Design of LP and CP microstrip antennas covered by lossy thermal protection system

Abstract

Low-temperature antenna system that covered by a dedicated thermal protection system (TPS) is an indispensable component of hypersonic vehicle. However, electromagnetic interactions between the installed antennas and the TPS tend to impair the antenna's performance, such as the resonant frequency, radiation efficiency, and polarization purity. To mitigate these negative effects of placing a thick, lossy TPS in close proximity to the microstrip patch antennas, this article proposes a concept of near-field matching technique. The magnetic field distribution of the installed antenna is calculated in the near field, followed by adopting a surface fitting method to determine the optimal shape of a modified TPS. Two patch antennas with linear polarization (LP) and circular polarization (CP) are analyzed by this method, respectively. It is discovered that different TPS shapes suit LP and CP antennas, respectively. Both experimental and numerical results show that the proposed TPS structure improves the impedance matching and radiation properties of the microstrip antennas simultaneously. The proposed design achieves a harmonious balance between the electrical and thermal protection performance, surpassing that of a traditional flat TPS. To verify the design, a prototype CP antenna is fabricated and measured.