Connection cable length

[OTLabs]

I would like to contribute with data for several antennas and Contribution Guidelines were of great help.

I missed just one more comment/recommendation: how long should be the coaxial cable between antenna and VNA? About 2 wavelengths or longer/shorter?

[rjDipcord]

To answer your question, cable length should have no affect on your measurements by way of wavelength. What matters most is that the coax is as short as possible to avoid losses, and the quality of the coax should be high. I do not advise using the included cables in a NanoVNA unless you need to. Keep in mind, the coax and position of the antenna while testing can significantly affect readings. Most antennas need a ground plane. An example of an antenna that does not need a ground plane would be something like a dipole. I think testing antennas (rubber duckies) directly attached to the VNA without any coax is the best because it provides the closest readings to a real-world situation. The VNA probably has a similar amount of ground plane surface as a meshtastic radio does.
Finally, make sure to re-calibrate your VNA for the frequency band you're using. And if using coax, perform a loss calibration as well, to remove those from your readings.