A compact 81–86 GHz branch line coupler using end-loaded transmission lines

This paper presents a reduced-size 81-86 GHz branch line coupler using end-loaded transmission lines and implemented in a 0.15-μm GaAs HEMT technology. The fabricated coupler has a size-reduction of 50% in chip-area compared to a conventional branch line coupler. The measured results demonstrated a phase imbalance of 90° at 83 GHz with a phase error of less than +/-1° over the frequency band of interest. Over a frequency range of 81-86 GHz the measurements showed an amplitude imbalance of less than 1.1 dB, a return loss of less than -11 dB, and an isolation close to 15 dB. The obtained results confirm the potential of the proposed branch line coupler for low-cost, high performance, small size GaAs-based System-on-Chip radio transceivers for wireless and radio-over-fiber ultra high speed communication systems.