An antenna unit comprising: a conductive ground plate; a first antenna element; and a second antenna element, wherein the first antenna element includes a first end connected to a feedpoint and a second end containing an open end, wherein a part of the first antenna element is disposed along the conductive ground plate, wherein the second antenna element branches off the first antenna element at a branch point on the first antenna element, and the second antenna element is disposed between the part of the first antenna element disposed along the conductive ground plate and the conductive ground plate, wherein the first antenna element is configured to resonate at a first frequency, and wherein the second antenna element and a segment between the first end and the branch point of the first antenna element are configured to resonate at a second frequency that is higher than the first frequency, a first parasitic element having a first end and a second end, the first parasitic element being disposed relative to the first antenna element such that the first end of the first parasitic element is electromagnetically coupled to the open end of the first antenna element and the second end of the first parasitic element is remoter from the feedpoint than the first end of the first parasitic element is, wherein the first parasitic element has no electrical connection with the conductive ground plate, and the first parasitic element is configured to resonate at a third frequency other than the first and the second frequencies (f1, f2), wherein the second antenna element has an open end, and characterized in that the distance between the parasitic element and the second antenna element is larger than the distance between the parasitic element and the first antenna element. a conductive ground plate; a first antenna element; and a second antenna element, wherein the first antenna element includes a first end connected to a feedpoint and a second end containing an open end, wherein a part of the first antenna element is disposed along the conductive ground plate, wherein the second antenna element branches off the first antenna element at a branch point on the first antenna element, and the second antenna element is disposed between the part of the first antenna element disposed along the conductive ground plate and the conductive ground plate, wherein the first antenna element is configured to resonate at a first frequency, and wherein the second antenna element and a segment between the first end and the branch point of the first antenna element are configured to resonate at a second frequency that is higher than the first frequency, a first parasitic element having a first end and a second end, the first parasitic element being disposed relative to the first antenna element such that the first end of the first parasitic element is electromagnetically coupled to the open end of the first antenna element and the second end of the first parasitic element is remoter from the feedpoint than the first end of the first parasitic element is, wherein the first parasitic element has no electrical connection with the conductive ground plate, and the first parasitic element is configured to resonate at a third frequency other than the first and the second frequencies (f1, f2), wherein the second antenna element has an open end, and characterized in that the distance between the parasitic element and the second antenna element is larger than the distance between the parasitic element and the first antenna element.