Agilent Technologies FieldFox N9913A User Manual page 61

For all filter shapes T is equal to T , and the filter is the same on both sides of
2 3
the center time.
Minimum gate span is twice the cutoff time. Each gate shape has a minimum
recommended gate span for proper operation. This is a consequence of the finite
cutoff rate of the gate. If you specify a gate span that is smaller than the
minimum span, the response will show the following effects:
 distorted gate shape that has no passband
 distorted shape
 incorrect indications of start and stop times
 may have increased sidelobe levels.
Time Domain - Option 010 61