Generation of powerful subnanosecond microwave pulses in the range of 38-150 GHz

Experimental measurements of coherent stimulated radiation from intense, subnanosecond electron bunches moving through aperiodic waveguide and interacting with a backward propagating TM/sub 0.1/ wave are presented. The ultra-short microwave pulses in Ka, W, and G band were generated with repetition frequencies of up to 25 Hz. Observation of RF breakdown of ambient air, as well as direct measurements by hot-carrier germanium detectors, gives an estimate of the peak power up to 140 MW for the 300-400 ps pulses at 38 GHz. The initial observation of 75 GHz 10-15 MW radiation pulses with duration less than 150 ps, and of 150 GHz microwave spikes with a risetime of 75 ps are also reported.