Tunable millimeter-wave filters using a coplanar waveguide and micromachined variable capacitors

In this paper, new micromachined tunable bandpass filters for multi-band mi llimeter-wave telecommunication systems are proposed. Two types of millimet er-wave tunable filters have been fabricated using micromachining technolog y and the responses of the filters have been measured: one type is a two-po le lumped element filter and the other a two-pole resonator filter. The fre quency tunability of the filter has been achieved by changing the gap betwe en a common coplanar waveguide ground plate and a movable cantilever beam c onnected to the transmission line with a controllable range of 2.5 mum. The deflection of the cantilever beam has been measured with applied dc voltag e. With the applied bias voltage from 0 to 50 V, the fabricated filters hav e shown center frequency shifts of 0.6 GHz (2.3%) at 26.6 GHz and 0.8 GHz ( 2.5%) at 32 GHz for the lumped element and resonator filters, respectively. The mechanical lifetime of the fabricated gold cantilever structure has be en tested by observing the existence of the spring memory phenomenon; there is no memory phenomenon or breakdown until a repeated actuation of 1.6 x 1 0(8) cycles.