Analysis of beam-steering and directive characteristics of adaptiveantenna arrays for mobile communications

摘要

Radiation patterns of planar, circular, and three-segment adaptive antenna arrays are analyzed and compared in view of applications in mobile radio. It is assumed that each array consisted of several subarrays, which themselves present vertical linear arrays (columns) of patch radiators, with prescribed magnitude and phase distributions that determine the beam shape in the vertical (elevation) direction. Weighting signals applied to the subarray inputs provide beam steering in the horizontal (azimuth) plane. The scan-angle range and directive properties of such arrays are analyzed and simulated. For relatively small and moderate-sized base-station adaptive arrays, consisting of N=4, ..., 7 subarrays, the planar configuration may not be an appropriate choice, as the planar array has limited scan-angle range. Steering its beam toward the edges of a 120° sector leads to a rise in the grating lobe in the opposite azimuth direction, which, in turn, entails an additional decrease in antenna gain. Circular and three-segment configurations are good and relatively simple alternative variants. These have some degree of curvature, which allows beam steering in a wider angular range when compared to the planar geometry, although at the expense of a wider beam and lower directivity. Their geometrical parameters should be carefully chosen, so as to provide the required scans at the least loss in directivity. The three-segment form is closely related to its planar counterpart and, in some applications, may be more preferable than the circular form. For larger arrays, consisting of N⩾8 subarrays, the planar geometry can attain the required 120° scans, and has advantages in directivity and gain when compared to any curved configuration