Design of Circularly Polarized Array Antennas with a Rotated Sequential Feeding Network for Antenna-in-Package Applications

In this study, a circularly polarized antenna-in-package array antenna with an expandable axial ratio bandwidth was proposed using a rotating sequential feed structure. Each antenna in the proposed design had a hexagonal shape for a triangular array configuration and featured a circular radiating patch. In addition, it was fed by two pins through a feed line with a 90° phase difference to implement circular polarization characteristics. A 2×2 subarray antenna was designed to enhance the axial ratio bandwidth by rotating each antenna by 90° and ensuring beam symmetry. This maintained stable axial ratio characteristics. A 90° phase distribution layer was used to rearrange the feed positions and correct the phase differences, allowing the use of conventional beam steering algorithms. A 4×4 array antenna model was designed based on the proposed configuration, and the antenna characteristics were analyzed. The simulation results showed that the 90° phase distribution layer exhibited an error within 5° in the target bandwidth, and the axial ratio bandwidth expanded from 7.1 % to 75 %. Furthermore, during beam steering within the range of θ0=60°, the axial ratio characteristics remained stable compared with those of conventional array antennas.