3D Smith chart constant quality factor semi-circles contours for positive and negative resistance circuits

TL;DR

This paper characterizes constant Q factor contours on 3D Smith charts for passive and active circuits, introduces a CAD method for Q analysis, and applies it to novel inductor and tunnel diode circuits.

Contribution

It extends the geometric understanding of Q contours to 3D Smith charts for active and passive circuits and develops a CAD tool for direct Q analysis from reflection coefficients.

Findings

Q contours form semi-circles on 3D Smith charts

Negative resistance circuits have complementary Q contours

Q analysis applied to Vanadium dioxide inductors and tunnel diodes

Abstract

The article proves first that the constant quality factor (Q) contours for passive circuits, while represented on a 2D Smith chart, form circle arcs on a coaxal circle family. Furthermore, these circle arcs represent semi-circles families in the north hemisphere while represented on a 3D Smith chart. On the contrary we show that the constant Q contours for active circuits with negative resistance form complementary circle arcs on the same family of coaxal circles in the exterior of the 2D Smith chart. Also, we find out that these constant Q contours represent complementary semi-circles in the south hemisphere while represented on the 3D Smith chart for negative resistance circuits. The constant Q - computer aided design (CAD) implementation of the Q semi-circles on the 3D Smith chart is then successfully used to evaluate the quality factor variations of newly fabricated Vanadium dioxide inductors first, directly from their reflection coefficient, as the temperature is increased from room temperature to 50 degrees Celsius ({\deg}C). Thus, a direct multi-parameter frequency dependent analysis is proposed including Q, inductance and reflection coefficient for inductors. Then, quality factor direct analysis is used for two tunnel diode small signal equivalent circuits analysis, allowing for the first time the Q and input impedance direct analysis on Smith chart representation of a circuit, including negative resistance