Broadband Dual-CP Multistage Sequential Rotation Arrays With Independent Control of Polarizations Based on Dual-CP Magnetoelectric Dipole Elements

In this article, broadband dual-circularly polarized (dual-CP) antenna arrays with independent control of polarizations are proposed and demonstrated at the K-band. By introducing folded $\Gamma $ -shaped end loadings and corner truncation, a dual-CP magnetoelectric dipole (ME-dipole) element with a compact footprint and a broad bandwidth of 22.5% is realized. Based on such element, a $2\times2$ -element sequential rotation (SR) subarray is constructed. By employing a high dielectric constant substrate, a stacked array feeding configuration is devised by placing two sets of microstrip feeding circuits above and below the ground plane for independent dual-CP beamforming. Importantly, the feeding circuitry is fully confined within the area of the array elements without occupying any extra space. Furthermore, a $4\times4$ -element array is synthesized for obtaining dual-CP radiated beams over a broad bandwidth with improved CP purity and port isolation via exploiting the double-stage SR feeding strategy. The fabricated array prototype experimentally achieves a 3-dB axial ratio bandwidth of wider than 28.5%, a 3-dB gain bandwidth of about 23.2%, as well as a −10 dB impedance bandwidth of greater than 50% within which the port isolation is higher than 15 dB. Moreover, the dual-CP beamforming is also showcased by a second array example that generates an LHCP pencil beam and an RHCP vortex beam pointing at distinct directions, confirming the capability of independent control of polarization.