R&S ZNA67 - Page 243

Concepts and features
R&S
®
ZNA
243User Manual 1178.6462.02 ─ 20
signal (from a local oscillator, LO) is applied to the RF mixer's LO port, resulting in an
output signal at the mixer's Intermediate Frequency (IF) port. For a given RF signal, an
ideal mixer would produce only two IF outputs: one at the frequency sum of the RF and
LO (IF = RF + LO), and another at the frequency difference between the RF and LO (IF
= |RF – LO|). Filtering can be used to select one of these IF outputs and reject the
unwanted one.
Meaning of S-parameters
The frequency-converting property of the mixer (i.e. the fact that incident and transmit-
ted waves are at different frequencies) causes a loss of phase information. While a
scalar measurement is active, the reverse transmission parameter S
12
is unavailable;
the magnitude of the forward transmission parameter S
21
describes the conversion
gain. The conversion gain measurement can be improved by a source match correc-
tion (included in the SMARTerCal) and a load match correction (optional). The phase
information, including the group delay, is meaningless.
The phase or group delay of mixers can be analyzed in a vector mixer measurement.
In the scalar mixer mode the analyzer provides the following functionality:
●
Configuration of the RF and LO signals and measurement of the generated IF sig-
nal.
●
System error correction and power calibration of the signal sources and of the IF
receiver. A SMARTerCal is recommended for this purpose; see Chapter 4.7.3.1,
"Calibration options", on page 235.
●
The mixer mode can be used to test important performance parameters of RF mix-
ers such as frequency ranges, conversion loss, compression, and isolation.
Two-stage mixer measurements
The scalar mixer measurement is also suited for measuring a system of two mixers
with frequency multipliers at their RF and LO inputs. The RF and LO input frequencies
of the first mixer are both multiplied by an integer fraction; the converted output signal
f
int
is fed to the second mixer, together with the multiplied second LO signal. The ana-
lyzer measures the output signal of the second mixer at its IF input port. The general
test setup is shown below; the mixer system under test (MUT) is enclosed in a blue
rectangle.
Optional extensions and accessories