A novel planar leaky-wave antenna (LWA) based on quasi-periodic width-modulated printed strips is investigated. Each single strip is obtained by a repetition of several unit cells with different lengths and modulations in order to keep the desired value of the phase constant when changing the attenuation along the line. The overall antenna surface consists of an arrangement of 9 such transversely periodic printed strips. Therefore, the radiated field can be fully controlled geometrically. This results in backward radiation by the n = spatial harmonic; i.e., the pointing angle p = 19 in the E (0) plane is realized by a proper design of the periodic sequence of the proposed array of unit cells enabling aperture control. A numerical example with an incident surface-wave excitation demonstrates the validity of the method.