from typing import Union


def _get_antenna_from_scene_dir_second(scene_dir_second: str) -> Union[str, None]:
    """If there is antenna datum inside `scene_dir_second` string, then return it.
    Otherwise, return None."""

    valid_antennas = ('CB11', 'CP5', 'ETC2')

    # return antenna datum from scene_dir_second, if it exists
    for antenna in valid_antennas:
        if antenna in scene_dir_second:
            return antenna

    # default value when antenna datum does not exist
    return None