EP0921587B1 - Mikrowellenfilter mit steiler Oberflanke - Google Patents

Mikrowellenfilter mit steiler Oberflanke Download PDF

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Publication number
EP0921587B1
EP0921587B1 EP19980402978 EP98402978A EP0921587B1 EP 0921587 B1 EP0921587 B1 EP 0921587B1 EP 19980402978 EP19980402978 EP 19980402978 EP 98402978 A EP98402978 A EP 98402978A EP 0921587 B1 EP0921587 B1 EP 0921587B1
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EP
European Patent Office
Prior art keywords
guides
filter
waveguide
filter according
cutoff frequency
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.)
Expired - Lifetime
Application number
EP19980402978
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English (en)
French (fr)
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EP0921587A1 (de
Inventor
Olivier Maas
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Thales SA
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Thales SA
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    • 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 we want to obtain.
  • band pass corresponding to the side of the low pass filter that we want to obtain.
  • the number of resonant cells of this bandpass filter depends on the ratio ⁇ '/ ⁇ ' 1 ( ⁇ ' 1 and ⁇ ' being respectively the maximum frequency of the bandwidth 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 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 charge 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 cut-off 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 subject of the present invention is 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 cut-off frequency of the filter, a load being placed at the end of each of the connected guides and these guides being arranged substantially regularly along the line section of propagation, the filter being characterized in that the length of the guides plugged in is greater than about eight times the wavelength in air corresponding to the filter cutoff frequency.
  • 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 coupled 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 (measured parallel to the longitudinal axis of guide 7) 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 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 at 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 cutoff 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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  • Control Of Motors That Do Not Use Commutators (AREA)

Claims (7)

  1. Bandpaßfilter für eine Übertragungsleitung mit einem Leitungsabschnitt (7), der in die Übertragungsleitung (1) eingefügt ist und an den mehrere Hohlleiter (11) angeschlossen sind, deren Grenzfrequenz jenseits der für das Filter geforderten Grenzfrequenz liegt, wobei eine Last (20) am Ende jedes der angeschlossenen Hohlleiter liegt und diese angeschlossenen Hohlleiter im wesentlichen regelmäßig entlang des Leitungsabschnitts angeordnet sind, dadurch gekennzeichnet, daß die Länge der angeschlossenen Hohlleiter größer als etwa die achtfache Wellenlänge in Luft entsprechend der Grenzfrequenz des Filters ist.
  2. Filter nach Anspruch 1, dadurch gekennzeichnet, daß der gegenseitige Achsabstand der Hohlleiter entlang des Leitungsabschnitts, an den sie angeschlossen sind, etwa 1/6 der Wellenlänge in Luft entsprechend der Grenzfrequenz des Filters beträgt.
  3. Filter nach Anspruch 1 oder 2, dadurch gekennzeichnet, daß die Längen der aufeinanderfolgenden angeschlossenen Hohlleiter ungleich sind.
  4. Filter nach Anspruch 3, dadurch gekennzeichnet, daß die Längen der aufeinanderfolgenden angeschlossenen Hohlleiter zufällig variieren.
  5. Filter nach einem der vorstehenden Ansprüche, dadurch gekennzeichnet, daß es aus drei Bauteilen besteht, nämlich zwei Halbschalen (12, 13) symmetrisch bezüglich einer Symmetrie-Ebene (14) des Leitungsabschnitts und einem U-förmigen Bauteil (15), das zusammen mit einer der Wände (10) der Einheit aus den beiden Halbschalen einen Hohlleiter bildet.
  6. Filter nach einem der vorstehenden Ansprüche, in dem die Kopplung zwischen dem Leitungsabschnitt und den angeschlossenen Hohlleitern durch Kopplungsöffnungen (21) erfolgt, wobei dieser Leitungsabschnitt ein Hohlleiter mit nur einer zentralen Längsrippe (8) ist und an einen Hohlleiter mit zwei zentralen Längsrippen (3, 4) angeschlossen ist, dadurch gekennzeichnet, daß die Kopplungsöffnungen in der Mitte des Leitungsabschnitts eine gleiche Länge (L1), an den Enden eine geringere Länge (L2) und dazwischen eine Länge (Ln) besitzen, die von der Länge (L2) an den Enden zur Länge (L1) in der Mitte im wesentlichen linear zunimmt.
  7. Filter nach einem der vorstehenden Ansprüche mit einer Grenzfrequenz im Mikrowellenbereich, dadurch gekennzeichnet, daß es mindestens dreißig angeschlossene Hohlleiter besitzt.
EP19980402978 1997-12-03 1998-11-27 Mikrowellenfilter mit steiler Oberflanke Expired - Lifetime EP0921587B1 (de)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
FR9715228A FR2771857B1 (fr) 1997-12-03 1997-12-03 Filtre hyperfrequence a flanc superieur raide
FR9715228 1997-12-03

Publications (2)

Publication Number Publication Date
EP0921587A1 EP0921587A1 (de) 1999-06-09
EP0921587B1 true EP0921587B1 (de) 2003-09-03

Family

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Family Applications (1)

Application Number Title Priority Date Filing Date
EP19980402978 Expired - Lifetime EP0921587B1 (de) 1997-12-03 1998-11-27 Mikrowellenfilter mit steiler Oberflanke

Country Status (3)

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EP (1) EP0921587B1 (de)
DE (1) DE69817744T2 (de)
FR (1) FR2771857B1 (de)

Family Cites Families (4)

* Cited by examiner, † Cited by third party
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
FR2565416B1 (fr) * 1984-05-30 1987-06-26 Alcatel Thomson Faisceaux Filtre du type guide d'ondes principal charge par des guides d'ondes lateraux

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Publication number Publication date
FR2771857A1 (fr) 1999-06-04
DE69817744D1 (de) 2003-10-09
FR2771857B1 (fr) 2000-02-18
EP0921587A1 (de) 1999-06-09
DE69817744T2 (de) 2004-07-15

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