Measurement of reflection coefficient (s11) without network analyzer

[Rahulkishor]

Hello all,

I am in need of a way to measure the reflection coefficient - S11 of a one port SAW (surface acoustic wave) device without using a network analyzer (cos the one we are having is send out for repair). If someone is aware of any method , please help me!!!!!


Thanks in advance!
Rahul Kishor

 

[BigBoss]

A directional coupler and power meter+signal generator can help you but the accuracy will not be satisfying and you will not able to measure the phase of S11..
I think you should wait for your VNA..

 

[G0HZU]

I suppose you could make/borrow a dual directional coupler and use a modern two channel digital scope and a signal generator (with low harmonic content) if the SAW frequency is within the range of the scope.

If you have access to a decent two channel digital scope you could use the scope maths functions to help you measure the phase. So you get amplitude AND relative phase with this method.
Note that you have to connect to the scope with equal length coax cables from the FWD and REV ports on the coupler and also you set the scope to a 50R input termination on each channel.

You could do it manually in maybe 50 frequency steps. It would probably take a couple of hours to do it and plot the results. The results wouldn't be as good as a VNA but if the coupler has high directivity and a flat response then it would give useful data (a lot better than nothing anyway )

 

[FvM]

Before VNA and RF pahse measuring devices have been available, engineers used slotted transmision lines to determine S11 from observed standing waves. The method is still available and doesn't require other instruments than a generator and a level meter.