JPH0529816A - Band-pass filter - Google Patents

Abstract

PURPOSE:To provide a band-pass filter capable of maintaining a good temperature characteristic. CONSTITUTION:A blocking part on side where the variable short-circuit board 3 of a cylindrical hollow resonator 1 is present is constituted of a movable cover 6 and a tube axial length L2 is made variable. The L1 for tube diameter D is properly set by the variable short-circuit board 3 so that the resonator 1 resonates (TE011 mode) with a desired frequency. The L2 is adjusted by the movable cover 6 so that the temperature characteristic of the resonator 1 is optimum. Since the adjustments are independent with each other, the temperature characteristic is improved even if the resonance frequency is changed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a cylindrical cavity resonator as a TE.
[0111] The present invention relates to a bandpass filter used by resonating in the 11 mode.

[0002]

2. Description of the Related Art As a band-pass filter used for resonating a cylindrical cavity resonator in a TE011 mode, the one shown in FIG. 2 is conventionally known. In FIG. 2, 10 is a cylindrical cavity resonator. The cylindrical cavity resonator 10 is open at one end in the tube axis direction and closed at the other end. And
On the tube wall on the other end side (closed part side) of the cylindrical cavity resonator 10,
Two coupling holes 2 are provided facing each other.

A disk-shaped variable short-circuit plate 3 is provided on one end side (opening side) of the cylindrical cavity resonator 10 so as to be orthogonal to the tube axis. The variable short-circuit plate 3 is used for the cylindrical cavity resonator 10
The disk has a diameter slightly smaller than the inner diameter D of the disk, and on the back surface facing the opening side, the threaded portion 4 is provided at the center and the absorber 7 is attached. Then, the opening of the cylindrical cavity resonator 10 is closed by the cover 8, but a fixing nut 5 is provided at a portion of the cover 8 that penetrates the screw portion 4, and the screw portion 4 is screwed to these. The variable short-circuit plate 3 is supported so as to be movable in the tube axis direction.

In the above structure, the cylindrical cavity resonator 10
Is the length of the tube axis L so that it resonates in TE011 mode.
2. The inner diameter is selected as D, but the TE111 mode can resonate with the same size. The variable short-circuit plate 3 is provided in order to remove the influence of the TE111 mode, and by finely moving it, the length from the surface of the variable short-circuit plate 3 to the closed portion on the other end side of the cylindrical cavity resonator 10 is set to L1. Then, make TE011 mode dominant. The TE111 mode is a cylindrical cavity resonator 10
A large loss is caused by the gap between the inner wall surface of the and the outer peripheral surface of the variable short-circuiting plate 3, and the Q is further lowered by the absorber 7, so that the resonator generally resonates only in the TE011 mode. If an electromagnetic wave is transmitted through the coupling hole 2, a band pass filter using the TE011 mode is constructed. In addition, in order to make the band pass characteristic sharp, a plurality of cylindrical cavity resonators 10 may be used with their coupling holes 2 connected to each other. FIG. 2 shows a basic configuration.

By the way, the temperature characteristic of the resonance frequency f ₀ of the cylindrical cavity resonator 10, that is, the band-pass filter is expressed by the following mathematical expression 1. In the equation, C is the speed of light, α1 is the linear expansion coefficient of the cylindrical cavity resonator material, α2 is the linear expansion coefficient of the variable short-circuit plate material, and t is the temperature.

[0006]

[Equation 1]

As is clear from the above equation, by appropriately selecting L1, L2 and D, and further selecting materials having appropriate linear expansion coefficients for the cylindrical cavity resonator 10 and the variable short-circuit plate 3, respectively, A cylindrical cavity resonator (that is, a bandpass filter) having excellent temperature characteristics can be realized.

[0008]

However, in reality, since there are variations due to manufacturing precision and the like, in order to obtain a desired resonance frequency, the variable short-circuit plate is slightly moved each time to obtain L.
It is necessary to adjust 1. Therefore, in the above-described conventional bandpass filter, since L1 changes, it becomes difficult to maintain the ideal relationship between L1, L2, and D, resulting in the cylindrical cavity resonator, and thus the bandpass filter. There is a problem of degrading the temperature characteristics of the wave filter.

An object of the present invention is to provide a bandpass filter which can stably maintain good temperature characteristics by providing a structure in which the tube axis length of the cylindrical cavity resonator itself can be varied.

[0010]

In order to achieve the above object, the band pass filter of the present invention has the following structure. That is, the band-pass filter of the present invention comprises a cylindrical cavity resonator, a variable short-circuit plate movably provided in the tube axis direction at one end side of the cylindrical cavity resonator in the tube axis direction, and the cylindrical cavity. A band-pass filter having two coupling holes provided on the tube wall on the other end side in the tube axis direction of the resonator so as to face each other, and used by resonating in a TE011 mode by adjusting the position of a variable short-circuit plate. One of the blocking portions on both sides of the cylindrical cavity resonator in the tube axis direction is movable in the tube axis direction.

[0011]

Next, the operation of the bandpass filter of the present invention constructed as described above will be described. In the present invention, one of the blocking portions on both sides of the cylindrical cavity resonator in the tube axis direction is movable in the tube axis direction. Therefore, after the desired resonance frequency is obtained by adjusting the position of the variable short-circuit plate, it is possible to set the tube axis length of the cylindrical cavity resonator that obtains the optimum temperature characteristic.

As a result, it is possible to realize a bandpass filter which can maintain good temperature characteristics even when the resonance frequency is changed.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a bandpass filter according to an embodiment of the present invention. The same components as those in the conventional example (FIG. 2) are designated by the same reference numerals. In the present embodiment, the closed portion of the cylindrical cavity resonator 1 on the side where the variable short-circuit plate 3 is present is constituted by the movable cover 6 so that the tube axis length L2 can be varied. A mechanism for moving the movable cover 6 in the tube axis direction is omitted because it can be configured with a concept similar to that of the moving mechanism of the variable short-circuiting plate 3, but the moving distance is short, so that even if the closing portion on the coupling hole 2 side is movable. good.

In the above structure, the resonance frequency is the pipe diameter D.
And L1 set by the variable short circuit plate 3. So D
Since the cylindrical cavity resonator 1 composed of the above and L1 has the length L2 that optimizes the temperature characteristic, the movable cover 6 adjusts L2.

Even when a plurality of cylindrical cavity resonators are used, a bandpass filter having good temperature characteristics as a whole can be realized by adjusting each resonator in the same manner.

[0016]

As described above, according to the bandpass filter of the present invention, one of the blocking portions on both sides of the cylindrical cavity resonator in the tube axis direction is configured to be movable in the tube axis direction, and the variable short circuit is provided. After adjusting the position of the plate to obtain the desired resonance frequency, the tube axis length of the cylindrical cavity resonator that obtains the optimum temperature characteristics can be set, so that good temperature characteristics are maintained even if the resonance frequency is changed. There is an effect that can realize a possible band pass filter.

[Brief description of drawings]

FIG. 1 is a schematic side sectional view of a bandpass filter according to an embodiment of the present invention.

FIG. 2 is a schematic side sectional view of a conventional bandpass filter.

[Explanation of symbols]

 1 Cylindrical cavity resonator 2 Coupling hole 3 Variable short-circuit plate 4 Screw part 5 Fixing nut 6 Movable cover 7 Absorber

Claims (1)

Claim: What is claimed is: 1. A cylindrical cavity resonator, a variable short-circuit plate provided at one end of the cylindrical cavity resonator in the tube axis direction so as to be movable in the tube axis direction, and the cylindrical cavity resonance. A band-pass filter that is provided with two coupling holes provided on the tube wall on the other end side in the tube axis direction of the vessel so as to face each other, and is used by resonating in a TE011 mode by adjusting the position of the variable short-circuit plate; A band-pass filter, wherein one of the blocking portions on both sides of the cavity resonator in the tube axis direction is movable in the tube axis direction.