The issue of intermodulation distortion in superconducting devices for rf and microwave applications is discussed. The classical frequency conversion theory for nonlinear two-port devices in the small signal limit is shown to apply to microstrip resonators regardless of their geometry and material. Two tone, third order intermodulation measurements allow more sensitive detection of nonlinearity compared to surface impedance measurements, provided a low noise, spurious free experimental setup is adopted. Measurements carried out on high quality Nb meanderline microstrip resonators show that at very low power level nonlinearity is dominated by intrinsic device properties. Film defects start to play a predominant role above a critical power level that strongly depends on the defect’s nature.

Abstract-Low-frequency (LF) dispersive phenomena due to device self-heating and/or the presence of "traps" (i.e., surface state densities and bulk spurious energy levels) must be taken into account in the large-signal dynamic modeling of III-V field-effect transistors when accurate performance predictions are pursued, since these effects cause important deviations between direct current (dc) and dynamic drain current characteristics. In this paper, a new model for the accurate characterization of these phenomena above their cutoff frequencies is presented, which is able to fully exploit, in the identification phase, large-signal current-voltage ( -) measurements carried out under quasi-sinusoidal regime using a recently proposed setup.

A planar superconducting single stage dual mode filter has been investigated and tested. The basic element of the device is a square patch resonator diagonally crossed by unequal slots to provide both a size reduction and a simple way to couple the two degenerate modes. The effect of further cuts, realized on the conductor surface, is also investigated with respect to the power handling capability and miniaturization requirements. Two different filter topologies operating in C band with 1% fractional bandwidth have been designed and fabricated using Nb and YBa2Cu3O7 films grown on 10×10×0.5 mm3 LaAlO3 (100) substrates. Device response is studied performing power and intermodulation measurements. Third order products start to appear above the noise floor (−120 dBm) at input power Pin≈−20 dBm, whereas thermomagnetic breakdown is observed above 20 dBm.

We report on microwave measurements of the surface impedance Z s ϭ R s ϩ iX s of Nb 3 Sn superconducting films deposited by planar magnetron sputtering on sapphire substrates. The samples show the A15 structure with maximum T c (R ϭ 0) of 17.4 K and residual resistivity ratios up to ␤Ϸ3. The measurements are performed by a microstrip resonator technique using a meander line geometry. The power dependence of Z s is studied at different temperatures and frequencies in the range of 1-10 GHz using the fundamental and higher order modes of the resonator. The effect of a dc magnetic field applied with different orientations is also studied. The data are analyzed in the context of a simple model able to describe most of the reported loss mechanisms.

Abstruct-A new kind of dual-mode filter based on cross and transverse slotted square resonators is presented. A pair of unequal crossed slots formed on a square patch resonator provides both a reduction of the filter size and a simple and controllable way to couple the two degenerate modes. Transverse cuts opportunely realized on the patch further decrease the operating frequency without any appreciable change in the power handling capability of the device. Three examples of single stage filters operating in C-band with 1% and 10% fractional bandwidth are designed with a commercial 2.5D software and fabricated using Nb and YBazCu307 films grown on LaA103 (100) substrates. The filters response is characterized at different temperatures and the insurgence of non-linearity investigated varying the input power and carrying out intermodulation measurements.