Multi-frequency Beam Switchable Microstrip Antenna Design

With the rapid development of mobile communication technology,the research and design of antennas with beam switching and scanning characteristics has attracted increasing attention.For providing a systematic and hierarchical idea for antenna design,Characteristic mode analysis theory(CMA)has been widely applied to antenna design.In this thesis,two microstrip antennas with beam switching and scanning characteristics are designed with CMA.The research contents mainly include the following two points:(1)A vertically polarized dual-frequency beam switchable microstrip antenna is designed based on CMA.By loading the shorting pins,the original current distribution on the patch is changed,thus generating modes J₁,J₂,and J₃.Adjusting the pins'spacing on different patches would tune the resonance frequencies of J₁ and J₃.By investigating the inherent difference between the far-field phase and characteristic angles of these modes,J₁and J₂ are superposed to form a unidirectional beam at low frequency.In contrast,J₂ and J₃ are superposed to form a beam in the opposite direction at a higher frequency.The proposed antenna has generated a beam with a tilted angle of 60 at4.20?4.31 GHz,with a gain of 7.24 d Bi,and the sidelobe level is lower than-9 d B;at4.64?4.84 GHz,it generate a 45°beam with a gain of 6.17 d Bi,and the sidelobe level is lower than-11 d B.(2)Based on CMA,a frequency scanning planar antenna with high gain has designed.By loading the shorting pins on the patch,the mode analysis has been performed on the four adjacent modes J₁,J₂,J₃,and J₄.It is found that J₃ with the beam direction perpendicular to the array limits the scanning range.Besides that,J₄ is not sensitive to changes in the distance and number of shorting pins,while significant frequency shifts arise with J₁,J₂,and J₃.Therefore,J₃is excluded from the frequency range of J₁,J₂,and J₄ by dense shorting pin loading and slot coupling feed structure.J₁ and J₂ generate bidirectional patterns with an inclination angle of 70°and 40°respectively,and J₄ is an endfire mode.By combining these modes in pairs,the proposed antenna achieves 10°?53°beam scanning at 4.32?4.72 GHz,the gain can reach 7.5?8 d Bi,the sidelobe level is lower than-11 d B,and the beam can be switched by changing the feeding port.