Research And Design Of Wideband Circularly Polarized Antenna Based On Crossed Dipole

Compared with linearly polarized antennas,circularly polarized（CP）antennas have the advantages of reducing polarization mismatch,reducing multipath interference,and suppressing Faraday rotation effects,which are widely used in various wireless communication systems.As a structure to realize CP,crossed dipole antenna has attracted a lot of attention dues to its advantages of simple structure,convenient feeding and directional radiation.In order to meet the development demands of wireless communication system toward high performance,this thesis carried out the research of broadband,miniaturization,filtering and high gain based on crossed dipole antenna,and completed the physical processing test.The details are as follows:（1）A broadband CP crossed dipole antenna with compact size is proposed.The antenna is mainly composed of two orthogonal half-wave dipoles,a delay ringing with 90°phase shift,four square open resonant rings,four parasitic patches and a metal floor.The orthogonal dipoles are connected through the delay rings in sequence to achieve 90°phase difference,thus realizing CP radiation.In order to expand the impedance bandwidth（IBW）of the antenna and achieve the compact characteristic of the antenna,symmetrical open resonant rings are introduced on the front and back of the dielectric plate,which makes the antenna produce axial ratio（AR）points at low and high frequencies and improves the AR bandwidth.In order to further extend the operating bandwidth of the antenna,parasitic patches are introduced around the resonant ring to generate perturbation,which combines multiple AR points to achieve broadband CP characteristics.Finally,the measured results show that the antenna has an IBW of 69.1%（1.39-2.84 GHz）and an AR bandwidth of 57.7%（1.43-2.59 GHz）.The antenna has a compact size of 0.6λ₀×0.6λ₀（λ₀ is the spatial wavelength corresponding to the center frequency of the antenna）,which has a smooth gain in the whole operating bandwidth,and beamwidth of the radiation pattern is 76°±3°.（2）A wideband CP filter antenna based a crossed dipole is proposed.The antenna uses a CP crossed dipole as the main radiator.Two radiation zeros are introduced outside the band by loading a fan-shaped open resonant ring,which realizes the filtering characteristics and improves the IBW and AR bandwidth of the antenna.In order to improve the sideband selection characteristics of the antenna,a radiation zero is introduced by loading a fan-shaped patch with two symmetrical slots,thus achieving good band-pass filtering characteristics and obtaining a wide AR bandwidth.Finally,the measured results show that the out-of-band radiation zero is consistent with the simulation results and has good filtering characteristics.The antenna has a 73%（1.28-2.75 GHz）IBW and 42%（1.67-2.55 GHz）AR bandwidth,and the gain fluctuation within the operating bandwidth is less than 1.5 d B.（3）A high gain CP array antenna is proposed.Firstly,the effects of translation and rotation on the performance of the array antenna are studied.Compared with the translation arrangement,the rotation arrangement has a wider AR bandwidth.Secondly,the equal phase feed network and the sequential rotation feed network with broadband characteristics are designed.By combining a translational array antenna with an equal phase feed network,75%（1.19-2.78 GHz）of IBW and 63%（1.3-2.49 GHz）of AR bandwidth are obtained.Combining a rotational array antenna with a sequential rotational feed network,91.7%（1.18-3.18 GHz）of IBW and 70%（1.26-2.62 GHz）of AR bandwidth are achieved.The in-band peak gain reaches 13.2 d Bic and 13 d Bic respectively,which are 5.4 d B and 5.2 d B higher than that of the antenna unit,and the antenna directivity is improved.