A two-dimensional grid of isotropic dipole scatterers excited by an obliquely incident plane wave is considered. Analytical formulas are obtained for the so-called interaction constant of the grid. To validate our theory, a comparison is done between the obtained approximate relation for the interaction constant, the result of the numerical summation of dipole fields, and a known accurate result for a special case. The theory results in the grid impedance of arrays which does not depend on the wave incidence angle. We show that the grid of nearly resonant electric dipoles turns out to be prospective as a constitutive element of novel high-impedance surfaces whose impedance is unique for the whole angular spectrum of plane waves.