Measurement of the Dielectric Constant and Loss Tangent of Isotropic Films at Millimeter Wavelengths

A technique for measuring the dielectric constant and loss tangent of isotropic films of electrical thickness less than about 60° has been developed. The method is adapted specifically to a cavity system constructed from 1.111 cm i.d. waveguide for use with the TE°₀₁ mode from 50 to 60 Gc. The approximate limits on the measurable loss tangent of ordinary plastics by this technique are: 1×10⁻⁴≲tanδ≲1×10⁻¹. Measurements at 55.2 Gc were made on three materials. The results are as follows: $$\begin{array}{ccc}\mathrm{\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}}\mathrm{Material}& {\mathrm{\hspace{0.17em}\epsilon }}_2\prime & \hspace{0.17em}\tan {\delta }_2\\ \mathrm{Plexiglas}& \text{2.55}& \text{0.0048}\\ \mathrm{General\; Electric\; varnish\; No}\text{.\hspace{0.17em}1202}& \text{2.65}& \text{0.012}\\ \mathrm{Mylar\; film}& \text{3.145̄}& \text{0.0044}\end{array}$$