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In this manuscript, a miniature high-temperature superconductor (HTS) bandpass filter (BPF) with multi-transmission zeros (TZs), high selectivity, and great attenuation of stopband is presented. A couple of dual-mode resonator (DMR) is employed to achieve the proposed BPF, which can be characterized by using the classical even-odd mode analysis technique. The presented cascaded DMR can excite four resonant modes, which can be individually managed. Plus, a pair of intrinsic transmission zeros can be yielded at both the lower and upper edges of the passband, which results in sharp shirt performance. As an example, the HTS BPF is designed, fabricated, and tested, in which the center frequency is centred at 3.95 GHz and the 3-dB fractional bandwidth (FBW) is 2.5%. The proposed HTS BPF is implemented by using Tl2Ba2CaCu2O8 (Tl-2212) thin films which are fabricated by two-step processing and the superconducting critical temperatures (Tc) of the HTS films can reach 103 K. The design methodology is confirmed since the experimental results are in good agreement with theoretical results, showing desired bandpass characteristics, high selectivity, and the attenuation of lower and upper stopbands above −50 dB. Further, the circuit size is only 0.4 cm2. [ABSTRACT FROM AUTHOR]

A quad-band microstrip bandpass filter (BPF) based on a 13-mode resonator is proposed in this article with compact size, high band‐to‐band isolation, and multiple transmission zeros (TZs). The proposed filter is constructed by two transmission paths from the input to the output port, which employs the transversal cancellation mechanism of two transition paths to introduce extra nine TZs. Therefore, a total of 12 TZs are located at 0.2, 1.8, 2, 3.88, 4.61, 5.24, 5.9, 9.26, 9.51, 12.32, 12.75, and 13.27 GHz, respectively, realizing high selectivity. Moreover, the designed filter can achieve quad passbands with centered frequency at 0.95, 2.78, 7.32, and 10.63 GHz for the requirement of multi-service in modern communication systems, with wide bandwidth of 235, 790, 2200, and 1540 MHz, respectively. The measured results agree well with the simulation results, which proves the feasibility of the design method. [ABSTRACT FROM AUTHOR]

This paper presents the design of frequency-tunable dual-band, tri-band and quad-band bandpass filters (BPFs). The proposed three BPFs can be independently tuned and individually switched by varying the capacitances of the varactors. In the designed tunable dual-band BPF (TD-BPF), common input/output feed lines are utilized for two tunable dual-mode resonators (TDRs). Further, three TDRs and four TDRs are employed to achieve tunable tri-band BPF (TT-BPF) and tunable quad-band BPF (TQ-BPF), respectively. Then, the TD-BPF and the TT-BPF are fabricated and measured to verify individual tunability and independent switchability. For the TD-BPF, the measurement results show that the center frequency (CF) of the first passband varies from 1.37 to 1.62 GHz, and the CF of the second passband varies from 2.3 to 2.64 GHz. In the measured TT-BPF, the tuning ranges of CFs of three passbands are 1.3–1.5 GHz, 2.36–2.6 GHz, and 3–3.54 GHz, respectively. [ABSTRACT FROM AUTHOR]