Radiation of a Circular Waveguide Through Thermal Protection with Allowance for Side Waves

The onboard antennas of reentry spacecraft, which are weakly directional emitters, are covered with a heat-resistant radio-transparent heat shield for protection from aerodynamic heating. Under conditions of aerodynamic heating, the electrical characteristics of thermal protection change significantly, and a melt layer appears on the outer surface [1]–[4]. The electromagnetic energy emitted by the onboard antenna, under conditions of change in the electrical characteristics of thermal protection and taking into account the effect of plasma formation, decreases so much due to losses due to absorption in these media and to reflection from the interfaces of these media that radio communication between the spacecraft and the earth is interrupted. To ensure continuous radio communication on the descent trajectory of the spacecraft, numerous studies are carried out in order to reduce the above-mentioned type of losses [5]–[7] However, when radiation through dielectric thermal protection, part of the radiated energy can be converted into side waves that do not participate in maintaining radio communication. Determination of the lateral wave structure and the power removed by them will make it possible to estimate the losses caused by the action of the lateral waves. In this work, relations are obtained to take into account the effect of side waves on the radiation pattern of a circular waveguide through a flat uniform radio-transparent heat shield.