What is BS EN 61189-2-721 - Relative permittivity and loss tangent about?   
BS EN 61189-2-721 is an international standard that covers test methods for electrical materials. A printed circuit board (PCB) is a laminated sandwich structure of conductive and insulating layers.  printed boards, and other interconnection structures and assemblies.  The main objective of the BS EN 61189 series is to demonstrate the reliability of laminate materials and assemblies and avoid printed circuit board failures.  
BS EN 61189-2-721 outlines a way to determine the relative permittivity ( ε r) and loss tangent (tanδ ) (also called dielectric constant (DK) and dissipation factor (Df)) of copper-clad laminates at microwave frequencies (from 1,1 GHz to 20 GHz) using a split post dielectric resonator (SPDR).
BS EN 61189-2-721 is applicable to copper-clad laminates and dielectric base materials.
Who is BS EN 61189-2-721 - Relative permittivity and loss tangent for?  
BS EN 61189-2-721 on Relative permittivity and loss tangent is useful for:  
- Manufacturers of electronic devices   
- Manufacturers of printed circuits and boards   
- Quality testing agencies  
- Electronics industry  
- Electronic engineers  
Why should you use BS EN 61189-2-721 - Relative permittivity and loss tangent?   
Relative permittivity is essential information to have when building capacitors and other  materials that are expected to introduce capacitance into a circuit.  Relative permittivity and loss tangent are detailed in BS EN 61189-2-721 to evaluate signal attenuation and to ensure that all-important information is recorded over the appropriate frequency range to accurately capture the magnitude of the resonances' peaks.  
With the help of BS EN 61189-2-721, you can find the frequency, measurement point, averaging number, and smoothing level, as well as increase the signal-to-noise ratio. Also, helps you with variable temperature tests, verifies the test system regularly with a standard reference sample.
Overall, BS EN 61189-2-721 will assist you in providing an alternative method for quantifying the effect of loss on an electromagnetic field within a material. These are required while constructing capacitors. Using BS EN 61189-2-721 you can demonstrate the reliability of laminate materials and assemblies and avoid printed circuit board failures.
