changing polarisation through a change in medium

[yefj]

Hello, I have the theory from the books shown below where we can change the polarization of an incident wave.
suppose we have TEM wave where E field is in X direction.
so if n1=1 (vacuum) and n2=sqrt(4) )=2 FR-4
phi=(1-2)*(2*pi*lambda*0.25)/lambda=pi/2
so by this logic after quarter wavelength in FR-4 ,linear polarized wave will have circular polarization?

https://eceweb1.rutgers.edu/~orfanidi/ewa/ch04.pdf

 

[FvM]

The linked textbook excerpt is discussing anisotropic media which is necessary to achieve intended polarisation change. FR4 isn't anisotropic.

 

[yefj]

Hello FVM, in the formulas they did presented n1 and n2, which is prettu isotropic.
Thanks.

 

[albbg]

The linked textbook excerpt is discussing anisotropic media which is necessary to achieve intended polarisation change. FR4 isn't anisotropic.

Not sure FR4 is isotropic; usually is treated so, but in practice should be anisotropic even if the differences of permittivity along X,Y and Z could be almost negligible depending from the frequency.

 

[FvM]

Agreed, but we are talking about noticeable anisotrpy that causes relevant polarisation changes.

 

[yefj]

Hello ,the math doesnt take it into account.The math uses in the calculation isotropic material.
we have n1 and n2 and thats it.
Where did i go wrong?
Thanks.

crystalline materials may have different indices of refraction associated with different crystallographic directions. A common situation with mineral crystals is that there are two distinct indices of refraction, and they are called birefringent materials. If the y- and z- directions are equivalent in terms of the crystalline forces.