Research On Wideband Miniaturized Antenna And The Band-Notch Technology

With the continuous expansion of wireless communication frequency band,many communication systems need broadband antennas with stable radiation pattern to cover multiple working frequency bands.However,notched band should be introduced to suppress the interference signals between multiple frequency bands.Since the physical size of the wideband antenna is determined by the lowest frequency of the antenna,the miniaturization design of the wideband antenna is of great significance for reducing the physical size of the communication system.The radiation pattern and gain of the wideband antenna usually change with frequency.Therefore,it is difficult to ensure the stability of the radiation pattern when designing the wideband antenna.Introducing the band-notch structure inside the wideband antenna can not only realize the band-notched characteristic without increasing the antenna volume,but also not deteriorate other antenna characteristics and even improve the antenna performance.In order to meet the needs with radiation stability,broadband,miniaturization and band notch,this dissertation mainly explores the research on wideband crossed dipole antenna and ultra-wideband monopole antenna with stable radiation characteristics and the band-notched designs.The thesis mainly consists of following parts:Wideband dual-polarized antenna for base station application and its band-notch technology.To meet the demand of miniaturized 2G/3G/4G base station antenna,a double-layer feeding structure is proposed.The crossed dipole antenna with the double-layer feeding structure can achieve stable radiation characteristics within the wide bandwith of 1.7-2.85 GHz for VSWR<1.5 and miniaturize the size of antenna down to 45×45 mm~2.With the development of 5G communication system,in order to meet the demand of 2G/3G/4G/5G base station application,a double-loop crossed dipole antenna is proposed to extend the working band of crossed dipole antenna to1.7-3.7 GHz.In order to suppress the signals in the interference frequency band of2.9-3.1 GHz,a coplanar waveguide filtering structure was proposed.Without increasing antenna volume and difficulty in processing and assembly,notched band was introduced to suppress the minimum gain within 2.9-3.1 GHz from 8 d Bi to-13.5 d Bi.Ultra-wideband dual-polarized antenna for WLAN application and its band-notch technology.For the ultra-wideband dual-polarized applications,such as 2.4-5.85 GHz WLAN,an ultra-wideband dual-polarized crossed dipole antenna fed by double-layer feeding structure is proposed with a wide working band of 2.38-6.42 GHz(91.8%)for VSWR<2 and stable radiation characteristic.Since bluetooth/Wi MAX/5G and other communication systems working in the 3.4-3.6 GHz band may interfere with WLAN communication,a C-shaped split-ring-resonator notch structure designed inside the antenna is proposed.Introducing the band-notched structure inside the antenna can not only suppress the minimum gain in the 3.4-3.6 GHz frequency band to-9 d Bi,but also improve the matching of the working frequency band of the antenna,reduce the height of the antenna and increase the gain in the 5-GHz WLAN band from 6 d Bi to 9.7 d Bi.Wideband high-gain circularly-polarized antenna and its band-notch technology.Aiming at realizing the broadband and high gain of directional wideband circularly-polarized antenna at the same time,the circularly-polarized realization of crossed dipole is studied and analyzed,and a kind of ultra-wideband circularly-polarized antenna with metallic wall is proposed.The impedance bandwidth is greater than 99.3%(1.51-4.49 GHz)for VSWR<1.5,the 3-d B axial ratio(AR)working band covers 1.68-3.79 GHz(77.1%),and the left-hand circularly polarized gain within the AR bandwidth is greater than 7.1 d Bi.For the WLAN application with dual bands,C-shaped split-ring resonator is introduced to realize band-notched characteristic.Meanwhile,the band-notched structure can also improve the the AR chacracterisic,and hence the 3-d B AR working band of 2.38-2.51 GHz and 4.08-5.91 GHz(85.2%)for VSWR<2 can be realized.The left-hand circularly polarized gain of the 2.4-GHz band of WLAN is greater than 6.8 d Bi,and the left-hand circularly polarized gain of the5-GHz band is greater than 8.9 d Bi.Ultra-wideband low-profile vertically-polarized omnidirectional monopole antenna and its band-notch technology.Firstly,by studying the radiation pattern distortion in the high frequency and the miniaturization of the vertically-polarized omnidirectional ultra-wideband antenna,a kind of asymmetrical inverted-F vertically-polarized omnidirectional ultra-wideband antenna fabricated by 3-D metal printing is proposed.The antenna uses a triangular feeding structure and trapezoidal shorting structure to improve the antenna matching,and utilizes two parasitic metal posts to enhance the omnidirectionality of the antenna in the azimuth plane.The asymmetrical inverted-F structure can not only solve the radiation patterns distortion of the high frequency band,but also achieve the miniaturized size and volume(0.19?_L×0.19?_L×0.06?_L).The impedance bandwidth is greater than 10:1(2.96-30 GHz)for VSWR<3,and the bandwidth with horizontal radiation pattern ripple better than±5 d B is more than 4.9:1(2.96-14.5 GHz).Secondly,a split gap notch structure was introduced into the antenna,which can not only realize the 3.4-3.6 GHz stopband,but also could further miniaturize the antenna size.The proposed band-notched antenna can realize the working band of2.4-2.5 GHz and 5-10 GHz for VSWR<2 with good horizontal radiation pattern omnidirectionality,which can be used for wireless communication such as the WLAN application.