Superconducting filters using spiral resonators have been demonstrated. Compared with meander lines, errors in track width have a smaller effect on the total inductance; fabrication tolerance, simulation accuracy, power handling, and quality factor are consequently improved. The coils do not require air bridges, which are difficult to produce in superconductors. The devices can be designed using a standard procedure based on the coupling coefficients between resonators and coupling to source and load. Fourth- and sixth-order Chebyshev filters employing single and twin spirals are demonstrated for 0.86% bandwidth filters with center frequency of approximately 1750 MHz. A new coupling structure has been introduced for the single-spiral resonators. Despite the very small size of approximately 1.7/spl times/1.7 mm, the resonators have a quality factor of approximately 30000 at 77 K and the filters can handle approximately 20 mW.

Ultra-compact superconducting narrow-band filters using single- and twin-spiral resonators

Novel resonators composed of double-spiral inductors and interdigital capacitors are developed, which not only are compact in size but also have no harmonics up to three times of the fundamental frequency. The center frequency is insensitive to the thickness of the substrate. A miniature seven-pole narrow-band HTS bandpass microstrip filter has been designed, fabricated and tested for an astronomy observation application, which requires a center frequency at 610 MHz and 0.82% fractional bandwidth. The computed and measured results are found in excellent agreement.

Superconducting microstrip filters using compact resonators with double-spiral inductors and interdigital capacitors

The compact meander-shape configuration of planar resonators is suggested for applications in narrowband filters with quasi-elliptic characteristic. The quasi-elliptic frequency response with two transmission zeroes at the edges of the passband is provided by the specific symmetry of the coupled resonators and is controlled by an appropriate choice of the resonator dimensions and the couplings between the resonators. The 12-pole quasi-elliptic filter with 0.5% fractional bandwidth at 1.775 GHz has been designed using meander-line microstrip resonators and manufactured on a double-sided YBCO film on a LaAlO/sub 3/ substrate. The filter exhibited the in-band insertion loss less than 0.5 dB at T=60 K, the return loss of 20 dB, the out-of-band rejection better than 75 dB, and 40 dB/MHz slope of the characteristic.

Narrowband Y-Ba-Cu-O filter with quasi-elliptic characteristic

Accurate design of microwave planar high-temperature superconducting (HTS) filters is obtained using a computer-aided design tool, which provides simulation of characteristics of the multicoupled transmission-line structures. The quasi-static spectral-domain method is applied. In order to achieve a good correspondence between measured and simulated filter performance, correct models of the microwave propagation characteristics of HTS planar transmission lines have to be used in the simulation procedure. The goal of this paper is to demonstrate that it is possible to design the planar HTS filters that do not need additional trimming after manufacturing. The trimmingless filters can be used in mass production for the next generation of mobile communication systems.

Development of CAD tool for a design of microwave planar HTS filters

A practical design technique for a compact forward-coupled microstrip bandpass filter structure is introduced based on a computer-aided simulation and optimization software TUMIC. The structure consists of a parallel array of fully aligned half-wavelength resonators. Aimed at the application in the front-end receiver of a GSM base station, a 9-pole high-temperature superconductor filter with 2.6% fractional bandwidth at 1732.5 MHz was designed and fabricated using double-sided YBCO thin films on a 30-mm/spl times/30-mm/spl times/0.5-mm LaAlO/sub 3/ wafer. The S-parameter measurements show a good agreement with the simulated results. At 30 K, the filter has less than 0.4-dB insertion loss, 0.3-dB passband ripple, and better than 12-dB return loss.

Design and performance of a compact forward-coupled HTS microstrip filter for a GSM system

10-pole HTS microstrip band-pass filters with central frequency 175 GHz have been designed, manufactured, and investigated without any trimming in the linear and nonlinear regimes A high filter performance with insertion loss not more than 05 dB and power handling capability up to 10 W of input power at T=60 K has been observed Different commercial and home-made software were used to simulate the filter characteristics

High-temperature superconductor filters: modeling and experimental investigations

The high-quality resonators and pass-band filters based on high-Tc superconducting (HTS) films are of the most interest for practical applications The industrial application of the devices is retarded by nonlinearity of the film surface impedance under microwave power of a high level The phenomenological model of nonlinear characteristics of HTS resonators was developed and applied to different kinds of planar resonators: disk, parallel plate, and micro-strip resonator A comparison of experimental and modeled characteristics of the resonators revealed the distinctive difference in the model parameters Some limiting characteristics are discussed

Investigation and Modeling Nonlinear Characteristics of High-Tc Superconducting Resonators

Carbon materials are promising for use as electrodes for supercapacitors and lithium–ion batteries due to a number of properties, such as non-toxicity, high specific surface area, good electronic conductivity, chemical inertness, and a wide operating temperature range. Carbon-based electrodes, with their characteristic high specific power and good cyclic stability, can be used for a new generation of consumer electronics, biomedical devices and hybrid electric vehicles. However, most carbon materials, due to their low electrical conductivity and insufficient diffusion of electrolyte ions in complex micropores, have energy density limitations in these devices due to insufficient number of pores for electrolyte diffusion. This work focuses on the optimization of a hybrid material based on porous carbon and carbon nanotubes by mechanical mixing. The purpose of this work is to gain new knowledge about the effect of hybrid material composition on its specific capacitance. The material for the study is taken on the basis of porous carbon and carbon nanotubes. Electrodes made of this hybrid material were taken as an object of research. Porous carbon or nitrogen-containing porous carbon (combined with single-, double-, or multi-layer carbon nanotubes (single-layer carbon nanotubes, bilayer carbon nanotubes or multilayer carbon nanotubes) were used to create the hybrid material. The effect of catalytic chemical vapor deposition synthesis parameters, such as flow rate and methane-to-hydrogen ratio, as well as the type of catalytic system on the multilayer carbon nanotubes structure was investigated. Two types of catalysts based on Mo12O28 (μ2-OH)12{Co(H2O)3}4 were prepared for the synthesis of multilayer carbon nanotubes by precipitation and combustion. The resulting carbon materials were tested as electrodes for supercapacitors and lithium ion intercalation. Electrodes based on nitrogen-containing porous carbon/carbon nanotubes 95:5% were found to be the most efficient compared to nitrogen-doped porous carbon by 10%. Carbon nanotubes, bilayer carbon nanotubes and multilayer carbon nanotubes synthesized using the catalyst obtained by deposition were selected as additives for the hybrid material. The hybrid materials were obtained by mechanical mixing and dispersion in an aqueous solution followed by lyophilization to remove water. When optimizing the ratio of the hybrid material components, the most effective porous carbon:carbon nanotubes component ratio was determined.

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V.V. Kondratiev

Papers

Narrowband Y-Ba-Cu-O filter with quasi-elliptic characteristic

Development of CAD tool for a design of microwave planar HTS filters

High-temperature superconductor filters: modeling and experimental investigations

Investigation and Modeling Nonlinear Characteristics of High-Tc Superconducting Resonators

Improvement of Hybrid Electrode Material Synthesis for Energy Accumulators Based on Carbon Nanotubes and Porous Structures