JPH0514573Y2 - - Google Patents

Description

[Detailed description of the invention] (Field of industrial application) This invention is used in the final stage power amplifier of medium/short wave oscillation amplifier equipment, and eliminates VHF band spurious generated in the output circuit of this final stage power amplifier over a wide band. Regarding low-pass filters.

(Prior art) The basic circuit configuration of this type of low-pass filter is shown in Figure 2a.
Shown below. This basic circuit is an n-type low-pass filter circuit in which two capacitors C are connected in parallel to the input and output sides of a coil L, and the typical filtering characteristics of this circuit are shown in Figure 2b. . In Figure 2b, _c is the cutting frequency, and there is sufficient attenuation for the VHF band. FIG. 3a shows an example of the structure of a conventional low-pass filter for realizing the circuit of FIG. 2a. In this figure, L is a coil formed using a linear conductor, C is the input side and output side capacitors (capacity), L ₁ and L ₂ are the inductance of the lead wire connecting the coil and the capacitor, respectively, 4 and 10 is a glass insulator 15
These are the input and output side terminals that are held through the .

FIG. _3b shows an equivalent circuit of the low-pass filter of FIG. Figure 3c shows the filtering characteristics of the equivalent circuit in Figure 3b, where _c is the switching frequency and 1 and ₂ are given by ₁ = ₁ /2π√ ₁ and ₂ = 1/2π√ _2, respectively. is the resonant frequency.

(Problems to be Solved by the Invention) The above-described conventional low-pass filter shown in FIG. 3a uses lumped constant elements as circuit elements, and therefore has the following drawbacks.

(1) The filtering characteristics of the equivalent circuit shown in Fig. _3b are as shown in Fig. _3c .
As can be easily seen by comparing the filtering characteristics in FIG. b, it is not possible to obtain a sufficient amount of attenuation in the high frequency band over a wide band.

(2) Since the elements are arranged in a three-dimensional structure, the shape becomes large and electrical characteristics are likely to fluctuate due to mechanical vibration.

(3) Even with the same shape, there are large variations in electrical characteristics, and it takes time to adjust after assembly.

(Means for Solving the Problems) In order to solve the above-mentioned problems, the low-pass filter provided by the present invention includes an inductance formed by making a spiral cut in a flat conductor; a first capacitor formed by stacking a first insulating flat plate of a dielectric and a first flat electrode in this order on one side of the capacitor, the flat conductor and the first flat electrode serving as both poles; A second insulating flat plate, a second flat electrode, a third insulating flat plate of dielectric material, and a third flat electrode are stacked in this order on the other side of the flat conductor, and the second insulating flat plate and the third flat electrode are stacked in this order. a second capacitor having a flat electrode and the third flat electrode as its opposite poles; means for fixing the inductance and the first and second capacitors together; fixed to the third flat electrode; an output-side coaxial terminal; an internal conductor of the output-side coaxial terminal includes the third flat electrode, a third insulating flat plate, a second flat electrode, and a second insulating flat plate; and is connected to the flat conductor and the second flat electrode near the center of the spiral cut, and the outer conductor of the output side coaxial terminal is connected to the third flat electrode. are connected to each other and form an output side grounding terminal, the flat conductor in an area outside the portion where the spiral cut is provided forms an input side terminal, and the first flat conductor is It is characterized by serving as a ground terminal on the input side.

(Example) Next, the present invention will be explained with reference to the drawings.

FIG. 1a is a perspective view of an embodiment of a low-pass filter according to the present invention, FIG. 1b is an exploded perspective view of FIG. 1a, and the inductance L shown in FIG.
The coil corresponding to this is realized by a coil in which a spiral slit is formed in a flat copper plate 3. The input side capacitor C shown in FIG. 2a is composed of a first flat copper plate electrode 1 on the ground side, a dielectric plate (Teflon sheet) 2, and a coiled copper plate 3. The output side capacitor C shown in FIG. It is completed. The input terminal 4 is a copper plate 4 that is integrated with the copper plate 3 of the coil. The output side terminal 10 shown in FIG. 2a consists of the inner conductor 10 of the coaxial terminal in FIG.
is connected to the spiral center of the coil 3 and the center of the second flat copper plate electrode 6. The ground end of the input capacitor C is a portion of the first flat electrode 1 that is bent downward. Also, the grounding end of the output side capacitor C is connected to the outer conductor 9 of the coaxial tube terminal.
It is. FIG. 1a shows a state in which the elements shown in FIG. 1b are stacked and assembled. FIG. 1c shows an example in which the low-pass filter of the present invention is mounted in a medium/short wave oscillation amplifier.

The low-pass filter according to the present invention has filtering characteristics as shown in FIG. 2b, and can provide sufficient attenuation even in the VHF band.

Note that FIG. 1b is merely an example of the present invention, and a desired low-pass filter can be realized even if the structure of each part is changed.

(Effects of the invention) As explained above, the low-pass filter according to the invention stably blocks spurious signals in the VHF band generated from the final stage power amplifier circuit of the medium/short wave oscillation amplifier over a wide band. You can. The present invention has such effects.

[Brief explanation of drawings]

Fig. 1a is a perspective view showing an embodiment of the low-pass filter according to the present invention, Fig. 1b is an exploded perspective view showing the low-pass filter of Fig. 1a, Fig. 1c is Figure 1a
FIG. 2a is a circuit diagram showing the basic configuration of a π-type low-pass filter, and FIG. Characteristic diagram showing the filtering characteristics of the low-pass filter of circuit a, 3rd
Figure a is a perspective view showing an example of the structure of a conventionally used lumped constant type low-pass filter, Figure 3 b is an equivalent circuit diagram of the lumped constant type low-pass filter of Figure 3 a, and Figure 3 3c is a characteristic diagram showing the filtering characteristics of the low-pass filter having the equivalent circuit shown in FIG. 3b. DESCRIPTION OF SYMBOLS 1... First flat electrode, 2, 7... Dielectric plate, 3... Coil, 4... Coil input end, 5...
Insulating flat plate, 6... second flat electrode, 8... third
9... Outer conductor of the output side coaxial terminal, 10... Inner conductor of the output side coaxial terminal (coil output end), 11... Insulating bushing, 12... Assembly bolt, 21... Equipment casing Body, 22...Low-pass filter, 23...Low-pass filter output side coaxial feeder, 1
5... Glass insulator, 16... Assembly chassis, L...
...Inductance, L ₁ , L ₂ ... Lead wire inductance, C ... Capacitor, C ₃ ... Stray capacitance.

Claims (1)

[Claims for Utility Model Registration] An inductance formed by making a spiral cut in a flat conductor; a first insulating flat plate of a dielectric and a first flat electrode stacked on one side of the flat conductor in this order; a first capacitor having the flat conductor and the first flat electrode as both poles; a second insulating flat plate, a second flat electrode, and a dielectric on the other side of the flat conductor; A third insulating flat plate and a third flat electrode are stacked in this order, and the second flat electrode and the third flat electrode are stacked in this order.
a second capacitor having flat plate electrodes as both poles;
means for fixing the inductance and the first and second capacitors together; an output-side coaxial terminal fixed to the third flat electrode; and an internal conductor of the output-side coaxial terminal. penetrates the third flat electrode, the third insulating flat plate, the second flat electrode, and the second insulating flat plate, and connects the flat conductor and the first insulating plate near the center of the spiral cut. The outer conductor of the output side coaxial terminal is connected to the third flat plate electrode, forming a ground terminal on the output side, and the spiral cut is connected to the second flat plate electrode. A low-pass filter characterized in that the flat conductor in a region outside the provided portion constitutes an input side terminal, and the first flat conductor constitutes an input side ground terminal.