The ornamental design for an antennamast, as shown and described.
FIG. 1 is a top perspective view of an antenna mast;
FIG. 2 is a rear view thereof,
FIG. 3 is a front view thereof;
FIG. 4 is a right side view thereof,
FIG. 5 is a left side view thereof;
FIG. 6 is a top thereof; and,
FIG. 7 is a bottom view thereof.
The broken lines in the drawings illustrate portions of the antenna mast which form no part of the claimed design. The antenna mast is shown with a symbolic break in its length. The appearance of any portion of the article between the breake lines forms no part of the claimed design.