Concepts and features
R&S
®
ZND
209
User Manual 1173.9557.02 ─ 61
blue arrow
= direct signal
red and green arrows = reflected signal
TD S
VSWR
Calculation
The ANSI time-domain method relies on a complex transmission measurement (S
21
)
using a vector network analyzer (VNA).
A time-domain transformation of the frequency domain data shows the impulse
response between the two antennas. Since the direct antenna-to-antenna response is
related to the shortest distance, the earliest impulse is the direct antenna response.
Reflections from the test site are from farther distance away, thus come at later time. It
is therefore possible to separate the direct antenna response S
21, direct
from reflections
S
21, reflected
by using time gating and to calculate
TD
S
VSWR
= (1+r) / (1-r)
,
where r = S
21,reflected
/ S
21,direct
.
Measurement Procedure for ANSI C63.25
See the Rohde & Schwarz Application Card "Fast validation of EMC Test Sites above 1
GHz with Time-domain S
VSWR
", published on the Rohde
&
Schwarz internet site.
4.7.6
Distance-to-fault measurements
Option R&S
ZND-K3
With option K3 "Distance-to-Fault", the R&S
ZND can locate faults and discontinuities
on cables and transmission lines.
Faults produce peaks on the impulse response (in the time domain) that is calculated
from the measured reflection S-parameter trace via inverse Fourier transformation. The
distance between the reference plane and the fault can then be calculated from the
propagation time, accounting for the electrical properties of the transmission line.
Moreover it is possible to define the peaks to be considered as being caused by a fault.
The following example shows the reflection at the end of a faultless open cable con-
nected to test port 2. A full one-port calibration ensures that the distance is measured
from the test port position (reference plane = distance zero). The horizontal position of
marker "M2" corresponds to the cable length of 1417
mm, the additional peak at posi-
tion "M1" is due to a bad connection between the cable and the test port.
Optional extensions and accessories
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