Micromachined based narrow band Fabry-Perot tunable bandpass filter

A micromachined based narrow band Fabry-Perot tunable bandpass filter is designed, fabricated and measured. The narrow bandpass characteristic is due to the cavity formed in the bandgap structures by the insertion of a transmission line resonator between the two Bragg reflectors. The parametric analyses of the Fabry-Perot electromagnetic bandgap (EBG) filter are investigated by considering (i) the effect of the EBG cells on the Q factor; (ii) the change in the cavity length and the slot dimension to influence the filter performance characteristics; and (iii) the propagation characteristics of the Fabry-Perot EBG filter. The Fabry-Perot EBG tunable filter is fabricated on a silicon substrate using a surface micromachining process. The measurement result of the fixed Fabry-Perot filter shows a 3-dB bandwidth of around 250 MHz with an insertion loss of 4 dB. Capacitive microelectromechanical system switches are fabricated in the cavity to develop a tunable filter. The switch heights are varied with a bias voltage from 0 to 34 V, and the resonant frequency is tuned. The result shows a tuning range of 7.5% with an insertion loss that varies from 4.1 to 7.35 dB.