A D-Band Single-Waveguide Single-Substrate Doubler Using Vertically Mirrored Schottky Diodes for Low-Loss Power Combining

This letter presents a D-band frequency doubler employing a novel single-waveguide single-substrate (SWSS) structure, integrating two vertically mirrored Schottky barrier diode (SBD) chips on a 50-<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu $</tex-math> </inline-formula>m quartz substrate for low-loss power combining. The optimal diode embedding impedance is extracted using broadband load-pull techniques and transformed through a hybrid waveguide-microstrip matching network. Independent bias control for the two SBD chips enables partial compensation for performance degradation caused by the SBD chip imbalance. For verification, the proposed SWSS doubler is fabricated and measured with an output power of 12–14 dBm and an efficiency of 10%–15.8% across 120–158 GHz. Compared with similar reports, this work exhibits superior overall performance in bandwidth, output power, and efficiency.