One often sees some misconceptions about the relationship between VSWR and impedance. The maths of the relation is explained at Telegrapher’s Equation. The relationship is not trivial and will challenge readers who do not understand complex numbers and exponentials.
Even if you do not have the requisite maths, the following examples may dispel some wooly thinking.
By example
|Z|=50
I have created a SimNEC model to simulate a load Z of specified |Z|, and to sweep the phase of Z from -90 to +90°, and to display VSWR50.
Above is the result where |Z|=50 and for phase of Z from -90 to +90°.
The blue dashed curve is |Z| and the magenta dotted curve is phase of Z.
The blue curve is VSWR, and note that it is 1 when phase of Z = 0°, and NOWHERE else.
There is only one impedance that results in VSWR50=1, it is 50+j0Ω or 50∠0.
|Z|=60
Above is the result where |Z|=60 and for phase of Z from -90 to +90°.
The blue dashed curve is |Z| and the magenta dotted curve is phase of Z.
The blue curve is VSWR, and note that it is a minimum when phase of Z = 0°, and NOWHERE else.
So, talking antenns systems, is knowing |Z| alone of much value?
No, not usually.
To measure / know VSWR of an antenna system is usually much more useful.
If you have a NanoVNA and would like to apply it to antenna measurement, see NanoVNA setup for common antenna system measurement tasks.