Design Of High Gain Antenna Based On Railroad Communication System

Railway wireless communication has the characteristics of linear distribution,so the antenna used in railway communication should have the characteristics of narrow beam and high gain.Based on the theory of dipole antenna and Yagi-Uda antenna,a high-gain and narrow beamwidth antenna which can be used in railway wireless communication was studied and designed,and its broadband characteristic was explored.A dual-band high gain antenna for railway communication and a dual-polarization high-gain antenna for tunnel environment are designed based on the high-gain broadband Yagi-Uda antenna.In this paper,a 900 MHz band high gain Yagi-Uda antenna was designed firstly.A printed dipole antenna was adopted as active radiation unit,and metal reflector plate and a certain number of directors was added to improve the gain of antenna and made the antenna has narrow beamwidth.By adding two square branch structures to both ends of the dipole,a wide bandwidth characteristic can be obtained,and the matching characteristic can be improved by adding coupling patches.The antenna adopts non-equal spacing and non-equal length directors,which maximizes the gain and the width of the band.The-10 dB bandwidth of the antenna is 256MHz(0.744–1GHz),and the relative is 29.3%.Compared with the high-gain Yagi-Uda antenna without square branches and coupling structure,the absolute bandwidth is increased by 83 MHz,and the relative bandwidth is increased by about 10%.Within-10 dB work frequency band,the average of the maximum gain of the antenna is 14.2dB,the average of the maximum gain of the antenna in the band of 885-935 MHz is 15.9dB.The average beamwidth of the E plane and H plane are 35°and 36°,respectively.The front-to-back ratio is more than 24 dB.Because there is multiple frequency of railway wireless communication,a high gain Yagi-Uda antenna work in 450 MHz band was designed based on the high gain antenna work in 900 MHz band.Then combined two antenna,placed by orthogonal way to reduce the coupling between the two antennas,implemented the dual-band work of 450 MHz and 900 MHz band.By adding a metal bar as reflector,the matching characteristic of the dual-band antenna was improved at the band around 900 MHz,and the gain raise of 4.7dB in this band also.The isolation of the two ports is greater than 30 dB.In the band of 455-470 MHz and 885-935 MHz,the average gain are 13.6dB and 14.9dB,the half power beamwidth within 50°and 35°,respectively.A dual-polarization high gain antenna was designed to overcome the multipath fading caused by electromagnetic wave propagate in the tunnel.The antenna based on the broadband high gain Yagi-Uda antenna work in 900 MHz band,and two linear polarization antennas was placed in orthogonal way.Through reasonable dislocation configuration,realize the dual-polarization and make the isolation more than 30 dB of the two ports.The S11 of two ports is less than-15 dB.The average of the biggest gain is 15.3dB.The half power beamwidth of the antenna is less than 40°.The antenna has strong directivity,which can solve the problem of multipath fading effectively.