Scattering from array antennas is a complicated problem, containing the structural and mode items in nature. The complexities in analyzing the latter one also come from the feeding network that follows antenna unit ports, where active or anisotropy devices may exist. Therefore, it is significant that an efficient method can be constructed to analyze array antenna scattering with arbitrary port reflections. In this work, we address this problem by adopting the S-matrix model for the antenna array, aiming to efficiently and accurately compose the mode scattering in case of arbitrary reflections at feeding ports. In the numerical process, the antenna reciprocity is utilized in obtainning the basis for the scattering composition analysis. In case of various loading conditions, numerical results are presented, showing that the composed scattering results by the S-matrix model agree well with that obtained by direct full scale simulations. Then the methods for obtaining radiation and scattering of a large antenna array based on results of a small array, are reviewed and extended in composing the large antenna array scattering in case of variable loading conditions. And, promising results are obtained.
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