A Wide-Band Reflection-Type Phase Shifter at S-Band Using BST Coated Substrate

The design and experimental results of a wide-band monolithic reflection-type phase shifter are presented in this paper. The phase shifter fabricated on Ba0 6Sr0 4TiO3 (BST)/sapphire consists of a coplanar waveguide (CPW) Lange coupler, a series resonated LC termination, and a bias network. The CPW Lange coupler results in a power split of 3.5 dB 0.5 dB in the range of 1.6–3.2 GHz. The BST interdigital capacitor has a tunability ( max min) of 3.1 with 140 V. Measured and simulated performance of a series resonated LC termination was described. The phase shifter has achieved a phase-shift range of over 90 with an insertion loss of better than 2.0 dB and a return loss of higher than 14 dB in the frequency range of 1.9–2.5 GHz over a bias voltage range from 0 to 160 V. A figure-of-merit of maximum 72 /dB at 2 GHz was obtained. The smaller phase shifter using the folded-type CPW Lange coupler, which maintains a smaller aspect ratio for easier packaging, has an insertion loss of better than 2.3 dB with a phase-shift range of over 130 at 2.5 GHz. Two-tone measurements of the phase shifter indicate an input 3 of 32 dBm with 0 V and 41.9 dBm with 60 V. Total size of the monolithic BST phase shifter is 11.2 mm 4.9 mm 0.43 mm for the straight coupler design and 5.4 mm 6.5 mm 0.43 mm for the folded-type design.