A novel microstrip filter structure consisting of transversal resonator array and its fully canonical bandpass filter design

A new and simple microstrip filter structure for a transversal array bandpass filter with multiple transmission zeros (TZs) is proposed, which is constructed by the parallel arrangement of even- and odd-mode half-wavelength resonators. The odd-mode resonators having open ends produce an intrinsic negative coupling with respect to the even-mode resonators with shorted ends, resulting in the cancellation of signals passing through parallel paths at stopbands. Thus, the proposed filter can generate multiple TZs with the control of external Q factors for multiple resonators, without using any couplings between adjacent/non-adjacent resonators. The resonant frequencies and the external Q factors required for resonators are synthesized with a coupling-matrix optimization, and then a fully canonical bandpass filter with 2-GHz center frequency, 6% bandwidth, and four TZs is designed. A very sharp roll-off response is achieved by TZs located at the passband edge, which is confirmed by both simulations and measurements.