“…In order to extend the coverage range, one obvious solution is to resort to high gain antennas. Up to now, various kinds of antennas have been designed for the 60 GHz band, such as patch [8], dipole [9], slot [10], grid [11], and metamaterial-mushroom antennas [12]. Many extra components, such as superstrate [13], metamaterial [14] or parabolic reflector [15], are adopted to enhance the antenna gain.…”