AbstractIn this paper, we present a new model to determine the dielectric constant and the loss tangent of dielectric material in the sheet/slab form, with both low and high relative permittivity. A non‐destructive testing method is used, based on the microstrip patch and line resonators. This method provides consistently accurate results, as compared to the nominal value of data given by the manufactures. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 36: 483–486, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10797