A novel reconfigurable tri-mode resonator and its application to bandpass filter

A reconfigurable tri-mode resonator and its application to tri-band bandpass filter have been demonstrated. The proposed filter exhibits 32.8% fractional tuning range of the first passband from 1.12-1.56 GHz and 12.73% of the third pass-band from 2.50-2.84 GHz, and a fixed second passband at 2 GHz, respectively. The first and third frequency passbands can be tuned independently without interfering with each other. Especially, the filter uses a hybrid technique of lumped inductors and microstrip lines, resulting in a very compact mechanical size of 0.12 ?g ? 0.08 ?g, where ?g is the guided wavelength on the substrate at the central of the first passband frequency. The measured results agree well with the simulated ones.