JPS62241401A - Filter circuit - Google Patents

Abstract

PURPOSE:To improve mass-productivity and to improve filter characteristics by composing a series inductor of a microstrip line and a parallel capacitor of a chip capacitor, and providing a tip open stub which is <=1/4 as long as wavelength to the connection part between the series inductor and parallel capacitor. CONSTITUTION:Inductance is composed of the microstrip line instead of an air-core coil and tip open stubs 9a-9c which are <=1/4 as long as the wavelength are provided to the connection parts between microstrip line inductors 6a-6d and chip capacitors 7a-7c, thereby realizing fine capacity. A filter circuit of this constitution have its air-core coil formed in a strip pattern, so variance in inductance is small. Further, the fine capacity is realized by the tip open stubs 9a-ic, so superior filter characteristics are obtained. Furthermore, the length of the tip open stubs is only adjusted for variance in capacity value among the chip capacitors, so the mass-productivity is superior.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a filter circuit used in satellite broadcast receivers, microwave communication devices, and the like.

2. Description of the Related Art Conventionally, this type of filter circuit used in relatively low frequency microwave bands has been constructed by cascading an air-core coil and a chip capacitor as shown in FIG. Second
In the figure, 1a, 1b.

1c and 1d are air-core coils, and 2a, 2b, and 2c are chip capacitors. The inductance of the air-core coils 1a to 1d and the capacitance of the chip capacitors 2a to 2C are constants determined according to the specifications of the filter.

Problems to be Solved by the Invention In a filter circuit with such a conventional configuration, it is difficult to adjust the pass characteristics and selection characteristics of the filter in response to variations in capacitance of the chip capacitors 2a to 2C and variations in inductance of the air core coils 1a to 1d. Adjustments were essential to achieve the specifications. Furthermore, it is difficult to realize a minute capacitance value of several PF or less with a commercially available chip capacitor, and a filter having a capacitance value calculated from the filter specifications cannot be produced, and as a result, deterioration of filter characteristics is unavoidable.

The present invention has been made in view of the above points, and provides a filter circuit in which the constant of the filter element is close to the theoretical value, has excellent filter characteristics, and is suitable for mass production.

A foolproof way to solve problems The technical means of the present invention to solve the above problems is as follows.

The inductance is constructed by a microstrip line instead of an air-core coil, and a quarter inductance is used at the connection between the microstrip line inductor and the chip capacitor.
A stub with an open end below the wavelength is provided, thereby achieving a very small capacitance.

action The effect of this technical means is as follows.

That is, the inductance of the series air-core coil can be realized by a series microstrip line, and the characteristic impedance and length of the microstrip line are determined so as to obtain the desired inductance. In addition, the capacitance value of the parallel capacitor determined by the filter specifications is realized by a chip capacitor and an open-ended stub with a diameter of 1/4 wavelength or less. In other words, most of the desired capacitance value is achieved by a chip capacitor, and the remaining minute capacitance value is achieved by an open-ended stub.

In a filter circuit with such a configuration, the air-core coil is formed into a strip pattern, so there is little variation in inductance, and the open-end stub allows a small capacitance to be achieved, so excellent filter characteristics can be obtained. Furthermore, to account for variations in the capacitance of chip capacitors, all you have to do is adjust the length of the open-ended stub.

Excellent for mass production.

EXAMPLE Hereinafter, an example of the present invention will be described based on the accompanying drawings.

FIG. 1 is a diagram showing an embodiment of the filter circuit of the present invention. In the figure, 3 is a dielectric substrate with a relative dielectric constant of 2.6. It is a Teflon substrate with a thickness of 0.8 rtrm, and the back side has a ground pattern on the entire surface.

4 is an input line, 6 is an output line, 6a, 6b, 6c.

6d is a microstrip line inductor, 7a,
7b and 7a are chip capacitors, and 8a.

8b and 8c are stubs/I/holes, and 9a, 9b, and 9c are stubs with open ends. Note that the filter of the embodiment of the present invention has a cutoff frequency of 600 MHz and a ripple of 0.05.
dB, a 7-stage Chebyshev characteristic low-pass filter with a characteristic impedance of 60Ω.

The series inductance and parallel capacitance for constructing this filter are as shown in the table below. The filter element values of this example are as follows: for the microstrip line inductors 6a and 6d whose series inductance is shown in the table below, the characteristic impedance is 150Ω, and the length is 20.5Ω.
．． , also 6b.

For 6C, characteristic impedance 150Ω, length 38
．． 5 TTM microstrip line. Further, as for the parallel capacitance shown in the table, 7 pF for 7a and 7c is a chip capacitor, and the remaining 0.62 pF is composed of open-ended stubs 9a and 90. Also.

For 7b, 8py is a chip capacitor and the remaining 0.5
7 pF- is realized by the open-ended stub 9b.

(Left below) Effects of the Invention As described above, according to the present invention, a minute capacitance is realized by the open-end stub without using an air-core coil, and the capacitance value of the chip capacitor can be compensated for by this. It is suitable for mass production and has the effect of providing excellent filter characteristics.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an example of a filter circuit according to an embodiment of the present invention. 3... Dielectric substrate, 4... Input line,
5...Output line, 6a-6d...Microstrip line inductor, 7a-7c...Group...
chip capacitor. 8a-8c...Group/Through hole, 9a-9c/Old...Open tip stub. Name of agent: Patent attorney Toshio Nakao and 1 other person 2nd
figure

Claims (1)

[Claims] It is configured by cascade-connecting a plurality of series inductors and parallel capacitors mounted on a dielectric substrate, the series inductor is a microstrip line, the parallel capacitor is a chip capacitor, and the series inductor and the parallel capacitor are connected in series. A filter circuit characterized in that a parallel capacitor connection portion is provided with an open-ended stub having a length of 1/4 wavelength or less.