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# Why there's a phase jump of S11 at the resonant frequency

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#### dynaren

##### Newbie level 5
frequency jump phase jump

Hi All,

I have a basic question - what causes the phase jump of S11 from -180 to -180 at the resonant frequency in a resonate structure.
(The resonant structure is equivalent to LC in series. )
In experiment, the jump is less than 180.

Re: Why there's a phase jump of S11 at the resonant frequen

Could you try to repair your question?

what causes the phase jump of S11 from -180 to -180 at the resonant frequency

There is no jump from -180 to -180. (Even if you meant -180 to +180 there is no jump).

In experiment, the jump is less than 180.

Do you mean you are comparing an experiment with some theoretical result/simulation result?

V
Points: 2
Re: Why there's a phase jump of S11 at the resonant frequen

Yes, I am comparing experimental result to CST simulation result.
In simulation result is showing in the picture attached.

V
Points: 2
Re: Why there's a phase jump of S11 at the resonant frequen

What I am trying right now is to derive this phase from Zin.
And Zin = R+jwL+1/iwC
S11 = (Zin-Z0)/(Zin+Z0)
Hope I'm on the right track.

V
Points: 2
in fact, there is no phase jump.
if you add 360deg to the part before the resonant frequency, which can not change phase, you will find the phase is continuous.
the phase is turning anticlockwise in polar coordinates.

V
Points: 2