A design of tunable UWB filters

A novel design method is proposed for UWB filters using a ring resonator structure with a stub. A five stage UWB filter with 86.6% relative bandwidth is fabricated based on a design method which shows an excellent performance, i.e. low insertion loss of 0.58 dB and flat group delay of 1.6 nsec. We also extend the design method to the one for a wide range tunable filter. Simulated results show that more than 40% tunable range can be obtained with a single capacitor for each ring resonator.