Patent ID: 8412137

Claim:
A radio transmitter comprising: a radio module; a battery from which power is fed to the radio module; a metal plate; and a mounting substrate having a first principal surface facing the metal plate and a second principal surface opposite to the first principal surface, wherein the radio module comprises a transmission module generating a transmission signal and an antenna configured to wirelessly transmit the transmission signal, the metal plate is located so as to cover a part of the battery and a part of the antenna, the battery is electromagnetically coupled to the antenna, a main radiation direction of the antenna is parallel to a principal surface of the metal plate, the radio module is formed on the first principal surface, and a ground electrode of the radio module is formed on the second principal surface, the mounting substrate being located between the radio module and the ground electrode, and the antenna has a spiral shape, a helical shape, or a meander shape on the mounting substrate, and has pieces on both the first and second principal surfaces of the mounting substrate.