Design of a High-Order Dual-Band Superconducting Filter With Controllable Frequencies and Bandwidths

This paper presents the design of an eight-pole dual-band bandpass high-temperature superconducting (HTS) filter with modified stub-loaded resonators (SLRs) and dual-feeding structures. The proposed modified SLRs are found to be advantageous because the even-mode and odd-mode couplings are separated from paths. The two bandwidths can be separately adjusted by two coupling paths. The proposed modified SLRs can conveniently be used to tune the two bandpass frequencies. Therefore, both the frequencies and bandwidths of each bandpass can be easily controlled. Moreover, the proposed modified SLRs can be also used to design high-frequency and high-order dual-band bandpass filters. A dual-feeding structure is adopted to match the external Q factor and internal couplings at two bandpass frequencies simultaneously. An eight-pole HTS dual-band bandpass filter operating at 2.55 and 3.53 GHz is designed and fabricated with a compact size of 18.14 mm × 9.36 mm to demonstrate the proposed design.