The ornamental design for the frequency selective surface, as shown and described.
FIG. 1 is a perspective view of the front, right and top sides of a frequency selective surface of showing our new design;
FIG. 2 is a front view thereof;
FIG. 3 is a rear view thereof;
FIG. 4 is a left side view thereof;
FIG. 5 is a right side view thereof;
FIG. 6 is a top view thereof;
FIG. 7 is a bottom view thereof;
FIG. 8 is a cross sectional view at line 8-8 in FIG. 2; and,
FIG. 9 is a reference perspective view showing a usage state where the frequency selective surface is continuously extended in the left, right, top and bottom in the front view.
The broken lines shown represent unclaimed subject matter of the frequency selective surface or environments and form no part of the claimed design.