18.3 Basic Dielectric Measurement Theory

As most dielectric measurements make use of cells to contain the dielectric, and as we can regard the cell as an RF and MW component, many dielectric measurement techniques, viewed at the instrumental level, are similar to other S-parameter measurement techniques that are covered in-depth in other chapters and also in textbooks on RF and MW measurements (e.g. [15 17]). A more comprehensive version of the treatment given here can be found in the Good Practice Guide [1].

Dielectric measurement methods and measurement cells largely fall into two broad classes:

1. Those in which the dielectric properties are measured as an impedance, Z, as in Figure 18.2a, or more commonly, as an admittance, Y, as in Figure 18.2b. These may collectively be called lumped-impedance methods and are generally used at low frequencies (LF) and in the RF region of the spectrum up to 1 GHz.

2. Those in which the dielectric is considered to be interacting with travelling and standing electromagnetic waves - these may collectively be called' Wave Methods'.

Both lumped-impedance and wave techniques can be used in resonators. Resonators are measurement cells with resonating EM-fields inside them that are used to obtain high sensitivity for measuring the loss of low-loss dielectrics (see below).