Research And Design Of Omnidirectional High Gain Vehicle Antenna

With the rapid development of wireless communication,UHF band vehicle antenna has been widely used in military and civil fields.Due to the particularity of military vehicle antenna,it often faces some complex geographical environment,which puts forward higher requirements for the electrical performance of the antenna.Therefore,the vehicle antenna with high gain and broadband has become a research hotspot.According to the actual engineering requirements,the broadband and high gain theoretical research and experimental verification of vehicle antenna and array based on Gradual structure and coupled feed are carried out in this paper.Two omnidirectional high gain vehicle antennas in UHF band are designed.The main research contents and conclusions are as follows:(1)Research and design of omnidirectional broadband vehicle antenna.Based on the theory of dipole antenna and broadband antenna,this chapter studies the structural equivalent model method.In order to effectively expand the antenna bandwidth,a stepped gradient structure is added to the ordinary dipole antenna to make it equivalent to a biconical antenna.The impedance transformation is realized by adjusting the slenderness ratio between each part of the gradient structure and the internal air coaxial.In view of the gain deterioration caused by current imbalance,the slot coupling feed form is adopted.At this time,the antenna is equivalent to an equal amplitude in-phase binary array,so that its gain is improved.In order to adapt to the vehicle environment,the anti lodging device is installed at the bottom of the antenna and simulated and tested.Finally,the antenna prototype is tested.The results show that the VSWR is less than 2.5,the directional pattern is horizontal and omnidirectional,and the gain is greater than 4dbi in the working frequency band.(2)Research and design of omnidirectional high gain array antenna.In order to further improve the antenna gain,based on the above antenna,the antenna feed form is adjusted from single-layer coupling feed to double-layer coupling feed.The antenna is equivalent to an equal amplitude in-phase quaternion array.The antenna is processed and tested to achieve the goal of VSWR less than 2,horizontal omnidirectional pattern and gain greater than 6dbi in the working frequency band.Since both antennas work in UHF band and some frequency bands overlap,a T-shaped coaxial adapter is designed to integrate the two antennas,and the two antennas are placed vertically and coaxially.Aiming at the problem of frequent manual replacement of the adapter caused by the dual port feeding of T-shaped coaxial adapter,a duplexer is designed to change the antenna from dual port feeding to single port feeding.Finally,the integrated antenna achieves the goal of VSWR less than 2.5,relative bandwidth of 40% and gain greater than 5d Bi in the working frequency band.