EP1568098B1 - Wide band microwave band separating device - Google Patents

Abstract

The separator comprises an assembly of pairs of pass-band and low-pass filters (2.1 - 2.5). All the filters are made of super-conducting material, cooled in operation to a temperature less than the critical temperature of the material. The filters are arranged in order of decreasing frequency band. The separator for wide band hyperfrequency receivers comprises an assembly of pairs of pass-band and low-pass filters (2.1 - 2.5). Each pair of filters relates to a band of frequencies (Fbn - Fhn) which are to be separated from a range of bands. The pass-band filter has a pass-band lying between Fbn and Fhn (with Fbn less than Fhn), whilst the low-pass filter has a cut-off frequency situated at Fhn-1. All the filters are made of super-conducting material, cooled in operation to a temperature less than the critical temperature of the material. The pairs of filters are arranged in order of decreasing bands of frequency to be separated (channel 5 - channel 1) with respect to distance from the input of the separator.

Description

The present invention relates to a broadband microwave band separator device.

• ■ l'amplificateur de tête (celui qui suit immédiatement l'antenne réceptrice) présente des non-linéarités entraînant la génération de fréquences harmoniques ;
• ■ les mélangeurs des étages hétérodynes génèrent des produits d'intermodulation ;
• ■ la largeur de bande instantanée de ces récepteurs est limitée;
• ■ les filtres des séparateurs introduisent des pertes d'insertion non négligeables ;
• ■ ces mêmes filtres ont une raideur insuffisante des flancs de leur courbe caractéristique atténuation/fréquence ;
• ■ du fait de cette raideur insuffisante, les bandes contiguës se chevauchent ;
• ■ si l'on veut éviter ce chevauchement, on doit écarter les unes des autres les fréquences centrales des canaux, et donc des filtres correspondants, ce qui crée des trous entre bandes contiguës.

Microwave band separators (also called "multiplexers") are devices used in particular in broadband microwave receivers. These receivers receive multichannel signals with adjacent channels that the separators are responsible for separating individually. The performance of these broadband microwave receivers is limited by the following points:

• ■ the head amplifier (the one immediately following the receiving antenna) has non-linearities leading to the generation of harmonic frequencies;
• ■ Mixers of heterodyne stages generate intermodulation products;
• ■ the instant bandwidth of these receivers is limited;
• ■ separator filters introduce significant insertion losses;
• These same filters have an insufficient stiffness of the flanks of their attenuation / frequency characteristic curve;
• Due to this insufficient stiffness, the contiguous bands overlap;
• ■ If this overlap is to be avoided, the center frequencies of the channels, and therefore of the corresponding filters, must be separated from one another, which creates holes between adjacent bands.

Bandpass filters currently used in microwave frequencies are generally of the type with straight lines or folded in "U". Such filters have insufficient stiffness of the flanks of their frequency / attenuation characteristic and insertion losses.

No. 5,838,675 discloses a microwave channel separator having a "manifold" type structure and including limiting amplifiers, which makes it difficult to implement.

The present invention relates to a separator device for broadband microwave receiver of the aforementioned type, this separator device does not have the aforementioned drawbacks of the devices of the prior art.

The separator device according to the invention comprises a set of pairs of band-pass and low-pass filters, and in each pair of filters relating to a frequency band Fb _n -Fh _n to be separated from a set of bands, the band-pass filter has a bandwidth between Fb _n and Fh _n (with Fb _n <Fh _n ), while the low-pass filter has a cutoff frequency located at Fh _n-1 , all the filters being of superconducting material cooled in operation at a temperature below the critical temperature of this material, each pair of filters being made on the same individual bar and having a common input to which these filters are connected directly.

• la figure 1 est un bloc-diagramme d'un dispositif séparateur conforme à l'invention ;
• la figure 2 est une vue en plan d'une paire de filtres faisant partie d'un dispositif séparateur conforme à l'invention ;
• la figure 3 est une vue en plan d'un mode de réalisation préféré d'un filtre passe-bande faisant partie de la paire de filtres de la figure 2 ; et
• la figure 4 est une vue de détail agrandie du filtre de la figure 1.

The present invention will be better understood on reading the detailed description of an embodiment, taken by way of nonlimiting example and illustrated by the appended drawing, in which:

• Figure 1 is a block diagram of a separator device according to the invention;
• Figure 2 is a plan view of a pair of filters forming part of a separator device according to the invention;
• Fig. 3 is a plan view of a preferred embodiment of a bandpass filter forming part of the pair of filters of Fig. 2; and
• Figure 4 is an enlarged detail view of the filter of Figure 1.

The separator device 1 shown diagrammatically in FIG. 1 comprises several pairs of filters, each pair of filters consisting of a bandpass filter and a low-pass filter. In the present case, the separator device comprises five pairs of filters, respectively referenced 2.1 to 2.5, but it is understood that the number of filter pairs of the separator device of the invention may be different, depending on the number of channels contained in the signal received by the microwave receiver to which this separator device belongs.

According to an important characteristic of the invention, the first pair of filters 2.1 connected just after the input 3 is that relating to the highest frequency channel (channel 1 in the example), the second pair, 2.2; connected just downstream of the first pair, refers to the channel (channel 2) at frequencies just below those of channel 1, and so on up to the pair of filters 2.5 (channel 5).

According to an exemplary embodiment, the channels 1 to 5 respectively have the following frequency bands (in GHz): 16-18, 12-16, 8-12, 4-8 and 2-4, but it is understood that these values may be different in other applications.

Each pair of filters 2.1 to 2.5 (2.1 to 2.n in the most general case) is made on the same single support substrate strip, as described below with reference to FIG. separator 1 are fixed in a box with separate cells 4, parallel to each other, and decoupled from each other by electromagnetic shields 5.1 to 5.4 formed on the walls of the boxes of the housing 4. The inlet 3 is connected to the point 5 which is the common input of filters 2.1. The output 6 of the pair of filters 2.1 to the next pair 2.2 is the output of the low-pass filter of the pair 2.1 (opposite its input 5). This output 6 is connected to the input 7 of the pair 2.2 which is the common input of the filters of the pair 2.2 and so on up to the pair 2.5 (outputs 8, 10, 12 respectively connected to the inputs 9, 11 , 13). Finally, the output 14 of the low-pass filter of the pair 2.5 is connected either to a suitable dummy load (in order to absorb residuals from the incident signal) or, for example, to a spectrum analyzer. On the outputs 15 to 19 of the band pass filters pairs 2.1 to 2.5 respectively, the signals from channels 1 to 5 are collected, and only these signals (without harmonics or end parts of the contiguous channels).

FIG. 2 shows one of the strips of the separator 1, for example the bar 2.1. Its bandpass filter is made as follows.

The bandpass filter described here has a bandwidth of 2 or 4 GHz, for a center frequency of between 3 and 20 GHz, but it is understood that the invention is not limited to these values, and that a person skilled in the art will be able, on reading the present description, to modify these values while obtaining the same advantages as with the present example.

The band-pass filter 20 shown in FIGS. 2 to 4 of the drawing comprises, for the present example, twelve lines of electrical length λ / 2 coupled together and referenced L1 to L12, but it is understood that the number of lines d a filter may be different, advantageously between 12 and 16. The stiffness of the flanks of the frequency / attenuation characteristic being a direct function of the number of lines, it may be necessary to seek a compromise between a high stiffness and a large bulk ( generally, devices comprising such filters should have a large number to improve their characteristics, while their size must be limited, for example when these devices are airborne).

L1 and L12 lines are "folded" lines with a general "V" shape. However, according to an important feature of the invention, the two branches of this "V", instead of being rectilinear, are each in the form of a "step" having, at mid-height, a bearing perpendicular to the axis of symmetry of the "V" at each end of which is connected an "amount" parallel to the axis of symmetry of the "V". The successive lines are arranged head-to-tail, so as to be optimally coupled and to reduce the size of the filter. The free end of the line L12 is directly connected to a metallized block E formed on a support bar 21 and constituting the input terminal of the filter 20. The free end of the line L1 is directly connected to a metallized block S formed on the substrate 21 and constituting the output terminal of the filter 20. Of course, the shapes and dimensions of the terminals E and S are determined so as to give them an adequate impedance. It is also understood that, if only the bandpass filter 20 is used, the input of the filter may be on the side of the line L1, and its output on the side of the line L12.

The lines L1 to Ln (n = 12 in the present example) are formed by depositing thin layers of superconducting material on the strip 21 of material having low dielectric losses, such as MgO. The bar 21 has for example a rectangular shape, and the lines L1 to Ln follow one another in a direction 22 parallel to a long side of the bar 21. These lines have a general shape of "V" and the axes of symmetry of these " V "are all parallel to a direction 23 which is perpendicular to the direction 22, the openings of the" V "being alternately directed in the direction otherwise. The common "height" of all the lines L1 to Ln is referenced h (dimension of the lines measured parallel to the direction 23). In detail, and as represented in FIG. 4 for four successive lines Lm-1, Lm, Lm + 1, Lm + 2, all the lines are produced in the following manner, as explained below for the line Lm, identical to all other lines, only the orientation of lines alternating from one line to the next.

The axis of symmetry of the line Lm is referenced 24, and only half of this line is described here (to the left of the axis 24, as seen in FIG. 4), while the other half is deducing the symmetry with respect to the axis 24. The line Lm comprises a first rectilinear section 25 extending over substantially half the height h. This section is parallel to the axis 24 and is distant about h / 2. The section 25 is followed by a section 26 which is perpendicular to it and moves towards the axis 24 without however reaching it. The section 26 is extended by a section 27 parallel to the axis 24, which extends itself by a section 28 perpendicular to the axis 24 and reaching the axis 24. The other half of the line Lm consists of sections 25a to 28a, respectively symmetrical sections 25 to 28 with respect to the axis 24.

Let D be the distance between the sections 25 and 25a. According to a preferred embodiment, the sum of the lengths of the sections 28 and 28a is substantially equal to D / 3, and as a result, the lengths of the sections 26 and 26a are substantially equal to each other at D / 3.

The successive lines L1 to Ln are very close to each other, in order to ensure optimal coupling between them. As indicated in FIG. 4, the distance d between two adjacent lines is advantageously a few tens of micrometers and preferably less than 100 μm for filter lines that can operate at frequencies between 2 and 20 GHz, for example.

The low-pass filter 29 of the strip 2.1 is made in a manner known per se with regard to its topology, the important difference compared to known low-pass filters operating at similar frequencies residing in the fact that the conductive elements of FIG. Low-pass filters of the invention are not conventional metal layers (Cu, Au, ...) but are composed of thin superconducting layers deposited on the same substrate strip 21 as that carrying the band-pass filter described above. -above. For this reason, the low-pass filter 29 will be described here only briefly. This filter 29 comprises several LC cells, for example nine cells 30.1 to 30.9. Each of these cells 30.1 to 30.9 consists of a narrow line, possibly folded in meanders and acting as inductance (referenced 31.3 for the cell 30.3 only, to simplify the drawing) and a rectangular plate (referenced 32.3 for the cell 30.3) acting as a capacitor with the metallization of the other side of the substrate 21 (not visible in the drawing). In the example shown in FIG. 2, the electrodes of the capacitors of the cells 30.1 to 30.8 are of the same dimensions, whereas that of the cell 30.9 is of smaller dimensions. The inductances of the cells 30.2 to 30.8 are identical, while those of the cells 30.1 and 30.9 are smaller. The capacitor of the last cell 30.9 is connected to a small block S1 constituting the output terminal to the next pair (or to the termination for the pair 2.5). Of course, the relative dimensions of the inductances and capacitors of the different cells of the low-pass filter are determined as a function of the relative impedances of the filter and of the elements connected to its input and its output, the impedance matching being able to be taken into account. charge by the first and last cells, or be progressive and affect neighboring cells. Where appropriate, the shapes and dimensions of the conductors connecting the filter cells to the terminals 15 and 16 are such that these conductors provide part of the impedance matching. In the example shown in FIG. 2, the inductor 30.1 is not connected directly to the input terminal E, but to the line L12 of the band-pass filter, almost in the middle, but it is understood that this connection could be performed differently (inductor 30.1 connected directly to the terminal E or to another place of the line L12). Of course, not only all the elements of each bar 2.1 to 2.5 are superconducting material, but also the links between bars, all of the circuits shown in Figure 1 being brought to a temperature below the critical temperature of the superconducting material.

• grâce au fait que tous ses éléments conducteurs sont en matériau supraconducteur, les pertes d'insertion qu'il produit sont très réduites grâce à la faible résistance de surface de ce matériau ;
• grâce à ces pertes d'insertion réduites, on peut brancher le séparateur en tête, immédiatement derrière l'antenne. Ce séparateur est alors suivi d'amplificateurs, ce qui supprime ou diminue très fortement les harmoniques qui, autrement, seraient produites par ces amplificateurs ;
• on réduit la distorsion d'intermodulation des étages hétérodynes ;
• on augmente la largeur de bande instantanée ;
• on augmente la raideur des flancs de la caractéristique atténuation/fréquence des filtres passe-bas et passe-bande, car on peut augmenter le nombre de cellules de chaque filtre grâce à leur très faible résistance ;
• on supprime pratiquement tout chevauchement entre bandes contiguës grâce au fait que les circuits des filtres formés sur les barrettes (2.1 à 2.5) peuvent avoir des dimensions très précises et grâce au fait que les fréquences sont traitées dans l'ordre décroissant de leurs valeurs ;
• les trous entre bandes contiguës peuvent être supprimés par l'utilisation de deux séparateurs à bandes décalées.

The separator device described here has the following advantages:

• thanks to the fact that all its conducting elements are in superconducting material, the insertion losses that it produces are very small thanks to the low surface resistance of this material;
• thanks to these reduced insertion losses, you can connect the separator at the head, immediately behind the antenna. This separator is then followed by amplifiers, which eliminates or greatly reduces the harmonics that would otherwise be produced by these amplifiers;
• the intermodulation distortion of the heterodyne stages is reduced;
• we increase the instantaneous bandwidth;
• the stiffness of the flanks of the attenuation / frequency characteristic of the low-pass and band-pass filters is increased, since the number of cells of each filter can be increased by virtue of their very low resistance;
• virtually eliminating any overlap between adjacent bands by the fact that the filter circuits formed on the bars (2.1 to 2.5) can have very precise dimensions and because the frequencies are processed in descending order of their values;
• the holes between adjacent strips can be eliminated by the use of two offset band separators.

In addition, by cooling the superconducting circuits to a specific temperature, virtually eliminating phase drift and eliminate the need for frequent calibration of the receivers.

Claims (2)

1. Splitter device for wideband microwave receivers, characterized in that it comprises a set of pairs of band-pass and low-pass filters (2.1 to 2.5), and in that, in each pair of filters relative to a frequency band Fb_n-Fh_n to be split from a set of bands, the band-pass filter has a bandwidth between Fb_n and Fh_n (with Fb_n < Fh_n), whereas the low-pass filter has a cut-off frequency located at Fh_n-1, all the filters being made of a superconductive material, cooled in operation to a temperature below the critical temperature of this material, each pair of filters being produced on one and the same individual strip (21) and having a common input (E) to which are directly linked the low-pass filter and the band-pass filter of this same strip, and in that the split band output (S) is that of the band-pass filter, and that the output (S1) to the next pair (6, 8, 10, 12) or to a termination (14) is that of the low-pass filter.
2. Splitter device according to Claim 1, characterized in that the pairs of filters are disposed, from the input of the splitter, in descending order of the frequency bands to be split (channel 5 to channel 1).

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