Hi, I am self teaching myself how to use our VNA at school as I think it would be an important tool to learn in the real world. I have access to a 8722 VNA and a E8364B PNA and I want to find the characterisitic impedance, phase velocity, then use that to find the dielectric constant of a microstrip (up to 40GHz). I am looking for a sort of cook book method (step by step) if you will, on how to do these measurements. I have looked through the instruction manual but I didn't really get much out of how to actually find these parameters. Thank you.

> So after talking with some of my professors, it seems that using the s-parameters would actually be the better way to go with the VNAs. The S11 parameter actually shows what the characteristic impedance is, then I can use the S11 and S21 parameters to derive the dielectric constant. Does anyone know of a good source that shows how to do this?

I'm no expert on this - I have never done it myself.

However, I think your idea of using the time-domain options are best. You are going to have some discontinuity between the RF connector on your PCB (probably SMA) and the microstrip. Likewise at the end of the microstrip there is going to be some discontinutiy to whatever the line is terminated in. I think the way to do this is probably

* Use transform menu to look at the time domain.

* Put a gate around the middle of the microstrip, so the effect of the connectors is removed.

* Transform back to the frequency domain to look at the impedance etc of just the microstrip, without the discontinuty of the PCB/connector interface being evident.

There is a whole chapter in this book on the TDR functionality in this book, as well as another chapter on measuring passive devices. There will be the information you need in that book.

http://www.amazon.com/Handbook-Microwave-Component-Measurements-Techniques/dp/1119979552/

Edited by: drkirkby on Apr 30, 2013 3:27 PM

HP AN-380 and HP AN-? (this one dont have an no) explains several approaches to measuring ɛ.

As far as I remember there are 2 common metods for measuring ɛ, the capacitance method and resonance method.

By using the capacitance method, you should be able to come close to what the board is rated for (fringe capactiances are limiting), while the resonance method would not require vector analyzer and can be done with scalar tools like an spectrum analyzer.

The math for the resonance method can be a bit hairy, if you have taken electromagetics, you should know the equation for an cavity resonator. The PCB is treated as an re

For those measurment, I would reccomend you to start with an board with an known ɛ and work backwards. FR4 and such inexpencive laminates have ɛ that vary both between the manufacturers and from sheet to sheet, so get your procedure in place before you tackle those. You should try to get some samples from the local distributor of microwave laminates and do some experiments. This should make you more valuable to an employer, as you have actual experience doing microwave and RF measurements.

+ L. S. Napoli and J. J. Hughes, “A Simple Technique for the Accurate Determination of

the Microwave Dielectric Constant for Microwave Integrated-Circuit Substrates”, IEEE

Transactions on Microwave Theory and Techniques, July, 1971. +

and:

+ Howell, “A Quick Accurate Method to Measure the Dielectric Constant of Microwave

Integrated-Circuit Substrates”, IEEE Transactions on Microwave Theory and Techniques,

March, 1973 +

Your school library may be able to help you with those articles.

BR.

Thomas.

Edited by: ThomasSK on May 11, 2013 11:33 AM