Miniaturized high-temperature superconducting diplexer using common resonator and cross coupling structure

This paper presents a miniaturized high-temperature superconducting (HTS) diplexer for mobile (1.8 GHz) and wireless local area network (2.4 GHz). A stub-loaded spiral resonator is used as a signal splitter and a common resonator for both channels. A cross coupling between the common port and fourth resonator of the lower channel is introduced via a transmission line, transmission zeros have been realized in the transition band of the channel, improving the selectivity of the channel band. Meanwhile, the other transmission line is used to introduce a cross coupling between the common resonator and fourth resonator of the higher channel of the diplexer. The diplexer is fabricated on a YBa2Cu3Oy (YBCO) polished MgO substrate wafer, which has a compact size of 11.1 mm × 8.43 mm. Isolation in both channels is greater than 40 dB, maximum insertion loss in both channels is less than 0.05 dB, and minimum return loss in both channels is greater than 18.5 dB.