Radiation characteristics of a cavity-backed cylindrical gap antenna

The input impedance and the equatorial radiation patterns of a VHF cavity-backed cylindrical gap antenna are derived and compared with experiments. The experiments generally support the computations, provided that the gap dimension is neither larger than about 1/100 of a wavelength, nor so thin that mechanical tolerances in the feed design become important. The results show that the tuning, impedance bandwidth, and the radiation patterns of this antenna can be controlled very accurately by adjusting the internal radius and height of the cavity. Salient points of this antenna are its wide-band characteristics (10-percent bandwidth), its pattern circularity, and particularly the fact that it can be made an integral part of a space vehicle.