A Geometric Phase Presetting Technique for CP Agile and Beam-Steering Reconfigurable Array With Enhanced AR Bandwidth

In this article, the concept, design, and validation of a circularly polarized (CP) agile and beam-steering reconfigurable array based on geometric phase presetting technique (GPPT) are reported, featuring a significant axial ratio (AR) performance improvement for all states. The used CP agile 3-bit patch element is enabled by utilizing a reconfigurable feeding network (RFN) composed of two digital phase shifters and a single-pole four-throw (SP4T) switch. By altering the state of RFN, the polarization can be switched between left-handed CP (LHCP) and right-handed CP (RHCP), and eight phase states (i.e., 0°, 45°, 90°, 135°, 180°, 225°, 270°, 315°) can be provided simultaneously to realize the 3-bit element. By properly manipulating the array phase distribution, the radiation pattern of the designed
$1\times 8$
array can be dynamically steered in a range from −52° to 52° for each CP mode. Importantly, different from the uniform distribution of elements in traditional arrays, here the adjacent elements of the
$1\times 8$
array based on GPPT are rotated 90° in turn. Due to the opposite geometric phase response between the two CP waves, the co- and cross-polarization components of the array exhibit different phase distribution. Consequently, the cross-polarization in the main beam direction is significantly suppressed within the whole operating frequency band. The joint 3 dB AR relative bandwidth for all states is extended to 20.8%. To demonstrate the proposed methodology, a prototype of the GPPT-based array is fabricated and characterized. The measured results agree well with the simulated ones, thus validating the reconfigurability and the great advantages in broadening the AR bandwidth.