Thanks Andy, I've got contact with a guy at NIST who works at GHz.
Still, I don't have that value...
I have also the paper in your third link, but obviousely all the values are given in optical field, knowing that the wavelength of GHz is in mm.
Are there someones know about gold's index of refraction in micro-onde, for exemple in frequency 10GHz? Or a book in which I may find the value. Thanks a lot.