A new approach to circularly polarized dipole array antenna with polarization conversion technique

In this paper, we present a circularly polarized (CP) printed dipole array antenna (CP-PDA) with fractal-inspired dipole arms and parasitic elements in the form of stairs. By stacking five ellipses with increasing radiuses to form the semifractal dipole arms, the antenna's effective electrical length and bandwidth are enhanced while maintaining compactness. By generating orthogonal electric field components with a phase difference of 90°, stair-shaped parasitic elements convert linear polarization into circular polarization. Using Wilkinson power dividers and microstrip line phase shifters as a sequentially rotated feeding network, the array outputs can be accurately phased at 0°, 90°, 180°, and 270°, resulting in a high level of polarization purity. Tests of the fabricated prototype revealed that the results are consistent with simulations. In addition to covering WLAN, ISM, and satellite frequencies, the array antenna offers a wide impedance bandwidth of 41.12% (1.99-3.02 GHz) and an axial ratio bandwidth of 35.02% (2.12-3.02 GHz). With a peak gain of 14.16 dBic at 2.55 GHz and a polarization purity exceeding 27 dB, the array exhibits right-handed circular polarization (RHCP). The antenna is fabricated using standard PCB etching techniques on FR4 and Rogers RO4003 substrates and tested in the antenna laboratory, demonstrating robust performance under practical fabrication tolerances. The antenna's wide bandwidth and high polarization purity make it suitable for real-world deployments in WLAN routers, ISM-band IoT devices, and S-band satellite terminals, where resilience to polarization mismatch and multipath fading is critical.