EP1152483A1 - 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 according to two separate bands or two subbands with circular polarization in the context, for example, of radar type applications or satellite telecommunications in the microwave field.

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

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

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

Indeed, in this case, it is important that these frequency sub-bands are relatively far apart in order to avoid transmission and reception do not disturb each other.

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

We have been led, in a known manner, to develop elements radiant heaters operating in several bands or several sub-bands of the same frequency band.

We know, from European patent application 0 130 111, a source radar capable of transmitting at least two frequencies, so example of having a high resolution thanks to a high frequency, and a long range via a low frequency.

This radar source uses four waveguides surrounding a fifth guide.

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

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

Such known devices also require a power system bulky and complex to ensure correct radiation, which induces even more space and cost.

In addition, an antenna comprising such a source is intended for operate at an extreme frequency ratio greater than or equal to 6, report which does not impose significant operating constraints on the makes the difference between the extreme frequencies.

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

We know, in addition and in particular by the French patent application 98 06200, so-called "flat" antennas operating through circuits of the integrated circuit type and making it possible not to use hybrid coupler.

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

In this context, the present invention aims to overcome these disadvantages by proposing a dual-band microwave radiating element small in size and experiencing only small losses, the circular polarization being generated by the radiating part of the antenna itself without having to provide an additional circuit such as a coupler hybrid for example.

To this end, according to the invention, a microwave radiating element comprising first and second means capable of conveying electromagnetic waves at first and second respectively frequency bands, is characterized in that the first and second means are coaxial, the first means comprising a waveguide hollow and metallic capable of receiving the second means so coaxial.

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

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

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 polarizers being such that the polarization of the electromagnetic waves is circular.

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

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

Preferably, the core of the dielectric guide has 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 illustrative embodiment but in no way limiting, with reference to the appended drawings in which:

• Figure 1 is a schematic perspective view of a first embodiment of a radiating element according to the invention;
• Figure 2 a schematic wireframe perspective view of the radiating element of Figure 1 from another angle of view;
• Figure 3 is a side view of the radiating element of Figure 1;
• Figure 4 is a schematic perspective view of a second embodiment of a radiating element according to the invention.

Figure 1 shows a schematic perspective view of a first embodiment of a radiating element 1 according to the invention.

The radiating element 1 has a first excitation access 2 generating the wave intended to be propagated. The excitation access 2 is, in the embodiment of FIG. 1, of coaxial type, comprising a part tubular device 2a and a central part 2b, cylindrical and arranged in the center of the peripheral part 2a (see Figures 2 and 3).

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

The excitation access 2 is linked, via the central part 2b and in a known manner, at a first end of a first waveguide supply 3 capable of operating, for example, in the Ka band aux around 30 GHz, and more precisely between 27.6 and 29 GHz.

The feed guide 3 (hereinafter guide 3), perpendicular to the access excitation 2 and having the shape of a hollow and elongated conduit with an axis longitudinal Z, with rectangular cross section, propagates the linearly polarized electromagnetic waves.

At the opposite end from that where the excitation access 2 is located, the guide 3 comprises, in its extension in the direction of the axis Z 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 identical shape to that of guide 3 but of more dimensions large, except the longitudinal direction parallel to the Z axis.

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

In the extension of the adaptation 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 adaptation transformer 4.
In order to generate the circular polarization of the signal, the polarizer 5 is angularly offset by 45 degrees around the axis Z with respect to the matching transformer 4 which is itself aligned with the guide 3.

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

These three elements, the guide 3, the adaptation transformer 4 as well as the polarizer 5, are, for example, metallic and associated end to end, at level of one of their faces, by any known technique such as welding, machining, EDM or made by molding.

It will also be noted that several transition sections such as the matching transformer 4 can be provided in the form of embodiment shown in FIGS. 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 section rectangular but larger than the first guide 3. The respective faces of the guides 3 and 6 are mutually parallel.

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

This groove 6a, also called "ridge", makes it possible to limit the propagation of electromagnetic waves carried by the guide comprising such groove 6a in the fundamental mode only.

A guide comprising such a ridge 6a is said to be a ridged 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 another technique than the coaxial is also possible here.

The second guide 6 also works in the Ka band 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 level of the ridge 6a, the width of said ridge 6a corresponding to the width of the first guide 3.

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

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

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

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

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

Like polarizer 5, polarizer 9 is angularly offset by 45 degrees around the Z axis with respect 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, circular polarization.

In the embodiment of Figures 1 to 3, the geometry and the arrangement of the different parts of the radiating element 1 are such that polarizers 5 and 9 are oriented in the same way, their faces respective being parallel to each other. This relative provision of polarizers 5 and 9 provides circular polarization similarly sense for both bands.

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

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

Figure 2 is a schematic wireframe perspective view of the element radiating from Figure 1, from a different angle of view than that of the Figure 1, where the mutual orientation of the different parts appears.

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

The side view of Figure 3 again shows the relative arrangement of the different parts of the radiating element, including the relative position polarizers 5 and 9.

The polarizer 5 is largely contained in the polarizer 9, does not protruding only slightly in the direction of the Z axis. However, according to variant embodiments, polarizer 5 (30 GHz) can also be found totally included or entirely outside polarizer 9 (20 GHz).

The feed guides 3 and 6 open respectively, via the adaptation 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 sub-bands, one used for transmission (high band), the other used for reception (band low).
The particular geometry of the radiating element 1 also makes it possible to obtain circular polarization of the electromagnetic waves.

Figure 4 shows, in schematic wireframe perspective 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 Figures 1 to 3 bear the same references.

• 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 full low band (20 GHz) part of the radiating element 1 with:

• excitation access 7,
• the ridged feed guide 6,
• the adaptation transformer 8 but not comprising a ridge,
• the polarizer 9.

Besides the absence of a ridge on the adaptation transformer 8, the difference with the first embodiment of the radiating element 1 is located at high frequency circuit level.

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

In fact, the guide 10 has a cross section identical to that of the guide 3 but of shorter length (along the Z axis). The guide 10 is housed in the guide 6, at the level of the ridge 6a, in the same way as the guide 3 in FIGS. 1 to 3.
The guide 10 is substantially interrupted at the junction between the guide 6 and the adaptation transformer 8, any other configuration remaining possible. There, the guide 10 is coupled in a known manner to a microwave fiber 11 arranged in the extension of the guide 10.

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

Fiber 11 has, like an optical fiber, a solid core cylindrical 12 surrounded by a hollow sheath 13 of tubular shape. The heart 12 and the sheath 13, can be, for example, mounted one inside the other according to a tight or sliding fit with a fastening completed by a collage.

Ideally, the microwave fiber is produced in a manner known in dielectric material of the so-called "index jump" type, the sheath 13 having a relatively high index (minimum 10 for example) to ensure good confinement of hybrid mode H11. Ideally, the heart index 12 is slightly higher 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 done by through the heart 12 which has, at its end close to the access excitation 2, an extension 12a entering the guide 10. This extension 12a is of substantially conical shape flaring in the direction of the Z axis.

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

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

Unlike the shape of the part of the heart 12 which is surrounded sheath 13, the particular ellipsoidal shape (of major axis parallel to the axis Z) of the radiating part 12b of the core 12 of the fiber 11 allows a generation of circular polarization of waves in a simple and without have to provide additional rooms.

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

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

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

Whatever the geometry adopted, the invention makes it possible to obtain a dual-band radiating element having a reduced bulk, suitable for generate circular polarization without using circuits complementary, with independent access for each sub-band of frequencies and which may have a frequency ratio of operating between 1.22 and 2.

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

Claims (7)

Microwave radiating element 1 comprising first and second means able to convey electromagnetic waves respectively at a first and a second frequency band, the first means comprising a hollow and metallic waveguide 6 capable of receiving the second means coaxially , the second means also comprising a hollow and metallic waveguide 3, characterized in that the waveguides (3, 6) constituting the first and second means comprise, each at their end and nested one in the other, a polarizer (5, 9). Radiating element according to claim 1, characterized in that the second means comprise a guide comprising a core 12 and a sheath 13 both made of dielectric material. Radiating element according to claim 2, characterized in that the dielectric guide is a microwave fiber 11 capable of propagating only the hybrid mode H11. Radiating element according to claim 1, characterized in that the geometry of the polarizers (5, 9) is such that the polarization of the electromagnetic waves is circular. Radiating element according to claim 4, characterized in that the polarizers (5, 9) have a cross section of rectangular or elliptical shape. Radiating element according to one of claims 2 or 3, characterized in that the geometry of the dielectric guide is such that the polarization of the electromagnetic waves is circular. Radiating element according to claim 6, characterized in that the core 12 of the dielectric guide has an extension 12b, outside the sheath 13, having a cross section of elliptical, rectangular or ellipsoidal shape.

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