De-embedding S-Parameters in Waveguides for Material Parameter Extraction
One of the vital tasks while computing S-Parameters for material characterization of a sample placed inside the waveguide is to de-embed the S-parameters to the edges of the sample. This can be performed by scaling the S-Parameters appropriately.
Consider a X-band waveguide: a = 22.86 mm & b = 10.16 mm (WR-90) as shown in figure below.
Let a sample of thickness 'd' be placed in the cross section of the waveguide at a distance of '
' as shown in Figure below.
The S-Parameters at the edge of the port are given by
The reference simulation plane should be shifted from the port to the sample edge (as indicated by the red-line in the figure below) such that the effect of the empty waveguide sections are removed and the s-parameters represent just the unknown sample.
The process of de-embedding involves scaling the s-parameters appropriately. To do that, let us consider the standard s-parameter equations as below.
where,
The scaling is performed a follows.
The de-embedded s-parameters can now be used directly for material characterization using standard extraction techniques such as Nicolson-Ross-Weir.
In Feko, one can use the Post Feko scripting or mathematical equations to achieve the de-embedded s-parameters from a full waveguide simulation.