JPS61189701A - Band-pass filter - Google Patents

Abstract

PURPOSE:To obtain a wide band filter having a higher harmonic wave suppressing effect by using a 1/2 wavelength type strip line resonator having a linear taper part and an opened tip part and performing the connection between resonators and also between the input and the output with said taper part. CONSTITUTION:Resonators 101-103 have linear taper parts having large width at the center part and small width at the open end part respectively. Therefore the conductor loss can be reduced with these resonators since the line width is large at the center part where the current level is maximum and therefore applied suitably to a filter having low loss. Furthermore the higher harmonic wave suppressing effect is secured owing to the uneven line impedance, and a sufficiently large degree of bond is secured at the taper part. This attains a band-pass filter of a wide band. While resonators 201-203 have small width of line at the center part and large width at the open end part respectively. Thus the lengths of these resonators can be set shorter than the 1/2 wavelength.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a bandpass filter using a microstrip or strip line in a frequency band of several hundred MHz or higher, and is applicable to various wireless transceivers, measuring instruments, etc. used.

BACKGROUND ART Band-pass filters using microstrip line or strip line (hereinafter collectively referred to as strip line) resonators have a simple structure and are easy to manufacture, as shown in Figure 3, so they are suitable for microwave bands and It is a circuit that has received awards in the nearby frequency band, and its design method is also based on Micr.
owave Filters.

Impedance Matching Network
ks+ and Coupling Structure
s” (G, L+Mathaei, L, Young an
dE-M-T, 7hones, MiGraw,
New York, 1964).

In Fig. 3, 301, 302, and 303 are uniform line resonators with half wavelength open ends, and each resonator is parallel coupled with a quarter wavelength, and input/output lines 304, 30
5 are coupled in parallel with a quarter wavelength line to form a bandpass filter. However, in this filter, when the design center frequency of the resonator itself is 10, nfo (n=2
, s, 4. -) also has a resonance point, so the passband occurs not only in fo but also in 2f0, 3f0, 4f0..., so it is a power amplifier.

When used as an output filter for a circuit that has a high level of harmonic components in the output of an oscillator, etc., it not only has no harmonic suppression effect, but also has the disadvantage that there is little freedom in design regarding loss and shape. It is something.

In order to overcome these drawbacks, a strip line filter can be considered in which a resonator having an asymmetric impedance as shown in FIG. 4 is applied as a resonant element.

In Fig. 4, 401.402.403 are resonators, 4
04.405 indicates an input/output line. The resonator used in this filter is one in which the line impedance is different from the line impedance by changing the line width of the line near the open end and the line near the center. ), the line impedance is no longer uniform, so the high-order resonance point is not an integral multiple of the fundamental wave. Therefore, a filter having a high frequency suppression effect can be realized. If a low-loss design is still required, the line width at the center of the line may be widened. Also, make the shape smaller (shorten the resonator length)
If it is necessary to design it, it can be done by designing the central part of the line to be narrow, and it has the advantage that the degree of freedom in design is greater than that of the filter using the uniform line resonator shown in FIG.

Problems to be Solved by the Invention However, as can be seen from FIG. 4, this filter cannot have a sufficiently long coupling line;
It has the disadvantage that the degree of coupling cannot be increased and it can only be applied to narrow band filters.

In view of the above-mentioned drawbacks, the present invention aims to realize a strip line filter having a wide passband and having a harmonic suppressing effect.

Means for Solving the Problems In the present invention, a linear strip line resonator having an open-ended tip is used as a non-uniform line co-optation device, and the linear tapered portion connects between the resonators and input/output. It has a bond.

By making the line impedance non-uniform using a linear taper, the higher-order resonance point of the stripline resonator can be shifted from an integer multiple of the fundamental resonance point, and the linear taper By coupling, the coupling length can be made sufficiently long, so the degree of coupling can be designed to be strong and the passband can be expanded.

Example FIG. 1 shows a first embodiment of the present invention.

In FIG. 1, 101, 102, 103 are resonators, 1
04 and 105 are input/output coupling lines. Resonator 101.
102 and 103 are resonators having a linear channel with a wide line width at the center of the line and a narrow structure at the open end. These resonators 101, 102, and 103 have a large line width at the center of the line where the current is maximum, so that conductor loss can be reduced, making them suitable for low-loss filters. In addition, since the line impedance is non-uniform, it also has a harmonic suppression effect as a filter, and since a sufficiently thick coupling degree can be obtained with the four linear channels, a zero-order Next, another embodiment will be described.

FIG. 2 shows a second embodiment of the invention.

In Figure 2, 201.202.203 are resonators, 2
04.205 is an input/output coupling line.

In this example, the resonators 201, 202, and 203 have a narrow line width at the center and a wide open end, which is a resonator with nonuniform impedance. It has a harmonic suppression effect. A resonator with this structure is suitable for miniaturization because the resonator length can be designed to be shorter than the half-scale length.

In the description of this embodiment, a three-stage filter using three resonators is shown, but it goes without saying that the number of stages (number of resonators) can be arbitrarily selected.

Effects of the Invention As described above, the present invention uses a bipartite open-ended long strip line resonator having a linear tapered portion, and uses the tapered portion to perform inter-resonator and input/output coupling, so that it can be used as a filter. A broadband filter with harmonic suppression effect can be realized, and its industrial value is extremely large.

[Brief explanation of the drawing]

FIG. 1 is a plan view of a band-pass filter according to a first embodiment of the present invention, FIG. 2 is a plan view of a band-pass filter according to a second embodiment of the present invention, and FIG. 3 is a plan view of a conventional strip line resonator. FIG. 4 is a plan view of a conventional strip line resonator having a harmonic suppression effect. 101.102,103:201.202゜203...
...Resonator, 104,105 ;204°205・
...Input/output coupling line. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Zukan 2nd cause 3rd figure

Claims (2)

[Claims] (1) Using one or more linear tapered strip or microstrip line resonators with a wide line width at the center of the resonant line and narrow line widths at the two open ends, A bandpass filter in which the output line and resonator are coupled in parallel through a linear taper. (2) Using one or more linear tapered strip or microstrip line resonators with a narrow line width at the center of the resonant line and wide line widths at the two open ends, A bandpass filter in which the output line and resonator are coupled in parallel through a linear taper.