Micromachined filters in multilayer technology for on-board communication systems in Ka-band

A new concept for compact and low-loss Ka-band micromachined bandpass filters for next generation on-board communications is presented which combines micromachined cavities with multilayer technology on silicon. The resonator consists of a gold-plated micromachined shielding cavity with a longitudinal 20 μm thick gold-plated silicon membrane. The membrane is short-circuited at both anchored ends and it operates as a λ/2 TEM line resonator. The footprint of a single resonator is reduced by more than 50% with respect to conventional micromachined cavities using the TE₁₀₁ resonant mode. The measurements of single transmission-type resonators are in very good agreement with the full-wave simulations, demonstrating a high filter robustness to process tolerance. The expected unloaded Q of the resonators for 500 μm thick layers is 600, and the measured value is above 500. Qs above 1000 are feasible with the available technology by simply increasing the number and the thickness of the silicon layers. A 4^th order pseudo-elliptic filter at 30 GHz (FBW = 1.7%) has been designed and is under fabrication.