Phase shifters are critical components in scanned phased-array antenna systems for both commercial and military applications. Phase shifters can also be combined with transmitter power amplifiers to improve system linearity in cellular communications networks. By using different phase-shifting elements in an antenna array, a beam can be effectively steered electronically, rather than mechanically shifting an antenna. Phase shifters are traditionally based on switching diodes to achieve the different phase states. And research continues on using microelectromechanical- systems (MEMS) devices as components in high-frequency phase shifters. But an application note from Agile RF, Inc. (www.agilematerials.com), "Affordable Phase Shifters," explains how ferroelectric materials can be used to form affordable RF/microwave phase shifters.
Ferroelectric materials are ceramic compounds with unique dielectric properties. Thickfilm ferromagnetic materials have traditionally been used for large industrial capacitors. In recent years, however, several companies have explored the use of these materials in thin-film form for higher-frequency circuits and devices. Thin-film ferroelectric materials exhibit much different properties than bulk, thick-film ferroelectric materials, with a flat temperature response for controlled capacitance over wide temperature ranges. Thin-film ferroelectric materials maintain the high capacitance density of the thick-film materials, and lend themselves to stable, high-performance phase shifters.
The six-page application note explains how Agile RF uses barium strontium titanate (BST) thin-film ferroelectric material to form phase shifters that can be tuned with applied voltage, since the capacitance of these materials changes as a function of applied voltage. Because of the high capacitance density, a great many capacitors can be formed in a small area, to create variable capacitors or voltage-controlled delay lines. The capability to make delay lines also makes it possible to create compact phase shifters and filters. The BST material also exhibits the property of increasing capacitor quality factor (Q) with increasing control voltage, allowing for the development of high-frequency phase shifters with low loss as well as tunable microwave filters.
Agile RF, Inc.
93 Castillian Dr.
Santa Barbara, CA 93117
Fax: (805) 968-3279