Measurement of Noise Figure of Quasi-optical power combiner

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Measurement of Noise Figure of Quasi-optical
power combiner
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Spatial Power Combiner System
Features

• N-way power divider
• N-way power combiner
• High gain MMIC

MMIC Gain-G1 Noise Figure- NF1
Vout
V1out
Low reflection matching
Vin
V1in
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Power Combiner simple model
Single MMIC
(G1)
V1in
V1out
Low reflection Matching
Low reflection Matching
50?
50?
N50?
N50?
N
Single MMIC
(G1)
VNin
VNout
Low reflection Matching
Low reflection Matching
R50 ?
N50?
50?
50?
N50?
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Theoretical Analysis

• Vin V1in Vnin
• PinN P1in ... N PNin
• Vout V1out Vnout
• PoutN P1out ... N PNout
• The total Gain Gt is the same as G1

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Noise Figure of power combiner
Added Noise by MMIC Nadd
Singal MMIC
(G1, NF1)
Nadd
V1in
V1out
(G1, NF1)
Low reflection Matching
Low reflection Matching
Power Combiner
50?
50?
N50?
N50?
N
Nadd
VNin
VNout
(G1, NF1)
Low reflection Matching
Low reflection Matching
N50?
50?
50?
N50?
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Why they are the same?

• The reason is that the combining of irrelevant N
  channel noise is the same as one channel.
• That is NaddNaddt

Notice The power combiner is not a linear
amplitude summing network, but works as a spatial
power summing system.
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How the noise is added?

• The noise is evaluated with covariance.
• The covariance of the sum of N irrelevant
  variables are N times covariance of each variable.

Vn1out
NR
Vnout
N
R
VnNout
NR
Considering only the added noise by MMICs The
added noise by MMICs of power combiner is the
same as the added noise of single MMIC.
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Real System Noise Figure
Ideal Power Combiner
(G1, NF1)
Nadd
Insertion Loss L1
Real Power Combiner
V1in
V1out
(G1, NF1)
Low reflection Matching
Low reflection Matching
50?
50?
N50?
N50?
N
Nadd
Insertion Loss L1
VNin
VNout
(G1, NF1)
Low reflection Matching
Low reflection Matching
N50?
50?
50?
N50?
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Measurement System
Noise Figure Meter-8970B
Noise Source Driver
CW Generator-8673G Output power-8dBm
Noise Source - 346C
Noise Input
LO Signal Input
Test Set-8971B Working ModeSSB3 From
4-18GHz Down Convert to 450MHz Single Side Band
Noise
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Single MMIC Measurement
Biase For MMIC
Microstrip Probe
Noise Output
Noise Input
MMIC
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Power Combiner Measurement
Bias For MMICs
Noise Source Driver Input
Noise Input
Noise Source
Noise Output
Power Combiner
Heat Sink
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Measurement Theory
Output Noise Power No

• The Noise Figure Meter output noise at two
  different noise temperature
• Get the G and Na from the measurement
• Calibrate to eliminate the affect of the loss of
  the cable and connectors

N2
N1
Na
Noise Temperature-T
T1
T2
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Measurement Result _at_Vd7V
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Measurement Result Plot _at_Vd7V
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Measurement Result Plot _at_Vd6V
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Measurement Result Plot _at_Vd5V
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Summary

• The measurement result show that the Noise Figure
  of Power Combiner is the same as one single MMIC.