JPH0478041B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (1) Technical Field of the Invention The present invention relates to a dielectric filter used in VHF band and UHF band radio equipment.

(2) Background of the technology In general, filters used in portable radios called mobile radios and in-vehicle radio equipment are required to be small, lightweight, and less affected by temperature changes. For this reason, recently, dielectric filters, which are smaller, lighter, and less subject to temperature changes than helical filters and the like, are often used in these devices.

This type of dielectric filter generally consists of a rectangular parallelepiped-shaped dielectric block whose bottom and side surfaces are metallized and provided with an outer conductor film, and a plurality of rectangular parallelepiped dielectric blocks each having an axis in the vertical direction and whose inner surface is metallized and provided with an inner conductor film. It is configured as a band pass filter (hereinafter referred to as BPF) by providing a through hole and further providing a coupling part for connecting to an external circuit on the outside of the through hole located at both ends. In addition, in this type of dielectric filter, the attenuation charge in the attenuation band can be increased by increasing the number of through holes, that is, by increasing the number of resonator stages, but on the other hand, the dielectric block becomes larger. . Furthermore, the amount of attenuation generally required of a filter is often asymmetrical. That is, with respect to the passband, either the high band or the low band, for example, a specific limited band in the high band, needs to be attenuated by a predetermined attenuation amount or more, and the low band may not need to be attenuated so much. Of course, the opposite may also be the case. In such cases, instead of simply increasing the number of through holes to meet the above requirements, it is necessary to create a dielectric filter that can minimize the number of through holes and meet the above requirements. is desired.

(3) Problems with the prior art Figures 1 and 2 are diagrams for explaining a conventional dielectric filter, with Figure 1 being a partially cutaway perspective view, and Figure 2 being A of Figure 1. A cross-sectional view taken along the −A′ line is shown. In both figures, reference numeral 10 indicates the entire dielectric filter, 11 indicates a dielectric block, and 12 indicates a housing. A plurality of through holes 13 are provided in the dielectric block 11, and these through holes 1
An inner conductor film 13a (indicated by crosshatching in the figure) is formed on the inner surface of the dielectric block 11 by metallization using a method such as thick film firing, and the bottom and side surfaces of the dielectric block 11 are similarly metalized to form an outer conductor film 13a. 1
1a is formed. This dielectric block 11
is housed in a housing 12 having input/output connectors 14 and 15 and a frequency adjustment screw 16, thereby forming a dielectric filter 10. Further, in this case, since four through holes 13 are provided, a four-stage filter is formed. The through hole 13 provided in the dielectric 11 is open at one end (in this case, the upper end), and the other end is opened at the outer conductor film 11a.
Since the hole is short-circuited, it is formed as a resonant element that resonates at a frequency where the depth of the hole (or the height of the hole) is around 1/4 wavelength (λ/4). If a suitable excitation body 17 is used as a coupling part and connected to an external circuit via input/output connectors 14 and 15,
Operates as a BPF type dielectric filter. In the figure,
The excitation body 17 is formed of a metal rod fitted into a non-metalized hole 18 provided at both ends of the block 11, and the metal rod 17 and the through hole 13 having the conductive film 13a are connected.

The attenuation characteristics outside the passband (attenuation characteristics in the attenuation band) of such a dielectric filter are determined by the amount of attenuation required for a plurality of specific frequency bands in the attenuation band. That is, the number of stages of the filter is determined by the attenuation characteristic that provides the necessary attenuation amount for this specific frequency band. However, in many cases, the number of filter stages can be reduced if the amount of attenuation required for this specific frequency band is excluded. This is the third
This will be further explained with reference to the drawings.

FIG. 3 is a diagram showing an example of an attenuation characteristic curve of a conventional dielectric filter. In the figure, the vertical axis shows the attenuation amount (dB), the horizontal axis shows the frequency f (MHz),
Curve D shown by a solid line shows the attenuation characteristic curve of a five-stage filter, and curve E shown by a dotted line shows an attenuation characteristic curve of a six-stage filter. For example, if the filter's 3dB bandwidth is
At 25MHz, 35~45M from center frequency f ₀ to high band side
When designing a filter that requires attenuation of 50 dB or more in a specific band 19 separated by Hz, a 5-stage filter will have an attenuation of 50 dB or more from f ₀ to 38.1 MHz, as shown by curve D.
Attenuation of 50dB or more cannot be achieved unless the distance is 50dB or more.
In the case of a 6-stage filter, as shown by curve E, an attenuation amount of 56 dB or more can be obtained at a distance of 35 MHz from f ₀ . Therefore, even if the amount of attenuation on the low band side is equal to or less than curve D (5-stage configuration), it is necessary to form the filter in this case into a 6-stage configuration based on the curve. Also, in this case, the filter's no-load Q ₀ = 1000 (f = 800MHz)
Then, the passing loss at the center frequency f ₀ is 6
In the case of a stage configuration, it is approximately 1.1 dB, and in the case of a five-stage configuration, it is 0.9 dB, resulting in a difference of 0.2 dB. That is, the smaller the number of stages, the better the pass characteristics in the pass band. In this way, in conventional dielectric filters, it is necessary to form a six-stage configuration even under the above conditions, and as a result, the filter becomes larger and the pass loss within the pass band increases. Contains undesirable issues.

(4) Purpose of the invention Therefore, in view of the above-mentioned conventional problems, the present invention has been made to
When it is necessary to attenuate the amount of attenuation in a specific band outside the passband to a predetermined value or more, the number of stages in the filter is practically minimized to make the filter smaller and lighter, and the pass characteristics within the passband are also good. It is an object of the present invention to provide a dielectric filter that can maintain the following properties.

(5) Structure of the invention A plurality of through holes are formed in one dielectric block at predetermined intervals, and an inner surface of the hole forms a resonator whose resonant frequency is a predetermined passing frequency; metallizing all other surfaces of the dielectric block except for one surface including the opening of the hole;
In the 1/4 wavelength resonant coaxial dielectric filter, the coupling portions are provided at both ends of the dielectric block to couple with both end holes of the hole group and to connect to an external circuit, wherein the engagement portion further providing a hole with a metalized inner surface on at least one outer side of the
A specific band blocking resonator having a resonance frequency different from that of the resonant element and having an attenuation pole outside the passband of the filter is formed in the hole, and the coupling portion and the specific band blocking resonator are coupled. A dielectric filter characterized by:

(6) Embodiments of the invention Hereinafter, embodiments of the invention will be described in detail based on the drawings.

FIGS. 4 to 6 are diagrams for explaining embodiments of the present invention.

FIG. 4 is a diagram showing essential parts of an embodiment of a dielectric filter according to the present invention. In the figure, reference numeral 31
31a is a dielectric block, 31a is an external conductor film metalized on the bottom and side surfaces of block 31, and 32, 3 is a dielectric block.
3 and 34 are through holes for forming a resonator; 32
Reference numerals a, 33a, and 34a indicate internal conductor films metalized on the inner surfaces of the through holes, and 35 and 36 indicate capacitors forming coupling portions, respectively.
Further, reference numerals 37 and 38 respectively indicate through holes for forming a resonator for blocking a specific band outside the passband.

In this embodiment, the through holes 3 are metalized inside adjacent to the outside of the resonators 32 and 34.
7 and 38 are provided, and these are formed into a specific band rejection resonator, that is, a band rejection filter (hereinafter referred to as BRF), and through holes 32, 33,
In combination with the BPF formed by 34, a three-stage BPF and a two-stage BPF are formed in the same dielectric block 31.
It is equipped with BRF. Through holes 37, 38
has an internal conductor film 37 metallized on its inner surface.
a, 38a are formed, and these conductor films are formed into a resonant element set to be slightly longer than 1/4 wavelength. These resonators (through holes 37,
38) operates as an inductive element, is coupled with the input/output coupling parts (capacitors) 35 and 36, resonates in series, and operates as a BRF.

The depth (or height) of these conductor films 37a and 38a is set to be slightly longer than 1/4 wavelength of the frequency to be blocked. The dielectric block thus formed is housed in a housing and assembled as a dielectric filter, as in the conventional example shown in FIG. By configuring the BRF in an integrated dielectric filter using this method, a BRF with a simple configuration and high Q can be added. In addition, in FIG. 4, the resonators 37 and 38 may be replaced with either one as necessary
In this case, the amount of attenuation is only halved.

Next, with reference to FIG. 5, the attenuation characteristics of the embodiment shown in FIG. 4 will be explained.

FIG. 5 is a diagram showing the attenuation characteristic curve of the embodiment of the present invention, in comparison with the attenuation characteristic curve of the prior art example (FIG. 3) described above. Accordingly, curves D and E represent the attenuation characteristic curves for conventional filters with a five-stage configuration and a six-stage configuration, respectively. Reference numeral 40 indicates a specific band 35 to 45 MHz away from the center frequency f ₀ toward the lower band side, and indicates a position where the amount of attenuation is 50 dB. Now,
In the case of the embodiment (FIG. 4), since the BRF has a three-stage configuration, the attenuation characteristic of this alone becomes like a curve F shown by a dashed line. However, since the resonant elements 37 and 38 are configured to resonate with the frequency of the specific band 35, the attenuation characteristic of the specific band 35 portion becomes like the curve H shown by the two-dot chain line, and an attenuation amount of 50 dB or more is obtained. . Therefore, the low band side of the attenuation characteristic curve of this example is shown by a curve in which the F'' portion of curve F is changed to curve H, and the high band side is shown by curve F. In addition, the attenuation characteristic shown by curve F is sufficient on the high band side, and if it is necessary to attenuate only the specific band 35 on the low band side by 50 dB or more, in the conventional example, a 6-stage filter is required as described above. However, in this embodiment, as is clear from FIG. 4, the desired attenuation characteristics can be obtained with a filter having essentially a five-stage configuration, with the BPF having a three-stage configuration and the BRF having a two-stage configuration. According to the present invention, it is possible to configure a filter with at least one stage fewer than the conventional example, and as a result, a dielectric filter that is small, lightweight, and can maintain good passband characteristics is realized. can do.

Further, according to the present invention, the resonators 37 and 38 forming the BRF are the resonators 32, 33, and 34 of the BPF.
It is also possible to form it shorter than that. In this case, contrary to the example, the resonant element resonates at the frequency of a specific band on the high band side and blocks (attenuates) this frequency.
Therefore, the attenuation characteristic curve becomes as shown in FIG. That is, in this case, the BRF resonant element is formed so that it resonates in a specific band 19 that is 35 to 45 MHz away from the center frequency f ₀ toward the high band side and can attenuate the amount of attenuation in that band to 50 dB or more. become. Therefore, the high band side of this attenuation characteristic curve is shown by a curve in which the F' portion of curve F is changed to curve G,
The low band side is shown by curve F.

(7) Effects of the Invention As explained in detail above, the dielectric filter of the present invention has the following effects by providing a specific band rejection filter (BRF) having an attenuation pole outside the passband.
The advantage is that it has a simple configuration, can be made small and lightweight, and can maintain good pass characteristics within the pass band.

[Brief explanation of the drawing]

Fig. 1 is a partially cutaway perspective view of a conventional dielectric block, Fig. 2 is a cross-sectional view taken along line A-A' in Fig. 1, and Fig. 3 is a diagram showing the attenuation characteristic curve of a conventional dielectric filter. , FIG. 4 is a diagram showing a main part of an embodiment of a dielectric filter according to the present invention, FIG. 5 is a diagram showing an attenuation characteristic curve of the embodiment shown in FIG. 4, and FIG. It is a figure which shows the attenuation characteristic curve of an Example. 31...Dielectric block, 31a...Outer conductor film, 32, 33, 34...Through hole (resonator) of BPF, 32a, 33a, 34a...Inner conductor film of BPF, 35, 36...Capacitor, 37, 38...
...BRF through holes (resonators), 37a, 38a...
BRF internal conductor membrane.

Claims (1)

[Claims] 1. A plurality of through holes are formed at a predetermined interval in one dielectric block, and the inner surface of the hole that forms a resonator whose resonant frequency is a predetermined passing frequency, and the opening of the hole. All other surfaces of the dielectric block except one surface including the metallized surface are metalized, and coupling parts are provided at both ends of the dielectric block to respectively couple with both end holes of the hole group and to connect to an external circuit. In the 1/4 wavelength resonant coaxial dielectric filter, a hole whose inner surface is metallized is further provided on at least one outer side of the coupling part, and the hole has a resonant frequency different from that of the resonant element. 1. A dielectric filter comprising: a specific band blocking resonator having an attenuation pole outside the passband of the filter; and coupling the coupling portion to the specific band blocking resonator.