Radiation from a circularly polarized antenna through the ionized wake of a Mars-entry capsule

The effects of the ionized wake-of a Mars-entry capsule on radiation from a circularly polarized antenna operating at 400 and 2295 MHz are studied. The circularly polarized antenna is represented by a turnstile antenna above a ground plane, while the ionized wake is approximated by a cylindrically stratified plasma consisting of -plasma regions. Integral expressions for the fields are obtained for the antenna located in the wake and are evaluated using saddle-point integration to yield the radiation patterns. Computed patterns for the two simplest configurations and are presented. The radiation patterns for both near- and far-wake electron-density profiles develop a conical null region whose extent is proportional to the peak electron density in the wake. For the near-wake electron-density profile, sharp peaks which are attributable to leaky-wave radiation, appear within the null region of the patterns. The effect of the conical null region in the patterns is to prolong blackout time for communication cone angles that lie within the null region. There are no serious depolarization effects in the nonnull region and satisfactory communications can be carried out.