The periodically-loaded travelling-wave multiple-beam klystron

The periodically-loaded travelling-wave klystron (p.l.t.w.k.) is a fast-wave multi-beam microwave amplifier for very high power, having an operating bandwidth greater than 10%. A theoretical investigation has been carried out for small-signal conditions, relativistic corrections being included. Optimum conditions for the various parameters affecting the operation have been determined, and the results are presented in a series of contour diagrams. The investigation shows that, for a constant-impedance power-amplifier section, an efficiency of 35% is possible, while a power-amplifier section of tapered impedance could attain 50%. An iris-loaded ridge waveguide was found to give an impedance of 1 kilohm at the beams with a bandwidth of 20% between the cut-off points. In order that a p.l.t.w.k. should have a useful gain, the product of the gun perveance and number of guns must be high. A gun with a perveance of 2.4 ¿A/volt3/2 was developed for an S-band experimental model. The experimental work was limited to a single beam demountable device. By suitable experiments the behaviour of each beam in a multi-beam model was investigated and hence the performance of the whole klystron was calculated: there was reasonable agreement between theory and practice.