RF source including slow wave tube with lateral outlet ports

摘要

Multiple radio frequency (RF) outlet ports are provided along the side of a slow wave tube to establish a distributed RF output in response to the transmission of an e-beam through the tube. The tube has a periodically rippled inner surface, and the outlet ports are spaced along the tube by substantially integral numbers of ripple periods. When implemented as a backward wave oscillator, RF power is extracted during a single pass through the tube; a travelling wave tube amplifier implementation is also possible. The separation of the RF extraction from the absorption of the e-beam at the end of the tube eliminates RF reflections and permits water cooling of the e-beam absorber. The RF extraction ports are also preferably configured as built-in mode converters from a TM01 cylindrical tube mode to a TE10 rectangular extraction mode, with four symmetrically arranged rectangular extraction waveguides at each extraction location combining their energies into a single TE10 output. Reductions in the cylindrical tube diameter after each extraction location reflect radiation back through the tube to cancel back-scattered radiation losses from the extraction ports.