A Continuously Tunable Bandpass Filter Using Distilled Water Based on Multiple-Mode Resonator

© 2001-2012 IEEE. In this letter, a continuously tunable bandpass filter (BPF) with low insertion loss using distilled water based on the stripline triple-mode resonator (TMR) is first presented. The configurability of proposed BPF is achieved by using six polytetrafluoroethylene (PTFE) tubes located above the surface of the TMR circuit. These tubes are filled with distilled water. By adjusting the amount of distilled water inside these tubes, the equivalent electrical length of the transmission line changes, which can change the resonant frequency of the TMR. It is demonstrated in simulated and measured results that the center frequency tuning of the proposed BPF is ranged from 1.06 to 1.29 GHz with a fractional bandwidth (FBW) of 16.5%-19.2% and the measured insertion loss is varied within 1-0.4 dB. The measured results are highly consistent with the simulated results.