Dielectric measurement at wavelengths around 1 cm by means of an H01 cylinderical-cavity resonator

The flow of current in the end surfaces closing an Hoi cylindrical-cavity resonator is everywhere circumferential and this current has zero value at the wall surface. The resonant response can thus conveniently be delineated by variation of the length of the cavity about its resonant value, for which purpose a non-contact type of movable piston is used. The paper describes the technique by means of which this type of resonant system can be used to measure the permittivity and loss-factor values of low-loss solid and liquid dielectrics at wavelengths as low as one centimetre. The factors which determine the optimum size of dielectric specimen to be inserted into the resonator, for accurate permittivity and loss-factor evaluation, are discussed. Typical results are given showing the variation of loss-factor with concentration for solutions of benzophenone in benzene and benzo-phenone in liquid paraffin, and the accuracy of measurement is considered.