Communications: radio wave antennas – Antennas – With radio cabinet
Reexamination Certificate
1999-01-28
2001-03-13
Le, Hoanganh (Department: 2821)
Communications: radio wave antennas
Antennas
With radio cabinet
C343S895000
Reexamination Certificate
active
06201500
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an antenna device provided for a portable radio such as a portable cellular phone and, more particularly, to an antenna device which enables transmission and reception of signals at two different frequencies.
2. Description of the Related Art
In a portable radio device, such as a portable cellular phone, which is used while being carried outside, a whip antenna projecting from a housing of the radio is retracted into the housing so as to make the radio as compact as possible while the radio is being carried.
This type of portable radio uses a helical antenna constantly connected to feeding hardware to enable transmission and reception of a signal regardless of whether the whip antenna is housed in the housing or extended. Japanese Patent Publication of Translated Version (PCT) No. Hei-9-505956 discloses an antenna device which resonates at two radio different frequencies even while a whip antenna is retracted into the housing.
Referring now to
FIG. 9
, a prior art antenna device
100
comprises a fixed antenna section
130
and a slide antenna section
103
. The fixed antenna section
130
includes a first helical antenna element
116
consisting of a first coil and a second helical antenna element
114
consisting of a second coil. Both antenna elements are helically wrapped around a cylindrical insulating sleeve
104
. The coils are connected at one end to a conductive sleeve
109
attached to one end of the insulating sleeve
104
. The conductive sleeve
109
is electrically connected to transmission and reception circuits of a portable radio (not shown), thus constituting means for attaching the antenna device
100
to the portable radio.
The slide antenna
103
is a rod antenna element disposed below an insulating cover
125
. Slide antenna
103
passes through the insulating sleeve
104
and the conductive sleeve
109
. The slide antenna
103
can be extended from and retracted into the portable radio in the axial direction.
When the slide antenna
103
is retracted to a housed position, the rod antenna element is positioned below the conductive sleeve
109
. The rod antenna element is disconnected from the conductive sleeve
109
by means of the insulating cover
125
and hence is out of use. As shown in an equivalent circuit diagram shown in
FIG. 10
, the fixed antenna
130
is connected to the conductive sleeve
109
, and the first and second helical antenna elements
116
and
114
resonate at resonance frequencies f11 and f12.
As shown in
FIG. 11
, when compared with the capability of an antenna device having one helical antenna which resonates at frequency f10 (denoted by a dashed line in FIG.
11
), the bandwidth capability of the antenna device
100
covers a much wider range.
When the slide antenna
103
is extended, the lower end of the rod antenna element is electrically connected to the conductive sleeve
109
, and the rod antenna acts as a whip antenna resonating at the frequency f10.
The conventional antenna device
100
enables transmission and reception of a signal regardless whether the slide antenna
103
is housed or extended. Further, as shown in
FIG. 11
, while the slide antenna
103
is housed, the antenna device
100
enables transmission and reception of a radio signal at two frequencies f11 and f12.
In recent years, a frequency band used for mobile communications equipment has differed from field to field. For example, an automobile telephone is allocated a range of 900 MHz, and a personal handyphone system (PHS) is allocated a range of 1.9 GHz. There is a desire for a portable radio capable of being used with both communications system. For this reason, there has been desired what is called a dual-band-capable antenna device which enables transmission and reception of a signal at either of the bands.
However, in the previously-described conventional antenna device
100
, when the slide antenna section
103
is housed, the fixed antenna section
130
enables transmission and reception of a signal over a broad range. To this end, the two helical antenna elements are adjusted so as to resonate at comparatively close frequencies f11 and f12. Accordingly, the conventional antenna device
100
does not cope with communication at completely different frequency bands. If an attempt is made to cope with such communication through use of an antenna which is identical structure with the conventional antenna device
100
, there is a need to connect the two helical antenna elements
114
and
116
having completely different extended strengths to the conductive sleeve
109
with a side-by-side configuration. This results in not only impairment of appearance of the portable radio but also an increase in the number of components, thereby rendering assembly of the portable radio laborious.
The conventional antenna device
100
causes only the rod antenna elements to serve as an antenna while the slide antenna section is extended. Accordingly, the antenna device
100
cannot enable the rod antenna elements to cope with two completely different frequency bands. Consequently, the conventional antenna device
100
cannot cause the antenna elements to resonate at two completely different frequencies and to enable transmission and reception of a signal at respective frequencies regardless of whether the slide antenna is housed or extended.
OBJECTS AND SUMMARY OF THE INVENTION
The present invention has been conceived to solve the foregoing problems. Accordingly, it is an object of the present invention to provide an antenna device which enables a portable radio to transmit and receive signals in frequency bands used for two types of different communications systems, but using only one type of antenna element.
Another object of the present invention is to provide an antenna device which enables storage of a slide antenna and enables a portable radio to transmit and receive a signal in any of the frequency bands used by two types of different communications system.
To these ends, according to a first aspect of the present invention, there is provided an antenna device comprising:
feeding hardware attached to a housing of a portable radio; and
a helical antenna element whose base end is connected to the feeding hardware, wherein the helical antenna element is caused to resonate at a first frequency as a ¼-wavelength helical antenna and to resonate at a second frequency lower than three times the first frequency as a ¾-wavelength helical antenna, by adjustment of an extended length and a winding pitch.
The ¼-wavelength helical antenna resonating at a first frequency f1 again reaches an impedance close to that at which the helical antenna resonates at the first frequency f1, at a second frequency f2 which is lower than three times the first frequency f1. Even when the ¼-wavelength helical antenna is used as a ¾-wavelength helical antenna, its standing-wave voltage ratio (SWVR) does not change at all. Accordingly, it is possible to cause one helical antenna element connected at one end to feeding hardware to resonate at the first and second frequencies f1 and f2 by adjustment of an extended length and a winding pitch, thereby enabling transmission and reception of a signal in two different frequency bands.
According to a second aspect of the present invention, there is provided an antenna device comprising:
a rod antenna element which resonates at a first frequency as a ¼-wavelength whip antenna;
a movable contact section which is electrically connected to a base end of the rod antenna element and is continually provided in line with the rod antenna element;
an insulating cover which covers the rod antenna element;
a slide antenna section along an upper outer peripheral surface of which the insulating cover becomes exposed and along a lower outer peripheral surface of which the movable contact section becomes exposed;
feeding hardware which is attached to a housing of a portable radio, causes the slide antenna section to fit into a support ho
Le Hoang-anh
Morrison Law Firm
SMK Corporation
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