In this work, we propose a full-wave numerical approach for efficient analysis and design of printed leaky-wave phased arrays. The proposed technique is based on the method of moments in the spectral domain applied to a leaky structure in a periodic environment. The implementation exploits suitable analytical manipulations to strongly improve numerical convergence. Planar array configurations based on microstrip leaky lines have been considered in detail for accurate evaluations of the relevant dispersion and radiation properties. The effects of phase-shifted feeding of leaky lines have particularly been investigated as a function of the involved physical parameters, to achieve fundamental information on the beam scanning features both in elevation and azimuth. © 2002 Wiley Periodicals, Inc. Int J RF and Microwave CAE 12: 272–287, 2002.