JP2777501B2 - Dielectric filter - Google Patents

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 a high-frequency circuit of a radio communication device or the like.

[0002]

2. Description of the Related Art In recent years, dielectric filters have been used in high-frequency circuits of various wireless communication devices. In particular, in a wireless communication device or the like that can simultaneously transmit and receive a mobile phone or the like, a duplexer 1 as shown in the block diagram of the wireless communication device in FIG. 9 is used.
Are connected to the antenna 2, the receiving unit 3 and the transmitting unit 4. The signal generated by the transmitting unit 4 passes through the duplexer 1 and is transmitted to the antenna 2, and the signal received by the antenna 2 passes through the duplexer 1 and is transmitted to the receiving unit 3. Here, the frequency band of the transmission signal is different from the frequency band of the reception signal.

FIG. 10 is an internal configuration diagram of the duplexer 1 shown in FIG. The duplexer 1 is composed of two narrow band-pass filters (BPFs) 5 and 6. BPF
5 is connected to the transmitting unit 4 and the output terminal of the BPF 6 is connected to the receiving unit 3. The output terminal of the BPF 5 and the input terminal of the BPF 6 are connected to each other.
Connected to antenna 2. Here, the BPF 5 has a pass band for passing only the transmission signal, and the BPF 6 has a pass band for passing only the reception signal.

FIG. 11 shows the transmission characteristics of the duplexer 1 described above. In this figure, TX and RX represent the transmission characteristics of the transmission BPF 5 and the reception BPF 6, respectively. As shown in the figure, BPF5 and BPF
The six passbands are close to each other. Further, since the power of the transmission signal is usually about 1 to 5 W, the transmission signal may leak to the receiving unit via the reception BPF 6. Therefore, when designing the duplexer 1, in the transmission characteristics of the BPF 6, the attenuation characteristic at a frequency lower than the pass band must be steep.

Therefore, as a method of sharpening the attenuation characteristic at a frequency lower than the pass band of the filter, the following general characteristics of the filter have been conventionally used.
FIG. 12 shows transmission characteristics in a general dielectric filter when design parameters relating to the number of stages and the like are changed.

FIG. 12A shows transmission characteristics of a dielectric filter according to predetermined design parameters. In such a dielectric filter, when the passband is narrowed by changing the design parameters, the attenuation characteristics in the lower and higher frequencies than the passband, that is, the attenuation characteristics in both attenuation ranges become steeper (see FIG. 12B). If the passband is further narrowed, the attenuation characteristics of both attenuation regions are steeper than those in FIG. 12B (see FIG. 12C). Conversely, when the pass band is widened, the attenuation characteristics in both attenuation regions become gentler than those in FIG.

FIG. 13 is a perspective view showing the structure of a conventional dielectric filter 7 used in the duplexer 1 described above, and FIG.
FIG. 13 is a sectional view taken along line AA in FIG. As shown in FIGS. 13 and 14, reference numeral 8 denotes a substantially rectangular parallelepiped ceramic material, and rectangular tubular through holes 9 to 12 are provided from the front surface 8a to the back surface 8b. These through holes 9 to 12
The length that forms an opening in the front face 8a of the ceramic material 8 is L _1, and forms a rectangular hole 9a~12a the width W _1, and another opening at the rear surface 8b of the ceramic material 8 Length L
_2, is constituted by the width are connected rectangular hole 9b~12b and each of _{W 2 (W 1 <W 2} ). Further, through holes 13 and 14 for inputting and outputting signals are formed from the inner surfaces of the rectangular holes 9b and 12b located on the outer side to the side surfaces 8c and 8d of the ceramic material 8, respectively.

After the through holes 9 to 14 are formed, the ceramic material 8 is subjected to electroless plating or the ceramic material 8 is immersed in a conductive paste to form the through holes 9 to 14. On the inner surface, an inner conductor 15a,
An outer conductor 15b is formed on the outer surface of the ceramic material 8. The front surface 8a of the ceramic material 8 has a through hole 9
An arc-shaped notch 16 is formed from the bottom surface 8e to the top surface 8f of the ceramic material 8 so that the surface of each of the openings 12 to 12 is curved. Thereby, the notch 1
The inner conductor 15a and the outer conductor 15b reaching 6 are separated. Therefore, the inner conductor 15a forms an open end on the front surface 8a of the ceramic material 8, and forms a short-circuit end on the back surface 8b.

Further, the periphery of each of the through-holes 13 and 14 on the side surfaces 8c and 8d of the ceramic material 8 is formed by etching or cutting, etc.
b and 14b are formed, and input / output patterns 13a and 14a are formed to be continuous with the inner conductor 15a and insulated from the outer conductor 15b.

FIG. 15 is an equivalent circuit diagram showing an electrical configuration of the dielectric filter 7. As shown in FIG. In this figure, FIG.
The same reference numerals are given to the portions corresponding to No. 4 and the description is omitted. Here, 9z to 12z are distributed constant lines (hereinafter, referred to as lines) corresponding to the through holes 9 to 12 shown in FIG. 13 'and 14' are through holes 13 and 14, input / output patterns 13a and 14a, respectively.
The input / output terminal 17 is a ground. Further, one end of a capacitor 18 having a small capacitance is connected to the open ends of the lines 9z to 12z, and the other end is connected to the ground 17. This capacitor 1
8 is a fringing capacitance (when the dielectric constant of the dielectric is 100), which is caused by the discontinuity of the dielectric constant around the open ends of the lines 9z to 12z due to the formation of the cutout 16 described above. About several pF).

By the way, one end is opened as shown in FIG.
The input / output characteristics of the distributed constant circuit in which the lines 9z to 12z having the other ends short-circuited are provided in parallel can be obtained by superimposing electromagnetic field coupling between the lines. Generally, such electromagnetic field coupling includes an even mode and an odd mode. Here, the even-mode electromagnetic field coupling is a coupling in which currents in the same direction flow in two lines where the coupling occurs, and the odd-mode electromagnetic field coupling is the second.
The coupling is such that currents flowing in opposite directions flow in this line. Therefore, the electromagnetic field in the odd mode and the electromagnetic field in the even mode cancel each other. The mode of the electromagnetic field coupling between the two lines is determined by parameters such as the dielectric constant of the dielectric between the lines, the line length, the frequency of the signal propagating in the line, and the like, whether the line is short-circuited or open-ended. , And impedance elements connected to the line.

Generally, odd-mode electromagnetic field coupling is dominant on the open end side of the line, and even-mode electromagnetic field coupling is dominant on the short-circuit end side. Further, in the case of rectangular tubular transmission lines each having a uniform width, if their lengths are ４ of the wavelength of the signal propagating through the transmission lines, the electromagnetic field due to the odd mode coupling and the electromagnetic field due to the even mode coupling Are cancelled, and the electromagnetic field between the lines is not coupled. Therefore,
If the electromagnetic field coupling of either the even mode or the odd mode between the lines is weakened, a certain amount of coupling can be obtained in the superposed electromagnetic field. Therefore, in the conventional dielectric filter 7 described above, as shown in FIG. 14, the width W ₁ of the rectangular hole 9a~12a is an open-end side
A short-circuit end side by less than the width W ₂ of the square hole 9B～12b, since is weaker than the electromagnetic coupling even mode electromagnetic field coupling odd mode at the open end side of the short-circuit end side, the line Bonding occurs between 9z and 12z.

Next, the transmission characteristics of the dielectric filter 7 will be described. The curve shown by the broken line in FIG. 16 shows the transmission characteristics of the dielectric filter 7. Dielectric filter 7
Is constituted by a resonance circuit of the lines 9z to 12z and the capacitor 18, as shown in FIG. The resonance frequency in these resonance circuits is such that their line length is 1/4.
The frequency is lower than the frequency that becomes the wavelength, and exists in the pass band of the dielectric filter 7. Further, at a frequency slightly higher than the pass band and a line length of 1/4 of the wavelength, a state where the electromagnetic field is not coupled, that is,
There is a state where the amount of attenuation is infinite. On the other hand, when the frequency is lower than the pass band, the amount of attenuation becomes infinite when the frequency is zero, that is, in the case of DC. Therefore, in the transmission characteristics of the dielectric filter 7, the attenuation characteristics at frequencies higher than the pass band are steep, but the attenuation characteristics at frequencies lower than the pass band are moderate.

[0014]

In the above-mentioned conventional dielectric filter 7, the attenuation characteristic at a frequency lower than the pass band is moderate. Therefore, when the conventional dielectric filter 7 is used for the BPF 6 of the duplexer 1 of a wireless communication device such as a car phone which requires a steep attenuation characteristic at a frequency lower than the pass band, the number of filter stages is increased. Therefore, there is a problem that the shape of the dielectric filter 7 is large and the manufacturing cost is high. By changing the design parameters related to the number of stages,
If you try to make it steeper, the passband becomes narrower and
There is a problem that a pass band cannot be obtained. The present invention has been made in view of the above circumstances, and has a steep attenuation characteristic at a frequency lower than the pass band ,
An object of the present invention is to provide a dielectric filter having a wide pass band in a high frequency band .

[0015]

Means for Solving the Problems Four dielectric blocks penetrating from the front surface to the rear surface of the dielectric block and arranged in a predetermined direction are provided.
And more through holes, they and inner conductors on the inner surface of each through-hole, a dielectric filter comprising an outer conductor provided on the outer peripheral surface other than the front surface of the dielectric block, the dielectric It is provided at the rear side of the block, out of the through hole
The two through-holes adjacent to the inside of the
An extension extending as a through hole, and an inner surface of the common through hole
And the inner conductor provided on the outer surface of the extension.
And an outer conductor .

[0016]

According to the above dielectric filter, the dielectric filter is disposed adjacent to the inside.
An extension part that combines two side-by-side through-holes into a common through-hole
Is extended, and an inner conductor is provided on the inner surface of the extension.
The inner conductor of this extension is provided on the inner surface of the two through holes.
As a result, the passband in the high frequency band is widened while the attenuation characteristic in the frequency band lower than the passband is steeper than when no extension inner conductor is provided .

[0017]

FIG. 1 shows the structure of a dielectric filter 19 according to a first embodiment of the present invention. FIG. 1 (a) is a perspective view showing its appearance, and FIG. FIG. In this figure, parts corresponding to those in FIGS. 13 and 14 are denoted by the same reference numerals, and description thereof will be omitted.

The structure of the dielectric filter 19 according to the present embodiment is the same as that of the conventional dielectric filter 7 shown in FIGS.
Is equivalent to an extension of the ceramic material 8 around the through holes 10 and 11 on the back surface 8b.

As shown in FIG. 1, on the back surface 20b of the ceramic material 20, the through holes 10, 11 and the periphery thereof are formed.
Extending extension 21 of a length L ₃ and is formed. The extension 21 has one opening on its rear surface and has a length L ₃ , which is continuous with the through holes 10 and 11.
The width is W ₃ (W ₃ = 2W ₂ + W, W is the square holes 10b, 11b
A hole 22 having a width (between) is formed.

Also, in this ceramic material 20,
A conductor is formed in the same manner as in the conventional example, and the through holes 9 to 1 are formed.
4. On the inner surface of the hole 22, an inner conductor 23a, a notch 16 and a non-conductive portion 13 around the input / output patterns 13a and 14a.
An outer conductor 23b is formed on the outer surface of the ceramic material 20 except for the outer conductors b and 14b. Then, a short-circuit conductor 23c is formed inside the hole 22 and on the end face of the ceramic material 20 which is continuous with the through holes 10 and 11.

Next, an equivalent circuit of the dielectric filter 19 according to the present embodiment shown in FIG. 2 will be described. In this figure, parts corresponding to the respective parts in FIGS. 1 and 15 are denoted by the same reference numerals, and description thereof will be omitted. The equivalent circuit of this dielectric filter 19 is composed of two lines 10 shown in FIG.
The short-circuit ends of z and 11z are connected at connection point 24 in FIG.
Is connected to one end of a common line 22z formed by the inner conductor 23a of the hole 22 shown in FIG.

FIG. 3A shows the transmission characteristics of the conventional dielectric filter 7, and FIGS. 3B and 3C show the transmission characteristics of the dielectric filter 19 of the present embodiment. Hereinafter, the attenuation characteristics of the dielectric filter 19 according to the present embodiment in the attenuation range will be described with reference to FIGS. In these figures, among the design parameters of the dielectric filter 7 and the dielectric filter 9, the number of stages, the dielectric constant of the ceramic materials 8 and 20, and the thickness of the ceramic materials 8 and 20 (the bottom surface 8e and the upper surface 8f
And the bottom surface 20e and the top surface 2 of the ceramic material 20.
The same value is used for (interval with 0f).

FIG. 3B shows the transmission characteristic of the dielectric filter 19 when a certain design parameter value relating to the line 22z shown in FIG. 2 is added to the dielectric filter 7 having the transmission characteristic shown in FIG. It is. When comparing the attenuation characteristics in the attenuation region between FIG. 3A and FIG. 3B, there is almost no difference in the attenuation characteristics at frequencies lower than the pass band. This is because, in the dielectric filter 19, when the frequency of the signal is lower than the pass band, the impedance of the line 22z becomes small, and the connection point 24 where the lines 10z, 11z and 22z are short-circuited is directly grounded. This is because the configuration becomes close to the configuration of the dielectric filter 7 of the example.

On the other hand, in FIG. 3B, when the frequency is higher than the pass band, the impedance of the line 22z increases, and the connection point 24 between the lines 10z, 11z and the line 22z has a high potential. The transmission is performed on the route of 10z → connection point 24 → line 11z.
Therefore, there is no frequency at which the attenuation becomes infinitely high at a frequency slightly higher than the passband.
The attenuation characteristics at frequencies higher than the passband are shown in FIG.
It is slower than.

The above-mentioned line 10z → connection point 24 →
Since the signal path of the line 11z is composed of the two through holes 10, 11 and the inner conductor 23a and the short-circuit conductor 23c of the hole 22 shown in FIG. 1B, when the frequency is higher than the pass band, The amount of coupling between the two lines 10z, 11z is very large, and the passband width is wide. However, since the pass band width is too wide in this state, the characteristics of the general filter described above are used. That is, FIG.
In order to obtain a pass band width similar to the transmission characteristic shown in (a),
If narrow ratio, or the lengths L _1, L _2, pass band width by changing the ratio of L ₃ or the like of the width W ₁ and the width W ₂ of the through-holes 9 to 12 shown in FIG. 1 (b), both Fig. 3 shows the attenuation characteristics in the attenuation region.
It becomes steeper than the attenuation characteristic shown in FIG.

In FIG. 16 described above, the transmission characteristics when the dielectric filter 19 according to the present embodiment is designed so that the pass band width is the same as that of the conventional dielectric filter 7 are indicated by solid lines. As shown in the figure, the attenuation characteristic of the dielectric filter 19 according to the present embodiment can be steeper at a frequency lower than the pass band as compared with the conventional filter.

FIG. 4 is a view showing an external configuration of a dielectric filter 25 according to a second embodiment of the present invention, and FIG. 5 is a perspective view of a metal case 26 attached to the dielectric filter 25 shown in FIG. 6 and 7 are cross-sectional views of the ceramic material 27 and the dielectric filter 25 in FIG. 4 taken along the line CC. Hereinafter, the dielectric filter 2 will be described with reference to these figures.
5 will be described. Here, the broken line part shown in FIG. 7 is the metal case 26 shown in FIG.

The ceramic material 27 of the dielectric filter 25 according to the second embodiment has a cylindrical shape having a uniform thickness instead of the rectangular through holes 9 to 12 of the dielectric filter 19 according to the first embodiment. Through holes 28 to 31 are formed, and the back surface 27 b
In the same manner as in the first embodiment, an extended portion 32 is formed, and a hole 33 continuous with the through holes 29 and 30 is formed. In this embodiment, the through holes 13, 14 and the notch 16 of the first embodiment are not provided.
Further, pins 34 which are input / output conductor bars and a tubular spacer 35 which is a dielectric member different from the ceramic material 27 are inserted into the through holes 28 and 31 located on the outside from the front surface 27 a of the ceramic material 27. Have been.

As shown in FIG. 6, this ceramic material 27
In this case, the conductor is formed in the same manner as in the conventional example and the first embodiment. An inner conductor 36a is formed on the inner surface of the through holes 28 to 31 and the hole 33, and an outer conductor 36b is formed on the outer surface of the ceramic material 27 except for the front surface 27a of the ceramic material 27. Further, inside the hole 33, a short-circuit conductor 36c is provided on an end face of the ceramic material 27 which is continuous with the through holes 29 and 30.
Around the through holes 29, 30 in the front surface 27a of the ceramic material 27, a rectangular outer conductor 36d continuous with the inner conductor 36a is provided.
Is formed. In this case, the front surface 27 of the ceramic material 27
In a, portions other than the outer conductor 36d are such that the formed conductor is deleted or the conductor is not formed.

As shown in FIG. 7, one end of the dielectric spacer 35 is tapered so as to be easily inserted into the through holes 28 and 31, and the other end is formed into the through holes 28 and 3.
1 are thicker than the through holes 28 and 31 so as not to enter the inside of the hole 1. Further, a coaxial through hole provided in the dielectric spacer 35 has a front surface 27 of the ceramic material 27.
A pin 34 is inserted from the side a. One end of the pin 34 protrudes from the dielectric spacer 35 on the front surface 27a of the ceramic material 27 so as to be connected to the outside.

The metal case 26 has two pins 3
Inside 4, the front surface 27a of the ceramic material 27 is covered so as to be in contact with the dielectric spacer 35 and not to contact the outer conductor 36d. Also, the metal case 26
Is in contact with the outer conductor 36b at the bottom surface 27c and the top surface 27d of the ceramic material 27.

FIG. 8 is an equivalent circuit of the dielectric filter 25 of this embodiment. In this figure, lines 29z to 31z
9 correspond to the through holes 29 to 31 shown in FIG. The capacitor 37 is constituted by the pins 34, the inner conductor 36a and the dielectric spacer 35, and the capacitor 38 is constituted by the short-circuited ends of the through holes 28 to 31, the outer conductor 36b and the ceramic material 27. It is. Reference numeral 34 'denotes an input / output terminal corresponding to the pin 34, and reference numeral 39 denotes a ground. Note that the operation in this embodiment is the same as that in the first embodiment, and a description thereof will be omitted.

[0033]

As described above, according to the present invention, in the dielectric filter having four or more stages, the dielectric filter adjacent to the inner side is used.
Extends as a common through hole by combining two through holes
Part is extended, and an inner conductor is provided on the inner surface of the extension part.
The inner conductor of this extension is provided on the inner surface of the two through holes.
The inner conductor is connected to the
-Due to the formation of the dance line , the attenuation characteristics at frequencies lower than the pass band can be sharpened, and
The pass band of the filter can be widened . Therefore, when a filter having a steeper attenuation characteristic at a frequency lower than the pass band is required, a small and inexpensive filter can be provided.

[Brief description of the drawings]

FIG. 1 shows a dielectric filter 19 according to a first embodiment of the present invention.
FIG. 2 is a perspective view showing the configuration of FIG.

FIG. 2 is an equivalent circuit of a dielectric filter 19 according to the embodiment.

FIG. 3 is a diagram showing transmission characteristics when a design parameter is changed in the dielectric filter 19 according to the embodiment.

FIG. 4 shows a dielectric filter 25 according to a second embodiment of the present invention.
It is a perspective view which shows a structure of.

FIG. 5 is a perspective view of a metal case 26 attached to the dielectric filter 25 according to the same embodiment.

FIG. 6 is a perspective view of a ceramic material 27 when the dielectric filter 25 shown in FIG. 4 is cut along a CC section.

FIG. 7 is a cross-sectional view of the dielectric filter 25 shown in FIG.

FIG. 8 is an equivalent circuit of the dielectric filter 25 according to the same embodiment.

FIG. 9 is a block diagram of a wireless communication device capable of transmitting and receiving.

10 is an internal configuration diagram of the duplexer 1 used in the wireless communication device of FIG.

11 shows transmission characteristics in the duplexer 1 shown in FIG.

FIG. 12 is a diagram illustrating transmission characteristics of a general filter.

FIG. 13 is a perspective view showing a configuration of a conventional dielectric filter 7.

14 is a sectional view of the dielectric filter 7 shown in FIG. 11 taken along the line AA.

FIG. 15 is an equivalent circuit of a conventional dielectric filter 7;

FIG. 16 is a diagram showing transmission characteristics of the dielectric filter 19 according to the conventional example and the first embodiment of the present invention.

[Explanation of symbols]

9-14, 29-31 Through-holes 9a-12a, 9b-12b Rectangular holes 13a, 14a Input / output pattern 16 Notch portion 19, 25 Dielectric filter 20, 27 Ceramic material 20a, 27a Front surface 20b, 27b Back surface 21, 32 extension 22, 33 hole 23a, 36a inner conductor 23b, 36b outer conductor 23c, 36c short-circuit conductor 34 pin 35 dielectric spacer

Claims (1)

(57) [Claims] 1. Four or more through-holes penetrating from a front surface to a rear surface of a dielectric block and arranged in a predetermined direction.
When the inner conductors on the inner surface of each of these through-holes, a dielectric filter comprising an outer conductor provided on the outer peripheral surface other than the front surface of the dielectric block, the rear surface of the dielectric block Provided , said through hole
The two through-holes arranged adjacent to the inside of the
And extension extending as a through hole, the dielectric filter, wherein the the inner conductors on the inner surface of the common through-holes, comprising an outer conductor provided on the outer surface of the extension portion.