EP0557176A1 - Feeding device for a plate antenna with two crossed polarizations and array equipped with such a device - Google Patents

Abstract

The invention relates to a feed device intended for an array of plate antennas with dual crossed polarisation and to an array employing such a device. The plate antennas (S) are fed via two completely separate lines. A first transmission line, of the three-plate type, consists of a track (T) and two earth planes (M, CP). A second line, of the microstrip type, comprises a track (R) and an earth plane (M). The unit is produced by metallising three printed circuits (CI1 to CI3); there are several variant embodiments. Application to the feeding of satellite receiving antennas having dual crossed polarisation. <IMAGE>

Description

The present invention relates to plate antennas, and more particularly relates to a supply device, or "distributor", intended for a network of plate antennas with double cross polarization, advantageously produced in printed circuits. The double feed device according to the invention is specially designed to be integrated into a network which may include several hundred plate antennas.

In the known art, several solutions have been proposed for the design and supply of such antennas.

As an example, one solution consisted in providing that one of the distributors, in a tree, could be on the printed circuit carrying the radiating sources and the other on another printed circuit with as many passages as radiating sources. (or group of radiating sources constituting for example resonant subnets). This solution in triplate embodiment for the two distributors and tested in the Ku band, is difficult to implement when several hundred sources are envisaged. In addition, it uses four juxtaposed printed circuits. Such a configuration is described in the article by G. DUBOST: "Dual Polarized Microstrip Arrays in S, C, X and Ku Bands", PIERS 1991, July 1.5, Cambridge, Massachussets (USA).

Other solutions have been proposed, but they do not provide sufficient decoupling required for certain applications.

The invention aims to overcome the shortcomings of the known art.

To do this, it offers a supply device comprising two completely independent transmission lines: a first transmission line of the triplate type and a second transmission line of the microstrip type.

It thus provides a very significant decoupling between the two channels corresponding to the two crossed polarizations.

The subject of the invention is therefore a device for feeding at least one plate antenna with double crossed polarization, characterized in that it comprises, for each source, a first line of triplate type comprising a first ground plane, a second ground plane and an elongate track parallel to a first direction and disposed between the first and second ground plan; a second microstrip type line comprising the first ground plane and an elongated track of direction perpendicular to the first direction, and in that the tracks, the first and second ground planes are arranged in four distinct planes which are parallel to each other .

The subject of the invention is also a network of double polarized plate antennas fitted with such a device.

• la figure 1 illustre un dispositif d'alimentation pour antenne plaque à double polarisation croisée selon l'invention ;
• les figures 2 et 3 illustrent un sous-réseau d'antennes plaques incorporant le dispositif selon l'invention.

The invention will be better understood and other characteristics and advantages will appear from the following description and the appended figures, among which:

• FIG. 1 illustrates a feed device for a plate antenna with double crossed polarization according to the invention;
• Figures 2 and 3 illustrate a sub-array of plate antennas incorporating the device according to the invention.

FIG. 1 illustrates a supply device for plate antennas with double crossed polarization according to the invention.

More specifically, the bottom of Figure 1 illustrates the antenna and its feeder seen from above, by convention. The top of the figure illustrates these same elements in section CC ′, that is to say in a direction parallel to one of the supply lines R which will be described later.

The source used S is a plate antenna, with double crossed polarization. This source, in a preferred embodiment of the invention, is in accordance with the main lessons of the European patent application published under the number EP-A- 0 243 289, on October 28, 1987. Reference may be made, as a non-limiting example, to the alternative embodiment shown in Figures 1 and 2 of this application. It will however be seen that the antenna is powered according to the invention only more by two triplate lines, contrary to the arrangements made in the aforementioned European patent application.

The main characteristics of the plate antenna that can be used in the context of the invention will now be recalled.

The source S consists of two doublets plates, folded and interlaced, metallized on the same face of a printed circuit. To allow its use in a very large number of copies in a network, it is decoupled from the metallic plane M common to all the sources using four non-conductive windows F₁ to F₄.

The main characteristic of the invention consists in supplying such a dual-polarization source using two completely independent transmission lines. Three juxtaposed printed circuits CI₁, CI₂ and CI₃ are necessary. These printed circuits can naturally consist of successive layers of a multilayer printed circuit.

One of the transmission lines, of the triplate type, has a T track and two ground planes M and CP. The other, of the microstrip type, comprises a track R and again the ground plane M. The length of the two lines open at their ends is close to the quarter-wave. These lengths are noted l₁ and l₂ in FIG. 1. Insofar as the thickness of the metal plane M is large compared to the thickness of the skin (for example a thickness of printed circuit of 17.5 μm), the coupling between the two transmission lines is very weak.

The windows F₁ to F₄ are produced, for example, by removing the metallization. They are in the form of a portion of crowns, the common center O being at the point of intersection of the tracks R and T, center of the source S, when we look at the source in projection.

Track widths R and T are noted, respectively, w₁ and w₂. The thicknesses of the printed circuits CI₁ to CI₃ have been noted in FIG. 1: H₁, H₂ and H₃. All these parameters depend on the application envisaged or on technological choices.

Tests were carried out on a device according to the invention. With the values of the parameters characterizing the device as below:
H₁ = H₂ = H₃ = 0.8 mm
ε _r = 2.2 (relative permittivity of the substrate of the printed circuit)
w₁ = 0.68 mm
w₂ = 0.3 mm
l₁ = 4.5 mm
l₂ = 3.55 mm

• a) "rapport d'ondes stationnaires" (R.O.S.) de l'impédance rapportées à 100 Ω :
     R.OS. < 1,5 entre 11,7 et 12,1 GHz (R.O.S. moyen inférieur à 1,2)
• b) le découplage entre les deux accès de la source reste inférieur à -30dB de 11,85 à 12,2 GHz.

The following radio characteristics have been measured in the frequency band used for reception of the "DBS"("Direct Broadcasting Satellite")

• a) "standing wave ratio" (ROS) of the impedance reported at 100 Ω:
  R.OS. <1.5 between 11.7 and 12.1 GHz (average ROS less than 1.2)
• b) the decoupling between the two source ports remains below -30dB from 11.85 to 12.2 GHz.

The input impedances have been adapted using quarter-wave transformers. These were carried out either in a three-ply line for the three-ply transmission line, or in a microstrip line for the microstrip transmission line. They will be illustrated later with reference to Figures 2 and 3.

We see that the main object of the invention, that is to say to obtain a very significant decoupling between crossed polarizations is well achieved.

The production of a device according to the invention as described above is susceptible of several variants of practical embodiments.

Table I, placed at the end of this description, shows four solutions, denoted A, B, C and D, for metallizing the elements R, M, T and CP. The choice is made according to data functions essentially of a technological nature, in particular the tolerances for metallization of the printed circuits and the precision necessary to ensure a good mechanical position for the coincidence of the three juxtaposed printed circuits. In this table, it is indicated on which printed circuit and on which face of this circuit is made such a metallization element. By convention, the faces denoted "face 1" are the upper faces (FIG. 1) and "face 2", the lower faces.

By way of example, if we consider the variant denoted A, the metallization of R is carried out on the "face 1" of the printed circuit CI₁, the metallization T on the "face 2" of CI₂, the metallization of M on the "face 2" of CI₁ and the metallization of CP on the "face 2" of CI₃.

In addition, for the variant denoted D, the circuit CI₂ is simply constituted by a dielectric sheet. It should be noted that the metallization CP, on the printed circuit CI₃, can be replaced by a metal plate if one wishes a rigidity of the assembly more important. In this case, and only for solutions A and B, the printed circuit CI₃ can be replaced by a simple metal sheet and a dielectric sheet between this metal sheet and the printed circuit CI₂.

A network using devices conforming to the invention will now be described with reference to FIGS. 2 and 3. In reality, these figures show two resonant sub-networks of ten radiating sources each. More particularly, these subnetworks were produced according to variant denoted B in Table I.

More particularly, FIG. 2 corresponds to the supply by triplate lines of each resonant sub-network whose directivity is maximum in the "plane E" or electrical polarization. FIG. 3 corresponds, for its part, to the supply by microstrip lines of each resonant sub-network whose directivity is maximum in the "H plane" or magnetic polarization.

In these two figures, two bands of ten sources are shown, each distributed parallel to an axis Δ. These sources have been labeled S₁₀₀ to S₁₀₉ and S₂₀₀ to S₂₀₉. Only the source S₂₀₄, in the central zone of the sources S₂₀₀ to S₂₀₉, has been detailed by way of a more complete illustration of the invention.

In FIG. 2, the sub-network shown is supplied by two primary lines notably comprising the tracks T₁₀ and T₂₀. These lines supply in turn, in a central area, two secondary lines T₁₀₀ and T₂₀₀ which also branch into individual supply lines from the sources. The primary supply lines T₁₀ and T₂₀ as well as the secondary lines T₁₀₀ and T₂₀₀ extend parallel to the axis Δ between two source bands. Individual lines, such as the line T₂₀₄, are first of all perpendicular to Δ, between two contiguous sources then again parallel to Δ to cross the ribbon lines (Figure 3). The line T₂₀₄ constitutes an example for the source S₂₀₄.

FIG. 2 also shows adaptation transformers between the primary and secondary lines: transformers Tr₁₀ and Tr₂₀; and between the secondary lines and the individual supply lines, for example the transformer Tr₂₀₄. They are produced in the same way as the lines themselves, that is to say in triplate technology for the part of the sub-network of FIG. 2. The role of these transformers has been specified previously in relation to the description of figure 1.

relation dans laquelle λ₀ est la longueur d'onde dans l'air et ε_r la permittivité relative du substrat du circuit imprimé.The centers of two contiguous sources are distant by a distance d. This width is given by the relation

relation in which λ₀ is the wavelength in air and ε _r the relative permittivity of the substrate of the printed circuit.

This configuration of tree distributors makes it possible to supply all the sources in phase, on the one hand, and on the other hand, makes it possible to obtain a balanced network due to the symmetry in the supply of the sources of the same subnet.

Since solution B has been described more particularly, presented in table I placed at the end of this description, the lines T₁₀, T₂₀, T₁₀₀, T₂₀₀ and the individual supply lines such as the line T₂₀₄ are produced by metallization of the "face 2" of the printed circuit CI₂ (Figure 1). The ground plane M is produced by metallization of the "face 1" of this printed circuit and the ground plane CP, known as a metal counterweight, is produced by metallization of the "face 2" of the circuit CI₃.

Figure 3 corresponds to the supply by microstrip lines. The same resonant subnetwork has been represented comprising two bands of ten sources S₁₀₀ to S₂₀₉ distributed regularly parallel to the axis Δ. The configuration of the microstrip lines is similar to that shown in Figure 2 for the triplate lines. We find primary lines R₁₀ and R₂₀ and secondary R₁₀₀ and R₂₀₀ by bands of ten sources. The junction between these two types of lines is made in the middle of the secondary lines.

It should however be noted that the translation distance, equal to d = 17 mm between adjacent sources of a sub-network, corresponds to 11.9 GHz, the central frequency of the reception frequency band of the DBS satellite (11.7 to 12, 1 GHz), at a phase wavelength in the triplate line. As we saw previously, the distance d is given by the relation $$\text{d =}\frac{\text{λ₀}}{\sqrt{{\text{ε}}_{\text{r}}}}\text{= 0.674 λ₀}$$

For the microstrip line, the phase wavelength is greater and this is the reason why the supply lines R₁₀₀ and R₂₀₀, which must have between two adjacent sources a length greater than 17 mm, are sinuous as shown. in Figure 3.

Finally, for each source, such as the source S₂₀₄, branch off from the lines R₁₀₀ or R₂₀₀, perpendicular to the axis Δ and from the individual supply lines. An example is given by the line R₂₀₄ (source S₂₀₄).

In the same way as for FIG. 2, FIG. 3 shows adaptation transformers T'r₁₀, T'r₂₀ and T'r₂₀₄. They are naturally produced in microstrip type line technology.

This configuration of tree distributors therefore also ensures for this polarization of the sub-network a phase supply of all the sources and makes it possible to obtain a balanced network due to the symmetry of the supply.

Still in the case of solution B, the lines R₁₀, R₂₀, R₁₀₀, R₂₀₀ and the particular supply lines from sources such as the line R₂₀₄ are produced by metallization of the "face 1" of the printed circuit CI₁ (FIG. 1), the ground plane M being produced on the "face 1" of the printed circuit CI₂ as previously indicated.

To fix the ideas, without this being limiting, we have indicated in Figures 2 and 3 some constructive details.

In FIG. 2, in addition to the translation distance d, the distance l separating two source centers has been shown. In the example of the antenna tested, with ε _r = 2.2, l = 0.944 λ₀ (with λ₀ wavelength in a vacuum at the central frequency).

The individual supply lines, such as the line T₂₀₄, have a wider section in the connection area with the secondary lines T₁₀₀ and T₂₀₀. This extends over a length, for example l₂₀₄, given by the relation l₂₀₄ = 0.17 λ₀.

The axes of the two rows of sources are distant by a distance d₂, given by the relation d₂ = 0.944 λ₀.

The distance d is naturally given by the same relationship for Figures 2 and 3. As indicated d = 0.674 λ₀.

In reality, an array of plate antennas generally has more resonant subarrays shown in Figures 2 and 3. A complete array (not shown) will typically have hundreds of plate antennas. It is obtained simply by increasing the number of sub-networks The set will have the configuration of a regular matrix of n sub-networks each comprising p source.

Resonant subnets conforming to those which have just been described in relation to FIGS. 2 and 3 have been produced.

• le rapport d'onde stationnaire (R.O.S.) de l'impédance d'entrée rapportée à 100 ohms reste inférieur à 1,85 entre 11,8 et 12,2 GHz.
• le découplage entre polarisations croisées d'une même colonne (par exemple pour les sources S₁₀₀ à S₁₁₀), c'est-à-dire entre les deux accès du sous-réseau, reste meilleur que -30dB ; les fréquences variant de 11,7 à 12,1 GHz.

The experimental results obtained on these two resonant sub-networks are the following:

• the standing wave ratio (ROS) of the input impedance reported at 100 ohms remains less than 1.85 between 11.8 and 12.2 GHz.
• the decoupling between crossed polarizations of the same column (for example for sources S₁₀₀ to S₁₁₀), that is to say between the two accesses of the sub-network, remains better than -30dB; frequencies ranging from 11.7 to 12.1 GHz.

The main aim of the invention, a very good decoupling between the two crossed polarizations, is therefore well achieved.

A second advantage of the supply devices according to the invention is that the number of tracks of the supply lines located between two adjacent sub-networks is reduced to two. This is important to avoid unwanted couplings between lines, since the radiating source has a diameter close to 0.65 λ₀ (λ₀ being the wavelength of the vacuum at the central frequency) and where the distance between adjacent sub-arrays must remain less than λ₀ to avoid the lobes of the arrays.

The invention is not limited to the supply device described precisely. In particular, sources of the type described in relation to FIG. 1, although specially adapted, can be replaced by other sources of known art insofar as they can be supplied in accordance with the teachings of the invention.

The invention applies more particularly to dual polarization satellite reception antennas, in particular for the reception of the DBS satellite, and more generally to the reception of television broadcasts.

Claims (12)

Device for feeding at least one plate antenna (S) with double crossed polarization, characterized in that it comprises, for each source (S), a first line of triplate type comprising a first ground plane (M), a second ground plane (CP) and an elongate track (T) parallel to a first direction and arranged between the first and the second ground plane; a second microstrip type line comprising the first ground plane (M) and an elongated track (R) of direction perpendicular to the first direction, and in that the tracks (T, R), the first (M) and second (CP) ground planes are arranged in four distinct planes which are parallel to each other. Device according to Claim 1, characterized in that the track (T) of the triplate type line and the track (R) of the microstrip type line intersect in a central zone (O) of each source (S) and intersect extend over lengths (l₁ and l₂), to form, respectively, a quarter wave line of triplate type and a quarter wave line of microstrip type, these lines being open at their ends. Device according to any one of claims 1 or 2, characterized in that said four planes each constitute one of the faces, lower or upper, of a stack of three printed circuits (CI₁ to CI₃) superimposed. Device according to claim 3, characterized in that the microstrip type line consists of a metallized track (R) on the upper face of the upper printed circuit (CI₁) of said stack and of a ground plane (M) produced by metallization of the underside of this printed circuit (CI₁), and in that the three-ply line consists of said ground plane (M), a track (T) produced by metallization of the underside of the intermediate printed circuit (CI₂) of said stacking and a second ground plane produced by metallization of the lower face of the lower printed circuit (CI₃). Device according to claim 3, characterized in that the microstrip type line consists of a track (R) metallized on the upper face of the upper printed circuit (CI₁) of said stack and of a ground plane (M) produced by metallization of the upper face of the intermediate printed circuit (CI₂), and in that the three-ply line is formed by said ground plane (M), a track (T) produced by metallization of the face bottom of the intermediate printed circuit (CI₂) and a second ground plane produced by metallization of the underside of the lower printed circuit (CI₃). Device according to claim 3, characterized in that the microstrip type line consists of a track (R) metallized on the upper face of the upper printed circuit (CI₁) of said stack of a ground plane (M) produced by metallization of the upper face of the intermediate printed circuit (CI₂), and in that the three-ply line consists of said ground plane (M), a track (T) produced by metallization of the upper face of the lower printed circuit (CI₃) of said stack and a second ground plane produced by metallization of the underside of this printed circuit (CI₃). Device according to claim 3, characterized in that the microstrip type line consists of a metallized track (R) on the upper face of the upper printed circuit (CI₁) of said stack and of a ground plane (M) produced by metallization of the lower face of this printed circuit (CI₁), and in that the three-ply line consists of said ground plane (M), a track (T) produced by metallization of the upper face of the lower printed circuit (CI₃) of said stack and a second ground plane (CP) produced by metallization of the lower face of the lower printed circuit (CI₃). Device according to any one of Claims 4 to 7, characterized in that the metallization forming the second ground plane (CP) is replaced by a rigid metal plate. Array of plate antennas organized according to a matrix of n resonant sub-arrays each comprising p sources (S₁₀₀ to S₂₀₉), characterized in that it is equipped with a supply device according to any one of claims 1 to 8 , and in that each feed line, of the triplate type, respectively of the microstrip type, consists of a distributor configured in the form of a shaft comprising, per line, a main line (T₁₀ and T₂₀, R₁₀ and R₂₀) s 'extending parallel to said column and a secondary line (T₁₀₀ and T₂₀₀, R₁₀₀ and R₂₀₀), parallel to this line and connected in a middle zone, and, for each source (S₂₀₄), an individual supply line (T₂₀₄, R₂₀₄), the connections with the secondary lines being regularly distributed along these. Network according to claim 9, characterized in that inside a resonant sub-network (S₁₀₀ to S₁₀₉, S₂₀₀ to S₂₀₉), the sources are regularly distributed and their centers spaced by a distance d such that d = λ₀ / √ε _r , with λ₀ the wavelength of the radiation in the air and ε _r the relative permittivity of the medium forming the lines. Network according to claim 10, characterized in that the lengths of tracks (T) forming the line of triplate type between two of said connections, connecting the secondary lines (T₁₀₀ and T₂₀₀) to the individual supply lines (T₂₀₄), are equal to the distance d, these lengths themselves being equal to a phase wavelength in the triplate line, and in that the secondary lines consist of segments of lines of lengths d. Network according to claim 11, characterized in that the track lengths (R) forming the microstrip type line between two of said connections connecting the secondary lines (R₁₀₀ and R₂₀₀) to the individual supply lines (R₂₀₄) being equal to the length phase wavelength of a microstrip type supply line, this phase wavelength being greater than the phase wavelength in the triplate type supply line, the secondary lines (R₁₀₀ and R₂₀₀) are sinusoidal.

Images