TABLE OF CONTENTS In all passive waveguide structures, the primary circuit elements resistance and conductance act like absorbers of electromagnetic wave energy. As such, their mathematical sign is, by convention, positive. However, certain active electrical devices exist whose equivalent circuit can most conveniently be represented by negative resistance or negative conductance elements. Negative resistance and negative conductance circuit elements act more like sources than absorbers of electromagnetic wave energy.
Electrical devices such as parametric and tunnel diode reflection amplifiers, which can be schematically represented by negative resistance or negative conductance in combination with conventional circuit elements, are frequently used in connection with waveguides. In order to properly represent their characteristics on a SMITH CHART for graphical analysis, it is important to understand the effect of negative resistance or negative conductance upon the associated waveguide electrical characteristics. This will be discussed more fully herein. It will be found, for example, that when a waveguide is terminated in a circuit which has a resultant negative resistance or negative conductance component, the complex reflection coefficients and the complex transmission coefficients at all points along the waveguide are different from what they would have been had the sign of the resistance or conductance been positive.
Negative resistances and negative conductances do not actually produce energy, but rather act to transform and release energy from an associated source (such as a battery) into electromagnetic energy whose frequency is controlled by a primary source of smaller energy level. Negative resistance is defined [7] as the property...
