Circular Focal Plane Array for Astronomic Applicationscsas.ee.byu.edu/docs/Workshop/Sarkis_Workshop on Phased Array.pdf · Circular Focal Plane Array for Astronomic Applications Rémi

UCL - École Polytechnique de Louvain

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Circular Focal Plane Array for Astronomic Applications

Rémi Sarkis, Christophe Craeye

International Workshop on Phased Array Antenna Systems for Radio Astronomy

May 3-5, 2010 Provo, Utah, USA


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Outline

Introduction

Rectangular Arrays Vs Circular Arrays.

ASM in Circular Arrays

ASM – MoM gives the exact solution for the circular array.

Design of 3D Vivaldi Single Antenna

Return loss and Radiation pattern.

Analysis of Wideband arrays of 3D Vivaldi antennas

Return loss and Radiation pattern.

Future Works

Conclusion


Rectangular Arrays Vs Circular Arrays

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Less truncation effect at the border of the array.

Advantage of the rotation similarity of the radiation pattern.

Polarimetric advantage using different polarizations.

Rotational symmetry: pattern calibration is made easier.

Periodic sector


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ASM-MoM applied to Circular Array

European Conference on Antennas and Propagation, EuCAP 2010.


Wave phenomenology in finite arrays

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Finite array: direct and reflected waves

Generated by single source in periodic structure

Reflected by array ends


The current on a given point can be regarded as progressive waves launched by the excited element and reflected by the ends of the array.

Craeye et Sarkis, ACES Journal 2008.


Array Scanning Method

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Aliasing:

Repetition of the source every N elements

Infinite-array solution for phase shift ψ between elements

Current at ant. m for ant. 0 excited

(B. Munk et al., 1979)


Array Scanning Method

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ASM aliased source ASM aliased sourceFinite array: direct and reflected waves

Generated by single source in periodic structure



Aliased through discrete array scanning method

If Array Scanning Method is implemented with the help of finite summation, the source is repeated. (see figure auxiliary peaks)


ASM applied to Circular Array

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Repeated source every N elements,i.e. always on the same element inN-element circular array : with thealiased source, the exact solution isobtained !


ASM applied to Circular Arrays

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11 12 1 1 1 1 1

21 22 2 1 2 2 2

11 12 1 1 1 1 1

1 2 1

N N

N N

N N N N N N n n

N N NN NN n n

Z Z Z Z I VZ Z Z Z I V

Z Z Z Z I VZ Z Z Z I V

−

−

− − − − − − −

−

=

Method of Moments(N*M)x(N*M) system of equations

N Reduced systems of (MxM).

( ) ( )1

0

1 pN

jmp

pI m I e

Nψψ

−−∞

=

≈ ∑2 with (0 1)p p p NNπψ = < < −

ASM approximation

[ ] ( ) ( )c p pZ I Vψ ψ∞ =

[ ]1 2 1T

c N NZ Z C C C C−=

( )* pjmpC U N e ψ=

Equivalent to DFT approaches to solving block circulant matrix: R. Vescovo: “Inversion of Block-Circulant Matrices and Circular Array Approach”, IEEE Transactions on Antennas and Propagation, Vol. 45, No. 10, October 1997, pp. 1565-1567


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Design of 3D Vivaldi Antenna



Design of 3D Vivaldi Antenna

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a

b

Width a = 24 cm.Height b = 20cm.Circular cavity of diameter d = 2.4 cm.Thickness of 2cm.

Discretization of the 3D Vivaldi antenna.

y

x

z

E-planeH-plane

Coaxial cable will arrive here from inside the 3D

structureNo transitions

required


Manufacturing

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Mazak Variaxis 200 5-axis machineAt the department of mechanical

engineering at UCL

Perspective viewInside view

Coupe viewThe coaxial feeding

The feedDesign characteristics:-Manufacturing precision-Aluminum used for light weight-Almost no soldering is required-Fed via SMA connector on the back


Bandwidth

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This antenna enhance a 4:1 bandwidth

1 2 3 4 5

-50

-40

-30

-20

-10

0

Frequency (GHz)

S11

(dB

)

Return Loss

CST simulationMeasurementMOM3D simulation

Good matching between MoM , CST and Measurements.


Patterns

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MoMCST

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MoMCST

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MoMCST

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MoMCST

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MoMCST

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MoMCST

E-plane(xOz)

H-plane(yOz)

1GHz 3GHz 4GHz


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Circular Array of Wideband Tapered-slot Antennas



Circular Array Design

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Sector of the array without the connection Sector of the array

with the connections

Array structure

This arrays is in manufacturing process


Return Loss

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Connected elements ⇒ No sharp reflection at ends of slots ⇒ Smoother frequency response


Radiation patterns and connecting BF

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E-Plane(xOz)

H-Plane(yOz)

At 2GHz At 3GHzAt 1GHz

With connecting basis functions in red


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Dense circular array for focal plane arrays



Dense Hexagonal Array

20Periodic element of the array

Dense Hexagonal Array


Outer

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E-plane(xOz)

H-plane(yOz)

1GHz 2GHz 3GHz


Inner

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H-plane(yOz)

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E-plane(xOz)

"to be fixed"


Bi-concentric Circular Array

23Periodic element of the array Bi-concentric Circular Array


Outer

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E-plane(xOz)

H-plane(yOz)

1GHz 2GHz 3GHz


Inner

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E-plane(xOz)

H-plane(yOz)

2GHz 3GHz 4GHz

"to be fixed"


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Further studies



Circular structures

27Dense Hexagonal Cells Array ?Concentric Circular Array ?


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Conclusion

Link between ASM and Block circulant matrix solution.

Novel design of 3D Vivaldi antenna

Light weight of the antenna.

Precise fabrication technology.

Suitable to host LNA.

Effect of the connecting functions: smoother frequency response

Study of different circular array structures

Dense and Concentric Hexagonal arrays.

Easier Calibration: Radiation pattern can be compensated.

Proposed further studies.


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Thank You

Documents

Circular Focal Plane Array for Astronomic Applicationscsas.ee.byu.edu/docs/Workshop/Sarkis_Workshop on Phased Array.pdf · Circular Focal Plane Array for Astronomic Applications Rémi