Can I get away with a $60 dollar N-to-N 1 meter cable from a reputable vendor for use in the scenario below? I have limited practical experience with a new VNA that just has an N connector output and in the past I have gotten the plane of calibration right up to the connector that attaches to the DUT.

Here is the scenario

  • looking for an antenna match S11 around 2500 MHZ, widest bandwidth 80MHz at 2480MHZ
  • Rhode and Schwarz 0-6GHZ open through load calibrator is not assigned any coefficients by Rhode & Schwarz
  • calibration plane is at end of 1 meter N-to-N cable, after which port extension will have to compensate for an N-to-UFL adapter in series with 4 inch UFL to UFL cable.
  • able to provide good short and open at DUT instead of estimating Td for port extension
  • N-to-N cable will be taped so it doesn't flex after calibration.
  • Not really planning on using a torque wrench

The cable should be fine, but if you calibrate at the end of the N-to-N cable and then add a N-to-UFL transition then another UFL-to-UFL coax cable, you'll have a problem with these transitions. If should be able to calibrate to the end of the last UFL connector close to the antenna input, that is more accurate.

You can make a calibration PCB, using same stackup/characteristics of your antenna PCB, or even just adding three terminations at some corner of your antenna PCB. Add three UFL connectors with an open, short and load (50 Ohm) terminations, respectively. Measure S parameters of each termination so that you can calibrate up to the antenna input.

You can create a set of calibration parameters from this SOL (Short, Open, Load) trio and load to the VNA, you'll have to check you VNA manual if and how this can be done for your particular model. OR You can measure the S parameters of the SOL loads, measure the S parameters of your antenna and then apply calibration afterwards in a PC using a script in MATLAB or Python. Check the scikit-rf package for Python, they have a page about calibration, can be very useful: https://scikit-rf.readthedocs.io/en/latest/tutorials/Calibration.html

  • \$\begingroup\$ Thanks. I do have a UFL calibration board from the manufacturer. On one hand, the board is low cost, and it isn't clear whether using port extension or depending on this board to have a 50.000 ohm load is the better choice. On the other hand, it actually has 9 open, short, and load calibrations-one triplet for 3 different PCB stack ups. We pick the stackup closest to the DUT. But you say put some SOL loads on the DUT and measure their S parameters....I cannot do that because the plane of calibration is at the VNA output, not at the point I could measure S params. I will post a figure \$\endgroup\$ – BHS Mar 3 at 22:58

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