JPH1093306A - Dielectric filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the dielectric filter whose pass characteristic in the vicinity of a resonance frequency for harmonics is improved. SOLUTION: The dielectric filter is provided with a base board 4 having input/output terminals 6a, 6b, input/output coupling strip lines 7a, 7b, and a ground pattern 8 as its conductor pattern and with a plurality of 1/4 wavelength coaxial dielectric resonators arranged adjacent to each other on an upper side of the base board 4. In this case, the line width of the input/output coupling strip lines 7a, 7b is formed wider in the vicinity of a part in contact with an open end face of a dielectric material and in the vicinity of a part apart from the open end face by about 2/3 of the length of the resonators than the other parts.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dielectric filter used for high-frequency signals of several hundred MHz to several GHz.

[0002]

2. Description of the Related Art Various high-frequency filters are used in communication devices. In particular, with the spread of mobile communication devices such as mobile phones and the increase in use of communication, various filters have been reduced in size and have improved filter characteristics. Improvement is required.
Conventionally, as a filter used at a high frequency, there is a dielectric filter using a coaxial dielectric resonator, which is described in, for example, JP-A-6-283904. As shown in FIG. 3, the dielectric filter is disposed adjacent to each other on a base substrate (4) having a conductive pattern formed on the surface of a dielectric substrate (5), and on an upper surface of the base substrate (4). A plurality of coaxial dielectric resonators (10a) (10b).

As shown in FIG. 2, the coaxial dielectric resonator (10) has a dielectric member (2) formed with through holes (22) passing through both end surfaces (20) and (21) thereof. Outer peripheral surface of member (2), through hole (22)
On either one of the inner surface and the end surface (21) of the dielectric member (2),
This is a quarter-wavelength coaxial resonator provided with conductor layers (30), (31), (32). Further, as shown in FIG. 2, the coaxial dielectric resonator (10) has a bottom surface (23) by removing one surface of the conductor layer (30) on the outer peripheral surface.
A part of the conductor layer (30) on the side surface of each of the adjacent coaxial resonators (10a) (10b) is deleted to form an interstage coupling window (90). As shown in FIG. 10, the base substrate (4) has input / output terminal portions (6a) (6b),
The strip lines (7a) and (7b) for input / output coupling and the ground pattern (8) are formed. The input / output coupling strip lines (7a) and (7b) are provided on the upper surface of the dielectric substrate (5) inside the contact surfaces of the input / output stages with the bottom surfaces (23) of the coaxial resonators (10a) and (10b). From the area, the respective input / output terminal portions (6a) and (6b) are formed. As shown in FIGS. 10 (a) and 10 (b), the ground pattern (8) is formed on the upper and lower surfaces of the dielectric substrate (5) inside the contact surface with the bottom surface (23) of the coaxial resonator (10), and I / O terminal sections (6a) (6b) and I / O coupling strip lines (7
a) It is formed excluding the peripheral region of (7b).

By arranging a plurality of coaxial resonators (10) adjacent to each other on a base substrate (4) having a conductor pattern formed on the surface of a dielectric substrate (5) as described above, input / output is achieved. A capacitive coupling between the coupling strip lines (7a) (7b) and the conductor layers (31) on the inner surfaces of the holes of the input / output coaxial resonators (10a) (10b) is made, and a band-pass dielectric filter is used. Is formed.

[0005]

Generally, in a quarter-wave resonator, not only a fundamental wave whose quarter of one wavelength is equal to the resonator length, but also a harmonic whose frequency is an odd multiple of the fundamental wave. Also resonate. Therefore, a band-pass filter using a quarter-wavelength coaxial dielectric resonator has a low attenuation with a small signal attenuation not only in a frequency band near a desired fundamental wave but also in a frequency band near the harmonic. Bandwidth will result. In particular, as shown in FIG. 6, since the low attenuation band generated near the frequency three times the frequency f ₀ of the fundamental wave is closest to the desired low attenuation band near the frequency f ₀ , it is necessary to increase the attenuation. is there.

[0006]

SUMMARY OF THE INVENTION The present inventor has devised the following solution by paying attention to the amplitude shapes of a fundamental wave and a harmonic generated in a 1/4 wavelength coaxial resonator. FIG. 5 shows a fundamental wave among the standing waves that resonate in the 1/4 wavelength coaxial dielectric resonator (10),
The lowest-order third harmonic among the harmonics is indicated by the one-dot chain line and the solid line curve, respectively. Since the electromagnetic wave resonating in the coaxial resonator is a TEM wave, the wave shown in FIG. 5 represents the electric field distribution in the resonator, and the amplitude of the wave represents the strength of the electric field. The arrow in the resonator indicates the direction of the electric field of the third harmonic at a certain point in time. As can be understood from FIG. 5, the fundamental wave has an open end face (2
At the position A in (0), the wave becomes an antinode, and the intensity of the electric field becomes maximum. The third harmonic is located at the position A on the open end face (20).
Then, at a position B which is away from the position A by about 2/3 of the resonator length in the axial direction, the antinode becomes a wave antinode, and the electric field strength becomes maximum. Further, since the phase of the third harmonic at the position A is shifted by a half wavelength as compared with that at the position B, the position A
The direction of the electric field of the third harmonic is opposite to that at the position B. The present invention relates to a base substrate
It is an object of the present invention to provide a dielectric filter having excellent transmission characteristics by changing the shape of the coupling strip line (7) in (4).

[0007]

In order to solve the above-mentioned problems, the present invention provides a dielectric filter using a quarter-wavelength type coaxial dielectric resonator, wherein at least one of the input / output coupling strip lines is made of a dielectric material. The line width between the vicinity of the open end face of the body member and the vicinity of a position separated from the open end face by about 2/3 of the resonator length is wider than other positions.

[0008]

[Function] The third harmonic resonating in the 1/4 type coaxial dielectric resonator is located at a position A on the open end face (20) and at a position axially away from the position A by about 2/3 of the resonator length. In B, the strength of the electric field is maximum, and the direction of the electric field is opposite at each position. Accordingly, the input / output coupling strip line is formed with a large line width in the vicinity of the positions A and B, so that the capacitive coupling with the coaxial dielectric resonator is strongly performed at the positions A and B. , The electric fields at the positions A and B cancel each other. As a result, it becomes difficult for the dielectric filter to resonate the third harmonic.

[0009]

At this time, the pass characteristic of the dielectric filter is as shown by the solid line in FIG. 6, and the attenuation near the frequency of the third harmonic is lower than that of the conventional pass characteristic indicated by the broken line in FIG. Can be increased. Thus, according to the present invention,
The pass characteristic of the dielectric filter is improved.

[0010]

Embodiments of the present invention will be described below in detail with reference to the drawings. (First Embodiment) FIG.
The two quarter-wavelength coaxial dielectric resonators (10a) and (10b) are adjacent to each other on the upper surface of the base substrate (4) in which the conductor pattern is formed on the surface of the dielectric substrate (5). This is a surface-mount type dielectric filter arranged in a manner as described above. The quarter-wave coaxial dielectric resonator (10) has a prismatic dielectric member as shown in FIG.
With respect to (2), a through hole (22) passing through both end surfaces (20) and (21) is formed, and the outer peripheral surface of the dielectric member (2), the inner surface of the through hole (22), and the dielectric member (2) One of the end faces (21) is coated with a conductive material to form conductor layers (30), (31) and (32). Then, the conductive material is removed from one surface of the outer peripheral surface of the dielectric member (2) to form a bottom surface (23), and the coaxial resonators (10a) and (10b) are coated with the conductive material from a part of the adjacent side surface. Removed and window for interstage coupling
(90) is formed. As the material of the dielectric member (2), high dielectric constant ceramics such as barium oxide, titanium oxide, and neodymium oxide are suitable. Further, as the conductive material, a high conductivity material such as silver or copper is suitable.

The coaxial resonator (10) is provided on the base substrate (4).
a) On the surface of a dielectric substrate (5) having a size that allows two (10b) to be placed side by side, as shown in FIGS. 1 (a) and (b), by a pattern of a conductive material. Input / output terminal (6a)
(6b), input / output coupling strip lines (7a) and (7b) and a ground pattern (8) are formed. The input / output terminals (6a) and (6b)
At the edge of the substrate (4), the coaxial resonator (10
a) Formed near the open end face (20) of (10b). The input / output coupling strip lines (7a) and (7b) corresponding to the input / output stage coaxial resonators (10a) and (10b) are provided on the upper surface of the dielectric substrate (5), respectively, with the bottom surface (23) of each resonator. The input / output terminal portions (6a) and (6b) are formed from the inner region of the contact surface, through the contact portion with the open end surface (20) of each resonator. According to the present invention, the coupling strip lines (7a) and (7b) are located near the position in contact with the open end face (20) of the dielectric member (2) and about two-thirds of the resonator length from the open end face (20). The line width near the position just apart is formed wider than other positions (70). Further, with respect to the resonance frequency (fundamental frequency) f ₀ of the fundamental wave, the coupling strip lines (7a) (7b) and the coaxial resonator (10a) (10b) of each capacitive coupling between the conventional and to the same extent And the strip line for coupling (7
In (a) and (7b), the line width of the portion other than the wide portion (70) is formed narrower than the conventional one (FIG. 9). The ground pattern (8)
On the upper and lower surfaces of the dielectric substrate (5), the coaxial resonator (1
(0) and the area inside the contact surface with the bottom surface (23), and the input / output terminals (6
a) (6b) and the peripheral areas of the input / output coupling strip lines (7a) and (7b). The material of the dielectric substrate (5) is suitably a low dielectric material such as alumina. Also,
In order to connect the upper and lower conductor patterns, a concave material (50) formed on the edge of the dielectric substrate (5) is coated with a conductive material.

As described above, the coaxial resonators (10a) and (10b)
And the base substrate (4) is formed, and as shown in FIG.
The coaxial resonators (10a) and (10b) are bonded on the base substrate (4) with an insulating adhesive, and the conductor layers (30) and (32) on the outer surfaces of the resonators (1a) and (1b) are grounded. Solder to pattern (8). Then, in order to meet the desired specifications, each coaxial resonator (10a)
The dielectric filter is completed by trimming and fine-tuning the open end face (20) of (10b) and the window (90) for inter-step coupling.

FIG. 4 is a sectional view of the dielectric filter.
FIG. 4 is a longitudinal sectional view taken along line AA of FIG. 3 and viewed in a direction indicated by an arrow. FIG. 5 is a simplified version of the conductor layers (30), (31) and (32) taken out of FIG. 4, and FIG. 5 shows the basic structure of the quarter-wave coaxial dielectric resonator (10). Waves and third harmonics are shown. As can be understood from FIG. 5, the third harmonic has an electric field strength at a position A on the open end face (20) and at a position B about 2/3 of the resonator length in the axial direction from the position A. Is maximum, and the direction of the electric field is opposite at each position. Therefore, the input / output coupling strip line (7)
This means that the wide portion (70) near the positions A and B is more strongly capacitively coupled to the coaxial resonator (10) than at the other positions, thereby canceling the electric fields at the positions A and B. Become. As a result, the dielectric filter, taken third harmonic hardly resonate, as shown in FIG. 6, with respect to passing characteristic, it is possible to increase the attenuation of the resonance frequency 3f ₀ near the third harmonic. In addition, I / O coupling strip lines (7a) (7b)
In the above, by forming the line width of the portion other than the wide portion (70) narrow, the entire strip line (7a) (7b),
Capacitive coupling to the fundamental frequency f ₀ of the coaxial resonator (10a) (10b) may be a conventional level, and as a result, FIG. 6
As in, for pass characteristics of the dielectric filter can be maintained the characteristics of the fundamental frequency f ₀ near the frequency band is desired band.

(Second Embodiment) The dielectric filter of the present embodiment is different from the first embodiment in that two quarter-wavelength coaxial dielectric resonators (10a) and (10b) are used instead of two. In this example, two half-wavelength open-ended coaxial dielectric resonators (11a) and (11b) are used. As shown in FIG. 8, the half-wavelength open-ended resonator (11) is a quarter-wavelength resonator (10a) (1) used in the first embodiment.
0b) Compared to (FIG. 2), both end surfaces (20) and (21) are not covered with the conductive material and are open end surfaces, and further, the coaxial resonators are separated from the center on adjacent side surfaces. A portion of the conductive material is removed to form an interstage coupling window (90). At this time, the standing wave that resonates in the half-wavelength resonator (11) includes a fundamental wave in which half of one wavelength is equal to the resonator length, and a harmonic in which the resonance frequency is an even multiple of the fundamental frequency. It is. Therefore, in the band-pass filter using the half-wavelength resonator (11), the low attenuation band occurs not only in the frequency band near the desired fundamental wave but also in the frequency band near the harmonic. Become. In particular, the low attenuation band generated near the frequency of the second harmonic whose resonance frequency is twice the fundamental frequency is closest to the desired fundamental frequency, and therefore, it is necessary to increase the attenuation. Half-wavelength open-ended resonator (1
The fundamental wave and the second harmonic that resonate in 1) have shapes shown by a chain line and a solid line in FIG. 9, respectively. As can be understood from FIG. 9, the intensity of the electric field at the position C of the open end face (20) and at the position D which is about 1/2 of the resonator length in the axial direction from the position C is higher than that of the second harmonic. Is maximum, and the direction of the electric field is opposite at each position.

Accordingly, a strip line for input / output coupling with respect to the coaxial dielectric resonators (11a) and (11b) open to both ends at 1/2 wavelength.
(7a) and (7b) show that the line width in the vicinity of the position C of the open end face (20) and the position of the line D in the vicinity of the position D which is about 1/2 of the resonator length in the axial direction from the position C as shown in FIG. By being formed wide (70), the wide portion (70) near the positions C and D is more capacitively coupled to the coaxial resonator (11) than at the other positions. Will be canceled out. As a result, as the dielectric filter, the second harmonic is less likely to resonate, and the attenuation in the pass characteristic near the resonance frequency of the second harmonic can be increased. Furthermore, in the input / output coupling strip lines (7a) and (7b), the wide portions (7
0), the entire line width of the strip lines (7a) (7b) and the coaxial resonators (11a) (11
The capacitive coupling with respect to the fundamental frequency with b) can be made approximately the same as that of the related art. As a result, the pass characteristic of the dielectric filter can maintain the characteristic near the fundamental frequency which is a desired band.

Incidentally, both end faces (20) and (21) of the dielectric member (2).
However, even in the case of using a half-wavelength double-ended short-circuit type coaxial dielectric resonator covered with a conductive material and serving as a short-circuit end face, considering the same manner as described above, the input / output coupling strip lines (7a) (7b ), The line width is increased near the position about 1/4 of the resonator length in the axial direction from the position of the short-circuit end face (20) and near the position about 3/4 away from the resonator length (70). As for the pass characteristics of the dielectric filter, the attenuation in the vicinity of the resonance frequency of the second harmonic can be increased. Further, in the above embodiment, the wide portion (70) is formed on both the input / output coupling strip lines (7a) and (7b), but the harmonic component is generated by the coaxial resonator in either the input stage or the output stage. Cancels out, the pass characteristics are improved, so that only one of the input / output coupling strip lines (7a) and (7b) has a wide area.
Even if (70) is formed, the effect of the present invention can be realized.

Further, in the present application, the cancellation of the harmonic component in the dielectric filter is realized by strengthening the capacitive coupling of the portion corresponding to the antinode of the harmonic.
It is expected that this can also be realized by devising the shape of the interstage coupling window (90) to strengthen the inductive coupling.

The description of the above embodiment is for the purpose of illustrating the present invention, and should not be construed as limiting the invention described in the claims or reducing the scope thereof. or,
The configuration of each part of the present invention is not limited to the above-described embodiment, and it is needless to say that various modifications can be made within the technical scope described in the claims. For example, in the above embodiment, two coaxial resonators have been described, but the present invention relates to the shape of the input / output coupling strip lines (7a) and (7b). The number of resonators can be freely selected. Further, in the above embodiment, the input / output terminal section (6a)
Although (6b) is formed on the opposite side on the base substrate (4), it may be formed on the same side, in which case the end faces (20) and (21) of the coaxial resonator in the input / output stage Direction is the same. As described above, the orientation of the end faces (20) and (21) of the coaxial resonator can be freely selected, and the conductor pattern on the base substrate (4) changes correspondingly.

[Brief description of the drawings]

FIGS. 1A and 1B are diagrams showing a base substrate used in a dielectric filter according to a first embodiment, wherein FIG. 1A is a plan view and FIG. 1B is a bottom view.

FIG. 2 is a perspective view showing a quarter-wavelength coaxial dielectric resonator used in the dielectric filters of the related art and the first embodiment.

FIG. 3 is a perspective view showing a dielectric filter according to the first embodiment.

FIG. 4 is a cross-sectional view taken along a line AA of FIG. 3 and viewed in a direction indicated by an arrow.

FIG. 5 is an explanatory diagram schematically showing a fundamental wave and a third harmonic resonating in a quarter-wavelength coaxial dielectric resonator.

FIG. 6 is a diagram illustrating transmission characteristics of the dielectric filter according to the first embodiment.

FIG. 7 is a plan view of a base substrate used in a second embodiment.

FIG. 8 is used in the dielectric filter of the second embodiment.
FIG. 2 is a perspective view showing a half-wavelength open-ended coaxial dielectric resonator.

FIG. 9 is an explanatory diagram schematically showing a fundamental wave and a second harmonic resonating in a coaxial dielectric resonator having a half wavelength open at both ends.

10A and 10B are diagrams showing a base substrate used in a conventional dielectric filter, wherein FIG. 10A is a plan view and FIG. 10B is a bottom view.

[Explanation of symbols]

 (4) Base board (6) I / O terminal (7) I / O coupling stripline (8) Ground pattern (10) Quarter-wavelength coaxial dielectric resonator (70) Wide part of coupling stripline ( 90) Interstage coupling window

Claims (3)

[Claims] An input / output terminal section (6a) (6b), an input / output coupling strip line (7a) (7b), and a ground pattern (8) are formed as conductor patterns on the surface of a dielectric substrate (5). A plurality of coaxial dielectric resonators are placed on the base substrate (4) and the input / output coupling strip lines (7a) and (7b) and the ground pattern (8) on the upper surface of the base substrate (4). A dielectric filter disposed adjacently, wherein said coaxial dielectric resonator forms a through-hole (22) passing through both end faces (20) and (21) in a dielectric member (2), Conductor layers (30) and (31) are provided on the outer peripheral surface of the member (2) and the inner surface of the through hole (22), and one surface of the conductor layer (30) on the outer peripheral surface is further removed to form a bottom surface (23). A part of the side surface of each adjacent coaxial resonator is deleted to form an interstage coupling window (90), and the input / output coupling strip lines (7a) (7b) of the base substrate (4) are ,Respectively In the dielectric filter formed from the area inside the contact surface with the bottom surface (23) of the coaxial resonator of each input / output stage to each input / output terminal (6a) (6b), the input / output coupling strip At least one of the lines (7a) and (7b) is a position corresponding to the antinode of the electric field distribution in the standing wave having a higher frequency next to the fundamental wave among the standing waves resonating in the coaxial dielectric resonator. (70) The dielectric filter, wherein a line width in the vicinity is formed wider than other positions (70). 2. The coaxial dielectric resonator according to claim 1, wherein the conductor layer is disposed on one end face of the dielectric member. The wide portion (70) of the input / output coupling strip lines (7a) and (7b) is located near the position in contact with the open end face (20) of the dielectric member (2) and the resonator from the open end face (20). The dielectric filter according to claim 1, wherein the dielectric filter is formed near a position separated by about 2/3 of the length. The coaxial dielectric resonator is a half-wavelength open-ended coaxial dielectric resonator (11) in which conductor layers are not provided on both end faces of the dielectric member (2), The wide portion (70) of each of the strip lines (7a) and (7b) is close to the position in contact with the open end face (20) of the dielectric member (2), and is about 1/2 of the resonator length from the open end face (20). 2. The dielectric filter according to claim 1, wherein the dielectric filter is formed in the vicinity of a position separated by only a distance.