WO2006061865A1 - High efficiency antenna and related manufacturing process - Google Patents

Abstract

The invention concerns an array plane antenna (1, 1’), comprising a set of at least two reception and/or5 transmission radiating elements fed by means of at least one beam forming network or BFN of the parallel type, characterised in that each one of said radiating elements comprises a shaped aperture (2), and in that at least one BFN network is made through wave guides (3) directly obtained from the bulk of the antenna (1, 1’), so that each one of the shaped apertures (2) is an input and/or output horn (4) of a wave guide (3) of the BFN network. The invention further concerns the process of manufacturing such plane antenna.

Description

HIGH EFFICIENCY ANTENNA AND RELATED MANUFACTURING PROCESS

The present invention concerns a plane antenna, in particular employable in fixed and mobile terminals adapted for reception of satellite TV and for multimedia satellite links, that is reliable, simple and efficient, having a wide operation bandwidth, a very limited volumetric dimensions, and being extremely inexpensive with reference to the manufacturing, installation, and maintenance costs. The present invention further concerns the process of manufacturing such plane antenna.

It is known that for reception of satellite TV and multimedia satellite links, for instance belonging to the Internet, reflector antennas are presently normally used. However, reflector antennas suffer from some drawbacks, such as an insufficient aperture efficiency, significant volumetric dimensions, the need of an accurate electric adjustment, and high manufacturing, installation, and maintenance costs.

In order to solve these problems of reflector antennas, radiating element array plane antennas have been developed.

However, even this type of antennas suffers from some drawbacks, substantially due to the fact that this antenna architecture has considerable combination losses of the feeding network or BFN (Beam Forming Network) of the individual radiating elements. In fact, differently from the reflector, a plane antenna benefits in terms of antenna gain from the coherent sum of the contributions due to the individual elements constituting the plane antenna. Such contributions must be coherently added through a Radio Frequency or RF combiner.

The implementing technology of a plane antenna is nowadays essentially based on the microstrips. Although the microstrip approach entails advantages in terms of dimensions, ensuring very small thicknesses, microstrip plane antennas have significant losses due to ohmic dissipation of the same microstrip lines. Some recently developed solutions in planar technology may mitigate this problem but certainly they cannot solve it, especially at high frequencies, particularly starting from 10 GHz, usuallly used in satellite applications.

The ohmic loss associated with the BFN, that grows with the increase of the antenna dimensions, limits the attainment of the antenna gain, at the same time making the same antenna inefficient. This means that the antenna does not fully exploit its size.

Technologies developed in order to obviate the BFN ohmic losses, resulting in the "active antennas", are based on active components. These, suitably arranged within the BFN as close to the radiating element as possible, allows to minimise the contribution of such losses, thus improving the efficiency and hence the gain of the antennas.

The possibility of directly inserting onto the radiating element an active element, such as a Low Noise Amplifier or LNA, a Solid State Power Amplifier or SSPA, or a transmitter/receiver or Tx/Rx module, further allows to control, for instance through the use of phase shifters, the shape and the aim of the antenna radiation pattern.

However, active antennas suffer form the drawback of being particularly complex and, consequently, expensive. Moreover, the use of active elements requires an accurate tracking in amplitude and phase (tuning) of the same, that is hard to achieve and it depends on environmental parameters (for instance temperature), especially with the increase of the operating frequency.

A further antenna type is the slotted array antenna one. These antennas essentially consist in a wave guide provided with suitably designed slots which interrupt the current lines present onto the same guide and which consequently become small radiating elements.

Depending on the desired antenna radiative characteristics, the wave guide structure may terminate with either a resistive termination, and in this case there is a so-called traveling wave antenna, or a simple short circuit termination, and this case there is a resonant antenna.

However, even slot antennas suffer from some drawbacks. First of all, form the configuration point of view, this antenna architecture substantially achieves a linear, not planar, antenna. Hence, in the case when a planar antenna is required, it is necessary to have a set of linear slot antennas provided with a series of combiners which allow the coherent sum of the inputs/outputs of the individual linear antennas. Consequently, the resulting planar antennas are complex, they have significant ohmic losses, and their dimensions are increased by the thickness required by the various components.

Moreover, the simultaneous double polarization, as well as the circular polarization, are obtainable only with difficulty and by considerably 000703

3 increasing the antenna complexity.

Furthermore, the aim of the radiation pattern peak moves with frequency.

Still, in case of a short circuit, or resonant, termination antenna, the operating bandwidth is limitated to few percents, of the order of 3-5%, around the central frequency, and a very high accuracy in manufacturing the slots is also necessary.

Finally, in case of use of a resistive termination, or traveling wave, antenna the efficiency of the individual linear antenna is lower than the theoretical one, since, due to design requirements, for its own operation, the antenna must absolutely dissipate part of its power on the end resistive load.

It is therefore an object of the present invention to provide a plane antenna, in particular employable in high frequency applications, that is reliable, simple, and efficient, and that has a wide operation bandwidth.

It is still an object of the present invention to provide such an antenna that has a radiation pattern peak which is constant over the operation bandwidth, and that is extremely inexpensive with reference to the manufacturing, installation, and maintenance costs.

It is specific subject matter of the present invention an array plane antenna, comprising a set of at least two reception and/or transmission radiating elements fed by means of at least one beam forming network or BFN of parallel type, characterised in that each one of said radiating elements comprises a shaped aperture, and in that said at least one BFN network is made through wave guides directly obtained from the bulk of the antenna, so that each one of the shaped apertures is an input and/or output horn of a wave guide of the BFN network.

Always according to the invention, the antenna may comprise one BFN network for each wave polarization which the antenna is capable of receiving and/or transmitting.

Still according to the invention, the antenna may comprise at least one input and/or output wave guide connection, arranged either sideways and/or onto the surface opposite to that of the shaped apertures. Furthermore according to the invention, at least one shaped aperture may have square or rectangular or circular or exagonal or octagonal shape. Always according to the invention, at least one shaped aperture may be tapered.

Still according to the invention, said at least one shaped aperture may have a truncated pyramid or truncated cone shape. Furthermore according to the invention, the antenna may be capable of simultaneously receiving and/or transmitting dual polarization waves.

Always according to the invention, the shaped apertures may be arranged in a square array, each one of the shaped apertures having truncated square based pyramid shape and being fed by an output of a corresponding square wave guide of said at least one BFN network the cross section of which is tilted by 45 degrees in respect to the square base of the truncated pyramid of the shaped aperture.

Still according to the invention, each one of the shaped apertures may have a truncated square based pyramid shape and may be fed by an output of a corresponding square wave guide of said at least one BFN network the cross section of which corresponds to a square base of the truncated pyramid of the shaped aperture, the set of the shaped apertures being arranged in an array having a substantially rhombus-like configuration, wherein the number of shaped apertures in the vertical columns of the array decreases from the centre of the antenna towards the sides of it.

Furthermore according to the invention, the antenna may further comprise micro wave active components. Always according to the invention, the antenna may be capable of operating in C band and/or in Ku band and/or in Ka band and/or in Q/V band and/or in W band.

Still according to the invention, the antenna may be made in metallic material and/or in plastic material, the surfaces of the wave guides and of the shaped apertures being metallised.

It is still specific subject matter of the present invention a process of manufacturing an array plane antenna as previously described, characterised in that it comprises the following steps:

- manufacturing at least two layers, so as to make in each one of said at least two layers at least one respective portion of the wave guides of the BFN network and/or of the shaped apertures;

- integrally coupling said at least two layers, so as to make the 0703

5 respective portions of adjacent layers correspond to each other.

Always according to the invention, the antenna to manufacture is may be made in metallic material, and the step of manufacturing said at least two layers may be a step of mechanical and/or electrical micromachining.

Still according to the invention, the step of integrally coupling said at least two layers may be a step of welding.

Furthermore according to the invention, the antenna to manufacture may be made in plastic material, and the process may further comprise the following step:

- metallising the surfaces of the wave guides and of the shaped apertures

Always according to the invention, the step of manufacturing said at least two layers may be a step of moulding. Still according to the invention, the step of integrally coupling said at least two layers may be a step of welding.

The present invention will now be described, by way of illustration and not by way of limitation, according to its preferred embodiments, by particularly referring to the Figures of the enclosed drawings, in which:

Figure 1 shows a perspective view of a first embodiment of the antenna according to the invention, exploded into the forming layers; Figure 2 shows a particular of the antenna of Figure 1 ; Figure 3 shows a perspective view of a first section of the antenna of Figure 1 ;

Figure 4 shows a perspective view of a second section of the antenna of Figure 1 ;

Figures 5a and 5b respectively show an arrangement of the antenna of Figure 1 and the related amplitude distribution over the aperture in the horizontal plane; and

Figure 6 show a second embodiment of the antenna according to the invention.

In the Figures, alike elements are indicated by same reference numbers. With reference to Figures 1-4, it may be observed that the preferred embodiment of the array antenna 1 according to the invention comprises a set of shaped apertures 2 tapered as a truncated square 0703

6 based pyramid, each one of which constitutes an array radiating element. However, it should be understood that the square shape of the shaped apertures 2 of the antenna of Figures 1-4 is shown by way of example and not by way of limitation, other embodiments being able to adopt different shapes of the base of the truncated pyramid of the apertures 2, such as for instance rectangular, circular, exagonal, octagonal shapes, depending on the electromagnetic characteristics which are desired to obtain for the specific applications of the antenna. Similarly, the truncated pyramid shape of the apertures 2 is shown by way of example and not by way of limitation.

The apertures 2 are fed by means of a BFN network of parallel type for a fine control of the characteristics of the antenna 1 in terms of operative bandwidth, gain, minimum movement of the beam within the band, purity of polarization. The BFN network is based on the use of wave guides 3 directly obtained from the bulk of the antenna 1 , underneath the radiating elements 2 of the antenna 1. In particular, it may be observed that outputs 4 of the square wave guides of the BFN network are arranged with the cross section tilted by 45 degrees in respect to the bases of the truncated pyramid of the apertures 2. The antenna also comprises a wave guide input (or an output) (not shown), having square section, that is preferably arranged either sideways to the antenna 1 or backwards, onto the surface opposite to that of the radiating apertures 2.

Obviously, the size and the shape of the wave guides 3, as well as the BFN network configuration, depends on the electromagnetic characteristics which are desired to obtain for the specific applications of the antenna, such as for instance on the frequency band wherein the antenna is used.

As shown in Figures 1-4 (and more in particular in Figures 1 and 2), the antenna 1 comprises a lower layer 5, an intermediate layer 6, and an upper layer 7 (that corresponds to the radiating elements 2), each one of which is obtained from the machining of the material(s) used for manufacturing the antenna 1. Such machining of the three layers 5, 6, and 7 makes a portion of the wave guides 3 of the BFN network. At the end of the machining, the three layers 5, 6, and 7 are integrally coupled to each other so as to make the respective portions of the BFN network wave guides 3 and the apertures 2 correspond to each other (by way of example and not by way of limitation, through the aid of shaped pins of a layer 3

7 which insert into corresponding notches of the adjacent layer).

In particular, the material may be either metallic or low-cost material, such as for instance plastic that is subsequently metallised.

In the case when the used material is metallic, the machining of each one of the three layers is a micromachining, for instance a mechanical and/or electrical one, and the integral coupling of the three layers 5, 6, and 7 may be obtained through standard techniques (by way of example and not by way of limitation, through laser welding).

In the case when the used material is plastic, the machining of each one of the three layers may be simply a moulding, and the integral coupling of the three layers 5, 6, and 7 may be obtained through standard techniques (by way of example and not by way of limitation, through welding). In particular, after the machining of the plastic layers, and either before or after the integral coupling, the surfaces of the wave guides 3 and horns constituiting the shaped apertures 2 are metallised.

The antenna 1 of Figures 1-4 comprises apertures 2 and two BFN networks capable to operate with two orthogonal polarizations, linear and/or circular ones. The antenna of Figure 1 thus allows to obtain 2 largely insulated simultaneous polarizations. Other embodiments of the antenna according to the invention may comprise radiating apertures and one single BFN network capable to provide a single polarization.

The characteristics of the two operating polarizations, corresponding to two separated inputs (or outputs) of the antenna 1 , are very similar over the whole operating band.

In particular, the antenna according to the invention may be used both in passive configuration, (such as that shown in Figures 1-4) since it is characterised by extremely reduced ohmic losses of the BFN network, and in "active antenna" configuration, i.e. provided (always within the antenna body) with a LNA amplifier and/or a SSPA amplifier and/or a Tx/Rx module and/or a phase shifter.

The different embodiments of the antenna according to the invention may comprise a number of machined layers different from three, depending on the complexity of the BFN network that is to be made, and on the possible active components of an "active antenna" configuration.

The advantage offered by the antenna according to the present invention in respect to the presently available reflector antennas and plane antennas piatte and slot antennas are considerable.

First of all, it has a percentage operating frequency bandwidth at least up to 50%.

Moreover, the antenna according to the invention may operate with any type of polarization, for instance single linear, dual linear, single circular, dual circular, with a separation of the orthogonal components better than 30 dB. The circular polarization may be obtained either at BFN network level, or through the insertion of suitable dielectric "slabs" into the radiating apertures, or through the use of an external polariser. Furthermore, the antenna according to the invention has an aperture efficiency substantially equal to the theoretical value, with a whole antenna efficiency better than 85%.

Still, the technology of the antenna, based on the wave guides, causes it to be preferably used at high frequencies, up to the order of 100 GHz.

Still, ease of manufacturing and possibility of making the antenna according to the invention even in low-cost material, such as for instance metallised plastic, make it particularly attractive for mass productions. The antenna according to the invention may be used in great many applications, as for instance: TV satellite reception in Ku band; multimedia satellite link in Ku band; multimedia satellite link in Ka band; high definition TV satellite reception in Ka band; connection between radio links from Ku band upwards; use as mobile terminal on transport means, such as trains, cars, airplanes, and shifts, in C, Ka, Ku, QA/, and W bands; use as fixed terminal; and use for terrestrial remote sensing applications (repeater/calibrator) in C band and in X band.

In particular, for most of the aforementioned applications, the antenna according to the invention may need a spatial discrimination among contiguous satellites.

As shown in Figure 5a, this is easily obtainable by positioning the antenna 1 at 45 degrees (in case of square antenna as that of Figures 1-4) and exploiting the natural taper of amplitude illumination (amplitude taper) towards the edge of the same antenna 1 in the horizontal plane, resulting in very low side lobes of the radiation pattern. In other words, this shape of amplitude distribution corresponds to an antenna far field radiation pattern characterised by extremely low side lobes, capable of discriminating the reception of the desired signal from that of interfering signals coming from other satellites located close to that of interest. In particular, the antenna 1 of Figures 1-4 provides for linear polarizations which are parallel (horizontal) and perpendicular (vertical) in respect to the aforesaid horizontal plane (that is the reason because the output square wave guide horns 4 of the BFN network are placed with the cross section tilted by 45 degrees in respect to the bases of the truncated pyramid of the apertures 2).

Another manner for obtaining an amplitude taper capable of providing for a spatial discrimination, slightly more complex in terms of layout of the BFN network, is the one shown in Figure 6, wherein an antenna 1' according to the invention comprises a set of square radiating apertures 2 arranged in an array having a substantially rhombus-like configuration, wherein the number of radiating apertures 2 in the vertical columns decreases from the centre of the antenna towards the sides of it.

The preferred embodiments have been above described and some modifications of this invention have been suggested, but it should be understood that those skilled in the art can make other variations and changes, without so departing from the related scope of protection, as defined by the following claims.

Claims

1. Array plane antenna (1, 1'), comprising a set of at least two reception and/or transmission radiating elements fed by means of at least one beam forming network or BFN of parallel type, characterised in that each one of said radiating elements comprises a shaped aperture (2), and in that said at least one BFN network is made through wave guides (3) directly obtained from the bulk of the antenna (1 , 1'), so that each one of the shaped apertures (2) is an input and/or output horn (4) of a wave guide (3) of the BFN network.

2. Antenna according to claim 1 , characterised in that it comprises one BFN network for each wave polarization which the antenna is capable of receiving and/or transmitting.

3. Antenna according to claim 1 or 2, characterised in that it comprises at least one input and/or output wave guide connection, arranged either sideways and/or onto the surface opposite to that of the shaped apertures (2).

4. Antenna according to any one of the preceding claims, characterised in that at least one shaped aperture (2) has square or rectangular or circular or exagonal or octagonal shape.

5. Antenna according to any one of the preceding claims, characterised in that che at least one shaped aperture (2) is tapered.

6. Antenna according to claim 5, characterised in that said at least one shaped aperture (2) has a truncated pyramid or truncated cone shape

7. Antenna according to any one of the preceding claims characterised in that it is capable of simultaneously receiving and/or transmitting dual polarization waves.

8. Antenna according to any one of the preceding claims characterised in that the shaped apertures (2) are arranged in a square array, each one of the shaped apertures (2) having truncated square based pyramid shape and being fed by an output (4) of a corresponding square wave guide (3) of said at least one BFN network the cross section of which is tilted by 45 degrees in respect to the square base of the truncated pyramid of the shaped aperture (2).

9. Antenna according to any one of claims 1 to 7, characterised in that each one of the shaped apertures (2) has a truncated square based pyramid shape and is fed by an output (4) of a corresponding square Way© guide (3) of said at least one BFN network the cross section of which corresponds to a square base of the truncated pyramid of the shaped aperture (2), the set of the shaped apertures (2) being arranged in an array having a substantially rhombus-like configuration, wherein the number of shaped apertures (2) in the vertical columns of the array decreases from the centre of the antenna towards the sides of it.

10. Antenna according to any one of the preceding claims, characterised in that it further comprises micro wave active components.

11. Antenna according to any one of the preceding claims, characterised in that it is capable of operating in C band and/or in Ku band and/or in Ka band and/or in QA/ band and/or in W band.

12. Antenna according to any one of the preceding claims, characterised in that it is made in metallic material.

13. Antenna according to any one of claims 1 to 11 , characterised in that it is made in plastic material, the surfaces of the wave guides (3) and of the shaped apertures (2) being metallised.

14. Process of manufacturing an array plane antenna (1 , 1') according to any one of the preceding claims 1-13, characterised in that it comprises the following steps: - manufacturing at least two layers (5, 6, 7), so as to make in each one of said at least two layers (5, 6, 7) at least one respective portion of the wave guides (3) of the BFN network and/or of the shaped apertures

(2);

- integrally coupling said at least two layers (5, 6, 7), so as to make the respective portions of adjacent layers correspond to each other.

15. Process according to claim 14, characterised in that the antenna to manufacture is an antenna according to claim 12, and in that the step of manufacturing said at least two layers (5, 6, 7) is a step of mechanical and/or electrical micromachining.

16. Process according to claim 15, characterised in that the step of integrally coupling said at least two layers (5, 6, 7) is a step of welding.

17. Process according to claim 14, characterised in that the antenna to manufacture is an antenna according to claim 13, and in that it further comprises the following step:

- metallising the surfaces of the wave guides (3) and of the shaped apertures (2).

18. Process according to claim 17, characterised in that the step of manufacturing said at least two layers (5, 6, 7) is a step of moulding.

19. Process according to claim 17 or 18, characterised in that the step of integrally coupling said at least two layers (5, 6, 7) is a step of welding.