Research of low profile circularly polarized loop antenna based on backward radiation suppression

In order to adapt to the development trend of miniaturization of mobile terminals at present, a compact circular polarization ring antenna with low profile and high fronttoback ratio is proposed in this paper, covering the two operating bands of BDS-B1 and GPS-L1. The radiator of the antenna is a loop patch, and two coupled feeding branches with different areas are used to feed the antenna to achieve circular polarization radiation. In addition, the mechanism of backward radiation suppression of the parasitic loop is deeply discussed, which enables the antenna to achieve a high fronttoback ratio on the basis of compact structure, and the exchange between the fronttoback ratio and the radiation efficiency can be realized. The measured results show that in the operating frequency band, the designed antenna has achieved a fronttoback ratio of more than 10 dB, the realized gain is higher than 3.25 dBi, and the antenna has a righthanded circular polarization gain of not less than 3.19 dBic in the 3-dB axial ratio bandwidth. In addition, the size of the designed antenna radiator is 0.148λ0×0.148λ0(λ0 is the vacuum wavelength), and the overall size is 0.236λ0× 0.236λ0× 0.028λ0, which can be applied to the terminal equipment with high degree of miniaturization.