High Temperature Superconducting Microwave Research Articles

Recent progress of superconducting electronics in China

It has been nearly 110 years since the discovery of superconductors, and more than 30 years since the discovery of high temperature superconductors (HTS). Great progress has been made in the application of superconducting electronics in the last two decades. HTS microwave devices have shown much higher perfomance than the traditional ones and have found their ways to the industry applications in mobile communication, radar, and special communication applications. Owing to the ultrahigh sensitivity to magnetic fields and currents, superconducting quantum interference devices (SQUIDs) have been used as the irresplacible sensors in geological surveying, magnetic resonanc imaging, biomagnetic imaging, and other areas. The sensitivity of superconducting radiation detectors such as superconducting SIS mixer, superconducting hot electron bolometer, superconducting transition edge sensor, superconducting nanowire single photon detector, and superconducting microwave kinetic inductance detector are near the quantum limitation. They are now key technology in geophysics, astrophysics, quantum information science, biomedicine, and so on. Superconducting Josephson parametric amplifier has become a key element for superconducting quantum computing. Superconducting integrated circuit has been included in the international roadmap for devices and systems, and shows that having the potential to become one of the mainstreams for post-Moore information processing technology. In metrology, superconducting Josephson effect and Josephson junction array devices have been widely used in the redefinition of quantum voltage reference and basic units of the International system of Units. Superconducting electronics plays an important role in the current quantum information technology boom, which in turn promotes the development of superconducting electronics. This review will brief introduce the research and application of superconducting electronics in China in recent years.

A Thirty-year History of Superconducting Microwave Devices and Fundamental Studies Thereof

Thirty years have passed since the discovery of high-temperature superconductors (HTS), and practical applications of HTS equipment and devices are moving into full-swing. From the beginning of their discovery, the use of HTS in microwave devices has been recognized as one of their most practical applications. This is because the surface resistance of HTS is about 1/1000 of that of pure copper at 1 GHz and 77 K. From early on, researchers have recognized that high performance of microwave passive devices could be realized by utilizing the characteristics of HTS. In addition, the size of HTS microwave devices is relatively small, and they can be cooled by a small cryocooler. Furthermore, we were able to establish high-quality HTS thin-film fabrication technology essential for producing high performance microwave devices in a short period of time. In view of the above, I would like to present an overview of the past thirty years of superconducting microwave devices and fundamental studies thereof.

The high temperature superconducting filters and its application progress

Microwave filters are essential elements in many areas of RF/microwave engineering. The crowded frequency spectrum has put forward higher requirements on channel filters. Not only very high close-to-band rejections are required to prevent interference to or from closely neighboring channels, but also very low insertion loss is required to reduce system noise figure. Some RF/microwave system require in-band group-delay and amplitude flatness to minimize signal degradation even further. Surface resistance of high temperature superconducting (HTS) material is about 1000 times less than the best conventional metals such as copper and silver at microwave frequency. So a significant effort has been put into the research and realization of high performance microwave HTS filters since the discovery of HTS materials. HTS microwave filters with remarkably high performance have been constructed in the past 30 years. For example, by selecting appropriate resonators with high quality factors and employing well-designed coupling structures with week coupling coefficients, some HTS filters can have fractional band width (FBW) blow 0.1% with very high selectivity. The insertion loss of some HTS filters can be as low as 0.05 dB. With above excellent performance, HTS filters can not only eliminate unwanted interference but also minimize noise figure of the microwave system. HTS filters and their front-end subsystems have also been successfully applied to many fields and brought multiple economic returns and social benefit. It is reported that HTS receiver front-end subsystem, which integrate with narrow-band highly selective HTS filters and low noise amplifiers (LNA) in a cryocooler, has been employed in more than 10000 base stations in America. According to the promotion materials, the ultra-low-loss and high sensitivity of the HTS receiver can translate into 10%–15% or more increased base station coverage area and data throughput. In some cases carriers could add 8% or more usable resource blocks and capacity due to the high selectivity of the HTS receiver, valued at hundreds of millions of dollars. Design technology of HTS filters has been developed rapidly at an incredible speed. In recent years, many efforts have concentrated on novel HTS filter design technologies, including those in high power handling capability filters, multiplexer or multiband filters and frequency tunable filters. Some research groups are trying to develop all-HTS integrated microwave front-end receivers, which integrate HTS filter, oscillators, mixers and antenna into a whole chip. The all-HTS integrated front-end receiver could make the system compact, efficient, and be able to exploit the full potential of the superconductive components. In this paper, the research status, trend of development and application progress about HTS filters are reviewed. The best performances of HTS filters ever reached in specifications such as insertion loss, FBW, out of band rejection, skirt slope and in band group delay are firstly reviewed. Then the remarkable progress in the most recent years which stand for the research trends of HTS filter technology is presented in detail. At last the application of HTS filters and their front-end subsystems to mobile communications, space or satellite communication technology, radar detective system, deep space detection and radio astronomy is also reviewed.

A 36 GHz HTS MMIC Josephson Mixer—Simulation and Measurement

Modeling, simulation, and measurement of a compact 36 GHz high-temperature superconducting (HTS) monolithic Josephson junction mixer are presented in this paper. A full HTS microwave monolithic integrated circuit (MMIC) simulation was carried out for the circuit combining HTS passive devices and the Josephson junction. Optimal impedance matching and bias conditions were investigated, and the circuit layout was designed accordingly. The HTS circuit has a compact dimension of 5 × 4 × 0.3 mm3, including filters, resonators, and impedance matching circuits. The HTS MMIC mixer was fabricated and packaged with an LNA to realize a receiver front end with a total dimension of 28 × 25 × 15 mm3. Measurement result showed an overall conversion gain around 35 dB, with local oscillator driving power around −45 dBm at operating temperature of 40 K.

Insight into the structural, electrical and photoresponse properties of individual Fe:SrTiO3 nanotubes

Titanates are suitable for many applications such as oxygen sensing and tunable HTS (high temperature superconducting) microwave filters. The potential advantages of the nanostructured forms have been however scarcely explored compared to other oxides. In this work, the structural and electrical properties of individual iron-doped strontium titanate nanotubes (Fe:SrTiO3) grown by electrophoretic deposition (EPD) were assessed for the first time, showing high stability and reproducibility. This result paves the way to further development of more complex titanate-based devices, as for instance nanostructured oxygen STFO sensors. From experimental data, it was concluded that the polycrystalline form of Fe:SrTiO3 nanotubes is the major limitation to attain high photoconductivity gains when exposed to UV-light.

Recent Progress of HTS Microwave Applications in Satellite Receiver, Meteorological Radar, Mobile Communication and Radio Astronomy

The applications of high-temperature superconductor (HTS) filters or subsystems to radio astronomy, the third generation (3G) mobile communications, meteorological radar, and satellite are introduced. A wideband HTS filter for the Miyun 50-m radio telescope in Beijing was presented, and a novel resonator and a new style interleaved coupling structure were proposed for the design of the wideband filter. An HTS transceiver subsystem was constructed. A field trial in commercial TD-SCDMA base station network was carried out in Beijing and remarkable improvements were achieved for RF performance in both transmitting and receiving chains. A demonstration HTS meteorological radar station was set up in Beijing and it showed great enhancements in sensitivity and anti-interference ability in urban area wind profile measurements. An experimental HTS microwave receiver front end for satellite applications had been constructed and passed all the space qualification tests. As a payload of an experimental satellite, it was ready for launch.

Closed Form Formulas for Distributed Circuit Model of Discontinuities in HTS Microstrip Transmission Lines

A distributed circuit model for different kinds of discontinuities in high temperature superconducting (HTS) microstrip transmission lines (TLs), is proposed. In each case, closed form formula for lumped element model is presented based on the configuration of the discontinuity and the characterizations of HTS microstrip TLs. These discontinuities consist of steps in width, open ends, gaps and 90-degree bends. In the case of normal conductor microstrip TLs there are a lot of numerical and analytical equations that can accurately model them, however those formulas are not efficient for HTS TLs. Thus modified relations are extracted utilizing the superconducting characterizations to obtain much more accurate formulas. Additionally temperature dependence of HTS TLs is considered in the relations. Moreover regarding the kinetic inductance in HTS TLs a closed form formula is proposed for characteristic impedance of HTS TLs. Furthermore correction factors based on fringe fields is used to optimize all formulas. Using these formulations can lead to modeling and analysis of some superconducting microwave devices such as resonators, microwave filters, couplers, etc. In contrast to EM analysis, using the distributed circuit model is much easier for analysis of HTS microwave devices. The accuracy of the proposed model is confirmed in comparison with some electromagnetic full-wave simulations. This full analytical approach shows great accuracy in this test case as well.

A miniaturized HTS microwave receiver front-end subsystem for radar and communication applications

This paper presents a miniaturized high performance high temperature superconducting (HTS) microwave receiver front-end subsystem, which uses a mini stirling cryocooler to cool a high selective HTS filter and a low noise amplifier (LNA). The HTS filter was miniaturized by using specially designed compact resonators and fabricating with double-sided YBCO films on LAO substrate which has a relatively high permittivity. The LNA was specially designed to work at cryogenic temperature with noise figure of 0.27 dB at 71 K. The mini cryocooler, which is widely used in infrared detectors, has a smaller size (60 mm × 80 mm × 100 mm) and a lighter weight (340 g) than the stirling cryocoolers commonly used in other HTS filter subsystem. The whole front-end subsystem, including a HTS filter, a LNA, a cryocooler and the vacuum chamber, has a size of only φ120 mm × 175 mm and a weight of only 3.3 kg. The microwave devices inside the subsystem are working at 71.8 K with a consumed cooling power of 0.325 W. The center frequency of this subsystem is 925.2 MHz and the bandwidth is 2.7 MHz (which is a fractional bandwidth of 0.2%), with the gain of 19.75 dB at center frequency and the return loss better than −18.11 dB in the pass band. The stop band rejection is more than 60 dB and the skirt slope is exceeding 120 dB MHz −1. The noise figure of this subsystem is less than 0.8 dB. This front-end subsystem can be used in radars and communication systems conveniently due to it’s compact size and light weight.

Investigation of HTSC digital trunking communication receiver subsystem

The application of HTSC (high temperature superconductor) microwave devices in a UHF digital trunking communication system is introduced. The replacement between the HTSC microwave devices and the normal microwave devices is conducted. The digital sensitivity of the base station in complex electromagnetic environment has been increased to 6 dB, as the results of the experiment indicated, and this means that the coverage radius of the base station has been improved about twice, that is to say, the coverage area can be extended to four times as large as that of the current method.

On the Power Handling Properties of High Temperature Superconducting Microwave Contiguous Duplexer

The power handling properties of a high temperature superconducting (HTS) microwave contiguous duplexer are measured in this letter. The HTS contiguous duplexer was fabricated using YBa2Cu3O7 (YBCO) thin films on a 0.5-mm-thick LaA1O3 substrate, operation frequencies of which are centered at 3.25 GHz and 3.75 GHz with 500-MHz-wide channels. The tested frequency response of power handling property of the HTS contiguous duplexer shows that there is a decreased power handling property on the crossover region; however, this microwave nonlinearity does not affect the engineering application of HTS contiguous duplexers and multiplexers.

Nonlinear buffer layers relevant for reduced nonlinear effects in HTS microwave devices

Microwave devices made of a High-Temperature Superconductor (HTS) exhibit a nonlinear response as the microwave power increases. The HTS nonlinearities generate a nonlinear inductance Ld(irf) and a nonlinear resistance Rd(irf) in a device. Ld(irf) and Rd(irf) are responsible for an increase of the device loss, a small frequency dispersion as well as the generation of spurious signals like Intermodulation Distortion (IMD). Nevertheless, the HTS nonlinearities in a microwave device can be reduced using a nonlinear dielectric like a ParaElectric Material (PEM). This assumption has recently been demonstrated theoretically. In a microwave device made of a HTS and a PEM, the nonlinear contribution to the capacitance Cd(vrf) from the PEM acts oppositely to the nonlinear contribution to Ld(irf). This may cancel the effect of the HTS inductive nonlinearities. The PEM also produces a nonlinear conductance Gd(vrf) in a device. All these nonlinear terms contribute to the IMD output power and the nonlinear quality factor (Q0) of a resonant passive microwave device. In this paper, the dependence of the different nonlinear contributions on frequency and applied dc bias voltage (Vdc) is investigated. The relevance to employ PEM in order to reduce the nonlinearities in HTS microwave devices is discussed.

Study of optically controlled high temperature superconducting microwave variable attenuator

AbstractA novel optically controlled HTS (high temperature superconducting) microwave variable attenuator was proposed and a sample was tested, which can be used solely, or be integrated into the HTS system. Utilizing the very low microwave superficial resistance and superexcellent optically response character of YBCO film, the insertion loss of sample is lower than 0.2 dB and variable attenuation precision is 0.01 dB at least. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 1539–1541, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22494

Planar tunable high-temperature superconductor microwave broadband phase shifter withpatterned ferroelectric thin film

A planar tunable high-temperature superconductor (HTS) microwave phase shifter withpatterned ferroelectric thin film is presented in this paper. The circuit is based on a coplanarstrip (CPS) transmission line periodically loaded with planar varactors. The CPS line istransformed to microstrip input/output by baluns. The patterning of the ferroelectric thinfilm reduces the conductor loss and eliminates unwanted tuning comparing with circuitswhere a whole layer of ferroelectric thin film is used. The circuit is optimized for hightunability following analytical equations. The phase shifter thus fabricated has abroadband response from 7 to 11 GHz. At 200 V DC bias, an average phase shift of20° is achieved.

Unified Description of Nonlinear Effects in High Temperature Superconductor Microwave Devices

We experimentally demonstrate the equivalence of different manifestations of nonlinear response in high temperature superconductor (HTS) microwave devices. Using a combination of analytical and numerical analysis, we show that the results of intermodulation distortion measurements, harmonic generation measurements, and power-dependent resonator measurements of different coplanar waveguide structures patterned onto the same HTS thin-film sample all yield approximately the same values for the nonlinear penetration depth. The extraction of an underlying nonlinear material parameter that is independent of the specific device geometry and experimental configuration will allow our results to be quantitatively compared with other nonlinear measurements, and will therefore help in determining the dominant source(s) of nonlinear response in HTS microwave devices.

Relating intermodulation distortion to the generating nonlinearity for high-temperature superconductor microwave experiments

We demonstrate how to derive from the intermodulation distortion (IMD) measured as a function of signal power the respective relative increase function $\mathrm{\ensuremath{\Delta}}Z∕{Z}_{0}$ of the governing nonlinear response function $Z$. We apply this approach to our IMD investigations on the microwave properties of high-temperature superconductors (HTS) and show how the experimental input and output quantities can be related to their theoretical model counterparts. The quantitative comparison of $\mathrm{\ensuremath{\Delta}}Z∕{Z}_{0}$ with the relative increase of the hf surface resistance $\mathrm{\ensuremath{\Delta}}{R}_{S}∕{R}_{S0}$ and of the hf surface reactance $\mathrm{\ensuremath{\Delta}}{X}_{S}∕{X}_{S0}$, both measured as functions of hf power, allows us to conclude that the IMD generation in HTS must be predominantly due to the hf-power-induced increase $\mathrm{\ensuremath{\Delta}}{R}_{S}$, with a negligible respective contribution from $\mathrm{\ensuremath{\Delta}}{X}_{S}$.

Analysis of a flip-chip bonded tunable high-temperature superconducting coplanar waveguide resonator using the conformal mapping technique

We have studied the tuning properties of a high-temperature superconducting (HTS) half-wavelength coplanar waveguide (CPW) resonator operating at 5 GHz. The tuning schemes are based on flip-chip bonding of an electrically tunable ferroelectric (FE) thin film and a mechanically movable low-loss single crystal on top of the resonator. Using the conformal mapping method, closed-form analytical expressions have been derived for a flip-chip bonded conductor-backed and top-shielded CPW transmission line. The obtained expressions are used to analyse the volume effect of the FE thin film and the gap between the flip-chip and the CPW resonator on the tuning properties of the device. It has been found that large frequency modulation of the resonator produces impedance mismatch, which can considerably enhance the insertion loss of high-performance HTS microwave devices. Analysis also suggests that, for electrically tunable devices, flip-chip bonded FE thin films on HTS CPW devices provide a relatively higher performance compared to bilayer HTS/FE tunable devices.

Microwave superconductivity

This paper provides an overview of the microwave applications of high-temperature superconductor (HTS) technology. The main characteristics of HTS materials are outlined, highlighting the differences between superconductors and normal conductors. This paper presents recent progress in the development of HTS filters, multiplexers, cryogenic receivers, delay lines, and antennas. A brief summary of cryocooler technology and cryopackaging requirements is presented. The benefits of using HTS technology in wireless and satellite systems are also discussed. The intent of this paper is to provide perspective to newcomers in the field and to empower the potential end-users with current status and performance capabilities of HTS microwave devices.

Power-dependent impedance of high temperature superconductor thin films: Relation to harmonic generation

We present measurements of the power-dependent microwave surface impedance of YBa2Cu3O7−δ thin films, performed using patterned coplanar waveguide (CPW) resonators at 5.87 GHz and 76 K. We compare these resonator measurements with third-harmonic generation measurements performed on CPW transmission lines of the same geometry patterned onto the same thin-film sample at the same frequency and temperature. We find that the power-dependent surface reactance Xs(Prf) is directly related to the magnitude of the generated third-harmonic signal, indicating a common origin for both of these manifestations of nonlinearity in high temperature superconductor (HTS) devices. These results are consistent with the nonlinear response generated by a current-dependent penetration depth λ(J), which provides a material limitation on the linearity that can be achieved in any practical HTS microwave device.

Optical-microwave interaction modeling in high-temperature superconducting films

Optical-microwave interaction in high-T/sub c/ superconductors is investigated for performing basic optoelectronic functions in cryogenic environment. A fast bolometric photoresponse in conjunction with the unique electrical properties of high-temperature superconductor (HTS) materials allows us to explore a series of novel optoelectronic devices with low-noise/low-power and high-speed/high-frequency characteristics. After reviewing the HTS photoresponse categories, we describe the fast bolometric photoresponse and its condition with heat transfer analysis. The analytical solution of heat diffusion equation for an HTS strip mounted on a substrate will be presented for three different type of optical sources. Then the effect of optical irradiation will be incorporated in the two-fluid model by thermomodulation concept in order to model the interaction of optical radiation with electrical signal. The current-field relationship and the supercurrent response time are evaluated in the presence of both optical and electrical signals. Our numerical simulations for YBaCuO film demonstrate the possibility of RF harmonic generation when the laser beam is modulated by the RF signal in the presence of dc bias current and RF signal mixing when the HTS film is fed by a time-harmonic microwave source. The developed model can also be used to study optical control and tunability techniques for HTS microwave devices for analog signal processing.

Electrical tuning of passive HTS microwave devices using single crystal strontium titanate

Over the last few years several groups have fabricated High Temperature Superconducting (HTS) thin film microwave devices which have included a ferroelectric thin film layer in their design. The electric field dependence of the ferroelectric promises desirable in-situ tuning of the frequency response. Here we present the results of our experiments on the tuning of a coplanar HTS resonator using single crystal strontium titanate (STO). We have patterned a simple coplanar resonator device onto Y-Ba-Cu-O thin films deposited on [100] magnesium oxide substrates. Careful consideration of the size, position and biasing of these high permittivity STO crystals with respect to the planar device allows us to minimise the perturbance to the plain resonators response whilst at the same time maximising the degree to which we are able to tune the device. We have also performed a series of capacitance measurements on our STO crystals to obtain reliable data for the dependence of the permittivity on temperature, applied bias and crystallographic orientation.