An antenna illuminated by a cavity resonator

A microwave aperture antenna with small phase errors has been constructed by utilizing the plane field configuration inside a box-shaped resonator to directly excite the aperture, which is the same shape as the resonator. The antenna is narrow band, as Q of the resonator should be sufficient for selecting the proper mode in the resonator. The possible bandwidth of the antenna is thus inverse proportional to the desired gain. Reasonable agreement between theory and measurements was obtained.