Analysis and Design of Novel 180° Hybrid for U-Band Monolithic Subharmonic Mixer in 0.15-μm GaAs pHEMT Technology

In this brief, a novel reduced-size 180° hybrid is presented to implement a ${U}$ -band subharmonic mixer (SHM) via a 0.15- $\mu \text{m}$ GaAs pHEMT process. The isolations between $\Sigma $ -port and $\Delta $ -port of the proposed 180° hybrid are significantly enhanced by two structures: one is a compact multiconductor edge-coupled line balun with artificial transmission line and the other is an in-phase power divider composed of ${\lambda }_{\mathrm{ LO}}$ /4 coupled line. As a proof-of-principle demonstration, a single balanced SHM with an antiparallel diode pair configuration is designed and fabricated, which exhibits a conversion gain of −12.25 dB ± 1.55 dB within the operating RF frequency of 40 to 60 GHz under 14 dBm LO pumping power. The improved isolations of LO-to-RF and 2LO-to-RF are 33 to 47 dB and 44 to 57 dB, respectively. The measured results surpass previously reported performance of SHMs.