The circular cavity for antennas, periodic structures, and power combiners

Abstract

Circular cylindrical cavity resonators have been studied in three configurations. First, a slot antenna backed by a circular cylindrical cavity was analyzed. The resonant frequency of the cavity is found using power conservation considerations. Three resonant frequencies were found. The first resonance occurred because the slot resonated on its own. The second resonance was a closed cavity resonance. The third resonance was due to the coupled slot and cavity resonance. The theoretical results were found to be within 2% of experimental results for most cases. The theory was used to predict the resonant frequency for a structure fed through the cavity sidewall. The antenna pattern for a dielectric filled slot was also examined. The dielectric was shown to lower the operation frequency and had little effect on the shape of the antenna pattern. A periodic string of resonant cavities was the second structure studied. The cavity string was examined using cavity perturbation theory and the Bethe small aperture theory. A string of T M qio mode cavities was examined to find the phase and frequency characteristics, the distribution of fields on the structure, and the S-parameters of the structure when fed with a waveguide. The phase was shown to vary from 0° to 180°; the bandwidth of the cavity chain was shown to depend upon the aperture size. The final topic examined was the waveguide E-plane star junction. An X-band star junction was shown to have a bandwidth of 2.58 GHz and an insertion loss of 6 dB. Coupling apertures were placed upon four ports of the star junction ports to increase the isolation between the four ports while keeping the coupling to the fifth port at 6 dB. Without the coupling apertures, the star junction was tested as a power combiner; the star junction demonstrated a combining efficiency of 70%.