Analysis of Three-Conductor Coupled-Line 180$^{\circ}$ Hybrid for Single-Balanced Subharmonic Mixer Design in 0.15- $\mu{\hbox {m}}$ pHEMT Technology

A novel 180
^°
hybrid with two λ/4 sections of three-conductor coupled-line structure inhered different operating frequencies with overlapped characteristic and perfect isolation between the Σ-port and Δ-port is employed to implement a Ka- to M-band single-balanced subharmonic mixer (SHM) in a 0.15- μm GaAs pHEMT process with a compact die size of less than 0.82 × 0.83 mm
²
. The thorough analysis based on the scattering matrix of the 180
^°
hybrid is also presented. Incorporating the inherent features of the 180
^°
hybrid with an antiparallel diode pair configuration, the proposed SHM achieved a wide operating bandwidth from 37 to 85 GHz with low conversion loss from 9 to 14 dB, enhanced local oscillation (LO)-to-RF isolation and 2LO-to-RF isolation under 10-dBm LO power level. This proposed architecture is really attractive to SHM design in modern millimeter-wave territory.