Submillimeter-Wave Waveguide-to-Microstrip Transitions for Wide Circuits/Wafers

Microstrip transitions for wide circuits/wafers are proposed using stub arrays (SAs) and indented waveguides (IWs). Full-wave analysis is performed to show that the proposed techniques can effectively suppress the resonances excited in the slit region which is needed to accommodate wide substrates. H-band waveguide-to-microstrip transitions consisting of two directors, dipole antenna, and balun were fabricated including the proposed techniques, accommodating a 1220-μm-wide substrate which is about three times the width of WR-03 standard waveguide (430 μm). The slit region is 1300 μm wide and 90 μm high. The comparison of measurement results between four transitions proves that the proposed SAs and IWs can successfully eliminate in-band resonances and greatly enhance the bandwidth of the transitions. The transition with both SAs and IW exhibits the best performance, a back-to-back loss of 2.3 dB across 234-314 GHz, where the variation in the insertion loss was less than ±0.5 dB. This insertion loss includes the losses in the microstrip line and 3-cm-long waveguide section. The return loss is better than 13.7 dB in this frequency range. Bandwidth for 10-dB return loss is as large as 97 GHz from 227 to 324 GHz.