The field of gratings of large cylinders in a unit cell of square, rectangular, or infinite-strip pattern is studied. Solutions are provided for alternating potential use being made of suitable arrangements of line charges. The complex potential corresponding to a given cylinder is found by correlation of the spacing of the line charges and the size of the cylinder. This method is also suitable for solution of fields of one-dimensional gratings of elliptical cylinders at alternating potential. Detailed results are presented in tables as well as in plots of typical field configurations.