1. An antenna comprising: • at least one central longitudinal radiating element; and • at least one outer element comprising at least one rolled-up electrically- conductive sheet disposed around the central element, without electrical contact therebetween, wherein the outer element presents a height that is strictly decreasing, or alternatively that increases and decreases along the roll.

2. An antenna according to claim 1, wherein the conductive sheet possesses a first side defining a maximum height of the outer element, and a second side, in particular a side perpendicular to the first, defining a base of the outer element.

3. An antenna according to claim 2, wherein the conductive sheet presents the shape of a right-angled triangle.

4. An antenna according to claim 2, wherein the conductive sheet has a third side interconnecting the first two sides and presenting the shape of a decreasing exponential.

5. An antenna according to claim 2, wherein the conductive sheet has a third side interconnecting the first and second sides and formed by a succession of crenellations.

6. An antenna according to claim 1, wherein the minimum height of the outer element is not zero.

7. An antenna according to claim 1, wherein the outer element comprises a rolled-up conductive sheet having the shape of an isosceles triangle with its base defining the maximum height of the outer element.

8. An antenna according to claim 1, wherein the outer element is rolled in a spiral, in particular a variable-pitch spiral.

9. An antenna according to claim 1, wherein the outer element is arranged to operate without contacting ground. 9

10. An antenna according to claim 9, wherein the central radiating element is a dipole.

11. An antenna according to claim 1, wherein the outer element is arranged to operate in contact with ground.

12. An antenna according to claim 11, wherein the central radiating element is a monopole.

13. An antenna according to claim 1, including a dielectric material surrounding the central radiating element and the outer element. Dated this 14th day of September 2007. 10 The present invention relates to an antenna comprising: • at least one central longitudinal radiating element; and • at least one outer element comprising at least one rolled-up electrically- conductive sheet disposed around the central element, without electrical contact therebetween, the outer element presenting a height that is strictly decreasing, or alternatively that increases and decreases along the roll.

The present invention relates to a broadband antenna that conserves its radiation
pattern.
BACKGROUND
There are various topologies for antennas that are broadband in terms of voltage
standing wave ratio (VSWR) and that can be used in various application fields
(commercial, military, industrial,...).
Thus, as examples, the topologies in the most widespread use are the following:
antennas that are independent of frequency (spiral, log-periodic); and broadband dipoles
(elliptical, volume, planar, ...). These topologies can be used in the context of making
antennas that are directional or that are omnidirectional.
In another form, passband can be increased by means of an added matching
network that can incorporate some number of discrete or pseudo-lumped components
(capacitors, inductors, resistors, transformers, etc.).
One of the problems associated with using a matching network lies in the physical
limitations that arise from making use of components. Thus, such solutions do not in any
way make it possible to modify or shape the radiation characteristics of the individual
radiating element. Furthermore, a matching network reduces the intrinsic power
performance and efficiency of the radiating element. Nevertheless, in spite of certain
radiation-shaping properties, the use of the above-mentioned broadband topologies does
not make it possible to provide structures that are compatible with all applications.
Thus, with respect to form factor, such antennas need to present dimensions that
are close to wave lengths. In addition, in order to obtain omnidirectional coverage,
conventional form factors (wire antennas) cannot be satisfied, thereby making it more
complicated to integrate beam-conserving antennas in applications of the portable or
vehicle type.
With the arrival of new communications standards making use of time-division
signals, such antennas also suffer from problems of dispersion relative to the position of
the phase center, making it difficult if not impossible to implement such systems.
2

Nevertheless, several structures have been developed for the purpose of mitigating
the above-mentioned problems.
US patent No. 6 339 409 discloses an antenna formed by rolling up a single
electrically-conductive sheet having the shape of a right-angled triangle.
US patent application No. 2006/0071873 describes an antenna as mentioned above
connected to a ground-forming disk.
US patent No. 4 527 163 describes a monostrip antenna having an outer element
formed by a sheet cut out to present a Y-shape.
SUMMARY
The present invention seeks in particular to remedy the above-mentioned
drawbacks associated with known antennas by means of a construction that is innovative.
The invention thus provides an antenna comprising:
• at least one central longitudinal radiating element; and
• at least one outer element comprising at least one rolled-up electrically-
conductive sheet disposed around the central element, without electrical contact
therebetween, the outer element presenting a height that is strictly decreasing, or
alternatively that increases and decreases, along the roll.
The antenna of the invention can be used on its own or as an antenna element in an
array of antennas that are identical or different, and where appropriate either contacting or
not contacting ground.
In an embodiment of the invention, the electrically-conductive sheet forming the
outer element has a first side defining the maximum height of the outer element and a
second side, in particular a side perpendicular to the first side, defining a base of the outer
element.
By way of example, the conductive sheet may present the shape of a right-angled
triangle, or it may have a third side interconnecting the first two sides and presenting a
shape that decreases exponentially.
3

In a variant, the conductive sheet may have a third side interconnecting the first and
second sides and formed by a succession of crenellations.
The minimum height of the outer element may be zero, or in a variant, it may be
non-zero.
By way of example, the conductive sheet may have the shape of a right-angled
triangle, which triangle may optionally be truncated at a vertex.
In an embodiment of the invention, the outer element comprises a rolled-up
conductive sheet having the shape of an isosceles triangle, with the base of the triangle
defining the maximum height of the outer element.
The outer element may be rolled in a spiral, in particular a variable-pitch spiral,
specifically a logarithmic spiral.
The profile of the sheet constituting the outer element may be continuous, or it may
be formed by a succession of plane portions.
The conductive sheet may be rolled up from one or the other of its ends, and from
the inside towards the outside or from the outside towards the inside relative to the central
radiating element.
The central radiating element may be of any type.
For example, the radiating element may be of the dipole type, in particular it may
be a printed or a cylindrical dipole.
The outer element may be considered as an impedance transformer when it is
arranged to operate without contacting ground and purely by electromagnetic coupling.
The antenna is then said to have a "continuous profile".
In another embodiment of the invention, the outer element is arranged to operate
while in contact with ground and can be considered as being an extension of that ground.
The antenna is then said to have a "matching sleeve".
4

The radiating element may be a monopole, a dipole, a helix, an ellipse, or a
combination of these elements.
The radiating element may be a printed or cylindrical dipole, for example.
All of the elements of the antenna may be made of conducive materials or may
comprise printed circuit cards.
The central radiating element and the outer element may be surrounded by a
dielectric material, in particular by being embedded at least in part in the dielectric
material. In a variant, it is possible to use a dielectric material in sheet form that is rolled
around the central radiating element and the outer element.
Whether or not the outer element is associated with ground, and depending on the
periodicity of the outer element, the antenna of the invention may be ultra-broadband or of
the multi-band type.
The broad bandwidth and the high efficiency of the antenna of the invention
enables it to operate at high power.
The invention also enables the antenna to be miniaturized, using dimensions that
are of the order of one-tenth of the wavelength.
The antenna of the invention can thus be used in all types of application, in
particular in appliances that are portable or vehicle-mounted.
The invention can be used in particular for mobile applications, in particular in the
field of portable appliances or vehicles, or in a variant it can be used in infrastructure, for
example in the field of base stations.
The invention also makes it possible to obtain a radiation pattern that can be
selected to be directional, sector-shaped (antenna in an array), or omnidirectional.
The invention enables the following advantages to be achieved in particular:
• a substantially constant radiation pattern to be obtained in dipole mode, whether
directional or otherwise, over its operating band;
5

• high efficiency because of the topology of the antenna;
• conserving its broadband characteristic in a wide variety of integration
environments, in particular in environments that make use of a ground plane; and
• compactness, given its broadband characteristic.
BRIEF DESCRIPTION OF THE DRAWING
The invention can be better understood on reading the following detailed
description of non-limiting embodiments of the invention and on examining the
accompanying drawing, in which:
• Figure 1 is a diagrammatic fragmentary view of an antenna with a dipole radiating
element and in accordance with the invention;
• Figure 2 is a diagrammatic plan view of the Figure 1 antenna;
• Figure 3 is a diagrammatic and fragmentary view showing the conductive sheet
used for forming the outer element of the Figure 1 antenna;
• Figures 4 to 7 are diagrammatic and fragmentary views showing other examples
of sheets that can be used to form the outer element of the antenna of the invention; and
•Figure 8 is a diagrammatic and fragmentary view of a monopole antenna
constituting an embodiment of the invention.
MORE DETAILED DESCRIPTION
Figure 1 shows a so-called "continuous profile" antenna 1 comprising a central
radiating element 2 of the dipole type having a longitudinal axis X, and an outer element 3
drawn in dashed lines and that can be said to be partially parasitic, surrounding the
radiating element 2.
The antenna 1 shown has a dielectric material 4 in which the radiating element 2
and the outer element 3 are embedded, at least in part.
6

In a variant, the radiating element 2 and the outer element 3 may be separated by
air.
The radiating element 2 may be of any type, for example a printed or cylindrical
dipole, and it is may be in the form of a rod.
The outer element 3 can be considered as being an adaptive load, and it is not
connected to any ground.
In the example shown, the outer element 3 is formed by a rolled-up electrically
conductive sheet 5 that has the shape of an isosceles triangle, as shown in Figure 3. In a
variant, the shape of the triangle may be arbitrary.
The sheet 5 may be rolled in a spiral, for example a variable-pitch spiral, as can be
seen in Figure 2.
The maximum height H of the outer element 3 measured along the axis X
corresponds to the length H of the base of the isosceles triangle of the sheet 5.
In the example described, the outer element 3 presents a minimum height along the
roll axis that is zero, corresponding to the vertex H of the isosceles triangle opposite from
its base.
The antenna 1 may be of the type presenting an ultra-broad band.
The outer element 3 may present other shapes.
For example, as shown in Figure 4, the outer element 3 may be made from a
conductive sheet 5 in the shape of a right-angled triangle.
In a variant, the conductive sheet 5 may be in the form of a truncated right-angled
triangle, so that the outer element 3 presents a minimum height along the roll axis that is
not zero.
In a variant, as shown in Figure 6, the conductive sheet 5 may have two sides that
are perpendicular and a third side of a shape that is curvilinear, being of the decreasing
exponential type.
7

As shown in Figure 7, the conductive sheet 5 may have a side that is formed by a
succession of crenellations, with the height of the outer element varying along the roll,
alternately increasing and decreasing.
Figure 8 shows an antenna 10 of the so-called "matching sleeve" type constituting
another embodiment of the invention.
This antenna 10 is of the monopole type, and comprises a central radiating element
11, an outer element 12 rolled around the radiating element 11, and a ground element 13 to
which the outer element 12 is connected. The outer element may be made integrally with
the ground element.
The elements 11 and 12 may be made of conductive material, or in a variant they
may be made using printed circuit cards.
In another variant, the radiating element 11 may be of the dipole type.
The outer element 12 may be considered as an extension of the ground element 13.
In the example described, the outer element 12 is constituted by rolling up a sheet
that has the shape of a right-angled triangle.
Naturally, the outer element 12 may present one of the other shapes described
above.
The antenna 10 makes it possible to obtain a bandwidth that is ultra-broad.
The influence of the ground element 13 on the operation of the antenna can be
made to be very small by means of the invention.
The radiating element 11 may be a single piece or it may be assembled from a
plurality of elements.
In the examples shown, the central radiating element and the outer element are
concentric.
In a variant, the central radiating element could be off-center relative to the outer
element.
8

WE CLAIM:
1. An antenna comprising:
• at least one central longitudinal radiating element; and
• at least one outer element comprising at least one rolled-up electrically-
conductive sheet disposed around the central element, without electrical contact
therebetween, wherein the outer element presents a height that is strictly decreasing, or
alternatively that increases and decreases along the roll.

2. An antenna according to claim 1, wherein the conductive sheet possesses a first side
defining a maximum height of the outer element, and a second side, in particular a side
perpendicular to the first, defining a base of the outer element.
3. An antenna according to claim 2, wherein the conductive sheet presents the shape of a
right-angled triangle.
4. An antenna according to claim 2, wherein the conductive sheet has a third side
interconnecting the first two sides and presenting the shape of a decreasing exponential.
5. An antenna according to claim 2, wherein the conductive sheet has a third side
interconnecting the first and second sides and formed by a succession of crenellations.
6. An antenna according to claim 1, wherein the minimum height of the outer element is
not zero.
7. An antenna according to claim 1, wherein the outer element comprises a rolled-up
conductive sheet having the shape of an isosceles triangle with its base defining the
maximum height of the outer element.
8. An antenna according to claim 1, wherein the outer element is rolled in a spiral, in
particular a variable-pitch spiral.
9. An antenna according to claim 1, wherein the outer element is arranged to operate
without contacting ground.
9

10. An antenna according to claim 9, wherein the central radiating element is a dipole.
11. An antenna according to claim 1, wherein the outer element is arranged to operate in
contact with ground.
12. An antenna according to claim 11, wherein the central radiating element is a
monopole.
13. An antenna according to claim 1, including a dielectric material surrounding the
central radiating element and the outer element.
Dated this 14th day of September 2007.

10

The present invention relates to an antenna comprising:
• at least one central longitudinal radiating element; and
• at least one outer element comprising at least one rolled-up electrically-
conductive sheet disposed around the central element, without electrical contact
therebetween, the outer element presenting a height that is strictly decreasing, or
alternatively that increases and decreases along the roll.