Abstract: This arrangement is formed by two receive branches (1) and (4) for receiving a wave whose frequency spectrum is practically constant in a predetermined frequency band, a combining circuit (15) for combining the waves at the output of the receive branches and a servo-control for keeping the spectrum of the signal at the output of the combining circuit constant by adjusting a phase shifting circuit (12) inserted in said branch (4). The servo-control is constituted by a frequency discrimination circuit (25) for analyzing the combined waves, an adjustable selective circuit (27) for obtaining a frequency band of the spectrum of the combined signal as a function of the output signal of the frequency discriminator and by a control circuit (29, 31) which adjusts the phase shifting circuit for optimizing the output signal of the selective circuit.