noise coupling in focal plane arrays jacki van der merwe msceng stellenbosch university
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Noise Coupling in Focal Noise Coupling in Focal Plane ArraysPlane Arrays
Jacki van der MerweJacki van der Merwe
MScEngMScEng
Stellenbosch UniversityStellenbosch University
OutlineOutline
Focal Plane ArraysFocal Plane Arrays Receiver NoiseReceiver Noise Low Noise AmplifiersLow Noise Amplifiers Introduction to Noise CouplingIntroduction to Noise Coupling Calculating Noise CouplingCalculating Noise Coupling Active Noise Figure and Noise Active Noise Figure and Noise
TemperatureTemperature ExamplesExamples
Focal Plane ArraysFocal Plane Arrays Large, dense phased Large, dense phased
arrays of antennasarrays of antennas
Placed in focal plane of Placed in focal plane of reflectorreflector
In theory, any number of In theory, any number of beams can be formedbeams can be formed
Enables complete Enables complete collection of the entire collection of the entire electric field in the focal electric field in the focal plane of the reflectorplane of the reflector
Because they are densely Because they are densely packed, there exists a high packed, there exists a high level of mutual coupling level of mutual coupling between the elementbetween the element
Receiver NoiseReceiver Noise
Noise Temperature Noise Temperature and Gain of the and Gain of the first element have first element have the greatest effect the greatest effect on overall noise on overall noise temperature of the temperature of the systemsystem
Usually Low Noise Usually Low Noise Amplifier (LNA)Amplifier (LNA)
Low Noise Amplifiers (LNA)Low Noise Amplifiers (LNA)
Designed to add very Designed to add very little noise to systemlittle noise to system
Very Little ≠ NoneVery Little ≠ None
Most of the noise Most of the noise travel toward the loadtravel toward the load
A small portion travels A small portion travels back toward the back toward the antenna and is antenna and is radiatedradiated
Noise CouplingNoise Coupling
Noise signals from Noise signals from LNA travel towards LNA travel towards antennas and are antennas and are radiatedradiated
Radiated noise are Radiated noise are received by other received by other elements and elements and amplifiedamplified
This is referred to This is referred to as as Noise CouplingNoise Coupling
Calculating Noise CouplingCalculating Noise Coupling
Represent coupled, noisy network as Represent coupled, noisy network as equivalent circuit diagramequivalent circuit diagram
Direction of noise coupling
LNA Noise ModelLNA Noise Model Optimum Source Optimum Source
Admittance (YAdmittance (Yss=Y=Ymm))
• Specific source admittance Specific source admittance allowing for optimum allowing for optimum noise matchnoise match
Minimum noise Figure (FMinimum noise Figure (Fm m ))
• Noise Figure resulting Noise Figure resulting from optimum noise from optimum noise matchmatch
Equivalent Noise Equivalent Noise Resistance (RResistance (Rnn))
• Representation in Ohm of Representation in Ohm of the spectral density of a the spectral density of a noise-voltage generatornoise-voltage generator
Coupled AntennasCoupled Antennas
2 Coupled Antennas 2 Coupled Antennas at a timeat a time
All elements are All elements are identical, only identical, only coupling terms coupling terms differdiffer
Use superposition Use superposition to calculate total to calculate total couplingcoupling
Calculating Noise CouplingCalculating Noise Coupling
Equivalent Circuit diagram now…Equivalent Circuit diagram now…
Direction of noise coupling
Calculating Noise CouplingCalculating Noise Coupling
Reduce Circuit diagramReduce Circuit diagram
Calculate noise power coupled to Calculate noise power coupled to each elementeach element
Active Noise Figure and Active Noise Figure and TemperatureTemperature
Problem:Problem: If coupled noise is considered input noise, the If coupled noise is considered input noise, the input SNR is degraded, this results in false impression that input SNR is degraded, this results in false impression that the Noise Figure of the LNA improved.the Noise Figure of the LNA improved.
All LNAs are seen as one “multiport LNA bank”All LNAs are seen as one “multiport LNA bank”
Add coupled noise from other LNAs in the bank to the noise Add coupled noise from other LNAs in the bank to the noise power generated by the isolated LNApower generated by the isolated LNA
Verification ExampleVerification Example
Active Noise Temperature of 8x8 Active Noise Temperature of 8x8 Vivaldi ArrayVivaldi Array
Added noise Added noise temperature of 14 temperature of 14 KelvinKelvin
≈ ≈ 9% of Isolated 9% of Isolated Noise TemperatureNoise Temperature
For SKA ≈ 1.3 K !!!For SKA ≈ 1.3 K !!!
SKA TSKA Tsyssys Budget Budget
Estimate Estimate ΔΔT TableT Table
Any Questions?Any Questions?