A High-Gain Transmitarray for Generating Dual-Mode OAM Beams

This paper proposes a novel transmitarray antenna which can achieve high gain and produce dual-mode orbital angular momentum (OAM) beams in Ku band. Two back-to-back wideband dual-polarized microstrip antennas are employed as the unit cells, which are connected using metalized via holes. Full 360 o phase ranges can be obtained by varying the length of feeding lines in two orthogonal polarizations. Due to high isolation between the two orthogonal polarizations, dual-mode OAM beams can be formed simultaneously by tuning phase distributions in x- and y-polarizations, respectively. The approach for generating OAM beams is explained. To verify this concept, one prototype carrying 0 and +1 mode OAM beams is designed, fabricated and measured. Experimental results demonstrate that the both 0 and +1 mode OAM beams can be generated successfully, and the measured results agree well with the simulated results. Because of high directivity and focusing effects of transmitarray, the proposed +1 mode OAM beam has stable performance at a long propagation distance. The maximum gain reaches 26 dBi and 20 dBi in 0 and +1 mode OAM beams, respectively. Meanwhile, a narrow divergence angle of +/-5 o is obtained in +1 mode OAM beam. Compared to other OAM antennas reported, main advantages of the proposed antenna include high gain, narrow divergence angle?low cost, planar structure and the capability of producing dual-mode OAM beams