JP3399747B2 - Microwave circuit shield case - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a microwave circuit shield case, and more particularly to a microwave circuit provided with a local oscillator circuit such as a satellite broadcast receiving converter (LNB). The structure of the shield case.

[0002]

2. Description of the Related Art For example, a satellite broadcast converter (L
Conventionally, a microwave device including a local oscillator circuit such as NB) is configured as shown in FIG. It should be noted that, in the figure, the respective constituent portions are drawn apart for the sake of understanding, but in reality, they are in contact with each other as described below. In the figure, 2
Is a microstrip line substrate, on the surface of which a circuit pattern and a ground pattern 2a are provided, and a local oscillator circuit and other circuit parts are mounted on this surface. Further, the ground conductor 2b is provided on the entire back surface. Reference numeral 3 denotes a shield case (referred to as a first shield case) as a main body housing mainly made of aluminum die-cast, which has a box-like shape. The substrate 2 is attached to the first shield case 3 as illustrated. As shown in the figure, the ground conductor 2b on the back surface of the substrate is brought into surface contact with the inner bottom surface of the shield case 3.

Further, as in the above description, 1 is a shield case (hereinafter referred to as a second shield case) mainly made of aluminum die cast, and has a box shape. This second
The shield case 1 is attached so as to contact the inside of the first shield case 3, and the opening sides (1a, 1b, etc.) of the second shield case 1 contact the ground pattern 2a on the substrate surface. By shielding the substrate 2 in the above manner, leakage of electromagnetic waves from the local oscillation circuit or the like to the outside or jumping of unnecessary electromagnetic waves from the outside is prevented. In order to enhance the shield effect, a method of connecting the front surface ground pattern 1a of the substrate 2 and the back surface ground conductor 2b with a through hole is generally used together.

[0004]

However, in the case of the conventional shield method, the contact between the opening side of the second shield case 1 and the ground pattern 2a on the substrate surface may be insufficient. In such a case, the shield effect is reduced and the electromagnetic wave leakage to the outside is increased. In particular, since the level of the local oscillation signal is usually high, if there is a contact insufficient portion as described above, external leakage of the same signal component increases. Therefore, there is a demand for a shield technique that suppresses leakage of a specific frequency such as a local oscillation signal to the outside even when the contact is insufficient as described above. The present invention has been made from such a background,
An object of the present invention is to provide a shield case for a microwave circuit, which can enhance the shield effect in the microwave circuit.

[0005]

DISCLOSURE OF THE INVENTION The present invention provides a box-shaped first shield in which a microstrip line substrate having a circuit pattern and a ground pattern on the front surface and a ground conductor on the back surface is opened. The front surface of the board is attached to the inner bottom surface of the case so that the ground conductor on the back surface of the board is in surface contact, and the opening side of a box-shaped second shield case having an opening at the bottom is attached to the first shield case. Which is attached so as to be in contact with the ground pattern provided on the periphery of the second shield case, a specific frequency for which leakage to the outside is desired to be suppressed at the periphery of the opening of the second shield case.
A microwave circuit shield case is provided in which a slit groove having a required width and depth set according to the wavelength is provided, and the peripheral edge is in contact with the peripheral edge of the substrate surface.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION A slit groove is provided on the opening side (all sides) of a box-shaped second shield case provided so as to cover the surface (component side) of a microstrip line substrate. For example, the depth of the slit groove is set to a length of about ½ of a wavelength of a specific frequency at which leakage to the outside such as a local oscillation signal is desired to be suppressed, and the width of the slit groove is set to about ½ of the same wavelength. Make it 20 or less. This further suppresses external leakage for the specific frequency. Further, the slit groove may be provided not on the entire opening side but on the opening side in the vicinity of a large oscillation level, such as in the vicinity of the local oscillation circuit. Further, the slit groove may be filled with a dielectric. Thereby, the depth of the slit groove can be shortened by the length determined by the relative permittivity of the dielectric.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A microwave circuit shield case according to the present invention will be described below with reference to the drawings in the same manner as the above (prior art)
An LNB (satellite broadcast receiving converter) will be described as an example.
For convenience of description, FIG. 5 used in the description of the conventional technique is also used. FIG. 1 is an embodiment of a shield case for a microwave circuit according to the present invention, and is a bottom view (A) and a side sectional view (B) of a main part of a second shield case 1 of FIG. 2 is for explaining FIG. 1, and is an enlarged view of a side sectional view of a main part based on FIG. 5, FIG. 3 is an explanatory view of input impedance, and FIG. It is a principal part bottom view of the shield case 1 of FIG. LN
B is configured such that the microstrip line substrate 2 is shielded by the first shield case 3 as the main body casing and the second shield case 1 as already described in FIG. 5 (FIG. 5). .

As shown in FIG. 1, the present invention is characterized in that a slit groove 11 is provided on the opening sides 1a, 1b, 1c (1d is omitted because it is a sectional view) of the second shield case 1 having the above-mentioned structure. To do. In FIG. 1, slit grooves are provided on all the opening sides (a method of providing the slits on one side will be described later). FIG. 2 is an enlarged view of the vicinity of the slit groove based on FIG.
Is a second shield case, 2 is a microstrip line, and 3 is a first shield case. The structural relationship between them is as described above with reference to FIG. 5.
The grounding pattern 2a is attached so that the surface 2b is in surface contact with the inner bottom surface of the first shield case 3, and the second shield case 1 is provided with the opening sides 1a and the like on the peripheral edge of the substrate surface.
Attach so that it touches.

The depth and width of the slit groove 11 provided in the second shield case 1 are set as follows. The depth L1 of the slit groove 11 is set to L1 = λ / 2.
The width t of the slit groove 11 is set to t ≦ λ / 20. Here, λ is a wavelength, for example, the wavelength of the local oscillation signal when the local oscillation signal has a shield effect.

The following results can be obtained by setting the depth L1 of the slit groove 11 as described above. 2 and 3, the input impedance Zin when the tip C is seen from the end A or the end B of the slit groove 11 in contact with the ground pattern 2a is expressed as follows. Zin = jZo · tan (β · L1) where Zo is the characteristic impedance of the slit groove and β is the phase constant. Further, for the above β, β = 2π / λ
Is. Therefore, L1 = λ / 2 and β = 2π / λ are set to Zin
Substituting into the expression, the result is as follows. Zin = jZo · tan {(2π / λ) · (λ / 2)} = jZo
・ Tan π = 0

As in the above equation, the input impedance Zin becomes zero. This means that the signal component of the wavelength λ (local oscillation signal or the like) is grounded through the points A and B and does not leak to the outside. In this way, by providing the slit groove, a shielding effect is exerted on a specific frequency component (local oscillation signal or the like). Therefore, by providing the slit groove 11 on the entire opening side of the second shield case 1, the shield effect is maximized. On the other hand, depending on the level of the specific frequency component, such as the local oscillator circuit, the slit groove 11 may be provided only on the opening side near the oscillator circuit (FIG. 4). The slit length S (FIG. 4) in this case may be set according to the desired effect.

Next, a method of filling the slit groove 11 with a dielectric will be described. Up to the above, the inside of the slit groove 11 was air. When the slit groove is filled with a dielectric material, the required slit groove depth L2 is as follows. L2 = L1 / (square root of εs) where εs is the relative permittivity of the filled dielectric. In this way, when the dielectric is filled, the slit groove depth L2
Can be shorter than the depth L1 when the dielectric is not filled, and the slit groove can be easily formed.

[0013]

As described above, according to the present invention, there is provided a microwave equipment such as a satellite broadcast receiving converter (LNB) which is provided with an oscillating circuit and whose shield case covers the microstrip line substrate. , Approximately 1 of the wavelength at a specific frequency is provided at the required location of the shield case
By providing the slit groove having a depth of / 2, it is possible to further suppress the external leakage of the specific frequency. Therefore, the effect of suppressing the external leakage of the specific frequency is added to the conventional ordinary shielding effect. Further, in the past, in order to strengthen the suppression of the external leakage of the specific frequency, a double shield structure has been dealt with, but the present invention eliminates the need for them, and the shield structure is inexpensive, easy and highly reliable. Can be

[Brief description of drawings]

1A and 1B are views showing an embodiment of a shield case for a microwave device according to the present invention, in which FIG. 1A is a bottom view of an essential part of a second shield case 1, and FIG. FIG.

FIG. 2 is an enlarged view for explaining FIG. 1 and is a side cross-sectional view of a main part of a microwave device using an LNB as an example.

FIG. 3 is an explanatory diagram of input impedance.

FIG. 4 is a view showing another embodiment of the shield case for a microwave device according to the present invention, and is a bottom view of a main part of the second shield case 1.

5A and 5B are views for explaining the related art and FIG. 1 and the like, and are a side sectional view (A) of a main part and a top view (B) of the main part of a microwave device using an LNB as an example.

[Explanation of symbols]

1 Second shield case 1a, 1b opening side 2 Microstrip line substrate 2a Ground pattern 2b Ground conductor 3 First shield case 11 slit groove

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Claims (5)

(57) [Claims] 1. A microstrip line board having a circuit pattern and a ground pattern on the front surface and a ground conductor on the back surface, and the back surface of the board on an inner bottom surface of a box-shaped first shield case having an upper opening. Of the box-shaped second shield case, which is attached so that the ground conductors of the above are in surface contact with each other, and the opening side of the box-shaped second shield case is attached to the ground pattern provided on the peripheral edge of the substrate surface attached to the first shield case. In the case where the second shield case and the second shield case are attached so as to come into contact with each other,
A shield case for a microwave circuit, characterized in that a slit groove having a required width and depth set from a wavelength of a specific frequency at which leakage is desired to be suppressed is provided, and the peripheral edge is in contact with the peripheral edge of the substrate surface. 2. The shield case for a microwave circuit according to claim 1, wherein the depth of the slit groove is approximately ½ of a wavelength of a frequency that suppresses leakage to the outside. Wherein the width of the slit groove, claims 1 to 2 shield case for microwave circuit, wherein it has substantially less than one-twentieth of the wavelength of the frequency to suppress the leakage to the outside. Wherein said slit groove, the second shield case according to claim 1 to 3 shield case for microwave circuit according to characterized in that provided on a part of the periphery of the opening of. 5. Some of the slit groove, filled with a dielectric, claims 1 to 4, wherein it has shallow depth equivalent to the length the slit groove which is determined by the dielectric constant of the dielectric Shield case for microwave circuit.