With this double resonator, small and flat dielectric samples can be examined with regard to their properties. The arrangement is based on a classical cavity resonator. A coaxial line is terminated with a parallel-plate capacitor. This capacitance results from the arrangement of the second reflected cavity resonator. The test object can be introduced between the plates. As a result of the high quality of the product, the system reacts very sensitively to variations of the dielectric. The phase position of the transmitted signal can be used for the evaluation of changes in the properties.