# The meaning and role of the phase in antenna measurements with VNA

VNA measurements of an antenna return Z, RL, Xs, Rs... and also phase. I usually check Z=50 and Xs=0 to reach the max Return Loss and the lowest SWR 1.0:1, without having care of phase values.

However I noticed that in some cases even if Z and Xs are 50 snd 0 the SWR is high (even 6:1... 10:1) becouse of a particular high value of phase.

What's the best value of phase I have to reach for a perfect matching?

Do I need to have always care of the phase like Z and Xs?

• 'phase' indicates TIME DELAY, in cables or across the air. – analogsystemsrf Oct 28 '18 at 11:09
• The VNA measurement is made directly at the antenna connector, so what does "time delay" mean? What's the best value I need to reach? If the antenna is perfectly "matched" Zo=50 and Xs=0 why the SWR is high? – Kevin White Oct 28 '18 at 12:30

## 1 Answer

VNA measurement results are just complex numbers. Complex numbers can be expressed in either "magnitude (Z) + phase (P)" or "resistance (Rs) + reactance (Xs)".

You don't want to mix these complementary notations of complex numbers. So Z=50 and Xs=0 is not what you are looking for.

For SWR=1 with a load of Rl=50 Ohms you need Z=50,P=0 or Rs=50,Xs=0, which is the same.

• Thanks Stefan Wysss, so when I want to adjust an antenna for the perfect match and for the max power transfer it's sufficient I reach i.e. Z=50 and P=0 that automatically means Xs=0? The complex number I consider(ed) necessary and sufficient is (Z,Xs) without giving importance to phase (that automatically reach the optimum value). – Kevin White Oct 28 '18 at 13:35
• No, Z=50 and Xs=0 is not sufficient. Let's make an example: You try to match an antenna impedance of ZL=50 Ohms with some matching elements and your VNA displays an impedance of Zm=-50 Ohms which is Z=50,P=pi or Rs=-50,Xs=0. So you have Z=50,Xs=0 but the matching is not correct because it has P=pi or Rs=-50. – Stefan Wyss Oct 28 '18 at 14:09