Design of Thin Wire Metamaterial-Based Interaction Structure for Backward Wave Generation

摘要

In this article, a thin wire (TW) metamaterial (MTM)-based interaction structure has been reported as a potential candidate for realizing a backward wave oscillator (BWO). The interaction structure has been designed by arranging an array of connected TWs periodically along the axis of a hollow rectangular waveguide. The TW array exhibits negative permittivity along the transverse dimensions and allows mode propagation below the transverse magnetic (TM) mode cutoff of the hollow waveguide. Two TW array variants, one with wires of square cross section (STW) and the other of circular cross section (CTW), have been considered. The frequency range (similar to 12.3-13.3 GHz) of the fundamental backward TM mode has been verified using both the eigenmode and S-parameter simulations. For a stable operation, the operating point has been chosen at similar to pi/2 point on the fundamental backward mode at 12.8 GHz. The TW array has been designed in such a way so as to avoid the interception with the electron beam propagating down the interaction structure. A prototype of STW array inside a rectangular waveguide has also been fabricated. Preliminary beam-wave interaction simulation has also been carried out, and an output power of 12.98 kW has been observed with an electronic efficiency of 13.61%. This TW array is a simpler structure to realize and hence has the advantage of reduced fabrication complexity. This makes it a viable choice as a filling medium to realize an MTM-based BWO.