A 20-40GHz MMIC 180° Filtering Phase Shifter with 5° Phase Error in 0.25-μm GaAs Technology

This paper proposes a transformer-based ultra-wideband switchable 180° phase shifter, featuring consistent trisection filtering responses in both states. All adjacent resonators are coupled through electric (E) or magnetic (M) paths, with the E coupling formed by reusing the intrinsic transistor parasitics and the M coupling provided by the transformer-based balun. Benefiting from the symmetric structure, transistor switching reconfigures the signal paths while preserving symmetric equivalent circuits in the two states, thereby enabling consistent three-pole filtering responses and a stable 180° phase shift across states. Fabricated in a 0.25-μm GaAs process, the proposed filtering phase shifter demonstrates a gain error below 0.4 dB and a phase error less than 5° across 20–40 GHz.