On the shaping of the main lobe in wide-band arrays

This paper describes a method to obtain a wide-band beam pattern whose main lobe has the desired shape and, at the same time, the level of the side lobes is acceptable. The aim is to reproduce a main lobe profile as close as possible to the desired one through the synthesis of the array-weighting window. A typical goal is to obtain, in wide-band conditions, a flat-top shaped beam similar to the ones produced by specific narrow-band windows. To achieve this result, an optimization process based on simulated annealing is developed and applied under different operating conditions, including two wide-band beam pattern definitions and different values of the fractional bandwidth. Although the shape of the resulting main lobe is not as good as the one obtained in narrow-band conditions (the reasons for this drawback are given), it is shown that the adoption of windows synthesized by the proposed method is more suitable than the direct application of narrow-band windows in wide-band conditions. In addition to providing better performances, it is shown that the windows synthesized by the proposed method also result in greater robustness to random perturbations of weight values, which are unavoidable in real systems.

[1]  A. Trucco.  Weighting and thinning wide-band arrays by simulated annealing. , 2002, Ultrasonics.

[2]  Richard O. Nielsen,et al.  Sonar Signal Processing , 1991 .

[3]  V. Murino,et al.  Stochastic optimization of linear sparse arrays , 1999 .

[4]  Vittorio Murino,et al.  Beam pattern formulation and analysis for wide-band beamforming systems using sparse arrays , 1997, Signal Process..

[5]  G. Cincotti,et al.  Optimization of wide-band linear arrays , 2001, IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control.

[6]  G. Cincotti,et al.  Design of wide-band arrays for low side-lobe level beam patterns by simulated annealing , 2002, IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control.

[7]  A. Macovski.  Ultrasonic imaging using arrays , 1979, Proceedings of the IEEE.

[8]  A. Trucco,et al.  Thinning and weighting of large planar arrays by simulated annealing , 1999, IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control.

[9]  W. E. Engeler,et al.  Windowing of wide-band ultrasound transducers , 1996, 1996 IEEE Ultrasonics Symposium. Proceedings.

[10]  William E. Engeler,et al.  WINDOWING OF WIDEBAND ULTRASOUND TRANSDUCERS , 1996 .

[11]  M. A. Ingram,et al.  Pattern Synthesis for Arbitrary Arrays Using an Adaptive Array Method , 1999 .

[12]  Andrea Trucco,et al.  A STOCHASTIC APPROACH TO OPTIMISE WIDE-BAND BEAM PATTERNS , 2002 .

[13]  Andrea Trucco,et al.  Optimisation of Wide-Band Beam Patterns by Means of a Joined Synthesis of Weighting Coefficients and Pulse Envelope , 2002 .

[14]  J. S. Bird,et al.  Synthesis of symmetric flattop radiation patterns , 1996 .

[15]  Gabriella Cincotti,et al.  Computation and Properties of the Wide-Band Beam Pattern , 2004 .

[16]  Andrea Trucco,et al.  On the stability of wideband beam patterns with respect to weighting and envelope fluctuations. , 2004, Ultrasonics.

[17]  S. Curletto,et al.  Flattening the side-lobes of wide-band beam patterns [acoustic arrays] , 2003 .

[19]  A. Trucco,et al.  Three-dimensional image generation and processing in underwater acoustic vision , 2000, Proceedings of the IEEE.

[20]  B. Steinberg,et al.  Ultrasparse, ultrawideband arrays , 1998, IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control.

[21]  C. D. Gelatt,et al.  Optimization by Simulated Annealing , 1983, Science.

[22]  Fauzia Ahmad,et al.  Coarray analysis of the wide-band point spread function for active array imaging , 2001, Signal Process..

[23]  F. Ares,et al.  Multiple-pattern linear antenna arrays with single prefixed amplitude distributions: modified Woodward-Lawson synthesis , 2000 .

[24]  P. J. 't Hoen.  Aperture apodization to reduce the off-axis intensity of the pulsed-mode directivity function of linear arrays , 1982 .

[25]  F. Ares,et al.  Phase-only control of antenna sum and shaped patterns through null perturbation , 2001 .