User`s guide

4-4 Agilent Technologies E5500 Phase Noise Measurement System
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. Figure 4-3 shows that the
National Institute Science and Technology (NIST) defines L(f) as the ratio
of the power (at an offset (
f) Hertz away from the carrier) The phase
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
(f) equals the Fourier frequency or offset
frequency.
= single sideband (SSB) phase noise to carrier ration (per Hertz)
Figure 4-3 Deriving
L(f) from a RF Analyzer Display
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 Figure 4-4. This chapter,
except where noted otherwise, will use the logarithmic form of as
follows: .
L f
()
power density in one phase modulation sideband
()
total signal power
----------------------------------------------------------------------------------------------------------------------------------------
P
ssb
P
s
------------
==
Lf()
L f()
S
∆ f
f() 2f
2
L f()=