PSpice simulations of nonlinear transmission lines based on ferroelectric dielectrics

The search for efficient, compact, high-power conversion of electrical impulses into high power microwave energy is driving a modern rebirth of nonlinear transmission line studies. A nonlinear transmission line utilizes the nonlinear permittivities and permeabilities, ε_r and μ_r for dielectrics and magnetics, respectively, to transform a fast-rising pulse front into microwave energy. The amplitude dependent phase velocity of nonlinear materials enables an input pulse of relatively slow rise time to be converted into a pulse exhibiting an extremely fast rise-time through the formation of an electromagnetic shockwave. A majority of research today is conducted on nonlinear magnetic materials, namely ferrites, with an impressive degree of success. By contrast, the University of Missouri - Columbia (UMC) has focused upon nonlinear transmission lines comprised of nonlinear dielectric materials in order to take advantage of some unique materials and techniques recently developed at UMC. Pulsed power generated from the nonlinear transmission lines indicate power levels on the order of 100 MW and response frequencies into the GHz range with simultaneous compression of pulses. A simulation study of nonlinear transmission line behavior under different parametric constraints is reported. The simulations were conducted in PSpice and utilize a custom-developed nonlinear dielectric model based upon laboratory data provided by commercial manufacturers of ferroelectric material. The model implemented in the study is discussed in detail and the compromises made to balance model accuracy with numerical convergence are discussed. A one-dimensional model of a coaxial transmission line filled with a ferroelectric material was implemented and the results are discussed.