Novel Approach for Center Frequency and Bandwidth Tuning in Multimode Resonator Based Microstrip Dual-Mode Bandpass Filter

Abstract

In this paper, a novel approach for both center frequency and bandwidth tuning in a dual mode bandpass filter is demonstrated. The proposed filter is configured from a half wavelength multimode resonator structure. The Ultra-wide bandpass response of the multimode resonator is extracted using an inter-digital feed structure which provides good input/output coupling. By deploying stepped admittance structure perturbation element into the symmetrical plane of the multimode resonator, the dual-mode response is achieved with three upper stopband transmission zeros (TZs). The coupling between two degenerative mode frequencies is controlled by the admittance ratio (Y) of the stepped admittance structure. Changing admittance ratio (Y) of stepped admittance structure, resulted in the change in even mode resonance frequency and location of three upper stopband transmission zeros while keeping odd mode frequency fixed. The proposed filter has a size of 14.0 x 30.0 mm2.