High Isolation Superconducting Diplexer Designed with Double-Side Structure
This paper presents a new type superconducting diplexer designed with double-side structure. The two channels of the diplexer are located on the different layers of the superconducting thin films. One channel consists of four-pole microstrip stepped impedance resonators(MSIR) on the upper side, while the other channel consists of four-pole slotline stepped impedance resonators (SSIR) on the back side. In this paper, the coupling of MSIR-SSIR and MSIR-MSIR is compared, and the simulated results show that the latter is weaker than the former in a certain distance. High isolation between the two channels is therefore achieved because of their highly suppressed unwanted cross-coupling. The diplexer is fabricated on a MgO substrate with a double-side-coated 500-nm-thick YBCO HTS thin films and exhibits high performance. The measurements agree well with the simulations, and the isolation is over 45dB.