Engineering topics

Shamansky, Harry T.

Publications and source records attributed to Shamansky, Harry T..

3 records

NASA NTRS1993

A physical basis formulation for the electromagnetic backscattering by a finite-length rectangular trough in a ground plane

The electromagnetic backscattering from a finite-length rectangular trough in an infinite ground plane is examined. A physical basis formulation, as introduced by Richmond (1985), is used to express the unknown currents in the trough aperture in terms of a forced wave resulting from the incident plane wave, and one or more pairs of oppositely directed traveling waves propagating along the trough. A Galerkin solution is employed to solve a very small system of equations to determine the weights of the postulated aperture currents, and then radiated to compute the radar cross section (RCS). These results are then compared with a measurement of a trough in a finite ground.

Shamansky, Harry T.↗

NASA NTRS1989

Electromagnetic scattering by a straight thin wire

The traveling-wave energy, which multiply diffracts on a straight thin wire, is represented as a sum of terms, each with a distinct physical meaning, that can be individually examined in the time domain. Expressions for each scattering mechanism on a straight thin wire are cast in the form of four basic electromagnetic wave concepts: diffraction, attachment, launch, and reflection. Using the basic mechanisms from P. Ya. Ufimtsev (1962), each of the scattering mechanisms is included into the total scattered field for the straight thin wire. Scattering as a function of angle and frequency is then compared to the moment-method solution. These analytic expressions are then extended to a lossy wire with a simple approximate modification using the propagation velocity on the wire as derived from the Sommerfeld wave on a straight lossy wire. Both the perfectly conducting and lossy wire solutions are compared to moment-method results, and excellent agreement is found. As is common with asymptotic solutions, when the electrical length of wire is smaller than 0.2 lambda the results lose accuracy. The expressions modified to approximate the scattering for the lossy thin wire yield excellent agreement even for lossy wires where the wire radius is on the order of skin depth.

Shamansky, Harry T.↗

NASA NTRS1988

The determination of the propagation constant for the traveling wave in an infinite ground plane

The propagation constant for the traveling wave in a trough in an infinite ground plane is examined. The null-field integral is used to determine the EM field in the trough structure, and pulse basis functions give the distribution of the aperture fields. From this, the propagation constant is solved for, using the Newton-Raphson iterative scheme. Various sizes of geometries are examined. The far-field patterns are calculated and compared with other solutions, thereby validating the integral formulation which subsequently provided the propagation constant. Measurements of two trough geometries are performed to validate the theoretical results.

Shamansky, Harry T.↗