Multi-order Miniaturized Dual Transmission Zeros HTS Filter without Cross Coupling

A Miniaturized high temperature superconducting filter applied to mobile communication is designed based on a novel double-folded microstrip hairpin resonator which can be used to adjust the intensity of electromagnetic coupling. The filter has the characteristics of small size and a pair of transmission zeros to improve out-of-band suppression without cross coupling. According to the theory of complex electromagnetic coupling, the circuit structure of the double folded microstrip hairpin resonator is analyzed. By adjusting the lengths of different circuit parts of the microstrip resonator, the exchange of electromagnetic coupling characteristics can be realized, thus introducing transmission zeros. At the same time, the mutual cancellation of electromagnetic coupling can reduce the distance between resonators, so the overall size of the filter is reduced. A double transmission zeros miniaturized microstrip HTS 11-order filter with the center frequency of 1300MHz and bandwidth of 200MHz without cross-coupling is designed. The measured indexes of the filter at 77 K: the center frequency is 1300 MHz, 3 dB relative bandwidth is 15%, in-band insertion loss is less than 0.25 dB, the size is 24.81 mm X 11.60 mm (0.26λgc X 0.12λgc), and out-of-band rejection is more than 70dB. The overall size test results are consistent with the simulation results.