Radio Telescope Receivers - Australia Telescope National ... · Radio Telescope Receivers CSIRO ASTRONOMY AND SPACE SCIENCE Alex Dunning. 25. th. September 2017

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

Receiver Systems for Radio Astronomy | Alex Dunning3 |

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

Receiver Systems for Radio Astronomy| Alex Dunning4 |

Feed Horns

Vacuum Dewar

Control and Monitoring electronics

On the outside…

Receiver Systems for Radio Astronomy| Alex Dunning5 |

On the inside…

Receiver Systems for Radio Astronomy| Alex Dunning6 |

Feed Horn

Receiver Systems for Radio Astronomy| Alex Dunning7 |

Detour: Reciprocity

Microwave Network

A

B

Forward𝑉𝑉𝐵𝐵 = 𝑆𝑆𝐵𝐵𝐵𝐵𝑉𝑉𝐵𝐵

Reverse𝑉𝑉𝐵𝐵 = 𝑆𝑆𝐵𝐵𝐵𝐵𝑉𝑉𝐵𝐵

Reciprocal𝑆𝑆𝐵𝐵𝐵𝐵 = 𝑆𝑆𝐵𝐵𝐵𝐵

Receiver Systems for Radio Astronomy| Alex Dunning8 |

Receiver Systems for Radio Astronomy| Alex Dunning9 |

θ

α

Receiver Systems for Radio Astronomy| Alex Dunning10 |

Receiver Systems for Radio Astronomy| Alex Dunning11 |

-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

Receiver Systems for Radio Astronomy| Alex Dunning12 |

Feed

Signal

Noise source

Coupler

7mm waveguide couplerNoise coupled in

through small holes

Noise coupled in through vane

21cm waveguide coupler

12mm noise source

Receiver Systems for Radio Astronomy| Alex Dunning13 |

Ortho-mode Transducer

Feed

Signal

Noise source

Coupler

Pol B

Pol A

A output

B output

Input

Receiver Systems for Radio Astronomy| Alex Dunning14 |

Separating the Polarisations: The OMT

Receiver Systems for Radio Astronomy| Alex Dunning15 |

Ortho-mode Transducer

Feed

Signal

Noise source

Coupler LNA

LNAPol B

Pol A

High Electron Mobility Transistor

(HEMT)Low Noise Amplifier

Receiver Systems for Radio Astronomy| Alex Dunning16 |

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

Receiver Systems for Radio Astronomy| Alex Dunning17 |

32

4

2

321 GGGain

TGGain

TGain

TTTLNALNALNA

system ××+

×++=

Feed

Signal

LNA Second Stage

Amplifier

Third Stage Amplifier

T1 T2 T3

Receiver Systems for Radio Astronomy| Alex Dunning18 |

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

Receiver Systems for Radio Astronomy| Alex Dunning19 |

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

Receiver Systems for Radio Astronomy| Alex Dunning20 |

15K section

70K section

Helium Lines

Helium Compressor

Helium Refrigerator

Refrigerator in the Parkes 12mm receiver

Cold finger

Receiver Systems for Radio Astronomy| Alex Dunning21 |

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

Receiver Systems for Radio Astronomy| Alex Dunning22 |

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

Receiver Systems for Radio Astronomy| Alex Dunning23 |

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

Receiver Systems for Radio Astronomy| Alex Dunning24 |

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

Receiver Systems for Radio Astronomy| Alex Dunning25 |

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)

Receiver Systems for Radio Astronomy| Alex Dunning26 |

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)

Receiver Systems for Radio Astronomy| Alex Dunning27 |

Signal 1

Mixer (Multiplier)

Frequency

Pow

er

Frequency

Pow

er

Δf Δf

Local Oscillator

flo

Band pass filter

Receiver Systems for Radio Astronomy| Alex Dunning28 |

The modern radio telescope 0.000001 megapixels

Receiver Systems for Radio Astronomy| Alex Dunning29 |

Photo credit: Wheeler Studios

Receiver Systems for Radio Astronomy| Alex Dunning30 |

Receiver Systems for Radio Astronomy| Alex Dunning31 |

Receiver Systems for Radio Astronomy| Alex Dunning32 |

Digital beamformer

Weighted (complex) sum of inputs

Receiver Systems for Radio Astronomy| Alex Dunning33 |

CSIRO Astronomy and Space ScienceAlex Dunning

t +61 2 9372 4346e [email protected] www.csiro.au/cass

CSIRO ASTRONOMY AND SPACE SCIENCE

Thank you