JPH0744365B2 - High frequency filter - Google Patents

Description

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 high-frequency filter that uses a comb-shaped dielectric block and has a polar low-pass filter section and a band-stop filter section integrally formed therein.

This filter is useful, for example, in mobile communication in the microwave band, satellite communication, and the like.

[Prior Art] A filter in which a low-pass filter unit and a band-elimination filter unit are combined is known. For example, a plurality of λ / 4-type dielectric resonators each having a single resonator hole are arranged side by side on a substrate, and a plurality of chip capacitors stacked vertically (the same number as the resonators). It is arranged near the open surface of the resonator, and the ends of the coil are inserted and connected between the chip capacitors of each set to connect the sets (between filter stages) to each other, and the conductor film of each resonator hole And a top electrode of each set of chip capacitors are connected by a lead wire.

[Problems to be Solved by the Invention] Since a large number of chip capacitors are used in the above configuration,
Variations in individual capacitances directly affect the filter characteristics.
Therefore, capacity selection must be performed, and the number of adjustment steps increases. In addition, the number of parts is large, and the man-hours for assembly and management are also large. Since the λ / 4 type coaxial resonator is used, the shape cannot be reduced.

Furthermore, because the chip capacitors are stacked in two layers,
Positioning is required, and a coil terminal needs to be inserted and connected between the two-stage capacitors, which complicates the assembly work, resulting in poor reliability and poor yield.

Further, in order to make the low-pass filter part polar, it is necessary to add additional parts and the structure becomes complicated, which is not practical.

An object of the present invention is to solve the above-mentioned drawbacks of the prior art, and to integrate a low-pass filter unit and a band-elimination filter unit. Therefore, the size is reduced, the number of assembly steps and adjustment steps are small, and the polarized feedback circuit is provided. It is to provide a high-reliability high-frequency filter having excellent filter characteristics.

[Means for Solving the Problems] The present invention is basically a dielectric block in which a polar low-pass filter section and a band-pass filter section are integrally formed. A plurality of grooves are provided in parallel on one of the opposite surfaces of the dielectric block to form a comb shape, and a conductor film is formed on the wall surface and the bottom surface of each groove. A common ground electrode and individual electrodes facing the bottom surface of the groove are provided on the other surface. And connecting the conductor films of the groove with a first coil,
A second coil connects each individual electrode and the ground electrode.

The surface on which the ground electrode and the individual electrode are formed may be a flat surface, but if a recess (including a step and a groove) is provided and the second coil is housed in the recess, the coil will not interfere when mounting. Not preferred.

[Operation] A ground capacitance is formed between the conductor film at the bottom of the groove of the dielectric block and the ground electrode, and an inductance is generated in the first coil connecting between the conductor films of the groove. A basic low-pass filter characteristic is obtained by a 4-terminal LC network in which a plurality of these coils are connected in series and grounding capacitors are connected in parallel between the interconnection points of the coils. Further, an opposing capacitance is generated between the wall surface conductor films of the adjacent grooves, and a parallel resonance circuit is formed by the capacitance and the inductance of the coil, and an attenuation pole for blocking passage is created. This attenuation pole can be formed near the pass band by selecting the inductance and the opposing capacitance to appropriate values, so that the pass band becomes steep and the filter characteristics are improved.

Further, since the conductor film at the bottom of the groove and the individual electrode are arranged so as to face each other, another capacitance is formed by them, and the capacitance and the second coil form a multistage band elimination filter portion. With this, a large attenuation is obtained in a predetermined frequency band.

In the high frequency filter of the present invention, the attenuation band of the band elimination filter unit is set within the pass band of the low pass filter unit, and unnecessary signals and noise are cut in the high frequency side attenuation band of the low pass filter unit.

[Embodiment] FIGS. 1A and 1B are perspective views 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 dielectric constant material for microwaves is one in which four grooves 12 are provided in parallel on one of a pair of opposed surfaces (upper surface in FIG. 1) of a rectangular parallelepiped. It has a comb shape when viewed in a vertical section.
Then, the conductor film 14 is provided on the inner surface of each groove 12, that is, both the wall surfaces and the bottom surface. The other surface of the dielectric block 10 (lower surface in FIG. 1)
A ground electrode 16 is formed on one side in the longitudinal direction, and an individual electrode 18 is further formed at a position facing the bottom surface of each groove 12. And between the inlet / outlet terminal 20 and the conductor film of the groove located at both ends,
And the conductor films of the respective grooves are connected by the first coil 22, and further the second coil is connected between the individual electrodes 18 and the ground electrode 16 on the lower surface.
Connect with 24.

In FIG. 1, in order to make the drawing easy to understand, the portions where the conductor film is not present and the base material of the dielectric is exposed are shown by fine dots, and the shaded portions represent the conductor film. The ground electrode 16 and the individual electrode 18 are conductor films. The dielectric block 10 is manufactured by press-molding powder into a predetermined shape and firing. The conductor film may be an extremely thin conductive layer formed by, for example, baking a silver paste.

FIGS. 2A and 2B are explanatory views showing the state of capacity distribution seen from the p direction and the q direction in FIG. 1A, respectively. Fig. 2A
As shown in FIG. 3, ground capacitances C ₁ , ..., C ₄ are formed between the groove bottom conductor film and the ground electrode 16 in the dielectric block 10,
Opposing capacitors C ₅ , ..., C ₇ are formed between the wall surface conductor films of the adjacent grooves. L ₁ , ..., L ₅ represent the inductances of the first coil 22. When the width of the dielectric block is fixed, the ground capacitances C ₁ , ..., C ₄ can be adjusted by the width of the groove 12, the distance between the ground electrode 16 and the bottom of the groove, and the width of the ground electrode 16, and the opposing capacitance
C ₅ , ..., C ₇ can be adjusted by the width of the convex portion between the grooves and the groove depth. In addition, the capacitance C ₈ between the conductor film on the bottom surface of each groove 12 and each individual electrode 18,
…, C ₁₁ is formed. L ₆ , ..., L ₈ represent the inductance of the second coil 24.

An equivalent circuit of the high frequency filter of the present invention is shown in FIG. Grounding capacitances C ₁ , ..., C ₄ and inductances L ₁ , ..., L ₅ realize basic low-pass filter characteristics, and opposing capacitances C ₅ ,…, C ₇ and inductances L ₂ ,…, L ₄ An attenuation pole for blocking passage is created by parallel resonance with. A low-pass filter section is constituted by these. Also, the capacitances C ₈ , ..., C ₁₁ and the inductances L ₆ , ..., L ₈
Becomes an equivalent circuit similar to that of a conventional dielectric resonator, and constitutes these band elimination filter sections. The low pass filter section and the band pass filter section are combined to form a high frequency filter.

An example of the filter characteristics obtained by this high frequency filter is shown in FIG. The insertion loss is extremely small, and a sufficiently large amount of attenuation can be obtained in a predetermined frequency band. For example, when this is used as a transmission filter, the stop band (region with large attenuation) is set to the reception band a as shown in FIG.
Becomes The transmission band b, which is slightly shifted to the low frequency side from the reception band a, has very little attenuation (the insertion loss is very small).
These depend on the characteristics of the band elimination filter section. The part indicated by reference sign c is a region where the effect of the low-pass filter section is effective, and the high frequency side is cut.

An antenna duplexer used in a car telephone or the like can be constructed by using two dielectric filters having different central resonance frequencies as described above and combining one as a transmission filter and the other as a reception filter.

In the present invention, the shape of the groove formed in the dielectric block is not limited to the above-mentioned U-shape, but may be a square cross-section, a semicircle, or the like. The capacitance can be adjusted by changing the width and depth of the groove.

The lower surface electrode pattern of the dielectric block may be as shown in FIG. Here, the ground electrode 26 is provided so as to surround the individual electrode 18.

6 to 8 show another embodiment of the present invention. FIG. 6 shows a step provided on the lower surface of the dielectric block 30. The ground electrode 32 is formed on the lower side of the block and the individual electrode 34 is formed on the higher side. The example shown in FIG.
Longitudinal ridges 38 are formed in the center of the lower surface of the dielectric block 36, individual electrodes 40 are provided thereon, and ground electrodes 42 are provided on both lower surfaces. In both cases of FIG. 6 and FIG. 7, the second coil 24 connects the ground electrode 32 and the individual electrode 34, and the ground electrode 42 and the individual electrode 40. coil
24 is accommodated in the recess created by the step.

In FIG. 8, recesses 46 are formed on the lower surface of the dielectric block 44 at positions facing the grooves, and individual electrodes 48 are provided on the bottom surface thereof. The ground electrode 50 is provided on the flat portion in a strip shape. Also here, each individual electrode 48 and the ground electrode 50 are connected by the second coil 24, and the coil 24 is housed in the recess 46. It is preferable to store the coil in the recess as described above because the coil can be protected and the parts can be downsized, and the coil does not become an obstacle during mounting.

In each of the above embodiments, four grooves are provided, but the number of shapes may be changed as appropriate.

[Effects of the Invention] As described above, according to the present invention, since the capacitance portion is integrated in the dielectric block, variation in capacitance can be suppressed, and the number of parts is small, which facilitates the assembly and the manufacturing cost. Is reduced and reliability is increased. Further, since the capacitors are formed three-dimensionally, the occupied mounting area is reduced and the board mounting density is improved. In particular, in the present invention, the band elimination filter portion is integrally incorporated in the dielectric block, so that the size can be reduced.

Further, according to the present invention, as described above, since the band elimination filter section is provided in the frequency region where the desired attenuation is desired, it is sufficiently large
Since the amount of attenuation is obtained and the low-pass filter unit in which the capacitance part is integrated is combined, the insertion loss is small on the low band side, the amount of attenuation on the high band side is sufficiently large, and the filter characteristics are improved as a whole.

The low-pass filter section has a polar feedback circuit, and the attenuation pole for blocking the passage can be formed near the pass band by selecting the value of the opposing capacitance, so that the pass band becomes steep and the filter characteristic is further improved.

[Brief description of drawings]

1A and 1B are exploded perspective views showing an embodiment of a high frequency filter according to the present invention, and FIGS. 2A and 2B are explanatory views of a capacitance distribution state viewed from p and q directions in FIG. 1A, respectively. FIG. 3 is an equivalent circuit diagram of the filter according to the present invention, FIG. 4 is an explanatory view of a characteristic example of the filter of the present invention, and FIGS. 5, 6, 7, and 8 are other examples of the present invention. It is a perspective view showing an example of. 10 ... Dielectric block, 12 ... Groove, 14 ... Conductor film, 16 ...
… Earth electrode, 18 …… Individual electrode, 20 …… I / O terminal, 22
...... First coil, 24 ...... Second coil.

Continuation of the front page (56) Reference JP-A-3-234102 (JP, A) JP-A-3-205903 (JP, A) Actually open 3-115401 (JP, U)

Claims (2)

[Claims] 1. A plurality of grooves are provided in parallel on one surface of a dielectric block facing each other to form a comb shape, a conductor film is formed on a wall surface and a bottom surface of each groove, and a common ground is formed on the other surface. A high-frequency filter in which electrodes and individual electrodes facing each other on the bottom surface of the groove are provided, the conductor films of the groove are connected by a first coil, and the individual electrodes and the ground electrode are connected by a second coil. 2. A recess is provided on the surface on which the ground electrode and the individual electrode are formed, and the second coil is housed in the recess.
The listed filters.