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; a second end connected to a first connection point on the conductive ground plate; and a fold disposed between the first and the second ends, wherein a part of a segment between the first end and the fold 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 that is disposed on the segment between the first end and the fold of 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 segment between the first end and the fold of 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 characterized in that the second end of the first antenna element is connected to the first connection point on the conductive ground plate via a trap circuit, the trap circuit including a first capacitor and an inductor in parallel, as well as a second capacitor connected in series with these parallel-connected first capacitor and inductor, and wherein the trap circuit is configured to disconnect the second end of the first antenna element from the first connection point on the conductive ground plate at the second frequency. 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; a second end connected to a first connection point on the conductive ground plate; and a fold disposed between the first and the second ends, a first end connected to a feedpoint; a second end connected to a first connection point on the conductive ground plate; and a fold disposed between the first and the second ends, wherein a part of a segment between the first end and the fold 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 that is disposed on the segment between the first end and the fold of 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 segment between the first end and the fold of 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 characterized in that the second end of the first antenna element is connected to the first connection point on the conductive ground plate via a trap circuit, the trap circuit including a first capacitor and an inductor in parallel, as well as a second capacitor connected in series with these parallel-connected first capacitor and inductor, and wherein the trap circuit is configured to disconnect the second end of the first antenna element from the first connection point on the conductive ground plate at the second frequency.