EP0617477B1 - H-shaped waveguide structure defining a principal and two secondary waveguides for transporting waves having distinct frequencies. - Google Patents

Description

The present invention relates to a waveguide line with two symmetrical internal ribs, arranged to provide a median constriction in the guide and reduce the cut-off frequency of the guide, and to an excitation probe plunging into the constriction.

On board a missile, for example, it can be used, which is also radiated at the end to serve as an antenna, between a transmitter, for example again, for telemetry or trajectography, and an orifice made in the skin of the missile. Telemetry is carried out in a frequency band around 2 GHz, trajectography in a band around 5 GHz.

Since a waveguide has a cross section adapted to a single frequency range, as many radiation guides and orifices are needed as there are applications. It is an expensive and cumbersome solution because the orifices must be protected by materials transparent to radiation and often withstand heating. In addition, the radiation holes are very troublesome, because they can create a surface discontinuity and alter the aerodynamics of the craft.

The article by J.E. STORER et al., Published in IRE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES, vol. 3, no 2, March 1961, New York (US), pages 116 to 123, entitled "TEM impedance and cross-coupling for small circular center conductors in a double ridged waveguide" proposes a waveguide structure with median throttling, that is to say, an H guide, in which a central conductor is arranged in each of the spaces situated on either side of the constriction so as to transmit signals in TEM mode.

In addition, American patent US-A-4 119 967 describes a probe coupling structure introduced into the throttle of an H wave guide.

The present invention therefore aims to propose a waveguide line adapted to at least two distinct frequency ranges.

To this end, the invention relates to a line of the type defined above in which two secondary split guides of cross section smaller than that of the waveguide line with two ribs, called primary, being thus formed on both sides. other of the median constriction, constituting a median slot for the secondary guides, there is provided a another excitation probe plunging into one of the two secondary guides.

It will be emphasized that, for the person skilled in the art, it was the shape and size of a waveguide which determined, in the fundamental mode, the only range of frequencies that can be transmitted and that it therefore appeared to be a priori excluded from wanting to transmit several frequency ranges in the same guide.

Thus, the primary guide is designed to transmit a first frequency band, thanks to the fact that the constriction creates a primary guide with double groove and two lateral secondary guides.

Each secondary guide can transmit, without being disturbed, despite the constriction acting as a median slot, a second frequency in a second frequency band which is specific to it.

A rib makes it possible to reduce the section of the primary waveguide line for the same band of transmitted frequencies, or else, with a maintained section, to reduce the cut-off frequency.

As each secondary guide has a smaller section than that of the primary guide, the frequencies of the band of the secondary guides are higher than those of the primary band.

Advantageously, the secondary guides are internally ribbed, with the advantages mentioned above.

In particular, the ribs of the primary guide can be shaped to constitute a rib in each ribbed secondary guide.

Advantageously, the cross section of the primary guide is a rectangle.

In the preferred embodiment of the invention, the line is open at one end, to form a waveguide antenna with radiation at the end.

• la figure 1 est une vue en coupe transversale de la ligne guide d'ondes de l'invention, selon un plan proche de son extrémité d'excitation et
• la figure 2 est une vue en coupe analogue à celle de la figure 1, mais dans un plan proche de son extrémité de rayonnement.

The invention will be better understood using the following description of the preferred embodiment of the antenna line of the invention, with reference to the attached drawing in which:

• FIG. 1 is a cross-sectional view of the waveguide line of the invention, along a plane close to its excitation end, and
• Figure 2 is a sectional view similar to that of Figure 1, but in a plane close to its radiation end.

The line guide of Figures 1 and 2 is a guide with a rectangular cross section. It has two internal ribs 4 and 6, T-shaped which extend over the entire length of the guide. Transversally, they extend, by their feet, from the middle of the long sides of the rectangle of the guide section. The two ribs 4 and 6 are symmetrical with respect to a longitudinal median plane 10 of the guide and form between them a median longitudinal throttle 8.

The constriction 8, of rectangular section in FIG. 1, constitutes the central part of a cavity 12, forming a primary guide, which therefore comprises two secondary cavities 14 and 16 physically connected by the constriction 8. The secondary cavities 14 and 16 are arranged symmetrically on either side of a plane of symmetry 11 of the ribs 4 and 6, thus than the guide. Each secondary cavity 14 and 16 forms a secondary guide of generally rectangular cross section, the length of which extends parallel to the width of the cross section of the primary guide 12. The walls 7 and 9, each arranged along a width of the cross section of the primary guide 12, respectively form two walls of the two secondary guides 14 and 16 and constitute lengths of the cross sections of the secondary guides.

The ends of the bars of the T of the ribs 4 and 6 form, in each secondary guide 14 and 16, a pair of ribs, respectively 41, 61 and 42, 62. The distance separating the ribs 4 and 6 being relatively small compared to the length of the walls 7 and 9, the ribs of each secondary guide can be considered as adjacent, as if the constriction did not exist.

A bore 22, passing through the base of the rib 4, substantially in the plane 11, receives an excitation probe 23 disposed perpendicular to the median plane 10 and the end of which plunges into the constriction 8. The probe 23 is arranged to excite the primary waveguide line in linear polarization at a first frequency, of a value chosen so that the corresponding electromagnetic wave propagates in the guide line using the entire volume of the primary guide 12.

The secondary guide 14 has a bore 24 formed in the wall 7 in the median plane 10. An excitation probe 25, passing through the bore 24 perpendicular to the wall 7 and plunging into the secondary guide 14, transmits to the latter a electromagnetic excitation in linear polarization at a second frequency whose value allows the propagation of the corresponding electromagnetic wave along the single secondary guide line 14.

In the present example, the waveguide lines radiate at their ends opposite to that of the excitation probes 23 and 25.

The operation of the waveguide lines is as follows.

The two electromagnetic waves generated by the probes 23 and 25 propagate perpendicular to the plane of FIG. 1, in the direction of the radiation end close to the cross section shown in FIG. 2.

The wave at the first frequency propagates occupying the entire volume of the primary guide 12.

In the secondary guide 14, the wave at the second frequency propagates with a polarization orthogonal to that of the first wave, so that there is absence of coupling and corresponding loss. Measurements have shown that decoupling exceeds 40 decibels. The direction of the polarization of the wave at the second frequency prevents a transfer of energy from this wave from the first secondary guide 14 to the other secondary guide 16 through the throttle 8.

The end of the constriction 8 opening into the secondary guide 14 constitutes a slot extending along the length of the secondary guide line, perpendicular to the plane of the figures. In the plane of these, the slot described above is located in the median plane 10. As is known, a slot of this kind does not cause losses as long as its width is small relative to the length of the wall in which it is formed, which is the case here.

For the sake of clarity, it has not been planned to transmit a third frequency in the secondary guide 16.

The radiating opening of the waveguide line, primary or secondary, forms an antenna, shown in cross section in Figure 2, the other end of the line being closed. Unlike what is shown in FIG. 1, the upper bar of the T of each rib 4 and 6 has a central notch 65, 66, here rectangular, between its ends, respectively 41, 42 and 61, 62, which widens the constriction 8 in the central part of its cross section, while keeping the width of the constriction 8 constant at its outlet forming a slot in each secondary guide 14 and 16. For other guide line sections parallel to that of Figure 2 and adjacent to it, the depth of the notch indicated above is all the greater the closer the section considered is to the radiating opening.

The modification of the shape of the throttle 8 has the effect of adapting the characteristic line impedance to that presented by the load at the end of the line, that is to say the air. The progressiveness of the transition avoids the creation of significant parasitic reflections, the report standing waveform being less than 1.5 in the vicinity of the central frequency of the primary guide 12.

The modification of the shape of the constriction 8 exposed above is only a particular example and other modifications of shape are possible. In particular, they can also bear on the shape of the ribs 41, 42, 61 and 62 of the secondary guides 14 and 16. Similarly, the secondary guides 14, 16 could comprise a second rib, like that (63, 64) s' extending along the wall 7, 9 opposite the slot 8, and shown in broken lines in Figure 1, for example in one piece with the associated wall.

Claims (9)

1. A wave guide line with two symmetrical internal ribs (4, 6) arranged to provide a median restriction (8) in the guide and to decrease the cut-off frequency of the guide, and with an excitation probe (23) plugged in the restriction (8), characterised in that two secondary slit guides (14, 16) with a transverse section smaller than that of the wave guide line with two ribs, called primary (12), being thus formed on both sides of the median restriction (8) constituting a middle slit for the secondary guides, another excitation probe (25) is provided which is plugged one of the two secondary guides (14).
2. A line according to claim 1, wherein both secondary guides (14, 16) are also internally ribbed (41, 61, 63; 42, 62, 64).
3. A line according to one of claims 1 and 2, wherein the ribs (4, 6) of the primary guide (12) are formed so as to constitute a rib (41, 61; 42, 62) in each ribbed secondary guide (14, 16).
4. A line according to one of claims 1 to 3, wherein the two probes (23, 25) are disposed to produce two orthogonal fields respectively.
5. A line according to one of claims 1 to 4, wherein the restriction (8) of the primary guide (12) is relatively thin in relation to the dimensions of its transverse section (7).
6. A line according to one of claims 1 to 5, wherein the transverse section of the primary guide is a rectangle.
7. A line according to claim 6, wherein the restriction (8) of the primary guide (12) extends in parallel with the length of the said rectangle.
8. An end radiating wave guide antenna characterised in that it is made of the wave guide line according to one of claims 1 to 7, which, further, is also open at one end.
9. An antenna according to claim 8, wherein the ribs of the ribbed primary guide (12) and ribbed secondary guide (14, 16) of the line which is open at one end are formed to match the impedances at the opening of the line.

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