JPH0349301A - Band pass filter - Google Patents

Abstract

PURPOSE:To make the entire band pass filter small without deteriorating an out-band attenuation by bending microstrip line resonators at each center part and making each bent resonator opposite to an adjacent resonator in parallel respectively. CONSTITUTION:Resonators 13-16 each made of a half wavelength microstrip line are formed on a dielectric base 1 whose rear side is made of a conductor. A half (1/4 wavelength) of each resonator is coupled with an adjacent resonator or input/output lines 11, 12 as a parallel line, Since the resonators 13-16 are bent at the center by an angle of 90 deg., the length of the entire band pass filter is decreased by nearly a half in comparison with the case of straight line resonators 23-26 like a conventional band pass filter. Since the resonator lines other than the adjacent resonators are not arranged in parallel closely different from the conventional filter, the deterioration of attenuation in out-band, especially at high frequency is not caused.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a bandpass filter using a microstrip line provided on a dielectric substrate.

[Conventional technology]

Conventionally, this type of bandpass filter has a resonator 2 consisting of a half-wavelength microstrip line, as shown in FIG.
A structure in which 3 to 26 are formed in a straight line has generally been used. That is, the resonators 23 to 26 are sequentially arranged in one direction while the halves (1/4 wavelength) of the resonators 23 to 26, each having a half wavelength, are opposed in parallel to each other to provide coupling between the resonators. It had a structure.

[Problem to be solved by the invention]

However, the conventional bandpass filter described above requires a total length equal to or longer than 1/4 wavelength multiplied by the number of stages, so the length of each resonator is long, especially when the frequency is low. The disadvantage is that the shape becomes larger.

On the other hand, in order to compensate for the drawbacks of the bandpass filter shown in FIG. 2, conventionally, as shown in FIG.
The structure is made more compact by bending it at two places and bending it at 180 degrees as a whole. However, in this structure, the 1/4 wavelength parts of all the resonators are arranged close to each other in parallel, so coupling occurs not only between adjacent resonators but also between resonators further apart. However, there is a drawback that the amount of attenuation is degraded outside the band, especially on the high frequency side.

[Means to solve the problem]

The bandpass filter of the present invention includes at least one resonator made of a half-wavelength microstrip line provided on a dielectric substrate whose back surface is a conductor, and the half-length portion of the resonator is connected to the adjacent resonator. In the bandpass filter having a structure in which the resonators or the input/output lines are connected to each other by facing each other in parallel, each of the resonators has a shape bent at one point in the central portion in the longitudinal direction.

〔Example〕

Next, the present invention will be explained with reference to the drawings.

FIGS. 1(a) and 1(b) are a plan view and a side view of an embodiment of the present invention.

Resonator 13 consisting of a half-wavelength microstrip line
16 are formed on a dielectric substrate 1 whose back surface is a conductor. Each resonator is connected to an adjacent resonator or an input/output line ix, 12 at a half (1/4 wavelength) portion thereof as a parallel line. Here, each of the resonators 13 to 16 is bent at 90 degrees at its center, so compared to the case where each of the resonators 23 to 26 is a straight line as in the conventional example (not shown in FIG. 2),
The overall length of the bandpass filter can be reduced to about 1/72. In addition, as seen in the third and first conventional example, the lines of resonators other than those between adjacent resonators are not lined up close to each other in parallel, so the amount of attenuation outside the band, especially on the high frequency side, deteriorates. There is no. Figure 4 shows an example of its characteristics. curve 41
curve 42 shows the out-of-band attenuation characteristic of the embodiment shown in FIG. 1 or the conventional example shown in FIG. 2, and the curve 42 shows the out-of-band attenuation characteristic of the conventional example shown in FIG. Center frequency of passband (f o ” 4
GHz) twice the frequency (2fo = 8GHz
> deterioration of attenuation due to higher-order resonance mode is seen, but in the conventional example shown in Fig. 3, the 6G H
It can be seen that the attenuation decreases significantly near z.

In the embodiment shown in FIG. 1, the bending angle of each resonator is 90
However, the bending angle can be further increased to achieve further miniaturization as long as the amount of out-of-band attenuation is not significantly degraded.

〔Effect of the invention〕

As explained above, in the present invention, by bending the microstrip line resonator at one point in the center thereof, it is possible to downsize the overall shape of the bandpass filter without deteriorating the out-of-band attenuation. This is particularly effective when the passband frequency is low and the length of the half-wavelength resonator is long.

3-16...Resonator.

Claims (1)

[Claims] At least one resonator consisting of a half-wavelength microstrip line is provided on a dielectric substrate whose back surface is a conductor, and a half-length portion of the resonator is parallel to the adjacent resonator or input/output line. 1. A band-pass filter having a structure in which each of the resonators is coupled by facing each other, wherein each of the resonators has a shape bent at one point in a central portion in the longitudinal direction.