AbstractOne of the challenges faced in using ferroelectrics in high frequency devices is how to effectively use the material in a circuit design. A compact reflection-type phase shifter fabricated on sapphire substrates coated with ferroelectric barium strontium titanate (BST) thin-films has been built which shows the promise of using BST thin films in the design of tunable microwave devices. The phase shifter, fabricated as one monolithic assembly, consists of a 3dB coupler, meandered line inductors and tunable interdigital capacitors. A continuously variable phase shift range of more than 100° using the branch-line coupler was obtained at a center frequency of 2.95 GHz, and more than 90° phase shift over 200 MHz bandwidth with a bias voltage range from 0 V to 175 V. The phase shifter using the Lange coupler has over 700 MHz bandwidth centered at 2.2 GHz with a phase shift of more than 90° and an insertion loss less than 2 dB and return loss of greater than 14 dB, over a bias voltage range from 0 V to 160 V. The loss of the BST phase shifter presented in this work is on the order of other commercially available RF front-end components, such as bandpass filters and RF switches. This holds promise for the practical realization of smart antenna systems in cellular handsets and wireless LAN cards.