Study On Wideband Antennas Based On The Tightly Coupling Effect

With the rapid development of wireless communication technology,the radio frequency system is gradually showing the trend of multi-functional integration development.Therefore,the technology of wideband antenna has attracted extensive attention of experts and scholars in antenna field.The array antenna based on the tightly coupling effect,which uses the strong electromagnetic coupling effect between elements to broaden operating bandwidth,shows remarkable advantages such as ultra-wideband,low profile and wideangle scanning.Thus,it has become a promising candidate for high-performance radar wideband antennas,and has wide application prospects in both commercial and military wireless communication systems.In consideration of research subjects and practical requirements of modern communication systems,this thesis is mainly concerned with the wideband antenna based on tightly coupling effect,especially the ultra-wideband dualpolarized array and wideband circularly polarized antenna.The author's major works are as follows: 1.The theory and design method of the tightly coupled array antenna are investigated.Firstly,the basic principle of phased array and the difficulties of traditional wideband array antenna design are analyzed.Then,the working principle and the equivalent circuit model of the tightly coupled array antenna are studied.With the help of the software of ADS and HFSS,the equivalent circuit model is analyzed and the tightly coupled array element is designed.In addition,the design methods of the tightly coupled array is analyzed from three aspects: the design of feeding structure,the removal method of common mode resonance,and the technology of the wide-angle impedance matching(WAIM)layer.2.Based on the theory of tightly coupled array antenna,an ultra-wideband tightly coupled array antenna is realized.Firstly,the unbalanced feeding structure is used to feed the short dipole.Based on the waveguide cut-off frequency theory,the coupled shorting via is utilized to move the common mode resonance out of the operating band.In order to realize the wideband impedance matching of the antenna element,the parallel coupled plate structure is introduced.Then,the scan performance of the antenna is analyzed from two aspects: the introducing of WAIM layer and the elimination of scan blindness.After that,the truncation method of tightly coupled finite array is investigated.The dummy element loading method is used to truncation the 1-D infinite array,and the impedance bandwidth and scan performance are analyzed.Finally,the 8 × 8 tightly coupled array is designed,and the simulation results and measuring methods are analyzed and discussed.3.The electromagnetic coupling effect is introduced into the research of circularly polarized antenna,and two wideband circularly polarized antennas are proposed.In the first antenna design,the single arm coupling effect is introduced into the asymmetric dipoles,leading to the improvement of the impedance matching.After that,the impedance matching strips and interdigital structure are introduced to further enhance the operating bandwidth.Finally,the measured results show that the proposed single-arm coupled asymmetric dipole antenna achieves 108% impedance bandwidth and 96% axial ratio(AR)bandwidth,with stable wideband circularly polarized performance.In the second antenna design,based on the single-arm coupled asymmetric dipole,a wideband circularly polarized antenna with lowprofile is realized by introducing the artificial magnetic conductor(AMC)surface.The measured results show that the presented antenna achieves a wide impedance bandwidth of 107% and an AR bandwidth of 97% in the condition of low profile.