JPH098505A - Dielectric filter - Google Patents

Abstract

PURPOSE: To obtain the dielectric filter that passes or attenuates two waves at a low cost without increasing the entire size. CONSTITUTION: One side S2 of a TEM mode dielectric resonator is used for a short-circuit side and the other side S1 is used for an open side, and a 1st wave passes through the filter in the fundamental wave resonance mode and a 2nd wave passes in the 3rd harmonic resonance mode. Thus, two waves are passed or attenuated by one band pass filter. Furthermore, since it is not required to provide a matching circuit to connect two filters, the size is made entirely small and the cost is reduced.

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 in high frequency circuits such as mobile communication equipment.

[0002]

2. Description of the Related Art With the recent expansion and development of a cellular type mobile communication system, it has been applied to a filter used in a device that can be used in both two different mobile communication systems or to two mobile communication systems. A filter commonly used by different devices has been desired. For example, in a high frequency circuit applied to both a mobile communication system using the 800 MHz band and a mobile communication system using the 1.5 GHz band, when configuring a filter that passes or attenuates the two waves, according to the conventional technology,
As shown in FIG. 14, a filter F1 that passes or attenuates the 800 MHz band and a filter F2 that passes or attenuates the 1.5 GHz band are connected in parallel to form a filter circuit.

By combining two band pass filters having different center frequencies of the pass band in this way, as shown in FIG. 15, a band pass characteristic of passing two waves f1 and f2 is realized, and an attenuation band is obtained. By combining two band attenuating filters having different center frequencies, the band attenuating characteristics for attenuating two waves f1 and f2 are realized as shown in FIG.

[0004]

However, in such a conventional structure, simply connecting two sets of filters in parallel interferes with each other and the desired characteristics cannot be obtained. Therefore, a matching circuit is needed.

17 and 18 show an example of the matching circuit. In FIG. 17, portions indicated as BPF1 and BPF2 are bandpass filters using two-stage dielectric resonators, and M1 and M2 are phase adjusting circuits. In this way, the two band pass filters are matched by the phase adjusting circuit. Also, in FIG.
The portions indicated as EF1 and BEF2 are band attenuating filters using dielectric resonators of three stages, M1 and M, respectively.
Reference numerals 2 are phase adjusting circuits. In this way, the two band attenuation filters are matched by the phase adjusting circuit.

As described above, in the conventional configuration, not only two sets of filters are required, but also a matching circuit for connecting the two sets of filters is required, resulting in an increase in size and an increase in cost. It was

An object of the present invention is to provide a dielectric filter that allows the two waves to pass or be attenuated without increasing the overall size and reducing the cost.

[0008]

The dielectric filter according to the present invention comprises one of the TEM mode dielectric resonators according to claim 1 for passing or attenuating two waves by a set of filter circuits. The short-circuited end and the other end are opened, and the frequencies of the fundamental wave resonance mode and / or the third-order resonance mode are set so that the first wave passes or is attenuated by the fundamental wave resonance mode and the second wave by the third-order resonance mode. Passes or attenuates waves.

In order to set the frequencies of the first wave and the second wave to a predetermined value, the dielectric filter of the present invention has the short-circuit end side and the open end side as described in claim 2. By changing the impedance ratio, the frequencies of the fundamental resonance mode and the third resonance mode are set to predetermined values.

In the dielectric filter of the present invention, in order to provide the attenuation pole on the high band side or the low band side of the pass band of the first wave or the second wave, adjacent dielectric resonances are provided. A reactance element is provided between the dielectric resonator and the coupling circuit for coupling between the capacitors and the external circuit to set the frequency of the attenuation pole.

[0011]

In the dielectric filter according to the first aspect of the present invention, since one of the TEM mode dielectric resonators has a short-circuited end and the other has an open end, at least two of the fundamental resonance mode and the third-order resonance mode are provided. Two resonance modes occur. By setting the frequencies of both resonance modes, the first wave passes or is attenuated by the fundamental resonance mode, and the second wave is passed or attenuated by the third resonance mode. This allows two waves to pass or be attenuated by a set of dielectric filters.

In the dielectric filter according to the second aspect, the impedance ratio between the short-circuited end side and the open-end side is changed so that, for example, the resonance frequency of the fundamental wave resonance mode is 800 MHz and the frequency of the third-order resonance mode is 1.5 GHz. By this, it becomes possible to pass or attenuate two waves of 800 MHz band and 1.5 GHz band.

In the dielectric filter according to the third aspect of the present invention, a coupling circuit for coupling between adjacent dielectric resonators or coupling with an external circuit and a reactance element provided between the coupling circuit and the dielectric resonator are provided. By the action of, the attenuation pole is generated on the high band side or the low band side of the first wave or the second wave, and the unnecessary frequency signal on the high band side or the low band side of the first wave or the second wave is efficiently generated. It can be greatly attenuated.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The structure of a bandpass filter according to a first embodiment of the present invention will be described below with reference to FIGS.

FIG. 1 is a perspective view of the bandpass filter with the shield cover removed. In the figure, Ra and Rb are respectively λ / 4 type TEM mode dielectric resonators, which form through holes in the central axes of the prismatic dielectrics 1a and 1b and form inner conductors on their inner peripheral surfaces. , S
Outer conductors 2a and 2b are formed on five surfaces, respectively, with the surface indicated by 1 as the open end and the surface indicated by S2 as the short-circuited end. The terminals 3a and 3b are inserted into the through holes, respectively. The two dielectric resonators Ra and Rb are attached to the upper part of the substrate 7, and the dielectric plate 4 is attached. The terminals 3a and 3b inserted into the through holes of the dielectric resonator are connected to the two electrodes provided on the upper surface of the dielectric plate 4, and the electrodes provided on the back surface side of the dielectric plate 4 and the input terminals provided on the substrate side. The output electrode 8 is electrically connected.

2A and 2B are a top view and a bottom view of the dielectric plate shown in FIG. Two electrodes 5a and 5b are provided on the upper surface of the dielectric plate 4, and two electrodes 6a and 6b are formed on the back surface. Thereby, the electrodes 5a-6a
Capacitance C1 between them, capacitance C3 between the electrodes 5b-6b,
And an electrostatic capacitance C2 is generated between the electrodes 5a and 5b.

FIG. 3 is an equivalent circuit diagram of the bandpass filter shown in FIG. In this way, a bandpass filter circuit composed of two-stage dielectric resonators is constructed.

FIG. 4 is a characteristic diagram of the bandpass filter shown in FIG. In the figure, the horizontal axis represents frequency, the vertical axis represents attenuation amount (dB), S21 is a pass characteristic between input and output, and S11 is
Is a reflection characteristic on the input side, and S22 is a reflection characteristic on the output side. In this way, the fundamental wave resonance mode frequency of the resonators Ra and Rb is 800 MHz, and the third resonance mode frequency is 1.
By setting it to 9 GHz, the 800 MHz band and 1.9
A band pass filter characteristic that passes two waves in the GHz band is obtained.

By the way, in order to set the frequencies of the fundamental wave resonance mode and the third order resonance mode to predetermined values,
The impedance ratio between the short-circuited end side and the open end side of the dielectric resonator is changed. 5 and 6 are diagrams showing an example thereof.
For example, as shown in FIG. 5A, if the inner conductor diameter on the open end side is made larger than that on the short-circuited end side, the electrostatic capacitance component becomes large in the region where the electric field energy in the fundamental resonance mode is large. , The resonance frequency of the fundamental wave resonance mode decreases. On the other hand, in the third resonance mode, since both peaks and troughs of the electric field energy are distributed in the region L1 having a large inner conductor diameter, the resonance frequency of the third resonance mode does not change much.
As a result, as shown in FIG. 6A, the frequency f2 of the third-order resonance mode becomes relatively high with respect to the frequency f1 of the fundamental wave resonance mode. That is, the frequency difference between f1 and f2 is widened. On the contrary, as shown in FIG. 5B, if the inner conductor diameter on the short-circuit end side is made larger than that on the open end side, the electrostatic capacitance in the region where electric field energy in the third resonance mode is relatively concentrated. 3 because the component becomes large
The resonance frequency of the secondary resonance mode decreases. On the other hand, in the fundamental wave resonance mode, the electric field energy in the region L2 where the inner conductor diameter is large is relatively small, so the resonance frequency of the fundamental wave resonance mode does not change much. As a result, as shown in FIG. 6B, the frequency f2 of the third-order resonance mode becomes relatively low with respect to the frequency f1 of the fundamental wave resonance mode.
That is, the frequency difference between f1 and f2 is narrowed.

Instead of changing the diameter of the inner conductor, the size of the outer conductor may be changed as shown in FIGS. 5 (C) and 5 (D). For example, as shown in (C), by making the outer conductor size on the short-circuited end side smaller than that on the open end side, the frequency difference between f1 and f2 is narrowed by the same effect as in (B), and (D). As shown in, by reducing the outer conductor size on the open end side from the short-circuited end side,
Due to the same effect as in the case of (A), the frequency difference between f1 and f2 is widened.

As indicated above, the axial dimension L1,
By setting L2 and the inner conductor diameter or the outer conductor size, the frequency of the fundamental wave resonance mode and the frequency of the third-order resonance mode are set to predetermined values.

Next, the structure of the bandpass filter according to the second embodiment of the present invention will be described with reference to FIGS.

FIG. 7 is a plan view of the bandpass filter,
Two TEM mode dielectric resonators Ra,
A dielectric plate 4 is provided together with Rb. The difference from the first embodiment shown in FIG. 1 is that the electrodes 10a, 1
0b is provided, chip inductors 11a and 11b as reactance elements are mounted between the two electrodes 10a and 10b and the other two electrodes 5a and 5b, and terminals 3a and 3b of the dielectric resonator are connected to the electrodes 10a and 10b. The point is that they are connected.

FIG. 8 is an equivalent circuit diagram of the bandpass filter shown in FIG. 7, and FIG. 9 is a characteristic diagram thereof. In FIG. 8, La and Lb are inductors corresponding to the chip inductors 11a and 11b. By connecting the inductor between the resonator and the coupling circuit in this manner, attenuation poles are generated between the first wave f1 and the second wave f2 and on the high frequency side of the second wave f2, as shown in FIG. In this case, inductor L
When the inductances of a and Lb are increased, the frequency fd1 of the attenuation pole becomes lower and fd2 becomes higher. On the contrary, when the inductances of the inductors La and Lb are reduced, the frequency fd1 of the attenuation pole becomes high and fd2 becomes low.

Although the chip inductor is used in the example shown in FIG. 7, it may be a coil, and the length of the terminals 3a and 3b drawn from the dielectric resonator (dielectric resonator and dielectric The value of the inductance may be determined by changing the distance from the plate 4.

Next, the structure of the bandpass filter according to the third embodiment is shown in FIGS. The third embodiment is an example of a single dielectric block.

In FIG. 10, (A) is an overall perspective view,
FIG. 3B is a partially cutaway perspective view in a state where it is turned upside down. The dielectric block 1 is provided with two through holes 12a and 12b having a step structure, and the inner conductor 1 is provided on the inner peripheral surface of each of the through holes 12a and 12b.
5 is formed. Part of the inner conductor 15 has a gap 1
6 is provided to generate an electrostatic capacitance at that portion. The outer conductor 2 and the input / output conductor 14 are formed on the outer surface of the dielectric block.

FIG. 11 is an equivalent circuit diagram shown in FIG. In FIG. 11, Ra and Rb are through holes 12a and 12
The dielectric resonators Ca, Cb, which are composed of the inner conductor on the inner peripheral surface of b, the dielectric block, and the outer conductor, are external coupling capacitances generated between the inner conductor and the input / output conductors.

As shown in FIG. 10, the through holes 12a, 1
The inner diameter of 2b is made different between the short-circuit end side and the open end side to change the impedance ratio between the short-circuit end side and the open end side, and the axial length of the resonator, the pitch between the through holes 12a and 12b, and the inner conductor A bandpass filter characteristic that allows two waves to pass is obtained by determining the size of the gap provided in a part.

Next, the structure of the band attenuation filter according to the fourth embodiment is shown in FIGS. FIG. 12 is a plan view of the band attenuation filter. On the substrate 7, electrodes to which the back surfaces of the chip capacitors 17a, 17b and 17c are connected, input electrodes 8 and 9 and λ / 4 transmission lines 18a and 18b are formed. Three TEM mode dielectric resonators Ra, Rb, Rc and a chip capacitor 1 are provided on the substrate 7.
7a, 17b, 17c are mounted, and the terminals 3a, 3b, 3c of the dielectric resonator are connected to the chip capacitor 17a,
17b and 17c are respectively connected to the surface electrodes.

FIG. 13 is an equivalent circuit diagram of the band attenuation filter shown in FIG. Ca, Cb and Cc correspond to the chip capacitors 17a, 17b and 17c in FIG. If the electrical length of the λ / 4 transmission lines 18a and 18b is equal to a quarter wavelength at the frequency of the fundamental resonance mode, the electrical length is approximately equal to the quarter wavelength at the frequency of the third resonance mode. In addition, since the phase difference between the adjacent resonators is substantially equal to 90 °, the filter shown in FIG. 12 exhibits band attenuation characteristics even at the frequency of the third resonance mode.

The characteristics of the band attenuation filter according to the fourth embodiment are the same as those shown in FIG. When this filter is used as a transmission filter, for example, A in FIG.
810 to 830MHz attenuation band, B 940 to 96
If 0MHz pass band, C is 1429 to 1453MHz pass band, and D is 1477 to 1501MHz attenuation band, it can be shared by mobile communication system using 800MHz band and mobile communication system using 1.5GHz band. Becomes

[0033]

According to the dielectric filter according to the first aspect of the present invention, two waves can be passed or attenuated by one set of dielectric filters, and moreover, two sets of filters are connected. Since a matching circuit is also required, the overall size can be reduced and the cost can be reduced.

According to the dielectric filter of claim 2,
By changing the impedance ratio between the short-circuited end side and the open end side, it becomes possible to easily set the fundamental wave resonance mode frequency and the third-order resonance mode frequency to the first wave and the second wave, respectively.

According to the dielectric filter of claim 3,
Since the attenuation pole is generated on the high frequency side or the low frequency side of the first wave or the second wave, the unnecessary frequency signal on the high frequency side or the low frequency side of the first wave or the second wave can be efficiently and largely attenuated. .

[Brief description of drawings]

FIG. 1 is a perspective view of a bandpass filter according to a first embodiment.

FIG. 2 is a diagram showing a structure of a dielectric plate shown in FIG.

FIG. 3 is an equivalent circuit diagram of the bandpass filter according to the first embodiment.

FIG. 4 is a characteristic diagram of the bandpass filter according to the first embodiment.

FIG. 5 is a diagram showing an example of adjusting the impedance ratio between the short-circuit end side and the open end side.

FIG. 6 is a diagram showing an example of a change in the frequency difference between the third-order resonance mode and the fundamental wave resonance mode due to the adjustment shown in FIG.

FIG. 7 is a plan view of a bandpass filter according to a second embodiment.

FIG. 8 is an equivalent circuit diagram of a bandpass filter according to a second embodiment.

FIG. 9 is a characteristic diagram of the bandpass filter according to the second embodiment.

FIG. 10 is a perspective view of a bandpass filter according to a third embodiment.

FIG. 11 is an equivalent circuit diagram of a bandpass filter according to a third embodiment.

FIG. 12 is a plan view of a band attenuation filter according to a fourth embodiment.

FIG. 13 is an equivalent circuit diagram of a band attenuation filter according to a fourth embodiment.

FIG. 14 is a configuration diagram of a conventional filter circuit.

15 is a diagram showing a characteristic example of the circuit shown in FIG.

16 is a diagram showing a characteristic example of the circuit shown in FIG.

FIG. 17 is a diagram showing an example of a matching circuit in a conventional bandpass filter.

FIG. 18 is a diagram showing an example of a matching circuit in a conventional band attenuation filter.

[Description of Reference Signs] 1, 1a, 1b-dielectric (dielectric block) 2, 2a, 2b-outer conductors 3a, 3b-terminal 4-dielectric plate 5a, 5b, 6a, 6b-conductor 7-substrate 8, 9-input / output electrodes 11a, 11b-chip inductors 12a, 12b-through holes 13a, 13b-conductor 14-input / output conductor 15-inner conductor 16-gap portions 17a, 17b, 17c-chip capacitors 18a, 18b-λ / 4 Transmission line

Claims (3)

[Claims] 1. A dielectric filter using a single or a plurality of TEM mode dielectric resonators, wherein one of the TEM mode dielectric resonators is a short-circuited end and the other is an open end, and a fundamental wave resonance mode and And / or a frequency of a third-order resonance mode is set so that the first wave passes or is attenuated by the fundamental wave resonance mode and the second wave is passed or attenuated by the third-order resonance mode. 2. The dielectric filter according to claim 1, wherein the impedance ratio between the short-circuited end side and the open end side is changed to set the frequencies of the fundamental wave resonance mode and the third-order resonance mode to predetermined values. 3. The dielectric filter according to claim 1 or 2, wherein a coupling circuit for coupling between the dielectric resonators or coupling between the dielectric resonator and an external circuit is provided, and the coupling circuit is provided. A reactance element between the dielectric resonator and the dielectric resonator to provide bandpass characteristics for passing the first wave and the second wave.
A dielectric filter having an attenuation pole in a band other than a wave and a second wave.