220 GHz Dual-Mode Dual-Band Waveguide Filter in Stackable Multilayer MEMS Technology

The development of next-generation transceiver system on the terahertz (THz) band demands the integration of key waveguide filters. In this paper, a dual-band filter using TM dual-mode cavities is proposed based on the stackable multilayer MEMS technology to achieve a highly compact design. TM120 and TM210 dual modes in the nearly square cavity have been introduced into the waveguide filter for obtaining the dual-band response. In addition, the non-resonating mode of TM110 in the cavity can be exploited as modal bypass coupling, which can generate two transmission zeros in the vicinity of each passband. Finally, such 220 GHz 3rd-order dual-band waveguide filter with quasi-elliptical response is fabricated through the silicon-based micromachining and nine stacked silicon platelets packaging techniques to achieve the compact thickness of only 2.34 mm. The measurement exhibits that the packaged filter has obtained the 3-dB fractional bandwidths of 4% from 217.5 to 226.5 GHz and 2.9% from 235.5 to 242.5 GHz, low insertion loss of about - 1.2 dB, as well as four obvious transmission zeros in the out-of-band, respectively. The exploitation of the advanced TM multi-mode cavity exemplifies innovation for highly compact THz waveguide filters, which are ideally suitable for multilayer silicon-based micro-processing.