Discrete amplitude shading for sidelobe suppression of sources

Abstract

Amplitude shading techniques are used in arrays to achieve reduced sidelobe levels with reasonably small major lobe width. Most papers on shading consider arrays without restriction of amplitude and location of the shading function to discrete choices. For some arrays such as resonant sonar arrays, it is desirable to achieve the amplitude shading by series‐parallel combinations of discrete elements of the array. Such an arrangement forces a relationship between the width and amplitude of discrete zones. This problem is illustrated in the design of a linear array of 24 elements for which the sidelobe level must be less than −20 dB. One discrete shading configuration had −21.9 dB sidelobe level. The best choice of series‐parallel combinations achieved a narrower beamwidth and a −25.7 dB sidelobe level. [Work supported by Naval Sea Systems Command.]