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8-3 VNA Master Implementation
8-3
VNA Master Implementation
The Time Domain implementation in the VNA Master is trace based, which makes it very
flexible to use. Each of the four traces in the VNA Master can be configured independently
and can be in the frequency, time, or distance domain. Each trace can also be configured to
represent any of the S-parameters. The VNA Master (as an example) can simultaneously
view S
in the frequency, distance, and time domains using three traces. Alternatively, you
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can view all four of the S-parameters in the distance domain or the time domain or both. This
flexibility could be useful when tuning complex filters or analyzing long cable problems with
multiple discontinuities.
One Way versus Round Trip
With the ability to transform any S-parameter, one question that arises is whether the time
or distance that is plotted represents a one-way or a round-trip propagation. The one-way
propagation represents the transmission (or 2-port) measurement, in which the signal is
transmitted from one port, propagates through the device under test, and is received on the
second port. One-way propagation occurs when transforming S
The round-trip propagation represents a reflection (1-port) measurement, in which the signal
is transmitted from one port, propagates through the device under test, fully reflects at the
end of the device, and is received back at the same port. Round-trip propagation occurs when
transforming S
or S
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For reflection measurements, the VNA Master can handle the two cases of one-way and
round-trip propagation differently in the Time and Distance domains. In the distance domain,
the VNA Master compensates for the round trip reflection propagation by showing the actual
length of the device under test (essentially dividing the distance by 2 for the reflection
measurements). This compensation renders the distance reflection measurement as a
One-Way measurement in terms of the distance value that is reported. In the Time Domain,
you can choose to set the reflection measurement to be either One-Way or Round-Trip (press
the following keys: Shift 8 (System), Application Options, Time Domain, and
Reflection Calc in Time). When set to One Way (which is the default setting), the VNA Master
compensates for the round-trip reflection measurement as it does in the Distance Domain.
When set to Round Trip, the VNA Master plots the response against the actual time that the
signal travels from the transmission port to the receiving port, without accounting for the
2-way propagation (reflection and return).
For example, look at the results of measuring a cable that is 3.05 meters (10 ft) long. For a
transmission measurement, approximately 14.4 ns are taken by a signal when traveling from
one end of the cable to the other end of the cable. For a reflection measurement, the time is
twice as long, or approximately 29 ns are taken by a signal when traveling from one end of
the cable, reflecting from the far end, and returning.
domain response of a cable of this length for both reflection (S
that for this example, the VNA Master Reflection Calc in Time parameter is set to Round Trip.
The top trace of
Figure 8-1
(MK1 at the near end, and MK2 at the far end). You can see that the far end peak at MK2 is
at approximately 29 ns. Looking at the bottom trace, you can see that the peak at MK3 (which
represents the signal received at the end of the cable) is at approximately 14.4 ns.
8-2
.
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is the S
plot showing the reflections from both ends of the cable
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PN: 10580-00289 Rev. K
Time Domain, Option 2
or S
.
21
12
Figure 8-1
shows a measured time
) and transmission (S
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Vector Network Analyzer MG
). Note
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