# Delta phase meassurement of long cable/waveguide

Question asked by jacegu on Oct 20, 2016
Latest reply on Oct 30, 2016 by drkirkby

Dear All,

I’m finding some difficulties in a phase meassurement with an Agilent E5071C Network Analyzer at 3 GHz, SPAN 0 Hz and a slow sweep. I hope you can give me some advise about how to procced.

I want to meassure the Delta Phase between 3 different propagation paths. Please take a look of the diagram attached. The objetive is to check the diferent phases in one side of the installation when in the other side the same signal is injected. The installation contains one coaxial cable (CX) and two waveguides (WGA and WGB).

My first approach was to meassure individually the phase of each path with the help of an auxiliar cable (switching from one to the other), and then just make the numbers:

Delta Phase CX_WGA = [Phase CX] – [Phase WGA] = Phase [A_B_C1_D1] - Phase [A_B_C2_D2]

Delta Phase CX_WGB = [Phase CX] – [Phase WGB] = Phase [A_B_C1_D1] - Phase [A_B_C3_D3]

Delta Phase WGA_WGB = [Phase WGA] – [Phase WGB] = Phase [A_B_C2_D2] - Phase [A_B_C3_D3]

But I found that for each single phase measurament ([Phase CX], [Phase WGA] and [Phase WGB]) I can see a big phase drift over the time. Like I’m not able to do a quick switch between the paths, I’m afraid my Delta Phase calculation is impacted for this phase drift.

So now some questions:

1.- Where is coming this phase drift over the time? In short cables I’m not seeing this effect, but in this meassurement of a long installation (about 80 m with the auxiliar cable) the phase drift I saw can go until 15 degress per hour. Is there any indicated configuration to delete or at least mitigate this effect?

2.- My network analyzer only has 2 ports… Is there any other better option to make this Delta Phase meassurement? Maybe with an external signal generator?

Please let me know if you need some more details by my side.

Thanks a lot for your time.

Best regards,

Javier