T. Touya and D. Auroux (France)
Array antenna, multi-beam, topological optimization, ac tive chain reduction.
We consider Direct Radiating Arrays (DRA) as reconfig urable multibeam transmit antennas. The antenna diame ter is determined by directivity and isolation specifications, and the grid lattice is constrained by grating lobe rejection outside the Earth. As high directivity beams are mostly re quired, adding these two constraints leads to a prohibitive number of antenna elements (so of active chains). In order to reduce the number of active chains without affecting antenna pattern characteristics, we consider non regular aperture sampling by dividing the radiating aperture into non-regular subarrays. Industrial constraints lead to gather small identical elements in rectangular groups with various sizes. The basic elements are small enough to avoid any grating lobe on the Earth disk; as the 2nd-step aperture meshing (by non-regular groups) is non-periodic, no other grating lobes appear on the Earth. We first present a mathematical algorithm for the op timization of the antenna alimentation for a given spot on the Earth, by defining a cost function able to warrant con vergence of a gradient-type method, and then we combine these solutions found for each beam in a single power dis tribution on the aperture, using the Singular Value Decom position (SVD) method. Finally, we optimize the topology of the antenna by sampling the obtained distribution into amplitude values that can be provided by gathering ele ments by 1, 2, 3, or 4. And the best rectangles arrangement is found in an iterative process using the topologic gradient method. A clever association of these various steps leads to a non-regular subarrays distribution saving nearly 50% of the initial elements number, while complying for all beams with typical requirements on gain and isolation, and using equal-power feeding, so better efficiency and lower cost for a single amplifiers class.
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