A Low-Loss and Wideband Quadrature Hybrid Coupler for Millimeter-Wave Attenuators

In this paper, a novel quadrature hybrid coupler, composed of parallel-stripline (PSL) and a 180-degree phase inverter, is employed for millimeter-wave attenuator design. For verification, a reflection-type attenuator using this hybrid coupler has been implemented in a 0.13-μm SiGe BiCMOS process. The different attenuation levels of 0 dB (reference state), 2 dB, 4 dB, and 8 dB are achieved by adjusting the reflective loads. Capacitive compensation is used to improve the phase variation at high attenuation levels of 8 dB. The proposed attenuator demonstrates a simulated insertion loss (in the reference state) of less than 1.5 dB, a phase shift of less than 3.2 degrees, and an input/output return loss better than 15 dB within the operating frequency range of 170 GHz to 200 GHz.