Reflection-canceling of slotted waveguide antenna by using a circular pit

A slot cut on a metal waveguide produces scattered fields in the internal region as well as the external region. It causes reflection in the waveguides and deteriorates the VSWR of the antenna. This paper proposes a novel technique to cancel the reflection by placing a pit on the bottom of the waveguide. Only the original slots exist on the aperture and the pit is in the waveguide. Thus, the radiation pattern design by the slots and the pit design for reflection cancelling can be conducted independently. We design a circular pit for a transverse slot in a rectangular waveguide. The analysis and design are validated by experiments. These results are applicable for parallel plates such as radial lines as well.