JPS62164301A - Strip line filter - Google Patents

Abstract

PURPOSE:To obtain a small strip line filter having a satisfactory narrow band characteristic by forming the electrode forming area of the part close to the open edge of respective mutually adjoining resonance electrodes larger than other part of respective resonance electrode respectively. CONSTITUTION:A ground electrode 2 is continuous with a guard electrode 3 formed on other main surface through one side surface of a dielectric substrate 1. From a guard electrode 3, plural resonance electrodes 41-44 constituted by a strip line are extended and formed. Parts 81-84 close to the open edge of respective resonance electrodes 41-44 are formed to a step type extended to both sides in the pulling-out direction and formed larger than other parts 91-94 of the resonance electrodes 41-44. Thus, the narrow band characteristic can be realized, the mutual distance between resonance electrodes and the length of respective resonance electrodes can be shortened and the whole shape of a filter can be miniaturized.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a stripline filter used, for example, as a bandpass filter.

<Prior Art> FIG. 2 is a plan view of a conventional combline type stripline filter. Note that in the figure, the shaded area indicates the electrode formation area. In the filter shown in this figure, a ground electrode I2 is formed on the entire surface of one main surface of the dielectric substrate 11. This ground electrode 12 extends through the side surface of the dielectric substrate 11 to a guard electrode 13 formed on the other main surface.

On the other main surface, a plurality of (four in the figure) resonant electrodes 14 are formed of rectangular strip lines extending from the guard electrode 13. 144 are drawn out in parallel so that they are parallel to each other. In addition, the resonant electrode 14 at the end of the array. ．．
144 is an external lead electrode 17. as an input/output electrode. ,
+7. is brought out. As a result, each resonant electrode 14.
One end of ~144 is an open end 16. -16. and the other end is connected to the ground electrode 12 to form a short-circuited end +5. -154.

<Problems to be Solved by the Invention> In a multistage filter having such a configuration, in order to obtain narrow band characteristics, the distance S between adjacent resonant electrodes 141 to 144 must be increased to some extent. The overall shape becomes larger.

Therefore, the resonant electrode 14. ~14. If a filter is made using a dielectric substrate 11 with a low relative dielectric constant in order to shorten the distance S, the length ρ of each resonant electrode 14□ to 144 must be increased, resulting in miniaturization. The problem is that it cannot be done.

SUMMARY OF THE INVENTION In view of these conventional problems, it is an object of the present invention to provide a small stripline filter having good narrowband characteristics.

<Means for Solving the Problems> In order to achieve such an object, the present invention sets the electrode formation area of the open end portion of each adjacent resonant electrode as follows:
Each of the resonant electrodes is characterized by a structure in which the resonant electrodes are formed larger than other parts.

<Example> Hereinafter, the present invention will be described in detail based on an example shown in the drawings. Note that the shaded area does not indicate the electrode formation area.

FIG. 1 is a perspective view of a combline type stripline filter according to this embodiment. The filter shown in this figure is a bandpass filter that grows four stages of resonators, and includes a dielectric substrate 1. A ground electrode 2 made of Ag or the like is formed on one main surface of the dielectric substrate 1 over its entire surface. This ground electrode 2 is a dielectric substrate ■
It is continuous with the guard electrode 3 formed on the other main surface through one side surface of the main surface. From the guard electrode 3, a plurality of (four in the figure) resonant electrodes 4 composed of strip lines are connected.
．． .about.44 are formed to extend.

Each resonant electrode4. ~4. are mutually adjacent resonant electrodes 4, ~
44 and are arranged in parallel at a predetermined distance S, one end of each is connected to the ground electrode 2 via the guard electrode 3 as short-circuit ends 5I to 54, and the other end is an open end 61.
~64.

In addition, the resonant electrodes 4 at both ends. ．． 4. From the middle part of
External extraction electrode as an output electrode7. ．． 7. is drawn out to the side surface of the dielectric substrate 1.

The open end portions 81 to 84 of each of the resonant electrodes 4□ to 44 are formed in a step shape projecting on both sides in the drawing direction. -44 is formed larger than the other parts 91-94.

In this way, each resonant electrode 4. ~44 and ground electrode 2
Since the capacitance formed between the two is larger than that of the conventional example, the resonant frequency is lowered accordingly. Therefore, the lengths of the resonant electrodes 41 to 44 can be shortened as long as they have the same resonant frequency.

In addition, in a stripline filter having such a configuration, since the odd mode resonance frequency is usually higher than the even mode resonance frequency, each resonance electrode 4. - Portion near the open end of 44 8. By increasing the area of .about.84, adjacent resonant electrodes 4. With respect to a change in the coupling capacitance fi C between . Therefore, the difference in resonance frequency between odd mode and even mode is greatly reduced compared to the conventional example, thereby making it possible to obtain a filter with a narrow bandwidth. In addition, each resonant interelectrode type #IS
It is also possible to shorten the time.

Note that the open end portion 8. 84 can be selected from any shape such as a step shape or a circular shape.

Further, the guard electrode 3 is provided as necessary, and may be omitted. In addition, the manner in which people and outputs are connected is not limited to the embodiments described above. Furthermore,
Of course, the number of stages of the resonant electrodes 4I to 44 is not limited to four stages.

<Effects of the Invention> As described above, according to the present invention, the electrode formation area of the open end portions of each adjacent resonant electrode is formed larger than the other portions of each resonant electrode.
Not only can a narrow band characteristic be realized, but also the distance between the resonant electrodes and the length of each resonant electrode can be shortened, and the overall shape of the filter can be made smaller. Therefore, the cost of materials such as the material of the dielectric substrate can be reduced, and manufacturing costs can be reduced.

[Brief explanation of drawings]

FIG. 1 is a perspective view of an embodiment according to the present invention, and FIG. 2 is a plan view of a conventional example. DESCRIPTION OF SYMBOLS 1... Dielectric substrate, 2... Ground electrode, 41-44... Resonant electrode, 5,-54... Short-circuited end of resonant electrode, 6I-64... Open end of resonant electrode, 8 , ~84... Portion near the open end of the resonant electrode.

Claims (1)

[Claims] (1) A dielectric substrate is provided, a ground electrode is formed on one main surface of the dielectric substrate, and a plurality of resonant electrodes consisting of strip lines are formed in parallel on the other main surface of the dielectric substrate. , in a strip line filter in which one end of each resonant electrode is connected to the ground electrode to form a short-circuited end, and the other end of the resonant electrode is an open end, forming electrodes in portions of adjacent resonant electrodes near the open end; A stripline filter characterized in that each resonant electrode has a larger area than other parts.