JPH03216001A - Dielectric filter - Google Patents

Abstract

PURPOSE:To realize a dielectric band pass filter with ease of manufacture with high Q and able to be sufficiently made small by providing a slot in the center of both upper and lower sides of a dielectric block, and connecting plural blocks in the direction of tube axis. CONSTITUTION:Each resonator 10 is formed by forming a conductor film 12 to nearly all the faces of a dielectric block made of a high dielectric constant ceramics sintered body made of a material such as barrium titanate to obtain a waveguide type resonator. A slot 14 prolonged in a tube axial direction is provided in the middle of both upper and lower sides of the dielectric block and a coupling part (coupling window) 16 without any conductor film is provided at the end in the direction of tube axis. Then, for example, three resonators 10 are connected in the direction of the tube axis to be coupled mutually at coupling windows 16 and an input output section is provided to both ends of the connected structure. Thus, the filter is made small, the band pass characteristic is obtained, the structure is comparatively simple, the manufacture is easy and the Q is high.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a dielectric filter used in microwave bands, etc., and more specifically to a waveguide type resonator in which a conductive film is formed on almost the entire surface of a dielectric block. This concerns a bandpass filter that uses . This dielectric filter is useful, for example, in fields such as microwave multiplex communication, satellite communication, and mobile communication. [Prior art] As one of the bandpass filters used in the microwave band,
There is a waveguide filter that uses a square cavity resonator. In this waveguide filter, resonators equipped with inductive metal windows are connected in multiple stages, and screws are installed on the resonator walls to adjust the resonant frequency. Another technology uses dielectric resonators. A typical example of this is to alternately provide resonator holes and coupler holes in the longitudinal direction of a rectangular parallelepiped dielectric block, and to make resonance This is a quarter wavelength resonant coaxial filter with a conductive film formed on the inner surface of the hole. [Problems to be Solved by the Invention] However, waveguide filters have the disadvantage that they are too large in the microwave band.

On the other hand, dielectric filters have the advantage of being miniaturized because they use a dielectric material with a high relative permittivity, but the structure required to obtain appropriate coupling between each resonant element is complex and requires design, manufacturing, and adjustment. It is complicated, and the Q value is also slightly inferior.

The purpose of the present invention is to eliminate the drawbacks of the prior art as described above, and to provide a dielectric bandpass filter that is easy to manufacture, has a large Q value, and can be sufficiently miniaturized. The present invention, which can achieve the above object, uses a waveguide type resonator in which a conductor film is formed on almost the entire surface of a dielectric flock, and the dielectric blocks extend in the axial direction of the tube. It has a shape with a groove, and a connecting part without a conductive film is provided on the end face in the tube axis direction, and a plurality of the resonators are connected in the tube axis direction and connected to each other at the connecting part, and the resonators are connected to each other at both ends of the connecting structure. This is a dielectric filter equipped with an input/output section.

Here, the shape of the dielectric block is preferably H-shaped in cross section with a groove provided in the center of both upper and lower surfaces. The coupling part between the resonators can be a coupling window without a conductive film at positions facing each other, or a structure in which coupling pins are inserted into each dielectric block in half. The length of the dielectric block in the tube axis direction is 17 times the tube axis wavelength λg.
It is 2.

[Function] Considering the TE mode of a rectangular waveguide, the 1t magnetic field within the waveguide resonates in the width direction and propagates in the tube axis direction.

The lateral resonance satisfies the condition that the lateral width of the waveguide is an integral multiple of a half wavelength. Therefore, the rectangular waveguide basically operates as a Takagi pass filter with a cutoff frequency determined by the geometry of its cross section. If the inside of the rectangular waveguide is made of dielectric material, its large dielectric constant lowers the cutoff frequency and allows miniaturization. When the dielectric block has a groove extending in the direction of the tube axis as in the present invention, the electric field is concentrated in the part of the dielectric lowered by the groove, so that a capacitance (capacitance component) appears to be inserted as a lumped constant. Be like what was done. This capacitance lengthens the overall resonant wavelength and shifts the resonant frequency to a lower value. This allows for further miniaturization. Since the present invention uses a resonator with conductor films on both end faces and dimensions in the tube axis direction in a predetermined direction, the electromagnetic waves introduced inside are reflected at both end faces in the tube axis direction and return to the original direction. resonate. This resonator is coupled to the next resonator by a coupling part. By connecting multiple resonators in the tube axis direction in this way, a good band l! A filter exhibiting excessive characteristics is obtained.

[Embodiment] FIG. 1 is an exploded perspective view showing an embodiment of a dielectric filter according to the present invention, and is an example of a three-stage configuration in which three dielectric resonators are combined.

Each resonator 10 is a waveguide type resonator in which a conductor film 12 is formed on almost the entire surface of a dielectric block of a predetermined shape made of a high dielectric constant ceramic sintered body such as halium titanate. The dielectric block has a groove 14 extending in the tube axis direction at the center of its upper and lower surfaces, and has an H-shaped cross section. The length E of each resonator 10 in the tube axis direction is half the tube axis wavelength λg (ie, l=λg/2).

In the present invention, a joint portion without a conductive film is provided at the end portion in the tube axis direction. In this embodiment, the coupling portions are coupling windows 16 provided on both sides of the lower end face. Three such resonators 10 are connected in the tube axis direction and coupled to each other through a coupling window 16. Although not shown in FIG. 1, input/output sections as described later are provided at both ends of these connecting structures.

In the drawings, the parts marked with small dots are the parts where there is no conductor film and the dielectric base is exposed, and the other parts are covered with the conductor film. The conductor film may be formed by baking silver paste, for example.

FIG. 2 shows the shape of the end face of the resonator IO in the tube axis direction. In the figure, arrows indicate the direction of the electric field. Width aI+
When the height is b1, the width of the groove is al+the height of the dielectric portion sandwiched between the grooves is b2, the cutoff frequency λC is expressed by the following equation.

Note that εr is the relative dielectric constant of the dielectric. For example, εr-90
, al =10mm, ax =5+as,
bI=5o+m. If b2 = 2.5 mm, λ
C is approximately 210mm, and the cutoff frequency fc is approximately 714M.
It becomes H2. Therefore, a microwave band filter can be constructed with a resonator as small as described above.

Also, TE2 when . , T.E. . mode can be placed higher than the fundamental mode and can operate over a wide band.

The structure of the joint is not limited to the above embodiment.
In FIG. 3, a coupling window 18 without a conductor film is provided at one place on the end face of the resonator in the tube axis direction, and the coupling window 18 is brought into close contact with the other to couple with each other. In the example shown in FIG. 4, a common coupling pin 20 is inserted in each half at the center of the end face, and the coupling pins 20 are coupled by the coupling pins 20.

For example, as shown in FIG. 5, the input/output parts provided at both ends of the connecting structure are provided by providing holes 22 in the height direction in the grooves 14 of the resonator 10, and inserting spring input/output terminals 24 into the holes 22. , or insert the coaxial input/output terminal 26. In addition, as shown in FIGS. 6 and 7, portions 28 without a conductive film are provided at both lower portions of the end faces of the resonator 10 located at both ends,
A structure may also be used in which the L-shaped connection terminal 30 connects the bifurcated strinoplane 32 of the board and the input/output conductor pattern 34 of the resonator by soldering or the like. In this case, a portion 36 without a conductive film is formed on the lower surface where the human output portions at both ends of the resonator are provided, to prevent short circuits at that portion. The input/output section may be provided only on one side, but in order to strengthen the coupling, it is preferable to excite from both sides as shown in FIG.

Further, as another embodiment of the present invention, as shown in FIG. 8, there is also a configuration in which a rejection filter 38 is mounted using a groove in a resonator. In this way, a characteristic in which the pass band of the filter becomes even steeper can be obtained.

The above embodiments all have an H-shaped cross section with grooves on the top and bottom surfaces, but depending on the case, a concave cross-sectional structure with grooves on only one side may be used. However, since the Q value decreases in a concave structure, it is preferable to provide grooves of the same size symmetrically like an H-type structure. Further, the number of connected resonators, that is, the number of stages, may be the above two or four or more.

[Effects of the Invention] Since the present invention forms a groove extending in the tube axis direction in a waveguide resonator using a dielectric as described above, the electric field concentrates on the dielectric near the groove and appears concentrated. Since a constant capacitor is inserted, the resonant wavelength becomes longer and the device can be made smaller. In addition, in the present invention, since a plurality of resonators having coupling portions are connected in the tube axis direction and coupled to each other, the present invention exhibits bandpass characteristics and has a relatively simple structure.
It is easy to manufacture, and the Q value is larger than that of conventional coaxial dielectric filters.

[Brief explanation of drawings]

FIG. 1 is an exploded perspective view showing one embodiment of a dielectric filter according to the present invention, and FIG. 2 is an explanatory view showing the dimensions of its cross section and the direction of the electric field. FIGS. 3 and 4 are perspective views showing examples of the configuration of other joints of the present invention. FIG. 5 is an explanatory diagram showing an example of the input/output section in the present invention, FIG. 6 is an explanatory diagram showing another example of the input/output section, and FIG. 7 is an enlarged view thereof. FIG. 8 is a partial perspective view of another embodiment of the present invention. 10... Resonator, l2... Conductor film, 14... Groove,
16.18... Combined window, 20... Combined bin, 24.
... Spring input/output terminal, 26... Coaxial input/output terminal.

Claims (4)

[Claims] 1. In a dielectric filter using a waveguide type resonator in which a conductor film is formed on almost the entire surface of a dielectric block, the dielectric block has a shape having a groove extending in the tube axis direction, and a conductor is provided on the end surface in the tube axis direction. A dielectric filter characterized in that a coupling part without a membrane is provided, a plurality of resonators thereof are connected in the tube axis direction and coupled to each other at the coupling part, and input/output parts are provided at both ends of the coupling structure. . 2. 2. The dielectric filter according to claim 1, wherein the dielectric block has an H-shaped cross section with a groove in the center of both upper and lower surfaces. 3. 3. The dielectric filter according to claim 1, wherein the coupling portion between the resonators is a coupling window without a conductive film provided at positions facing each other. 4. 3. The dielectric filter according to claim 1, wherein the coupling portion between the resonators comprises coupling pins partially inserted into dielectric blocks facing each other.