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A simple Fresnel zone plate for indoor focusing of 2 GHz band signals is proposed and studied. It consists of concentric metal rings mounted on the outside of an exterior wall. A three-ring zone plate has a through-wall focusing efficiency of 15 dB (measured) and 14 dB (calculated), and axial defocusing of 0.22 m.
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Hristov et al. (2003) studied this question.
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