A quasi-optical beamformer includes a power distributor composed of a succession of parallel-plate dividers extending in a YZ-plane from a first stage to a last stage, each parallel-plate divider comprising, in each of the stages of the corporate structure located under a higher stage, first and second parallel-plate waveguide branches leading to respective parallel-plate dividers of the following stage of the corporate structure, the beamformer furthermore including a plurality of lenses extending longitudinally along the X-axis in at least one stage of the power distributor, so as to apply a delay that is continuously variable along the X-axis, the lenses being placed in each of the branches of the dividers of at least one stage in the power distributor.