Interspectral line noise and increased gains in coherent injection-locked TWT and IBCFA loop amplifiers

Static and dynamic theories for the injection-locking of distributed linear beam microwave loop feedback oscillators are presented and verified by experimental results. The frequency lock range is inversely proportional to the product of the square root of the realized injection gain and the total loop length, while the characteristic time to acquire lock is directly proportional to that product. Loop phase variations in a lock condition are also magnified by the square root of the injection gain. The evolution of a dual mode X-band Injected Beam Crossed-Field Amplifier (IBCFA), designed for use as a multimode coherent radar transmitter, is discussed. Measurements of pulsed excess noise contributed by the CFA are presented. CFA excess noise is down better than 115 dBc/Hz at 2 kHz from a pulsed spectral line and that noise emanates from the beam supply. Excess pulsed noise with positive feedback and injection-locking increases in direct proportion to the injection gain.