Re: Properties of FR4
I don't know. Where did you see the term λ0? That does not mean much to me.
Any frequency you choose, from 10 MHz, to 10 GHz, will have a unique wavelength λ for a line on the board. They are all different, and are a function of the frequency and the line type (microstrip, stripline, coplanar, and the various impedances and line widths for each). As we discussed above, if the dielectric contant εr of FR4 is not constant, it is difficult to figure out the wavelength on a transmission line of a particular frequency ahead of time!