A flat scanning antenna comprises at least one slotted waveguide array comprising two dielectric substrates, one superposed above the other. The two substrates comprise the same number of waveguides, which are in mutual correspondence and communicate between them, pairwise, via corresponding coupling slots. Each waveguide of the upper substrate further includes a plurality of radiating slots, all the radiating slots being mutually parallel and oriented in the same direction and each waveguide of the lower substrate includes an individual internal supply circuit comprising an individual phase-shift/amplification electronic circuit.