B-1 Introduction - Anritsu MS2024B Manual

Appendix B — Windowing
B-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 because the spectrum is cut off at a finite
frequency. Windowing reduces the side lobes by smoothing out the sharp transitions at the
beginning and the end of the frequency sweep. As the side lobes are reduced, the main lobe
widens, thereby reducing the resolution.
In situations where a small discontinuity may be close to a large one, side lobe reduction
windowing helps to reveal the discrete discontinuities. If distance resolution is critical, then
reduce the windowing for greater signal resolution.
If strong interfering frequency components are present, but are distant from the frequency of
interest, then use a windowing format with higher side lobes, such as Rectangular Windowing
or Nominal Side Lobe Windowing.
If strong interfering signals are present and are near the frequency of interest, then use a
windowing format with lower side lobes, such as Low Side Lobe Windowing or Minimum Side
Lobe Windowing.
If two or more signals are very near to each other, then spectral resolution is important. In
this case, use Rectangular Windowing for the sharpest main lobe (the best resolution).
If the amplitude accuracy of a single frequency component is more important than the exact
location of the component in a given frequency bin, then choose a windowing format with a
wide main lobe.
If you are examining a single frequency, and if the amplitude accuracy is more important
than the exact frequency, then use Low Side Lobe Windowing or Minimum Side Lobe
Windowing.
Vector Network Analyzer MG PN: 10580-00289 Rev. K B-1