A novel structure for dc bias on varactors in composite right/left-handed transmission lines phase shifter using Ba0.25Sr 0.75TiO3 thin film

Abstract

Tunable ferroelectric varactors, consisting of two series connected capacitors using Ba0.25Sr0.75TiO3 thin film, have been applied in composite right/left-handed (CRLH) transmission lines (TLs) phase shifters. The CRLH circuit, with a length of 3330 νm, is a coplanar design integrated on a high resistive Si substrate. A novel circuit of dc bias pads is designed to provide direct connection and therefore ensure the same applied dc voltage across each varactor. Both simulation and experimental results demonstrated the unique features of CRLH TLs, showing a differential phase shift with flat frequency dependence characteristics. Under 10 V dc voltages, the phase shift is 35° and the differential phase shift is flat between 6.8 and 8.8 GHz. The figure of merit is 4.1° dB-1 around 7.5 GHz. © 2009 IOP Publishing Ltd.