Research On Wideband Dual-polarized Antenna With High Isolation

Dual-polarized antenna is widely used in wireless communication system owing to its mer-its of avoiding multi-path fading and increasing channel capacity.With the change of the communication era,communication equipment has continuously evolved,and more strin-gent requirements have been imposed on dual-polarized antennas.Modern communication expects dual-polarization antenna element to cover as many communication working fre-quency bands as possible,while keeping miniaturized aperture size,low-profile structure,and high isolation.Bandwidth enhancement of dual-polarized antenna element can help de-crease the number of antennas needed in the communication base station,thus leading to low complexity of the feeding network.Also,miniaturized and low-profile dual-polarized element is a preferable choice for a base station antenna array for the sake of lightweight.In addition,high isolation can guarantee channel independence,thus improve the effect of multi-path fading and the overall performance of the base station.In this thesis,several common methods to realize dual polarization are investigated and analyzed,including microstrip patch antenna,crossed dipole antenna,multi-dipole antenna,and slot antenna.Furthermore,many representative results of these methods are analyzed and compared to understand their advantages,disadvantages,and evolution trends.Based on the research above,a wideband low-profile dual-polarized multiple-microstrip dipole antenna with high isolation is firstly proposed.Radiation structure of the proposed antenna consists of four microstrip dipoles adjacent to each other,which are excited by a slot coupler.Introducing multiple dipoles and the slot coupler allow a wide bandwidth with a low-profile structure.The slot coupler is cross-shaped,with its junction connected to t-wo orthogonal baluns and its four ends located beneath the four dipoles.Technically,the slot coupler works as a two-to-four power divider.Supposed one balun is excited,the other balun will then be isolated,and differential signals generated by the excited balun will be divided into four equal-amplitude parts by the slot coupler.Afterwards,these four signals will be respectively coupled to four dipoles,then radiate,synthesize and generate a slant linear polarization.Two baluns account for±45?linear polarizations,respectively.The slot coupler can guarantee approximately differential signals within the desired wide bandwidth,resulting in common-mode suppression and high isolation.A good agreement of simulated and experimental results proves the validity of realizing a wide-10dB operating band of48%and a high isolation of 37dB with a low profile of 0.18?₀.Based on the multi-mode fusion technology,a compact broadband dual-polarized crossed s-lot antenna is designed in this paper.The antenna's radiation structure is a square patch with four center-symmetrical funnel-shaped slots along the diagonals of the patch.Each slot has a driven branch in the middle.One end of the driven branch is open,and the other end is con-nected to a differential balun.A pair of driven branches distributed along the same diagonal are connected to the same differential balun.When one balun is working,a pair of driven branches connected to it generates a pair of differential signals and couples the signals to the main radiator,forming a linear polarization.When two orthogonal differential baluns are excited,respectively,they would produce±45?linear polarization.When the main radiator obtains low-frequency signal,the radiator operates at a quarter-wavelength resonance mode of the patch.When the main radiator obtains high-frequency signal,the radiator operates at quarter-wavelength resonance mode of the slot.The fusion of the patch mode and the slot mode realizes the maximum use of the radiator,thereby achieving the miniaturization of the radiation aperture while ensuring a wide working bandwidth.The simulation current distri-bution confirms this working principle.And the measurement results show that the antenna can achieve a differential working bandwidth of 55.3%and an isolation of 39dB with a radiation aperture of 0.36?₀×0.36?₀.