Micromachined W-band waveguide and filter with two embedded H-plane bends

A micromachined W-band through waveguide together with a passband filter embedded with a pair of H-plane bends is presented here. The novel design of the bend enabled direct and accurate connection between the micromachined circuit and standard waveguide flanges. The devices were fabricated using thick SU-8 photoresist technology. They were constructed with six gold- or silver-coated SU-8 layers, each of a thickness of 0.635 mm. These layers were then bonded on top of each other to form the waveguide and filter. A measured average insertion loss of 0.5 dB or 0.0278 dB/mm has been achieved by the 18 mm long through waveguide, and the return loss is better than 18.8 dB in the whole W-band. The asymmetrical capacitive irises coupled filter shows a 3 dB bandwidth of 8.61 GHz at a central frequency of 88.47 GHz. The passband insertion loss was measured to be between 0.97 and 1.1 dB and reflection loss is better than 15 dB. This performance demonstrates the potential of employing this micromachining and multi-layered technique to fabricate millimetre and submillimetre waveguide components.