1
INAF – Institute of Radioastronomy- Bologna – Italy
2
Elettronica s.p.a. – V. Tiburtina Valeria, Rome – Italy
3
University “Tor Vergata” – Electronic Eng. Dept. – Rome - Italy
Reduction of the Uncertainty Reduction of the Uncertainty
on Noise Figure Measurements on Noise Figure Measurements
A. Cremonini
1, M. De Dominicis
2, S. Mariotti
1, E. Limiti
3, A.Serino
3WHY WHY
Reduce Uncertainty?
Reduce Uncertainty?
Uncertainty should be much lower than the value to be measured
3.5E-02
1E-13
5E-07
5E-03
1.E-14 1.E-12 1.E-10 1.E-08 1.E-06 1.E-04 1.E-02 1.E+00
Time Voltage RF Impedance Noise Figure
Absolute Uncertainty +/- 3.5 % = +/- 0.15 dB
For a receiver:
NF = 0.3 +/-0.15 dB
Te = 21 +/- 11 K
• Looking for and Find Sources of Uncertainty (U)
How How
Reduce Uncertainty?
Reduce Uncertainty?
• Analyze and propagate uncertainty
• Minimize the sources wherever it is possible
• Since U(ENR) is dominant, let do calibration of Noise Source with a Secondary Standard (liq. N
2)
• Let Practical operations accurate as possible
Involved Environments Involved Environments
Room Temperature
Room Temperature Cryogenic /on Dewar Cryogenic /on Dewar - easier
- faster
- accurate
- less jitter
- more realistic
- accurate
10.11 0.02 0.077 0.098
2 2 2 20.167
u NF
c dB
Sources (causes) of Uncertainty:
Sources (causes) of Uncertainty:
Propagation, Math Formulation Propagation, Math Formulation
12 1 2
1
1 F F F
G
2 2
2 12 2 2 2
1 12 2
1 1 1
2 2
2 2
2 12 2
1
1 1 1 1 1
1
c
dB dB
F F
u NF u NF u NF
F F G
F F F
u G u ENR
F G F F G
F
12F
2= 10dB F
1= 3 dB
G
1= 15 dB
• Depend on many causes, even Depend on many causes, even U(ENR) U(ENR) Depend on
Depend on U(ENR) U(ENR)
Causes of Uncertainty:
Causes of Uncertainty:
Graphical - Intuitive Graphical - Intuitive
T
eT
cT
hP
cP
hT
eT
cT
hP
cP
hReducing T
c, will reduce U(T
e)
T
eT
cT
hP
cP
hReducing U(T
h) and U(T
c) will reduce U(T
e)
Increasing T
hdon’t reduce U(T
e) , because U(T
h)/T
his a constant
Instead increase T
hmay generate non-linearity . Yopt 2…5
Causes of Uncertainty:
Causes of Uncertainty:
Practical, Tips&Tricks Practical, Tips&Tricks
|S
11 ON| , |S
11 OFF| < - 33 dB Selected Attenuator
PT 100 A Cascade Ferrite Isolators
Environment: Thermostatic room, NO cables movement
Precision Connectors / Connector Care
Type A Uncert. << Type B Uncert.
10 dB
6 dB
Other causes of Uncertainty:
Other causes of Uncertainty:
Approximate Expression T e
1
1 NS DUT 2
1 290 T e
0.1 1.0 10.0 100.0
0 10 20 30 40 50 60 70
R.L. NoiseSource + R.L. DUT [dB ]
+/-
Te [oK ]
NS DUT
Mismatch: A closed form expression doesn’t exist
Liq. N2
77 K POWER METER
800 W
Liq. N2
77 K POWER METER
3200 W
Liq. N2
77 K POWER METER
9400 W
Liq. N2
77 K POWER METER
800 W
Liq. N2
77 K POWER METER
3200 W
Liq. N2
77 K POWER METER
9400 W
Principle of Operation 1/3 Principle of Operation 1/3
Noise Source +
Attenuator
Principle of Operation 2/3 Principle of Operation 2/3
1
Switch Isolators 2
LNA
Receiver
0 1
2
Px
02
01
M0,crio
Noise Source Ta–TH
77 K
7mm-K
M0,x
HP 8971C
HP 8970B
Pad 3dB
Att. Step 1dB Att. Step 10dB Cold Load
IF 20 MHz
Power Meter
PA PA
IF 6 dB
e iso
crio x x
, crio ,
a crio
a
x T
Y Y M
T M T
T
T
1
1
02 0
01 0
Vector Correction
Pictures Pictures
•Coaxial 1-18 GHz
•WR 28
26.5-40 GHz
•WR 22
33-50 GHz
Data Analysis Data Analysis MatLab
MatLab ® ® codes has been used to: codes has been used to:
Process spar of non insertable Adapter Compute Mismatch and Available Gain
Instruments control and automatic data collection
Calculate ENR and associated Uncertainty
Uncertainty of the Result Uncertainty of the Result
21 '
2 2 2
2 2 2
0.0045 1.72 0.74 1.87 K
trans
crio crio Ta crio S crio T
u T u T u T u T
2 2 2 2
2 2 2 2
18.0 1.83 8.68 23.5 30.9 K
hot hot s hot a hot Y hot S
u T u T u T u T u T
Uncertainty of VNA is dominant ( 0.045 dB - hp 8510C )
S par Uncertainty Depend on U(T
cryo)
S par Uncertainty
Results and Results and
Associated Uncertainty Associated Uncertainty
U(ENR) was +/- 0.15 dB U(ENR) = +/- 0.06 dB
Spin-off for the LNAs Spin-off for the LNAs
80 100 120 140
18 20 22 24 26
Frequency [ GHz ] N o is e T em p er at u re [ K ]
Simulation80 100 120 140
18 20 22 24 26
Frequency [ GHz ] N o is e T em p er at u re [ K ]
SimulationCommon U(ENR)
80 100 120 140
18 20 22 24 26
Frequency [ GHz ] N o is e T em p er at u re [ K ]
SimulationCommon U(ENR)Low U(ENR)