JPH0434287B2 - - 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 and exceeding the UHF band.

BACKGROUND OF THE INVENTION Conventionally, bandpass filters used in the above-mentioned frequency range include ones in which dielectric coaxial resonators are connected in multiple stages. However, in the case of such a filter, since the dielectric coaxial resonator is cylindrical, a filter in which the dielectric coaxial resonator is arranged in multiple stages is bulky.

Therefore, in order to solve these problems, the applicant of the present invention proposed the following small-sized bandpass filter (Japanese Patent Application No. 1973-97315).

As shown in FIG. 11, this bandpass filter includes a front surface 51a and a back surface 51b of a dielectric substrate 51.
Conductive patterns 52 to 55 are formed thereon. Each conductive pattern 52 to 55 includes two capacitor electrode patterns 52a, 52b, 53a, 53
b, 54a, 54b, 55a, 55b and one coil pattern 52c, 53c, 54c, 55c. Capacitor electrode pattern 52a
and 53a, 52b and 53b, 54a and 55a, 5
4b and 55b are opposed to each other with a dielectric substrate 51 in between, and capacitors C51, C52, C53, C
54 is formed. In addition, the coil pattern 52
c, 53c, 54c, and 55c form coils L51, L52, L53, and L54 in terms of high frequency.

Problems to be Solved by the Invention By the way, if this bandpass filter is constructed using a dielectric substrate 51 with a dielectric constant of 80 and a thickness of 400 μm, for example, if the frequency characteristic is a center frequency of 644 MHz, the capacitor C51, C52 is 11pF and 53pF respectively, coils L51 and L52 are both
It takes a value of 2.77nH. To get these values,
Each conductive pattern 52 to 55 has l51=7 mm, l52=
The required sizes are 1.5 mm, l53 = 7 mm, l54 = 3.5 mm, and l55 = 6 mm. Therefore, two resonators (R
The vertical and horizontal dimensions of the entire bandpass filter inductively coupled with 40, R50) are 14 x 9 mm,
Compared to a filter in which dielectric coaxial resonators are connected in multiple stages, the size can be considerably reduced.

However, in recent years, there has been a strong demand for electronic devices to be smaller and lighter in weight, and the bandpass filters described above still pose an obstacle to making the device smaller and lighter.

SUMMARY OF THE INVENTION In view of the above problems, it is an object of the present invention to provide a small and lightweight bandpass filter.

Means for Solving the Problems The present invention for achieving the above object includes a substrate,
Two coil patterns formed on the surface of the substrate,
The four capacitor electrode patterns extending from both ends of both coil patterns and formed on the substrate surface face both the capacitor electrode pattern extending from one coil pattern and the capacitor electrode pattern extending from the other coil pattern. The structure is characterized in that a plurality of resonators each formed of two capacitor electrode patterns formed inside a substrate are connected in multiple stages by coupling them together.

Embodiment FIG. 1 shows the configuration of a bandpass filter as an embodiment of the present invention, in which FIG. 1 is a front view and FIG. In the figure, 1 is for example
A dielectric substrate made of FRDR material etc., whose surface 1a
, there are four coil patterns 2a, 2b,
2c, 2d are formed, and each coil pattern 2a,
At both ends of 2b, 2c, 2d, capacitor electrode patterns 3a, 4a, 3b, 4b, 3c, 4c, 3
d, 4d are formed. These coil patterns 2a, 2b, 2c, 2d and capacitor electrode patterns 3a, 4a, 3b, 4b, 3c, 4c,
3d and 4d are formed by screen printing silver paste, for example. Inside 1b of dielectric substrate 1, the capacitor electrode patterns 3a and 3b, 4a and 4b, 3c and 3d, 4c and 4 are arranged.
capacitor electrode patterns 5ab, 6ab, 5cd for configuring a capacitor, respectively facing d and
6cd is formed at a distance d from the surface 1a. These capacitor electrode patterns 5ab, 6ab,
The 5cd and 6cd can be formed by a lamination method used for forming internal electrodes of multilayer capacitors. The capacitor electrode patterns 3a, 3
b and capacitor electrode patterns 5ab, 4a, 4b
and 6ab, 3c, 3d, and 5cd, and 4c, 4d, and 6cd are formed in opposing states, respectively, as described above, and have a capacitance determined by the dielectric constant ε of the dielectric substrate 1, the distance d, and the opposing area of the capacitor. capacitors C ₁₁ , C ₁₂ , C ₁₃ , C ₁₄ , C ₁₅ , C ₁₆ , C ₁₇ , C ₁₈ are formed, among which capacitors C ₁₁ and C ₁₃ are connected in series to form capacitor C1, and similarly To,
C2 for C ₁₂ , C ₁₄ , C3 for C ₁₅ , C ₁₇ , C for C ₁₆ , C ₁₈
4 are configured. Also, coil pattern 2
a, 2b, 2c, and 2d form a coil at high frequency, so their inductances are L1, L2,
Let them be L3 and L4. 11 and 13 are input/output lead terminals, and 12 and 14 are grounding terminals.

In the above configuration, as shown in Figure 2, another capacitor C2 (C4) is connected to an LC series circuit in which two coils L1 and L2 (L3, L4) are connected in series on both sides of one capacitor C1 (C3). Resonator R1 (R2) represented by an equivalent circuit connected in parallel
As shown in FIG. 1, they are inductively coupled by two coil patterns 2b and 2c that are adjacent to each other at a distance t, so that a bandpass filter having an equivalent circuit as shown in FIG. 3 is constructed. In the figure, M is 2
Mutual inductance, L12, L14, representing the degree of magnetic coupling between the two coil patterns 2b and 2c
is the inductance of the lead wires 12 and 14. 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 represents the coupling capacity. By changing the interval t between the two coil patterns 2b and 2c, the degree of coupling (including both magnetic and capacitive coupling) can be changed, thereby adjusting the passband width of the bandpass filter. .

FIG. 4 shows the frequency characteristics of the bandpass filter having the above configuration. It has steep characteristics with a center frequency of 644MHz and a bandwidth of 20MHz. The dimensions of the dielectric substrate 1 and the coil pattern and capacitor electrode pattern constituting one resonator R1 to obtain such frequency characteristics are as follows.

(a) Dielectric substrate: dielectric constant 80, thickness 400μm, distance d
= 20 μm, vertical and horizontal dimensions 11 x 7.5 mm, (b) Capacitor electrode patterns 3a, 4a, 3b,
4b and capacitor electrode patterns 5ab, 6ab
Dimensions: l1 = l2 = l3 = l4 = 2 (mm), l5 = 0.26 (mm), l6 = 0.61 (mm), l7 = l8 = 6.0 (mm).

with this, C1=11(pF), C2=53(pF), L1=L2=2.77(nH), becomes.

(c) Spacing t between coil patterns 2b and 2c = 1 mm.

Note that the width W of the coil pattern is not related to the inductance value, but the larger the width, the smaller the resistance, and therefore the higher the Q, which is preferable.
In this embodiment, W=1.0 mm.

Moreover, in this embodiment, two resonators R1, R
Coupling between the two is done by coil patterns 2b and 2c, and in combination, at least one place between the resonators is made of a member (for example, a metal piece) that equivalently constitutes a coil, or a member that equivalently constitutes a coil. Connection can also be made using a member (for example, a capacitor with leads) constituting a series circuit of capacitors. By doing so, a pole can be created in the filter characteristic, thereby making it possible to obtain a steeper filter characteristic.

Next, FIG. 5 shows another embodiment of the present invention. This embodiment shows an example in which three resonators R of one unit in the previous embodiment are used and coupled in multiple stages. Here, each resonator is R1, R2,
R3, resonator R3 is coil pattern 2
e, 2f, capacitor electrode patterns 3e, 4f, and capacitor electrode patterns 5ef, 6ef, and since the resonators R1, R2 and R2, R3 are arranged at intervals t1, t2, the coil patterns 2b, 2c, 2d, and 2e to form a bandpass filter having an equivalent circuit as shown in FIG. In the figure, L12, L1
4 and L15 are coil components of the terminals 12, 14, and 15.

An example of the frequency characteristics of the filter of this embodiment is shown in FIG. As in the previous embodiment, the intervals t1, t2
The width of the passband can be adjusted by changing . Also, at least one of each resonator spacing
By connecting the points with a coil component or a series circuit of a coil and a capacitor, it is also possible to create poles in the filter characteristics.

FIG. 8 shows still another embodiment of the present invention. Three resonators R1, R2, R3 on one dielectric substrate 1
This is the same as the second embodiment in that a bandpass filter is formed by coupling these in multiple stages, but in this embodiment, the coupling between each resonator R1, R2, and R3 is mainly performed by capacitive coupling. This embodiment differs from the previous embodiment in that the following points were followed. That is, as shown in the figure, adjacent capacitor electrode patterns 3b, 3c, and 3d, 3e are extended in the relative direction 2 at the joint portion.
1, 22 and 23, 24, and a capacitor electrode pattern 2 is provided inside the substrate 1b so as to face the extensions 21, 22, 23, 24.
5, 26, and these extension portions 21, 22, the capacitor electrode pattern 25 and the extension portion 23,
24 and the capacitor electrode pattern 26, each resonator R1, R
2, R3 is bonded. However, the extension part 2
1, 22, 23, and 24 also have a coil component in terms of high frequency, so it is difficult to say that the coupling is pure capacitive coupling, and it can be said that coupling is performed even if capacitive coupling is the main component.

An equivalent circuit of a bandpass filter having this configuration is shown in FIG. 9, and its frequency characteristics are shown in FIG. 10.
It can be seen that this example also has good spurious characteristics. Note that in this embodiment as well, as in each of the above embodiments, poles can be created by connecting the resonators with a coil component or a series circuit of a coil component and a capacitor.

In each of the above embodiments, all the resonators are provided on one dielectric substrate 1, but each resonator is formed on one dielectric substrate and the required number of resonators are connected. Even if you do this, the same effect and effect can be obtained.

Effects of the Invention As described above, the bandpass filter of the present invention has the following features:
Since one of the capacitor electrode patterns constituting the capacitor is buried inside the substrate, the distance between the capacitor electrode pattern formed on the surface of the substrate and the capacitor electrode pattern formed inside the substrate can be easily narrowed. If the capacitor capacitance is the same, the area occupied by the capacitor electrode pattern can be reduced, so by reducing the capacitance of one resonator, a bandpass filter in which the resonators are coupled in multiple stages can be made smaller. Electronic equipment equipped with a pass filter can be configured to be small and lightweight.

In addition, since the resonator having the above-mentioned equivalent circuit has a high Q, the filter of the present invention, which is constructed by combining the resonators in multiple stages, also has the effect of having a high Q and good selectivity.

[Brief explanation of drawings]

Figure 1 shows a bandpass filter as an embodiment of the present invention, where Figure A is a front view and Figure B is an X in Figure A.
-X-ray sectional view, Figure 2 is an equivalent circuit diagram of the resonator constituting the filter in Figure 1, Figure 3 is an equivalent circuit diagram of the filter in Figure 1, Figure 4 is the frequency characteristic of the filter, Figure 5 A is a front view of a bandpass filter as another embodiment of the present invention, and Figure B is a Y-Y line in Figure A.
6 is an equivalent circuit diagram of the filter in FIG. 5, FIG. 7 is a diagram showing the frequency characteristics of the filter in FIG. 5, and FIG. 8A is a band diagram as yet another embodiment of the present invention. Front view of pass filter, figure B is Z in figure A
-Z line sectional view, Figure 9 is an equivalent circuit diagram of the filter in Figure 8, Figure 10 is a diagram showing the frequency characteristics of the filter in Figure 8, Figure 11A is a front view of the conventional filter. Figure B is a side view, and figure C is a rear view. 1...Dielectric substrate, 2a, 2b, 2c, 2d,
2e, 2f...Coil pattern, 3a, 4a, 3
b, 4b, 3c, 4c, 3d, 4d, 3e, 4
e, 3f, 4f...Capacitor electrode pattern, 5
ab, 6ab, 5cd, 6cd, 5ef, 6ef...Capacitor electrode pattern, C1, C2, C3, C4, C
5, C6, C7, C8... Capacitor, L1, L
2, L3, L4, L5, L6...Coil, R1,
R2, R3...Resonator.

Claims (1)

[Claims] 1. A substrate, two coil patterns formed on the substrate surface, four capacitor electrode patterns formed on the substrate surface extending from both ends of both coil patterns, and a capacitor electrode pattern extending from one coil pattern. A multi-stage connection is achieved by combining a plurality of resonators each consisting of two capacitor electrode patterns formed inside the substrate so as to face both capacitor electrode patterns extending from the other coil pattern. Features a bandpass filter.