Chalmers University of Technology

Development of a Coolable Decade Bandwidth Eleven Feed System for SKA &

VLBI 2010 Radio Telescopes

Per-Simon Kildal

Chalmers University of Technology

Gothenburg, SWEDEN15 cm diameter for 2-13 GHz

Chalmers University of Technology

Start in 2003: ATA array, forrunner of US SKA (500 MHz – 10 GHz)

Chalmers University of Technology

Size and complexity for fmin = 500 MHz

ATA feed:Too large

& Problem

with phase center

variations

Eleven feed:Eleven times

smaller&

No problem with phase

center variations

Chalmers University of Technology

Size and complexity for fmin = 500 MHz

ATA feed:Too large

& Problem

with phase center

variations

Eleven feed:Eleven times

smaller&

No problem with phase

center variations

Chalmers University of Technology

Idea behind Chalmers feed• Two parallel dipoles over ground

– from book about Radio Telescopes by Christiansen and Högbom– equal E- and H-plane patterns– phase center is locked to the ground plane – low far-out sidelobes and backlobes.

• Bandwidth by– Logperiodic– Folded dipoles

• ”Eleven” name inspired by– Basic dual-dipole geometry– Directivity 10-11 dBi and S11 <-10 dB– Over more than decade bandwidth (>11)– And size eleven times smaller than

classical log-periodic feeds

Chalmers University of Technology

Interdisciplinary team developing coolable VLBI2010 hardware from Sept 2008

• Interdisciplinary research at Chalmers– Department of Signals and Systems, Chalmers

– Department of Radio and Space Sciences, Chalmers

– Department of Microtechnology and Nanoscience

– Chalmers Industriteknik (CIT) for helping to commercialize:

• No dedicated SKA funding since 2003-2005 (US SKA project)

• Hardware orders from VLBI 2010 partners: – Vertex (BKG) in Germany

– Statkart in Norway

– Haystack radio telescope in USA

Chalmers University of Technology

Main contributions• Dr Jian Yang: “Electrical design”

• Dr Miroslav Pantaleev and Leif Helldner: “Mechanical and cryogenic design”

• Benjamin Klein, South Africa “Noise modeling”

• Drawing, assembled feed, cooled feed

Chalmers University of Technology

Assembled 2-13 GHz hardware and drawing

Chalmers University of Technology

The following choices were made during the project

• All materials MUST stand cryogenic temp

• 4 separate panels (petals) with log-per. dipoles

• PCB technology for antenna petals

• Minimize thickness of dielectric in center

• 2x4 ports with no crossing lines in center puck

• Differential feed line impedance 200 Ohms

• Experimental model has 2x4 coaxial ports, transf to 50 Ohms

• We work also with 4 differential 200 Ohms LNAs, 2 per polarization

Chalmers University of Technology

Front and back sides of Eleven feed with 8 single-ended ports

Chalmers University of Technology

Integration with differential 200 ohm LNAs from Caltech

• Four cryogenic differential 200 ohm LNAs from Caltech mounted on the back side of the ground plane

• Requires in addition two power combiners to get two polarizations out from the cryostat

• Expected delivery of LNAs: June 2010

Chalmers University of Technology

Early computed still valid efficiency vs. subtended half angle

Optimum subtended angle >50 deg

Chalmers University of Technology

Early computed figure of Merit versus F/Doptimum F/D = 0.4 (i.e. 64 deg)

Useful range 0.33 < F/D < 0.50, i.e. 75 deg < 55 deg

Chalmers University of Technology

Simulations and Measurements at Chalmersof input reflection coefficient (4 ports excited)

(power dividers and cables were calibrated away)

1 3 5 7 9 11 13 15 1718-20

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eff

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measuredsimulated

Chalmers University of Technology

Co- and crosspolar patterns in 45 deg planetotal and with removed higher order variations

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theta (deg)

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2GHz2.1GHz

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2.4GHz2.5GHz

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2.00 GHz2.10 GHz

2.20 GHz

2.30 GHz

2.40 GHz2.50 GHz

2.60 GHz

2.70 GHz

2.80 GHz2.90 GHz

Chalmers University of Technology

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3.00 GHz3.10 GHz

3.20 GHz

3.30 GHz

3.40 GHz3.50 GHz

3.60 GHz

3.70 GHz

3.80 GHz3.90 GHz

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3GHz

3.1GHz3.2GHz

3.3GHz

3.4GHz

3.5GHz

3.6GHz

3.7GHz3.8GHz

3.9GHz

Co- and crosspolar patterns in 45 deg planetotal and with removed higher order variations

Chalmers University of Technology

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4.00 GHz4.10 GHz

4.20 GHz

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4.40 GHz4.50 GHz

4.60 GHz

4.70 GHz

4.80 GHz4.90 GHz

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4GHz

4.1GHz4.2GHz

4.3GHz

4.4GHz

4.5GHz

4.6GHz

4.7GHz4.8GHz

4.9GHz

Co- and crosspolar patterns in 45 deg planetotal and with removed higher order variations

Chalmers University of Technology

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5.00 GHz5.10 GHz

5.20 GHz

5.30 GHz

5.40 GHz5.50 GHz

5.60 GHz

5.70 GHz

5.80 GHz5.90 GHz

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5GHz

5.1GHz5.2GHz

5.3GHz

5.4GHz

5.5GHz

5.6GHz

5.7GHz5.8GHz

5.9GHz

Co- and crosspolar patterns in 45 deg planetotal and with removed higher order variations

Chalmers University of Technology

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6.00 GHz6.10 GHz

6.20 GHz

6.30 GHz

6.40 GHz6.50 GHz

6.60 GHz

6.70 GHz

6.80 GHz6.90 GHz

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6GHz

6.1GHz6.2GHz

6.3GHz

6.4GHz

6.5GHz

6.6GHz

6.7GHz6.8GHz

6.9GHz

Co- and crosspolar patterns in 45 deg planetotal and with removed higher order variations

Chalmers University of Technology

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7GHz

7.1GHz7.2GHz

7.3GHz

7.4GHz

7.5GHz

7.6GHz

7.7GHz7.8GHz

7.9GHz

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7.00 GHz7.10 GHz

7.20 GHz

7.30 GHz

7.40 GHz7.50 GHz

7.60 GHz

7.70 GHz

7.80 GHz7.90 GHz

Co- and crosspolar patterns in 45 deg planetotal and with removed higher order variations

Chalmers University of Technology

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8.00 GHz8.10 GHz

8.20 GHz

8.30 GHz

8.40 GHz8.50 GHz

8.60 GHz

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8.80 GHz8.90 GHz

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8GHz

8.1GHz8.2GHz

8.3GHz

8.4GHz

8.5GHz

8.6GHz

8.7GHz8.8GHz

8.9GHz

Co- and crosspolar patterns in 45 deg planetotal and with removed higher order variations

Chalmers University of Technology

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9.00 GHz9.10 GHz

9.20 GHz

9.30 GHz

9.40 GHz9.50 GHz

9.60 GHz

9.70 GHz

9.80 GHz9.90 GHz

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9GHz

9.1GHz9.2GHz

9.3GHz

9.4GHz

9.5GHz

9.6GHz

9.7GHz9.8GHz

9.9GHz

Co- and crosspolar patterns in 45 deg planetotal and with removed higher order variations

Chalmers University of Technology

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10.00 GHz10.10 GHz

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10.40 GHz10.50 GHz

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10.80 GHz10.90 GHz

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10GHz

10.1GHz10.2GHz

10.3GHz

10.4GHz

10.5GHz

10.6GHz

10.7GHz10.8GHz

10.9GHz

Co- and crosspolar patterns in 45 deg planetotal and with removed higher order variations

Chalmers University of Technology

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11.00 GHz11.10 GHz

11.20 GHz

11.30 GHz

11.40 GHz11.50 GHz

11.60 GHz

11.70 GHz

11.80 GHz11.90 GHz

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11GHz

11.1GHz11.2GHz

11.3GHz

11.4GHz

11.5GHz

11.6GHz

11.7GHz11.8GHz

11.9GHz

Co- and crosspolar patterns in 45 deg planetotal and with removed higher order variations

Chalmers University of Technology

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12.00 GHz12.10 GHz

12.20 GHz

12.30 GHz

12.40 GHz12.50 GHz

12.60 GHz

12.70 GHz

12.80 GHz12.90 GHz

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12GHz

12.1GHz12.2GHz

12.3GHz

12.4GHz

12.5GHz

12.6GHz

12.7GHz12.8GHz

12.9GHz

Co- and crosspolar patterns in 45 deg planetotal and with removed higher order variations

Chalmers University of Technology

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13.00 GHz13.10 GHz

13.20 GHz

13.30 GHz

13.40 GHz13.50 GHz

13.60 GHz

13.70 GHz

13.80 GHz13.90 GHz

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13GHz

13.1GHz13.2GHz

13.3GHz

13.4GHz

13.5GHz

13.6GHz

13.7GHz13.8GHz

13.9GHz

Co- and crosspolar patterns in 45 deg planetotal and with removed higher order variations

Chalmers University of Technology

Sub-efficiencies from measured radiation patterns at TUD

2 3 4 5 6 7 8 9 10 11 12 13-4

-3.5

-3

-2.5

-2

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Frequency (GHz)

Eff

icie

ncy

(dB

)

esp

eBOR1

epol

eill

e

eap

Looks good, except for BOR1 efficiency below 2.5 GHz and above 9 GHz.

BOR1 efficiency is power lost in sidelobes due to higher order variations.

Chalmers University of Technology

After survival test

to 14 K

Three stages of cryostat

(Dewar) can be seen

Chalmers University of Technology

Deformation simulations and testing at cryogenic temperatures

Chalmers University of Technology

Integration of Eleven feed in cryostat

The MIL infrared filter reduces the temperature to 25K

The 70K shield has infrared window of one layer Teflon

The temperature on the Feed surface is measured with temperature sensor Lakeshore DT-470 mounted on thin copper support soldered at the edge of the third dipole.

Chalmers University of Technology

Front and back sides of Eleven feed with 8 single-ended ports

Chalmers University of Technology

Noise Temperature Measurements

Chalmers University of Technology

Noise temperatures

Ohmic loss

LNA

Sky and ground

Total predicted and measured

Chalmers University of Technology

Summary of measurement results

• Hardware: Good. Appears solid and appealing• Matching: abs(S11) < -10 dB up to 13 GHz

– measured by removing effects of power dividers and cables by calibration

• Independent gain measurements at Technical University of Denmark – Losses smaller than 0.5 dB (Uncertainty due to multiple reflections between

180 deg hybrid, 3dB power divider and antenna, which were not calibrated out in this case)

– Radiation patterns: Good between 2.5 and 9 GHz. Otherwise low BOR1 efficiency

– Overall efficiency in reflector better than -2 dB between 2.5 and 9 GHz

• Promising system noise measurements with TLNA = 5 – 10 K

Chalmers University of Technology

Integration with differential 200 ohm LNAs from Caltech

• Four cryogenic differential 200 ohm LNAs from Caltech mounted on the back side of the ground plane

• Requires in addition two power combiners to get two polarizations out from the cryostat

• Expected delivery of LNAs: June 2010

Chalmers University of Technology

Planned work• Design and test compact 1-10 GHz SKA model

• Improve low BOR1 efficiency above 9 GHz

• More studies of radiation fields and S11 in cryostat

• Improve noise models

• Test with 4 differential LNAs

• Integrate and test with passive balun and 2 single-ended LNAs

• More optimizatioins and compare with horn solutions (narrow band)

Chalmers University of Technology

Comparison of figure of merit A/T (predicted)

A/T of the Eleven feed system• For a reflector of 1 m2 area with subtended half angle of 60o, i.e. F/D = 0.433. • Cooled system is with Caltech cryogenic LNA and cryostat is at 30 K. • The uncooled system is with Chalmers room temperature LNA at room temperature.