Current Issue : October - December Volume : 2012 Issue Number : 4 Articles : 7 Articles
A new, rigorous, field-based, seminumerical analysis method is presented to obtain the reflection and transmission coefficients of\r\n2D planar periodic structures with arbitrarily shaped metallization patterns for both normal and oblique incidence conditions. It is\r\nuseful for the analysis, design, and optimization of many single-layer and multilayer planar structures, such as frequency-selective\r\nsurfaces (FSSs), artificial magnetic conductor (AMC) surfaces, electromagnetic bandgap (EBG) structures, some metamaterials\r\nand high-impedance surfaces. In this coupled-field expansion method (CFEM), the x- and y-components of the vector magnetic\r\npotential in each homogeneous region in a unit cell are expanded in terms of Bloch-Floquet modes and the solution to the coupledfield\r\nproblem is formulated. The unique, analytical formulation presented here leads to a linear system with reasonably simple\r\nmatrix elements. By cascading the matrices representing each interface,multilayer periodic structures are analyzed in a very flexible\r\nway. Being field based, CFEM does not require substrate Green�s functions to analyze surfaces printed on dielectric substrates. The\r\nmethod was validated by analyzing one single-layer periodic surface (a printed AMC on a dielectric substrate) and one multilayer\r\nperiodic surface (a circular polarizer) and comparing CFEM results with HFSS results....
In search for isotropic radiators with reasonable quality Factor (Q), bandwidth, and efficiency, one looks for practical radiators\r\nwith a typical resonant length of ?/4.We present here a Green�s function analysis in Fourier of a ?/4 microstrip element and a farfield\r\nintegral method in configuration (real) space of single and dual U-shaped ?/4 elements. Both solutions analytically prove that\r\nthe power radiation patterns are isotropic in nature (while the thickness and the width tend to zero), although the polarizations\r\nare not symmetrical in all cuts. It is also shown that the power isotropic U-shaped radiator, for which the surface current density\r\nis infinite, can be replaced by another finite-size radiator, having finite-surface current density, such that its far-field is exactly the\r\nsame as the far-field of the U-shaped isotropic radiator....
This paper discusses over-the-air (OTA) test setup for multiple-input-multiple-output (MIMO) capable terminals with emphasis\r\non channel modelling. The setup is composed of a fading emulator, an anechoic chamber, and multiple probes. Creation of\r\na propagation environment inside an anechoic chamber requires unconventional radio channel modelling, namely, a specific\r\nmapping of the original models onto the probe antennas. We introduce two novel methods to generate fading emulator channel\r\ncoefficients; the prefaded signals synthesis and the plane wave synthesis. To verify both methods we present a set of simulation\r\nresults.We also show that the geometric description is a prerequisite for the original channel model....
A novel printed ultrawideband (UWB) CPW-fed Koch fractal slot antenna is proposed. The UWB bandwidth is largely enhanced\r\nby the three-iteration Koch fractal slot whose extrusive angle is 900 instead of 600 to obtain better convoluted shape and selfsimilarity.\r\nThe -10 dB impedance bandwidth is 3400MHz (1270ââ?¬â??4670 MHz) or about 114% in comparison with 1290MHz\r\n(1620ââ?¬â??2910 MHz) or about 57% of the referenced square slot antenna. Details of the proposed antenna design and performance\r\nare presented and discussed....
This paper presents optimization problem formulations to design meander-line antennas for passive UHF radio frequency\r\nidentification tags based on given specifications of input impedance, frequency range, and geometric constraints. In this\r\napplication, there is a need for directive transponders to select properly the target tag, which in turn must be ideally isotropic. The\r\ndesign of an effective meander-line antenna for RFID purposes requires balancing geometrical characteristics with the microchip\r\nimpedance. Therefore, there is an issue of optimization in determining the antenna parameters for best performance. The antenna\r\nis analyzed by a method of moments. Some results using a deterministic optimization algorithm are shown....
The equivalent dipole-moment method (EDM) is extended and applied in the analysis of electromagnetic (EM) radiation by\r\narbitrarily shaped microstrip antenna in this paper. The method of moments (MoM) is used to solve the volume-surface integral\r\nequation (VSIE). A strip model is applied in the treatment of the feeding probe of the microstrip antenna, in which the discretized\r\ntriangular elements of the excitation source are equivalent as dipole models. The proposed approach is sufficiently versatile in\r\nhandling arbitrarily shaped microstrip antenna and is easily constructed through a simple procedure. Numerical results are given\r\nto demonstrate the accuracy and efficiency of this method....
There is a growing interest in detecting and processing Global Navigation Satellite System (GNSS) signals in indoors and urban\r\ncanyons by handheld devices. To overcome the signal attenuation problem in such adverse fading environments, long coherent\r\nintegration is normally used. Moving the antenna arbitrarily while collecting signals is generally avoided as it temporally decorrelates\r\nthe signals and limits the coherent integration gain. This decorrelation is a function of the antenna displacement and geometry\r\nof reflectors and angle of arrival of the received signal. Hence, to have an optimum receiver processing strategy it is crucial to\r\ncharacterize the multipath fading channel parameters. Herein, Angle of Arrival (AoA) and Angle Spread (AS) along with signal\r\nspatial correlation coefficient and fading intensity in GNSSmultipath indoor channels are defined and quantified theoretically and\r\npractically. A synthetic uniform circular array utilizing a right-hand circular polarized (RHCP) antenna has been used to measure\r\nthe spatial characteristics of indoor GNSS fading channels. Furthermore, rotating effect of a circular polarized antenna on the\r\nsynthetic array processing and AoA estimation has been characterized. The performance of the beamforming technique via array\r\ngain is also assessed to explore the advantages and limitations of beamforming in fading conditions....
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