An antenna structure has a stack of dielectric layers and metal layers. The antenna structure includes a radiator and a grounding structure. The radiator has a parasitic radiator element, a main radiator element and a ground plane element respectively in a first metal layer, a second metal layer and a third metal layer of the metal layers. The parasitic radiator element and the main radiator element are physically spaced by a first dielectric layer of the dielectric layers. The main radiator element and the ground plane element are physically spaced by a second dielectric layer of the dielectric layers. The grounding structure laterally surrounds between the main radiator element and the ground plane element for blocking electromagnetic radiation, but not between the parasitic radiator element and the main radiator element.