Abstract: For improving 3D focussing and side lobe suppression in a direction finding system identical groups of transducers are provided at each side of a first and a second axis, which are inclined by an angle 0°≠&psgr;<180°, preferable &psgr;=90°. A first magnitude summation signal is derived from the first pair of transducer groups associated with the first axis and a second magnitude summation signal is derived from the second pair of transducer groups associated with the second axis. Furthermore, a differential signal is derived between the complex output signal of each pair of transducers. For each axis the absolute value of said differential signal is subtracted from the associated magnitude summation signal. The resulting two output signals, associated with said two axis, are then combined to finally obtain a three-dimensionally focussed beam pattern.

Abstract: For improving the focussing of a direction finding system comprising at least two identical transducers or groups of transducers (W.sub.L, W.sub.R), on the one hand a magnitude summation signal (.vertline..vertline.+.vertline..vertline.) and on the other hand a differential signal (.vertline.-.vertline.) are derived from the transducer output signals (,). Thereafter the magnitude of the differential signal is subtracted from the magnitude summation signal.