JPH03296315A - High frequency filter - Google Patents

Abstract

PURPOSE:To suppress dispersion in the capacitance of the filter by integrating all capacitive components in a dielectric block. CONSTITUTION:A dielectric block 10 made of a sintered body of a microwave use high dielectric constant material is formed by providing four grooves 12 in parallel with one of sets of faces opposite to each other on a rectangular parallelopiped and formed to be a comb shape when observed in a longitudinal cross section. Then a conductor film 14 is provided to inner faces of the slots 12, that is, both wall faces and a bottom face. A ground electrode 16 is formed to the entire other faces of the dielectric block 10. Then input and output terminals 18 and a conductor film of grooves placed at both ends, and conductor films of the grooves are interconnected by a 1st coil 20 respectively and each conductor film 14 and ground are interconnected by a 2nd coil 22.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a filter used in a high frequency band such as a microwave band. More specifically, the present invention relates to a bandpass filter in which a capacitive portion is integrated using a comb-shaped dielectric block.

This filter is used, for example, in mobile communications in the microwave band, satellite communications, and the like.

[Prior art] As a bandpass filter used in a high frequency band, λ/
There are dielectric filters, stripline filters, LC filters, etc. that use type 4 coaxial resonators.

A filter using a λ/4 type coaxial resonator has an integrated structure in which multiple resonator holes are arranged in parallel in a dielectric block and connected by a coupling hole, or a filter that uses multiple resonators with a single resonator hole. There is a structure in which they are lined up. When using single resonators, they can be coupled together using a capacitor formed using a dielectric substrate or an individual chip capacitor, or by providing a window on the side of the resonator.

[Problems to be Solved by the Invention] In a dielectric filter using a 2/4 type coaxial resonator, its height is inversely proportional to the product of the square root of the effective dielectric constant and the frequency. Therefore, a material with a high dielectric constant is required, but the relationship k (constant) = Q/f·ε is generally established, and as the dielectric constant increases, Q decreases. Currently in practical use ε, = 91~9
If a material of about 3 is used, a height of about 9 am is required at a frequency of 900 MHz, and there is a limit to miniaturization.

On the other hand, stripline filters can be miniaturized, but their Q is poor, and since LC filters use many individual components (chip capacitors and coils), variations in the characteristics of individual components directly affect the filter characteristics. , the number of adjustment steps increases. In any case, if the selected parts are not carefully attached (soldered or connected by conductive adhesive), the characteristics will change and the yield will decrease. In other words, even if the structure is simple, there are actually many parts, and the disadvantage is that it requires a lot of assembly and management man-hours.
It was not possible to reduce the price due to low reliability.

The purpose of the present invention is to eliminate the above-mentioned drawbacks of the conventional technology, to integrate the capacitor part, to reduce variations in capacitance, to reduce assembly and adjustment man-hours, to reduce the size, to reduce the cost, and to improve reliability. The objective is to provide a high frequency filter with high performance.

[Means for Solving the Problems] A high frequency filter according to the present invention has a plurality of parallel grooves formed in one of the opposing surfaces of a dielectric block to form a comb shape,
A conductive film is formed on the wall and bottom surface of the good conductor, and a common ground electrode is provided on the opposite side, and the conductive films in the groove are connected by a first coil, and the conductive film of the good conductor and the ground are connected. It is connected by a second coil.

For the input/output part, connect the conductive film in the groove located at both ends and the input/output terminal with a coil, or form input/output electrodes at both ends of the dielectric block and connect the input/output terminal with a coil. Configure by connecting.

[Opposing capacitance occurs between the wall conductor films of adjacent grooves of the working dielectric block. Further, a ground capacitance is formed between the conductive film at the bottom of the groove and the earth electrode, and inductance is generated in the second coil. These constitute a parallel resonant circuit. These parallel resonant circuits are inserted in parallel between the mutual connection points of the opposing capacitors and the ground, respectively.
The terminal LC network provides the basic bandpass filter characteristics.

Furthermore, since the inductance by the first coil is provided in parallel with the opposing capacitance, a resonant circuit is created, thereby creating an attenuation pole for blocking high-frequency passage. This attenuation pole can be formed near the passband by selecting appropriate values for the inductance and opposing capacitance, so the passband becomes steeper and the filter characteristics are improved.

[Embodiment] FIG. 1 is a perspective view showing an embodiment of a high frequency filter according to the present invention. A dielectric block 10 made of a sintered body of a high-permittivity material for microwave use has four grooves 12 provided in parallel on one side (the top surface in FIG. 1) of a pair of opposing surfaces of a rectangular parallelepiped. It is comb-shaped when viewed in longitudinal section.

Then, a conductive film 14 is formed on the inner surface of the lead 12, that is, on both walls and the bottom surface.
will be established. A ground electrode 16 is formed on the entire surface of the other surface (lower surface in FIG. 1) of the dielectric block 10. A first coil 20 is used to connect the input/output terminal 18 and the conductor films in the grooves located at both ends, and between the good conductor films, and a second coil 22 is connected between each conductor film 14 and the ground. Connect with.

In order to make the drawing easier to understand in Figure 1, the parts where there is no conductor film and the dielectric base is exposed are shown as small dots, and the parts where the conductor film (including electrodes) has been formed are shown with shadow lines. The table is attached. Dielectric block 10
is manufactured, for example, by press-molding powder into a predetermined shape and firing it. Further, the conductive film may be an extremely thin conductive layer formed by baking a silver paste, for example.

FIG. 2 shows the distribution of capacitance. In the dielectric block 10, ground capacitances C1, . C1 is formed. When the width of the dielectric block is constant, the ground capacity C
0C4 can be adjusted by the width of the groove 12 and the distance between the ground electrode 16 and the bottom of the groove, and the opposing capacitance C6,..., C? can be adjusted by adjusting the width of the protrusion between the grooves and the groove depth. Ll..., La represents the inductance due to the second coil 22, LS,
..., L represents the inductance of the first coil 20.

The equivalent circuit is shown in Figure 3. Four parallel resonant circuits are constituted by the grounding container C C4 and the inductances Ll, . . . , L. They are the opposing capacitance Cs,...
・Tsumata opposing capacitance Cs,...C? and inductance L! , . . . , Ls create an attenuation pole for pass blocking. In this way, a high frequency filter exhibiting band pass filter characteristics is obtained.

An example of filter characteristics obtained by this high frequency filter is shown in FIG. Since the capacitive part is integrated, the insertion loss is small and a large attenuation can be obtained in the part indicated by the symbol a.

In the present invention, the shape of the groove formed in the dielectric block is not limited to the U-shape described above, but may also have a square cross section, a semicircular shape, or the like. Capacity can be adjusted by changing the width and depth of the groove. Although four grooves are provided in the above embodiment, the number of grooves formed may be changed as appropriate.

FIG. 5 shows another example of the input/output terminal structure. Input/output electrodes 32 are provided on both end faces of the dielectric block 30, and a coil 34 is connected thereto to draw out input/output terminals. There is capacitive coupling between the input/output electrode 32 and the wall conductor film of the groove located at the end. FIG. 6 shows the equivalent circuit of that part.

The input/output coupling capacitance is expressed as 00, and the inductance of the coil 34 is expressed as 0. Expressed as

[Effects of the Invention] As described above, in the present invention, since all the capacitance portions are integrated within the dielectric block, variations in capacitance can be suppressed. Each capacity depends only on the dimensions and the uniformity of the material, but the dimensional relationship can be solved by molding technology, and the uniformity of the material is one piece, so the capacity hardly differs between individual parts, so fine adjustment can be made. The uniformity and reproducibility are so high that there is no need for In addition to the small number of parts, the present invention facilitates assembly, reduces manufacturing costs, has high reliability, and can be miniaturized. Furthermore, since the capacitance is formed three-dimensionally,
Occupied mounting reduces the area and improves board mounting density.

In addition, since the present invention has a structure in which the capacitive part is integrated, insertion loss is small, and large attenuation can be obtained on the high frequency side.
Overall, the filter characteristics are improved.

[Brief explanation of drawings]

Fig. 1 is a perspective view showing an embodiment of the high frequency filter according to the present invention, Fig. 2 is an explanatory diagram of its capacitance distribution state, Fig. 3 is an equivalent circuit diagram of the filter, and Fig. 4 is an example of filter characteristics. An explanatory diagram, FIG. 5 is an explanatory diagram showing another example of the input/output terminal structure,
FIG. 6 is an equivalent circuit diagram of that part. 10... Dielectric block, 12... Groove, 14...
Conductor film, 16... Earth electrode, 18... Input/output terminal, 20... First coil, 22-... Second coil.

Claims (3)

[Claims] 1. A plurality of grooves are provided in parallel on one of the opposing surfaces of the dielectric block to form a comb shape, a conductive film is formed on the wall and bottom surface of each groove, and a common ground electrode is provided on the opposite surface. A high frequency filter in which a first coil connects the conductor films in the grooves, and a second coil connects the conductor film in each groove and the ground. 2. 2. The filter according to claim 1, wherein the conductor film of the groove located at both ends and the input/output terminal are connected by a coil. 3. 2. The filter according to claim 1, wherein input/output electrodes are formed at both ends of the dielectric block, and the input/output terminals are connected by a coil.