Wideband bow‐tie antenna with increased gain and directivity by using high impedance surface

Metamaterial surfaces offer a wide range of advantages in terms of antenna design. One such metamaterial is designed to capture the benefits of both high‐impedance surfaces as well as artificial magnetic surfaces. The confluence of both these properties delivers an added advantage to planar antennas by delivering high gain and directivity simultaneously. Bidirectional radiation pattern has been transformed to a directional radiation pattern by placing the metamaterial as substrate beneath the antipodal bowtie antenna. In addition, zero separation between the antenna and metasurface ensures low profile. The proposed design has been verified both by simulation and measurement which have shown an improvement on gain of 3.2 dBi with an almost steady gain response inside the resonating band of the antenna which lies between 12 and 16 GHz.     

Analytical study of surface wave multiple refraction in boundary of a scalar impedance surface with a tensor impedance surface

In this paper, the multiple refraction phenomenon is investigated on the boundary of a scalar impedance surface (SIS) and a tensor impedance surface (TIS). When a surface wave (SW) propagates on the SIS and radiates to the boundary of the TIS, the propagation direction of it is changed and the refraction phenomenon is accrued. The method that is proposed in this paper can predict the multiple refraction for the SW. Moreover, another analytical method is introduced for designing the proposed structure which the double refraction (DR) occurs at arbitrary angles on it. Using it, a sample of the structure is designed by printed circuits in 15.2GHz and the results are verified by the full‐wave simulation and measurement. The results are shown that in the structure, DR is occurred in 2° and 22° as predicted. The proposed method can provide many applications such as design of SW power dividers based on the TISs, impedance surface based waveguides, holographic antennas, and feeding of array antennas.     

An efficient solution of the input impedance of a half‐wave dipole near a human head

This article combines the Galerkin method of moments with the complex image technique to find the current distribution, input impedance, return loss, and frequency bandwidth of a half‐wave dipole near a human head. It also finds the specific absorption rate distribution inside the human head which is modeled as three planar layers of lossy dielectrics. Comparisons with IE3D commercial simulator verify the accuracy and speed of the proposed method. It is found that the input resistance of the dipole is significantly reduced as the dipole is brought closer to the human head causing a reduction in the frequency bandwidth. The proposed method can be modified to solve other types of antennas on different human head planar geometries. © 2011 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2012.     

Semi‐analytical calculation for sensitivities of the method of moments impedance and excitation matrices

A novel method is presented in this article for calculating the sensitivities of the impedance and excitation matrices of the method of moments. The proposed method evaluates the required derivatives with respect to a design variable semi‐analytically. It is demonstrated that one matrices' fill is enough to achieve the required sensitivities. Two such fills would be necessary to obtain similar results using the conventional finite‐difference approximation method. A microstrip patch antenna example is used to demonstrate the validity of the proposed method. By comparing its results with those obtained using finite‐difference numerical approximation, a high degree of agreement is observed. The accuracy of the numerical approximation is found to be sensitive to the selected value of perturbation. © 2007 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2007.     

Radiation analysis of on‐platform antenna using MoM‐PO combined with surface–surface configuration

In this article, wire antennas installed on electrically large structures are modeled by surface–surface configuration. The surface–surface configuration is applied to the hybrid method of moments–physical optics (MoM‐PO) to solve electromagnetic radiation problem of wire antennas mounted on electrically large conducting platform. Numerical results for the arbitrary shaped perfectly electric conducting are considered. Compared with the wire–surface configuration, the surface–surface configuration is easy to ensure the current continuity at the junction and maintain the required good accuracy. Additional complex basis functions are not required in surface–surface junction model compared with wire–surface junction model. © 2010 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2010.     

Platform tolerant dual‐band UHF‐RFID tag antenna with enhanced read range using artificial magnetic conductor structures

In this work, a platform tolerant novel dual band tag antenna is proposed for UHF‐RFID bands used in Europe (855‐867 MHz ) and Japan (950‐955 MHz). Asymmetrical shunt stub feed network is employed to effectively match its impedance to the microchip (Alien Higgs‐4). The antenna miniaturization is achieved by embedding inverted L‐shaped slit on left side of the patch. Also, asymmetrical stepped rectangular slot is embedded to further achieve the optimized dual band response at the desired resonant frequencies (f₁ = 866 MHz and f₂ = 953 MHz). To further enhance its radiation performance on conductive objects like metallic surfaces, the proposed tag is integrated with artificial magnetic conductor (AMC) structure. Also, antenna parameters such as main lobe gain, directivity, front‐to‐back ratio parameters are examined for the integrated tag in free space and on metallic sheet. The proposed integrated tag exhibits directional radiation pattern making it insensitive to underlying object and thus platform tolerant. Further, the proposed integrated tag exhibits steady gain response inside the resonating bands on different sized metallic sheets. The proposed integrated tag is compact (2635 mm³) covering European band with a read range of 7.3 m and Japanese band with a read range of 10.8 m.     

Genetic algorithm optimization of a planar slot array using full wave method‐of‐moments analysis

Waveguide‐fed slot arrays in standing wave mode have been employed successfully in space based remote sensing radars because of their high efficiency, ease of deployment and their ability to withstand the radiation environment. Although the bandwidth requirement in such systems is minimal, at Ka band and above manufacturing tolerances in the order of 1 mil (25 μm), achieved in the dip brazing process, may affect their performance. To produce designs that are less sensitive to manufacturing tolerance, genetic algorithm (GA) optimization is employed in conjunction with a full wave analysis utilizing the method‐of‐moments solution to the pertinent integral equations of slot apertures of a planar array. In this work, a single 8 × 10 sub‐array of an interferometric antenna, proposed previously for a planetary mapping application, was investigated. The array was first designed by the Elliott's procedure and subsequently the design parameters were perturbed by GA optimization using the moment method analysis. The fitness parameter is a weighted function of return loss and gain over a number of frequencies in the operating band. A matching waveguide section consisting of inductive irises is also optimized using GA and mode matching technique. Optimum designs producing nearly constant gain and good return loss over 6% bandwidth are found to be less sensitive to manufacturing tolerance than the initial Elliott design. © 2013 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2013.     

Galerkin versus razor‐blade testing in the method of moments formulation for multiconductor transmission lines

In this paper, the effect of the testing technique in the method of moments (MoM) solution for multiconductor transmission lines is investigated. Two important testing techniques, namely, Galerkin and razor‐blade testing, are used and compared. The problem is formulated using the mixed potential integral equation. The analysis shows that the solution of the longitudinal modal current near the edge of the conductor is significantly affected by the testing scheme in the MoM kernel. For the selected expansion functions, razor‐blade testing gives more reasonable modal current distribution than Galerkin testing. © 2000 John Wiley & Sons, Inc. Int J RF and Microwave CAE 10: 132–138, 2000.     

A microstrip wideband monopole antenna for multisystem integration by utilizing stepped‐impedance structure and L‐shaped slot

In this article, a coplanar‐waveguide (CPW)‐fed dual‐band antenna for applications of the multisystem integration has been demonstrated. The resonance analysis of the stepped‐impedance (SI) monopole is presented by using the transmission‐line analysis method. The frequency‐response characteristics of the SI‐monopole, such as the resonance condition and harmonic response, are systematically summarized. Furthermore, utilizing several simple techniques, such as bent feeding topology, asymmetric ground plane, and an L‐shaped slot etched in the ground plane, a right‐hand circularly polarized (RHCP) radiating wave at 1.57 GHz and a left‐hand circularly polarized (LHCP) radiating wave at 2.33 GHz are excited for the applications of the global positioning system (GPS) and the satellite digital audio radio (SDAR) service system. After optimization of the geometrical parameters of the proposed antenna, the measured impedance bandwidths of a reflection coefficient less than ?10 dB range from 1.40 to 2.98 GHz and from 4.48 to 6.27 GHz, and thus covers most of the commercial wireless communication systems, such as GPS, digital cellular system (DCS), personal communication system (PCS), international mobile telecommunications (IMT)?2000, wireless local area networks (WLAN), and long‐term evolution (LTE) 2300/2600. The measured 3‐dB axial ratio (AR) bandwidths are about 80 MHz at 1.57 GHz and 100 MHz at 2.33 GHz.     

Fast solution of volume–surface integral equation for scattering from composite conducting‐dielectric targets using multilevel fast dipole method

This article presents a fast solution to the volume–surface integral equation for electromagnetic scattering from three‐dimensional (3D) targets comprising both conductors and dielectric materials by using the multilevel fast dipole method (MLFDM). This scheme is based on the concept of equivalent dipole‐moment method (EDM) that views the Rao–Wilton–Glisson and the Schaubert–Wilton–Glisson basis functions as dipole models with equivalent dipole moments. In the MLFDM, a simple Taylor's series expansion of the terms R^α (α = 1, ?1, ?2, ?3) and R? R? in the formulation of the EDM transforms the interaction between two equivalent dipoles into an aggregation–translation–disaggregation form naturally. Furthermore, benefiting from the multilevel grouping scheme, the matrix‐vector product can be accelerated and the memory cost is reduced remarkably. Simulation results are presented to demonstrate the efficiency and accuracy of this method. © 2012 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2012.     

Wide‐band analysis of wire antenna using MoM combined with best uniform rational approximation and surface–surface configuration

In this article, an efficient method based on the method of moments (MoM) combined with the best uniform rational approximation and surface–surface configuration is presented for the wide‐band analysis of wire antenna. Compared with the asymptotic waveform evaluation technique, the major advantage of the Maehly approximation is that it can be easily implemented into an existing MoM computer code. Compared with the wire‐surface configuration, the surface–surface configuration is easy to ensure the current continuity at the junction and maintain the required good accuracy. Numerical results including the input admittance and return loss show that the CPU time took by Maehly approximation is about 1/10 of the CPU time used by the traditional MoM. Good agreement between the presented method and the exact solution is observed. © 2010 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2010.     

Dual‐polarized low sidelobe Fabry‐Perot antenna using tapered partially reflective surface

A novel dual‐polarized Fabry‐Perot (FP) cavity antenna with low sidelobes is proposed. Low sidelobes are obtained by using a tapered partially reflective surface (PRS) in the form of circular lattice instead of the conventional rectangular lattice. As the PRS can be regarded as a 2D leaky wave surface on which cylindrical waves propagate outward radially in the form of concentric rings, so arranging the PRS elements in the form of circular lattice and then applying tapering on it yields low sidelobes in both the E‐ and H‐planes. The performance of the proposed PRS is validated by fabricating a dual‐polarized FP antenna and measuring its radiation patterns. Peak realized gains of 18.6 and 18.5 dBi are obtained for horizontal and vertical polarizations respectively, giving an aperture efficiency of around 42%. Measured sidelobe levels are reduced to lower than ?21.3 dB in both the E‐ and H‐planes for the two orthogonal polarizations.     

Electro‐optic properties of an intrinsic half‐V‐mode FLCD and its application to field‐sequential full‐color LCDs using a poly‐Si TFT matrix array

Abstract— An intrinsic half‐V‐mode ferroelectric liquid‐crystal display (FLCD) exhibiting a high contrast ratio (300:1), owing to defect‐free gray‐scale capability, with a high response speed (τ ? 400 μsec) and good switchability with TFTs, has been developed. Furthermore, this FLCD features high‐temperature reliability owing to the use of a special hybrid alignment technique. We successfully fabricated an active‐matrix poly‐Si TFT field‐sequential full‐color (FS FC) LCD with XGA specifications and a 0.9‐in. diagonal using a half‐V‐mode FLCD and an RGB light‐emitting‐diode (LED) array microdisplay. It is shown that the fabricated active‐matrix FS FCLCD exhibits good moving‐image performance with high full‐color display capability.     

Analysis of line to line coupled coplanar waveguides with W‐shaped conductor backing using conformal mapping method

A W‐shaped microshield coupled parallel coplanar waveguide (CP CPW), which is a new type of CP CPW, is proposed. Closed‐form expressions are presented for calculating the quasistatic parameters of this coupled structure by using conformal mapping techniques. The effect of the W‐shaped conductor backing on the coupling between CPWs is also discussed. Comparisons are made between the present numerical results and the results available in the microwave literature for CPW V‐shaped microshield coupled lines (CWVMCLs) and CP CPWs with a flat conductor backing. In addition, the coupling coefficient of the coupled CPWs is shown to be significantly lower than that of the CWVMCLs in the literature. © 2002 Wiley Periodicals, Inc. Int J RF and Microwave CAE 12: 354–359, 2002. Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mmce10035     

Bandwidth‐enhancement of circularly‐polarized fabry‐perot antenna using single‐layer partially reflective surface

In this article, we investigate bandwidth‐enhancement of a circularly‐polarized (CP) Fabry‐Perot antenna (FPA) using single‐layer partially reflective surface (PRS). The FPA is composed of a single‐feed truncated‐corner square patch antenna, which is covered by the PRS formed by a square aperture array. We revealed that the finite‐sized PRS produces extra resonances and CP radiations for the antenna system, which broadened the impedance matching and axial ratio (AR) bandwidths significantly. For verification, a broadband CP FPA prototype operating near 5.8 GHz was realized and tested. The fabricated antenna with overall size of 125 mm × 125 mm × 23.5 mm achieves a |S₁₁| < ?10 dB bandwidth of 31.7% (5.23‐7.2 GHz), an AR < 3‐dB bandwidth of 13.7% (5.45‐6.25 GHz), the peak gain of 13.3 dBic, a 3‐dB gain bandwidth of 22.38% (5.0‐6.26 GHz), and a radiation efficiency of >91%.     

Parametric interpolation of the moment matrix in surface integral equation formulation

In the analysis of electromagnetic scattering and radiation from objects of arbitrary shape using the method of moments (MoM), it is desirable to fill the impedance (or moment) matrix efficiently so that larger size problems can be solved. This article describes a general MoM technique in which the matrix is filled by spatial interpolation with respect to a parametrized electrical separation between source and test elements. The parametrization is accomplished such that the same algorithm also provides frequency interpolation, thus facilitating efficient computations over a wide frequency band. The spatial interpolation method is illustrated by application to the analysis of radiation from tunable microstrip patch antennas over multiple frequency bands. By specializing the interpolation scheme to a surface integral equation formulation that employs rooftop basis functions on a grid of rectangular cells, it is shown that the interpolation method results in considerable reduction of the storage and CPU time requirements. ©1999 John Wiley & Sons, Inc. Int J RF and Microwave CAE 9: 474–489, 1999.     

Backlight unit with double‐surface light emission using a single micro‐structured lightguide plate

Abstract— A novel illumination system for a liquid‐crystal‐display (LCD) module used in a dual‐display cellular phone has been developed. A double‐surface light‐emitting backlight uses a single light‐guide plate to illuminate both LCDs. A single lightguide, two prism sheets, and four light‐emitting diodes (LED) were used in the new structure, compared with ten components and two sets of light sources with six LEDs in the current backlight. The thickness and power consumption of the new backlight were reduced by a factor of 0.59 and 0.67, respectively.     

Basis functions for an MoM solution of a corner‐truncated patch antenna

A new set of entire‐domain basis functions for the numerical solution of corner‐truncated patch antennas via a method of moments (MoM) algorithm is proposed in this article. The basis functions used here allow improvement of the computational efficiency and/or the accuracy of the numerical method, compared to the analysis techniques previously presented in the literature and commonly employed in practical designs. Some numerical results showing the capabilities of the new basis functions proposed here and good agreement with the measurements are also presented. © 2005 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2005.     

Design of an efficiency‐enhanced Greinacher rectifier operating in the GSM 1800 band by using rat‐race coupler for RF energy harvesting applications

Radio frequency energy harvesting (RFEH) circuits can convert the power of communication signals from radio frequencies (RF) in the environment into direct current and voltage (DC power). In this study, the Greinacher full‐wave rectifier circuit topology was combined with a 180° hybrid ring (rat‐race) coupler which was a passive RF/microwave circuit. Thus, higher RF‐DC conversion efficiency was obtained. First, using the Greinacher rectifier topology, RFEH circuit operating at the center frequency of 1850 MHz was designed. Then, at this frequency, designing of the rat‐race coupler having 1000 MHz bandwidth was made. The S‐parameter measurements and simulation data of the designed coupler circuit were compared. Finally, the high efficiency rectifier circuit where these two circuits were used together was designed. The proposed rectifier circuit was constructed on 70 × 70 × 1.6 mm³ FR4 substrate material with a permittivity of 4.3 (ε_r = 4.3). The power conversion efficiency (PCE) of the rectifier circuit, which had 125 MHz bandwidth at the center frequency of 1850 MHz and was developed with rat‐race coupler, was calculated as 71% at 4.7 dBm input power. In addition, with this study, at ?15 dBm input power, which was a relatively low power level, 40% PCE value was obtained.