A slot antenna located on a substrate with a first surface and a second surface opposite to the first surface includes a feeding portion and a radiating portion. The feeding portion is located on the first surface of the substrate to feed electromagnetic signals. The radiating portion is located on the second surface of the substrate and defines a sector-shaped slot, a first rectangle-shaped slot, a second rectangle-shaped slot, and a third rectangle-shaped slot, wherein the sector-shaped slot is defined by a first semidiameter, a second semidiameter, and an arc connected one by one.