Design And Realization Of Wideband Circularly Polarized Microstrip Antennas

In recent years,the density of wireless communication networks is increasing continuously,and the communication of devices has become diversified.The traditional star network gradually develops toward the mesh network,making the communication area of single point-to-multipoint constantly expanding.The traditional linear polarized antenna restricts the development of the wireless network because of the high requirements on the direction of antenna.The problem can be solved by using the circularly polarized antenna.Circularly polarized microstrip antenna is widely studied because of its low profile,easy integration,strong anti-interference and insensitive directionality.However,the shortcoming of the narrow bandwidth of the ordinary circularly polarized microstrip antenna limits its application.Therefore,the wideband circularly polarized microstrip antenna has become an important research topic in wireless communications.In this thesis,the physical properties of microstrip antenna and circular polarization are described in details and two broadband circularly polarized microstrip antennas are designed emphatically.One is a wideband circularly polarized microstrip antenna with CPW-fed,and the other is a wideband circularly polarized microstrip antenna with wide-slot proximity coupled feed.Each antenna is mainly studied from several aspects including antenna structure,model building,the influence of main structural parameters on antenna performance,the optimization of antenna bandwidth and so on.In the end the antennas are fabricated,and the simulation results and return loss measurement results are shown.The CPW-fed wideband circularly polarized microstrip antenna has a footprint of40*40mm².The antenna is composed of a“human type”feed terminal,a ground plate and a single layer dielectric substrate.The“L”type microstip in the upper left corner and the lower right corner of the“human type”is perturbation segments,and the polarized waves is generated by adjusting the perturbation branches of“human type”feed terminal.The simulated results show that the resonant frequency is 2.45GHz and the maximum gain of the antenna is 2.7dBi.The simulated results demonstrate a-10-dB impedance bandwidth(S₁₁?-10dB)covers a total of 1200MHz from 2200MHz to3400MHz,giving FBW=42.8%.The 3dB axial ratio bandwidth of the antenna covers a total of 350MHz from 2250MHz to 2600MHz,and the relative bandwidth is about14.4%.The reflection coefficient of the prototype was measured by using a vector network analyzer?VNA?.The measured results show that the actual impedance bandwidth of the antenna covers a total of 1150MHz from 2250MHz to 3400MHz,and the results meet the requirements of bandwidth.It was equipped with a wireless communication device to test the communication distance,and the communication distance is about 150 meters.The bandwidth of the circularly polarized microstrip antenna is further extended by using wide-slot proximity coupled feed.The antenna has a footprint of 41*41mm²,and consists of the microstrip feeder at the bottom of the antenna,the radiation patch and the dielectric substrate.The resonant mode is excited by a perturbation unit of two 90°“L-shaped”structures at the middle square wide slot of the top radiation patch to radiate circularly polarized waves.The simulation results reveal that the maximum gain is 3dBi which is increased by 0.3dB.The simulated impedance bandwidth cover a total of1850MHz from 2050MHz to 3900MHz,which is increased by 650MHz.The 3dB axial ratio bandwidth covers a total of 500MHz from 2100MHz to 2600MHz,which is increased by 150MHz.The actual impedance bandwidth of the antenna covers a total of2100MHz from 1800MHz to 3900MHz,which is increased by 950MHz.The antenna is capable of realizing an communication distance of 200 meters on a wireless communication device.The two broadband circularly polarized microstrip antennas designed in this thesis meet the requirements of broadband.The two antennas have good double direction circularly polarized radiation capability and certain practical value.The thesis will provide a solution for the follow-up study on the wideband circularly polarized microstrip antennas.