S-Band Active Circulator with Reactive Load Tuning for Isolation Recovery

This work presents a $3.4-\text{GHz}$ gallium nitride (GaN) active circulator with independently tunable reactive loads, which can compensate for impedance mismatch and maintain isolation that results from phased array scan impedance. Simulated results demonstrate isolation improvements of 13.4, 10.5, 19.7 and 31.8 dB for $|\Gamma|$ mismatches of $0.2\left(\theta=180^{\circ}\right.$ and $\left.\theta=270^{\circ}\right)$ and 0.3 $(\theta=0^{\circ}$ and $\theta=90^{\circ})$, respectively. This concept shows promise for application in full duplex phased array front ends, where high isolation is critical.