Linear-Nonlinear Interaction and Passive Intermodulation Distortion

This paper describes several consequences of a linear-nonlinear interaction that was recently found to be of importance in microwave circuits that produce passive inter-modulation (PIM) distortion. This paper briefly discusses how this linear-nonlinear interaction operates in an example system. It then discusses how an understanding of the linear-nonlinear interaction allows us to distinguish between different types of nonlinearities from the power dependence of the third-order intermodulation distortion product. Next, an example uses a multiphysics simulator to demonstrate that electrothermal nonlinearities behave as expected from the linear-nonlinear interaction model. Lastly, it illustrates how simple nonlinear models characterized with one circuit can accurately predict distortion levels when the nonlinearity is placed within a very different circuit, showing that knowledge of the interaction gives the ability to accurately predict the behavior of PIM-producing components in a variety of circuits such as resonators, filters, and matching networks

Binnengekomen

By adding controlled thicknesses of nickel and gold plating to the conductors of a coaxial transmission line, the magnitude of passive intermodulation produced by the transmission line can be controlled with precision. Theoretical predictions of distortion magnitude as a function of plating thicknesses are presented, along with an experimental validation. These adjustable-magnitude passive intermodulation sources are used to give a fourfold improvement in the bandwidth of techniques presented previously, demonstrating that cancellation can for the first time be achieved in bandwidths needed for cellular systems

Prediction of passive intermodulation from coaxial connectors in microwave networks

Coaxial connectors are frequently the dominant contributors to passive intermodulation (PIM) distortion in high-frequency networks. This paper reports on a circuit model enabling estimation of PIM distortion by coaxial connectors in the design of high-frequency networks. A method of modeling the effect of multiple point sources of PIM is applied to coaxial connectors, allowing the prediction of the PIM of networks with several connectors. Typical ranges of PIM produced by common connectors in a two-tone test are reported. The stability and repeatability of PIM produced by a single connector is examined. Nonlinear current-voltage curves for coaxial connectors are given that predict the PIM distortion output by coaxial connectors over a broad range of input powers. An experimental verification is given showing that PIM of a system can be predicted if the characteristics of the individual components are known

The seasonal distribution of immune thrombotic thrombocytopenic purpura is influenced by geography: Epidemiologic findings from a multi‐center analysis of 719 disease episodes

Abstract Prior studies have suggested that immune thrombotic thrombocytopenic purpura (iTTP) may display seasonal variation; however, methodologic limitations and sample sizes have diminished the ability to perform a rigorous assessment. This 5‐year retrospective study assessed the epidemiology of iTTP and determined whether it displays a seasonal pattern. Patients with both initial and relapsed iTTP (defined as a disintegrin and metalloprotease with thrombospondin type motifs 13 activity <10%) from 24 tertiary centers in Australia, Canada, France, Greece, Italy, Spain, and the US were included. Seasons were defined as: Northern Hemisphere—winter (December–February); spring (March–May); summer (June–August); autumn (September–November) and Southern Hemisphere—winter (June–August); spring (September–November); summer (December–February); autumn (March–May). Additional outcomes included the mean temperature in months with and without an iTTP episode at each site. A total of 583 patients experienced 719 iTTP episodes. The observed proportion of iTTP episodes during the winter was significantly greater than expected if equally distributed across seasons (28.5%, 205/719, 25.3%–31.9%; p = .03). Distance from the equator and mean temperature deviation both positively correlated with the proportion of iTTP episodes during winter. Acute iTTP episodes were associated with the winter season and colder temperatures, with a second peak during summer. Occurrence during winter was most pronounced at sites further from the equator and/or with greater annual temperature deviations. Understanding the etiologies underlying seasonal patterns of disease may assist in discovery and development of future preventative therapies and inform models for resource utilization