Study Of Multi-Band Dual-Polarized Antennas And Circularly-Polarized Antennas Borne On Specific Platforms

To effectively transmit and receive electromagnetic signals,antennas paly a great role in wireless communication systems.In specific platforms（such as aircrafts,ships,satellites,etc.）,a large number of communication devices need to be arranged in a limited space,As a result,requirements on miniaturized,multi-band and multi-polarization antennas are raised.On the other hand,the axial-ratio（AR）performance of multi-band circularly-polarized antennas is an urgent bottleneck technology in communication systems.On the basis of research topics and scientific projects,this dissertation aims to investigate multi-band dual-polarized antennas borne on specific platforms and circularly-polarized antennas.Contents of this dissertation are summed up as follows:1.Multi-band dual-polarized antenna borne on unmanned aerial vehicle（UAV）.A multi-band dual-polarized antenna borne on UAV has been creatively developed by combining multi-antenna combination technology and special-shaped back cavity.The antenna includes a L-band antenna,two S/C-band antennas and two X-band antennas.In the L-band,a printed umbrella monopole is used to achieve a wide beamwidth.In the S/C-band and X-band,broadband dual-polarized antennas are designed by using wide crossed-slot coupled patches and a special-shaped back cavity,where the S/C-band antennas have an impedance bandwidth（IBW）of 89%and the X-band antennas have an IBW of 44%.The overall size of the hybrid antenna isΦ0.38λ_L×0.22λ_L.The measured results show that the designed multi-band dual-polarized antenna has wideband,wide-beamwidth and dual-polarized characteristics.Compared with other simliar studies,the designed antenna has smaller size and better electrical performance.2.Multi-band dual-polarized antenna array with large frequency reconfigurability.A multi-band dual-polarized antenna array with a 106-octave frequency range is studied.The multi-band characteristic is realized by using frequency reconfigurable techniques.Specificly,a dipole with a coupled microstrip-slotline is used as a reconfigurable antenna unit,and its IBW is 87%.Then arms of 16 dipole units are cascaded to switch the operation bands between M1（30～110 MHz）,M2（110～200 MHz）,M3（200～600 MHz）,M4（600～1300 MHz）and M5（1300～3200 MHz）.Further a dual-polarized 3×3 antenna array is designed in the lower frequency band.The measured results show that the designed multi-band frequency-reconfigurable dual-polarized antenna array has good radiation characteristics within a 106-octave frequency range.Compared with other related published literatures,the designed antenna has the widest octave bandwidth.3.Wideband circularly-polarized antenna based on magneto-electric dipole.In order to solve the problem that the axial-ratio bandwidth of wideband circularly-polarized antenna is narrow,a pair of magnetic dipoles below the elliptical crossed dipole antenna is used to improve the 3 d B AR bandwidth of 73%（2.54～5.51 GHz）,and the IBW is 79%（2.50～5.78 GHz）.Among the whole operating frequency band,the half-power beamwidths（HPBW）are greater than 74°,the 3 d B AR beamwidths are greater than 76°and the gain is above 7.5 d Bic.Compared with other related published literatures,the designed magnetic dipoles have wider axial-ratio bandwidth broadening effect,and its structure is simple.4.Dual-band circulaly-polarized antenna based on AMC.In order to solve the problem that the axial-ratio beamwidth of the multi-band circularly-polarized antenna is narrow,the in-phase reflection property of the AMC is utilized to improve the circularly-polarized characteristic of the planar printed qudrifiliar helix antenna,and the multi-resonant branching technique is applied to achieve a dual-band characteristic.The size of the designed antenna is 0.36λ₀×0.36λ₀×0.106λ₀.The measured results show that the operating bandwidth is 1.17～1.39 GHz and 1.49～1.58 GHz.The HPBWs are greater than 104°/119°at 1.268/1.561 GHz,and the AR beamwidths are greater than 171°/201°at 1.268/1.561 GHz.Compared with other related published literatures,the designed dual-band circulaly-polarized antenna has wider beamwidth and smaller size.Finally,the research progress and the further study on these issues are discussed.