A Broadband 220-GHz Converter From Rectangular Waveguide TE $_{10}$ Mode to SIW TE $_{20}$ Mode for Terahertz Planar Integration

This article presents a 220-GHz wideband converter for terahertz (THz) applications, which facilitates the transition from the TE
$_{10}$
mode of the rectangular waveguide (RWG) to the TE
$_{20}$
mode of the substrate-integrated waveguide (SIW). This converter consists of waveguides, a dipole antenna, a grounded slotline, and a SIW. The dipole antenna effectively couples the TE
$_{10}$
-mode guided wave from the RWG into the slotline. Due to the quasi-slotline mode and SIW TE
$_{20}$
mode being odd modes with similar electric field distributions, the longitudinal slotline effectively excites the TE
$_{20}$
mode within the SIW. This study elucidates the converter’s principles and propagation properties through electric field analysis and electromagnetic (EM) simulations. Besides, a back-to-back converter prototype was fabricated and measured, exhibiting an insertion loss of 2.1–5.0 dB from 198 to 238 GHz (18.3% bandwidth) and a return loss better than 6.1 dB. The estimated loss for a single converter is 1.1–2.5 dB, including the loss of a 1.4-mm-long SIW. Furthermore, based on the proposed mode converter, an SIW bandpass filter and a balun were designed and demonstrated, providing further evidence of the existence of the TE
$_{20}$
mode in SIW. To the best of our knowledge, this article presents the first 220-GHz converter from the RWG TE
$_{10}$
mode to the SIW TE
$_{20}$
mode, demonstrating its potential applications in THz planar integration.