1. Field of the Invention
The present invention is related to a structure of a helix antenna, and especially to an antenna which suits a communication instrument, by cooperation of the related members thereof, a fixed length, a loading added to the antenna and impedance matching of an inner helix coil make it surely suit two or multiple frequencies.
2. Description of the Prior Art
Coils used as signal receiving and emitting elements are well known, the coil pitch and the coil diameter of a conventional helix antenna are both fixed, and can only be used for a single frequency. However, frequencies used nowadays for communication instruments (such as a mobile phone) are all of two or multiple frequencies. It needs frequency matching to make a conventional helix antenna suit two or multiple frequencies. Nevertheless, this generally involves more complicated structures and higher cost of production.
Thereby, Ericsson company No. W 098/15028 provided a multi band non-uniform helical antenna, the pitch angle, coil diameter, number and spacing of the coil turns of the helical antenna are set ununiform in order to get the-function of two or multiple frequencies. For example, the helical coil has a section with a denser group of turns, and has another section with a looser group of turns; alternatively, a section can be of a larger coil diameter, while the other section can be of a smaller coil diameter; in these modes, different lengths can be used for different consonant frequencies (such as 900 MHZ and 1800 MHZ).
However, the content disclosed in this patent shows that the helical coil is not compressed, and its antenna can not be added to with a top loading, such as is shown in FIG. 1, it can not obtain the desired VSWR. Even if it is added with a top loading, such as is shown in, FIG. 2, the desired VSWR still can not be obtained. Only when the non-uniform helical antenna is compressed, the desired VSWR can be obtained. When the frequency is 880 MHZ, its VSWR is 4.33.
The object of the present invention is to provide a structure of a helix antenna, wherein, a load can be added on the top of a non-uniform helical coil, in cooperating with a fixed length of the helical coil formed by melting connecting the inner to the outer insulating sleeves, as well as with the impedance matching of a metallic connecting seat on the bottom thereof with an elastic contact piece, to construct a brand-new dual or multi-frequency helix antenna.
In the preferred embodiment, the top of the helical coil is extended toward the center thereof with a length to be an added loading of the antenna.
In a practicable preferred embodiment, the inner and the outer insulating sleeves of the antenna is provided respectively with an annular recess and an external protruding annulus able to matchably connect with each other for melting connecting with each other, so that the helical coil can be assembled to have a fixed length of a predetermined type.
The bottom of the helical coil has a dense section of turns assembled on the metallic connecting seat to make impedance matching with the elastic contact piece.