I have designed a reflection-type phase shifter operating at 10 GHz using a 3 dB quadrature hybrid coupler. The design achieves nearly 0–360° phase shift range by tuning the reflective loads.

However, I observe that S11 shifts in frequency while tuning the loads—for example, the input match moves down toward ~8 GHz instead of staying centered at 10 GHz.

How can I make the input remain matched at 10 GHz over the full tuning range

1) Should I improve the coupler design (wideband hybrid)? or should I redesign the reflective load for constant-|Γ| behavior?

2) Any practical methods (e.g., λ/4 transformers, all-pass load networks, pads, dual-resonant matching) that are effective at X-band?