| Nowadays,with the development of wireless communication systems,people have entered the 5G Era.5G is an abbreviation for the fifth generation of mobile communications.Compared with previous generations of mobile communications,it has higher requirements on antenna size,operating frequency band,and channel capacity.To solve problems in 5G and its network,the research object of this paper is orbital angular momentum antenna.Orbital angular momentum antenna is a subset of multiple input multiple output antennas that can achieve maximum channel capacity,and can generate vortex electromagnetic fields with orbital angular momentum components.The vortex electromagnetic fields of different modes are orthogonal to each other,and their modes can be used as a new degree of freedom to improve the anti-interference ability of the beam.Therefore,the corresponding orbital angular momentum antenna has the ability to further increase the channel capacity under limited spectrum resources.It can also be used as an important component of the new system radar system to improve imaging resolution.However,at the same time,existing orbital angular momentum antennas have some problems such as large size,small bandwidth,and phase singularities.In response to these problems,this paper studies compact and wideband orbital angular momentum antenna without phase singularities.The main tasks are as follows:First,a 2×2 uniform circular array based on a double-layer feed-back rectangular patch unit is proposed to generate a 3-modal vortex field,and the effect on the size of the circular array on the impedance bandwidth is studied.Through analysis,when the radius of the circular array is reduced to 0.46?0,the impedance bandwidth is about 8.5%and the in-band isolation is lower than-20dB;when the radius of the circular array is reduced to 0.37?0,the impedance bandwidth is about 3.5%and The in-band isolation is less than-10d B.When the radius of the circular array is less than 0.37?0,the impedance bandwidth will be significantly smaller.The antenna's in-band gain can reach 7.2dBi.Secondly,a compact 2×2 orbital angular momentum antenna based on metamaterial characteristics is proposed to achieve high bandwidth.This metamaterial characteristic refers to the use of periodic metalized vias to change the equivalent relative dielectric constant.Utilizing 4 groups of 3×4 metalized through holes,although the distance between the rectangular patch units can be reduced to 2mm,the port isolation of the corresponding orbital angular momentum antenna is still below-10dB within its bandwidth of 11.3-17.3GHz.It is lower than-20dB in the frequency range of 13.9-14.5GHz,and the in-band gain is 8.02dBi.Finally,a compact 2×2 uniformly rotating circular array based on a half-mode substrate integrated waveguide is proposed to achieve a vortex field without phase singularities.This antenna has high port isolation at the same time.Adjacent cells of a uniformly rotating circular array have high isolation due to different polarizations.Opposite cells also have high isolation due to the back-to-back substrate integrated waveguide structure.In addition,due to the inclusion of a differential feed structure,the 1-modal vortex field does not have a phase singularity.Based on this,the designed antenna operates in the frequency range of7.98-8.03GHz,the in-band isolation is lower than-20dB. |
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