In this paper, a compact dual-mode hairpin ring resonator (HRR) with two controllable resonances is proposed to design high-order dual-band high-temperature superconducting (HTS) bandpass filters. Its noncoupled dual-mode resonant characteristics and the mechanism for inherent transmission zero (TZ) production are studied. Moreover, a general dual-path coupling scheme is introduced for high-order coupling realization and applied to the third-order and eighth-order dual-band filter design. Also, two coupling structures for the adjacent HRRs with different orientations are proposed to excite TZs between the passbands for high selectivity. Besides, dual-parallel input–output feeding structure is adopted to tune the external quality factors of the dual-mode HRR individually so that the two passband are realized easily using high-order structure. For demonstration, an eighth-order dual-band HTS filter both operating at 1.9 and 2.6 GHz for mobile communications application are designed and analyzed. Compared with the third-order one, the selectivity of the eighth-order filter has at least 4.2 times improvement and five TZs are produced for high band-edge selectivity. Finally, the eighth-order dual-band filter is fabricated on MgO substrate with YBCO thin films. Measured results agree well with the simulations and show the excellent performance with 0.12-dB minimum insertion loss and better than −75-dB rejection level up to 5 GHz. In addition, the nonlinear characteristics of the fabricated HTS filter is observed by experiment, which shows the temperature dependence of filter center frequency performance and microwave insertion loss.

High-Order Dual-Band Superconducting Bandpass Filter With Controllable Bandwidths and Multitransmission Zeros

In this article, a flexible high-selectivity single-layer coplanar waveguide (CPW) bandpass filter using interdigital spoof surface plasmon polaritons (SSPP) of bow-tie cells is proposed, simulated, and fabricated. The low and high cut-off frequency can be adjusted independently, which is one of the characteristics of the presented bandpass filter. The SSPP of bow-tie cells is used to adjust the high cut-off frequency, while the interdigital coupling structure of the SSPP is designed to adjust the lower one. The proposed filter also has advantages of single-layer structure and high selectivity. Simulated results of the proposed filter show a theoretical 3-dB bandwidth from 2.28 to 5.12 GHz (about 76.8%) with high selectivity ( $\vert S_{11}\vert dB and −0.4 dB $> \vert S_{21}\vert > -1.1$ dB in the passband), and measured results agree well with simulated ones. Since the filter in this article is designed based on the flexible printed circuit (FPC) board, the circuit can be tested in bent, folded, and even twisted states, and these measured results are all basically consistent with the test result of the flat state circuit. This characteristic can greatly reduce the size of the filter and increase the flexibility of the circuit application.

A Flexible High-Selectivity Single-Layer Coplanar Waveguide Bandpass Filter Using Interdigital Spoof Surface Plasmon Polaritons of Bow-Tie Cells

This paper presents a novel tri-band high- temperature superconducting bandpass filter based on the tri-mode resonance of an embedded stub-loaded resonator (ESLR). This ESLR is analyzed using the even- and odd-mode method, demonstrating the emergence of three resonant frequencies and two transmission zeros in the ESLR circuit. The coupling structure, using capacitively loaded parallel coupled lines, is studied to realize the equal coupling coefficients at three resonant frequencies. Two tapped lines are used to achieve the desired external coupling under prior specifications. The lossless lumped-element equivalent circuits for three passbands are proposed. Finally, a third-order tri-band filter with the 4% fractional bandwidth is designed and fabricated with three passbands centered at 1.8, 2.4, and 3.5 GHz, respectively, corresponding to the GSM, WLAN, and WiMAX communication applications. The measured results agree well with simulated ones, showing very low in-band insertion loss, i.e., 0.07, 0.08, and 0.11 dB, in the three passbands, respectively.

A Novel Tri-Band Superconducting Filter Using Embedded Stub-Loaded Resonators

https://iopscience.iop.org/article/10.1088/1361-6668/aa69f1/pdf

Progress on applications of high temperature superconducting microwave filters

This paper presents a synthesis design method for superconducting dual-mode dual-band filters. A low-pass to dual-band bandpass frequency transformation is proposed based on lossless lumped-element dual-mode resonator circuits. Formulas for extracting the coupling coefficient $k$ and external quality factor $Q_e$ of dual-mode microstrip resonators are derived using the coupling matrix theory and the proposed frequency transformation formula. This makes the design process of dual-mode dual-band filters similar to that of the single bandpass filter. For the demonstration, four dual-band superconducting filters with different dual-mode resonator structures, such as stepped-impedance, stub-loaded, and embedded resonators are designed and fabricated. The measured results match well with the simulations.

Design of Dual-Mode Dual-Band Superconducting Filters

We have designed a miniaturized high-temperature superconducting dual-band bandpass filters (DBPFs) using stub-loaded meander line resonators and their applications to tri-band bandpass filters (TBPFs). The DBPF enables independent control of the center frequencies of the first and second bands. The bandwidths of the DBPF can be flexibly adjusted using a capacitance-loaded microstrip line between the resonators. The DBPF was designed and analyzed using an electromagnetic simulator and fabricated using an YBa 2 Cu 3 O y thin film on an Al 2 O 3 substrate. The center frequencies are 3.5 and 5.0 GHz; two bands have 2% bandwidth. The measured frequency responses of the DBPF were in good agreement with the simulated frequency responses. The TBPF was realized by combining the DBPF and a single-band bandpass filter (SBPF) that uses a folded stepped-impedance resonator with common input and output. The DBPF constructs the first and third bands of 3.5 and 5.0 GHz, and the SBPF forms the second band of 4.25 GHz. The frequency responses of the simulated TBPF meet the design parameters.

Design of Miniaturized HTS Dual-Band Bandpass Filters Using Stub-Loaded Meander Line Resonators and Their Applications to Tri-Band Bandpass Filters

A high-temperature superconducting tri-band bandpass filter (TBPF) has been developed. The TBPF is realized by combining a three-pole dual-band bandpass filter (DBPF) which uses stub-loaded meander line resonators with an additional capacitance-loaded microstrip line, and a three-pole single band bandpass filter (SBPF) which uses folded stepped-impedance resonator with common input and output. The DBPF constructs the first and third bands, and the SBPF forms the second band. The DBPF enables independent control of the center frequencies of the first and second bands. The bandwidths of the DBPF can be flexibly adjusted using the additional microstrip lines. The TBPF was designed and analyzed using an electromagnetic simulator based on moment method. The TBPF was fabricated using YBa2Cu3Oy thin film on a 25×25×0.5 mm Al2O3 substrate. The center frequencies of the three-pass-bands are 3.5, 4.25, 5.0 GHz; three bands have a 2% bandwidth. The measured frequency response of the TBPF was in good agreement with the simulated one.

Design of Tri-Band Superconducting Bandpass Filters with Independently Controllable Bandwidths

Synopsis: A high-temperature superconductor (HTS) dual-band bandpass filter (BPF) has been developed using stub-loaded hair-pin resonators. The main advantage of the filter is to allow independent control of the center frequency of the first and second bands. Flexible adjustment of the coupling coefficient can be achieved using a pair of H-shaped waveguides. We designed and analyzed a 3-pole HTS dual-band BPF. The filter was fabricated using YBa2Cu3Oy thin film on an Al2O3 substrate. The measured frequency responses of the filter agree well with those obtained during simulation.

Shunsuke Sugiyama

Papers

Design of Miniaturized HTS Dual-Band Bandpass Filters Using Stub-Loaded Meander Line Resonators and Their Applications to Tri-Band Bandpass Filters

Design of Tri-Band Superconducting Bandpass Filters with Independently Controllable Bandwidths

Design of Superconducting Dual-band Bandpass Filter using Stub-loaded Hair-pin Resonators