Design Of Pre-Multi Flat-Top Beam Antenna Array

With the rapid development of communication technology,the contradiction between the surge of mobile communication traffic and limited spectrum resources has become increasingly prominent.Smart antenna can significantly improve spectrum utilization,so it has attracted widespread attention.There are two schemes for smart antenna:quasi-dynamic pre-multi-beam smart antenna and fully adaptive array smart antenna for automatically tracking users.Among them,the quasi-dynamic pre-multi-beam smart antenna has good overall performance.Compared with the fully adaptive array smart antenna,it has simple structure and low cost.At present,in the pre-multi-beam smart antenna,because the radiation intensity is not uniform in each beam coverage area,the received signal of the user moves in the WLAN signal coverage area,which seriously affects the reception effect.Therefore,it is necessary to study the design method of pre-multi-beam smart antenna with stable signal reception effect.Therefore,it is necessary to study the design method of pre-multi-beam smart antenna with stable signal reception effect.Beamforing technology is a signal preprocessing technology applied to antenna array.Its principle is to control the beam direction and shape of antenna array by adjusting the feed current amplitude and phase of each element of antenna array.It can also significantly improve the gain of antenna array and reduce the sidelobe level.It has the advantages of enlarging the signal coverage,improving edge throughput and suppressing interference.Therefore,this paper proposed a solution of pre-multi flat-top beam smart antenna by combineing quasi-dynamic pre-multi-beam smart antenna with beamforming technology,and made a comprehensive study to the implementation methods of the solution,and achieved the following main results:(1)microstrip quasi-Yagi antenna is designed,and then four quasi-Yagi antennas are composed into a four-element linear antenna array,which achieves higher gain and is convenient for beamforming and radiation direction control.The antenna operates in the frequency range of 2.4 GHz to 2.48 GHz.(2)Flat-top beam antenna arrays are designed according to beamforming principle,and the corresponding feeding network is designed.The Woodward-Watson and Fourier transform methods are selected as the comprehensive beamforming methods to calculate the amplitudes and phases of the feed currents of flat-top beam antenna array elements.In order to pre-set the antenna beam pointing,Butler matrix is chosen as the feed network of the antenna array in this design.Butler matrix is widely used in communication system as a simple and low-cost beam switching device.However,the outp.ut signals of traditional Butler matrix feeding network are equal-amplitude and equal phase difference,which can not meet the requirement of the output current amplitudes for flat-top beamforming.Therefore,this paper uses Wilkinson power divider to improve it.A 4×4 new Butler matrix feed network can not only output the current with different equal phase differences at the output end,but also output current amplitude with stable amplitude weighting,which can realize the control of antenna beam shape and beam pointing at the same time.(3)A SP4T RF switch is designed.PIN diode is selected as the control device of the switch circuit,and the series-parallel switch array structure is used to design the RF switch.Based on the above design results,the microstrip quasi-Yagi antenna array,feed network and RF switch control network are processed and tested.The results show that the antenna-fed system can switch among four beams of 39°-68°,62°-91°,87°-116° and 110°-140°.In each beam,the gain varies within 3dB,with flat gain directivity pattern,the received signals are stable when user moving within the beam coverage.Therefore,the problem of signal instability of pre-multi-beam smart antenna can be solved well.