Re: Er @ other frequency
For a data signal, it isn't the clock frequency or pulse repitition rate that matters - it is the edge rate. The data in a digital signal is all in the pulse edges. The pulse rate only determines how soon the edges get sent. Rise and fall times determine the true bandwidth of your data.
If you have exceptionally fast pulse edges, you should be using the Er measured at 1GHz or above. However, the variation in Er from 1MHz to 1Ghz probably is going to cause less impact on your controlled impedance than other manufacturing variables. Remember that the fab is only able to etch the trace width to +/- 5-10% accuracy at best. Most fabs will only guarantee controlled impedance to +/- 10%. The roughness of the trace edges, undercutting while etching, and variations in dielectric thickness from weave and lamination pressures and temperatures are all going to affect the finished impedance.
The bottom line is that the 1MHz Er value is probably good enough for the impedance calculations in your application. If the material you are going to use is capable of producing tighter manufacturing tolerances, the material vendor will supply Er values for other frequencies. Your fab should have the data sheet from his material vendor, or should be able to tell you exactly who makes the material he will be using. There's no way for you to calculate the dielectric constant for board material without having your fab make some test coupons and measuring it yourself at different frequencies.
Remember that the frequencies you are interested in for signal integrity are the equivalent frequencies calculated from the rise and fall times of your data pulses - that's the part of the signal you need to protect.