JPS6360605A - Band pass filter - Google Patents

Abstract

PURPOSE:To suppress the spurious resonance mode effectively without using a band stop filter by fitting a prescribed resonator to the mid-point part of a pi/2 line resonator. CONSTITUTION:A dielectric resonator 15 having a resonance frequency near the frequency 2f0 twice the pass band center frequency f0 is fitted to the midpoint part of the pi/2 line resonator 13. Thus, the midpoint part of the resonator 13 is grounded in terms of high frequencies with respect to the fundamental wave f0 and open in terms of high frequencies with respect to the frequency 2f0. Since the resonator 15 fitted to the midpoint part of the resonator 13 is coupled and resonated with respect to the frequency 2f0, the spurious resonance mode near the frequency 2f0 is attenuated largely by the resonance. Thus, the spurious resonance mode is suppressed effectively without using a band stop 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 end to the output side in the drawing. It's a railroad.

Reference numeral 3.4.5 denotes three λ/2 line resonators arranged along the lines between the input and output external connection lines 12 on the surface of the dielectric substrate. Here, λ is the line wavelength corresponding to the passband center frequency f.

Each of the λ/2 line resonators 3, 4.5 is coupled in parallel to the adjacent resonators 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 21o, 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 f0) is provided between the external connection lines for human power and output, and the λ/ The two-line resonator has the passband center frequency f in its middle part. The device is characterized in that a dielectric resonator having a resonant frequency is installed near the frequency 2, which is twice as high as the frequency 2.

The effects of this configuration are as follows.

That is, since the dielectric material 85 is attached to the middle part of the λ7/2 line resonator, the spurious resonance mode near 2f0 is 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 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.

+2.13.14 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 close to the external connection line 10 and 11 side
．． Reference numeral 14 has the same configuration as the conventional example shown in FIG.

The embodiment is characterized by the configuration of the λ/2 line resonator 13 placed in the center. That is, this λ/2 line resonator 1
3 has a passband center frequency r in its middle part. A dielectric resonator 1 having a resonant frequency near twice the frequency 2fo
5 is attached.

FIG. 2 is an enlarged view of the λ/2 line resonator I3. Second
As shown in the figure, the dielectric resonator 15 is
3, ie 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. is in a ground state (minimum electric field j3) in terms of high frequency, and conversely, the frequency 2fo which is twice the fundamental wave ro
It is in an open state (maximum electric field state) in terms of high frequency. Therefore, a dielectric resonator 15 is attached to the middle part of this resonator 13, and the dielectric resonator 15 hardly couples the fundamental wave f0 with the microstrip line, and with respect to 2f, Because they combine and resonate,
Due to this resonance, electromagnetic energy near 2f is confined here, and as a result, spurious resonance modes near 2f are greatly attenuated.

FIG. 4 is a characteristic diagram of the bandpass filter according to the embodiment of the present invention when the dielectric resonator 15 is attached.

As shown in FIG. 4, the spurious resonance mode at 2f0 in this bandpass filter is largely suppressed. This is due to the effect of the dielectric resonator 15, 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 f. is 3.95GHz, bandwidth is 8
00MHz, a third-order bandpass filter designed with a flat passband amplitude characteristic, and configured with a microstrip line using a dielectric substrate with a dielectric constant of 2.5 and a thickness of 0.76mm. Ta.

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.

Although this embodiment has been described using 3g of λ/2 line resonators, it is also possible to use one or other than three.

(Effects of the Invention) As explained above, in the present invention, since the dielectric resonator is provided in the middle part of the λ/2 line resonator, the excellent effect is that the spurious resonance mode in the stop band is sufficiently suppressed. is demonstrated.

[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. to, tt are external connection lines for input and output, +2.1
3.14 is a λ/2 line resonator, and 15 is a dielectric resonator.

Claims (1)

[Claims] (1) A λ/2 line resonator (where λ is the line wavelength corresponding to the passband center frequency f_0) is provided between the input and output external connection lines, and the λ/2 line resonator is A bandpass filter characterized in that a dielectric resonator having a resonant frequency in the vicinity of a frequency 2f_0, which is twice the passband center frequency, is attached to an intermediate portion.