Design and Characterization of a $W$-Band Micromachined Cavity Filter Including a Novel Integrated Transition From CPW Feeding Lines

This paper demonstrates a novel coplanar waveguide (CPW) to rectangular waveguide (RWG) transition and its application as an integration enabling structure for filters at W-band for the first time to the best of the authors' knowledge. In the proposed wideband transition, the CPW and RWG are integrated on one side of the substrate, while the coupling probe is patterned directly on the substrate instead of being made separately. The transition is fabricated using silicon micromachining and thick-film surface micromachining techniques with high precision, which is suitable for millimeter-wave subsystems and are easily extendable to terahertz applications compared to the existing approaches. In the proposed filter design, the metallized probes are used to couple signals from the CPW to waveguide resonant cavities, therefore, the need for waveguide input/output ports is eliminated. This significantly reduces the size of the filter by approximately 30%. The transition and filter components are optimized using Ansoft's high frequency structure simulator 10 (HFSS 10). The measured response of the filter has the center frequency at 96.6 GHz, 2.9% bandwidth, and a 4.14-dB insertion loss in the passband.