Circularly polarized waveguide antenna loaded with a slotted spherical resonator

In this paper, a circularly polarized waveguide antenna loaded with a slotted spherical resonator is proposed. The antenna consists of two perpendicular SMA ports, a rectangular waveguide, and a slotted spherical resonator. Two vertical crossed slots are introduced onto the spherical resonator. The antenna is fed by the two perpendicular SMA ports in the same phase, and thus the TE
10
and TE
01
modes can be generated in the waveguide. Two polarization degenerate TM
11
modes are excited in the spherical resonator. The electromagnetic energy which satisfies the radiation condition of a circularly polarized wave radiates into the free space through the two crossed slots. At the center frequency of 15 GHz, the radiation efficiency is over 95%, and the left-handed circular polarization (LHCP) gain is 7dB with a cross-polarization level of less than -28dB. The impedance bandwidth is 1% within which the axial ratio is less than 2dB. The proposed antenna has the advantages of high efficiency, excellent circular polarization purity, and low cross polarization level.