We use the general coupled matrix method to design the planar microwave diplexer on the superconductivity YBa2Cu3O7 (YBCO) thin film with the MgO substrate, which has an attenuation pole near cutoff frequency with each one filter. Both two high performance bandpass filters can be synthesized by using multiple λ/2-resonators and can be combined the two filters to form a diplexer. The attenuation poles will improve the selectivity of the diplexer and can be obtained by modifying the traditional Chebyshev frequency response. A practical design technique using coupling matrix synthesis algorithm with Chebyshev filtering function, including theoretical and simulated results will be demonstrated.
