Communications: radio wave antennas – Antennas – With radio cabinet
Patent
1996-04-26
1998-06-23
Hajec, Donald T.
Communications: radio wave antennas
Antennas
With radio cabinet
343895, 343900, H01Q 124
Patent
active
057710236
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a broadband antenna means for casing-carried equipment.
Portable equipment, and then particularly hand-carried telephones, are often provided with helical antennas. Such antennas are convenient because they can be made more robust and take up less space than straight wire antennas for instance. However, they do not always give satisfactory antenna performance.
One problem is that a helical antenna is short and can therefore easily be screened or obstructed by a user or by objects in its vicinity. The helical antenna is therefore often combined with an extendable straight wire antenna, which is not screened as easily and which also gives better antenna performance. For instance, the Patent Specifications U.S. Pat. No. 4,121,218, U.S. Pat. No. 5,204,687 and U.S. Pat. No. 4,868,576 describe different antenna means for portable equipment in which a helical antenna has been combined with an extendable straight wire antenna.
Another problem encountered with the use of helical antennas resides in their limited bandwidth. This renders conventional helical antennas unusable in those cases when an antenna function having a very broad band is required, for instance in the JDC mobile telephone system. In cases such as these, it would be desirable to provide an antenna means which has the positive properties of helical antennas coupled with a bandwidth which is much greater than the bandwidth of a conventional helical antenna.
It is, of course, conceivable to provide portable equipment with two separate helical antennas which have mutually different resonance frequencies. Such an antenna arrangement would be unnecessarily space consuming, however.
The problems concerning bandwidth and space requirements are solved by a broadband antenna means according to the present invention. There is thus obtained a helical structure that is resonant at two frequencies which result from the different lengths of respective coils and whose difference is due to the difference in the lengths of the coils.
SUMMARY OF THE INVENTION
The problems relating to screening of the short helical antennas is solved by combining the helical antennas with a straight wire antenna.
Further advantageous embodiments of the invention are defined in the depending Claims. For instance, a helical structure which is resonant at more than two frequencies can also be obtained in a similar manner, by combining three or more coils.
It may also be problematic and require very high precision in manufacture to achieve a well-defined mutual capacitance/inductance between the coils when they are mounted close to one another. This can be alleviated by twisting the coils together prior to being wound to their final helical shape, for instance.
BRIEF DESCRIPTION OF THE DRAWINGS
Two preferred embodiments of the invention will now be described in more detail with reference to the accompanying drawings, in which
FIG. 1 is view of a first embodiment of the invention which includes, among other things, a first helical antenna incorporated in a sleeve provided with an attachment means, a second helical antenna, an antenna rod or pin which encloses a straight wire antenna and the second helical antenna;
FIG. 2a illustrates a second embodiment of the invention which includes, among other things, a first helical antenna and a second helical antenna embodied in a sleeve provided with an attachment means, and an antenna rod or pin which embraces a straight wire antenna;
FIG. 2b shows elements of the second embodiment illustrated in FIG. 2a;
FIG. 3 is a circuit diagram which illustrates an electric function of the helical antennas of the first embodiment illustrated in FIG. 1;
FIG. 4 is a circuit diagram which illustrates an electric function of the helical antennas of the second embodiment shown in FIGS. 2a and 2b; and
FIG. 5 shows three curves in a bandwidth diagram of a conventional helical antenna of a helical structure according to the invention, and of a straight wire antenna.
DESCRIPTION OF THE PREFERRED EM
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patent: 5446469 (1995-08-01), Makino
patent: 5469177 (1995-11-01), Rush et al.
patent: 5479178 (1995-12-01), Ha
patent: 5504494 (1996-04-01), Chatzipetros et al.
patent: 5594457 (1997-01-01), Wingo
Derwent's Abstract, No. 93-366142/46, Week 9346, Abstract of SU, 1758726, Aug. 30, 1992.
Allgon AB
Hajec Donald T.
Ho Tan
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