Excitaiton Signal in CST Time and fourier reprentation

Hey I opened MWS new project without any template. Set units, background material etc. As soon as I define the freq of operation say 0.8 to 1.2 GHz a default excitation signal is generated? In its properties it says its gaussian with Fmin 0.8 Fmax 1.2 GHz. Again after running the simulations I check the 1D Results ->Discrete port-> Voltages It has two signal. One is same signal shown in Excitation signal NT other is frequency representation of that signal which shows a straight line at 1 from 0.8 to 1.2 GHz. But this is not the case. I exported the time domain signal and computed its FFT in MATLAB. Its not the rectangular pulse as given in CST. Can anyone resolve the discrepancy?

Thanks