An antenna device includes a first elliptic reflective surface, a first antenna and a second antenna. The first elliptic reflective surface has a first focus and a second focus. The first antenna is disposed on the first focus, and the second antenna is disposed on the second focus. The first antenna transmits a first signal and a second signal, and the second antenna receives the first signal and the second signal. The first signal is transmitted directly to the second antenna from the first antenna. The second signal is reflected by the first elliptic reflective surface and transmitted to the second antenna.