In a multi-band U-slot planar antenna, a limited ground plane is provided. A connector includes a ground terminal connected to the ground plane and a feeding terminal for feeding a signal. A planar radiation device includes a feeding point connected to the feeding terminal, a central U-slot having a symmetrical configuration about a central axis thereof, the central axis extending vertically from the feeding point, and at least one pair of auxiliary U-slots symmetrical with each other about the central axis. In the multi-band U-slot planar antenna, alternatively, at least one auxiliary U-slot may have a symmetrical configuration about the central axis.