Non resonant microwave measurement techniques

The main difficulty arises due to the low losses of many microwave oxide materials including insulator and superconducting metals. Therefore, approaches based on a sample being just a small perturbation of the dut, such as a cavity resonator with a small piece of material inside, are of limited use, because the effect of the sample absorption on the resonator Q is too small. Therefore, in most cases the geometry of the sample has to be selected in a way that the sample itself represents a dominant part of the dut. 

For bulk dielectrics, a dielectric resonator can be formed by a cylindrically shaped piece of dielectric material. Dielectric thin films are more difficult to investigate, in particular when the loss tangent is very small. Planar resonator techniques as well as specially designed dielectric resonators can be used to examine their properties. For high-temperature superconductors both dielectric resonators and planar resonators represent an ideal tool to examine their surface impedance values. 

Non resonant techniques are only of limited use to determine microwave losses with high precision, in particular when the losses are very small. Flowever, for the investigation of nonlinear absorption phenomena (i.e. rf power dependent on surface impedance or loss tangent) by intermodulation distortion measurements broad-band test devices are more common. Typically, a planar transmission line with an impedance of 50 Ohms can be employed for intermodulation 

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