Research On Space-time Orbital Angular Momentum Antenna Array Based On Sequential Control

To achieve multi functions,such as suppressing sidelobe,generating beam carrying Orbital Angular Momentum(OAM),generating sum and differential beam,and fast beam scanning,the traditional antenna arrays are required to make precisely amplitude and phase modulation for each element in the array.Therefore,a great number of attenuators and phase shifters are necessary in the feed network,which make the design complicate and expensive.However,the dependence on the attenuation and phase shifting devices is greatly reduced when the functions above are realized by using space-time antenna array(STAA),which is formed by introducing the time factor as a new dimension to the traditional antenna array.Compared with the traditional antenna array,the attenuators and phase shifters are replaced by a group of Radio Frequency(RF)switches controlled by field programmable gate array(FPGA)in STAA.The RF switches are modulated by the time function,so that the antenna element can obtain the time weighting,which can be equivalent to the amplitude weighting at the center frequency and the amplitude and phase weighting at the sideband frequency,so the amplitude and phase modulation can be realized.The design freedom is improved and the cost is reduced by introducing “time” dimension,which can achieve good reconfigurability.Based on the above background,the relationship between STAA’s characteristics and time function is studied from the perspective of time domain and frequency domain in this paper,which mainly contains the following three aspects,1.A novel multi-frequency phase switch screen(PSS)model is constructed based on the multifrequency artificial magnetic conductor structure.Through spectrum analysis and reflection coefficient analysis of PSS,it can be found that if the time functions are selected properly,PSS can realize radar stealth and frequency reconstruction.Based on isotropic antenna element,the ideal STAA model is constructed.By calculating the radiation patterns when STAA is loaded with different time functions,it can be found that if the time function changes,STAA can synthesize different patterns.2.The improved patch antenna element is used to constructed an eight-element uniform circular antenna array,and a Gysel power divider is designed to produce eight-channel RF signal with equal amplitude and phase.Time functions for controlling RF switches is coded in Verilog language,and the codes are burned to FPGA.When suitable RF switches are selected,the space-time OAM antenna array system is constructed by connecting the previously designed devices and modules with RF cables.3.The constraint condition for the range of OAM beam model values and the array factor expression of STAA system are given.The active radiation pattern of STAA system is calculated by combining the full-wave simulation and numerical calculation.The ARC values of each radiation element of STAA in a time function period are calculated by combining practical measurement and numerical calculation,and the calculated results are analyzed in detail.It is found that the ARC value of each element will change with the switching of RF switch.