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This paper proposes a reconfigurable bandpass filter with a wide tunable range, which is achieved by connecting two tunable passbands with switching diodes. A pair of transmission zeros (TZs) are introduced through the cross‐coupling structure to improve the passband selectivity of the filter, and one more transmission zero is added by the interdigital coupling line to enhance the out‐of‐band suppression and broaden the upper stopband. The simulation and experimental results show that the designed filter with an absolute bandwidth of 100 MHz realizes a tunable frequency band covering 1.5–3 GHz, corresponding to a fractional tunable range of 66.7%. The dimension of the fabricated filter is 0.32 λg × 0.34 λg. [ABSTRACT FROM AUTHOR]

A high-temperature superconductor (HTS) bandpass filter with special asymmetric cul-de-sac units (SACUs) is introduced and a compact low-radiating microstrip resonator is suggested for the filter realization. Such a filter is capable of providing better selectivity and higher out-of-band rejection and hence a decrease in adjacent-channel interference, which is of critical importance for mobile communication. This improvement of the filter characteristics results from an increase in the number of pairs of transmission zeros (TZs) on the imaginary axis on the complex plane when using the filter composed of the introduced SACUs, each providing a pair of TZs. An 11-pole filter consisting of two SACUs was fabricated using MgO substrate of 0.5 mm thickness with double-sided YBCO HTS film. Characterization of the filter at 77 K gave a central frequency of 2345 MHz, insertion loss 0.19 dB, an overall in-band return loss better than 15 dB, and an ultra-high band-edge steepness as a consequence of the two pairs of TZs. The measured characteristics are in good accord with those obtained by electromagnetic simulation. [ABSTRACT FROM AUTHOR]

A novel multimode dual-ring ultrawideband (UWB) bandpass filter is proposed in this article, which is constructed by loading open stubs in the horizontal and vertical directions of the dual-ring resonator. Five modes are evenly distributed in the passband, and a pair of transmission zeros are introduced to the left and right transition bands to enhance selectivity. Parallel-coupled lines ensure external coupling strength for realizing the UWB, and a cross junction suppresses spurious in high frequencies to expand the upper stopband. For demonstration, a quintuple-mode high-temperature superconducting UWB bandpass filter is designed on the 0.5 mm thick MgO substrate with double-sided YBa2Cu3O7 (YBCO) films. The test results show that the 3-dB bandwidth covers 2.56 to 11.15 GHz, the in-band return loss greater than 15 dB. [ABSTRACT FROM AUTHOR]

A miniaturized eight-order quasi-elliptic function filter configuration with controllable transmission zeros (TZs) is proposed. Without changing the overall layout of the filter, two pairs of TZs are introduced by adopting two cascaded quadruplet (CQ) units to improve the suppression of the filter. At the same time, a cross capacitance coupling is introduced to combine the two CQ units to realize the synchronous adjustment of these two pairs of TZs. Through using this configuration, it not only helps realize the miniaturization of the filter, but also reduces the complexity of adjusting the two CQ units individually. Finally, an eight-order high-temperature superconducting filter with two pairs of TZs is designed on a double-sided YBCO/MgO/YBCO thin film with a size of 15.95 mm × 7.91 mm, a thickness of 0.5 mm, and a dielectric constant of 9.8. At 77 K, the measured central frequency of the filter is 2000 MHz, the bandwidth is 35 MHz, the out-of-band rejection is greater than 60 dB/MHz, the insertion loss is less than 0.22 dB, the return loss is better than 15.8 dB, and the test results are in good agreement with the simulated ones. [ABSTRACT FROM AUTHOR]

A miniaturized high temperature superconducting (HTS) ultra‐wideband (UWB) bandpass filter (BPF) is presented based on stub‐loaded multi‐mode resonator (SLMMR) in this letter. This SLMMR constructed by loading three sets of different open stubs on a stepped‐impedance resonator brings five resonant modes into the passband for UWB bandwidth and a pair of transmission zeros in the transition bands for high selectivity. The filter is finally designed and fabricated on a 0.5‐mm thick MgO substrate with double‐sided YBCO HTS films. At 77 K, the measured results show that the 3‐dB bandwidth covers 3.0 GHz‐12.0 GHz; the minimum insertion loss is 0.11 dB; the return loss is better than 15.75 dB; the out‐of‐band rejection is greater than 24.35 dB in the lower stopband, and the upper stopband with 20 dB attenuation level is extended to 16.77 GHz. [ABSTRACT FROM AUTHOR]

In this paper, a novel trapezoidal meander-line resonator (TMLR) is proposed to design compact high-order high-temperature superconducting (HTS) linear phase bandpass filters with cascaded quadruplet (CQ) structures. By changing the conventional rectangle half-wavelength meander-line microstrip resonator into a trapezoidal resonator, unnecessary cross coupling between nonadjacent resonators in the CQ units can be avoided. And using the proposed TMLR to design the CQ unit, electric field cross coupling or magnetic field cross coupling can be easily achieved and tuned without the cross-coupling line. To further demonstrate the feasibility of using this configuration for miniaturized circuit design, an 8-order HTS linear phase filter with one pair of transmission zeros was designed. The measured responses agree very well with the simulated results. The physical HTS filter has a center frequency of 1935 MHz and bandwidth of 70 MHz. The out-of-band rejection is greater than 50 dB, and the effective bandwidth of group delay fluctuation less than ±3 ns takes up more than 65% in the whole passband. [ABSTRACT FROM AUTHOR]

In this paper, a reconfigurable filter is designed by adjusting the microstrip line impedance for the first time, which breaks the single situation that the resonator can only adjust the electrical length in the previous microstrip reconfigurable circuits. This fully reconfigurable filter loads varactors between three parallel coupling lines to realize the reconfiguration of equivalent impedance. Changing the equivalent impedance of the resonator can use harmonics to introduce transmission poles (TPs) and transmission zeros (TZs), which not only effectively improves the selectivity of the filter but also greatly improves the stopband suppression. Finally, this fully reconfigurable filter can not only tune the center frequency but also the bandwidth. A total of six TZs are introduced, three can be generated by the resonator itself, and the other three are introduced by loading adjustable stubs. The final size of this filter is 0.34 λ g × 0.25 λ g. The measured results are in good agreement with the simulation results. [ABSTRACT FROM AUTHOR]