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Feeds and LNA’s for SKATDP Progress Report, June 4, 2010

S. WeinrebCaltech

1. Caltech EE group2. SKA-Mid receiver requirements3. Five candidate feeds4. Quadridge update5. ATA feed update6. Eleven update7. QSC update (by G. Cortes)

Ahmed Akgiray – Ph.D. student SKA feed design and integration

Hamdi Mani – Research technician worked on everything

Glenn Jones - Ph.D. graduate 2009 works on wide bandwidth processing

Zan Zhang – MSEE graduate 2010 SKA feed design and tests

Caltech EE Radio Astronomy Group, May, 2010Damon Russell – Ph.D. student LNA design and testing

Steve Smith – Research engineer, LNA’s, systems

Hector Navarette – Research technician, LNA’s construction

Joe Bardin – Ph.D. graduate SiGe Cryogenic LNA’s

SKA Mid Reflector Array – Receiver Requirements

1. Operation from 0.3 to 10 GHzA. > 60 % EfficiencyB. Tsys < 35K for 0.8 to 10 GHz

2. Secondary but important considerationsA. Power consumptionB. ManufacturabililtyC. MaintainabilityD. Cost including IP rightsE. Stabiliy for dynamic range and polarization

3. Reference designA. Uncooled 0.3 to 1.4 GHz receiver with 0.8m diameterB. Cooled 1.4 to 10 GHz receiver with 0.3m diameter dewarC. Benchmark against octave band receiver (0.7 to 1.4 or

5 to 10 GHz)

Status of Candidate Feeds

QUADRIDGE – Cooled 3.5 to 14 GHz on 34m telescope with measured efficiency and Tsys. Versions for 0.3 to 1.5 and1.4 to 10 GHz in design.

ATA – Uncooled 0.5 to 11 GHz on 42 ATA antennas with 40 to 100K Tsys. Prototypes of cooled 1 to 10 GHz versions are under test.

QSC - Uncooled 0.4 to 4 GHz prototype constructed and tested showing good patterns and return loss. Update by G. Cortes follows.

ELEVEN – Cooled 2 to 12 GHz prototype with measured patterns, return loss and noise. A 1 to 10 GHz cooled prototype under construction and will be delivered to Caltech this summer.

SINUOUS – In design and test at NRAO. Uses foam support and dewar.

Improvements to Quadridge Feed Good return loss is achieved from 1.4 – 11GHz

5mm

LNA

LNA

Probe coupling 100 ohm slot line to microstrip;

Concept for Integration of LNA’s Into Dual-Polarized Quad-Ridge Feed

• Single-ended 100 ohm LNA’s are mounted on bottom side of fins with probe coupling across slot to opposite fin.• Coaxial output and bias lines of LNA will be routed along back of fin• LNA will be on a bolt-in copper carrier for easy replacment

LNA on 10mm base could be repackaged to 5mm x 20mm area

Secondary (shadow)

2-14 GHz Cooled Feed 0.5-4 GHz Feed, Cooled LNA

Rotatable Tertiary

Photograph of 0.5 to 14 GHz System at Goldstone DSS28, October, 2008

Efficiency and Tsys of Quadrige Feed Measured on 34m GAVRT Telescope

Two Concepts for Cooling of the ATA Feed

• Current ATA feed is uncooled (with LNA cooled to 65K) and covers 0.5 to 11 GHz with system noise temperature of 40 to 100K• Two concepts to cool the feed to reduce Tsys to < 35K over the band of 1 to 10 GHz or higher are being investigated.

Cooled feed in aluminum vacuum chamber with Mylar window

Cooled feed in glass bulb vacuum chamber

Coolable Prototype of ATA Feed at Caltech for Tests of Impedance, Pattern, and Noise

Temperature• Feed made of copper (to be plated) and is ~40 cm long• Feed tips are connected to LNA within pyramid by 93 ohm coaxial cable as shown at right below.• Tests will be conducted during summer of 2010

Eleven Feed - Noise of Cryogenic Feed and LNA Now Measured(Beaudoin, Klein, Yang, Kildal, and others)

•Noise measured for feed, baluns, and LNA’s at 20K•Measured patterns predict good efficiency

Very Low Noise Amplifier Development Summary - 2009

• InP HEMTS - Indium-phosphide high-electron-mobility transistors have been implemented in almost all low-noise amplifiers in radio astronomy for the past 10 years with little change in performance. They are usually cooled to 15K to reduce the noise by an order of magnitude. The noise performance from wafer to wafer can vary by a factor of two due to unknown reasons.

• Room Temperature Very Low Noise Amplifiers. - The cost of the large number of receivers required by arrays could be greatly reduced if LNA’S with sufficiently low noise could be realized at room temperature. Transistor device improvements may enable this. Current performance is around 17K noise or 0.25 dB noise figure at 1.4 GHz; a goal is < 10K of noise (0.14 dB NF) at 1.4 GHz.

• SiGe HBT - A promising new transistor, the SiGe HBT, is being rapidly developed for high speed computer and communication applications. These transistors greatly improve in current gain and transconductance when cooled. During the past year SiGe amplifiers with noise temperatures of <5K at frequencies under 4 GHz have been built and tested at Caltech using transistors from IBM and STM. Advantages are: 1) simultaneous noise and power match by feedback, 2) high gain stability, 3) can be integrated with CMOS on the same chip. 4) rapidly developing technology.

6 Models, @ 15K

SiGe HBT

001 to 1 GHz < 6K

1 to 3 GHz < 8K

InP HEMT

0.5 to 11 GHz, Tn < 6K

4 to 14 GHz, Tn < 8K

6 to 20 GHz, Tn < 12K

11 to 26 GHz, Tn < 20K

Differential InP HEMT

0.5 to 11 GHz,Tn <18K at 60K

Caltech-Developed Cryogenic LNA’s

eCaltech EE has Delivered 400 LNA’s to Other Research Centers During the Past 6 Years

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Packaged Differential Cryogenic LNA

Will be used for tests of ATA, QSC, and Eleven feeds and is available if a differential transition to a quadridge feed is desired. Optimum

generator impedance is in the 200 ohm range.

200 ohm differential

input

50 ohmcoaxial output

InP HEMT MMIC LNA

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Noise Temperature Measurement of Differential LNA’s• Noise temperature of a differential amplifier can be measured with the Y factor method by dipping a termination resistor in LN2 at 77K

• The resistance change vs temperature can be measured very accurately at DC with on ohmmeter. The change in typical thin-film resistance is negligible.

• Shown below is a small board with two 270 ohm resistors connected to two differential LNA’s with a gold-plated SS tubing quad transmission lines.