Abstract
This letter presents the design of a wideband circularly polarized antenna, operating at Ka band. The proposed antenna comprises a circular microstrip patch antenna that is coupled to a microstrip feedline through a modified L-shaped aperture slot. The antenna radiates a wideband right-hand circularly polarized wave with high polarization purity and a wide axial ratio (AR) angular beamwidth. A 4 <inline-formula><tex-math notation="LaTeX">\times </tex-math></inline-formula> 4 antenna subarray has been designed, fabricated, and measured to validate the proposed concept. The array exhibits a reflection coefficient <inline-formula><tex-math notation="LaTeX">S_{11}\, < </tex-math></inline-formula> −10 dB over the frequency band 27-31 GHz. Moreover, the 4 <inline-formula> <tex-math notation="LaTeX">\times</tex-math></inline-formula> 4 antenna subarray yields a high level of polarization purity, as well as a flat measured AR <inline-formula><tex-math notation="LaTeX">\leqslant</tex-math> </inline-formula> 1.15 dB over the frequency range 27.55-30.45 GHz (10<inline-formula><tex-math notation="LaTeX"> \%</tex-math></inline-formula> bandwidth).