Hi,

Electrical signals on wires and traces travel at the speed depending on the dielectric constant of the board material. I am wondering how can I perform measurements on the signal propagation speed with a Network Analyzers. I have a network analyzer E5071B. I would like to show the difference in propagation speed with different materials having different dielectric constant.

Thanks a lot.

Best wishes,

kohim

Electrical signals on wires and traces travel at the speed depending on the dielectric constant of the board material. I am wondering how can I perform measurements on the signal propagation speed with a Network Analyzers. I have a network analyzer E5071B. I would like to show the difference in propagation speed with different materials having different dielectric constant.

Thanks a lot.

Best wishes,

kohim

Thank you for your help.

May I have more information about how to config my network analyzer to perform such measurements and what am I going to obtained from the measurements?

Best wishes,

kohim

An even easier thing to do, and not worry about phase wrapping, or converting phase to velocity, is to measure S11 of a cable with the other end open circuited. S11 will look like an open circuit at low frequencies (far right side of Smith Chart), and will extend clockwise along the outer edge of the Smith Chart with increasing frequency. Agilent VNAs have the ability to mathamatically cancel out a length of 50 ohm transmission added to the calibrated test port. This is called "Port Extension". Find the Port Extension adjustment (I think it is under the Cal menu tree), and dial the value until S11 sweep for the open cable looks close to a dot on the right side of the Smith Chart. The adjustment reads directly in seconds. Measuring the length of the cable, you can calculate velocity. You can then use c=1/(sqrt(e*u)) to calculate u.

(edit) I mentioned the S11 with Port Extension because it is a technique I use quite a bit, but I just realized that it can be done with S21 without needing a full calibration. I just went back in the lab to try it. I connected port1 to port2 with a through cable and did a quick "Thru Cal". I inserted a cable that measured 30.6 cm and looked at S21 phase for which I see a sawtooth waveform (constant phase shift versus frequency with phase wrapping). I dialed the port extension until S21 phase was a flat line, at which point it was 1.451nsec. So the velocity in the cable is .306/1.451ns = 2.109e8 m/s. Velocity of em wave in free space is 2.998e8 m/s, therefore the "velocity factor" is 2.109/2.998 = 0.678. Velocity factor is 1/sqrt(dielectric constant), so I calculate the dielectric constant of the material in my cable to be 2.17. My guess is that the dielectric of this cable is polyethylene, so this makes sence.