JPH0468608A - Low pass filter with feedback circuit - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a low-pass filter with a comb-shaped structure used mainly in the microwave band. More specifically, in the present invention, a plurality of grooves are arranged in parallel on one surface of a dielectric block, a conductor film is formed on the opposite surface and the inner surface of the groove, thereby forming a plurality of capacitor parts, and the conductor film in the groove is This relates to a bridge-type low-pass filter in which a feedback circuit is constructed by connecting the grooves with a coil and connecting arbitrarily distant grooves with a capacitor.

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

[Prior Art] A stripline structure is commonly used as a low-pass filter used in the microwave band.

This is a structure in which a plurality of electrodes are formed on the front surface of a substrate such as alumina, a ground electrode is formed on the entire surface of the substrate, and the surface electrodes are connected by strip lines.

A grounded capacitance (C component) is formed between the electrodes on both the front and back sides of the board, and the strip line connecting the surface electrodes becomes an inductance (L component), and the LC circuit network created by them achieves low-pass filter characteristics. ing.

Here, the ground capacitance changes depending on the dielectric constant and thickness of the substrate and the electrode area, and the inductance changes depending on the width and length of the conductor pattern.

[Problems to be Solved by the Invention] In order to miniaturize the above-mentioned low-pass filter, it is conceivable to use a material with a high dielectric constant as the substrate. When a substrate with a high dielectric constant is used, the area of both the ground capacitance and inductance becomes smaller, but the variation in capacitance becomes larger, and the characteristics vary greatly. Since electrodes and the like are formed by screen printing, variations in characteristics are determined by printing accuracy, making it difficult to adjust the electrode area.

Furthermore, it is a separate matter to perform polarized feedback with the above filter! It is necessary to provide poles, which increases the number of man-hours in design and manufacturing, resulting in higher costs and disadvantages in that the size of the board becomes larger.

SUMMARY OF THE INVENTION An object of the present invention is to provide a low-pass filter having a polarized feedback circuit, which can eliminate the drawbacks of the prior art as described above, can be made smaller, can reduce the number of assembly and adjustment steps.

[Means for Solving the Problems] The present invention, which can achieve the above object, has a comb shape in which a plurality of grooves are provided in parallel on one side of the V's 'E1 body flock, and at least eight grooves. A conductive film is formed on the bottom surface, and a ground electrode is provided on the other surface, and the conductive films in adjacent grooves are connected by a coil, and the conductor layers in any distant (non-adjacent) grooves are coupled via a capacitor capacitance. This is a low-pass filter with a feedback circuit.

Here, a conductor film may be formed on both wall surfaces in addition to the bottom surface of the groove.

In this specification, [sJ] refers to a long and narrow groove, and in addition to the usual groove with walls on both sides, it also refers to a groove with no wall on one side when located at the end of a dielectric block. It is used in a broad sense, including.

Coupling between arbitrarily distant grooves by capacitor capacitance may be achieved by a plurality of conductor patterns having opposing portions formed on the surface of the dielectric block, or by forming holes in the vicinity of predetermined grooves. A structure may be used in which both ends of the conductive wire of the mold are inserted.

[Operation] A ground capacitance is formed between the conductor film at the bottom of the groove and the earth electrode, and inductance exists in the coil that couples the conductor films in the groove. A basic low Mi! 4-terminal LC network in which these multiple coils are connected in series and each ground capacitor is connected in parallel between the interconnection points of the coils! A 1-in-1 filter characteristic can be obtained.

Furthermore, if a coupling is formed between arbitrarily distant grooves by capacitor capacitance, a feedback circuit is formed and an attenuation pole is created.

Further, when a conductive film is formed on the wall surface of the groove, opposing capacitance is generated between the wall surface conductive films of adjacent grooves, and this and the inductance of the coil form a parallel resonant circuit, creating an attenuation pole for blocking passage.

These attenuation poles can be formed near the passband by selecting appropriate values for the capacitor capacitance, inductance, and opposing capacitance, so that the passband becomes steeper and the filter characteristics are improved.

[Embodiment] FIG. 1 is a perspective view showing an embodiment of a low-pass filter with a feedback circuit according to the present invention, and FIG. 2 is an explanatory diagram showing an equivalent circuit thereof.

The gN body block IO made of a high dielectric constant material for microwaves such as barium titanate is a rectangular parallelepiped with four grooves 12 provided in parallel on one of the opposing surfaces (the top surface in the drawing). , is comb-shaped as shown in Figure 2. Conductor films 14a and 14 are formed on the bottom and both walls of the eight grooves 12, respectively.
b, and a ground electrode 16 is formed on the entire other surface (lower surface in the drawing) of the dielectric block 10. A coil 20 is connected between the input/output terminal 18 and the groove conductor films located at both ends, and between the good conductor films.

Further, on the front surface of the dielectric block IO, two conductor patterns 22a and 22b are provided, one end of which is electrically connected to the conductor film of the groove located at each end, and the other end of which is opposite to each other with a slight gap between them.
form.

In FIG. 1, in order to make the drawing easier to understand, portions where there is no conductor film and the dielectric base is exposed are shown as small dots. The dielectric block can be manufactured, for example, by press-molding powder into a predetermined shape and firing it.

Alternatively, the grooves may be formed by cutting a rectangular parallelepiped-shaped fired crystal, and the conductor film or conductor pattern may be formed by, for example, baking a silver paste.

As shown in FIG. 2, ground capacitances C+ and Cz are formed between the conductor film 14a at the bottom of the groove and the ground electrode 16, and opposing capacitances C3 and C are formed between the wall conductor films 14b of adjacent grooves. Ru. LL represents the inductance due to the coil. Basic low-pass filter characteristics are realized with grounded capacitance c,, C2 and inductance L..., Lx, and opposing capacitance Cx
, Ca and inductance . . . , L3 resonate in parallel, creating an attenuation pole for blocking passage. Also, two conductor patterns 22a, 2 facing each other with a small gap between them.
2b forms a capacitor capacitance C, and the grooves at both ends are coupled to form a feedback circuit.

Note that when the width of the dielectric block is constant, the ground capacitance C
,,C, can be adjusted by the groove width and the distance between the ground electrode and the groove bottom, and the opposing capacitances Cs and C- can be adjusted by the width of the protrusion between the grooves and the groove depth. The capacitor capacitance C can be adjusted by adjusting the length and spacing of the opposing portions of the conductor pattern.

FIG. 3 shows another embodiment of the invention.

A dielectric block 10 is used, which has four grooves 12 similar to those in the previous embodiment and has conductor films 14a and 14b provided on the bottom and wall surfaces of the grooves 12. Holes 24a24b are formed in the vicinity of the grooves located at both ends in the same direction as the grooves. and both holes 24
Insert both ends of the U-shaped conducting wire 26 into a24b. This connects the grooves at both ends.

By adjusting the insertion amount l of the conducting wire 26, the capacitor coupling capacity between the conductive film of the groove and the inserted conducting wire can be varied.

Next, we will discuss the experimental results. FIG. 4 is an explanatory diagram of the dielectric filter used in the experiment, and FIG. 6 is a diagram of the obtained filter characteristics. The dielectric block is made of a material with a dielectric constant ε=39, and its dimensions are as shown in FIG.

The unit is -. Note that the width of the dielectric block is 6.3-1. The input/output coil has 2 turns, and the coil between the grooves has 3 turns, and two tin-plated coated wires 30 (core wire diameter 0.4 m) are attached to the conductor film of the grooves at both ends of 6 using wire rods with a wire diameter of 0.4 m. 8
The core wire portions (m*φ, insulation coating diameter 1.2-■φ) were each soldered, and the other ends were wrapped once to provide a capacitor coupling capacity. As can be seen from FIG. 6, an attenuation pole P was generated near the passband, and steep filter characteristics were obtained.

When the coupling capacitance is increased (in this case, when the number of windings is increased), the i1m overband does not change, and the attenuation pole P moves in the direction of arrow a (the state shown by the imaginary line).

Although the preferred embodiments of the present invention have been described above in detail, the present invention is not limited to only such configurations. The number of grooves is arbitrary, and the groove shape etc. may be changed as appropriate.
For example, a groove having a rectangular cross section may be used. By changing the groove width and groove depth, the capacity of each groove section can be adjusted. Also, the outer wall portions of the grooves at both ends may be omitted and can therefore be deleted. This allows for miniaturization and also saves on material costs.

Capacitor coupling between distant grooves is not limited to the grooves at both ends, but can be performed between any grooves depending on the required characteristics.The amount of feedback changes and the characteristics change depending on which groove is selected. When coupling with a groove located at the end, it is also possible to form a conductive film on the wall of the groove and provide an electrode on the end face of the dielectric block to form a capacitor capacity, thereby coupling with other grooves. be.

[Effects of the Invention] As described above, the present invention provides a dielectric block with a plurality of grooves arranged in parallel, and forms a conductive film on the bottom of the groove to provide grounding capacity between the bottom of the groove and the opposing earth electrode. Since the conductor films in the grooves are successively connected by coils, the LC circuit network as described above can be formed in an equally economical manner, and the desired low-pass filter characteristics can be achieved. Since the arbitrary distant (non-adjacent) grooves are coupled via the capacitor capacitance, a feedback circuit is formed, and the attenuation pole for pass blocking can be formed near the pass band, resulting in a steep pass band and improved filter characteristics. be done.

Furthermore, if a conductive film is formed on the wall surfaces of the grooves, polarization can also be achieved by the opposing capacitance generated between the wall surfaces of adjacent grooves and the inductance of the coil.

Since the filter of the present invention is integrated, the capacitance is uniform, and by making the groove shape accurate, variations in capacitance can be suppressed. High-precision screen printing technology is not required to form the conductor film, and therefore the filter can be manufactured easily. Costs are reduced. Also, by changing the inductance and width, the filter characteristics can be changed freely.

Furthermore, unlike the conventional flat plate type, since the capacitor is formed three-dimensionally, the occupied mounting area is reduced and the board mounting density is improved.

[Brief explanation of drawings]

FIG. 1 is a perspective view showing one embodiment of a low-pass filter with a feedback circuit according to the present invention, FIG. 2 is an explanatory diagram showing its equivalent circuit, and FIG. 3 is a perspective view showing another embodiment of the present invention. Figure, 4th
FIG. 5 is an explanatory diagram of the filter used in the experiment, FIG. 5 is an explanatory diagram of the dimensions of its grooves, etc., and FIG. 6 is a graph showing an example of the characteristics of the filter. 10... Dielectric block, 12... Groove, 14a14
b... Conductor film, 16... Earth electrode, 18... Input/output terminal, 20... Coil, 22a, 22b... Conductor pattern, 24a, 24b... Hole, 26... Conductor wire . Patent applicant Fuji Electrochemical Co., Ltd.

Claims (4)

[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 at least the bottom surface of each groove, and a ground electrode is provided on the other surface, and the conductive film of the adjacent groove is formed. A low-pass filter with a feedback circuit that connects conductor films in arbitrary separated grooves with a coil through a capacitor. 2. Claim 1: A conductive film is formed on the bottom and both wall surfaces of each groove.
Filters listed. 3. A plurality of conductor patterns are formed on the surface of the dielectric block, one end of which conducts with the conductor film of the groove, and the other ends of which face each other with a slight gap therebetween, whereby arbitrary distanced grooves are connected to each other. 1 or the filter described in 1. 4. 3. The filter according to claim 1, wherein holes are formed in the vicinity of the grooves in the dielectric block, and both ends of a U-shaped conducting wire are inserted into the two holes, respectively, thereby coupling the grooves at arbitrary distances.