MS20xxA VNA Master UG 10580-00166 Rev. C C-1
Appendix C — Windowing
C-1 Introduction
The theoretical requirement for inverse FFT is for the data to extend from zero frequency to
infinity. Side lobes appear around a discontinuity due to the fact that the spectrum is cut off
at a finite frequency. Windowing reduces the side lobes by smoothing out the sharp
transi-tions at the beginning and at the end of the frequency sweep. As the side lobes are
reduced the main lobe widens thereby reducing the resolution.
In situations where there may be a small discontinuity close to a large one, side lobe
reduc-tion windowing should be used. When distance resolution is critical windowing can be
reduced.
C-2 Windowing Examples
The types of windowing in order of increasing side lobe reduction are: rectangular, nominal
side lobe, low side lobe, and minimum side lobe. Figures C-1 through C-4 show examples of
the types of windowing.
Figure C-1. Rectangular Windowing Example
10580-00166C.book Page 1 Thursday, February 21, 2008 12:52 PM
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