Rohde & Schwarz R&S SMU200A, Руководство по обслуживанию

Страница: 50 / 294

R&S SMU200A Test Procedures
1007.9845.82 1.23
E-12
Output Impedance
Test assembly
See section " Test Assembly for Output Impedance (VSWR)" , page 1.5 .
Test method Since the VSWR of a source must be measured, a purely passive
measurement using the VSWR bridge is only possible with levels where
the VSWR is determined by the output impedance of the attenuator only.
This applies to attenuations of more than 20 dB.
With higher levels, the effect of level control must be taken into account.
For this purpose, an auxiliary generator is used which transmits a wave
with a slightly offset carrier frequency (difference frequency within the
control bandwidth of the level control) into the DUT, on which the
outgoing wave of the DUT is superimposed. In the case of an ideal
source impedance, only the outgoing wave of the DUT flows back into the
bridge, in the case of a deviating source impedance, the two components
are superimposed on one another, which, due to the frequency offset,
results in a beat, from the amplitude ratio of which the VSWR can be
derived.
Recommended test frequencies
and levels
Test frequencies: every 50 MHz as from 1 GHz.
Test levels: first the (frequency dependent) switching level of the first
step attenuator has to be determined (see section “
Preparation,
Recommended Test Frequencies and Levels
”). 2.5 dB above is the
first measurement level. Then the first 5 attenuator steps are
measured by reducing the level in steps of 5 dB. This way all possible
output impedances are recorded.
With options R&S B31, -B32, -B36, -B37 the measurement has to be
performed in Attenuator Mode Normal, and an additional
measurement has to be performed in Attenuator Mode High Power at
15 dBm.
For the measurements in Attenuator Mode High Power and at the first
two attenuator steps the procedure for high levels has to be used.
The other measurements are performed following the procedure for
lower levels.