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A Ka‐band reflectarray consisting of modified cross loop is investigated in this article for millimeter‐wave broadband dual‐polarization applications. It consists of 40 × 40 unit cells that covered an area of 200 × 200 mm2 and a multimode conical horn antenna which is connected to an orthomode transducer as the offset feed. Its unit cell is composed of a solid cross inside and a cross loop outside, which can lead to nearly 550° linear phase shift curve by varying its length. After this proposed structure has been analyzed and compared with the traditional wideband element (i.e., double cross loop), it is used in the reflectarray. An equivalent circuit model with an insightful field distribution is used to analyze their different behaviors when it resonated at the same operating frequency. For vertical and horizontal polarization modes, the peak gain are measured to be 34.3 and 33.5 dB, the aperture efficiency are 48.6% and 40.4% at the center frequency of 32 GHz, respectively. The 1.5 dB gain bandwidth are close to 18% and 15%, which is better than conventional millimeter‐wave single‐layer ones. This new reflectarray antenna is especially useful for millimeter‐wave broadband dual‐polarization applications. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:287–293, 2014

An X-band reflectarray, which consists of double square loop loaded by spiral stubs (DSL-SS) unit, is investigated in this communication. The DSL-SS unit is composed of a modified double square loop loaded by four spiral stubs and is analyzed by a simple circuit approach, which can analyze the complex multiple resonance structure and guide the design, to reveal its characteristic. The reflectarray is designed according to a detailed design procedure and is then fabricated on a single-layer FR-4 substrate, which covers an area of 192×192 mm 2 . The proposed reflectarray has a wider gain bandwidth and lower cross-polarization when compared with the conventional single-layer reflectarrays, and its measured gain, the aperture efficiency and 1-dB gain bandwidth are 24.4 dBi, 53.5% at the center 10 GHz, and about 38% (9.4~13.2 GHz), respectively. This new reflectarray antenna is especially useful for low-cost broadband communication applications. Index Terms-Broadband antennas, reflectarray, resonance.0018-926X (c)

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