The beamforming is used to increase the transmit power and reduce the losses in the array antenna. Minimizing the side lobe level and enhancing the main lobe level is very important to improve the target detection accuracy and jamming stability for an underwater acoustic transducer array.
We investigated how to effectively reduce the side lobe level while minimizing the main lobe width increase for the uniformly spaced arc array of omnidirectional underwater acoustic transducers, even at low signal-to-noise ratio (SNR).
First, we proposed a new cost function to effectively reduce the side lobe level while minimizing the main lobe width increase, using the simulated annealing algorithm (SAA) for the uniformly spaced arc array of omnidirectional underwater acoustic transducers, even at low signal-to-noise ratio (SNR). A cost function was constructed that reflects the deviation between the beam width of interest and the beam width by the weight vector, and the ratio of the sum of all the side lobe levels to the main lobe level.
Second, the proposed cost function was used to obtain the weighting coefficients for the elements and to compare them with various windowing methods.
The array weighting by the proposed method can reduce the side lobe level by about 8dB lower than uniform method while minimizing the main lobe width increase for low SNRs. Other methods except Cosine method increase the main lobe width considerably, although those may lower the side lobe level more than the proposed method. Therefore, the proposed method can effectively suppress the noise while maintaining the resolution of the underwater acoustic transducer array.
According to the evaluation of directivity by the various methods based on the cost function, for the SNR equal to-5dB, the value of cost function by the proposed method is 1.55, 1.44, 1.77, 1.39, 2.69 and 1.41 times lower than those by Uniform method, Cosine method, Hanning method, Hamming method, Blackman method and Triangular method, respectively. For uniform arc arrays with underwater acoustic transducers, it is confirmed that array element weighting with weight vectors obtained by using the proposed cost function and simulated annealing based on weight factor updating can effectively reduce the side lobe level while minimizing the main lobe width increase of array directivity even at low SNR. The results are shown in Fig.
The research results were published in "Archives of Acoustics" under the title of "A side lobe level reduction method using simulated annealing algorithm in a uniform arc array"(https://doi.org/10.24425/aoa.2024.148783).
