In this paper, different arrangements of infinite arrays of nonlinearly loaded antennas are analyzed in the frequency domain by an efficient approximate method and compared with the exact one which are respectively based on the nonlinear current and harmonic balance techniques. In one hand, although the exact method is suitable for strongly nonlinear load, it is suffering from gradient operation and initial guess in the iteration process especially under multi-tone excitations. On the other hand, although the approximate method is very efficient, it is limited to weakly nonlinear loads and low-valued incident waves. Finally, acceptable ranges for application of the approximate method versus different parameters such as nonlinearity effect of the load and the magnitude of incident wave are extracted.