Abstract: A compact size antenna operating in LTE frequency bands includes a radiation element, a ground plane, a connecting piece, and a ground extension element. The radiation element at least includes a first radiation branch extending toward a first direction, wherein a connection end of the radiation element has a signal feeding point. The connecting piece is coupled to the ground plane. The ground extension element includes: a metal arm, coupled to the ground plane through the connecting piece; a first ground branch, coupled to the metal arm, and extending toward the first direction; a second ground branch coupled to the metal arm, and extending toward a second direction opposite to the first direction; and a third ground branch, coupled to the metal arm, coupled to the second ground branch, and extending toward the first direction.

Abstract: An antenna structure includes a matching circuit, a flexible printed circuit board, and an external metal element. The matching circuit is configured to provide impedance. The flexible printed circuit board has a variable shape, wherein a metal wire is disposed on the flexible printed circuit board. The external metal element is coupled to a signal source through the metal wire disposed on the flexible printed circuit board and the matching circuit.

Abstract: A compact size antenna operating in LTE frequency bands includes a radiation element, a ground plane, a connecting piece, and a ground extension element. The radiation element at least includes a first radiation branch extending toward a first direction, wherein a connection end of the radiation element has a signal feeding point. The connecting piece is coupled to the ground plane. The ground extension element includes: a metal arm, coupled to the ground plane through the connecting piece; a first ground branch, coupled to the metal arm, and extending toward the first direction; a second ground branch coupled to the metal arm, and extending toward a second direction opposite to the first direction; and a third ground branch, coupled to the metal arm, coupled to the second ground branch, and extending toward the first direction.