Miniaturized 150-GHz Branch-Line Coupler Using Capacitive Compensation in Quartz-IPD Technology

This paper presents the design and characterization of 150-GHz branch-line couplers, fabricated in a quartz-IPD process. Based on C-L-C miniaturization structures, two versions are proposed to reduce the core area by 64% and 59%. A compact modelling approach is introduced to determine the optimal transmission-line electrical length and compensation capacitance under layout constraints, while a capacitor-rotation strategy is proposed to effectively suppress high-frequency parasitic coupling. On-wafer measurements are performed using a crossover-based termination scheme to provide proper termination. The coupler achieves 0.35 dB insertion loss and 3.3° phase error with a normalized area of 0.025 λ₀², whereas the 1st and 2nd-order designs exhibit 0.85 dB and 0.58 dB insertion loss with phase errors of 8° and 5° and areas of 0.009 λ₀² and 0.01025 λ₀², respectively.