Microwave Generation in Coaxial, Composite Nonlinear Transmission Lines

Abstract

Nonlinear transmission lines (NLTLs) can sharpen electric pulses to generate high power microwaves with high repetition rate 1 . This work uses COMSOL Multiphysics to model coaxial, NLTLs composed of ferroelectric and/or ferromagnetic composites to construct a hybrid, distributed NLTL. We have measured the linear electromagnetic properties 2 and nonlinear permeability 3 of such composites from 1-4 GHz to demonstrate the feasibility of adjusting inclusion selection and volume loading to tune electromagnetic properties to adjust NLTL performance. These results justify our use of hyperbolic tangent functions to model the nonlinear electromagnetic properties. Treating an NLTL containing a ferromagnetic composite as a homogeneous domain allows us to assume an effective gyromagnetic ratio and damping factor in the Landau-Lifshitz (LL) equation for specific ferromagnetic composites based on our NLTL experiments. We then solve the LL equation for the gyromagnetic rotation of the magnetization of the composite 4 exposed to an applied external magnetic bias. The NLTL simulation results are compared with our experimental results. Implications to NLTL system design, particularly integrating with an antenna for HPM propagation, will be discussed.