Multicavity magnetron anode structure

A magnetron is provided having a hollow anode 10 surrounding a cathode 11 with resonant cavity defining anode vanes 12 extending radially inwardly towards the cathode. The hollow interior of the anode is closed at each end by a pole piece 13, 14 consisting of a disc having a hub or boss extending into the interior of the anode towards the other hub or boss. The vanes are tapered in step fashion with an axial length adjacent the cathode which is shorter than the axial length at the interior of the anode cylinder whereby to permit the hubs or bosses to enter further into the anode cylinder, and thus approach each other more closely, than would be the case if the vanes were not tapered.