J. H. Tarng
Y. F. Lin
Inst. of Commun. Eng., Natl. Chiao-Tung Univ., Hsin-Chu, Taiwan, R.O.C.
In this report, effects of surface scattering on beamforming technique operated by a linear array are investigated. The array pattern, synthesized by conventional beamforming, is illustrated as an index to show the scattering effects. Both the cases of a wave scattered by randomly rough and smooth surfaces are considered, which are solved by the image and Kirchhoff methods, respectively. It is found that the latter case gives stronger interference to the array pattern than the former one. In the randomly rough surface case, the array pattern is interfered more severely when the array focuses the main beam in the direction of the scattering surface. It is found that the pattern interference can be smoothed by the roughness of the surface. The rougher the surface is, the weaker interference is. It is also demonstrated that the longer range between the array and source may lead to stronger interference. The three-dimensional as well as two-dimensional problems are investigated. In the former problem, the sidelobe is interfered more severely and its level is much higher than those in the latter one. Here, a Gaussian correlation function of rough surface fluctuation is assumed.