A wideband coaxial-to-waveguide transition devised with topology optimization

Topology optimization is a powerful technique that utilizes the distribution of material properties along with surface topology as parameters to expand a specified performance. While primarily used as a foundational step in regenerative design for structural mechanics, the general TO framework is also applicable to many of the complex issues in electromagnetics such as frequency agile mode converters. This is considered a difficult parameter to optimize since RF components operate on resonance. TO is used on the coaxial-to-rectangular waveguide converter in the range X band. The radiative element chosen is a patch antenna with a ground stop. The original design is transformed into a binary material distribution matrix, where each cell is assigned a value of 0 or 1, while ensuring connectivity between the cells. Then the cell values are altered via a BPSO algorithm to optimize the width of the operating band, resulting in a complex structure that yields a bandwidth 38% larger than the control. The optimized patch structure is fabricated and its performance verified in the frequency range 8-12 GHz.