Agilent Technologies E5070B, User Manual

Page: 346 / 769

340 Chapter 9
Analysis in Time Domain (Option 010)
Transformation to time domain
Effect of the window function on the response resolution
Lowering the sidelobe level with the window function elongates the width of the impulse
signal and the rise time of the step signal. As described in “Effect of frequency sweep
range on response resolution” on page 339, because the response resolution is equal to the
width of the impulse signal and the rise time of the step signal, lowering the sidelobe level
enlarges the response resolution. Table 9-3 shows the relationship between the response
resolution and the window setting.
Table 9-3 Correspondence of window setting and response resolution
Window Low pass step Low pass impulse Band pass
Minimum 0.45/frequency span 0.60/frequency span 1.20/frequency span
Normal 0.99/frequency span 0.98/frequency span 1.95/frequency span
Maximum 1.48/frequency span 1.39/frequency span 2.77/frequency span
Figure 9-6 shows how the response changes as the window shape changes. If the
magnitudes of adjacent peaks are comparable, you need to make the resolution higher; if
they differ significantly, you need to set the window so that smaller peaks with lower
sidelobes appear.
Figure 9-6 Effect of window on response resolution
Effect of the transformation type on the response resolution
Although both transformation types, band pass and low pass impulse, simulate the
response of the impulse signal, the impulse width in the low pass impulse mode is half the
width of that in the band pass mode as shown in Table 9-1. Therefore, the resolution is
better in the low pass mode. If the DUT can be measured in the low pass mode, response
data with better resolution is obtained in the low pass mode.