Micromachined based narrow band Fabry–Perot tunable bandpass filter

Abstract

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.