Agilent Technologies E5070B, User Manual

Page: 343 / 769

Chapter 9 337
Analysis in Time Domain (Option 010)
Transformation to time domain
9.
Analy
sis in T
ime Domain
(O
ption
010
)
Setting the window
Because the E5070B/E5071B transforms data within a finite frequency domain to data in
the time domain, an unnatural change of data at the end points within the frequency domain
occurs. For this reason, the following phenomena occur.
• Width of impulse signal and rise time of step signal
A time width occurs in the impulse signal and a rise time occurs in the step signal.
• Sidelobe
Sidelobes (small peaks around the maximum peak) occur in the impulse signal and the
step signal. Ringing occurs on the trace due to sidelobes, which reduces the dynamic
range.
By using the window function, you can lower the level of sidelobes. However, the width of
the impulse and the rise time of the step become larger as a penalty. You can select from
three types of windows: maximum, normal, and minimum. Table 9-2 shows the relation
between the window and the sidelobe/impulse width.
Table 9-2 Characteristics of windows
Window Sidelobe level of
impulse signal Width of impulse
(50% in low pass
mode
*1
)
Sidelobe level of
step signal Rise time of step
signal (10
−
90%)
Minimum
−
13 dB 0.60/frequency span
−
21 dB 0.45/frequency span
Normal
−
44 dB 0.98/frequency span
−
60 dB 0.99/frequency span
Maximum
−
75 dB 1.39/frequency span
−
70 dB 1.48/frequency span
The window function is available only when the response in the time domain is displayed.
It does not have any effect when the response in frequency domain is displayed. Figure 9-3
shows the effect of the window when measuring the reflection of a short circuit in the time
domain.
Figure 9-3 Effect of window on response from a short circuit in time domain
*1.The value in the band pass mode is twice the value in the low pass mode.