A microelectronic wireless transmission device including: a substrate able to be traversed by radio waves intended to be emitted by the device, an antenna, an electrical power supply, an integrated circuit, electrically connected to the antenna and to the electrical power supply, and able to transmit to the antenna electrical signals intended to be emitted by the antenna in the form of the said radio waves, a cap rigidly connected to the substrate and forming, with the substrate, at least one cavity in which the antenna and the integrated circuit are positioned, where the cap comprises an electrically conductive material connected electrically to an electrical potential of the electrical power supply and/or of the integrated circuit, and able to form a reflector with regard to the radio waves intended to be emitted by the antenna.