Advanced Technology for Modern Radio Telescopes and some history
Gie Han Tan
5th EIROforum School on Instrumentation The radio spectrum
Radio astronomy operates between ~10 MHz (30 m) up to >1,5 THz (0,2 mm)
5th EIROforum School on Instrumentation A condensed history of radio telescopes
Radio astronomy is a relatively young discipline in experimental astronomy but has seen a very rapid development ….
Karl Jansky – 1932 Grote Reber – 1937 Lovell Telescope – 1957 Westerbork Synthesis Radio detected radiation at 9 m parabolicantenna 76 m parabolicantenna Telescope (WSRT) – 1970 20.5 MHz from the Milky Way Operating at 3.3 GHz Operating up to ~5 GHz 14 X 25 m parabolic antenna / 900 MHz / 160 MHz Operating up to ~8.4 GHz
5th EIROforum School on Instrumentation A condensed history of radio telescopes
… and continues to make technological progress.
Green Bank Telescope – 2000 Low Frequency Array (LOFAR) 100 m off-set parabolic antenna 2012 Phased array Operating up to ~116 GHz Operating range 10-250 MHz
Atacama Large Millimeter/submillimeter FAST Telescope – 2016 Array (ALMA) - 2013 500 m spherical antenna 54 x 12 m / 12 x 7 m Operating up to ~3 GHz Operating range 30-950 GHz 5th EIROforum School on Instrumentation Outline
Key performance drivers for radio telescopes Sensitivity Angular resolution Frequency coverage Design examples of modern radio telescopes Atacama Large Millimeter/submillimeter Array (ALMA) Square Kilometre Array (SKA) Some new receiver technologies Phased array feeds Aperture arrays Radio Frequency Interference
5th EIROforum School on Instrumentation Sensitivity
Sensitivity equation expressed in flux density S
Ssys 2 k Tsys S Ssys B t Aeff
Increase collecting area Aeff (larger dishes / combining multiple dishes) Reduction of system noise sources Tsys (e.g. amplifiers, antenna spill over) Increase observing bandwidth B (only works for continuum sources, e.g. thermal radiation)
5th EIROforum School on Instrumentation A sensitivity comparison
LOFAR: > 1 km2 (@ 30 MHz) SKA1-Low:465.500 m2 (@ 100 MHz)
2 SKA1-Mid: 26.555 m (ηap = 80%) JVLA: 13.250 m2
5th EIROforum School on Instrumentation Sky noise
Below < 100 MHz sky noise is becoming a dominant
contributor to Tsys
1E+9
1E+8
1E+7 Cosmic noise towards 1E+6 Galactic pole Man made noise (quiet rural) 1E+5 Atmospheric noise (day) 1E+4 Atmospheric noise (night)
1E+3 Total antenna noise (day)
1E+2
Equivalent noise temperature [Kelvin] 1E+1
1E+0 1 10 100 1000 10000 Frequency [MHz]
5th EIROforum School on Instrumentation Angular resolution
• Antenna Half-Power Beam Width (HPBW) as a measure for angular resolution 휆 휃 = 푘. 퐻푃퐵푊 퐷 Increase aperture size D Increase frequency → smaller λ
• Practical limits to increasing D • Aperture synthesis • WSRT (3 km), VLA (27 km), SKA Phase 1 (150 km) • Very Long Baseline Interferometry • < 100 – > 300.000 km
5th EIROforum School on Instrumentation Angular resolution
• Very Long Baseline Interferometry • Groundbased VLBI • Event Horizon Telescope • Baseline • 230 / 450 GHz • Resolution: 10 μas (goal) • Space VLBI • HALCA - VSOP • 1997 - 2005 • 8 m diameter reflector • Baseline 56 – 21.400 km • 1.6 GHz / 5 GHz / 22 GHz • Resolution: ~120 μas • Radioastron – Spektr-R • 2011 • 10 m diameter reflector • Baseline 10.000 – 339.000 km • 327 MHz / 1.6 GHz / 5 GHz / 22 GHz • Resolution: ~8 μas
5th EIROforum School on Instrumentation Angular resolution comparison
5th EIROforum School on Instrumentation What is ALMA?
The Atacama Large Millimeter/submillimeter Array - a global endeavor to build an interferometric array of radio telescopes operating at wavelengths between 10 and 0.3 mm (30 to 950 GHz) 7000 m2 collecting area (54 12-m antennas & 12 7-m antennas) 5000-m altitude site in Chile Reconfigurable antennas allowing baselines up to 14 km
The ALMA Partners Europe (ESO on behalf of its 16 member states) North America (US/NSF and Canada/NRC ) East Asia (Japan/NAOJ, Korea and Taiwan/ASIAA)
5th EIROforum School on Instrumentation Geographical location of ALMA
Northern Chili Atacama desert
5th EIROforum School on Instrumentation San Pedro de Atacama (2400m), AOS (5000m) OSF (2900m)
December 2007 5th EIROforum School on InstrumentationChile Observatories Earthquake Preparedness Workshop 14 Llano de Chajnantor
Chajnantor plateau, elevation 5000+ m
5th EIROforum School on Instrumentation ALMA baseline instrument
Key technical parameters: 54 & 12 antennas: • 12 m / 7 m diameter, Cassegrain configuration • Surface accuracy: < 25 μm rms / 12 m - < 15 μm rms / 7 m • Pointing accuracy: 0.6 arcsec (offset, 2 deg in position and 15 min time), 2.0 arcsec (absolute) • Nutating sub-reflector (4 antennas) Zoom configuration: • Baseline length up to 14 km • 192 antenna stations • All antennas fully reconfigurable over all antenna pads Front ends: • Dual polarisation • IF bandwidth: 8 GHz / polarisation Correlator: • Number of baseband inputs: 8 / antenna • Maximum sampling rate per baseband input: 4 GHz • Digitising format: 3 bit - 8 level • Correlation format: 2 bit - 4 level 5th EIROforum School on Instrumentation ALMA Front End key specifications
Receiver noise temperature ALMA Frequency Mixing Receiver Band Range TRx over 80% of TRx at any RF scheme technology the RF band * frequency *
1 31.3 – 45 GHz 17 K 28 K USB HEMT
2 67 – 90 GHz 30 K 50 K LSB HEMT
3 84 – 116 GHz 37 K (40K) 62 K (50K) 2SB SIS 4 125 – 169 GHz 51 K (45K) 85 K (55K) 2SB SIS
5 163 - 211 GHz 65 K 108 K 2SB SIS
6 211 – 275 GHz 83 K (45K) 138 K (60K) 2SB SIS 7 275 – 373 GHz 147 K (80K) 221 K (90K) 2SB SIS 8 385 – 500 GHz 196 K (160K) 294 K (270K) 2SB SIS 9 602 – 720 GHz 175 K (100K) 263 K (150K) DSB SIS 10 787 – 950 GHz 230 K 345 K DSB SIS
* In brackets achieved noise temperature
5th EIROforum School on Instrumentation Simplified ALMA block diagram
Receiver systems: Super heterodyne Antenna based electronics Central back end architecture
R I ADC Dual frequency conversion L Digital correlator (only single conversion shown) 1 Optical transmission systems for digitised IF (120 Gb/sec Data storage each antenna) and LO reference distribution The depicted system is Antenna based electronics located at the Array R I ADC Operations Site at 5000+ m. L Central frequency reference Remotely controlled from the Operations Support Facility 64 at ≈2800 m.
5th EIROforum School on Instrumentation ALMA Antenna based electronics
General specs: IF sub-system Bandwidth: Front end RF R I ADC • 8 GHz / pol 31 - 950 GHz L
IF1 4 - 12 GHz T Dual orthogonal R I o
L o
Band p t
polarisation LO1 selector R I ADC i c
27 - 938 10:1 L a l
GHz channels T Frequenc X
y s
multiplier u b
N = 1 .. 6 - s
Front end: R I ADC y s
L t e 31 GHz - 950 GHz m
10 bands R I ADC L
IF2 IF: 2 - 4 GHz LO2 8 - 10 GHz / 4 x 2 GHz out / 12 - 14 GHz polarisation LO reference frequencies (27 - 122 GHz, 2 GHz, 25 MHz, 20 Hz) on optical fiber from central distribution
5th EIROforum School on Instrumentation ALMA / Front End Assembly
5th EIROforum School on Instrumentation ALMA Band 7 Cartridge
Cold Cartridge Warm Cartridge
5th EIROforum School on Instrumentation ALMA Band 9 Cartridge
4 + 110 K Stage Assembly (NOVA/SRON) SIS Junction Lay Out (TUD)
nd Partially 2 Optics Assembled Assembly 110K Stage Integrated on 4K Plate
1st Optics 4-12 GHz Block Isolators Warm Cartridge Assembly (NRAO)
Cartridge Assembly (NOVA/SRON) YIG Oscillator (15-20 GHz)
LO Phase Lock
LO Bias Electronics Space for Cartridge WR8 Waveguide Bias Electronics Outputs (2) 5th EIROforum School on Instrumentation Cryogenic sub-mm Low Noise Amplifiers
Replacing SIS-mixers by III-V transistor technology Increased RF bandwidth Reduced cooling requirements: ~20 K instead of < 4 K
1000 5000 )
900 4500 × )
♦ 800 4000
700 3500
600 3000
500 2500
400 2000 Low Noise Factory 300 1500 LNF-LNC65_115WA
[K] for cryogenic LNAs ( for [K] cryogenic RECK et al - 2014
n 200 1000
T [K] for room temperature LNAs LNAs ( temperaturefor [K] room
n RECK et al - 2014
100 500 T
0 0 DEAL et al - 2016 0 200 400 600 800 1000 Frequency [GHz] Ratio left / right y-axis is 1 / 5
Demonstrated reduction in Tn when cooling LNA from room temperature to ~ 25 K (see e.g. Reck et al)
5th EIROforum School on Instrumentation SKA Phase 1 / Phase 2
Phase 1: ~130,000 Phase 2: antennas across 80km 500,000 antennas across 200km (2025 – 2033)
Phase 1: 197 dishes Phase 2: 2500 across 150km dishes across 3500km of southern Africa (2025 – 2033)
5th EIROforum School on Instrumentation SKA1-Low / Mid Main Characteristics
SKA1-Low SKA1-Mid Frequency range 50 MHz – 350 MHz Band 1: 350 MHz – 1050 MHz Band 2: 950 MHz – 1760 MHz Band 5: 4.6 GHz - 13.8 GHz 2 2 Collecting area (effective) 465,500 m (@ 100 MHz) 26,555 m (ηap = 80%) Antenna type Log-Periodic Dipole Array Off-set Gregorian parabolic reflector Number of antennas ~ 130,000 197 (incl. 64 MeerKAT) Maximum baseline > 65 km 120 - 150 km Sub-arrays 4 4 Correlator channels 65536 65536 Instantaneous bandwidth 300 MHz Band 1: 700 MHz Band 2: 810 MHz Band 3: 2 x 2500 MHz Minimum channel width 256 Hz 256 Hz Brightness dynamic range > 50 dB > 60 dB
5th EIROforum School on Instrumentation SKA1-Low / AAVS1 system layout
MRO Main Building Internet I/F
Station box “TM” MWA TPMs Control Controller Power System 1
4 Data Data Switch Splice MCCS MCCS Box Servers Servers 3
Fibre cables Fibre 3
Data Data Switch Beams to
576-core …. splicing MWA 2 Correlator Power RF over fibre Signal data Patch Recorder (server) cables Internet 1 25 …. Signal data I/F Power Clock Dist recorder (server) Clocks from MWA/Maser
5th EIROforum School on Instrumentation SKA1-Low / Log Periodic Dipole Antenna
• Improved antenna base structure
5th EIROforum School on Instrumentation SKA1-Low / Full station EM simulation
5th EIROforum School on Instrumentation SKA / AAVS0 Beam Measurements
. Located at Cambridge/Lord’s Bridge . Hexacopter beam test
5th EIROforum School on Instrumentation SKA1-Mid array configuration
1 km 50 km
Each red dot represents a SKA1-Mid 15 m reflector antenna Each black dot represents a MeerKAT dish.
5th EIROforum School on Instrumentation SKA1-Mid / Offset-optics antenna design
Multiple Feeds to cover multiple bands
15-m Effective Diameter DVA-C (China)
DVA-1 (Canada + MeerKAT Dish Design some US heritage) South Africa (13.5 m)
5th EIROforum School on Instrumentation SKA1-Mid Optics Design
Primary optics design optimization parameter is sensitivity High aperture efficiency • Shaped, unblocked reflectors Low noise • Unblocked aperture, sub-reflector extension
5th EIROforum School on Instrumentation SKA1-Mid / SPF Band 1
Room Temperature (Uncooled) Feed Horn and LNA
5th EIROforum School on Instrumentation SKA / Science data transport
0.68 Tb/s 4.5 Tbps
8.8 Tbps
100Gb/s 100Gb/ s
7.2Tbps 3.1Tbps 4.9Tbps
SKA1_Low SKA1_Mid
5th EIROforum School on Instrumentation SKA Telescope to world – data rates
• Image cubes of sky maps 18PB n*/year ~30Gbit/s o SDP Fourier transform of CSP time series o Moderate external compute and model fitting • Epoch of Re-ionisation 1.6PB/ 6 Hr ~600 Gbit/s o Uses calibrated aperture plane o Enormous compute of power spectra • Weak gravitational lensing 70PB/2500Hr 60Gbit/s o Uses further processed aperture plane data o Considerable compute of galaxy ellipticity • Pulsars 4-5 PBytes/y ≤10Gbits o Discovery and in depth study; timing 10 ns in 10 years o Large physics compute • VLBI we do 4 Gbit/s now ! o Data direct from the beamformer ~ 10 Gbit/s UDP
5th EIROforum School on Instrumentation Multiple feeds in focal plane
Enlarging of FOV with multiple feed in focal plane
Under sampled focal plane (d > ½ ʎ) Densely sampled focal plane (d < ½ ʎ) Focal plane arrays Phased array feeds Mainly at (sub-)mm telescopes Focus at cm telescopes
5th EIROforum School on Instrumentation PAF Development – CSIRO (AUS)
• Focussed on 650 – 1700 MHz • Concepts demonstrated 5 x 4 array (40 Elements)
5th EIROforum School on Instrumentation PAF Development - NRC (CA)
Array Noise Temperature
Thick Vivaldi element and LNA 5th EIROforum School on Instrumentation PAF Development – ASTRON / JBCO
• PHAROS Cryogenic receiver MMIC 0.2-2GHz LNA (ASTRON) Analog beamformer
5th EIROforum School on Instrumentation Aperture arrays - MFAA
A very large field of view, and the opportunity of transient buffering A fast response time and pointing Multiple beams, concurrent observations A very high survey speed capability High sensitivity < 1.4 GHz Relatively low capital and operational costs Low post-processing costs (large stations) No moving parts No vacuum, helium, cryogenics
5th EIROforum School on Instrumentation MFAA demonstrator
Located on the South African SKA site Demonstrate feasibility and technological maturity Technical verification Science observations 2 Ae ~2000 m
Parameter Value or range Units 2 Aeff/Tsys at 1GHz 40 m /K Frequency range 500 - 1500 MHz Bandwidth >500 MHz Baseline length 300 - 1000 m
Compactness 50% Aeff inside 100m Number of stations 10 - 20 Independent fields-of- ≥2 view HPBW (FoV) at 1GHz 15 (175) deg (deg2) Polarizations Full Stokes
5th EIROforum School on Instrumentation MFAA front-end development
5th EIROforum School on Instrumentation MFAA front-end development
Integrated receiver
5th EIROforum School on Instrumentation Radio Frequency Interference
RFI is increasing threat to radio astronomy Passive service
SKA monitoring 2010, annotated power flux spectra, core site SA -140 , 99 perc. c Global RFI map @ 1,4 GHz N = 6 , 90 perc. c , median -160 N (B1..B9) = 0 0 0 0 47 1 0 0 0 c from NASA Acquarius flag detection flag
-180
-200
))
-1 -220
Hz
-2
(dB(Wm
c -240
-250
RAS Misc.SAT Mil.SAT INMARSAT,IRIDIUM Sat.Broadc Galileo,GPS,Glonass Aero Com/Nav Terr.MobileComm Terr.Broadc SA Fut Terr.Broadc SA Private&Public Com
70 80 90 100 120 150 200 250 300 350 400 500 600 700 800 900 1000 1200 1400 1600 2000 f (MHz) 5th EIROforum School on Instrumentation Thank you!
5th EIROforum School on Instrumentation