Planar tunable high-temperature superconductor microwave broadband phase shifter with patterned ferroelectric thin film

A planar tunable high-temperature superconductor (HTS) microwave phase shifter with patterned ferroelectric thin film is presented in this paper. The circuit is based on a coplanar strip (CPS) transmission line periodically loaded with planar varactors. The CPS line is transformed to microstrip input/output by baluns. The patterning of the ferroelectric thin film reduces the conductor loss and eliminates unwanted tuning comparing with circuits where a whole layer of ferroelectric thin film is used. The circuit is optimized for high tunability following analytical equations. The phase shifter thus fabricated has a broadband response from 7 to 11 GHz. At 200 V DC bias, an average phase shift of 20° is achieved.