A method of measuring the complex permittivities of lossy dielectrics at microwave frequencies

A new method is described for the measurement of the complex permittivities of lossy dielectrics at microwave frequencies. The method has been devised for use when the sample is in the form of a thin film or coating, and may not readily be obtained in a form suitable for the methods already described. Measurements are made of the changes in the attenuation and phase-change coefficients of a TE01 wave propagating in a length of rectangular waveguide, when one broad wall is coated with a film of the dielectric material. The method is of particular value in the investigation of dielectric-lined circular waveguide transmission. The accuracy of measurement is comparable with that of other methods suitable for lossy dielectrics, and improves with increase in the loss tangent and with decrease in the permittivity. Examples are given of some measurements carried out in waveguide no. 22 at 35 Gc/s, and comparison is made where possible with the values obtained by other methods.