A dielectric filled cavity structure is currently being used to estimate the
dielectric constant and loss factor over a wide range of frequencies of a dielectric
material which fills the cavity structure [Saed, 1987]. A full field analysis is used
to compute the effective complex permittivity of the sample material based on
reflection coefficient measurements of the cavity structure and associated
geometrical dimensions. The method has previously been used successfully to
determine the dielectric constant of materials, but limitations in the Inethod have
created difficulties in accurate determination of the dielectric loss factor. The
effective loss in this method yields an estimate of the total cavity loss, including
both the dielectric loss and that of the cavity conductor walls.
In this dissertation a perturbation approach is used to separate the
conductor loss from the total loss. The loss-free full-field analysis is used to
determine the electric current at the conductor boundaries. This current is used to
evaluate the perturbed power dissipated in the cavity walls based on known
conductor properties. By subtracting the loss due to the conductor walls from the
total loss measured in the structure, the dielectric loss and the resultant dielectric
loss factor may be estimated.
Measurements are presented for sample dielectric materials. The dielectric
loss tangents computed by this new technique improve the unperturbed estimates
in the microwave frequency range.
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