Agilent Technologies E1420B, User Manual

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50 Agilent E5505A User’s Guide
3
Phase Noise Basics
Where BW (bandwidth is negligible with respect to any changes in versus
the fourier frequency or offset frequency (f).
L(f)
Another useful measure of noise energy is L(f), which is then directly
related to by a simple approximation which has generally negligible error
if the modulation sidebands are such that the total phase deviation are much
less than 1 radian (
∆φ
pk
<< radian).
L(f) is an indirect measurement of noise energy easily related to the RF power
spectrum observed on an RF analyzer.
Figure 16 shows that the National
Institute of Standards 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 15 CW signal sidebands viewed in the frequency domain
S
φ
f
( )
∆φ
2
rms f
( )
BW used to measure
∆φ
rms
--------------------------------------------------------------------------
rad 2
Hz
------------
= =
S
φ
S φ f
( )
L
f
( )
1
2
---
S
∆φ
f
( )
=
e5505a_user_CW_sidebands_freq.ai
rev2 10/20/03
L
f
( )
p ower d ensity in one ph ase modu lation sideban d
( )
to tal signa l power
----------------------------------------------------------------------------------------------------------------------------------------
Pssb
Ps
------------
= =