A 5 kW wideband coupled cavity tube with PPM focusing for 11 GHz to 17 GHz

A wideband PPM-focused coupled cavity tube for Ku-band has been developed that operates over a 43 percent bandwidth. Previous wideband coupled cavity tubes have bandwidths of up to about 30%. Increased cold bandwidth is achieved by eliminating the stop-band between fundamental and next higher mode ("slot" mode) so that the two adjacent modes are coalescent. In addition, the beam hole and ferrule diameter are chosen to be relatively small. The tube provides internal gain equalization with staggered bandwidths of the four gain sections and with frequency selective loss. Small signal gain is about 40 dB with maximum gain variations of less than 15 dB over the bandwidth. Without the internal gain equalization design the gain variation would have been on the order of 40 dB. The tube uses double period permanent magnet focusing with Alnico 8 magnets. The gun has a non-intercepting grid.