Juan M. O'Callaghan

Analysis and simulation of the effects of distributed nonlinearities in microwave superconducting devices

This paper presents a comprehensive study of microwave nonlinearities in superconductors, with an emphasis on intermodulation distortion and third-harmonic generation. It contains the analysis of various resonant and nonresonant test devices and its validation using numerical simulations based on harmonic balance (HB). The HB simulations made on test devices show that the closed-form equations for intermodulation and third-harmonic generation are only valid at low power levels. The paper also contains examples of application of HB to illustrate that this technique is useful to simulate superconductive devices other than simple test devices, and that the validity of the simulations is not restricted to low drive power levels. Most of the analyses and simulations of this paper are based on electrical parameters that describe the nonlinearities in the superconducting material. These parameters are compatible with many existing models of microwave nonlinearities in superconductors. We discuss the particulars on how to relate these electrical parameters with one of the existing models that postulates that the nonlinear effects are due to a dependence of the penetration depth on the current density in the superconductor.

FET noise-parameter determination using a novel technique based on 50-/spl Omega/ noise-figure measurements

A novel method for measuring the four noise parameters of a field-effect transistor (FET) is presented. It is based on the determination of its intrinsic noise matrix elements [C/sub 11//sup INT/, C/sub 22//sup INT/, Re(C/sub 12//sup INT/), Im(C/sub 12//sup INT/)] by fitting the measured device noise figure for a matched source reflection coefficient (F/sub 50/) at a number of frequency points, thus, a tuner is not required. In contrast to previous works, no restrictive assumptions are made on the intrinsic noise sources. The receiver full-noise calibration is easily performed by using a set of coaxial and on-wafer standards that are commonly available in a microwave laboratory, thus, an expensive broad-band tuner is not required for calibration either. On-wafer experimental verification up to 26 GHz is presented and a comparison with other F/sub 50/-based and tuner-based methods is given. As an application, the dependence of the FET intrinsic noise sources as a function of the bias drain-current and gate-length is obtained.

Analysis and Simulation of distributed nonlinearities in ferroelectrics and superconductors for microwave applications

This paper gives closed-form equations for the intermodulation and third harmonic signals generated in a nonlinear transmission line with distributed quadratic nonlinearities in the conductor and dielectric. Although the formulation developed is general, it is intended to be used in planar devices combining high-temperature superconductor (HTS) and oxide ferroelectrics. The analysis in this paper shows that the intermodulation and third harmonic signals produced by an HTS tend to cancel those of a ferroelectric, and that full cancellation is theoretically possible. This opens the way for using HTS/ferroelectric multilayers, not (only) for their tunable or phase-shifting properties, but for highly linear spurious-free planar HTS devices.

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.

Nonlinear simulation and characterization of devices with HTS transmission lines using harmonic balance algorithms

This work presents the use of Harmonic Balance to simulate the nonlinear behavior of HTS transmission lines. Good agreement with theoretical cross-checks is found. We also show the use of this algorithm to fit the model of HTS lines from experimental measurements. We illustrate this by fitting several types of experimental data, and discuss how to avoid ambiguity in this fitting.

Nonlinear Distributed Model for Bulk Acoustic Wave Resonators

This work expands the model proposed by Krimtholz, Leedom, and Matthaei (KLM) model to account for the nonlinear effects occurring in acoustic devices due to the nonlinear stiffened elasticity. We show that a nonlinear distributed capacitance in the acoustic transmission line of the KLM model can account for the distributed nature of the nonlinear effects. Specifically, we use the nonlinear telegraphers equation to find closed-form equations for intermodulation distortion and harmonic generation. We confirm the validity of these equations by comparing their results with those provided by a KLM equivalent circuit in which the nonlinear transmission line is implemented by cascading many L-C cells having a voltage-dependent capacitance. To further confirm the model, we show measured nonlinear effects in a thin film bulk acoustic resonator in close agreement with the equivalent circuit simulations.

Passive Intermodulation Due to Self-Heating in Printed Transmission Lines

This paper proposes a mechanism by which third-order intermodulation distortion, due to self-heating, is generated in transmission lines. This work shows how transmission lines made of several materials, whose properties are independent of the electric and magnetic fields, can generate important levels of intermodulation distortion. A circuit model supported by finite-element simulations is presented to account for the temperature generation and also for its impact on the nonlinear performance. Closed-form expressions are used to calculate the generated intermodulation products and are derived from the circuit model and compared with simulations. Finally, measurements and simulations of different transmission lines are presented, showing very good agreement.

Intermodulation Distortion in Coupled-Resonator Filters With Nonuniformly Distributed Nonlinear Properties—Use in HTS IMD Compensation

We present a general procedure for calculating intermodulation distortion in coupled-resonator filters that allows one to predict the performance of a nonlinear filter as a function of the general nodal matrix defining the filter and the material parameters that cause the nonlinear behavior. It is valid for almost any type of nonlinear distributed effects, including those produced by high-temperature superconductors, nonlinear dielectrics such as ferroelectrics, or superconductor/ferroelectric bilayers, and it is valid when the spatial distribution of nonlinearities is not uniform. The procedure has been validated with experimental measurements in an eight-pole quasi-elliptic superconducting filter. Using this procedure, we have assessed a combination of materials with different types of nonlinear effects to partially or completely mitigate the filters nonlinear response. This includes superconducting filters with a ferroelectric pre- or post-distorter stage or even with intermediate ferroelectric compensation stages

Modeling Superconducting Transmission Line Bends and Their Impact on Nonlinear Effects

This paper reports on a numerical technique to obtain the current distribution in the annular bent sections of planar layouts. This is used to obtain the linear and nonlinear circuit distributed parameters modeling a superconducting strip bend and its impact on intermodulation distortion. As an example, we analyze a superconductive open-loop resonator and assess the linear and nonlinear contribution of its bends in its overall linear and nonlinear performance. These simulations are very useful for optimizing the resonators of a filter in order to minimize its nonlinear distortion

Nonlinear distributed model for IMD prediction in BAW resonators

This work presents a distributed nonlinear equivalent circuit to asses the intermodulation distortion (IMD) occurring in a BAW resonator. Closed-form expressions for intermodulation distortion at 2f1-f2 are obtained. Comparisons between analytical and simulated results are in good agreement. Extension of this analysis could be used to predict the nonlinear performance of more complex systems using BAW resonators, such as filters. Finally, measurements are presented and explained using the proposed approach.