JPH08148902A - Microstrip line filter and adjustment method therefor - Google Patents

Abstract

PURPOSE: To provide the microstrip line filter of a wide band without degrading other characteristics by adding side electrodes to grounding electrodes on the outer side of microstrip lines on both ends. CONSTITUTION: Input/output electrodes 22 and 24 are connected to the open ends of the microstrip lines 16a and 16c on both ends. Then, the grounding electrodes on the respective outer sides of the microstrip lines 16a and 16c are formed as wide width parts 14a and 14c and the side electrodes 26 and 28 are added to the grounding electrodes. In this constitution, the width or length E of the side electrodes 26 and 28 is set so as to let the length A'+B of the microstrip line 16a on the outer side and the input/output electrode 22 be approximately the same as the length C and D of the other microstrip lines 20a, 20b and 16b. Thus, the balance of a resonance frequency is not lost between the microstrip lines 16a and 16c on the outer side and the other microstrip lines 20a, 20b and 16b.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a microstripline filter and a method of adjusting the same, and more particularly to a combline type or interdigital type microstripline filter and a method of adjusting the same.

[0002]

2. Description of the Related Art For example, U.S. Pat. No. 4,266,206 issued May 5, 1981 discloses a microstrip line filter having microstrip lines formed on a dielectric substrate. FIG. 1 shows an example of an interdigital microstrip line filter of this type. In this conventional microstripline filter 1, the outermost microstriplines 2 and 3 are generally used.
Get an outer bond at. That is, input / output electrodes 4 and 5 are connected to the microstrip lines 2 and 3 at both ends, respectively, and the input / output electrodes 4 and 5 couple the microstrip lines 2 and 3 to the outside. In such a microstripline filter 1, it is necessary to strengthen (increase) the external coupling by the outermost microstriplines 2 and / or 3 in order to widen the filter bandwidth.

Therefore, as shown in FIG. 1 or 2, the input / output electrodes 4 and 5 are brought close to the open ends of the microstrip lines 2 and 3. That is, in such a microstrip line 1, the input / output electrodes 4 are
The closer the connection position of the microstrip lines 2 and 3 with the microstrip lines 2 and 3 is to the open ends of the microstrip lines 2 and 3, the larger the coupling becomes, and as shown in FIG. It is considered that the external coupling can be maximized by connecting the electrodes.

[0004]

In the microstripline filter 1 shown in FIG. 1, the lengths of the microstriplines 2 and 3 for obtaining external coupling are the input / output electrodes 4.
Since it is considered to be “A + B” including 5 and 5, it is relatively long as compared with the length C or D of other microstrip lines. Therefore, the balance of the resonance frequency of each microstrip line is lost, and the reflection loss is deteriorated. Along with this, there is a problem that the insertion loss also increases.

More specifically, the microstrip line filter shown in FIG. 2 basically has a filter characteristic as shown in FIG. When the input / output electrodes as shown in FIG. 1 are connected to widen the relative band in such a microstripline filter 1, as shown in FIG. 4, the reflection characteristic at the input side S11 is greatly deteriorated, and the output is accordingly reduced. The pass characteristic on the side S21 also deteriorates.
Particularly, in the example of FIG. 4, the insertion loss near 2400 MHz is greatly deteriorated.

Therefore, a primary object of the present invention is to provide a broadband microstrip line filter without degradation of other characteristics. Another object of the present invention is to provide a method for adjusting a microstrip line filter, which can easily adjust the band. Still another object of the present invention is to provide a microstrip line filter which can adjust a pole position to obtain desired electric characteristics.

Another object of the present invention is to provide a method for adjusting a microstrip line filter, which can easily adjust the pole position.

[0008]

A first aspect of the present invention is a microstrip line filter including a plurality of microstrip lines each having one end commonly connected to a ground electrode, the microstrip lines at both ends being connected to the outside. A microstrip line filter, wherein side electrodes having dimensions according to a desired band are added to the ground electrodes outside the microstrip lines at both ends.

A second invention comprises a plurality of microstrip lines each having one end commonly connected to a ground electrode,
In a microstrip line filter in which microstrip lines at both ends are coupled to the outside, a side electrode having a dimension according to a desired pole position is added to a ground electrode outside the microstrip lines at both ends, It is a stripline filter.

A third invention includes a plurality of microstrip lines each having one end commonly connected to a ground electrode,
A method for adjusting a microstrip line in which the microstrip lines at both ends are coupled to the outside, wherein the band is adjusted by changing the width dimension of the ground electrode outside the microstrip lines at both ends. Adjustment method.

A fourth invention includes a plurality of microstrip lines each having one end commonly connected to a ground electrode,
A method for adjusting a microstrip line in which microstrip lines at both ends are coupled to the outside, wherein a pole position is adjusted by changing a width dimension of a ground electrode outside the microstrip lines at both ends. Is the adjustment method.

[0012]

[Operation] In the microstrip line filter,
The resonance frequency of the microstrip lines at both ends can be controlled by adding side electrodes to the ground electrodes outside the microstrip lines at both ends. Specifically, by setting the dimensions of the side electrodes so that the total of the lengths of the microstrip lines at both ends and the lengths of the input / output electrodes connected thereto are about the same as the lengths of the other microstrip lines, The resonance frequency of the microstrip lines at both ends can be set to a value similar to the resonance frequencies of the other microstrip lines. Therefore, a wide band filter characteristic can be obtained without deteriorating the reflection characteristic and the insertion loss.

Also, by adding side electrodes to the ground electrodes outside the microstrip lines on both sides, the electrical length of the microstrip line can be changed without changing the electrical length of the input / output coupling portion, and thereby the attenuation pole. Can be set to a desired position. Therefore, in order to adjust the band of the microstrip line filter, the width dimension of the ground electrode outside the microstrip lines at both ends may be changed.

Similarly, the position of the attenuation pole can be adjusted by changing the width dimension of the ground electrode outside the microstrip lines at both ends.

[0015]

According to the present invention, a wideband microstrip line filter can be obtained without degrading reflection characteristics and insertion loss. Furthermore, according to the present invention, by simply changing the width dimension of the ground electrode outside the microstrip lines at both ends,
The band can be adjusted.

Further, according to the present invention, a microstrip line filter having an attenuation pole at a desired position can be obtained by adding side electrodes to the ground electrodes outside the microstrip lines at both ends. And
According to the present invention, by changing the width dimension of the ground electrode outside the microstrip line at both ends,
The position of the attenuation pole can be easily adjusted.

The above-mentioned objects, other objects, features and advantages of the present invention will become more apparent from the detailed description of the following embodiments made with reference to the drawings.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION The microstripline filter 10 shown in FIG. 5 is an interdigital type microstripline filter, which includes a dielectric substrate 12, like the conventional microstripline filter 1 shown in FIG. A ground electrode 14 is formed on the upper end of the dielectric substrate 12, and extends from the ground electrode 14 to form, for example, λ / 4 microstrip lines 16a, 16b and 16c. The ground electrode 1 is provided on the lower end of the dielectric substrate 12.
8 is formed and extends from the ground electrode 18 and extends, for example, λ / 4 microstrip lines 20a and 20.
b is formed. The microstrip line 20a is formed between the microstrip lines 16a and 16b, and the microstrip line 20b is formed between the microstrip lines 16b and 16c. Therefore, the microstrip lines 16a to 16c and the microstrip lines 20a to 20b are formed. And are combined into an interdigit. Input / output electrodes 22 and 24 are connected to the open ends of the microstrip lines 16a and 16c at both ends.

In this embodiment, it should be noted that the side electrodes 26 and 28 are added to the ground electrodes outside the microstrip lines 16a and 16c on both sides. That is, in the embodiment shown in FIG. 5, the ground electrode 14 includes wide portions 14a and 14c at both ends and a narrow portion 14b at the center. Wide parts 14a and 14
In c, the width E of the side electrodes 26 and 28 is larger than the original width W of the ground electrode 14 (width of the narrow portion 14b).
Has an added width.

On the other hand, the outer microstrip line 1
The length of 6a and the input / output electrode 22 is "A '" in FIG.
+ B ”. Then, the width or length E of the side electrodes 26 and 28 is set so that the length "A '+ B" is approximately the same as the lengths C and D of the other microstrip lines 20a and 20b and 16b. Thus, the resonance frequencies of the outer microstrip lines 16a and 16c and the resonance frequencies of the other microstrip lines can be made substantially the same, and the outer microstrip lines 16a and 16c and the other microstrip lines 20a and 20b can be made. There is no loss of balance in the resonance frequency between and 16b.

Therefore, according to the embodiment of FIG. 5, even if the band of the microstrip line having the basic filter characteristic as shown in FIG. 3 is widened, as shown in FIG. There is no deterioration in characteristics. The microstrip line filter 10 of the embodiment shown in FIG. 7 is a comb line type filter. Therefore, in the microstrip line filter 10, the ground electrode 1 formed on the main surface of the dielectric 12 is
4 from which microstrip lines 16a, 16a ', 16b and 16c of λ / 4, for example, are formed. The input / output electrodes 22 are formed on the microstrip lines 16a and 16c at both ends, as in the embodiment of FIG.
And 24 are connected. Further, also in the embodiment shown in FIG. 7, the ground electrode 14 includes wide portions 14a and 14c at both ends and a narrow portion 14b at the center, as in the embodiment shown in FIG. Then, in the wide portions 14a and 14c, side electrodes 26 and 28 having a width E are added to the original width W of the ground electrode 14. Therefore, also in the combline type microstrip line 10 in the embodiment of FIG. 7, the width E of the side electrodes 26 and 28 is equal to the lengths of the other microstrip lines 16a ', 16b and 16b'. By setting the resonance frequency of the outer microstrip lines 16a and 16c to be substantially the same as the resonance frequency of the other microstrip lines, the reflection characteristics and the insertion loss are adversely affected. It is possible to widen the band without giving.

The combline type microstripline filter 10 shown in FIG. 7 originally has, for example, a bandpass filter characteristic as shown in FIG. However, in reality, as shown in FIG. 9, it has a so-called polar characteristic in which an attenuation pole is generated on the higher side of the pass band. Such an attenuation pole is not intentionally provided in the circuit design,
This is unique to the structure of the microstrip line filter. And although the attenuation pole itself is generally beneficial in the electrical properties of the filter, its pole position could not be controlled arbitrarily. However, due to the side electrodes 26 and 28 described above,
It has been discovered that the position of the damping pole can be controlled.

FIG. 10 partially shows an electrode pattern of the combline type microstripline filter, and FIG. 11 shows an equivalent circuit thereof. In the equivalent circuit, the coupling impedance Zij is

[0024]

## EQU1 ## This is represented by Zij = Zk tan θij. That is, by setting the electrical length θij to π / 2, the coupling impedance Zij becomes infinite, and no coupling occurs (attenuation pole). By the way, the electrical length θi of the microstrip line and the electrical length θij of the coupling portion
Are the same in the physical length L of FIG. 10, but since the microstrip line has the tip capacitance Cs,
At the resonance point (pass band) of the microstrip line,
θi <θij <π / 2. Therefore, the attenuation pole generated in the combline type microstripline filter as shown in FIG. 7 is generated in the higher band side than the pass band. This is because θ increases as the frequency increases.

Therefore, the principle of the attenuation pole is applied to change the electric length of the microstrip line and the width or length E of the side electrodes 26 and 28 without changing the electric length of the coupling portion. It is possible to control the relationship between the pass band and the frequency of the attenuation pole by shifting the relationship between θi and θij.

That is, when the width E of the side electrodes 26 and 28 (FIG. 7) is short, the attenuation pole is on the high band side far away from the pass band as shown in FIG. However,
When the width E of the side electrodes 26 and 28 is increased, as shown in FIG.
As shown in FIG. 3, the attenuation pole is closer to the pass band. Therefore, the position of the attenuation pole can be arbitrarily controlled by adjusting the width E of the side electrodes 26 and 28 (FIG. 7).

The widths E of the side electrodes 26 and 28 are made large in advance, and then, by cutting (trimming) using a tool such as a lutor, the position of the attenuation pole is adjusted so as to move away from the pass band. be able to. Therefore, the yield of products is improved.
Further, the idea of controlling the position of the attenuation pole by the width E of the side electrodes 26 and 28 can be similarly applied to the interdigital microstrip line filter shown in FIG.

However, in the interdigital microstripline filter, as can be seen from the electrode pattern shown in FIG. 14, the relationship between the electrical lengths θi and θij is opposite to that of the above combline microstripline filter. , Θi> θij. Therefore, in the interdigital microstripline filter as shown in FIG. 5, the attenuation pole is generated in the lower band side than the pass band. However, even in this case, since the relationship between the electrical lengths θi and θij can be changed by changing the width E of the side electrodes 26 and 28 (FIG. 5), the positions of the attenuation poles can be changed. It can be controlled by the width E of.

[Brief description of drawings]

FIG. 1 is an illustrative view showing one example of a conventional interdigital microstripline filter.

FIG. 2 is an illustrative view showing another example of a conventional interdigital microstripline filter.

FIG. 3 is a graph showing reflection characteristics and insertion loss of an interdigital microstripline filter.

FIG. 4 is a graph showing reflection characteristics and insertion loss of an interdigital microstripline filter.

FIG. 5 is an illustrative view showing one embodiment of the present invention.

FIG. 6 is a graph showing reflection characteristics and insertion loss in the example of FIG.

FIG. 7 is an illustrative view showing another embodiment of the present invention.

FIG. 8 is a graph showing filter characteristics of a general bandpass filter.

FIG. 9 is a graph showing that an attenuation pole is formed in the microstrip line filter.

10 is an illustrative view showing one example of an electrode pattern of the combline type microstripline filter of the embodiment in FIG. 7. FIG.

11 is an equivalent circuit diagram of FIG.

FIG. 12 is a graph showing the position of the attenuation pole when the width of the side electrode is small in the embodiment of FIG.

FIG. 13 is a graph showing the position of the attenuation pole when the width of the side electrode is large in the example of FIG.

FIG. 14 is an illustrative view showing an electrode pattern of the interdigital microstripline filter of the embodiment in FIG. 5;

[Explanation of symbols]

10 ... Microstrip line filter 12 ... Dielectric 14 ... Ground electrode 14a, 14c ... Wide part 14b ... Narrow part 16a, 16a ', 16b, 16b', 16c, 20
a, 20b ... Microstrip line 22, 24 ... Input / output electrode 26, 28 ... Side electrode

Claims (4)

[Claims] 1. A microstrip line filter having a plurality of microstrip lines each having one end commonly connected to a ground electrode, the microstrip lines at both ends being coupled to the outside, wherein the microstrip lines outside the both ends are provided. A microstrip line filter, wherein a side electrode having a dimension according to a desired band is added to the ground electrode. 2. A microstrip line filter having a plurality of microstrip lines each having one end commonly connected to a ground electrode, the microstrip lines at both ends being connected to the outside, wherein the microstrip lines outside the both ends are provided. A microstrip line filter, wherein a side electrode having a dimension according to a desired pole position is added to the ground electrode. 3. A method of adjusting a microstrip line, wherein each end includes a plurality of microstrip lines commonly connected to a ground electrode, and the microstrip lines at both ends are connected to the outside. A method for adjusting a microstrip line filter, wherein the band is adjusted by changing the width dimension of the ground electrode outside the line. 4. A method for adjusting a microstrip line in which each end includes a plurality of microstrip lines commonly connected to a ground electrode, and the microstrip lines at both ends are connected to the outside, wherein the microstrips at both ends are provided. A method for adjusting a microstrip line filter, wherein the pole position is adjusted by changing the width dimension of the ground electrode outside the line.