A gain enhancement and cross-polarization suppression in wideband circularly polarized filter antenna

A circularly polarized filter antenna suitable for the fifth generation (5 G) frequency band is proposed. The antenna consists of a feed network, a rectangular patch with corners cut, and surrounding parasitic patches. A fourth-order E-shaped bandpass filter is incorporated into both branches of the Wilkinson power divider within the feed network, enabling the antenna’s filtering functionality. The rectangular patch with corners cut and the parasitic patches together form the radiation structure, where the parasitic patches not only enhance the antenna gain within the operating band but also enable effective widening of the axial ratio beamwidth in the range of 4.8–6.0 GHz by etching slots, achieving a maximum expansion of 76.55° A key innovation of this study is the simultaneous realization of axial ratio beamwidth expansion and gain optimization within the same structural layer, significantly improving the overall antenna performance without increasing design complexity. The final antenna design has dimensions of 0.81λ₀ × 1.078λ₀ × 0.075λ₀. Fabrication and measurement results verify that the proposed antenna achieves a 43.5 % impedance bandwidth and a 43.13 % axial ratio bandwidth within the operating frequency range, along with a peak gain of 8.73 dBi, demonstrating excellent electromagnetic performance. These characteristics make the proposed antenna particularly suitable for sub-6 GHz 5 G communication systems.