| Since the entering the information age,wireless communication has become a necessary means of daily communication.As an indispensable part of the communication link,the wireless base station directly determines the communication quality.Modern life and work require high quality wireless communication which mainly occurs indoors,so the demand for indoor base stations is huge,especially in urban areas,with dense buildings and high population density,outdoor base stations are far from being able to meet the communication needs.The solution of indoor base station mainly includes the directional base station antenna installed on the wall and the omnidirectional base station antenna installed on the ceiling,and the latter is more widely used.For indoor ceiling base station antennas,good omni-directional coverage and large operating bandwidth are required in engineering applications.The miniaturization of the physical structure of the antenna,especially the low profile height,has been the continuous pursuit of commercial applications because of its low cost,high stability and aesthetics.According to the application requirements of different polarization,three miniaturized omni-directional base station antennas used in LTE system are proposed.The main work of this thesis includes:1.A vertically polarized omnidirectional antenna is designed,which is composed of three orthogonal PCB boards and four shorting metal posts.First of all,the radiation structure which is similar to the single cone antenna is realized by two crossed substrates,and then the triangular patch and shorting posts are loaded to reduce the working frequency of the antenna.It thus reduces its profile height equivalently.In addition,the Interdigital capacitor is applied near the input port of the antenna to improve the impedance matching.The working band of the designed antenna covers 1.67-3.46 GHz with the overall physical size of30×30×14.5mm3 and electrical size0.166×0.166×0.081?3mi n,where?mi n is the free space wavelength corresponding to the lowest operating frequency.The antenna has the advantages of a novel structure,small size,low production cost and good stability.And it is suitable for mass production.The design method of this antenna can be flexibly applied to the same type of antennas and has a good guiding significance for the design of tridimensional antenna.2.A horizontally polarized omnidirectional antenna is designed.The antenna is implemented on a circular PCB board.The antenna is fed at the center of the substrate,and four Vivaldi slot antennas directly fed through a 1-4 power divider.In addition,a straight slot is arranged between every two Vivaldi antennas to expand the antenna bandwidth and improve the pattern roundness of the antenna in the Azimuth plane.The overall physical size of the antenna is?×602×1mm3,and the electrical size is?×(0.32)2×0.005?3min.3.A dual-polarization omni-directional antenna is designed.The horizontally polarized omnidirectional radiation is realized by a circular array of eight open slots,and the vertically polarized omnidirectional radiation is realized by using the characteristics of the TM0n mode of a cylindrical cavity.Specifically,eight copper plates are used to excite the TM01 and TM02 modes.In addition,the horizontally polarized antenna is used to replace the top metal disk of the vertically polarized antenna element.Eight slots are etched on the ground of the vertically polarized antenna element,which well solves the problem of matching deterioration when the horizontally polarized antenna is close to the ground.In the band of 1.7-2.7 GHz,the reflection coefficients of horizontal polarization unit and vertical polarization unit are both less than-10 d B,and the port isolation is about35 d B.The antenna achieves a very low profile height of 12.3mm(0.07?min),and avoids the problem of feeder interference in the practical application of the traditional dual-polarization omnidirectional antenna. |
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