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Relative phase and Phase shift

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rsx4729

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Hi all,

I am studying about phase shifter. Some papers presented the "phase shift" versus frequency, some other papers showed the graphs "Relative phase" versus frequency. What is the different between "phase shift" and "Relative phase"? Or they are similar?

Thank in advanced.
 

Absolute phase refers to the phase of a waveform relative to some standard (strictly speaking, phase is always relative). To the extent that this standard is accepted by all parties, one can speak of an absolute phase in a particular field of application.

Relative phase is defined as the relative timing difference between two spike trains normalized by the associated interspike interval of one cell. This phase measurement is intended to reveal the relative timing relationship between spike trains at different firing rates.
 
yep, what he said.

the difference is, when you sweep frequency over a band and it is set at "zero degrees", is the ang[S21] a constant, or a moving number (i.e. an increasing ramp of phase vs frequency).
 
ahmed saad said:
Absolute phase refers to the phase of a waveform relative to some standard (strictly speaking, phase is always relative). To the extent that this standard is accepted by all parties, one can speak of an absolute phase in a particular field of application.

Relative phase is defined as the relative timing difference between two spike trains normalized by the associated interspike interval of one cell. This phase measurement is intended to reveal the relative timing relationship between spike trains at different firing rates.
Click to expand...

biff44 said:
yep, what he said.

the difference is, when you sweep frequency over a band and it is set at "zero degrees", is the ang[S21] a constant, or a moving number (i.e. an increasing ramp of phase vs frequency).
Click to expand...

Assume I have a phase shifter as a two port network. I simulate the S-parameter by ADS, then plot the phase(S21). I think that is "phase shift", isn't it? If I am correct, in what case of simulation I can get the "relative phase"?
 

S21 phase is depending on reference planes, which can be set arbitrarily in a real measurement or a simulation.

To consider a simple case, you are simulating a transmission line coupler with some electrical length. You could e.g. substract a delay according to this length when displaying S21 phase, achieving a "relative phase".
 
biff44 said:
yep, what he said.

the difference is, when you sweep frequency over a band and it is set at "zero degrees", is the ang[S21] a constant, or a moving number (i.e. an increasing ramp of phase vs frequency).
Click to expand...

FvM said:
S21 phase is depending on reference planes, which can be set arbitrarily in a real measurement or a simulation.

To consider a simple case, you are simulating a transmission line coupler with some electrical length. You could e.g. substract a delay according to this length when displaying S21 phase, achieving a "relative phase".
Click to expand...

Hi biff and FvM,

I think I may misunderstand what you explained in the previous reply. Hence I asked this question: I simulated a quadrature wavelength transmission line at 2 GHz. The phase(S21) in the attached image is "phase shift", isn't it? Otherwise, if the graph shows Phase(S21) is constant, that is "relative phase"??

Thank you so much!

Phase shift.jpg
 

Yes, a λ/4 transmission line it will shift the phase by 90 degrees (faithfully).
 

vfone said:
Yes, a λ/4 transmission line it will shift the phase by 90 degrees (faithfully).
Click to expand...

Hi vfone,

I agree that λ/4 transmission line it will shift the phase by 90 degrees. But I am confused that figure is "phase shift" graph or "relative phase" graph?
 

As was stated above by other posters, all the "phase shifts" are related to a relative/initial phase.
 
So, the figure (which I had attached above) shows the relative phase between output and input. And y-axis should be named as "Relative phase"?
 

As vfone stated, phase is always relative. In so far, "relative phase" could be considered as pleonasm.

In case of the λ/4 transmission line, phase shift is like a length, in can be unequivocally assigned to a piece of cable if the operation frequency is fixed. Talking of relative phase seems inappropriate then.

I don't see a clear distinction between phase and relative phase, I would emphasize the relative nature if a phase measurement is normalized by an arbitrary time delay which is different from the actual propagation delay.
 
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