Losses in Cavity Resonators

The problem investigated was the measurement of the Q, or figure of merit, of a resonant cavity and observation of the variation in Q with changes in the size and shape of the coupling holes. A method of measurement was developed using a spectrum analyzer as a detector and a signal with a known spectrum to calibrate the analyzer for frequency changes. The results indicate that the Q is lowered if the size of the coupling windows is increased. There are two contributions to the losses which may be considered separately; the losses on the inner walls of the resonator, and the losses due to energy radiated out of the coupling hole.