SKA AA-low: LPD antenna (SKALA) &

path towards AAVS0 at Cambridge

Eloy de Lera AcedoUniversity of Cambridge

1AAVP 2011:

Taking the AA programme into SKA Pre-Construction12-16 December, 2011 - ASTRON, Dwingeloo

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

IntroductionParameter Specification Remarks

Low frequency MHz 70 Lowest frequency expected for the EoR

Nyquist frequency MHz 100 Frequency with element spacing is λ/2, defines max A eff

High frequency MHz 450 Freq where sky noise is low, overlaps with AA-hi and/or dishes

Frequency coverage contiguous There are no gaps between low and high frequency

Bandwidth, max MHz 380 Individual beams can operate over the full frequency range

Polarisations 2 Orthogonal

Station diameter m 180 Determined from SKA2. Uses 250 arrays for expected SKA2 sensitivity

Geometric area m2 ~25,000

No. of element types 1 A single wide-band element type e.g. bow-tie or conical spiral

No. of elements ~10k Each element is low gain, dual polarisation

Scan angle range deg ±45 Will operate at larger scan angles, but sensitivity not defined

Sensitivity @ 100 MHz m2/K 17Single array, sensitivity varies over the band.

Assumes Tsky= 1000K, 70% for appodisation.

Frequency channel kHz 250Assumes 2048 channels splitting the full sample rate, further channelization will be required at correlator

Output data rate Tb/s 16Defines the survey performance of the array.

Can be used flexibly for frequency, bandwidth and number of beams

Evolution: from BLU to SKALA

BLU

ImpedanceDual polarisationSky coverageCost

Toothed log periodic

ImpedanceDual polarisationSky coverageCost

SKALA

ImpedanceDual polarisationSky coverageCost

w-SKALA

ImpedanceDual polarisationSky coverageCost

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

0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45-20

-18

-16

-14

-12

-10

-8

-6

-4

-2

0

Freq /GHz

S11

/dB

0.08 0.1 0.12 0.14 0.16 0.18 0.2-20

-18

-16

-14

-12

-10

-8

-6

-4

-2

0

Freq /GHz

S11

/dB

SimulationMeasurement

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

Static discharge path

Balun Coaxial output

LNA1

LNA2

DC block

Dual Matched Low Noise RF FETs Required

SchematicAVAGO MGA-16516

Board layout

Picture

LNA & antenna performance0 1.0

1.0

-1.0

10.0

1 0 . 0

-10.0

5.0

5 .0

-5.0

2.0

2.0

-2.0

3.0

3 .0

-3.0

4.0

4 .0

-4.0

0.2

0.2

- 0. 2

0.4

0.4

- 0. 4

0.6

0.6

-0.6

0.8

0.8

-0.8

A n te n n a S 1 1 a n d L N A N o ise C ir c le sS w p Ma x

4 5 0 MH z

S w p Min

7 0 MH z

p8

p7

p6

p5

p4

p3

p2p1

4 5 0 M H zr 1 .5 8 1 3 5x - 0 .0 3 2 4 0 5

7 0 M H zr 0 .4 6 2 5 9 1x - 0 .2 3 6 8 5 4

D B (N FC IR (1 ,0 .1 ))L N A _ M G A 1 65 1 6_ a ll_ in _ on e .$ FS W P 1

S (1 ,1 )S K A L A _ C C L _5 _ s im p le _1 p o lL o ad e d_ W ing _ d iff_ m e ta lP o le G o od _ no n M eta l.$FP R J

p 1 : F R E Q = 7 0 M H zN F = 0 .5 3 9 5 3 d B

p 2 : F R E Q = 7 0 M H zN F = 0 .6 3 9 5 3 d B

p 3 : F R E Q = 1 3 0 M H zN F = 0 .4 1 3 5 5 d B

p 4 : F R E Q = 1 3 0 M H zN F = 0 .5 1 3 5 5 d B

p 5 : F R E Q = 3 0 0 M H zN F = 0 .4 1 0 0 5 d B

p 6 : F R E Q = 3 0 0 M H zN F = 0 .5 1 0 0 5 d B

p 7 : F R E Q = 4 5 0 M H zN F = 0 .4 3 0 0 3 d B

p 8 : F R E Q = 4 5 0 M H zN F = 0 .5 3 0 0 3 d B

70 170 270 370 450Frequency (MHz)

SK A Lo LNA Transducer Gain and Noise Figure in dB

0

10

20

30

40

50

dB

70 MHz44.1 dB

449.3 MHz0.4301 dB

448.3 MHz40.94 dB

70 MHz0.7654 dB

DB(NF())LNA_MGA16516_all_in_one.$FPRJ

DB(GT())LNA_MGA16516_all_in_one.$FPRJ

Operating with Cambridge Log Periodic

LNA+antenna simulated performance (includes a 20dB gain second stage on chip)

LNA+antenna simulated performance (includes a 20dB gain second stage on chip)

70 170 270 370 450Frequency (MHz)

Noise Figure of SK A Lo LNA operating with Cambridge Log Periodic

0.4

0.5

0.6

0.7

0.8

No

ise

Fig

ure

dB

70 MHz0.7654 dB

103.3 MHz0.4528 dB

255.2 MHz0.4608 dB

449.5 MHz0.4301 dB

DB(NF())LNA_M GA16516_all_in_one.$FPRJ

Simulated A/T for SKA1 (with log-periodic antenna)

• 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 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.

* Peak is at 2452 m^2/K

200

200

400600

8001000

12001400

16001800

2000

2200

2400

30o

45o

60o

A/T for polarization 1 [m 2/K] for SKA1 (based on SKALA) @ 170 MHz

sin()*cos()

sin

()*

sin

()

-1 -0.5 0 0.5 1-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

* Peak is at 2452 m^2/K

200

2002

00

40060080010001200140016001800

2000

2200

2400

30o

45o

60o

A/T for polarization 2 [m 2/K] for SKA1 (based on SKALA) @ 170 MHz

sin()*cos()

sin

()*

sin

()

-1 -0.5 0 0.5 1-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

* Peak is at 3468 m^2/K

5001000

1500

2000

2500

3000

3400

30o

45o

60o

A/T Stokes I [m2/K] for SKA1 (based on SKALA) @ 170 MHz

sin()*cos()

sin

()*

sin

()

-1 -0.5 0 0.5 1-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.450

500

1000

1500

2000

2500

3000

3500

4000

A/T Stokes I [m2/K] for SKA1 (based on SKALA)

Freq /GHz

A/T

/m

2 /K

Zenith

30o

45o

60o

Effect of Soil/GND – (Soil B – 5% humidity)

Even a bigger pitch may be possible!

0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.450

20

40

60

80

100

120

Freq /GHz

Tg

nd /K

10 cm pitch5 cm pitchNo ground

X-pol

0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45-50

-45

-40

-35

-30

-25

-20

-15

-10

-5

0

Freq /GHz

x-p

ol /

dB

Zenith

22.5 o H-plane

22.5 o E-plane

45 o H-plane

45 o E-plane

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.

– Cost:• Estimated total cost is 5-10 K€ depending on

tools and equipment needed for the tests.

e/o

e/o

e/o

Analogue

ADC: 1GS/s

Data

Control

Sync.

50- 100m all optical

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)

SKALA3(Cambridge)

SKALA4(ASTRON)

SKALA0miniSKALA

(Cambridge)