TABLE OF CONTENTS In this section, we will examine methods by which the beamforming patterns of a 1-D linear array can be modified and optimized.
Beamforming can be achieved by suitably applying weights and delays to the array elements to obtain the desired adaptive directional sensitivities and optimal array gains. The general principles of phased-array beamforming and signal processing were extensively presented by Johnson and Dudgeon (1993). Several other authors have also done extensive investigation in this field (Godara, 1997; Sundararaman and Adams, 2002, 2004, 2005). It seems that there are many ways to achieve the phased array beamforming, including:
conventional beamforming by simple delay-and-sum algorithms;
null-steering beamforming which assumed that the interference is known;
optimal beamforming.
Mainlobe quality degrades when the beam is steered closer to the array, i.e., around 0 and 180 . In many applications, a 16-element array may be sufficient to ensure reasonably good directivity. Beam directivity improves with increasing d/ ? values. However, if d/ ? increased beyond 1/2, grating lobes start to show up; their number gets larger as d/ ? increases.
Optimization of the phase array beamforming can be obtained by adjusting several parameters: (a) number of sensors, M; (b) sensor spacing, d; (c) the d/ ? ratio; (d) the weights of the array. Once these parameters are fixed, the mainlobe width, grating lobes size and location, and sidelobes magnitude are...
