JPS6231843B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a dielectric filter structure that is small and has good electrical characteristics.

FIG. 1 shows a perspective view of a conventional interdigital filter. In the figure, 1-1 to 1-5 are inner conductors, 2-
1 to 2-4 are the gaps between the inner conductors, 3 is the case,
3-1 to 3-3 are the bottom surfaces of the case. Further, the lid 3-4 is omitted in the figure. 4 is an excitation antenna connected to an external terminal and serves as an input/output coupling means. The length of inner conductors 1-1 to 1-5 in the figure is approximately 1/4
wavelength, and one end is located on the bottom of the case 3-1.
and 3-2 are alternately shorted, and the other end is open.
In this case, the necessary amount of coupling between adjacent resonators cannot be obtained unless the short circuit parts are arranged alternately. This type of filter has the disadvantage that the inner conductor is fixed alternately to the two bottom surfaces, which requires a lot of effort to manufacture and is expensive.

FIG. 2 shows a perspective view of a conventional comb line filter. In the figure, 11-1 to 11-5 are inner conductors, one end of which is open, and the other end of which is the same bottom surface 1 of the metal case 13.
Short circuited to 3-1. Inner conductor 11-1 to 11-5
The length of is selected to be sufficiently shorter than 1/4 wavelength. This rod acts as an inductance L, while a capacitance C resonating with L is provided at the tip of the rod by suitable means. In the example of FIG. 2, this capacity is the disk 11a-1
11a-5 and the other bottom surface 13-2 of the case 13. In order to obtain the necessary amount of coupling between adjacent resonators, a gap 12-1~ is created between the inner conductors.
A filter is obtained by providing a coupling antenna 12-4 and further providing a coupling antenna 14 as an input/output coupling means between the external line and the resonators at both ends. In this type of filter, the inner conductors 11-1 to 11-5
Since it is fixed to the same bottom surface 13-1 of the capacitor, the manufacturing cost is reduced in this respect, but on the other hand, it has the disadvantage that it is difficult to manufacture the value of capacitance C with an accuracy of, for example, several percent, which ultimately increases the cost. There is almost no merit to this, the only advantage is that it can be made smaller than an interdigital filter.

Now, in Fig. 1, the inner conductor 1-1 of the resonator
We have described the case where the medium in the space between 1-5 and case 3 is air, but if a material with a large dielectric constant εr is filled, the length of inner conductors 1-1 to 1-5 can be reduced to approximately √
It can be shortened to 1/r. However, the circular inner conductors 1-1 to 1-5 and the flat outer conductor (case 3)
It is difficult to fill the entire area in between with solid dielectric material. The situation during this period is exactly the same in the case of Figure 2.

Therefore, an invention was made that uses concentric dielectrics 31-1 to 31-5 as shown in FIG. 3 (Japanese Patent Application No. 53-142306).

If a resonator structure having the cross section shown in FIG. 3a is used, a filter as shown in FIG. 3b can be constructed, and the electrical coupling between the resonators 31-1 to 31-5 becomes large. 1/4 wavelength resonators 31-1 to 31 as shown in FIG. 3 without using the cross arrangement as shown in FIG.
-5 can be provided with a shorted end on the same bottom surface 33-1 of the case to obtain a filter with the required bandwidth. Therefore, it can be realized at a lower cost than those shown in FIGS. 1 and 2.

However, the filter of FIG. 3 has two drawbacks. First, the circumferences of the dielectrics 31-1 to 31-5 are the same as the bottom surface of the flat plate of the case 3 and the lids 33-3, 3.
3-4 at an extremely narrow portion, and it is difficult to keep the width of the contact portion constant, so the coupling between the resonators tends to fluctuate. Second, since the dielectric columns 31-1 to 31-5 are concentric cylinders, it is difficult to process the dielectrics, and there is a limit to how low the cost can be reduced. Note that the lid 33-4 of the case 3 is omitted in FIG. 3b.

In order to eliminate these drawbacks, the purpose of the present invention is to improve the reproducibility of a certain amount of coupling between resonators by using dielectric columns with a rectangular cross section, to reduce the cost, and to further reduce the size of the resonators. It's about moving forward.

FIG. 4 shows a conventionally considered filter with a cross structure. Figure 4a uses a dielectric with a rectangular cross section.
Fig. 4b is a cross-sectional view of a 1/4 wavelength resonator.
This is a cross-arranged filter made up of the 1/4 wavelength resonators shown in Figure a. In Figure 4, 41-1~
41-5 is a rectangular dielectric column, 41a-1 to 41a
-5 is a circular inner conductor inserted in the central part of the dielectric pillars 41-1 to 41-5 in the hand direction, and 43 is a case formed of a flat metal plate. Said dielectric pillar 41-1
41-5 are in contact with the upper and lower surfaces of the case 43.

In order to simplify the explanation in the sectional view of FIG. 4a, first consider the case where there is no gap 42-1 between the dielectric pillars 41-1 and 41-2.
A filter is obtained by arranging resonators each consisting of an inner conductor 41a-2 and a dielectric column 41-2 in an intersecting manner as shown in FIG. 4B. However, if no gap is provided between adjacent resonators, the amount of coupling between the resonators becomes very large. Therefore, in order to realize a filter with an appropriate bandwidth, the inner conductor 41a-1
Since the distance between the inner conductor 41a-2 and the inner conductor 41a-2 must be increased, it is difficult to miniaturize the filter.

On the other hand, if a gap 42-1 is provided between the dielectric pillars 41-1 and the dielectric pillars, and they are arranged in an intersecting manner as shown in FIG. -1, the dielectric pillar 41
-1 and 41-2 due to the gap 42-1, and as a result, the inner conductor 41a-1 and the inner conductor 41
The distance a-2 can be shortened, and the filter can be made smaller. However, the amount of coupling between the resonators changes quite rapidly with respect to the distance of the gap 42-1. According to experiments, the change in coupling amount between 1 mm and 2 mm gap is 1.9 × 10 ^-2 /mm. For example, if the variation in coupling amount between each resonator is designed to be ±3%, other Assuming that there is no influence, the tolerance of the gap 42-1 must be within ±30 μm. If other factors related to the amount of coupling are taken into consideration, the tolerance of the gap 42-1 will be on the order of microns, making it difficult to actually mass-produce the filter.

Furthermore, it is actually extremely difficult to cross-arrange the resonators within the case 43, which increases the price of the filter.

Examples of the present invention are shown in FIGS. 5, 6, 7, and 11. That is, in the present invention, the shorted ends of the inner conductors of all resonators are arranged on the same bottom surface of the case, and gaps are provided between the resonators. Considering the case where there is no space between the resonators, the electric field coupling and the magnetic field coupling cancel each other out, and as a result, the amount of coupling between the resonators becomes almost zero. If we now create a gap between adjacent resonators, the amount of electric field coupling will decrease rapidly. On the other hand, the amount of magnetic field coupling is hardly affected by the presence of a gap, and as a result, by providing a gap, the amount of coupling between resonators can be increased and a filter with an appropriate bandwidth can be realized. That is, the effect of the gap is exactly the opposite of that in the case of FIG. 4.

According to experiments, when the resonators are placed on the same bottom surface, the sensitivity of the coupling amount to a gap of 1 mm to 2 mm is roughly 5×10 ^-3 . For this reason, the tolerance of the gap is on the order of 0.1 mm, for example, if the variation in the amount of coupling is designed within ±3%, and the filter can be easily realized. However, since the resonators are placed on the same bottom surface, assembly is easy.

FIG. 5 shows a first embodiment of the present invention. FIG. 5a is a partially omitted cross-sectional view, and FIG. 5b is a perspective view of the filter. In Figure 5, 51-1 to 51
-5 is a rectangular dielectric column, 51a-1 to 51a-5 are circular inner conductors, 52-1 to 52-4 are gaps formed between the rectangular dielectric columns 51-1 to 51-5, and 53 is a metal sealed case, 53
-1 to 53-3, 53-4 are flat plates forming the case 53; 54 is a coupling antenna of input/output coupling means;
55a-1 to 55a-5 are protruding electrodes formed on the flat plate 53-3, and 55b-1 to 55b-5 are protruding electrodes formed on the flat plate 53-4. Note that FIG. 5b is a diagram in which the flat plate 53-4 forming the lid is omitted for ease of explanation.

The circular inner conductors 51a-1 to 51a-5 are fixed only on a flat plate 53-1 forming the bottom surface of the case 53. In addition, rectangular dielectric pillars 51-1 to 51-5
1-5 has an insertion hole in the longitudinal direction of the center, into which the circular inner conductors 51a-1 to 51a-5 are inserted. In this inserted state, the rectangular dielectric columns 51-1 to 51
-5 are projecting electrodes 55a-1 to 55a-5, 55b-1 provided on the flat plates 53-3, 53-4 of the case 3.
In contact with ~55b-2.

In addition, in FIG. 5a, 510 is a dielectric column 51
-1 is the part exposed to space, 51c
is a shielding portion where the dielectric pillar 51-1 is in contact with the protruding electrodes 55a-1, 55b-1 of the flat plates 53-3, 53-4. Although no reference numerals are given in FIG. 5b, the same applies to the exposed portions 510 and shielded portions 51c of the dielectric columns 51-2 to 51-5.

Therefore, the protruding electrodes 55a-1 to 55a-
The effect of 5, 55b-1 to 55b-5 is to make the exposed portions 510 of the dielectric pillars 51-1 to 51-5 larger than the shielded portions 51c, so that gaps 52-1 to 52-1 from the resonators are The purpose is to increase leakage of electromagnetic field to 52-4. Therefore, the amount of inter-resonator coupling can be increased regardless of the cross structure or Combuline coupling.

FIG. 5c is a partially omitted cross-sectional view of the second embodiment, in which protrusions 51b and 5 are shown on the rectangular dielectric 51-1.
1d is provided. These protrusions 51b, 51c are in contact with the flat plates 53-3, 53-4 of the case 3, and the projecting electrodes 55a-1 to 55a in FIGS.
-5, Similar to 55b-1 to 55b-5, the exposed portions 510 of the rectangular dielectric columns 51-1 to 51-5 are made larger than the shielded portions 51c, increasing the amount of inter-resonator coupling. be able to. In this case, the flat plates 53-3 and 53-4 of case 3 are
Electrodes 55a-1 to 55a-5, 55b as shown in b
The rest is the same as in FIG. 5b except that 1 to 55b-5 are not provided.

FIG. 6 is a partially omitted cross-sectional view of the third embodiment. 61-1, 61-2 are dielectric columns with a rectangular cross section 61a-1, 61a-2 are circular inner conductors, 63-
3, 63-4 is a flat plate in a sealed metal case. The dielectric pillars 61-1 and 61-2 are fixed to the same bottom surface of the case as in FIG. 5. In the case of FIG. 6, there is no gap between the flat plates 63-3, 63-4 and the opposing dielectrics 61-1, 61-2, but the portion 610 exposed to the space is
The contact portion 61c is made larger than the contact portion 61c. That is, as H in FIG. 6 becomes larger than W, the electromagnetic field of the resonator tends to leak into the gap 62, and the inter-resonator coupling tends to increase.

Furthermore, as a fourth embodiment, as shown in FIG. 7, the amount of coupling can be increased by placing a thin conductor rod 76 on the case surface between the circular conductors at right angles to the circular conductors.

Since the third embodiment has a simple structure, it is possible to theoretically calculate various characteristics of the resonator. Theoretical values and calculated values for the third example will be shown below, and the calculations were performed by analyzing the electromagnetic field using a relaxation method.

Note that the characteristics of the filter are determined by the characteristics of each resonator that is its element.

FIG. 8a shows the theoretical value of the height H of the rectangular dielectric material versus the unloaded Q of the resonator when the diameter 2Rm of the circular inner conductor is used as a parameter, and FIG. 8b shows the experimental value. The experimental value of Q was about 80% of the theoretical value.
The dielectric constant εr of the dielectric used in the calculation is 20, and its
tanδ is 1.4×10 ^-4 and the width of the rectangular dielectric is W = 12
It is [mm].

Figure 9 shows the distance between conductors in the circle Xd (see Figure 6)
The solid line shows the theoretical value of the coupling coefficient between the resonators, and the broken line shows the experimental value. The experimental value is approximately the theoretical value.
50% (width W = 10 [mm], distance between conductors in the circle Xd = 11 [mm]).

FIG. 10 shows the theoretical value of the equivalent dielectric constant εeff, which determines the longitudinal dimension of the resonator. This is the equivalent dielectric constant εeff versus the width W of the rectangular dielectric when the diameter 2Rm of the circular inner conductor is used as a parameter. The height H of the rectangular dielectric is 12 [mm], and the relative permittivity εr of the dielectric is
20, its tanδ is 1.4×10 ^-4 .

The equivalent permittivity εeff is the wavelength in the longitudinal direction of the resonator as λg, and the free space wavelength in the absence of a dielectric as λo.
Then, εeff=(λo/λg) ² (1). Therefore, the length of the circular inner conductor of the 1/4 wavelength resonator is chosen to be 1/4λg, It is. If the space inside the resonator is entirely occupied by a dielectric material with a permittivity of εr, then εfee=εr (3). When a gap exists as in the present invention, the equivalent dielectric constant εeff becomes smaller than the dielectric constant εr of the dielectric into which the circular inner conductor is inserted. FIG. 10 shows this calculated result.

From the above analysis, the unloaded Q of the resonator to minimize filter loss is optimally determined by the height H of the rectangular dielectric and the inner conductor diameter 2Rm. In addition, the amount of coupling between the resonators, which determines the bandwidth of the filter, can be appropriately determined by the distance between the inner conductors Xd (the width W of the rectangular dielectric and the distance S between the dielectrics (see Figure 6)). .

FIG. 11 shows the longitudinal shape of the resonator. Figure 11a shows the length L ₁ of the circular inner conductor and rectangular dielectric.
is approximately 1/4λg, and the tip is opened by a space 100. Figure b shows the case where the capacitor 101 is loaded at the tip of the resonator. It is well known that the length L ₂ of the resonator in FIG. 1B is shorter than the length L ₁ of the resonator in FIG.

In the prototype example of the 850MHz band filter, the volumes of the five-stage filter are approximately 60c.c., 20c.c., and 28c.c. in the structures shown in Figures 3, 5, and 6, respectively. The effect of miniaturization was 1:1/3:1/2, and the effect of miniaturization was most remarkable in the case shown in FIG.

On the other hand, the loss of the filter is 1dB,
They were 1.5dB and 1.1dB.

Therefore, in terms of loss, the one shown in FIG. 7 is better than the one shown in FIG. 5, and has almost the same characteristics as the one shown in FIG. 3.

All of the filters of the present invention have a gap between the resonators, so when designing the filter, it is possible to easily prevent electromagnetic leakage into the gap by changing the width of the gap or inserting and removing conductors from the gap as appropriate to configure the filter. In addition to being able to change the amount of energy, since dielectric columns with a rectangular cross section are used, it is possible to improve the reproducibility of a fixed amount of coupling between resonators after the filter is assembled. Moreover, since the inner conductor is fixed only to one bottom surface of the case without using a cross structure or a comb-line connection, it is possible to produce an extremely inexpensive and compact filter.

In the description of the present invention, the inner conductor is limited to a cylinder, but as a result of theoretical analysis, if the inner conductor is a square cylinder or a flat plate with appropriate thickness and width, the loss will be lower than that of a cylinder. It is clear that miniaturization is not possible.

[Brief explanation of the drawing]

1, 2, and 3 are diagrams showing the structure of a conventional filter, and FIG. 4 is a diagram for explaining a conventional cross-arranged dielectric filter. Figure 5b is a perspective view, and Figure 5a is the first diagram of the present invention.
Figure b is a perspective view of the first embodiment of the invention, Figure c is a cross-sectional view of the second embodiment of the invention, and Figure 6 is a third embodiment of the invention. FIG. 7 is a perspective view of the fourth embodiment of the present invention.
Figure 8 is a diagram showing the height H of the rectangular dielectric versus the unloaded Q of the resonator, Figure 9 is a diagram showing the distance between conductors in a circle versus the coupling coefficient between the resonators, and Figure 10 is the equivalent dielectric constant. FIG. 11 is a diagram showing the longitudinal shape of the resonator according to the present invention. 41-4 ~ 41-5, 51-1 ~ 51-5, 6
1-1~61-2...Rectangular dielectric column, 41a-1~
41a-5, 51a-1 to 51a-5, 61a-
1~61a-2...Circular inner conductor, 42-1~42-
4,52-1 to 52-4,62...Gap, 4
3,53,53-1~53-3,63-3~63
-4...Metal housing, 44, 54...Antenna, 55a-1 to 55a-5, 55b-1 to 55
b-5...Protruding electrode, 51b-1 to 51b-2,5
1d-1 to 51d-2...Protrusions of dielectric material.

Claims (1)

[Claims] 1. A plurality of distributed constant line resonators each comprising a sealed metal housing, a columnar dielectric, and an inner conductor inserted in the longitudinal direction of the center of the dielectric;
In a dielectric filter having input/output coupling means, the columnar dielectric has a substantially rectangular cross section, the inner conductor is substantially cylindrical, and one end of the cylindrical inner conductor is fixed on the same bottom surface of the metal housing. the columnar dielectric is in contact with the metal housing on both opposing sides, and the exposed side of the columnar dielectric is
A dielectric filter characterized in that it is larger than the side surface that is in contact with the metal housing. 2. The dielectric filter according to claim 1, wherein the columnar dielectric member has a substantially rectangular cross section, and the surface that contacts the metal housing is smaller than the surface that does not contact the metal housing. 3. The dielectric filter according to claim 1, wherein the columnar dielectric having a substantially rectangular cross section has a protrusion, and the protrusion contacts the metal housing. 4. The dielectric filter according to claim 1, wherein a protruding electrode is provided on the surface of the metal housing that comes into contact with the columnar dielectric having a substantially rectangular cross section. 5. The dielectric filter according to claim 1 or 2, wherein the amount of electrical coupling between the resonators is obtained by changing the distance between the inner conductors. 6. The amount of electrical coupling between the resonators is obtained by fixing a thin conducting wire in the gap between the dielectrics between the opposing bottom surfaces of the metal housing, or 2. The dielectric filter according to item 2. 7. Claim 3, characterized in that one end of the inner conductor is fixed on the same bottom surface of the metal housing, and a capacitor electrode is provided on the surface of the metal housing opposite to the other end of the inner conductor. The dielectric filter described.