JPH0481891B2 - - 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.

As a related invention, the applicant has proposed a device 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. 1983-97316.

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 it is an object of the present invention 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 provides a structure in which a capacitor electrode pattern is formed at two opposing locations on both the front and back surfaces of a dielectric substrate, and a capacitor electrode pattern is formed between the electrode pattern and the dielectric substrate in between. forming first and second capacitors, on the other hand, a coil pattern is formed between two capacitor electrodes on the front surface of the substrate and between two capacitor electrodes on the back surface, and the first capacitor and A plurality of resonators are formed by forming an LC series circuit with the coil constituted by the coil pattern connected in series on both sides, and the second capacitor being connected in parallel to this LC series circuit. The present invention is characterized in that the coil of each resonator is magnetically coupled to the coil of another resonator for multi-stage connection, and that at least one resonator is connected by a coil.

Function As described above, by forming a predetermined conductive pattern on both sides of a dielectric substrate, a low-volume resonator can be created, and by connecting these resonators in multiple stages, the entire bandpass filter can be constructed with a low volume. Moreover, since the capacitor electrode pattern and the coil pattern can be formed in the same pattern, the filter can be manufactured easily and at low cost. Further, by connecting a plurality of multi-stage coupled resonators at least at one point with a coil, poles are generated near both sides of the pass band due to the characteristics of the filter. When poles occur on both sides of the passband in this way, the rise in frequency characteristics 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, reference numeral 1 denotes a dielectric substrate made of FRDR material or the like with a dielectric constant of 80 and a thickness of 0.4 mm, and conductive patterns 2, 3, 4, and 5 having a U-shape are formed on the front surface 1a and the back surface 1b, respectively.
is formed by screen printing silver paste, for example, 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 coil patterns 2c, 3c, 4c, 5c and 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, are opposed to each other via the dielectric substrate 1, and have capacitances determined by the dielectric constant and thickness of the substrate, and the facing area of the electrodes of the capacitors C1, C2,
It forms C3 and 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 without being 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,
Relative permittivity 80 (b) Conductive pattern: l1 = 7 (mm), dimensions are the same as each pattern) l2 = 1.5 (mm), dimensions are common) 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) Distance d between coil patterns 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 (2, 4, 10) (3, 5,
11) The conductive patterns 2 and 4 are formed at intervals d1 and d2, and are connected via the conductive coil pattern 6 on the surface 1a side. In the figure, 12,1
3 is a lead terminal for grounding a part of the intermediate stage resonator Q2, and 14 and 15 are lead terminals for input/output, respectively. In this way, the resonator is
In the stage-coupled filter as well, 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 a third embodiment of the 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 lead terminals for input and output, respectively, and 18 and 19 are ground terminals for grounding, respectively. In the bandpass filter of the third embodiment, as in the first and second embodiments, the passband width can be widened or narrowed by changing the spacing between the resonance groups 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, since the filter is constructed 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. Moreover, if all the resonators are formed on one dielectric substrate so that the substrate can be shared, an even smaller and more compact structure can be obtained.

Since the resonant group with the above equivalent circuit has a high Q,
The filter of the present invention, which is constructed by combining these in multiple stages, also has a high Q and good selectivity.

Since the capacitor electrode pattern and the coil pattern can be formed in the same pattern on both the front and back sides of the dielectric substrate, the same printing mask can be used by using technology such as screen printing, making it possible to easily and inexpensively create a bandpass filter with simple work. Can be formed.

Since at least one of the multiple resonators coupled in multiple stages is connected by a coil, a pole can be created in the immediate vicinity of 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 constitutes the filter of Fig. 1. Figure 3 is an equivalent circuit diagram of the resonator, Figure 3 is an equivalent circuit diagram of the filter in Figure 1, Figure 4 is a diagram showing the frequency characteristics of the filter, Figure 5 is a frequency diagram showing an example of the case where no coil is connected. Characteristic diagrams, 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. 6C is a rear view, Fig. 7
6 is an equivalent circuit diagram of the filter of FIG. 6, FIG. 8 is a diagram showing the frequency characteristics of the filter of FIG. 6, and FIG. 9A is a front view of a bandpass filter as a third embodiment of the present invention. Figure B is a side view, Figure C is a rear view, Figure 10 is an equivalent circuit diagram of the filter in Figure 9, and Figure 11 is an equivalent circuit diagram of the filter in Figure 9.
The figure shows the frequency characteristics of the filter. C1, C3, C5...first capacitor, C
2, C4, C6...Second capacitor, L1, L
2, L3, L4, L5, L7, L8...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 between them form first and second capacitors, while the surface of the substrate A coil pattern is formed between two capacitor electrodes located on the back surface of the first capacitor and between two capacitor electrodes located on the back surface thereof, and the coil is constituted by the first capacitor and the coil pattern connected in series on both sides of the first capacitor. by forming a LC series circuit with a plurality of resonators in which the second capacitor is connected in parallel to the LC series circuit, and magnetically coupling the coil of each resonator with the coil of another resonator. A bandpass filter characterized in that it is connected in multiple stages and at least one resonator is connected by a coil.