The antennas for the propulsion plume attenuation test

Jet engines are widely used in various high-speed aircraft. After firing the propulsion fuel, hot gas is ejected from the tail of the engine. Because of its high temperature and the chemical effect of the fuel combustion, the gas around the tail of the propulsion is ionized, which then generates a non-uniform, high temperate, compound body of plasma called the plasma plume. When a microwave beam travels through the plasma plume, energy attenuation, which is very important for aircraft development, is inevitable. Microwave beams which are sent by an antenna are received by another antenna and tested by the receiver. The plasma plume attenuation is the ratio of the signals that travel through the plasma to those that pass it. It is obvious that the effect of the antennas during the attenuation test is critical. We discuss the relationship between the radius of the plasma plume and the microwave beam radius of the antenna, and the effect of the alignment of the antennas and the plasma plume center on the test results. We also determine the antenna design criteria, present an implemented lens antenna and provided the test results.