Coherent power combining of four-way injection-locked 5.8-GHz magnetrons based on a five-port hybrid waveguide combiner

A high-efficiency power-combining method for four-way 5.8-GHz magnetrons based on the external injection-locking technique is presented in this article. The method uses a nonisolated, lossless five-port hybrid waveguide combiner for power combining. Meanwhile, the injection-locking technology has been applied to magnetrons for achieving coherent power combining. The phase fluctuation of the injection-locked magnetron, without the presence of a phase-locked loop, measured nearly 2.5 degree. In contrast, when a phase-locked loop was introduced, the phase fluctuation reduced significantly to approximately 0.5 degree. This phase accuracy can fully meet the requirements of combining experiments. Four magnetrons worked in injection-locked states without phase-locked loop. The proposed power-combining system is designed, measured, and analyzed. Measurement results show that a high-power-combining efficiency of over 95% is achieved by injection-locked magnetron without PLL, with the best efficiency reaching up to 97.7% with phase control of the injected signals. Experimental results reveal that the magnetron phase-pushing effects and the ripple in high-power dc voltage and current have a minor impact of approximately 4% on the combining efficiency.

💡 Research Summary

This paper presents a high‑efficiency power‑combining scheme for four 5.8 GHz magnetrons using external injection‑locking and a lossless, non‑isolated five‑port hybrid waveguide combiner. Magnetrons, which are limited in output power by their resonant cavity size, become especially low‑power at higher frequencies. To overcome this, the authors synchronize four magnetrons by injecting a low‑power reference signal into each device, thereby forcing the oscillators to lock in frequency and phase. Without a phase‑locked loop (PLL), the injection‑locked magnetrons exhibit a phase jitter of ±2.5°, which is reduced to ±0.5° when a PLL is added, satisfying the stringent phase‑accuracy requirements for coherent combining.

The combiner is a quasi‑symmetric five‑port network derived from a 3‑dB E‑plane tee and a 3‑dB H‑plane tee. Ports 2 and 3 feed the H‑plane tee, ports 4 and 5 feed the E‑plane tee, and port 1 serves as the single combined‑output port. Theoretical analysis shows that if the input amplitudes are equal and the relative phases are either 0° (E‑plane) or 180° (H‑plane), the intrinsic maximum efficiency of the network approaches 100 %. Measured and simulated S‑parameters confirm excellent matching (|S₁₁| < ‑20 dB) and the required phase relationships, indicating that the combiner is essentially lossless and non‑isolated.

The authors derive the combining efficiency η as a function of amplitude and phase mismatches:
η =