Impact of Topology on the Performance and Spectral Behavior of THz Schottky Mixers

This work presents a comparative analysis of two full-band WR-3.4 sub-harmonic mixers (SHM) based on Schottky diodes, using alternative anti-parallel and cross-bar diode balancing configurations. Both mixers share equivalent technology and design techniques, offering a very unique opportunity for a direct experimental comparison. Through detailed simulations, we analyze signal coupling, harmonic emission, and intermodulation (IM) products to understand their performance differences. While conversion loss (CL) degradation in anti-parallel mixers is typically attributed to epitaxial layer properties, this study reveals that a significant portion of the degradation is also linked to the architecture itself and is associated with the generation and propagation of unwanted IM products outside the diode cell. Experimental measurements, closely aligned with simulation results, show a 1.5–3 dB CL degradation, which mainly comes from propagation of IM products, with an additional loss attributed to IF and RF coupling in the anti-parallel configuration. In contrast, the cross-bar mixer exhibits minimal susceptibility to these effects, at the expense of reduced LO harmonic suppression and extra required LO power.