The Spectral Background Mask block removes all spurios or any other signal from the spectrum to offer a perfect clean spectrum to measure your DUT within a noisy RF environment.
More information about this block can be found in the SPECTRAN V6 Forum: https://v6-forum.aaronia.de/forum/topic/spectral-background-mask-block/
We have some quite strong LTE signals and want to eliminate those since our DUT will operate within the same frequency band:
After recording and automatic filter mask setup we activate the filter mask and now have a clean noise floor with our DUT signals only: