Research On Planar Endfire Circularly Polarized Antennas And Arrays

With the rapid development of information technology,information interchange increasingly depends on the wireless network and other contemporary technologies.As a key part of the wireless network communication systems,antennas play an indispensable role in them.The planar end-fire antennas with circularly polarization have gradually received widespread attention and research because of their advantages such as good orientation,low profile and strong anti-interference ability.Therefore,this thesis did a detailed study on the basic principles and design ideas of planar end-fire antennas with circularly polarization.Then,three new types of planar end-fire circularly polarized antennas are designed.The main research contents are as follows:1.The main purpose of this thesis is to design planar end-fire circularly polarized antennas.In order to provide a certain theory for the related design,we study the basic principles of end-fire antennas,circularly polarized antennas and microstrip Yagi antennas.2.Based on the conventional design idea,two types of circular polarized antennas without ground structure,including single semi-circle dipole antennas and double semi-circle dipole antennas,are designed by using the complementary dipole methods.Both of them contain a feeding port and a pair of microstrip lines which are used to connect the semi-circular ring oscillator with rectangular magnetic dipole.The phase difference can be adjusted by changing the length of the microstrip line.Besides,a semi-circle patch which acts as a director is added in front of the antenna.Meanwhile,the director can be used to adjust the impedance matching of the antenna,which makes the-10-d B impedance bandwidth and the 3-d B axial ratio bandwidth in the same frequency band.The resonant frequencies of two antennas are 4.17 GHz and 4.40 GHz respectively.The relative bandwidths are 8.0% and 9.3%,respectively.And the maximum gains in the working frequency band are 3.88 d Bi and 4.20 d Bi,respectively.Meanwhile,both of the antennas achieve good end-fire circular polarization performance.In addition,we also study the performance of the array which is composed of two semi-circular ring dipole antennas.3.A new type of planar end-fire circularly polarized antenna with ground is proposed: a microstrip Yagi antenna based on the high impedance surface(HIS).To avoid the influence of the ground plane on the beamwidth of the radiation pattern,we use HIS to replace the ground plane in the design.Thanks to the HIS,which supports TE and TM modes at the same time,the influence of the ground plane on the radiation pattern is reduced significantly.Then,a new type of microstrip Yagi antenna based on HIS structure that works near 9.9 GHz is designed.Compared with the antenna with traditional metal ground,the radiation beam of the propsed antenna is colser to the end-fire direction.The main radiation beam has a maximum gain of 8 d Bi at 59° from the normal direction,and achieves a good circular polarization in the end-fire direction.The measured results are basically consistent with the simulated results,proving the feasibility of the design.