Study And Design Of Ground-Based Navigation Omnidirectional Antennas

As a kind of antenna which has uniform radiation in the horizontal plane,the omnidirectional antenna has been widely used in the field of communication,navigation and so on.The omnidirectional antennas consist of dipoles are popular in practical applications with the advantages of simple structures,low cost,processing and integrating with the feeder network easily.At present,many radio systems need to improve the performance of antennas to complete some special tasks,such as forming special beams to cover specific areas.Array pattern synthesis is the method to solve these problems.In this thesis,high gain omnidirectional antennas are studied in the field of zero padding,which is a kind of array pattern synthesis in the background of the navigation system.Firstly,we study the basic principles of array antennas and the characteristic parameters of the dipole,from which the feasibility of constructing a high gain omnidirectional antenna by using dipoles to form the longitudinal array is determined.Then,the basic structure and advantages of the printed dipole are studied and the common feed forms are introduced.On that basis,an omnidirectional array antenna with four printed dipoles as the elements is proposed.Two arms of each element are printed on the upper and lower layers respectively of the substrate and four elements are equidistant.The antenna is feed by a smoothing line with the method of series feed,so the equivalent method in characteristic impedance of the smoothing line and the microstrip line are studied.The simulation results show that in the horizontal plane the minimum gain is greater than 5.8d Bi and the ellipticity is less than 0.65 d B.In the vertical plane,the first zero points in the upper half are greater than-19.7d Bi.The VSWR is less than 1.5 in the working frequency band.Secondly,in order to fill the first zero points in the upper half in the vertical plane,we need to change the excitation phase distribution of the elements.In view of the structure of the antenna mentioned above,we optimize the gap and the position of the elements and adding metal sleeves in combination with the stub in the top of the antenna to pad zero points and improve the ellipticity.The simulation results show that in the horizontal plane the minimum gain is greater than 5.2d Bi and the ellipticity is less than 0.48 d B.In the vertical plane,the first zero points in the upper half are greater than-8.3d Bi.The VSWR is less than 1.5 in the working frequency band.We obtain that the effect of zero padding is excellent from the results.Finally,we need to study the feeding network to learn the methods of zero padding to grasp the intuitive effect.We use DE algorithm as an optimization method.At the same time,another omnidirectional array antenna with eight wideband dipoles as the elements is designed.The simulation results show that in the horizontal plane the minimum gain is greater than 8.2d Bi and the ellipticity is less than 0.54 d B.In the vertical plane,the first zero points in the upper half are greater than-13.4d Bi.The VSWR is less than 1.5 in the working frequency band,meeting design requirements.