Communications: radio wave antennas – Antennas – Spiral or helical type
Reexamination Certificate
2000-10-27
2002-02-12
Wimer, Michael C. (Department: 2821)
Communications: radio wave antennas
Antennas
Spiral or helical type
Reexamination Certificate
active
06346926
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
Recently, mobile telephones for cellular systems and simple mobile phone systems (PHS) have become widely popular, and these mobile telephones are provided with antennas for the transmission and reception of call traffic and data traffic. Usually, for these antennas, a whip antenna is used, which is made of a retractable whip element that, for the sake of convenience when carrying the mobile telephone and anticipating a call, can be stowed away in a casing of the mobile telephone.
2. Description of the Related Art
However, when the whip element has been stowed away in the casing, transmission and reception with the mobile telephone are almost impossible, so that a small antenna element has to be provided outside the casing when the whip element is stowed away in the casing. Thus, this small antenna element can be used for transmission and reception when the whip element is stowed away in the casing.
A characteristic feature of helical antennas is that the physical length can be made shorter than the effective antenna length, so that helical antennas are used for the afore-mentioned small antenna elements. Conventionally known are configurations, in which the helical antenna is provided at the casing of the mobile telephone, or at the tip of a retractable whip element.
The configuration of such a conventional helical antenna is shown in
FIGS. 10
a
and
10
b
. However, the helical antenna
100
shown in these drawings is of the type that is attached to the wireless device casing of a mobile telephone or the like, and the cover covering its outer surface is not shown.
FIG. 10
a
is a plan view of the helical antenna
100
, and
FIG. 10
b
is a cross-sectional view thereof. As shown in these drawings, a through hole
101
a
is formed in the insulating bobbin
101
, which is made by resin casting, passing from the top to the bottom along the axis of the bobbin
101
. The through hole
101
a
is provided for slidably inserting the whip antenna into it.
A single thread of helical protrusion portions
105
is formed on the peripheral outer surface of the bobbin
101
. The helical protrusion portions
105
form a single thread, but for illustrative reasons, the numerals
105
a
to
105
g
are associated with the helical protrusion portions in
FIGS. 10
a
and
10
b
. The helical protrusion portion
105
g
is taken as the leading end of the helical protrusion portions
105
. The helical protrusion portions
105
a
to
105
g
form helical groove portions between them, and a helical element
122
is arranged in these helical groove portions. The helical element
122
is made of a wire of, for example, phosphor bronze, which is formed into helical shape. The helical element
122
is screwed from the upper end of the bobbin
101
into the helical groove, which leads to the situation shown in
FIGS. 10
a
and
10
b.
The lower end of the bobbin
101
is provided with a threaded portion, and this threaded portion of the bobbin
101
is screwed into a threaded portion formed on an inner peripheral surface at the upper end of an attachment fitting
115
. This fixes the attachment fitting
115
to the lower end of the bobbin
101
. The lower portion of the helical element
122
that has been screwed onto the bobbin
101
is also wound around an upper cylindrical portion
115
d
formed in the upper portion of the attachment fitting
115
, and the helical element
122
is in electrical contact with this upper cylindrical portion
115
d
. Furthermore, a through hole
115
a
connected to the through hole
101
a
is formed also in the attachment fitting
115
. A collar portion
115
b
is formed in an intermediate portion of the peripheral side surface of the attachment fitting
115
, and a threaded portion
115
c
is formed at a lower portion of the peripheral side surface. The threaded portion
115
c
is screwed to the wireless device casing until the lower surface of the collar portion
115
b
abuts against the wireless device casing, whereby the helical antenna
100
is attached to the wireless casing device. Thus, the attachment portion
115
connects the transmission/reception portion provided inside the wireless device casing with the helical element
122
.
The helical antenna
100
with the conventional configuration shown in
FIGS. 10
a
and
10
b
has a small outer diameter of several mm, so that the helical element
122
is provided with a wire diameter of about 0.6 mm. When this helically shaped helical element
122
is screwed from the upper end of the bobbin
101
, it will be moved beyond the helical protrusion portion
105
g
, or the leading end and wound around the upper cylindrical portion
115
d
. Thus, the inner peripheral surface of the helical element
122
will be brought into contact with the upper cylindrical portion
115
d
. However, since the wire diameter of the helical element
122
is small, as mentioned above, and the screwing is performed manually, already small differences in the screwing force can lead to a vertical displacement of the position of the helical element
122
contacting the upper cylindrical portion
115
d
. Thus, when the position of the helical element
122
contacting the upper cylindrical portion
115
d
is shifted vertically, there are the problems that the effective number of windings of the helical element
122
changes, and the resonance frequency of the helical antenna
100
shifts.
This is explained with reference to
FIGS. 11
a
,
11
b
, and
11
c
. As shown in
FIG. 11
a
, the helical element
122
g
is in contact with the upper cylindrical portion
115
d
. The helical element
122
g
and the upper cylindrical portion
115
d
contact each other at the contact point
123
located on the right side in
FIG. 11
a
. When the position of the helical element
122
g
is shifted slightly upwards as shown in
FIG. 11
b
, then the helical element
122
g
and the upper cylindrical portion
115
d
contact each other at the contact point
123
located approximately at the center as shown in
FIG. 11
b
. Furthermore, when the position of the helical element
122
g
is shifted even more upwards as shown in
FIG. 11
c
, then the helical element
122
g
and the upper cylindrical portion
115
d
contact each other at the contact point
123
located on the left side in
FIG. 11
c
. Thus, there is the problem that when the helical antenna
100
is used, for example, for the 900 MHz band, then this shifting of the contact point
123
causes a resonance shift of about 20 MHz for the shift shown in
FIG. 11
b
, and a resonance shift of about 40 MHz for the shift shown in
FIG. 11
c.
It is therefore an object of the present invention to provide a helical antenna, in which the helical element and the attachment fitting contact one another at a stabilized location.
SUMMARY OF THE INVENTION
In a helical antenna in accordance with the present invention, a leading end of the helical protrusion portions formed at the lower end of the bobbin has substantially the same diameter as the second collar portion, which is connected to this leading end, and the depth of the helical groove portions becomes gradually shallower toward this leading end, so that the helical element can be easily moved beyond the leading end and positioned on the side surface of the second collar portion. Since the outer diameter of the second collar portion and the outer diameter of the leading end are substantially the same and there is almost no difference in level between them, the helical element is better prevented from shifting vertically, and the helical element contacts the side surface of the second collar portion of the attachment fitting at a stabilized location. Consequently, deviation of the resonance point can be prevented.
When the helical protrusion portions including the leading end, which form the helical groove portion whose depth becomes gradually shallower, are formed higher, then this helical groove portion becomes deeper, and the position of the helical element within this groove portion is stabilized, so that the position
Izumi Yutaka
Nakaya Takashi
Shimabara Masataka
Connolly Bove Lodge & Hutz
Nippon Antena Kabushiki Kaisha
Wimer Michael C.
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