A cylindrically stratified model of the plasma wake of a dipole antenna entering a planetary atmosphere

The radiation characteristics of a dipole antenna are calculated in a high-velocity wind of ionized gases representing the wake region of an antenna located on the aft portion of a probe entering a planetary atmosphere. The antenna and the support structure are assumed to give rise to a cylindrically stratified plasma flow field, which is allowed to possess a radial distribution in the electron concentration and collision frequency. Each cylindrical layer of the plasma shell moves at a uniform axial velocity with respect to the antenna and is biased magnetically along the axis of the cylinder. The antenna is represented by a circularly polarized turnstile antenna mounted off-axis a quarter wavelength above a ground plane and is oriented transverse to the axis of the cylinder. The antenna operates at frequencies near the cutoff frequency of the plasma in the wake. Integral expressions for the cylindrical components of the electric and magnetic field intensities are derived and are evaluated in the rest frame of the antenna using the techniques of asymptotic expansions. The resulting far-field gain patterns of the antenna are given and are compared with the free-space patterns.