Wideband Circularly Polarized Crossed-dipole Antenna

Compared with linearly polarized(LP)antenna,circularly polarized(CP)antenna is more capable to mitigate polarization mismatch and suppress multipath interferences,and is therefore more preferable to global positioning system(GPS),satellite communication/navigation system and radio frequency identification(RFID)system.On the other hand,with the rapid development of modern wireless communication systems,the bandwidth requirement of modern systems is higher than ever.Wideband circularly polarized antenna can cover multiple working band of the wireless communication systems simultaneously so that the number of the antennas in the system can be reduced,and thus can make the overall system simpler and more compact.In recent years,crossed-dipole antenna has received extensive attentions due to its broad CP bandwidth.However,traditional crossed-dipole antenna has the problems of high profile,insufficient bandwidth and unstable beamwidth within the passband.To tackle these problems,the major work of this paper can be summarized as follows.Firstly,a low-profile wideband CP crossed-dipole antenna has been proposed.Two adjacent axial ratio(AR)passbands with AR<3 dB are generated due to the stepped rectangular patches,and they are merged together by adding an additional dielectric slab above the ground plane.Therefore,the proposed antenna can achieve a very wide AR bandwidth of 55.1%with a low profile of 0.13?0.Also,an irregular ground plane is used for the proposed antenna,which can desirably enhance the boresight gain to~10.4 dBic.Then,an ultra-wideband CP crossed-dipole antenna has been proposed.Four vertical metallic plates are introduced beside the crossed dipoles.Due to the coupling between the crossed dipoles and vertical plates,additional axial ratio passband can,therefore,be generated beside the original operating band,enhancing CP bandwidth of the proposed antenna from about 30%to 106.1%.It is worth emphasizing that the proposed method possesses great universality and is applicable to almost all patch-type antennas.Finally,a wideband and wide-beam CP crossed-dipole antenna has been proposed.Four parasitic triangular patches which are shorted to the ground plane are symmetrically intervened between the crossed dipoles and the ground plane.Due to the strong coupling between the crossed dipoles and parasitic elements,orthogonal currents can be induced on the parasitic elements.It has been found that the parasitic elements can not only decrease the antenna profile to as low as 0.1?0,but also can increase the usable CP bandwidth significantly to 63.4%.Besides,a wide AR beamwidth(ARBW)of more than 120~o and a wide half-power beamwidth(HPBW)of more than 110~o can be maintained within a very wide frequency band of 50.7%.