Novel multi-mode ring resonator transversal array bandpass filter with very high skirt selectivity using multiple transmission zeros

In this paper, we propose a novel transversal array bandpass filter composed of multi-mode ring resonators, and design a bandpass filter with very high skirt selectivity. Based on a conventional filter theory, a bandpass filter is constructed by cascade connection of resonators, while in our proposed filter, two ring resonators are arranged in parallel connection with respect to the input/output lines. The filter can be modeled with a five-path circuit formed by both four resonant modes and direct source/load coupling, thereby enabling to generate multiple transmission zeros. The designed fourth-order Chebyshev-type filter realizes a very sharp roll-off response because of the transmission zeros located very close to the passband edge. The novel filter configuration is validated through the circuit analysis and the measurement of the test filter.