A fully tunable two‐pole bandpass filter using the resonator with asymmetrical capacitances

A fully tunable second‐order bandpass filter based on novel resonator is proposed. The resonating frequency and the coupling coefficient between the resonators can be controlled by two varactor diodes. Theoretical expressions have been derived for the coupling coefficient. Four types of filter responses can be reconfigured by setting different bias voltage combinations, including tunable bandwidth filter, constant absolute bandwidth filter, constant fractional bandwidth filter, and decrease bandwidth filter. The simulation and measured results of the four responses are in good agreement with each other, and excellent tunable characteristics are achieved.