Communications: radio wave antennas – Antennas – With radio cabinet
Patent
1995-05-24
1998-05-26
Hajec, Donald T.
Communications: radio wave antennas
Antennas
With radio cabinet
343895, 343901, H01Q 124
Patent
active
057573255
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to an antenna device for portable equipment, particularly for hand portable telephones.
BACKGROUND OF THE INVENTION
Antennas for mobile telephones may be divided into two main groups, quarter-wave and half-wave antennas, although types somewhere between and outside these may occur.
Characteristics of a quarter-wave antenna are: (portion length approximately 8 cm at 900 MHz), to the 50 ohm of the telephone, without impedance transformation, disturbing,
Characteristics of a half-wave length antenna are: (portion length approximately 16 cm at 900 MHz), transformation to the 50 Ohm of the telephone, including a connector,
In the specification and claims below the terms half-wave antenna and quarter-wave antenna refer to antennas having substantially the above characteristics, respectively.
One disadvantage in using the quarter-wave antenna, which is dependent on a ground plane, is that the ground plane offered in hand portable telephone is in most cases smaller than one wavelength in a radius from the feeding point of the antenna. As a result, the ground plane becomes resonant and, consequently, it must be tuned to the antenna for optimal performance. Moreover, the ground plane characteristics change (and so the antenna performance) depending on whether the telephone is placed freely, whether the telephone (the ground plane) is held with the hand, whether the user is perspiring, whether the telephone is moved to the ear etc.
Another disadvantage in using a quarter-wave antenna for a hand portable telephone is, in fact, its small length. This causes the antenna, while in call position, to be strongly screened in a substantial angle sector by the head of the user.
In spite of the above mentioned disadvantages, the most common antenna for hand portable telephones is a quarter-wave length antenna, since a small antenna is needed to regard the telephone as hand portable or a pocket telephone. Recently, a type of hand portable telephone has appeared, which are provided with extendable half-wave antennas. This is an acceptable solution from the handling point of view, since the antenna requires a small space in the retracted position. The problem in this case is that the antenna function is so poor in the retracted position that it might be difficult to receive an incoming call.
Another known type of mobile telephones employs in combination a considerably more compact helical antenna of quarter-wave type as an antenna for receiving an incoming call, and a half-wave antenna which is extended in call position. However, this arrangement is unsatisfactory due to the ground plane dependence of the helical antenna and the switching between the helical antenna and the half-wave antenna being complicated, since only one antenna at the time may connected. Also, a helical antenna has a lower degree of efficiency than e.g. a rod antenna.
All the above mentioned disadvantages are overcome by an antenna device according to the present invention.
SUMMARY OF THE INVENTION
This new antenna device for portable equipment uses in combination a helical antenna of half-wave length type arranged outside of a main body of said portable equipment, an extendable half-wave antenna, and an impedance transformer. Therefore, no ground plane is required for the antenna function. Further, due to the sufficient length of the half-wave length antenna, the problem of the user's head screening the antenna is substantially reduced. Yet further, a very simple switching may be performed, since the helical antenna and half-wave length antenna may utilize the same impedance transformer. The half-wave length antenna, when in use, may even be connected parallel to the helical antenna due to impedance differences. According to the invention this possibility is utilized and, therefore, only a very simple switching device is required. The switching device may be operated by extending and retracting of the antenna.
In the retracted position (see FIG. 3a) the half-wave length antenna is neither galvanically nor
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Allgon AB
Hajec Donald T.
Ho Tan
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