Sub-THz Inline Transition From Microstrip Line to Waveguide for Large-Sized MMICs

This article presents a wideband sub-terahertz (sub-THz) inline transition from microstrip line (MSL) to rectangular waveguide (RWG). The transition employs the bow-tie antenna to achieve a compact inline transition and wideband impedance matching with the RWG, resulting in bigger bandwidths than the transitions using dipoles. In order to overcome the substrate width limitations of conventional probes, the perfect magnetic conductor (PMC) packaging concept is used in this article, resulting in a better integration ability with large-sized monolithic microwave integrated circuits (MMICs). Two back-to-back transition prototypes related to different angles of the bow-tie antenna have been fabricated to evaluate the transition performances in the sub-THz band. The tested large-sized substrates have a large width of 10.826 mm and a length of 10.8 mm, and the length of the MSL is 9.28 mm. According to the experimental results, in the 110–170-GHz band, prototype I has a reflection coefficient of less than -11 dB and an insertion loss of 1.79–2.6 dB, while prototype II has a reflection coefficient of less than -8.5 dB and an insertion loss of 1.52–2.5 dB.