Band-pass filter

Abstract

 A band-pass filter includes a first substrate (10) having a first triangular microstrip conductor (11) formed thereon, a second substrate (20) having a second triangular microstrip conductor (21) formed thereon, and a shielding case (18) mounted on the first substrate (10) to cover the first microstrip conductor (11). The second substrate (20) is mounted on the inner surface of the top plate (18a) of the shielding case (18) such that the second microstrip conductor (21) faces the first substrate (10) and does not overlap the first microstrip conductor (11) in plan view. In this manner, the first microstrip conductor (11) is coupled with the second microstrip conductor (21).

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

[0001] The present invention relates to a band-pass filter having microstrip conductors, and particularly to a band-pass filter having triangular microstrip conductors.

2. Description of the Related Art

[0002] Nowadays, band-pass filters having triangular microstrip conductors (sometimes called cymbal band-pass filters) are being studied.

[0003] Fig. 4 is an exploded perspective view of a conventional cymbal band-pass filter, which includes a substrate 30 having two triangular microstrip conductors 31 and 32 formed on the upper surface thereof. The first microstrip conductor 31 and the second microstrip conductor 32 are shaped like isosceles triangles of the same size, and are disposed so that corresponding sides (bases) of the two microstrip conductors 31 and 32 are parallel to each other. The distance between the parallel bases and the sizes of the microstrip conductors determine characteristics such as the band-pass center frequency, bandwidth, loss, and skirt characteristics. In order to achieve a band-pass center frequency of 25 GHz, for example, the length W of each base is about 4.77 mm, the distance G between the bases is 0.15 mm, and the height K from each base to the opposite apex is 0.6 mm. The thickness H of the substrate 30 is 0.25 mm.

[0004] Referring again to Fig. 4, the substrate 30 has a first conductive line 33, a second conductive line 35, and an amplifier 34. The first conductive line 33 is connected to the apex opposite to the base of the first microstrip conductor 31. The input terminal (or output terminal) of the amplifier 34 is connected to the apex opposite to the base of the second microstrip conductor 32. The output terminal (or input terminal) of the amplifier 34 is connected to the second conductive line 35. The substrate 30 further includes a grounding conductor (not shown in Fig. 4) formed on its back surface. The conductive lines 33 and 35 have a characteristic impedance of, for example, 50 ohm. One of the conductive lines 33 and 35 is used for signal input and the other for signal output. Useful information about these band-pass filters can be found in non-patent document, IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES, VOL. 50. NO. 5, MAY 2002, P. 1431-1432, for example.

[0005] Referring again to Fig. 4, the substrate 30 further includes bar conductors 36 and 37 along both sides of the first microstrip conductor 31 and the second microstrip conductor 32. The bar conductors 36 and 37 are connected to the grounding conductor on the back surface of the substrate 30 by means of conductive holes (not shown in Fig. 4). The band-pass filter includes a U-shaped shielding case 38 covering the first microstrip conductor 31 and the second microstrip conductor 32. The shielding case 38 has legs 38a and 38b soldered to the bar conductors 36 and 37, respectively.

[0006] In the band-pass filter described above, the apexes opposite to the bases of the two triangular microstrip conductors function as the input terminal and the output terminal of the band-pass filter, where the distance between the input and output terminals is about 1.35 mm. Furthermore, the band-pass filter has the amplifier as a peripheral circuit connected thereto, and therefore requires a certain area for the amplifier. This area for the amplifier adds to the footprint of the band-pass filter.

SUMMARY OF THE INVENTION

[0007] Accordingly, an object of the present invention is to provide a band-pass filter requiring a smaller footprint while still including a peripheral circuit.

[0008] In order to achieve the object described above, a band-pass filter according to an aspect of the present invention includes a first substrate having a first triangular microstrip conductor formed on one surface thereof and a grounding conductor formed on the other surface thereof; a second substrate having a second triangular microstrip conductor formed on one surface thereof and a grounding conductor formed on the other surface thereof; and a shielding case covering the first microstrip conductor. The shielding case includes a top plate and side plates, the side plates being connected to the first substrate. The second substrate is mounted on the inner surface of the top plate of the shielding case such that the second microstrip conductor faces the first substrate and does not overlap the first microstrip conductor in plan view. In this manner, the first microstrip conductor is coupled with the second microstrip conductor, while a space for a peripheral circuit can be allocated on the first substrate, below the second microstrip conductor. Thus, the present invention can provide a compact band-pass filter which requires only a small footprint while still including a peripheral circuit.

[0009] Furthermore, one side of the second microstrip conductor may be substantially directly above and parallel with one side of the first microstrip conductor. Thus, the two microstrip conductors can be sufficiently coupled with each other.

[0010] An amplifier may be formed in an area of the first substrate, namely, the area facing the second substrate, such that the apex opposite to the side of the second microstrip conductor is connected to the input terminal or the output terminal of the amplifier. Thus, the present invention can provide a band-pass filter with an integrated amplifier.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] 

Fig. 1 is an exploded perspective view of a band-pass filter according to the present invention;

Fig. 2 is a sectional view of a relevant part of a band-pass filter according to the present invention;

Fig. 3 is a plan view illustrating the positional relationship between a first microstrip conductor and a second microstrip conductor of a band-pass filter according to the present invention; and

Fig. 4 is an exploded perspective view of a conventional band-pass filter.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] A band-pass filter according to the present invention is illustrated in Figs. 1 to 3. Fig. 1 is an exploded perspective view of the band-pass filter. Fig. 2 is a sectional view of a relevant part of the band-pass filter. Fig. 3 is a plan view illustrating the positional relationship between two microstrip conductors of the band-pass filter.

[0013] Referring to Figs. 1 to 3, a band-pass filter according to the present invention includes a first substrate 10, a second substrate 20, and a shielding case 18.

[0014] The first substrate 10 includes a first isosceles-triangle-shaped microstrip conductor 11 formed on its upper surface, a peripheral circuit 12, such as an amplifier, adjacent to one side (base) of the first microstrip conductor 11, a first conductive line 13 connected to the apex opposite to the base of the first microstrip conductor 11, a second conductive line 14 connected to the input terminal (or output terminal) of the peripheral circuit 12, and a grounding conductor 17 formed on its entire lower surface.

[0015] The first microstrip conductor 11 has a side (base) length W of about 4.77 mm and a distance (height) K between the base and the apex opposite to the base of about 0.6 mm. The first conductive line 13 and the second conductive line 14 extend away from each other. One of the conductive lines 13 and 14 is used for signal input and the other for signal output.

[0016] The first substrate 10 further includes bar conductors 15 and 16 extending along both sides of the first microstrip conductor 11 and the peripheral circuit 12, that is, the two sides parallel to the direction in which the first microstrip conductor 11 and the peripheral circuit 12 are arranged. The grounding conductor 17 is connected to the bar conductors 15 and 16 by means of, for example, conductive holes (through-holes) (not shown in Figs. 1 to 3).

[0017] The shielding case 18 is U-shaped, having a top plate 18a and two side plates 18b and 18c formed by bending the top plate 18a. The side plates 18b and 18c are soldered to the bar conductors 15 and 16, respectively, on the first substrate 10, in order to cover the first microstrip conductor 11 and the peripheral circuit 12.

[0018] The second substrate 20 has a second isosceles-triangle-shaped microstrip conductor 21 formed on its lower surface and a grounding conductor 22 on its upper surface. The second microstrip conductor 21 has the same shape and size as the first microstrip conductor 11. The second substrate 20 is mounted on the shielding case 18 such that the grounding conductor 22 is in surface contact with the inner surface of the top plate 18a and one side (base) of the second microstrip conductor 21 is perpendicular to the surfaces of the side plates 18b and 18c. When mounted on the shielding case 18, the second substrate 20 occupies substantially half the area of the inner surface of the top plate 18a.

[0019] Referring to Figs. 2 and 3, with the shielding case 18 mounted on the first substrate 10, the second microstrip conductor 21 does not overlap the first microstrip conductor 11 in plan view; the second microstrip conductor 21 is disposed above the peripheral circuit 12. The base of the first microstrip conductor 11 is aligned and parallel with the base of the second microstrip conductor 21 in plan view, the two microstrip conductors 11 and 21 being symmetrical with respect to the base line, as shown in Fig. 3. The vertical distance G (not shown in Figs. 1 to 3) between the first substrate 10 and the second substrate 20 is about 0.15 mm.

[0020] The apex opposite to the base of the second microstrip conductor 21 is connected to the input terminal (or the output terminal) of the peripheral circuit 12 with a lead wire 23 such as a bonding wire.

[0021] According to the structure described above, the first microstrip conductor 11 and the second microstrip conductor 21 are coupled with each other near their bases to function as a band-pass filter with a center frequency of 25 GHz.

[0022] The footprint of the band-pass filter including the peripheral circuit 12 is small because the peripheral circuit 12 is formed on the first substrate 10 disposed below the second substrate 20.

Claims

1. A band-pass filter comprising:

a first substrate including:

a first triangular microstrip conductor formed on one surface thereof; and

a grounding conductor formed on the other surface thereof;

a second substrate including:

a second triangular microstrip conductor formed on one surface thereof and coupled with the first triangular microstrip conductor; and

a grounding conductor formed on the other surface thereof; and

a shielding case covering the first microstrip conductor, the shielding case including:

a top plate; and

side plates connected to the first substrate,

   wherein the second substrate is mounted on the inner surface of the top plate such that the second microstrip conductor faces the first substrate and does not overlap the first microstrip conductor in plan view.

2. The band-pass filter according to claim 1, wherein a first side of the second microstrip conductor is substantially directly above and parallel with a first side of the first microstrip conductor.

3. The band-pass filter according to claim 2, further comprising an amplifier formed in an area of the first substrate, the area facing the second substrate, wherein the apex opposite to the first side of the second microstrip conductor is connected to an input terminal or an output terminal of the amplifier.

Drawing