JPH0481889B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a bandpass filter that is suitably used in a frequency range including the UHF band and beyond. Prior art 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. was 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 capacitively 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 bandpass filter of the present invention has a capacitor electrode pattern formed at two opposing locations on both the front and back surfaces of a dielectric substrate, and a gap between the electrode pattern and the capacitor electrode pattern. First and second capacitors are formed with the dielectric substrate, and a coil pattern is formed between the two capacitor electrodes on the front surface of the substrate and between the two capacitor electrodes on the back surface of the substrate, and and a capacitor of
The capacitor formed by the capacitor pattern connected in series on both sides forms an LC series circuit, and the second capacitor is connected in parallel to the LC series circuit to form a plurality of resonators. At least one capacitive coupling between the resonators
The gist is that the points were connected by coils. EXAMPLES Hereinafter, the present invention will be explained in detail based on illustrated examples. FIG. 1 shows the configuration of a bandpass filter as an embodiment of the present invention, in which FIG. A is a front view, FIG. B is a side view, and FIG. C is a rear view. In the figure, 1 is for example
A dielectric substrate made of FRDR material etc., whose surface 1a
U-shaped conductive patterns 2 to 5 are formed on the back surface 1b, respectively, and the conductive patterns 2 and 4 on the front surface 1a are connected via a conductive pattern 6 formed in a substantially concave shape. There is. The conductive patterns 2 to 5 are two capacitor electrode patterns 2a, 2b, 3a, 3b, 4a, 4b, 5a, 5.
b and one coil pattern 2c, 3c, 4c, 5
It consists of c. Of these, the capacitor electrode patterns 2a and 3a, 2b and 3b, 4a and 5a, and 4b and 5b are opposed to each other with the dielectric substrate 1 in between, and the dielectric constant and thickness of the substrate 1 and the opposing area of the capacitor electrode patterns are The capacitor capacity C determined accordingly
1, C2, C3, and C4. On the other hand, the coil patterns 2c, 3c, 4c, and 5c are formed using high frequency at positions that do not face each other, and each coil pattern has an inductance of L1, L2, L3, and L4.
have. Further, among the capacitor electrode patterns 2 to 5, the capacitor electrode patterns 2a and 4a on the substrate surface 1a side are formed with extending portions 2d and 4d in a direction approaching each other.
A conductive pattern 7 is formed on the back side of the substrate 1b so as to have a capacitor Cs of a predetermined capacity between capacitors b and 4b. 8, 9 are input/output lead terminals, 10,
11 indicates a grounding terminal. The conductive patterns 2 and 3 (or the conductive patterns 4 and 5) are represented by an equivalent circuit as shown in FIG. 2, and constitute a resonator Q. That is, the resonator Q is connected to the first capacitor C1 (C3)
A second capacitor C2 is connected to the LC series circuit formed by connecting coils L1 and L2 (L3, L4) on both sides of the
(C4) are connected in parallel. FIG. 3 shows the bandpass filter shown in FIG. 1 in terms of a value circuit. That is, in the bandpass filter, two resonators Q1 and Q2 having the equivalent circuit shown in FIG. 2 are capacitively coupled by the capacitor Cs, and the resonators Q1 and Q2 are connected by a connecting coil L5. It becomes. In the figure, L10,L
11 is an inductance that the lead terminals 10 and 11 have. In this bandpass filter, the degree of capacitive coupling can be changed by changing the capacitance of the capacitor Cs, and therefore the passband width can be adjusted thereby. 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. The center frequency of both is 504MHz. As is clear from the comparison of these two figures, the resonators Q1 and Q2 are connected to the connected coil L5.
It was confirmed that poles P and P are formed on both sides of the center frequency by connecting to the coil L5, and steeper characteristics can be obtained than in the case where the connecting coil L5 is not provided. Moreover, as described above, since the bandpass filter is made of a conductive pattern having the equivalent circuit shown in FIG. 3, it is compact without being bulky, and requires no effort during manufacture.
The dimensions of the substrate 1 and the conductive patterns 2 to 7 to obtain the frequency characteristics shown in FIG. 4 are as follows. (a) Dielectric substrate: thickness 0.4 mm, length and width dimensions 12 x 14 mm,
Dielectric constant 80 (b) Conductive pattern (same for each pattern): Capacitor electrode pattern 2a, 2b l1 = 6.5 (mm) l2 = 1.5 (mm) l3 = 6.5 (mm) l4 = 3.5 (mm) C1 = 20 (PF ) C2 = 44 (PF) Coil pattern 2c, 3c l5 = 5.6 (mm) L1 = L2 = 2.49 (nH) Capacitor electrode pattern 2d, 4d, 7 l6 = l7 = 1.5 (mm) l8 = 0.5 (mm) l9 = 1.3 (mm) Cs = 1.0 (PF) Coil pattern 6 l10 = l11 = 1.5 (mm) l12 = l13 = l14 = 1.0 (mm) l15 = 3.5 (mm) L5 = 3.0 (nH) In addition, the width of the coil pattern W 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=1.5 (mm). FIG. 6 shows another embodiment (second embodiment) in which resonators having the equivalent circuit shown in FIG. 2 are coupled in three stages. In this embodiment, three U-shaped conductive patterns 2, 4, 12 and 3, 5, 1 are used.
3 are formed on both the front and back surfaces 1a and 1b of one dielectric substrate 1 at predetermined intervals, and
The conductive patterns 2 and 12 on the a side are connected via the conductive pattern 6. Furthermore, the conductive patterns 2, 4, and 12 are partially extended to form extension portions 2.
d, 4d, 12d, and 12e, and conductive patterns 17 and 14 are formed on the back surface 1b of the substrate, partially facing the extended portions 2d, 4d, 12d, and 12e. FIG. 7 shows an equivalent circuit representation of the bandpass filter shown in FIG. 6. That is, the conductive pattern 2 formed on both the front and back surfaces of the substrate 1
and 3, 4 and 5, 12 and 13 make resonators Q1, Q2,
Configuring Q3, extending portions 2d, 4d, 12d, 12
e and conductive patterns 7 and 14 constitute coupling capacitors Cs ₁ and Cs ₂ , and also form resonators Q1 and Q3.
are connected to each other by a connecting coil L5. In the diagram, C
5, C6, L6, and L7 are capacitors and coils forming the resonator Q3, and L15 is a coil component of the lead terminal 15. FIG. 8 shows the frequency characteristics of the bandpass filter, and shows the case where the coil L5 is not provided. Both center frequencies are 400MHz
It is. As is clear from this diagram, the connected coil L
5, two poles P and P were formed at both ends of the center frequency, and it was confirmed that steep characteristics were obtained. The dimensions of each part of the conductive pattern 6 of the bandpass filter for obtaining such frequency characteristics are as follows. l16 = 1.0 (mm) l17 = 3.5 (mm) L5 = 2.0 (nH) Figure 10 is yet another example (third example)
Similar to the second embodiment, three stages of resonators having the equivalent circuit shown in FIG. 16, and a similar protrusion 17 is also provided on the conductive pattern 5 on the back side 1b so as to face the protrusion 16, and the protrusion 16,
17 is provided with a through hole 18 for electrically connecting it. Note that the through hole 18 is filled with a conductive paste such as silver. FIG. 11 shows an equivalent circuit of the bandpass filter shown in FIG. 10. The protrusions 16 and 17 also form a coil L5. FIG. 12 shows its frequency characteristics. As is clear from this figure, the center frequency
It can be seen that poles P and P are formed on both sides of 405 Hz, resulting in steep frequency characteristics. The dimensions of each part of the conductive patterns 16 and 17 are shown below. l18 = 1.0 (mm) l19 = 2.5 (mm) Through hole 18 = 0.5 (mmφ) L5 = 2.0 (nH) It was confirmed that by connecting the resonators with the coil in this way, steep characteristics were obtained. It was done. Further, since the bandpass filter according to the present invention has a resonator formed of a conductive pattern, it is compact and does not become bulky even when connected in three or more stages. It should be noted that the present invention is not limited to the above-mentioned embodiments, and it goes without saying that the design can be changed within the scope of the invention. For example, there is no limit to the number of resonator stages, and three resonator stages can be placed on one substrate.
It is also possible to connect more than one resonator in multiple stages. Furthermore, the lead terminals can be led out at any point, and the bandwidth can be changed by changing the spacing between the resonators. In addition, in the embodiments shown in FIGS. 2 and 3, the frequency of the pole P is
By moving 5 in the direction of arrow A as shown in FIGS. 6 and 10, a bandpass filter can be selected arbitrarily and has filter characteristics suitable for the purpose. In addition, the conductive pattern can be easily formed by screen printing silver paste, etc., and the connection between the resonators can be made at least one connection point, but it is possible to set two or more connection points. Needless to say, it's a good thing. Effects of the Invention As detailed above, the bandpass filter of the present invention has a resonance circuit 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. In this configuration, a plurality of resonators are capacitively coupled, and at least one point between the resonators is connected by a coil, so that poles are formed on both sides of the center frequency, and steep filter characteristics can be obtained. Further, since the capacitor electrode pattern and the coil pattern are formed with the same pattern on both the front and back surfaces of the dielectric substrate, a printing mask with the same pattern can be used during manufacturing, and manufacturing can be performed at low cost. In addition, unlike a dielectric coaxial resonator, the capacitance of the capacitor, which is a component of the resonator, can be changed and adjusted independently, making impedance matching easier.

[Brief explanation of drawings]

Fig. 1 shows a bandpass filter as an embodiment (first embodiment) of the present invention, in which Fig. A is a front view, Fig. B is a side view, Fig. C is a back view, and Fig. 2 is a
Fig. 3 is an equivalent circuit diagram of the resonator constituting the filter in Fig. 1, Fig. 4 is a frequency characteristic diagram of the bandpass filter in the first embodiment, Fig. 5 is a coil 6A is a front view of the bandpass filter showing the second embodiment, FIG. 6B is a side view, FIG. Its equivalent circuit diagram, FIG. 8 is a frequency characteristic diagram of the bandpass filter in the second embodiment, FIG. 9 is a frequency characteristic diagram showing an example when the coil is not connected, and FIG.
Figure 0 A is a front view of the bandpass filter showing the third embodiment, Figure B is a side view, Figure C is a rear view, and Figure 11 is a front view of the bandpass filter showing the third embodiment.
The figure is an equivalent circuit diagram of the filter, and Figure 12 is the third
FIG. 3 is a frequency characteristic diagram in an example of FIG. 1...Dielectric substrate, 2a, 2b, 3a, 3b,
4a, 4b, 5a, 5b...capacitor electrode pattern, 2c, 3c, 4c, 5c...coil pattern, C1, C3, C5...first capacitor,
C2, C4, C6...Second capacitor, L1, L
2, L3, L4, L5, L6, L7...Coil,
Q1, Q2, Q3...resonator.

Claims (1)

[Claims] 1 Capacitor electrode patterns are formed at two opposite locations on the front and back surfaces of the dielectric substrate, and the electrode patterns and the dielectric substrate therebetween form first and second capacitors, while the surface of the substrate A coil pattern is formed between two capacitor electrodes on the back side and between two capacitor electrodes on the back side, and the capacitor is configured by the first capacitor and the capacitor pattern connected in series on both sides of the first capacitor. form an LC series circuit with
A bandpass filter characterized in that a plurality of resonators each having the second capacitor connected in parallel to the LC series circuit are capacitively coupled, and at least one point between the resonators is connected by a coil. .