JPH0580169B2 - - Google Patents

Description

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

Conventional technology Conventionally, bandpass filters used in the above frequency range have generally consisted of dielectric coaxial resonators connected in multiple stages. Because of their shape, filters arranged in multiple stages had the disadvantage of being bulky. Therefore, the present applicant requested a patent application filed in 1983.
-97316, a bandpass filter as shown in FIG. 5 has been filed.

In Figure 5, Figure A is a front view, Figure B is a side view,
Figure C is a rear view. In the figure, 1 is a dielectric substrate 1 made of FRDR material, for example, and its front surface 1a and back surface 1
b and U-shaped conductive patterns 2,
3, 4, and 5 are formed by screen printing silver paste, for example.

Each conductive pattern 2 to 5 has two capacitor electrode patterns 2a, 2b, 3a, 3b, 4a, 4b,
5a, 5b and one coil pattern 2c, 3c,
It consists of 4c and 5c. Among these, capacitor electrode patterns 2a and 3a, 2b and 3b, 4a
and 5a, 4b, and 5b are opposed to each other via the dielectric substrate 1, and form capacitors C1, C2, C3, and C4 with capacities determined by the dielectric constant and thickness of the substrate and the opposing areas of the electrodes of the capacitor. are doing. On the other hand, the coil patterns 2c, 3c, 4c, and 5c are
They are formed at positions that do not face each other. Each coil pattern 2c, 3c, 4c, 5c forms a coil at high frequency. Here, the inductance of each coil pattern is assumed to be L1, L2, L3, and L4. 11 and 13 are input/output lead terminals. 12 and 14 are grounding terminals.

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 are connected in parallel to form a resonator represented by an equivalent circuit. A resonator having this equivalent circuit (hereinafter, these two resonators are referred to as Q1 and Q2).
However, as shown in FIG. 5, since the two coil patterns 2c and 4c are provided close to each other with a distance d, the two coil patterns 2c and 4c create magnetic coupling, as shown in FIG. Construct a bandpass filter with an equivalent circuit as shown below. In the figure, M is 2
Mutual inductance L12 and L14 representing the degree of magnetic coupling between the two coil patterns 2c and 4c are the inductances of the lead wires 12 and 14, respectively. 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.

Problems to be Solved by the Invention Incidentally, the bandpass filter shown in FIG. 5 above has the advantage of being flat and not bulky, but on the other hand, it cannot be mounted on a printed circuit board in which other circuits are incorporated. In some cases, the electromagnetic field distribution is disturbed by nearby electronic components, metal pieces, etc., resulting in a problem in that the frequency characteristics shift toward higher frequencies.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a bandpass filter whose frequency characteristics do not change after mounting.

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. Multiple resonators are formed on the substrate,
and a bandpass filter in which a coil of each resonator is magnetically coupled to a coil of another resonator, comprising: a ground electrode formed on the back surface of the substrate; a side plate portion electrically connected to the ground electrode of the substrate; The bandpass filter is covered with a metal cover consisting of a top plate portion continuous with the top plate portion, and is electromagnetically shielded from the outside.

Embodiment FIG. 1 shows an external view of a bandpass filter as an embodiment of the present invention, and FIG. 2 shows a configuration diagram. Furthermore, Figure 3 A is a front view, B is a bottom view,
C is a side view. The bandpass filter is assembled from a bandpass filter main body 20, a metal cover 21, and a printed circuit board 22.

The bandpass filter main body 20 has a structure in which a plurality of resonators are formed on a substrate by pattern printing or the like, and the resonators are coupled together, similar to that shown in FIG. However, unlike FIG. 5, the periphery of the substrate is molded with an exterior resin 31.

The metal cover 21 is made by bending a single metal plate, and includes a top plate portion 21a and left and right side plate portions 21b, 2.
1c. Two tongue pieces 21d, 21e are provided inwardly at the lower ends of the left and right side plate parts 21b, 21c.
are being brought out in different rows. One tongue piece 21
d is a ground electrode 30a on the bottom surface of the printed circuit board 22
The other tongue piece 21e is connected to the upper surface of the printed circuit board 22 by soldering. Further, as shown in FIG. 3, a ground terminal 28 extends from one side of the upper plate portion 21a.

The printed circuit board 22 has lead terminals 2 extending from the bandpass filter main body 20 toward one side.
4 to 27 are inserted, and the back side has the third hole 23...
As shown in Figure B, the ground terminal 2 occupies approximately the front surface.
8 and the lead terminal 2
4, 26, 27 attachment electrodes 30b... are formed.

To assemble the bandpass filter, each lead terminal 24 to 27 of the bandpass filter main body 20 is bent into an inverted L shape, and the holes 23 of the printed circuit board 22...
The lead terminals 24 to 27 are soldered to predetermined electrodes 30b on the back surface of the printed circuit board while keeping the bandpass filter main body 20 at a predetermined height from the printed circuit board 22. After that, the metal cover 21 is attached to the printed circuit board 22, and the tongue piece 21d is attached.
solder to the ground electrode 30a on the back of the printed circuit board.

The height of the bandpass filter main body 20 in the installed state is preferably slightly above or below the middle (center position) between the ground electrode 30a on the back surface of the printed circuit board and the top plate portion 21a of the metal cover 21. In the embodiment, it is set slightly above the center position.

Further, an example of the dimensions of each part of the band pass filter is as follows with reference to FIG.

l ₁ = 23 (mm) l ₂ = 4.5 (mm) l ₃ = 14 (mm) l ₄ = 5 (mm) With the above structure, the bandpass filter has a structure that connects the metal cover 21 and the ground electrode on the back of the printed circuit board 22. 30a, so even if other electronic components or metal pieces exist nearby after mounting, the electromagnetic field distribution will be disturbed and the frequency characteristics of the bandpass filter will not change. effectively prevented.

On the other hand, the distance between the bandpass filter body 20 and the top surface 21a of the metal cover, or the distance between the bandpass filter body 20 and the ground electrode 30a on the back surface of the printed circuit board.
The frequency characteristics change by changing the distance from the

FIG. 4 shows frequency characteristic curves when the distance between the bandpass filter and the metal cover is changed. Curve 1 is for the normal position of the bandpass filter, Curve 2 is for the bandpass filter placed close to the metal cover (upper side), and Curve 3 is for the bandpass filter placed at the intermediate position between the ground electrode and the top surface of the metal cover. (downward).

As is clear from this graph, when the bandpass filter is moved to the metal cover side (above),
It can be seen that when the center frequency moves to a higher side and the band pass filter is moved to an intermediate position, the center frequency moves to a lower side. Due to this,
Fine adjustment of frequency characteristics can be made at the manufacturing stage by changing the distance between the metal cover and the bandpass filter.
As a result, the product yield has improved. In addition,
After finishing the fine adjustment, as shown in FIG.
It is preferable to put a wedge 29 between it and a to prevent the frequency characteristics from changing unexpectedly. In the above embodiment, the lead terminals of the bandpass filter are used as they are, but it is also possible to eliminate the lead terminals and make them chip-shaped.

Effects of the Invention As explained above, according to the present invention, since the upper and lower sides of the bandpass filter are shielded with a metal cover and a printed circuit board, after mounting, the electromagnetic field distribution is disturbed by the approach of external metal pieces, etc. There are no longer any changes in characteristics. or,
Depending on the distance between the metal cover and the bandpass filter,
Since the frequency characteristics change, it is possible to fine-tune the frequency characteristics at the product stage, which also has the effect of improving product yield.

[Brief explanation of the drawing]

Fig. 1 is an external view of a bandpass filter that is an embodiment of the present invention, Fig. 2 is a block diagram of Fig. 1, and Fig.
Figure A is a front view of the bandpass filter, B is a bottom view, C is a side view, Figure 4 is the frequency characteristic curve of the bandpass filter in Figure 1, Figure 5A is a front view of a conventional bandpass filter, B shows a side view, C shows a rear view, FIG. 6 shows an equivalent circuit of a resonator, and FIG. 7 shows an equivalent circuit of a bandpass filter. 20...Band pass filter, 21...Metal cover, 21a...Top plate portion of metal cover, 21
b, 21c... side part of metal cover, 21d, 2
1e... tongue piece, 22... printed circuit board, 23...
Terminal hole, 24...Input terminal, 25, 26...Earth terminal, 27...Output terminal, 28...Earth terminal, 29...Wedge, 30a...Earth electrode, 3
0b...electrode, 31...bandpass filter exterior resin.

Claims (1)

[Claims] 1. A plurality of resonators are formed on a substrate, 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 a bandpass filter in which a coil of each resonator is magnetically coupled to a coil of another resonator, comprising: a ground electrode formed on the back surface of the substrate; a side plate portion electrically connected to the ground electrode of the substrate; A bandpass filter is characterized in that the bandpass filter is electromagnetically shielded from the outside by being covered with a metal cover consisting of a top plate portion continuous with the top plate portion.