Wideband superconducting diplexer with stepped-impedance cross-structure

A stepped-impedance cross-structure (SICS), consisting of a centre rectangular patch loaded with two pairs of stubs, is proposed for the designing of a wideband superconducting diplexer. Each pair of the stubs is designed for one channel of the diplexer, and is coupled by the centre rectangular patch with a strong coupling property required by the wide bandwidths. The frequencies and the coupling strengths of the two pairs of the stubs can be controlled independently. A superconducting diplexer has been successfully designed and fabricated with the proposed structure. The two channels are centred at 2.9 and 5.8 GHz with fractional bandwidths of 26.9 and 24.5%. The measured results of the fabricated device show low insertion losses and high isolations and agree well with the simulated ones.