Showing papers in "Progress in Electromagnetics Research-pier in 2003"

Electromagnetic scattering by a conducting cylinder coated with metamaterials

Abstract: The electromagnetic scattering from a conducting cylinder coated with metamaterials, which have both negative permittivity and permeability, is derived rigorously by using the classic separation of variables technique. It is found that a conducting cylinder coated with metamaterials has anomalous scattering cross section compared to that coated with conventional dielectric materials. Numerical results are presented and discussed for the scattering cross section of a conducting cylinder coated with metamaterials.

Measurement of complex permittivity of liquids using waveguide techniques

Abstract: Complex permittivity of a number of liquids and binary mixtures has been studied by measurement using the waveguide techniques at the X and Ku band. Particular pieces of WR90 and WR62 waveguides were designed for the measurement of liquid materials. The custom designed TRL calibration kits are applied for calibration of the waveguide system. The measured results of complex permittivity of liquid dielectrics, such as methanol, propyl alcohol, ethyl alcohol, chlorobenzene, dioxane, cyclohexane and binary mixtures, are presented. Particular pieces of open-ended waveguides for the X and Ku bands were also designed for holding liquids and the measured data using the open-ended waveguide technique were compared with those measured using the waveguide technique. Some of the measured results are also compared with calculated data using the Debye equation and published data measured by the Fourier transform spectroscopy.

Modeling of RF Absorber for Application in the Design of Anechoic Chamber

Abstract: A proper model of RF absorber must be developed based on information such as absorber reflectivity, in magnitude and phase, for various angles of incidence, and for parallel and perpendicular polarizations. Unfortunately, these data are not available due to the practical limitations of the test fixtures to measure the RF absorber performance. Manufacturer data sheets normally specify only the magnitude of the absorber reflectivity for normal incidence. A model has been developed in this paper for pyramidal RF absorber with pyramid length shorter than a quarter wavelength and poor reflectivity performance. Since the reflection from the metal backing would be much higher than the reflection and scattering from the pyramid tips, the metal boundary may be modeled as a lossy dielectric with certain effective dielectric constant, e eff , and effective conductivity, σ eff , and the thickness extends to infinity. The appropriate values of e eff and σ eff can be derived based on the reflectivity information given by the manufacturer's data sheet. The reflectivity at oblique incidence is calculated and compared with the results of method of homogenization and moment method. A reasonable match between the different models is obtained. The plane-boundary dielectric model can be used to evaluate the degradation of reflectivity level with respect to angle of incidence. It can be used in a simulation tool for design of anechoic chamber.

Microwave Applications of Photonic Crystals

Abstract: We have demonstrated guiding and bending of electromagnetic (EM) waves in planar and coupled-cavity waveguides built around three-dimensional layer-by-layer photonic crystals. We observed full transmission of the EM waves through these waveguide structures. The dispersion relations obtained from the experiments were in good agreement with the predictions of our waveguide models. We also reported a resonant cavity enhanced (RCE) effect by placing microwave detectors in defect structures. A power enhancement factor of 3450 was measured for planar cavity structures. Similar defects were used to achieve highly directional patterns from monopole antennas.

Electromagnetic scattering from a circular target above or below rough surface

Abstract: The electromagnetic scattering from a perfectly electric conducting (PEC) target located above or below rough surface is investigated, for the case of TM polarization, using the Method of Moments (MoM). The rough surface with Gaussian profile is used to emulate the realistic situation of a statistically-rough surface, while the tapered incident wave is chosen to reduce the truncation error. The Monte-Carlo procedure is employed to calculate the angular correlation function (ACF), which is dependent on the depth, size and horizontal position of the buried target, as well as the moisture content in the soil, and the properties of the rough surface. The enhancement of the ACF on the non-memory line can be used to detect a target below the rough surface. The analysis on the statistical characteristics is also carried out, in view of the study on target detection.

An introduction to photonic band gap (pbg) materials

Abstract: This paper introduces photonic band gap (PBG) materials that are periodic dielectric or metallo-dielectric materials conceived to control the propagation of electromagnetic waves. Firstly, the principle of these materials is explained. Doped PBG materials are then presented with their main properties and applications. New phenomena like super-prism or super-lens are also introduced. A review of different numerical methods used to study photonic band gap materials and to analyze their properties is given next. Manufacturing processes are then briefly described and foreseen applications are presented. Finally, the new field of the controllable photonic band gap materials is introduced.

Three dimensional photonic crystals in the visible regime

Abstract: dimensional photonic bandgap structures working in the visible have been given increasing attention in recent years encouraged by the possibility to control, modify or confine electromagnetic waves in all three dimensions, since this could have considerable impact on novel passive and active optical devices and systems. Although substantial progress has been made in the fabrication of 3D Photonic crystals by means of nano-lithography and nanotechnol- ogy, it still remains a challenge to fabricate these crystals with feature sizes of the half of the wavelength in the visible. Self-assembling of colloidal particles is an alternative method to prepare 3-dimensional photonic crystals. The aim of this article is to show how to use col- loidal crystals as templates for photonic crystals and how to monitor the changes of their optical properties due course of the modification.

Analysis and Applications of Uniplanar Compact Photonic Bandgap Structures

Abstract: This paper reviews recent advancements in the research and development of Uniplanar Compact Photonic Bandgap (UCPBG) structures for microwave and millimeter-wave applications. These planar periodic structures are particularly attractive and have been intensively investigated due to their easy fabrication, low cost, and compatibility with standard planar circuit technology. In this paper, basic properties of UC-PBG will be studied such as the slowwave effect, distinct stopband and passband, leakage suppression of surface waves, and realization of a magnetic surface. Owing to the different features of UC-PBG, these structures have been applied to microwave circuits to improve microstrip filters and patch antennas, to perform harmonic tuning in power amplifiers, to suppress leakage in conductor-backed coplanar waveguide, to realize TEM waveguides, and to implement low-profile cavity-backed slot antennas.

Potential of reflected GNSS signals for ice sheet remote sensing

Abstract: Earth-reflected GNSS (Global Navigation Satellite System) signals have become an attractive tool for remote sensing, eg, ocean altimetry and scatterometric ocean wind measurements For ice sheets, the large penetration capability and the large-scale surface averaging of the L-band signals could open a new look on firnpack characteristics like accumulation rates In this paper we investigate theoretically reflections of GPS (Global Positioning System) signals from ice sheets We derive a model of the reflection signal and perform simulations of airborne and spaceborne measurements The results show that the signal, though complex, is sensitive to the roughness of the snow surface (and internal interfaces) and to firn parameters like accumulation rates To extract valuable and concise information from the complex signal, we derive all example procedure that focusses on particular ground zones during a satellite receiver pass The results indicate that it should be possible in principle to separately infer surface and firnpack parameters from the measurements We conclude that GNSS reflections over ice sheets should be further persued, in particular by obtaining experimental data

Radio propagation in rural residential areas with vegetation

Abstract: In this paper we describe radio wave propagation within mixed residential area consisting of vegetation and houses. We assume no specific knowledge of the houses and vegetation location, but only of their statistical parameters. A three-dimensional (3D) stochastic approach, which is based on the statistical description of the terrain features, houses and vegetation, and deterministic description of signal decay is presented. The scattering and diffraction from trees and buildings, as well as the diffused reflection from the rough structures of the obstructions are modeled using the statistical description of an array of non-transparent phase screens randomly distributed on the rough terrain. The model, which accounts for single scattering and diffraction phenomena and a similar model, which accounts for multiple scattering effects without effects of diffraction are compared with measurements carried out in typical rural mixed residential areas with vegetation. The accuracy of the theoretical prediction is analyzed accounting possible variations of the terrain features. The approach presented here is applicable in many cases, where specific topographical information is not available.

FDTD modeling of a vibrating intrinsic reverberation chamber

Abstract: The field conditions inside a vibrating intrinsic reverber- ation chamber (VIRC) are examined. By the use of the Finite Differ- ence Time Domain (FDTD) method,the field strength in the VIRC is calculated,and an investigation of the field uniformity and the field distribution is performed. The modes inside the cavity are excited by applying an appropriately modulated waveform on a dipoles gap. The use of this kind of waveform enables the study of the field conditions over a wide frequency range. On the contrary,an implementation of the field excitation with an unmodulated carrier would require a sim- ulation of the FDTD method at each frequency of interest. Thus,a considerable reduction in the simulation time is achieved. The results presented,describing the field behavior inside the enclosure,agree with theory to a high degree.

Spatial Correlation Functions for Fields in Three - Dimensional Rayleigh Channels

Abstract: Starting from a continuous plane-wave representation of the electric and magnetic fields, spatial auto- and cross-correlation functions for field components and their modulus are derived in the three-dimensional Rayleigh channel case. It is shown that existing results, generally relying on two-dimensional or isotropic models, can significantly differ from those obtained thanks to a three-dimensional approach.

Numerical and Theoretical Study of Photonic Crystal Fibers

Abstract: In this work, we study a novel type of optical waveguide, whose properties derive from a periodic arrangement of fibers (not necessarily circular), and from a central structural defect along which the light is guided. We first look for propagating modes in photonic crystal fibers of high indexcore region which can be single mode at any wavelength (1-4). Unlike the first type of photonic crystal fibers, whose properties derive from a high effective index, there exists some fundamentally different type of novel optical waveguides which consist in localizing the guided modes in air regions (4-5). These propagating modes are localized in a low-indexstructural defect thanks to a photonic bandgap guidance for the resonant frequencies (coming from the photonic crystal cladding). We achieve numerical computations with the help of a new finite element formulation for spectral problems arising in the determination of propagating modes in dielectric waveguides and particularly in optical fibers (7). The originality of the paper lies in the fact that we take into account both the boundness of the crystal (no Bloch wave expansion or periodicity boundary conditions) and the unboundness of the problem (no artificial boundary conditions at finite distance). We are thus led to an unbounded operator (open guide operator) and we must pay a special attention to its theoretical study before its numerical treatment. For this, we choose the magnetic field as the variable. It involves both a transverse field in the section of the guide and a longitudinal field along its axis. The section of the guide is meshed with triangles and Whitney finite elements are used, i.e., edge elements for the transverse field and node elements for the longitudinal field. To deal with the open problem, a judicious choice of coordinate transformation allows the finite element modeling of the infinite exterior domain. It is to be noticed that the discretization of the open guide operator leads to a generalized eigenvalue problem, solved thanks to the Lanczos algorithm. The code is validated by a numerical study of the classical

Length Reduction of Evanescent-Mode Ridge Waveguide Bandpass Filters

Abstract: Length reduction of evanescent-mode ridge waveguide bandpass filters is investigated extensively. Based on the conventional filter configuration, two new filter configurations are proposed: one is the generalized filter, and the other is the folded filter. In the generalized filter configuration, the cross sections of the evanescent waveguide and the ridge waveguide are not necessarily the same. It is found that the filter length can be reduced by enlarging the evanescent waveguide height. In the folded filter configuration, the filter is folded back at the middle coupling section. The folded junction is ridged to provide the required coupling between the two ridge waveguide resonators it connects. A design example demonstrates the feasibility of this filter configuration.

Antennas on High Impedance Ground Planes: on the Importance of the Antenna Isolation

Abstract: Photonic Band-Gap materials (PBG) are periodic structures composed of dielectric materials or metal. They exhibit frequency bands for which no propagation mode can propagate. Unfortunately, they are bulky and their period has to be at least a quarter wavelength. One extension of the PBG structures is called High impedance ground planes (High Z). Their period is much smaller and they exhibit frequency bands in which no surface wave can propagate. Their electromagnetic characteristics make them particularly interesting for antenna applications. On the one hand, they reduce the interaction between an antenna and its backward surroundings, with smaller size than usual ground planes. On the other hand, they can be used for planar antenna solutions, as the radiating element can be placed right on the top of the ground plane. After a presentation of the steps which lead to High Impedance ground planes, the electromagnetic characteristics of such ground planes are presented. Then, some antenna applications illustrate the interest of such structures. 1 High Impedance Ground History 1.1 Photonic Band-Gap Materials 1.2 Metallo-Dielectric PBG 1.3 High Impedance Ground Planes 2 Electromagnetic Characteristics of High Impedance Ground Planes 2.1 Corrugated Surfaces 2.2 High Z Equivalent Circuit Model 2.3 High Z Electromagnetic Characteristics

Dispersion diagrams of bloch modes applied to the design of directive sources

Abstract: We present an original study which makes use of a convenient representation of the dispersion diagrams of Bloch modes for the design of angular selective sources. These diagrams provide us all the pertinent information about the radiative properties of the photonic crystal, and a guideline to optimize the structure in order to obtain the suitable properties. We apply these tools in two cases: when the radiated field propagates normally to the device, and also for an off-axis radiating device. Several numerical examples obtained from a rigorous numerical method show the relevance of this approach.

Identification of radar targets in resonance zone: e-pulse techniques

Abstract: Radar scattering amplitudes contain pole singularities whose importance was recognized in the context of the Singularity Expansion Method: S.E.M. This method uses the fact that the late time domain response rt(t) of a target, illuminated by an E.M. wave, is mainly defined in a frequency band corresponding to the resonance region of the object. The knowledge of the singularities is useful information for discrimination of radar targets and has been used for different purposes of discrimination and identification. In this paper, we propose a modified scheme of radar target identification. The method presented is based on E-Pulse technique. In practical cases, direct application of classical E-Pulse techniques is not very efficient. Its performances are damaged by the characteristics of the exciting signal (antenna output signal). We propose a modified scheme of E-Pulse technique, which allows more accurate target discrimination and improves radar target identification. This procedure requires the deconvolution of the target response by the antenna signal and the application of an equivalent gaussian impulse excitation. This process has been successfully tested to FDTD simulations and measurements in anechoic chamber. 40 Toribio, Saillard, and Pouliguen

Rayleigh multipole methods for photonic crystal calculations

Abstract: —Multipolemethodshaveevolvedtobeanimportantclassof theoretical and computational techniques in the study of photoniccrystalsandrelatedproblems. Inthischapter,wepresentasystematicand unified development of the theory, and apply it to a range ofscatteringproblemsincludingfinitesetsofcylinders,two-dimensionalstacks of grating and the calculation of band diagrams from thescattering matrices of grating layers. We also demonstrate its utilityin studies of finite systems that involve the computation of the localdensityofstates.1 Introduction2 TheoreticalFormulation2.1 BackgroundandContext2.2 GeneralFramework2.3 InfiniteStructures—Arrays2.4 InfiniteStructures—Gratings2.5 InfiniteStructureswithComplexUnitCell2.6 InfiniteStructures—CrossedGratingsand“Woodpiles”3 FromScatteringMatricestoBandDiagrams4 DisorderedPhotonicCrystals5 Green’s Tensor and Local Density of States for 2DPhotonicCrystals5.1 Background5.2 LDOSforTMPolarisation5.3 LDOSforTEPolarisation6 DiscussionandOutlookReferences1. INTRODUCTIONWhile there exist a variety of theories [1–3] for solving generalscattering and propagation problems, methods that are stronglyadapted to particular scattering geometries or profiles can be quiteadvantageous. Such techniques yield highly accurate results withrelatively short computation times, permitting the study of largeror more complex structures, and facilitating asymptotic analyses incertainlimitingcases.

Numerical studies of disordered photonic crystals

Abstract: Since the first demonstration of a complete photonic band gap by E. Yablonovitch in 1987 [1], photonic band gap materials have attracted a very significant interest in Electromagnetism but also in Solid State Physics. Doped photonic crystals that have a point defect (a local disturbance) have been extensively studied with the emergence of this new area of Physics. They present localized modes in the band gap and triggered many potential applications. Fewer papers have been devoted to strongly disordered photonic crystals that are periodic on the average. These structures are disturbed on the overall feature and the defect corresponding is referred to as extended. Analogue at a first glance to amorphous semiconductors, these materials could present interesting properties. Moreover, manufacture of photonic crystals is still a real challenge for the optical domain and undesirable extended defects can appear leading to a compulsory study of the tolerances of periodicity for such new materials.

Electromagnetic scattering from a dielectric cylinder with multiple eccentric cylindrical inclusions

Abstract: A simple and direct method to the problem of two- dimensional electromagnetic scattering from a dielectric cylinder with multiple eccentric cylindrical inclusions is proposed. The method is based on the T-matrix approach. An aggregate T-matrix of the external cylinder for TM-wave and TE-wave excitations is derived in terms of the T-matrices of individual cylinders isolated in the host medium. The backscattering and differential scattering cross- sections of the host cylinder are easily obtained by matrix calculations for the aggregate T-matrix. Numerical investigation is presented for the case where all cylinders have circular cross-sections. Numerical examples for up to three inclusions demonstrate that the scattering characteristics are significantly influenced by the internal asymmetry and inhomogeneity pertinent to the locations and material of the inclusions.

Radio wave propagation in perpendicular streets of urban street grid for microcellular communications. part I: channel modeling

Abstract: This paper proposes a spatial variant wideband propagation model for perpendicular street of urban street grid. Analytical expression of the spatial variant multi-ray channel transfer function is derived. The model provides characteristics of each ray in explicit expressions. The ray characteristics are given in terms of complex amplitude for both vertical and horizontal polarizations, path length, angle of arrival and departure. A set membership criteria is proposed to determine the coupling radio paths. The proposed model is not only capable in providing macroscopic quantities like mean field values and mean delay spread, but also the full wideband channel information, i.e., space dependent complex channel responses with a high time dispersion resolution. The proposed model can be used for studying different propagation problems in urban street grid for microcellular communications with applications e.g., antenna diversity techniques, multi-input multi-output (MIMO) channel capacity analysis, etc.

2D Cavity Modeling Using Method of Moments and Iterative Solvers

Abstract: The method of moments (MoM) and the electric field integral equations (EFIEs), for both parallel and perpendicular polarization were applied to simulate scattering from 2D cavity structures. This code employed several matrix equation solvers, such as the LU decomposition, conjugate gradient (CG) method, bi-conjugate gradient (BCG) method, generalized conjugate residual (GCR) method, and generalized minimal residual (GMRES) method. The simulated results can be used for future reference and benchmarking. A comparison on the convergence behavior of the CG, BCG, GCR, and GMRES methods was made for the benchmark geometry, such as offset bend cavity, rectangular waveguide with hub, double-bend Sshaped cavity, etc. Some comments on the performance of the various iterative solvers will be highlighted.

Stripline transition to ridge waveguide bandpass filters

Abstract: Full wave optimization is implemented to design a wide band transition from shielded stripline to ridge waveguide. A bandpass ridge waveguide filter, with input/output realized through tapped-in stripline is designed. Using rigorous mode matching technique the generalized scattering matrices of all the building blocks are obtained. Design procedure is described and examples are given to demonstrate the features of the tapped-in coupling structure. The tapped-in structure results in a considerable reduction of the filter's total length compared to the use of two transitions.

FDTD Simulations of Reconfigurable Electromagnetic Band Gap Structures for Millimeter Wave Applications

Abstract: Metallo-dielectric electromagnetic bandgap (EBG) structures are studied in the millimeter regime with a finite difference time domain (FDTD) simulator. Several EBG waveguiding structures are considered for millimeter-wave power splitting, switching and filtering operations. It is demonstrated that triangular EBG structures lend themselves naturally to the design of Y-power splitters. Square EBG structures with circular and square rods are shown to lead naturally to straight in-line waveguide filter applications. Comparisons between EBG millimeter-wave waveguide filters formed with dielectric and metallic rods are given. It is shown that high quality broad bandwidth, millimeter-wave bandstop filters can be realized with square EBG structures with circular metallic rods. It is demonstrated that multiple bandstop performance in a single device can be obtained by cascading together multiple EBG millimeter-wave waveguide filters. It is also demonstrated that one can control the electromagnetic power flow in these millimeter-wave EBG waveguide devices by introducing additional local defects. It is shown that the Y-power splitter can be made reconfigurable by using imposed current distributions to achieve these local defects and, consequently, that a millimeter-wave EBG switch can be realized.

Numerical studies of Metallic PBG Structures

Abstract: Abstract—Photonic Bandgap (PBG) materials have been investigated for their versatility in controlling the propagation of electromagnetic waves [1, 2]. In order to determine PBG structures responses, several analytical or numerical methods are used, such as: • The plane wave method applied to solve Maxwell’s equations [3]. • The transfer matrix method, based on the wire grating impedance developed by N. Marcuvitz [4]. • The Finite Element Method (FEM) exhibits, e.g., the frequency response of reflection and transmission coefficients of the PBG materials when they have infinite surfaces and are excited by plane wave. The FEM method can be also used in the case of finite structure fed by a dipole. • The Finite Difference Time Domain method (FDTD). This method solves the discretized Maxwell’s equations in the time domain and evaluates the electromagnetic field components. These EM fields are then obtained in the frequency domain thanks to a Fourier Transform.

Simulated and Measured Performance of a Patch Antenna on a 2-Dimensional Photonic Crystals Substrate

Abstract: This paper deals with the use of Photonic Crystal (PC) structures as substrates in patch antenna configurations in order to mitigate the effect of the surface wave mode propagation. The case of a single antenna has been studied. A comparison between a conventional substrate based patch and a patch with a PC as substrate has been performed. The antennas were fabricated and measured. Improvements in all the main parameters of the antenna were obtained when using a PC. The frequency dependence of the radiation patterns is significantly reduced when using a PC as substrate.

A Practical Approach to Modeling Doubly Curved Conformal Microstrip Antennas

Abstract: Designers are increasingly integrating conformal microstrip antennas into the curved structures of either air or land vehicles. Quite often, these structures are doubly curved (e.g. curved along two orthogonal surface directions). This practice necessitates the development of accurate codes versatile enough to model conformal antennas with arbitrarily shaped apertures radiating from doubly curved surfaces. Traditional planar-structure-based design techniques are not well suited for this application. A hybrid finite element-boundary integral formulation appropriate for the high-frequency analysis and design of doubly curved conformal antennas is introduced in this paper. The novelty of this approach lies in its use of an asymptotic prolate spheroidal dyadic Green’s function to model the physics of curved surface diffraction. To demonstrate the utility of this approach, the effects of curvature on the resonant frequency and input impedance of both a doubly curved conformal square and circular patch antenna are investigated. Different feed positions are also considered. Due to a paucity of published experimental data, the numerical results are benchmarked by comparison with the results for planar square and circular patch antennas. The planar results are obtained by using an experimentally validated planar finite element-boundary integral code. 296 Macon, Trott, and Kempel

Genetically Evolved Phase-Aggregation Technique for Linear Arrays Control

Abstract: This paper presents a modified Genetic Algorithm (GA) technique in which the large phase perturbations are calculated by aggregating small phase increments. The proposed aggregation GA technique overcomes the major drawback of the large solution space required by the classical GA techniques. The proposed method adopts small ranges for increments of the parameters and the optimality is reached via aggregation of the best increments of phases. Consequently, the GA searches in a smaller solution space and finds the solution with reduced number of iterations. Simulation results show the achieved improvement of the proposed technique over the classical GA. The suppressed sectors using phase-only control are accomplished with and without element failures. Problems like imposing symmetrical nulls around the mainbeam and compensation for the failure of center element have been achieved.

Wave propagation in a curved waveguide with arbitrary dielectric transverse profiles

Abstract: A rigorous approach is derived for the analysis of electromagnetic (EM) wave propagation in dielectric waveguides with arbitrary profiles, situated inside rectangular metal tubes, and along a curved dielectric waveguide. The first objective is to develop a mode model in order to provide a numerical tool for the calculation of the output fields for radius of curvature 0.1 m ≤ R ≤∞ . Therefore we take into account all the terms in the calculations, without neglecting the terms of the bending. Another objective is to demonstrate the ability of the model to solve practical problems with inhomogeneous dielectric profiles. The method is based on Fourier coefficients of the transverse dielectric profile and those of the input wave profile. These improvements contribute to the application of the model for inhomogeneous dielectric profiles with single or multiple maxima in the transverse plane. This model is useful for the analysis of dielectric waveguides in the microwave and the millimeter-wave regimes, for diffused optical waveguides in integrated optics, and for IR regimes.

Study on Bandwidth of 2-D Dielectric PBG Material

Abstract: �H by extending Bloch theorem to the vector field Maxwell equations, the characteristics of 2-D dielectric rod array with square cross-section elements arranged in square lattice is analyzed in detail. From the numerical results, empirical expressions for both the relative bandwidth of frequency band gap and the midgap frequency with respect to the average permittivity, under the optimal filling fraction of dielectric/air in cross-section for wider bandwidth, are formulated by means of data fit.