An inline waveguide-to-microstrip transition for wideband millimeter-wave applications

A low-cost wide Ka-band inline waveguide-to-microstrip transition is proposed, which facilities the integration of planar transmission lines with waveguide structures. By employing a circular patch above a wedge-shaped cavity, the quasi-TEM mode wave in the microstrip line can be transformed into the TE₁₀ mode wave in the rectangular waveguide. A transition prototype in a back-to-back configuration is manufactured and experimentally tested. Measured results show that the return loss is greater than 13 dB from 28 to 38 GHz and the insertion loss remains less than 0.4 dB for the proposed single-side transition. With the features of wideband, compact structure and easy integration, the proposed transition can be applied in the low-loss and high-integration millimeter-wave systems.