JPH08335807A - Band pass filter - Google Patents

Abstract

PURPOSE: To surely eliminate the undesired signal bands and also to easily reduce the element size of a high frequency band filter. CONSTITUTION: A stub type resonator 2 is connected in series to the output line of a band pass filter main body 1 which defines high frequency bands as its pass bands. The spurious signals which are produced in the bands excluding those of the main body 1 are eliminated by the resonator 2. This resonator 2 is required to have a coaxial line having its tip opened in a T shape against the line itself and also to have a microstrip line constitution. In this constitution, a pattern is formed on a printed board or an electrode is formed on a ceramic substrate where the main body 1 is mounted. Then the pattern or the electrode is unified with the main body 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bandpass filter for high frequency band.

[0002]

BACKGROUND OF THE INVENTION Microwave in (MH _Z ~GH _Z), a bandpass filter is used in the oscillation circuit and signal processing circuit. As the bandpass filter used in this band, a filter element such as a surface acoustic wave filter, a dielectric filter, a crystal filter or a ceramic filter is used.

[0003]

The ideal characteristic of a bandpass filter is to pass only a desired frequency band and remove an unnecessary band.

However, when a filter element is actually created, an unwanted signal (spurious signal) such as a harmonic wave may occur in a band other than a desired band. FIG. 5 shows an example of frequency characteristics of a general filter.

Ideally, a bandpass filter is required to be designed so as to have no unnecessary signal, but it is difficult to completely remove it. When these unwanted signals occur, it is conceivable to remove the unwanted signal band with a low-pass filter or a high-pass filter using an LC element.

However, it is difficult to design and manufacture a filter using an LC element having desired characteristics in a high frequency band having a high frequency. That is, when the frequency becomes high, the design constant of the LC element becomes small, and a component having a general constant has a large error in the constant, which cannot be dealt with.

An object of the present invention is to provide a bandpass filter which surely and easily removes an unnecessary signal band.

Another object of the present invention is to provide a bandpass filter which facilitates miniaturization of elements.

[0009]

In order to solve the above problems, the present invention provides a bandpass filter main body having a high frequency band as a pass band, and a bandpass filter main body connected in series to an output line of the bandpass filter main body. And a stub type resonator for removing spurious signals generated outside the band.

According to the present invention, the stub type resonator is
It is characterized in that it is constituted by a microstrip line on a printed circuit board.

According to the present invention, the stub type resonator is
A microstrip line is formed on the surface of the ceramic substrate on which the bandpass filter body is mounted.

[0012]

The unnecessary signal (spurious signal) generated in the main body of the band pass filter is removed by the stub type resonator instead of the low pass filter or the high pass filter by the LC element. This stub type resonator obtains an accurate design constant even when the design constant is made small, and can reliably remove spurious signals.

By constructing the stub type resonator as a microstrip line on the printed circuit board, it is possible to save the mounting work as compared with the filter configuration using the LC element and to eliminate the need for special components.

Further, the stub type resonator is formed integrally with the bandpass filter body by forming it on the surface of the ceramic substrate on which the bandpass filter body is mounted.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a filter configuration showing an embodiment of the present invention. The bandpass filter body 1 has the same structure as the conventional one. The stub type resonator 2 is connected in series to the output line of the bandpass filter body 1, and a filter output is obtained from the output end of the stub type resonator 2.

In this configuration, the filter frequency characteristic of the bandpass filter body 1 is such that the insertion loss is small in the pass band as shown in FIG. 2A, but the insertion loss is small outside the pass band. Spurious regions are generated and pass unwanted signals.

As shown in FIG. 2 (b), the stub type resonator 2 acts as a notch filter having a spurious region of the bandpass filter body 1 as a stop region, and a signal passing through the bandpass filter body 1 is processed. Remove included spurious signals.

As a result, the bandpass filter in which the bandpass filter body 1 and the stub type resonator 2 are connected in series can obtain a frequency characteristic with an unnecessary signal removed, as shown in FIG. 2 (c). You can

FIG. 3 shows an embodiment of the stub type resonator 2. (A) of the same figure shows the case where a coaxial line is used for the transmission line, and a T-shaped open end coaxial line is inserted in the middle of this coaxial line. The stop band at this time is determined by changing the stub length L.

FIG. 3B shows a case where the stub type resonator is constructed as a microstrip line of a printed circuit board, and in this case also, the stop band is determined by changing the stub length L.

The structure of this microstrip line is as follows:
It can also be configured on the surface of the ceramic substrate on which the bandpass filter is mounted. FIG. 4 shows a case where it is formed on the surface of a ceramic substrate. The bandpass filter body 1 is placed on the ceramic laminated substrate 3, connected to the electrodes on the ceramic laminated substrate 3 by wire bonding, and these are integrally packaged.

In the ceramic laminated substrate 3, pattern electrodes constituting a circuit are formed on each ceramic substrate, and necessary circuit connections are made by using via holes.

Here, the stub type resonator has an integrated structure in which electrodes are formed in a microstrip line structure on one ceramic substrate surface of the ceramic laminated substrate 3 and are connected in series to the bandpass filter body 1.

[0024]

As described above, according to the present invention, a stub type resonator is connected in series to the output line of the bandpass filter body to remove spurious signals that cannot be blocked by the bandpass filter body. effective.

(1) In the stub type resonator, even when the design constant is made small, the stop band can be accurately determined by the stub length L, and the unnecessary signal is removed as compared with the removal of the unnecessary signal by the conventional LC filter circuit. Reliable and easy removal.

(2) The stub type resonator can be constituted by a coaxial line or a microstrip line, and the number of constituent parts can be reduced and the size can be reduced as compared with the conventional LC filter circuit.

(3) When the stub type resonator is formed on the surface of the printed circuit board, it can be realized by forming a pattern on the printed circuit board on which the bandpass filter main body is mounted, which eliminates the trouble of mounting and requires no special component parts. become.

(4) The stub type resonator can be integrally formed by using the ceramic substrate on which the main body of the bandpass filter is mounted and can be miniaturized as a bandpass filter. Further, the temperature condition equivalent to that of the bandpass filter main body can be provided, and stable characteristics can be obtained even with temperature fluctuation in the frequency band.

[Brief description of drawings]

FIG. 1 is a filter configuration diagram showing an embodiment of the present invention.

FIG. 2 is a frequency characteristic diagram of a bandpass filter body and a stub type resonator according to an embodiment.

FIG. 3 is an example of a stub type resonator.

FIG. 4 is an example of forming a stub type resonator on a ceramic substrate.

FIG. 5 shows an example of frequency characteristics of a conventional bandpass filter.

[Explanation of symbols]

 1 ... Bandpass filter body 2 ... Stub type resonator 3 ... Ceramic laminated substrate

Claims (3)

[Claims] 1. A bandpass filter body having a high frequency band as a passband, and a stub type resonator connected in series to an output line of the bandpass filter body for removing spurious signals generated outside the passband of the body. A bandpass filter characterized by being provided. 2. The bandpass filter according to claim 1, wherein the stub type resonator is formed of a microstrip line on a printed circuit board. 3. The bandpass filter according to claim 1, wherein the stub type resonator is formed of a microstrip line on a surface of a ceramic substrate on which the main body of the bandpass filter is mounted.