Multiband telecommunication antenna

Details Multiband telecommunication antenna Multiband telecommunication antenna

2002-03-05

2003-11-11

Phan, Tho (Department: 2821)

Communications: radio wave antennas

Antennas

With radio cabinet

C343S797000, C343S815000, C343S817000

Reexamination Certificate

active

06646611

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to multiband telecommunication antennas, in particular for cellular telephone systems.
2. Description of the Prior Art
Cellular telephone systems use various frequency bands corresponding to various existing telecommunication systems. Several telecommunication systems are used simultaneously at present, for example the digital cellular system (DCS) (1 710-1 880 MHz), and the Global System for Mobile communications (GSM) (870-960 MHz). New telecommunication systems are currently being installed, such as the Universal Mobile Telephone Service (UMTS) (1 900-2 170 MHz).
Telecommunication network operators must therefore provide a network of antennas operating in the various frequency bands used. Some operators install complementary networks of antennas, each network operating in accordance with one telecommunication system. Thus operators use a network of GSM antennas and a network of DCS antennas while they are installing a network of UMTS antennas.
However, the multiplication of antenna networks leads to increasing costs for the operators—purchase of antennas, leasing of locations, installation—and damages the environment. For this reason other operators use antennas operating in accordance with more than one telecommunications system. This reduces the installation cost and damage to the environment.
Two types of antennas are then used:
A first type of antenna, known as a “wideband” antenna, uses a sufficiently wide operating band to be able to send and receive calls in accordance with more than one telecommunication system. For example, an antenna using a frequency band from 870 MHz to 1 880 MHz is used as a combined GSM and DCS antenna.
A second type of antenna, known as a “multiband” antenna, combines, in a single antenna chassis, respective radiating elements conforming to more than one telecommunication system. For example, there are GSM and DCS dual band antennas including respective radiating elements for the GSM and the DCS.
FIG. 1
shows a prior art GSM and DCS dual band antenna. The dual band antenna
10
includes radiating elements
12
operating in accordance with the GSM and radiating elements
14
operating in accordance with the DCS. In this kind of antenna the GSM radiating elements
12
are connected to two GSM connectors
16
and
18
transmitting waves with frequencies in the GSM band. Similarly, the DCS radiating elements
14
are connected to two DCS connectors
20
and
22
transmitting waves with frequencies in the DCS band.
FIG. 1
does not show the connection between the connectors and the GSM or DCS radiating elements.
Two independent connectors transmitting waves in the same frequency band are used because of the nature of the radiating elements used. Each radiating element—the operation of which is described in U.S. Pat. No. 6,025,798, for example—is equivalent to two independent dipoles at 90° to each other. Accordingly, the radiating elements
12
and
14
receive and/or send telecommunication signals correctly regardless of the position of a sending or receiving antenna relative to the radiating elements.
The set of radiating elements for the same band of frequencies forms a transmission device. Accordingly, the GSM radiating elements
12
form a GSM transmission device and the DCS radiating elements
14
form a DCS transmission device. To optimize the operation of each of these devices, two criteria are taken into account in the design of this prior art antenna:
In accordance with a first criterion, the radiating elements for the same band of frequencies are separated by a distance substantially equal to 0.95×&lgr;
m
, where &lgr;
m
represents the average wavelength of the band of frequencies associated with those radiating elements. It is known that this disposition of the radiating elements is favorable to the operation of the device positioned in this way.
In accordance with a second criterion, the radiating elements of the same device are placed in the same vicinity, i.e. they are similarly surrounded by other nearby radiating elements and by metal partition walls whose function is described below.
In the case of a DCS and GSM dual band antenna, one feature of the wavelengths used facilitates the production of an antenna meeting the above two criteria. The average wavelength &lgr;
DCS
of the DCS band is approximately equal to half the average wavelength &lgr;
GSM
of the GSM band. It is therefore possible to produce an antenna having a periodic structure with the pitch for the DCS radiating elements equal to twice the pitch for the GSM radiating elements. Because of this feature, any GSM radiating element
12
is equidistant from two GSM radiating elements
12
and equidistant from two DCS radiating elements
14
. Similarly, any DCS radiating element
14
is equidistant from two DCS radiating elements
14
.
The symmetry in the disposition of the radiating elements of the two devices considerably reduces the consequences of radio frequency interference because each radiating element of the same device is affected by similar interference. The performance of a device—for example its signal to noise ratio—is improved if the radiating elements of the device operate under similar conditions.
Coupling between radiating elements of the same device substantially reduces its performance. To reduce such coupling, the radiating elements are partitioned off by metal walls whose positions also determine various characteristics of the radiation of each device, for example the horizontal aperture. Thus walls
26
perpendicular to a longitudinal axis
27
of the antenna partition off the GSM radiating elements
12
within rectangular enclosures also defined by the longitudinal walls
27
a
and
27
b
of the chassis of the antenna. The walls
26
reduce the coupling between the GSM radiating elements
12
, thereby increasing the gain of the GSM device.
The gain of the GSM device is a function of the distance between the lateral walls
27
a
and
27
b
and the GSM radiating elements
12
and of the height of the walls
27
a
and
27
b
. If the GSM radiating elements
12
are substantially equidistant from the partition walls
27
a
,
27
b
and
26
, an optimum configuration is obtained enabling the GSM device to operate in accordance with transmission criteria imposed by operators. Furthermore, the operation of the GSM device is optimized in terms of the second criterion previously referred to, because all the radiating elements of the device are similarly partitioned off.
Furthermore, the walls
26
are also used conjointly with fixed walls
24
along the axis
27
of the antenna to partition off the DCS radiating elements
14
. This partitioning determines operating characteristics of the DCS device, such as its horizontal aperture or its gain. Nevertheless, the GSM radiating elements
12
are also placed along the axis
27
of the antenna. Metal walls close to a radiating element disturb its operation. For this reason the longitudinal walls
24
have a chamfer
25
near the GSM radiating elements
12
.
The DCS radiating elements
14
are partitioned off in pairs of radiating elements in rectangular enclosures formed by the walls
24
,
26
and
27
b
. To limit coupling between the DCS radiating elements
14
of each pair, a wall
28
is placed perpendicularly to the axis
27
between the radiating elements
14
of the pairs. Each wall
28
is equidistant from the two DCS radiating elements
14
separated in this way. Accordingly, these walls
28
are in the vicinity of a GSM radiating element
12
equidistant from the said two DCS radiating elements. The walls
28
therefore interfere with the GSM radiating elements
12
in the same way as the walls
24
, because of the proximity of a partition wall to the GSM radiating elements
12
. For this reason the walls
28
have a length which is less than the width of the enclosures partitioning off the DCS radiating elements
14
. Moreover, the height of the walls
28
decreases as they approach the GSM radiating elements

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