Multifunctional OAM Antenn

With the rapid development of science and technology,5G wireless communication networks are rapidly popularized.To meet more demands of the future network,we are preparing for the 6G era of the interconnection of everything.Since orbital angular momentum has been introduced into the field of radiofrequency,it has the potential to improve spectral efficiency in wireless communication and realize super-resolution radar imaging because of its physical characteristics of infinite multiple orthogonal modes.At present,orbital angular momentum has attracted extensive attention and research both in academia and industry,it has become one of the hot technologies of 6G.To further realize the application of orbital angular momentum in low-frequency band and millimeter band,implement its application in wireless communication and stealth system,this paper mainly studies the orbital angular momentum antenna from three aspects.Firstly,a compact multimode orbital angular momentum antenna with a sequentially rotation structure is proposed to realize modal reuse of orbital angular momentum in the low-frequency band of the microwave.Primarily,the principle of generating vortex electromagnetic wave by sequential rotation array based on circular polarization element is discussed,and an isosceles right triangle circular polarization patch element with acute angles symmetrically cut off is designed to realize the compactness of array.The four elements sequential rotation array is used to verify the above theory,its compact principle is analyzed as well.Based on the compact four-cell array,a concentric uniform circular array with a radius of 0.76λ₀ is finally designed and fabricated.Simulation and experimental results show that the proposed antenna has a working bandwidth of 8.7%in the X band,and can effectively generate vortex electromagnetic waves in-1 and-2 modes.The maximum gain of the two modes is 5.7d Bi and7.8d Bi,respectively,and both have high modal purity in the range of 8.8-9.6GHz.Secondly,to realize the application of orbital angular momentum in the millimeter band,a compact broadband orbital angular momentum antenna working in Ka-band is proposed,and the array is extended to achieve high gain radiation.In the first place,four wideband patch unit shaped like an isosceles right triangle with acute Angle cut off,as well as a simple T-shaped equal power allocation feeding network are designed to form a sequential rotation array to generate a±1 mode vortex electromagnetic waves.The simulation results show that the impedance bandwidth of the array is 32.79%,the maximum gain of the main polarization is4.7d Bi,the beam divergence angle is 35°,and the array has high modal purity in the wide-band.In addition,an extended array based on sequential phase shift feeds is used to generate high-gain vortex waves in+1 mode.Simulation results show that the impedance bandwidth of the array is 15.2%,the maximum gain of the main polarization can reach 11d Bi,and the divergence angle is only 13°.Compared with the four-cell array,the radiation performance of the extended array is significantly improved.Finally,a multi-functional orbital angular momentum antenna with high radiation and low scattering performance is proposed for the application of an orbital angular momentum antenna in a stealth system.Based on the radiation enhancement principle of the F-P cavity and the basic theory of scattering reduction of antenna,a frequency selective absorber combining frequency selective surface and the absorbing surface was designed to improve the radiation performance of the antenna and reduce its out-of-band scattering at the same time.Simulation results show that the sequentially rotated concentric uniform circular array loading frequency selection absorber can effectively generate OAM waves in-1 and-2 modes,and the main lobe gain is5.9d Bi and 7.3d Bi,respectively.Compared with the case without loading,the array can effectively reduce the radar cross section in the 5-15GHz or even wider band without affecting the radiation performance,which is reduced by about 16d B at 13.8GHz.