Novel Low Profile Circularly Polarized Antennas

With the rapid development of wireless communication technology,antennas are used in many new scenes.The environment which antennas have to deal with are becoming more complex.The CP antenna is very effective in combating multi-path interferences or fading.CP antenna is able to reduce the ‘Faraday rotation' effect.Due to the features of circular polarization,recent decades have seen a lot of research and development activities in CP antennas from industries and institutes worldwide.In many applications,low profile feature is "rigid demand" today.Because of meeting the needs of low profile feature and circular polarization characteristics,two antennas are designed in this thesis.They are all low profile CP antennas.For the first antenna,emphasis will be placed on miniaturization and broadband.With the combination of CPW and slot-loop structure,broadband is realized.The proposed antenna attains an S11 ?-10 d B impedance matching bandwidth of 88%,from 2.32-5.95 GHz,and a broadband 3 d B AR bandwidth of 35%,ranging from2.97-4.25 GHz.By using a new feeding structure,miniaturization is realized.The single feed structure contains a microstrip transition-to-coplanar waveguide conversion structure.By using this conversion structure,the two modes of CPW are excited by the same time.And the 90° phase difference can obtain if the dimensions are carefully designed.This antenna is fabricated and measured.The measured results are agreement with the simulation results.After that,this paper presents a design of a new low profile quasi-omnidirectional circularly polarized antenna.This antenna centered at 2.4 GHz?It combined H-plane fan-shaped horn antenna and dipoles to generate Circular polarized radiation.This design use single feed and simple impedance matching method to keep the antenna structure simple.It has the end-fire property,meanwhile,it also maintains the advantages of low profile.by integrating multiple basic structures on the same substrate symmetrically.Its radiation pattern has the quasiomnidirectional property.Its radiation pattern almost has the ideal omnidirectional property in xoy-plane.This antenna meets the needs of many application scenarios.For example,the antenna is suitable for embedding in a small metallic UAV.