A Miniature 200-GHz Subharmonic Mixer With a Folded 180° Hybrid Using Equal-Length Edge- and Broadside-Coupled Lines

A miniature 180° hybrid is proposed to demonstrate a 200-GHz subharmonic mixer (SHM) using a 0.18-μm SiGe BiCMOS process. The reduced-size 180° hybrid is achieved by folding the shared coupled lines between the in-phase power divider and the out-of-phase Marchand balun. The shared coupled lines demand an equal length design for the coupled lines at both Δ and Σ ports of an 180° hybrid. For the SHM, edge coupling for the Σ section and broad-side coupling for the Δ section are employed to compensate the different input frequencies at Δ and Σ ports. The SHM achieves a conversion gain around -21 dB from 175 to 200 GHz with 0-dBm LO pumping power. The LO-to-RF isolation is better than 32 dB within the operating bandwidth.