Design and implementation of a narrow-band superconducting X-band diplexer with high isolation

This paper presents a high performance X-band diplexer with a 65 MHz bandwidth operating at central frequencies of 9.90 and 10.02 GHz. Outstanding six-pole channel filters with a high out-of-band rejection are realized by utilizing a double-folded resonator and suppressing nonadjacent couplings on the basis of coupling analysis to improve the filtering performance of the diplexer. Two types of diplexers are compared in terms of isolation and packaging box's influence. The T-type topology is better than Y-type, and its isolation exceeds 70 dB. Moreover, the return loss and insertion loss is better than 13 dB and 0.4 dB respectively. The measurements agree well with the simulations, demonstrating that a high performance X-band diplexer with a compact size can be realized by HTS film apart from waveguide structure.