Measurement Principles
R&S
®
RT-ZZ80
28
User Manual 1409.7689.02 ─ 02
Application range of transmission line probes
Use the R&S
RT-ZZ80 only for measurements of low-impedance sources,
preferably in 50
Ω
or 75
Ω
impedance controlled environments.
The advantage of transmission line probes is the nearly constant input impedance
over the frequency range, even at very high frequencies. Thus, transmission line
probes are qualified also for measurements of very broadband signals, which
cannot be measured using traditional passive probes.
4.2.2
Input Impedance
The input signal loading caused by the probe is determined by its input impe-
dance Z
in
presents an equivalent circuit model.
Z
in
consists of the following probe-specific parameters.
●
Input resistance R
in
●
Input capacitance C
in
●
Minimum input impedance |Z
min
|
The resulting input impedance versus frequency is indicated in
. The
trace shows three characteristic areas that can be assigned to R
in
, C
in
, and |Z
min
|.
The resulting loading of a step signal at the input of the probe is given in
.
The connection inductance L
con
has only a minor effect on the signal loading and
is therefore not taken into account in the following.
Signal Loading of the Input Signal
