JPS6360604A - Band pass filter - Google Patents

Abstract

PURPOSE:To suppress the spurious resonance mode effectively without using a band stop filter by providing a current absorbing body to the midpoint part of a lambda/2 line resonator. CONSTITUTION:The radio wave absorbing body 15 is provided at the midpoint of the lambda/2 line resonator, that is, at a position of lambda/4 from each end. Thus, the midpoint part of the resonator 13 is grounded in terms of high frequencies with respect to a fundamental wave f0 and open in terms of high frequencies to a frequency being twice the fundamental wave f0. Thus, even when the radio wave absorbing body 15 is fitted to the midpoint part of the resonator 13, the pass characteristic at the center of the fundamental wave f0 is almost effected and the radio wave absorbing body 15 acts on the spurious resonance mode only near the frequency 2f0. The spurious resonance mode is suppressed efficiently without using the band block filter.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to a bandpass filter composed of a strip line or the like having a harmonic suppression effect.

(Prior Art) FIG. 6 is a schematic configuration diagram of a conventional band-pass filter. In FIG. 6, symbols I and 2 are external connections for input and output formed on the surface of a dielectric substrate (not shown), respectively, along a line diagonally downward to the right from the input side to the output side in the drawing. It's a railroad.

Reference numeral 3.4.5 designates three λ/2 line resonators arranged along the lines between the input and output external connection lines 1.2 on the surface of the dielectric substrate. Here, λ is the line wavelength corresponding to the passband center frequency fo.

Each of the λ/2 line resonators 3, 4.5 is coupled in parallel with the adjacent resonator at λ/4, which is half the length of the resonator.

Band-pass filters with such a structure are often used in microstrip lines and the like because a design method has been established. However, on the other hand, since it is based on a λ/2 line, spurious resonance modes that lead to deterioration of the stopband characteristics tend to occur near 2ro, as shown in the characteristic diagram of the bandpass filter in FIG.

For example, if a bandpass filter that is prone to generate spurious resonance modes is used in a receiver, it may not be able to sufficiently attenuate signals outside the required band, resulting in a decrease in reception sensitivity, and the oscillator or When used in conjunction with a nonlinear circuit such as a multiplier, there is a problem in that harmonic components are not suppressed sufficiently, leading to the generation of unnecessary waves.

Therefore, in order to suppress such spurious resonance modes, an extra circuit such as a band rejection filter has conventionally been required. When a band-elimination filter is used, problems arise in that the insertion loss caused by the band-elimination filter adversely affects the passband, or that the circuit shape becomes large and complicated.

(Object of the Invention) The present invention has been made to solve these problems, and it is possible to effectively suppress spurious resonance modes without using a band-stop filter, and to achieve wide rejection. The purpose of this invention is to provide a bandpass filter with

(Structure of the Invention) In order to achieve the above object, the present invention has the following structure.

That is, in the bandpass filter of the present invention, a λ/2 line resonator (where λ is the line wavelength corresponding to the passband center frequency) is provided between the input and output external connection lines, and the input/2vA The road resonator is characterized in that a radio wave absorber is attached to its intermediate portion.

The effects of this configuration are as follows.

That is, since the radio wave absorber is attached to the intermediate portion of the λ/2 line resonator, spurious resonance modes are suppressed.

(Example) FIG. 1 is a schematic configuration diagram of a bandpass filter according to an example of the present invention. In FIG. 1, reference numeral IO is an input external connection line formed extending in the left-right direction in the drawing on the surface of a dielectric substrate (not shown), and 11 is an input external connection line 11 formed diagonally downward to the right of the input external connection line IO. Similarly, it is an output external connection line formed to extend in the left-right direction.

12.13.14 is also on the dielectric substrate surface,
A plurality of, in this embodiment three, are arranged and formed along the diagonal line and extending in the left and right direction.
It is a λ/2 line resonator.

λ/2 line resonator 12 near the external connection line 10.2 side.
Reference numeral 14 has the same configuration as the conventional example shown in FIG.

The embodiment is characterized by the configuration of the 72-line resonator 13 placed in the center. That is, this λ/2 line resonator 1
3, a radio wave absorber 15 is attached to the middle portion thereof.

FIG. 2 is an enlarged view of the λ/2 line resonator 13. Second
As shown in the figure, the radio wave absorber 15 has its resonator 13
, at a position λ/4 from either end of the resonator 13 .

In this case, as the fundamental wave mode of the λ/2 line resonator 13 is shown in FIG. 3, the intermediate part of the λ/2 line resonator 13 has a fundamental wave f. For a frequency 2f, which is twice the frequency of the fundamental wave f, it is in a ground state (minimum electric field state) in terms of high frequency. Therefore, even if the radio wave absorber 15 is attached to the middle part of the resonator 13, the fundamental wave f remains. It has almost no effect on the passband characteristics centered around , and acts only on spurious resonance modes around 2ro.

FIG. 4 is a characteristic diagram of the bandpass filter according to the embodiment of the present invention when the radio wave absorber 15 is attached. 2 in this bandpass filter as shown in FIG.
The spurious resonance mode at f is largely suppressed. This is because the radio wave absorber 15 has an effect in addition to the fact that the intermediate portion has almost no effect on the pass band characteristics of the band pass filter as described above.

FIG. 5 is a characteristic diagram of bandpass filters based on experiments of the conventional example and the present embodiment. In FIG. 5, the solid line is the conventional example, and the broken line is the present embodiment.

In the experiment, the center frequency r0 was 3.95 GHz and the bandwidth was 8
00MI (z, 3rd-order bandpass filter designed with passband amplitude flatness characteristics and configured with a microstrip line using a dielectric substrate with a relative dielectric constant of 2.5 and a thickness of 0.76 mm. I went there.

As shown in FIG. 5, it was found that in this example, the spurious resonance mode was suppressed to a greater extent than in the conventional example.

In this embodiment, the λ/2 line resonator is described as having 3 g, but it goes without saying that it may be tg, or it may be other than 3.

(Effects of the Invention) As explained above, in the present invention, since the radio wave absorber is provided in the middle part of the λ/2 line resonator, the excellent effect of sufficiently suppressing the spurious resonance mode in the stopband is achieved. Be effective.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of a bandpass filter according to an embodiment of the present invention, Fig. 2 is a block diagram of a λ/2 line resonator which is the main part of the embodiment, and Fig. 3 is a block diagram of a λ/2 line resonator. Fundamental wave mode diagram, Figure 4 is a characteristic diagram of the band-pass filter of the embodiment, Figure 5 is a characteristic diagram of the band-pass filter based on experiments of the conventional example and the embodiment, and Figure 6 is the band-pass filter according to the conventional example. FIG. 7 is a characteristic diagram of a conventional band-pass filter. 10.11 is the external connection line for input and output, 12.1
3.14 is a λ/2 line resonator, and 15 is a radio wave absorber. Applicant Sharp Co., Ltd. Agent Patent Attorney Kazuhide Okada Haka 1 Figure 1 (Configuration diagram of a bandpass filter according to an embodiment of the present invention)
n Figure 2 Figure 3 (Resonance mode diagram of λ/2 line resonator) □ Recommendation □ Figure 4 (Characteristics diagram of the band pass filter of the example) Figure 5

Claims (1)

[Claims] (1) A λ/2 line resonator (where λ is the line wavelength corresponding to the passband center frequency) is provided between the input and output external connection lines, and the λ/2 line resonator is located between the two. A bandpass filter characterized by having a radio wave absorber attached to a portion.