A planar bi-directional radiation antenna (100, 400, 500, 600, 700), comprising: a substrate, comprising a first surface and a second surface opposite to said first surface; a first reflecting element (140, 140', 140"), disposed on the first surface of the substrate; an antenna element, disposed on the substrate; and a second reflecting element (120, 120'), disposed on the second surface of the substrate; said antenna element comprises a first radiating element and a second radiating element, said first radiating element having a first arm and a second arm, said second radiating element having a first arm and a second arm, said second arm of the first radiating element and said second arm of the second radiating element being symmetrical to a mirror plane perpendicular to said substrate and in parallel with a predetermined direction in a projection onto a plane in parallel with said substrate, characterized in that said first reflecting element (140,140',140") has a first concavely recessed edge, said first edge forms a first notch (101,101') of said first reflecting element (140,140',140"); said second reflecting element (120,120') has a second concavely recessed edge, said second edge forms a second notch of said second reflecting element (120,120'); said first radiating element is disposed in said first notch; said second radiating element is disposed in said second notch; said planar bi-directional radiation antenna further comprises a third reflecting element (150, 150') comprising a first coverage portion and a second coverage portion, said first coverage portion being disposed on the first surface of the substrate and opposite to the second arm of the first radiating element, said second coverage portion being disposed on the second surface of the substrate and opposite to the second arm of the second radiating element, said first and second coverage portions (151, 152) covering an opening of the first and second notches (101, 101') towards said predetermined direction, respectively, at least partially, so that the planar bi-directional radiation antenna (100, 400, 500, 600, 700) generates two beams radiated in different directions, each beam including a first angle (θ 1, θ 2, θ 3) with said substrate, wherein said first edge of the first reflecting element and said second edge of the second reflecting element face the third reflecting element along the predetermined direction, wherein a first end of the first coverage portion is electrically connected to the first reflecting element (140, 140', 140"), a second end of the first coverage portion is an open end, wherein a first end of the second coverage portion is electrically connected to the second reflecting element (120, 120'), and a second end of the second coverage portion is an open end. a substrate, comprising a first surface and a second surface opposite to said first surface; a first reflecting element (140, 140', 140"), disposed on the first surface of the substrate; an antenna element, disposed on the substrate; and a second reflecting element (120, 120'), disposed on the second surface of the substrate; said antenna element comprises a first radiating element and a second radiating element, said first radiating element having a first arm and a second arm, said second radiating element having a first arm and a second arm, said second arm of the first radiating element and said second arm of the second radiating element being symmetrical to a mirror plane perpendicular to said substrate and in parallel with a predetermined direction in a projection onto a plane in parallel with said substrate, characterized in that said first reflecting element (140,140',140") has a first concavely recessed edge, said first edge forms a first notch (101,101') of said first reflecting element (140,140',140"); said second reflecting element (120,120') has a second concavely recessed edge, said second edge forms a second notch of said second reflecting element (120,120'); said first radiating element is disposed in said first notch; said second radiating element is disposed in said second notch; said planar bi-directional radiation antenna further comprises a third reflecting element (150, 150') comprising a first coverage portion and a second coverage portion, said first coverage portion being disposed on the first surface of the substrate and opposite to the second arm of the first radiating element, said second coverage portion being disposed on the second surface of the substrate and opposite to the second arm of the second radiating element, said first and second coverage portions (151, 152) covering an opening of the first and second notches (101, 101') towards said predetermined direction, respectively, at least partially, so that the planar bi-directional radiation antenna (100, 400, 500, 600, 700) generates two beams radiated in different directions, each beam including a first angle (θ 1, θ 2, θ 3) with said substrate, wherein said first edge of the first reflecting element and said second edge of the second reflecting element face the third reflecting element along the predetermined direction, wherein a first end of the first coverage portion is electrically connected to the first reflecting element (140, 140', 140"), a second end of the first coverage portion is an open end, wherein a first end of the second coverage portion is electrically connected to the second reflecting element (120, 120'), and a second end of the second coverage portion is an open end.