# Showing papers in "IEEE Transactions on Antennas and Propagation in 1981"

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TL;DR: A survey of microstrip antenna elements is presented, with emphasis on theoretical and practical design techniques, and critical needs for further research and development for this antenna are identified.

Abstract: A survey of microstrip antenna elements is presented, with emphasis on theoretical and practical design techniques. Available substrate materials are reviewed along with the relation between dielectric constant tolerance and resonant frequency of microstrip patches. Several theoretical analysis techniques are summarized, including transmission-line and modal-expansion (cavity) techniques as well as numerical methods such as the method of moments and finite-element techniques. Practical procedures are given for both standard rectangular and circular patches, as well as variations on those designs including circularly polarized microstrip patches. The quality, bandwidth, and efficiency factors of typical patch designs are discussed. Microstrip dipole and conformal antennas are summarized. Finally, critical needs for further research and development for this antenna are identified.

1,485Â citations

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TL;DR: In this paper, a technique for controlling the operating frequency and polarization of microstrip antennas is proposed, which is achieved by placing shorting posts at appropriate locations within the antenna's boundaries.

Abstract: A technique is investigated for controlling the operating frequency and polarization of microstrip antennas. The control is achieved by placing shorting posts at appropriate locations within the antenna's boundaries. By changing the number and locations of the posts, the operating frequency can be tuned over a 1.5-to-1 range, and the polarization can be changed from horizontal to vertical, right-hand circular, or left-hand circular. All of these changes are obtained without significantly altering the input impedance or radiation patterns of the antenna and without increasing the complexity of the external microwave feed network. The frequency and polarization can be electronically controlled by using microwave switching diodes for the shorting posts. Antennas that have two feeds and operate simultaneously in two orthogonal polarizations have been constructed with the capability to switch between linear and circular polarization. Also, a thin frequency-scanned array has been built with the frequency-agile microstrip elements.

303Â citations

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TL;DR: In this article, an efficient algorithm is presented to compute the shape of perfectly conducting cylinders via knowledge of scattering cross sections, and mathematical analysis is performed in terms of operator and functions, and the fundamental instability of the problem is demonstrated.

Abstract: An efficient algorithm is presented to compute the shape of perfectly conducting cylinders via knowledge of scattering cross sections. This choice of scattering data avoids the difficulties linked with the phase measurements or reconstructions. The mathematical analysis is performed in terms of operator and functions, and the fundamental instability of the problem is demonstrated. Then the stability is restored by means of a Tikhonov-Miller regularization. The efficiency of the method is outlined by numerical examples. References are given which show that the same algorithm applies to other electromagnetic inverse problems, especially to gratings.

291Â citations

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TL;DR: Past and present technological developments in microstrip antenna arrays are summarized and emphasis is on exploring the potential of such arrays for satisfying the requirements of advanced military and commercial applications.

Abstract: Past and present technological developments in microstrip antenna arrays are summarized. Emphasis is on exploring the potential of such arrays for satisfying the requirements of advanced military and commercial applications.

263Â citations

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TL;DR: In this paper, the current distribution, input impedance, and radiation pattern of wire antennas printed on a dielectric substrate are computed by solving Pocklington's equation by moment methods.

Abstract: Printed dipole antennas find increasing use in microwave as well as far infrared frequencies. The current distribution, input impedance, and radiation pattern are computed for wire antennas printed on a dielectric substrate. The current distribution is obtained by solving Pocklington's equation by moment methods. The Green's function pertinent to the problem involves improper Sommerfeld-type integrals. These integrals are computed by a real-axis integration technique which involves analytical and numerical steps. The effect of surface modes is carefully taken into account.

225Â citations

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TL;DR: A method for analyzing characterisitcs of open microstrip disk structures is presented, based on the spectral domain immittance matrix approach, and all the wave phenomena associated with the structures are incorporated.

Abstract: A method for analyzing characterisitcs of open microstrip disk structures is presented. The method is based on the spectral domain immittance matrix approach, and all the wave phenomena associated with the structures are incorporated. The method provides a number of unique and convenient features both in analytical and numerical phases. A numerical example illustrating the usefulness of the method is included. Some numerical results are compared with experimental data.

215Â citations

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TL;DR: Many of the popular methods for the solution of large matrix equations are surveyed in this paper with the hope of finding an efficient method suitable for both electromagnetic scattering and radiation problems and system identification problems.

Abstract: Many of the popular methods for the solution of large matrix equations are surveyed with the hope of finding an efficient method suitable for both electromagnetic scattering and radiation problems and system identification problems.

184Â citations

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TL;DR: In this paper, a series of measurements of the S -parameters was carried out to investigate the mutual coupling between L-band rectangular, nearly square, and circular microstrip antennas.

Abstract: Mutual coupling between L -band rectangular, nearly square, and circular microstrip antennas has been investigated experimentally by a series of measurements of the S -parameters. The mutual coupling level decreases monotonically with increasing separation between elements with the E -plane coupling down 20 dB and the H -plane coupling down 25 dB for typical adjacent element spacings. For 1/16 in and 1/8 in substrates at L -band the predominant coupling mechanism is via the space wave since the surface wave is shown experimentally to be small.

178Â citations

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TL;DR: Approximate boundary conditions are a means for simulating material and surface effects in scattering and propagation as discussed by the authors, and criteria for their validity are given for the validity of these conditions.

Abstract: Approximate boundary conditions are a means for simulating material and surface effects in scattering and propagation. A number of conditions are discussed, and criteria are given for their validity.

167Â citations

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TL;DR: In this article, an approximate asymptotic solution for the electromagnetic fields induced on an electrically large perfectly conducting smooth convex surface by an infinitesimal magnetic or electric current moment on the same surface is presented.

Abstract: An approximate asymptotic solution is presented for the electromagnetic fields which are induced on an electrically large perfectly conducting smooth convex surface by an infinitesimal magnetic or electric current moment on the same surface. This solution can be employed to calculate the mutual coupling between antennas on a convex surface in an efficient and accurate manner. In this solution, the surface fields propagate along Keller's surface ray paths, and their description remains uniformly valid within the shadow boundary transition region including the immediate vicinity of the source. Furthermore, the effect of surface ray torsion on the surface fields is indicated in the present solution, through a factor T/k , where T denotes the surface ray torsion and k is the surface curvature in the ray direction. This solution is deduced from the asymptotic solutions to simpler canonical problems. Numerical results for the mutual coupling between slots in cylinders and cones are presented, and are shown to compare very well with experiments.

159Â citations

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TL;DR: In this paper, a compact approximate asymptotic solution for the field radiated by an antenna on a perfectly conducting smooth convex surface was developed for the GPDD field.

Abstract: A compact approximate asymptotic solution is developed for the field radiated by an antenna on a perfectly conducting smooth convex surface. This high-frequency solution employs the ray coordinates of the geometrical theory of diffraction (GTD). In the shadow region the field radiated by the source propagates along Keller's surface diffracted ray path, whereas in the lit region the incident field propagates along the geometrical optics ray path directly from the source to the field point. These ray fields are expressed in terms of Fock functions which reduce to the geometrical optics field in the deep lit region and remain uniformly valid across the shadow boundary transition region into the deep shadow region. Surface ray torsion, which affects the radiated field in both the shadow and transition regions, appears explicitly in the solution as a torsion factor. The radiation patterns of slots and monopoles on cylinders, cones, and spheroids calculated from this solution agree very well with measured patterns and with patterns calculated from exact solutions.

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TL;DR: A general framework for regularization and approximation methods for ill-posed problems is developed in this paper, where three levels in the resolution processes are distinguished and emphasized: philosophy of resolution, regularization-approximation schema, and regularization algorithms.

Abstract: A general framework for regularization and approximation methods for ill-posed problems is developed. Three levels in the resolution processes are distinguished and emphasized: philosophy of resolution, regularization-approximation schema, and regularization algorithms. Dilemmas and methodologies of resolution of ill-posed problems and their numerical implementations are examined in this framework with particular reference to the problem of finding numerically minimum weighted-norm least-squares solutions of first kind integral equations (and more generally of linear operator equations with nonclosed range). A common problem in all these methods is delineated: each method reduces the problem of resolution to a "nonstandard" minimization problem involving an unknown critical "parameter" whose "optimal" value is crucial to the numerical realization and amenability of the method. The "nonstandardness" results from the fact that one does not have explicitly, or a priori, the function to be minimized; it has to built up using additional information, convergence rate estimates, and robustness conditions, etc. Several results are developed that complement recent advances in numerical analysis and regularization of inverse and ill-posed (identification and pattern synthesis) problems. An emphasis is placed on the role of constraints, function space methods, the role of generalized inverses, and reproducing kernels in the regularization and stable computational resolution of these problems. The results will be applied specifically to problems of antenna synthesis and identification. However the thrust of the paper is devoted to the interdisciplinary character of operator-theoretic and numerical methods for ill-posed problems.

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TL;DR: In this article, a traveling-wave design technique for microstrip series arrays is discussed, which is applicable to both resonant and nonresonant array configurations, and experimental results for both configurations are presented.

Abstract: A traveling-wave design technique for microstrip series arrays is discussed. The technique is applicable to both resonant and nonresonant array configurations. Experimental results for both configurations are presented.

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TL;DR: In this paper, the method of moments is used to analyze microstrip antennas of rectangular and nonrectangular shape, and surface currents are used to model the microstrip patch and volume polarization currents for the dielectric slab.

Abstract: The method of moments is used to analyze microstrip antennas of rectangular and nonrectangular shape. Surface currents are used to model the microstrip patch and volume polarization currents for the dielectric slab. The method requires unusually precise computation of the impedance matrix but is capable of accurately predicting currents, impedance, and resonant frequency of the antenna.

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TL;DR: In this paper, it was shown that due to the vector nature of electromagnetic waves, electromagnetic remote sensing and inverse scattering techniques, if applied rigorously, require incorporation of polarization information into their formulation.

Abstract: The complete description of electromagnetic scattering processes implies polarization since an electromagnetic scatterer acts like a polarization transformer. The main objective is to show that due to the vector nature of electromagnetic waves, electromagnetic remote sensing and inverse scattering techniques, if applied rigorously, require incorporation of polarization information into their formulation. By applying this approach to existing and some novel theories, remarkable improvements in quality and fidelity of the reconstructed profiles and/or images can be obtained. Thus there is ample justification for continuing efforts in developing methods and theories of vector inverse scattering for the electromagnetic polarization-dependent case or in the even more complicated seismic case of p - and s -wave interaction in elastic media as for example encountered in vertical seismic profiling.

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TL;DR: In this paper, the performance of an adaptive array using three mutually perpendicular dipoles (a "tripole") is studied, where a desired signal and an interference signal, each with arbitrary angle of arrival and polarization, are assumed incident on the array.

Abstract: The performance of an adaptive array using three mutually perpendicular dipoles (a "tripole") is studied. A desired signal and an interference signal, each with arbitrary angle of arrival and polarization, are assumed incident on the array. Uncorrelated thermal noise is also assumed present on each element signal. The output desired signal-to-interference-plus-noise ratio (SINR) is computed as a function of the signal arrival angles and polarizations. It is shown that for most angles of arrival and polarizations, the array has an excellent ability to protect a desired signal from interference. Certain special cases where the performance is not good are discussed in detail.

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TL;DR: In this paper, the inverse problem of solving an integro-differential operator with a given set of inputs and outputs is studied. But the authors focus on the problem of regularizing an ill-posed problem to a well-posed one.

Abstract: Many problems of mathematical physics can be formulated in terms of the operator equation Ax = y , where A is an integro-differential operator. Given A and x , the solution for y is usually straightforward. However, the inverse problem which consists of the solution for x when given A and y is much more difficult. The following questions relative to the inverse problem are explored. 1) Does specification of the operator A determine the set \{y\} for which a solution x is possible? 2) Does the inverse problem always have a unique solution? 3) Do small perturbations of the forcing function y always result in small perturbations of the solution? 4) What are some of the considerations that enter into the choice of a solution technique for a specific problem? The concept of an ill-posed problem versus that of a well-posed problem is discussed. Specifically, the manner by which an ill-posed problem may be regularized to a well-posed problem is presented. The concepts are illustrated by several examples.

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TL;DR: In this paper, a unique aspect-invariant excitation waveform is proposed for an isolated scatterer, which is used in the singularity expansion method (SEM) or for target identification.

Abstract: Two general classes of inversion techniques may be distinguished: those utilizing angular or spatial frequency analysis over as wide a range of target aspects as practicable, and those involving relatively few aspects but employing as wide a frequency spectrum as possible. The latter technique is discussed, and a special excitation waveform called the "kill-pulse" or K-pulse is proposed. By analogy with lumped and distributed networks, a unique aspect-invariant excitation waveform is postulated for an isolated scatterer. This waveform, of finite and minimal duration, then characterizes the pole spectrum of the scatterer as used in the singularity expansion method (SEM) or for target identification. The derivation of this excitation waveform and its relation to one or more surface waves is illustrated by several examples. Using surface waves initiated at certain points of an object, the complex attenuation of circumnavigating waves is estimated by the geometrical theory of diffraction. Three-parameter characteristic equations are derived which predict pole strings with excellent accuracy for conducting spheres and cylinders and lesser accuracy for prolate spheroids of several axial ratios. For spheres and cylinders, the same characteristic equation also yields good estimates of cavity resonance frequencies.

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TL;DR: In this paper, a new class of printed circuit radiator consisting of a microstrip dipole electromagnetically coupled to the microstrip feed line is described, and several configurations which differ in bandwidth, efficiency, and construction simplicity are presented.

Abstract: A new class of printed circuit radiator consisting of a microstrip dipole electromagnetically coupled to a microstrip feed line is described. Several configurations which differ in bandwidth, efficiency, and construction simplicity are presented. A geometry which has been found to be optimum for many applications is noted. Radiation characteristics of both isolated elements and arrays of elements are examined. Experimental and theoretical results are presented.

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TL;DR: A theoretical analysis of an elliptical microstrip antenna is presented in this article, where it is shown that radiation from this antenna is left-hand or right-hand circularly polarized in a narrow frequency band when the eccentricity of the ellipse is small.

Abstract: A theoretical analysis of an elliptical microstrip antenna is presented. It is shown that radiation from this antenna is left-hand or right-hand circularly polarized in a narrow frequency band when the eccentricity of the ellipse is small. The theoretical result agrees with the experimental data.

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TL;DR: In this paper, the mutual impedance between microstrip dipoles printed on a grounded substrate is computed, and the significance of surface waves to mutual coupling is discussed, in broadside, collinear, and echelon arrangements.

Abstract: The mutual impedance between microstrip dipoles printed on a grounded substrate is computed. Results for the microstrip dipoles in broadside, collinear, and echelon arrangements are presented. The significance of surface waves to mutual coupling is discussed.

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TL;DR: In this article, the problem of a circular microstrip disk excited by a probe is solved using rigorous analysis using vector Hankel transforms, from which the unknown current can be solved for.

Abstract: The problem of a circular microstrip disk excited by a probe is solved using rigorous analysis. The disk is assumed to have zero thickness, and the current on the probe is taken to be uniform. Using vector Hankel transforms the problem is formulated in terms of vector dual-integral equations, from which the unknown current can be solved for. Due to the singular nature of the current distribution arising from probe excitation, the direct application of Galerkin's basis function expansion method gives a slowly convergent result. Therefore the singular part of the current is removed since the singularity is known a priori. The unknown current to be solved for is then regular and tenable to Galerkin's method of analysis. It is shown that this analysis agrees with the single-mode approximation when the dielectric substrate layer is thin, and that it deviates from the single-mode approximation when the substrate layer is thick. Excellent agreement of both the computed real and imaginary parts of the input impedance with experimental data is noted. The radiation patterns and the current distributions on the disk are also-presented.

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TL;DR: In this article, a full-wave analysis of a circular disk conductor printed on a dielectric substrate backed by a ground plane is presented based on the Galerkin's method applied in the Hankel transform domain and is numerically quite efficient.

Abstract: A full-wave analysis of a circular disk conductor printed on a dielectric substrate backed by a ground plane is presented. The method is based on the Galerkin's method applied in the Hankel transform domain and is numerically quite efficient. Several numerical examples are compared with available experimental data. The agreement is found to be quite good and the validity of the present method is confirmed.

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TL;DR: In this paper, the ability of a least mean square (LMS) adaptive array to adapt to the electromagnetic polarization of incoming signals is considered and the output signal-to-interference-plus-noise ratio (SINR) from the array is computed as a function of the signal angles of arrival and polarizations.

Abstract: The ability of a least mean square (LMS) adaptive array to adapt to the electromagnetic polarization of incoming signals is considered. An array of two pairs of crossed dipoles is studied. A desired signal and an interference signal are assumed to arrive from arbitrary directions with arbitrary elliptical polarizations. The output signal-to-interference-plus-noise ratio (SINR) from the array is computed as a function of the signal angles of arrival and polarizations. It is shown that as long as certain special desired signal polarizations are avoided, the array is difficult to jam with a single interference signal. To produce a poor SINR, an interference signal must both arrive from the same direction and have the same polarization as the desired signal.

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Raytheon

^{1}TL;DR: In this paper, an antenna consisting of an interconnected wire grid formed by etching metallic lines on a dielectric sheet backed by a metallic ground plane is described, and the theory of operation, analytical model, and experimental findings for this approach to a printed array are described.

Abstract: A description is given of an antenna consisting of an interconnected wire grid formed by etching metallic lines on a dielectric sheet backed by a metallic ground plane. The theory of operation, analytical model, and experimental findings for this approach to a printed array are described. The device is low cost, light weight, and has sufficient bandwidth to be of use in a variety of applications. An analytical model is developed which establishes transmission line equivalent circuits for the wire grid elements. Current distributions determined from the model are shown to predict accurately the measured pattern performance of a typical implementation. The bandwidth as established by various pattern parameters is quantitatively assessed. Particular emphasis is given to methods of amplitude control through control of line impedances. A particular design implementation is presented for a five-wavelength circular array with independent quadrant control. Measured results from this configuration are compared to theory.

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TL;DR: In this paper, reference beam addition, apodization and the use of multiple intensity distributions have been proposed for phase retrieval in a one-dimensional field, where the phase ambiguity arises as the result of the possibilities of conjugating the zeros of F(z), z = x + jy.

Abstract: The phase retrieval problem arises in applications of electromagnetic theory in which wave phase is apparently lost or impractical to measure and only intensity data are available. The mathematics of the problem provides unusual insights into the nature of electromagnetic fields. The theory is reviewed and illustrated. The basic issue of the phase retrieval problem, stated for a one-dimensional field, is that although a unique Fourier transform relation exists between the field F(x) in the Fraunhofer plane and the field u(x') in the object plane, the infinite fold phase ambiguity which appears as the result of the possibilities of conjugating the zeros of F(z), z = x + jy implies that additional information or processing of the object wave must be available to obtain the phase. Among the possible solutions which are described are reference beam addition, apodization and the use of multiple intensity distributions, permitting the use of iterative computational procedures in some applications.

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Abstract: A theoretical study is presented of the input impedance of a circular microstrip disk antenna excited by a coaxial line. The theory is based on Green's function technique applied to the disk cavity with the boundary admittance at the edge. Both the feed pin size and the boundary admittance are shown to be important in deriving the analytical expression for the input impedance. The boundary admittance is obtained by considering the radiated power and the electric and magnetic stored energies in the fringe capacitance. The analytical expression for the input impedance includes the feed location, the feed pin size, the disk size and thickness, and the dielectric constant of the material, and is useful for optimizing various parameters. The calculations are compared with experimental data showing a good agreement.

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TL;DR: In this article, a numerical method is presented to compute one unknown constitutive parameter of an inhomogeoeous lossy dielectric slab from the reflected field in the time domain.

Abstract: A numerical method is presented to compute one unknown constitutive parameter of an inhomogeoeous lossy dielectric slab from the reflected field in the time domain. The method is based upon a space-time discretization of the integral equation for the reflected field. In the inversion, especially those space-time points where the numerical computation of the electric-field strength in the slab is most accurate are taken into account. This is achieved by computing the unknown parameter iteratively. Alternately solving equations for an approximate direct-scattering problem and an approximate inverse-scattering problem yields successive approximations for the electric field in the slab and the unknown constitutive coefficient. Both problems lead to an infinite system of linear equations from which a finite subsystem is selected. General criteria for this selection are presented. Various profiles have been reconstructed numerically from the reflected field due to a sine-squared incident pulse.

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TL;DR: Its algorithm for imaging ground-based targets is described and experimental results are given for a 3 cm wavelength demonstration system using a distorted 27-m random sparse array, confirming the validity of the technique.

Abstract: High angular resolution radar imaging may be achieved with a large-aperture antenna even if the aperture is distorted, provided that adaptive signal processing compensates for the distortion. The radio camera is an instrument designed for this purpose. Its algorithm for imaging ground-based targets is described and experimental results are given for a 3 cm wavelength demonstration system using a distorted 27-m random sparse array. The measured beamwidth of 1 mrad conformed to theory, confirming the validity of the technique. Extension of the algorithm to accommodate isolated targets such as aircraft and ships also is discussed.

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TL;DR: In this article, a variable coordinate system associated with the local features of two-dimensional rough surfaces with arbitrary slope is derived for the depolarization of the scattered radiation fields, and the analytical procedures used in the derivations of the solutions are presented.

Abstract: Employing a variable coordinate system associated with the local features of two-dimensionally rough surfaces with arbitrary slope, full-wave solutions are derived for the depolarization of the scattered radiation fields. An outline of the analytical procedures used in the derivations of the solutions are presented. Furthermore, the engineer who is not familiar with them can also use the final result which is expressed as a definite integral whose integrand is given explicitly and in closed form. These full-wave solutions are compared with the quasi-optics solution and the iterative or perturbational solutions for slightly rough surfaces, and they are shown to bridge the wide gap that exists between them. The full-wave solutions are consistent with energy conservation, duality, and reciprocity relationships in electromagnetic theory. These solutions account for upward and downward scattering of the incident waves with respect to the horizontal reference plane, thus shadowing and multiple scattering are considered. Applications to two-dimensionally periodic structures and random rough surfaces are also presented. The fullwave solutions are examined for Brewster, grazing, and specular angles and backscatter. Special consideration is also given to good conducting boundaries.