JPS6126722B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a bandpass filter composed of microstrip lines. The first example of a conventional bandpass filter consists of a closed line with a length of one wavelength, which is made up of a microstrip line in which the conductor on the bottom surface of a dielectric substrate with conductors arranged on both sides is grounded, and a line arranged on the top surface. Figures a, b, c,
Shown in d and e. FIG. 1a shows a one-stage bandpass filter in which the one-wavelength closed line 4 is configured in a circular shape, and FIG. 1b shows a one-stage bandpass filter in which the one-wavelength closed line 4 is configured in a rectangular shape. Figure 1c shows a two-stage circular one-wavelength closed line 4, Figure 1d shows a two-stage rectangular one-wavelength closed line 4, and Figure 1e shows a rectangular one-wavelength closed line 4. railroad track 4
This is a two-stage bandpass filter in which the following are arranged in parallel. In the figure, 1 is an input line, 2 is an output line,
3 is a coupling line. In these conventional examples, in order to obtain attenuation outside the passband, the one-wavelength closed line 4 is connected to the coupled line 3.
A method is used in which multiple stages are connected in series via a filter, or a combination of bandstop filters is used. However, when multiple stages of one-wavelength closed lines are connected in series, there is a drawback that the loss in the passband becomes large. Furthermore, the shape of the filter also tends to become larger. When combined with a bandstop filter, there is a drawback that not only the loss in the pass band is large but also the shape becomes large. An object of the present invention is to eliminate the above-mentioned drawbacks of the prior art, and to provide a microstrip bandpass filter that has low loss in the passband, can provide a large degree of attenuation outside the band, and can easily finely adjust the resonant frequency. It is something. In order to achieve the above object, in the present invention, two rectangular one-wavelength lines are arranged in parallel to constitute a two-stage bandpass filter, and one end is connected between the input line and the output line. By providing a second coupled line connected to the line and leaving the other end open on either the input line or the output line, or both, and creating electromagnetic coupling between the input and output, resonance outside the passband can be achieved. A trap is created at a frequency position that is almost symmetrical with respect to the frequency, and the attenuation characteristics outside the band are improved. In addition, in a single-wavelength closed line, a strip line with one end open is connected at a position approximately 1/4 wavelength away from the input and output ends, and the resonant frequency is finely adjusted by changing the length of this strip line. FIG. 2 shows an embodiment of the present invention. The figure shows the configuration of the microstrip bandpass filter section of a tuner IF filter with a resonance frequency of 3GHz and a trap frequency of 3.114GHz. In the figure, 5 is an input line, 6 is an output line, 7 and 8 are rectangular single-wavelength closed lines, 9 is a coupled line of input line 5 and output line 6, and 10 is a strip line for fine tuning the resonant frequency (hereinafter referred to as 11 is a coupling line that electromagnetically couples the two one-wavelength closed lines 7 and 8, the input line 5 is adjacent to the input part 7a of the one-wavelength line 7, and the output line 6 is one-wavelength closed line 7. The coupled line 9 is adjacent to the output part 8b of the line 8, and the coupled line 9 is adjacent to the output part 7b of the one-wavelength line 7.
and is arranged adjacent to the input section 8a of the single-wavelength line 8. The signal input from the 50Ω input line 5 is approximately 95Ω.
A 3GHz staggered tuning circuit consisting of a single-wavelength closed line 7 having a characteristic impedance of The signal is output to the output line 6 through the . At this time,
The band characteristics and loss of single tuning depend on the coupling state of the input line 5, the output line 6 and the one-wavelength closed lines 7, 8, the coupling state of the coupled line 11 and the one-wavelength closed lines 7, 8, and the coupling state of the one-wavelength lines 7, 8. Determined by load Q and no load Q. In this example, a 3 dB bandwidth of 12 MHz and a loss of 5.5 dB are obtained at 3 GHz. In this bandpass filter, the input line 5
Due to the coupling between the input and output by the coupling line 9 and
Due to the staggered tuning characteristics of 3GHz, traps occur at almost symmetrical frequency positions with respect to the center frequency. Third
The figure shows frequency on the horizontal axis and attenuation with respect to the passband on the vertical axis, and shows the state of the trap frequency when the length l of the coupled line 9 is changed. In the case of an IF filter for the tuner of a television receiver, it is necessary to form an image trap that attenuates the image signal appearing at 3.114 GHz with respect to the center frequency of 3 GHz. The solid line A in FIG. 3 shows that the length l of the coupling line 9 is set to _l1 , and the trap is adjusted to the image frequency band. At this time, the attenuation degree of the image frequency band with respect to the passband is 3.114GHz±4M
65dB can be obtained at Hz. The broken line B in FIG. 3 shows the case where the length l of the coupling line 9 is made larger than _l1 , and the dashed line C shows the case where l is made smaller than _l1 . Although the coupling line 9 is provided on the output line 6 side, the same effect can be obtained even if it is provided on the input line 5 side. Moreover, the same effect can be obtained even if it is provided on both the input line 5 and the output line 6. Since this bandpass filter obtains the required passband characteristics by staggered tuning using the two closed lines 7 and 8, the shift in the resonance frequencies of the closed lines affects the passband characteristics. Minor adjustments are required. Fine adjustment of the resonant frequency is performed by changing the length of the line 10, changing the capacitance added to the connecting portion, and changing the resonant frequency of the single-wavelength closed line 7. The adjustment line 10 is the input part 7a or the output part 7 of the closed line 7.
It is provided at a position approximately 1/4 wavelength away from b to sufficiently reduce the influence on single tuning characteristics. The adjustment line 10 for fine adjustment is provided on the input side single wavelength closed line 7, and the output side single wavelength closed line 8.
Alternatively, instead of just one, a plurality of them may be provided. FIG. 4 is a pattern diagram of a microstrip bandpass filter used to obtain the characteristic diagram shown in FIG. 3, and the dimensions of each part shown in FIG. 4 are shown in a table.

[Table] FIG. 5 is a pattern diagram showing another embodiment of the present invention, in which the one-wavelength closed lines 7 and 8 are formed into an oval shape, and this embodiment is also similar to the first embodiment shown in FIG. It is possible to obtain almost the same characteristics as in the example. According to the present invention, a trap can be formed at a frequency position symmetrical to the tuning frequency of the staggered tuning characteristic of single tuning, and the resonant frequency can be easily finely adjusted. Therefore, it is possible to increase the degree of attenuation outside the passband without increasing the loss in the passband, and it is possible to obtain a narrow passband characteristic in a staggered tuning characteristic with a single peak characteristic, which improves television reception. As a 3GHz IF filter for aircraft, it is possible to realize a narrow band microstrip bandpass filter with low loss and good attenuation in the image frequency band.

[Brief explanation of the drawing]

Figures 1a, b, c, d, and e are pattern diagrams of a conventional bandpass filter using microstrip lines, and Figures 2 and 4 are pattern diagrams of a bandpass filter according to the present invention. FIG. 3 is a characteristic diagram showing the attenuation characteristic, and FIG. 5 is a pattern diagram showing another embodiment of the bandpass filter according to the present invention. 5: Input line, 6: Output line, 7, 8: Single wavelength closed line, 9: Coupling line, 10: Adjustment line, 1
1: Combined line.

Claims (1)

[Claims] 1. In a microstrip line disposed on the upper surface of a dielectric substrate having a ground conductor disposed on the lower surface, a first single-wavelength line and a first single-wavelength line adjacent to the first single-wavelength line are provided. a second one-wavelength line arranged in parallel with each other, an input line arranged adjacent to the input part of the first one-wavelength line, and adjacent to the input line, and
an output line disposed adjacent to the output section of the second one-wavelength line;
The first
A microstrip bandpass filter comprising: a coupled line; and a second coupled line coupled to at least one of the input line and the output line and disposed protrudingly between the input line and the output line. 2. In a microstrip line disposed on the upper surface of a dielectric substrate with a ground conductor disposed on the lower surface, a first one-wavelength line and a first one-wavelength line are arranged adjacent to and parallel to each other. a second one-wavelength line, an input line disposed adjacent to the input part of the first one-wavelength line, and an input line adjacent to the input line, and
an output line disposed adjacent to the output section of the second one-wavelength line;
The first
a second coupled line coupled to at least one of the input line and the output line and protrudingly arranged between the input line and the output line, and at least one of the first and second one-wavelength lines. A microstrip bandpass filter consisting of one wavelength line and an adjustment line coupled at a position approximately 1/4 wavelength away from the input or output part.