| As a new mechanism,vortex electromagnetic(EM)wave can carry infinite number of orbital angular momentum(OAM)modes which are orthogonal to each other at the same frequency.Utilizing the orthogonality of OAM modes,vortex EM waves can be used as information carriers to simultaneously transmit multipath information at the same frequency in wireless communication,which will not only effectively solve the problems in modern wireless communication systems,including the ever-increasing exhausted spectrum resource and finite data rate,but also offer a new solution to realize the high performance wireless communications with high speed and large capacity.In order to apply the new technology of vortex EM waves to wireless communication,we need to study the generation of vortex EM wave with multiple OAM modes.Therefore,this paper focuses on studying and designing a device for generating vortex EM wave with multiple OAM modes,where each mode is independent and simple in realization.Meantime,exploring the application of vortex EM wave in wireless communications is performed.The main research contents of this thesis are as follows:1)Introducing the basic principle of OAM and structure characteristics of vortex EM wave,the basic theory of the vortex EM wave generated by the circular array is analyzed in detail.By changing the phase of antenna elements,the vortex EM wave with desired OAM mode can be generated.It is very simple and flexible for generating vortex EM waves with arbitrary OAM modes.2)Three kinds of circular antenna arrays for generation of vortex EM wave with single OAM mode are simulated by the CST software,thus verifying the basic theory of circular array for generating the vortex EM wave.Based on the method of generating the vortex EM wave with single OAM mode,a device for generating vortex EM wave with multiple OAM modes is studyed and designed.For example,simulations of two patch circular arrays and three monopole circular arrays are given to generate the vortex EM wave with multiple OAM modes.3)The effects of relevant parameters such as OAM mode,the number of array elements,the radius of array and the initial phase of the first array element are analyzed in detail.Taking all factors into considerations,the three circular arrays,working at X band,are designed to generate vortex EM wave with multiple OAM modes.The phase distribution of electric fields,far-field radiation pattern and far-field phase distribution are analyzed.4)In order to satisfy the excitation requirements for each antenna element of the three circular arrays,we designed a three-way unequal power divider with the power ratio of 6:8:12 and three equal power dividers working at X band,which are six ways,eight ways and twelve ways.The four power dividers are implemented and examined,and results from measurements agree well with the simulations.By assembling power dividers and phase shift line into feeding network,the performance of the three monopole circular arrays is tested,and the normalized far-field pattern and far-field phase distribution in diffrent working states are given.There is a good agreement between the measured results and the simulation results of the three circular arrays in the seven working states.The three circular array is simple and easy to implement for generating the vortex EM wave with multiple OAM modes,which offers a new solution to realize the high performance wireless communications with high speed and large capacity. |
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