Advanced Array Antennas: Conformal Arrays and Digital Beamforming

Transcription

1 Advanced Array Antennas: Conformal Arrays and Digital Beamforming Professor Lars Josefsson Lars Microwave, Sweden Dr. Patrik Persson Ericsson AB, Sweden Dr. Hans Steyskal S4 Inc, Hanscom AFB, MA, USA

2 Advanced Array Antennas Welcome to CEI Course # 21 on Conformal Arrays & Digital Beamforming Lars Josefsson Lars Microwave, Göteborg, Sweden Patrik Persson Ericsson AB, Göteborg, Sweden Hans Steyskal S4 Inc., Hanscom AFB, MA, USA 1. Intro Advanced Array Antennas 3. Planar Arrays - a short overview To be discussed: The Element/Array factor Grating lobes. Phase scanning Mutual coupling blind angles representations Single mode elements Array mismatch Scan dependence Frequency sensitivity 3. Pl. Array

3 Advanced Array Antennas 4. Circular Arrays Uniform Circular Array Omni patterns Phase mode theory Isotropic elements Directive elements Cylindrical wave impedance Phase mode impedance Dipole array Slot array Cophasal excitation UCA phased to radiate in 45 direction 4. Circ. Array Mechanical: Sphere with facets Mobile satellite communication terminal (prototype) 40 6 crossed dipoles 360 az, -10 to 90 elev. TX RHC, RX LHCP (Roke Manor Research Ltd., UK) Dodecahedron: 12 pentagons, each with five triangles GaAs MMICs and control elecronics on triangular tile 7. Charct.

4 Doubly curved array, ct d. Radiating elements lined up in the main beam direction. But viewed from a different angle [Josefsson et al. 2002] 12. Pol. Design Chart N (kr = 20 30) [No of elements] 80 N fixed (anti aliasing: M < N/2) (N > M + kr) Distortion modes limitation Move limit to minimize harmonics (N>M+αkR, α ~1.5) (M < kr) Cylinder size cutoff, kr limitation [ total No. of modes = 2M+1] Can push limit, but noise increases (M<α kr, α ~1.5) M For wide bandwidth reduce No of modes! 14. Synth.

5 The wave equation A basic feature of Maxwells equations is the existence of traveling wave solutions. The waves represent transport of energy. EM theory: interested in how the waves propagate, not so much in how they were originated. Antenna theory: interested in how to get a certain pattern/ performance. 2. EM Geodesics, the key parameter! Geodesic surface ray(s) 6. Geod.

6 PEC cyl.: Ripple vs. element spacing, R = 5 Progressive narrowing of the pattern due to the endfire grating lobe (as in the planar case). The ripple is reduced when decreasing the element spacing. It is not caused by an edge effect (no discontinuity). Instead, it is due to the mutual coupling. 10. Singly Rad Doubly curved surfaces 11. Doubly

7 Mutual coupling: Polarization effect Isolated coupling! The polarization must also be accounted for, not only the geodesic length and the radius of curvature. The angular dependence follows element far field radiation pattern: sin 1 sin Doubly DBF

8 CEI/Barcelon 2010 CEI/Barcelona O010

9 CEI/Barcelona October 2010 CEI/Barcelona October 2010