Theory of waveguide-fed slots radiating into parallel-plate regions

Slotted waveguide arrays feeding into parallel-plate regions have been used in some high speed scanners. Parallel-plate regions also have been used for the suppression of second-order beams of high-gain arrays. A theoretical expression is derived for the conductance of a longitudinal shunt-slot in a rectangular guide when the slot is radiating into a parallel-plate region of arbitrary plate spacing. Some peculiarities of the theoretical results are discussed. There is good agreement between theory and experiment.