Introduction
The Tracking and Data Relay Satellite System (TDRSS) is a constellation of geosynchronous satellites, which are the primary source of space-to-ground voice, data and telemetry for the Space Shuttle [1]. The satellites also provide communications with the International Space Station and scientific spacecraft in low-Earth orbit such as the Hubble Space Telescope. Integral to the design of the TDRSS class of satellites is an architecture consisting of a multiple access (MA), S-band, phased array antenna. This MA system receives and relays data simultaneously from five lower data-rate users and transmits commands to a single user.