Antenna adapted to receive or emit at least one working frequency, comprising: - at least two non-ferrous metal plates extending mainly according to a horizontal plane, at least one first plate forming a radiating portion (4 H; 4 H1, 4 H2, 4 H3, 4 H4; 4 H1, 4 H2, 4 H3, 4 H4, 4 H5, 4 H6, 4 H7, 4 H8) and a second plate forming a mass plane, - at least one substrate (1; 1 1, 1 2; 1 1, 1 2, 1 3, 1 4) extending mainly according to a horizontal plane, arranged between the mass plane (4 B) and the radiating portion (4 H), - an excitor of length at least equal to the thickness of the substrate, extending between the mass plane (4 B) and the radiating portion (4 H) and connected to the radiating portion (4 H), and adapted to supply the antenna, said antenna being characterised in that: a) said at least one working frequency is comprised in a kilometric comprised between 30 kHz and 300 kHz, or a hectometric comprised between 0.3 MHz and 3 MHz, or a decametric comprised between 3 MHz and 30 MHz, or a metric comprised between 30 MHz and 300 MHz band of frequencies, b) the substrate is a dispersive ferromagnetic substrate, called dispersive ferrite, presenting at said at least one working frequency, as magnetic features, a high relative magnetic permeability comprised between 10 and 10,000 and a high magnetic loss tangent greater than 0.1, c) said antenna comprises local modification means of the magnetic features of the dispersive ferrite, which are a magnet arranged on one of the non-ferrous metal plates (4 B; 4 H), wherein said magnet does not cover the whole surface of the dispersive ferrite, said magnet generating a magnetic field leading to a gradual and local reduction of the relative magnetic permeability and the magnetic losses of the dispersive ferrite. - at least two non-ferrous metal plates extending mainly according to a horizontal plane, at least one first plate forming a radiating portion (4 H; 4 H1, 4 H2, 4 H3, 4 H4; 4 H1, 4 H2, 4 H3, 4 H4, 4 H5, 4 H6, 4 H7, 4 H8) and a second plate forming a mass plane, - at least one substrate (1; 1 1, 1 2; 1 1, 1 2, 1 3, 1 4) extending mainly according to a horizontal plane, arranged between the mass plane (4 B) and the radiating portion (4 H), - an excitor of length at least equal to the thickness of the substrate, extending between the mass plane (4 B) and the radiating portion (4 H) and connected to the radiating portion (4 H), and adapted to supply the antenna, a) said at least one working frequency is comprised in a kilometric comprised between 30 kHz and 300 kHz, or a hectometric comprised between 0.3 MHz and 3 MHz, or a decametric comprised between 3 MHz and 30 MHz, or a metric comprised between 30 MHz and 300 MHz band of frequencies, b) the substrate is a dispersive ferromagnetic substrate, called dispersive ferrite, presenting at said at least one working frequency, as magnetic features, a high relative magnetic permeability comprised between 10 and 10,000 and a high magnetic loss tangent greater than 0.1, c) said antenna comprises local modification means of the magnetic features of the dispersive ferrite, which are a magnet arranged on one of the non-ferrous metal plates (4 B; 4 H), wherein said magnet does not cover the whole surface of the dispersive ferrite, said magnet generating a magnetic field leading to a gradual and local reduction of the relative magnetic permeability and the magnetic losses of the dispersive ferrite.