EP1842265B1

EP1842265B1 - High efficiency antenna and related manufacturing process

Info

Publication number: EP1842265B1
Application number: EP05823808.0A
Authority: EP
Inventors: Pasquale Russo; Alessandro Rosa; Alfredo Catalani; Annamaria D'ippolito
Original assignee: Space Eng SpA; Space Engineering SpA
Current assignee: Airbus Italia SpA
Priority date: 2004-12-10
Filing date: 2005-11-29
Publication date: 2017-11-01
Anticipated expiration: 2025-11-29
Also published as: EP1842265A1; WO2006061865A1; ES2657869T3; ITRM20040605A1

Description

The present invention concerns a planar 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 planar 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 planar 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 planar antenna benefits in terms of antenna gain from the coherent sum of the contributions due to the individual elements constituting the planar antenna. Such contributions must be coherently added through a Radio Frequency or RF combiner.
The implementing technology of a planar antenna is nowadays essentially based on the microstrips. Although the microstrip approach entails advantages in terms of dimensions, ensuring very small thicknesses, microstrip planar 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 from 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 travelling 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 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 limited 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 travelling 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.
Document US 6246264 discloses a lightweight modular low-level reconfigurable beamformer for array antennas, wherein the BFN is designed by dividing a large array into a discrete number of smaller subarrays of radiating elements.
Document US 6225960 discloses a microwave planar antenna, and the related manufacturing process, including a pair of rectangular section channel pluralities, communicating with cavities of receiving square-section horns, each plurality of channels acting as waveguides for differently polarised microwave signals separated by the specific conformation of the cavities.
Document US 5909191 discloses a multiple beam or phased array antenna and beamforming network integrated into a single package, wherein the antenna element and beamforming network comprises a plurality of radiators and a number of microwave components.
It is therefore an object of the present invention to provide a planar 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 planar antenna as defined in independent claim 1.
Further embodiments of the array planar antenna are defined in the dependent claims 2-13.
It is still specific subject matter of the present invention a process of manufacturing an array planar antenna as defined in independent claim 14.
Further embodiments of the process are defined in the dependent claims 15-19.
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 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, hexagonal, 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 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 constituting 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 planar antennas 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, Q/V, 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

Array planar antenna (1, 1'), comprising a set of at least two reception and/or transmission radiating elements and wave guides (3) arranged within the bulk of the antenna (1, 1'), each one of said radiating elements comprising an aperture (2), characterised in that said at least two reception and/or transmission radiating elements are fed by means of at least one beam forming network or BFN of parallel type, said at least one BFN network being made through said wave guides (3) arranged within the bulk of the antenna (1, 1'), whereby each one of the apertures (2) is an input and/or output horn (4) of a wave guide (3) of the BFN network.
Array 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.
Array 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 apertures (2).
Array antenna according to any one of the preceding claims, characterised in that at least one aperture (2) has square or rectangular or circular or hexagonal or octagonal shape.
Array antenna according to any one of the preceding claims, characterised in that at least one aperture (2) is tapered.
Array antenna according to claim 5, characterised in that said at least one aperture (2) has a truncated pyramid or truncated cone shape.
Array antenna according to any one of the preceding claims, characterised in that it simultaneously receives and/or transmits dual polarization waves.
Array antenna according to any one of the preceding claims, characterised in that the apertures (2) are arranged in a square array, each one of the 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 aperture (2).
Array antenna according to any one of claims 1 to 7, characterised in that each one of the apertures (2) has a truncated square based pyramid shape and is fed by an output (4) of a corresponding square wave 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 aperture (2), the set of the apertures (2) being arranged in an array having a rhombus-like configuration, wherein the number of apertures (2) in the vertical columns of the array decreases from the centre of the antenna towards the sides of it.
Array antenna according to any one of the preceding claims, characterised in that it further comprises micro wave active components.
Array 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 Q/V band and/or in W band.
Array antenna according to any one of the preceding claims, characterised in that it is made in metallic material.
Array 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 apertures (2) being metallised.
Process of manufacturing an array planar 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 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.
Process according to claim 14, characterised in that the array antenna to manufacture is an array 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.
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.
Process according to claim 14, characterised in that the array antenna to manufacture is an array 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 apertures (2).
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.
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.