Analysis and Optimization of CP Antenna Covered by Thermal Protection System for Broadband Applications

Installed antenna on a hypersonic vehicle is protected by thermal protection system (TPS), but it may deteriorate the antenna’s performance. This article analyzes electromagnetic interactions between a circularly polarized (CP) antenna and TPS through multilayer Green’s function and reciprocity theorem. Two orthogonally placed Hertzian diploes represent an equivalent CP antenna. Radiation pattern and axial ratio (AR) are rigorously calculated. With TPS, the AR beamwidth is compromised and the main lobe splits. An impedance ground (IG) is proposed to replace metallic ground for alleviating the negative effects of TPS. An Archimedean spiral antenna is fabricated and measured for verification. The AR beamwidth is widened by 32° on average in the frequency range of 3–8 GHz. Additionally, the split of the main lobe existing in the frequency range of 4.6–5.4 GHz is repaired and the realized gain in the broadside is improved by ~1.8 dBi. As a price, the radiation efficiency of the spiral antenna is reduced by ~14% since partial radiation is absorbed by IG. High-temperature (HT) heating experiment reaching up to 800 °C is conducted to verify the thermal protection performance. The proposed method does not change the structure of TPS or increase the antenna profile, and hence it is potentially useful for broadband systems on hypersonic vehicles.