EP0360692A1 - Composite duplex antenna with circular polarisation - Google Patents

Abstract

The invention relates to a composite duplex antenna with circular polarisation. It comprises at least one pair of radiators (7,8) with orthogonal linear polarisation and powered with a 90 DEG phase shift; in each pair, each radiator operates at two different frequencies (F1, F2) having mutually orthogonal polarisations. The invention applies in particular to antennas used in space technology. <IMAGE>

Description

The present invention relates to composite antennas operating in simultaneous transmission and reception on two frequencies. To separate the receiver channel from the transmitter channel whose power is significantly higher, a diplexer is generally used. It is necessary to provide a duplexer for each active element of the antenna so that the number of duplexers is equal to the number of active elements.

The duplexers generally have a volume and a weight greater than that of the radiator element; therefore, the use of duplexers leads to a significant increase in weight and size, which is particularly troublesome in the case of space applications. This is why it is desirable to reduce the weight and the bulk of the duplexer or even to remove it.

One solution is to use opposite polarizations for transmission and reception, the polarizer achieving the necessary separation; however, this solution is generally not acceptable at the complex system level.

Another solution, which is described in the article by T SHIOKAWA et al in the journal IECE of Japan, technical report, AP 86-60, proposes the use of duplexing radiators to obtain operation in circular polarization. The radiators which are proposed in this document provide 20 to 30 dB isolation between transmission and reception and it is currently necessary to provide band pass filters to complete the desired separation.

In the two cases which have just been described, the radiators are composed of two elementary radiators, one operating in transmission, and the other operating in reception, which are mounted in a clever configuration in order to occupy the same surface. In a first embodiment, the radiator consists of a dual duplex patch (PATCH) consisting of two plates of dielectric material provided with metallic coatings. Frequency selectivity is used between the top pad and the bottom pad; this solution is interesting but it complicates the structure of the radiator and consequently increases, the weight and the bulk.

Impedance, cross-polarization performance and configuration are affected by the asymmetry of the power system. In addition to this, it is necessary to strongly review the design to achieve the double assembly of the pellets and their duplexing.

Another solution is described in French Patent ^No. 84 14189 of 17 September 1984 (Published under ^No. 2570546) of the applicant; it is a helical multi-wire antenna, made up of independent radiation strands, helically wound around the same core, said strands being angularly offset in a regular manner with respect to each other, at least two radiation strands of said antenna being each connected continuously to a separate transmitting or receiving device.

The latter solution is not frequency selective and results in loss of gain.

The present invention relates to an antenna of the aforementioned type which makes it possible to avoid the problems which have just been exposed as well as to eliminate the duplexers. In addition, the invention proposes to deal with the problems of the products. passive intermodulation, which can be a decisive factor in avoiding the use of two separate sets of antennas for transmission and reception.

The invention also makes it possible to eliminate the crossed axial polarization and to produce symmetrical radiation configurations.

The subject of the invention is a composite duplex antenna of the circular polarization type. It is notably remarkable in that it comprises at least one pair of radiators with orthogonal linear polarizations (vertical and horizontal), the two radiators of the same pair being supplied with a relative phase shift of 90 °, and in that, in each pair of radiators, each radiator receives and / or emits signals at two different frequencies having orthogonal polarizations between them, a radiator working at a first frequency (F₁) in vertical polarization and a second frequency (F₂) in horizontal polarization, and the other radiator working at the first frequency (F₁) in horizontal polarization and at the second frequency (F₂) in vertical polarization.

The use of radiators with circular polarization allows the simultaneous transmission and reception of two circularly polarized signals having the same polarization mode at different frequencies, and this without mutual interference.

According to one embodiment, one of the frequencies is assigned to reception and the other frequency is assigned to transmission. According to another embodiment of the invention, the antenna works either in transmission or in reception on the two frequencies.

According to one embodiment of the invention, the composite antenna comprises two pairs of radiators.

According to another characteristic of the invention, feed power distributors are used, constituted by 3 dB hybrid couplers; this makes it possible to obtain two circular polarizations per frequency.

Advantageously, uncompensated power distributors are used in the edge area of the array antenna.

According to a practical embodiment of the invention, the radiators are constituted by pads in printed circuit in the form of a microstrip, and the supply lines are located in the same plane as the radiators; advantageously, the supply lines are printed on the same substrate as the pellets.

Finally, it can also be provided that the supply lines of each frequency are located at different levels, which limits the possibility of possible intermodulation coupling from one band to the other.

• - la figure 1 représente un couple de radiateurs fournissant une polarisation circulaire,
• - la figure 2 représente deux couples de radiateurs disposés et alimentés pour fournir une polarisation circulaire,
• - la figure 3 est un schéma plus détaillé de l'antenne de la figure 1, et
• - la figure 4 est un schéma plus détaillé de l'antenne de la figure 2.

Other characteristics and advantages of the invention will emerge from the description which follows, with reference to the attached drawings in which:

• FIG. 1 represents a pair of radiators providing circular polarization,
• FIG. 2 represents two pairs of radiators arranged and supplied to provide circular polarization,
• FIG. 3 is a more detailed diagram of the antenna of FIG. 1, and
• - Figure 4 is a more detailed diagram of the antenna of Figure 2.

The present invention is based on the use of composite antennas or array antennas which comprise at least a pair of radiator elements with orthogonal linear polarizations, these two radiators being arranged relative to each other and supplied in a manner performing circular polarization; the supply of the two torque radiators being made simply under a mutual phase shift of 90 °, it is possible to work in simultaneous transmission and reception without having to use duplexers.

The possibility of obtaining circular polarization using linear polarized radiator elements was described in the article JOHN HUANG "A Technique for an array to Generate Circular Polarization with Linearly Polarized Elements" published in the journal "IEEE Transactions and propagation "volume AP-34, ^No. 9, Sept. 1986. figures 1 to 4 illustrate such antennas with circular polarizations.

FIG. 1 represents a first array antenna comprising a single pair of radiating elements whose polarization modes are coplanar and orthogonal. These two elements, which can be constituted by pads in printed circuit 1 and 2, of rectangular shape, are arranged perpendicular to each other and supplied with a phase shift of 90 °, a first element 1 being supplied without phase shift and a second element 2 being supplied with a phase shift of 90 °.

In Figure 2, there is shown a set of two pairs of elements with orthogonal polarization radiators; the elements or pads 5 and 6 with vertical polarization are combined with pads 3 and 4 with horizontal polarization. The excitation of the horizontally polarized elements 3 and 4 presents a 90 ° phase shift relative to the excitation of the vertically polarized elements 5 and 6. One can obtain a right or left circular polarization depending on the orientation and the phase of the excitation.

The invention proposes to use this type of power supply generating circular polarization with a selection of the frequencies of the two radiator elements of the same couple. FIG. 3 schematically represents the feed circuit of such an antenna constituted by a single pair of two elements 7 and 8 with orthogonal linear polarizations. Each radiator element of the couple shown receives and / or emits two frequencies F₁ and F₂ according to orthogonal linear excitation modes; thus, the radiator element 7 is supplied at a frequency F₁ for which it radiates in vertical linear polarization and at a frequency F₂ for which it radiates in horizontal linear polarization. The second radiator element of the torque 8 is supplied in reverse, that is to say it receives or transmits the frequency F₁ and radiates in horizontal linear polarization and the frequency frequency F₂ by radiating in vertical linear polarization. In other words, each radiator element supports two orthogonal linear polarization modes at two different frequencies.

The phase shift of the power supply for each frequency is achieved by means of dividers or distributors such as hybrid power distributors at 3 dB D₁ and D₂; it is also possible to use other power distributors or dividers such as T-dividers with different supply line lengths, to create the phase shift.

The supply of the pads 7 and 8 at the frequencies F₁ and F₂ is such that the assembly of the two pads creates a left circular polarization or right according to the frequency distribution on each of the pads.

It is necessary that the radiating elements of each pair are adapted in impedance on the two frequencies in their two orthogonal directions, so as to avoid a reduction in gain. The resonant frequencies are determined by an appropriate choice of the dimensions L1 and L2 of the patch constituting the radiator element.

To produce the linearly polarized radiator elements, all types of suitable radiators can be used, such as printed crossed dipoles, slots, horn radiators, etc., in place of the microstrip pads shown in the figures.

It is also possible, in the case of pastilles, to use pastilles printed with two layers. In this case, the space between the elements is tighter than with pellets with double excitation in circular polarization for which, there is more mutual coupling.

The supply networks can be in the same plane as the elements; they are printed on the same substrate in the case of elements produced in the form of printed circuits. One can also provide, still in the context of flat elements, that the different supply lines are at different levels. In particular, it is possible to arrange the supply networks corresponding to the two frequencies on two separate levels, which limits the possibilities of coupling of any intermodulation or the erratic signals from one band to the other.

The antenna shown in Figure 3, which has a single pair of elements, can be used either in simultaneous transmission-reception, a frequency being reserved for transmission and a frequency for reception, either for transmission or reception on both frequencies.

In the case of a composite antenna comprising a single pair of radiating elements, that is to say in the case of FIG. 3, the radiation in the line of sight can be polarized in a perfectly circular manner but the radiation patterns will not be symmetrical.

It is also possible to use a network antenna comprising two pairs of radiator elements as shown in FIG. 4. In this case, the radiation configurations will be symmetrical due to the symmetry of the configuration itself and such an antenna with two couples d 'elements is therefore preferable.

If the distribution of the power is carried out by means of T-dividers, it will only be possible to have a frequency by circular polarization; on the other hand, if 3 dB hybrid couplers are used, it will be possible to generate two circular polarizations per frequency if this proves necessary.

The embodiment shown in FIG. 4 makes it possible to obtain all the supply lines on the same level; they can be produced in the form of printed circuits at the same time as the radiator elements; they can also be produced in the form of microstrips (microstrip), in the form of lines (stripline) or in the form of rectangular axes (squareaxe) fixed below the base plane.

It can be seen that the invention makes it possible to produce an antenna which is very simple compared to the complex duplexing antennas of the prior art. Furthermore, the feeding method is compatible with any type of double linear polarized radiator.

One of the reasons for the simplicity of the antenna according to the invention is that there is no need to modify the design of the radiator element.

Optimizing the performance of the radiator, particularly with regard to cross-polarization and reduction of mutual coupling, also improves the configuration symmetry of the radiation.

The passive intermodulation products generated in the transmitter circuit are isolated from the receiver channel, which is not the case with conventional network antennas in which the transmit and receive channels use the same supply network upstream of the duplexer . This must be a decisive factor to avoid having to use two separate array antennas for transceiver operation.

The method of supplying a duplexing network according to the invention includes networks of the F band and allows the application to networks and sources of data relay satellites, the active ARAMIS network, LOCSTAR radiators etc ... (European Data Relay Satellite).

The above description has been provided by way of non-limiting example only and it is obvious that modifications or variants can be made without departing from the scope of the present invention.

In particular, the invention applies to array antennas comprising any number of pairs of linearly polarized radiator elements provided that their orientation and their phase shift are appropriate. Furthermore, as indicated above, the invention applies to any type of radiator elements linearly or even elliptically polarized.

Uncompensated distribution may be necessary using a T-divider or hybrid dividers, particularly in the edge region of a network in which the conditions of mutual coupling would not be symmetrical and could induce polarization crossed with a balanced system.

Claims (9)

1) Composite antenna with circular polarization duplexing, characterized in that it comprises at least one pair of radiators (1,2; 3,5; 4,6; 7,8) with orthogonal linear polarizations (vertical and horizontal), the two radiators of the same couple being supplied with a relative phase shift of 90 °, and in that in each pair of radiators, each radiator receives and / or emits signals at two different frequencies having orthogonal polarizations between them, a radiator working at a first frequency (F₁) in vertical polarization and at a second frequency (F₂) in horizontal polarization, and the other radiator working at the first frequency (F₁) in horizontal polarization and at the second frequency (F₂) in vertical polarization . 2) Composite antenna according to claim 1, characterized in that a frequency is assigned to the transmission and another frequency is assigned to the reception. 3) Composite antenna according to claim 1, characterized in that the antenna works either in transmission or in reception on the two frequencies (F₁ and F₂). 4) Composite antenna according to claim 1, characterized in that it comprises two pairs of radiator elements (3,5; 4,6). 5) Composite antenna according to any one of claims 1 to 4, characterized in that the power supply distributors (D₁, D₂) are 3 dB hybrid couplers. 6) Composite antenna according to any one of claims 1 to 5, characterized in that provision is made for non-compensated power distributors in the edge area of said composite antenna. 7) Composite antenna according to any one of claims 1 to 6, characterized in that the supply lines are arranged in the same plane as the radiator elements. 8) Composite antenna according to claim 7, characterized in that the radiating elements are produced in the form of printed circuits on a substrate and in that the supply lines are also produced in printed circuits on the same substrate. 9) Composite antenna according to any one of claims 1 to 6, characterized in that the supplies of the two frequencies (F₁, F₂) are arranged at different levels.

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