The Study On Broadband And Multi-Band Circularly Polarized Antennas

Due to the rapid development of modern communication technology,the communication electronic equipment has the characteristics of miniaturization,and its ability to process communication information data also requires the characteristics of broadband.Antenna has always been the main part of the wireless communication system.Due to linear polarization antenna in mobile communication process will exist polarization mismatch,and the circularly polarized antenna has its own advantages in resisting multi-path interference and inhibiting cloud and rain interference,also it can receive incoming waves with any polarization form,thus,circularly polarized antenna naturally becomes the best choice for mobile satellite communication system.Since all kinds of modern wireless communication systems require broadband high-speed information processing capability,the antenna is also required to have broadband or multi-band characteristics.However,for the conventional circularly polarized microstrip antenna,the relative bandwidth is very narrow because of its high quality factor.In recent years,due to the continuous improvement of printing technology,printed antenna has the advantages of low cost,light quality,wide working bandwidth and easy processing and debugging.Therefore,in order to meet the needs of various mobile wireless communication devices,this dissertation conducts an in-depth study on circularly polarized printed antennas.The main research contents of this dissertation include:planar broadband dipole antenna,planar broadband circular polarization antenna based on dipole structure,printed wideband circularly polarized slot antenna and array,printed multi-band circularly polarized slot antenna and wideband dual-wideband printed dual-circular polarization slot antenna.1.The plane broadband dipole antenna is studied in depth.(1)Aiming at the complex feed-balun structure in the application of low-profile electric dipole antenna in ultra-wideband communication system,a feed-balun structure is proposed in this dissertation,which is similar to vivaldi antenna structure,to realize broadband matching characteristics.This simple feed structure can greatly improve the impedance bandwidth of the electrical dipole antenna,and this feed structure has little effect on the antenna impedance matching performance when the size changes,which indicates that the antenna has low requirements on machining accuracy and is easy to realize impedance matching.In order to meet the requirement of low profile and high gain of antenna for communication system,a reflective cavity structure is adopted in this dissertation.The profile height of the final optimized antenna is only 0.17?.(2)In order to meet the demand of UWB system for circularly polarized antennas,the wideband circularly polarized performance is achieved by using rotational symmetric dipole structure in this dissertation.The rotating dipole structure can produce another electric field with orthogonal direction of the direction of the dipole,and the phase difference between this electric field and the dipole excitation direction is 90°.As a result,the dipole-based rotationally symmetrical structure causes surface currents to produce circular polarization wave radiation.(3)In order to meet the requirements of different communication systems for different antenna polarization forms,a frequency selective polarization antenna is realized in this dissertation by using the rotational symmetric dipole structure.The polarization form of this frequency selective polarization antenna varies with its working frequency.2.The printing broadband circularly polarized slot antenna is studied.(1)A new type of annular planar slot antenna is designed in this dissertation to meet the requirements of modern wireless communication systems for circularly polarized antennas with wider impedance bandwidth and 3-dB axial-ratio bandwidth.At the same time,in order to optimize its circular polarization characteristic,a patch resistor is used to absorb the residual energy to reduce the secondary radiation.(2)In order to avoid using absorption resistance to realize broadband circularly polarized slot antenna,another new planar circularly polarized slot C-shaped slot antenna is designed in this dissertation.The low circularly polarized frequency of the antenna is mainly generated by the C-shaped slot,and the high circularly polarized frequency is mainly generated by the offset feed structure.A wideband circularly polarized slot antenna(3-dB axial-ratio bandwidth of 95.7%,1.20~3.40 GHz)can be designed by shortening the two circularly polarized frequency bands.At the same time,in order to improve the gain and realize directional radiation,a circularly polarized array with 2×2 rotary feeding network is designed based on the circularly polarized C-shaped slot antenna unit.(3)In order to further expand the circularly polarized bandwidth of C-shaped slot antenna,L-shaped metal strip is used in this dissertation to replace rectangular metal strip,and another L-shaped slot structure is cut on the antenna ground plane.It will generate another circularly polarized resonance point in high frequency.By the above operations,the circularly polarized bandwidth of antenna unit is further explaned(3-dB axial-ratio bandwidth is 115.2%,1.26~4.68 GHz).3.Multi-band circularly polarized antenna is studied.(1)In view of the characteristics of modern wireless communication system working in multiple frequency bands,a dual-band circularly polarized plane printed antenna is designed in this dissertation.The antenna uses an L-shaped metal strip to generate dual-frequency bandwidth.By adding two rectangular metal patches on the two symmetrically corners of ground plane,dual-frequency circular polarization radiation can be realized.(2)In order to meet the demand of antenna miniaturization for many modern dual-band wireless communication systems,another small-size dual-band circularly polarized plane printed slot antenna is designed in this dissertation.By using the inverted L-shaped metal strip and offset center feeding structure,the rdual-band with circular polarization is realized.The inverted L-shaped metal strip is used to realize low frequency circular polarization wave,and the offset center feeding structure is used to realize high frequency circular polarization wave.The size of the antenna is0.32?×0.32?=0.1?~2.Due to its bent structure,the antenna is more compact.Moreover,its circularly polarized operating bandwidth is wider and can perfectly cover the WLAN and wi-fi working frequency bands.4.The dual-port dual-circularly polarized planar printed slot antenna is studied.(1)In view of the demand of modern wireless communication system for broadband with various circular polarizations,this dissertation designed a wideband dual-circularly polarized plane printed slot antenna.This antenna consists of a U-shaped slot and two offset feeding ports to achieve broadband circularly polarized radiation.In the same frequency band,by changing the excitation and matching of two feeding ports,the radiation of right-hand circular polarization and left-hand circular polarization can be realized.(2)A dual-band dual-circular polarization plane printed slot antenna is designed in this dissertation to meet the demand of modern wireless communication systems for multi-band with multi-circular polarizations.The antenna is radiated by a Horseshoe-shaped slot and two offset feed L-shaped metal strips to achieve dual-band circular polarization.When one port is excited another one is matched,the antenna can achieve left-hand circular polarization radiation in lower frequency band and right-hand circular polarization radiation in higher frequency band.When the excitation port is opposite to the matching port,its circular polarization mode changes accordingly.