JPH0135524B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a variable bandpass filter that can vary the center frequency of its passband, and particularly relates to a variable bandpass filter using microstrip lines.

Generally, a tuner for receiving satellite broadcasting uses a superheterodyne system, which selects one wave with a width of about 30 MHz from among intermediate frequency signals with a width of 300 MHz or 500 MHz or more in the 1 GHz band, and converts the frequency. Due to the above selection, it has a passband of about 30MHz, and the center frequency of that passband is about 500MHz.
A variable bandpass filter is required. Conventionally, such a variable bandpass filter has been provided with a plurality of bandpass filters each having a different center frequency of a pass band, and these bandpass filters are used by switching. In addition, there were some devices that provided one or more variable band elimination filters and constituted a variable band pass filter as a whole. However, these variable bandpass filters require a large number of bandpass filters and variable band elimination filters, which poses a problem in that the circuit configuration becomes complicated.

An object of the present invention is to provide a variable bandpass filter that has a simple circuit configuration and can obtain bimodal frequency characteristics.

Therefore, the present invention has a length dimension of approximately 1/4 wavelength of the center frequency of the frequency band used, one end is an input end to which a signal of the frequency band used is supplied, and the other end is an open end. a first input side microstrip line having approximately the above-mentioned length dimension, which is arranged parallel to the first input side microstrip line with a small gap therebetween, and an end portion on the same side as the input end portion; The second input side microstrip line, which has an open end, and the first and second input side microstrip lines, which have approximately the above-mentioned length dimensions, are connected to each other so as not to be coupled in a distributed manner. a first intermediate microstrip line having one end adjacent to the end opposite to the open end of the line and having the other end open; and first and second inputs having substantially the above length dimension. It is arranged parallel to the first intermediate microstrip line with a small interval so as not to be distributedly coupled to the side microstrip line, and the end of the side adjacent to the second input side microstrip line is a second intermediate microstrip line having an open end, and first and second intermediate microstrip lines having substantially the above-mentioned length at ends opposite to the open end of the second intermediate microstrip line. A first output side microstrip line having one end adjacent to the line and the other end being an open end so as not to be distributedly coupled to the line, and a first and second output side microstrip line having approximately the above length dimension. An end on the same side as the open end of the first output microstrip line, which is arranged parallel to the first output microstrip line with a small interval so as not to be distributedly coupled to the intermediate microstrip line. A second output side microstrip line is formed on the dielectric substrate, and the second output side microstrip line is an output end and the opposite end is an open end.
A first variable capacitance element is connected between adjacent ends of the intermediate microstrip line, and a second variable capacitance element is connected between adjacent ends of the second intermediate and first output side microstrip lines. , a variable voltage circuit for the first and second variable capacitance elements is connected between the second input side and the middle part of the first intermediate microstrip line, and a variable voltage circuit is connected between the second intermediate part and the middle part of the first output side microstrip line. This is a configuration in which the parts are connected.

With this configuration, the first and second input side microstrip lines equivalently constitute a first tuning circuit. Similarly, the first and second intermediate microstrip lines and the first and second output side microstrip lines also constitute second and third tuning circuits, respectively. Each variable capacitance element constitutes a variable capacitor together with the variable voltage circuit, one of which is connected in series between the secondary side of the first tuned circuit and the primary side of the second tuned circuit, The other one is connected in series between the secondary side of the second tuned circuit and the primary side of the third tuned circuit. The tuning frequency is changed by changing the values of both variable capacitance capacitors. Therefore, a variable bandpass filter can be realized with a simple configuration of six microstrip lines, a variable capacitance element, and a variable voltage circuit. Moreover, by providing the first and second intermediate microstrip lines, a bimodal frequency characteristic can be obtained.

Hereinafter, the present invention will be explained in detail based on one embodiment shown in the drawings.

In FIG. 1, reference numeral 1 denotes a first input microstrip line, which has a length of about 34 mm and a width of about 2 mm, and is constructed on a dielectric substrate (not shown) with a dielectric constant of 4.2. A 1 GHz band signal is supplied to one end 2 of the first input microstrip line 1. That is, one end 2 is used as an input end. Further, the other end 3 is open. A second input microstrip line 4 is arranged parallel to the first input microstrip line 1 with a minute gap of about a fraction of a millimeter therebetween, that is, distributedly coupled to the first input microstrip line 1. The second input microstrip line 4 has almost the same length and width as the first input microstrip line 1, and the end 5 on the same side as the input end 2 is open. There is.

A first intermediate microstripline 8 is arranged so that one end 7 is spaced apart from the other end 6 of the second input microstripline 4 by about 3 mm and at a substantially right angle. This stripline 8 has almost the same length as the first input side microstripline 1, but its width is almost double, and the other end 9 opposite to the one end 7 is It's open. A second intermediate microstrip line 8 is spaced apart from the first intermediate microstrip line 8 by a fraction of a millimeter, and is parallel to the side further away from the first input microstrip line 1 so as to be distributed and coupled to the first intermediate microstrip line 8.
An intermediate microstrip line 10 is arranged. Second intermediate microstrip line 10
has an open end 11 on the same side as one end of the first intermediate microstrip line 8, and has substantially the same length and width as the first intermediate microstrip line 4.

One end 13 is located at a distance of about 3 mm from the other ends 9, 12 of the first and second intermediate microstrip lines 8, 10, and the first and second input side microstrip lines are arranged at a substantially right angle. A first output side microstrip line 14 is arranged in the opposite direction to the direction of the lines 1 and 4, and the other end 15 is open. The first output microstrip line 14 also has substantially the same length and width as the first input microstrip line 1. A second output microstrip line 16 is arranged parallel to the first output microstrip line 14 with an interval of about a fraction of a millimeter therebetween. In other words, it is distributedly coupled. The second output microstrip line 16 also has substantially the same length and width as the first input microstrip line 1. An appropriate approximately 30MHz wide signal in the 1GHz band is extracted from the other end of the second output microstripline 16 (the end farthest from the first and second input microstriplines 1 and 4) 18. be done. In other words, it is an output end. The end 17 opposite to the output end 18 is open.

Between the adjacent ends 6 and 7 of the second input side and first intermediate side microstrip lines 4 and 8, there are variable capacitance diodes 19 connected to each other with opposite polarities.
20 are connected at the shortest distance, and the interconnection point of these variable capacitance diodes 19 and 20 is the resistor 2.
It is grounded via 1. Similarly, the second intermediate and first output side microstrip lines 10, 1
Variable capacitance diodes 22 and 23, which are connected with opposite polarities to each other, are also connected between the adjacent ends 12 and 13 of 4 at the shortest distance, and their interconnection point is connected to the resistor 2.
It is grounded via 4.

Second input side, first and second intermediate and first output side microstrip lines 4, 8, 10, 14
The intermediate portions of the resistors 25, 26, 27,
28. These resistors 2
The interconnection points 5, 26, 27, and 28 are connected to the arms of a variable resistor 29, and both ends of the variable resistor 29 are connected to both ends of a DC power source 30. The negative side of this DC power supply 30 is grounded. Therefore, by changing the position of the arm of the variable resistor 29, the capacitance of each variable capacitance diode 19, 20, 22, 23 changes. By changing the capacitance in this way, a large capacitance change can be obtained with a small voltage change.

FIG. 2 shows an equivalent circuit of the circuit shown in FIG. 1st
The first and second input microstrip lines 1 and 4 shown in the figure are arranged in parallel with a small gap between them, so they are distributed and coupled to each other, forming a tuned circuit 31 as shown in FIG. are doing. Similarly, the first and second intermediate microstrip lines 8, 1
0, the first and second output side microstrip lines 14 and 16 also form tuning circuits 32 and 33, respectively. And a variable capacitance diode 19,
20 forms a variable capacitor 34, and the tuning circuit 3
1 and the primary side of the tuned circuit 32 to form a resonant circuit. Similarly, the variable capacitance diodes 22 and 23 are connected to the variable capacitor 3.
5 and the secondary side of the tuned circuit 32 and the tuned circuit 3
It is connected in series with the primary side of No. 3 to form a resonant circuit. Therefore, by changing the position of the arm of the variable resistor 29, the variable capacitor 34,
35 changes, the resonant frequency of each resonant circuit changes, and the frequency characteristics shown in Figure 3 are obtained.
A bimodal variable bandpass filter can be realized. In addition, microstrip lines 4, 8, 14, 1
When considering 6 alone, these ends 6, 7, 1
The voltage at points 2 and 13 is zero, and between these ends 6 and 7,
Variable capacitors 34 and 3 are connected between the ends 12 and 13.
It is thought that the resonant frequency does not change even if the microstrip lines 4, 8, 14, and 16 are connected respectively. However, in reality, the microstrip lines 4, 8, 14, and 16 are connected to each other. , same 14
are distributedly coupled to the same 16, so the voltage at the ends 6, 7, 12, 13 does not become zero due to this influence, and the variable capacitor 34 is connected between the ends 6, 7 and between the ends 12, 13. , 35, by connecting
Resonant frequency can be changed. Furthermore, the resistors 25, 26, 27, and 28 are connected to the intermediate portions of the microstrip lines 4, 8, 10, and 14 because the impedance changes at this point are small and virtually zero at high frequencies. This is because it is not easily affected by the real frequency.

In the above embodiment, the variable capacitance diodes 19 and 20 are connected between the second input side and the first intermediate side microstrip lines 4 and 8 with mutually opposite polarities, but instead of this, one variable capacitance diode is connected. The cathode is connected to the second input microstrip line 4 side, the anode is connected to the first intermediate microstrip line 8, and the resistor 25
may be connected to the positive side of the DC power supply. The same applies to the variable capacitance diodes 22 and 23.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of one embodiment of a variable bandpass filter according to the present invention, FIG. 2 is an equivalent circuit diagram of FIG. 1, and FIG. 3 is a frequency characteristic diagram of the circuit of FIG. 1. 1...1st input side microstrip line,
4...Second input side microstrip line, 8
...First intermediate microstrip line, 10...
...Second intermediate microstrip line, 14...
1st output side microstrip line, 16...
2nd output side microstrip line, 19,2
0, 22, 23...variable capacitance element, 21, 24,
25, 26, 27, 28, 29, 30...variable voltage circuit.

Claims (1)

[Claims] 1. A first input side having a length of approximately 1/4 wavelength of the center frequency of the frequency band used, with one end serving as an input end to which a signal in the frequency band used is supplied, and the other end serving as an open end. microstripline and
a second input side micro strip line having approximately the above length dimension, arranged parallel to the first input side micro strip line with a small gap therebetween, and having an open end on the same side as the input end side; strip line and
It has approximately the above length dimension, and one end is located at the end opposite to the open end of the second input microstrip line so as not to be distributedly coupled to the first and second input microstrip lines. The first intermediate microstrip line, which is arranged adjacent to the other end and whose other end is an open end, and the first and second input side microstrip lines, which have approximately the above-mentioned length, are arranged so as not to be coupled in a distributed manner. The first intermediate microstrip line is a second intermediate microstrip line that is arranged parallel to each other with a small interval and whose end adjacent to the second input side microstrip line is an open end. , having approximately the above-mentioned length dimension, one end thereof is adjacent to the end opposite to the open end of the second intermediate microstrip line so as not to be distributedly coupled to the first and second intermediate microstrip lines. The first output-side microstrip line, which is arranged so that the other end is an open end, and the first and second intermediate microstrip lines, which have approximately the above-mentioned length dimensions, are arranged so that they are not coupled in a distributed manner. It is arranged in parallel with the first output side microstrip line with a small interval, and the end on the same side as the open end of the first output side microstrip line is the output end, and the end on the opposite side is the output end. A second output side microstrip line having an open end is formed on a dielectric substrate, and a first variable capacitance element is formed between adjacent ends of the second input side and the first intermediate microstrip line. A second variable capacitance element is connected between adjacent ends of the second intermediate and first output side microstrip lines, and a variable voltage circuit for the first and second variable capacitance elements is connected to the second input side. A variable bandpass filter is connected between the intermediate portions of the side and first intermediate microstrip lines, and between the intermediate portions of the second intermediate and first output side microstrip lines.