Novel Materials Form Tunable Components

Nov. 1, 2003
Tiny voltage-tuned phase shifters are among the first components offered by a company with unique thin-film ferroelectric technology.

Tuning a high-frequency circuit usually involves trimming a variable capacitor or turning a mechanical tuner. By using innovative circuit materials formed of barium-strontium-titanate (BST) dielectric, however, Agile Materials & Technologies (Goleta, CA) offers components that can be tuned with an applied voltage. The company's thin-film ferroelectric technology offers tuning benefits at RF through millimeter-wave frequencies for commercial and military applications, including for antennas, filters, phase shifters, and linearization circuitry.

Since the dielectric constant of BST-based substrate materials changes with applied DC voltage, circuits can be readily fabricated with voltage-tunable capacitances. As with trimmer capacitors, as the capacitance is varied, the impedance and phase responses of an active or passive circuit are adjusted in a predictable way. In the case of Agile's components, however, the circuit board is the trimmer capacitor. For a variable capacitor formed on BST substrate with zero-voltage value of 32 pF, the capacitance drops to half 16 pF with an applied voltage of ±4 VDC. Once the tuning voltage has been applied to affect the capacitance shift, additional voltage need not be applied to maintain the change in capacitance and only a small leakage current is consumed.

At the recent IEEE MTT-S exhibition in Philadelphia, PA, the company demonstrated several BST components, including tunable phase shifters. The phase shifters operate with a single analog tuning voltage, requiring a maximum control voltage of 20 V. Since only passive components are used in the phase shifters (compared to diodes in conventional phase shifters), and the control voltage draws zero amperes of nominal current, the power consumption for this design is negligible. The phase shifters, which are available at frequencies from below 1 GHz to beyond 40 GHz (L-band through Ka-band), achieve better than 360-deg. Phase-shift rage with 6 to 7 dB or less typical insertion loss at 0-deg. phase shift, improving to 4 to 5 dB or less of insertion loss with increased phase shift. The phase shifters feature a distributed design with uniform group delay, and can handle more than +20 dBm (100 mW) input power over wide instantaneous bandwidths. They take up only 3 to 6 mm2 circuit-board area, depending upon frequency, allowing designers to shave the size of circuit layouts. Agile Materials & Technologies, Inc., 93 Castilian Dr., Goleta, CA 93117; (805) 968-5159, FAX: (805) 968-3279, Internet:

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