EP0068919B1 - Microwave resonator of the variable capacitor type, comprising dielectric material - Google Patents

Description

The present invention relates to a microwave resonator of the variable dielectric capacitor type placed in a cavity having a longitudinal axis of symmetry AA, the resonator comprising a first and a second cylindrical part, of the same axis XX perpendicular to the axis AA, coupled respectively with two walls facing the cavity, the first part passing right through the wall to which it is coupled and comprising a plunger whose position relative to the second part is adjustable.

Such resonators are known, the first and second parts of which are respectively associated with two walls opposite the cavity to form, for example, with this cavity and other identical resonators, an agile frequency filter, that is to say a filter intended to work in several frequency ranges, or channels and capable of passing quickly from one range or from one channel to another.

French patent number 1 046 593 describes one of these resonators using its figure 5. In this figure are represented a cavity and a resonator of the variable dielectric capacitor type, comprising a first part consisting of a plunger which slides at through a hole drilled directly in a first wall of the cavity, and a second part consisting of a fixed frame disposed on a second wall opposite the first. The plunger comprises a metal rod which is in contact with the cavity in the crossing of the hole; this rod constitutes the movable element of the capacitor. The plunger also comprises, towards the end of the metal rod close to the fixed frame, a layer of dielectric material which constitutes the dielectric of the capacitor.

Although this is not mentioned in the aforementioned patent, the sliding contact between the movable frame and the hole in the wall of the cavity poses production problems; it must indeed be of very good quality so as not to hinder the passage of surface currents between the movable armature and the cavity. Such contact is difficult to achieve, and therefore expensive, especially if the resonator is subjected to frequent adjustment modifications which cause contact wear as is the case in frequency agile filters.

The object of the present invention is to remedy these defects.

This is achieved by preventing sliding contact from occurring in places where currents are present.

According to the invention a resonator of the type indicated at the beginning of this description, the first part of which also includes a metal part pierced right through with a cylindrical hole of axis XX and located at a given distance from the second part, and the plunger of which is adjustable by displacement along the axis XX in the hole so that only one end portion of the plunger can come out of the hole in the direction of the second part, is characterized in that at least this end portion is entirely made of dielectric, allowing to modify only the capacitance of the capacitor without modifying the lines of the electric field in the space located between the two armatures of the capacitor.

It should be noted that resonators having the appearance of the resonator according to the invention are also known, but are not dielectric resonators and, in these known resonators, the plunger is entirely metallic, so that the problem of contact is poses in the same way as with the known dielectric resonators described above.

The present invention will be better understood and other characteristics will appear from the following description and the related figure which shows a resonator according to the invention.

The figure is a partial view, in section, of an agile frequency filter which shows a resonator according to the invention.

The figure represents a portion of a cavity, 1, made in a square guide, of axis of longitudinal symmetry AA. The section plane of the figure is a plane of longitudinal symmetry of the waveguide, parallel to two of the sides of the guide; this section makes it possible to see the internal face of a first side, 12, of the guide as well as the walls 10, 11 which constitute the two sides of the guide perpendicular to the first side 12.

• - une pièce métallique, 20, ayant sensiblement la forme d'une vis munie dune tête et qui est percée sur toute sa longueur d'un trou cylindrique, 24, d'axe XX; la pièce 20 traverse de part en part la paroi 10 du guide à travers un trou fileté,
• - un plongeur 21, 22 comportant: une tige 21, munie d'une tête, et présentant un corps cylindrique de diamètre légèrement inférieur au diamètre du trou 24 et un bâtonnet cylindrique de diélectrique, 22, d'axe XX; le bâtonnet 22 a un diamètre sensiblement égal à la moitié de celui du trou 24 et est collé à l'extrémité de la tige 21 opposée à la tête de cette tige; à cette même extrémité la tige 21 est creusée d'un trou 23 d'axe XX, dans lequel s'enfonce légèrement le bâtonnet de diélectrique 22. Le plongeur 21, 22 est introduit dans le trou 24 par l'ouverture de ce trou extérieure à la cavité de manière que sa tête, de même d'ailleurs que la tête de la pièce métallique 20, soit à l'extérieur de la cavité.

The resonator comprises a first part, 2, and a second part, 3, cylindrical, the axis XX of which is contained in the cutting plane and is perpendicular to the longitudinal axis AA of the guide. Part 2 is fixed to the wall 10 and includes:

• - A metal part, 20, having substantially the shape of a screw provided with a head and which is pierced over its entire length with a cylindrical hole, 24, of axis XX; the part 20 passes right through the wall 10 of the guide through a threaded hole,
• - A plunger 21, 22 comprising: a rod 21, provided with a head, and having a cylindrical body of diameter slightly less than the diameter of the hole 24 and a cylindrical dielectric rod, 22, of axis XX; the rod 22 has a diameter substantially equal to half that of the hole 24 and is glued to the end of the rod 21 opposite the head of this rod; at this same end, the rod 21 is hollowed out with a hole 23 of axis XX, in which the dielectric stick 22 is slightly inserted. The plunger 21, 22 is introduced into the hole 24 by the opening of this external hole to the cavity so that its head, as well as the head of the metal part 20, is outside the cavity.

- a helical spring 25 disposed between the head of the metal part 20 and the head of the rod 21, the role of which is to tend to bring the plunger out of the cavity when by pressure it is pressed towards the interior of the cavity to through hole 24.

Part 3 consists of a cylinder of axis XX, fitted at one of its ends in the wall 11 and comprising at the other of its ends a cylindrical hole 30, also of axis XX and of diameter equal to the diameter of the hole 24 of the metal part 20.

• - un réglage par vissage ou dévissage de la pièce métallique 20 dont l'écartement, e, par rapport au cylindre 3, détermine la fréquence de fonctionnement la plus haute du résonateur,
• - un réglage par enfoncement du plongeur 21, 22 à l'intérieur de la cavité entre deux positions extrêmes: une position où le bâtonnet de diélectrique 22 est tout entier dans le trou 24 et une position où le bâtonnet pénètre, sur une longueur êgale environ au tiers de l'écartement e, dans le trou 30; ces deux positions extrêmes correspondent respectivement à la fréquence la plus haute et à la fréquence la plus basse de fonctionnement du résonateur compte tenu de la position de la pièce métallique 20.

As it is made, the resonator according to the figure allows two adjustments:

• an adjustment by screwing or unscrewing the metal part 20 whose spacing, e, relative to the cylinder 3, determines the highest operating frequency of the resonator,
• - an adjustment by pressing the plunger 21, 22 inside the cavity between two extreme positions: a position where the dielectric stick 22 is entirely in the hole 24 and a position where the stick penetrates, over an equal length approximately a third of the distance e, in the hole 30; these two extreme positions correspond respectively to the highest frequency and to the lowest operating frequency of the resonator taking into account the position of the metal part 20.

It should be noted that, in the case of the example described, the rod 21 of the plunger is a metal rod which, like the metal part 20, the cylinder constituting the part 3 and the interior of the cavity, is made of metal. silvery, but the sliding of this rod 21 in the hole with a metal wall 24 poses practically no problem. In fact, this metal rod 21, at the maximum of the depression of the plunger, remains distant from the orifice of the hole 24 in the cavity; this hole 24 is too small for the waves which circulate in the cavity to propagate therein and for the rod 21 to be subjected to an electric field; there are therefore no surface currents at the level of the sliding contact between the plunger and the metallic part 20. On the other hand, in the case where the stick 22 instead of being in dielectric would have been metallic, this stick, playing the role of antenna, would have led to the formation of surface currents at the level of the sliding contact, with the drawbacks that this represents and which have been indicated above. The dielectric rod, 22, makes it possible to modify the capacitance of the capacitor unipuously, meaning to modify the lines of the electric field in the space situated between the two capacitor plates formed by the metal part 20 and the metal cylinder 3.

It should also be noted that the value of the capacity of the resonator according to the invention is not greatly modified by a slight lack of coaxiality between the plunger and the parts 20 and 3, unlike what occurs with all-metal plunger resonators.

• - diamètre extérieur du cylindre 3 et de la partie en regard de la pièce 20: 5 mm
• - diamètre des trous 24 et 30: 3,5 mm
• - profondeur du trou 30: 10 mm
• - possibilité de réglage de l'écartement e: entre 2,5 et 4 mm
• - fréquence la plus haute d'utilisation comprise entre 1,8 GHz et 3 GHz (fonction de la position de la pièce métallique 20)
• - bande couverte par le résonateur pour une position de réglage de la pièce 20, grâce au déplacement du plongeur 21, 22: 500 MHz (pour une permittivité de diélectrique égale à 20).

The above description refers to a filter made in a waveguide with a square section of 30 mm side. The resonator 2, 3 of this filter has the following dimensions and characteristics:

• - outside diameter of cylinder 3 and of the part opposite the part 20: 5 mm
• - diameter of holes 24 and 30: 3.5 mm
• - depth of hole 30: 10 mm
• - possibility of adjusting the distance e: between 2.5 and 4 mm
• - highest frequency of use between 1.8 GHz and 3 GHz (depending on the position of the metal part 20)
• - band covered by the resonator for a setting position of the part 20, thanks to the displacement of the plunger 21, 22: 500 MHz (for a dielectric permittivity equal to 20).

The invention is not limited to the example described and shown, this is how, for example, the cavity 1 can be produced in a rectangular or round guide and that the rod 22 can be of a diameter just less than that holes 24 and 30. Similarly, the plunger 21, 22 can be made entirely of dielectric and the metal part 20 can be fixed. As for the fixed part, 3, of the resonator, it may not have a hole such as 30, the adjustment of the plunger 21, 22 being effected by bringing the fixed part closer but without penetration. It is also possible to replace, for the plunger, the adjustment system with pressure effect and return spring by a system of the screw-nut type where the screw is constituted by the plunger and the nut by the metal part 20 whose hole 24 is tapped at its upper end.

Claims (3)

1. A microwave resonator of the variable capacitor type, comprising dielectric material and located in a cavity (1) presenting a longitudinal axis of symmetry AA, the resonator including a first (2) and a second cylindrical part (3) of a common axis XX perpendicular to the axis AA, each part being coupled to one of two walls (10, 11) facing the cavity, the first part fully passing through the wall (10) to which it is coupled and comprising a diver (21, 22), the position of which with respect to the second part is adjustable, the first part (2) further comprising a metal piece (20) perforated from one end to the other by a cylindrical hole (24) along the axis XX and located at a given distance (e) with respect to the second part (3), the diver being adjustable by displacement along the axis XX in the hole in such a way, that only a terminal portion (22) of the diver can protrude from the hole towards the second part, characterized in that at least this terminal portion is entirely constituted of dielectric material making it possible to modify only the capacity of the capacitor without modifying the electric field lines in the interspace between the two capacitor plates constituted by the metal piece (20) and the metal cylinder (3).

2. A resonator according to claim 1, characterized in that the given distance (e) is adjustable by adjusting the penetration rate of the metal piece (20) into the wall (10) of the cavity to which the first part is coupled.

3. A resonator according to claim 1, characterized in that the second part (3) is a cylinder which presents a hole (30) at the end disposed facing the first part (2), hole (30) into which the terminal portion (22) of the diver can penetrate.

Images