Tunable Capacitive Coupling for Cavity Resonator Filters

In this paper two different bandpass filters are discussed, which consists of 4 and 5 stepped coaxial resonators, respectively. The resonators have different size. Therefore, different temperature compensation arrangements need to be applied to guarantee stable performance in the temperature range from -40degC to 85degC. Both filters have a center-frequency of 2.0175 GHz, a bandwidth of 15 MHz and cross-coupling by a cascaded quadruplet for improved blocking performance. The cross-coupling is realized by a tunable capacitive coupling. The tuning capability is validated by measurements and simulations. As a result, the coupling strength is tunable by factor 5.