Research On Wideband Band-Notched Antenna In The Communication System

Nowadays,with the rapid development of wireless communication technology,the rapid spread of information has brought great convenience to people’s work and life.Accordingly,people also have higher requirements for wireless communication equipment,which promotes the development of wireless communication system to the direction of multi-frequency,broad bandwidth and miniaturization.As a device transmitting and receiving signals,antenna plays an increasingly important role in wireless communication system,and the performance of antenna will affect the performance of the whole communication system.Broadband antennas are usually used to cover multiple operating bands,but are interfered by signals from other narrowband communication systems.In order to suppress the interference signals between multiple working bands,band-notched characteristic should be introduced.Introducing band-stop filter or band-notch structure into wideband antenna is an effective method to achieve notch property.However,cascading band-stop filter at the antenna input port will increase the complexity of the antenna structure and the overall volume,deteriorate the antenna matching,increase the insertion loss and increase the antenna manufacturing cost,and is not conducive to the integration of the antenna.The integrated design of band-notch structure and broadband antenna can not only introduce the notch function without increasing the antenna size,but also not affect the other performance of the antenna,and even improve the radiation performance of the working band.In order to meet the needs of broadband,miniaturization and notch characteristics of antennas in communication systems,this dissertation carries out the research on wideband band-notched antennas in communication systems through the in-depth study of broadband dual-polarized directional antennas and broadband vertically-polarized omnidirectional antennas.The research content of this dissertation mainly includes following parts:Wideband dual-polarized 2G/3G/4G base station band-notched antenna.A coplanar waveguide dual-polarized band-notched crossed dipole antenna for 2G/3G/4G base stations is proposed.Firstly,a wideband dual-polarized crossed dipole antenna is designed using coplanar waveguide feed structure.Then,second-order coplanar waveguide defective gound structure(DGS)filter is proposed.The second-order coplanar waveguide DGS filter and the antenna are printed on the same substrate,so two radiation zeros are introduced to achieve 2.2-2.5 GHz stopband.For VSWR < 1.5,compared with the original broadband antenna covering 1.7-2.7 GHz,the minimum gain of the notched band of the proposed notch antenna is suppressed from 8.4 d Bi to-10.9 d Bi.The minimum gain of the notched band is reduced by 19.3 Db,compared with the gain of the operating band.Therefore,the proposed dual-polarized band-notched antenna works at 1.7-2.2 GHz and 2.5-2.7GHz,and is suitable for 2G/3G/4G base station applications requiring band-notched characteristic.Wideband dual-polarized WLAN band-notched antenna.A wideband dual-polarized crossed dipole antenna for 2.4/5-GHz WLAN is proposed.The proposed antenna for VSWR < 2 covers the bandwidth of WLAN 2.4-GHz(2.4-2.48 GHz)and 5-GHz(5.15-5.85 GHz)and has two radiation zeros within the 3.4-3.6 GHz band.In the design of the antenna,firstly,the ultra-wideband dual-polarized crossed dipole antenna with operating frequency of 2.4-5.8 GHz is designed by using coplanar waveguide feed structure.Secondly,a miniaturized coplanar waveguide defected transmission line structure(DMS)filter is embedded in the coplanar waveguide feed structure to introduce stopband characteristic.Finally,combined with the design of C-shaped split ring resonator(SRR)on the dipole antenna arm,a notched band(3.4-3.6 GHz)with two radiation zeros is realized.The two radiation zeros can be adjusted independently to achieve wide stopband performance.The results show that compared with the original wideband dipole antenna,the notch antenna can suppress the gain from 8 d Bi to less than-8 d Bi in the band of 3.4-3.6 GHz.The antenna can achieve a stable directional radiation pattern and gain of about 7 d Bi and 8.5 d Bi in the2.4-GHz and 5-GHz bands of WLAN.Therefore,for VSWR < 2,the dual-polarized band-notched antenna proposed in this chapter works in WLAN 2.4-GHz(2.4-2.48 GHz)and 5-GHz(5.15-5.85GHz)bands,and can be used in the dual-polarized WLAN applications that require the band-notch characteristic.Wideband dual-polarized 2G/3G/4G/5G base station band-notched antenna.Two kinds of broadband dual-polarized band-notched crossed dipole antennas based on coplanar waveguide filter for 2G/3G/4G/5G base stations are proposed.These two antennas have two radiation zeros and three radiation zeros,respectively.Firstly,a wideband crossed dipole antenna with coplanar waveguide filter as feed structure is designed,and its coverage frequency is 1.7-3.6 GHz.Then,for VSWR < 1.5,a coplanar waveguide DMS-DGS hybrid second-order band-stop filter is designed.The miniaturized highly selective coplanar waveguide filter and the antenna are printed on the same dielectric substrate to achieve stopband of 2.9-3.1 GHz.For VSWR < 1.5,compared with the original broadband antenna covering 1.7-3.6 GHz band,the proposed band-notched antenna works in two bands of 1.7-2.7 GHz and 3.4-3.6 GHz,and at the same time introduces the notched-band of2.9-3.1 GHz.The average gain of the proposed band-notched antenna is about 8.3 d Bi at low frequency and 7.1 d Bi at high frequency.In the stopband,the antenna gain is less than 0 d Bi and the minimum gain is-14.5 d Bi.Finally,for VSWR < 2,in this paper,a coplanar waveguide DMS-DGS hybrid third-order band-stop filter is designed.The miniaturized highly selective coplanar waveguide filter and the antenna are printed on the same dielectric substrate to realize the stopband covering 2.9-3.1 GHz.For VSWR < 2,compared with the original broadband antenna covering1.7-3.6 GHz band,the proposed band-notched antenna works in two bands of 1.7-2.7 GHz and3.4-3.6 GHz,and at the same time introduces the notch band covering 2.9-3.1 GHz.The average gain of the proposed band-notched antenna is about 8.3 d Bi in low band and 6.9 d Bi in high band.In the range of 2.87-3.17 GHz,the antenna gains are all lower than 0 d Bi,and the minimum gain is-14.5 d Bi.Compared with the antenna using DMS-DGS hybrid second-order filter,the antenna using DMS-DGS hybrid third-order filter has three radiation zeros and a stopband of 2.87-3.17 GHz with gain less than 0 d Bi,which has wider stopband and higher selectivity.Wideband vertically-polarized omnidirectional WLAN band-notched antenna.Planar wideband omnidirectional band-notched antenna and band-notched monopole antenna with large ground are proposed for WLAN applications with omnidirectional coverage.Firstly,the wideband characteristics and band-notched technology of crossed dipole antenna are introduced to omnidirectional antenna,and a vertically-polarized omnidirectional WLAN band-notched antenna is designed.The proposed omnidirectional band-notched antenna can cover WLAN 2.4-GHz(2.4-2.48 GHz)and 5-GHz(5.15-5.85 GHz)bands.The SRR is used to introduce notch zero at the frequency of 3.5 GHz,and the VSWR in the stopband is greater than 20.In the WLAN band of2.4-GHz,the horizontal maximum gain is about 2 d Bi,and in the WLAN band of 5-GHz,the horizontal maximum gain is 3.5-4.2 d Bi.In the notched band,the maximum gain of the antenna in the horizontal plane can be suppressed from 3 d Bi to-15 d Bi,and the maximum gain suppression can reach 18 d B.Secondly,for WLAN applications with large ground,an omnidirectional monopole antenna with large ground is designed by adopting the broadband characteristics and notch technology of planar vertically polarized antenna.The proposed band-notched antenna with large ground working in WLAN band also introduces a transmission zero.Besides,the proposed band-notched antenna has a larger rectangular coefficient,and the VSWR is greater than 50 in the notch band of 3.4-3.6 GHz.That is,the suppression effect is better.The maximum gain of the proposed band-notched antenna in horizontal plane is less than-13 d Bi,and the minimum gain is 12 d B smaller than that of the planar omnidirectional band-notched antenna.Maximum gain in the horizontal plane is about 1.3 d Bi in WLAN 2.4-GHz band,and is 1.8 to 2.5 d Bi in 5-GHz band.