A Compact Circuit Model for Frequency-Selective Limiters With Strong Field Nonuniformity

A compact nonlinear circuit model is developed for frequency-selective limiters (FSLs) based on thin film magnetic materials. The model contains a three-port coupled inductor circuit called a spin unit that represents the dynamic spin precession behaviors of a single spin, which is derived rigorously from the Landau-Lifshitz–Gilbert (LLG) equation. The spin units are then combined with external circuitry to represent the coupling between the RF signal in the form of electromagnetic (EM) waves and the spin waves. Specifically, two types of coupling are considered, parallel pumping and perpendicular pumping. The former contributes to the power-limiting effects of FSLs, while the latter accounts for the small signal insertion loss. In addition, the RF magnetic fields provided by coplanar waveguide (CPW)-FSLs are spatially nonuniform. Such nonuniformity can be modeled by creating an array of inductors based on the field distribution in both the width and the thickness directions. The circuit model is implemented in the advanced design system (ADS) and is capable of predicting the small signal $S$ -parameters, large signal insertion loss, power threshold, time delay, intermodulation (IM) spectrum, and frequency selectivity for CPW-FSLs. The model may also be used for modeling other RF magnetic devices based on similar physics.