Apparatus and method for a radio wave transmission

Radio end device, comprising: having an antenna (210) for transmitting a radio wave, the antenna has a first terminal (210a) and a second terminal (210b); a power circuit (24) for receiving a battery voltage and for supplying a driver output voltage to the antenna; a switch circuit (25) which is provided between the power circuit and the antenna to switch the direction of application of the driver output voltage between a first direction and a second direction to that of the first port to the second port or from extending the second terminal to the first terminal; a driver circuit (22) for driving said switch circuit (25) in response to a carrier wave frequency of the radio wave; and a modulator circuit (11) to modulate an output of the driver circuit in an ON / OFF manner, namely by a digital baseband signal having a frequency which is lower than the carrier wave frequency, wherein the power circuit (24) consists of a variable power circuit which contains a command input circuit (24e) to feed a command value of the driver output voltage, and a voltage converter circuit (24a) is provided to the battery voltage in the driver output voltage implement in accordance with the command value, the command value is variable, so that the coverage area of ​​the radio wave emitted from the antenna is variable in correspondence to the command value; the switching circuit (25) an H-bridge circuit having a first switching transistor (251), a second switching transistor (252), a third switching transistor (253) and a fourth switching transistor (254) includes; all of the transistors are made in accordance with the first to fourth switching transistors (251 to 254) of N-channel MOSFETs; the driver circuit (22) includes a booster circuit (23) for supplying a gate drive voltage to the gate terminals of N-channel MOSFETs to turn it on, the gate drive voltage is a threshold voltage higher than the driver output voltage ; and the booster circuit (23) includes a charge pump circuit for boosting the battery voltage to the gate drive voltage of the N-channel MOSFET.