Characteristics Of Response In Time Domain; Masking - Agilent Technologies ENA Series User Manual

Analysis in Time Domain (Option 010)

Characteristics of response in time domain

Characteristics of response in time domain
This section describes masking and the identification of the mismatch type that are
important for analyzing the response in time domain.

Masking

Masking is a phenomenon in which a mismatch at a location near the calibration surface
affects the response at the next mismatch location. This occurs because energy reflected by
a mismatch at a location nearest to the calibration surface does not reach the next mismatch
location. For example, when you measure the reflection of a cable that has 2 mismatch
locations reflecting 50% of the input voltage, the first mismatch reflects 50% of the
measurement signal. The remaining 50% reaches the next mismatch and its 50%, which is
25% of the entire measurement signal, is reflected. Therefore, in the response in time
domain, the 2nd mismatch looks smaller.
NOTE In this example, the transmission line is assumed to have no loss. However, because there
is loss in fact, the signal is attenuated as the distance from the calibration surface becomes
greater.
Figure 8-11 shows an example of masking due to loss. It compares masking when a short
termination is directly connected to the calibration surface and masking when a 6-dB
attenuator is inserted. In either case, total reflection occurs at the short termination. In the
latter case, the signal is attenuated in both ways, the return loss looks -12 dB.
Figure 8-11 Example of masking
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