JPS606564B2 - dielectric filter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a dielectric filter suitable for use particularly in a VHF band to a relatively low frequency microwave band.

Conventionally, as this type of compact filter for the purpose of miniaturization, those using a coaxial resonator or a semi-coaxial resonator are known. For example, outside the dielectric fill using a conventional semi-coaxial resonator, there is generally an outer conductor that also serves as a case, and an inner conductor of a predetermined length whose one end is short-circuited to this outer conductor and whose end is open.
It is composed of a dielectric core inserted between the inner and outer conductors (see FIG. 3). In addition, it is considered effective to manufacture the inner and outer conductors with a resin mold with a conductor coating on the surface in order to reduce the weight and cost of the outside of the electrical conductor film. . However, in a dielectric filter having such a structure, as is well known, a gap is created between the electromagnetic core and the inner and outer conductors due to processing tolerances, and this gap causes variations in the resonant frequency of the resonator. The problem was that it became extremely large.

Furthermore, when molded with resin as described above, problems arise with the temperature characteristics of the resin, particularly the linear expansion coefficient of the resin.
One possible solution to the above-mentioned gap problem is to remove the gap by charging the gap (particularly the gap between the inner conductor and the dielectric core) with a flea-conducting adhesive. However, this method has the disadvantage that extremely large electrical losses occur due to the current flowing on the surface of the inner conductor and the resistance of the adhesive. Therefore, in order to avoid such a phenomenon, it is conceivable to apply a metal coating to the conductor core and to solder the metal coating to the inner conductor. However, in this case, conditions are required such that the resin mold does not deform due to the heat generated for soldering and the metal coating does not peel off. However, in reality, this is extremely difficult, and for this reason, it was conventionally thought that it was impossible to manufacture this type of high-frequency power transfer filter by resin molding. Furthermore, even if the above-mentioned soldering is actually performed, solder flux remains in the void and soldering is difficult, even though the loss in the inner conductor is the dominant loss in the transfer body filter. For these reasons, there was a problem in that losses were not actually improved much. The present invention has been made based on the above-mentioned circumstances, and it is possible to effectively use a resin material with extremely poor temperature characteristics to provide a transparent filter that has a high standard of temperature characteristics and can be produced at low cost and lightweight. The purpose is to provide.

Embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

First, considering the constituent factors that determine the temperature characteristics of the dielectric filter prior to the example, {1' expansion due to temperature of the inner conductor, {2) temperature change in yield rate of the dielectric core and thermal expansion. There are three possible causes: thermal expansion of the outer conductor that also serves as the case.

First, when ceramic is selected as the material for the dielectric core, its linear expansion is about 8'°C, and its variation is extremely small.

On the other hand, the thermal expansion of resin has the disadvantage that it not only has a large coefficient of thermal expansion, but also that the coefficient of thermal expansion differs depending on the direction, and the dispersion of these values is extremely large. Therefore, if the inner and outer conductors of the resonator are made of resin,
As mentioned above, the temperature characteristics are extremely poor, and the variation thereof is extremely large, making it impossible to compensate for the temperature by appropriate means. Therefore, when considering the effect of the resonator on temperature changes theoretically using the cross-sectional view and plan view of the coaxial resonator shown in Figs. 1 and 2, 1 in the figure is the inner conductor,
2 is an outer conductor, solid arrows in FIG. 2 indicate electric field distribution, and broken arrows indicate magnetic field distribution.

The coaxial line impedance ZL when looking from the inner conductor 1 to the coaxial line side in a coaxial line using such a coaxial resonator is expressed by the following formula.・zL=i Australia・1 person {
10 (Q2-Q・)T}.・・・．・・・． ...'11
m/2-PL above formula tl) The middle is the specific impedance, bamboo is the pi, 8 is the propagation constant of the coaxial line, r is the radius of the inner conductor 1, r2 is the radius of the outer conductor 2, Q is the inner The coefficient of linear expansion of conductor 1, Q2 is the coefficient of linear expansion of outer conductor 2, T is the changing temperature, 1
, respectively indicate the height of the inner conductor 1.

Here, since the radius r and the height 1 of the inner conductor 1 are made of the same material, they have the same coefficient of linear expansion.

Furthermore, even if the coefficients of linear expansion Q, Q2 of the inner conductor 1 and the outer conductor 2 are different, the coefficients of linear expansion are usually extremely small, on the order of several tens of times 10-6. {1
10(Q2-Q・)T} is approximately constant as shown in the equation below. ln issue {10 (Q2-Q・)T} ln Sat--
---...-[2}rl Therefore, the above equation {11 can be approximately expressed as the following equation.

・zL〒i ticket・ln2・ ・．・・・．・・・． glue r, m/
2-81, However, in the design of a semi-coaxial resonator, since it is usually designed as Suga-B11go0, a slight change in the height 1 of the inner conductor 1 due to temperature (the coaxial line impedance Z shown in equation 11) I will make a big change.

As mentioned above, it will be understood that the influence of temperature changes on the outer conductor 2 can be almost ignored, and that the influence of temperature changes is mostly due to the expansion of the inner conductor 1. The present invention has been made with attention to such points, and FIG. 3 is a schematic cross-sectional view of a dielectric filter using a semi-coaxial resonator according to an embodiment thereof.

That is, the outer conductor 2, which also serves as a case, and the bottom plate 3 are integrally manufactured by a molding method using a suitable resin material such as polycarbon. On the other hand, the metal inner conductor 1 is fixed to the thin metal plate 11 by caulking, and then heated and press-fitted into the resin case. Further, the surfaces of the inner conductor 1, outer conductor 2 and bottom plate 3 are uniformly and continuously coated with a low resistance metal 5 such as silver, as shown in FIG. Then, the gap between the inner conductor 1 and the outer conductor 2 is filled with the flexible body core 4 and inserted. Here, if the wavelength of the inner conductor and other lines is ^g, it is formed to have a length g, and as shown in the figure, it is installed so that one end is short-circuited to the outer conductor 2 and the other end is open. Ru.
Note that the metal thin plate 11 is electrically unrelated and is simply an inner conductor 1.
used for the sole purpose of mechanical retention. Further, in the figure, 6 is a hole provided in the outer conductor 2 for coupling between adjacent resonators, 7a is a gap between the outer conductor 2 and the dielectric core 4, and 7 is a hole provided in the outer conductor 2 for coupling between adjacent resonators.
b is the air gap between the inner conductor 1 and the dielectric core 4, 8 is the frequency adjustment screw, 9a is the input end loop, 9b is the output end loop,
10 is a shielding plate. According to the dielectric filter configured in this way, when a predetermined high-frequency magnetic field is excited from the input end loop 9a, the low A high frequency current flows through the resistance metal 5 (hereinafter referred to as conductor coating).

The plating thickness required for this conductor coating 5 is sufficient if it is equal to or greater than the skin depth 6 shown in the formula below. 6=, E Tsumaun; sudden;
...-----'41 In the above formula (4), the angular frequency is used, the crest o indicates the vacuum magnetic permeability, and the circle indicates the electrical conductivity of the plated metal.

Thus, in the example shown in FIG. 3, the unloaded Q of the obtained resonator was 1600-2200.

On the other hand, in FIG. 3, the outer conductor 2 is made of brass and the conductor coating 5
When it is silver-plated, the unloaded Q is 1700-1800
Met. Therefore, it can be understood that these two values agree well within the measurement error range, and there is no deterioration in the no-load Q due to the use of the resin. Furthermore, the temperature coefficient of the dielectric filter according to the first embodiment of the present invention shown in FIG. It was exactly the same as the case.

This is in good agreement with the theoretical consideration explained using Equations 11 to [3' above. Therefore, as is clear from the above, the electric power generated by using resin for the outer conductor 2 and the bottom plate 3 is Moreover, when using plated resin as shown in this example, the specific gravity of the resin is 1.4 (in the case of polycarbon) and the specific gravity of metal is 8 (
The weight can be reduced by approximately 1'5 compared to brass (in the case of brass), and there is no need for the cutting time required when using metal materials, making it possible to easily manufacture a uniform dielectric filter that can be easily mass-produced. There are advantages.

As a result, in mass production, compared to the case where the outer conductor 2 and the bottom plate 3 are manufactured by machining cutting from metal materials, when molded from plastic as described above, the material cost including processing cost can be reduced to about 1'10. There are also advantages.

In this type of filter, the resonance frequency of each resonator forming the filter varies due to the influence of the air gap between the dielectric core 4 and the inner conductor 1 and outer conductor 2.

Therefore, in the embodiment shown in FIG. 3, a frequency adjustment screw 8 is provided for adjusting the resonance frequency of each resonator.

FIG. 4 is a schematic cross-sectional view of a main part of a dielectric filter according to another embodiment of the present invention.

That is, in the embodiment shown in FIG. 3, only the inner conductor 1 is made of metal, and the outer conductor 2 and the bottom plate 3 are made of resin mold, but in the embodiment shown in FIG. 4, the inner conductor 1 and the bottom plate 3 are made of metal. This embodiment differs from the embodiment shown in FIG. 3 in that only the outer conductor 2 used is constructed using a resin mold. In other words, when the inner conductor 1 is made of metal and the bottom plate 3 is made of resin mold as in the first embodiment shown in FIG. Due to the distortion caused by the difference in coefficients, cracks occur in the conductor coating 5 at the connection between the inner conductor 1 and the bottom plate 3.

On the other hand, the high frequency current density flowing through the conductor coating 5 is
It is maximum at the connection part between the bottom plate 3 and the bottom plate 3. therefore,
If a crack occurs in the conductor coating 5 at this connection portion as described above, the resistance loss increases and the no-load Q of the resonator decreases. On the other hand, according to the second embodiment shown in FIG. 4, since both the inner conductor 1 and the bottom plate 3 are made of metal, even after long-term use, the inner It is possible to prevent cracks in the conductor coating 5 at the connection between the conductor 1 and the bottom plate 3.As a result, it is possible to eliminate an increase in resistance loss and obtain a high no-load Q that is stable for a long period of time in each resonator. 2 is a resin mold, and there is a risk that cracks will occur in the conductor coating 5 at the joint between the outer conductor 2 and the metal bottom plate 3. However, since the high frequency current density flowing through the conductor coating 5 at that joint is small, the crack will not occur. Even if this occurs, there is little effect on the increase in resistance loss and the decrease in the no-load Q of each resonator.As described above, according to the second embodiment shown in FIG. Although it may be inferior to the first embodiment, when compared with the conventional example, it is possible to obtain the same effect as the first embodiment, and also to prevent a decrease in the no-load Q of the resonator due to cracks in the conductor coating 5. As detailed above, according to the present invention, it is possible to effectively use a resin material with extremely poor temperature characteristics to produce a dielectric filter that is lightweight, low cost, and excellent in mass production without deteriorating electrical characteristics. According to the present invention, since the inner surface of the case, the inner bottom surface, and the inner conductor surface are coated uniformly and continuously with metal, there are no point contact parts during assembly. ,
Constructed so that no contact resistance occurs. Therefore, the no-load Q of each resonator constituting the filter increases, and the insertion loss of the filter decreases. Further, with this configuration, variations in the no-load Q of the resonators forming the filter can be reduced. Furthermore, in the present invention, since the dielectric core is inserted, the filter can of course be made smaller. Furthermore, if the bottom of the case and the inner conductor are made of metal, it is possible to prevent cracks in the coating metal at the connection between the inner conductor and the bottom of the case, thereby preventing an increase in resistance loss, thereby increasing the no-load Q of each resonator. It can be maintained stably and high for a period of time.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a coaxial resonator, FIG. 2 is a plan view of the resonator of FIG. The figure is a schematic cross-sectional view of a main part of a dielectric filter according to another embodiment of the present invention. Wings...inner conductor, 2...outer conductor, 3...bottom plate, 4...dielectric core 5...low resistance metal. Figure 1 Figure 2 Figure 3 Figure 4

Claims (1)

[Scope of Claims] 1 Consists of an inner conductor of a predetermined length, one end of which is short-circuited to the bottom of the case that also serves as a ground conductor and the other end is open, and a dielectric core filled between the inner conductor and the case. 1/4
In a general dielectric filter comprising a wavelength coaxial resonator and appropriate electrical coupling means between the resonator and the outside or between adjacent resonators, the inner conductor is made of metal, and the inner conductor is made of metal; 1. A dielectric filter characterized in that the entire case is made of a resin mold, and the inner surface, inner bottom surface, and each surface of the inner conductor of the case are uniformly and continuously coated with metal. 2. A 1/2-meter conductor consisting of an inner conductor of a predetermined length with one end shorted to the bottom of the case that also serves as a ground conductor and the other end open, and a dielectric core filled between this inner conductor and the case.
In a general dielectric filter comprising a four-wavelength coaxial resonator and appropriate electrical coupling means between this resonator and the outside or between adjacent resonators, the inner conductor and the inner conductor are short-circuited. A bottom surface of the case is made of metal, and a portion of the case other than the bottom surface is made of resin mold, and each surface of the case inner surface, inner bottom surface, and inner conductor is made of metal and is uniformly continuous. A derivative filter characterized by being coated with