JPS6094502A - Variable band-pass filter - Google Patents

Abstract

PURPOSE:To obtain a variable BPF with simple circuit constitution and double peak frequency characteristic by providing four microstrip lines, a varactor diode, a variable voltage circuit and further two intermediate microstrip lines. CONSTITUTION:Input microstrip lines 1, 4 are coupled in a way of distribution and form a tuning circuit 31. Similarly, intermediate microstrip lines 8, 10 and output microstrip lines 14, 16 also form tuning circuits 32, 33 respectively. Moreover, varactor diodes 19, 20, form a variable capacitor 34, which is connected in series between the tuning circuits 31 and 32 to constitute a resonance circuit. Similarly, varactor diodes 22, 23 form a variable capacitor 35, which is connected in series between the tuning circuits 32 and 33 to form a resonance circuit. Thus, the value of variable capacitors 34, 35 is changed by adjusting the slider of a variable resistor 29 to change the resonance frequency of each resonance circuit. Thus, the variable BPF having double peak frequency characteristic is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a variable bandpass filter that can vary the center frequency of its pass band, and particularly relates to a variable bandpass filter that uses a microstrip line.

-The tuner for receiving satellite broadcasting uses a super-hetero gain method, and supports 300 GHz in the IGHz band.
A lucky wave of about 30 MHz is selected from intermediate frequency signals with a width of MHz or 500 MHz or more, and the frequency is converted. The /2 of the above selection has a passband of about 30MHz, and the center frequency of the passband is about 500MHz.
A bandpass filter with variable z is required. Conventionally,
Such a variable bandpass filter includes a plurality of bandpass filters each having a different center frequency in its passband, and one or more variable band rejection filters for each of these bandpass filters, which collectively constitute a variable bandpass filter. There was something to do. However, these variable band-pass filters require a large number of band-pass filters and variable tracking removal filters, resulting in a complicated circuit configuration.

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 approximately equal to the 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 end micro-strip line having the above-mentioned length dimension and arranged parallel to the first input end micro-string line with a small gap therebetween, and an end on the same side as the above-mentioned input end. The second input end microstrip line, which has an open end, and the first and second input end 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 the other end being open; The end microstrip line is arranged parallel to the second input end microstrip line so as not to be distributedly coupled to the end microstrip line, and at a small distance from the first intermediate microstrip line, and is adjacent to the second input end microstrip line. a second intermediate microstrip line having an open end of 111!, and having a length dimension of approximately 111!
The first output side microstrip line is arranged such that one end thereof is adjacent to the first and second intermediate microstrip lines so as not to be distributedly coupled to the first and second intermediate microstrip lines, and the other end is an open end. However, the first and second intermediate microstrip lines are arranged in the iF row with a small interval from the WJ1 output side microstrip line so that the first and second intermediate microstrip lines are distributed and connected. A second output side microstrip line whose end on the same side as the open end of the side microstrip line is an output end and an end on the opposite side from this as an open end is placed on a dielectric substrate. form,
A first variable capacitance element is connected between adjacent ends of the second input end and the first intermediate microstrip line, and a second variable capacitance element is connected between adjacent ends of the second intermediate and first output side microstrip lines. The variable capacitance elements are connected, and the variable voltage circuit for the first and second variable capacitance elements is connected to the second input terminal and the first
In this configuration, it is connected between the intermediate portions of the intermediate microstrip lines, and between the intermediate portions of the second intermediate and first output side microstrip lines.

With this configuration, the first and second input end microstrip lines equally constitute a first tuning circuit. Similarly, the first and second intermediate microstrip lines/
, 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, One more
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 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,
Bimodal frequency characteristics can be obtained.

The present invention will now be described in detail based on the embodiment shown in FIG.

In FIG. 1, reference numeral 1 denotes the first input side microstrip line, which is approximately 34+ nm long and approximately 2 ytrm wide, and is constructed on a dielectric substrate (not shown) with a dielectric constant of 4.2. . A signal in the 1 GHz band is supplied to one end 2 of the microstrip line 1 on the il input side. That is, one end portion 2 is used as an input end portion. Further, the other end portion 3 is open. The second input end microstrip line 4 is connected to the first input end microstrip line 1 with a small gap of a fraction of the diameter, that is, distributedly coupled to the first input end microstrip line 1.
are arranged in parallel. 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. ing.

A first intermediate microstrip line 8 is arranged so that one end 7 is spaced apart from the other end 6 of the second input end microstrip line 4 by about 311 m and at a substantially right angle. This strip line 8 has almost the same length dimension as the first input side microstrip line l, but its width dimension is almost double, and the other end 9 opposite to the one end 7 is open. has been done. A second intermediate microstrip line Io parallel to the first input end microstrip line l is spaced apart from the first intermediate microstrip line 8 by a distance of a few l6rm, that is, distributedly coupled to the first intermediate microstrip line 8. It is located. The second intermediate microstrip line IO has the same shape as one end of the first intermediate microstrip line 8.

1st and a52 intermediate microstrip line 8.1
One end 13 is located at a distance of about 3 mm from the other end 9.12 of 1. t I, (, the hill is at the j;
and the second input end microstrip line], the first output side microstrip line 14 is arranged in the direction 1 opposite to the direction 4, and the other end 15 of the pl is open. This first output (1m microstrip line 14
The microstrip line 1 also has substantially the same length and width as the first input microstrip line 1. The distance between the first output side microstrip line 14 and the second output side microstrip line 16 is l'A;
is arranged δ in the 11th row. That is, it is distributed coupled. The second output microstrip line 16 also has substantially the same length and width as the first input microstrip line 1.

The other end of the second output microstrip line 16 (the end farthest from the first and second input microstrip lines 114) 18 to an appropriate approximately 3 GHz band.
A signal with a width of 0 MHz is extracted. In other words, it is an output end. The end 17 opposite to the output end 18 is open.

Second input end and first intermediate side microstrip line 4
．． Between the adjacent ends 6.7 of 8, variable capacitance diodes lq, 20 connected with mutually opposite polarities are connected at a distance of NLI, and the 1st interconnection point of these variable capacitance diodes 19.20 is as follows. It is grounded via a resistor 21.

Similarly, variable capacitance diodes 22.23 connected with mutually opposite polarities are connected at the shortest distance between the adjacent ends 12.13 of the second intermediate and first output side microstrip lines 10, 14. The interconnection point is grounded via a resistor 24.

Second input end, first and second intermediate and first output microstrip lines 4.8.10. ．． 14 are each connected via a resistor 25.26.2'7.2B. The interconnection points of these resistors 25, 26, 2', 7, 28 are connected to the arms of a variable resistor 29, and both ends of this variable resistor 29 are connected to both ends of a DC power supply 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 11 of each town variable capacitance diode 19, 20, 22, 23 changes. By changing the capacitance in this way, a large amount of capacitance can be reduced with a small voltage change.

FIG. 2 shows an equivalent circuit of the circuit shown in FIG. 1 in Figure 1
The microstrip lines 1.4 and the second input end microstrip lines are disposed in parallel with a small gap between them, so that they are distributed and coupled to each other, forming a tuned circuit 31 as shown in FIG. Similarly, the first and second intermediate microstrip lines 8, 10.degree. and the first and second output microstrip lines 14,16 also form tuning circuits 32,33, respectively.

The variable capacitance diodes 19 and 20 form a variable capacitor 34, and connect the secondary side of the tuned circuit 31 and the tuned circuit 32.
A resonant circuit is configured by connecting a series IC between the primary side of the Similarly, the variable capacitance diodes 22 and 23 form a variable capacitor 35, and two of the tuned circuits 32 form a resonant circuit. Therefore, by changing the position of the arm of the variable resistor 29, the value of the variable capacitor 34.35 changes, the resonant frequency of each resonant circuit changes, and the frequency characteristics shown in FIG. 3 are obtained. A bimodal variable bandpass filter can be realized. In addition, resistor 25, 26, 27
．． 28 to each microstrip line 4, B, 11, 1
The reason why it was connected to the middle part of 4 is that the impedance at this point becomes zero at high frequencies and is not easily affected by high frequencies.

In the above embodiment, the variable capacitance diodes 19.20 are connected between the second input terminal and the first intermediate microstrip 4.8 with mutually opposite polarities, but instead of this, one variable capacitance diode is connected to the cathode of may be connected to the second input end microstrip line 4 side, the anode may be 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. ■...1st input side microstrip line, 4...
・Second input end microstrip line, 8...1st
Intermediate microstrip line, 10...second intermediate-
Microstrip line, 14... First output side microstrip line, 16... Second output side microstrip line, 19.20.22.23... Variable capacitance element, 21.24.25.26 .21 no, 28.29
．． 30...Variable voltage circuit. Patent applicant: Diex Antenna Co., Ltd. Representative: Satoshi Shimizu, and two other talented artists

Claims (1)

[Claims] [1] A first input end having a length dimension that is almost a dead wavelength of the center frequency of the frequency band used, and one end of which is an input end to which a signal of the frequency band of use is supplied, and the other end is an open end. The microstrip line is arranged parallel to the first input side microstrip line with a small gap, and the end on the same side as the input end is an open end. The second input end microstrip line is distributed between the first and second input side microstrip lines, and the second input end microstrip line has a length dimension of 2. One end is arranged adjacent to the end opposite to the open end of the strip line, and the other end is the open end 1 part. The first intermediate microstrip line is arranged parallel to the first intermediate microstrip line with a small interval so as not to be distributedly coupled to the first and second input end microstrip lines. a second intermediate microstrip line having an open end at an adjacent end; The second intermediate microstrip line has one end adjacent to the second intermediate microstrip line so as not to be distributedly coupled, and the other end is an open end, and the first output side microstrip line has approximately the above length dimension. The first and second intermediate microstrip lines are arranged in parallel with each other with a small distance apart from each other so as not to be distributedly coupled to the first and second intermediate microstrip lines, and the open end of the first output microstrip line is A second output side microstrip line having an end on the same side as an output end and an end on the opposite side as an open end is formed on a dielectric substrate, and a second input end and an if l of intermediate microstrip line! A first variable capacitance element is connected between the ends in contact with A, a second variable capacitance element is connected between the adjacent ends of the second intermediate and first output side microstrip lines, and the first and second A variable voltage circuit for the variable capacitance element is connected between the second input terminal and the intermediate portion of the first intermediate microstrip line, and
(second intermediate and first output side micros) A variable bandpass filter connected between the intermediate portions of the IJ tube line.