JPH1028005A - Dielectric filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the spurious characteristic of a dielectric filter without deteriorating the pass characteristic (insertion loss) of the filter and, at the same time, to improve the performance of the filter and reduce the size and the cost of the filter. SOLUTION: A capacitor C0 is connected in parallel with an inductance L2 constituting a band elimination filter-side low-pass filter and the capacitance of the capacitor C0 is set so that the parallel resonance frequency of the inductance L2 and capacitor C0 can become twice or thrice the frequency 2f0 or 3f0 of the passing band of a dielectric filter. When the parallel resonance frequency is set at twice or thrice the frequency 2f0 or 3f0 of the passing band, the impedance to the parallel resonance frequency is open circuited and the spurious characteristics of the dielectric filter at the frequency 2f0 or 3f0 can be attenuated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention
The present invention relates to a dielectric filter used for a mobile communication device such as a mobile phone.

[0002]

2. Description of the Related Art FIG. 11 is a circuit diagram of a so-called antenna duplexer as a dielectric filter used in mobile communication devices such as a mobile phone and a mobile phone. In this antenna duplexer, the transmission unit side constitutes a two-stage band elimination filter using two dielectric coaxial resonators 1 and 2,
On the receiving side, a two-stage band-pass filter using two dielectric coaxial resonators 3 and 4 is provided. An antenna is connected to the central antenna terminal ANT.

[0003] In FIG 11, a band elimination filter of the transmitter side of the antenna duplexer, the above dielectric coaxial resonators 1 and 2, the capacitance C ₁ -C _5, consists of the inductance L _1, L _2, etc. I have. Further, the bandpass filter of the receiver side, the dielectric coaxial resonators 3 and 4 above, and a capacitance C ₆ -C ₈ and the like.

Here, at the antenna terminal ANT of the band elimination filter of the antenna duplexer, the capacitances C ₄ and C _{4 are set} so that the reflection phase is open in the pass band of the band pass filter on the receiving side.
The phase is adjusted by a π-type low-pass filter having C ₅ and inductance L ₂ . FIG. 12 shows the pass characteristics of this band elimination filter. 12, the horizontal axis represents frequency, the left vertical axis represents insertion loss (dB), and the right vertical axis represents reflection loss (dB).

[0005] A curve (a) shows the pass characteristic S _{2 1,} curve (b) shows the reflection characteristic S _{1 1.} A of the curve (a) indicates a pass band, and B indicates an attenuation band. FIG. 13 shows a case where the frequency domain is expanded (500 to 3).
000 MHz).

[0006]

FIG. 13 shows the pass characteristics of such a conventional band elimination filter.
As shown in (2), the band elimination filter on the transmitting side doubles and triples the pass band of the important transmission wave (2f ₀ , 3
The attenuation at the frequency f ₀ ) is insufficient. Therefore, the transmission band is twice or three times (2f ₀ , 3f)
_In order to improve the attenuation at the frequency ₀ ), FIG.
And a method as shown in FIG.

[0007] That is, in FIG.
On the TX side, additional capacitance C ₉And inductance
L_ThreeInsert a low-pass filter consisting of
The low-pass filter (capacitance C_Four,
C_Five, Inductance L_Two)
In addition, two or three times the passband (2f₀, 3f
₀), The amount of attenuation at the frequency was improved. Also figure
In No. 15, the antenna terminal ANT side is
Pacitance C₉, C_Ten, Inductance L_ThreeConsists of
A low-pass filter is inserted and, as in the case of FIG.
-Pass filter (capacitance C_Four, C_Five, Indac
Tance L_Two) Supplements the lack of the low-pass function
And twice or three times the pass band (2f₀, 3f₀) Frequency
The amount of attenuation in was improved.

However, in FIGS. 14 and 15, although the attenuation at frequencies twice and three times (2f ₀ , 3f ₀ ) the passband can be improved, a low-pass filter including a plurality of components is further added. There is a problem that the number of parts increases and the size also increases due to the addition. Also, to improve spurious characteristics,
If the cutoff frequency of the low-pass filter is reduced, the pass characteristics (insertion loss) will be deteriorated.

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and aims to improve spurious characteristics without deteriorating transmission characteristics (insertion loss), and to achieve high performance, small size, and low cost. It is intended to provide a dielectric filter aimed at.

[0010]

According to the present invention, there is provided a dielectric filter which couples dielectric coaxial resonators with an inductance and blocks or passes a predetermined frequency band, and causes the inductance to resonate in parallel at a predetermined frequency. A capacitor is connected in parallel.

According to a second aspect of the present invention, a predetermined frequency band is blocked or passed by using a dielectric coaxial resonator.
In a dielectric filter that couples with an external circuit using an inductance, a capacitor that performs parallel resonance at a predetermined frequency is connected to the inductance in parallel.

In a third aspect of the present invention, in a dielectric filter for blocking or passing a predetermined frequency band using a dielectric coaxial resonator and a π-type low-pass filter, a capacitor constituting the low-pass filter includes a capacitor. A multilayer chip capacitor that performs series resonance at a frequency is used.

[0013]

According to the present invention, it is possible to improve spurious characteristics by causing a parallel resonance with an inductance and a capacitor and setting the parallel resonance frequency to, for example, twice or three times the pass band. And high performance can be achieved. In addition, since the capacitor is simply connected in parallel to the inductance, and a low-pass filter is not added unlike the related art, the configuration can be made small and inexpensive.

According to a second aspect of the present invention, there is provided a dielectric filter in which a predetermined frequency band is blocked or passed by using a dielectric coaxial resonator and coupling with an external circuit is performed using an inductance. By connecting a capacitor that performs parallel resonance at a frequency in parallel, the inductor and the capacitor perform parallel resonance, and the parallel resonance frequency is set to be, for example, twice or three times the passband. Spurious characteristics can be improved, and higher performance can be achieved. In addition, simply connect a capacitor in parallel with the inductance,
Since a low-pass filter is not added unlike the related art, a small and inexpensive configuration can be achieved.

According to a third aspect of the present invention, in a dielectric filter for blocking or passing a predetermined frequency band by using a dielectric coaxial resonator and a π-type low-pass filter, a capacitor constituting the low-pass filter may have a predetermined frequency band. The use of the multilayer chip capacitor in which self-series resonance occurs at the frequency described above makes it possible to improve spurious characteristics at a desired frequency without deteriorating insertion loss. Moreover, in order not to add a low-pass filter as in the past,
The filter can be reduced in size.

[0016]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a circuit diagram of an antenna duplexer including a band elimination filter and a band-pass filter similar to those in the related art. The same members as those in the related art are denoted by the same reference numerals and the description thereof will be omitted, and the gist of the present invention will be described in detail.

[0017] That is, in this embodiment, is obtained by connecting a capacitor C ₀ in parallel with the inductance L ₂ constituting a band elimination filter side of the low-pass filter. Then, the set inductance L ₂ and 2 times the passband parallel resonance frequency of the capacitor C _0, the capacitance of the capacitor C ₀ to be three times the frequency (2f _0, 3f _0). Set the parallel resonance frequency to 2
Double and triple the frequency (2f ₀ , 3f ₀ ), the impedance to the parallel resonance frequency is open.
And the frequency (2f ₀ , 3f) twice and three times the pass band
₀ ) can attenuate the spurious characteristics,
The spurious characteristics can be improved.

(Embodiment 2) FIG. 2 shows a second embodiment. In this embodiment, a capacitor C ₀ is connected in parallel with an inductance L _1.
Are connected. In this embodiment, as in the previous embodiment, twice the passband parallel resonant frequency of the inductance L ₁ and the capacitor C _0, 3 times the frequency (2f
_0, so that the 3f ₀₎ is set to the capacitance value of the capacitor C _0. Thereby, spurious characteristics can be improved.

FIGS. 3 and 4 show conventional examples shown in FIGS.
FIG. 4 shows pass characteristics in Examples 1 and 2 corresponding to FIG. 3, and as shown in FIG. 4, parallel resonance of LC occurs near 3000 MHz, and the frequency (2
f ₀ , 3f ₀ ) are attenuated more than before. In FIG. 3, as in the prior art, the curve (a) shows the pass characteristic S _{2 1,} curve (b) shows the reflection characteristic S _{1 1.} A of the curve (a) indicates a pass band, and B indicates an attenuation band.

Embodiment 3 FIG. 5 is a circuit diagram of a two-stage band-pass filter using two dielectric coaxial resonators 1 and 2. Even in the case of such a bandpass filter, as shown in FIG. 6, and a capacitor C ₃ to parallel resonance in parallel with the inductance L _1, by setting the value as in the previous embodiment, improvement in spurious characteristic Can be achieved.

[0021] (Embodiment 4) FIG. 7 shows a fourth embodiment, the band-pass filter, a case of using the inductance L ₁ for binding to the external circuit. Even such a case, to connect the capacitor C ₃ in parallel with the inductance L _1, by setting the value as in the previous embodiment,
The spurious characteristics can be improved.

In each of the embodiments described above, the case of a two-stage band elimination filter and a two-stage band-pass filter has been described. The invention can be applied. Further, the present invention can be applied to a single configuration of a band elimination filter or a combination of a band elimination filter, a band-pass filter, a low-pass filter, a high-pass filter and the like, regardless of the antenna duplexer.

(Embodiment 5) FIG. 8 shows Embodiment 5 and is a circuit diagram of a three-stage band elimination filter using three dielectric coaxial resonators 1 to 3. In addition, C ₁ ~
C ₆ is the capacitance. Here, the inductance L ₂ and the capacitance C _5, C ₆ are realized and a quarter-wave transmission line connecting between resonators same function and inductance L _1, a capacitor C _4, C consists of ₅ [pi type 2 times the pass band, 3 times
The spurious characteristics at the double frequency (2f ₀ , 3f ₀ ) are improved.

Conventionally, however, the capacitances C _{4 to} C ₆ shown in FIG. 8 are not formed by forming an electrode film on a base substrate made of a dielectric material. There was no way to further curb the situation. Therefore, in this embodiment, the capacitance C
Either ₄ -C _6, or is obtained by the use of multilayer chip capacitors all.

In the multilayer chip capacitor, series resonance occurs due to its structure. Therefore, by performing self-resonance at a frequency that suppresses spurious characteristics, spurious characteristics at a desired frequency can be improved without deteriorating insertion loss. Further, FIG. 9 shows a circuit diagram of a band elimination filter in two stages, shows a case of using a multilayer chip capacitor to the capacitance C ₅ for phase adjustment.

FIG. 10 is a diagram showing the relationship between the capacitance value of the multilayer chip capacitor and the resonance frequency. As shown in the figure, the self-resonance frequency differs depending on the capacitance of the multilayer chip capacitor. To use. In the case of the embodiment shown in FIGS. 8 and 9, a series resonance is caused between both ends of the capacitances C ₆ and C ₅ using the multilayer chip capacitor to short-circuit each end, so that the insertion loss is not deteriorated. The spurious characteristics are improved.

For example, in the experimental results, when the capacitances C _{4 to} C ₆ in FIG. 8 are set between the electrode films of the base substrate, the attenuation at a frequency twice the passband is 25 dB.
Was one of the capacitances C _{4 to} C ₆ ,
Alternatively, when a multilayer chip capacitor was used for all, the attenuation at a frequency twice the passband was 33 dB.

In this embodiment, the case of a two-stage or three-stage band elimination filter has been described.
When a filter in which a capacitor is connected between a transmission line between an input / output end and an earth line is configured, the present invention is applicable not only to a band elimination filter but also to any filter. Further, the present invention is not limited to the number of stages of the dielectric coaxial resonator, and can be applied to a case of three or more stages.

[0029]

According to the present invention, in a dielectric filter that couples dielectric coaxial resonators with an inductance and blocks or passes a predetermined frequency band, a capacitor that resonates in parallel with the inductance at a predetermined frequency is provided. Since they are connected in parallel, it is possible to improve spurious characteristics by causing parallel resonance with an inductance and a capacitor and setting the parallel resonance frequency to be, for example, twice or three times the passband. And high performance can be achieved. In addition, since the capacitor is simply connected in parallel to the inductance, and a low-pass filter is not added unlike the related art, it is possible to achieve a small and inexpensive configuration.

According to a second aspect of the present invention, there is provided a dielectric filter in which a predetermined frequency band is blocked or passed by using a dielectric coaxial resonator and coupling with an external circuit is performed by using an inductance. By connecting a capacitor that performs parallel resonance at a frequency in parallel, the inductor and the capacitor perform parallel resonance, and the parallel resonance frequency is set to be, for example, twice or three times the passband. Spurious characteristics can be improved, and higher performance can be achieved. In addition, simply connect a capacitor in parallel with the inductance,
Since a low-pass filter is not added unlike the related art, a small and inexpensive configuration can be achieved.

According to a third aspect of the present invention, in a dielectric filter for blocking or passing a predetermined frequency band by using a dielectric coaxial resonator and a π-type low-pass filter, a capacitor constituting the low-pass filter may have a predetermined frequency band. The use of the multilayer chip capacitor in which self-series resonance occurs at the frequency described above makes it possible to improve spurious characteristics at a desired frequency without deteriorating insertion loss. Moreover, in order not to add a low-pass filter as in the past,
The filter can be reduced in size.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of an antenna duplexer according to an embodiment of the present invention.

FIG. 2 is a circuit diagram of an antenna duplexer according to a second embodiment of the present invention.

FIG. 3 is a diagram showing transmission characteristics and reflection loss of an example of the present invention.

FIG. 4 is a diagram showing a transmission characteristic of the embodiment of the present invention.

FIG. 5 is a circuit diagram of a bandpass filter according to a third embodiment of the present invention.

FIG. 6 is a circuit diagram of a bandpass filter according to a third embodiment of the present invention.

FIG. 7 is a circuit diagram of a bandpass filter according to a fourth embodiment of the present invention.

FIG. 8 is a circuit diagram of a band elimination filter according to a fifth embodiment of the present invention.

FIG. 9 is a circuit diagram of a band elimination filter according to a fifth embodiment of the present invention.

FIG. 10 is a diagram illustrating the relationship between the capacitance of a multilayer chip capacitor and a self-resonant frequency according to a fifth embodiment of the present invention.

FIG. 11 is a circuit diagram of a conventional antenna duplexer.

FIG. 12 is a diagram showing transmission characteristics and reflection loss of a conventional example.

FIG. 13 is a diagram showing pass characteristics of a conventional example.

FIG. 14 is a main part circuit diagram of another conventional antenna duplexer.

FIG. 15 is a circuit diagram of still another conventional antenna duplexer.

[Explanation of symbols]

1-3 dielectric coaxial resonators L ₂ the inductance C ₀ capacitor

Claims (3)

[Claims] 1. A dielectric filter that couples dielectric coaxial resonators with an inductance and blocks or passes a predetermined frequency band, wherein a capacitor that performs parallel resonance at a predetermined frequency is connected to the inductance in parallel. Characteristic dielectric filter. 2. A dielectric filter that blocks or passes a predetermined frequency band using a dielectric coaxial resonator and couples with an external circuit using an inductance, wherein a capacitor that resonates in parallel with the inductance at a predetermined frequency is provided. A dielectric filter, which is connected in parallel. 3. A dielectric filter for blocking or passing a predetermined frequency band by using a dielectric coaxial resonator and a π-type low-pass filter, wherein a series of resonances at a predetermined frequency are added to a capacitor constituting the low-pass filter. A dielectric filter using a chip capacitor.