A technique is presented combining the advantages of the spatial and spectral versions of the method of moments for a general electromagnetic problem involving a printed structure. The metalizations are of arbitrary shape and are described by a shape-conforming mesh with subdomain basis functions. The technique is based on the extraction of the leading singular terms of the Green's function, in which space and frequency dependences are separated. The part of the impedance matrix associated with these terms is efficiently evaluated in the space domain, once for all frequencies. The eigenfunctions of these singular parts (expressed in terms of the subdomain basis functions) are then used as entire-domain basis functions for the remaining regular part, whose associated impedance matrix is evaluated in the spectral domain. This appears to be the generalization to arbitrary patch shapes of the use of entire-domain functions (like orthogonal polynomials or cavity modes) and drastically reduces the number of unknowns, showing potential for the full-wave analysis of printed arrays.