The present disclosure relates to an earphone antenna through which a mixture of a radio-frequency signal (RF signal) and a low-frequency signal (such as audio signal and acoustic signal; hereafter collectively referred to as audio signal) is transmitted.
Mobile wireless electronic devices such as mobile liquid crystal television receivers, mobile radio receivers, and pagers which use earphone antennas have been offered (see, for example, JP-A-2003-163529 (patent reference 1)). Such an earphone antenna uses a signal line as an antenna to transmit audio signals to a rod antenna or to earphones.
In an antenna using a coaxial cable, a dedicated connector is used. A ferrite bead is inserted under the headphone terminal to remove noise superimposed on the audio signal (see, for example, JP-A-H9-199237 (patent reference 2)).
The present applicant has already offered an earphone antenna in which an antenna line is formed by an earphone cord and a coaxial cable. The total length of the earphone cord is about ½λ. The earphone cord and coaxial cable are connected to intermediate parts of the antenna line. The earphone antenna is equipped with a relay portion having a separation-superimposition circuit for separating or superimposing audio signals from or onto RF signals. In this earphone antenna, the relay portion is formed by a substrate on which a given pattern and ground are formed, as well as plural ferrite beads and chip capacitors mounted on the substrate.
This earphone antenna is constructed as described above. The relay portion is mounted in an intermediate part of the antenna line. Consequently, the cost is increased. Furthermore, the antenna is somewhat large in size and heavy. Therefore, it has been pointed out that the antenna may not be routed as freely as desired. Furthermore, in an earphone antenna, as described previously, a structure for interconnecting the earphone code and coaxial cable is mounted in the relay portion constituting a feeding point for the antenna line. In addition, the substrate on which the separation-superimposition circuit for separating or superimposing audio signals from or onto RF signals is mounted, as well as other components. For these reasons, the antenna characteristics are somewhat inferior to those of an independent antenna line.
Additionally, another problem common to earphone antennas is that noise countermeasure on the part of the connector portion connecting the earphone antenna with the body of the device is important. That is, in the connector portion made up of contact elements, an earphone antenna suffers from the problem that a countermeasure implemented by shielding independent transmission lines of the coaxial cable that transmits RF signals increases the size. In an earphone antenna, insertion of ferrite beads or other countermeasure is used to cope with the problem. However, this presents the problem that the design of the body of the device is limited.
Accordingly, it is desirable to provide an earphone antenna which alleviates the foregoing problems with the earphone antenna and thus reduces the cost and improves the antenna characteristics.