Automatic Frequency Control of Magnetrons

A practical AFC system for both X-band and Ku-band magnetron radar transmitters has been developed. This system meets the needs of three radar systems currently in production. Frequency stabilization is accomplished by electronically controlling the magnetron load impedance. Therefore, the magnetron ``pulling figure'' is put to use. The closed loop AFC system maintains frequency stability to better than ±2 Mc at Ku-band and ±1.5 Mc at X-band frequencies over wide environmental conditions. The system dynamically compensates for deviations in frequency due to temperature, vibration, shock, changes in duty cycle, drift with life, and poor voltage regulation. The response time of the AFC system is such that, starting at the limits of thle capture range, ``on frequency'' response is Obtained within the first five pulses of the magnetron. One of the radar systems requires a considerable delay between groups of pulses. For this radar, the AFC system provides a memory to hold the conditions for ``on frequency'' response during the delay periods. A qualitative analysis of the closed-loop system is made with reference to the Rieke Diagram. It is shown how a single magnetron has been used to meet two different sets of system performance requirements. System operation and hardware are discussed with reference to practical difficulties.