Hi, This email's title is a bit long but it is exactly a question annoying me. I'm trying to find out whether there is a proven relationship between a dielectric material's real part and imaginary part. Imaginary part is dielectric loss tangent. And real part is the dielectric constant. For a material like FR4 or Rogers, their dielectric constants all change over frequency. And their loss tangents are also different. Is there any inner relationship between the value of loss tangent and how the dielectric constant (real part) changes over frequency? Thanks,Neo ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List technical documents are available at: http://www.si-list.net List archives are viewable at: //www.freelists.org/archives/si-list Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu