Bandpass filters with mixed hairpin and patch resonators

This paper presents a new implementation technique of transmission zeros in an in-line coupled filter. Neither cross couplings between non-adjacent resonators nor separate side-line resonators have been used. Instead a mixture of single-mode hairpin resonators and dual-mode patch resonators have been adopted in a bandpass filter with one asymmetric transmission zero. The introduction of the patch led to an improved frequency selectivity through an independently controllable transmission zero. This approach has been verified by a three-pole filter at 2.6 GHz with 8% bandwidth and a transmission zero at 2.4 GHz. Good agreement has been shown between the measurements and the simulation.