JPH05206704A - Band pass filter - Google Patents

Abstract

PURPOSE:To allow the performance of a band pass filter to be almost unchanged even when the shock is applied to a casing in its longitudinal direction and/or vertical direction. CONSTITUTION:The base band filter in which plural dielectric resonators 4a, 4b, 4c are arranged in the casing 1 at a prescribed interval in a line whose prescribed pass band frequency is less than the prescribed band is made of a foamed plastic whose dielectric constant is 1.05 or below, and a foamed plastic 7 is used to fill a space in the casing 1 and to support the dielectric resonators 4a, 4b, 4c into the casing.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bandpass filter, and more particularly to a bandpass filter in which a spherical dielectric is arranged in a cutoff waveguide.

[0002]

2. Description of the Related Art Conventionally, a bandpass filter of this type has a plurality of resonators arranged in a group and electromagnetically coupled between adjacent resonators to obtain a predetermined bandpass characteristic. .. The performance required for such a bandpass filter is that the insertion loss is small within the passband frequency and the insertion loss is large outside the passband frequency in the widest possible frequency range. In order to satisfy such specifications, the Q value of the resonator must be high.

Further, the conventional bandpass filter uses a dielectric resonator which operates in a cylindrical mode, particularly in the TE01δ mode. This dielectric resonator maintains a resonance mode even if it is not supported by a metal, so that a high Q can be obtained, and therefore, one having a small insertion loss and a good cutoff performance can be obtained.

The TE01δ mode resonator is not of the fundamental resonance mode. On the other hand, the resonator of the fundamental resonance mode TM010 cannot maintain the resonance unless the dielectric is supported by the metal, while the Q value due to the loss in the metal. Will be lower.

On the other hand, there is also a bandpass filter which uses a dielectric sphere as a resonator and operates in a spherical mode. This bandpass filter is equipped with a dielectric resonator, and by supporting the minimum electric field portion with a dielectric material having a dielectric constant smaller than that of the resonator, the resonance condition is hardly affected and the inside of the housing is not affected. Fixed to. The minimum electric field is determined by the angle of the antenna for driving the filter.

As a conventional bandpass filter, there is one having a structure as shown in FIG. The structure of this bandpass filter is disclosed in Japanese Patent Application No. 2-266386 filed by the present applicant on October 5, 1990.

In FIG. 7, reference numeral 1 denotes a cylindrical casing,
A coupling loop 2a is attached to the end face 1a in the long axis direction. One end of the coupling loop 2a has an input / output connector 3
It is connected to a. An input / output connector 3b is connected to the end surface 1b opposite to the end surface 1a. A coupling loop similar to the coupling loop 2a is also provided on the end face 1b, but it is located behind the end face 1b and is not shown.

In the housing 1, three spherical dielectric resonators 4a, 4b, 4c are arranged at substantially equal intervals along the central axis X. The dielectric resonators 4a, 4b, and 4c are supported by plate-shaped supports 5a, 5b, and 5c so that the mounting positions of the dielectric resonators 4a, 4b, and 4c do not shift due to external force such as impact. Each of the supports 5a, 5b, 5c is made of a plastic material having a low dielectric loss, is extended in the radial direction, and is supported by coming into contact with the inner wall of the housing 1.

In operation, the electromagnetic wave signal input from the input / output connector 3a is converted into the dielectric resonators 4a, 4b, 4c.
An electric field indicated by a solid line arrow and a magnetic field indicated by a dotted line arrow are generated at the portion of (1) and are output from the input / output connector 3b.

In such a dielectric resonator, the resonance of the spherical dielectric resonates in a floating state even in the fundamental mode, and it is not necessary to support it by a metal, so that the Q value does not decrease due to the resistance loss of the metal. .. The fundamental resonance mode of the spherical dielectric resonator is TM01. When the dielectric constant is 24, the diameter of the resonator is about 0.178λ, and TE01
The size is about 15% smaller than that of the δ-mode resonator.

The next higher mode of the spherical dielectric resonator is TE
And the dielectric constant is 24, the dielectric constant is about 64.
Since it resonates at a high frequency, a wide pass band can be obtained. When the TE01δ mode resonator is constructed using the same dielectric, the next higher mode (EH11δ) is generated at a frequency about 17% higher.

[0012]

However, in the conventional band pass filter, the work of adhering the support for supporting the resonator in the minimum electric field position in the housing and the work of positioning it on the central axis of the housing are complicated. However, there was a drawback that it was not easy to manufacture.

The present invention is mechanically and electrically stable in order to overcome the drawbacks of conventional bandpass filters,
It is an object of the present invention to provide a bandpass filter that is easy to manufacture.

[0014]

A bandpass filter according to the present invention comprises a plurality of dielectric resonators linearly arranged at a predetermined interval in a housing so as to have a predetermined pass frequency band or less. A foamed plastic having a dielectric constant of 1.05 or less, the foamed plastic filling the space in the housing and supporting the dielectric resonator in the housing. Is.

[0015]

According to the present invention, by holding the dielectric resonator in the housing with the foamed plastic, even if an impact force in the lengthwise direction and / or the vertical direction is applied to the housing, it functions as a bandpass filter. Stabilize its performance by keeping the coupling coefficient almost unchanged.

[0016]

Embodiments of the present invention will be described in detail below with reference to the drawings, and the same elements as those already described in FIG. 7 will be described using the same reference numerals. FIG. 1 is a view showing the internal structure of a bandpass filter according to the present invention, and for ease of explanation, the upper portion of the housing 1 is shown broken away along the length direction of the housing 1. In FIG. 1, an input / output connector 3 is provided on each end surface 1a, 1b of the housing 1.
a and 3b are attached. I / O connector 3a,
The other ends of 3b respectively project into the housing 1, the former is connected to the coupling electrode 6a, and the latter is also hidden by the end face 1b and connected to the coupling electrode on the end face 1b side not shown. In the case 1, the configuration on the end face 1a side is also the end face 1b.
Since the configuration on the side is also the same, the following description will focus on the former.

Here, in the coupling electrode 6a, as shown in FIG. 2, the distance between the coupling electrode 6a and the dielectric resonator 4a changes due to an impact perpendicular to the length direction of the housing 1. In order to avoid a change in the coupling coefficient between them, it is formed in a cylindrical shape.

In the housing 1, three spherical dielectric resonators 4a, 4b, 4c are arranged at substantially equal intervals on a plane on the central axis X including the coupling electrode 3a. The center axis of the dielectric resonator 4a is, as shown by the solid line in FIG.
It coincides with the central axis of the length direction. Dielectric resonator 4b
Similarly, 4c and 4c coincide with the central axis.

The influence of the surrounding medium on the resonance frequencies of the dielectric resonators 4a, 4b, 4c is determined by the permittivity of the dielectric itself and the permittivity of the surrounding medium. The dielectric constants of the surrounding medium are described below.
When the permittivity of the resonators b and 4c is 20 or more, and the permittivity of the medium around them is 1.05 or less,
The resonance frequency of the resonator is hardly affected by the surrounding medium. Even if there is an influence, this is within the range that can be corrected based on theoretical calculation in advance. The dielectric loss (ε ″) related to the dielectric will be described. The dielectric loss of the dielectric resonators 4a, 4b, and 4c is 1 / (expansion ratio) of the bulk material. Is small, the Q value of the resonator is hardly influenced.

Further, in order to keep the dielectric resonators 4a, 4b and 4c arranged at substantially equal intervals around the plane, the inside of the housing 1 is filled with foamed plastic 7. FIG. 1 shows the lower side of the foamed plastic 7 for the sake of simplicity.

Since the dielectric constant of the foamed plastic 7 acts to lower the resonance frequency when it is large, it is preferable that it is as small as possible. Furthermore, if the dielectric loss of the foamed plastic 7 is large, the dielectric resonator 4a,
It is preferable to be as small as possible, because it lowers the Q of 4b and 4c, and therefore increases the insertion loss of the band pass filter to lower the pass band characteristic. For this reason, it is preferable that the foamed plastic 7 is made of foamed polyethylene that has a small dielectric constant and a small dielectric loss, is rich in mechanical flexibility, and is chemically stable.

The dielectric constant (ε ') of foamed polyethylene is obtained from the following equation according to the expansion ratio. ε '= 1 + (2.2-1) / (expansion ratio) (1) For example, if the expansion ratio is 40, ε' = 1.03, and the resonance frequency is corrected by perturbation calculation. It becomes possible to do. Since foamed polyethylene has a small dielectric loss, the effect of dielectric loss on performance is as follows:
Can be ignored.

Further, on the plane of the foamed plastic 7 including the central axis X, a plastic having a hole having a diameter slightly larger than the diameter of the dielectric resonators 4a, 4b, 4c.
A spacer 8 made of a film is arranged. Spacer 8
The dielectric resonators 4a, 4b, 4c are respectively arranged in the respective holes of, and cooperate with the foamed plastic 7 to ensure the maintenance of these positions.

This is because when the relative distances between the dielectric resonators 4a, 4b and 4c are shifted in the central axis direction by an external force such as vibration and impact, their coupling coefficient is a predetermined value, that is, the pass frequency band. This is because the dielectric resonators 4a, 4b, and 4c are accurately held in the housing 1 so that the inconvenience that the performance does not reach a predetermined value does not occur. Therefore, the spacer 8 is made of a polyimide resin film having a high mechanical rigidity and a small dielectric loss and a thickness of 50 μm.

In operation, the electromagnetic wave signal input from the input / output connector 3a is converted into the dielectric resonators 4a, 4b, 4c.
Output from the input / output connector 3b by generating an electric field indicated by a solid arrow above.

Now, an impact force is applied to the bandpass filter in the lengthwise direction thereof, and the dielectric resonators 4a, 4b, 4c are displaced in the lengthwise direction as shown by the dotted line in FIG. And In this case, the dielectric resonators 4a, 4b, 4
Since the relative positional relationship between c is maintained by the presence of the spacer 8, there is no change in the pass band performance, that is, it is not affected by the impact force. Further, such an impact force also changes the distance between the coupling electrode 6a and the dielectric resonator 4a. However, since the dielectric resonators 4a, 4b, 4c supported by the spacer 8 are displaced together,
Since the distance between the coupling electrode 6a and the dielectric resonator 4a decreases, the distance between the coupling electrode 6b and the dielectric resonator 4c increases, and the effect is canceled out as a whole. The coupling coefficient between them does not change.

On the other hand, an impact force perpendicular to the length direction of the housing 1 is applied, so that the dielectric resonators 4a, 4b and 4c are separated from the central axis in the vertical direction as shown by the dotted line in FIG. Even if displaced, the dielectric resonators 4a, 4b, and 4c do not change the lengthwise distance of the housing 1. But,
Since the distance between the dielectric resonator 4a and the coupling electrode 6a changes, the coupling coefficient between them does not have a change canceling effect such as the displacement in the direction of the central axis described above, and the bandpass filter passes through. Bandwidth performance may vary. Therefore, as described above, in order to avoid the change in the coupling coefficient between the coupling electrode 6a and the dielectric resonator 4a due to the impact in the direction of the vertical axis on the housing 1, as shown in FIG. Since the shape of 6a is cylindrical, the coupling electrode 6a and the dielectric resonator 4a are
The electric field distribution generated between and shows a shape in which the letter M lies sideways as shown in FIG. 5, when an impact force perpendicular to the length direction of the housing 1 is not applied, The electric field troughs are located on the longitudinal axis. When an impact force perpendicular to the length direction of the housing 1 is applied, as shown in FIG.
Although one peak of the electric field moves away from the dielectric resonator 4a, the edge effect of the coupling electrode 6a that the other peak of the electric field approaches makes the coupling coefficient as a whole almost unchanged.

In order to obtain such an electric field, the combined electrode 6a
The diameter and wall thickness of the cylinder are determined by the diameter and permittivity of the dielectric resonator 4a and the required coupling coefficient between the coupling electrode 6a and the dielectric resonator 4a. Good.

[0029]

As described above, according to the present invention, since the dielectric resonator in the housing is held by the foamed plastic, impact force is applied to the housing in the longitudinal direction and / or the vertical direction. Even if is applied, the coupling coefficient of the bandpass filter can be prevented from substantially changing, and stable performance can be obtained as the bandpass filter.

[Brief description of drawings]

FIG. 1 is a perspective view of a bandpass filter showing a partially cutaway view of an embodiment of a bandpass filter according to the present invention.

FIG. 2 is a diagram showing a structure of a coupling electrode.

FIG. 3 is a cross-sectional view taken along the center of the bandpass filter shown in FIG. 1 in the longitudinal direction.

FIG. 4 is a diagram for explaining the displacement of the dielectric resonator in the housing with respect to the vertical impact force of the housing 1.

FIG. 5 is a diagram showing an electric field formed between a coupling electrode and a dielectric resonator.

FIG. 6 is a diagram showing an electric field formed between a coupling electrode and a dielectric resonator.

FIG. 7 is a perspective view of a conventional bandpass filter with a part thereof cut away.

[Explanation of symbols]

 1 Housing 4a, 4b, 4c Dielectric resonator 6a Coupling electrode 7 Foamed plastic 8 Spacer

Claims (3)

[Claims] 1. A band pass filter having a plurality of dielectric resonators linearly arranged at a predetermined interval in a housing so as to have a predetermined pass frequency band or less, and a dielectric constant of 1.05 or less. And a foamed plastic which is filled with a space inside the housing and supports the dielectric resonator in the housing. 2. A plurality of the plurality of dielectric resonators are arranged on a plane including a central axis in a diameter direction of the housing and longitudinally cut through the foamed plastic, and are slightly larger than substantially the diameter of the dielectric resonator. The band pass filter according to claim 1, further comprising a spacer having a hole, wherein each of the dielectric resonators is supported in each of the holes. 3. The method according to claim 1, further comprising a cylindrical electrode attached to an inner end surface of the housing, wherein the electrode drives the dielectric resonator.
Bandpass filter as described.