A novel varactor tuned dielectric resonator filter

This paper presents a novel structure for tunable dielectric resonator (DR) filters using varactor tuning. The varactor is mounted outside the filter housing while interacting with the resonator through a PCB circuit board. The concept is analyzed both theoretically and experimentally. A prototype tunable DR filter employing this concept is designed, implemented and tested. The filter operates at 5 GHz with a bandwidth of 60 MHz demonstrating a tuning range of more than 300 MHz and a spurious free window larger than 1.0 GHz.