This sort of antenna apparatus is disclosed in the publication No. B-1-51 issued by Japanese Electronic Information Communication Institute Society in 1997.
FIG. 13 is a structure diagram showing a helical antenna equipped with a mobile communication terminal housing, indicated in the above-explained publication.
The helical antenna 11 shown in FIG. 13 can have the better gain and circularly polarized wave characteristics over the wide range as shown in FIG. 14 to FIG. 17. That is, this helical antenna 11 is uprighted over a metal housing 10 keeping a predetermined interval "d", and while 2 sets of line-shaped elements are intersected with each other, the respective line-shaped elements are bent in a helical shape. Then, the electric power is fed to the summit portions of the first line-shaped element and the second line-shaped element maintaining such a phase relationship of 90 degrees.
In other words, FIG. 14 to FIG. 17 are characteristic diagrams showing the test results performed in such that the adverse influences are given to the radiation characteristic of the metal housing 10 when the helical antenna 11 is employed as the antenna for the mobile communication terminal. As apparent from the changes in the vertical plane directivity caused by the interval "d" shown in FIG. 14 and FIG. 15, there is substantially no adverse influence given to the directivity caused by the metal housing 10 in the vertex direction. Also, as apparent from the axial ratio characteristics indicated in FIG. 16 and FIG. 17, there is a relatively small adverse influence caused by the metal housing 10. As a result, it may be seen that since there is a small adverse influence given to the various characteristics caused by the metal housing 10, the helical antenna 11 is suitable for the antenna mounted on the mobile communication terminal housing.
However, the length of the metal housing 1 shown in FIG. 13 is 150 mm, and the length of the helical antenna 2 is 80 mm. When the interval "d" between this helical antenna 2 and the metal housing 1 is involved, the total length exceeds 230 mm, which may deteriorate portability.
One solution is conceivable to avoid this deterioration of portability. That is, the antenna main body may be stored into the mobile communication terminal housing. However, if the helical antenna main body is storable into the mobile communication terminal housing, there arises a problem that it is difficult that the power feeding circuit is made movable.
In other words, FIG. 18 indicates the power feeding circuit unit described in "A New GCPW Resonant Quadrifiler Helix Antennas for GPS Land Mobile Applications" of IEEE AP-S 1997 Digest 664 in FIG. 1. The electric power supplied from the power feeding circuit unit 12 is branched from a single feeding cable provided in the cylinder via a balun shortcircuit unit 13 to 2 pairs of feeding cables so as to energize the respective radiation elements 17 of the helical antenna. In this case, 4 sets of the feeding cables provided in the cylinder and for supplying the electric power to the respective radiation elements 17 cannot be made of flexible structures, but are constructed of the fixed circuit arrangement. As a result, there is a problem that it is difficult to make the power feeding circuit movable.
The present invention has been made to solve the above-described problems, and therefore has an object to provide such an antenna apparatus for a portable telephone. That is, since the movable radiation elements are provided in the vicinity of a fixed antenna for energization purpose in such a manner that these movable radiation elements are stacked on this fixed antenna in a coaxial manner but are not electrically connected to this fixed antenna, this antenna apparatus for the portable telephone can have the better circularly polarized wave characteristic and the superior portability.