An improved resonant-cavity method of measuring high-frequency losses in materials

The measurement of h.f. losses in a sample of material is often made by observing the reduction in the Q-factor of a resonant cavity when the sample is introduced into it. Unfortunately, materials of high permittivity and large losses tend seriously to disturb the distribution of the field in the cavity and thus to make precise measurements difficult. In the present proposal an attempt is made to avoid that problem by placing the sample not in the cavity itself but in a short length of evanescent guide coupled to it. The case is discussed of a cavity resonant in the H01 mode and coupled through the end wall to a corresponding evanescent guide into which the sample can be introduced, and it is shown that this arrangement should be capable of yielding accurate values of loss tangent for such materials as semiconductors, which present difficulties in conventional equipment.