Multiplicative receiving arrays: the angular resolution of targets in a sonar system with electronic scanning

The advantages of the multiplicative system of reception, namely the reduction of beamwidth to half that of the same array used normally and the virtual suppression of all minor lobes of the directional pattern, appear at first sight to be not fully realizable when more than one signal source is present owing to cross-product terms in the output. The theoretical examination of the problem given here shows that, in fact, these cross-product terms do not seriously interfere with the attainment of the improved angular resolution, and indeed they add a ¿winking¿ effect which may actually improve the recognition of double targets in an echo-ranging system. Preliminary trials in a reservoir, followed by sea trials of an experimental electronic sector-scanning sonar equipment using the multiplicative principle, show that in practice the angular resolution is approximately twice as good as that of the corresponding additive system, this improvement being accompanied by other advantages due to the reduction of sidelobe effects; among the latter advantages is the absence of the ¿smearing¿ of the display trace which otherwise occurs when strong echoes are received on a display unit which has been adjusted for a lower general signal level.