Tunable microstrip ring bandpass filter

The simulated and experimental results of a tunable microstrip ring bandpass filter are presented in this paper. A meander path is loaded in the ring resonator for achieving different resonator lengths by using the ON or OFF state of PIN diodes and then switch the passband from 2.47GHz to 5.1GHz. When the PIN switch turns to ON state, which is equivalent to a resistance, the bandpass filter has a center frequency of 5.1GHz, with a passband bandwidth of 520MHz and an insertion loss of 1.37dB. When the switch turns to OFF state, which is equivalent to a capacitance, the filter works in the center frequency of 2.47GHz, with a passband bandwidth of 10MHz and an insertion loss of 3.11dB.