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# significance of reflection coefficient phase vs theta plot?

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#### kae_jolie

##### Full Member level 4
What is the significance of reflection coefficient phase vs theta plot? What information does it convey? What would this information be used for?

Correct me if I am wrong, but I think it tells me the difference in angle between the incident and reflected wave over the various angles of incidence, but what do I need this info for? Also, I read it's desirable to have linear phase and constant group delay? Again, why is that? Is it the more linear the phase is, the less noise the system has? Why?

Thank you.

Hello,

First:"A negative reflection coefficient means that the reflected wave receives a 180°, or PI, phase shift".
The phase delay is very important to be compensated otherwise the meassurements will have errors and the results will not be corected.Try to understand that a phase delay will bring noise and shifted signals and this is what we don't need.So if you want to have good results compensate this phase delay.(for ex, i had a RF circuit, with some components, but there was a phase delay so i used a Coplanar Waveguide before introducing the signal in the circuit;something like:signal power-port1-coplanar waveguide-RFcircuit and I measured the S11 coefficient.The results was as expected to be).When I rejected the coplanar , there was a wrong phase shift.
Third, the linear phase is required because in this way the signal will pass through a circuit with no delay.

And yes, if the phase is linear, the best accurate results you get, because the noise is reduced.

Regards

kae_jolie

### kae_jolie

Points: 2
Thanks a lot Manuel. Would a natural logarithm curve be considered linear phase. It plateaus at the top. What would be considered linear phase? How about constant phase? Is constant phase acceptable/ideal?

Hi jolie,

I think a natural logarithm phase is not a linear phase, because the curve is not simetric. In the follow link you have the differences between the linea and non-linear phase : https://en.wikipedia.org/wiki/Linear_phase and the natural log phase seems to be non-linear : https://en.wikipedia.org/wiki/Natural_logarithm .
About the phase constant, i can't give you any sugestion, but I think this reffers to propagation type(see the link) https://en.wikipedia.org/wiki/Propagation_constant#Phase_constant)

Regards

kae_jolie

Points: 2