Electrical Modeling of Ferroelectric Tunable Microwave Components and Circuits

Abstract

Ba(1−x)Sr x TiO 3 (BST) is currently being investigated for applications in tunable microwave devices and circuits. Our group has demonstrated several working ferroelectric tunable microwave circuits in collaboration with NASA Glenn Research center in the past several years. Current work is underway in optimizing the ferroelectric thin-films properties at microwave frequencies, in collaboration with Air Force Research Laboratories. Ferroelectric tunable filters, couplers, and phase shifters have been demonstrated in the past using two-layered microstrip or coplanar waveguide configuration. Accurate electrical modeling of ferroelectric tunable components and circuits will be presented in detail in this work. With known material properties such as dielectric tunability, capacitance vs voltage, and Q values over a wide frequency range, one could model any circuit and estimate the circuit's performance over a wide frequency range. Electrical models can be developed that predict the frequency tunability, and the effect of the dielectric tunability on various circuit parameters. For example, in the tunable filters, the effect of dielectric tunability of the ferroelectric thin-film on the filter's passband insertion loss, return loss, bandwidth, and frequency shift could be assessed using a simple lumped element circuit models. We have also developed models for MEMS capacitive shunt switches using BST thin-film as a dielectric layer for phase shifter applications.