High-temperature Superconducting Filter Research Articles

Design of HTS linear phase bandpass filter based on the inline topology

Abstract Inline topology filters have the advantages of a simple structure and fewer coupling coefficients. Based on the inline topology, this paper constructs a phase compensation topology of the filter, which can independently and controllably introduce two types of transmission zeros (TZs), and is convenient to realize the Chebyshev-like function response and compensate group delay. The finite frequency transmission zero is directly introduced through the source and load (S/L), and the real zero point is introduced and adjusted through the cross-coupling unit of the main path in this inline phase compensation topology. The two types of TZs can be introduced and regulated independently, so the side-band suppression and group delay compensation can be freely adjusted. A High-temperature superconducting (HTS) filter with inline is designed and processed with a typical structure based on application requirements. The filter introduces two pairs of symmetrical real TZs to improve sideband rejection and a pair of real TZs to control group delays to realize the linear phase. In addition, it has a small size and straightforward construction, and the results of the full-wave analysis method and the theoretical analysis approach match well with the measured results of the frequency response characteristics.

A tunable dual-narrowband HTS filter using coding superconducting metamaterials aided by grey wolf algorithm

Abstract The design of tunable dual-narrowband high-temperature superconducting (HTS) filter based on coding superconducting metamaterials aided by grey wolf algorithm (GWA) is proposed in this paper. By virtue of the characteristics of right/left-handed bands and scale of deep sub-wavelength, the tunable metamaterials unit loaded with varactor is designed, with coupling types of coding pairs further studied. A tunable sixth-order HTS filter circuit is then constructed, whose layout is effectively optimized by newly developed GWA method. Simulated frequency responses demonstrate that the center frequencies of dual-band respectively locate at 170.1-177.2 MHz (Band I) and 185.2-194.1 MHz (Band II), with 3-dB fractional bandwidth (FBWs) of 0.65%-0.61% and 0.62%-0.57%. The deeply miniaturized circuit size is 0.037×0.046 λ2 g, and the close-to-band rejection level reaches 80-dB. Experimental results of fabricated prototype measured at 70 K validate the feasibility of described design method for high order tunable HTS filter.

A High-Temperature Superconducting Wideband Bandpass Filter at the L Band for Radio Astronomy

In order to ensure the normal operation of radio astronomy observations, an extremely sensitive receiver system needs to be equipped in front of the large radio telescope. An 8-pole wideband high-temperature superconducting (HTS) filter using a Coplanar Spiral Resonator Structure with a passband of 1160∼1670 MHz is developed to suppress strong radio interference. The filter is fabricated on a 36 mm × 14 mm YBCO HTS film, which is deposited on a 0.5 mm thick MgO substrate. The minimum insertion loss measured in the liquid nitrogen temperature region is 0.03 dB, and the first parasitic passband appears at 2600 MHz. The measured results are in good agreement with the simulations. The filter can be used in radio telescope receivers for the observation of neutral hydrogen and pulsars, as well as in high-sensitivity satellite navigation instruments.

Development of highly selective compact high-temperature superconducting quad-band bandpass filter using interdigital feeding structure for radio astronomy

Astronomers at the Mizusawa Very Long Baseline Interferometry Observatory of the National Astronomical Observatory of Japan are promoting the development of broadband receivers in the ultra-high frequency (UHF) band. The presence of extensive radio frequency interferences (RFI) in the UHF band hinders continuous broadband radio observations in this band. A promising technical solution to this problem is to use a superconducting multi-band bandpass filter as it enables the bundling of several RFI-free bands. We have developed a high-temperature superconducting compact quad-band bandpass filter (QB-BPF) at 0.7, 1.4, 1.6, and 2.1 GHz with low loss and steep cutoff characteristics for broadband receivers. That consists of two six-pole dual-band bandpass filters. We have devised an interdigital feeding structure with a high degree of freedom that enables the external quality factor to be designed individually for each band. A compact QB-BPF was fabricated using double-sided YBa2Cu3Oy thin films on a 36.4 mm × 42.0 mm (0.22λ g × 0.25λ g) Al2O3 substrate. The measurement results agreed well with the simulated ones, indicating that the QB-BPF overcomes the problem of extensive RFI in the UHF band.

Synthesis and design of asymmetric cul-de-sac structure HTS filter with transmission zero introduced in Pairs

An asymmetric prototype of a cul-de-sac topology filter to introduce finite frequency transmission zeros (FTZs) in pairs with the least cross-coupling is synthesized and designed in this paper, which is suitable for the design of the high temperature superconducting (HTS) narrowband filter with high selectivity sideband suppression and symmetrical frequency response about the central frequency, especially. The resonator in the cul-de-sac structure filter can adopt the same frequency resonator without self-coupling so that the cul-de-sac structure filter can have fewer coupling coefficients and fewer resonator types. These characteristics of cul-de-sac structure filters are convenient for the design of high-order HTS filters with temperature shifts. A typical 7-order HTS filter with a central frequency of 4000 MHz, 5% relative bandwidth, five coupling coefficients, one cross-coupling, and one pair of FTZs is designed and fabricated on a 0.5 mm-thick MgO wafer with double-sided YBa2Cu3O7 (YBCO) thin films employing this cul-de-sac filter theory. The analyzed frequency response characteristic obtained with full-wave tools of this filter agrees well with the synthesis results and measured results at 77 K (Kelvin temperature).

Recent progress on high-temperature superconducting filters

Since the discovery of high temperature superconducting (HTS) materials in 1987, the performance of microwave filters such as insertion loss, selectivity, and out-band rejection has been significantly improved by utilizing HTS films. Nowadays, HTS filters have been widely used in wireless communications, space exploration, satellite communications, and several other fields. HTS filters with a special performance, such as wideband, dual-band or multiband, frequency tunable, and high power-handling capability have been designed and fabricated in recent years to meet the increasing requirements of practical applications and to further extend the application areas. This paper reviews the various types of above-mentioned HTS filters as well as the developments of novel design methodologies.

Application of Stirling pulse tube cryocoolers in high temperature superconducting filters subsystems

The application of high temperature superconducting(HTS)filter has penetrated into various fields. In recent decades, GM-type pulse tube cryocooler and Stirling-type pulse tube cryocooler (SPTC) are two common cryocoolers. Due to the advantages of PTCs, such as no moving parts at the cold end, simple structure, small mechanical vibration and longer lifetime, pulse tube cryocoolers is gradually replacing oil-lubricated Stirling-coolers and G-M cryocoolers to cool down HTS magnets. In this paper, the development of PTC in HTS magnet cooling in the past 20 years is summarized firstly. Secondly, the development of HTS cooling system in our lab are reported. At last, the further development direction of HTS’s cooling system is discussed.

Design and development of a lightweight cryogenic system for high temperature superconducting (HTS) filters subsystem

Design and development of a lightweight cryogenic system for high temperature superconducting (HTS) filters subsystem

Wide stopband single layerquasi‐elliptic ultra‐widebandbandpass filter

This paper presents the design of a microstrip ultra-wideband (UWB) bandpass filter that exhibits desirable characteristics of low-loss, high selectivity, wide stopband and high out-of-band rejection at room temperature. These characteristics are normally achieved with high temperature superconductor filters that require cryogenic cooling. The design of the proposed filter was realized by exciting multiple resonant modes in a unique Z-shaped microstrip resonator. The admittance of the filter configuration can be tuned prior to fabrication to adjust its center frequency by about 11.5% without affecting the profile of the bandpass response however this can have an impact of the loss. The proposed configuration allows adjustment of the upper and lower transmission zeros defining the bandpass response by 20.5% and 11.4%, respectively, without degrading the overall filter response. The low-loss quasi-elliptic function UWB bandpass filter design was fabricated on a commercially available dielectric substrate using standard PCB technology and its performance verified. The fabricated filter exhibits insertion-loss of 0.68 dB and return-loss better than 17 dB.

Design of a dual-wideband high temperature superconducting filter

A 7-pole dual-wideband high temperature superconducting (HTS) filter based on a quarter-wavelength stub-loaded dual-mode resonator is introduced. The resonance characteristics, coupling patterns, external factor and cross coupling structure are discussed in turn. The filter is fabricated on a double side DyBa2Cu3O7 HTS thin film with a 2 inch-diameter and 0.5-mm-thick MgO substrate. The fabricated filter is measured at 77 K. The measured results show that the filter has an excellent in-band performance with center frequencies of 240 MHz, 541 MHz and passbands of 40 MHz, 140 MHz, respectively. Due to the introduction of transmission zeros, the selectivity of filter is further improved. The measured results agree with the simulated ones substantially.

Miniaturized ultra-narrowband HTS linear phase filter with CQ units sharing quarter-wavelength resonators

This paper proposes a method for designing a miniaturized ultra-narrowband high-temperature superconducting (HTS) linear phase filter based on the resonator-shared cascaded quadruplet (CQ) units constructed by the quarter-wavelength microstrip line. Two types of CQ unit with different coupling configurations are utilized to introduce transmission zeros and realize the linear phase. The introduction of transmission zeros increases the transition band roll-off rate, and the in-band group delay characteristic is improved through the phase compensation. The number of resonators and the filter size further decrease by sharing a resonator between two adjacent CQ units. Finally, a ten-order compact ultra-narrowband linear phase HTS filter with three CQ units is designed to demonstrate the feasibility. The central frequency of the filter is 450 MHz with the fractional bandwidth of 2.22%, and the dimension is 38.7 mm × 12.5 mm (0.141λ g0 × 0.047λ g0, λ g0 is the guided wavelength at the central frequency f 0). The measured results show an excellent performance in the insertion loss, the out-of-band rejection, the return loss, and the passband selectivity. Moreover, the bandwidth with a group delay ripple within 30 ns occupies 70% of the entire passband, highlighting the linear phase feature. In addition, the first parasitic passband is located at 3.8 times of the fundamental frequencies. The test results are in good agreement with the simulated ones.

High Selectivity Single Wideband and Quad-Band HTS Filters Using Novel Quad-Mode Resonators With Self-Coupled Structure

This paper presents improved quad-mode resonators based on the open/short-end load of the center stub, which introduces the self-coupled structure. Compared with the traditional stub-loaded stepped impedance resonator (SLSIR), the proposed quad-mode resonators can significantly reduce the circuit size and further increase the design freedom. First of all, a comprehensive theoretical analysis is performed to infer the resonant characteristics of the proposed resonator. Then, two design prototypes based on different center loads of the resonator were demonstrated to verify the feasibility of the design method. First, a prototype of a wideband high temperature superconducting (HTS) filter with an FBW of 89% is proposed, whose center frequency (CF) can be flexibly controlled. Next, a quad-band HTS filter using different central stub load is proposed, which centered at 1.20, 2.52, 3.51, 4.44 GHz with the 3-dB FBW of 4.8%, 3.96%, 3.97% and 2.2%, respectively. The internal and external coupling mechanisms are also carefully studied to meet the specified requirements. The two prototypes proposed in this paper both have the advantages of compact size, ultra-low insertion loss and steep suppressed skirts. In addition, the measured results are in good agreement with the EM full-wave simulated results.

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.

Tri‐band superconducting filter based on crossed resonators with controllable coupling and feeding structures

In this article, a compact tri-band high-temperature superconducting filter with controllable coupling and feeding structures based on crossed resonator which consists of two-end-open UIR with a short stub and an open stub shunted at the resonator center is proposed. Due to the symmetrical structure of the proposed resonator, the odd- and even-mode analysis method can be used to derive their resonance frequencies. Then, a capacitance-loaded microstrip line is added between the resonators to flexibly control the bandwidths. Furthermore, one tapped line and one coupled line are utilized to realize the acquired external coupling under prior specifications. For demonstration, a tri-band filter operating at 1.6 GHz (Global Positioning System), 2.45 GHz (Wireless Local Area Networks), and 3.5 GHz (WiMAX) is designed, analyzed using the electromagnetic simulator, and fabricated using an YBa2Cu3Oy thin film on an MgO substrate. The measured results agree well with the simulated ones.

A 12-pole VHF band high selective high temperature superconducting filter

A 12-pole VHF band high temperature superconducting (HTS) filter with a spiral quarter-wavelength resonator is introduced. The coupling characteristics of the proposed resonator, cross structure and external quality factor is analyzed in detail. The HTS filter is fabricated on a 3-inch-diameter double-sided DyBa2Cu3O7 HTS thin film with a LAO substrate and measured with a low-temperature test system at 77 K. The measured filter has a center frequency of 119.93 MHz and a 1-dB passband of 10.04 dB. Due to the introduction of transmission zeros, the rectangular coefficient (BW60dB/BW1dB) of the measured filter is about 1.20, which shows excellent selectivity. The measured results are in good agreement with the simulated ones.

Compact triple‐band HTS filter with high selectivity using self‐coupled stepped impedance resonator

A compact triple-band high-temperature superconducting (HTS) filter with high selectivity based on self-coupled stepped impedance resonator is proposed in this Letter. By folding the two-opened arms of the λ/2 stepped impedance resonator, inter-resonator coupling has been evolved. Due to theoretical analysis of the resonator, the first three resonant frequencies are used to construct three passbands with controllable frequency ratios and bandwidths by changing coupling coefficient, impedance ratios and length ratio. Finally, a triple-band filter example with frequencies centred at 1.72/4.05/7.6 GHz (frequency ratios of 1:2.4:4.4) is designed, fabricated and tested, which has multiple transmission zeros and compact size. Good agreement between the simulated and the measured results validates the design method.

Design of special asymmetric cul-de-sac unit configuration high temperature superconductor filter with multi-pair of transmission zeros

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.

Compact ultra-narrowband superconducting filter using N-spiral resonator with open-loop secondary coupling structure**Project supported by the National Key Scientific Instrument and Equipment Development Project of China (Grant No. 2014YQ030975).

A novel N-spiral resonator with open-loop secondary coupling structure (OLSCS) is proposed to realize a compact ultra-narrowband high temperature superconducting (HTS) filter. The coupling strength and polarity between the resonators can be significantly reduced and changed by introducing OLSCS, thus the required weak coupling can be achieved in a very compact size. A six-pole superconducting filter at 1701 MHz with a fractional bandwidth of 0.19% is designed to validate this method. The filter is fabricated on MgO substrate with a compact size of 15 mm × 10 mm. The measured insertion loss is 0.79 dB, and the return loss is better than 17.4 dB. The experimental results show a good agreement with the simulations.

A Wide Stopband Wideband HTS Filter Using Stepped-Impedance Resonators With an Interdigital Capacitor Structure

A stepped-impedance resonator with an interdigital capacitor (IDC) structure has been proposed to design a wideband filter with a wide and deep stopband. With the increase of the IDC part, there is always a maximum ratio of a spurious resonance frequency to a fundamental resonance frequency whether we change the length or number of interdigital fingers. We increase the width of a microstrip line loaded with the IDC structure to reduce the fundamental resonance frequency and increase the spurious resonance frequency. The harmonic ratio of the proposed resonator is raised to 5.6. Moreover, we bend the narrow microstrip line into a meander line to realize the strong coupling for a wideband filter. A ten-pole high-temperature superconducting filter centered at 2.128 GHz with a 22.7% bandwidth is fabricated for demonstration. The filter is fabricated on a 0.5-mm-thick MgO substrate with a circuit size of 26 × 10 mm. The measured maximum insertion loss in passband is 0.11 dB and the return loss is better than 17.3 dB. The measured out-of-band rejection is better than 80 dB up to 8.728 GHz, which is about 4.1 times of the center frequency.

A Wideband HTS Filter Using Strong Coupling Coplanar Spiral Resonator Structure

A novel coplanar spiral resonator structure, which has a stronger coupling strength than a normal coplanar waveguide (CPW) structure, is introduced. This structure helps to realize the remarkable strong coupling required for low-frequency wideband filters. Although no grounded stubs are deployed to balance the ground plane, the slot-line mode of the filter is not excited. An eight-pole wideband high-temperature superconducting filter, with a fractional bandwidth of 50% and a center frequency of 322 MHz, is developed. The filter is designed and fabricated on a 0.5-mm-thick LaAlO$_3$ substrate with a core size of 41 mm × 22 mm. The measured minimum insertion loss is 0.05 dB and the first spurious peak appears at 842 MHz, which is about 2.6 times the center frequency. The measured results agree well with the simulated results.