[Patent document 1] JP 2008-205604 A
An antenna is mounted in a vehicle for executing various communications such as GPS, vehicle-to-vehicle communications, or road-to-vehicle communications. Such an antenna in a vehicle is required to enable downsizing and favorable transmission and reception performance.
Several wireless communication modules with antennas are provided for the several kinds of communications in a vehicle, respectively; the several wireless modules are required to be arranged collectively at the same place (for example, a predetermined place on the roof of the vehicle). Therefore, the various wireless communication modules with the antennas are required to achieve further downsizing.
To that end, Patent document 1 discloses a technology to downsize a wireless communication module with an antenna as follows. A radio frequency circuit board is mounted on a ground structure serving as a ground of a wireless terminal. A circuit board has a feed point at one end and a variable capacity reactive element at the other end. The feed point has one end connected with one end of a ground conductor of the circuit board and the other end connected with the ground structure via a first contact terminal. The variable capacity reactive element has one end connected with the other end of the ground conductor of the circuit board and the other end connected with the ground structure via a second contact terminal.
This forms a current loop that flows from the one end of the feed point, via the first the ground structure, the second contact terminal, the variable capacity reactive element, and the earth conductor, to the other end of the feed point. This configuration achieves a radiating pattern shape as an antenna without using an antenna element, thereby enabling downsizing.
However, the feed point and the variable capacity reactive element are arranged at both the ends of the circuit board, respectively, to achieve a function as one antenna; thus, the downsizing is not fully achieved.
Further, in the antenna apparatus of Patent document 1, the above-mentioned current loop is formed, thereby causing both the ground structure and the earth conductor to be radiation source. This requires the design to consider the both. Therefore, the design of the antenna apparatus may become complicated; the configuration of the antenna apparatus may become complicated.