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Keysight Technologies
Understanding the
Fundamental Principles of
Vector Network Analysis
Application Note
Introduction
Network analysis is the process by which designers and manufacturers
measure the electrical performance of the components and circuits used
in more complex systems. When these systems are conveying signals with
information content, we are most concerned with getting the signal from one
point to another with maximum efficiency and minimum distortion. Vector
network analysis is a method of accurately characterizing such components
by measuring their effect on the amplitude and phase of swept-frequency and
swept-power test signals.
In this application note, the fundamental principles of vector network analysis
will be reviewed. The discussion includes the common parameters that can be
measured, including the concept of scattering parameters (S-parameters). RF fun-
damentals such as transmission lines and the Smith chart will also be reviewed.
Keysight Technologies, Inc. offers a wide range of portable and benchtop vector
network analyzers for characterizing components from DC to 110 GHz. These
instruments are available with a wide range of options to simplify testing in the
field, laboratory, and production environments.
Measurements in Communications Systems
In any communications system, the effect of signal distortion must be consid-
ered. While we generally think of the distortion caused by nonlinear effects
(for example, when intermodulation products are produced from desired carrier
signals), purely linear systems can also introduce signal distortion. Linear
systems can change the time waveform of signals passing through them by
altering the amplitude or phase relationships of the spectral components that
make up the signal.
Let's examine the difference between linear and nonlinear behavior more closely.
Linear devices impose magnitude and phase changes on input signals (Figure 1).
Any sinusoid appearing at the input will also appear at the output, and at the
same frequency. No new signals are created. Both active and passive nonlinear
devices can shift an input signal in frequency or add other frequency components,
such as harmonic and spurious signals. Large input signals can drive normally
linear devices into compression or saturation, causing nonlinear operation.
A
A * Sin 360