Agilent Spectrum Analysis Basics - Agilent Technologies

Adjacent channel power measurements
TOI, SOI, 1 dB gain compression, and DANL are all classic measures of
spectrum analyzer performance. However, with the tremendous growth of
digital communication systems, other measures of dynamic range have
become increasingly important. For example, adjacent channel power (ACP)
measurements are often done in CDMA-based communication systems to
determine how much signal energy leaks or “spills over” into adjacent or
alternate channels located above and below a carrier. An example ACP
measurement is shown in Figure 6-9.
Figure 6-9. Adjacent channel power measurement using PSA Series
Note the relative amplitude difference between the carrier power and the
adjacent and alternate channels. Up to six channels on either side of the
carrier can be measured at a time.
Typically, we are most interested in the relative difference between the
signal power in the main channel and the signal power in the adjacent or
alternate channel. Depending on the particular communication standard,
these measurements are often described as “adjacent channel power ratio”
(ACPR) or “adjacent channel leakage ratio” (ACLR) tests. Because digitally
modulated signals, as well as the distortion they generate, are very noise-like
in nature, the industry standards typically define a channel bandwidth
over which the signal power is integrated.
In order to accurately measure ACP performance of a device under test
(DUT), such as a power amplifier, the spectrum analyzer must have better
ACP performance than the device being tested. Therefore, spectrum analyzer
ACPR dynamic range has become a key performance measure for digital
communication systems.
82