Research On Anti-Interference Antenna Front-End Technology Of Beidou

The Global Navigation Satellite System(GNSS)provides precise positioning and accurate timing at any time,and has penetrated into various industries such as communication systems,transportation,and smart grids.The BeiDou Navigation Satellite System is a global navigation satellite system independently developed and operated by China.Due to the extremely weak satellite signals,which are usually 20 dB lower than noise signals,the system is vulnerable to various malicious or unintentional interferences,making it difficult to maintain secure and reliable services.Improving the anti-interference performance of the BeiDou system has always been an important research topic.As the receiver of BeiDou signals,the antenna directly affects the system’s ability to process signals and interferences.As the system moves towards miniaturization and integration,the distance between antennas is getting closer,and the anti-interference performance is getting worse.How to achieve anti-interference performance requirements in a limited size is a difficult problem that designers constantly face.Researchers have found that the decline in the anti-interference performance of the BeiDou system is due to the mutual coupling between antennas,which causes the received signals to be non-linearly independent and the output signal-to-noise ratio to decrease.Therefore,decoupling the antennas is an important part of the research on the front-end technology of BeiDou antiinterference antennas within a limited size.Currently,there is still a significant gap in research on decoupling of circularly polarized antennas for BeiDou.Circular polarization is a combination of two orthogonal phase differences of 90 degrees,so the decoupling of circularly polarized antennas is much more difficult than that of linearly polarized antennas.After studying the decoupling methods for linearly polarized antennas,the advantages and disadvantages of different methods were summarized,and the feasibility of applying them to circular polarization decoupling was analyzed.Finally,the mode cancellation method was used to decouple the circularly polarized BeiDou antenna to improve the system’s anti-interference performance.The original mode cancellation method was proposed for decoupling of two-element linearly polarized antennas,but to apply it to BeiDou array design,it was developed into two-element circularly polarized antenna decoupling design,and further developed into decoupling design of three-element linear arrays and four-element parallel arrays.Taking the B3(1268MHz)BeiDou patch antenna with an edge-to-edge spacing of 4mm(0.017λ)as the research object,the mode cancellation method was used to design the decoupling of binary linear arrays,three-element linear arrays,and four-element parallel arrays.Compared with the uncoupled antenna array,the antenna array designed using the pattern cancellation method can improve the isolation by about 15 dB,make the directional pattern more symmetrical,effectively improve the low elevation gain,and widen the 3dB axial ratio beamwidth.The coupling between antenna array elements is the main cause of the decreased anti-interference performance of the BeiDou system,but this is also a problem that the miniaturization of the system has to face.Therefore,achieving isolation between antenna array elements on small platforms is an important research topic for anti-interference antenna front-end technology of the BeiDou system.Using mode cancellation method for decoupling design of circularly polarized antenna arrays can effectively improve the isolation between antenna arrays and the radiation characteristics of antennas.