Circular Focal Plane Array for Astronomic Applications

Transcription

1 International Workshop on Phased Array Antenna Systems for Radio Astronomy Circular Focal Plane Array for Astronomic Applications Rémi Sarkis, Christophe Craeye May 3-5, 21 Provo, Utah, USA 1

2 Introduction Outline 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 2

3 Rectangular Arrays Vs Circular Arrays Periodic sector 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. 3

4 European Conference on Antennas and Propagation, EuCAP 21. ASM-MoM applied to Circular Array 4

5 Wave phenomenology in finite arrays Craeye et Sarkis, ACES Journal 28. Finite array: direct and reflected waves Reflected by array ends 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. 5

6 Array Scanning Method (B. Munk et al., 1979) Current at ant. m for ant. excited Infinite-array solution for phase shift ψ between elements Aliasing: Repetition of the source every N elements 6

7 Array Scanning Method ASM aliased source Finite array: direct and reflected waves ASM aliased source Reflected by array ends Generated by single source in periodic structure Reflected by array ends 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) 7

8 ASM applied to Circular Array Repeated source every N elements, i.e. always on the same element in N-element circular array : with the aliased source, the exact solution is obtained! 8

9 ASM applied to Circular Arrays Method of Moments (N*M)x(N*M) system of equations 1 jmψ p N 1 ( ) ( ψ p ) I m I e N p= 2π ψ p = p with ( < p< N 1) N N Reduced systems of (MxM). Z11 Z12 Z1N 1 Z1N I1 V1 Z21 Z22 Z2N 1 Z 2N I 2 V 2 = ZN 11 ZN 12 ZN 1N 1 ZN 1N In 1 Vn 1 Z Z Z Z I V N1 N 2 NN 1 NN n n ASM approximation [ Zc] I ( ψ p) = V ( ψ p) [ ] Z = Z CC C C c 1 2 N 1 N p C = 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. 1, October 1997, pp p jm T 9

10 European Conference on Antennas and Propagation, EuCAP 21. Design of 3D Vivaldi Antenna 1

11 H-plane E-plane Design of 3D Vivaldi Antenna a b Coaxial cable will arrive here from inside the 3D structure No transitions required z y x Width a = 24 cm. Height b = 2cm. Circular cavity of diameter d = 2.4 cm. Thickness of 2cm. Discretization of the 3D Vivaldi antenna. 11

12 Manufacturing Inside view Perspective view Mazak Variaxis 2 5-axis machine At the department of mechanical engineering at UCL Design characteristics: -Manufacturing precision -Aluminum used for light weight -Almost no soldering is required -Fed via SMA connector on the back The coaxial feeding The feed Coupe view 12

13 Return Loss Bandwidth -1 S11 (db) CST simulation Measurement MOM3D simulation This antenna enhance a 4:1 bandwidth Frequency (GHz) Good matching between MoM, CST and Measurements. 13

14 3 Patterns 1GHz 3GHz 4GHz E-plane (xoz) MoM CST MoM CST MoM CST H-plane (yoz) MoM CST MoM CST MoM CST

15 European Conference on Antennas and Propagation, EuCAP 21. Circular Array of Wideband Tapered-slot Antennas 15

16 Circular Array Design Sector of the array without the connection Array structure Sector of the array with the connections This arrays is in manufacturing process 16

17 Return Loss Connected elements No sharp reflection at ends of slots Smoother frequency response 17

18 E-Plane (xoz) Radiation patterns and connecting BF 3 At 1GHz At 2GHz At 3GHz H-Plane (yoz) With connecting basis functions in red 18

19 European Conference on Antennas and Propagation, EuCAP 21. Dense circular array for focal plane arrays 19

20 Dense Hexagonal Array Periodic element of the array Dense Hexagonal Array 2

21 E-plane (xoz) H-plane (yoz) Outer 1GHz 2GHz 3GHz

22 Inner 1GHz 2GHz 3GHz H-plane (yoz) E-plane (xoz) "to be fixed"

23 Bi-concentric Circular Array Periodic element of the array Bi-concentric Circular Array 23

24 E-plane (xoz) H-plane (yoz) Outer 1GHz 2GHz 3GHz

25 E-plane (xoz) H-plane (yoz) Inner 2GHz 3GHz 4GHz "to be fixed" 25

26 European Conference on Antennas and Propagation, EuCAP 21. Further studies 26

27 Circular structures Concentric Circular Array? Dense Hexagonal Cells Array? 27

28 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. 28

29 European Conference on Antennas and Propagation, EuCAP 21. Thank You 29