Numerical Analysis Of Antenna Maximum Bandwidth And Topology Optimization Of Antenna In Limited Space

As the front-end part of transceiver,antenna plays an important role in the communication system.Besides,it is widely used in radar,remote sensing and medical detection.In order to realize the requirement of large capacity data transmission in modern communication system and reduce the antenna installation space,antenna usually has the design requirements of multi-band,broadband and miniaturization.However,the contradiction between miniaturization and multi-band,broadband and specific radiation modes makes the design very difficult.In fact,the performance of antenna is limited by the limited space,which limits the possibility of antenna design.In this paper,the ultimate bandwidth performance of antenna in limited space will be analyzed,and topology optimization will be adopted to complete the design task of antenna.The main work of this thesis includes:Firstly,the research background and development status of the antenna physical bounds are analyzed,and the numerical modeling of the antenna physical bounds is completed,including the antenna Q and the antenna Q with radiation mode limits.The bandwidth of antenna is determined by two factors: matching network and antenna Q,which is the ratio between space energy storage and radiation energy.Antenna Q belongs to the essential attribute of antenna.The smaller the antenna Q,the more likely the broadband characteristic can be obtained by matching the network.More generally,antenna Q is approximately inversely proportional to the bandwidth for resonant antennas.In this thesis,the physical bounds such as Q and Q with radiation mode limit are solved according to the surface current of the antenna,then the maximum bandwidth can be obtained according to the inverse ratio relation between bandwidth and antenna Q.In addition,topology optimization based on genetic algorithm and method of moments is proposed.Topology optimization has the characteristic of high design freedom and is more suitable for multi-functional antenna.Different from traditional antenna design method,topology optimization allows any shape change of optimization area.In order to achieve multi-band and broadband antenna,the antenna Q is introduced into the fitness function.In the optimization example of small base station antenna,the working bandwidth of high frequency band is increased from 1690MHz-1920 MHz to 1680MHz-2710 MHz.Topology optimization based on sub-structure characteristic mode is proposed in this thesis according to the idea of "shape first and feed later".This method firstly finds the potential radiation mode of the antenna structure based on the sub-structure characteristic mode theory,and then finds the characteristic mode that meets the design requirements by iteratively changing the antenna shape.Then,the impedance map is used to find the most suitable feeding point.In addition,based on the orthogonality of far-field modes between characteristic modes,a dual-antenna topology is designed,which can be used in MIMO system.Without decoupling structure,the isolation between the two antennas can be achieved up to-13 dB.