A HTS Balun on Lanthanum Aluminate Substrate

This paper presents a high temperature superconducting (HTS) planner balun. The balun was fabricated using double sided HTS YBCO films on a 3 inch 0.5 mm-thick LAO substrate. The balun demonstrates a wideband operation and a low insertion loss. The center frequency of the blun is 1.25 GHz. The -18 dB return loss bandwidth is 1.02 GHz with the fractional bandwidth of 82%. The phase imbalance is less than 7° and the amplitude imbanlance is less than 0.7 dB. The insertion loss is less than 0.31 dB.