Modern communications systems use multi-beam antennas for the sectorization of 360° azimuthal coverage or diversity and MIMO concepts. One suitable antenna realization is based on the phased array principle, where four elements placed at the edges of a square are required in order to form four overlapping beams in azimuth. In its basic form, excitation phases of 0°, 90° and 180° are required for beam forming. The paper presents a novel multi-beam matrix network created by four 90°-hybrid couplers which realizes the required excitation for four beams spaced by 90° in the azimuth plane. A proof-of-concept antenna was designed which employs miniature surface-mount couplers in a microstrip feed network and uses vertical monopole radiators.