Generation of powerful subnanosecond microwave pulses throughout the band of 38-150 GHz

Experimental results of the observation of coherent stimulated radiation from dense, subnanosecond electron bunches moving through a periodic waveguide and interacting with a backward propagating TM/sub 01/ wave are presented. The 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, leads to an estimate of the peak power as high as 60 MW for the 300 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.