EP1152483B1 - Dual-band microwave radiating element - Google Patents

Abstract

A microwave radiating element including first and second means for conveying electromagnetic waves in respective first and second frequency bands, wherein the first and second means are coaxial.

Description

The present invention relates to a radiating element operating in two bands or two distinct and circularly polarized subbands in the context, for example, of radar type applications or of satellite telecommunications in the microwave domain.

In the case of telecommunications, this type of radiating element is more particularly intended to be integrated in an antenna disposed on board a satellite or on the ground to allow communication between the different sets of the system.

The operation of different frequency bands or different ranges of the same band, such as in the Ka 20/30 GHz band, for example, requires the use of radiant devices capable of operating over a very wide band.

This need for a relatively wide frequency band is even more obvious when the radiating element has to operate in two sub-bands of different frequencies for transmission and reception.

Indeed, in this case, it is important that these sub-frequency bands are relatively far apart to prevent the transmit and receive signals from mutually interfering.

However, the known radiating devices operating on a relatively wide band are volumieux, so expensive to manufacture and complex to implement.
In addition, this type of broadband device has, because of their structure, a relatively limited surface efficiency.

In known manner, it has been possible to develop radiating elements operating in several bands or several subbands of the same frequency band.

We know, by the request of European patent EP-0 130 111 , a radar source capable of emitting at least two frequencies, for example to have a high resolution thanks to a high frequency, and a long range via a low frequency.

This radar source employs four waveguides surrounding a fifth guide.

The four peripheral guides are able, for example, to operate according to the Ku band centered on 16 GHz and the central guide in X band centered on 10 GHz.

However, such a device operates only in a linear polarization, the circular polarization requiring the addition of a hybrid coupler which causes an increase in the size of the device as well as its cost. In addition, hybrid high frequency couplers cause significant losses in the circuit.

Such known devices also require a voluminous and complex power system to ensure proper radiation, which leads to an even larger size and cost.

In addition, an antenna comprising such a source is intended to operate in an extreme frequency ratio greater than or equal to 6, a ratio that does not impose significant operating constraints due to the difference existing between the extreme frequencies.

However, in the case of an extreme frequency ratio between 1.22 and 2, such an antenna is not effective because of the interactions between the different parts of the antenna.

It is known, moreover, and in particular by the request for French patent 98 06200 , so-called "planar" antennas operating via circuits of integrated circuits type and making it possible not to use a hybrid coupler.

However, the operation of the planar antennas in a frequency ratio of between 1.22 and 2 causes, due in particular to their compactness, significant losses due to the coupling of the elements working in high and low bands.

The document EP-A-0 443 526 discloses a microwave element according to the preamble of claim 1 and the document US-A-5,258,768 discloses a polarizer.

In this context, the object of the present invention is to overcome these drawbacks by proposing a reduced-band dual-band microwave radiating element with only low losses, the circular polarization being generated by the radiating part of the antenna itself. without having to provide additional circuit such as a hybrid coupler for example.

To this end, according to the invention, a microwave radiating element comprising first and second means able to convey electromagnetic waves respectively to a first and a second frequency band, is characterized in that the first and second means are coaxial, the first means comprising a hollow and metallic waveguide adapted to receive the second means coaxially.

According to a first embodiment, the second means also comprise a hollow waveguide and metal.

According to a second embodiment, the second means comprise a guide comprising a core and a sheath both made of dielectric material, said dielectric guide being, for example, a microwave fiber capable of propagating only the hybrid mode H11.

Advantageously, in the first embodiment, the waveguides constituting the first and second means comprise, each at their end and nested one inside the other, a polarizer, the geometry of the polarizers being such that the polarization of the waves electromagnetic is circular.

Preferably, the polarizers have a cross section of rectangular or elliptical shape.

According to a preferred form of the second embodiment of the radiating element of the invention, the geometry of the dielectric guide is such that the polarization of the electromagnetic waves is circular.

Preferably, the core of the dielectric guide comprises an extension emerging from the sheath of said guide and having a cross section of elliptical, rectangular or ellipsoidal shape.

• La figure 1 est une vue schématique en perspective d'une première forme de réalisation d'un élément rayonnant selon l'invention ;
• La figure 2 une vue schématique filaire en perspective de l'élément rayonnant de la figure 1 selon un autre angle de vue ;
• La figure 3 est une vue de côté de l'élément rayonnant de la figure 1 ;
• La figure 4 est une vue schématique en perspective d'une seconde forme de réalisation d'un élément rayonnant selon l'invention.

The invention will be better understood in the light of the following description relating to an exemplary embodiment but in no way limiting, with reference to the accompanying drawings in which:

• The figure 1 is a schematic perspective view of a first embodiment of a radiating element according to the invention;
• The figure 2 a wired schematic view in perspective of the radiating element of the figure 1 according to another angle of view;
• The figure 3 is a side view of the radiating element of the figure 1 ;
• The figure 4 is a schematic perspective view of a second embodiment of a radiating element according to the invention.

The figure 1 is a schematic perspective view of a first embodiment of a radiating element 1 according to the invention.

The radiating element 1 comprises a first excitation access 2 generating the wave intended to be propagated. The excitation access 2 is, in the mode of realization of the figure 1 , of coaxial type, comprising a tubular peripheral portion 2a and a central portion 2b, cylindrical and disposed in the center of the peripheral portion 2a (see figures 2 and 3 ).

Note that the excitation access 2 could use any other known excitation technique such as triplate and other, or be constituted by another guide.

The excitation access 2 is connected, via the central portion 2b and in known manner, to a first end of a first power waveguide 3 able to operate, for example, in the band Ka around 30 GHz, and more exactly between 27.6 and 29 GHz.

The feed guide 3 (hereinafter guide 3), perpendicular to the excitation port 2 and having an elongated hollow longitudinal axis shape Z, with a rectangular cross-section, makes it possible to propagate the polarized electromagnetic waves. linearly.

At the opposite end of the one where the excitation access 2 is located, the guide 3 comprises, in its extension in the direction of the Z axis of the guide 3, a transition section composed of an adaptation transformer. 4.

The adaptation transformer 4 consists of a hollow guide having a section of shape identical to that of the guide 3 but of larger dimensions, except the longitudinal direction parallel to the Z axis.

The guide 3 is centered and aligned on the matching transformer 4, the different faces constituting the guide 3 and the matching transformer 4 being parallel to each other.

In the extension of the matching transformer 4 is a polarizer 5, working at 30 GHz, also hollow, parallelepiped, of rectangular cross-section and of larger dimensions than that of the matching transformer 4.
In order to generate the circular polarization of the signal, the polarizer 5 is angularly offset by 45 degrees about the Z axis relative to the matching transformer 4 which is itself in alignment with the guide 3.

The polarizer 5, here of rectangular section, may also be of elliptical shape in order to obtain the circular polarization of the signal.

These three elements, the guide 3, the matching transformer 4 as well as the polarizer 5, are, for example, metal and end-to-end, at one of their faces, by any known technique such as welding, machining, electroerosion or made by molding.

It should be noted, in addition, that several transition sections such as the matching transformer 4 may be provided in the embodiment shown in FIGS. Figures 1 to 3 between the guide 3 and the polarizer 5.

The first guide 3 is arranged, coaxially, inside a second feed guide 6, hollow and of substantially rectangular section but of larger dimensions than those of the first guide 3. The respective faces of the guides 3 and 6 are parallel to each other.

The second guide 6 comprises, on one of its larger faces, a slight recess inwardly forming a groove 6a of rectangular section and parallel to the axis Z of the guide 3.

This groove 6a, also called "ridge", limits the propagation of electromagnetic waves carried by the guide having such a groove 6a in the single fundamental mode.

A guide comprising such a ridge 6a is said riddled guide.

The second guide 6, shorter than the first guide 3 in the direction of the Z axis, is associated with a second excitation port 7 of the coaxial type. Any other technique than coaxial is also possible.

The second guide 6 also works in the Ka band at around 20 GHz and for example between 17.8 and 19.2 GHz.

The first guide 3 is secured to the second guide 6 at the ridge 6a, the width of said ridge 6a corresponding to the width of the first guide 3.

In the extension of the second feed guide 6 is a transition section composed of an adaptation transformer 8.

The adaptation transformer 8 is a guide comprising a ridge 8a (rifled guide), whose cross section is of the same shape as that of the second feed guide 6 but of larger dimensions.

The ridges 6a and 8a are thus aligned and parallel to the Z axis of the first guide 3.

On the side opposite to that where the second guide 6 is located, the matching transformer 8 is associated with a polarizer 9.

The polarizer 9 has a substantially rectangular cross section, large enough to contain, at least in part, the polarizer 5 of the high band.

Like the polarizer 5, the polarizer 9 is angularly offset by 45 degrees about the Z axis relative to the matching transformer 8 and the guide 6 so as to generate a circular polarization of the signal.

The polarizer 9 may have a different shape such as, for example, an elliptical cross section, capable of generating, from the linear polarization of the signal propagating in the guide 6 and the matching transformer 8, a circular polarization.

In the embodiment of the Figures 1 to 3 , the geometry and the arrangement of the different parts of the radiating element 1 are such that the polarizers 5 and 9 are oriented in the same way, their respective faces being parallel to each other. This relative arrangement of the polarizers 5 and 9 makes it possible to obtain a circular polarization of the same direction for the two bands.

However, in the case of opposite circular polarizations, the polarizers 5 and 9 will be oriented relative to 90 °.

Thus, the radiating element 1 of the present invention makes it possible to obtain, according to the relative arrangement of the polarizers 5 and 9, four configurations different from circular polarization: right / right, right / left, left / right and left / left.

The figure 2 is a wired schematic perspective view of the radiating element of the figure 1 according to a different angle of view from that of the figure 1 , where the mutual orientation of the different pieces appears.

The radiating element 1 thus consists of a first and a second independent access coaxial circuit: the first compound of the excitation access 2, the supply guide 3, the adaptation transformer 4 and the polarizer 5 and working in the high band (30 GHz), the second circuit comprising the excitation access 7, the ruled power supply guide 6, the matching transformer 8 and the polarizer 5 and working in the low band (20 GHz) ).

The side view of the figure 3 shows again the relative disposition of the different parts of the radiating element, and in particular the relative position of the polarizers 5 and 9.

The polarizer 5 is largely contained in the polarizer 9, projecting only slightly in the direction of the Z axis. However, according to alternative embodiments, the polarizer 5 (30 GHz) can also be completely included or entirely outside the polarizer 9 (20 GHz).

The supply guides 3 and 6 open respectively, through the matching transformers 4 and 8, in the polarizers 5 and 9.

The radiating element 1 is therefore able to operate according to two different frequency bands, or more exactly two independent access subbands, one serving for transmission (high band), the other for receiving (band low).
The particular geometry of the radiating element 1 also makes it possible to obtain a circular polarization of the electromagnetic waves.

The figure 4 shows, in schematic perspective wire view, a second embodiment of a radiating element 1 according to the invention.

The parts of the radiating element 1 identical to those of the first embodiment of the Figures 1 to 3 bear the same reference.

• l'accès d'excitation 7,
• le guide d'alimentation ridgé 6,
• le transformateur d'adaptation 8 mais ne comportant pas de ridge,
• le polariseur 9.

We thus find the complete low band (20 GHz) part of the radiating element 1 with:

• the excitation access 7,
• the ridged feeding guide 6,
• the adaptation transformer 8 but having no ridge,
• the polarizer 9.

In addition to the absence of ridge on the matching transformer 8, the difference with the first embodiment of the radiating element 1 is at the level of the high frequency circuit.

The high frequency element has a coaxial excitation access 2 identical to that of the embodiment of the Figures 1 to 3 associated with a first end of a metal feed guide 10 similar to the guide 3 of the preceding figures.

Indeed, the guide 10 is of identical cross section to that of the guide 3 but of length (along the Z axis) lower. The guide 10 is housed in the guide 6, at the ridge 6a, in the same way as the guide 3 in the Figures 1 to 3 .
The guide 10 stops substantially at the junction between the guide 6 and the matching transformer 8, any other configuration remaining possible. Here, the guide 10 is coupled in known manner to a microwave fiber 11 arranged in the extension of the guide 10.

The microwave fiber 11 is a dielectric guide axis coincident with the Z axis and propagating only hybrid mode H11 (fundamental mode).

The fiber 11 comprises, in the manner of an optical fiber, a cylindrical solid core 12 surrounded by a hollow sheath 13 of tubular form. The core 12 and the sheath 13 may, for example, be mounted one inside the other in a tight fit, or slid with a fastening completed by gluing.

Ideally, the microwave fiber is made in a known manner dielectric material of the type called "index jump", the sheath 13 having a relatively high index (minimum 10 for example) to ensure good confinement hybrid mode H11. Ideally, the index of the core 12 is slightly greater than that of the sheath 13.

The materials that can be used are for example: synthetic sapphire, Berilium oxide, alumina ...

The coupling between the guide 10 and the microwave fiber 11 is via the core 12 which has, at its end close to the excitation port 2, an extension 12a penetrating the guide 10. This extension 12a is substantially conical shape flaring in the direction of the Z axis.

Advantageously and in order to dispense with the use of a polarizer for the high frequency, the microwave fiber 11 has a geometry that allows the generation of a circular polarization through the generation of two orthogonal modes H11.

For this, the core 12 of the microwave fiber 11 extends outside the sheath 13 on the opposite side to that of the first extension 12a in a second extension 12b in shape, seen in cross section, elliptical.

Unlike the shape of the portion of the core 12 which is surrounded by the sheath 13, the particular ellipsoidal shape (of large axis parallel to the Z axis) of the radiating portion 12b of the core 12 of the fiber 11 allows a generation of the circular polarization of the waves simply and without having to provide additional parts.

As for the first embodiment of Figures 1 to 3 , the part of the radiating element 1 working in high band is arranged coaxially in the hollow metal part working in low band.

Thus, the feed guide 10 and the microwave fiber 11 pass through the rusted feed guide 6, the adaptation transformer 8 and the polarizer 9.

The invention is not limited to the embodiments described in connection with the Figures 1 to 4 , other geometries or arrangements being conceivable for the various elements, in particular for the supply guides 3, 6, 10, the polarizers 5 and 9 or the fiber 11, in order to generate a circular polarization of the waves in the radiating element coaxial 1.

Whatever the geometry adopted, the invention makes it possible to obtain a dual-band radiating element having a small overall size, capable of generating a circular polarization without using complementary circuits, having an independent access for each sub-frequency band. and may have an operating frequency ratio of between 1.22 and 2.

This type of radiating element is particularly suitable for high frequencies, such as those of the Ka band for example.

Claims (7)

1. Hyperfrequency radiating element (1) comprising first and second means capable of carrying electromagnetic waves respectively in a first and a second frequency band, the first means comprising a hollow metallic waveguide (6) capable of coaxial accommodation of the second means, the second means also comprising a hollow metallic waveguide (3), characterized in that the waveguides (3, 6) constituting the first and second means each comprise a polarizer (5, 9) at their ends and fitted inside one another.
2. Radiating element according to claim 1, in which the geometry of the polarizers (5, 9) is such that the polarization of the electromagnetic waves is circular.
3. Radiating element according to claim 2, in which the polarizers (5, 9) have a cross-section which is rectangular or elliptical in shape.
4. Radiating element according to claim 1, in which the second means comprise a guide having a core (12) and cladding (13), both of dielectric material.
5. Radiating element according to claim 4, in which the dielectric guide is a hyperfrequency fibre (11) capable of propagating only the H11 hybrid mode.
6. Radiating element according to one of claims 4 or 5, in which the geometry of the dielectric guide is such that the polarization of the electromagnetic waves is circular.
7. Radiating element according to claim 6, in which the core (12) of the dielectric guide comprises an extension (12b), outside the cladding (13), having a cross-section elliptical, rectangular or ellipsoidal in shape.

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