EP0164050B1 - Filter with a main waveguide loaded with lateral waveguides - Google Patents

Description

The present invention relates to a filter comprising a main waveguide, the two ends of which are coupled to the two ports of the filter, and also comprising at least one lateral guide which opens, at one of its ends, into a hole drilled in the wall of the main guide and which is generally loaded, at its other end, with an absorbent material.

Such filters are known and are, for example, plugged into the output switches of power amplifiers working in centimeter waves, so as to reduce the level of harmonics radiated in space.

Known filters are produced by means of a rectangular main guide whose four sides, or at least one of the two long sides, are loaded by lateral guides, which are also rectangular but of smaller cross section than that of the main guide. These filters sometimes include, at their two accesses, an impedance adapter of the progressive fitting type (type in Anglo-Saxon literature) or of the discontinuous fitting type in steps (steps in Anglo-Saxon literature); this impedance adapter, which constitutes a rectangular guide connection, is intended to increase the coupling of the lateral guides by reducing the distance between the two long sides of the main guide, that is to say by taking, for the main guide, an internal section whose short sides are smaller than those of the filter connection ports; the long sides, on the other hand, keep the same dimension as the long sides of the external rectangular guides to which the filter is connected.

These known filters have a high cost price due to the generally large number of lateral guides which must be associated with the main guide; moreover, they are very difficult to produce by electro-erosion or electro-forming.

The object of the present invention is to avoid or at least reduce these drawbacks.

This is obtained, in particular, by using, as lateral guides, cylindrical guides whose production, on the one hand, and positioning relative to the main guide, on the other hand, are simpler than those of the rectangular guides . It should be noted that, while the replacement of the cylindrical lateral guides seems to go without saying, it poses, in fact, problems which, it seems, had not been seriously studied and especially resolved; this explains why, until then, only filters with rectangular lateral guides have been produced; the rest of the description will show what precautions must be taken for the correct operation of filters with cylindrical lateral guides.

According to the invention a filter comprising a rectangular main guide, n secondary guides with n integer at least equal to 1, coupled at one of their ends, to the main guide by holes passing through the wall of the main guide, and two adapters d impedance of the connection type rectangular guide-rectangular guide, respectively coupled to the two ends of the main guide, is characterized in that the n secondary guides are cylindrical guides and in that the impedance transformers have, at their ends, sections internal rectangulars of which both the length and the width are smaller on the side coupled to the main guide than on the side opposite the main guide.

The present invention will be better understood and other characteristics will appear with the aid of the description below and of the figures relating thereto which represent:

• - la figure 2, le filtre de la figure 1 vu de bout,
• - la figure 3, une coupe transversale du filtre des figures 1 et 2.

FIG. 1, a filter according to the invention seen from the side,

• FIG. 2, the filter of FIG. 1 seen from the end,
• - Figure 3, a cross section of the filter of Figures 1 and 2.

The references given to the elements correspond from one figure to another.

Figure 1 shows a filter according to the invention in partial side view, with a part shown in broken away.

• - une bride de fixation 3,
• - un adaptateur d'impédance, 2, qui, avec la bride 3 a une longueur de 30 mm et qui passe d'une section interne de 15,8 x 7,9 mm à son extrémité située du côté de la bride 2, à une section interne de 14 x 7 mm à son autre extrémité,
• - un guide principal, 1, rectangulaire, d'une section interne de 14 x 7 mm et de 270 mm de longueur; sur le pourtour de ce guide principal sont fixés quarante ensemble latéraux comportant chacun six guides secondaires, cylindriques, tels que A1, B1, C1, D1, E1, F1; placés dans un même plan transversal du guide principal,
• - un adaptateur d'impédance 4, symétrique de l'adaptateur 2 par rapport à un plan de symétrie constitué par le plan transversal, non représenté, passant par le milieu du guide 1,
• - une bride de fixation, 5, symétrique de la bride 3 par rapport au plan de symétrie mentionné ci-avant.

Figure 2, which shows the filter seen at the end, has an axis line, XX, which indicates the cutaway of Figure 1; in addition to this cutaway, the passage from FIG. 2 to FIG. 1 is done by removing the part H from FIG. 2. The filter comprises, with reference to FIGS. 1 and 2:

• - a mounting flange 3,
• - an impedance adapter, 2, which, with the flange 3 has a length of 30 mm and which passes from an internal section of 15.8 x 7.9 mm at its end situated on the side of the flange 2, to an internal section of 14 x 7 mm at its other end,
• - a main guide, 1, rectangular, with an internal section of 14 x 7 mm and 270 mm in length; around the periphery of this main guide are fixed forty lateral assemblies each comprising six secondary, cylindrical guides, such as A1, B1, C1, D1, E1, F1; placed in the same transverse plane of the main guide,
• an impedance adapter 4, symmetrical with the adapter 2 with respect to a plane of symmetry constituted by the transverse plane, not shown, passing through the middle of the guide 1,
• - A fixing flange, 5, symmetrical with the flange 3 with respect to the plane of symmetry mentioned above.

It should be noted that, in the embodiment which is described, it is not only the flanges 3, 5 and the impedance adapters 2.4 which are symmetrical with respect to the plane of symmetry but the whole filter and that thus the filter is perfectly reversible.

• - les six guides secondaires, cylindriques, tels que A1, B1, C1, D1, E1, F1, répartis dans un même plan transversal du guide principal 1 et dont deux, tels que A1, B1, figure 2, débouchent dans l'un des grands côtés du guide 1, et deux autres, tels que D1, E1, débouchent dans l'autre grand côté du guide 1; les deux derniers guides secondaires, tels que C1 et F1, débouchent respectivement dans les deux petits côtés du guide 1; les guides secondaires de ces quarante ensembless ont tous un diamètre intérieur de 5,38 mm et une longueur de 30 mm; dans le sens de la longueur du guide 1 les guides secondaires forment six alignements de quarante guides parallèles, jointifs, tels que B1-B40 et D1-D40 sur la figure 1,
• - des capots qui recouvrent les extrémités des guides secondaires opposées au guide principal; les capots des extrémités des guides secondaires sont associés pour former quatre grands capots G, H, I, J qui recouvrent respectivement tous les guides secondaires tels que A1, B1, tels que C1, tels que D1 et tels que F1,
• -des charges, telles que Lb1, Lb9, Lb40 (figure 1), réalisées en matériau absorbant de 2 mm d'épaisseur, pénètrent dans chacun des guides secondaires par les extrémités situées à l'opposé du guide principal 1; les charges des quarante guides secondaires d'un même alignement sont reliées entre elles à travers des encoches, telles que K, figure 1, pratiquées à l'extrémité des guides secondaires opposée au guide 1, dans la partie jointive des guides successifs d'un même alignement; ces charges forment ainsi six lames de scie, telle que L figure 1, dont les quarante dents constituent donc quarante charges de guides secondaires.

Each of the forty sets discussed above includes:

• - the six secondary, cylindrical guides, such as A1, B1, C1, D1, E1, F1, distributed in the same transverse plane of the main guide 1 and two of which, such as A1, B1, FIG. 2, open into one long sides of guide 1, and two others, such as D1, E1, open into the other long side of guide 1; the last two secondary guides, such as C1 and F1, open respectively into the two short sides of the guide 1; the guides secondary of these forty assemblies all have an internal diameter of 5.38 mm and a length of 30 mm; in the lengthwise direction of the guide 1, the secondary guides form six alignments of forty parallel, contiguous guides, such as B1-B40 and D1-D40 in FIG. 1,
• - covers which cover the ends of the secondary guides opposite the main guide; the covers of the ends of the secondary guides are associated to form four large covers G, H, I, J which respectively cover all the secondary guides such as A1, B1, such as C1, such as D1 and such as F1,
• charges, such as Lb1, Lb9, Lb40 (FIG. 1), made of absorbent material 2 mm thick, penetrate into each of the secondary guides by the ends situated opposite the main guide 1; the loads of the forty secondary guides of the same alignment are connected to each other through notches, such as K, FIG. 1, formed at the end of the secondary guides opposite to guide 1, in the contiguous part of the successive guides of a same alignment; these loads thus form six saw blades, such as L FIG. 1, the forty teeth of which therefore constitute forty loads of secondary guides.

The secondary guides of the filter open into guide 1 through circular holes with a diameter of 5.38 mm, equal to the inside diameter of the guides, except for the first five and the last five guides of each alignment, for which the coupling are of a smaller diameter so as not to capture too large a fraction of the energy of the main guide, 1. In each alignment and from each of the ends of the alignment, the first five holes have respective diameters 4.16, 4.40, 4.67 and 4.95 mm; thus, from the filter ports, the couplings of the secondary guides are progressively increasing, which reduces the power applied to the first loads and makes it possible to avoid destroying them when the input power is high; as this progressive growth of the couplings of the secondary guides is found on each side of the filter, the two ports of the filter can serve as inlet access since there is no need to choose one rather than the other for reasons for power dissipation in the first charges. The thirty other secondary guides of each alignment being all identical to each other and emerging through identical holes in the guide 1, the middle part of the filter in FIG. 1 has not been drawn so that, depending on the space available for Figure 1, the parts shown are drawn to a scale allowing a good understanding of their details.

Figure 3 is a cross section of the filter of Figures 1 and 2, at the height of the eighth side assembly, counting from the left end in Figure 1; this section shows the six secondary guides A8, B8, C8, D8, E8, F8 with their respective loads La8, Lb8, Lc8, Ld8, Le8, Lf8 and their cover G, H, I, J. The loads are fixed in the lids by gluing.

The filter which has just been described is a harmonic filter 2, intended to pass a fundamental frequency between 17.3 and 18.1 GHz. Its performance, for a test power of 1.3 kW, is as follows: for the fundamental the losses are 0.11 dB and the standing wave ratio is 1.035 while for a harmonic 2 of between 34, 6 and 36.2 GHz losses are greater than 50 dB and the standing wave ratio is 1.23.

The realization of this filter posed problems; indeed it had been tried to start from a conventional filter, with rectangular secondary guides, and to simply replace the rectangular secondary guides by circular guides; but it appeared, in addition to the TE11 mode, parasitic modes TE01 and TE02 (called TE10 and TE20 in the Anglo-Saxon literature). The explanation of this phenomenon can be sought in the fact that the rectangular secondary guides of the known art were of small thickness compared to their width, which made that their internal section and therefore their hole for coupling to the main guide were small. ; therefore there was no creation of disturbances in the main guide. On the other hand, with cylindrical secondary guides, the sections are important, since it is no longer possible to reduce a thickness without reducing a width, and this results in significant discontinuities in the wall of the main guide; these discontinuities bring about an artificial widening of the main guide; therefore, the cutoff frequency of the first two parasitic modes TE01 and TE02 is lowered, which creates parasitic resonances which appear, in particular, in the band 17.3-18.1 GHz.

It would have been possible to reduce the dimension of the coupling holes of each of the secondary guides in order to avoid these disturbances; but, still due to the transverse dimensions of the cylindrical secondary guides, it would not have been possible to have enough cylindrical guides to capture the same amount of energy per unit length of the filter and these filters would have been, for the same performances than rectangular secondary guide filters, on the order of twice as long; in most use cases this is not acceptable.

The solution adopted to avoid these drawbacks is, as appears from the description made with the aid of FIGS. 1 to 3, to reduce not only the thickness of the main guide but also its width and, incidentally, to progressively reduce the coupling of the secondary guides in the vicinity of the access points of the filter, the coupling being all the weaker as the secondary guide is closer to an access point.

The present invention is not limited to the example described, thus the main guide of the filter can be associated with secondary guides only by its two long sides or even by only one of its long sides. Likewise the number of secondary guides, if it must at least be equal to 1, is only limited by the space available for the filter; moreover, it is possible to fill the secondary guides with dielectric in order to reduce their section without increasing their cut-off frequency; it is also possible to distribute the secondary guides in different ways along the main guide and, in particular, the distribution may not be regular. As for the impedance adapters at the filter ports, such as 2 and 4 in FIG. 1, they can be of the progressive fitting or discontinuous fitting type.

Claims (4)

1. A filter comprising a rectangular primary waveguide (1), n secondary guides (A1, B1, C1, D1, E1, F1,...), (n being an integer at least equal to 1) coupled by one of their ends to the primary guide via apertures through the wall of said primary guide, and two impedance matching means (2, 4) of the rectangular-guide-to-rectangular- guide coupling type, respectively coupled to the two ends of the primary guide, wherein said secondary guides are cylindrical guides, characterized in that the ends of the impedance transformers are provided with rectangular internal cross sections both the length and width whereof are smaller on the primary guide coupling side than on the side remote from the primary guide.

2. A filter according to claim 1, wherein a number m of the n secondary waveguides (B1...B2...B40) (m and n being at least equal to 3 and m being at most equal to n) are arranged in a row along said primary guide and issue into the primary guide respectively via m apertures in a same side of the primary guide, characterized in that k and p apertures (k and p being integers never greater than m/2) among the m which are respectively the closest to the ends of the primary guide, have cross-sections which are all the smaller for the aperture's closeness to the nearest end of the primary guide.

3. A filter according to claim 1, comprising n loads (Lb1, Lb9, Lb40, La8, Lb8, Lc8, Ld8, Le8, Lf8) of an absorbing material, disposed in the secondary guides in their ends remote from the primary guide, wherein j of the n secondary guides (j and n being at least equal to 2 and j at most equal to n) form a row of juxtaposed guides, characterized in that j of said n loads are juxtaposed to form a saw-blade whose j teeth respectively project into said j secondary guides.

4. A filter according to claim 3, characterized in that a cover (G,H,I,J) is attached to the j juxtaposed loads and covers the remote ends of the j secondary guides with respect to the primary guide.

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