Design Of Adjustable Yagi Antenna And Dual-band Dual-mode Handheld Terminal Antenna

With the rapid development of wireless communication technology,the wireless communication system is constantly updated,and the communication frequency band shows a trend of diversification,which makes a communication system need to take into account multiple frequency bands to meet different functions.In the face of this practical demand for different communication systems,two antennas working in different communication systems are designed to meet the communication needs of a communication system for multiple frequency bands.The main contexts of the thesis are as follows: 1.An adjustable Yagi antenna used in shortwave communication system is designed.By replacing part of the fixed length antenna element in the traditional Yagi antenna with the length adjustable antenna element,and combining the adjustable antenna element and the fixed length antenna element,arranging the position of the antenna element reasonably,the normal operation of the Yagi antenna in the wider working frequency band is realized.The antenna is divided into two basic types: one is the high gain type adjustable Yagi antenna,to achieve the high gain index,the total number of antenna elements is 14,in different working frequency bands,adjust the antenna element length reasonably,change the actual number of participating radiation elements,make the antenna maintain the normal working state;One is a miniaturized adjustable Yagi antenna with four antenna elements,the number of antenna elements is reduced,the adjustable range of the antenna is more flexible,and the antenna can achieve a wider working frequency band.The simulation and optimization design of the adjustable Yagi antenna is carried out by the simulation software ANSYS HFSS.The simulation results show that the high-gain adjustable Yagi antenna can work normally in the 7MHz?20MHz frequency range,and the antenna gain is over 14.2 d Bi at the resonant frequency,while the miniaturized adjustable Yagi antenna can work normally in the 7MHz?25MHz frequency range,and the antenna gain at the resonant frequency is greater than 12.2d Bi.In addition,the expansion type adjustable Yagi antenna is designed,including low frequency expansion type adjustable Yagi antenna,high frequency expansion type adjustable Yagi antenna and two-way working type adjustable Yagi antenna,to be suitable for different working environments.2.A dual-band dual-mode handheld terminal antenna used in a personal communication terminal is designed.Through the integrated design of VHF/UHF-band linearly polarized monopole antenna and S-band circularly polarized quadrifilar helical antenna,the communication terminal can realize the function of short-range communication in VHF/UHF band and mobile satellite communication in S-band at the same time.First,the S-band antenna is designed,which is in the form of the quadrifilar helical antenna.By adding a spiral arm next to the spiral arm of the antenna,the antenna can meet the bandwidth requirement of S-band satellite communication.By loading spiral branches on the top of the antenna,the gain of the low elevation is guaranteed.Then,the VHF/UHF antenna is designed,and the S-band quadrifilar helical antenna is taken as a part of the VHF/UHF band radiator.To realize the integrated design of the antenna,and to avoid the interaction between the S-band antenna and the VHF/UHF band antenna,based on the ?/4 transmission line theory,a metal four-arm cylindrical structure is designed at the antenna connection to isolate the two antennas.Second,the two band radiators of the antenna are fed through two ports,and to eliminate the mutual influence of the two feed ports,a choke balun is designed.Finally,the antenna is processed and tested,and the test results show that the VSWR of the S-band antenna is less than 1.5:1 in the 1.98GHz?2.01 GHz and 2.17GHz?2.2GHz frequency range,and the antenna gain is greater than 2d Bi in the upper half space of ?=±35°.The VSWR of the VHF/UHF band antenna is less than 3.0:1 in the 225MHz?678MHz frequency range,and the antenna gain is greater than 0.5d Bi in the horizontal plane.