Abstract: 1. A system for detecting in bearing a source of sound in a predetermined plane and for measuring the frequency of said sound comprising in combination: two hydrophone dipoles sustantially arranged in said plane, each having at least two hydrophones, the axis of said dipoles being at right angles to each other said hydrophones receiving said sound and providing output signals these hydrophones having respective axes perpendicular to said plane; means for detecting the respective phase shifts between said output signals of the same dipole and providing phase shift indicating signals; and display means having two inputs for receiving respectively said phase shift indicating signals.

Abstract: 1. A direction finding system for determining the direction from which short sonic or ultrasonic pulses are incoming, comprising: a plurality of electroacoustic transducers forming a circular arrangement; electronic means for sequentially switching in and out pairs of diametrically opposed transducers; differential means having two inputs, respectively connected by said electronic means to said switched-in transducers, and an output for providing the differential output signal of each of said pairs; and means for deriving the phase of said output signal.

Abstract: In order to compensate for the displacement of a coherent pulse airborne radar, the latter is provided with means for alternately linearly moving forward and backward the phase centre of its antenna system, at the reception, from one cycle radar to the next.The displacement of the phase centre is carried out by introducing a controllable dissymmetry in the illumination of the linear radiating aperture of the antenna system.