|
(11) | EP 0 977 303 A3 |
| (12) | EUROPEAN PATENT APPLICATION |
|
|
|
|
|||||||||||||||||||||||
| (54) | Antenna for radio telephone |
| (57) Provides an antenna for a radio telephone whereby, in a state wherein a rod-shaped
antenna (10) is extended to outside the case (50) of the radio telephone, the effects
of the human body are negligible and emission of radio waves at an angle close to
the horizontal direction is possible, and in a state wherein the rod-shaped antenna
(10) is retracted within the case (50), no unwanted radiation is produced. For this
purpose, a helical antenna (20) having an electrical length of λ/4 and the rod-shaped
antenna (10) extendable and retractable with respect to the case (50) through the
hollow central portion of the helical antenna (20) and having an electrical length
of about 3λ/8 and inductive reactance, are electrically coupled by means of an electrostatic
coupling portion (30) having capacitive reactance such that, in the state wherein
the rod-shaped antenna (10) is extended from the case (50), the inductive reactance
of the rod-shaped antenna (10) is canceled out. The length of the bottom portion (12a)
of the connecting member (12) is preferably set to a length such that when the rod-shaped
antenna (10) is retracted within the case (50), the bottom portion (12a) of the connecting
member (12) passes through the helical coil (20) over the entire length thereof, severing
electrical coupling between the helical antenna (20) and the rod-shaped antenna (10). |