How to plot a graph on frequency domain when i don't have any time parameter?

I have plotted a graph in comsoll Frequency vs S11 plot,i need to transform it in frequency domain spectrum.How to do it?

[Walter Roberson]

What input do you have? You have a signal? The distance between adjacent entries in the signal corresponds to how many of what units?

[shahriar sowad]

i Have frequency values in the x axis and S11 values in the y axis,i now want to plot the frequency domain from these values,how do i do it?

[Walter Roberson]

plot(frequency_values, S11)

??

[shahriar sowad]

I was told to use FFT to plot in the frequency domain,i have no idea hopow to do it when i have no time values in the x axis

Answer 1

[Girijashankar Sahoo]

You are calculating return loss parameter with frequency.

Calculate PSD input and PSD of return signal

X(K)=(1/N)*fft(x(n)); PSDX=Pi=abs(X(K)*X(K)')

Y(K)=(1/N)*fft(y(n));PSDY=Pr=abs(Y(K)*Y(K)')

S11= 10log(Pi/Pr)

plot(f,S11)

[shahriar sowad]

i Have frequency values in the x axis and S11 values in the y axis,i now want to plot the frequency domain from these values,how do i do it?