X-Band Reflection-Type Phase Shifters Using Coupled-Line Couplers on Single-Layer RF PCB

In this letter, an X-band reflection-type phase shifter is presented. It is based on a single-layer stub-loaded coupled-line coupler loaded by two-varactor tuning circuits. This choice of coupler significantly improves on the phase shifter bandwidth achievable with a branch-line coupler, as it features a lower phase imbalance across the band of interest. The proof-of-concept prototype achieves better than 10-dB return loss across a 20% fractional bandwidth. The phase shifter further exhibits insertion loss of 2.1 ± 1.3 dB and maximum phase shift of 392° at 10 GHz, leading to a state-of-the-art figure of merit at X-band of 115°/dB. The occupied area is 0.25λ_g ².