Step Response Versus Impulse Response - Anritsu MS2024B Manual

8-3 VNA Master Implementation Time Domain, Option 2

Step Response versus Impulse Response

The screen capture in Figure 8-4 shows both impulse and step responses of the same Beatty
standard. Step responses may seem more intuitive because they are a representation of
impedance versus distance. A negative reflection off the leading edge of the low-impedance
section of transmission line causes the purple step response to drop down as the step travels
through the low-impedance portions of the Beatty standard. A positive reflection off the
trailing edge of the low-impedance section of transmission line causes the step response to
rise back up. A secondary reflection off the trailing edge eventually brings the step response
back to zero. Secondary reflections can be seen with large impedance mismatches such as the
Beatty standard.
Figure 8-4. Beatty Standard – Impulse and Step Response
Low Pass versus Band Pass
The VNA Master uses two types of processing to transform frequency domain data to time
data (or distance data). Bandpass processing is the standard processing technique that can be
applied to all frequency sweep setups. Only impulse response can be displayed in this mode.
Lowpass processing is a technique that can be used only where frequency content that is
fairly close to DC is available. This technique creates a pure real transform and can produce a
step response in addition to an impulse response. For the same frequency sweep width,
lowpass processing produces time (or distance) resolution that is a factor of 2 better than that
of bandpass processing.
8-6 PN: 10580-00289 Rev. K Vector Network Analyzer MG