Radio Technical Characteristics of Space Vehicle Board Antennas
V. Mikhailov *
Saint Petersburg State University of Aerospace Instrumentation, Saint-Petersburg, Russia.
*Author to whom correspondence should be addressed.
Abstract
Continuous radio communication is required for the effective operation of spacecraft. The radio-technical characteristics of the antenna window that affect radio communication include the radiation pattern, efficiency, aperture conductivity, and a number of other characteristics that describe more subtle electrodynamic effects. In this study, a method for calculating the radio-technical characteristics of onboard antennas of returned spacecraft is considered. Analytical expressions for the radiation pattern, side and surface waves, efficiency factor, aperture conductivity, and reflection coefficient are derived. These characteristics determine the radio-communication range and whether communication can be maintained. Because these antennas must have a wide radiation pattern, they are configured as the open end of a transmission line. The emitter is modelled as the open end of a rectangular waveguide enclosed by radio-transparent thermal protection against aerodynamic heating. Because the electrodynamic problem must be solved in the antenna's resonant region, the electric and magnetic components of the electromagnetic field are represented by the angular spectrum of plane waves using a direct Fourier transform, and the resulting wave equations are solved. The results of the solution, using the boundary conditions, are converted into the electric and magnetic components of the radiation field and the fields of the side and surface waves using an inverse Fourier transform. These results yield expressions for the antenna characteristics described above. The obtained expressions depend on the electrical characteristics of the thermal protection material. Given the temperature dependence of the electrical characteristics and the temperature profile along the Earth-return trajectory, it is possible to calculate the characteristics of the onboard antenna as a function of the flight trajectory. The developed mathematical models are relevant because knowledge of the radio-engineering characteristics of onboard antennas under aerodynamic-heating conditions is important for ensuring continuous radio communication on the descent trajectory.
Keywords: Onboard antenna, spacecraft, aerodynamic heating, thermal protection, antenna characteristics, calculation expressions