A High-Conversion-Gain Compact W-Band Distributed Doubler With Second Harmonic Positive Feedback Using Cross-Coupled Capacitor

This paper presents a compact and high conversion gain (CG) W-band differential distributed doubler. The proposed two-stage distributed doubler consists of two push-push frequency doubler (PPFD), utilizing a compact in-phase and quadrature-phase generator with a 90˚ electrical length of transmission line. Furthermore, cross-coupled capacitors are connected from the output of the PPFD to the input of the other PPFD, forming a second harmonic positive feedback (SHPF) and enhancing CG of 2f0. Comparing the measurement results of the distributed doublers with and without the SHPF, 6-dB improvement in CG, resulting in a peak CG of 0.1 dB. The doubler achieves a 3-dB bandwidth of 13.9 GHz, which is from 74.8 to 88.7 GHz. The saturated output power is 6.7 dBm with 35-mW DC power consumption. The fundamental rejection ratio is >36 dBc and the core size is only 0.05 mm2.