JPH0638481Y2 - Filter using composite coaxial resonator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention relates to a composite coaxial resonator filter configured by using a plurality of coaxial resonators.

[Prior Art] For example, in a bandpass filter using a coaxial resonator, a configuration in which a trap filter is added is often adopted when improving the attenuation characteristic. In such a case, conventionally, in addition to the original coaxial resonator for bandpass filters, a coaxial resonator for trapping and a ring resonator have been externally connected.

[Problems to be Solved by the Invention] In the bandpass filter to which the conventional trap filter is added, an extra space is required for the trap filter, which inevitably increases the size of the entire filter. In particular, with the recent miniaturization of electronic devices, such a demand for miniaturization of a filter cannot sufficiently meet the above-mentioned conventional configuration.

An object of the present invention is to provide a filter using a composite coaxial resonator, which is suitable for downsizing a bandpass filter to which a trap filter is added.

[Means for Solving Problems] A filter using the composite coaxial resonator according to the present invention has the following configuration.

A central conductor located in the center.

A cylindrical inner dielectric that coaxially covers the center conductor from the outer peripheral side.

A cylindrical inner conductor that coaxially covers the inner dielectric from the outer peripheral side.

A cylindrical outer dielectric that coaxially covers the inner conductor from the outer peripheral side.

A cylindrical outer conductor that coaxially covers the outer dielectric from the outer peripheral side.

A first input / output terminal connected to the center conductor.

A second input / output terminal connected to the inner conductor.

The central conductor, the inner dielectric, and the inner conductor form a first coaxial resonator. The inner conductor, the outer dielectric, and the outer conductor, the second
Of the coaxial resonator. Therefore, both coaxial resonators are directly connected at the inner conductor portion.

For example, by setting the first input / output terminal on the input side and the second input / output terminal on the output side, the second coaxial resonator functions as a bandpass filter element, and the first coaxial resonator is used. Functions as a trap filter element.

[Operation] Since the first coaxial resonator is concentrically arranged inside the second coaxial resonator as described above, an extra space for the trap filter is not required, and the filter is increased in size. Instead, the attenuation characteristic can be improved.
That is, according to the present invention, the filter provided with the trap circuit can be downsized.

Example As shown in FIG. 1, the composite coaxial resonator according to the present example is composed of a first 1/4 wavelength coaxial resonator 1 and a second 1/4 wavelength coaxial resonator 2. Has been done.

The first quarter-wave coaxial resonator 1 has a rod-shaped central conductor 3 arranged at the center, a cylindrical inner dielectric 4 that covers the central conductor 3 from the outside, and an inner dielectric 4 that covers the inner dielectric 4 from the outer peripheral side. The inner conductor 5 has a cylindrical shape. Further, a disk-shaped short-circuit electrode 6 is provided at the lower end of the first coaxial resonator 1.
The inner conductor 5 and the short-circuit electrode 6 are formed of a metal electrode film such as silver or copper. Also, the center conductor 3
Protrudes upward from the inner dielectric 4 so that its axial length is longer than that of the inner dielectric 4. Further, the short-circuit electrode 6 is arranged slightly above the lower end of the inner conductor 5, its center is electrically connected to the center conductor 3, and its outer peripheral edge is electrically connected to the inner conductor.

The second coaxial resonator 2 includes the inner conductor 5, a cylindrical outer dielectric 7 that covers the inner conductor 5 from the outer peripheral side, and a cylindrical outer conductor 8 that covers the outer dielectric 7 from the outer peripheral side. There is. The axial length of the outer conductor 8 is set shorter than the length of the inner conductor 5, and as a result, the upper end of the inner conductor 5 is arranged above the upper end of the outer conductor 8. Further, the second coaxial resonator 2 has an annular plate-shaped short-circuit electrode 9 at the lower end thereof. Similar to the inner conductor 5, the outer conductor 8 and the short-circuit electrode 9 are integrally formed of a metal electrode film such as silver or copper.

A perspective view of the composite coaxial resonator is shown in FIG.

On the other hand, the central conductor 3 is connected to the input terminal 21 via the capacitor 20.
Are connected. An output terminal 23 is connected to the upper end of the inner conductor 5 via capacitors 22 ,. In addition, another resonance element 24, 2 is provided between each capacitor 22 ,.
5, ... are properly connected.

An equivalent circuit of the bandpass filter shown in FIG. 1 is shown in FIG. As is clear from FIG. 3, the resonance element 26 corresponding to the first coaxial resonator 1 has the function of a trap filter element. Further, the resonance element 27 corresponding to the second coaxial resonator 2 constitutes a part of a general bandpass filter element like the other resonance elements 24 and 25.

Next, the operation of this embodiment will be described.

In the embodiment shown in FIG. 1, the lower end of the central conductor 3 and the lower end of the inner conductor 5 are short-circuited by the short-circuiting electrode 6, and both lower ends of the inner conductor 5 and the outer conductor 8 are short-circuited by the short-circuiting electrode 9. There is. Therefore, in the embodiment of FIG. 1, the dielectric constant ε ₂ ,
Length l ₂ lambda / 4 coaxial resonator (second coaxial resonator 2), the dielectric constant epsilon _1, the length l ₁ lambda / 4 coaxial resonator (first coaxial resonator 1)
Is built in (λ is the wavelength). Here, the resonance frequencies ₁ and ₂ of the two coaxial resonators ₁ and ₂ are, respectively, Can be obtained at. Here, C represents the speed of light.

The filter according to the present embodiment including the both resonators 1 and 2 having the resonance frequency characteristic has the attenuation pole at a certain frequency, and thus the attenuation characteristic can be improved. In this case, the frequency of the attenuation pole can be set appropriately by appropriately selecting the dielectric constant ε ₁ and the length l ₁ .

[Other Embodiments] (a) As the central conductor 3 and the inner dielectric body 4 constituting the first coaxial resonator 1, a coaxial cable such as a semi-rigid cable may be used.

(B) As shown in FIG. 4, the short-circuit electrode 6 provided in the embodiment of FIG. 1 may be omitted, whereby the first coaxial resonator 1 may be a λ / 2 type coaxial resonator.

(C) In the embodiment shown in FIG. 1, the composite coaxial resonator according to the present invention is used only for the first-stage resonant element 2, but the composite coaxial resonator according to the present invention may be used in other places. Good. Further, the resonance elements 24 and 25 may be omitted.

(D) The composite coaxial resonator shown in FIG. 1 or 4 may be used for at least one filter portion of the antenna duplexer.

(E) In the embodiment shown in FIG. 1, a capacitor is selected by appropriately selecting the characteristic impedance of the first coaxial resonator 1.
20 can be omitted.

(F) By using the composite coaxial resonator according to the present invention, it is also possible to configure an integrated filter in which a plurality of resonant elements are formed in one dielectric block or an antenna duplexer in which the filters are combined.

(G) Instead of the first coaxial resonator 1, as shown in FIG. 5, a configuration having an inner conductor 31 and an outer conductor 32 unique to the first coaxial resonator may be adopted.

[Advantage of the Invention] According to the filter using the composite coaxial resonator of the present invention, the attenuation characteristic can be improved by adding the trap filter, and even if the trap filter is added, the size of the filter as a whole is not large. Instead, the size of the filter as a whole can be reduced.

[Brief description of drawings]

FIG. 1 is an explanatory view showing a configuration of a filter according to an embodiment of the present invention and a longitudinal section of a composite coaxial resonator used therein, FIG. 2 is a perspective view of the composite coaxial resonator, and FIG. Equivalent circuit diagrams, FIG. 4 and FIG. 5 are vertical sectional views corresponding to different embodiments. 1 is a first coaxial resonator, 2 is a second coaxial resonator, 3 is a central conductor, 4 is an inner dielectric, 5 is an inner conductor, 7 is an outer dielectric, 8
Is an outer conductor, 21 is an input terminal, and 23 is an output terminal.

Claims (1)

[Scope of utility model registration request] 1. A central conductor arranged at the center, a cylindrical inner dielectric that coaxially covers the central conductor from the outer peripheral side, a cylindrical inner conductor that coaxially covers the inner dielectric from the outer peripheral side, and an inner conductor. A cylindrical outer conductor that coaxially covers the outer peripheral side, a cylindrical outer conductor that coaxially covers the outer dielectric from the outer peripheral side, a first input / output terminal connected to the central conductor, and the inner conductor A second coaxial input / output terminal connected to the central conductor, the inner dielectric body, and the inner conductor to form a first coaxial resonator, and the inner conductor, the outer dielectric body, and the outer conductor. To form a second coaxial resonator, whereby the first and second coaxial resonators are directly connected by the inner conductor, and the first coaxial resonator is connected to the first input / output. Functioning as a trap filter between the terminal and the second input / output terminal, A filter using a composite coaxial resonator, wherein the second coaxial resonator is made to function as a bandpass filter.