Slot-mode propagation in rectangular waveguide

A previously observed discrepancy in the near-field pattern of a leaky-wave rectangular-waveguide antenna has been attributed to the presence of a second mode, in addition to the well known perturbed-waveguide mode. In this letter, a quantitative investigation of the properties of this so called slot mode is reported, and it is revealed that the cutoff frequency decreases with slot height and is strongly sensitive to it, in contrast to the other leaky-wave modes. Experimental observations of leaky-wave radiation at S band frequencies from a slotted Q band rectangular waveguide substantiate the theoretical predictions.