RADAR ANTENNA PATTERN ANALYSIS FOR THE SPACE SHUTTLE USING NEC-BSC

Abstract

In order to improve tracking capability, radar transponder antennas will be mounted on the space shuttle solid rocket boosters (SRB). These four antennas, each being identical cavity-backed helices operating at 5.765 GHz, will be mounted near the top of the SRB's, adjacent to the intertank portion of the external tank. The purpose of this study is to calculate the roll-plane pattern (the plane perpendicular to the SRB axes and containing the antennas) in the presence of this complex electromagnetic environment. The large electrical size of this problem mandates an optical approach, thus a general purpose code, the Numerical Electromagnetics Code - Basic Scattering Code, was chosen as the computational tool. This code is based on the modern Geometrical Theory of Diffraction and allows computation of scattering of bodies composed of canonical shapes such as plates and elliptic cilinders. Apertures mounted on a curved surface (the SRB) cannot be accommodated by the code, so an antenna model consisting of wires was devised that approximated the actual performance of the antennas. Although the method of moments (MM) was not used in developing the antenna model, the code's MM input option proved instrumental in implementing the scheme. The improvised antenna model matched well with measurements taken at the NASA/Marshall Space Flight Center (MSFC) range. The SRB's, the external tank, and the shuttle nose were modeled as circular cylinders, and the code was able to produce what is thought to be a reasonable roll-plane pattern. [Vol. 5, No. l, pp. 39-46 (1990)]