ASKAP Feeds

David DeBoerASKAP Project Director05 May 2009

ASKAP Design Goals

High-dynamic range, wide field-of-view imagingNumber of dishes 36 (3-axis)Optics prime focus f/D 0.5Dish diameter 12 mSurface < 1mmPointing 30 Max baseline 6kmSensitivity 65 m2/KSpeed 1.3x105 m4/K2.deg2

Observing frequency 700 – 1800 MHzField of View 30 deg2

Processed Bandwidth 300 MHzChannels 16kFocal Plane Phased Array 188 elements

+ Infrastructure for new SKA-ready observatory Murchison Radio Observatory (MRO)+ Support of other projects (MWA, PAPER, +)

Two Views of the System Architecture

L ~20mIF

FocalPlaneArray

12mReflector

Receivers200 off feeds700MHz -1800MHz

LO's

2000Gbps

SMF G6525km

Round trip Measurement

All Antennas Other Arrays

400kmSMF G655

>10Gbps

ScienceCentre

FutureRemote Antennas

OADM

ASKAP SITE

LA

N

LAN

LAN

Atomic ClockLO Reference

REPRESENTATIVE ANTENNA

RFoF or Coax

FO

BO

T

AD

C

Supe

rhet

Coa

rse

PFB

FO

BO

T

Bea

mfo

rmer

P

FB

Correlator

192Coarse

filterbankover 48 FPGAs

16 way cross

connecton ATCA

backplane

4 way connection on boardBW per FPGA 19MHz

Beam forming

Data reordering

DRAM

A/DsFine

Filterbank

At Antenna At Central site one ATCA chassis per antenna

192 10G

optical links

Field-of-View

Receivers/Data Transport

High-Z, differential low-noise amplifiers

~3:1

Up-conversion

Analog fiber to BF

Receiver-on-a-chip

Receiver elements

LNA 700-1300 MHz

700-1800 MHz

Band selection

1000-1800 MHz

Mixer1BPF

Mixer2 Anti Alasing filterAmp

LO2=4430MHz(Low side LO)

LO1=5850-6650MHz(High side LO)

IF=570MHzBW=300MHz

IF=5GHzBW=300MHz

To ADCIF1 IF2

Antenna/LNA Sub-octave band selection

Conversion module

DigitalAttenuator

Gain control

RF Cable(20-25m)

DIGITAL SLIDE

Digital Uniboard

CSIRO. SKA2008

ASKAP data flow, processing, and storage

Analog Systems IPT team

• Low-noise amplifier design• Rob Shaw • Peter Axtens

• Receiver electronics• K. Jeganathan • Simon Mackay • Suzy Jackson• Yoon Chung

• Plus consultation services of:• Pat Sykes• Michael Brothers• Matt Shields• Mark Bowen • Santy Castillo• Henry Kanoniuk• Les Reilly

Russell Gough (IPT leader)

John O'Sullivan (IPT scientist)

• Electromagnetic design of FPA and calibration system

• Stuart Hay

• Rong-Yu Qiao

• Francis Cooray

• Doug Hayman

• Aaron Chippendale

• Mechanical design

• Deszo Kiraly

• Russ Bolton

• Paul Doherty

• Eliane Hakvoort

• Workshop staff (3 EFT)

Projected staff resources (2009 – 2012)

Russell Gough (IPT leader) 80%

John O'Sullivan (IPT scientist) 40%

Stuart Hay 100% K. Jeganathan 100%

Rong-Yu Qiao 100% Simon Mackay 100%

Francis Cooray 100% Suzy Jackson 100%

Doug Hayman 100% Yoon Chung 50%

Aaron Chippendale 50% Plus consultation services of:

Rob Shaw 60% Pat Sykes 10%

Peter Axtens 80% Michael Brothers 20%

Deszo Kiraly 40% Matt Shields 20%

Russ Bolton 70% Mark Bowen 20%

Paul Doherty 30% Santy Castillo 20%

Eliane Hakvoort 30% Henry Kanoniuk 10%

Workshop staff (3 EFT) 100% Les Reilly 10%

Total ~16 EFT

Introduction - Analog Systems

• The ASKAP analog system • amplifies astronomical signals, frequency translates (twice) and

filters the signals before they are sampled by the ADC.

• The ASKAP analog system includes

• the “Chequer-board” Focal Plane Array

• the prime focus electronics package

• the pedestal analog electronics package

• calibration signalling system

• The calibration signalling system• allows the complex gain of each receiver channel to be

measured and monitored.

• uses three dual polarisation radiators on the reflector surface. (One radiator on bore-sight the other two off-axis)

Scope of Analog Systems IPT

• The “Chequer-board” Focal Plane Array

• Electromagnetic design

• Optimisation of Chequer-board array and low-noise amplifiers

• The prime focus electronics package, which includes:

• the balanced low-noise amplifiers, each with a post-amplifier gain-slope equalizer

• broadband bandpass filters and switchable sub-band select filters

• driver amplifiers to send the RF signals from the prime focus electronics package to the pedestal analog electronics package

• control and monitor electronics and power supply filtering

• The calibration signalling package.

Analog System specifications

• Frequencies• RF band 700 – 1800 MHz• Instantaneous bandwidth 300 MHz• Sampled band 424 – 724 MHz• Sample clock 768 MHz

• Low-noise amplifiers• Low-noise amplifier noise temperature 40 Kelvin • Low-noise amplifier gain 27 dB

• Gain• Nominal total nett gain 72 dB• Nominal nett gain at prime focus 68 dB• Assumed loss in cable 17dB at 0.7 GHz

(from prime focus to pedestal) 31dB at 1.8 GHz• Nominal nett gain in pedestal 21dB at 0.7 GHz

35dB at 1.8 GHz• Output power (to digitiser)

• Nominal output power -19 ±1 dBm into 50 Ohms

Timeline and Milestones

• March 2009: Analog Systems PDR

• March 2009 - September 2009

Build and test first prototype of Analog System

• September 2009: Analog Systems CDR

• September 2009 - April 2010

Build and test Analog System for Antenna #1

• April 2010: Antenna 1 construction complete

• April 2010 - June 2010

Install Analog System in Antenna #1

• June 2010: Complete installation of equipment in Antenna #1

• June 2010 - November 2010

Build and test Analog Systems for Antennas #2 - #6

Install Analog Systems in Antennas #2 - #6

• November 2010: Complete installation of equipment in Antennas #2 - #6

Other design options

System-on-a-chip

Microcooling

FPA concept

• Connected checkerboard array

Patches Transmission lines

Ground plane

Digital beamformer

Low-noiseamplificationandconversion

Weighted sum of inputs

Currents

FPA Electronics housing

FPA Package design

RFI shield and weather proof

octagonal enclosure

Rigid focal plane baseplate

Additional Antenna leg attachment point

Main Antenna leg bracket fixture

RF outputs in weatherproof ports

DC / Control and cooling ports

FPA Package internal design

Isolated cable interface bulkheads

Module conduction cooling plates

Centralised cooling

Circulation fans on air baffle

Cooling conduction and air circulation

Module mounting and cooling plate

Module guides and heat conduction path

Cooling air upward vents

LNA RF shield and heatsinks

LNA assembles and RFI shield heatsinks

Cooling air galleries

FPA mounting

FPA dielectric weather shield

Baseplate relief for conduction reduction

Antenna legmounting points

Phased Array Feed

Approach to the design

• Development of modelling capability• Modelling and experimental investigations of 5x4 array

• Refined and enlarged design for ASKAP

Modelling capability

• YA: CBFMoM, GEMS, MWS, PO• YL and LNA noise: MO, measurements on LNA, MWS transitions• Vb (signal + noise) by cascading Y and equivalent-current covariance matrices• Software checking by independent codes

1,ow

2,ow

1,oV

2,oV

Array and reflector

LNA+

AY

LY

Plane wave/radiation patternports

Array ports(eg at groundplane)

Sourcesand spillover

Temperature TFlux density S

Vbeam=wt

oVo

Gmaxavailable

Loading/beamforming configurations

D

iL

D

i

N

ibeam VwV ,

1

)(,,

1

iLiiLi

N

ibeam VwVwV

VL,iD

IA,i¯

IL,iD

IA,i+

IS,i¯

IL,i+

VL,iC

ZL,iC ZL,i

D

VA,i¯

VA,i+

IL,i¯

IL,iC

IS,i+IA,i¯

VA,i¯

IA,i+VA,i+

i+

i¯

g

2a

2b

VA,,i¯

IA,i¯IL,i¯

IS,i¯

IA,i+

IS,i+

IL,i+

VL,i+

ZL,i

ZL,i

VL,i¯VL,i+

VA,i+

Differential:

Single-ended:

Differential single-ended: )(,,

1

iLiL

D

i

N

ibeam VVwV

22ie ,,,. iLC

iLiLD

iL ZZZZ

ηtot verses loading/beamforming configurations

f/D=0.4 f/D=0.5Differential: LNA stability and array resonance problemsSingle-ended: Good but not worth x2 electronicsDifferential single-ended: Current focus

Optimum ηtot impedances

Radiation-pattern test configuration

• SE patterns easiest to test before LNA available

• SE ports :50ohm SMA connectors• Differential loads: nominal 300ohm resistors

GEMS vs measured radiation patterns

CBFM conduction and polarization currents

Effects of dielectric PCB (RO4003C)

• Noticeable in radiation patterns• Some variation in Zopt (eg 30% increase at 1.5GHz)• Small addition to Tsys: (conductor+dielectric) < 3K

MWS vs measured radiation patterns

• Adaptive meshing has also resulted in much improved agreement with measurements

Mutual coupling test configuration

Differential radiation patterns

• LNA asymmetry requires general 3-port model to characterize

• Patterns dependent on LNA port / array port mapping

Preliminary design of ASKAP-sized array

• FoV 30 sq deg requires larger array• 11x10 minus some corner elements• 188 diff ports (112) patches

LNA Schematic

ATF-35143 PHEMTs

Symmetric structure

These are the generations

• Version 1: the design I inherited, with slight revisions. Installed on Parkes 5x4.

• Version 2: redesigned for lower input capacitance.

A sample noise temperature measurement

Version 1 noise temperature

Performance (I)

Version 2 noise temperature

Performance (II)

Version 2 diff-mode input impedance

Performance (III)

Version 2 gains

Shielding, shielding, shielding

Inside the screened room . . .

And outside . . .

Parkes Observations

• Phase 1• Single dish, single 8 by 8 real time full

correlator 0.875 MHz BW• GPS L2 (1227.6 MHz, 10 Mchip/sec) 10 MHz to

nulls broad band signal to calibrate array and set beamformer weights.

• Strong astronomical source (Virgo A) drift scans to measure Tsys/eff (not Dicke switched hence vulnerable to gain variations and also is astronomical source confusion limited)

• Tsys/eff ~ 175 K +/-?

Parkes Observations

• Phase 2• Single dish• Polyphase filter to 0.875

MHz BW channels, record samples all inputs to disk

• Software correlate to produce covariances for up to 48 inputs (40 from array)

• Measure GPS and Virgo A as before

• Roughly consistent with Tsys/eff ~ 175 K but still fundamentally inaccurate

• Peak beamformed efficiency ~ 4 times single element efficiency

• Beamformed Tsys 0.8 times element Tsys

Phased Array Feed Results

Parkes ObservationsCaveats and next steps

• 1st version installed LNA was sub-optimal• Preferred LNA version with lower input parasitics, better match

was marginally stable on array and was pulled at last minute• Next steps

• Resolve if possible modelling vs measurement inconsistencies• Install new version LNA - should be better match, broader

response• Use array with “popcorn box” enclosure, software correlator and

64 m to get array only Tsys, efficiency using sky vs absorber measurements

• Array on 12 m with 64 m to repeat previous measurements plus beamforming

• Improve modelling vs measurement match• Extend to polarization• Refine calibration methods using reflector sources and

astronomical measurements.

Where does the noise come from?

• Sky noise• Spillover: feed radiation past dish to ground modelled,

no feed scattering at this stage• Array resistive losses: based on surface resistive loss

in each MoM basis element• Optional matching network losses• LNA: 2 Port Rn, Gammaopt, Fmin or full 3 port S par

plus noise wave• Derived from mix or model (MWS), transistor manufacter

specs (measurement + extrapolation), measurement (S par, F)

• Noise from later receiver stages• Hot absorbing load enclosing array• Signal contributions via array system model plus

reflector physical optics

Noise contributions• Noise at beamformer output

• Conjugate match,• Max SNR• Aperture fit (best

beamshape)• Using 3 Port model of old LNA

• still somewhat idealized• PCB-connector parasitics

and input component losses not yet accounted for

• Differential combiner gain mismatch not properly modelled

• Probably optimistic overall but matches 300 Ohm lab noise temp measurements

• Receiver noise dominates• Array resistive losses, LNA

load, matching network are insignificant

Receiver block diagram (high level)

Assumption: NTreceiver elements= 5°KNTantenna Spillover = 135°KRF cable loss = 26dB at 1400MHz

Receiver elements

LNA

700-1800 MHz

RF cable

700-1300 MHz

1000-1800 MHz

RF amp

Sub-octaveband selection

RF amp

700-1800 MHz

BPF Mixer1BPF

Mixer2Anti-alasing

filter

LO2=4424MHz(Low side LO)

LO1=5848-6648MHz(High side LO)

IF=574MHzBW=300MHz

IF=4998 MHzBW=300MHz

To ADC

IF1 IF2

Conversion module

DigitalAttenuator

Gain control

Prime focus RF gain block

Gain -- 27 41 -26 30

Noise Temperature (°K) 140 40 338 115161 16681

Noise Figure (dB) -- 0.56 3.35 26 17.67

Added NT (°K) 140 40 0.67 0.02 1.05

Cascaded NF (dB) 1.711 2.097 2.103 2.103 2.113

Cascaded Gain (dB) -- 27 68 42 72

I/P power density (dBm/MHz) -- -116 -89 -48 -74

O/P power density (dBm/MHz) -116 -89 -48 -74 -44

DC power consumption: per channel (Watts) -- 0.36 2.4 -- 3.6 per Antenna (Watts) -- 72 480 -- 720

Conversion module block diagram

RF mixer RF BPF

Digital Attenuator

IF-mixer

IF BPFIF amp-1

Anti-aliasing Filter

ADC

IF amp-2

PAD

RF amp-3

RF Amp-2

Gain control (4/5lines)

PAD

PAD

PAD

PAD

IFDetector

14 dB coupler

32dBcoupler

Self test control

LO1

LO2

IF limit pass/fail

Coupler

PAD

Vdd

RF Amp-1Equalizer

Lo trap

Divider(÷4)

RF Coaxial cable

DCPOWER

DC Power

Power overload Power enable

RF IN

IF OUT424-724MHz424-724MHz

Summary

• More work required on modelling and characterizing LNAs and associated transitions from array

• Modelling indicates Tsys/effap goals should be achievable with better control of these effects

• Lowering array impedance should help (scope exists)

Conclusion

• We need to reconcile telescope measurements, lab LNA measurements and modelling

• Biggest uncertainty is probably the LNA full noise model accounting for various parasitics etc

• Work in progress – has been delayed

• Further array and PAF on telescope measurements as well as processing of existing data are needed

• Also work in progress – also delayed

• A better or more simple understanding of the relevant signal and noise matching parameters for a PAF is desirable for design and optimisation

• However, brute force application of full EM + circuit modelling is also possible.

• A production array will ideally have lower impedance levels in order to ease some of the difficulties