JPS5842301A - Distributed constant filter - Google Patents

Abstract

PURPOSE:To obtain the desired blocking characteristics, by making the shape of parts disposed closely together nonlinear through alternate connection of capacitive and inductive lines and the disposition of the two adjacent capacitive lines closely. CONSTITUTION:In wide lines 22, 23 and 24, adjacent parts of the lines 22, 23 and 23, 24 are formed wave-shape. Thus, the coupling length of electromagnetic waves can be taken sufficiently for the two pairs of adjacent lines 22, 23 and 23, 24, and a large coupling can be obtained. As a result, a required capacitance can be obtained as capacitors. On the other hand, the width of the lines 22, 23 and 24 is almost the same same as that of conventional lines, no effect can be given on the selection of capacitance.

Description

[Detailed description of the invention] This invention is a finter used in the microwave band.

For example, the present invention relates to an elliptic function-type distributed constant filter constituted by a distributed constant line such as a microstrip line.

In recent years, one example is a microwave band filter.

Distributed constant lines such as micro-strip lines are used. It is well known that by deforming this type of microstrip line, a reactance element is equivalently formed, and by combining the reactance elements, an elliptic function distributed constant filter with excellent selectivity can be obtained. There is.

FIG. 1 is a plan view showing the structure of an elliptic function low-pass filter applied to a microstrip line according to the above-mentioned conventional method.

In the figure, 1 is an inductive electric board, 2, 3.4 is a wide line,
5 and 6 are narrow lines, and 7 and 8 are input/output lines. As shown in the figure, the wide lines 2.3.4 and the narrow lines 5.6 are connected alternately, and two mutually adjacent wide lines 2 and 3 and 3 and 4 are arranged close to each other. Although not shown in FIG. 1, there is a ground conductor on the back surface of the substrate 1. By configuring it like this, the wide lines 2, 3, and 4 are connected in parallel. The narrow-width lines 5 and 6 are equivalent to having an inductance inserted in series. Furthermore, since the two adjacent wide lines 2 and 3 and 3 and 4 are close to each other, there is capacitive coupling between the two lines due to coupling in the direction of electromagnetic wave propagation. It is equivalent to inserting a cano-9 sitance in series.

FIG. 2 is a diagram showing an equivalent circuit of the embodiment of FIG. 1. As is clear from the above, the wide line 2°3.4 corresponds to the capacitor sis 13, 14.15, and the narrow line 5, 6 corresponds to the inductance 16.17. Furthermore, wide tracks 2 and 3,
The coupling capacitance existing between 3 and 4 is capacitance 18.19, and input/output lines 7 and 8 are connected to terminals 9 and 10
and the ground conductors on the back side of the substrate l correspond to terminals 11 and 12, respectively. From this, it can be seen that the distributed constant filter of FIG. 1 constitutes an elliptic function type low-pass filter.

An elliptic function low-pass filter as described above.

When applied to high frequencies, restrictions are imposed on the actual dimensions of the line, making it difficult to obtain the necessary frequency characteristics. Especially regarding the capacitance 18.19 due to the coupling between the adjacent wide lines 2 and 3, and 3 and 4,
In order to obtain the required value for capacitance 18.19 in order to obtain the required characteristics, the gaps between the wide lines 2 and 3, and between 3 and 4 must be narrowed, but it is not possible to narrow the gaps beyond a certain level. This is almost impossible in terms of implementation. for example,
In order to obtain the necessary capacitance for capacitance 18.19, it is possible to increase the facing width of wide line 2.3.4, but capacitance 13.14.1
5 will deviate from the correct value, making it unusable. in this way.

If a distributed constant filter as shown in FIG. 1 is applied to high frequencies, the capacitance 18.19 will not reach the required value, making it impossible to obtain desired blocking characteristics.

FIG. 3 is a graph showing an example of the frequency characteristics of the conventional filter. In the figure, the vertical axis is the amount of passing attenuation, and the horizontal axis is the frequency. Further, f+ is a passing frequency, and +fz to f4 are harmonics of 2, for example, h, and there is a frequency range f in which all of them should be blocked. here.

Actual @20 shows the required properties. However, as described above, when the low-pass filter shown in FIG. 1 is used at high frequencies, the characteristics shown by the broken line 21 occur, and sufficient attenuation cannot be obtained at the blocked frequencies fv and f+. The above-mentioned problems are exactly the same even when an elliptic function filter is constructed using a distributed constant line other than a microstrip line.

The purpose of this invention is to solve the above problems,
The distributed parameter filter of the present invention, which has excellent selectivity when applied to high frequencies, has a capacitive line in which a capacitance is inserted in series in a distributed constant line, and an inductance in series in an equivalent manner. It has a structure in which the inserted inductive lines are alternately connected, and the two capacitive lines adjacent to each other are arranged closely, and the shape of the adjacent part is non-linear. It is characterized by the presence of

Hereinafter, this invention will be applied to a micro strip line,
Refer to one drawing for an embodiment in which an elliptic function type low-pass filter is constructed in the same manner as in FIG. 1. FIG. 4 is a plan view showing an embodiment of the present invention. In the figure, the same symbols as in Figure 1 indicate the same structure.

I want it to be understood as having a function. 22, 23, and 24 are wide lines. In the wide lines 22, 23, and 24, the proximate portions of the two adjacent wide lines 22 and 23 and 23 and 24 are corrugated.

For this reason, each of the two adjacent lines 22 and 23°23
A sufficient coupling length in the direction of electromagnetic wave propagation between and 24 can be obtained, and a large coupling can be obtained. Therefore.

As a capacitance of 18.19, the required amount of capacitance can be easily obtained. On the other hand, the width of the wide line 22°23.24 is l? ! Since there is almost no change, the selection of capacitances 13, 14, and 15 has no effect. Also,
The shape of the waveform in the vicinity of the mutually adjacent wide lines 22 and 23, and 23 and 24 is sufficiently small compared to the line width, so that changes in the characteristic impedance of the line etc. are negligibly small.

Therefore, the equivalent circuit of the elliptic function low-pass filter seen in this embodiment is the same as that shown in FIG.

is iZl. As a result, the single frequency characteristic becomes like the solid line 20 in FIG. 3, and the initial objective can be achieved. FIG. 5 is a plan view showing the configuration of another embodiment of the present invention. In the figure, 25, 26, and 27 are wide lines, and two adjacent wide lines 25, 26, and 2 are connected to each other.
The adjacent portions of 6 and 27 are uneven. Therefore, according to this embodiment.

The capacitances 18 and 19 have a larger value than in the embodiment shown in FIG. 4, thereby making it possible to meet demands for a wider range of characteristics.

In the first and second embodiments described above, the cases where the shape of the adjacent portions of two adjacent wide lines are wavy and the shape of convexes and convexes are explained as examples. It goes without saying that the same effects as in the present embodiment can also be obtained with other non-linear shapes. Although the embodiment of this invention has been explained using a micro-strip line as an example, it is also possible to construct a filter using other distributed constant lines.
As long as you are constructing an elliptic function filter.

It is also clear that exactly the same effect can be obtained. For example, a triplate line or a slot line can be considered as the other distributed constant line, and a thick metal rod can be used as the wide line, and a metal wire can be used as the narrow line.

In the above embodiment, three wide lines and two narrow lines are used.
The explanation is clear by taking a filter made up of two as an example.

As is clear from the above explanation, the distributed constant filter according to the present invention has excellent selectivity when applied to high frequencies, and also provides sufficient attenuation in the stop band. When applied to circuits in the high microwave band, the effect of improving their performance is significant.

[Brief explanation of drawings]

Figure 1 is a plane showing an example of the configuration of a conventional distributed constant filter.
1. Figure 2 shows the conventional circuit shown in Figure 1. 3 is a frequency characteristic diagram of the conventional example shown in FIG. 1, and FIG. 4 is a plan view showing the configuration of an embodiment according to the present invention. FIG. 5 is a plan view showing the configuration of another embodiment of the invention. In the figure, 1 is a dielectric substrate, 2, 3, 4, 22
゜23.24.25.26.27 are wide lines, 5゜6 are narrow lines, '7 and 8 are input/output lines, 9.10 are input/output terminals, 11.12 are ground terminals, 13, 14゜15.18
．． 19 is a capacitance, and 16.17 is an inductance. ” Figure 1 Rod 2 Bad Frequency Figure 3 Figure 4 Figure 5

Claims (1)

[Claims] 1. Equivalently to the distributed constant line! Capacitive lines in which capacitances are inserted in parallel and inductive lines in which inductances are equivalently inserted in series are alternately connected, and the two capacitive lines adjacent to each other are arranged closely. A distributed constant filter characterized in that the shape of the adjacent portion is non-linear.