A 360° BST phase shifter with moderate bias voltage at 30 GHz

Paraelectric BaSrTiO3 films deposited by sol-gel have been investigated from 1 kHz to 40 GHz using coplanar waveguides, resonators, and inter-digitated capacitances. At room temperature and without bias, the dielectric constant epsilon(r) is around 300 and the loss tangent is 5 x 10(-2). Tunability is 40% for a 40-V bias voltage. Analog phase-shifter circuits were subsequently fabricated in order to obtain a 360 degrees phase shift in the K a-band with a moderate bias voltage. The lowest bias value was 17 V at 40 GHz, whereas 40 V were necessary at 30 GHz. For the latter condition, the insertion loss was -6 dB. The best figure-of-merit of the phase shifters with a loading factor of 1.4 was 27 degrees/dB. These results show an improvement in terms of voltage-controlled tunability.