High-temperature Superconducting Bandpass Filter Research Articles

Miniaturized Quadband High-Temperature Superconducting Bandpass Filter with a Wide Frequency Ratio

This paper presents a miniaturized quadband high-temperature superconducting (HTS) bandpass filter based on a multistub-loaded resonator. Owing to the symmetrical structure of the proposed resonator, the odd- and even-mode analysis method can be used to derive its resonance frequencies. First, the frequency ratio between passbands may be significantly changed by adjusting the impedance ratio and fold spacing of the resonator. Moreover, the proposed filter exhibits well-controlled center frequencies and bandwidths for the four passbands, resulting in a considerably enhanced design possibility of quadband bandpass filters. A low insertion loss within each band is obtained using HTS technology. Additionally, the proposed filter was etched on an MgO substrate with a thickness of 0.5 mm and combined with YBCO thin films for demonstration. The results obtained were highly consistent with those of the simulation, validating the effectiveness and viability of the proposed method.

A High-Temperature Superconducting Bandpass Dual-Mode Filter with Tunable Relative Bandwidth and Center Frequency.

This study proposes a high-temperature superconducting (HTS) bandpass filter with a continuously tunable bandwidth and center frequency. The proposed filter combines several gallium arsenide varactors and a dual-mode resonator (DMR). The even and odd modes of the DMR can be tuned simultaneously using a single bias voltage. The capacitive value of varactors in the circuit is tuned continuously under continuous voltage and frequency tunability. External couplings and the interstage can be realized using an interdigital coupling structure; a fixed capacitor is added to the feeder to improve its coupling strength. A low-insertion loss within the band is obtained using HTS technology. Additionally, the proposed filter is etched on a 0.5 mm-thick MgO substrate and combined with YBCO thin films for demonstration. For the as-fabricated device, the tuning frequency range of 1.22~1.34 GHz was 9.4%; the 3-dB fractional bandwidth was 12.95~17.39%, and the insertion loss was 2.28~3.59 dB. The simulation and experimental measurement results were highly consistent.

Balanced Dual-Band HTS BPF With Controllable Frequency Ratio and Transmission Zeros Using Mixed Cross-Coupling

In this brief, a fourth-order balanced dual-band high temperature superconducting (HTS) bandpass filter (BPF) is presented based on modified stub-loaded resonators (SLRs). Firstly, the differential mode (DM) and common mode (CM) resonant characteristics of the modified SLRs are analyzed. Under DM operation, two types of mixed cross-coupling topologies are constructed by placing the spiral modified SLRs and their DM equivalent structures in an appropriate way. Then, a dual-band response with controllable center frequencies, bandwidths, and transmission zeros (TZs) is achieved. Under CM operation, an effective CM suppression circuit is proposed for improving the in-band CM suppression level. Finally, for verification, a fourth-order balanced dual-band HTS BPF with center frequencies of 3.494/4.797 GHz and insertion loss of 0.26/0.21 dB is designed and fabricated on MgO substrate with double-sided YBCO thin films. The measured results agree well with the simulated ones, and the BPF shows the attractive features of low insertion loss and good out-of-band rejection.

High-Order Balanced Dual-Band HTS BPF With Flexible Frequency Ratio and Sharp Rejection Skirts

In this article, a new class of high-order balanced dual-band high-temperature superconducting (HTS) bandpass filter (BPF) based on modified multimode stub-loaded resonators (SLRs) is presented. First, a detailed theoretical analysis of the multimode SLRs is provided to obtain insight into their frequency response characteristics under the differential-mode (DM) and common-mode (CM) operations. Specifically, the SLRs under the DM operation are designed to generate their second and third resonant modes in the two specified passbands, and they are sequentially cascaded by alternate <inline-formula> <tex-math notation="LaTeX">$J$ </tex-math></inline-formula> and <inline-formula> <tex-math notation="LaTeX">$K$ </tex-math></inline-formula> inverters for sharp rejection skirts. Following that, the working mechanism of the CM rejection of the resonator is investigated for achieving good CM suppression performance for this filter. Finally, for experimental validation, an eighth-order prototype filter is designed and fabricated on the MgO substrate with double-sided YBa2Cu3Oy (YBCO) thin films. Good agreement between measured and simulated results is obtained, and the filter is at the same time with low insertion loss, flexible frequency ratio, sharp rejection skirts, and good CM suppression level.

A Compact Four-Pole Tunable HTS Bandpass Filter at VHF Band

This article presents a compact, low loss, wide tuning range, high temperature superconducting (HTS) bandpass filter at very high frequency (VHF) band. The filter consists of four zigzag open-loop resonators loaded with gallium arsenide (GaAs) varactors as tuning elements. Each resonator is biased independently. The filter circuit is fabricated on a 3-inch HTS thin film deposited on a LaAlO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> substrate. The filter demonstrates a frequency tuning range of 73.2-118 MHz, which is a tunability of 48%, an insertion loss of 0.6-2.2 dB, and a 3-dB fractional bandwidth of 3.2-4.3%. Besides, the return loss of the filter is better than 16.6 dB in the whole tuning range, with slight adjustment of bias voltages for different resonators.

Design of Dualband Bandpass High-Temperature Superconducting Filter With Group Delay Equalization

A novel dualband high-temperature superconducting (HTS) bandpass filter is proposed with group delay equalization for 5G emergency communication receivers with N41 and N79 bands in this paper. The dual-folded stub-loaded stepped impedance resonator (DSLSIR) is applied to realize dualband performance. The proposed DSLSIR has miniaturized circuit size and more design freedom to independently adjust the two designed center frequencies, comparing with other reported DSLSIRs. Two cross-coupling transmission lines are added at the top and bottom parts of the cascaded sixth-order filter with DSLSIRs to flatten the group delay of the passband at both bands. A dualband bandpass HTS filter etched on the YBCO superconducting material is fabricated to verify the proposed design method. The measurement is actualized at the temperature of 77 K to make YBCO microstrip lines perform superconducting features. The results show that the first center frequency is 2.595 GHz with 6.2% bandwidth for N41 band and 0.3 dB insertion loss while the second center frequency is 4.85 GHz with 2% bandwidth for N79 band and 0.4 dB insertion loss. Meanwhile, the group delays at the N41 and N79 bands keep 2 ns fluctuations in the 60% passband. The agreement between the measured and simulated results indicates that the proposed dualband bandpass HTS filter with low insertion loss, sharp roll-off skirt and flat group delay is a promising candidate for emergency communication receiver.

Compact narrowband high-order dual-band superconducting bandpass filters using stub-loaded double-folded resonators

Compact narrowband high-pole dual-band high-temperature superconducting (HTS) bandpass filters (BPF) have been developed that use newly developed stub-loaded double-folded microstrip resonators. The resonators have a weak coupling property that enables the distance between resonators to be reduced and that suppresses unwanted nonadjacent coupling. Moreover, it enables independent control of the resonant frequencies of the first and second passbands. Additional microstrip lines and a dual-feeding structure are introduced to enable flexible adjustment of the internal and external couplings of the two passbands. A prototype ten-pole dual-band HTS BPF operating at 1.5 and 2.0 GHz was designed and constructed. The filter for both passbands has a 1% fractional bandwidth and was fabricated using YBa2Cu3Oy thin film on an Al2O3 substrate. The measured frequency responses of the filter were in good agreement with the simulated ones. These results demonstrate that the compact filter has high selectivity, low insertion loss, and good stop-band rejection.

Balanced Dual-Band Superconducting Filter Using Stepped-Impedance Resonators With High Band-to-Band Isolation and Wide Stopband

A balanced dual-band and wide-stopband high-temperature superconducting (HTS) bandpass filter (BPF) with deep stopband rejection is designed using modified stepped impedance resonators (SIRs) in this brief. The center frequencies of the two differential-mode (DM) passbands can be controlled by adjusting two electrical length ratios of the proposed SIR, while keeping the third spurious frequency far away for wide-stopband design. An inherent common-mode (CM) suppression can also be obtained due to the discriminating CM resonant frequencies different from the DM ones. Multiple transmission zeros (TZs) are achieved to realize high passband selectivity and enhanced DM stopband by multipath coupling and shunt stubs loaded on the I/O ports. The proposed balanced dual-band filter operating at 1.78/4.0 GHz is eventually fabricated using HTS YBCO thin films on a MgO substrate, which can significantly lower the insertion losses. The circuit was measured at the temperature of 77 K, which shows maximum insertion losses of 0.42/0.37 dB and a DM stopband of 5.0f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</sup> with 40-dB attenuation, respectively.

Design of High-Temperature Superconducting Dual-Band Filter With Multiple Transmission Zeros

A multiorder dual-band high-temperature superconducting (HTS) bandpass filter (BPF) with multiple transmission zeros (TZs) is designed in this paper. The theoretical characteristics of the introduction of TZs by the electric and magnetic mixed coupling and the cascade quadruplet (CQ) cross-coupling structures are analyzed, respectively. These two methods can be applied to the design of the multimode compact dual-band HTS BPF with controllable central frequency, bandwidth, and TZs. For demonstration, a Y-shape tunable resonator structure, which can simultaneously implement the internal electric and magnetic mixed coupling, and the external cross coupling are constructed to achieve the proposed dual-band BPF. The external quality factors required by the two passbands and the feasibility of independently adjusting the coupling strength between adjacent resonators are analyzed. Finally, a six-order dual-band HTS BPF with the center frequencies of 1490 (bandwidth of 40 MHz) and 2340 MHz (bandwidth of 80 MHz) is designed and fabricated on the double-sided YBCO/MgO/YBCO HTS thin films with the size of 17.2 mm × 14.7 mm (0.20 λg × 0.17 λg), and there are multiple of TZs located outside the two passbands, respectively. The out-of-band rejections are greatly improved to 70 and 80 dB due to these TZs, which fully exhibits the advantages of the proposed dual-band BPF. The measured results are in good agreement with the simulated ones.

Miniaturized High Temperature Superconducting Bandpass Filter Based on D-CRLH Resonators

In this paper, a novel high temperature superconducting (HTS) dual composite right/left-handed (D-CRLH) resonator is proposed, which is constructed by microstrip spiral coupled lines and microstrip high-impedance lines. Moreover, by using an equivalent circuit model and a admittance matrix method, the characteristics of the D-CRLH resonator is obtained and analyzed, which makes it suitable for implementing the miniaturized high-performance filter. For demonstration, a second-order D-CRLH bandpass filter is designed on a 0.5-mm-thick MgO wafer with double sided YBa <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sub> films. Multitransmission zeros are obtained in the stopband of the filter, improving the selectivity and stopband characteristics of the filter. Good agreement between the measurements and design goals can be observed.

Compact Dual-Band HTS Bandpass Filter Using Coplanar Waveguide Short-Circuited Stub-Loaded Ring Resonator

A compact coplanar waveguide (CPW) dual-band high-temperature superconducting (HTS) bandpass filter using a short-circuited stub-loaded ring resonator (SC-SLRR) is introduced in this paper. The equivalent circuit of the SC-SLRR is built and its resonant formulas are presented. The relationship between the parameters of electrical length and resonant performances are deduced. Resonant modes of the proposed resonators can be simultaneously excited and easily tuned for a dual-band application. To verify this methodology, a second-order CPW HTS dual-band bandpass filter operating at 2.36/4.93 GHz is designed. This filter is implemented on a 0.5-mm thick MgO wafer with a one-sided YBa 2 Cu 3 O 7 film, and it has the compact size of 0.146λg × 0.083λg. Measured results agree well with the simulated ones, which show that the minimum insertion losses of both bands are less than 0.15 dB.

Superconducting Filter Based on Split-Ring Resonator Structures

A design of high-temperature superconducting bandpass filter based on split-ring resonator (SRR) structures is presented in this paper. The SRR has been considered as a classical element for metamaterials and exhibits characteristics of subwavelength resonator, hence can aid in the compact design of filters. Filter has been simulated and optimized using Sonnet software. The measured results of the filter have good consistency with the simulated results and show good band pass characteristics. The center frequency of the filter measured at 70 K was 2.515 GHz, the rectangle coefficient was 1.22, and the insertion loss was 0.1 dB at the center frequency.

Novel Tri-Band High-Temperature Superconducting Bandpass Filters Using Asymmetric Shunted-Line Stepped-Impedance Resonator (SLSIR)

In this paper, a tri-band high-temperature superconducting (HTS) bandpass filter (BPF) is proposed with a pair of asymmetric shunted-line stepped impedance resonators (SLSIRs). Compared with the conventional SIRs, the proposed asymmetric SLSIR has more degrees of freedom in controlling multi-mode operating characteristics. Moreover, design graphs for the relationship of electric characteristic parameters and the resonant frequency ratio are built and applied to multiband device design. For demonstration, a two-order tri-band HTS BPF is well designed with center frequencies of 1.575/2.4/3.5 GHz. The external quality factor and the coupling coefficient have also been analyzed to satisfy the bandwidth of the BPF. The designed filter is fabricated on the YBCO superconducting material and measured under superconducting conditions (at the temperature of 77 K). The measurement results are in good agreement with the simulation results, indicating that the insertion loss of the three passbands is about 0.1 dB, showing the advantage of in-band insertion loss.

A compact high-temperature superconducting band-pass filter with wide upper stopband

A novel hair-pin resonator(NHR) composed of interdigital capacitor and fractal resonator is developed, which not only has compact in size but also has no harmonics up to three times of the fundamental frequency. The results show that the equivalent capacitance introduced by the interdigital capacitor at the conventional hair-pin resonator terminal plays a major role in suppressing the spurious harmonics, whereas the equivalent inductance has no improved harmonic rejection ability. A miniature five-pole wide-band HTS bandpass microstrip filter has been designed and fabricated with this NHR on a double-sided MgO-based DBCO thin film. Measurement at 79.4K shows that the fabricated HTS filter has less than 0.11 dB insertion loss and better than 20 dB return loss in the passband, and an ultra high spurious passband at about 3.3f0. Moreover, the simulated and measured results are found in excellent agreement in wideband response.

Wide-Stopband Superconducting Bandpass Filter Using Slitted Stepped-Impedance Resonator and Composite Spurline Structure

In this paper, a wide-stopband high-temperature superconducting (HTS) bandpass filter (BPF) is presented using slitted stepped-impedance resonators (slitted-SIRs). The use of SIR is essential in widening the filter stopband. Besides, it is found that introduced slits in SIRs provide additional freedoms to control resonance modes when compared with a conventional SIR. Hence, four types of slitted-SIRs are arranged at same fundamental mode f 0 and different higher order modes by adjusting the slits. The coupling of higher order modes is reduced and wide stopband is achieved. In addition, a composite spurline structure is employed to generate two independently controllable transmission zeros, which further improves the stopband performance. Finally, a cascade quadruplet HTS BPF is designed and fabricated on an MgO wafer with double-sided YBCO films. Measurement shows the passband of the BPF is operated at 2.35 GHz and its minimum insertion loss is less than 0.15 dB. The rejection level is better than 21.9 dB in the stopband up to 13.26 GHz (about 5.64 f 0 ). The designed HTS filter tends to the potential application for the desired wide stopband and the high selectivity performance.

Trimming Mechanism of External Quality Factor in HTS Bandpass Filter Using Bulk Resonators

We investigated the usability of a trimming mechanism for varying an external quality factor (Q e ) in a hightemperature superconducting bandpass filter (BPF) using bulk resonators at around 5 GHz. The proposed trimming mechanism was composed of air space between an input port and the first resonator in a Cu cavity, a center conductor of the coaxial through the space, and a dielectric or metallic trimming rod. We decided the geometrical dimensions of the trimming mechanism and estimated the Q e by varying the height of rod (h Q ) using an electromagnetic simulator. These simulated results indicate that the proposed mechanism could function for theoretical Q e values up to those of 8-pole BPF. We then fabricated the trimming mechanism for Q e and measured the Q e by using a vector network analyzer. The measured data almost matched the simulated data. Next, we fabricated a 5-pole BPF with the trimming mechanisms for Q e and obtained good filtering responses.

Miniaturized Multiband HTS Bandpass Filter Design Using a Single-Perturbed Multimode Resonator With Multitransmission Zeros

This paper presents a miniaturized quint-band high-temperature superconducting (HTS) bandpass filter (BPF) based on a single-perturbed multimode resonator (PMMR). By properly adjusting the lengths and the position of the perturbation line in a PMMR, the intrinsic resonance modes can be controlled, which is advantageous for multiband design. The source-load coupling, spurlines, and matching stubs on feedlines are introduced to improve impedance matching and to generate multi transmission zeros, so that enhanced isolation and harmonics suppression can be realized. A low insertion loss (IL) within each band is obtained by using an HTS technology. The filter is fabricated on an MgO substrate with the YBCO thin films, and measured at the temperature of 77 K. The passband measurement is consistent with the simulation, which verifies five passbands located at 0.56, 1.52, 3.8, 4.7, and 5.3 GHz, respectively. A low-measured IL with less than 0.2 dB level is obtained due to the application of a superconducting technology. The proposed HTS BPF owns the great merits of a simple structure, a miniature size (0.008λ g 2 ), an enhanced upper stopband, and a low IL.

A wideband UHF high-temperature superconducting filter system with a fractional bandwidth over 108%

A High-temperature superconducting (HTS) bandpass filter system containing a lowpass filter, a highpass filter and an LNA has been fabricated to meet the demands of wideband wireless signal receiving system. The filter system has an ultimate fractional bandwidth over 108% with the passband from 820 MHz to 2750 MHz. Besides, the filter system showed good frequency selectivity and out-of-band rejection. The 40 dB to 3 dB rectangle coefficient of our filter system is 1.4, which is better than that of an 8-pole Chebyshev filter, and the out-of-band rejection is better than 40 dB. Through systematical optimization, a return loss of better than 9.8 dB was received in the filter system. This system also showed advantages in design and fabrication precision.

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

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-temperature superconducting filter using self-embedding asymmetric stepped impedance resonator with wide stopband performance and miniaturized size**Project supported by the National Natural Science Foundation of China (Grant No. 61371009) and the National High Technology Research and Development Program of China (Grant No. 2014AA032703).

In this study, a novel self-embedding asymmetric stepped impedance resonator (SE-ASIR) topology is proposed. By embedding asymmetric stepped impedance resonators in themselves, circuit sizes of ASIRs can be reduced effectively, while the ability to control spurious modes of ASIRs remains. Therefore, SE-ASIRs are suitable for being used to design filters with wide stopbands and miniaturized sizes. Furthermore, the construction process of the SE-ASIR is described in detail, and an equivalent model of the SE-ASIR is proposed. For demonstration, a high-temperature superconducting bandpass filter centered at 1112 MHz is designed and fabricated. The measured result agrees well with the simulation result and shows that the out-of-band rejection is better than 60 dB up to 4088 MHz, which is about 3.7 times the center frequency. The filter circuit size is 31 mm × 13 mm or , where is the guided wavelength at 1112 MHz.