JPH0481890B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a bandpass filter that is suitably used in a frequency range including the UHF band and beyond.

Conventional technology and its problems The filter characteristics of a bandpass filter in the above frequency range are required to have relatively high sharpness (hereinafter referred to as Q), and in the past, dielectric coaxial resonators were connected in multiple stages. Things were common.

By the way, the above-mentioned dielectric coaxial resonator is represented by an equivalent circuit consisting of a series circuit consisting of a capacitor and a coil and another capacitor connected in parallel, but when used as a bandpass filter,
A separate coupling means such as a capacitor is required, resulting in a complicated structure, an increase in size, and a time-consuming assembly process.

The applicant has proposed a related invention in which a conductive pattern constituting a resonator circuit is formed on a single substrate, and a plurality of resonator circuits are magnetically coupled, thereby realizing compactness. This was already proposed in patent application No. 1983-97317.

However, although the invention as filed above has become more compact, it cannot be said that its "Q" is necessarily satisfactory in terms of filter characteristics, and there is still room for improvement.

The present invention has been made in view of these problems, and an object of the present invention is to provide a bandpass filter that is compact and has improved filter characteristics.

Means for Solving the Problems In order to achieve the above object, the present invention has an equivalent circuit in which a second capacitor is connected in parallel to an LC series circuit in which a coil is connected in series on both sides of a first capacitor. The present invention is characterized in that a plurality of resonators are connected in multiple stages by magnetically coupling the coil of each resonator with the coil of another resonator, and that at least one resonator is connected by a coil.

Effect By coupling at least one resonator of a plurality of multi-stage coupled resonators with a coil, poles are generated near both sides of the pass band due to the characteristics of the filter, although the reason is unknown. When such a pole occurs on the town side of the passband, the rise of the frequency characteristic becomes steep.

Embodiment FIG. 1 shows the configuration of a bandpass filter as a first embodiment of the present invention, in which figure A is a front view, figure B is a side view, and figure C is a rear view. In the figure, 1 is a dielectric substrate made of, for example, FRDR material, with a dielectric constant of 80 and a thickness of 0.4 mm, and conductive patterns 2, 3, 4 in a U-shape are formed on the front surface 1a and the back surface 1b, respectively. 5
is formed, for example, by screen printing silver paste, and the conductive patterns 2 and 4 on the surface 1a side are connected via a rectangular conductive coil pattern 6. Each conductive pattern 2
-5 are two capacitor electrode patterns 2a, 2
It consists of one coil pattern 2c, 3c, 4c, 5c. Among these, capacitor electrode patterns 2a and 3a, 2b and 3b, 4a and 5a, 4b and 5
b is opposed to capacitors C1, C2, C with a capacitance determined by the dielectric constant and thickness of the substrate and the facing area of the capacitor electrodes.
3, forming C4. On the other hand, the coil patterns 2c, 3c, 4c, and 5c are formed at positions that do not face each other. Each coil pattern 2c, 3
c, 4c, and 5c form a coil at high frequency.
Here, the inductance of each coil pattern is assumed to be L1, L2, L3, and L4. 7 and 9 are lead terminals for input/output, respectively, and 8 is an earth terminal for grounding.

In the above configuration, the conductive patterns 2 and 3 and 4 and 5 facing each other on the front and back surfaces of the dielectric substrate 1 are connected to the first capacitors C1 and C3, respectively, as shown in FIG.
A second capacitor C2, C is connected to an LC series circuit in which series coils L1, L2, L3, and L4 are connected on both sides of the
4 constitute resonators Q1 and Q2 represented by an equivalent circuit connected in parallel. The resonators Q1 and Q2 having this equivalent circuit are magnetically coupled, and
Since they are connected by the conductive coil pattern 6, a bandpass filter having an equivalent circuit as shown in FIG. 3 is constructed. In the figure, M is the mutual inductance representing the degree of magnetic coupling between the two coil patterns 2c and 4c, L5 is the inductance of the conductive coil pattern 6, and L6 is the inductance of the lead terminal 8. Note that since the two resonators described above use the dielectric substrate 1, not only magnetic coupling but also capacitive coupling is performed.
In the figure, Cs schematically indicates its binding capacity.
Coupling by changing the distance between the two resonators Q1 and Q2 (including both magnetic and capacitive coupling)
The degree of this can be changed, thereby adjusting the passband width of the bandpass filter.

In this case, narrowing the spacing widens the bandwidth, and widening the spacing narrows the bandwidth.

FIG. 4 shows the frequency characteristics of the bandpass filter having the above configuration, and FIG. 5 shows an example in which the connecting coil L5 is not provided. Both center frequencies are 458MHz. As is clear from the comparison of these two figures, the resonator Q
It was confirmed that by connecting 1, Q2 to the connecting coil L5, poles P and P are formed on both sides of the center frequency, and that steeper characteristics can be obtained compared to the case where the connecting coil L5 is not provided. . Furthermore, as described above, the bandpass filter is made of a conductive pattern having the equivalent circuit shown in FIG. 3, and is compact and not bulky. The dimensions of the substrate 1 and the conductive patterns 2 to 6 to obtain the frequency characteristics shown in FIG. 4 are as follows.

(a) Dielectric substrate: thickness 0.4 mm, length and width dimensions 14 x 9 mm,
Dielectric law 80 (b) Conductive pattern: l1 = 7 (mm), (each pattern and dimensions are common l2 = 1.5 (mm), l3 = 7 (mm), l4 = 3.5 (mm), l5 = 6 (mm) , l6 = 3.5 (mm), l7 = 1.1 (mm), C1 = 11 (PF), C2 = 53 (PF), L1 = L2 = 2.77 (nH), L5 = 2 (nH), (c) Coil pattern Distance d between 2c and 4c = 1mm
Although the width W of the coil patterns 2c to 5c is not related to the inductance value, the larger the width, the smaller the resistance, which is preferable as the Q becomes higher. In this embodiment, W=1.5 mm.

Although the first embodiment shows an example in which two resonators Q1 and Q2 are provided on one dielectric substrate and the resonators are coupled in two stages, the present invention is not limited to two-stage coupling. , it can be applied to a combination of 3 or 4 or more stages. Furthermore, the method of magnetic coupling is also arbitrary. FIG. 6 shows a case of three-stage coupling as an example. That is, in this embodiment, three U-shaped conductive patterns are formed on both surfaces 1a and 1b of one dielectric substrate 1 (3, 4, 10) (3, 5,
11) The conductive patterns 2 and 4 on the front surface 1a are connected via the conductive coil pattern 6, which is formed at intervals d1 and d2. In the figure, 12, 13
14 and 15 are lead terminals for grounding a part of the intermediate stage resonator Q2, respectively, and lead terminals 14 and 15 for input/output, respectively. In this way, the resonator is
In the stage-coupled filter, the interval d between the resonators Q1, Q2, and Q3 is the same as in the two-stage coupled filter.
By changing 1 and d2, the passband width can be widened or narrowed.

FIG. 7 shows an equivalent circuit of the bandpass filter of this embodiment, and FIG. 8 shows an example of frequency characteristics. In the figure, L12 and L13 are the inductances of the lead terminals 12 and 13.

From FIG. 8, it can be seen that the bandpass filter of this embodiment has poles P1 and P very close to both sides of the center frequency of 400MHz.
2, and it can be seen that it has a steep rise characteristic. At the same time, a pole P3 is generated on the higher frequency side than the pole P2, but this pole P3 does not affect the steep rise characteristics.

In the embodiment shown in FIG. 6, by moving the connection position of the lead terminal 12 provided in the intermediate stage resonator Q2 as shown by arrows A and B in the figure, the frequencies of the poles P1 and P2 can be adjusted to the center frequency. or bring it closer to
You can make them go away.

FIG. 9 shows the embodiment of FIG. 3 of the present invention. This is similar to the second embodiment described above, in which the resonators are coupled in three stages, and the conductive patterns 2 and 4 on the surface 1a side of the dielectric substrate are connected via the conductive coil pattern 6. Although a detailed explanation of each structure will be omitted, the lead terminal positions are different from those in the second embodiment. In the figure, 16 and 17 are input/output lead terminals, and 18 and 19 are ground terminals, respectively. Similarly to the first and second embodiments, in the bandpass filter of the third embodiment, the passband width can be adjusted wide or narrow by changing the spacing between the resonators Q1, Q2, and Q3.

FIG. 10 shows an equivalent circuit diagram of the bandpass filter of the third embodiment. In the figure, L16 and L17 are inductances of lead terminals 16 and 17, respectively. FIG. 11 shows the frequency characteristics of the third embodiment. From the figure, it can be seen that the bandpass filter of this embodiment has poles P1 and P2 on both sides of the center frequency of 404 MHz, and has steep characteristics. Recognize.

In each of the above embodiments, a plurality of resonators are formed on one dielectric substrate, but it is not necessarily necessary to form them on one substrate, and it is possible to use a plurality of substrates. It's okay.

Furthermore, if slits are provided between the resonators in each of the above embodiments, spurious signals can be prevented, which is even more convenient.

Effects of the Invention Since the bandpass filter according to the present invention is configured as described above, it has the following effects. That is, as shown in the above embodiment, by connecting in multiple stages low-volume resonators each having a predetermined conductive pattern formed on both surfaces of a dielectric substrate, the entire filter can be constructed with low bulk. Furthermore, if all the resonators are formed on one substrate and the substrate is shared, it is possible to obtain a smaller and more compact configuration.

Since at least one of the multiple resonators coupled in multiple stages is connected by a coil, a pole can be created very close to the passband, and steep frequency characteristics can be obtained.

[Brief explanation of the drawing]

Fig. 1 shows a bandpass filter as a first embodiment of the present invention, Fig. A is a front view, Fig. B is a side view, Fig. C is a rear view, and Fig. 2 shows the configuration of the filter of Fig. 1. Fig. 3 is an equivalent circuit diagram of the filter shown in Fig. 1, Fig. 4 is a diagram showing the frequency characteristics of the filter, and Fig. 5 shows an example when no coil is connected. Frequency characteristic diagram, Fig. 6A is a front view of a bandpass filter as a second embodiment of the present invention, Fig. 6B is a side view, Fig. C is a rear view, and Fig. 7 is an equivalent circuit of the filter of Fig. 6. 8 is a diagram showing the frequency characteristics of the filter in FIG. 6, FIG. 9 A is a front view of a bandpass filter as a third embodiment of the present invention, FIG. 9 is a side view, and FIG. C is a rear view. figure,
Figure 10 is an equivalent circuit diagram of the filter in Figure 9,
FIG. 1 is a diagram showing the frequency characteristics of the filter. C1, C3, C5...first capacitor, C2,
C4, C6...Second capacitor, L1, L2, L
3, L4, L5, L6, L7, L8...Coil,
Q1, Q2, Q3...resonator.

Claims (1)

[Claims] 1 A plurality of resonators each having an equivalent circuit in which a second capacitor is connected in parallel to an LC series circuit in which coils are connected in series on both sides of a first capacitor, and the coil of each resonator is connected to the other resonator. A bandpass filter characterized in that it is connected in multiple stages by magnetically coupling with a coil, and at least one resonator is connected by the coil.