1. Field of the Invention
The present invention relates to an antenna, and more particular to a miniature combo built-in antenna structure.
2. Description of Prior Art
In a global positioning system (GPS), the time of transmitting a radio signal is used to measure distance by basic trigonometric positioning principles, and three or more GPS satellites are adopted for cross comparisons. By converting signal receiving speed and time to obtain the distance from the satellite as well as using an electronic map built in a GPS receiver, the position of an object or a person can be located or identified.
At present, automobile personal navigation devices (PND) become increasingly popular. To allow users to access current road conditions and weather reports while driving a motor vehicle, a traffic message channel (TMC) receiving module is usually built in the personal navigation device (PND). Since ground broadcasting uses a FM Radio Data System (RDS) to broadcast current traffic and weather information, and such communication application is generally called Radio Data System (RDS)/Traffic Message Channel (TMC) and provides three kinds of services as listed below:
1. The area, road section and direction affected by a recent car accident.
2. The time duration of a continuous traffic or weather condition.
3. The suggested driving route based on the aforementioned information. Traffic message is updated once every five minutes. The way for the RDS/TMC to collect traffic information is substantially the same as that of satellite broadcasting, and sensors and cameras installed at roadsides by local traffic departments are used for collecting information and statistics.
After a personal navigation device (PND) is built in a TMC receiving module, an antenna slot of a TMC receiving module is created on a housing of the personal navigation device (PND), so that users can plug an external earphone into the antenna slot and use it as a dedicated antenna or a TMC receiving module. The earphone is used as an antenna, and thus there is no issue of installing an antenna in a motor vehicle. As to drivers, it is not safe to listen to the road condition and weather report while driving a motor vehicle. However, the size of the dedicated antenna of a general TMC receiving module is large and uneasy-to-install, and thus causing tremendous inconvenience to users.