Agilent Technologies E5500A User Manual page 37

Phase Noise Basics
What is Phase Noise?
L(f) is an indirect measurement of noise energy easily related to the RF
power spectrum observed on an RF analyzer.
National Institute Science and Technology (NIST) defines L(f) as the ratio
of the power (at an offset (
modulation sideband is based on a per Hertz of bandwidth spectral density
and or offset frequency in one phase modulation sideband, on a per Hertz of
bandwidth spectral density and
frequency.
power density in one phase modulation sideband
L f ( )
--------------------------------------------------------------------------------------------------------------------------------------- -
=
= single sideband (SSB) phase noise to carrier ration (per Hertz)
L
Figure 4-3 Deriving
L f ( )
is usually presented logarithmically as a spectral density plot of the
phase modulation sidebands in the frequency domain, expressed in dB
relative to the carrier per Hz (dBc/Hz) as shown in
except where noted otherwise, will use the logarithmic form of
S ∆ f f ( )
follows:
4-4 Agilent Technologies E5500 Phase Noise Measurement System
f)
Hertz away from the carrier) The phase
(f)
equals the Fourier frequency or offset
(
total signal power
(f) from a RF Analyzer Display
2f 2 L f ( )
= .
Figure 4-3 shows that the
)
=
Figure 4-4. This chapter,
L f ( )
as
P ssb
----------- -
P s