Showing papers by "Constantine A. Balanis published in 1988"

Attenuation distortion of transient signals in microstrip

Abstract: Attenuation distortion, and combinations of dispersion and attenuation distortions, of transient signals in microstrip lines are investigated. Conduction losses are considered for the general case where the strip conductor resistivity is different from that of the ground plane. Dielectric losses are examined for commonly used isotropic substrates. Attenuation and dispersion distortions of short pulses are shown to vary as microstrip and pulse parameters are changed. >

Pulse dispersion distortion in open and shielded microstrips using the spectral-domain method

Abstract: The spectral-domain method is used to compute the effective dielectric constant ( epsilon /sub r///sub eff/(f)) of open and shielded microstrip lines to analyze the dispersion distortion of short electrical pulses. Precise expressions for the longitudinal and transverse current distributions allow a high level of accuracy for epsilon /sub r///sub eff/(f). It is determined that computation time can be minimized for the open microstrip calculations by using the shielded microstrip formulation provided large dimensions for the conducting walls are assumed. >

Pulse time-delay method for geophysical tomography

Abstract: Geotomography methods are presented for reconstructions of index-of-refraction distributions for time-delay measurements. Two versions of the algebraic reconstruction technique (ART) are compared to the conjugate residual (CR) method with Lagrange multiplier conditioning. The CR method with Lagrange multiplier conditioning provided the best reconstructions for good anomaly boundary definition under noisy conditions. A ray bending model to account for refraction is also used in the reconstructions. Modifications are made in the algorithm to simplify its use and to improve the convergence stability. Two image filters, the two-group minimum-variance partition-average (MVP2-AVE) one and the selective smoothing (SS) one, are used in succession and some of the limitations of each filter are eliminated. This improves the implementation of the filters and the accuracy of the reconstructions. >

Comparison of higher-order diffractions in scattering by a strip

Abstract: The authors consider the far-field scattering of a plane wave from a perfectly-conducting, finite-width, infinitely-long strip using the geometric theory of diffraction/uniform theory of diffraction (GTD/UTD). Formulations for monostatic and bistatic scattering for both TE and TM polarizations are given. The results are compared with extended spectral theory of diffraction and moment method (MM) results to determine guidelines on the accuracy of the traditional GTD/UTD formulation. >

Scattering patterns of dihedral corner reflectors with impedance surface impedances

Abstract: The radar cross section patterns of lossy dihedral corner reflectors are calculated using a uniform geometrical theory of diffraction for impedance surfaces All terms of up to third order reflections are considered for patterns in the principal plane The surface waves are included whenever they exist for reactive surface impedances The dihedral corner reflectors examined have right, obtuse, and acute interior angles, and patterns over the entire 360 deg azimuthal plane are calculated The surface impedances can be different on the four faces of the dihedral corner reflector; however, the surface impedance must be uniform over each face Computed cross sections are compared with a moment method technique for a dielectric/ferrite absorber coating on a metallic corner reflector The analysis of the dihedral corner reflector is important because it demonstrates many of the important scattering contributors of complex targets including both interior and exterior wedge diffraction, half-plane diffraction, and dominant multiple reflections and diffractions

Interior impedance wedge diffraction with surface waves

Abstract: The exact impedance wedge solution is evaluated asymptotically using the method of steepest descents for plane wave illumination at normal incidence. Uniform but different impedances on each face are considered for both soft and hard polarizations. The asymptotic solution isolates the incident, singly reflected, multiply reflected, diffracted, and surface wave fields. Multiply reflected fields of any order are permitted. The multiply reflected fields from the exact solution are written as ratios of auxiliary Maliuzhinets functions, whereas a geometrical analysis gives the reflected fields as products of reflection coefficients. These two representations are shown to be identical in magnitude, phase and the angular range over which they exist. The diffracted field includes four Fresnel transition functions as in the perfect conductor case, and the expressions for the appropriate discontinuities at the shadow boundaries are presented. The surface wave exists over a finite angular range and only for certain surface impedances. A surface wave transition field is included to retain continuity. Computations are presented for interior wedge diffractions although the formulation is valid for both exterior and interior wedges.

Reflections, diffractions, and surface waves for an interior wedge with impedance surfaces

Abstract: The exact solution for the interior impedance wedge was evaluation asymptotically to yield a geometrical theory of diffraction (GTD). The geometrical-optics terms correspond identically to simple ray-tracing results. The diffraction field is analogous to the perfectly conduction case with suitable multiplying factors to account for the lossy reflections. The surface-wave contribution and its associated transition field are included to account for complex poles of the auxiliary Maliuzhinets function. Numerical integration using an adaptive quadrature routine was used to verify the accuracy of the technique. The analysis of the interior wedge geometry extends the work of M.I. Herman and J.L. Volakis (1987) to allow the study of complex structures which may include many multiple reflections and diffractions within interior wedges. >