Suspended-grooved dielectric resonators for high Q, dual-mode, mobile communications filters

A new suspended and grooved dielectric resonator configuration is used for realizing high unloaded Q-factor, wide spurious-free operating window and tight coupling either to input or between dual-mode resonances. The latter couplings are obtained by inserting probes inside the dielectric resonator groove. This approach allows significant values of coupling/tuning to be obtained while metallic contacts with the dielectric resonator are avoided. Experimental results, on a three-pole filter with an asymmetric transmission zero, confirm the validity of the proposed resonator for realizing transmit filters for UMTS cellular-radio base stations.