Measurement of dielectric constant and loss tangent of PCB

Abstract

This report describes the theory and methodology of measuring dielectric constant and loss tangent by using a spherical open resonator. The dielectric constant measurement method consists of perturbing the resonant frequency of a spherical open resonator by inserting a sheet of plane dielectric sample at the centre of the resonator normal to its axis. The dielectric constant can be calculated by measuring the resonant frequency of a symmetrical mode and of the adjacent lower-frequency asymmetrical mode easily by Network Analyzer. The measurement of loss tangent is basically by finding the energy stored inside the sample obtaining the resonant frequencies with and without sheet of dielectric substrate, and then. Apart from the theory, this report described the dimension, configuration and connection of the open resonator. The computer program written with MatLab 6.5 would also be introduced. By applying the Gaussian Beam theory, the basic field expressions can be well approximated inside a spherical open resonator. Two transcendental equations are derived for microwave and millimetre-wave in its symmetrical and asymmetrical resonant mode with the perturbation technique. By solving the two transcendental equations with the reflective index, n, by computer, the dielectric constant can then be determined. At this experiment, sets of mirrors with different spherical radius of curvature and dielectric substrates are tried to place in the open resonator. In the measurement, Network Analyzer is used to record the change of resonant frequency. The measurement result is shown at following chapter.