Receiver Systems - Australia Telescope National Facility | · PDF fileThe Basic Structure of a...
Transcript of Receiver Systems - Australia Telescope National Facility | · PDF fileThe Basic Structure of a...
Receiver Systems
Alex Dunning
The Basic Structure of a typical Radio Telescope
CSIRO. Receiver Systems for Radio Astronomy
Antenna
Receiver
Conversion
Digitiser
Signal Processing / Correlator
They are much the same
CSIRO. Receiver Systems for Radio Astronomy
Radiotelescope
Receivers
CSIRO. Receiver Systems for Radio Astronomy
Radio Receivers
CSIRO. Receiver Systems for Radio Astronomy
“A radio receiver
converts signals from a
radio antenna to a
usable form” Wikipedia
Ours look more like this...
CSIRO. Receiver Systems for Radio Astronomy
Compact Array
3/7/12mm Receiver
• Captures the signal
reflected from the
antenna
• Amplifies the signal
Or this...
CSIRO. Receiver Systems for Radio Astronomy
Parkes 10/50cm
Receiver
Or this...
CSIRO. Receiver Systems for Radio Astronomy
ASKAP Phased
Array Receiver
Some even look like this...
CSIRO. Receiver Systems for Radio Astronomy
Allen Telescope Log
Periodic Receiver
The Receiver
CSIRO. Receiver Systems for Radio Astronomy
On the outside...
Vacuum
Dewar
Feed Horns
The Receiver
CSIRO. Receiver Systems for Radio Astronomy
On the inside...
Amplifiers Ortho-Mode
Transducers
CSIRO. Wide Band Receiver Upgrade of the CASS Compact Array
RFe
sys
A
TS
system temperature
Integration Time
minimum detectable
flux
Effective Collecting
Area
Observing Bandwidth
The Australia Telescope Receivers
CSIRO. Receiver Systems for Radio Astronomy
10
cm
-25cm
12
mm
-18.7
mm
6m
m-1
0m
m
O2 a
bso
rptio
n
2.8
mm
-3.5
mm
4.6
cm
-6.7
cm
3.2
cm
-3.7
cm
2.5
cm
-7cm
Current upgrade
L/S C/X
K Q W
1:1.25 bandwidth 1:1.65 bandwidth 1:2.5 bandwidth
Parkes Receiver Bands
CSIRO. Receiver Systems for Radio Astronomy
Where do they go?
CSIRO. Receiver Systems for Radio Astronomy
In a prime focus...
CSIRO. Receiver Systems for Radio Astronomy
The Receiver
goes here
In a Cassegrain system...
CSIRO. Receiver Systems for Radio Astronomy
The Receiver
goes here
Receiving the signal – Feed horns
CSIRO. Receiver Systems for Radio Astronomy
Feed
Signal
Waveguide
output
Captures the focused
microwaves into a
waveguide output
Feed Horns
CSIRO. Receiver Systems for Radio Astronomy
Feed Horns
CSIRO. Receiver Systems for Radio Astronomy
t
EJB
t
BE
B
E
000
0
0
Detour: Waveguides
CSIRO. Receiver Systems for Radio Astronomy
• Replace cables at high
frequencies
• Operate like optical
fibres for microwaves
• Only work over a limited
frequency range
• Can support signals with
two polarisations
A Tale of Two Feedhorns
CSIRO. Receiver Systems for Radio Astronomy
A Tale of Two Feedhorns
CSIRO. Receiver Systems for Radio Astronomy
-25 -20 -15 -10 -5 0 5 10 15 20 25Theta [deg]
0
50
100
150
200
250
300
Ga
in
-25 -20 -15 -10 -5 0 5 10 15 20 25Theta [deg]
0
50
100
150
200
250
300
Ga
in
Corrugated Smooth Walled
E-Field At
Feed mouth
X and Y Feed
Patterns
CSIRO. Receiver Systems for Radio Astronomy
dd
1sin
Coupling noise into the System
CSIRO. Receiver Systems for Radio Astronomy
Feed
Signal
Noise source
Coupler
7mm waveguide
coupler Noise coupled
in through
small holes
Noise coupled
in through vane
21cm waveguide
coupler 12mm noise source
Separating Polarisations –
Ortho-mode Transducers (OMTs)
CSIRO. Receiver Systems for Radio Astronomy
Polariser Feed
Signal
Noise source
Coupler
Pol B
Pol A
Separates incoming
signal into two linear or
circular polarisations
Linear OMTs exhibit
higher polarisation purity
over broad frequency
bands (usually)
12mm Ortho-mode
transducer
4cm Ortho-mode transducer
3mm Ortho-mode
transducer
Separating Polarisations –
Ortho-mode Transducers (OMTs)
CSIRO. Receiver Systems for Radio Astronomy
Low Noise Amplifiers (LNA)
CSIRO. Receiver Systems for Radio Astronomy
Polariser Feed
Signal
Noise source
Coupler LNA
LNA
To conversion
System
Pol B
Pol A
High Electron
Mobility Transistor
(HEMT)
32
4
2
321
GGGain
T
GGain
T
Gain
TTT
LNALNALNA
system
Feed
Signal
LNA Second
Stage
Amplifier
Third
Stage
Amplifier
T1 T2 T3
Why is the first Low Noise Amplifier so important?
CSIRO. Receiver Systems for Radio Astronomy
….so although receiver topologies can be quite
varied I’m saying that this is a pretty typical
structure of our receivers
…………and the Compact Array 3/7/12 mm
systems reflect this.
Polariser Feed
Signal
Noise source
Coupler LNA
LNA
To conversion
System
Pol B
Pol A
CSIRO. Receiver Systems for Radio Astronomy
CSIRO. Receiver Systems for Radio Astronomy
The Phased Array
Approach
CSIRO.
Getting more from each antenna
4/20
• Simple Receiver Collects
CSIRO.
Getting more from each antenna
• Simple Receiver Collects
• Phased Array Feed
• collects more (~every /2)
4/20
CSIRO.
Getting more from each antenna
• Phased Array Feed
• collects more (~every /2)
• allows corrections
4/20
• Simple Receiver Collects
CSIRO.
Connected Array
• Start with a simple array of dipoles
LNA +
Conversion +
Filtering
Digital beamformer
Weighted (complex) sum of inputs
5/20
• Join them together
CSIRO.
Connected Chequerboard Array
LNA +
Conversion +
Filtering
Digital beamformer
Weighted (complex) sum of inputs
• Complete sampling of focal region fields
• Digital beamforming
6/20
Single Beam Excitation of a Phased Array
CSIRO. Receiver Systems for Radio Astronomy
What is the rest of the stuff?
CSIRO. Receiver Systems for Radio Astronomy
What’s this?
What’s this?
Electronics
CSIRO. Receiver Systems for Radio Astronomy
• Supplies and monitors
all amplifier voltages
and currents
• Monitors system
temperatures and
pressures
Cryogenics
CSIRO. Receiver Systems for Radio Astronomy
15K section
80K section
Helium Lines
Helium Compressor
Helium Refrigerator
Refrigerator in the Parkes
12mm receiver
Cold finger
CSIRO. Receiver Systems for Radio Astronomy
Copper Radiation
Shield 80K
Helium Refrigerator
cold finger
Vacuum Dewar
Thermal Isolation
waveguide
15K section
Low Noise
Amplifiers
Gap
CSIRO. Receiver Systems for Radio Astronomy
….but why do we need to cool
our receivers at all?
…………well first
How weak is the signal?
CSIRO. Receiver Systems for Radio Astronomy
Your Hand →
1.38× 10-23 W Hz-1K-1 × 300K × 1 × 109 Hz
= 4 × 10-12 W
10Jy radio source →
10 × 10-26 W m-2Hz-1 × 1900m2 × 1 × 109 Hz
= 2× 10-13 W
Mobile Phone →
≈ 1W
Mobile Phone on the moon→
≈ 1W ÷ 4π (3.8×108m)2 ÷ 5×106Hz
≈ 10Jy
Effective area of Parkes
telescope dish
Bandwidth of Digital Filter
Bank 3 Boltzmann's
constant
Lunar
Distance 3G transmit
bandwidth
Like your hand all the components in the
receiver system contribute a thermal noise
signal which masks the astronomical signal
we are trying to observe.
By cooling the receiver we reduce these
thermal sources of noise and improve the
sensitivity of the receiver by 7-10 times.
CSIRO. Receiver Systems for Radio Astronomy
Reduce noise by cooling
CSIRO. Receiver Systems for Radio Astronomy
Electronic
device
generates
a signal
Cold stuff (liquid nitrogen)
Contact Us
Phone: 1300 363 400 or +61 3 9545 2176
Email: [email protected] Web: www.csiro.au
Thank you
CSIRO Astronomy and Space Science
Alex Dunning
RF Engineer
Phone: 02 9372 4346
Email: [email protected]
Web: www.csiro.au/org/CASS