Communications: radio wave antennas – Antennas – Slot type
Reexamination Certificate
1999-09-27
2001-05-01
Phan, Tho (Department: 2821)
Communications: radio wave antennas
Antennas
Slot type
C343S770000
Reexamination Certificate
active
06225958
ABSTRACT:
TECHNOLOGICAL FIELD
The present invention relates to a multifrequency antenna to be used mainly as a built-in antenna of a small and in radio communication terminal such as a mobile telephone, and more particularly to a multifrequency antenna for receiving radio waves of a plurality of desired frequency bands without enlarging the size of the communication terminal by use of high-order mode resonance frequency generated in a plane antenna with a short-circuit plate.
BACKGROUND ART
As a built-in antenna of a small and thin radio communication terminal such as a mobile telephone, a plane antenna with a short-circuit plate having a structure as shown in
FIG. 18
is well known.
In
FIG. 18
, in a plane antenna
210
with a short-circuit plate, a radiator conductor plate
212
which is a radiator conductor is arranged on a grounded conductor plate, that is, a ground plate
211
, and the radiator conductor plate
212
is connected to the ground plate
211
via a short-circuit plate
213
. Power is supplied to a feeding point
212
a
on the radiator conductor plate
212
by a feeder cable
214
from a power-feeding source
215
through a hole
211
a
bored in the ground plate
211
.
The plane antenna
210
with a short-circuit plate shown in
FIG. 18
is known to resonate at a frequency when the length of L
0
shown in the drawing is about &lgr;g/4 (&lgr;g indicates an effective wavelength).
Meanwhile, in such a plane antenna, for example, to apply this antenna to a system having 2 or more built-in radio terminals, a multifrequency antenna for receiving two or more different frequency bands together may be required.
Conventionally, as a multifrequency antenna for receiving two or more different frequency bands, the constitution shown in
FIG. 19
or
20
is known.
A multifrequency antenna
220
shown in
FIG. 19
is structured so that two radiator conductor plates
222
-
1
and
222
-
2
different in size are arranged in parallel with a ground plate
221
, and these two radiator conductor plates
222
-
1
and
222
-
2
are connected to the ground plate
221
via short-circuit plates
223
-
1
and
223
-
2
respectively, and power is supplied to a feeding point
222
-
1
a
on the radiator conductor plate
222
-
1
from a power-feeding source
225
-
1
via a feeder cable
224
-
1
, and power is supplied to a feeding point
222
-
2
a
on the radiator conductor plate
222
-
2
from a power-feeding source
225
-
2
via a feeder cable
224
-
2
.
Namely, the multifrequency antenna
220
shown in
FIG. 19
is structured so that two single-frequency plane antennas resonating in different frequency bands respectively are arranged side by side and by use of such a constitution, a problem arises that the arrangement of the two single-frequency plane antennas increases the mounting area. A multifrequency antenna
230
shown in
FIG. 20
is structured so that two radiator conductor plates
232
-
1
and
232
-
2
different in size are stacked and arranged on a ground plate
231
, and these two radiator conductor plates
232
-
1
and
232
-
2
are connected to the ground plate
231
via short-circuit plates
233
-
1
and
233
-
2
respectively, and power is supplied to a feeding point
232
-
1
a
on the radiator conductor plate
232
-
1
from a power-feeding source
235
-
1
via a feeder cable
234
-
1
, and power is supplied to a feeding point
232
-
2
a
on the radiator conductor plate
232
-
2
from a power-feeding source
235
-
2
via a feeder cable
234
-
2
.
Namely, the multifrequency antenna
230
shown in
FIG. 20
is structured so that two single-frequency plane antennas resonating in different frequency bands respectively are stacked and arranged and by use of such a constitution, a problem arises that the stacking arrangement of the two single-frequency plane antennas increases the height of the mounting portion and increases the mounting volume.
As mentioned above, in a conventional multifrequency antenna, compared with a single-frequency plane antenna with a short-circuit plate, the mounting area and mounting volume are larger and it may cause obstacles to miniaturization and thinning of a radio terminal accommodating this multifrequency antenna.
DISCLOSURE OF THE INVENTION
An object of the present invention is to provide a small multifrequency antenna requiring no increase in mounting area and mounting volume.
The present invention constitutes a multifrequency antenna using the main mode resonance frequency and high-order mode resonance frequency of a single-frequency plane antenna with a short-circuit plate.
Generally, in a single-frequency plane antenna with a short-circuit plate having a main mode resonance frequency, there is a high-order mode resonance frequency integer times of this main mode resonance frequency. However, this high-order mode resonance frequency may be often different from a desired frequency band and cannot be used as it is.
Therefore, according to the present invention, a single-frequency plane antenna with a short-circuit plate is structured so that a cut portion is formed in a predetermined location of the radiator conductor plate thereof and a predetermined high-order mode resonance frequency is shifted to a desired frequency band by this cut portion and by doing this, both of them can be received in a plurality of desired different frequency bands.
Namely, the present invention is characterized in that a multifrequency antenna has a ground plate, a radiator conductor plate arranged opposite to the ground plate, a short-circuit plate for connecting the ground plate and radiator conductor plate, and a power supply means for supplying power to the radiator conductor plate, and the radiator conductor plate has at least one cut portion for shifting at least one high-order mode resonance frequency to a predetermined frequency, and the multifrequency antenna operates at least at two frequencies such as the main mode resonance frequency and at least one high-order mode resonance frequency shifted by the cut portion.
The cut portion is formed at least in one of the locations integer times of the distance C/2 fn (where n indicates the order of an odd-order mode (n=3, 5, 7, c a light speed, fn an n-order mode resonance frequency) from the short-circuit plate on the radiator conductor plate.
The cut portion may comprise a slot with a length of SL and a width of SW formed orthogonally to the current flowing on the radiator conductor plate.
Furthermore, the cut portion may comprise a hole in an optional shape formed on the radiator conductor plate. Furthermore, the cut portion may comprise a cut-out portion with one end open in an optional shape formed in the radiator conductor plate.
The multifrequency antenna may be structured so that the distance between the ground plate and the radiator conductor plate varies with the distance from the short-circuit plate on the radiator conductor plate.
Furthermore, the cut portion may be structured so as to be formed in the location at a predetermined distance shifted from the center on the radiator conductor plate.
Furthermore, the ground plate may be structured so as to be formed in the location at a predetermined distance shifted from the center on the radiator conductor plate.
The multifrequency antenna further has a dielectric of a predetermined dielectric constant arranged between the ground plate and the radiator conductor and the cut portion is formed at least in one of the locations integer times of the distance C/(2 fn{square root over ( )}r)(where n indicates the order of an odd-order mode (n=3, 5, 7, c a light speed, fn an n-order mode resonance frequency, &egr;r the dielectric constant of the dielectric) from the short-circuit plate on the radiator conductor plate.
In this case, the dielectric can be structured so that the dielectric constant thereof varies with the distance from the short-circuit plate on the radiator conductor plate.
Furthermore, the power supply means may be structured so as to supply power to the location at a predetermined distance shifted from the center on the radiator conductor
Amano Takashi
Chiba Norimichi
Iwasaki Hisao
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Kabushiki Kaisha Toshiba
Phan Tho
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