Vector network analyzer basics
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Vector network analyzer basics
4.1
Introduction
A vector network analyzer is used to measure the performance of circuits or networks such as amplifiers,
filters, attenuators, cables and antennas. It does this by applying a test signal to the network to be tested,
measuring the reflected and transmitted signals and comparing them to the test signal. The vector network
analyzer measures both the magnitude and phase of these signals.
4.2
Structure of the VNA
The VNA consists of a tunable RF source, the output of which is split into two paths. The signal feeds to the
couplers are each measured by their respective reference receivers through power dividers. In the forward
mode, the test signal is passed through a directional coupler or directional bridge before being applied to the
DUT. The directional output of the coupler, which selects only signals reflected from the input of the DUT, is
connected to the Port1 receiver where the signal’s magnitude and phase are measured. The rest of the
signal, the portion that is not reflected from the input, passes through the DUT to the Port2 receiver where its
magnitude and phase are measured. The measurements at the Port1 and Port2 receivers are referenced to
the measurements made by the Ref1 and Ref2 receivers so that any variations due to the source are
removed. The Ref1 and Ref2 receivers also provide a reference for the measurement of phase.
Simplified vector network analyzer block diagram
In reverse mode, the test signal is applied to the output of the DUT, and the Port2 receiver is used to
measure the reflection from the output port of the DUT while the Port1 receiver measures the reverse
transmission through the DUT.
