Dual circularly polarized 3-D printed broadband dielectric reflectarray with a linearly polarized feed

A broadband dual circularly polarized (dual-CP) reflectarray based on three-dimensional (3D) printed dielectric materials is proposed in this paper. A novel 3D dielectric array element that enables the broadband linearly polarization (LP) to CP transformation is proposed. The unit cell consists of two orthogonal dielectric cuboids, which adjust the phases of the two orthogonal LP waves independently and then combine them into a CP wave. The innovative unit cell design provides an extra degree of freedom in varying the geometries of the array elements in all three dimensions, which enables us to independently control the phases of the two LP waves. This maintains an equal amplitude and 90° phase difference condition across the entire reflectarray surface, realizing a broadband and high gain LP-CP reflectarray. The placement of the feed is also optimized to achieve the highest aperture efficiency. Finally, an off-set reflectarray was designed and fabricated using lost-cost 3D printing. The reflectarray is able to provide both left-hand circular polarization (LHCP) and right-hand circular polarization (RHCP), with just an LP feed. The measurements agree well with simulated results where the maximum realized gain and directivity at 34 GHz are measured as 27.9 dBi and 28.1 dBi, respectively. The measured 3-dB gain bandwidth and aperture efficiency are 30% and up to 38%, respectively. More importantly, a broad 3-dB axial ratio (AR) bandwidth greater than 40% has been achieved for both LHCP and RHCP, covering almost the entire frequency band of interest, ranging from 26 to 40 GHz.