WO2007071475A1

WO2007071475A1 - Reconfigurable antenna

Info

Publication number: WO2007071475A1
Application number: PCT/EP2006/067583
Authority: WO
Inventors: Eliana Palmieri; Massimo Di Fabrizio; Mario Fulvio Caramanico
Original assignee: Thales Italia S.P.A. - Land & Joint Systems Division
Priority date: 2005-12-22
Filing date: 2006-10-19
Publication date: 2007-06-28
Also published as: ITRM20050640A1

Abstract

Antenna (1) comprising: - a first (2) and a second (3) reflector in metal material, spaced from and facing each other so as to define a region (4a, 4b, 4c) of dielectric material lying between said reflectors, the first and the second reflector and said region forming a radial waveguide for propagating between said reflectors an electromagnetic signal transmitted or received by said antenna (1), characterized in that, the antenna (1) further comprises an array of reflecting elements (21, 61) which can be activated according to different configurations in the region of dielectric material (4a, 4b, 4c) so as to vary and control the radiation characteristics of the antenna (1).

Description

"Reconfigurable Antenna" DESCRIPTION

The present invention relates in general to the technical sector of radio telecommunication systems and, in particular, relates to a reconfigurable antenna as defined in the preamble of the first claim.

As is known, an antenna is a device suitable to emit and receive radiofrequency electromagnetic signals and it is characterized by a series of parameters which define its radiation properties and which generally depend on the size of the antenna and its geometrical structure. Said parameters are, for example, expressed as numeric values (input impedance, beam width, band width, directivity) or at most as three-dimensional or two- dimensional diagrams (such as a radiation solid and a radiation diagram respectively) .

At present there exist both antennas where the above parameters are generally fixed, i.e. they cannot be varied once the physical structure and the position of the antenna have been defined, and antennas where at least some of the above parameters can be varied, by an operator or by an automatic control system, while the antenna is being used. This last type of antenna is generally known in the sector as a reconfigurable antenna. For example, in modern telecommunication systems, the use of reconfigurable antennas with variable pointing is widespread, i.e. antennas whose directivity, which represents the direction in which the radiation solid or, more commonly, the radiation diagram reaches maximum, can be varied both in space or on a plane respectively. Regarding this, various solutions which make it possible to vary and control the directivity of an antenna belong to the prior art. In particular, solutions are known which are based both on the use of mechanical or electromechanical means (for example motorized devices) and exclusively on electronics. Among the latter, an important place is occupied by the so-called Phased Array Antennas, which generally include a plurality, or array, of radiating elements. In said antennas, the reciprocal phase displacements of said radiating elements can be electronically controlled so as to be able to vary the radiation diagram (i.e. its shape and/or orientation on a plane) resulting from the interference of the electromagnetic signals emitted/received from said elements .

The prior art solutions present some disadvantages, in particular in some cases they are expensive compared to their use and in other cases they are considerably complex to produce. Moreover, the solutions based on the use of electromechanical means have very high reaction times compared to the requirements of modern telecommunication systems.

Object of the present invention is to provide a reconfigurable antenna which overcomes the above- described disadvantages with reference to the prior art.

Said object is reached by means of an antenna as defined and characterized in general in attached claim 1. Preferred embodiments are defined in the dependent claims.

Further features and advantages of the present invention will become more apparent from the following detailed description of an exemplary but non-limiting embodiment thereof, as illustrated in the accompanying drawings, in which: figure 1 shows a lateral cross section of some components of an antenna according to the invention;

- figure 2 shows a frontal view of a first embodiment of an antenna according to the invention; - figure 3 shows a perspective view from below the antenna in figure 2;

- figure 4 shows a further perspective view from below the antenna in figure 3 with some parts separated;

- figure 5a shows the antenna in figure 3 and 4 and a particular operational configuration; - figures 5b and 5c show radiation diagrams corresponding to the particular configuration in figure 5a; and figure 6 shows a second embodiment of an antenna according to the present invention, including plasma nanotubes as reflecting elements.

In the figures, equal or similar elements are indicated with the same reference numbers.

The particular antenna embodiments described herein with reference to the attached drawings can advantageously be used for transmitting and/or receiving signals with a frequency between approximately 4 GHz and approximately 5 GHz. However, it should be noted that a person skilled in the art, on the basis of the teachings of the present invention, can easily design the size of the antenna in such a way that it can be used in different frequency bands, generally in the range of 2

GHz - 50 GHz.

In general, an antenna according to the present invention can be used in various applications. Non- limiting examples of said applications are the following: use in transmission stations for radio and television signals, use in telecommunication systems both military and civil, telephony, use in data transmission systems, use in microwave satellite communication systems. Figure 1 illustrates a lateral cross-section of some of the components of an antenna 1 according to the present invention, which can be used for transmitting and/or receiving electromagnetic signals.

Advantageously, as illustrated in figure 1, the antenna 1 includes a first reflector 2 and a second reflector 3, both made of metal material. The two reflectors 2 and 3 are spaced from and facing each other.

In the antenna 1, there is a region of dielectric material 4a, 4b, 4c lying between the reflectors 2 and 3 in such a way that the first reflector 2, the second reflector 3 and the region 4a, 4b, 4c form a radial waveguide for propagating between said reflectors an electromagnetic signal transmitted or received by the antenna 1. For example, the dielectric material of the region 4a, 4b, 4c can simply be air.

A further waveguide 5 is coupled to the centre, or along the axis Z, of the radial waveguide formed by the reflectors 2, 3 and the region 4a, 4b, 4c. Said further guide 5 represents, in practice, an input/output waveguide, i.e. a guide by means of which an electromagnetic signal to be transmitted can be supplied to the antenna 1 or by means of which an electromagnetic signal received by the antenna 1 can be acquired. Preferably, the input/output waveguide 5 is a coaxial guide perpendicular to the radial guide and having a coating 6 connected to the reflector 2 of the antenna 1, and a core 8 connected to the other reflector 3 of the antenna 1. In practice, said core 8 passes through a hole 9 provided in the centre of the reflector 2 connected to the coating 6 of the input/output guide 5 to be connected to the other reflector 3 from the side facing the region 4a, 4b, 4c lying between the two reflectors 2 and 3. In the particularly preferred embodiment illustrated in figure 1, the core 8 has a threaded cavity 16 on the side facing the reflector which is to be connected to the reflector 3 by means of a screw 18. However, equivalent fixing means can be provided between the reflector 3 and the core 8, for example the latter could comprise, instead of the threaded cavity 16, a pin so that it can be connected to the second reflector 3 by means of a special nut.

Preferably, coupling means are provided in the antenna 1 such as to improve impedance matching between the radial guide and the coaxial input/output guide 5. More preferably, the coating 6 of the coaxial guide 5 is finished by means of a tapered funnel, or horn, ending connected to the central opening 9 of the reflector 2. As can be seen in figure 1, in a particularly advantageous embodiment, the core 8 of the coaxial guide 5 also has a tapered ending 19 which preferably, as illustrated in figure 1, changes its tapered profile while passing from the coaxial guide 5 to the region 4b, i.e. in correspondence with the central opening 9.

In a particularly advantageous embodiment, the antenna 1 has a cylindrical symmetry around an axis Z and the two reflectors 2 and 3, as shown in figure 1, are substantially disc-shaped and are concave. Preferably, each of the two reflectors 2 and 3 has a central portion 10, 11, substantially disc-shaped and flat, and a peripheral annular portion 12 and 13, connected to the flat portion 10, 11 and at an angle to it. Other embodiments are possible where the above-mentioned peripheral annular portion 12 and 13 are absent, to the detriment of optimization of the side lobes. In a particularly advantageous embodiment, as can be seen in figure 1, the external edges 14 and 15 of the two disc-shaped reflectors are circular edges with a rounded rim, preferably with a substantially circular cross section. Advantageously, by means of experimental tests and numerical simulations, it has been seen that the rounding of the external edges 14, 15 is such as to improve the impedance matching between the radial guide defined between the two reflectors 2 and 3 and the free space and to reduce the extent of the side lobes, so limiting the effect of edge diffraction. In the antenna 1, the central portion 10 of the first reflector 2 is facing, spaced from and parallel to the central portion 11 of the second reflector 3, so that the concave parts of the two reflectors 2 and 3 are both facing the side opposite the region 4a, 4b, 4c lying between the two reflectors. In a preferred embodiment, the distance between the two central disc-shaped portions 10, 11 of the two reflectors 2 and 3 is approximately between 0.3 cm and 5 cm, and preferably equal to 1 cm (in the case of an antenna operating in the 4-5 GHz range) , and the external diameter of the two reflectors is approximately between 3 cm and 25 cm and preferably equal to approximately 18 cm (in the case of an antenna operating in the 4-5 GHz range) . The diameter of the two disc-shaped central portions is preferably between 2 cm and 24 cm and preferably equal to approximately 10 centimeters (in the case of an antenna operating in the 4-5 GHz range) . Preferably, the overall height of the antenna 1 (measured between the edge 14 and the edge 15, edges included) is between 4 cm and 10 cm and is preferably equal to approximately 7 cm (in the case of an antenna operating in the 4-5 GHz range) .

In a particularly advantageous embodiment, between the two reflectors 2 and 3 of the antenna 1, a spacing element 20 in dielectric material is provided which extends between the first and the second reflector and which can be fixed, for example by glue, to the first and to the second reflector in order to keep said reflectors united and spaced from each other. For example, said spacing element 20 is made of a plastic material with a dielectric constant preferably lower than 2. Preferably, as shown in figure 1, the spacing element 20 is a tubular element. In an alternative embodiment, not shown in the figures, said spacing element 20 is a filling element, essentially disc-shaped, which substantially fills the portion of dielectric material 4a placed between the two central portions 10 and 11 of the two reflectors 2 and 3.

It should be observed that the antenna 1 with a base structure with the components as illustrated in figure 1 has a cylindrical symmetry around the axis Z of the coaxial guide 5 and, for this reason, it has a radiation diagram which, on planes perpendicular to the axis Z, is substantially omnidirectional.

Advantageously, an antenna 1 according to the present invention, further comprises an array of reflecting elements which can be activated according to different configurations in the dielectric region 4a, 4b, 4c lying between the first 2 and the second 3 reflector so as to vary and control the radiation characteristics of the antenna 1. A first embodiment of an antenna 1 according to the present invention and including the components already illustrated and described with reference to figure 1, is shown in figure 2. In figure 2, the spacing element 20 has not been illustrated in order to make some details of the antenna 1 visible.

In said embodiment, the reflecting elements are metal elements 21 each of which can be operated so as to be moved axially between: - a forward position (or active position) where said element occupies the dielectric region lying between the first 2 and the second 3 reflector; and

- a backward position (or inactive position) where said element is placed outside said dielectric region. Preferably, as illustrated in figure 2, said metal elements 21 are substantially cylinder-shaped metal elements. More preferably, said elements are arranged along two concentric circumferences and centered substantially around the axis Z. Preferably said circumferences include the same number of reflecting elements (21) .

In a particularly preferred embodiment, the reflecting elements 21 arranged along one of the two circumferences are staggered by half a pitch (i.e. intercalated) with respect to the reflecting elements 21 arranged on the other circumference. Preferably, each of the two circumferences includes a number of reflecting elements 21 between 3 and 40.

For the purposes of this description, the terms active or inactive shall refer to the capacity, or not, of an element 21 to act as a reflecting body inside the dielectric region lying between the two reflectors 2 and

3.

As can be seen in figure 2, special holes 22 are provided in the flat circular portion of one of the two reflectors (in this case reflector 2), so that the metal elements 21 can pass through the reflector during their axial movement. In the particular embodiment in figure 2, a particular configuration of the antenna 1 is shown where some reflecting elements 21 are active in the dielectric region and where other reflecting elements are inactive, i.e. in the backward position (therefore not visible in the figure) .

In a particularly preferred embodiment, each of the metal elements 21 is a piston, preferably of an electromagnetic motor, including said piston 21, which in practice represents the mobile part of the motor, and an energizable field coil to eject or return the piston to its backward position. Preferably, the pistons 21 are made of ductile iron. The electromagnetic motors can be individually controlled, for example by means of a micro-controller, known in the art and therefore not described further here. Alternatively, the motors can be controlled in groups, for example of two or three motors.

As can be seen in figure 3, the electromagnetic motors are preferably arranged on the concave side of one of the reflectors 2 and 3 (in this case the reflector 2) and are fixed to said reflector 2. Preferably, two plates 31 and 32 are provided, opposite to and spaced from each other, one of which 31 holed and fixed immediately below the central part of the reflector 2, for mounting the motors 30 to the remaining part of the structure of the antenna 1. The other plate 32 advantageously makes it possible to establish a common stop position for the pistons 20 when they are in the backward position. Preferably, elastic means 33, for example in the form of helical springs, are provided to hold/return the pistons 21 to the backward position when the coils of the respective electromagnetic motors 30 are not energized.

In figure 3, compared to figures 1 and 2, the coaxial guide 6 is shown as having a greater length and is provided with a coaxial connector 34, of the "N" type, so that a coaxial cable, not shown in the figure, for example with an impedance equal to 50 ohm, can be connected to the antenna 1.

In figure 4, the antenna in figure 3 is shown with the plate 32 removed. In this embodiment, the plate 32 can be fixed to a flange 40 provided on the coaxial guide 6. Moreover, in figure 4 the pistons 21 of the electromagnetic motors 30 are provided with a flat and extended base 35 intended to abut against the plate 32

(removed in figure 4, but visible in figure 3) . In the particular embodiment in figure 3, the antenna 1 includes twenty-four electromagnetic motors 30, arranged on two concentric circumferences, each including twelve electromagnetic motors 30. Therefore, the respective pistons 21, which in this particular embodiment represent the reflecting elements, are also arranged on two concentric circumferences.

Figure 5a illustrates a particular operational configuration of the antenna 1. In said configuration, where the antenna 1 is illustrated schematically from above with the upper reflector 3 removed, eleven reflecting elements 21 (represented by a dark dot) are active in the dielectric regions 4a, i.e. they are in a "forward" position, while the remaining thirteen reflecting elements 21' are inactive (represented by a light dot), i.e. they are in a backward position. It should be noted that the reflecting elements (both the active and the inactive ones) are arranged along two concentric circumferences, Cl and C2 respectively.

The radiation diagram in the horizontal plane

(azimuth) of the antenna 1 in the configuration in figure 5a is shown in figure 5b. By observing figure 2, it can be deduced that, in the configuration in figure 5a, the antenna is characterized by an elevated directivity, with a very narrow main lobe and very reduced secondary lobes.

Figure 5c shows the radiation diagram in the vertical plane (zenith) of the antenna 1, in the same particular configuration in figure 5a.

It should be observed that the configuration in figure 5a can be rotated at will by activating in sequence some reflecting elements and deactivating others, so that the main lobe of the diagram in figure 5b completes a scan at 360° on the horizontal plane (azimuth) .

On the basis of the above, a person skilled in the art can easily deduce that, by varying the number and the position of the active reflecting elements 21, the radiation characteristics of the antenna 1 can easily be modified. More particularly, by selecting suitable configurations of the active reflecting elements 21, it is possible to control electronically the width of the main lobe, the antenna pointing (i.e. the direction of maximum directivity) and the band width. However, in the configuration where all the reflecting elements are inactive, the antenna 1, given its cylindrical symmetry, has an omnidirectional radiation diagram on the horizontal plane.

In a particularly advantageous embodiment, the various configurations of the antenna 1, (except for the configuration where all the elements are inactive) , are characterized in that the active reflecting elements 21 are arranged consecutively along the first or along the second circumference so as to form "arcs" of active reflecting elements. Preferably, said configurations, as in the embodiment shown in figure 5a, are formed by a first and a second arc of active reflecting elements 21 arranged respectively on the first Cl and on the second C2 circumference, the first and the second arc being substantially centered with each other.

Figure 6 shows a second embodiment of the antenna 1 according to the present invention. In this case, the base components already described with reference to figure 1, are the same. However, the reflecting elements, which can be activated in the dielectric region lying between the two reflectors 2 and 3, change.

In particular, the reflecting elements 61 of the antenna 1 in figure 6 are plasma nanotubes, they are fixed and they are placed between the first reflector 2 and the second reflector 3.

Preferably, the plasma nanotubes 61 are arranged along two concentric circumferences Cl, C2 and centered substantially around the axis Z. In a particularly advantageous embodiment, the plasma nanotubes arranged along one of the two circumferences are staggered respect to the nanotubes arranged on the other circumference.

The plasma nanotubes 61 are, in practice, glass tubes containing ionizable gas and can be controlled either singly or in groups, for example of two or three tubes 61. If the gas is not ionized, the plasma nanotubes 61 behave as inactive reflecting elements, i.e. they are not such as to reflect an electromagnetic signal transmitted or received by the antenna 1 and which propagates inside the dielectric region lying between the two reflectors 2 and 3. Otherwise, if the gas is ionized, said nanotubes 61 behave as active reflecting elements, i.e. they are such as to reflect an electromagnetic signal transmitted or received by the antenna 1 and which propagates inside the dielectric region lying between the two reflectors 2 and 3. Since the plasma nanotubes 61 are substantially cylinder-shaped elements, their behavior in the active state is essentially comparable to that of the pistons 21 of the antenna described above with reference to figures 2-5. Compared to said antenna, the antenna in figure 6 has the advantage that it does not include moving mechanical parts. The nanotubes can be ionized in accordance with methods known to the skilled in the art, such as excitation by means of a radiofrequency signal or excitation by means of an optical frequency signal (for example, a laser signal) .

Moreover, since in the case of the antenna in figure 6 the nanotubes act as spacing elements between the first 2 and the second reflector, the spacing element 20 in dielectric material can be omitted.

Therefore, also in this case, since the behavior of the antenna in figure 6 is substantially similar to that of the antenna 1, by varying the number and the position of the active reflecting elements 61 (in other words containing ionized gas), i.e. by varying the possible configurations of the active elements, the radiation characteristics of the antenna 1 can easily be modified. More particularly, by selecting suitable configurations of the active reflecting elements 61, it is possible to control electronically the width of the main lobe, the antenna pointing (i.e. the direction of maximum directivity) and the band width. However, in the configuration where all the reflecting elements 61 are inactive (i.e. they contain non-ionized gas), the antenna 1, given its cylindrical symmetry around the axis Z, has an omnidirectional radiation diagram on the horizontal plane .

As can be understood from the above, the objects of the invention are fully reached. In fact, an antenna according to the invention can be made with limited costs and the radiation diagram can be completely reconfigured. Experimental tests have demonstrated that, advantageously, an antenna according to the invention, has a high pointing speed and requires a simple electric interface for control of directivity.

Furthermore, experimental tests have demonstrated that the particular structure of the reflectors and of the input/output guides in the above-described antenna embodiments also make it possible to obtain excellent impedance matching.

Naturally, in order to satisfy contingent and specific requirements, a person skilled in the art may apply to an antenna according to the invention many modifications and variations, all of which, however, are included within the scope of protection of the invention as defined by the following claims.

Claims

1. Antenna (1) comprising: a first (2) and a second (3) reflector in metal material spaced from and facing each other and a region (4a, 4b, 4c) of dielectric material lying between said reflectors, the first and the second reflector and said region forming a radial waveguide for propagating between said reflectors an electromagnetic signal transmitted or received by said antenna, characterized in that, the antenna (1) further includes an array of reflecting elements (21, 61) which can be activated according to different configurations in the region of dielectric material (4a, 4b, 4c) so as to vary and control the radiation characteristics of the antenna (1).

2. Antenna (1) according to claim 1, wherein the array of reflecting elements (21, 61) includes reflecting elements arranged along two concentric circumferences

(Cl, C2) .

3. Antenna (1) according to claim 2, wherein the reflecting elements (21, 61) arranged along one of said circumferences (Cl) are staggered with respect to the reflecting elements (21, 61) arranged along the other (C2) of said circumferences.

4. Antenna (1) according to claims 2 or 3, wherein said configurations are characterized in that the active reflecting elements (21, 61) are arranged consecutively along one of said circumferences in such a way as to form arcs of active reflecting elements (21, 61).

5. Antenna (1) according to any of the claims from 2 to 4, wherein said configurations are formed by a first and a second arc of active reflecting elements (21, 61) arranged respectively on one (Cl) and on the other (C2) of said circumferences, the first and the second arc being substantially centered with each other.

6. Antenna (1) according to any of the previous claims, wherein each of said reflecting elements (21, 61) is substantially cylinder-shaped.

7. Antenna (1) according to any of the previous claims, wherein the antenna (1) has a cylindrical symmetry around an axis Z and wherein said reflectors (2, 3) are essentially disc-shaped and concave.

8. Antenna (1) according to claim 7, wherein each of said reflectors (2, 3) includes a disc-shaped and flat central portion (10, 11), and a peripheral annular portion (12, 13) connected to the flat portion (10, 11) and at an angle to it.

9. Antenna (1) according to claims 7 or 8, wherein each of said reflectors (2, 3) includes an external circular edge (14, 15) with a rounded profile or a substantially circular cross section.

10. Antenna (1) according to claim 1, further comprising an input/output coaxial waveguide (5) perpendicular to said radial guide and connected to the centre of it.

11. Antenna (1) according to claim 10, wherein the coaxial waveguide (5) includes a coating (6) connected to the first reflector (2) and a core (8) connected to the second reflector (3) .

12. Antenna (1) according to claim 11, wherein the first reflector (2) includes a central opening (9) and wherein the coating (6) is connected to said opening (9) by means of a tapered funnel, or horn, ending (7), said core (6) passing through said opening (9) to be connected to the second reflector (3) and having a tapered ending (19) with a tapered profile which changes near said opening ( 9) .

13. Antenna (1) according to any of the previous claims, wherein said reflecting elements are metal elements (21), each of which can be operated to be moved axially between:

- a forward active position wherein said element (21) occupies said region of dielectric material; and

- a backward position where said element is placed outside said region.

14. Antenna (1) according to claim 13, wherein said metal elements (21) are pistons of corresponding electromagnetic motors (30) included in said antenna (1).

15. Antenna (1) according to claim 1, wherein said reflecting elements (21, 61) include plasma nanotubes

(61), containing ionizable gas, placed between said first (2) and said second (3) reflector and which can be activated by ionizing the gas contained in them.

16. Antenna (1) according to claim 15, wherein said gas can be ionized by means of a radiofrequency signal or by means of an optical frequency signal.