Research On Omnidirectional Circularly Polarized Slot Antenna

Antenna is in the front of the wireless communication link,and its performance is directly related to the performance of the entire communication system.In the field of vehicle-mounted and satellite communication,omnidirectional coverage and circular polarization technology are required in order to resist the polarization mismatch caused by the change of relative positions between communication nodes.And it is usually necessary to achieve conical beam so as to point to a specific angle.In addition,in order to improve channel utilization and capacity,a technique of polarization diversity is needed.The above technical difficulties is key to the system performance.In this paper,based on the perpendicular slots as the basic circular polarized unit,according to the specific application requirements,we achieve two types of omnidirectional circularly polarized antenna,the main contents are as follows:Firstly,based on the demand of vehicle-mounted satellite communication,an antenna with an omnidirectional circularly polarized conical beam is designed.There are two circles of perpendicular rectangular slots that cut on the outer conductor of the truncated cone and they make up the antenna radiation part.The research shows that by reasonably designing the distance between two circle of slot pairs and making good impedance matching,the direction of the conical beam can be perpendicular to the truncated cone busbar(the surface of the outer radiation conductor),and the conical beam circular polarization performance is good.And it is easy to change the beam direction simply by changing the slant angle of the outer conductor to meet any actual system requirements.Simulation and experimental results show that the antenna achieves good performance of the omnidirectional circularly polarized conical beam,which can meet the actual communication requirements.Then,based on the demand of larger system capacity and higher spectrum utilization,an omnidirectional circularly polarized polarization diversity antenna that can be excited by the same side of the antenna is designed.By using the T-shaped feed structure,the problem that the original antenna needs to be fed from both ends of the antenna which would affect the actual performance is improved.One port of the T-shaped feed structure excites the slot array from bottom to top to realize the right hand circular polarized(RHCP)radiation characteristic.Learning from the feeding method of the above-mentioned CP conical beam antenna,we use the other port to excite the slot array from top to bottom by inserting a coaxial line,to achieve left hand circularly polarized(LHCP)radiation characteristics.Simulation and experimental results show that the antenna has good dual circular polarization property and can meet the needs of wireless communication.At last,this article discusses the characteristics and shortcomings of the designed antenna,as well as the possibility of improvement.