Research And Design Of High Performance Omnidirectional Antenna

The azimuthal omnidirectional antenna has omnidirectional radiation patterns in the horizontal direction.This special radiation characteristic is widely used in the wireless communication fields such as broadcast TV,mobile communication,indoor distributed system,vehicle-mounted station,satellite communication and so on.With the rapid development of the wireless communication system market,people also put forward higher challenges to the performance requirements of omnidirectional antennas.In this thesis,combined with the research on the project during the internship,three high-performance omnidirectional antennas with different polarization methods are proposed,namely linear polarization,high gain dual-frequency double-fed omnidirectional antennas,broadband miniaturization and horizontal polarization antenna and vertical / horizontal dual-polarized omnidirectional antenna.The main works of this thesis are: 1.A dual-band double-fed vertically polarized omnidirectional antenna is proposed.The proposed antenna consists of a broken-line dipole array with two arms printed on the front and back sides of the dielectric board,respectively.A parallel double-line structure is used to feed the antenna with equal magnitude and phase.The antennas operating in the high and low bands are designed with two independent branches.By optimizing the array spacing,a high isolation can be achieved without any decoupling structure.The measured results show that the-10 d B reflection coefficient bandwidth of the antenna can cover the bands of 2.4 ? 2.5 GHz and 5.15 ? 5.85 GHz.In the absence of other decoupling structures,the antenna isolation is better than 20 d B and has good omnidirectional radiation characteristics.2.A printed broadband miniaturized horizontally polarized omnidirectional antenna is proposed.The design consists of four ''F-shaped” dipoles,a broadband feed network,four parasitic bands,and four directors.Four groups of ''F-shaped” dipoles form two large rings to achieve broadband omnidirectional radiation characteristics.Moreover,loading parasitic strips can effectively expand the impedance bandwidth.The director can be used to enhance the axially oriented radiation characteristic of each group of dipoles,which increases the gain and reduce the gain variation in the horizontal plane.The measurement results show that the-10 d B reflection coefficient bandwidth of the antenna can cover the band of 1.7-3.9 GHz,and the entire size is only 100 mm×1.5 mm.The out-of-roundness in the horizontal plane is within 2 d B.3.A vertical / horizontal dual-polarized omnidirectional antenna for vehicle-mounted mobile communication systems is proposed.The design consists of a horizontally polarized antenna and a vertically polarized antenna placed with a reasonable distance in the vertical direction.The vertically polarized antenna adopts the form of a disc cone antenna.The antenna is fed by a 50? RF coaxial cable and a round patch is loaded on the top of the disc cone to improve impedance matching.The horizontally polarized antenna uses four sets of arc dipole antennas to form a circular ring as the radiating unit.A feed network composed of a one-fourth power divider,a gradient impedance transformation section and a balun combination is utilized to feed the radiating unit the same amplitude and in phase,which makes the current distribution on the ring uniform;and achieves horizontal omnidirectional radiation characteristics.Finally,by combining the vertically polarized antenna and horizontally polarized antenna the practical engineering applications,a reasonable outer cover size is obtained.In order to simulate results show that isolation between the two ports of the dual-polarized antenna is greater than 35 d B,the out-of-roundness of the horizontally and vertically polarized antennas are within 0.5 d B and 1 d B.The thesis has conducted in-depth research on high-performance omnidirectional antennas with different polarization modes,investigated the working principle and design theory of omnidirectional antennas,and accumulated richer design ideas and data support for engineering design.