[0001] The present invention pertains to a dual-polarization antenna's radiating element.
[0002] So-called "butterfly" radiating elements which are made up of multiple assembled
parts, as described in the document
EP-0 895 303. The radiating element comprises two orthogonal dipoles each comprising two conducting
elements; each conducting element is folded into a V to form two wings, mounted on
a reflector or ground plane. However, this configuration has a directivity limitation.
As the surface currents traveling through the wings are limited, it is at best equivalent
to two half-wave dipoles arranged orthogonally.
[0003] So-called "TV" radiating elements are also known, used in television transmission
antennas. Their cast structure is fairly difficult to construct. Additionally, this
structure requires that the radiating element is supplied by four coaxial cables,
[0004] So-called "patch" radiating elements are also known, printed on a printed circuit
board (PCB), for which multilayer techniques should be used in order to achieve the
desired characteristics. These radiating elements are generally made up of a square
conducting surface which is approximately a half-wavelength on each side. However,
the currents, which are neither concentrated nor guided, are distributed across the
entire square surface, which results in lower polarization purity. Furthermore, the
usable frequency band is narrow, about ± 5% around the central frequency.
[0005] The purpose of the present invention is to implement a dual-polarization antenna's
radiating element having a very large current surface area, and consequently a maximized
directivity.
[0006] Another purpose of the invention is to propose a dual-polarization antenna's radiating
element whose radio-etectric characteristics are stable over a very large frequency
band.
[0007] Another purpose of the invention is to propose a dual-polarization antenna's radiating
element whose volume and cost are minimized:
[0008] The object of the present invention is a dual-polarization antenna's radiating element
comprising a pair of half-wave dipoles for each polarization, each dipole forming
a conductive rectangular plane whose ends are folded onto the central section, and
a junction formed of a conducting strip ensuring the connection between the two dipoles
with the same polarization. According to the invention, the dipoles are arranged on
a first face of a dielectric medium, each dipole pair being respectively supplied
by a microband conducting line arranged on the second face opposite the dielectric
medium. Also according to the invention, the conducting lines respectively supplying
each of the dipole pairs are placed within the same plane, and a jumper cable ensures
that one line overlaps the other at the crossing point.
[0009] According to one preferred embodiment, the junction is connected to the dipole at
a point where the current is at a maximum and voltage is at a minimum, which makes
it possible not to change the distribution of currents within the radiating element.
[0010] According to another embodiment, each polarization's pair of dipoles is supplied
by a single coaxial cable. The coaxial cable is connected to a supply line, for example
a microstrip, which supplies each pair of dipoles.
[0011] According to another embodiment, a single pair's dipoles are separated from one another
by a distance of a half-wavelength.
[0012] According to a first embodiment, the dipoles are printed onto the lower surface of
the dielectric medium, and the conducting lines are printed onto the upper surface
of the dielectric medium.
[0013] According to a second embodiment, at least one of the components of the radiating
element chosen from among the dipoles, injunctions, and the supply lines is cut from
a thin metal plate.
[0014] According to one variant, a pair of dipoles and the corresponding junction is cut
from a single piece within a thin metal plate.
[0015] The invention discloses a radiating element which is equivalent to two half-wave
dipoles for each polarization, owing to surface currents traveling over a larger surface
area than in a "butterfly" radiating element of the prior art. As this radiating element's
directivity is greater than for the radiating elements of the prior art, only a reflecting
plane with lower dimensions is needed to lead to an equivalent beamwidth. As the radiating
element is more directive, the backfire value is lower. Consequently, the double-polarization
antennas resulting from the joining of these radiating elements is smaller and thicker
than the antennas of the prior art.
[0016] The inventive radiating element is mechanically very simple, and includes fewer parts
than the radiating elements of the prior art. In particular, it includes only two
coaxial cables, a ground plane or reflector with reduced surface area, and potentially
an insulating plane substrate, for example such as the one used for a printed circuit
board, compared with the many parts used for constructing the radiating elements of
the prior art. The construction of the inventive radiating element does not require
any welding, and minimizes the materials used.
[0017] From an impedance standpoint, the radiating element is large-band, owing to the coupling
of the half-wave dipoles, which makes it possible to reduce the distance between the
dipoles and the reflector, and therefore to achieve a less thick antenna. It is no
longer necessary to add a balun.
[0018] The inventive radiating element may be used in large-band antennas, typically including
multiple bands, for example DCS, PCS, and UMTS. It is possible to adapt the impedance
to a large frequency band by using the significant surface area available for the
microstrip line.
[0019] A further object of the invention is a double-polarization antenna comprising radiating
elements as described above.
[0020] Other characteristics and advantages of the invention will become apparent while
reading the following description of embodiments, which are non-limiting and given
for purely illustrative purposes, and in the attached drawing, in which:
- Figure 1 depicts a perspective view of a radiating element according to one embodiment
of the invention,
- Figure 2 shows in detail the pairs of dipoles of the radiating element of Figure 1,
- Figure 3 depicts a top view of another embodiment of a radiating element,
- Figure 4 is the co-polarization and cross-polarization radiation pattern of the radiating
element of Figure 1. The intensity of the radiation R in dB is given as the y-axis,
and the radiation angle ϕ in degrees is the x-axis.
- Figure 5 depicts the reflection coefficient of each of the pairs of dipoles of Figure
1 both during co-polarization and cross-polarization, and the insulation between the
two pairs of dipoles. The reflection coefficient and the insulation I in dB is given
as the y-axis, and the frequency F in GHz as the x-axis.
[0021] In the embodiment of the invention depicted in Figures 1 and 2, a radiating element
1 is mounted onto a metal plate serving as a reflector
2 placed a short distance away, about one quarter-wavelength of the radiating element
1. The reflector's
2 edges are folded or shaped so as to enable adjustment of the radiation pattern.
[0022] The double-polarization radiating element
1 comprises, for the first polarization, a first dipole
3 and a second dipole
4, and for the second polarization, a third dipole
5 and a fourth dipole
6. The dipoles
3, 4, 5, 6 are rectangular planes forming "C" shapes, the two ends
7 being folded onto the central section
8 so as to create a T-shaped slope
9 between these sections. Between the two dipoles
3, 4 and
5, 6 of the same polarization, positive or negative, a junction
10, 11 in the form of a strip joins the two dipoles
3, 4 and
5, 6 of the same pair. The jonction
10, 11 is connected to the dipoles
3, 4, 5, 6 at points where the current is at a maximum and voltage is at a minimum, which makes
it possible to not change the distribution of currents within the radiating element.
The dipoles of each pair
3, 4 and
5, 6 are separated from one another by a distance of a half-wavelength.
[0023] The dipoles
3, 4, 5, 6 as well as their respective junctions
10, 11 are printed onto the lower face of the dielectric medium
12 of a printed circuit. The upper face of the dielectric medium
12 supports the microstrip supply lines
13 of each of the dipoles. The junctions
10, 11 of the dipoles
3, 4, 5, 6 are used as a ground plane for the microstrip line
13. As shown in detail in Figure 3, the pair of two dipoles
3, 4 and
5, 6 for each polarization is directly supplied near the center of the radiating element
1 by a single coaxial cable
14, each cable
14 supplying the microstrip lines
13 associated with one of the junctions
10 or
11.
[0024] As the microstrip lines
13 are coplanar, a jumper cable
15 ensures that the microstrip lines
13 overlap one another at their crossing point. Having coplanar microstrip lines
13 affords many advantages when constructing radiating elements
1, particularly in terms of form factor, complexity of assembly, and cost. The problem
of minimizing the volume and cost of the radiating element
1 in comparison to existing elements has thereby been solved. This is because when
the supply lines are arranged on either side of the dielectric medium, this requires
using two dielectric medium thicknesses separated by a ground plane. Additionally,
the grounding of the dipoles, via the braid surrounding the coaxial cable, becomes
very complicated. In this situation, it is understood that, particularly owing to
its more complicated construction and the increase in the quantity of materials needed,
the final product is much more expensive than the radiating element
1 of the invention.
[0025] Dipoles
3, 4, 5, 6 may be constructed by etching a copper substrate of the type used to create printed
circuit boards. A conductive paint can also be used, or the technique of screenprinting.
[0026] This concept enables the proximity between the radiating element
1 and the reflector
2 leading to a total antenna thickness which may be less than 80 mm. and preferentially
about 60 mm for the GSM 900 and, as opposed to 85 mm at present. The radiating element
1 enables satisfactory uncoupling (approximately 30 dB of insulation) between the two
layers of dipoles
3, 4 and
5, 6.
[0027] According to another embodiment depicted in Figure 3, the pair of dipoles
30, 31 and their junction
32 are directly tied into a thin conductive plate, for example from a single part. A
substrate with a large surface area is no longer necessary, and the supply lines
33 may be placed directly onto the cut plate, with a localized insulating substrate
being placed in between. The supply lines
33 may also be cut from a thin conductive plate. In this situation, the jumper cable
may be created directly by folding the cut plate.
[0028] Figure 4, which depicts the radiation pattern of the radiating element, will now
be considered. The bell-shaped group of curves
40 corresponds to the co-polarization components, and the V-shaped group of curves
41 corresponds to the cross-section polymerization component, respectively for frequencies
of 800 MHz, 900 MHz, 1 GHz, and 1.1 GHz. The cross-section polymerization depicted
by the V-shaped curves
41 must be minimized. The usable frequency band is about ± 21% around the central frequency.
At a radiation level R = -3dB, the beamwidth Δϕ
42 is about 60° to 65°, and the variation in the opening
43 (gap between the curves) remains very low within the frequency band studied (800
MHz to 1.1 GHz). The distinction between the two polarizations, shown as the distance
between the group of co-polarization curves
40 and the group of cross-polarization curves
41 is better than 32dB within the azimuth axis ϕ = 0°.
[0029] Figure 5 depicts the reflection coefficient C for the two pairs of dipoles and the
insulation I between these pairs. The reflection coefficient
50, 51 remains greater than 15dB for each of the two pairs of dipoles over a frequency band
of 850 MHz to 1180 MHz. The usable frequency band is about ± 16.5% around the central
frequency, as opposed to about ± 10% around the central frequency for a "patch" radiating
element of the prior art. The insulation
52 between the two pairs of dipoles remains better than 26dB over an extremely broad
frequency band.
[0030] These Figures 4 and 5 show that the radio-electric characteristics of the radiating
element, according to the embodiment of the invention just described, are advantageously
stable over a very broad frequency band.
1. A dual-polarization antenna's radiating element comprising a pair of half-wave dipoles
(3, 4) and (5, 6) for each polarization, each dipole forming a conductive rectangular
plate whose ends (7) are folded onto the central section (8), and a junction (10,
11) in the form of a conducting strip ensuring the link between these two dipoles
(3, 4; 5, 6) with the same polarization, characterized in that the dipoles (3, 4; 5, 6) are disposed upon a first surface of a dielectric medium
(12), each pair of dipoles a (3, 4) and (5, 6) being respectively supplied by a microband
conducting line (13) disposed upon a second surface opposite the dielectric medium,
and that the connecting lines (13) respectively supplying each of the pairs of dipoles
are placed within the same plane, a jumper cable (15) ensures that one line overlaps
the other at the crossing point.
2. A radiating element according to claim 1, wherein the junction (10, 11) is connected
to the dipole (3, 4, 5, 6) at a point where the current is at a maximum and the voltage
is at a minimum.
3. A radiating element according to one of the claims 1 and 2, wherein the pair of dipoles
(3, 4; 5, 6) of each polarization is supplied by a single coaxial cable (14).
4. A radiating element according to one of the claims 1 to 3, wherein the dipoles (3,
4; 5, 6) of a single pair are separated from one another by a distance of a half-wavelength.
5. A radiating element according to one of the claims 1 to 4, wherein the dipoles (3,
4; 5, 6) are printed onto the lower face of the dielectric medium (12), and the conducting
lines (13) are printed onto the upper face of the dielectric medium (12).
6. A radiating element according to one of the claims 1 to 4, wherein at least one of
the radiating element's components chosen from among the dipoles (30, 31), the junctions
(32), and the supply lines (33) is cut from a thin metal plate.
7. A radiating element according to claim 6, wherein one pair of dipoles (30, 31) and
the corresponding junction (32) are cut from a single piece within a thin metal plate.
8. A double-polarization antenna comprising radiating elements according to one of the
preceding claims.