test quality of VNA cables
I am doing some testing of S21/S11 with a vna. I am unsure about the quality of the current cables that are being used. Can you explain the best process and what to look for in measuring the quality of a cable for VNA measurements.
I know that the vna equipment is calibrating out some of the errors introduced by a cable, but I am unsure as to when to draw the line on using given cables for measurements.
Based on this information can you give me some test procedures and what to look for in determining if a cable is suitable for use with the VNA? Any links to such procedures?
Thanks.
What you have to look for is their phase and amplitude stability. You can test that by calibrating in SOLT, connecting both cables and mechanically move them. The variation in S21 and S11 is a baseline of what you can expect from your measurements in case your cables move. Good cables have a big mechanical coaxial structure around the microwave cable which prevents mechanical overstress and overbending.
Next you should check whether you can notice any glitches in S21 while moving your cables. If there is a failing outer conductor (cr@ck), it can result in sharp resonances which may vanish as you move them. Because it is hard to find the cause (which cable), you can go further by calibrating the VNA with just one cable and at the instument port. Then you can make a distinction between the performance of both cables.
Hope this helps you out a bit.
Instrumentation cables are an often ignored part of a measurement. To get more than very general responses that do little to help your situation one would need a better description of your measurement goals. Frequency? Which VNA? What are you trying to measure? What accuracy? Any active content? Production or R&D application?
Instrumentation cables often can be priced in the vicinity 0f S5000 each.
Talk to the manufacturer of your VNA and discuss your concerns and solicit suggestions. Then go test the instrumentation. Don't ignore the calibration kits and make sure your connectors are sound and clean. Throw all the adapters away and buy new ones.