JPH0720002B2 - Compound filter device - Google Patents

Description

TECHNICAL FIELD The present invention relates to a composite filter device using a dielectric filter having a dielectric resonator.

[Prior Art] In a conventional dielectric filter device, the number of filter stages is determined from the required attenuation outside the pass band, and this is realized using a dielectric resonator. At that time, in a filter in which the insertion loss in the pass band may be large, Q _{0 of} the resonator used may be small, so that the diameter can be made small to some extent.

On the other hand, the surface acoustic wave filter (SAW filter) has a characteristic that it is small and can obtain a large amount of attenuation.

[Problems to be Solved by the Invention] When high attenuation is required outside the pass band, it is wasteful to obtain all the required attenuation by the above-mentioned conventional dielectric filter because the insertion loss becomes large. In addition, there is a limit in reducing the diameter of the resonator due to molding of the resonator unit and subsequent assembly. Also, as the number of stages of the dielectric resonator increases, the group delay time characteristic in the pass band deteriorates.

On the other hand, since the SAW filter cannot withstand high input power, it cannot be used where a high power of several watts or more is simply applied in a filter device using the SAW filter.

An object of the present invention is to provide a filter device which is small in size, yet has a high attenuation outside the pass band, and can be used even under a high power condition, while compensating for the drawbacks of the dielectric filter and the SAW filter described above. Especially.

[Means for Solving Problems] A filter device according to the present invention is a composite filter device in which a SAW filter is coupled in series to a dielectric filter,
A W filter is coupled in series between the dielectric filter and the output terminal.

[Operation] When a SAW filter is connected in series with a dielectric filter, SAW
The filter provides a high amount of attenuation outside the pass band, and the filter device is compact as a whole.
Moreover, since the number of stages of the dielectric resonator required is reduced, the group delay time characteristic in the pass band is improved. Note that SA
The group delay time of W filters is generally flat in the pass band.

Since the SAW filter is coupled in series between the dielectric filter and the output terminal, the power level is first reduced in the dielectric resonator for high input power. Therefore, the SAW filter is protected against high input power.

[Embodiment] FIG. 1 shows a composite filter device according to an embodiment of the present invention.

In FIG. 1, a case 1 of a dielectric filter device includes a plurality of dielectric resonators 2, a coupling substrate 3 made of a dielectric material for capacitively coupling the dielectric resonators 2, and a coupling substrate 3. The attached SAW filter 4 is stored.

The dielectric resonator 2 is a coaxial TEM resonator made of, for example, a dielectric ceramic, and is arranged in the case 1 in parallel with each other. A coupling terminal 5 is attached to each inner conductor end of each dielectric resonator 2. On the other hand, a coupling electrode 6 corresponding to each coupling terminal 5 is fixed to the upper end surface of the coupling substrate 3. Each of the coupling electrodes 6 has a coupling terminal 5
The tip of is connected. The structure of the coupling substrate 3 portion realizes a capacitance for coupling the dielectric resonator 2.

The SAW filter 4 is arranged at the left end of FIG. As shown in FIG. 2, the SAW filter 4 is
It is arranged in the conventional dead space in the case 1 on the surface of the combined substrate 3 opposite to the connecting electrode 6. The SAW filter 4 shown in the figure is put in a cylindrical member having a low height such as a hermetic case. The SAW filter 4 may be an independent member or may be directly formed on the main surface of the combined substrate 3. In the latter case,
For example, a part of the coupling substrate 3 is made piezoelectric, and an interdigital transducer or the like is provided in that part to form a SAW.
Filter 4 is used. The input / output terminals 7 and 8 of the SAW filter 4 extend to the side where the coupling electrode 6 is formed through a pair of through holes formed in the coupling substrate 3. As shown in FIG. 1, the two terminals 7 and 8 are connected to each other on the combined substrate 3 by the connecting electrodes 6.
A pair of small square electrodes formed on the same side as
It is connected to 9,10 by soldering. On the other hand, among the coupling electrodes 6, the coupling electrode 6a arranged at the left end of FIG.
It is formed in a U-shape that opens to the left when viewed in the direction of FIG. The input side electrode 9 is arranged so as to be surrounded by the coupling electrode 6a with a space. That is, the capacitance between the coupling electrode 6a and the input side electrode 9 is the external coupling capacitance of the dielectric filter.

Next, the operation of this embodiment will be described.

When high power in a certain frequency band is input to the dielectric filter, the dielectric resonator 2 first filters the power. At that time, the high input power is SAW in the dielectric resonator 2.
It is reduced to a power level that the filter 4 can withstand. Next, it is filtered by the SAW filter 4 and output from the output side electrode 10. At this time, since the number of stages of the dielectric resonator 2 is smaller than that of the conventional one and the group delay time of the SAW filter 4 is flat in the pass band, the group delay time characteristic in the pass band is better than before. .

[Another Embodiment] (a) Instead of the above embodiment, the configuration of FIG. 3 can be adopted.

In FIG. 3, a small square electrode 11 is arranged in a portion surrounded by the U-shaped portion of the coupling electrode 6a.
A line 12 for impedance matching is formed integrally with the electrode 11. The line 12 extends to the left in FIG. 3 on the combined substrate 3, and an electrode 13 is integrally formed at the tip of the line 12. Like the electrode 9 (FIG. 1), the electrode 13 is connected to the input terminal 7 of the SAW filter 4 by soldering or the like.

In the case of this embodiment, the capacitance is not directly taken between the electrode 13 soldered to the input terminal 7 of the SAW filter 4 and the electrode 6a on the side of the dielectric resonator 2 to prevent the impedance mismatch of the SAW filter 4. It can be absorbed by line 12. Therefore, according to the structure shown in FIG. 3, even if the impedance of the SAW filter 4 varies, the SAW filter 4 can be adjusted by the line 12 to obtain a matching composite filter device as a whole.

(B) Instead of the line 12, a stub as shown in FIG.
It is also possible to adopt the line 15 in which 14 is formed.
Instead of the line 12 or the line 15, lands 16 are provided as shown in FIG.
It is also possible to adopt a configuration in which the bonding wire 18 and the line 17 are connected by a bonding wire 18.

If these configurations are adopted, it becomes possible to adjust the impedance variation more freely than the line 12 in FIG.

[Advantages of the Invention] According to the composite filter device of the present invention, since the SAW filter is coupled in series to the dielectric filter, it is possible to obtain a dielectric filter which is small but which can obtain high attenuation outside the pass band. it can. For example, the SAW filter is much smaller than the dielectric resonator, and the SAW filter can be easily miniaturized by inserting the SAW filter in the dead space of the dielectric filter device.

When the same amount of attenuation is obtained, the number of stages of the dielectric resonator can be reduced as compared with the conventional case, so that the cost can be reduced.

Since the number of stages of the dielectric resonator is reduced and the group delay time of the SAW filter is flat in the general passband, the group delay time characteristic in the passband is better than that of the conventional one composed of only the dielectric resonator. Will get better.

Since the SAW filter is coupled in series between the dielectric filter and the output terminal, the input power level is reduced by the dielectric resonator and therefore SA at high input power levels.
Since the W filter is protected, it can be used even under high power conditions.

[Brief description of drawings]

1 is a cross-sectional partial view of a composite filter device according to an embodiment of the present invention, FIG. 2 is a II-II partial cross-sectional view of FIG. 1, and FIG.
The drawing corresponds to FIG. 1 of another embodiment, and FIGS. 4 and 5 are plan partial views of another embodiment, respectively. Reference numeral 2 is a dielectric resonator, 4 is a surface acoustic wave filter, and 10 is an output side electrode.

Claims (1)

[Claims] 1. A composite filter device comprising a dielectric filter and a surface acoustic wave filter, wherein the surface acoustic wave filter is coupled in series between a dielectric filter and an output terminal.