Measurement of antenna radiation patterns coated with plasma

A plasma sheath forms on the surface of a spacecraft when it enters the atmosphere at hypersonic speeds. The radiation pattern of antennas can be influenced by the plasma sheath. In order to measure the radiation pattern of an antenna coated with plasma, this paper proposes an experimental method for measuring the radiation pattern of an antenna coated with high-speed plasma. In this experiment, L-band antennas with circular polarization and linear polarization are designed as the antenna under test (AUT) and placed within a blunt cone capable of operating in high-temperature plasma. In addition, the traditional antenna pattern measurement scheme is adjusted by rotating the position of the receiving antenna to equivalently simulate the rotation of the AUT. The receiving antenna is placed on the plasma side turntable, and a computer controls the movement of the receiving antenna. Then, the signal from the AUT in the horizontal direction ranging from −30° to 30° is captured and its amplitude and phase are recorded. The antenna pattern is generated using the collected data. The results indicate that as the experimental conditions shift from the low-frequency group to the high-frequency group, the maximum radiation direction approaches 0° and the radiation gain is attenuated from a positive value to below −2 dB. Moreover, in the circularly polarized antenna, as the plasma characteristic frequency increases, the axial ratio degrades to 8 dB within the direction range of −10°–0°.