Study On Asymmetrically Fed Dual-Mode Resonant Sectorial Dipole Antennas

Future mobile communications will evolve toward high frequency,millimeter wave bands.As one of the key components in the millimeter wave wireless communication system,the research and development of millimeter wave antenna has become a cutting-edge topic.Recently,microstrip antennas have been widely used in millimeter wave owing to their characteristics of compact size,low cost,and suitability for integration with other systems.Microstrip printed dipole have become common methods to design millimeter wave antenna.However,the TM mode microstrip feed line can no longer directly employed to excite the TE mode resonant dipole,which might produce high cross-polarization level.Therefore,it is always a big challenge to design a pure horizontally polarized printed dipole with low cross-polarization,simple structure and apply it in millimeter wave bands.Based on the theory of multi-mode resonance,this thesis designs a dual-mode resonant horizontally polarized,asymmetrically fed sectorial dipole and applies it to design of four-element millimeter wave array antennas.The main work is as follows:1.Firstly,base on the multi-mode resonance theory of 2-D sectorial full-wavelength dipole,a microstrip fed printed sectorial dipole is proposed.The feeder adopts a coplanar stripline(CPS)to microstrip line(MSL)transition structure with asymmetric-fed configuration and it is set at the radius of sectorial dipole finally.Cross-sectional E-field distributions transition from TM to TE mode.The antenna sample of 2.4GHz is fabricated and measured,and the measured results are in good agreement with the simulated,which fully proves the correctness of the design method of horizontally polarized,asymmetrically fed sectorial dipole.2.In order to further study the above design approach,it is extended to the 24 GHz millimeter wave band,and its correctness is verified by simulation.The sectorial dipole elements with flared angle of 270° and 290° are employed to implement four-element millimeter wave linear antenna array,which is applied above 24GHz-band.HFSS is used to optimize the element spacing.Finally,the antenna array samples are fabricated.As has been verified,the proposed antenna can exhibit low cross-polarization and wide beamwidth of H-plane(zx-plane).3.Subsequently,the zigzag topology is employed in the four-element millimeter wave antenna array.In the experimental verification,it is found that the proposed antenna can reduce the sidelobe level at high frequency and improve the gain within the impedance bandwidth.As is evidently revealed,an asymmetric CPS-MSL transition can serve as a successfully effective feeder to wideband,full-wavelength sectorial dipoles at both microwave and millimeter wave bands.