Waveguide cavity perturbation method for measuring complex permittivity of water

An accurate method of measuring the complex permittivity of high‐loss liquids like water by use of a waveguide perturbation technique is presented. The sample taken in a thin capillary tube of low‐loss material is inserted in the S‐band waveguide cavity. Resonance frequency and frequency shift are measured with a H. P. network analyzer and the complex permittivity is calculated. This method is particularly useful in the case of high‐loss liquids. Another advantage of this method is that only a very small quantity of liquid is needed for the study.