Measurements of micromachined submillimeter waveguide circuits

In this paper two calibrated measurement methods for submillimeter circuits are presented and micromachined waveguides operating between 220 and 325 GHz have been fabricated using thick SU-8 photoresist technology and tested. The first measurement method is achieved by employing a pair of micromachined embedded H-plane bends, which were specially designed to enable direct and accurate connection between the micromachined circuit and standard waveguide flanges. A 16 mm long WR-3 waveguide has been designed, fabricated and measured using this technology. The measured average insertion loss is 2.3 dB or 0.144 dB/mm over the frequency range of 220-321 GHz. The second measurement technology employs a conventionally machined metal block constructed with two separate pieces in which to mount the micromachined circuit. A choke flange has been adopted for eliminating the effect of air gap at the interfaces between the micromachined circuit and metal block. A 15 mm long WR-3 straight waveguide has been fabricated and tested. The measured insertion loss is between 1.4 dB and 3.2 dB corresponding to 0.093 and 0.213 dB/mm. A comparison between these two measurement technologies has been carried out and presented.