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This letter proposes a wide-range reconfigurable bandpass filter (WRBPF) based on the cross-shape triple-mode resonator. Varactor diodes and switching diodes are utilized at the ends of the resonator and the positions of external coupling, which combines the two working modes of the low-frequency band and high-frequency band, greatly broaden the tunable range of the center frequency ($f_{0}$). When the 3-dB bandwidth of WRBPF is 180 MHz, $f_{0}$ can be adjusted from 0.78 to 1.93 GHz, and the relative adjustment range is 84.9%. When $f_{0}$ is 1.355 GHz, the absolute bandwidth can be adjusted from 110 to 950 MHz, and the relative bandwidth adjustment range is 8.1%–70.1%. Moreover, the circuit size of WRBPF is only $0.29\,\,\lambda g\,\,\times 0.22\,\,\lambda g$. The experimental results show that WRBPF has not only a simple structure but also an excellent performance. [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 new method is proposed to produce even finite transmission zeros without any cross-coupling between the resonators of filter, by loading the second-order extracted-pole unit (EPU) composed of two mutual coupled resonators at the input or output port of the filter. An arbitrary distribution of finite transmission zeros on the imaginary axis can be achieved by adjusting the resonant frequencies of resonators in the EPUs and the coupling strength between them. The finite transmission zeros can be symmetrically or asymmetrically distributed about the center frequency of the filter, even all on the same side outside the passband of the filter. And the topological structures of these filters are given in this paper. Besides, Cauchy method is adopted to analyze the proposed EPU configuration filter as well. This paper not only discusses how to implement a pair and two pairs of finite transmission zeros, and how to control the distribution of finite transmission zeros, but also gives multiple sets of computer-aided synthesized normalized coupling matrices. Based on this, an eighth-order quasi-elliptic function high-temperature superconducting filter with two pairs of finite transmission zeros was designed on a double-sided YBCO/LaAlO3/YBCO films to verify the feasibility of this new structure. [ABSTRACT FROM AUTHOR]

A novel compact high-temperature superconducting low-pass filter (LPF) with an ultrawide stopband, excellent out-of-band rejection, and a low insertion loss is presented. This filter consists of a four-order LPF constructed by four interdigital hairpin stepped-impedance resonators (IHSIRs) and two pairs of radial stubs (RSs) in the input and output ports of the filter. The four-order IHSIR LPF brings transmission zeros for a high selectivity, and the RSs exhibit a characteristic of extending the LPF’s stopband effectively. The proposed LPF with cutoff frequency $f_{c}$ at 3 GHz is implemented on a 0.5-mm-thick MgO wafer with double-sided YBCO films. The measured results show a 30-dB harmonic suppression from $1.08f_{c}$ to $7f_{c}$ , a steep roll-off of 197.1 dB/GHz, and an in-band insertion loss less than 0.13 dB. Moreover, the LPF possesses a miniaturized size of $0.21\lambda _{\text {gc}} \times 0.03\lambda _{\text {gc}}$. [ABSTRACT FROM AUTHOR]

This letter presents a new multimode ring resonator ultrawideband (UWB) bandpass filter by loading a microstrip line on the vertical symmetrical plane of a ring resonator and a pair of stepped-impedance open stubs at the center of this microstrip line. Five modes are allocated within UWB band, and a pair of transmission zeros are introduced to improve the passband selectivity. By adopting the parallel-coupled lines, not only suitable external coupling is achieved, but also the performance of upper stopband is improved. This quintuple-mode high-temperature superconducting UWB filter is designed on a 0.5-mm-thick MgO substrate with double-sided YBCO films. The measured results show that 3-dB bandwidth covers 1.57–6.51 GHz, the return loss is better than 10.70 dB, the out-of-band rejection is greater than 24.75 dB in the lower stopband, and the upper stopband with 20-dB attenuation level is extended to about 9 GHz. [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]

A high-performance miniaturized multi-mode ultra-wide band (UWB) filter is proposed in this paper. The simple compact quintuple-mode resonator is constructed by loading three sets of open stubs on a modified conventional triple-mode resonator. Even and odd mode analytical methods are applied to analyze it. In addition, the function of each part of the filter is studied in cases of weak/strong coupling. In order to further improve the insertion loss, selectivity and out-of-band suppression, the designed filter is finally fabricated on double-sided YBCO/MgO/YBCO high-temperature superconducting (HTS) film. The test results show that the HTS UWB filter has excellent performance, and the simulation results are in good agreement with the test ones. The 3-dB bandwidth covers 3.6 ~ 13.2 GHz. The maximum insertion loss in the band was only 0.32 dB, and the reflection was better than –15.1 dB. The band-edge roll-off rate was 56 dB/GHz and the upper stopband with 20 dB rejection extended to 20.7 GHz. [ABSTRACT FROM AUTHOR]