Analysis and Numerical Modeling of a 20W Microwave Electrothermal Thruster

The microwave electrothermal thruster (MET) is an electric propulsion device that uses an electromagnetic resonant cavity within which free-floating plasma is ignited and sustained in a propellant gas. The thrust is generated when the heated propellant gas is exhausted out of a gas-dynamic nozzle. For an empty cavity without any perturbing regions—e.g., dielectric regions or antenna regions—it is fairly straightforward to accurately calculate the cavitys resonant frequency and describe the electric field intensity distribution within the cavity. However, actual METs do contain perturbing regions, which means that analytical solutions are no longer possible to fully characterize the device. Hence, the numerical methods to simulate the electric field intensity and distribution within the resonant cavity were employed. The simulation results are that with the cap height increasing, the resonant frequency and electric field strength decrease, also increasing the permittivity of dielectric material causes decreasing the resonant frequency and electric field strength. A decrease in resonant frequency and maximum electric field strength, and an increase in resonant bandwidth, were observed with increasing antenna depth. Rounding an antenna of a given depth equals decreasing the depth.