1. Field of the Invention
The present invention relates to a communication apparatus.
2. Description of the Related Art
An antenna which is used for radio communication radiates electromagnetic waves (radio waves) for radio communication after receiving input of a transmission signal (electric voltage or electric current) of a predetermined frequency. Conversely, the antenna also receives electromagnetic waves and converts into a reception signal (electric voltage or electric current). Here, when the antenna has a length corresponding to a wavelength which is used for the radio communication, receiving sensitivity and transmitting efficiency of electromagnetic waves can be improved.
Thus, the length of an antenna element (an antenna line) normally tends to be set at an approximate integral multiple of a quarter wavelength of the electromagnetic waves. In particular, the length of such an antenna element is an important factor for designing an antenna which is used for middle-range communication or long-range communication. It is similar to short-range communication as well. On the other hand, as disclosed in Japanese Patent Application Laid-Open No. 2007-36439, a technology of human body communication which utilizes a human body as a transmission path has been recently developed as for short-range communication. However, since a human body is utilized as the transmission path, the communication distance is limited. Therefore, it is difficult to apply the human body communication technology to middle-range communication or long-range communication.