JPH0744370B2 - 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 in which a polar type low pass filter section using a comb-shaped dielectric block and a band elimination filter section having a plurality of λ / 4 type dielectric coaxial resonators are combined.

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. This is because, for example, a plurality of λ / 4 type dielectric resonators having a single resonator hole are arranged side by side on a substrate, and two or more chip capacitors are stacked on the substrate (the same number as the resonator). By connecting and inserting the ends of the coil between the chip capacitors of each set, the sets (filter stages) are connected to each other, and the conductor film of each resonator hole and the top electrode of each set of chip capacitors are connected. It has a configuration in which and 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.

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 unit polar, it is necessary to add additional parts and the structure becomes complicated, which is not practical.

The object of the present invention is to eliminate the drawbacks of the prior art as described above, and to integrate the capacitors of the low-pass filter unit, so that the number of assembling steps and adjusting steps are small, and a polar feedback circuit is provided, and the filter characteristics To provide an excellent and highly reliable high frequency filter.

[Means for Solving the Problems] The present invention is basically configured by combining a polar low-pass filter unit and a band-pass filter unit. The low-pass filter section has a comb-shaped structure in which a plurality of grooves are provided in parallel on one of the surfaces of the dielectric block facing each other, and a conductor film is formed on the wall surface and the bottom surface of each groove and the ground electrode is formed on the other surface. It is provided and the conductor films of the groove are connected by a coil. The bandpass filter is configured by arranging a plurality of 1/4 wavelength dielectric resonators each having a single resonator hole, and providing a capacitance in each resonator. Then, the resonator holes and the conductor film of the groove are coupled to each other through the capacitance to form a high frequency filter.

Capacitive coupling between the resonator hole and the groove conductor film may be achieved by inserting a resin terminal into the resonator hole and connecting the terminal pin to the groove conductor film, or by connecting a coupling capacitor to the resonator hole open end. A method of mounting and connecting, attaching a metal terminal to the other electrode of the coupling capacitor, and connecting the metal terminal to the conductor film of the groove may be used.

[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 coil connecting between the conductor films of the groove. A basic low-pass filter characteristic can be obtained by a four-terminal LC network in which a plurality of coils are connected in series and grounding capacitors are connected in parallel between interconnection points of the coils. Further, a facing 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, thereby forming an attenuation pole for blocking passage. The 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 characteristic is improved.

A band rejection filter unit is configured by combining a plurality of quarter-wave dielectric coaxial resonators and capacitors provided therein, and thereby a large attenuation is obtained in a predetermined frequency band.

For example, in the case of a transmission filter, its stop band (frequency band in which large attenuation is obtained) is set in the reception band, and conversely, in the case of a reception filter, the stop band is set in the transmission band.

When the 1/4 wavelength type is used as the dielectric resonator, spurious appears in a frequency band that is an odd multiple of the fundamental wave center frequency f ₀ . Especially the spurious of 3f ₀ is large. In the present invention, the low-pass filter section reduces the 3f ₀ spurious.

[Embodiment] FIG. 1 is an exploded perspective view showing an embodiment of a high-frequency filter according to the present invention, and FIG. 2 is a plan view after assembly thereof.

A dielectric block 10 made of a sintered body of a high dielectric constant material for microwaves is provided on one of a pair of opposing faces (first
4 grooves 12 are provided in parallel on the upper surface in the figure,
When viewed in vertical section, it looks like a comb. A conductor film 14 is provided on the inner surface of each groove 12, that is, both wall surfaces and the bottom surface, and a ground electrode 16 is formed on the other surface (lower surface in FIG. 1) of the dielectric block 10. Then, the input / output terminal 18 and the conductor films of the grooves located at both ends and the conductor films of the grooves are connected by the coil 20.

Four λ / 4-type dielectric coaxial resonators 22 are arranged in parallel corresponding to each groove 12. The resonator 22 is provided with a resonator hole 24 at the center of a sinter of a square columnar high dielectric constant material for microwaves.
One of the open surfaces (the front surface in FIG. 1) is an open surface, and the conductor film 26 is formed on the other outer surface and the inner surface of the resonator hole 24. The resin portion 30 of the resin terminal 28 is inserted into the resonator hole 24 from the open end side, and the tips of the terminal pins 32 penetrating the center of the resonator hole 24 are respectively formed on the conductor films on the grooves 12.
Solder to 14.

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 dielectric block and the like are manufactured by press-molding powder into a predetermined shape and firing. The conductor film may be formed by baking silver paste, for example.

As shown in FIG. 3, ground capacitances C ₁ and C ₂ are formed between the groove bottom conductor film and the ground electrode 16 in the dielectric block 10, and opposing capacitances C ₃ and C ₃ are formed between the wall conductor films of the adjacent grooves. C ₄ is formed. L ₁ , ..., L ₃ represent the inductance due to the coil 20. When the width of the dielectric block is constant, the ground capacitances C ₁ and C ₂ can be adjusted by the groove width, the distance between the ground electrode and the groove bottom, and the opposing capacitances C ₃ and C ₄ are the width of the convex portion between the grooves, It can be adjusted by the groove depth.

An equivalent circuit of the high frequency filter of the present invention is shown in FIG. The grounding capacitances C ₁ and C ₂ and the inductances L ₁ , ..., L ₃ realize the basic low-pass filter characteristics, and the parallel resonance of the opposing capacitances C ₃ , C ₄ and the inductances L ₁ , ..., L ₃ To create an attenuation pole that blocks passage. The low-pass filter unit 40 is configured by these. Further, by inserting the resin terminal 28, the resin portion 30 is located between the terminal pin 32 and the conductor film 26 of the resonator hole 24, and the capacitor is formed by them. The capacitor C and the resonator 22 form a bandpass filter unit 42. The low pass filter unit 40 and the band pass filter unit 42 are combined to form a high frequency filter.

An example of the measurement result of the filter characteristics obtained by such a high frequency filter is shown in FIG. Measurement is 0.3 ~ 3000MHz
This is the amount of attenuation at. From this result, it can be seen that the insertion loss is extremely small and a sufficiently large attenuation amount can be obtained in a predetermined frequency band. When this is used as a transmission filter, the stop band (region where the amount of attenuation is large) becomes the reception band a as shown in FIG. 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 unit is effective.

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. By changing the width and depth of the groove, it is possible to adjust the ground capacitance and the counter capacitance.

The coupling between the λ / 4 type resonator 22 and the groove conductor film 14 may be configured by a coupling capacitor other than the above resin terminal. Examples thereof are shown in FIGS. 6 and 7. In FIG. 6, a conductor pattern 50 that extends radially is formed at the open end of the resonator hole 24 of the resonator 22, a coupling capacitor 52 is mounted and connected thereon, and an L-shaped metal terminal 54 is connected to the other electrode. To connect. With this configuration, when the coupling capacitor 52 is connected to the conductor pattern 50, the tip of the conductor pattern 50 protrudes from the coupling capacitor 52, so that the resonance frequency can be easily adjusted by cutting the tip of the conductor pattern. .

In the example shown in FIG. 7, a rivet-type metal terminal block 56 is inserted and fixed at the open end of the resonator hole 24, and a coupling capacitor is placed thereon.
52 is soldered and the metal terminal 54 is connected. Alternatively, a hole may be provided in the resonator in parallel with the resonator hole and a metal pin may be inserted.

In each of the above embodiments, four sets of grooves and resonators are provided, but the number of sets (number of filter stages) may be arbitrary.

EFFECTS OF THE INVENTION Since the present invention provides the band elimination filter section in the frequency region where desired attenuation is desired as described above, a sufficiently large amount of attenuation can be obtained even with a small number of resonators. Further, the low-pass filter section can suppress spurious of 3f ₀ , and the filter characteristics are improved as a whole. Further, the present invention is a combination of the band stop filter unit and the low pass filter unit, and since the number of resonators of the band stop filter unit can be reduced, the insertion loss is small and the size can be reduced.

In the low-pass filter section, a plurality of grooves are arranged in parallel in the dielectric block, a conductor film is formed on the inner surface of the dielectric block to provide a ground capacitance between the bottom of the groove and the opposing ground electrode, and Since the coils are sequentially connected to each other, the capacitance portion is integrated, and the insertion loss in the pass band is improved. In addition, a polar feedback circuit is formed by the opposing capacitance generated between the wall surfaces of adjacent grooves and the inductance of the coil.By selecting the value of the opposing capacitance, the attenuation pole for blocking the passage can be formed near the passband, so the passband becomes steep. The filter characteristics are improved.

Since the filter of the present invention has an integrated capacitive portion,
Accurate groove shape can suppress capacitance variation, does not require high-precision screen printing technology to form the conductor film, and has a small number of parts, which facilitates assembly, reduces manufacturing costs, and improves reliability. Becomes higher.

Further, since the capacitors are three-dimensionally formed, the occupied mounting area is reduced and the board mounting density is improved.

[Brief description of drawings]

FIG. 1 is an exploded perspective view showing an embodiment of a high-frequency filter according to the present invention, FIG. 2 is a plan view after assembly thereof, FIG. 3 is an explanatory view of a low-pass filter portion, and FIG. 5 is an equivalent circuit diagram of the filter according to the present invention, FIG. 5 is a graph showing an example of characteristics of the filter of the present invention, and FIGS. 6 and 7 are explanatory views showing examples of connection of coupling capacitors. 10 ... Dielectric block, 12 ... Groove, 14 ... Conductor film, 16 ...
… Ground electrode, 18 …… input / output terminal, 20 …… coil, 22…
… Resonator, 24 …… Resonator hole, 28 …… Resin terminal, 52 …… Coupling capacitor.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hisao Sato 5 36-11 Shinbashi, Minato-ku, Tokyo Fuji Electric Chemical Co., Ltd. (56) Reference JP-A-3-234102 (JP, A) JP A 61-191101 (JP, A) Actual Kaihei 3-82903 (JP, U)

Claims (3)

[Claims] 1. A plurality of grooves are provided in parallel on one of opposite surfaces of a dielectric block to form a comb shape, a conductor film is formed on the wall surface and the bottom surface of each groove, and an earth electrode is provided on the other surface. The conductor films of the groove are connected with a coil, and a plurality of 1/4 wavelength dielectric coaxial resonators each having a single resonator hole are juxtaposed, and a capacitance is provided between each resonator hole and the conductor film of the groove. Combined high frequency filter. 2. The filter according to claim 1, wherein a resin terminal is inserted into the resonator hole of the dielectric resonator, and the terminal pin is connected to the conductor film of the groove. 3. A coupling capacitor is mounted and connected to an open end of a resonator hole of a dielectric resonator, a metal terminal is attached to the other electrode of the coupling capacitor, and the metal terminal is connected to a groove conductor film. The filter according to item 1.