JPH0542174B2 - - 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.

BACKGROUND TECHNIQUES AND THEIR PROBLEMS Conventionally, bandpass filters used in the above frequency range are generally composed of dielectric coaxial resonators connected in multiple stages.

However, in the case of such a filter, since the dielectric coaxial resonator has a cylindrical shape, a filter in which the dielectric coaxial resonator is arranged in multiple stages has a drawback that it is bulky.

SUMMARY OF THE INVENTION In view of the above-mentioned problems, an object of the present invention is to provide a compact bandpass filter that can be easily constructed on a single substrate.

Means for Solving the Problems In order to achieve the above object, the bandpass filter of the present invention has capacitor electrode patterns formed at two opposing locations on the front and back surfaces of a dielectric substrate. 1st and 2nd with the board
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 is connected in series with the first capacitor on both sides thereof. A plurality of resonators are formed by forming an LC series circuit with a coil constituted by the above-mentioned coil pattern, and the second capacitor is connected in parallel to this LC series circuit. The resonators are connected in multiple stages by magnetically coupling them with the coils of other resonators, and a slit is formed in at least one location between the resonators of the dielectric substrate.

The above-mentioned resonator has a unique equivalent circuit, and is clearly distinguished from the equivalent circuit of a conventional dielectric coaxial resonator (parallel circuit of a coil and a capacitor, etc.).

In the present invention, since a bandpass filter is constructed by magnetically coupling resonators having such unique equivalent circuits, many problems in conventional filters can be solved.

Furthermore, since the slit is formed between the resonators of the dielectric substrate, it is possible to obtain excellent frequency characteristics with suppressed spurious generation.

Embodiment FIG. 1 shows the configuration of a bandpass filter as an 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. For example, 1 in the figure is
A dielectric substrate made of FRDR material etc., whose surface 1a
U-shaped conductive patterns 2, 3, 4, and 5 are formed on the and rear surface 1b, respectively, by screen printing silver paste, for example. Each conductive pattern 2 to 5 has two capacitor electrode patterns 2
a, 2b, 3a, 3b, 4a, 4b, 5a, 5b
and one coil pattern 2c, 3c, 4c, 5c
It consists of. Among these, capacitor electrode patterns 2a and 3a, 2b and 3b, 4a and 5a, 4
b and 5b are opposed to each other via the dielectric substrate 1, and are capacitors C1 and C whose capacitance is determined by the dielectric constant and thickness of the substrate and the opposing areas of the electrodes of the capacitor.
2, 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 2
c, 3c, 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. 11,
13 is a lead terminal for input/output. 12,14
is a grounding terminal.

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
The resonators Q1 and Q2 are formed by an equivalent circuit in which 4 connected in parallel. Since the resonators Q1 and Q2 having this equivalent circuit are provided with the two coil patterns 2c and 4c close to each other with a distance d as shown in FIG. 4c causes magnetic coupling and constitutes a bandpass filter having an equivalent circuit as shown in FIG. In the figure, M indicates two coil patterns 2c,
Mutual inductance L12 and L14 representing the degree of magnetic coupling between the lead wires 12 and 14 are the inductances of the lead wires 12 and 14, respectively.

A slit 15 is formed between the resonator Q1 and the resonator Q2 of the dielectric substrate 1, and prevents capacitive coupling between the coil pattern 2c and the coil pattern 4c. Since there is no capacitive coupling between the two, this bandpass filter has excellent frequency characteristics with suppressed spurious generation.

In addition, coil pattern 2c and coil pattern 4c
By changing the distance d between the two, the degree of magnetic coupling between the two can be changed, and thereby the passband width of the bandpass filter can be adjusted. In this case, narrowing the interval d widens the bandwidth, and widening the interval d narrows the bandwidth.

FIG. 4 shows the frequency characteristics of the bandpass filter having the above configuration. It has steep characteristics with a center frequency of 644MH and a bandwidth of 20MPH. What should be noted about this frequency characteristic is that the generation of spurious is suppressed on the higher frequency side than the passband. The coil pattern 2c and the coil pattern 4 are separated by the slit 15.
This effect is due to the prevention of capacitive coupling with c. FIG. 5 shows the frequency characteristics when the slit 15 is not formed.
As can be seen from a comparison with the figure (outside the present invention), by forming the slits 15, the bandpass filter of the present invention is able to suppress the generation of spurious in the range of 1 GHz to 1.8 GHz.

The dimensions of the substrate 1 and the conductive patterns 2 to 5 to obtain the frequency characteristics shown in FIG. 4 are as follows.

(a) Dielectric substrate 1: Thickness 0.4 mm, vertical and horizontal dimensions 14 x 9
mm, dielectric constant 80 (b) Conductive pattern: l1 = 7 (mm), (each pattern and dimensions l2 = 1.5 (mm), dimensions are the same) l3 = 7 (mm), l4 = 3.5 (mm), l5 = 6 (mm), C1 = 11 (PF), C2 = 53 (PF) L1 = L2 = 2.77 (nH) (c) Distance between coil patterns 2c and 4c d = 1 mm Vertical and horizontal dimensions of slit 15 0.3 x 9.5 mm Coil Although the width W of the pattern is not related to the inductance value, the larger the width, the smaller the resistance, and therefore the higher the Q, which is preferable. In this embodiment, W=1.5 mm.

Also, in this embodiment, two resonators Q1 and Q2
Coupling between them is done by coil patterns 2c and 4c, and in addition, at least one part of the resonator is equivalently connected to a member (for example, a metal piece) that constitutes a coil, or equivalently a coil and a capacitor connected in series. Connections can also be made using members constituting a circuit (for example, capacitors with leads). By doing so, a pole can be created in the filter characteristic, thereby making it possible to obtain a steeper filter characteristic.

Next, FIG. 6 shows another embodiment of the present invention. While the above embodiment is a two-stage connection, this embodiment is a three-stage connection. That is, there are three U-shaped conductive patterns 2, 4, and 6 on the front surface of the dielectric substrate 1, and three U-shaped conductive patterns on the back surface.
By forming U-shaped conductive patterns 3, 5, 7, three resonators Q1, Q2,
Q3 (the equivalent circuit is the same as the circuit shown in FIG. 2) is configured, and these are magnetically coupled in three stages. In the figure, 15 is a slit formed between resonators Q1 and Q2, and 16 is a slit formed between resonators Q2 and Q3. Further, 17 is a lead terminal for grounding a part of the intermediate stage resonator Q2.

FIG. 7 shows an equivalent circuit of the bandpass filter of this embodiment. In the figure, L12, L14, and L17 are coil components of the lead terminals. Moreover, the frequency characteristics are shown in FIG. As can be seen from the figure, it has steep characteristics with a center frequency of 465MHz and a bandwidth of 20MHz, and the generation of spurious is suppressed in the higher frequencies than the passband.

The above are two embodiments of the bandpass filter of the present invention, and it goes without saying that design changes can be made within the scope of the invention. For example, the number of magnetically coupled resonators is arbitrary, and is not limited to two-stage coupling or three-stage coupling as in the above embodiments, but may be four or more stages. Further, it is not necessary to form slits in all the spaces between the resonators, and in the second embodiment, one of the slits 15 and 16 may be omitted.

Effects of the Invention As described above, the bandpass filter of the present invention has
Multiple resonators are formed on a single dielectric substrate with a unique equivalent circuit in which a second capacitor is connected in parallel to an LC series circuit in which coils are connected on both sides of a first capacitor, and these are connected in multiple stages. Since the filter is magnetically coupled to the filter, it has the advantage of being small and compact, unlike a filter using a dielectric coaxial resonator.

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

Furthermore, since a slit is formed between the resonators of the dielectric substrate to prevent capacitive coupling between the two, the filter of the present invention suppresses the generation of spurious waves. , has excellent frequency characteristics.

[Brief explanation of the drawing]

FIG. 1 shows a bandpass filter as an embodiment of the present invention, in which figure A is a front view, figure B is a side view, and figure B is a side view.
Figure C is a rear 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, and Figure 4 shows the frequency characteristics of the filter. Figure 5 is a diagram showing the frequency characteristics of a filter other than the present invention, Figure 6 A is a front view showing a bandpass filter as another embodiment of the present invention, Figure B is a side view, and Figure C is a rear view. 7 are equivalent circuit diagrams of the filter, and FIG. 8 is a diagram showing the frequency characteristics of the filter. 1...Dielectric substrate, 2, 3, 4, 5, 6, 7...
...Conductive pattern, C1, C3...First capacitor, C2, C4...Second capacitor, L1, L
2, L3, L4...Coil, Q1, Q2, Q3...
...Resonator, 15, 16...Slit.

Claims (1)

[Scope of Claims] 1. A capacitor electrode pattern is formed at two opposing locations on both the front and back surfaces of a dielectric substrate, and the electrode pattern and the dielectric substrate therebetween form 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 a coil pattern is formed between the first capacitor and the coil pattern connected in series on both sides of the first capacitor. A plurality of resonators are formed by forming an LC series circuit with the coil configured as above, and the second capacitor is connected in parallel to this LC series circuit, and the coil of each resonator is connected to the coil of the other resonator. An LC bandpass filter that is connected in multiple stages by magnetically coupling with a coil, and has a slit formed at least at one location between resonators of a dielectric substrate.