I have simulate a broadband antenna in CST MWS 2019. I have done this in both time domain and frequency domain solvers within freq range of 2 GHz to 10 GHz. Comparing these two results, I don't get similarly for 4 GHz to 6 GHz. What is the reason behind this? Which result should be considered between them as the best for my work?
You should at first understand how time domain and frequency domain are related to each other and what the Fourier transform does.
How to do a discrete Fourier transform (FFT) and to plot the amplitude and phase spectrum in MATLAB
https://youtu.be/ZvYGqYOyesk
How to reconstruct a periodic signal as a sum of cosine functions from the freq. spectrum in MATLAB
https://youtu.be/OvyTRxZSolU
Hello,
There is difference in numerical techniques in both methods. The time domain solver in the CST Microwave Studio is based on the finite integration technique (FIT) describing Maxwell's equations on a time-grid space whereas the frequency domain solver is based on the finite element method (FEM).
Thanks,
So far we were talking about numerical approaches. But the question is also valid for measurements..it has been developed in the late 70th as a powerful method using S-parameters (S21 S11) measured in the frequency domain and then transforming into the time domain an taking advantage of certain techniques like time domain gating, this function is now standard on most modern VNAs. The first commercial instrument which had it was the HP8510 in 1983.But it only applicable (a priopri) for linear and time invariant DUTs.
one important point in the numerical analysis is that the time domain approach allows for "non perturbation theory based"approaches i.e. when the current distribution is a function of the resistivity of the material this can be quite important in certain cases. But dealing with sharp and high Q resonances is better in the frequency domain
Time domain is transient analysis with waveform transitions in time, frequency domain is like fft or ac analysis usually - in steady state or reaching steady state.
As an example for 1st order rc low pass filter, at DC you will see the cap charging and discharging, at frequencies below cutoff amplitude of sinusoid stays relatively the same and the it attenuates beyond corner, in frequency domain a spike at the frequency of interest and beyond the corner the spike attenuates, and in ac plot you see a low pass filter line that attenuates at 20db/dec beyond corner.
Note S parameters just like ac analysis is also a function of frequency.
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