Phase difference between 2 Transmission Lines

Hi,

I would like to measure the delay difference between 2 TLIN, see attached.

I try to measure each TLIN with VNA but because the VNA phase measurement lmit to +/-180 degrees, i do not which math operation i need to do between the numbers.

Please advice.

a network analyzer does not actually measure time delay. It instead measures Δ θ / Δ F = "group delay".

So you would measure phase at F1=1000 MHz in radians. You would then shift frequency to F2=1010 MHz, and measure phase again in radians. then compute group delay. Typically you keep measuring over a wider frequency range, average the answers, and that is your group delay.


Scope this out:
http://www.eng-tips.com/viewthread.cfm?qid=328069

Hi,

I want to measure the phase difference between the 2 transmission lines as describe in the figure.

But the Network Anlyzer phase measurement limit to +/-180 degrees.

Any ideas how to do it ?

Thanks

Yes, he does right according to the definition of phase which periodical with n*360 degrees.

Biff44 did show you how to determine the actual time delay with a VNA. It's quite easy because can can expect an almost frequency independent delay.

Hi FvM,

But i need to measure the phase difference between the transmission line - not the group delay.

Thanks,

Doron

The VNA does measure the phase difference. You can e.g. calibrate the VNA for TLIN1 and measure TLIN2. If you select a sufficient wide frequency range (e.g. 1 MHz to 3 GHz), the displayed phase starts at about 0° and will jump back to -180° when exceeding +180°. You may want to extrapolate the measured value by adding n*360 degree at each jump.

Good Idea !

I will check

One way you could do it on an old/basic VNA (i.e one without group delay capability) would be to extract s parameter data into a PC for both cases across a wide frequency range and then post process the data in the PC to predict (or reverse engineer) the total delay time for each microstrip line based on the data across frequency. i.e. you should be able to reverse engineer the time delay in terms of phase = N*360 degrees +C at any given frequency.

Not a perfect answer but it would work fairly well for something simple like comparing two microstrip transmission lines on an old VNA that has limited capability.

Hi,

OK, I measure the phase difference at frequency 4.28GHz and receive -153.8 degree ,there is 1 jump in the VNA so the total phase shift is: 360 x 1 -153.8 = 206.2 degree. (Thanks to FvM & Gohzu).

Now i will calculate the Er effective and i receive Er effective = 3.97.

I see that as the frequency increase the Er effective decrease.

Is there and idea how to calculate the Er (Not the Er effective) ?

Thanks !

so you did not write this?