IEC 61189-2-721:2015 outlines a way to determine the relative permittivity and loss tangent (also called dielectric constant and dissipation factor) of copper clad laminates at microwave frequencies (from 1,1 GHz to 20 GHz) using a split post dielectric resonator (SPDR). IEC 61189-2-721:2015 is applicable to copper clad laminates and dielectric base materials.