Research On Broadband Circularlypolarized Printed Antenna

The antenna is a device which can convert high frequency electric signals and space electromagnetic waves to each other.Because the circularly polarized antenna has the characteristics of being able to accept arbitrary linear polarization and the same direction of circular polarization,it has many obvious advantages in anti-multipath interference,restraining depolarization effect caused by rain and fog and so on.Moreover,modern wireless communication systems require faster and faster transmission speed to support the explosive growth of data demand,these have driven the study of broadband circularly polarized antennas.Printed antennas are widely used because of their flexible design,easy integration and compact structure.Because the broadband circularly polarized printed antenna has the advantages of low profile,simple fabrication and wide polarization bandwidth,this paper studies the broadband circularly polarized printed antennas deeply,and proposes three broadband circularly polarized antennas that are a broadband circularly polarized microstrip antenna,a broadband circularly polarized slot antenna and a coplanar waveguide broadband circularly polarized antenna.Based on the sequential rotation feed structure,a broadband circularly polarized microstrip antenna was proposed by the modified traditional patch and ground.Four square patches are arranged orthogonally around the ring feed network,and U-shaped slots are introduced into the radiation patches and ground,which greatly broadens the circular polarization bandwidth of the antenna.In addition,in order to expand the circular polarization bandwidth of the antenna at high frequencies,one of the square patches is miniaturized and chamfered.The measured impedance bandwidth is of 26.4%(5.25GHz-6.85GHz),and the measured polarization bandwidth is of 21.5%(5.40GHz-6.70GHz).The size of the antenna is 50mm*50mm*1.524 mm.Compared with the traditional broadband circularly polarized microstrip antenna,it has the smaller profile and the wider bandwidth,so it is convenient for broadband wireless communication system.A compact broadband circularly polarized slot antenna is designed by introducing the Cshaped feed structure and a C-shaped radiation slot.The antenna is excited by the eccentric feed structure,and a circular slot is added to the C-shaped ground to expand the circular polarization bandwidth of the antenna at 2.50 GHz and 5.75 GHz,which helps the antenna to achieve good miniaturization performance.The measured impedance bandwidth of the antenna is 98.9%(2.20GHz-6.50GHz),and the measured circular polarization bandwidth is of 95.5%(2.30GHz-6.50GHz).The size of the antenna is 35mm*35mm*1mm.Compared with the current slot circularly polarized antenna,it has the smaller size and the wider circular polarization bandwidth.Based on the coplanar waveguide(CPW)feed structure,a broadband circularly polarized antenna is proposed in the form of the modified ground and radiation patch.The ground is composed of two asymmetrical rectangular patches,and the circular polarization radiation performance is achieved by loading the rectangular slot and bending branches.Then the Wshaped metal patch is introduced to expand the antenna bandwidth.The measured impedance bandwidth is of 120%(1.50GHz-6.00GHz),and the measured circular polarization bandwidth is of 47.7%(3.25GHz-5.30GHz).