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How does the lattice constant (periodicity) of a metamaterial unit cell scale with the overall antenna footprint, and what are the design rules to avoid grating lobes and ensure effective medium behavior?

I'm designing a metasurface antenna where the unit cells are printed across a substrate. If my antenna aperture needs to be 10λ x 10λ at 10 GHz, how do I determine the unit cell size and spacing? I know the cell must be subwavelength (typically < λ/2) to avoid grating lobes, but is there a stricter limit (e.g., λ/5) to ensure the array behaves as a true effective medium? Also, does the total number of cells (aperture size divided by lattice constant) impact performance beyond just the beamforming resolution?

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By Ashish Chaurasiya Answered 1 year ago

The two key constraints are grating lobes and effective medium behavior. To avoid grating lobes in any array, the periodicity p must satisfy p < λ / (1 + |sin θ|), where θ is the maximum scan angle. For broadside radiation, p < λ suffices, but for scanning, a stricter limit like p < λ/1.5 is common. For effective medium behavior (where the array acts homogenously), you need p

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