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A dual-band reflectarray antenna with a double layer, employing concentric square rings as reflecting elements, is proposed. With a procedure of the steepest decent method (SDM), the impressed phases of the reflecting elements are synthesized for the proposed antenna to radiate an optimum field pattern in the near zone of array aperture. The reflectarray antenna is designed for two frequency bands, covering 915 MHz and 2.4 GHz, which both can be used in RFID applications.
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You et al. (2012) studied this question.
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