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.
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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:
In the Figures, alike elements are indicated by same reference numbers.
With reference to
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
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
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
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
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
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.
This list of references cited by the applicant is for the reader's convenience only. It does not form part of the European patent document. Even though great care has been taken in compiling the references, errors or omissions cannot be excluded and the EPO disclaims all liability in this regard.