Make network windowing centered on 0 Hz
Make network windowing centered on 0 Hz

Windowing function should be symmetric about 0 Hz.
Negative frequencies are not included, so cut out the negative
part of the window.

scikit-rf/scikit-rf,Ttl/scikit-rf,temmeand/scikit-rf,temmeand/scikit-rf,Ttl/scikit-rf,jhillairet/scikit-rf,temmeand/scikit-rf,scikit-rf/scikit-rf,jhillairet/scikit-rf,Ttl/scikit-rf,Ttl/scikit-rf,jhillairet/scikit-rf