Installation guide

6
How Does It Work? (continued)
E5071C ENA Vector Network
Analyzer
• To perform scalar analysis of a
frequency converter which requires
a VBA application through U2000
Series USB power sensor.
ENA has a frequency offset mode (FOM)
option used to measure the frequency
converter device accurately. The “offset”
of source and receiver port frequency
can be defi ned precisely. The receiver
port can detect the down-converter or
up-converter signal. There are limitations
to using FOM to measure the frequency
converter device. First, the local oscillator
(LO) signal of the device under test (DUT)
has to be known and locked to the source
or receiver port frequency of a network
analyzer. Otherwise, the difference
between predicted intermediate frequency
(IF) signal and actual IF signal is directly
converted to a magnitude error because
of the intermediate frequency bandwidth
(IFBW) fi lter shape implemented in these
network analyzers.
Figure 9 IFBW versus LO frequency drifts with FOM mode
Figure 9 shows the ENA setup in FOM
mode. IFBW is set to 1 kHz, and the 3 dB
BW of the IFBW fi lter is approximately
1kHz. If the actual output frequency of
the DUT has offset as 500 Hz (=BW/2)
from target frequency, the magnitude
result has a 3 dB error. When the output
signal drifts, the measurement results are
also changed at the same time.
You can overcome the limitation of FOM
by using the USB power sensor (with
network analyzer VBA, sample wizard
is available) as a “broadband power
detector” (see fi gure 10). The USB power
sensor is used to measure all power in its
bandwidth, and the measurement result is
stable and not infl uenced by output signal
offset or drift (see Figure 11). For instance,
the USB power sensor provides USB plug-
and-play connectivity and easy setup in
the network analyzer.
Figure 10 USB power sensor (broadband detect) versus LO Frequency drift
E5071C ENA Series Network Analyzer with USB Power Sensor
DUT
Port 1
f2
± Df
f1
U200x Power Sensor
Df does not infl uence the power
meter’s measurement accuracy
f1
RF
Port 2
LO
IF
IF
USB Connection
ADC
f1 – (f2 ± Df)
f1 – f2 + IF
E5071C ENA Series Network Analyzer with Frequency Offset Mode Option
f1
f1
Port 1 Port 2
f1 – f2 + IF
ADC
IFRF
f2
± Df
f1 – (f2 ± Df)
DUT
IF ± Df
When IFBW = 1 kHz, then
3 dB BW = 1 kHz
Df infl uences magnitude accuracy