EP0031275B1 - Microwave window and waveguide with such a window - Google Patents

Description

The present invention relates to microwave windows. It also relates to waveguides comprising such windows.

• - les tubes hyperfréquences et les accélérateurs de particules qui fonctionnent à des pressions sensiblement nulles;
• - les circulateurs, les isolateurs, les lignes coaxiales et les guides d'onde dans lesquels un gaz peut être emprisonné pour augmenter leur tenue en puissance. La pression de ce gaz peut atteindre 3 kg/cm².

A microwave device which operates at a pressure different from atmospheric pressure generally requires a sealed window intended both to isolate it from external atmospheric pressure and to allow the propagation of microwave waves without producing internal reflections or resonances. This is the case, for example, for:

• - microwave tubes and particle accelerators which operate at substantially zero pressures;
• - circulators, insulators, coaxial lines and waveguides in which a gas can be trapped to increase their power handling. The pressure of this gas can reach 3 kg / cm ² .

A microwave window must therefore have a solidity sufficient to withstand a pressure of 1 kg / cm ² , when associated with a microwave device operating at low pressure and to withstand a pressure of 3 kg / cm ² , when it is associated to a device operating at high pressure.

On the other hand, a microwave window must be able to be used in a wide frequency band in which it does not have internal resonances generally designated by the English term of ghost modes, and in which its standing wave rate is low , and therefore the unimportant reflections.

The present invention relates more particularly to microwave windows used in waveguides of rectangular section, but the windows according to the invention can also be used in waveguides of any section, cylindrical or elliptical for example.

Various types of windows are known in the prior art used in waveguides of rectangular section.

• - soit une plaque diélectrique d'épaisseur λ_o/2 occupant toute la section du guide, où Ào est la longueur d'onde correspondant à la fréquence centrale F_a pour laquelle la fenêtre a été réalisée;
• - soit une plaque diélectrique d'épaisseur λ_o/4 occupant toute la section du guide et prolongée en son milieu par deux parties latérales de longueur électrique Àj4 qui occupent le tiers environ de la hauteur totale du guide;
• - soit une simple lame diélectrique mince dans un tronçon de guide d'onde circulaire relié au guide d'onde rectangulaire.

These windows can only be made of dielectric material. In this case, they can include:

• - or a dielectric plate of thickness λ _o / 2 occupying the entire section of the guide, where Ào is the wavelength corresponding to the central frequency F _a for which the window has been produced;
• - or a dielectric plate of thickness λ _o / 4 occupying the entire section of the guide and extended in the middle by two lateral parts of electrical length jj4 which occupy about a third of the total height of the guide;
• - or a simple thin dielectric strip in a circular waveguide section connected to the rectangular waveguide.

These windows can also be formed by a self-closing shutter and by a thin dielectric strip substantially equal to that of the shutter.

Windows according to the prior art, which are used in waveguides of rectangular section, have the drawback of having a very narrow operating frequency band. This defect is essentially due to the presence of ghost modes, for the windows, which include a large volume of dielectric, and to a bad standing wave rate, for the windows comprising an inductive shutter and a dielectric strip because the adaptation does not can be performed only for a given frequency.

Thus, for the windows according to the prior art, the bandwidth of use is generally of the order of 10 to 20% of the central frequency relative to the central frequency with a standing wave rate less than or equal to 1.15.

à proximité d'une lame diélectrique, d'un côté ou des deux côtés de cette lame. On se réfèrerera notamment à la figure 6 de cette demande de brevet.The German patent application DE-A-1,765,640 seeks to attenuate the internal resonances in a transmission band while having a low reflection coefficient, by having one or more transformers in

near a dielectric strip, on one side or both sides of this strip. Reference will be made in particular to FIG. 6 of this patent application.

The problem that the present invention aims to solve is to have a window, more efficient than windows according to the prior art, which does not have internal resonances and has a standing wave rate substantially equal to 1, in a frequency band F, F ₂ of at least 35% _F. around F _o .

The present invention relates to a window for microwave waveguide comprising a half-wave impedance transformer, the wavelength considered corresponding to the center frequency for which the window was produced, characterized in that the half-wave transformer is surmounted in its middle by at least one inductive shutter, the rest of the window being constituted by at least one dielectric strip of thin thickness substantially equal to that of the shutter and in that the respective surfaces of the blades and shutters of the assembly above the transformer are chosen so that the reactance of the slat and shutter assembly is canceled for the central frequency and the height of the transformer is chosen so that in a frequency band centered around the central frequency, the reactance of the transformer which s cancels for the central frequency and the reactance of the blade assembly- shutter surmounting the transformer offset.

According to a preferred embodiment of the invention, the transformer is surmounted in its middle by two inductive flaps, of equal or non-equal dimensions, which surround a dielectric strip.

The windows according to the invention have the advantage of not having internal resonances throughout the normal band of use of the guide, in the fundamental mode. This makes it possible to multiply by 2 or 3, compared to windows according to the prior art, the bandwidth of use with respect to the central frequency, this with a standing wave rate less than 1.10.

• - les figures 1 à 4, des vues en perspective de fenêtres, selon l'art antérieur, utilisées dans des guides de section rectangulaire;
• - la figure 5, une vue en perspective d'un mode de réalisation d'une fenêtre selon l'invention, utilisée dans un guide de section rectangulaire;
• - les figures 6 à 8, des abaques de Smith illustrant le fonctionnement d'une fenêtre selon l'invention;
• - les figures 9 et 10, deux autres mode de réalisation, vus en perspective d'une fenêtre selon l'invention, utilisée dans un guide d'onde de section rectangulaire.

Other objects, characteristics and results of the invention will emerge from the following description, given by way of nonlimiting example and illustrated by the appended figures which represent:

• - Figures 1 to 4, perspective views of windows, according to the prior art, used in guides of rectangular section;
• - Figure 5, a perspective view of an embodiment of a window according to the invention, used in a guide of rectangular section;
• - Figures 6 to 8, Smith charts illustrating the operation of a window according to the invention;
• - Figures 9 and 10, two other embodiments, seen in perspective of a window according to the invention, used in a waveguide of rectangular section.

In the different figures, the same references designate the same elements, but for reasons of clarity, the dimensions and proportions of the various elements are not respected, all the hidden edges are not shown in broken lines and all the cut planes are not not hatched.

Figures 1 to 4 show perspective views of windows, according to the prior art, used in guides of rectangular section, and which has been discussed above. In these figures, a cutaway shows the position of window 2 in guide 1.

In FIG. 1, the window 2 is constituted by a dielectric plate, of thickness λ _o / 2, and of rectangular section which is arranged perpendicular to the sides of the guide and which is fixed to its sides, generally by brazing.

In FIG. 2, the window 2 consists of a dielectric plate 3 of thickness λ _o / 4 occupying the entire section of the guide which is extended in its middle by two lateral parts 4, also of electrical length λ _o / 4. The lateral parts 4 occupy about a third of the total height of the guide.

In FIG. 3, the window 2 is constituted by a simple thin dielectric strip inserted in a section of circular guide 5, connected to the rectangular wave guide 1.

Finally, in FIG. 4, the window 2 consists of an inductive shutter 6 and a dielectric strip 7, of thin thickness substantially equal to that of the shutter. In Figure 4, we distinguished the inductive flap by hatching its surface.

It is known that an inductive flap consists of a thin metal plate placed in the section of the waveguide perpendicular to the short sides of the guide.

FIG. 5 represents a perspective view of an embodiment of a window according to the invention, used in a guide 1 of the rectangular section.

This window 2 is constituted by a half-wave impedance transformer, λ _o / 2, 8. The AO wavelength corresponds to the center frequency _F. for which the window was made.

In the figure, the transformer 8 is produced by a metal plate covering approximately on a half-wavelength λ 2 one of the long sides of the guide.

The window 2 thus consists of a thin dielectric strip 9 surrounded by two inductive shutters 10, of the same dimensions.

The blade and the flaps have substantially the same thickness and they are arranged on the transformer, in its middle, perpendicular to the surface of the transformer and to three sides of the guide.

The blade and the flaps have rectangular sections and the assembly formed by the transformer surmounted by the blade and the flaps hermetically closes the guide.

Figures 6 to 8 represent Smith charts illustrating the operation of a window such as that shown in Figure 5.

In FIG. 6, the variations in the frequency band F ₁ F ₂ centered on F _o of the impedance presented by the assembly made up of the blade 9 and the two flaps 10 have been shown on the Smith chart.

The impedance of this set is pure reactance. After having chosen the thickness of the blade and of the flaps required to obtain the desired rigidity, the respective surfaces of the blade and of the flaps are chosen so that this reactance, which progressively passes through positive, zero and negative values in the direction of increasing frequencies of F, towards F ₂ , vanishes for F _o .

The variations in the impedance of the assembly consisting of the blade 9 and the two flaps 10 are therefore represented on the Smith abacus by a straight line, carried by the axis of the impedances q of the Smith abacus; this line segment is in the half plane of positive impedances for F ,, it passes through the center of the Smith abacus for F _o , then is in the half plane of negative impedances for F ₂ .

In FIG. 7, the variations of the impedance presented by the transformer, alone, connected to a suitable termination, at different points of the guide, have been represented on the Smith abacus for the frequencies F ₁ , F ₀ and F ₂ .

• - π₁, un plan du guide situé du côté du générateur avant le transformateur;
• - π₂, le plan d'entrée du transformateur;
• - π₃, le plan médian du transformateur;
• - π₄, le plan de sortie de transformateur;
• - et enfin π₅, un plan du guide situé du côté de la terminaison adaptée contre le transformateur. Ces différents plans sont indiqués sur la figure 5.

We call:

• - π ₁ , a plane of the guide located on the generator side before the transformer;
• - π ₂ , the transformer input plane;
• - π ₃ , the median plane of the transformer;
• - π ₄ , the transformer output plane;
• - and finally π ₅ , a plane of the guide located on the side of the termination adapted against the transformer. These different plans are shown in Figure 5.

Before the transformer, plane π ₁ , there is adaptation and whatever the frequency, the impedance is represented by the point A which is the center of the Smith chart.

The arrival at the plane π ₂ means, whatever the frequency, a purely resistive impedance decrease and the impedance is represented by point B to the left of point A on the p axis of the resistances of the abacus of Smith.

pour F,, et de

pour F₂.The displacement of the plane π ₂ to the plane π ₄ over the length λ _o / 2 causes a rotation on a circle of radius AB centered at point A in the trigonometric direction. The angle of rotation depends on the operating frequency: it is 2π for F ₀ , of

for F ,, and from

for F ₂ .

At plane π ₄ , the impedance is therefore represented by point C, located on the circle above point B, for F ₁ . The impedance is represented by point B for F ₀ and by point E, located on the circle below point B, for F ₂ .

Finally at plane π ₅ , the transformer is crossed and there is an increase in purely resistive impedance which compensates for the decrease which had occurred at plane π ₂ .

The impedance on the plane π ₅ is therefore represented at the frequencies F ₁ , F ₀ and F ₂ by the points D, A and F which are substantially aligned. on the q axis. Points D and F are located on either side of A.

de π₅ se déduit de l'impédance au plan π₅ par une rotation de 180° du segment de droite DAF.The impedant in the median plane π ₃ distant from

from π ₅ is deduced from the impedance on the plane π ₅ by a 180 ° rotation of the line segment DAF.

Figure 8 represents on the Smith chart the variations of the impedance in the plane π ₃ . In the plane π ₃ , the transformer impedance is therefore a reactance which successively takes negative, zero and positive values in the direction of increasing frequencies, from F ₁ to F ₂ , from D to F.

By comparing FIGS. 6 and 8, it can be seen that the variations in the frequency band F, F ₂ of the impedance of the transformer and of the assembly constituted by the window and the flaps are purely reactive and are in the opposite direction in frequency function.

The window according to the invention comprises both a transformer and an assembly consisting of two shutters and a dielectric strip which surmounts the transformer in its middle. According to the invention, the dimensions of the components of the window are determined so that the impedance of the transformer and that of the assembly formed by the window and the shutters compensate each other in a frequency band F, F ₂ of at least 35 % of F ₀ around F ₀ . There is therefore adaptation and the standing wave rate is substantially equal to 1, in the band F ₁ F ₂ .

As has already been said previously, the thickness of the blade and of the flaps required is generally first chosen to obtain the desired rigidity. The respective surfaces of the blade and of the flaps are then chosen so that the reactance of the blade and flaps assembly is canceled for F _o . Finally, the height h of the transformer is determined. This height conditions the radius AB of the circle centered in A on which the rotation of 2π, 2π F ₁ / F ₀ and 2π F ₂ / F _{0 takes place,} which makes it possible to obtain points C, B, E and then the points DAF. The height h of the transformer is therefore chosen so that the segment DAF obtained in FIG. 8 is the symmetrical with respect to the center of the abacus of the segment represented in FIG. 6, the reactance of the transformer, which is canceled for the central frequency F _o , and the reactance of the blade-shutter assembly overcoming the transformer thus compensating.

A window according to the invention has been tested on a waveguide of rectangular section of dimensions 72 × 34 mm. The thickness of the dielectric strip was 2 mm and that of the flaps 3 mm. It was found that in the entire frequency band of use of the guide from 2.6 to 3.95 GHz, there were no internal resonances. A standing wave rate less than or equal to 1.08 was obtained for a band of use F ₁ F ₂ of 35% of F ₀ around F _o . The use band can exceed 40% of F ₀ around F ₀ with a standing wave rate of 1.5 and 50% of F ₀ around F _o with a standing wave rate of less than 2.

Figures 9 and 10 show two other embodiments, seen in perspective, of a window according to the invention used in a waveguide of rectangular section and the operation of which is identical to that of the window in FIG. 5.

environ les deux grands côtés du guide.In Figure 9, the transformer consists of two metal plates, facing each other, which overlap on the half-wavelength

about the two long sides of the guide.

These metal plates do not necessarily have the same thickness.

environ.The half-wave transformer can also be produced by decreasing, symmetrically or not with respect to the longitudinal median plane of the guide ne (shown in FIG. 9), the height of the guide over the half-wavelength

about.

Likewise, the assembly which surmounts the transformer in its middle, can be constituted as in FIG. 9 with a dielectric strip 9 and with a single inductive flap 10.

The window according to the invention can also comprise an assembly consisting of a dielectric strip surrounded by two inductive shutters of different surfaces.

Finally, the inductive shutters can be constituted by a metal plate or by a metallic deposit partially covering, one or both faces, of the dielectric strip constituting the window which then occupies the entire section of the guide above the transformer.

In FIG. 10, the transformer 8 is produced by an asymmetrical reduction in the height of the guide and has a discontinuity in its middle. The assembly consisting of a dielectric strip 9 and two uneven inductive flaps 10 then rests directly on the walls of the guide. Better power handling is thus obtained.

A window according to the invention such as that shown in FIG. 5 is produced practically in several stages.

First, the assembly consisting of the dielectric strip 9 and the inductive shutters 10 is produced separately.

To do this, a thin copper strip (around 2 mm thick in the case of the window operating in S strip which was discussed above) is brazed around the periphery of the ceramic dielectric strip 9. of copper is simultaneously brazed on a molybdenum hoop, the shape of which is studied so that it constitutes the inductive flaps 10.

The blade-shutter assembly is then brazed at the junction of two half-guides at the same time as the half-guides are brazed to each other.

On each of these half-guides, a half-transformer 8 has previously been brazed.

What has just been described is of course only an embodiment of a window according to the invention.

Claims (9)

1. Hyperfrequency window for wave guide comprising a half-wave impedance transformer (A.) corresponding to the central frequency (F_o) for which the window has been realized, characterized in that the half-wave transformer is topped in its middle, by at least one inductance shutter (10), the remainder of the window being constituted by at least one dielectric blade (9) of slight thickness substantially equal to that of the shutter, and in that the respective surfaces of the blades and the shutters of the assembly topping the transformer are selected so that the reactance of the blades and shutters assembly is reduced to zero for the central frequency (F_o) and the height (h) of the transformer is selected so that, in a frequency band (F₁ F₂) centered about the central frequency (F_o), the reactance of the transformer that is reduced to zero for the central frequency (F_o) and the reactance of the blade-shutter assembly topping the transformer compensate each other.

2. Window according to claim 1, characterized in that it is constituted by two inductance shutters (10), having or not having equal dimensions, surrounding a dielectric blade (9).

3. Window according to one of claims 1 or 2, characterized in that it is realized by brazing a copper band, of slight thickness, both on the dielectric ceramic blade (9) and on a molybdenum collar that constitutes the inductance shutter(s) (10).

4. Window according to one of claims 1 or 2, characterized in that the inductance shutter or shutters are constituted by a metallic deposit, covering partially one or two faces of the dielectric blade (9) constituting the window.

5. Window according to one of claims 1 to 4, characterized in that the half-wave transformer (8) presents a discontinuity in its middle and in that the inductance shutter(s) and the dielectric blade(s) bear directly on the walls of the hyperfrequency wave guide.

6. Utilization of a hyperfrequency window according to one of claims 1 to 5 in a wave guide of rectangular, circular or elliptical section.

7. Utilization of a window according to one of claims 1 to 5 in a wave guide of rectangular section, characterized in that the half-wave transformer (8) is realized by diminution, symetrically or not with respect to the longitudinal median plane (π₆) of the wave guide, of the height of the guide on about a half-length of wave (λ/2).

8. Utilization of a window according to one of claims 1 to 5 in a wave guide of rectangular section, characterized in that the half-wave transformer (8) is constituted by a metallic plate covering on about a half-wave (A/2), at least one of the long sides of the guide.

9. Utilization of a window according to one of claims 1 to 5, in a wave guide of rectangular, circular or elliptical section, characterized in that the window is brazed at the junction of two half-waves at the same time as the half-guides are brazed to each other, each half-guide already comprising a half-transformer (8).

Images