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Equivalent circuits are proposed to model the radiation impedance of low-profile ultrawideband antenna arrays with strong interelement coupling. Previous approaches provided rudimentary equivalent circuits and referred to much smaller impedance bandwidth arrays. In this letter, we extend these models to include antenna sections that overlap with adjacent array elements (as is the case with interwoven arms of tightly coupled spirals). The proposed equivalent circuits include dielectric superstrates and representations of higher-order grating lobes. Design optimization is carried out for an array of coupled and interwoven antenna elements to develop a 20:1 impedance bandwidth aperture. It is demonstrated that the radiation impedance obtained via the proposed equivalent circuit is in excellent agreement with full-wave simulation.