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Microwave Nicholson Ross Wier question

Microwave Nicholson Ross Wier question

Microwave Nicholson Ross Wier question

Hello all
I’ve synthesized recently different magnetic nanomaterials, and as a trial, i pressed the powder into rectangular shapes and put them inside a rectangular waveguide with similar dimensions to study their electromagnetic properties in the microwave region.
Then using the Nicholson-Ross-Wier method i calculated Epsilon, which should be nearly constant for such systems.
Finally, i calculated the return loss RL using 20*log((Zin-Z0)/(Zin+Z0)) where Zin is Mu and Epsilon dependent and Z0 = 50 ohm
RL should be negative and dipping below -10 dB once with a large bandwidth
Images are available below
The sample dimensions are 2.3x1 cm, and they have a thickness around 2.4 mm. the 2.3 cm side is 0.1 mm to big for the waveguide so it requires some quick polishing, which sometimes leaves a small air gap due to human error
My main question is, what is causing such massive peaks and jumps in the calculated parameters?
It’s either from the setup, the small gap or some hidden error in the matlab NRW code? which after importing the real and imaginary S11 and S21 is:
S11 = s11r + 1i.*s11i;
S21 = s21r + 1i.*s21i;
X = (S11.^2-S21.^2+1)./(2.*S11);
G = X + sqrt(X.^2-1)
G(abs(G)>1) = X(abs(G)>1) - sqrt(X(abs(G)>1).^2-1) %%this is to guarantee that abs(Gamma)<1
T = (S11 + S21 - G)./(1-(S11 + S21).*G);
%% This is 1/Lambda^2
ils = -(1./(2*3.141592*L).*log(1./T)).^2;
%% This is 1/Lambda
il = sqrt(ils)
M = il.*((1+G)./(1-G))./sqrt((1./L0.^2) - (1./Lc.^2));
E = L0.^2./(M).*(1./Lc.^2+ils);
This code worked for the given example in the following pdf's explanation of the NRW method:
Any help is much appreciated

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