Showing papers by "Constantine A. Balanis published in 1993"

MFIE analysis and design of ridged waveguides

Abstract: This paper presents a unified approach for the analysis and design of ridged waveguides by a magnetic held integral equation (MFIE) formulation. The MFIE approach allows accurate and complete solution via a simple numerical implementation of pulse basis functions. The emphasis of the paper is oriented to the design of ridged waveguides for applications in microwave components and systems, rather than to details of numerical algorithms. Erroneous bandwidth estimates due to neglect of the TE/sub 11/ mode in previous works have been corrected; and various useful design curves on cutoff frequency, bandwidth, attenuation, and waveguide impedance are provided. The proposed theory is verified by comparison to exact closed-form solutions and other published results. >

Analysis of pyramidal horn antennas using moment methods

Abstract: A hybrid numerical technique is developed for electrically large pyramidal horn antennas radiating in free space. A stepped-waveguide method is used to analyze the interior surfaces of the horn transition. The electric field integral equation (EFIE) is employed on the outer surfaces of the pyramidal horn including the radiating aperture. Meanwhile, the magnetic field integral equation (MFIE) is used on the aperture to relate the aperture fields and those in the horn transition The resultant hybrid field integral equation (HFIE) is solved numerically by the method of moments. This formulation is both accurate and numerically stable so that high-gain microwave pyramidal horns can be analyzed rigorously. Far-field radiation patterns, both computed and measured, are presented for three electrically-large X-band horn antennas. The comparisons demonstrate that this method is accurate enough to predict the fine pattern structure at wide angles and in the back region. Computed far-field patterns and aperture field distributions of two smaller X-band horns are also presented along with a discussion on the validity of the approximate aperture field distributions routinely used in the analysis and design of pyramidal horns. >

Finite-difference time-domain method for electromagnetic radiation, interference, and interaction with complex structures

Abstract: The finite-difference-time-domain (FDTD) method is reviewed and then used to model and predict the radiation patterns of a monopole antenna mounted on the bottom of a perfectly conducting helicopter structure. The computed radiation patterns are compared with measurements to demonstrate the accuracy of the FDTD method. To study the effect of antenna interference, a second monopole antenna is mounted on the structure and the patterns are recalculated. The perfectly conducting helicopter model is then replaced by a partially composite/partially conducting material structure and the electromagnetic fields penetrating the structure from an incident plane wave are analyzed. A preprocessing geometry program, GEOM, is used to generate an FDTD geometry model, assuming solid surface helicopter structure. >

NEC and ESP codes: guidelines, limitations, and EMC applications

Abstract: The computer modeling and simulation of EMC programs of complex structures are addressed, using the NEC and ESP moment method codes. The rules and guidelines of modeling using the two codes are summarized. In addition, visualization and automation of the modeling process are made possible through an interface computer program GEOM developed at Arizona State University. Finally, the interference between two wire antennas mounted on a complex helicopter model is given as an example of using these codes in EMC applications. >

Enhanced dominant mode operation of a shielded multilayer coplanar waveguide via substrate compensation

Abstract: The cutoff frequency of the first higher-order even mode in a shielded multilayer coplanar waveguide (CPW) is studied using the spectral domain approach (SDA). The effective dielectric constant for the dominant odd and first higher-order even mode in a shielded multilayer CPW is computed and compared to other published numerical results. Dielectric constant and substrate height are varied with respect to even mode cutoff frequency and plotted for several CPW structures. Different combinations of internal substrates are shown to produce even mode cutoff frequency maximization for increased odd mode operation bandwidth. >

Analysis of double- or quadruple-ridged waveguides by a magnetic surface integral equation approach

Abstract: The authors present a unified approach to the analysis of ridged waveguides by a magnetic field integral equation (MFIE) formulation. The MFIE approach allows an accurate and complete solution via a simple numerical implementation of pulse basis functions. The emphasis in the present work is on the design of ridged waveguides for applications in microwave components and systems, rather than on details of numerical algorithms. The proposed theory is verified by comparison with exact closed-form solutions and other published results. >

A physical optics/equivalent currents model for the RCS of trihedral corner reflectors

Abstract: The scattering in the interior regions of both square and triangular trihedral corner reflectors is examined The theoretical model presented combines geometrical and physical optics (GO and PO), used to account for reflection terms, with equivalent edge currents (EEC), used to account for first-order diffractions from the edges First-order, second-order, and third-order reflection terms are included Calculating the first-order reflection terms involves integrating over the entire surface of the illuminated plate Calculating the second- and third-order reflection terms, however, is much more difficult because the illuminated area is an arbitrary polygon whose shape is dependent upon the incident angles The method for determining the area of integration is detailed Extensive comparisons between the high-frequency model, Finite-Difference Time-Domain (FDTD) and experimental data are used for validation of the radar cross section (RCS) of both square and triangular trihedral reflectors

Three-dimensional automatic FDTD mesh generation on a PC

Abstract: The authors present a program developed at Arizona State University to generate automatically three-dimensional surface FDTD (finite-difference time-domain) mesh for a complex object. The program is based on an efficient ray-tracing algorithm and has been tested in various numerical simulations. The mesh generator can be used for a complex object enclosed by conducting and thin-dielectric surfaces. The high efficiency of the algorithm allows the mesh generation to be performed on a special computer. As an example, the mesh generation for a scale helicopter is shown. >

Radar cross section evaluation of the square trihedral corner reflector using PO and MEC

Abstract: Physical optics (PO) and the method of equivalent currents (MEC) were applied to the square trihedral corner reflector to evaluate its monostatic radar cross section (RCS). PO was used for the calculation of first, second, and third reflections from the trihedral plates, whereas MEC was used for the calculation of the first order diffractions from the edges. A complex program has been developed to calculate both monostatic and bistatic RCS of the square trihedral corner reflector for E-theta polarization. The agreement between the two methods is very good. >

Improved performance of microstrip couplers through multi-layer substrates

Abstract: Edge-coupled microstrip directional couplers are widely used in microwave circuits, however practical limits on center conductor spacings limit the level of coupling that can be attained. In addition, differences in the even and odd mode phase velocities degrade the performance of broad-side coupled microstrip directional couplers. A new technique for equalizing the phase velocities is presented which enhances the coupling and directivity, but uses wider center conductor spacing than traditional designs. This new technique uses two substrate layers where the upper substrate dielectric constant is much larger than the dielectric constant of the lower substrate. This allows the design of directional couplers with tighter couplings and better performance.

Scale model helicopter antenna pattern measurements at ASU's EMAC Facility

Abstract: The ElectroMagnetic Anechoic Chamber (EMAC) facility has been in operation at Arizona State University (ASU) since 1988. In addition to providing experimental verification for theoretical prediction of radiation and scattering targets, this multi-purpose facility acts as a testbed for a unique, semicompact antenna test range. Antenna patterns of a scale model helicopter have been measured at 500 MHz and compared to Numerical Electromagnetics Code (NEC) prediction. These measurements demonstrate that accurate antenna patterns can be measured at frequencies much lower than expected according to the conventional wisdom concerning rectangular anechoic chambers and compact ranges. Measurements made at EMAC of a scale model helicopter at UHF demonstrate remarkable agreement with theoretical prediction, particularly in the case of the electrically small reflector, absorber, and chamber. >

Enhanced dominant mode operation of shielded multilayer coplanar waveguide

Abstract: The effects of substrate height and dielectric constant on the propagation characteristics of a multilayer shielded symmetrical coplanar waveguide (CPW) are examined using a full-wave spectral-domain analysis (SDA). It was found that the effective dielectric constant of the shielded CPWs displayed a cutoff frequency for the even mode which can be controlled by varying the height and dielectric constant of the substrate, especially those directly below the coplanar slots. The highest cutoff frequencies found in three-layer CPW configurations utilized air as the lower substrate dielectric. In certain multilayer CPW combinations, when the lower substrate was not air, a bandwidth maximization effect was demonstrated using internal substrates. >

High-frequency techniques for RCS prediction of plate geometries and a physical optics/equivalent currents model for the RCS of trihedral corner reflectors

Abstract: Part 1 of this report continues the investigation, initiated in previous reports, of scattering from rectangular plates coated with lossy dielectrics. The hard polarization coefficients given in the last report are incorporated into a model, which includes second- and third-order diffractions, for the coated plate. Computed results from this model are examined and compared to measured data. A breakdown of the contribution of each of the higher-order terms to the total radar cross section (RCS) is given. The effectiveness of the uniform theory of diffraction (UTD) model in accounting for the coating effect is investigated by examining a Physical Optics (PO) model which incorporates the equivalent surface impedance approximation used in the UTD model. The PO, UTD, and experimental results are compared. Part 2 of this report presents a RCS model, based on PO and the Method of Equivalent Currents (MEC), for a trihedral corner reflector. PO is used to account for the reflected fields, while MEC is used for the diffracted fields. Single, double, and triple reflections and first-order diffractions are included in the model. A detailed derivation of the E(sub theta)-polarization, monostatic RCS is included. Computed results are compared with finite-difference time-domain (FDTD) results for validation. The PO/MEC model of this report compares very well with the FDTD model, and it is a much faster model in terms of computational speed.

Accurate and efficient computation of dielectric losses in multi-level, multi-conductor microstrip for CAD applications

Abstract: An approach to accurate and efficient computation of dielectric losses in complex microstrip structures is proposed. It can be used in lieu of lossy, full-wave solutions to provide accurate and efficient data for the CAD of multilevel, multiconductor MIC and MMIC structures. Results that are as accurate as lossy full-wave techniques over a wide range of frequencies, including the dispersive region, are obtained. In addition to providing accurate results, the method is up to three times faster, depending on the number and type of substrates or superstrates. Results for various multiconductor, multilevel structures that compare well with the lossy, full-wave approach and require significantly less computer time to compute are shown. >

Electromagnetics at Arizona State University

Abstract: Several research areas being investigated in the Department of Electrical Engineering at Arizona State University's College of Engineering and Applied Sciences are discussed. The topics of research include antennas, propagation, scattering, microwave circuits and devices, microwave measurements, and optical communications. The University's electromagnetic anechoic chamber, which is designed to perform precision antenna-pattern and radar-cross-section (RCS) measurements in the microwave region, is described. >

Improvement of the NEC code's upper limit and pattern prediction of a helicopter structure

Abstract: The capacity of the NEC (numerical electromagnetics code) has been doubled by modifying its file type of matrix storage. The loss of I/O (input/output) access speed due to using a direct-access file to store an out-of-core matrix has been compensated by reorganizing the sequence of matrix block factorization. Some factors that are important to the geometry modeling of electrically large complex structures have been considered in an attempt to balance the numerical accuracy and computational efficiency. The mesh generating program GEOM is introduced, and used to compute the antenna patterns of a 1:7 helicopter model made up of nearly 6000 elements. The predicted antenna patterns of the helicopter are compared with measurements at 1.492 GHz. The results showed good agreement with measurements. >

Scattering from coated geometries

Abstract: The authors present simplified, computationally faster, versions of the dielectric-wedge UTD (uniform geometrical theory of diffraction) coefficients for the case of a wedge with one perfectly conducting face. Expressions for several scattering configurations are considered. Included are plane-wave incidence, far-field observation; cylindrical-wave incidence from a finite distance (/spl rho/'), far-field observation; plane-wave incidence, observation at a finite distance (/spl rho/); and surface-wave scattering with the appropriate transition terms. These variations allow one to incorporate higher-order diffraction terms into the analysis of typical, practical target geometries such as a flat plate or dihedral corner reflector. A model for predicting the RCS (radar cross section) of a flat plate coated with an electrically thin, lossy dielectric using the UTD coefficients for a coated half plane is presented. >

RCS Analysis of Plate Geometries, parts 1 and 2

Abstract: High-frequency techniques for Radar Cross Section (RCS) prediction of plate geometries and a physical optics/equivalent currents model for the RCS of trihedral corner reflectors are addressed. In part 1, a Uniform Theory of Diffraction (UTD) model for the principal-plane radar cross section (RCS) of a perfectly conducting, rectangular plate coated on one side with an electrically thin, lossy dielectric is presented. In part 2, the scattering in the interior regions of both square and triangular trihedral corner reflectors are examined.

Advanced electromagnetic methods for aerospace vehicles

Abstract: The Advanced Helicopter Electromagnetics (AHE) Industrial Associates Program has continuously progressed with its research effort focused on subjects identified and recommended by the Advisory Task Force of the program. The research activities in this reporting period have been steered toward practical helicopter electromagnetic problems, such as HF antenna problems and antenna efficiencies, recommended by the AHE members at the annual conference held at Arizona State University on 28-29 Oct. 1992 and the last biannual meeting held at the Boeing Helicopter on 19-20 May 1993. The main topics addressed include the following: Composite Materials and Antenna Technology. The research work on each topic is closely tied with the AHE Consortium members' interests. Significant progress in each subject is reported. Special attention in the area of Composite Materials has been given to the following: modeling of material discontinuity and their effects on towel-bar antenna patterns; guidelines for composite material modeling by using the Green's function approach in the NEC code; measurements of towel-bar antennas grounded with a partially material-coated plate; development of 3-D volume mesh generator for modeling thick and volumetric dielectrics by using FD-TD method; FDTD modeling of horn antennas with composite E-plane walls; and antenna efficiency analysis for a horn antenna loaded with composite dielectric materials.

Closed-form expressions for the design of microstrip lines with two substrate layers

Abstract: A simple closed-form expression for the effective dielectric constant of a microstrip on a two-layer substrate is presented. Results for single-layer cases are incorporated in the formula to simplify it and increase the accuracy. The formula is curve-fitted from results computed with the spectral domain approach and is accurate to within 3% relative error over a wide range of parameters. >

Wide-Band Reduction of Coupling and Pulse Distortion in Multi-Conductor Integrated Circuit Lines

Abstract: Ultrafast clock speeds and short rise times of digital signals give them a very large bandwidth. With clock speeds in the Gigabit /second range and rise times on the order of 10 picoseconds, these signals will have significant frequency components in the tens to hundreds of GHz. This wide frequency range requires a full-wave analysis, rather than a a quasi-static one, to accurately predict the distortion and coupling of highspeed digital signals. High speed circuits also have small inter-line spacing to increase packing density, which in turn increases coupling distortion and crosstalk. Successful design of these high-speed circuits requires accurate prediction of pulse distortion and coupling, as well as a technique to reduce coupling over a very wide band of frequencies.

Solution of EM wave scattering from inhomogeneous and anisotropic objects by edge-based FEM

Abstract: A hybrid finite element method (FEM) is applied to solve the problem of electromagnetic scattering from a complex inhomogeneous and anisotropic object. In the FEM implementation considered, the open space is truncated by a fictitious surface conformal to the scatterer. The interior region is modeled by edge-based vector finite elements, while the exterior region is coupled to the interior region by tangential electric and magnetic fields on the surface. The use of edge-based vector finite elements is preferred because they are divergenceless, and can model continuous tangential fields across dielectric interfaces and on conducting surfaces. It is shown that the formulation and its computer program are applicable to virtually any objects. >

Contour path FDTD method for pyramidal horns with composite E-plane walls

Abstract: The CPFDTD (contour-path finite-difference time-domain) method was used for analysis of pyramidal horn antennas with or without composite E-plane walls. For the metallic horn very accurate antenna gain patterns were computed compared to measurements. When the E-plane walls are coated with lossy magnetic material, for gain pattern control, the CPFDTD yields acceptable gain patterns compared to measurements. >