| With the advent of 5G era,millimeter wave frequency band has attracted extensive attention from many scholars and enterprises due to its rich spectrum resources,larger channel capacity and wider frequency band.However,due to the disadvantages of MMW mobile communication system,such as short transmission distance,poor penetration and diffraction ability,easy air absorption and great influence of climate environment,the most direct way to increase the antenna signal range is to use antenna array to improve the gain of the antenna system.Unfortunately,the high-gain antenna array can only focus on a certain direction,which is inconsistent with the principle of multi-directional movement of mobile communication system.Therefore,based on the high-gain antenna array,a scannable millimeter wave antenna array is proposed to achieve the target of mobile communication system.In order to realize that the beam can cover a wider angle,a millimeter wave antenna with wide beam characteristics is needed according to the theorem of pattern multiplication.Magnetoelectric dipole has the characteristics of wide beam and good stability due to its complementary antenna structure.Due to the limited space of scannable antenna array,the distance between antennas is small without grid lobes,which leads to strong coupling effect between multiple antenna elements.This strong coupling will directly destroy the performance of the antenna,such as reducing the radiation efficiency of the antenna and affecting the scanning characteristics.At the same time,due to the increase of channel interference,it will also directly affect the data throughput.How to solve the problem of strong coupling between antennas,the traditional decoupling method gives a variety of ideas,including electromagnetic band gap structure(EBG),defective ground structure(DGS),array decoupling surface(ads),decoupled network and so on.However,these methods need to add metal structure or destroy the original antenna structure.More importantly,the biggest defect of these decoupling methods is that the decoupling frequency band is too narrow,and it has a strong impact on the resonance or radiation characteristics of the antenna.Due to its unique method of using the structure or characteristics of the antenna to realize decoupling,self decoupling antenna has attracted the attention and research of scholars in recent years.This decoupling method can not destroy the structure of the antenna itself,and realize wide-band decoupling while ensuring the radiation characteristics.Based on the above application background and the proposed problems,this paper designs a millimeter wave scannable electromagnetic dipole antenna array model based on double-layer ADS and an improved antenna array model based on staggered array arrangement.Then a self-decoupling scanning millimeter wave antenna array is proposed based on the characteristic mode theory.1.A millimeter wave antenna array based on double-layer ADS is proposed.Starting from the design of electromagnetic dipole antenna,the electric dipole and magnetic dipole are placed cross because they have complementary characteristics,so the antenna with broadband and wide beam characteristics is obtained.The antenna can reach a 3dB beam width of 120 °,and the antenna works at 22.5-35GHz(S11 <-10 dB).In order to improve the strong coupling effect between antennas after forming the array,the ADS is added above the antenna,and the decoupling is realized by using the idea of coupling energy cancellation.The proposed 1x4 loaded double-layer ADS antenna array works at26.5-29.5GHz,and the isolation is better than 20 dB,which has good scanning performance in its frequency band.2.Aiming at the problem of narrow decoupling bandwidth of the previous model,an improvement is proposed.The antenna is miniaturized by using a dielectric plate with high dielectric constant,the physical size between the antenna and the antenna is increased,and the structure is improved to optimize the resonant characteristics of the antenna.At the same time,based on the use of single-layer ADS,the antenna array is staggered,which reduces the mutual impedance between antennas and realizes the broadband and high isolation characteristics of antenna array.The designed 2x4 antenna array works at24.25-29.5GHz,the isolation is better than 17 dB,and has good scanning characteristics.The model is processed and measured.Through the comparison between the measured and simulation results,the causes of the error are analyzed.3.A millimeter wave scanning antenna array with self-decoupling characteristics is proposed.By using the characteristics of the antenna itself,high isolation is achieved without adding any structure.Based on the characteristic mode theory,the relationship between mutual impedance and mode weight coefficient(MWC)is found.Then,through the analysis and regulation of the basic mode of the antenna,a group of cancellation modes are used to offset the coupling energy,so as to realize the characteristics of self-decoupling.The analysis process starts from binary array and extends to quaternary scanning array.The designed 1x2 antenna array works at 24-29.4GHz(about 20% relative bandwidth),and the isolation is better than 20 dB;The 1x4 antenna array works at 25.8-30.5GHz,and the isolation is better than 20 dB.It has good scanning performance in its frequency band.The two antenna arrays are processed and measured.Based on the previous experience of processing millimeter wave antenna arrays,a welding free implementation scheme is proposed.Through the comparison of simulation and measured results,it can be seen that the physical model of the antenna is in good agreement with the simulation model. |
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