Design of High Order HTS Duplexer Based on SIR Structure

A folded half-wavelength microstrip resonator with a stepped impedance structure (FSIR) is designed to extend the second harmonic and affect the strength of the external electromagnetic coupling. The FSIRs of electromagnetic mutual cancellation structure and strong electric coupling structures are designed to realize the design of narrowband and broadband filters with extended second harmonic, respectively. A T- junction is designed to cascade the two high-order filters to achieve high isolation between two channels. The duplexer is fabricated on a single piece of 2-in double-sided YBCO (YBa₂Cu₃O₇) thin film on an MgO substrate with a dimension of 34.86×26.30×0.50 mm³, a thickness of 0.5 mm, and a dielectric constant of 9.8. At 77K, the measured central frequency of the duplexer are 910 and 1100 MHz, the fractional bandwidths are 2.19% and 18.18%, the out-of-band rejections are greater than 60 dB, the two second harmonic are located at 2.4 GHz and 2.5 GHz, the insertion loss is less than 0.20 dB, and the return losses are better than 16.1 dB and 17.2 dB. The test results of the duplexer are in good agreement with the simulated ones.