Study On Broadband Circularly Polarized Non-uniform Square Loop Antenna

Circularly polarized?CP?antennas can be employed to mitigate the multipath interference effects in various wireless systems.Design approach to a broadband circularly polarized?CP?non-uniform square loop antenna with co-axis mutually embedded structure is studied in this thesis.Both the bidirectional and unidirectional circularly polarized antennas are designed and investigated.The main contents of this thesis are organized as follows:1.The loop antenna can produce inherent circularly polarization under the even-mode excitation.It is known that the loop structure exhibits an infinite perfect electric wall which occurs along the major diagonal,while an infinite perfect magnetic wall occurs along the minor one.In order to achieve model matching of the natural boundary conditions,the rectangular dipole can be used to properly excite the loop antenna and control its handedness.2.By introducing the co-axis,mutually embedded dual-loop configuration,both the impedance and axial ratio?AR?bandwidth of the antenna can be effectively enhanced.By adjusting the size of the two loops,the antenna can resonate at different frequencies and broadband circular polarization characteristic can be realized.The antenna is simulated by using HFSS.Two configurations,with two loops embedded on the same/different layer?s?,are respectively designed.The 3-dB AR bandwidth can be enhanced to 19.5%and the impedance bandwidth for|S₁₁|<-10dB can be enhanced to 86.1%.3.In order to realize the unidirectional radiation antenna,two feed configurations are used in this thesis.The first one is to use L-shaped probe above a ground plane,and the other one is to utilize a twin-line transition balun mounted above a metallic reflector.Two cases,with two loops embedded on the same/different layer?s?,are respectively investigated.Two configurations,with two loops embedded on the same/different layer?s?,are respectively designed.The unidirectional loop antenna exhibits excellent CP performance with a high front-to-back ratio up to 30dB.The 3-dB AR bandwidth can be enhanced to 21.2%and the impedance bandwidth for|S₁₁|<-10dB can be enhanced to 76.7%.