The Research And Deign Of Broadband Circularly Polarized Microstrip Antenna

With the development of modern communication technology,a wireless communication system usually needs to work in multiple frequency bands,such as Wireless Local Area Network(WLAN),Worldwide Interoperability for Microwave Access(Wi MAX),and even needs to work in a wide frequency band at the gigahertz level,such as Ultra Wideband Communication System(UWB).Higher requirements are placed on the working bandwidth of the antenna.At the same time,wireless communication systems pursue more stable communication quality.Compared with traditional linear polarization,circularly polarized antennas can reduce polarization loss,suppress multipath interference and electromagnetic interference,which can effectively improve the stability of communication.It has significant advantages in practical applications.Therefore,the broadband circularly polarized antenna has high academic research and practical application value.Based on the microstrip antenna with low cost,low profile,and easy integration in mobile devices,this thesis studies the broadband circularly polarized microstrip antenna that can work in various wireless communication systems such as WLAN/Wi MAX/UWB.The research results are as follows:Firstly,a broadband circularly polarized square slot antenna fed by coplanar waveguide is designed first.The overall size of the antenna is 25×25×0.8mm~3,the ground plane is changed to an asymmetric structure,and rectangular slots are inserted at the diagonal corners,which initially stimulates the circular polarization mode.Then to improve the antenna impedance matching and circularly polarized radiation performance,a semi-circular perturbation patch is extended on the right side of the microstrip feedline.By continuously adjusting the parameters of each structure,the impedance bandwidth of 75.1%(3.68-8.11GHz)and the axial ratio bandwidth of 42.5%(3.96-6.10GHz)are finally obtained.The antenna completely covers the C-band.Secondly,a wide-band circularly polarized wide-slot antenna with non-center feed is designed using a wide-slot structure similar to the first antenna as the basic model.In order to break the symmetrical structure of the antenna and realize the performance of circular polarization,two L-shaped strips are introduced at the diagonal corners of the wide-slot ground plate,and asymmetric rectangular tuning patches are extended on the left and right sides of the microstrip transmission line.The radiator and the right ground plane are moved to the left as a whole,optimizing the impedance characteristics and current distribution of the antenna.The axial ratio bandwidth is extended to 58.0%(4.65-8.45GHz),the impedance bandwidth is 105.5%(2.76-8.92GHz).The antenna can work in the WLAN/Wi MAX3.5/5.2/5.8GHz frequency band,and completely covers the C-band(4.0-8.0GHz).Next,based on the relatively wide impedance bandwidth of the monopole antenna,an open-loop broadband circularly polarized monopole antenna is designed.The radiator is improved from a circular shape to an open ring,which greatly improves the circular polarization performance of the antenna.By introducing the rectangular groove and short branche in the ground plate,the impedance bandwidth is extended to 112.8%(3.75-13.47GHz),and the axial ratio bandwidth is extended to 77%(3.75-8.54GHz).The axial ratio bandwidth of the antenna completely covers the C-band of 4.0-8.0 GHz,which can be applied to scenarios such as satellite TV broadcasting.The antenna can meet most frequency band requirements of UWB wireless communication system,and realize circularly polarized radiation in a wider frequency band.Finally,the advantages and disadvantages of microstrip line feeding and coplanar waveguide feeding are analyzed,and a double circular broadband circularly polarized monopole antenna is designed.The inverted L-shaped groove is etched inside the double circular radiator,which effectively reduces the overall axial ratio of the antenna and introduces a new return loss resonance point.Then,by adjusting the structure of the double circular radiating patch and the asymmetric ground plane,broadband circular polarization performance is achieved.The antenna model is processed and tested,and the impedance bandwidth is 117.8%(2.2-8.5GHz),and the axial ratio bandwidth is 62%(4.45-8.45GHz).The working bandwidth of the antenna can completely cover the WLAN 2.4/5.2/5.8GHz and Wi MAX 2.5/3.5/5.5GHz frequency bands.