I think you have to use linear values of S11 and S21 in the formula not in dB. Then your answer will be positive.

Abdullah Madni how can i get linear values?

In excel data file all the s- parameter are in dB.

Well, you know the definition of dB, right (if not: https://en.wikipedia.org/wiki/Decibel )? Accordingly you can use the inverse function of the decadic logarithm to obtain the linear values (and you can let Excel do the job... ;-).

Sana Rahim you can use the following online calculator for quick conversion to linear from dB.

http://www.mogami.com/e/cad/db.html

It will give you voltage ratio, power ratio and value in Nepers. Voltage ratio is your linear value. For example -10 dB gives voltage ratio 0.316.

i did the calculation after converting dB into linear but still i am unable to calculate the answer. By using linear values i am getting A=1 and log (1) = 0.

i attached the excel file with detail.

Thomas Mayerhöfer Abdullah Madni

Ok, I have looked through the Excel file. Where do the S22 and S12 values come from? The transmittance is so small that I doubt these values come from measurements. Also, the changes in reflectance are sometimes surprisingly strong. Or is this some kind of metamaterial absorber on a metallic groundplane? In any way, I don't think that in this case it makes sense to distinguish between A and Aeff. In short, mathematically this looks fine to me, but does it make sense physically? Can you provide us with some background information?

You do not understand what dBs are. Don't take the log of dBs. dBs are 10 times the log of the number you want. Divide by ten and then use antilog. Read about it and do examples so you understand. Until you do you won't be able to reliably use dBs and power and will never be able to rely on your own calculations or understand what they mean.

Malcolm White Have you read everything carefully before you put your answer?

You are right Thomas. I didn't examine the excel file. Looking at the excel file shows that Sana is confused between power and amplitude, and has not used brackets when needed in the excel formulae.

In the excel file the dB to linear conversion is incorrect because there are no brackets round the exponent. =10^A/10 doesn't do it right. It should be =10^(A/10). This gives relative power. It should not then be squared.

The use of the term "linear" is often confusing. Perhaps power and amplitude would be better. =10^(A/10) gives relative power. =10^(A/20) would give relative amplitude. The formula with squared terms in it uses amplitude, not power. After the terms are squared they are relative power. Because of this, transmission of -96 dB which should have been 2.5E-10 has been calcu;lated as 1E-96 squared, which is 1E-182. This is too small to make any difference when subtracted from numbers near 1 so give a ratio of 1 next which generates zeros and #NUM on the further columns.

Sana, you need to practice more in excel (learn when brackets are needed), and understand the difference between power and amplitude, and what dB actually mean. dB ALWAYS refer to the power ratio - even when it is amplitude that is talked about. For example the half power point is often plotted in amplitude where it is 0.707, but is still referred to as the 3 dB point. Also watch out for the sign. As in my previous sentence the minus sign is often left out.

The formulae you are using are power conservation formulae, so each term is power. The value A that you are calculating is the proportion of power that is not reflected or transmitted, so is probably absorbed in your component.

It could also have been radiated. It is just missing power that does not appear in the measurements that the VNA made. If your components are surrounded by metal boxes it is probably safe to assume nearly all of it has been absorbed and turned into heat.

Thomas

The data is from an HP vector network analyser - it is the standard format and I recognise the header - I work with these all the time. The data looks like it might be for something using x-band waveguide - it transmits above about 7 GHz, and is cut-off below.

Thomas Mayerhöfer its a polymer composties work as EMI shielding material.

thatwhy tranmittance is too small.

Malcolm White Thanks a lot for your kind response and concern.

Dear Malcolm White sir,

How can I calculate EMI shielding and also how can Calculate |S11| or |S21|?

I measured the S-parameters (S11 and S12) for the EMI shielding

here i uploaded my data file in which S parameters were obtained using VNA.

I read papers on EMI measurement. They provided that: The total EMI shielding effectiveness (SET) depends on the logarithm of the ratio of the incident wave PI to the transmitted wave PT obtained by the equation SET = 10log(PI/PT) dB. The reflection coefficient (R) and transmission coefficient (T) is calculated from the relations R = |S11|2 and T = |S21|2 with the waveguide method, respectively. The value of S11 and S21 can be directly obtained from the vector network analyzer. Meanwhile, the absorption coefficient (A) is obtained from the relation of A = 1−R−T. In addition, SET is the total value from reflection effectiveness (SER) and absorption effectiveness (SEA) given by SET = SER + SEA, SER = − 10log(1−R) dB, and SEA = − 10log(T/(1−R)) dB, respectively. I don't understand how to calculate (R) and (T). I know that R and T should be in the range of 0 - 1. and |S11|, |S21| were extracted from VNA in dB. What is the correlation between R, T, and |S11| and |S21|

The data in your files is magnitude (which is the square root of relative power) and angle.

square it to get relative power. Then you can work out what proportion of the power is reflected, transmitted or is missing.

See https://ibis.org/connector/touchstone_spec11.pdf for a Touchstone file format definition. It took me a while to find out what they meant by magnitude, for sure.

Thank sir

I will try to get my answer