High-T/sub c/ superconducting planar filter with pseudo-Chebyshev characteristic

This paper presents design and measurement results of a high-T/sub c/ superconducting planar filter based on a pair of coupled modified hairpin resonators considered to be a key constituent of the filter structure. This provides the filter characteristics, which are very close to the Chebyshev prototype of the same order.     

Tunable microwave filters with controlled ferroelectric capacitors

Microwave microstrip resonators and filters controlled by ferroelectric capacitors have been simulated and experimentally studied. Control at room temperature and under cryogenic conditions has been ensured by capacitors based on BSTO and STO films, respectively. Cooled devices based on YBa₂Cu₃O_7-δ high-temperature superconducting films have been fabricated. The developed filters are efficiently tuned by applying a control voltage, are small, and have a low level of introduced losses.     

Theory of digital phase shifters based on high-Tcsuperconducting films

A theory of digital phase shifters based on transition from a superconducting (S) state into a normal (N) state in high-T_c superconductor (HTS) films is developed. It is shown that the insertion-loss level in the phase shifters is determined by the commutation quality of the HTS film and does not depend on the S-N switching element shape and size. The procedure for designing the S-N phase shifter with minimum insertion loss is equivalent to designing a matching circuit for the termination Z=√R_SR_N (R_S and R_N are the resistances of the switching element in the S- and N-states, respectively). Different versions of S-N phase shifters are suggested and discussed. High-quality S-N phase shifters can be successfully designed in a 1-10 GHz frequency range and find application on the receiving end of microwave systems     

Power dependence of HTS disk-resonator quality factor

The simple closed-form model of nonlinear response of a high-temperature superconducting disk resonator on microwave power is proposed. The model is based on superconducting film nonlinearity and describes the dependence of unloaded quality factor on the incident power. The specified normalizing power is used as the only fitting parameter. Good quantitative agreement of modeled and measured data has been obtained. The results observed exhibit the kinetic nature of the nonlinearity of the disk resonator on an LaAlO₃ substrate at T=60 K and more complicated, presumably thermal, heating nature of the nonlinearity at lower temperature     

Investigation and Modeling Nonlinear Characteristics of High-Tc Superconducting Resonators

The high-quality resonators and pass-band filters based on high-T _c 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.     

Magnetic field intensity in near field zone of loop antenna for RFID systems

The structure of a loop antenna of electrically large diameter with the loop perimeter split by capacitors in the form of planar two-wire (PTW) lines is considered. The antenna characteristics are calculated for one- and two-sided arrangement of the PTW lines and the obtained data are compared to the results of measurements. It is shown that the arrangement of PTW lines significantly influences the distribution of current over the loop perimeter.     

Analysis of the dielectric spectra of composite sealing coatings in a wide frequency range

Polymer coatings on the basis of the biphenol-Novolac potting epoxy compound with a 65% content of spherical particles of fused quartz as a filler were studied by the method of dielectric spectroscopy in a wide frequency range. Dielectric measurements were performed in frequency and temperature ranges of (10⁻² to 5 × 10⁹) Hz and 20 to 200°C, respectively, on film samples of composite coatings formed on different substrates. It was shown that the application of dielectric spectroscopy allows one to study the effect of the degree of the adhesion interaction with the substrate on the processes of structuring in the epoxy polymer matrix and to investigate the degradation processes in the coatings under the effect of high temperature and relative humidity. It was also shown that the values of the glass transition temperature (T _g ) of the composite determined by applying the method of low-frequency dielectric spectroscopy agree well with the T _g values obtained by applying the method of dynamic mechanical analysis (DMA).     

Design of Trimmingless Narrowband Planar HTS Filters

The use of high temperature superconductor (HTS) films provides a higher selectivity of planar filters. The lower out-of-band interference increases the sensitivity of receiving systems and allows reduction of transmitter radiated power. Our goal was to show how these filters can be designed with a desired accuracy, and to give evidence for a real possibility of designing the trimmingless planar HTS filters. The analysis of filter performance is based on accurate models of the characteristics of the HTS planar transmission lines. The HTS film and substrate characteristic tolerance sensitivity is investigated. The design procedure of the trimmingless filter is proposed. Mass production of such filters requires a specific certification of the substrate materials and HTS films used.     

Investigation of electrical nonlinearity of HTS thin films as applied to realization of a microwave IC mixer

The nonlinear response of superconducting thin film bridges and transmission line sections at microwave frequencies has been investigated. A number of mixer prototypes have been designed and characterized. A model, based on analysis of experimental pulsedI-V characteristics, predicting results of mixing experiments, has been introduced and good agreement with the model has been obtained.     

CAD model of effective dielectric constant of microstrip line on M-cut sapphire substrate

Simple and correct formulas in regard to frequency dispersion are derived for the calculation of an isotropic effective dielectric constant for the microstrip line on m-cut sapphire substrate. The formulas were verified by comparison to the results of full-wave analysis based on the equivalent surface impedance approach. The temperature dependence of the dielectric permittivity of sapphire is taken into account.