Research On Wideband Multi-Mode Antennas And Arrays

With the rapid development of the modern communication technology,several wireless communication systems operating at different frequency bands exist simultaneously.Owing to their superior features of reducing cost,saving installation,increasing the channel capacity and combating the multipath fading effect,wideband dual-polarized antennas have been widely applied in the base-station communication system.This dissertation is mainly focused on the design methods of wideband dual-polarized antennas.The major innovative contributions of the dissertation are listed as follows: 1.Design methods on combining multiple resonant modes to broaden the impedance bandwidths of the antennas are presented.By loading open stubs,or bent microstrip lines and shorting stubs,or rectangular loop dipoles,a new resonant mode is induced at high frequency,enhancing the impedance bandwidths of the antennas.A four-element antenna array is designed,and a feeding network with wideband phase shifting characteristics is adopted to excite the antenna array for realizing beam down tilt.Prototypes of the mentioned antennas and array are fabricated and tested.Measured results show that the design methods on wideband dual-polarized antennas are reliable.2.A design guideline about reducing the profile of the wideband antenna is investigated.By embedding parasitic dipoles into the orthogonal loop dipoles,a new resonant mode is generated to widen the impedance bandwidth.An artificial magnetic conductor(AMC)surface is introduced to reduce the profile of the antenna due to the fact that the AMC surface features 0 degree reflection phase.A prototype of the antenna is fabricated and measured.The profile of the antenna is about 0.176?c(?c represents the wavelength at the center operating frequency).In addition,the antenna has a wide bandwidth,a high port-to-port isolation,and a stable radiation pattern.Finally,the proposed antenna is suitable for the three-sector modern mobile base-station communication system.3.Design principles on broadening the impedance bandwidths of the differentially fed dual-polarized antennas are studied.(a)Firstly,the slot excitations that symmetrically rotated with respect to the center of the antenna structure are proposed to transmit the differential signals.Then,a parasitic patch placed above the main patch is used to broaden the impedance bandwidth.Thirdly,a broadband differential-fed dual-polarized stacked patch antenna with tuned slot excitations is designed.(b)Originally,four parasitic patches are adopted to improve the impedance matching,enhancing the working bandwidth of the antenna.Then,a metal loop shorted to the ground plane is utilized to prevent the plane wave propagating toward the edge of the metal ground plane,contributing to a low backscattered radiation and a low cross-polarization radiation.As a result,the cross-polarization discrimination is significantly strengthened.Eventually,a wideband differentially fed dual-polarized antenna with high cross-polarization discrimination is developed.(c)The impedance matching of the antenna is improved by loading shorting stubs,resulting in widening the operating bandwidth.Moreover,an integrated balun feeding structure is developed to transmit the differential signals to the antenna.Hence,a high common-mode suppression performance is realized.Finally,a broadband differentially fed dual-polarized antenna with high common-mode rejection is proposed.A four-element differential-fed antenna array with dual polarizations is also presented,which features a high common-mode suppression performance.Prototypes of the mentioned antenna and array are fabricated and measured.Experimental results are highly consistent with the simulated ones,which show that the design method is viable.Ultimately,the proposed antenna and antenna array can be applied into the base-station communication systems with the differential signals.4.A dual-polarized magneto-electric dipole antenna operating at the band of 3300-3600 MHz is proposed.A slot-coupled feeding structure with dual excitations is designed to excite the proposed antenna,which is of great help to improve the impedance matching.Owing to the combination of the magnetic and electric dipoles,the antenna remains a stable radiation pattern across the operating band.Moreover,the loaded V-shaped sidewalls are used to further keep the radiation pattern stable.Experimental results show that the implemented bandwidth of the proposed antenna can cover the required operating bandwidth of 5G wireless communication system.Meanwhile,a stable antenna gain and a stable radiation pattern are also obtained within the band of operation.