In order to design reflectarray antennas within reasonable CPU times, fast and accurate numerical tools for the analysis of periodic multilayered structures are required. In this paper, a pole-zero matching technique is applied to the determination of the scattering matrix of periodic arrays of stacked rectangular microstrip patches as a function of the dimensions of the patches. The pole-zero matching technique makes it possible to obtain closed-form equations for the scattering matrix of the

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... eriodic structures from a reduced set of full-wave data. These closed-form equations are very useful because they lead to important CPU time savings when they are applied to the design of reflectarray antennas. In fact, in this paper we present a comparison between a reflectarray design based on a fullwave analysis of each element and a reflectarray design based on the derived closed-form equations. It is shown that the CPU time required by the full-wave approach is nearly one order of magnitude larger than that required by the approach based on closed-form equations 1 .