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how does NA realize the frequency to time transfermation

Question asked by fuchen on Feb 22, 2012
Latest reply on Feb 22, 2012 by fuchen
From Fourier transformation and Nyquist principle, assuming that the signal bandwidth is Bw and the number of sampling points is N, so in the time domain, the time interval Δt should be 1/Bw , while the time range is supposed to be N*1/Bw.

However, when we used the Network Analyzer with setting the stop frequency fs, end frequency fe and points number N, we got the frequency domain response (S11).
Here, fs = 390MHz, fe=440MHz, N=801. SoΔt should be 2E-8 s.
Then we transfered to time domain as was show in other figure, and set the start time ts = 0, end time te = 7E-6s. Strangely, we found there were 801 points in the arrange [ts, te] andΔt was 7E-6/801=0.87E-8 s. It violated the Fourier principle. Why?  

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