FR2531815A1 - DIELECTRIC RESONATOR PASSER FILTER HAVING NEGATIVE COUPLING BETWEEN RESONATORS - Google Patents

Abstract

1. A resonator filter comprising a rectangular waveguide (1-3) and n dielectric resonators (R1-R6) disposed inside the waveguide (with n being not less than 4), in which negative coupling is provided between two of the n resonators (R2, R5), the waveguide operating below its cutoff frequency, the filter being characterized in that the waveguide is folded back on itself with a wall (2) that is common between its two folded portions, the two negatively coupled resonators being situated on either side of the common wall, the dimensions of the cross-section of the waveguide being about 2 to 2.5 times the transverse dimensions of the resonators, and in that the filter includes a coupling rod (20) for providing the negative coupling, said rod passing through the common wall via a hole and being electrically separate from the common wall, at least apart from its ends.

Description

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  DIELECTRIC RESONATOR PASSER FILTER,

  HAVING NEGATIVE COUPLING BETWEEN RESONATORS

  The present invention relates to dielectric resonator filters in which at least one negative coupling is formed between two resonators; these filters have amplitude-frequency curves which make them call, as the case may be, elliptical or pseudo-elliptic filters or flat band-pass filters. Such filters are known; an article entitled "Generalized dielectric resonator filters" (see Comsat technical review,

  volume 11, number 4 of 1981 pages 321-343) describes filters comprising

  both cavities whose bottom is covered with a ribbon waveguide (stripline in the Anglo-Saxon literature), common to the cavities and, in each of these cavities, a dielectric resonator isolated from the ribbon waveguide by a dielectric support; the common walls with two cavities do not go down to the ribbon waveguide so as not to create short circuits In these filters, the coupling between resonators is obtained thanks to the ribbon guide which includes quarter-turn lines. wave and three-quarter-wavelength lines whose ends are arranged under the resonators to be coupled The vacuum overvoltage coefficient of these filters does not exceed, for example, 3500 to 4.7 G Hz, in particular because of

  resonance mode TE 011 used for resonators.

  The object of the present invention was mainly to propose a dielectric resonator filter having at least one negative coupling and having a much higher overvoltage coefficient than the

coefficient indicated above.

  This result is obtained, in particular, by using a guide

  rectangular waveform folded back on itself, making it operate

  below its cutoff frequency and performing the negative coupling to

  through the common wall to the two folded portions of the guide.

  According to the invention, a resonator filter comprising a rectangular waveguide and N dielectric resonators (n at least equal to 4) arranged inside the guide, in which a negative coupling is realized

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  between two of the N resonators, is characterized in that the waveguide

  operates below its cutoff frequency and is folded back on itself

  even with a wall common to its two folded parts, the two negatively coupled resonators being located on either side of the common wall, the dimensions of the cross section of the guide being of the order of 2 to 2.5 times the transverse dimensions of the resonators, and in that it comprises a coupling wire for making the negative coupling, this wire passing through the common wall through a hole and being, at least in

  out of its ends, electrically separated from the common wall.

  The present invention will be better understood and other characteristics

  ticks will appear using the following description and figures

which represent:

  Figure 1, a filter according to the invention, capa removed ,.

  FIG. 2, a diagram showing a dielectric resonator, FIGS. 3, 4 and 5 sectional views relating to the filter according to FIG. 1,

  FIGS. 6 to 8 different views of a second filter according to the invention;

  Figure 9 of the graphical results for the filter according to the

figure 6.

  In the different figures, the corresponding elements are

designated by the same references.

  Figure 1 shows a filter according to the invention removed cover This filter is a bandpass filter with dielectric resonators, the 6

  resonators, RI-R 6, are arranged in series in a rectangular waveguide

  folded U-shape which forms the casing, 1, of the filter Access AI, A 2 of this

  two antennal jacks, arranged respectively

  at both ends of the filter So as to resonate the resonators in the TMOII mode and to propagate in the guide a TM mode whose cutoff frequency is greater than that of the TMOII mode of the resonators, the dimensions of the cross section of the guide are taken from the order of 2 to 2.5 times larger than the dimensions

  transversal resonators, in this case it is 2.2.

  In addition, the antennas of the accesses AI, A 2 are directed according to the direction

of propagation in the guide.

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  In order to create in the filter according to FIG. 1 a negative coupling between two non-adjacent resonators (R1 and R5), a wire coupling 20 is produced through the common wall 2 which separates the two folded parts. constituting the U-shaped guide Three embodiments of the wire coupling 20 will be given with reference to FIGS. 3 to 5. The filter housing according to FIG. 1 is assembled by means of screws which pass through the unrepresented lid of the filter to come screw

  in six threaded holes, such as 10, drilled into the filter box.

  FIG. 2 is a diagram showing the distribution of the electromagnetic field around a resonator R for a resonance mode of the TMOII type; the lines of the electric field, Eiont been represented in fine broken lines and the lines of the magnetic field, h have been represented in fine continuous lines The resonance mode TM 01 I which has been chosen for the resonators of FIG. with the filter according to this FIG. 1, a high overvoltage coefficient greater than

4,000.

  FIG. 3 is a sectional view, along the axis XX indicated in FIG. 1, of the filter according to FIG. 1. The resonators R 2 and R 5, as well as the other resonators of the filter, are glued on a support ( 52 for R 2 and 55 for R 5) and this support is itself glued on the bottom of the waveguide The resonator supports, such as 52 and 55, are made of a dielectric material of dielectric constant equal to 2, 5 whereas the dielectric constant of the dielectric resonators such as R 2 and R 5 is equal to 36. In the case of FIG. 3, the wire coupling is produced by a wire 20 which ends with two antennas Ga, G'a arranged perpendicularly. at the wall 20 and at half height of this wall The two antennas G and G'a as they are placed in the vicinity of the resonators R 2 and R 5 carry out a negative coupling, by the lines of the

  electric field, between these two resonators, that is to say that they reduce

  Part of the energy of the resonator R 2 is in phase opposition in the vicinity of the resonator R 5 or vice versa. This negative coupling makes it possible to reduce attenuation peaks across the bandwidth of the filter in order to make more steep the flanks of the curve of

  amplitude-frequency response of the filter considered.

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  Figure 3 which has just been described corresponds to a coupling

  electrical connection between the resonators R 2 and R 5 FIG.

  imparts a magnetic-magnetic coupling between the resonators R 2 and R 5; for this purpose the antennas Ga and G'a of Figure 3 are replaced by two loops Gb, G'b made with the wire 20 which is folded in the vicinity of its ends so as to form two loops in a vertical plane and to come in contact, with its ends, on the wall 2 It should be noted that the conductor 20 is in electrical contact with the wall 2 at its ends, indeed as well in the case of the example of Figure 3 that in that of Figure 4 and in that of Figure 5 which will be described later,

  the wire 20, when it passes through the wall 2, is electrically isolated.

  FIG. 5 is an exemplary embodiment of the wire coupling 20 of FIG. 1 in which the coupling with the resonator R 2 is an electrical coupling produced by means of a Ga antenna similar to that of FIG. 3, while the coupling with FIG. the resonator R 5 is a magnetic coupling produced by means of a loop G'b similar to the G'b loop

of Figure 4.

  It should be noted that theoretically, given the distribution of the magnetic field lines as shown in FIG. 2, the magnetic couplings by the loops Gb and G'b of FIGS. 4 and 5 can only be done if the loops Gb and G 'b are arranged in a vertical plane; in practice it appears that it is also possible to achieve this magnetic coupling with loops arranged differently and even arranged in a horizontal plane; this is due to the fact that the magnetic field, HC is not exactly as shown in Figure 2 and that it undergoes deformations due to the proximity of the walls of the waveguide, so that a coupling loop disposed in a plane parallel to the bottom of the filter housing is still traversed by a portion of the magnetic field. The filter of FIG. 1 is a 6-pole filter constituted by the 6 resonators R1 to R6, the filter which will now be described with reference to FIGS. 6 to 9, is a four-pole filter, designed on the same model that

the filter according to FIG.

  Figures 6, 7 and 8 show respectively the cover filter housing removed, the filter cover and a filter section with its

253 18 1 5

  lid; the cut is made according to the plane whose trace in Figure 6 is noted YY, and only the housing 1 with its lid 3 are shown cut This four-pole filter consists of a rectangular waveguide folded U with series in this waveguide, four resonators R1 to R4 and at the ends of the two-access guide AI, A 2, each consisting of a plug terminated on the guide side by a coupling antenna. FIG. 1 shows the tapped holes such as II which

  allow the fixing of the lid 3 on the housing 1 of the filter.

  As in the previous example shown in FIG. 1, the filter according to FIGS. 6 to 8 is designed to resonate the resonators according to the TMO mode 11 and to propagate in the guide a TM mode whose cutoff frequency is higher than that of the TMOI I mode of the resonators This way of operating the filter makes it possible to obtain a very high free-voltage overvoltage coefficient; it requires, as previously seen, different conditions: the waveguide must operate below its cutoff frequency, the antennas of the accesses of the guide must be arranged according to the direction of propagation of the waves in the guide, the resonators must be arranged in series in the guide and the resonators must have transverse dimensions of the order of 2 to 2.5 times smaller than the transverse dimensions of the guide

considered.

  FIGS. 7 and 8 show that, in addition to holes such as 10 for the passage of screws for fixing the cover 3 in the threaded holes I 1 of the casing 1, the cover 2 has four other holes in which are fixed adjustment elements of the resonance of the resonators, El to E 4, and

  five tapped holes through which pass screws VI to V 5.

  The adjustment elements E1 to E4 are intended for adjusting the frequency of the resonators, they are arranged just above the resonators and are

  constituted by a dielectric disk that a screw also dielectrically

  that allows by screwing in the cover 3 to approach or away at will resonator above which the adjusting element is located The tuning screws VI to V 5 are metal screws to allow to change the couplings between, respectively, the antenna of the access AI and the resonator RI, the resonators RI and R 2, the resonators R 2 and R 3, the

  resonators R 3 and R 4 and the resonator R 4 and the antenna of the access A 2.

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  The filter shown in FIGS. 6 to 8 is a filter in which the dielectric resonators have a dielectric constant equal to 36. This filter, whose housing dimensions are 71.70 x 62 x 30 mm, has been designed to operate in a band. passanger whose center frequency is 6 720 M Hz; the amplitude-frequency response curve of this filter is given in FIG. 9. Two curves are shown in FIG. 9: a curve CI indicated in broken line which represents the response of the filter without the coupling by the coupling wire 20 and a curve C 2 indicated in a solid line which represents the response of the filter when the wire coupling between the resonators R 1 and R 4 is introduced. As it appears in FIG. 9, the sides of the filter response curve have become much stiffer around the bandwidth due to the negative coupling effect introduced by the wire coupling 20; it should also be noted that the bandwidth of the filter with the coupling 20 is narrower than that without the coupling, this being due to the fact that the position of the resonators R1 to R4 of FIG. 6 has been studied without the coupling 20 and was not modified then when the coupling 20 was introduced It is possible to give the bandwidth (with the coupling 20) a width substantially equivalent to that obtained initially (without the coupling 20); to do this we must redefine the position of the resonators in the guide and, subsequently, the

  position of the adjusting elements (E1 to E4) and tuning screws (VI to V5).

  The invention is not limited to the examples described, it is thus that, for example, the number of resonators may be greater than six and may be equal to an odd number, for example five or seven, and that then the U-folded guide will be folded preferably such that a resonator

  is located substantially in the extension of the common wall, that is to say

  in the horizontal bar of the U It is also possible to provide, for example in the case of FIG. 1, two couplings by wire: a first coupling as indicated in FIG. 1 which couples the resonators R 2 and R 5

  and a second coupling that couples the resonators R1 and R6.

2531815 -

  REVE Nb LICATIONS 1 Resonator filter comprising a rectangular waveguide (1-3) and N dielectric resonators (n at least 4) arranged inside the guide (RI-R 6), in which a negative coupling is formed between two (R 2, R 5) N resonators, characterized in that the waveguide operates below its cutoff frequency and is folded back on itself with a wall (2) common to its two folded parts, the two negatively coupled resonators being located on either side of the common wall, the dimensions of the cross section of the guide being of the order of 2 to 2.5 times the transverse dimensions of the resonators, and it comprises a coupling wire (20) for making the negative coupling, this wire passing through the common wall through a hole and being, at least outside its ends, electrically separated from the common wall. 2 filter according to claim 1, characterized in that the wire is

  ends in an antenna on both sides of the common wall (Figure 3).

  3 Filter according to claim 1, characterized in that, on each side of the common wall, the wire forms a loop to come into

  contact at its ends with the common wall (Figure 4).

  4. Filter according to claim 1, characterized in that the wire ends in an antenna of a first c 8 tee of the common wall and forms, on the second side of the common wall, a -boucle, to come into contact with his

  end with the common wall (Figure 5).