  Full-wave electromagnetic simulations of electrically large arrays of complex
antennas and scatterers are challenging, as they consume large amount of memory
and require long CPU times. This paper presents a new reduced-order modeling
technique to compute scattering and radiation from large arrays of complex
scatterers and antennas. In the proposed technique, each element of the array
is replaced by an equivalent electric current distribution on a fictitious
closed surface enclosing the element. This equivalent electric current density
is derived using the equivalence theorem and it is related to the surface
currents on the scatterer by the Stratton-Chu formulation. With the proposed
approach, instead of directly solving for the unknown surface current density
on the scatterers, we only need to solve for the unknowns on the equivalent
surface. This approach leads to a reduction in the number of unknowns and
better conditioning when it is applied to problems involving complex scatterers
with multiscale features. Furthermore, the proposed approach is accelerated
with the adaptive integral equation method to solve large problems. As
illustrated in several practical examples, the proposed method yields speed up
of up to 20 times and consumes up to 12 times less memory than the standard
method of moments accelerated with the adaptive integral method.
