ADS Envelope Simulator

Hi, I am currently trying to understand how the envelope simulator in ADS works. I have did some simple simulation but can't seem to understand how it works. E.g. from the diagram attached why does the spectrum from the output contains so many component when i only applied a single tone input.

Any help will be greatly appreciated

Thank you
Magneto

[/img]

Hi
Turn off! window parameter "Kaiser" in data display