Slot admittance for arbitrary outer cross sections

Analysis of waveguide slot antennas is often simplified, by assuming the outer structure of the antenna to be an infinite ground plane. We analyze longitudinal slot antennas radiating into arbitrary cylindrical structures. The method can be used for both radiation patterns and the equivalent slot admittance, but we restrict this paper to admittance. By using a spectrum of two-dimensional solutions, the problem with cylindrical boundary conditions is simplified through a Fourier transform along the z-axis. The analysis inside the waveguide is separated from the outer structure analysis by means of the equivalence principle. Stevenson´s Green´s function is used for the interior problem. For the exterior problem we analyze each spectral k/sub z/, component by a two-dimensional (2D) moment method. The spectrum is inverse Fourier transformed and matched to the interior solution by an additional overbuilt moment method. The theoretical results are tested against measurements on a specific geometry, showing good agreement.<>