Design and Characterization of Frequency Agile RF and Microwave Devices using Ferroelectrics

Abstract

A methodology for the optimized design of tunable distributed resonators is introduced and verified. This technique enables maximum tuning with minimum degradation in quality (Q) factor. The concept of a network transformation factor and a new figure-of-merit for tunable resonators is introduced and applied to experimental data. The figure-of-merit quantifies the trade-off between tunability and Q factor for a given tuning ratio of the variable reactance device. As such, it can be extended to the design of filters, phase shifters, antennas, matching networks and other frequency-agile devices where resonant elements are used. Varactors utilizing Barium Strontium Titanate (BST) thin-film were designed and fabricated in integrated form and also in discrete form as standard 0603 components. High frequency characterization and modeling of BST varactors is described. A novel characterization technique for the intrinsic loss extraction of symmetrical two-port networks was developed and verified experimentally. Both integrated and discrete BST thin-film varactors were used to design, fabricate and characterize frequency-agile circuits. Tunable bandpass and bandstop filters and matching networks are described. A dual-mode, narrowband microstrip patch antenna with independently tunable modes was developed and characterized. Tuning and nonlinear characterization results are presented. Investigation for the use of BST thin-film varactors for voltage-controlled oscillators and phase shifters are also presented. Design parameters, fabrication issues, and processing challenges are discussed.