A Compact Broadband Marchand Balun for Millimeter-wave and Sub-THz Applications

This paper presents a compact broadband millimeter-wave Marchand balun, realized using indium phosphide (InP) transferred substrate (TS) technology. The architecture of this balun is based on a folded-type Marchand balun, modified using a compensating transmission line. The core area of the balun is 0.35 × 0.16 mm
²
for operation at W-band. The measured results show a corrected insertion loss of less than 7.5 dB and a return loss better than 10 dB in the frequency range from 70 to 110 GHz. Amplitude and phase imbalance remain below 2 dB and 2.5 degrees, respectively, over a 40 GHz bandwidth. To the authors' knowledge, this is the highest RF center frequency published so far for a broadband Marchand type balun with low phase and magnitude imbalance.