Microwave Dielectric Resonator-tuning

Book excerpt: Dielectric resonators have applications as low-loss compact filters in the microwave region. Tuning characteristics of dielectric resonators that might allow for temperature compensation and frequency variability were investigated both theoretically and experimentally at L band. A secondary dielectric resonator that is offset in frequency from the tuned resonator provides a maximum tuning range of approximately 10 percent before an additional filter loss of 3 dB is incurred; the rate of tuning is slow since it is done by changing the resonator coupling (spacing). For fast tuning, a varactor is used in a coupled resonant circuit. Frequency changes can then be made in a time interval approaching 1/(filter bandwidth), but in this case the maximum tuning range before an additional filter loss of 3 dB is incurred is reduced to 2 percent of the filter frequency.