how can i test phase of the balun in VNA?

[akhilpaulv]

i want to design a marchand balun for my spiral antenna. how can i test phase of the balun in VNA? how know it working properly ??

 

[biff44]

use a 3 port VNA and measure it. Or terminate one output port in 50 ohms and measure half of it, then switch the load and measure the other half on a 2 port vna.

This will work fine just so long as the port VSWR on the balun is very good. If you have a poor VSWR, it will give you some amplitude/phase ripple when measuring over a big bandwidth. If you do have a bad VSWR and want to see pain/phase tracking between the two outputs, maybe use two 6 dB pads at the outputs and then make the measurement.

 

[BigBoss]

Check the phases and amplitudes of S21 and S31.There should be absolute 180 degree between the ports ( it can be in any combination of absolute 180 degree) and the insertion losses must be minimum.( they should practically be equal)

 

[akhilpaulv]

Thank you for your replays. i have attached the balun drawing . i have two port VNA. i connected port1(unbalanced coaxial) and port2(output) as per in the image. i found the impedance of the balun by terminating port2 with 50 ohm but i didnt understand how to measure the phase balance of the balun. i measure the phase at port 2 but where did i get reference phase for taking phase difference??

 

[BigBoss]

View attachment 119995
Thank you for your replays. i have attached the balun drawing . i have two port VNA. i connected port1(unbalanced coaxial) and port2(output) as per in the image. i found the impedance of the balun by terminating port2 with 50 ohm but i didnt understand how to measure the phase balance of the balun. i measure the phase at port 2 but where did i get reference phase for taking phase difference??

If it's 1:1 BalUn, you may connect either an identical balun back-to-back to measure the performance.
Or, you can terminate balanced ports by VNA and 50 Ohm, you can check the Phase only ( because Gain will be reduced )