A Topology Optimization Method For Metallic Antenna Design

As the development of the wireless communication technology and the corresponding improvement of the antenna performance,especially the miniaturization and the integration,multi-functions are expected to be integrated into a single communication module.To meet the versatile applications,the antennas of the wireless communication system should be designed to satisfy the specific application requirements,such as the specific multiple or wide band operations,high radiation efficiency or other requirements.Thus it is necessary to develop advanced methods to guide the design of antenna structures for performance improvements.Topology optimization is an effective structural design method,by which the desired requirements of the designed structure can be satisfied through finding the optimal material distributions within a given design domain.Currently this method has been widely and successfully used in the innovative design of various functional structures,such as the load-carrying elastic structures,heat dissipation structures etc.Therefore,it is important to establish a topology optimization based method to achieve the structural design of high-performance antennas with specifically multi-frequency operations.Focusing on the design requirements of the miniaturization and the multi-frequency operations,this thesis develops an artificial density method based topology optimization method for metallic antenna designs,with which the "air box" problem,the "skin effect"problem and the gray transition problem exciting in the current design methods can be resolved.The main contents are organized as follows:1)MoM-based topology optimization method for metallic antenna design.In order to alleviate the "skin effect" problem,the topological configuration of antenna structures is modeled by using a series of resistance sheets,through which the optimization problem becomes convenient for solving with the method of moments(MoM).Based on the MoM,the problem of electromagnetic waves radiating or scattering from the metallic antenna is solved within a finite domain,where no "air box" around the antenna needs to be meshed and the corresponding computational cost is avoided.By introducing the exponential interpolation function,the relationship between the material resistance and the design variables is built.And the volume-preserving Heaviside density filter is introduced to guide the optimal results tending to a 0-1 differentiation.Based on the MoM-based design method,a planar metallic antenna is optimized for miniaturization by minimizing the S11 of the antenna at a lower frequency.However,the performance of the design result arises a significant decrease while the remaining gray scale elements were removed using the outside penalty function method.2)Tangential interpolation function based topology optimization method for metallic antenna design.In order to resolve the sensitive problem of the remaining gray scale elements to the performance of the design results,a tangential interpolation function based topology optimization method for metallic antenna design is presented.The optimization formulation is re-established where the objective is modified as maximizing the antenna efficiency.The inappropriateness of the exponential interpolation function in solving the optimization problem with the objective of maximizing the antenna efficiency is revealed.To overcome both the difficulties of the huge difference between the resistance of candidate materials and the rapid dissipation of the resistance to the scattered electric fields,a novel tangential interpolation function is proposed.The reason for the gray scale elements remaining in the design results is explained,and a reasonable threshold technique for removing the remaining gray scale elements is suggested.3)TIPS-based topology optimization method for metallic antenna design.In order to resolve the problem of the remaining gray scale elements,a novel design parameterization with a self-penalization scheme is developed.Through investigating the reason for the remaining gray scale elements,a regularity is discovered that the form of the tangential interpolation function should be changed during the optimization process.Based on this regularity,the criteria of an appropriate interpolation function to establish a self-penalized scheme for the topology optimization problems is discussed.Then in order to eliminate the remaining gray scale elements,a strategy with adaptively increasing penalty factor during the optimization process is utilized,by which binary results can be directly obtained.The name of TIPS originates from the combination of the Tangential interpolation function and the Increasing Penalty-factor Strategy.Additionally,a perimeter constraint is imposed on the optimization to regulate the small structural features existing in the design result.4)Topology optimization based design of dual-band patch antenna.In order to verify the effectiveness of the proposed design method,the method is used for guiding the design of dual-band patch antennas.The optimization formulation suitable for dual-band or multi-band antenna design with maximizing the minimum antenna efficiency at the target frequencies is built.And a single-layer patch antenna is optimized for specific dual-frequency operations.In order to verify the validity of the numerical solutions,the designed antenna is fabricated and tested on a network analyzer.The responses(S11s)of the designed antenna obtained by simulation and experiment show a good agreement.Since both the simulation and the experimentation indicate that two operational frequency bands can be optimized to arise around the target frequencies,the effectiveness of the proposed design method is confirmed.