A topology optimization method for design of small GPR antennas

This paper proposes a design method for miniaturized planar bow-tie antennas typically used in Ground Penetrating Radar (GPR) based on topology optimization. To reduce the center operating frequency of the miniaturized antenna, a design strategy is given to determine a reasonable distribution of conductive material within a given domain. The skin-depth issue in the FEM-model is avoided by using the method of moments (MOM) and the degree of freedom is reduced by not discretizing the free-space box domain which can greatly improve the computational efficiency. Additionally, a novel method is proposed to model a non-conductive material by imposing infinite impedance through an exponential material interpolation function. Based on a series of numerical results, three technical problems in the electromagnetic structural topology optimization technique are identified, and a volume-preserving Heaviside density filter is introduced to guide the optimal result tending to a 0-1 differentiation. Numerical examples show that the proposed optimization method can reduce the center operating frequency of the antenna significantly, thus the effectiveness of our optimization method is verified.