| With the rapid development of wireless communication technology and increasingly scarce spectrum resources,there is an urgent need for antenna to have broadband and multi-band characteristics.Many wireless communication systems use circular polarization technology to improve their stability and reliability,such as Wireless Local Area Network(WLAN),Worldwide Interoperability for Microwave Access(Wi MAX)and Bluetooth.The purpose of this thesis is to study the microstrip antenna used in WLAN,Wi MAX,and Bluetooth.The aim is to achieve broadband,multi-band,and miniaturization of circularly polarized microstrip antennas.The specific research contents are as follows:Firstly,a coplanar waveguide fed dual-band circularly polarized microstrip antenna is designed,which realizes the dual-band circularly polarized characteristic through the asymmetry of ground height,the perturbation of two curved branches extending to slot and the vertical slit at lower right corner of ground plane.The three operating bandwidths of the antenna were 2.19-3.15 GHz,3.25-3.7 GHz and 4.14-7.02 GHz,respectively.And the two axial ratio bandwidths were 2.15-2.56 GHz and 4.58-5.88 GHz.Secondly,a tri-band circularly polarized microstrip antenna is designed based on the first antenna.The length of the feed is increased,and part of the disturbing branch is simplified,which together make the improved antenna structure more simple.The impedance bandwidths were 62%(2.22-4.21 GHz)and 21.4%(4.84-6 GHz).And the axial ratio bandwidth were 13%(2.17-2.47 GHz),8.3%(3.46-3.76 GHz),and 36%(4.17-6 GHz),respectively.The antenna exhibits a right-hand circularly polarized radiation characteristic in the boresight direction within the three axial ratio bandwidths.Next,based on the broadband characteristics of rectangular wide slot antenna and multi-resonant structure,a dual-band wide slot circularly polarized antenna is designed.In order to achieve dual-band circularly polarized characteristic,a reasonable perturbation structure is introduced to the rectangular slot antenna.The overall size of the antenna is35×35×1.6mm~3.The antenna has an operating bandwidth of 2.22-6 GHz,with a relative bandwidth of 92%.The axial ratio bandwidths were 2.94-3.44 GHz and 5.25-5.88 GHz,respectively,peak gain in the low band was about 3.4 d Bi and in the high band was 6.5 d Bi.The right-handed circularly polarized waves are radiated toward the boresight direction within two circularly polarized bandwidths.The working bandwidth of the proposed antenna can completely cover the WLAN 2.4/5.2/5.8 GHz band and Wi MAX 2.5/3.5/5.5 GHz band.Finally,an antenna,which designed on the basis of traditional microstrip monopole antenna,can achieve circular polarization in a broadband range by breaking the symmetry of current.That is to change the position of feed and monopole patch so that the radiation patch and ground plane can participate in the radiation at the same time.By introducing a slot in the ground plane to achieve broadband circular polarization,then the antenna finally achieved a axial ratio bandwidth of 50.8%(3.72-6.25 GHz),the peak gain in the axial ratio bandwidth was about 3.0 d Bi.The overall size of the antenna is 30×35×1.6mm~3,and it has two impedance bandwidths,which were 2.76-6.83 GHz and 7.53-9.72 GHz. |
