A dual polarization, broadband, millimeter‐wave reflectarray using modified cross loop element

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 mm2and 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.