Wideband or ultra-wideband sector antenna having a height H, a depth D and a width W, including a first ground plane acting as a reflector plane, at least one antenna array comprising at least one first strand and at least one second strand, the antenna operating in a frequency range [f 1, f 2], characterized in that: • said strands (101, 102) have an elliptical shape folded towards the ground plane at the centre of the antenna, an inside curvature F 1, F' 1 starting from a point A, A' positioned towards the centre O of the antenna, an outside curvature F 2, F' 2 located in the extension of the first inside curvature F 1, F' 1; • a first end of the first strand is located at a first point A in proximity to the ground plane and a first end of the second strand are located at a second point A' in proximity to the ground plane; • a second end of the first strand and a second end of the second strand are respectively positioned at two points C, C' positioned with regard to the ground plane; • the origin 0 of the Cartesian coordinate system corresponding to the centre of the ground plane, are A = x A 0 z A, B = x B 0 z B and C = x c 0 z C where x A, x B, x C, z A, z B, z C, are the coordinates of the points A, B and C in a Cartesian coordinate system and c 1 and c 2 are two curvature parameters, A-B belonging to the inside curvature F 1, F' 1, and B-C belonging to the outside curvature F 2, F' 2; • the inside curvature F 1, F' 1 of the first strand is defined in order to guarantee the stability of the radiation pattern at the maximum operating frequency of the antenna by: X = x B + x A − x B e zc 1 − e z B c 1 e z A c 1 − e z B c 1, ∀ z ∈ z A z B • the outside curvature F 2, F' 2 of the second strand is defined in order to guarantee the stability of the impedance that the antenna exhibits across its supply terminals at the minimum operating frequency, X = x B + x C − x B e zc 2 − e z B c 2 e z C c 2 − e z B c 2, ∀ z ∈ z B z C • the first strand and the second strand are supplied in phase opposition. • said strands (101, 102) have an elliptical shape folded towards the ground plane at the centre of the antenna, an inside curvature F 1, F' 1 starting from a point A, A' positioned towards the centre O of the antenna, an outside curvature F 2, F' 2 located in the extension of the first inside curvature F 1, F' 1; • a first end of the first strand is located at a first point A in proximity to the ground plane and a first end of the second strand are located at a second point A' in proximity to the ground plane; • a second end of the first strand and a second end of the second strand are respectively positioned at two points C, C' positioned with regard to the ground plane; • the origin 0 of the Cartesian coordinate system corresponding to the centre of the ground plane, are A = x A 0 z A, B = x B 0 z B and C = x c 0 z C where x A, x B, x C, z A, z B, z C, are the coordinates of the points A, B and C in a Cartesian coordinate system and c 1 and c 2 are two curvature parameters, A-B belonging to the inside curvature F 1, F' 1, and B-C belonging to the outside curvature F 2, F' 2; • the inside curvature F 1, F' 1 of the first strand is defined in order to guarantee the stability of the radiation pattern at the maximum operating frequency of the antenna by: X = x B + x A − x B e zc 1 − e z B c 1 e z A c 1 − e z B c 1, ∀ z ∈ z A z B • the outside curvature F 2, F' 2 of the second strand is defined in order to guarantee the stability of the impedance that the antenna exhibits across its supply terminals at the minimum operating frequency, X = x B + x C − x B e zc 2 − e z B c 2 e z C c 2 − e z B c 2, ∀ z ∈ z B z C • the first strand and the second strand are supplied in phase opposition.