JP3009331B2 - Broadband dielectric filter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a monolithic interdigital dielectric filter using a rectangular parallelepiped dielectric block. More specifically, the present invention relates to a resonator having a smaller hole diameter and a larger number of holes. The present invention relates to a broadband dielectric filter in which an output matching circuit includes a series inductance and a parallel capacitance. This dielectric filter is particularly useful for various satellite communication systems for the L band and requiring a bandwidth of 50% or more of the fractional band.

[0002]

2. Description of the Related Art In an IF frequency band such as a satellite broadcasting reception or a micro satellite communication earth station (VSAT) system,
In the 1.2 GHz band, a bandwidth of 500 MHz or more is required. Conventionally, as this kind of broadband filter,
Coaxial bandpass filters have been used. In this filter, a fractional bandwidth of about 57% is obtained.

[0003]

However, as is well known,
The coaxial filter has a large size, a large number of parts, and has a problem that it is difficult to manufacture. Therefore, in recent years, the filter has almost been replaced with a dielectric filter to the extent possible. However, in a band-pass filter in the microwave band, the relative band is about 10 to 10.
Although a 30% dielectric filter has been manufactured,
Broadband dielectric filters of 0% or more have not yet been developed. The conventional dielectric filter is designed such that the ratio (w / d) of the dielectric block width w to the resonator hole diameter d is about 3.3 due to the molding conditions and the maximum Q condition. However, the dimensional ratio is limited to a bandwidth of 30%, and further broadening of the bandwidth cannot be expected.

[0004] It is an object of the present invention to provide a dielectric filter exhibiting a broadband characteristic equal to or better than that of a conventional coaxial filter.

[0005]

According to the present invention, a plurality of resonator holes are provided in the longitudinal direction of a substantially rectangular parallelepiped dielectric block, and most of the outer surface of the dielectric block and the inner surface of the resonator hole are provided. A structure in which each resonator hole has one open end on the open side and the other open end on the short-circuit side, and the open side and the short-circuit side are alternately located with respect to adjacent resonator holes Is an interdigital dielectric filter. Here, the feature of the present invention is that each resonator hole has the same hole diameter, seven or more (however, an odd number) are provided on a straight line in the center, and the dielectric block width (inductance).
In the plane where the resonator hole of the electric block is open,
W is the length of the side in the direction perpendicular to the direction, and d is the resonator hole diameter.
Where the ratio (w / d) is set to 6 ≦ w / d, and a matching circuit having a series inductance and a parallel capacitance is connected to the input and output.

In the input / output matching circuit, one end of a coaxial cable is connected to a connector attached to a housing base, and the core wire of the other end of the coaxial cable is inserted into a first-stage resonator hole and soldered. It is configured by connecting a capacitor to the body ground. The ratio (w / d) between the dielectric block width w and the resonator hole diameter d is preferably set to 6 ≦ w / d ≦ 10. The most preferred configuration is to arrange 13 resonator holes,
w / d ≒ 7.

[0007]

The relative bandwidth is increased by reducing the resonator hole diameter d with respect to the dielectric block width w. Since the coupling between the resonators becomes stronger, it is necessary to further strengthen the first-stage coupling.
Connect I / O signals directly. Therefore, the first stage of input / output is directly connected to a 50Ω coaxial cable, but the impedance of the dielectric filter main body becomes small because the resonator hole diameter becomes small, so that the impedance adjustment of the dielectric filter main body becomes impossible. . Therefore, it is possible to adjust the impedance by adding a matching circuit consisting of a series inductance and a parallel capacitance to the input and output,
In-band return loss is improved.

[0008]

FIG. 1 is a perspective view showing an embodiment of a dielectric filter according to the present invention. The dielectric filter body 10 uses a substantially rectangular parallelepiped dielectric block made of a sintered body of a microwave high dielectric constant ceramic material. The dielectric block has a structure in which 13 resonator holes 12 having the same hole diameter are provided on the center straight line in the longitudinal direction in a shape in which only both end portions are slightly elevated, and the dielectric block has most of the outer surface thereof. A conductor layer is provided on the inner surface of each resonator hole 12. Here, each resonator hole 1
In No. 2, one open end is an open side and the other open end is a short-circuit side, and the open side and the short-circuit side are alternately provided on the same surface (upper surface or lower surface) of adjacent resonator holes. Here, the upper ends of the resonator holes at both ends are open sides. On the short-circuit side, the inner conductor layer of the resonator hole and the outer surface conductor layer of the dielectric block are electrically connected, and on the open side, the inner conductor layer of the resonator hole and the outer surface conductor layer of the dielectric block are connected. Are not electrically connected (separated) by an annular non-conductor portion (shown with fine dots).

In such a dielectric filter main body 10, after a conductor layer is formed on the entire surface of the dielectric block (including the inner surface of each resonator hole), the conductor layer near the opening end of the resonator hole on the open side is formed. It can be easily manufactured by peeling off.

In this embodiment, when the dielectric block width is w and the resonator hole diameter is d, their ratio (w / d)
Is set to w / d = 7. Actual dimensions are: dielectric block width = 7 mm, resonator hole diameter d = 1 mm, and resonator hole pitch = 1.3 mm. The dielectric filter main body 10 is joined to the housing base 20 by soldering or the like. Further, a coaxial cable 24 is directly connected from a connector 22 attached near both ends of the housing base 20 to the first resonator hole. That is, the core wire of the coaxial cable 24 is inserted into the first-stage resonator hole and soldered. Further, a flat plate capacitor 28 is connected from the connector 22 to the housing base 20 by a lead 26. These constitute an input / output matching circuit 30.
The housing base 20 is covered with a cover (not shown) to shield the dielectric filter inside.

The effective volume of the manufactured dielectric filter is 1
It is 5.4 cc (70 mm × 20 mm × 11 mm), and the effective volume of the conventional coaxial filter is 205.5 cc (118 mm × 67 mm).
mm × 26 mm).
The dielectric constant of the dielectric ceramic material used was 39.
0.

FIG. 2 shows an equivalent circuit of this dielectric filter. The configuration of the filter is an interdigital filter including a dielectric filter main body 10 to which a matching circuit 30 having an inductance L in series on both sides of the input and output and a capacitance C in parallel is added.

FIG. 3 shows the in-band pass characteristic of this dielectric filter. Main performances are center frequency 1.2 GHz, insertion loss 0.45 dBmax, and in-band reflection loss 18.5 dBmi.
n, the 3 dB ratio band is 57.5%. The in-band group delay deviation is 4 nsec or less. Then, it was confirmed that the replacement was possible as compared with the performance of the conventional coaxial filter.

In the present invention, the resonator hole diameter d is reduced as much as possible within the range in which molding is possible. Then, by reducing the distance between the resonator holes and increasing the dielectric block width w with respect to the resonator hole diameter d, the side capacitance is reduced and the coupling capacitance is increased.
Thereby, the degree of coupling between the resonators is increased, and the bandwidth can be widened. Dielectric block width w and resonator hole diameter d
FIG. 4 shows the relationship between the ratio band and the ratio w / d. As can be seen from the figure, a ratio bandwidth of 50% or more can be obtained when 6 ≦ w / d. The resonator hole diameter d has a limit in reducing the diameter in the forming operation and the conductor layer forming operation, and the limit is considered to be 0.8 mmφ. Even if w / d is larger than 10, the fractional band does not become too large, and the dielectric block becomes large due to the limit of reducing the diameter of the resonator hole, which is not practical. Therefore, w / d ≦ 10 is a preferable range.

The design of the dielectric filter is performed as follows. When aiming at miniaturization, the resonator hole diameter d is reduced to the limit that can be manufactured. High performance (insertion loss, reflection loss)
When aiming at, it is a value that satisfies the target value. Then, w / d is determined according to the required fractional band, and the pitch between the resonator holes is determined by calculation or experiment. This pitch between holes is
It is determined so that the necessary in-band reflection loss can be obtained. As the resonator hole diameter becomes smaller, the impedance becomes lower and the
Ω, sufficient matching cannot be obtained with only the dielectric filter body. Therefore, the input and output are adjusted by adding a matching circuit composed of a series inductance and a parallel capacitance. Specifically, the input / output impedance is adjusted to 50Ω by adjusting the length of the 50Ω coaxial cable and the capacitance of the flat plate capacitor.

Although the preferred embodiment of the present invention has been described in detail, the present invention is not limited only to such a configuration. The number of resonator holes (the number of steps) formed in the dielectric block is not limited to thirteen, but actually seven or more are considered necessary. Although a 50Ω coaxial cable is used in the input / output matching circuit, a coil may be used instead of the coaxial cable.

[0017]

As described above, the present invention provides a matching circuit comprising a series inductance and a parallel capacitance at the input and output of an interdigital dielectric filter body having a resonator hole diameter smaller than the dielectric block width. Are connected, whereby a broadband dielectric filter having a fractional bandwidth of 50% or more can be obtained. As a result, it becomes possible to use a dielectric filter in place of the conventional coaxial filter in the IF frequency band for satellite broadcast reception or the like, and it is possible to greatly reduce the size.

[Brief description of the drawings]

FIG. 1 is a perspective view showing one embodiment of a dielectric filter according to the present invention.

FIG. 2 is an equivalent circuit diagram thereof.

FIG. 3 is a characteristic diagram showing the in-band pass characteristic.

FIG. 4 is a graph showing a relationship between w / d and a bandwidth ratio.

[Explanation of symbols]

 Reference Signs List 10 dielectric filter body 12 resonator hole 20 housing base 22 connector 24 coaxial cable 28 flat plate capacitor

Continuation of the front page (56) References JP-A-4-292001 (JP, A) JP-A-3-143103 (JP, A) JP-A-7-283604 (JP, A) JP-A-6-125202 (JP) JP-A-3-187502 (JP, A) JP-A-61-99401 (JP, A) JP-A-59-75902 (JP, A) JP-A-2-73802 (JP, U) JP-A-73802 (JP, U) 1-67807 (JP, U) Japanese Utility Model Showa 62-121804 (JP, U) Table 6-6-507764 (JP, A) Table 2 2-500320 (JP, A) (58) Fields surveyed (Int. Cl. ⁷ , DB name) H01P 1/205 H01P 7/04

Claims (4)

(57) [Claims] A plurality of resonator holes are provided in a longitudinal direction of a substantially rectangular parallelepiped dielectric block, and a conductor layer is formed on most of an outer surface of the dielectric block and an inner surface of the resonator hole. The resonator hole has one open end on the open side, the other open end on the short-circuit side, and an adjacent resonator hole, in an interdigital dielectric filter having a structure in which the open side and the short-circuit side are alternately positioned. Each resonator hole has the same hole diameter, and seven or more (however, an odd number) are provided on the center straight line, and the dielectric block width (dielectric block) is provided.
In the longitudinal direction on the surface where the lock resonator hole is open
Assuming that w is the length of the side in the orthogonal direction) and d is the resonator hole diameter, the ratio (w / d) is set to 6 ≦ w / d,
A broadband dielectric filter, wherein a matching circuit having a series inductance and a parallel capacitance is connected to the input and output. 2. One end of a coaxial cable is connected to a connector attached to a housing base, and a core wire of the other end of the coaxial cable is inserted into a first-stage resonator hole and soldered. 2. The dielectric filter according to claim 1, wherein a capacitor is connected to form an input / output matching circuit. 3. The relationship between a dielectric block width w and a resonator hole diameter d.
3. The dielectric filter according to claim 1, wherein the ratio (w / d) is set to satisfy 6 ≦ w / d ≦ 10. 4. A dielectric block having thirteen resonator holes.
The ratio (w / d) between the lock width w and the resonator hole diameter d is w / d ≒
3. The dielectric filter according to claim 1, wherein said dielectric filter is set to 7.