An antenna comprises a medium substrate and grounding units attached on the medium substrate. The antenna further comprises a metal structure attached on the medium substrate. The metal structure comprises an electromagnetic response unit, a metal open ring enclosing the electromagnetic response unit and a feeding point connected to an end of the metal open ring. The electromagnetic response unit comprises an electric-field coupling structure. This design increases the physical length of the antenna equivalently, so an RF antenna operating at an extremely low frequency can be designed within a very small space. This can eliminate the physical limitation imposed by the spatial area when the conventional antenna operates at a low frequency, and satisfy the requirements of miniaturization, a low operating frequency and broadband multi-mode services for the mobile phone antenna. Meanwhile, a solution of a lower cost is provided for design of the antenna of wireless communication apparatuses.