JPH0135525B2 - - 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, this 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 as an open end; The opposite end and one end of the second input microstrip line are adjacent to each other so as not to be distributedly coupled to the second input microstrip line, and are separated from the first intermediate microstrip line by a small distance. a second intermediate microstrip line arranged in parallel with each other, and an end portion of the second intermediate microstrip line having substantially the above length dimension on the same side as the open side of the first intermediate microstrip line. a first output side microstrip line having one end adjacent to the opposite end so as not to be distributedly coupled to the first and second intermediate microstrip lines, and the other end being an open end; The first output side microstrip line has approximately the above length dimension and is arranged parallel to the first output side microstrip line with a small interval so as not to be distributedly coupled to the first and second intermediate microstrip lines. A second output side microstripline is formed on a dielectric substrate, with an end on the same side as the open end of the stripline serving as an output end, and an end on the opposite side serving as an open end. , the second input side and the first
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. a capacitor connected between adjacent ends of the second input side and the second intermediate microstrip line and between adjacent ends of the first intermediate microstrip line and the first output side microstrip line; This is a configuration in which the following 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 capacitance capacitor together with a 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. Therefore, by changing the values of both variable capacitance capacitors, the tuning frequency is changed. Therefore, six microstrip lines, a variable capacitance element,
A variable bandpass filter can be realized with a simple configuration of a variable voltage circuit. Moreover, by providing the first and second intermediate microstrip lines, it is possible to obtain bimodal frequency characteristics, and the capacitor forms a frequency variable trap together with the variable capacitance capacitor, thereby changing the image frequency band. It can be greatly attenuated.

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 portion 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 one end 5 on the same side as the input end 2 is open. There is.

The first intermediate microstrip line 8 is connected so that one end 7 of the first intermediate microstrip line 8 is located approximately 3 mm apart from the other end 6 of the second input side microstrip line 4, and at a substantially right angle. Pline 8 is arranged. This stripline 8
has almost the same length as the first input microstrip line 1, but its width is almost double, and one end 7 and the opposite end 9 are open. A second intermediate microstripline 10 parallel to the first input side microstripline 1 is spaced apart from the first intermediate microstripline 8 by a distance of a fraction of a millimeter, that is, distributedly coupled to the first intermediate microstripline 8. It is located. The second intermediate microstrip line 10 has one end 1 on the same side as the one end 7 of the first intermediate microstrip line 8.
1 and the other end 12 on the opposite side are not open and have substantially the same length and width as the first intermediate microstrip line 8.

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 at an interval of about a fraction of a millimeter, that is, in a distributed manner. The second output microstrip line 16 also has substantially the same length and width as the first input microstrip line 1. 2nd output side microstrip line 1
6 (the end farthest from the first and second input side microstrip lines 1 and 4) 17, a signal of a suitable width of about 30 MHz in the 1 GHz band is extracted. In other words, it is the output end. Further, one end portion 18 is open.

Between the second input side and the adjacent ends 6 and 7 of the first intermediate microstrip lines 4 and 8, variable capacitance diodes 19 and 2 are connected with opposite polarities to each other.
0 are connected at the shortest distance, and the interconnection point of these variable capacitance diodes 19 and 20 is the resistor 21.
is grounded through. Similarly, the second intermediate and first output side microstrip lines 10, 14
Variable capacitance diodes 22 and 23 connected with opposite polarities are also connected between adjacent ends 12 and 13 of
is grounded through.

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.

In addition, the second input side microstrip line 4
A small capacitor 31 is connected at the shortest distance between the adjacent ends 6 and 11 of the second intermediate microstrip line 10 and the second intermediate microstrip line 10.

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 32 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 33 and 34, respectively. And a variable capacitance diode 19,
20 becomes a variable capacitor 35, and a tuning circuit 32
is connected in series between the secondary side of the tuning circuit 33 and the primary side of the tuned circuit 33, forming a resonant circuit. Similarly, the variable capacitance diodes 22 and 23 are connected to the variable capacitor 36.
The resonant circuit is connected in series between the secondary side of the tuned circuit 33 and the primary side of the tuned circuit 34. A capacitor 31 is connected across two variable capacitors 35 and 36. Therefore, by changing the position of the arm of the variable resistor 29, the values of the variable capacitors 35 and 36 change, and the resonant frequencies of both resonant circuits change. Therefore, a variable bandpass filter can be realized. Moreover, the capacitor 31 forms a frequency variable trap together with the variable capacitors 35 and 36 and the tuning circuit 33,
Significantly attenuates the image frequency band. FIG. 3 shows a frequency characteristic diagram of this embodiment. In addition, when considering the microstrip lines 4, 8, 14, 16 individually, these ends 6, 7, 12, 13
The voltage between ends 6 and 7 is zero, and between ends 6 and 7, end 1
Even if the variable capacitance capacitors 35 and 36 are connected between the microstrip lines 4 and 13, it is thought that the resonance frequency will not change.
14 and 16 are actually microstrip lines 4 and 1, microstrip lines 8 and 10, and microstrip lines 14 and 16, respectively.
Since the voltages at the ends 6, 7, 12, and 13 do not become zero due to this influence, variable capacitors 35 and 36 are connected between the ends 6 and 7 and between the ends 12 and 13. By connecting, the resonant frequency can be changed. Also, resistors 25, 2
6, 27, and 28 are connected to the middle part of each microstrip line 4, 8, 10, and 14 because at this point, the change in impedance at high frequency is small and is virtually zero, so it has no effect on high frequency. This is because it is difficult to accept.

In the above embodiment, the variable capacitance diodes 19 and 20 are connected between the second input side and the first intermediate microstrip lines 4 and 8 with mutually opposite polarities.
Instead, one variable capacitance diode may be connected and the resistor 25 may be connected to the positive side of the DC power supply 30. The same applies to the variable capacitance diodes 22 and 23. Further, contrary to the above embodiment, the output end 17
A signal may be supplied from the input terminal 2 and a signal may be taken out from the input end 2.

[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...
Second output side microstrip line, 16...
1st output side microstrip line, 19,2
0, 22, 23...variable capacitance element, 21, 24,
25, 26, 27, 28, 29, 30... variable voltage circuit, 31... capacitor.

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 lines, which are arranged adjacent to each other and have the other end as an open end, and the first and second input side microstrip lines, which have approximately the above-mentioned length dimensions, are arranged so that they are not coupled in a distributed manner. 2, the opposite end and one end of the input side microstrip line are adjacent to each other, and the first
The intermediate microstrip line refers to a second intermediate microstrip line that is arranged in parallel with a minute interval, and a second intermediate microstrip line that has approximately the above length dimension.
One end of the intermediate microstrip line is connected to the end opposite to the end on the same side as the open side of the first intermediate microstrip line so as not to be distributedly coupled to the first and second intermediate microstrip lines. The first output-side microstrip lines which are arranged adjacent to each other and have the other end as an open end, and the first and second intermediate microstrip lines having substantially the above-mentioned length 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. side and the middle part of the first intermediate microstrip line, and connected between the middle part of the second intermediate and first output side microstrip line, and the second
A variable bandpass filter comprising a capacitor connected between adjacent ends of an intermediate microstrip line or between adjacent ends of a first intermediate microstrip line and a first output microstrip line.