JPH03284002A - Dielectric filter - Google Patents

Abstract

PURPOSE:To obtain a dielectric filter whose passing band width can be freely set by forming an electromagnetic field non-coupling slit of wide width having a conductive pattern connected to an outer conductor between resonators in which the open end faces of dielectric filters are neighbored. CONSTITUTION:In the dielectric filter 10, two dielectric resonators 1a, 1b are formed on a single dielectric block body 1. Inner conductors 3a, 3b are formed on the inner planes of the resonator through holes 2a, 2b of the block 1, and the outer conductor 4 on the outer peripheral end face of the block. An L-C resonance circuit for the resonators 1a, 1b is comprised of the capacitive component of a dielectric part sandwiched between the inner conductors 3a, 3b and the outer conductor 4, and an inductance component decided by the length of the current route of the inner conductors 3a, 3b and the outer conductor 4. The resonators 1a, 1b are coupled electromagnetically with each other, and decide the passing band width as a filter. The electromagnetic field non-coupling slit 6 of wide width having the conductor patters 5a, 5b connected from an open end face A side to the outer conductor 4 are formed between the resonators 1a, 1b, and an electromagnetic field coupling slit 8 on the bottom plane 7.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a dielectric filter used in a microwave band filter, and more specifically, to a structure that increases the degree of coupling between adjacent resonators. be.

[Prior art]

Conventionally, dielectric filters have been widely used in devices that utilize microwaves, such as personal radios and car telephones, due to their small size and high selectivity.

As shown in FIG. 6, a typical conventional dielectric filter has a single block body 61 made of press-molded and fired dielectric ceramic material, in which a plurality of resonator through holes 62a and 62b are formed, and further through holes 62a and 62b are formed in the block body 61. A conductive film 6 is formed on the inner surface of the holes 62a and 62b.
3a, 63b (inner conductor), and a conductive film (outer conductor) 6 on the outer peripheral surface of the dielectric block except for one surface A where the through hole is exposed.
It was composed of 4. That is, one end surface of the dielectric block body 61 is an open end surface A, and the surface opposite to the open end surface A is a short-circuit end surface B where the inner conductors 63a, 63b and the outer conductor 64 are electrically connected to each other, and one resonator through hole 62a is formed. When paying attention to the inner conductor 63a and outer conductor 64 of the through hole 62a,
An LC resonant circuit is formed by the capacitance component C between the two and the inductance component of the current path flowing from the outer conductor 64 to the inner conductor 63a.

A plurality of such resonators 62a and 62b are formed in the same block body 61 and act as a filter 60.

In this dielectric filter 60, two inner conductors 62a
, 62b includes an even mode that propagates in-phase and an odd mode that propagates in anti-phase. Now, the 6th
In the state shown in the figure, since the dielectric material between adjacent resonators is uniformly filled, the inductive coupling and capacitive coupling between the resonators 62a and 62b are equal, and the even mode resonance frequency Fr. and the resonance frequency Fr of the odd mode. become equal, resulting in a filter 60 with a narrow passband width.

Therefore, conventionally, as shown in FIGS. 7 and 8, in order to make the degree of coupling between adjacent resonators 62a and 62b non-uniform in both modes, an electromagnetic coupling slit 68 or an electromagnetic coupling through-hole There was a dielectric filter 70.80 provided with 69. (JP-A-58-9401, JP-A-58-114
(See No. 601) By forming such electromagnetic field coupling slits 68 and electromagnetic field coupling through holes 69, it becomes possible to generate a pass band width as a filter as shown in FIG.

[Technical Problem to be Solved by the Invention] However, in the dielectric filters 70 and 80 described above, a filter with a desired passband width can be obtained by changing the dimensions of the slits 68 and through holes 69. However, the band width that can change the passband width is small, the degree of freedom in coupling is narrow, and now that dielectric filters 70 and 80 are becoming smaller, the mechanical Due to the deterioration in strength, there was a limit to the shape (amount of removal) of the slit 68 and the through hole 69.

The present invention was devised in view of the above-mentioned problems, and its purpose is to provide a dielectric filter that is small, low-profile, can have a freely designed passband width, and has improved mechanical strength. It provides:

[Specific means for achieving the object] In order to achieve the above-mentioned object of the present invention, the present invention provides a dielectric block with a plurality of resonator through holes, and an inner conductor and an inner conductor on the inner surface of the through hole. An outer conductor is provided on the outer peripheral surface of a dielectric block, one end face is an open end face, the other end face is a short-circuit end face where the inner conductor and the outer conductor are electrically connected, and adjacent resonators are electromagnetically coupled. In the body filter, a wide electromagnetic field decoupling slit having a conductor pattern that conducts with the outer conductor is formed between adjacent resonators on the open end surface, and a through hole for electromagnetic field coupling is formed on the bottom surface of the electromagnetic field decoupling slit. A dielectric filter characterized by having holes or slits formed therein.

[Effect]

The electric field distribution of the two resonators of the dielectric filter is maximum on the open end surface side and zero on the short-circuit end surface side.

In even mode, there is in-phase propagation, so the potentials of both resonators are equal, so there is magnetic coupling between the resonators, and in odd mode, there is anti-phase propagation, so the potentials of both resonators are opposite in sign and negative, and between the resonators. are capacitively coupled.

As in the above structure, by forming an electromagnetic field decoupling slit on the open end face side that is electrically connected to the wide outer conductor, the coupling capacitance in the odd mode can be made smaller than before, and even mode resonance can be achieved. It is possible to shift the resonance frequency of the odd mode to a higher frequency side with respect to the frequency. In other words, by forming the electromagnetic field non-coupling slit from the open end surface side, the opening area of the electromagnetic field coupling slit or the electromagnetic field coupling through hole is not changed.
You can freely adjust the degree of coupling and determine the desired passband width.
The strength of the dielectric filter can be improved.

Also, focusing on a single resonator, the conductor pattern formed in the electromagnetic field decoupling slit has the same potential as the outer conductor,
The opposing area between the inner conductor and the outer conductor increases. This lowers the resonant frequency of the single resonator and increases the height of the resonator.
That is, the height of the entire filter is reduced.

〔Example〕

Hereinafter, the dielectric filter of the present invention will be explained in detail based on the drawings.

FIG. 1 is an external perspective view of a dielectric filter of the present invention. The embodiment will be explained using a filter in which two resonators are formed in a single dielectric block.

In the dielectric filter 10 of the present invention, two dielectric resonators 1a and lb are formed in a single dielectric block l.

Dielectric board o-7 1 is BaO-TiO2 based, ZrO2
-3n02TiO2 system, BaO-3m20. -TiO2
system, BaO-Nd203-TiOz system or Ca0-T
It is made of iO□-3iO□-based ceramic with a predetermined dielectric constant, and is set to a predetermined height depending on the resonance frequency. The dielectric block 1 is formed by press-molding the above-mentioned material and then firing it. During this press molding, the resonator through-holes 2a and 2b and the later-described slits between the resonators as necessary,
A through hole etc. is formed.

A conductor film (hereinafter referred to as inner conductor 3a, 3b) made of silver, copper, etc. is formed on the inner surface of the resonator through holes 2a-, 2b of the dielectric block l, and the openings of the resonator through holes 2a, 2b are formed. A conductor film (hereinafter referred to as "open end surface A") made of silver, copper, etc. is formed on the outer peripheral end surface except for the top surface (hereinafter referred to as open end surface A) of dielectric block l where appears.
An outer conductor 4) is formed. The outer conductor 4 or inner conductors 3a, 3b are also connected to the bottom surface of the block l facing the open end surface A.
The short-circuit end face B is formed so as to be electrically conductive.

The inner conductors 3a, 3b and outer conductor 4 described above are formed by depositing silver, copper, or the like by a method such as printing, coating, or transfer, and then firing.

As a result, the resonators 1a and Ib of the dielectric filter 10 have a capacitance component C of the dielectric portion sandwiched between the inner conductors 3a and 3b and the outer conductor 4, and a current path between the inner conductors 3a and 3b and the outer conductor 4. An LC resonant circuit is constructed by the inductance component determined by the length of .

The two resonators 1aXlb are electromagnetically coupled to each other to determine a predetermined passband width as a filter. As described above, there are two coupling modes of the two resonators 1a and Ib: an even mode and an odd mode. Figure 3 (
a) is a schematic diagram showing the bonding state of even mode;
FIG. 3(b) is a schematic diagram showing the combined state of the odd mode.

In FIG. 3, solid lines represent lines of electric force, and dotted lines represent lines of magnetic force due to coupling of magnetic fields. As is clear from the figure, in the odd mode, the two resonators, more specifically, the two resonator through holes 2a and 2b, are strongly coupled by an electric field, and in the even mode, they are coupled by a magnetic field. There is no electric field coupling. Furthermore, when looking at the distribution of the electric field strength from the open end surface A to the short-circuited end surface B, as shown in FIG. 5, it is stronger on the open end surface A side.

In such a coupling mode, the present invention combines two resonators 1a,
A wide and relatively shallow electromagnetic field non-coupling slit 6 having conductor patterns 5a and 5b electrically connected to the outer conductor 4 from the open end surface A side is formed between Ib, and the electromagnetic field non-coupling slit 6 An electromagnetic field coupling slit 8 is formed on the bottom surface 7 of the dielectric block 6 so that the surface of the dielectric block l is exposed. Since the electromagnetic field decoupling slit 6 is electrically connected to the outer conductor 4,
The dielectric block 1 is formed by press molding, the conductor patterns 5a and 5b are formed at the same time as the outer conductor 4 is attached, and then the electromagnetic field coupling slit 8 is formed by mechanical cutting or the like.

Generally, if the phase velocity Vp is V p = 1 / FTTτ, μ...magnetic permeability ε...Dielectric constant ε　2　ε　O″　E　r ε. ...Dielectric constant in vacuum ε7...Relative permittivity It is.

Here, by forming the electromagnetic field coupling slit 8,
Air (ε,=1) is present in the dielectric block 1, and the dielectric constant is greatly reduced compared to about 90 of the material of the dielectric block 1. This is especially true for the resonance frequency Fr of odd mode coupling. greatly contributes to On the other hand, as is clear from Figure 3(a), even mode coupling is unrelated to changes in relative permittivity ε,
The even mode resonance frequency Fr remains unchanged.

Therefore, the coupling capacitance between the resonators 1a and Ib in the odd mode can be reduced, and as shown in FIG. 4, the odd mode resonance frequency Fr is higher than the even mode resonance frequency Fr8. can be shifted to the higher frequency side. For example, in a filter with a center frequency of 820 MHz, the passband width of 35 MHz can be controlled by changing the depth of the electromagnetic coupling slit 8.

Since the non-coupling slit 6 is formed on the open end surface A side where the electric field strength is relatively strong, the electric field immediately connects to the outer conductor 4.
converges to the ground potential of , blocking this electric field coupling. Therefore, the shape of the non-coupling slit 6 enables control over a wider pass band in addition to the degree of coupling of the electromagnetic field coupling slit 8.

For example, in a filter with a center frequency of 820 MHz,
By further adding the non-coupling slit 6 to the electromagnetic field coupling slit 8, it is possible to control the passband width up to around 40 MHz.

By forming the electromagnetic field decoupling slit 6 in this way, control over a wider passband than before is possible, so when designing a filter with the same passband as before,
The depth of the electromagnetic field coupling slit 8 can be made shallow.

Thereby, the mechanical strength of the filter can be improved.

Furthermore, by forming the electromagnetic field decoupling slit 6,
Focusing on the single resonators 1a and lb, the inner conductors 1a and I
b and the outer conductor 4 and the conductive pattern 5 having the same potential as the outer conductor 4
This means that the facing area will increase. As a result, the capacitance C of the resonators 1a and 1b increases, and the individual resonators 1a and 1
The resonant frequency of resonator 1a can be lowered, and accordingly, the resonator 1a.

It becomes possible to reduce the height of lb.

Therefore, small and low profile resonators 1a and Ib, that is, dielectric filters can be achieved.

According to the present invention, it is possible to control the coupling between the resonators 1a and Ib over a wide range, and to perform control over a wide passband width. For example, to obtain a broadband dielectric filter lO,
This can be achieved by making the electromagnetic field coupling slit 8 deep and the electromagnetic field non-coupling slit 8 shallow. In this way, as described above, in the odd mode, the coupling capacitance is further reduced by forming the conductive patterns 5a, 5b that are electrically connected to the outer conductor 4 in the resonators 1a, 1b near the open end surface A where the coupling capacitance is the largest. This is because you can do what you want.

Conversely, in order to obtain a narrow band dielectric filter 10, the electromagnetic field coupling slit 8 may be made shallow and the electromagnetic field non-coupling slit 6 may be made deep.

FIG. 2 is a schematic perspective view showing another embodiment of the dielectric filter 20 of the present invention. Incidentally, the same parts as in the above-mentioned embodiment are given the same numbers.

In this embodiment, a through hole 9 is formed in a part of the bottom surface 7 of the electromagnetic field coupling slit 8 to reach the short-circuit end surface B.

In this embodiment, the coupling degree of the resonators 1a and lb is determined by the depth of the electromagnetic field non-coupling slit 6 and the size of the electromagnetic field coupling through hole 9, and the broadband dielectric filter l
In order to obtain O, the opening area of the electromagnetic field coupling through hole °9 should be made large and the depth of the electromagnetic field non-coupling slit 6 should be made shallow.

As described above, the resonators 1a, 1
Adjust the degree of coupling between b or dielectric filter IO
The depth of the electromagnetic field coupling slit 8 is determined in consideration of the strength of . That is, assuming that the height of the resonators la and lb is the depth d of the h1 electromagnetic field coupling slit 8, it is desirable that d/h be 0.9 or less. If d/h is 0.9 or more, the mechanical strength of the dielectric filter 1 will deteriorate, making it virtually impossible to achieve the dielectric filter IO.

Furthermore, regarding the electromagnetic field decoupling slit 6, it is desirable that the height of the resonators 1a and Ib be approximately 0.1 of h as an optimum condition.

For example, the electromagnetic field decoupling slit 6 is connected to the resonators 1a and 1b.
If the height of h is 0.3 or more, it becomes impossible to achieve a substantially broadband dielectric filter 10.

In the embodiments described above, the dielectric filter is composed of two resonators 1a and 1b, or the filter may be formed of any number of resonators such as 3, 4, . . . .

[Effects of the present invention]

As described in detail above, a wide electromagnetic field decoupling slit having a conductor pattern that conducts with the outer conductor is formed between adjacent resonators on the open end surface of the dielectric filter, and the electromagnetic field decoupling slit Since a through hole or slit for electromagnetic field coupling is formed on the bottom surface of the dielectric filter, the controllable passband width becomes wider, resulting in a dielectric filter that can be freely set.

Furthermore, by increasing the control width of the passband width, the through holes or slits for electromagnetic field coupling can be minimized, resulting in a dielectric filter with excellent mechanical strength.

Furthermore, by increasing the capacitance of the resonator itself, a resonator with a low resonant frequency becomes possible, resulting in a small, low-profile dielectric filter.

[Brief explanation of the drawing]

FIG. 1 is an external perspective view of the dielectric filter of the present invention,
FIG. 2 is an external perspective view of another embodiment of the dielectric filter of the present invention. 3(a) and 3(b) are schematic diagrams for explaining the combined state of even mode and odd mode, and FIG. 3(a)
) shows the combination state in even mode, and FIG. 3(b) shows the combination state in odd mode. Figure 4 shows the passband width and even mode resonance frequency,
FIG. 3 is a characteristic diagram showing the relationship between the odd mode and the resonance frequency. FIG. 5 is a schematic diagram showing the distribution of electric field coupling strength between the open end face side and the shorted end face side. FIG. 6, FIG. 7, and FIG. 8 are external perspective views showing the structure of a conventional dielectric filter. 10.20, 60, l a, l b, 61a. 221.2b, 62a. 3a, 3b, 63a. 4.64・ ・ ・ ・ 5th revision, 5′g ・′... 6 ・ ・ ・ ・ ・ ・ ・ ・ 7 ・ Medium ・ ・ ・ ・ ・ 8 ・ ・ ・ ・ ・ ・ ・ 9 ・ ・ ・ ・・ ・ ・ ・ A. . . . . Slit, bottom surface, electromagnetic coupling slit, electromagnetic coupling through hole, open end surface, shorted end surface

Claims (1)

[Claims] (1) Provide multiple resonator through holes in the dielectric block,
An inner conductor is provided on the inner surface of the through hole and an outer conductor is provided on the outer peripheral surface of the dielectric block, one end surface is an open end surface, the other end surface is a short-circuit end surface where the inner conductor and the outer conductor are electrically connected, and the inner conductor and the outer conductor are adjacent to each other. In a dielectric filter in which resonators are electromagnetically coupled, a wide electromagnetic field decoupling slit having a conductor pattern that is electrically connected to the outer conductor is formed between adjacent resonators on the open end face, and further the electromagnetic field decoupling slit is A dielectric filter characterized in that a through hole or slit for electromagnetic field coupling is formed on the bottom surface of the coupling slit.