The effects of radiation losses on the measurement of loss tangent using microstrip ring resonators

Measurement of dielectric properties of copper clad printed circuit boards using microstrip ring resonators is a well-studied problem widely in use. The problem addressed here is different from this as the sample under test is difficult to copper clad. The sample is placed on a ring resonator fabricated on a printed circuit board of known dielectric properties and the properties of the test sample are obtained from the measurement of the resulting multilayer stack. Although the measurement of dielectric constant does not pose problems, the calculation of the loss tangent needs the radiation and conduction losses. Out of the two losses, estimation of radiation loss is a difficult task, firstly because the problem is multi-layer and, secondly because the dielectric properties of one of the layers (test sample) are unknown. As a result it is usually assumed that the radiation losses are negligible. This paper examines the effects of this assumption using accurate electromagnetic simulations.