| Beamforming is one of the key technologies for the fifth-generation mobile communication system.It can increase the utilization ratio of spatial resources,and thus improve the system capacity several times.Digital beamforming(DBF)is a promising method in beamforming,and it is one of the recent research hotspots.In this paper,a digital beamforming system is designed first and then a wide-angle scanning phased array antenna is proposed to improve the usage of spatial resources in the DBF system.To realize wide-angle scanning phased array,an isotropic antenna is designed first and then based on the isotropic antenna,a wide E-and H-plane pattern reconfigurable antenna is designed.At last,we used the forward state to consist of a wide-angle scanning phased array antenna.The main work of this dissertation is as follows:(1)Based on the principle of phased array antenna,a DBF system is designed in softwaredefined radio(SDR)hardware platform.This DBF system mainly consists of a digital-signalprocessor(DSP),a field-programmable gate array(FPGA),digital to analog converters(DACs),analog to digital converters(ADCs),orthogonal up/down converters,RF front ends and so on.And to measure the radiation pattern of the digital phased array antenna in the anechoic chamber directly,one of the receive channels of the DBF system is connected to the Satimo nearfield measurement system.(2)A novel quasi-isotropic angled-dipole antenna is proposed.By adding a pair of nearfield parasitic elements(NFPEs)beside the angled dipole,the E-plane pattern of the angled dipole is broadened greatly.The isotropic performance in the full space is improved by about 5 d B.Thanks to the balanced feed of the printed double-sided parallel strip-line(DSPSL),and the weak ring current on the cable's outer conductor which is induced by the V-shaped current on the angled dipole,there is no need for a choke balun.The measured isotropic performance of the antenna can reach 1.57 d B,which is the best among the available public reports.(3)A novel wide-beam pattern reconfigurable angled-dipole antenna is proposed.Based on pattern superposition,the widths of the NFPEs in the angled-dipole antenna are broadened.Benefitting from the existence of a pair of long slots,the reference ground functions as a director.By adding PIN diode switches in the slots,the ground can be switched from directors to a reflector.Thus,the antenna has two radiation states.The half-power beam-widths(HPBWs)in these two states in the two main planes are over 180°.(4)A wide-angle scanning phased array antenna is proposed.Benefitting from the good performances of the wide-beam element,the E-plane array has good performances.It has the characteristics of wide-angle scanning,low mutual coupling,wide impedance bandwidth,wideangle impedance matching(WAIM),lower sidelobe level(SLL),and so on.To optimize the radiation pattern quickly,an equivalent circuit of the radiation field in a phased array antenna is proposed.At last,we optimized not only the scanning range of the antenna array but also realized the advanced DBF strategies,such as simultaneous multi-beam and beam nulling. |
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