Center frequency, bandwidth, and transfer function tunable bandpass filter using ring resonator and J-inverter

This paper proposes a tunable bandpass filter that can tune its center frequency, bandwidth, and transfer function. The filter comprises tunable ring resonators and tunable J-inverters. The tunable ring resonator can change its susceptance slope parameter independently of its resonant frequency. This feature helps us to change the bandwidth and transfer function of the filter while keeping the center frequency constant. The center frequency of the filter is also tuned by the tunable resonator. The tunable J-inverter maintains its phase difference between two adjacent tunable ring resonators of 90 degrees at the resonant frequency of the tunable resonator even if the tunable resonator varies its resonant frequency. This paper also presents an ideal tuning scheme for a tunable three-pole bandpass filter and the measured characteristics for the fabricated filter. Experimental results validate the feasibility of the proposed tunable filter architecture.