Broadband Transition from Waveguide to Substrate-Integrated Waveguide with Back-Short Structure in Multilayer Substrate at 300-GHz Band

A broadband transition from a hollow rectangular waveguide to a substrate-integrated waveguide (SIW) was designed in 300-GHz band. The prepreg layers in a multilayer substrate are unified through rectangular apertures opened in the inner printed patterns. A back-short structure was formed at one end of the thick SIW in the multilayer substrate by a via hole arrangement. The back-short length and the locations of matching via holes were optimized to produce double resonance for broadband characteristic. The simulated bandwidth of the proposed transition for
$S_{11}$
lower than −10 dB was 71.2 GHz, and the fractional bandwidth was 25.9%.