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Well I suppose that since in FDTD you know the used frequencies then you know the wavelength range. For example you may know that λ is between 1 and 5 mm hence you know the propagation constant for each frequency (I believe every freq has its own β)...However let me check it out and I'll come back to you ASAP
Added after 13 minutes:
Well according to Pozar there may be another way...
The formula for the resistance of a material is given by this :
η=sqrt(μ/ε)=ωμ/β
where μ is the permeability of the material and ε the permittivity. Of course ω is ω=2πf.
Hence you can easily calculate β for any media like this.
Of course the propagation constant is different for every frequency and every different material.
So in FDTD you'll have a diffrent β for vacuum and different for other materials for any frequency...
Lastly you can calculate η and therefore β using field values like this:
η=Ex/Hy or two filed components perpendicular to each other.
However I strongly suggest finding β for every material using the first formula since you'll have to do it once for every frequency and you won't have any error due to FDTD inaccuracies...
Hope it helps...If you need any help plz ask...
(PS. Thnx for the helped me. Glad to see there is some recognition)
but some dispersive materials like ferrites, the wave lenght change when the field pass this materials, then we don't can calculate the beta from the classical formulas, and we must use the numerical solution.
Well after questioning a professor the answer was:
"You don't calculate the propagation constant from the S parameters. You calculate the ABCD prameters from the S ones and then using those and by employing phase unwrapping you can calculate the propagation constant"
Up to the ABCD part things are easy since you use standard formulas...
Beyond that, it is beyond me. I don't know much on this but if I find out more I'll inform you...
edit: you need to calculate the transfer (ABCD) matrix from matrix. for 2 port networks this is easy using formulae from books. for more ports, you can still find a formula of conversion.
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