Design, fabrication and characterization of a sheet-beam 140 GHz folded waveguide based on multi-step SU-8 UV-LIGA

The dispersion property and interaction impedance of a novel sheet-beam 140 GHz folded waveguide was simulated. By CST Microwave Studio, the phase velocity was 0.227c and the dispersion remained flat when the frequency was 140 GHz. The interaction impedance was about 5 at 140 GHz. The beam-wave interaction simulation by CST Particle Studio showed the output power gain reached 24.6 dB. Sheet-beam design was compatible with MEMS micromachining process. Then the folded waveguide was fabricated by multi-step SU-8 UV-LIGA process. The tested return loss S11 and insertion loss S21 were close to -28 dB and -1.2 dB respectively and the output power gain reached 23 dB. Good accordance between test and simulation results indicates the reasonable design and high machining precision by multi-step SU-8 UV-LIGA.