The effects of the thermal protection system on the Space Shuttle S-band quad antennas

A theory is presented to determine the effects of the multiple dielectric thermal protection system on the Space Shuttle orbiter´s S-band quad antennas. A ray optics approach is developed which indicates internal reflections from the orbiter metallic skin and multiple dielectric layers. The results of the computer program developed show that the beamwidth of the two upper quad antennas is narrowed by a thermal protection system. The results also show that the thermal protection system will cause significant depolarization of a circularly polarized signal as the angle from the normal to the antenna surface is increased. Heating of the thermal protection surface or degradation due to multiple missions may also be predicted by incorporating changes in the complex permittivity as a function of temperature. Heating and multiple mission effects are found to be less than 1 dB