Abstract: A sonar that enables an already localized object to be found again uses a transmission antenna fitted out to transmit only the two .+-.first order secondary lobes. This antenna is supplied with a set of frequencies tiered so that each of these lobes determines a series of channels at transmission corresponding to these frequencies and filling two sub-sectors located to the right and to the left of the antenna. The reception is done by forming two wide channels, each of which covers one of the two transmission sub-sectors. The discrimination in bearing at reception is done by the discrimination of the frequencies. To cover a more extensive sector, including especially the central part located between two sub-sectors, the antenna can be made to rotate mechanically. This enables the construction of a simplified sonar which can be used in a consumable way.