the unit cell. The proposed circuit models are validated through electromagnetic simulation and experimental data. It is also pointed out that the analysis can be easily extended to negative permittivity transmission lines based on complementary split ring resonators (CSRRs). Jordi Naqui, Lijuan Su, Javier Mata, and Ferran Martín Copyright © 2015 Jordi Naqui et al. All rights reserved. Substrate Integrated Waveguide Leaky-Wave Antenna Conforming to Conical Shape Surface Sun, 04 Oct 2015 11:28:17 +0000 A conical conformal leaky-wave antenna based on substrate integrated waveguide (SIW) technology is proposed and demonstrated in this paper. This antenna conforms to a conical shape surface with the angle of 40°. It has a narrow beam that scans from 80° to 97° with varying frequency (34 GHz~37 GHz). Both conformal and nonconformal antennas are fabricated through the standard PCB process. Their performances are compared within the desired frequency. W. N. Huang, Y. J. Cheng, and H. Deng Copyright © 2015 W. N. Huang et al. All rights reserved. An Opportunistic Array Beamforming Technique Based on Binary Multiobjective Wind Driven Optimization Method Sun, 04 Oct 2015 11:26:26 +0000 We present a novel binary version of multiobjective wind driven optimization (WDO) for emitted beamforming of opportunistic array radar, which is assumed as a multiobjective optimization problem. Firstly, the emitted signal model and objective functions of optimization are presented. Then the algorithm proposes a new definition of the position vector of air parcel, and brings a good discretization interpretation of continuous WDO. For multiobjective optimization, the grey relational grade (GRG) is then used to measure the similarity between the best two solutions for these two objectives. The best pressure locations with the maximum GRG will be recorded as the best two candidate solutions to the problem, and a final optimization result will be selected according to the importance of the two objectives. Finally, the proposed improved WDO has been applied for the optimal design of beamforming of the opportunistic antenna array, which needs a trade-off between the 3 dB main beam width and sidelobe level. The simulation results show that the proposed method outperforms conventional particle swarm optimization (PSO) in the optimal beamforming by achieving more reduction in the sidelobe level and saving more runtime. Zhenkai Zhang, Sana Salous, Hailin Li, and Yubo Tian Copyright © 2015 Zhenkai Zhang et al. All rights reserved. Resonances in Reverse Vavilov-Cherenkov Radiation Produced by Electron Beam Passage over Periodic Interface Sun, 04 Oct 2015 11:21:04 +0000 Resonances in reverse Vavilov-Cherenkov radiation produced by the charged particles beam passage over periodic boundary of dispersive left-handed medium are found out and studied. Analysis and modeling are performed on the base of rigorous mathematical approaches. For the first time, several physical peculiarities owing to these effects are considered in the conditions of possible resonant scattering of electromagnetic waves. Gerard Granet, Petr Melezhik, Anatoliy Poyedinchuk, Seil Sautbekov, Yuriy Sirenko, and Nataliya Yashina Copyright © 2015 Gerard Granet et al. All rights reserved. Wideband Dual-Element Antenna Array for MIMO Mobile Phone Applications Sun, 04 Oct 2015 11:18:45 +0000 A printed dual-element antenna array for LTE MIMO mobile phone applications is presented in this paper. The two array elements are symmetrically placed with the same dimensions, and each of the them consists of a novel driven strip and a wandering shorting strip. The driven strip is a whole loop, which improves the impedance matching for the upper band. Therefore, the bandwidth coverage is expanded and the antenna size is minimized at the same time. In addition, thanks to the protruded ground on the ground plane, the antenna isolation between the two array elements is significantly enhanced. The proposed planar antenna array successfully covers the seven operating bands of GSM850/900/1800/1900/UMTS2100/LTE2300/2500, and the isolation is more than 10 dB. The prototype was fabricated and tested, with S parameters, efficiency, radiation patterns, envelop correlation coefficient (ECC), and ergodic capacity presented. From the measured results, it is indicated that the antenna array has excellent and reliable performances when it is applied in MIMO applications. Yuanqiang Wang, Jie Yang, Shangfu Hao, and Xiao Zhang Copyright © 2015 Yuanqiang Wang et al. All rights reserved. Polarization-Independent and Angle-Insensitive Metamaterial Absorber Using 90-Degree-Rotated Split-Ring Resonators Sun, 04 Oct 2015 08:51:07 +0000 We present the design, simulation, and measurement of a polarization-independent and angle-insensitive metamaterial absorber (MA) in X-band. Since the unit cell of the MA consists of four subwavelength split-ring resonators with 4-fold symmetric rotation, the MA is insensitive to the variation of both polarization and incident angle of the planar electromagnetic wave. The electromagnetic performances of the MA are studied by full-wave simulations based on finite-element method and the Naval Research Laboratory arch experimental measurements. The electric field distributions are numerically investigated, which confirm the polarization-insensitive property of the MA, as expected from the symmetric nature of the structure. When the incident angles vary from 0 to 45 degrees, the MA remains at full width at half maximum of 0.4 GHz (0.5 GHz) with peak absorptions of 99.9% (95.2%) at 10.27 GHz (10.3 GHz) by simulations (measurements). Jia-Qi Feng, Wei-Dong Hu, Qing-Le Zhang, Hua Zong, Hui Huang, Yu-Ting Jin, Yu-Ming Wu, Zhan Xu, Xin Lv, and Li-Ming Si Copyright © 2015 Jia-Qi Feng et al. All rights reserved. Compact Microstrip Bandpass Diplexer Based on Twist Revised Split Ring Resonators Sun, 04 Oct 2015 07:48:31 +0000 Based on the twist revised split ring resonators (TR-SRRs) inspired filter unit a microstrip bandpass diplexer with highly compact size and high frequency selection and isolation properties is synthesized and systematically characterized. The proposed filter unit exhibits both electric and magnetic coupling effects and possesses two resonance modes (magnetic and electronic resonances). The two resonance modes can be flexibly controlled by adjusting the gap between the two TR-SRRs. The synthesized diplexer has very simple configuration with size of and degree of freedom for impedance matching. Measurement and simulation demonstrations are performed in this paper and a good agreement is achieved. The measured results indicate two quite close frequency channels (centered at 2.16 GHz and 2.91 GHz) with isolation larger than 30 dB. The proposed diplexer can be easily integrated into miniaturized RF/microwave integrated circuits. Jian Li, Yongjun Huang, Xuefeng Zhao, and Guangjun Wen Copyright © 2015 Jian Li et al. All rights reserved. Highly Compact MIMO Antenna System for LTE/ISM Applications Thu, 01 Oct 2015 16:07:14 +0000 Planar monopole antenna is proposed as the antenna element to form a compact dual-element multiple-input-multiple-output (MIMO) antenna system for LTE2300 (used in Asia and Africa) and ISM band operation. The system can cover a 310 MHz (2.20–2.51 GHz) operating bandwidth, with the total size of 15.5 mm × 18 mm × 1.6 mm. Measured isolation higher than 16 dB is obtained without any specially designed decoupling structures, while the edge-to-edge element spacing is only 7.8 mm (0.08λ at 2.20 GHz). Radiation characteristics, correlation coefficient, and the performance of the whole system with a metal sheet and a plastic housing show this system is competitive for practical MIMO applications. The antenna element is further used to build an eight-element MIMO antenna system; also good results are achieved. Lingsheng Yang, Tao Li, and Su Yan Copyright © 2015 Lingsheng Yang et al. All rights reserved. Experimental Assessment of Linear Sampling and Factorization Methods for Microwave Imaging of Concealed Targets Thu, 01 Oct 2015 11:47:59 +0000 Shape reconstruction methods are particularly well suited for imaging of concealed targets. Yet, these methods are rarely employed in real nondestructive testing applications, since they generally require the electrical parameters of outer object as a priori knowledge. In this regard, we propose an approach to relieve two well known shape reconstruction algorithms, which are the linear sampling and the factorization methods, from the requirement of the a priori knowledge on electrical parameters of the surrounding medium. The idea behind this paper is that if a measurement of the reference medium (a medium which can approximate the material, except the inclusion) can be supplied to these methods, reconstructions with very high qualities can be obtained even when there is no information about the electrical parameters of the surrounding medium. Taking the advantage of this idea, we consider that it is possible to use shape reconstruction methods in buried object detection. To this end, we perform several experiments inside an anechoic chamber to verify the approach against real measurements. Accuracy and stability of the obtained results show that both the linear sampling and the factorization methods can be quite useful for various buried obstacle imaging problems. M. N. Akıncı, T. Çağlayan, S. Özgür, U. Alkaşı, M. Abbak, and M. Çayören Copyright © 2015 M. N. Akıncı et al. All rights reserved. 3D Imaging of Dielectric Objects Buried under a Rough Surface by Using CSI Thu, 01 Oct 2015 11:46:27 +0000 A 3D scalar electromagnetic imaging of dielectric objects buried under a rough surface is presented. The problem has been treated as a 3D scalar problem for computational simplicity as a first step to the 3D vector problem. The complexity of the background in which the object is buried is simplified by obtaining Green’s function of its background, which consists of two homogeneous half-spaces, and a rough interface between them, by using Buried Object Approach (BOA). Green’s function of the two-part space with planar interface is obtained to be used in the process. Reconstruction of the location, shape, and constitutive parameters of the objects is achieved by Contrast Source Inversion (CSI) method with conjugate gradient. The scattered field data that is used in the inverse problem is obtained via both Method of Moments (MoM) and Comsol Multiphysics pressure acoustics model. Evrim Tetik and Ibrahim Akduman Copyright © 2015 Evrim Tetik and Ibrahim Akduman. All rights reserved. Ultra Wide X-Band Microwave Imaging of Concealed Weapons and Explosives Using 3D-SAR Technique Thu, 01 Oct 2015 11:13:58 +0000 In order to detect and image concealed weapons and explosives, an electromagnetic imaging tool with its related signal processing is presented. The aim is to penetrate clothes and to find personal-born weapons and explosives under clothes. The chosen UWB frequency range covers the whole X-band. The frequency range is justified after transmission measurements of numerous clothes that are dry or slightly wet. The apparatus and the 3D near-field SAR processor are described. A strategy for contour identification is presented with results of some simulants of weapon and explosive. A conclusion is drawn on the possible future of this technique. P. Millot and L. Casadebaig Copyright © 2015 P. Millot and L. Casadebaig. All rights reserved. Gain Enhancement of a Microstrip Patch Antenna Using a Reflecting Layer Thu, 01 Oct 2015 11:09:31 +0000 A low profile, unidirectional, dual layer, and narrow bandwidth microstrip patch antenna is designed to resonate at 2.45 GHz. The proposed antenna is suitable for specific applications, such as security and military systems, which require a narrow bandwidth and a small antenna size. This work is mainly focused on increasing the gain as well as reducing the size of the unidirectional patch antenna. The proposed antenna is simulated and measured. According to the simulated and measured results, it is shown that the unidirectional antenna has a higher gain and a higher front to back ratio (F/B) than the bidirectional one. This is achieved by using a second flame retardant layer (FR-4), coated with an annealed copper of 0.035 mm at both sides, with an air gap of 0.04 as a reflector. A gain of 5.2 dB with directivity of 7.6 dBi, F/B of 9.5 dB, and −18 dB return losses () are achieved through the use of a dual substrate layer of FR-4 with a relative permittivity of 4.3 and a thickness of 1.6 mm. The proposed dual layer microstrip patch antenna has an impedance bandwidth of 2% and the designed antenna shows very low complexity during fabrication. Anwer Sabah Mekki, Mohd Nizar Hamidon, Alyani Ismail, and Adam R. H. Alhawari Copyright © 2015 Anwer Sabah Mekki et al. All rights reserved. Cylindrical Three-Dimensional Millimeter-Wave Imaging via Compressive Sensing Thu, 01 Oct 2015 09:41:08 +0000 Millimeter-wave (MMW) imaging techniques have been used for the detection of concealed weapons and contraband carried by personnel. However, the future application of the new technology may be limited by its large number of antennas. In order to reduce the complexity of the hardware, a novel MMW imaging method based on compressive sensing (CS) is proposed in this paper. The MMW images can be reconstructed from the significantly undersampled backscattered data via the CS approach. Thus the number of antennas and the cost of system can be further reduced than those based on the traditional imaging methods that obey the Nyquist sampling theorem. The effectiveness of the proposed method is validated by numerical simulations as well as by real measured data of objects. Guoqiang Zhao, Shiyong Li, Bailing Ren, Qingwei Qiu, and Houjun Sun Copyright © 2015 Guoqiang Zhao et al. All rights reserved. Assessing the Capabilities of a New Linear Inversion Method for Quantitative Microwave Imaging Thu, 01 Oct 2015 09:37:18 +0000 We investigate the imaging capabilities of a new linear microwave imaging approach, which allows to quantitative retrieve the complex permittivity distribution of unknown nonweak targets. To this end, we carry out a parametric numerical analysis for a canonical scatterer (a homogeneous dielectric cylinder with circular cross section) and derive a quantitative criterion to foresee the method’s applicability. The reliability of the criterion is then tested against noncanonical scatterers to show the effectiveness of the method in imaging nonweak targets and in outperforming the linearized inversion method based on the standard Born approximation. Loreto Di Donato, Roberta Palmeri, Gino Sorbello, Tommaso Isernia, and Lorenzo Crocco Copyright © 2015 Loreto Di Donato et al. All rights reserved. A Multiple Resonant Frequencies Circular Reconfigurable Antenna Investigated with Wireless Powering in a Concrete Block Thu, 01 Oct 2015 08:20:09 +0000 A novel broadband reconfigurable antenna design that can cover different frequency bands is presented. This antenna has multiple resonant frequencies. The reflection coefficient graphs for this antenna are presented in this paper. The new proposed design was investigated along with RF MEMS switches and the results are also presented. Investigations were carried out to check the efficiency of the antenna in the wireless powering domain. The antenna was placed in a concrete block and its result comparison to that of a dipole antenna is also presented in this paper. Shishir Shanker Punjala, Niki Pissinou, and Kia Makki Copyright © 2015 Shishir Shanker Punjala et al. All rights reserved. High Gain Superstrate Loaded Membrane Antenna Based on Substrate Integrated Waveguide Technology Thu, 01 Oct 2015 08:18:05 +0000 The design and the results of a single slot coupled substrate integrated waveguide (SIW) fed membrane antenna loaded with a superstrate layer are presented for 94 GHz communication system. The membrane antenna is designed using ANSYS HFSS and consists of 6 layers. The microstrip patch antenna (MPA) placed on the top pyralux substrate layer is excited by means of a longitudinal rectangular slot placed over the SIW structure in the bottom pyralux substrate. The simulated antenna impedance bandwidth is found to be 5 GHz (91.5–96.5 GHz) with a gain of 7 dBi. In order to improve the gain a superstrate layer is added above the membrane antenna. The maximum gain achieved is 14.4 dBi with an efficiency of 77.6% at 94 GHz. The results are verified using CST Microwave Studio and are found to be in good agreement. Hamsakutty Vettikalladi Copyright © 2015 Hamsakutty Vettikalladi. All rights reserved. A Simple Quantitative Inversion Approach for Microwave Imaging in Embedded Systems Thu, 01 Oct 2015 08:11:38 +0000 In many applications of microwave imaging, there is the need of confining the device in order to shield it from environmental noise as well as to host the targets and the medium used for impedance matching purposes. For instance, in MWI for biomedical diagnostics a coupling medium is typically adopted to improve the penetration of the probing wave into the tissues. From the point of view of quantitative imaging procedures, that is aimed at retrieving the values of the complex permittivity in the domain under test, the presence of a confining structure entails an increase of complexity of the underlying modelling. This entails a further difficulty in achieving real-time imaging results, which are obviously of interest in practice. To address this challenge, we propose the application of a recently proposed inversion method that, making use of a suitable preprocessing of the data and a scenario-oriented field approximation, allows obtaining quantitative imaging results by means of quasi-real-time linear inversion, in a range of cases which is much broader than usual linearized approximations. The assessment of the method is carried out in the scalar 2D configuration and taking into account enclosures of different shapes and, to show the method’s flexibility different shapes, embedding nonweak targets. M. Ambrosanio, R. Scapaticci, and L. Crocco Copyright © 2015 M. Ambrosanio et al. All rights reserved. Novel Miniaturized Octaband Antenna for LTE Smart Handset Applications Thu, 01 Oct 2015 07:44:57 +0000 A novel octaband LTE mobile phone antenna is presented, which has a compact size with the overall dimension of 35 mm × 9 mm × 3 mm. The miniaturized octaband antenna is implemented by a simple prototype of three parts which include a folded monopole as feeding element, main radiator element, and parasitic radiator element. The main and parasitic radiator elements are excited by the folded monopole feeding element coupling and shorting to the handset ground plane. A wide bandwidth in low-frequency bands covering from 747 MHz to 960 MHz (LTE Band13/GSM850/GSM900) is contributed by both main and parasitic radiator elements. In addition, the folded monopole is designed to resonate at 2530 MHz, and the coupling between the feeding element and main radiator element is designed to resonate at 1840 MHz. Subsequently, the wide bandwidth in high-frequency bands covering from 1710 MHz to 2690 MHz (DCS1800/PCS1900/WCDMA2100/LTE2300/LTE2500) is contributed by both structures. The antenna has the total efficiency up to 30% in low bands and up to 75% in high bands, respectively. At the same time, the proposed miniaturized octaband LTE mobile phone antenna is fabricated and tested to verify the design. Haixia Liu, Bo Lu, and Long Li Copyright © 2015 Haixia Liu et al. All rights reserved. Equilateral Triangular Dielectric Resonator Nantenna at Optical Frequencies for Energy Harvesting Thu, 01 Oct 2015 07:32:25 +0000 The last decade has witnessed a remarkable growth in the telecommunication industry. With the introduction of smart gadgets, the demand for high data rate and bandwidth for wireless applications have increased exponentially at the cost of exponential consumption of energy. The latter is pushing the research and industry communities to devise green communication solutions that require the design of energy saving devices and techniques in one part and ambient energy harvesting techniques in the other part. With the advent of nanocomponents fabrication technology, researchers are now able to tap into the THz frequency regime and fabricate optical low profile antennas at a nanoscale. Optical antennas have proved their potential and are revolutionizing a class of novel optical detectors, interconnectors, sensors, and energy harvesting related fields. Authors in this paper propose an equilateral triangular dielectric resonator nantenna (ETDRNA) working at 193.5 THz standard optical frequency. The simulated antenna achieves an impedance bandwidth from 192.3 THz to 197.3 THz with an end-fire directivity of 8.6 dBi, covering the entire standard optical window of C-band. Numerical demonstrations prove the efficiency of the nantenna at the frequencies of interest, making it a viable candidate for future green energy harvesting and high speed optical applications. Waleed Tariq Sethi, Hamsakutty Vettikalladi, Habib Fathallah, and Mohamed Himdi Copyright © 2015 Waleed Tariq Sethi et al. All rights reserved. Analysis of Secret Key Randomness Exploiting the Radio Channel Variability Thu, 01 Oct 2015 07:10:44 +0000 A few years ago, physical layer based techniques have started to be considered as a way to improve security in wireless communications. A well known problem is the management of ciphering keys, both regarding the generation and distribution of these keys. A way to alleviate such difficulties is to use a common source of randomness for the legitimate terminals, not accessible to an eavesdropper. This is the case of the fading propagation channel, when exact or approximate reciprocity applies. Although this principle has been known for long, not so many works have evaluated the effect of radio channel properties in practical environments on the degree of randomness of the generated keys. To this end, we here investigate indoor radio channel measurements in different environments and settings at either 2.4625 GHz or 5.4 GHz band, of particular interest for WIFI related standards. Key bits are extracted by quantizing the complex channel coefficients and their randomness is evaluated using the NIST test suite. We then look at the impact of the carrier frequency, the channel variability in the space, time, and frequency degrees of freedom used to construct a long secret key, in relation to the nature of the radio environment such as the LOS/NLOS character. Taghrid Mazloum and Alain Sibille Copyright © 2015 Taghrid Mazloum and Alain Sibille. All rights reserved. A Miniaturized Triple Band Monopole Antenna for WLAN and WiMAX Applications Thu, 01 Oct 2015 07:09:23 +0000 A miniaturized triple band monopole antenna with a small size is proposed and its performance is investigated both numerically and experimentally for worldwide interoperability for microwave access (WiMAX) and wireless local area network (WLAN) applications. The three resonance frequencies are realized by using a toothbrush-shaped patch (TSP), a meander line (ML), and an inverted U-shaped patch (IUSP). The center frequencies of the triple bands can be controlled by adjusting the dimensions of the TSP, ML, and IUSP. Simulated and measured results are presented to demonstrate that the proposed triband monopole antenna with a good impedance bandwidth and omnidirectional radiation patterns is well suitable for WLAN and WiMAX communication applications. Yingsong Li and Wenhua Yu Copyright © 2015 Yingsong Li and Wenhua Yu. All rights reserved. A Low-Profile and Compact Split-Ring Antenna with Horizontally Polarized Omnidirectional Radiation Thu, 01 Oct 2015 06:54:25 +0000 This paper presents a low-profile and compact printed antenna having an omnidirectional radiation pattern with horizontal polarization to the ground. The proposed antenna consists of an inner small fed ring, an outer coupled split ring, and a ground plane. The overall dimension of the proposed antenna is 45 mm × 50.5 mm × 11.6 mm (0.138λ0 × 0.155λ0 × 0.036λ0). The −10-dB of the antenna covers the 920-MHz RFID band, and the gain is about 1.45 dBi in the parallel direction to the ground plane. The measured results show good agreements with the simulated results. Furthermore, the reasons for the low-profile structure and the omnidirectional radiation pattern are also discussed. Kittima Lertsakwimarn, Chuwong Phongcharoenpanich, and Takeshi Fukusako Copyright © 2015 Kittima Lertsakwimarn et al. All rights reserved. Efficient Design of Flexible and Low Cost Paper-Based Inkjet-Printed Antenna Tue, 29 Sep 2015 06:29:46 +0000 A new, efficient, flexible, and cheap antenna designed at 1.57 GHz microstrip patch antenna based on simple inkjet printer with improved performance using silver nanoparticles ink is developed. The antenna is printed on a kind of flexible substrate “glossy paper,” to offer the advantage of light and flexibility for different applications. The performance of silver nanoparticles ink has been studied through inkjet printing versus postsynthesis annealing and multilayer printing. The conductivity has been improved to have promising values up to 2 Ω/cm at temperatures up to 180°C. The surface morphology of the circuits has been analyzed using SEM with mean diameter of the nanoparticles around 100 nm, uniform surface distribution, and mean thickness of the printed layer around 230 microns. Also, a simple design of a coplanar waveguide (CPW) monopole Z-shaped antenna has been considered as an application of fabricated printed antenna using the studied silver nanoparticles ink through a cheap printer. A. M. Mansour, N. Shehata, B. M. Hamza, and M. R. M. Rizk Copyright © 2015 A. M. Mansour et al. All rights reserved. Radiation-Induced Correlation between Molecules Nearby Metallic Antenna Array Tue, 29 Sep 2015 06:03:20 +0000 We theoretically investigate optical absorption of molecules embedded nearby metallic antennas by using discrete dipole approximation method. It is found that the spectral peak of the absorption is shifted due to the radiation-induced correlation between the molecules. The most distinguishing feature of our work is to show that the shift is largely enhanced even when the individual molecules couple with localized surface plasmons near the different antennas. Specifically, we first consider the case that two sets of dimeric gold blocks with a spacing of a few nanometers are arranged and reveal that the intensity and spectral peak of the optical absorption strongly depend on the position of the molecules. In addition, when the dimeric blocks and the molecules are periodically arranged, the peak shift is found to increase up to ~1.2 meV (300 GHz). Because the radiation-induced correlation is essential for collective photon emission, our result implies the possibility of plasmon-assisted superfluorescence in designed antenna-molecule complex systems. Yoshiki Osaka, Nobuhiko Yokoshi, and Hajime Ishihara Copyright © 2015 Yoshiki Osaka et al. All rights reserved.