JPS633211Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a coaxial filter in which a resonator is loaded on a coaxial line.

FIG. 1 shows the structure of a conventional band rejection type coaxial filter. This coaxial filter has a structure in which a semi-coaxial resonator 2 is loaded onto a coaxial line 1. The coaxial line 1 has a structure in which an outer conductor 4 is coaxially arranged around the outer periphery of a center conductor 3.
In the semi-coaxial resonator 2, a cylindrical outer conductor 6 is coaxially arranged around the outer periphery of a tubular central conductor 5, one end of the outer conductor 6 is closed with an end plate 7, and the other end is connected to a coaxial line 1.
is connected to the outer conductor 4 of the coaxial line 1, one end of the center conductor 5 is cantilevered by the end plate 7, and the other end is projected into the coaxial line 1 through a coupling hole 8 drilled in the outer conductor 4 of the coaxial line 1, A variable length stub 9 is inserted into the tubular concentric conductor 5, and the tip thereof protrudes into the coaxial line 1 opposite to the center conductor 3.

In such a coaxial filter, the degree of coupling between the coaxial line 1 and the half-coaxial resonator 2 is basically determined by the degree of coupling between the center conductor 3 of the coaxial line 1 and the half-coaxial resonator 2.
The capacitance between the center conductor 5 and the tip of the center conductor 5 increases.
becomes lower. Therefore, conventionally, a variable length stub 9 is used to change the protrusion length of the variable length stub 9 into the coaxial line 1 and change the distance between the tip of the variable length stub 9 and the center conductor 3 to control the load Q. I was trying to find a way to change it.

FIG. 2 shows an equivalent circuit of such a band rejection type coaxial filter. In the figure,
C is the capacitance between the center conductor 3 of the coaxial line 1 and the center conductor 5 of the semi-coaxial resonator 2, and L is the length l of the center conductor 5 of the semi-coaxial resonator 2, which is 1/4 wavelength of the resonant frequency. The inductance obtained by making the inductance slightly shorter than an odd multiple of R1 is the internal resistance of the power supply 10, R
2 is a load resistance. The parallel combined resistance of these R1 and R2 is the load resistance R seen from the resonator 2. This resonant circuit is a series resonant circuit, and its resonant angular frequency ω ₀ and load Q are ω ₀ =1/√ …(1) Load Q=1/(Rω ₀ C)=ω ₀ L/R …( 2) It is well known that it is given by.

By the way, based on equation (2), as shown in Fig. 1, the variable length stub 9 is brought closer to the center conductor 3 side of the coaxial line 1 to increase C, and the degree of coupling is increased to increase the load Q.
As can be seen from equation (1), lowering the resonant frequency lowers the resonant frequency, so the conventional structure had the disadvantage of requiring readjustment of the resonant frequency. If L is constant, if the load Q is lowered by 2%, the resonant frequency will also be lowered by 1%. In this case, the amount of change in L is extremely small compared to the amount of change in C, but since it is directly proportional to the length l of the center conductor 5 of the semi-coaxial resonator 2, the resonant frequency further decreases. Also, from a structural point of view, if the center conductor 5 of the semi-coaxial resonator 2 is thin, there is a drawback that it is extremely difficult to form a screw hole for passing the variable length stub 9 through.

An object of the present invention is to provide a coaxial filter that can prevent changes in resonance frequency even when the load Q is adjusted.

The present invention provides a coaxial filter in which a resonator is loaded on a coaxial line, and a variable length stub is provided at any position in the circumferential direction of the outer conductor of the coaxial line corresponding to the loading location of the resonator. It is characterized by this.

Embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 3 shows an example in which the present invention is applied to a band rejection type coaxial filter. In addition,
Portions corresponding to those in FIG. 1 are designated by the same reference numerals. In this embodiment, a variable length stub 9 is threaded and supported through the outer conductor 4 of the coaxial line 1 at a symmetrical position opposite to the center conductor 5 of the semi-coaxial resonator 2.

In such a coaxial filter, when the variable length stub 9 is brought close to the center conductor 3 of the coaxial line 1, the electric field around the center conductor 3 is reduced by the variable length stub 9.
, and the electric field coupling to the center conductor 5 of the semi-coaxial resonator 2 becomes small. That is, there is an effect similar to that of reducing the capacitance C between the center conductor 5 of the semi-coaxial resonator 2 and the center conductor 3 of the coaxial line 1, and the load Q
becomes larger. On the other hand, at the resonant frequency, the combined resistance of L and C of the semi-coaxial resonator 2 is zero, so there is no electric field in the coaxial line 1 near the resonator 2, and there is no influence from the variable length stub 9. Therefore, the resonant frequency does not change. Actually, resonant frequency 4650M
Hz, an experiment was conducted using a coaxial filter with an initial load Q of 127, and when the degree of coupling was changed until the load Q changed by +36%, the change in the resonant frequency was only +0.1%.

FIG. 4 shows an example in which the present invention is applied to a band-pass type coaxial filter, and the operating principle of the variable length stub 9 is the same as that shown in FIG. Note that parts corresponding to those in FIG. 3 are designated by the same reference numerals.

In the above embodiment, the variable length stub 9 was attached to the outer conductor portion of the coaxial line 1 at a symmetrical position opposite to the center conductor 5 of the semi-coaxial resonator 2, but the present invention is not limited to this. The position may be shifted in the circumferential direction of the coaxial line 1 as long as the semi-coaxial resonator 2 is not affected.

As explained above, in the coaxial filter according to the present invention, since the variable length stub is provided on the outer conductor side of the coaxial line rather than on the resonator side, the load Q of the resonator can be changed without changing the resonant frequency. , the load Q of the resonator can be easily adjusted.
Further, according to the present invention, the present invention can be implemented without being affected by the structure of the resonator, and the structure is simple, making it easy to manufacture.

[Brief explanation of the drawing]

1 and 2 are longitudinal sectional views of a conventional coaxial filter and their equivalent circuit diagrams, and FIGS. 3 and 4 are longitudinal sectional views of two embodiments of the coaxial filter according to the present invention. . 1... Coaxial line, 2... Half coaxial resonator, 3...
Center conductor, 4... Outer conductor, 5... Center conductor, 6
...outer conductor, 8...coupling hole, 9...variable length stub.

Claims (1)

[Scope of utility model registration request] A coaxial filter having a resonator loaded on a coaxial line, characterized in that a variable-length stub is provided penetrating any position in the circumferential direction of the outer conductor of the coaxial line corresponding to the loading position of the resonator.