Surrogate Model-Assisted Optimization for Ultrawideband Bidirectional Absorptive Common-Mode Filter Design

An efficient surrogate model-assisted optimization scheme for designing ultrawideband bidirectional absorptive common-mode filters (A-CMFs) is presented. The proposed A-CMF consists of a differential pair, two resistors, and a lossless network constructed by fragment-type defected ground structure (FTDGS). Excellent differential mode (DM) transmission and common mode (CM) absorption characteristics are achieved by optimizing the lossless network and resistors. The computationally efficient initial optimization uses coarse FTDGS grids and aims at obtaining the good candidate solution set to establish a low-cost surrogate model. Guided by the surrogate model, the subsequent optimization uses the improved initial values, which involves adjusting structure configuration and conducting effective structure initialization to improve circuit performance and optimization efficiency thus achieving an A-CMF with enhanced DM passband and CM absorption bandwidth. For demonstration, an ultrawideband bidirectional A-CMF is designed on a PCB with a design area of 0.0512λg2. Measurement results show that the A-CMF has a DM 3-dB cutoff frequency up to 11.7 GHz and a CM absorption band from 1.92 to 11.05 GHz (the fractional bandwidth is 140.8%), covering all communication bands of the public standard IEEE 802.11be.