High-Q evanescent-mode filters using silicon micromachining and polymer stereolithography (SL) processing

Evanescent-mode filters are realized by both silicon micromachining as well as layer-by-layer polymer stereolithography (SL) processing. Capacitive loading an enclosed resonator reduces the size of a distributed cavity to be much smaller than a wavelength but which has much higher unloaded Q than lumped elements. The loaded resonators are extended into reduced-size filters with a low insertion loss due to the relatively high quality factor. Size reduction of resonators and filters can be a full order of magnitude depending on the height of the capacitive post. A 14 GHz resonator micro-machined in silicon with 5 mm×5 mm×0.45 mm volume reduces the size by 76.8%. The polymer-based fabrication was used to create a resonator with a Q greater than 1,050. An insertion loss of 0.83 dB was measured in a 1.69% filter with a size reduction of 47%. Furthermore, the proposed filters are quasi-planar and capable of integration with other RF components.