JPS63257302A - Trap circuit in microstrip line - Google Patents

Abstract

PURPOSE:To make the high frequency characteristic steep by forming a split strip prolonged from a tip of an open stub toward the branch point of a microstrip line and dividing the open stub into two by the split strip in broadwise direction. CONSTITUTION:The split strip 11 prolonged toward the branch point of the microstrip line 3 is formed form the tip of the open stub 10 and the open stub 10 is divided into two in the broadwise direction by the split strip 11. Since the open stub is divided into two by the split strip in this way, the two frequency points are attenuated simultaneously by a single open stub and the high frequency characteristic is made steep by the coupling capacitance of each part of the split into two by the split strip and a minute inductance of the branch point.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to a trap circuit in a microstrip line suitable for use in, for example, a down converter of a microwave receiving circuit.

"Prior Art" As is well known, a microwave receiving circuit mixes the received microphone [1 wave (frequency Sa) with the output of a local oscillator (frequency Sb), and generates an intermediate frequency of 5ir (=15a-5bl).
A down converter is provided as a frequency converter to obtain the .

In such a down converter, a microphone wave is transmitted by a microphone strip line, and a trap circuit may be provided at a required location on this microstrip line to steeply attenuate a specific frequency.

FIGS. 4 and 5 are diagrams showing the configuration of a trap circuit provided in a conventional microstrip line.

In this figure, 1 is a substrate made of a dielectric material;
2 is a grounding plate provided in close contact with the bottom surface of the substrate I, and 3 is a microstrip line formed on the top surface of the substrate I. These grounding plate 2 and strip line 3 may be made of metal plates such as copper. It is configured.

4 branches off at right angles from the microstrip line 3 and has a frequency S1 that is attenuated! The oven stub has a length corresponding to /4 wavelength e and a width W, and its tip 4a is not short-circuited to the ground plate 2 and is an open end (oven). In this way, the trap circuit 5 is configured by the open stub 4 branched from the microstrip line 3.

Here, if the equivalent circuit of the trap circuit 5 described in ``2'' is shown, the sixth
As shown in the figure, Zl and Z are the characteristic impedances of the microstrip line 5, and Z3 is the characteristic impedance of the open stub 4.

According to such a trap circuit 5, as shown in FIG. 7, the attenuation characteristic has a peak value fO at the frequency).

"Problems to be Solved by the Invention" By the way, in the conventional trap circuit 5 described above,
There were the following problems.

■Since there is only one frequency point that can be attenuated, for example, in a down converter, etc., the image frequency (=
25b-Sa) and the local oscillator frequency 5b, it is necessary to separately provide a trap circuit, which is not preferable in terms of integration.

■If the frequency you want to attenuate is close to the frequency of the signal you want to pass, the trap circuit 5 will pass the signal.
Since even the desired signal is attenuated, it cannot be applied particularly to locations where insertion loss is important.

This invention has been made in view of the above-mentioned circumstances, and provides a trap circuit for a microstrip line that can simultaneously attenuate two frequency points with a single open stub and can make the frequency characteristics particularly steep on the high frequency side. It is intended to.

"Means to Solve the Problem" This invention is based on a microstrip line that is branched off from a microstrip line formed on a substrate, and that is connected to a
In a trap circuit consisting of an open stub with a length corresponding to the wavelength, a separation band is formed extending from the tip of the open stub in the direction of the branch point with the microstrip line, and the separation band allows the open stub to be separated in its width direction. It is characterized by being divided into two parts.

"By dividing the working co-open stub into two parts with a separation band, two frequency points can be attenuated simultaneously by a single open stub, and each part of the open stub divided into two parts can be attenuated through the separation band. Due to the coupling capacitance of and the minute inductance at the branch point, the frequency characteristics on the high frequency side become steep.

"Embodiments" Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a diagram showing the configuration of an embodiment of the present invention. In this figure, 10 is an open stub having a length a' that branches off from the microstrip line 3 at right angles, and its tip 10a is an open end. This open stub 1
0 is the tip! Microstrip line 3 from Oa
A slit (separation zone) of length d extending in the direction of the branching point with
11 is formed and this slit! Open stub IO is divided into two parts in the width direction by ■, parts 10a and 10
b is formed. As a result, each part 10a and IOb of the open stub 10 divided into two is connected to the slit 1■
An adjacent lateral trap circuit 12 is constructed via the traversal trap circuit 12.

Here, if the entire length e' of the oven stub lO is plotted, the equivalent circuit is as shown in Figure 2 (a),
Further, when paying attention to the length d of the slit 11, its equivalent circuit is as shown in FIG. 2(b).

Then, the length l' of the open stub 10 is set to a length corresponding to 1/4 wavelength of the lower frequency 5, + of the two frequencies to be attenuated, and the slit! By appropriately setting the length d of (2), a damping characteristic as shown in FIG. 3 can be obtained.

That is, the frequency SI' and the frequency S! which is slightly higher than this frequency S1'! A trap occurs. In this case, frequency 5! When the length d of slit ■1 is increased, the frequency becomes lower! , ', and conversely, if d is made small, it moves away from the frequency 51'.

In addition, each part 10a of the oven stub lO divided into two
, 10. Due to the coupling capacitance between b and the minute inductance at the branch point, a rise occurs (attenuation m becomes small) in a slightly higher frequency region than the frequency d, and compared with the conventional frequency characteristic shown by the dotted line C1 in the figure. As a result, the frequency characteristics on the high frequency side become steep. Therefore, frequency 5.
Attenuation of signals in the pass band B adjacent to the pass band B is reduced.

According to one embodiment described above, the trap circuit 12 consisting of the oven stub 10 divided into two parts can attenuate two frequency points simultaneously, for example, in a down converter when the image frequency is 1. ', when the frequency of the local oscillator is 5°, both of these can be attenuated steeply.

"Effects of the Invention" As explained above, according to the present invention, from the tip of the oven stub provided branching off from the microstrip line formed on the substrate 2, to the branching point with the microstrip line, Since an extending separation band is formed and the oven stub is divided into two in the width direction by the separation band, the following effects can be obtained.

■A single oven stub can simultaneously attenuate the first frequency corresponding to the entire length of the oven stub and the second frequency corresponding to the length of the separation band. For example, in a down converter, etc. Both the image frequency and the local oscillation frequency can be sharply attenuated, and the image suppression ratio and oscillator radiation can be improved.

■ Due to the coupling capacity between each part of the oven stub divided into two by the separation band and the minute inductance at the branch point,
The frequency characteristics on the high frequency side become steep, and as a result, even if a passband for passing signals is set on the high frequency side of the frequency point where you want to attenuate U, the attenuation m of the signal in this passband is reduced. It can be suppressed.

(2) By changing the length of the separation band, the second frequency to be attenuated can be arbitrarily set.

(2) Since two trap circuits are provided in the same space as in the past, this is extremely effective in terms of integration.

[Brief explanation of drawings]

FIG. 1 is a plan view showing the configuration of a trap circuit according to an embodiment of the present invention, FIG. 2 is an equivalent circuit of the trap circuit according to the embodiment, and FIG. 3 is a graph showing the attenuation characteristics of the trap circuit according to the embodiment. , Fig. 4 is a perspective view showing the configuration of a conventional trap circuit, Fig. 5 is a plan view of the trap circuit, and Fig. 6 is a perspective view showing the configuration of a conventional trap circuit.
The figure is an equivalent circuit of the trap circuit, and FIG. 7 is a graph showing the iIλ decay characteristics of the trap circuit. 3...Microstrip line, IO...
... Oven stub, IOa, IOb ... part, 11 ... slit (separation band), 12 ...
...Trap circuit. Applicant Alps Electric Co., Ltd. Figure 4

Claims (1)

[Claims] In a trap circuit consisting of an open stub branched from a microstrip line formed on a substrate and having a length corresponding to 1/4 wavelength of a frequency to be attenuated, the tip of the open stub includes: A trap circuit for a microstrip line, characterized in that a separation band is formed extending from the stub in the direction of a branch point with the microstrip line, and the open stub is divided into two in the width direction by the separation band.