Miniaturized stepped-impedance dual-mode resonator filter

Conventional dual mode filters are realized by perturbing the electromagnetic field of ring resonator structures such that two orthogonal resonant modes occur, yielding a dual mode response. Due to the inherent resonant characteristic, the electrical length needed to establish the resonant condition is 360°. However it is felt that the size is still too large and unacceptable for the design of high performance multi-pole filter. In this paper, a novel technique to construct a dual mode filter with significant size reduction is introduced. This is achieved by incorporating a novel stepped impedance dual-mode resonator. Theoretical analysis together with experimental prototype is presented.