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. <EOS>