SKA AA-low:
LPD antenna (SKALA) &
path towards AAVS0 at Cambridge
Eloy de Lera Acedo
University of Cambridge
AAVP 2011:
Taking the AA programme into SKA Pre-Construction
12-16 December, 2011 - ASTRON, Dwingeloo
1
Overview
•
•
•
•
•
•
Introduction
Current status of SKALA (LPD antenna)
Low Noise Amplifier for SKALA
SKALA tests and AAVS0 (16-element array)
Important numbers
Summary and conclusions
Introduction
Parameter
Specification Remarks
Low frequency
MHz
70
Nyquist frequency
MHz
100
Frequency with element spacing is λ/2, defines max Aeff
High frequency
MHz
450
Freq where sky noise is low, overlaps with AA-hi and/or dishes
Frequency coverage
Bandwidth, max
contiguous
MHz
Polarisations
380
2
Station diameter
m
180
Geometric area
m2
~25,000
No. of element types
1
No. of elements
Scan angle range
~10k
deg
±45
m2/K
17
Frequency channel
kHz
250
Output data rate
Tb/s
16
Sensitivity @ 100 MHz
Lowest frequency expected for the EoR
There are no gaps between low and high frequency
Individual beams can operate over the full frequency range
Orthogonal
Determined from SKA2. Uses 250 arrays for expected SKA2 sensitivity
A single wide-band element type e.g. bow-tie or conical spiral
Each element is low gain, dual polarisation
Will operate at larger scan angles, but sensitivity not defined
Single array, sensitivity varies over the band.
Assumes Tsky= 1000K, 70% for appodisation.
Assumes 2048 channels splitting the full sample rate, further channelization will
be required at correlator
Defines the survey performance of the array.
Can be used flexibly for frequency, bandwidth and number of beams
Evolution: from BLU to SKALA
Impedance
Dual polarisation
Sky coverage
Cost
BLU
Impedance
Impedance
Dual polarisation
Dual polarisation
Sky coverage
Sky coverage
Cost
Cost
Toothedw-SKALA
log periodic
Impedance
Dual polarisation
Sky coverage
Cost
SKALA
SKALA: SKA Log-periodic Antenna
1.6 m
1.3 m
* GND mesh is 1.5 x 1.5 m.
Current status of SKALA
Mass production of SKALA and LNA
Mass production of SKALA and LNA
• Some numbers:
– Cost of antennas for AAVS1 is around 150€/element.
– Cost of antenna for AAVS2 is targeted at 75€/element (this is for the 2
polarisations and includes the electronics).
– Weight of each arm would be 1.56 kg if made of steel wire.
First prototype
Performance
0
Simulation
Measurement
-2
-4
S11 /dB
-6
-8
-10
-12
-14
-16
-18
-20
0.1
0.08
0.150.1
0.2 0.12
0.25
0.14 0.3
Freq
Freq/GHz
/GHz
0.35
0.16
0.4
0.18
0.450.2
Low Noise Amplifier for SKALA
• Frequency range 70 to 450MHz
• Gain > 20dB
• Gain flatness, as flat as possible consistent with
meeting other spec. parameters
• Noise temperature < 30K at 450MHz
• P1dB, high enough to allow astronomical observations
to be made at Lords Bridge
• Power consumption < 100mW
• Unconditionally stable at both input and output ports
• Differential source (antenna), single-ended load
• High Level of Common Mode Signal Rejection
Concept
Diferrential input
LNA1
Static discharge
path
DC block
LNA2
Balun
Coaxial output
Dual Matched Low Noise RF FETs
Required
AVAGO MGA-16516
Schematic
Board layout
Picture
LNA & antenna performance
DB(NFCIR(1,0.1))
LNA_MGA16516_all_in_one.$FSWP1
S(1,1)
SKALA_CCL_5_simple_1polLoaded_Wing_diff_metalPoleGood_nonMetal.$FPRJ
Swp Max
450MHz
2.
0
6
0.
0. 8
1.0
Antenna S11 and LNA Noise Circles
0.
4
450 MHz
r 1.58135
x -0.032405
0
3.
0
4.
5. 0
0. 2
10 .0
5.0
4.0
3.0
2.0
1.0
0.8
0.6
0.4
70 MHz
r 0.462591
x -0.236854
p2
p7
p2: FREQ = 70 MHz
NF = 0.63953 dB
p3: FREQ = 130 MHz
NF = 0.41355 dB
p4: FREQ = 130 MHz
NF = 0.51355 dB
p5: FREQ = 300 MHz
NF = 0.41005 dB
p5
p3
-1 0. 0
2
-0 .
p6
4
.0
-5 .
0
0
0.2
p1
10.0
p8
p1: FREQ = 70 MHz
NF = 0.53953 dB
p4
-3
.0
-1.0
-0 .8
-0
.6
.0
-2
.4
-0
Swp Min
70MHz
p6: FREQ = 300 MHz
NF = 0.51005 dB
p7: FREQ = 450 MHz
NF = 0.43003 dB
p8: FREQ = 450 MHz
NF = 0.53003 dB
LNA+antenna simulated performance
(includes a 20dB gain second stage on chip)
SKA Lo LNA Transducer Gain and Noise Figure in dB
50
Operating with Cambridge Log Periodic
448.3 MHz
40.94 dB
40
70 MHz
44.1 dB
DB(NF())
LNA_MGA16516_all_in_one.$FPRJ
dB
30
DB(GT())
LNA_MGA16516_all_in_one.$FPRJ
20
70 MHz
0.7654 dB
449.3 MHz
0.4301 dB
10
0
70
170
270
Frequency (MHz)
370
450
LNA+antenna simulated performance
(includes a 20dB gain second stage on chip)
Noise Figure of SKA Lo LNA operating with Cambridge Log Periodic
0.8
DB(NF())
LNA_MGA16516_all_in_one.$FPRJ
70 MHz
0.7654 dB
Noise Figure dB
0.7
0.6
255.2 MHz
0.4608 dB
0.5
449.5 MHz
0.4301 dB
103.3 MHz
0.4528 dB
0.4
70
170
270
Frequency (MHz)
370
450
Simulated A/T for SKA
1
(with log-periodic antenna)
- A/T shown is A/T of 1
antenna x N (number of
antennas in a 180 m station
with elements spaced 1.5 m
apart) x 50 stations.
• η (radiation efficiency) = 90%
• D (directivity)
• Tsky (sky noise temperature) following Tsky = 1.691*(freq[GHz].^-2.751) + 4.875 K
• Tamb (ambient temperature) = 295 K
• Trec (receiver noise temperature) -> Assuming ideal amplifier with:
• Zopt (optimum noise impedance) = 100 Ω
• Rn (noise resistor) = 10 Ω
• Fmin (minimum noise figure) = 0.3 dB -> 21 K
A/T for polarization 1 [m 2/K] for SKA1 (based on SKALA) @ 170 MHz
1
200
400
600
800
1000
1200
1400
1600
1800
2000
2200
0.8
0.6
sin( )*sin( )
0.4
0.2
2400
0
-0.2
30o
-0.4
45o
-0.6
60o
-0.8
* Peak is at
2452 m^2/K
-1
-1
200
-0.5
0
sin( )*cos()
0.5
1
A/T for polarization 2 [m 2/K] for SKA1 (based on SKALA) @ 170 MHz
1
0.8
200
0.6
0
0
2400
0.2
0
-0.2
30o
-0.4
45o
-0.6
60o
20
0
sin( )*sin( )
0.4
200
220
0
20
640000
8
1 00
120000
140 0
160 0
0
180
0
-0.8
* Peak is at
2452 m^2/K
-1
-1
-0.5
0
sin( )*cos()
0.5
1
A/T Stokes I [m2/K] for SKA1 (based on SKALA) @ 170 MHz
1
500
100
0
150
0
0.8
200
0.6
0
2500
sin( )*sin( )
0.4
3000
0.2
3400
0
-0.2
30o
-0.4
45o
-0.6
60o
-0.8
* Peak is at
3468 m^2/K
-1
-1
-0.5
0
sin( )*cos()
0.5
1
A/T Stokes I [m2/K] for SKA1 (based on SKALA)
4000
Zenith
30o
3500
45o
60o
3000
A/T /m2/K
2500
2000
1500
1000
500
0
0.05
0.1
0.15
0.2
0.25
Freq /GHz
0.3
0.35
0.4
0.45
Effect of Soil/GND – (Soil B – 5% humidity)
Even a bigger pitch may be possible!
120
10 cm pitch
5 cm pitch
No ground
100
Tgnd /K
80
60
40
20
0
0.1
0.15
0.2
0.25
Freq /GHz
0.3
0.35
0.4
0.45
X-pol
0
Zenith
22.5 o H-plane
-5
22.5
-10
x-pol /dB
-15
o
E-plane
45
o
H-plane
45
o
E-plane
-20
-25
-30
-35
-40
-45
-50
0.1
0.15
0.2
0.25
Freq /GHz
0.3
0.35
0.4
0.45
SKALA tests and AAVS0
• 16 dual-polarised SKALA elements.
• Aim:
– Test realistic SKA AA-low front-end
technology in an array environment:
• Effect of cables.
• Effect of ground mesh/soil.
• Effect of mutual coupling on noise and pattern.
– Challenges:
• Measure the pattern in an array environment.
Options:
– Use of known field source: NF, FF.
– Use data from interferometry experiment.
ADC: 1GS/s
50 -100m all
optical
– Cost:
• Estimated total cost is 5-10 K€ depending on
tools and equipment needed for the tests.
e/o
Data
e/o
Control
e/o
Sync.
Analogue
Lord’s Bridge Observatory
SKALA-AAVS0
Upcoming tests:
• December 2011:
– Impedance test with “dummy” board.
• January 2011:
–
–
–
–
Single element pattern measurement in outdoor test range, Perth?
Single element pattern measurement in outdoor test range, UK.
Noise matching with integrated LNA in reverberation chamber, UK.
Impedance tests on AAVS0.
• February-March 2011: (with Roach back-end)
– Noise tests on AAVS0: pointing the array to hot and cold patches of the sky.
– Pattern tests on AAVS0: (compare with analytical/EM models - UCL)
• Interferometry experiment: full correlation/correlation with high gain antenna
• Known source: Near field source (no back-end needed), minicopter?
– More tests... Any suggestion? Plug into other back-ends?
Important numbers
• Noise:
– <30 K @ 450 MHz.
• Sky coverage – A/T:
– Meets DRM specifications down to +/- 45o at all frequencies.
• Frequency band:
– Potential to go down to 50 MHz (lower arm).
• Foot-print: 1x1 m possible (lower arm).
• Cost:
– Targeted to 75 € including LNA and ground mesh.
Single-Dual band
• Low-band: high gain element, OK.
• High-band: low gain element? Not so easy... Getting down to 30 K
with a low gain antenna in a 3:1 band is not that easy. You will
probably need a high gain element anyway and rather large.
Summary and conclusions
• Antenna+LNA pair meets DRM requirements.
• In early 2012 noise and pattern tests for AAVS0.
• Mass production prototypes are in their way (75€/element).
Thank you! Any questions?
SKALA1
(Cambridge)
SKALA2
(ICRAR)
SKALA0
miniSKALA
(Cambridge)
SKALA3
(Cambridge)
SKALA4
(ASTRON)