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Radio Telescope Receivers CSIRO ASTRONOMY AND SPACE SCIENCE Alex Dunning 25 th September 2017
Transcript of Radio Telescope Receivers - Australia Telescope National ... · Radio Telescope Receivers CSIRO...
Radio Telescope Receivers
CSIRO ASTRONOMY AND SPACE SCIENCE
Alex Dunning
25th September 2017
Receiver Systems for Radio Astronomy | Alex Dunning2 |
“A radio receiver is an electronic device that receives radio waves and converts the information carried by them to a usable form” Wikipedia
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Parkes 10/40cm Receiver
• Captures the signal reflected from the antenna
• Determines the beam shape
• Amplifies the signal
• Conditions the signal for digitisation
Ours look more like this
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Feed Horns
Vacuum Dewar
Control and Monitoring electronics
On the outside…
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On the inside…
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Feed Horn
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Detour: Reciprocity
Microwave Network
A
B
Forward𝑉𝑉𝐵𝐵 = 𝑆𝑆𝐵𝐵𝐵𝐵𝑉𝑉𝐵𝐵
Reverse𝑉𝑉𝐵𝐵 = 𝑆𝑆𝐵𝐵𝐵𝐵𝑉𝑉𝐵𝐵
Reciprocal𝑆𝑆𝐵𝐵𝐵𝐵 = 𝑆𝑆𝐵𝐵𝐵𝐵
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θ
α
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-25 -20 -15 -10 -5 0 5 10 15 20 25Theta [deg]
0
50
100
150
200
250
300
Gai
n-25 -20 -15 -10 -5 0 5 10 15 20 25
Theta [deg]
0
50
100
150
200
250
300
Gai
n
Corrugated Smooth Walled
E-Field At Feed mouth
X and Y Feed Patterns
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Feed
Signal
Noise source
Coupler
7mm waveguide couplerNoise coupled in
through small holes
Noise coupled in through vane
21cm waveguide coupler
12mm noise source
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Ortho-mode Transducer
Feed
Signal
Noise source
Coupler
Pol B
Pol A
A output
B output
Input
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Separating the Polarisations: The OMT
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Ortho-mode Transducer
Feed
Signal
Noise source
Coupler LNA
LNAPol B
Pol A
High Electron Mobility Transistor
(HEMT)Low Noise Amplifier
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Noiseless Amplifier
Noise
𝑃𝑃𝑜𝑜𝑜𝑜𝑜𝑜𝑜𝑜𝑜𝑜𝑜𝑜 = 𝐺𝐺𝐺𝐺𝐺𝐺𝐺𝐺 ∆𝑓𝑓 𝑘𝑘𝐵𝐵 𝑇𝑇𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑜𝑜𝑜𝑜𝑟𝑟
Low Noise Amplifier
Noise
Noise
𝑇𝑇𝑟𝑟𝑒𝑒𝑜𝑜𝑟𝑟𝑒𝑒𝑒𝑒𝑒𝑒𝑟𝑟𝑒𝑒𝑜𝑜 =𝑃𝑃𝑜𝑜𝑜𝑜𝑜𝑜𝑜𝑜𝑜𝑜𝑜𝑜
𝐺𝐺𝐺𝐺𝐺𝐺𝐺𝐺 ∆𝑓𝑓 𝑘𝑘𝐵𝐵
Noiseless Termination
Black body Termination
𝑃𝑃𝑜𝑜𝑜𝑜𝑜𝑜𝑜𝑜𝑜𝑜𝑜𝑜 ∝ 𝐺𝐺𝐺𝐺𝐺𝐺𝐺𝐺 ∆𝑓𝑓
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32
4
2
321 GGGain
TGGain
TGain
TTTLNALNALNA
system ××+
×++=
Feed
Signal
LNA Second Stage
Amplifier
Third Stage Amplifier
T1 T2 T3
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10Jy radio source → ~1K additional noise
Your hand → ~300K additional noise
Mobile Phone at 1 km→ ~1 × 1011 K !!(in primary beam)
Zirconicusso Freepik.com
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Part Room Temperature Cryogenic Ratio
Sky + CMB (Tsky) 6K 6K 1
Spillover (Tspill) 3K 3K 1
Feed + OMT 10K 2K 5
LNA (Tlna) 35K 5K 7
Rest of the System 1K 1K 1
Total (Tsys) 55K 17K ~3
Noise contributions of a typical receiver
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15K section
70K section
Helium Lines
Helium Compressor
Helium Refrigerator
Refrigerator in the Parkes 12mm receiver
Cold finger
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CSIRO. Receiver Systems for Radio Astronomy
Copper Radiation Shield 70K
Helium Refrigerator cold finger
Vacuum Dewar
Thermal Isolation waveguide
15K section
Low Noise Amplifiers
Gap
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The RF System
Contains:• More amplification• Band defining filters• Frequency conversion• Level adjustment• Signal detection• Band shaping
Frequency Conversion
Signal
Filter
To Digitiser
AmplifierLevel
Adjustment
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Signal 1
Signal 2
Signal 1 × Signal 2
Mixer (Multiplier)
Frequency
Pow
er
Frequency
Pow
er
cos(ω1t)cos(ω2t)=½[cos((ω1+ω2)t)+ cos((ω1-ω2)t)]
Δf Δf
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Signal 1
Signal 2
Mixer (Multiplier)
Frequency
Pow
er
Frequency
Pow
er
cos(ω1t)cos(ω2t)=½[cos((ω1+ω2)t)+ cos((ω1-ω2)t)]
Δf Δf
Low pass filter
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Signal 1
Mixer (Multiplier)
Frequency
Pow
er
Frequency
Pow
er
Δf Δf
Local Oscillator
flo
cos(ω1t)cos(ωLOt) → ½cos[(ω1-ωLO)t]
Upper Side Band (USB)
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Signal 1
Mixer (Multiplier)
Frequency
Pow
er
Frequency
Pow
er
Δf Δf
Local Oscillator
flo
cos(ω1t)cos(ωLOt) → ½cos[(ωLO-ω1)t]Lower Side Band (LSB)
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Signal 1
Mixer (Multiplier)
Frequency
Pow
er
Frequency
Pow
er
Δf Δf
Local Oscillator
flo
Band pass filter
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The modern radio telescope 0.000001 megapixels
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Photo credit: Wheeler Studios
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Digital beamformer
Weighted (complex) sum of inputs
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CSIRO Astronomy and Space ScienceAlex Dunning
t +61 2 9372 4346e [email protected] www.csiro.au/cass
CSIRO ASTRONOMY AND SPACE SCIENCE
Thank you
