Design And Research Of Low Profile Wideband Circularly Polarized Magnetic-Electric Dipole Antenna Array

Antenna is an important part in wireless communication systems nowadays.As the rapid development of modern communication technology,more different types of antennas are designed to meet the requirement of the communication systems especially the portable antennas such as circularly polarized(CP)antennas with wideband,high gain and low profile.Compared with linearly polarized(LP)antenna,CP antenna has many advantages like avoiding multipath effects,mitigating the polarization mismatch and so on.CP antenna can be used to receive linearly polarized waves in any direction of polarization.Similarly,CP waves generated by a CP antenna can be received by any LP antennaMagnetic-electric(ME)dipole antenna is a relatively new kind of antenna structure that has been widely studied in recent years.This antenna has a broad application prospect for its benefits of wide bandwidth,low cross polarization,broad beamwidth as well as stable gain.However,traditional ME dipole antenna usually has a profile of about 0.25?₀,and this relatively high profile limits its application in many portable communication systems.In this thesis,a new low profile circularly polarized magnetic-electric(CP ME)dipole antenna element working in S-band is proposed.We improve and modify the structure of the traditional ME dipole antenna,and successfully reduce the profile of the proposed antenna by 60%.In this design,CP radiation can be realized by appropriately changing the shape and dimensions of the electric dipole.As the antenna profile is reduced,the axial ratio bandwidth will also decrease.So the sequential-rotated feeding technique is adopted to broaden the axial ratio bandwidth when we form the 2×2 antenna array using the proposed antenna elements.The total size of the array is only 1.32?₀×1.32?₀×0.077×0.The impedance of 37%(VSWR<2)from 1.72GHz to 2.5GHz is achieved,and from 1.75GHz to 2.46GHz,the axial ratio is less than 3dB with the axial ratio bandwidth is about 34%.In the working frequency band,the gain is stable with the peak value is about 12.9dBic.A broader beamwidth can also be accomplished with 3dB beamwidth is about 40 degrees.The measurement results of the fabricated antenna are in good agreement with the simulation results.