A Compact $E$ -Plane Four-Port Junction Circulator

A compact $E$ -plane four-port junction circulator is proposed in this letter. It consists of an X-shape waveguide junction, two X-shape ferrite disks with fillets, and several matching metal posts. Based on the combinations of the TM ₂₁₀ and degenerate TM _±110 modes, a four-port gyromagnetic resonator is realized. By introducing the tuning elements, the bandwidth is improved. Measurements show that from 8 to 9 GHz, the return loss is better than 18 dB, the isolation is better than 17 dB, and the insertion loss is 0.3–0.6 dB. Measurements agree well with the simulations. Its cross-sectional size is less than $0.86\lambda \times 0.72\lambda $ at 8.5 GHz. High-power test shows that its pulsed power capacity is no less than 28 kW.