Phased Array Feed Design - Australia Telescope National ... · PDF file• Why phased array...

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Transcript of Phased Array Feed Design - Australia Telescope National ... · PDF file• Why phased array...

  • Phased Array Feed Design

    Stuart Hay23 October 2009

  • CSIRO. Connected Array CBFM

    Outline

    Why phased array feeds (PAFs) for radioastronomy? General features and issues of PAF approach Connected-array PAF approach in ASKAP

  • CSIRO. Connected Array CBFM

    Why PAFs?

    High sensitivity Wide field of view (FoV) (instantaneous and contiguous)

    Survey speed (apAphy/Tsys)2 x FoV Possibilities for discovery (eg transient phenomena)

    Large frequency range (0.7-1.8GHz)

  • CSIRO. Connected Array CBFM

    PAFs in general

    Concentrator (optics)

    Low-noise amplifier (LNA) +Digital conversion +Polyphase filter

    Beams (weighted sums of inputs)

    Beamformer (digital)

  • CSIRO. Connected Array CBFM

    PAFs vs existing multibeam feeds

    PAF gives complete high-sensitivity sampling of FoV

    Beamformer (digital)

    max/2

    4 2 0 2 40

    0.5

    1

    1.5

    2

    2.5

    Angle (deg)

    Sen

    sitiv

    ity (

    m2

    / K)

    Beams (colors) and combined correlations (black)

    4 2 0 2 40

    0.5

    1

    1.5

    2

    2.5

    Angle (deg)

    Sen

    sitiv

    ity (

    m2

    / K)

    Beams (colors) and combined correlations (black)

  • CSIRO. Connected Array CBFM

    PAFs vs existing multibeam feeds

    PAF has significant mutual coupling effects However beam Tsys amplifier Tmin with optimum (active) noise

    matching of array/amplifiers and optimum beamforming

    0 50 100 1500

    0.5

    1

    1.5

    2

    2.5

    Number of beamformer inputs

    Sen

    sitiv

    ity (

    m2

    / K)

    0 50 100 1500

    50

    100

    150

    200

    250

    Number of beamformer inputs

    Noi

    se te

    mpe

    ratu

    re (

    K)

    Beam Tsys

    Amplifier Tmin

  • CSIRO. Connected Array CBFM

    PAF optics - focal vs image plane

    #elements determined by magnification All elements must be beamformed for

    good FoV limited by subreflector size

    focal plane

    imageplane

    fD

    #elements (f/D)2 and area of FoV Compromise between f/D and Can beamform subsets of elements Can expand FoV by adding more

    elements (upgrade path)

  • CSIRO. Connected Array CBFM

    PAF optics - beam stability

    Beam stability with respect to the astronomical sources is required for high dynamic range image formation

    Possibly solutions in clear-aperture (offset-fed) optics and electronic beam rotation through beamformer weights

    ASKAP will use a 3-axis antenna design

  • CSIRO. Connected Array CBFM

    PAF optcis - beam stability

  • CSIRO. Connected Array CBFM

    PAF/LNA issues

    Uncooled LNAs with Tmin in 20-40K range over 0.5-2GHz have been developed

    Tsys/ap < 70K realistic target that would make PAFs competitive Cooling PAFs is not straightforward

    Many coupled elements distributed over large area However should be further considered

    Differential LNAs and LNAs with >50 noise-match impedance are desired for some PAF designs

    Reduce balun loss Minimize LNA Tmin LNA modelling and measurements require further work

  • CSIRO. Connected Array CBFM

    Connected-array approach to PAF

    Broaden PAF investigation Previously focussed on Vivaldi (ASTRON and DRAO)

    Planar connected arrays Alternative viewpoint emphasizing mutual coupling Possible advantages of planar and low-profile structure

    Cost Loss Integration Noise coupling? Cooling? Other?

    Prototype connected-patch FPA

  • CSIRO. Connected Array CBFM

    Connected-array approach

    Current continuity enhances bandwidth (element spacing

  • CSIRO. Connected Array CBFM

    Approach to the design

    Develop modelling capability Electromagnetic modelling of array Electronic modelling of LNA

    Numerical and experimental investigations of prototype

    Resonances and matching to LNA Radiation pattern in chamber Parkes 12m testbed

    Optimize larger design for ASKAP

    150 100 50 0 50 100 15035

    30

    25

    20

    15

    10

    5

    0

    (deg)

    Pow

    er (

    dB)

    CBFM pol. 1CBFM pol. 2GEMS pol. 1GEMS pol. 2CBFM pol. 1 (no diel.)CBFM pol. 2 (no diel.)

    y (m)

    x (m

    )

    0.2 0.18 0.16 0.14 0.12 0.1 0.08 0.06

    0.06

    0.04

    0.02

    0

    0.02

    0.04

    0.06

    50

    40

    30

    20

    10

    0

    10

    20

    30

    y (m)

    x (m

    )

    0.2 0.18 0.16 0.14 0.12 0.1 0.08 0.06

    0.06

    0.04

    0.02

    0

    0.02

    0.04

    0.06

  • CSIRO. Connected Array CBFM

    Connected-array matching

    Zdiff~377 LNA optimum noise-match impedance in mutually coupled array environment

    Lower Zdiff modifications to array will lessen sensitivity to parasitics

    0.5 1 1.5 2200

    100

    0

    100

    200

    300

    400

    500

    600

    700

    Frequency (GHz)

    Impe

    danc

    e (o

    hm)

    real Zopt

    imag Zopt

    real Zin

    imag Zin

    ZSE ZSE

    Vi+ Vi-

    Patch Patch

    A (Vi+-Vi-)

    Groundplane

    ie ZC=ZSE / 2ZD=ZSE x 2

  • Contact UsPhone: 1300 363 400 or +61 3 9545 2176

    Email: enquiries@csiro.au Web: www.csiro.au

    Thank you

    CSIRO ICT CentreStuart Hay

    Phone: +61 2 9372 4288Email: Stuart.Hay@csiro.auWeb: www.csiro.au/group