JPS58120301A - Band pass filter - Google Patents

Abstract

PURPOSE:To have an extremely sharp increment of a loss of insertion at bands excepting the pass band, by setting the distance between the coupling points of a transmission line connected to the 1st and the 2nd resonators at an odd-fold value as long as 1/4 wavelength of the center frequency of the pass band. CONSTITUTION:An earth conductor 2 is provided on the rear side of a dielectric substrate 1, and an input signal is supplied to a microstrip line muSTL11 of the 1st transmission line provided on the upper side of the substrate 1. The line muSTL11 is connected to the 1st dielectric resonator 12, and the resonator 12 is connected to a line muSTL15 of the 2nd transmission line. The line muSTIL15 is connected to the 2nd dielectric resonator 13. For the line muSTL15, the distance between the coupling points between the resonators 12 and 13 is set equal to an odd-fold value as long as 1/4 wavelength of the center frequency of the pass band. The resonator 13 is connected to a line muSTL17 of the 3rd transmission line via the muSTL15, muSTL16 having the same structure as the resonator 13 and a resonator 14. Then an output is extracted out of the muSTL17. As a result, a sharp increment is obtained for a loss of insertion at bands excepting the pass band.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a bandpass filter using, for example, a dielectric resonator.

Generally, it is desirable for a bandpass filter to have a characteristic in which the insertion loss increases by one degree outside the passband. In this case, in a bandpass filter using one resonator, the steepness of the increase in insertion loss k has a limit determined by the unloaded Q value of the resonator, so it is necessary to try to achieve a steeper increase k. teeth.

A method is used in which a filter is constructed by combining a plurality of resonators.

FIG. 1 shows an example of such a device. In the figure “cI”
l A ground conductor (2
) is provided. In addition, on the front side of 11, there is a microphone 4 strip twin (3) that serves as an input terminal, a dielectric resonator (4) * (5) * (6), and a strip line that serves as an output terminal (7). is provided.

And this device kTh has an input signal on line (3) K
When supplied, this line (3) and resonator (4) are coupled, this resonator (4) and resonator (5) are coupled, and this resonator (5) and resonator (6) are coupled. The resonator (6) and the line (7) are coupled to produce an output signal from the twin (7).

However, in this device, if the coupling between the resonators is not strong enough, or if the coupling between the resonators in Sgelius mode is strong, this method of directly coupling the resonators is not appropriate.

Therefore, in such a pigeon house, it has been proposed to connect the resonators with a transmission all to form a band-pass filter using a number of resonators.

The present invention provides such a bandpass filter with 5K so that the increase in insertion loss outside the passband can be made even steeper. An embodiment of the present invention will be described below with reference to the drawings. 5. In Figure 2, a substrate (1)
of! ! In a conventional manner, the input terminals are microphone-strip tin housings, dielectric resonators az, as, and a4, and the microphone four-strip twin α9, ae, which connects these resonators.
A microphone strip 2-in αη serving as an output terminal is provided.

In this device, an input signal is supplied to the 2-in I as the first transmission line, this twin aυ is coupled to the first resonator UKM, and this resonator I is connected to the twin ( 15 and this line 4 is coupled to the second resonator a3 as well as k.

Resonator a of line α9 is equal to the odd number times between the coupling points of line α and resonator I.
It is coupled to the twin aη as the third transmission line via a configuration (twin a19 and resonator a4) equal to the above, and an output signal is extracted from this twin fin.

In this device, the distance between the coupling points of the lines αs and ae with the resonators 0, aJ and as, a4, respectively, is made equal to an odd multiple of one wavelength of the center frequency of the passband. The increase in loss can be made the steepest. We perform this equality below.

For simplicity, consider a bandpass filter with two resonators, and assume that the two resonators are the same. At this time, the bandpass filter value is expressed as shown in FIG.

From this equivalent circuit, each element of the 8 matrix [S] of the 2-terminal network between terminals AB and the S-v matrix [S] of the 2-terminal network between terminals CD is determined as shown in 5 below.

・・・・・・(1) ・・・・・・(2) Here, if the 8Y) ricks of the entire two-terminal circuit network between terminals AD is (8), then [S] is as follows using [8]. like! ! I will be forgotten.

...(3) The insertion loss value of this bandpass filter is -10log
Since it is 151g "l", it is 181! tl''K...(4) 81! or 81m in equation (4) indicates a change of 5 as shown in Figure 4 from equation (1) or (2).From this, 8xs8xt ' changes as shown in Figure 5. Also, g
t Snow B ue''j 5i is just rotating 81!81! clockwise by 2g1/λ radians, so 1st mu'e''j at the same frequency! The value of 1ψ- does not change, that is, the numerator of equation (4) takes the same value at the same frequency regardless of the dew value. On the other hand, 82! in equation (4)! Alternatively, 8tt' shows a change as shown in Figure 6 from equation (1) or (2). From this, 8z*8ss'! 7. Do you want to change as shown in Figure 7? :, 8u8x/e-j”
'/' is 8xs8xt' rotated clockwise by 4πVλ radians, so t1λ/4(fi-1tR*
...), the opposite side of Fig. 7 with respect to the origin, k〈Y5 to 9, shows a change as shown in Fig. 8.

t −j TsuruVλ SaraK 11−&511e l f) Value C is the distance between the point 1 and the point 82ffi8oe on the complex plane s −j4πVλ, so when − moves away from ω0, that is, L+
When nλ/4t −j4πVλ is selected, K is set such that the value of 1l−8uSoel becomes the largest, and 18s of <4>t becomes smaller.

On the other hand, when 6 is 610, k is 1l-8t snow 8t 7e
It turns out that the value of -j4d/λ1 is almost constant regardless of iK, and it is +81! The l dependence of + on ω2ω0 is small.

It is clear from the above that 5 K m −nλ/4(n
=1*3...), the increase in insertion loss outside the passband becomes the steepest.

In this way, a bandpass filter is formed.
According to the present invention, since the distance between the coupling points of the twin resonators connecting the resonators is equal to an odd multiple of 7 wavelengths of the center frequency of the passband, the insertion loss outside the passband is can be made to have the steepest increase.

Further, FIG. 9 shows the insertion loss sieving results when one resonator is used. Moreover, FIG. 10 shows the insertion loss when 1-OX is selected using two resonators.

It can be seen from these figures that the out-of-band insertion loss increases somewhat more rapidly than when one resonator is used. On the other hand, in Fig. 11, two resonators are used to generate 1-λ
This is the insertion loss when selecting /4. In this figure, g
The increase in out-of-band insertion loss is even steeper than in the case of −6.

As described above, according to the present invention, the increase in insertion loss outside the passband can be made extremely steep.

Note that in the present invention, the m-wavenumbers of a plurality of resonators do not necessarily have to match, and the same effect can be obtained even in the case of a plurality of resonators having a resonant frequency t near the center. Furthermore, the resonator is effective not only for the above-mentioned dielectric resonator but also for all types of resonators such as planar circuits, cavity resonators, and ferrimagnetic resonators. Furthermore, as a transmission line connecting the resonators,! In addition to IkuP strip lines, it is effective for all kinds of transmission lines such as waveguides, parallel lines, and strip lines.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a conventional device, FIG. 2 is a block diagram of an example of the present invention, and FIGS. 3 to 11 are diagrams for explaining the same. 01) eQ5*(lfi*(17))lv(riOX)
IJ yfu94y, Q3 * (+31 * Q4)
is a resonator. 2nd figure

Claims (1)

[Claims] An input signal is provided to a first transmission line, a transmission line of sl of and is coupled to a first common 11i@, a resonator of @1 of is coupled to a second transmission line of this second 2nd transmission line
resonator, and the distance between the coupling points of the second transmission line and the first and second resonators is equal to an odd multiple of seven wavelengths of the center frequency of the passband,
The eighth resonator is coupled to the jIs transmission line directly or through one or more sets of the second transmission line and the second resonator, and the output signal is extracted from the third transmission line. Bandpass filter.