EP0921587A1 - Filtre hyperfréquence à flanc superieur raide - Google Patents
Filtre hyperfréquence à flanc superieur raide Download PDFInfo
- Publication number
- EP0921587A1 EP0921587A1 EP98402978A EP98402978A EP0921587A1 EP 0921587 A1 EP0921587 A1 EP 0921587A1 EP 98402978 A EP98402978 A EP 98402978A EP 98402978 A EP98402978 A EP 98402978A EP 0921587 A1 EP0921587 A1 EP 0921587A1
- Authority
- EP
- European Patent Office
- Prior art keywords
- guides
- filter
- section
- frequency
- waveguide
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Granted
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Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01P—WAVEGUIDES; RESONATORS, LINES, OR OTHER DEVICES OF THE WAVEGUIDE TYPE
- H01P1/00—Auxiliary devices
- H01P1/20—Frequency-selective devices, e.g. filters
- H01P1/207—Hollow waveguide filters
- H01P1/209—Hollow waveguide filters comprising one or more branching arms or cavities wholly outside the main waveguide
Definitions
- the present invention relates to a microwave filter with steep upper flank.
- the first and the most widespread, consists in producing a sufficiently wide band-pass filter, that is to say the lower flank of which is situated below the frequency band of the useful signal, the upper flank of this filter. band pass corresponding to the side of the low pass filter that is to be obtained.
- band pass corresponding to the side of the low pass filter that is to be obtained.
- the number of resonant cells of this bandpass filter depends on the ratio ⁇ '/ ⁇ ' 1 ( ⁇ ' 1 and ⁇ ' being respectively the maximum frequency of the passband for which the attenuation of the filter is considered negligible, and the frequency, greater than ⁇ ' 1 , for which the attenuation specified on the upper side of the filter is obtained).
- the second known possibility starts from the technique known as “leaky wave ”, generally used to make harmonic filters. She consists of connecting to a propagation line (waveguide or cable coaxial) a series of waveguides (connected guides) whose dimensions are such that their cut-off frequency is beyond the band of the useful signal and below the band of harmonic signals (including the frequency is an integer multiple of the fundamental signal). In the band passing of the useful signal, the connected guides do not provide disturbance, and the wanted signal travels along the main line without couple in the connected guides. The whole then presents no attenuation in this bandwidth. Beyond the cutoff frequency of the connected guides, the useful signal couples in these connected guides, inside of which it is absorbed by a load placed at the end of these guides connected.
- each connected guide takes a small fraction of the useful signal.
- At the end of the main line there is an attenuation proportional to the number of guides connected and the degree of coupling of each of them with the main line.
- This filtering technique presents the advantage of introducing very low losses in the bandwidth, because the connected guides are not crossed by the incident wave.
- we obtains an attenuation by absorption of the frequencies located beyond the cut-off frequency of the connected guides which is advantageous in particular for harmonic filters arranged at the output of transmitters with tubes.
- the response curve of these filters does not allow them to be use as low pass filters in applications where search for extremely low losses up to the cutoff frequency Fc. Indeed, as shown in Figure 1, well before this frequency of cutoff, (which is determined by the width of the connected guides), we observes a phenomenon of increased filter losses: this is zone Z in figure 1.
- the present invention relates to a low-pass filter for a transmission line, in particular for a microwave waveguide, exhibiting extremely low loss cutoff frequency low (less than about 0.3 dB) and high attenuation (at least 20 dB) from a frequency higher than the cut-off frequency and which as close as possible to this cutoff frequency.
- the low-pass filter according to the invention comprises a section of propagation line inserted in the transmission line on which are connected several waveguides whose cutoff frequency is located above the required cutoff frequency of the filter, and is characterized by that the length of the connected guides is more than about eight times the wavelength in air corresponding to the cut-off frequency of the filter, a load being placed at the end of each of the connected guides, and that these guides are arranged substantially regularly along the section of propagation line.
- the pitch of the guides along of the section of line to which they are connected is approximately 1 / 6th of the wavelength in air corresponding to the cut-off frequency of the filter.
- the lengths of the successive connected guides are uneven, and advantageously distributed randomly along the line.
- the invention is described above with reference to a low-pass filter inserted into a microwave transmission line which is a guide waves, but it is understood that the invention can also be applied to very high frequencies (less than about 1 Ghz) and the lines of coaxial transmission.
- the filter described below has a cutoff frequency of 9.1 Ghz, but it is understood that it can be different.
- this waveguide 1 (FIG. 3) is of the classic type with rectangular section with double central rib longitudinal, that is to say that it has on the internal face of its walls large 2, 3 a central longitudinal “rib” 4, 5 respectively.
- the filter 6 has a main waveguide portion 7 inserted between the two parts of the waveguide 1.
- the inner section of the waveguide 7 has dimensions close to those of waveguide 1, but it has only one edge 8.
- This edge 8 is formed on the face inside of the wide wall 9, corresponding to the wall 3 of the waveguide 1.
- the edge 8 is aligned with the edges 5 of the two parts of the guide 1 and has substantially the same dimensions as the latter.
- the wide wall of the waveguide section 7 opposite the wall 9 is formed by the wall "Lower” 10 of the set of connected guides 11, that is to say the wall in which the coupling irises of the connected guides are practiced.
- the assembly 11 consists of two metal half-shells (12, 13), symmetrical with respect to the plane of symmetry 14 of the waveguide 7.
- the filter body 6 consists of three metal parts 12, 13 and 15 assembled together for example by mechanical tightening.
- Exhibit 15 in "U” shape constitutes with the two "lower” half-walls of the parts 12 and 13 (together forming the wall 10) the waveguide 7 to which are connected the connected guides formed in parts 12 and 13.
- the assembly of parts 12, 13 and 15 constitutes, with the charges absorbent described below, an easy to assemble component for both parts of the waveguide 1.
- This component is called here "low pass filter ", Although strictly speaking the main waveguide 7 does not part of the filter (at least in theory, the main waveguide 1, forming the transmission line, could be uninterrupted and the guides connected, constituting the filter itself, could be coupled to such a guide main).
- the connected guides are produced by precision milling in metal plates intended to form the half-shells 12 and 13.
- long parallel grooves 16 are formed in these plates, leaving a peripheral partition around all of these grooves.
- the different sides of this peripheral partition are referenced 10, 17 and 18 (these two last sides being parallel to grooves 16) and 19 (side opposite to the side 10).
- These fillers 20 have, for example a wedge shape triangular.
- the useful length of the connected guides formed by the grooves is greater than or equal to about eight times the length wave (corresponding to the filter cutoff frequency) in the air.
- the corresponding wavelength is approximately 33 mm, which means that the useful length of connected guides (between wall 10 and load 20 corresponding) is greater than about 260 mm.
- the lengths of the different successive branched guides are unequal, so to avoid any periodicity of their effects.
- the width of all these grooves is approximately 4 mm (this width determines their cutoff frequency, which must be the same for all connected guides) and their pitch of about 5 mm.
- the number of connected guides is at least 30 approximately for an X-band cutoff frequency, and an attenuation of at least minus 30 dB above the cutoff frequency.
- the coupling between the connected guides and the main guide 7 is made by irises 21, that is to say openings made in the partition 10.
- the width (measured parallel to the longitudinal axis of the guide 7) of these irises is equal to or slightly less than that of the guides connected.
- Their length (measured perpendicular to the longitudinal axis of the guide 7, in a plane parallel to the wall 10) is variable in the way following ( Figure 5, on which the embodiment example at 30 is illustrated trendy guides): the ten central irises (referenced IC as a whole) have the same length L1, which is about 15 mm.
- the two extreme irises denoted IE
- IE have a length L2 of approximately 8 mm each
- the eight irises intermediate (on each side of the central irises, not including the IE irises), noted I.I. have a length Ln which increases substantially linearly between the values L1 and L2, which allows to compensate by a coupling transition crescent (iris of increasing length) the passage between the parts of the guide main 1 without guides connected and guide 7 with guides connected.
- a coupling transition crescent iris of increasing length
- the length of the connected guides is such that the loads (20) placed at their ends do not absorb evanescent waves (which in art filters previous, were absorbed, causing losses in the band of these filters).
- the stiffness of the flank results from the sudden passage of the guides connected in the on state, this which causes a frequency very close to the cutoff frequency Fc (and greater than the latter) a strong attenuation of the waves passing through the transmission line. This attenuation is also a function of the number of guides connected.
- These connected guides must all have the same cut-off frequency so that the stiffness of said anterior flank is the best possible. However, in the filter bandwidth, the losses are very low (0.2 dB or better). This is achieved in particular thanks to the three-part embodiment of the filter, which can be machined with high precision. Integration of coupling irises in the same room mechanical that their connected guides avoid electrical contact in an area of maximum electric field, where any resistance of contact generates losses.
- the filter is passed between 4.75 GHz and 9.1 GHz, and its insertion losses are less than 0.3 dB, and from a frequency equal to Fc + 200 MHz, it has attenuation greater than 30 dB.
- the ratio ⁇ '/ ⁇ ' 1 of the filter of the invention is less than 1.025 (whereas for a reactive filter of the prior art with 10 cells, this ratio is 1.18, its losses being approximately 1 dB in bandwidth).
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Abstract
Description
- la figure 1, déjà mentionnée ci-dessus, est un diagramme de l'atténuation en fonction de la fréquence pour un filtre passe-bas connu,
- la figure 2 est une vue en coupe, d'un mode de réalisation du filtre de l'invention,
- la figure 3 est une vue en coupe d'un guide d'ondes sur lequel est branché le filtre de la figure 2,
- la figure 4 est une vue en perspective d'un demi-ensemble de guides branchés du filtre de la figure 2, et
- la figure 5 est une vue de dessous de l'ensemble de guides branchés de la figure 2, montrant les iris de couplage des guides branchés.
Claims (7)
- Filtre passe-bande pour une ligne de transmission, comportant un tronçon (7) de ligne de propagation, inséré dans la ligne de transmission (1) sur lequel sont branchés plusieurs guides d'ondes (11) dont la fréquence de coupure est située au-delà de la fréquence de coupure requise du filtre, caractérisé en ce que la longueur des guides branchés est supérieure à environ huit fois la longueur d'onde dans l'air correspondant à la fréquence de coupure du filtre, une charge (20) étant placée à l'extrémité de chacun des guides branchés, et en ce que ces guides sont disposés sensiblement régulièrement le long du tronçon de ligne de propagation.
- Filtre selon la revendication 1, caractérisé en ce que le pas des guides le long du tronçon de ligne sur lequel ils sont branchés est d'environ 1/6ème de la longueur d'onde dans l'air l'air correspondant à la fréquence de coupure du filtre.
- Filtre selon la revendication 1 ou 2, caractérisé en ce que les longueurs des guides branchés successifs sont inégales.
- Filtre selon la revendication 3, caractérisé en ce que les longueurs des guides branchés successifs sont réparties aléatoirement.
- Filtre selon l'une des revendications précédentes, caractérisé en ce que son corps est réalisé en trois parties : deux demi-coquilles (12, 13) symétriques par rapport au plan de symétrie (14) du tronçon de ligne de propagation et une pièce en forme de « U » (15) formant guide d'ondes avec l'une des parois (10) de l'ensemble des deux demi-coquilles.
- Filtre selon l'une des revendications précédentes, dans lequel le couplage entre le tronçon de ligne de propagation et les guides branchés se fait par des iris de couplage (21), ce tronçon étant un guide d'ondes à une seule nervure centrale longitudinale (8) et étant raccordé à un guide d'ondes à deux nervures centrales longitudinales (3, 4), caractérisé en ce que les iris de couplage ont la même longueur (L1) au milieu du tronçon, une longueur plus petite (L2) aux extrémités, et une longueur (Ln) croissant sensiblement linéairement entre les valeurs (L2) aux extrémités et la valeur au milieu (L1).
- Filtre selon l'une des revendications précédentes, ayant une fréquence de coupure en bande X, caractérisé en ce qu'il comporte au moins 30 guides branchés environ.
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
FR9715228 | 1997-12-03 | ||
FR9715228A FR2771857B1 (fr) | 1997-12-03 | 1997-12-03 | Filtre hyperfrequence a flanc superieur raide |
Publications (2)
Publication Number | Publication Date |
---|---|
EP0921587A1 true EP0921587A1 (fr) | 1999-06-09 |
EP0921587B1 EP0921587B1 (fr) | 2003-09-03 |
Family
ID=9514106
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
EP19980402978 Expired - Lifetime EP0921587B1 (fr) | 1997-12-03 | 1998-11-27 | Filtre hyperfréquence à flanc superieur raide |
Country Status (3)
Country | Link |
---|---|
EP (1) | EP0921587B1 (fr) |
DE (1) | DE69817744T2 (fr) |
FR (1) | FR2771857B1 (fr) |
Citations (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
GB845957A (en) * | 1958-12-15 | 1960-08-24 | Standard Telephones Cables Ltd | Improvements in or relating to electric wave filters |
FR1252509A (fr) * | 1960-03-31 | 1961-01-27 | Thomson Houston Comp Francaise | Filtre pour hyperfréquences |
US4060778A (en) * | 1976-07-12 | 1977-11-29 | Microwave Research Corporation | Microwave harmonic absorption filter |
EP0164050A1 (fr) * | 1984-05-30 | 1985-12-11 | Alcatel Thomson Faisceaux Hertziens | Filtre du type guide d'ondes principal chargé par des guides d'ondes latéraux |
-
1997
- 1997-12-03 FR FR9715228A patent/FR2771857B1/fr not_active Expired - Fee Related
-
1998
- 1998-11-27 DE DE69817744T patent/DE69817744T2/de not_active Expired - Fee Related
- 1998-11-27 EP EP19980402978 patent/EP0921587B1/fr not_active Expired - Lifetime
Patent Citations (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
GB845957A (en) * | 1958-12-15 | 1960-08-24 | Standard Telephones Cables Ltd | Improvements in or relating to electric wave filters |
FR1252509A (fr) * | 1960-03-31 | 1961-01-27 | Thomson Houston Comp Francaise | Filtre pour hyperfréquences |
US4060778A (en) * | 1976-07-12 | 1977-11-29 | Microwave Research Corporation | Microwave harmonic absorption filter |
EP0164050A1 (fr) * | 1984-05-30 | 1985-12-11 | Alcatel Thomson Faisceaux Hertziens | Filtre du type guide d'ondes principal chargé par des guides d'ondes latéraux |
Also Published As
Publication number | Publication date |
---|---|
DE69817744T2 (de) | 2004-07-15 |
DE69817744D1 (de) | 2003-10-09 |
FR2771857B1 (fr) | 2000-02-18 |
EP0921587B1 (fr) | 2003-09-03 |
FR2771857A1 (fr) | 1999-06-04 |
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