Mesh low-pass filters for millimeter-wave applications: Is the square capacitive shape optimal?

The use of mesh filters for millimeter-wave applications using capacitive and inductive grids is well known, and they are widely used in cosmic microwave background instrumentation. We report on an investigation into whether the capacitive square shape typically used in low-pass filter designs could be improved. The microgenetic algorithm and the finite-difference time-domain, and electromagnetic modeling method were used to look for shape variations to the standard square shape. Any shape changes discovered were then analyzed to establish which variations had the most effect. We show that improvements found using pixelated patterns evolved by the genetic algorithm were somewhat mixed.