A circuit board transmission line structures has microstrip or stripline transmission line geometries and cross-hatch patterned return planes. The cross-hatch design structure of the return planes and the relative position of the cross-hatch pattern to the transmission lines are configured to increase the usable bandwidth of the transmission lines. By properly adjusting the size and shape of the cross-hatch pattern, the performance of the microstrip and stripline transmission lines can be largely restored to the performance where continuous, solid return planes are used.