High-temperature Superconducting Microstrip Research Articles

A Circularly Polarized HTS Microstrip Antenna Array with Controllable Cryostat

A high-temperature superconductor (HTS) microstrip antenna array with right-hand circular polarization is proposed for space communications. The proposed HTS antenna array can achieve high efficiency, which is able to reduce the antenna’s loss. The array consists of 16 antenna elements being fed by a T-network. A pair of symmetric meander slots is used in each antenna element to broaden the input matching bandwidth. A controllable cryostat is used as the refrigeration for HTS. The experiment shows that the gain of the proposed HTS antenna is 8.39 dB, whose 10 dB return loss bandwidth is 2.2% ranging from 5.75 GHz to 5.87 GHz. In comparison with a traditional conductor antenna array having the same configuration, the proposed array has an 8.1 dB improvement in the gain and a 69.2% enhancement in the radiation efficiency.

Thin Film Ferroelectric Compact Branch-Line Coupler Based on D-CRLH Unit Cell and YBCO HTS Microstrip

In this paper, two new compact branch-line couplers (BLCs) are proposed. The first is designed and implemented using D-CRLH unit cells made of copper microstrip line. The new design occupies only 52 % of the area of the conventional BLC that operates at 1.8 GHz. The structure has been fabricated and the experimental results have been compared to the simulated ones and very good agreement has been obtained. Advanced design system circuit simulator and the CST full wave EM simulator have been used to simulate the proposed BLCs. The second BLC is designed using YBCO high-temperature superconducting (HTS) microstrip rather than copper to achieve low insertion loss, and more compact size. Three cases of this coupler with different substrate materials are studied. The design of YBCO on lanthanum aluminate (LAO) substrate attains an optimum BLC performance compared to the one using D-CRLH. All parameters of the second design are enhanced compared to the first one, the insertion loss is enhanced from ?0.1268 to ?0.007 dB, return loss is enhanced from ?35 to ?41 dB, isolation is enhanced from ?25 to ?36 dB, and the area is reduced from 246 to 53.55 mm2. Moreover, the tunable frequency BLC is designed using thin film layer of BST ferroelectric material, the layer is sandwiched between the LAO substrate and HTS microstrip line, the response shows a variation of the center frequency work with the applied electric field, and the ferroelectric thickness.

Investigation of DC current injection effect on the microwave characteristics of HTS YBCO microstrip resonators

The DC current injection effect from a ferromagnetic (FM) La0.7Sr0.3MnO3 (LSMO) to a high temperature superconducting (HTS) Y1Ba2Cu3O7−x (YBCO) thin film was investigated by the microwave surface impedance measurements in a FM/HTS structure, formed as a microstrip resonator for improving the sensitivity of the experiments. The quality factor and the resonance frequency of this structure were found to strongly depend on the current strength, injected from the LSMO electrode into the HTS microstrip electrode. The magnetic penetration depth and the quasiparticle conductivity of the HTS component were determined to increase under DC current injection process, which in all probability stimulated breaking of Cooper pairs and led to a decrease of the superfluid concentration and an increase of the normal fluid concentration without significantly affecting the relaxation time of the quasiparticles.

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.

Technique for tuning center frequency of HTS microstrip filters without significantly changing bandwidth

We have developed a technique for tuning high-temperature superconducting (HTS) microstrip filters in which additional electric pads are placed at the open ends of the resonators for tuning the center frequency. Pads are placed along one side of the open ends of the resonators to enable the effective lengths of the resonators to be adjusted, thereby shifting the center frequency. Pads are also placed around the I/O coupled-line elements to enable the coupling strength between the coupled-line and resonator to be adjusted, thereby reducing the insertion loss caused by tuning. The pads consist of line-and-space patterns. The former are electrically connected to the resonators, and the latter are electrically connected to the coupled-line elements. Simulated application of this technique to a 3-pole superconducting microstrip combline bandpass filter with half-wavelength resonators, a 5.0-GHz center frequency, and a 120-MHz 3-dB bandwidth shifted the bandwidth 500 MHz. However, the 3-dB bandwidth was reduced about 14 MHz. Use of a modified 3-pole microstrip interdigital bandpass filter mitigated the reduction to 2 MHz. Using this modified filter with additional electric pads is thus an effective way to tune the center frequency of HTS bandpass filters without significantly changing the bandwidth.

Novel trimming technique for tunable HTS microstrip filters

We have developed a method using additional electric pads for trimming tunable high-temperature superconducting (HTS) microstrip filters. These filters are generally tuned by adjusting the gap between a dielectric floating plate above the filter. When the floating plate approached the filter, the center frequency was shifted to a lower frequency. However, the insertion loss increases due to variation in the external quality factors varying from the design parameter. The external quality factors are usually controlled by adjusting the length of the input/output (I/O) coupled-line elements and the gap between the elements and the resonator. In our method, additional electric pads are distributed at the open-end of the I/O coupled-line elements of a 3-pole hairpin bandpass filter to enable adjustment of the external quality factors so as to reduce insertion loss. The electric pads consist of line-and-space patterns. They are eclectically connected to the coupled-line elements to adjust the line length and gap width and thereby control the external quality factors. An electromagnetic simulator was used for the design and analysis. The simulation results showed that the additional electric pads are effective in improving the insertion loss of the HTS bandpass filter after tuning.

An HTS microstrip equalizer for improving the group delay of an HTS filter forthird-generation communications

This paper reports a high temperature superconducting (HTS) microstrip equalizer forimproving the flatness of the pass-band group delay of an HTS filter for third-generation(3G) communications. The HTS filter to be equalized is a ten-pole quasi-ellipticfunction filter with a bandwidth of 9.6 MHz centered at 1946.5 MHz. The one-portcoupled-resonator microstrip equalizers were designed to have three or four poles, andthe calculated and simulated group delay response curves of the filter with theequalizers are presented and discussed. A three-pole equalizer was fabricated on apiece of 0.5 mm thick MgO wafer with double-sided YBCO films. The measuredresponses show that after connecting with the HTS equalizer, the group-delayeffective bandwidth of the filter, defined as the ratio between the flat group delaypass-band width (a criterion of variation of pass-band group delay being less than50 ns was applied) and the equal ripple pass-band width, increased from 50% to70% without any noticeable degradation of the band-edge steepness of the HTSfilter.

Miniaturization of Superconducting Filters Using Hilbert Fractal Curves

This work presents novel compact high-temperature superconductor microstrip resonators and filters based on the Hilbert space-filling fractal curve. Several Hilbert resonator configurations have been assessed by using a full-wave electromagnetic simulator and their miniaturization performance has been investigated, emphasizing the parameters which allow obtaining good tradeoff between compact size and losses. These resonators have proved to be useful for filter design. A four-pole 2.45-GHz quasi-elliptic filter and a four-pole 1.9-GHz Chebyshev filter have been realized by patterning 10 mm/spl times/10 mm Y/sub 2/Ba/sub 3/Cu/sub 7-/spl delta//O thin films on MgO substrates. Insertion losses of the order of 0.2 dB have been measured, showing good agreement with the simulations.

Wideband high-temperature superconducting microstrip antenna

A novel high temperature superconductor microstrip antenna with the distributed Josephson inductance approach having been used is presented. The antenna shows a wide bandwidth property which is obtained by varying the DC current flowing through the patch.

A compact, higher order, high temperature superconductor microstrip bandpass filter ona two-inch lanthanum aluminate substrate for personal communication serviceapplications

A practical design methodology for a compact parallel-coupled microstrip bandpassfilter structure with steep attenuation is introduced using a computer-aidedfull wave electromagnetic simulation based on the method of moments. Thestructure consists of an array of fully aligned half-wavelength spiral meanderline resonators. Aimed at application in the front-end receiver of digital cellularcommunication service, a 12-pole high temperature superconductor filter with 2.27%fractional bandwidth at 883.0 MHz was designed. The filter is fabricated usingthallium–barium–calcium–copper oxide (TBCCO) thin films on a two-inch lanthanum aluminate(LaAlO3) wafer.The S-parameter measurements show a good agreement with the simulated results.At 70 K, the 12-pole filter shows less than 0.4 dB insertion loss, 0.3 dB passbandripple, better than 12 dB return loss. The out of band rejection at 3 MHz below thepassband edges is more than 60.0 dB. In order to estimate the power handlingcapability of the filter, the third-order intermodulation distortion was measured.A sensitivity analysis for the observed frequency shift in the filter is reported. Also fromthis analysis an approach for using the same design in 0.5% FBW applications is discussed.

Tunable HTS microstrip filters for microwave electronics

A simple and successful design of a tunable high temperature superconducting (HTS) microstrip filter is presented. The tunability of the filter is predicted using full wave electromagnetic simulations based on method of moments. The predicted results are compared with measured data and good agreement is reported.

Design and development of ferroelectric tunable HTS microstrip filters for Ku- and K-band applications

In the past few years, our group has designed, fabricated and tested several ferroelectric tunable components, in collaboration with NASA Glenn Research Center. Among the components studied are microstrip tunable resonators, filters, diplexers, and couplers. Tunable filters with gold as well as YBCO high temperature superconductor (HTS) electrodes have been studied using the conductor/ferroelectric/dielectric two-layered microstrip configuration. Tunability is achieved through the non-linear dc electric field dependence of the relative dielectric constant of the ferroelectric thin film. Two pole ferroelectric tunable HTS filters using the YBCO/STO/LAO two-layered microstrip yielded low insertion loss as low as 1.5 dB, and large frequency tunability (∼2.3 GHz) at 24 K, with a peak electric field of 80 kV cm −1 for electrical tuning. The critical design issues for realizing practical tunable filters will be addressed. These include design for (i) large tunability, (ii) low insertion loss, (iii) bandwidth considerations, and (iv) dc biasing for tuning the filters. HTS filters will be compared with their gold counter parts for their performance at Ku- and K-band frequencies. Also, our current work on BSTO based room temperature tunable filters will be presented.

Power handling capability improvement of an HTS microstrip resonator

The power handling capability of high temperature superconducting (HTS) microstrip filters is an important problem, which restricts their practical applications. This paper reports the modelling results of the capacitively coupled half-wavelength resonator based on a modified microstrip transmission line with improved power characteristics.

Accurate full wave estimation of quality factor and resonance frequency of HTS microstrip resonator

The spectral domain technique is employed to estimate characteristics of a high temperature superconducting (HTS) microstripline resonator taking into account most of the practical operating conditions to provide accurate representation of device performance. This analysis is expected to be quite useful in CAD of high Q resonators and sharp cutoff filters used in microwave communications.

Fabrication of novel 22 GHz hairpin type HTS microstrip filter using laser ablated thin films

The fabrication of high quality superconducting thin films using pulsed laser deposition (PLD) has been reported to find optimized processing conditions and to make millimeter-wave devices. High temperature superconducting (HTS) YBCO films were prepared on MgO (10mm×10mm×0.5mm) substrates by PLD. The 3-pole bandpass filter centered at 22GHz for satellite communication was designed consisting of hairpin type coupled-lines to reduce the configuration in size. YBCO films are c-axis oriented and show superconductive transition temperatures of 88–89K with the transition widths <0.5K. The insertion loss of passband at 70K was about 5dB. The measured frequency response of superconducting filter will be compared with the simulation result.

Design of HTS, lumped-element, manifold-type microwave multiplexers

Manifold-type frequency multiplexers are especially useful when a sizable number of channels are required. However, they normally use interconnecting transmission lines that could result in an overall structure many wavelengths across. Herein we investigate the design of compact manifold multiplexers using lumped-element filters which are convenient for high temperature superconductor (HTS) realization, while the transmission lines are replaced with lumped-element equivalents. Design examples calculated for frequencies in the vicinity of 0.8 GHz yield element values which are quite feasible for realization in HTS microstrip circuits. The examples indicate that very compact multiplexers should be obtainable.

A12‐GHZ high‐temperature superconducting semiconductor oscillator

AbstractIn view of a monolithic integration of high‐temperature superconducting (HTS) passive circuits and semiconductor (SC) active devices, we propose in this work a hybrid SC / HTS microstrip oscillator operating at 77 K and 12 GHz, combining a HEMT and a YBaCuO ring resonator. © 1995 John Wiley &amp; Sons, Inc.

Analysis of anisotropic high temperature superconductor planar structures on sapphire anisotropic substrates

A full-wave finite-difference time-domain technique is used to study the anisotropy associated with high temperature superconductor (HTS) planar structures. The analysis is performed on anisotropic YBCO film deposited on anisotropic sapphire substrate. The solution incorporates all the physical aspects of the HTS materials. The finite thickness of the anisotropic strip is rigorously modeled using a graded non uniform mesh generator. The propagation characteristics of HTS microstrip line are evaluated. The current distributions inside the HTS are calculated for both the normal and the super fluids. It is shown that the 90/spl deg/ r-cut sapphire substrate structure has lower loss and lower effective dielectric constant than the 0/spl deg/ r-cut substrate. Interesting aspects, concerning the anisotropy of HTS microwave structures, are presented. >

High-power HTS microstrip filters for wireless communication

The performance of narrowband microstrip filters with low insertion loss and high power-handling capabilities made from YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// (YBCO) high-temperature superconducting (HTS) thin films is presented. Results are shown for two different designs that were chosen to optimize the power-handling capability. Both filters have a 2-GHz center frequency and 5 poles that incorporate coupled resonators with 10-/spl Omega/ internal impedances. They were made on 5-cm-diameter LaAlO/sub 3/ substrates. Both designs use parallel-coupled feed lines to avoid current crowding, The first design includes backward- and forward-coupled filters, has 1% bandwidth, and has handled over 25 watts of input power at 10 K with less than 0.25 dB compression. The second design has 1.2% bandwidth and uses only forward-coupled resonators. The dissipation loss is less than 0.2 dB at 45 K and it has a third-order intercept of 62 dBm. Another similar filter handled 36 watts of power at 45 K with less than 0.15 dB compression across the passband. We have developed a technique to visualize the power dissipation of the filter by observing the bubbles created by the filter when submerged in liquid helium, showing areas with local defects or where the current distribution is at its peak value. We also discuss several planar high-power filter issues, including material selection and fabrication, device configuration trade-offs, filter structure optimization, and design approaches to maximize power-handling capacity.

HTS microstrip matching networks and filters

High-temperature superconducting (HTS) YBCO microstrip bandpass filters and microstrip impedance matching networks were fabricated, tested and compared with the predicted performance. Vector corrected measurements of these circuits were performed at cryogenic temperatures. Comparisons of the insertion loss for the HTS and corresponding Au filters are presented, as well as the predicted noise figure for the low-noise amplifiers using HTS and Au matching networks.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>