Full D-Band Superstrate-Enhanced Transition for Rectangular Waveguide-to-PCB Interfacing

A transition from air-filled rectangular waveguide (RWG) to substrate-integrated waveguide (SIW) is proposed that covers the entire D-band (110–170 GHz). Broadband operation is obtained by leveraging a resonant slot and an aperture-coupled patch antenna-in-waveguide, while co-optimisation with a dielectric-loading superstrate matches both resonances to the RWG and ensures full D-band operation. Special attention is devoted to the stringent design restrictions that originate from its implementation in a standard any-layer high density interconnect printed circuit board manufacturing process at D-band frequencies, omitting inductive via posts, to maximise the robustness of the design against fabrication tolerances. Measurements of the RWG-to-SIW transition demonstrate a fractional bandwidth of 46%, effectively covering the entire D-band, while ensuring a low insertion loss of 0.95 $\pm$ 0.15 dB.