Integrated Ferroelectrics, 111: 50–58, 2009 Copyright © Taylor & Francis Group, LLC ISSN 1058-4587 print / 1607-8489 online DOI: 10.1080/10584581003590926 Design and Simulation of Tunable Ka Band Filters with Graded Barium Strontium Titanate (BST) Varactors T. S. Kalkur, 1,* N. M. Sbrockey, 2 G. S. Tompa, 2 and S. P. Alpay 3 1 Department of Electrical and Computer Engineering, University of Colorado at Colorado Springs, Colorado Springs, CO 80933-7150, U.S.A. 2 Structured Materials Industries, Inc., 201 Circle Drive North, Unit #102, Piscataway, NJ 08854, U.S.A. 3 Materials Science and Engineering Program, Department of Chemical, Materials, and Biomolecular Engineering, University of Connecticut, Storrs, CT 06269, U.S.A. Tunable Ka band filters based on graded barium strontium titanate (BST) have been in- vestigated in terms of their associated parasitics, tunability, and temperature dependence of capacitance. The simulation results show that increase in parasitic resistance from 0.05 ohm to 1 ohm increases the insertion loss from 0 db to 25 db. The simulation results also show that, with 60% tunability for graded BST capacitors, the center frequency of the filter can be tuned from 29.489 GHz to 45.144 GHz. In addition, the bandwidth shift becomes temperature independent when the graded BST capacitor is biased at an electric field of 3e7V/cm. Keywords: Ka band, BST, tunability INTRODUCTION: TUNABLE FILTERS, PARASITICS, TUNABILITY, AND TEMPERATURE DEPENDENCE Tunable Filters Tunable filters are one of the important modules for future communication systems. A tunable filter can replace a bank of conventional filters [1, 2]. In addition, it also gives the flexibility to tune its performance after packaging. A variety of tunable devices such as p-n junction varactors, GaAs MESFETs, MEMS and ferroelectrics have been used to implement tunable filters [2,7,8]. Low loss, compact filters with ferroelectric varactors can be used effectively Received August 16, 2009; in final form December 2, 2009. ∗ Corresponding author. E-mail: kalkur@eas.uccs.edu 50 Downloaded by [University of Colorado Colorado Springs] at 15:16 21 June 2012