I had intended to start to show some examples of using the NanoVNA in this post, but I think that content is too interesting to be buried under all this basic setup info. POLAR – Same as SMITH, but provides marker readings as a complex number. The marker readings in this format will display the equivalent Resistance and Inductance/Capacitance for marker frequency. SMITH – This is just the LINEAR and PHASE plots combined onto a polar co-ordinate system. PHASE – The relative phase difference between the signal source(always top port for NanoVNA) and received signal. For S11 1 would be 100% power reflected, 0 would be 0% power reflected. LINEAR – Same as LOGMAG, but expresses as a ratio. You can use SWR for S21 measurements, but i’m not really sure why anyone would do so. An antenna SWR of 3:1 would normally be considered good, while better than 2:1 would be excellent. The figure is normally quoted as a ratio I.e 2:1. For S11 measurements and SWR of 1 is a perfect match(zero reflected power). I think this is purely for historic reasons, as LOGMAG or LINEAR are generally more easily understood. SWR – The Standing Wave Ratio, often also called Voltage Standing Wave Ratio(VSWR), is often used for measuring antennas. For S21 measurements this is the INSERTION LOSS in dB. For passive networks it will always be below negative. LOGMAG – For S11 measurements this is the Return Loss and is measured in dB.
I tend to use LOGMAG for transmission measurements(S21) and either LOGMAG or SMITH for S11. The most common use cases will probably be LOGMAG, SWR and SMITH.
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