Abstract:
This paper develops a beam pattern design procedure for general multidimensional
irregular sonar arrays that incorporates the not well understood effects of array geometry
into the design process. The procedure is implemented by generating a "penalty
function" in a spectral covariance function form. Processing the penalty function causes
beam pattern high sidelobes to be penalized and the main lobe to be emphasized. This
is accomplished by forming the penalty function in terms of an isotropic noise field of
specified strength modified with a finite sector of low coherent energy and stabilized with
incoherent sensor noise. By inputting the penalty function into a minimum variance
beamformer, the beam pattern and aperture weights are calculated based on the given
array geometry. The beamformer used is Capon's Maximum Likelihood Method. The
array used to test the procedure is located on a sixty degree sector of a cylindrical surface.
The procedure is implemented by two different methods, each with some desirable
characteristics. One method suppresses sidelobes directly by the placement of nulls. The
other method suppresses sidelobes indirectly by the enhancement of the main lobe with
anti-nulls. Both methods are evaluated in terms of a sensitivity factor which constrains
the maximum white noise array gain. Results show that both methods result in sidelobe
levels that range from 20 to 35 dB lower compared to a conventional beam pattern with uniform aperture weighting and that the design procedure is applicable to beam patterns
steered to both true broadside and to off-broadside directions.
