Analysis of a terminated-waveguide slot antenna by an equivalent circuit method

The pattern in a half-space of a slot in the wall of a waveguide is a function of the terminating impedance. The description of the far fields in such a configuration is simplified considerably by the adoption of a network viewpoint, whereby the half-space is represented approximately by two (or more) spherical transmission lines, the feeding waveguide by a single uniform transmission line, and the slot by a coupling network which is directly analogous to that for a hybrid junction. For a given waveguide termination, the spherical mode voltages are computed by a simple network calculation, and the gain pattern is obtained by modal synthesis. The slot equivalent circuit parameters are obtained readily by simple measurements or from available theoretical formulas. Described in detail both theoretically and experimentally is a symmetric rectangular slot cut in either the broad or narrow face of a rectangular waveguide.