Effects of a Hypersonic Plasma Sheath on the Performances of Dipole Antenna and Horn Antenna

This paper discusses the influences of plasma sheath on antennas during hypersonic flights. The practical plasma sheath around an RAM-C vehicle when flying at 25.91 Ma at the altitude of 71 km is evaluated with the fluid analysis method, both dipole antenna and horn antenna are located at the stagnation region and aft body region, respectively, and the antenna performances are compared with those when the plasma sheath does not exist. Numerical results show that when the antennas are located at the stagnation region covered by plasma sheath, for dipole antenna, the gain decreases 7.3 dB and the frequency shifts to higher band by 9.88%, while for the horn antenna, the gain can decrease 4.01 dB and the return loss gets worse. However, when the antennas are located at the aft body region, the antenna performances show hardly any changes no matter the plasma sheath exists or not. The conclusion obtained may provide useful insights for designing antennas on hypersonic vehicles.