EP0557176B1 - 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 an array 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 triple plate type and a second transmission line of 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 invention also relates to an array of dual polarization plate antennas equipped 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 feed 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-O 243 289, on October 28, 1987. Reference may be made, as 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. 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 with 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-conducting windows F ₁ to F ₄ .

The main characteristic of the invention consists in supplying such a dual-polarization source using two completely independent transmission lines. Three juxtaposed printed circuits CI ₁ , CI ₂ and CI ₃ are required. 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 l ₁ and l ₂ 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 small.

The windows F ₁ to F ₄ 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 crossing point of the tracks R and T, center of the source S, when looking at the source in projection.

Track widths R and T are noted, respectively, w ₁ and w ₂ . The thicknesses of the printed circuits CI ₁ to CI ₃ have been noted in FIG. 1: H ₁ , H ₂ and H ₃ . 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:
H ₁ = H ₂ = H ₃ = 0.8 mm
ε _r = 2.2 (relative permittivity of the printed circuit substrate)
w ₁ = 0.68 mm
w ₂ = 0.3 mm
I ₁ = 4.5 mm
I ₂ = 3.55 mm 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 (mean 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 just described 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 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 CI ₁ , the metallization T on the "face 2" of CI ₂ , the metallization of M on the "face 2" of CI ₁ and the metallization of CP on the "face 2" of CI ₃ .

In addition, for the variant denoted D, the circuit CI ₂ is simply constituted by a dielectric sheet. It should be noted that the metallization CP, on the printed circuit CI ₃ , 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 CI ₃ can be replaced by a simple metallic sheet and a dielectric sheet between this metallic sheet and the printed circuit CI ₂ .

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 the 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 S ₁₀₀ to S ₁₀₉ and S ₂₀₀ to S ₂₀₉ . Only the source S ₂₀₄ , in the central zone of the sources S ₂₀₀ to S ₂₀₉ , 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 tracks T ₁₀ and T ₂₀ . These lines feed in turn, in a central area, two secondary lines T ₁₀₀ and T ₂₀₀ which also branch into individual supply lines from the sources. The primary supply lines T ₁₀ and T _{20 as} well as the secondary lines T ₁₀₀ and T ₂₀₀ extend parallel to the axis Δ between two source bands. Individual lines, such as the line T ₂₀₄ , are first of all perpendicular to Δ, between two contiguous sources then again parallel to Δ to cross the ribbon lines (Figure 3). Line T ₂₀₄ is an example of this for source S ₂₀₄ .

FIG. 2 also shows adaptation transformers, between the primary and secondary lines: transformers Tr ₁₀ and Tr ₂₀ ; and between the secondary lines and the individual supply lines, for example the transformer Tr ₂₀₄ . 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 λ ₀ 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 T ₁₀ , T ₂₀ , T ₁₀₀ , T ₂₀₀ and the individual supply lines such as the line T ₂₀₄ are produced by metallization of the "face 2" of the printed circuit CI ₂ (FIG. 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 CI ₃ .

Figure 3 corresponds to the supply by microstrip lines. The same resonant sub-network has been represented comprising two bands of ten sources S ₁₀₀ to S ₂₀₉ distributed regularly parallel to the axis Δ. The configuration of the microstrip lines is similar to that shown in Figure 2 for the three-ply lines. There are primary lines R ₁₀ and R ₂₀ and secondary lines R ₁₀₀ and R ₂₀₀ in strips 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 center 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 $$\text{d =}\frac{{\text{<figure-callout id="0" label="λ" filenames="imgf0003.png" state="{{state}}">λ</figure-callout>}}_{\text{0}}}{\sqrt{{\text{ε}}_{\text{r}}}}{\text{= 0.674 <figure-callout id="0" label="λ" filenames="imgf0003.png" state="{{state}}">λ</figure-callout>}}_{\text{0}}$$

For the microstrip line, the phase wavelength is greater and this is the reason why the supply lines R ₁₀₀ and R _200, which must have between two adjacent sources a length greater than 17 mm, are sinuous as it is shown in Figure 3.

Finally, for each source, such as the source S ₂₀₄ , branch off from the lines R ₁₀₀ or R ₂₀₀ , perpendicular to the axis Δ and from the individual supply lines. An example is given by line R ₂₀₄ (source S ₂₀₄ ).

In the same way as for FIG. 2, FIG. 3 shows adaptation transformers T'r ₁₀ , T'r ₂₀ and T'r ₂₀₄ . 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 R ₁₀ , R ₂₀ , R ₁₀₀ , R ₂₀₀ and the particular supply lines from sources such as the line R ₂₀₄ are produced by metallization of the "face 1" of the printed circuit Cl ₁ (Figure 1), the ground plane M being produced on the "face 1" of the printed circuit Cl ₂ as indicated above.

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 λ ₀ (with λ ₀ wavelength in a vacuum at the central frequency).

Individual supply lines, such as line T ₂₀₄ , have a wider section in the connection area with the secondary lines T ₁₀₀ and T ₂₀₀ . This extends over a length, for example l ₂₀₄ , given by the relation l ₂₀₄ = 0.17 λ ₀ .

The axes of the two rows of sources are distant by a distance d ₂ , given by the relation d ₂ = 0.944 λ ₀ .

The distance d is naturally given by the same relationship for Figures 2 and 3. As indicated d = 0.674 λ ₀ .

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 S ₁₀₀ to S ₁₁₀ ), 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 λ ₀ (λ ₀ being the wavelength of the vacuum at the center frequency) and where the distance between adjacent sub-arrays must remain less than λ ₀ to avoid the lobes of the arrays .

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

TABLE I PCB number Cl ₂ Cl ₃ Cl ₁ Designation of the metal structure Face 1 Side 2 Face 1 Side 2 Face 1 Side 2 R A, B C, D T A, B CD M B, C A, D CP A, B CD Distribution of metal structures on the 3 printed circuits. (According to the 4 solutions A, B, C, D) A: Track of the microstrip line M: Metallic plane common to all radiating sources with double crossed polarization. T: Track of the triplate line. CP: Metal counterweights.

Claims (12)

1. A feed device for at least one plate antenna (S) with dual cross polarization, characterized in that it comprises, for each source (S), a first line of the triplate type including a first ground plane (M), a second ground plane (CP) and a track (T) with an elongated form parallel to a first direction and disposed between the first and the second ground planes; a second line of the microstrip type including the first ground plane (M) and a track (R) having a form elongated in a direction perpendicular to the first direction, and in that the tracks (T, R), the first ground plane (M) and the second ground plane (CP) are disposed in four distinct, mutually parallel planes.
2. The device as claimed in 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 are prolonged for lengths (l₁ and l₂) in order to form, respectively, a quarter wave triplate type line and a quarter wave microstrip type line, said lines being open at their ends.
3. The device as claimed in claim 1 or claim 2, characterized in that the said four planes each constitute one of the lower or upper faces of a stack of three superposed printed circuits (CI₁ through CI₃).
4. The device as claimed in claim 3, characterized in that the microstrip type line is constituted by a metallized track (R) on the upper face of the upper printed circuit (CI₁) of the said stack and a ground plane (M) produced by metallization of the lower face of said printed circuit (CI₁) and in that the triplate line is constituted by the said ground plane (M), a track (T) produced by metallization of the lower face of the intermediate printed circuit (CI₂) of the said stack and a second ground plane produced by metallization of the lower face of the lower printed circuit (CI₃).
5. The device as claimed in claim 3, characterized in that the microstrip type line is constituted by a metallized track (R) on the upper face of the upper printed circuit (CI₁) of the said stack and a ground plane (M) produced by metallization of plate antenna (S), the upper face of the intermediate printed circuit (CI₂) and in that the triplate line is constituted by the said ground plane (M), a track (T) produced by metallization of the lower face of the intermediate printed circuit (CI₂) and a second ground plane produced by metallization of the lower face of the lower printed circuit (CI₃).
6. The device as claimed in claim 3, characterized in that the microstrip type line is constituted by a metallized track (R) on the upper face of the upper printed circuit (CI₁) of the said stack and a ground plane (M) produced by metallization of the upper face of the intermediate printed circuit (CI₂) and in that the triplate line is constituted by the said ground plane (M), a track (T) produced by metallization of the upper face of the lower printed circuit (CI₃) of the said stack and a second ground plane produced by metallization of the lower face of said printed circuit (CI₃).
7. The device as claimed in claim 3, characterized in that the microstrip type line is constituted by a metallized track (R) on the upper face of the upper printed circuit (CI₁) of the said stack and a ground plane (M) produced by metallization of the lower face of the printed circuit (CI₁) and in that the triplate line is constituted by the said ground plane (M), a track (T) produced by metallization of the upper face of the lower printed circuit (CI₃) of the said stack and a second ground plane (CP) produced by metallization of the lower face of the lower printed circuit (CI₃).
8. The device as claimed in any one of the claims 4 through 7, characterized in that the metallization forming the second ground plane (CP) is replaced by a rigid metallic plate.
9. An array of plate antennas in the form of a matrix of n resonant sub-arrays each comprising p sources (S₁₀₀ through S₂₀₉), characterized in that it is equipped with a feed device as claimed in any one of claims 1 through 8 and in that each feed line, of the triplate or, respectively, microstrip type, is constituted by a distributor configured in the form of a tree comprising, for each line, a principal line (T₁₀ and T₂₀, R₁₀ and R₂₀) extending in parallelism to the said column and a secondary line (T₁₀₀ and T₂₀₀, R₁₀₀ and R₂₀₀), in parallelism to said line and connected to a median zone, and, for each source (S₂₀₄), an individual feed line (T₂₀₄, R₂₀₄), the connections with the secondary lines being regularly distributed along the length of the same.
10. The array as claimed in claim 9, characterized in that in the interior of a resonant sub-array (S₁₀₀ through S₁₀₉, S₂₀₀ through S₂₀₉), the sources are regularly distributed and the centers thereof are spaced at a distance d such that d = λ₀ / $\sqrt{{\text{ε}}_{\text{r}}}$

    

    , wherein λ₀ is the wave length of radiation in air and ε_r is the relative permittivity of the medium constituting the lines.
11. The array as claimed in claim 10, characterized in that the lengths of the tracks (T) constituting the triplate type line between two of the said connections connecting the secondary lines (T₁₀₀ and T₂₀₀) to the individual feed lines (T₂₀₄), are equal to the distance d, said lengths being themselves equal to a phase wave length in the triplate line and in that the secondary lines are constituted by segments of straight lines of a length d.
12. The array as claimed in claim 11, characterized in that the length of the tracks (R) forming the microstrip type line between two of the said connections connecting the secondary lines (R₁₀₀ and R₂₀₀) to the individual feed lines (R₂₀₄) being equal to a phase wave length in a microstrip type line, said phase wave length being greater than the phase wave length in the triplate type feed line, the secondary lines (R₁₀₀ and R₂₀₀) are of sinusoidal form.

Images