The ornamental design for an antennaadapter, as shown and described.
FIG. 1 is a front, right, top perspective view of the antenna adapter in accordance with the design;
FIG. 2 is a top view thereof;
FIG. 3 is a bottom view thereof;
FIG. 4 is a left side elevational view thereof;
FIG. 5 is a right side elevational view thereof;
FIG. 6 is a rear elevational view thereof; and,
FIG. 7 is a front elevational view thereof.
The broken lines in FIGS. 1-7, located on the body portion of the antenna adapter, illustrate surface etching, which forms no part of the claimed design. The broken lines in FIGS 1-7 located around the periphery of projections from the body portion, illustrate electrical connection structure of the antenna adapter, which form no part of the claimed design.