Functional Groups Of The Network Analyzer - Keysight N5221A Service Manual

Theory of Operation
Network Analyzer System Operation
Figure 5-2 2-Port System Simplified Block Diagram

Functional Groups of the Network Analyzer

The operation of the network analyzer can be separated into major functional groups. Each group consists of
assemblies that perform a distinct function in the instrument. Some of the assemblies are related to more
than one group, and all of the groups, to some extent, are interrelated and affect each other's performance.
The major functional groups are:
• Synthesized Source Group
• Signal Separation Group
• Receiver Group
• Digital Processor and Digital Control Group
• Power Supply Group
Synthesized Source Group
The built-in synthesized source generates a swept, stepped, or continuous wave (CW) signal in the
frequency ranges as listed in
incident signals. The LO signal and the four incident signals are offset in frequency by the receiver IF of
7.438 MHz (at tuned frequencies below 53 MHz the IF and the offset is 0.826 MHz).
The LO signal is sent directly to the mixers in the receiver group. The incident signals are routed to the front
panel test ports and then to the device under test (DUT) as the test signal. A portion of each incident signal
is coupled off (in the signal separation group) and sent to the mixers in the receiver group as reference
signals. These reference signals are compared (mixed) with the LO signal in the receiver group to produce
the 7.438 MHz (or 0.826 MHz at frequencies below 53 MHz) IF signal.
The incident signal output power is leveled by an internal automatic leveling control (ALC) circuit. The
maximum output power level of the network analyzer at the test ports can be found in the Data Sheet and
5-4
Table 5-1. The source group provides five signals: an LO signal and four
PNA Series Microwave Network Analyzers
Service Guide N5222-90001
N5221A/22A