Device for measuring electromagnetic field sensor gain comprising an electromagnetic wave source and an antenna connected to the electromagnetic wave source and radiating an electromagnetic field in the direction of the sensor, the antenna is a monocone antenna comprising a plane conductive element having a first face and a second face opposite the first face and a cone-shaped conductive part situated on the side of the first face, characterised in that: - the plane conductive element consisting of a plate furnished with an opening wherein a flexible metal foil furnished with an opening is attached, the flexible foil having a first face and a second face, the first face and the second face of the flexible metal foil being respectively situated on the side of the first face and on the side of the second face of the plane conductive element, the cone-shaped conductive part comprising a cone body and a cone apex attached to the cone body, one end of the cone apex being positioned facing the opening of the metal foil, the first face of the plane conductive element and an external face of the cone-shaped conductive part defining, with a wall covered with absorbent included in the measurement device and surrounding the cone-shaped part, an anechoic chamber wherein the sensor is positioned, - an electrical connection part traverses the opening of the flexible metal foil and has a first end attached in the end of the cone apex and a second end attached to a first end of a coaxial cable attached to the second face of the flexible metal foil by mechanical means, the second end of the coaxial cable being connected to the electromagnetic wave source, - a cable suspension system (k1, k2,..., kN) holds the cone-shaped conductive part above the plane conductive element, - a system for measuring voltage connected to the sensor is suitable for measuring a voltage output by the sensor, and - a computing device connected to the voltage measurement system is suitable for computing a sensor gain on the basis of the voltage measurements output by the voltage measurement system. - the plane conductive element consisting of a plate furnished with an opening wherein a flexible metal foil furnished with an opening is attached, the flexible foil having a first face and a second face, the first face and the second face of the flexible metal foil being respectively situated on the side of the first face and on the side of the second face of the plane conductive element, the cone-shaped conductive part comprising a cone body and a cone apex attached to the cone body, one end of the cone apex being positioned facing the opening of the metal foil, the first face of the plane conductive element and an external face of the cone-shaped conductive part defining, with a wall covered with absorbent included in the measurement device and surrounding the cone-shaped part, an anechoic chamber wherein the sensor is positioned, - an electrical connection part traverses the opening of the flexible metal foil and has a first end attached in the end of the cone apex and a second end attached to a first end of a coaxial cable attached to the second face of the flexible metal foil by mechanical means, the second end of the coaxial cable being connected to the electromagnetic wave source, - a cable suspension system (k1, k2,..., kN) holds the cone-shaped conductive part above the plane conductive element, - a system for measuring voltage connected to the sensor is suitable for measuring a voltage output by the sensor, and - a computing device connected to the voltage measurement system is suitable for computing a sensor gain on the basis of the voltage measurements output by the voltage measurement system.