JP2001185887A - High-frequency circuit unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high-frequency circuit unit for suppressing electromagnetic coupling between circuits, and at the same time reducing the costs and size. SOLUTION: Plurality types of high-frequency circuits connected by a transmission line are accommodated in conductive shield cases 10 and 20. In the case 10, a shield wall 21 with ground potential, whose tip points to a through hole 14 and a grounding pattern 15 is included between at least two high-frequency circuits. The height of the shield wall 21 is an integer multiple of half the transmission wavelength.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-frequency circuit unit including a plurality of high-frequency circuits operating in a microwave band or a millimeter-wave band, and more particularly, to a method for easily coupling electromagnetic fields between high-frequency circuits. Regarding the structure to prevent.

[0002]

2. Description of the Related Art In a microwave band or a millimeter wave band, a plurality of high-frequency circuits, such as a transmission circuit and a reception circuit, are generally unitized to achieve compactness. The circuits are connected by a transmission line such as a microstrip line formed on the same substrate, but these high-frequency circuits make the electromagnetic field on the transmission line discontinuous. Field leakage couples to other high frequency circuits (electromagnetic coupling). For example, the transmission circuit
In addition to amplifiers, driver amplifiers, power amplifiers, etc.,
Although it is configured to include a filter and a power monitor, the connection points of these circuits are all discontinuous points in terms of electromagnetic fields, and cause mutual interference due to electromagnetic field coupling. Therefore, in the conventional high-frequency circuit unit, as shown in FIG.
And the circuit is electromagnetically shielded, and the circuits are connected by a connector CN mounted on the metal case K. In this way, electromagnetic field coupling between circuits can be reliably avoided.

As shown in the external view of FIG. 10, a high-frequency circuit is mounted in each small room 31 of a metal case body 30 divided into a plurality of small rooms 31 by a shielding wall 32, and the upper part thereof is covered with a metal cover. A high-frequency circuit unit having a structure covered by 40 is also known. In the case of the high-frequency circuit unit having this structure, the shielding for preventing the electromagnetic field coupling is shown in FIG.
As shown in the cross-sectional view of FIG. 1, among the plurality of high-frequency circuits mounted on the substrate 11, the high-frequency circuits in each small room 31 are surrounded by a shielding wall 32 and a metal cover 40. What is important here is that the ground potential of the transmission line L connecting the high-frequency circuits and the potentials of the metal cover 40 and the shielding wall 32 are made equal to the ground potential in order to complete the shielding. Note that, in FIG. 11, a portion surrounded by a dotted line is a magnetic field component, and a portion indicated by a solid arrow is an electric field component.

[0004]

In the high-frequency circuit unit having a metal case shown in FIG. 9, as the number of circuits increases, the number of metal cases K increases accordingly. Therefore, the size of the unit increases. In the high-frequency circuit unit shown in FIG. 10, since the metal case body has a complicated shape,
The processing is difficult, and the manufacturing cost cannot be reduced. In addition, since it is necessary to ensure sufficient mechanical contact for setting the potential of the metal cover and the shielding wall to the ground potential, high processing accuracy is required. Therefore, the conventional high-frequency circuit unit is significantly disadvantageous in terms of mass productivity and miniaturization. SUMMARY OF THE INVENTION It is a main object of the present invention to provide a high-frequency circuit unit capable of reliably suppressing electromagnetic field coupling, easily realizing a structure therefor, and reducing manufacturing cost and size.

[0005]

According to the present invention, there is provided a high-frequency circuit unit in which a plurality of types of high-frequency circuits connected by transmission lines are accommodated in a conductive shield case. Of the plurality of types of high-frequency circuits, between at least two high-frequency circuits to be shielded from an electromagnetic field, a conductive shielding wall having a ground potential whose tip is directed to a ground portion is interposed. The height of the conductive shielding wall is an integral multiple of half the transmission wavelength. When the height of the conductive shielding wall is determined in this way, even if the grounding part is not in mechanical contact, the electromagnetic shielding is equivalent to a short circuit state, and the shielding of the electromagnetic field is prevented. Be perfect.

[0006] The shield case is usually composed of a case body and a conductive case cover. The case body is provided with the grounding portion in a pattern according to a mounting state of a high frequency circuit to be electromagnetically separated. Then, a conductive shielding wall having a shape corresponding to the pattern of the ground portion is formed integrally with the case cover. In a preferred embodiment, a plurality of types of high-frequency circuits to be shielded and transmission lines for connecting them are mounted on the same plane. In this case, the processing of the case body is facilitated, and the manufacturing cost can be reduced.

In order to mount them on the same plane, for example, a plurality of types of high-frequency circuits and a transmission line for connecting them may be mounted on a single substrate. In this case, preferably, a through hole is formed in the substrate along the pattern of the ground portion.

The transmission line may be a microstrip line or a coplanar line (coplanar transmission line). Further, since the shielding wall only needs to ensure conductivity, it may be made of a polymer material formed integrally with the case cover and having a metalized surface in addition to metal or the like.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will
An embodiment when applied to a high-frequency circuit unit operating in the GHz band will be described. This high frequency circuit unit
It comprises a case body and a case cover joined to the case body. A board is housed in the case body, as in the case of this type of the related art, and a high-frequency circuit is mounted on the board together with a transmission line for connecting them. As described above, these high-frequency circuits become discontinuous points on the transmission circuit and cause electromagnetic field coupling.

Here, in order to clarify the features of the present invention described below, a conventional high-frequency circuit unit having a conductive case body and a case cover will be described.
As shown in the cross-sectional view of FIG. 4, the conventional high-frequency circuit unit mounts a plurality of types of high-frequency circuits, for example, a transmission circuit and a reception circuit on the substrate 211 of the case main body 210,
While connecting each circuit with transmission lines L1 and L2,
The case body 210 is structured to be covered with a case cover 220. A ground pattern 214 is formed below the substrate 211 or around the substrate 211.

The transmission lines L1 and L2 are usually microstrip lines formed on the substrate 11. In FIG. 4, a dotted line indicates a magnetic field component, and a solid arrow indicates an electric field component. In the case of the high-frequency circuit unit having the structure shown in FIG. 4, the electromagnetic field M1 is provided between the transmission line L1 of one high-frequency circuit (for example, a transmission circuit) and the transmission line L2 of the other high-frequency circuit (for example, a reception circuit). No structure can prevent binding. Therefore, electromagnetic field coupling occurs according to the interval between the transmission lines L1 and L2 and the distribution of the electromagnetic field M1 at the discontinuous point. As a result, for example, the transmission wave from the transmission circuit affects the reception wave in the reception circuit as noise, and the noise figure of the reception circuit is deteriorated. If the transmitted wave is electromagnetically coupled to the receiving circuit at a high level, the low-level signal placed before the receiving circuit
The noise amplifier saturates, causing sensitivity suppression. If a loop is formed via the frequency conversion unit (mixer), there is a possibility of loop oscillation. Therefore, the structure shown in FIG. 4 is not always suitable for practical use depending on the operating frequency.

The problem of the high-frequency circuit unit having such a structure can be solved to some extent by improving the structure on the case body side. That is, as shown in the cross-sectional view of FIG. 5, the through hole 14 and the ground pattern 15 are formed in the substrate 11 on the case body 10 side. By doing so, the electric field components of the transmission lines L1 and L2 on the substrate 11 are absorbed by the ground pattern 15 of the through hole 14, so that
The radiation of the fundamental mode of the electromagnetic field M2 is suppressed, and the electromagnetic field coupling is reduced.

The method of forming the through hole 14 and the ground pattern 15 is well known, and a detailed description thereof will be omitted.

In this embodiment, in order to further reduce the electromagnetic coupling, a high-frequency circuit unit having a characteristic structure of the case cover as well as a characteristic structure of the case body as shown in FIG. 5 is used.

FIGS. 1A and 1B are exploded views of the high-frequency circuit unit according to the present embodiment. FIG. 1A is a rear view of a case cover 20 and FIG. FIG.
FIG. 3 is a cross-sectional view of the high-frequency unit in the AA direction.

The structure on the case body 10 side is basically the same as that shown in FIG. That is, the case body 1
A substrate 11 is mounted on the substrate 0, and a high-frequency circuit including a transmission circuit 12 and a reception circuit 13 to be shielded is mounted on the substrate 11. The circuits are connected by a transmission line L which is a microstrip line. The transmission line of the transmission circuit 12 is L1, and the transmission line of the reception circuit 13 is L2. Between the transmitting circuit 12 and the receiving circuit 13 on the substrate 11, a through hole 14 and a ground pattern 15 are formed. The ground pattern 15 is electrically connected to the conductive case body end 10a, and both are at the ground potential.

The case cover 20 is a flange-shaped member made of a conductive material, and its end 20a is connected to the end 1 of the case body.
0a. When the end portion 20a is joined to the case body end portion 10a, the entire shield case is set to the ground potential so that the internal high-frequency circuit group can be shielded from external electromagnetic waves.

The portion corresponding to the ground pattern 15 on the rear side of the case cover 20 is connected to the conductive shielding wall 2.
1 is protruding. The height of the shielding wall 21 is the end 2
The height G is shorter than the height 0a, and is a height at which a gap G1 is formed between the case body end 10a and the end 20a of the case cover 20 and the ground pattern 15. However, even if the gap G1 is mechanically formed, the height is a height that satisfies the condition equivalent to being electrically in contact with the ground pattern 15. Hereinafter, this principle will be described with reference to FIGS.

FIG. 6 is an equivalent circuit of a general transmission model in which two high-frequency circuits are connected by a transmission line. The characteristic impedance of the transmission line is Z, and the transmission electrical angle is represented by θ. In this transmission model, if a terminal of one high-frequency circuit is represented by c-c 'and a terminal of the other high-frequency circuit is represented by dd' by a four-terminal circuit, the transmission matrix F is defined by the following equation.

[0021]

F = | cos θ jZ sin θ | (1) | j sin θ / Z cos θ |

The terminals dd 'of this transmission model are short-circuited,
From the middle of the terminal cc ', the terminal a-
FIG. 7 shows a state where the connection is branched to a 'and bb'. FIG. 7 shows a model in which mutual interference due to electromagnetic field coupling occurs between two high-frequency circuits. That is, electromagnetic field coupling occurs in the middle of the terminals aa ′ and bb ′. In this case, the terminal cc ′
, The impedance Zcc ′ as viewed in the direction of dd ′ is defined by “jZtan θ” from the above equation (1). Transmission electrical angle θ is transmission line length 1 and transmission wavelength (free space wavelength)
Is defined as λg, and is defined by the following equation. θ = 2πl / λg (2)

In equation (2), if the transmission line length l is selected to be an integral multiple of 1/2 of λg, the transmission electrical angle θ becomes nπ (n: an integer), and the impedance Zcc ′ becomes zero. Z
The electrical circuit meaning that cc ′ is zero is “short circuit of connection end cc ′”. In other words, the transmission model (terminals aa ′, bb ′) assuming electromagnetic field coupling is short-circuited at the terminal cc ′ on the way, and the interference between the two high-frequency circuits is theoretically possible. Completely suppressed.

In the case of the high-frequency circuit unit having the structure shown in FIG.
On the surface of the shielding wall 21 protruding from the case cover 20, an electromagnetic wave (TEM wave: Tr
ansverse ElectroMagnetic wave). This T
The EM wave is equivalent to an electromagnetic wave transmitted through the branch circuit connected to the terminal cc ′ in FIG. That is, a transmission model assuming electromagnetic field coupling between the transmission circuit 12 and the reception circuit 13 is equivalent to the transmission model in FIG.

Therefore, assuming that the height of the shielding wall 21 is 1 and the transmission wavelength is λg, if l is an integral multiple of λ of λg, the ground pattern 15 and the shielding wall 21 are mechanically separated. Even if there is no contact, it is electromagnetically short-circuited, and a condition equivalent to the case where both are completely contacted by a conductor is established. Therefore, electromagnetic coupling between the two high-frequency circuits of the transmission circuit 12 and the reception circuit 13 can be reliably avoided.

However, the present invention does not mean that the ground pattern 15 and the shielding wall 21 must always be in a mechanically non-contact state. It simply means that it may be in a non-contact state. In other words, without having to precisely process the shield case as in the conventional high-frequency circuit unit,
This means that electromagnetic field coupling between the high-frequency circuits in the case can be avoided. As a result, manufacturing costs can be reduced. This has a very important meaning in manufacturing a unit used in a millimeter wave band.

The gap G1 at the time of non-contact depends on the operating frequency.
There is no problem within the range of 0.5.

Although the above description has been made on the assumption that the transmission lines L1 and L2 are microstrip lines, the transmission lines may be coplanar lines. FIG.
FIG. 4 is a sectional structural view of a high-frequency circuit unit when a coplanar line is used as a transmission line. Except that the ground pattern 14 is formed on the substrate 11, the configuration is the same as that when the microstrip line is used for the transmission line. The basic operation principle is the same as that of the microstrip line.

The description has been made on the assumption that the shielding wall 21 is formed integrally with the conductive case cover 20. However, after molding or processing a rigid polymer material such as plastic, the surface of the shielding wall 21 is formed. May be used as the shielding wall 21. However, in this case, it is necessary to make the thickness of the metallization sufficient to be five times or more the skin depth of the operating frequency.

FIG. 8 is a characteristic diagram showing the result of actually measuring the degree of electromagnetic field coupling of the high-frequency circuit unit. In the figure, the vertical axis represents the degree at which the transmission wave from the transmission circuit 12 acts on the reception circuit (transmission wave coupling degree: dB), and the horizontal axis represents the circuit operating frequency (GHz). The degree to which the transmission wave output from the transmission circuit 12 is coupled to the reception end of the reception circuit 13 is indicated by A when only the through hole 14 and the ground pattern 15 are used, and B when the shielding wall 21 is used in combination. From this figure, it can be seen that the combined use of the shielding wall 21 can reduce the electromagnetic coupling of about -27 dB as compared with the case where only the ground pattern including the through hole 14 is used.

[0031]

As is apparent from the above description, according to the present invention, even if there is a partial mechanical non-contact between the shielding wall in the shield case and the grounding portion, electromagnetically, Since both are equivalent to a short circuit, a specific effect is obtained in that unevenness in mechanical processing accuracy can be absorbed while reliably reducing electromagnetic field coupling between high-frequency circuits. As a result, it is possible to simultaneously satisfy the demand for reducing the manufacturing cost and the size of the unit.

[Brief description of the drawings]

FIG. 1 is an exploded view of a high-frequency circuit unit according to an embodiment of the present invention, wherein (a) is a rear view of a case cover of a shield case, and (b) is a top view of a case main body.

FIG. 2 is a cross-sectional view of the high-frequency circuit unit of the embodiment in the AA direction.

FIG. 3 is a cross-sectional view of a high-frequency circuit unit when a transmission line is a coplanar line.

FIG. 4 is a cross-sectional view of a high-frequency circuit unit in which electromagnetic field coupling is free.

FIG. 5 is a cross-sectional view of a high-frequency circuit unit having a through hole and a ground pattern.

FIG. 6 is an equivalent circuit (general model) of a transmission model showing the principle of the present invention.

FIG. 7 is an equivalent circuit of a transmission model showing the principle of the present invention (a model in which electromagnetic coupling occurs).

FIG. 8 is a characteristic diagram obtained by actually measuring an electromagnetic field coupling ratio according to the present invention.

FIG. 9 is an external perspective view of a conventional general high-frequency circuit unit.

FIG. 10 is an external perspective view of another conventional high-frequency circuit unit.

FIG. 11 is a sectional view of the high-frequency circuit unit of FIG. 10;

[Explanation of symbols]

 10, 30, 210 Case body of shield case 10a Case body end 11 Substrate housed in case body 12 Transmitting circuit as an example of high-frequency circuit 13 Receiving circuit as an example of high-frequency circuit 14 Through hole 15 Ground pattern 20, 40 , 220 Shield case cover 20a Case cover end 21, 32 Shielding wall CN connector K Metal case for each circuit

Claims (7)

[Claims] A plurality of types of high-frequency circuits connected by a transmission line are housed in a conductive shield case, and a ground potential between at least two high-frequency circuits whose tip is directed to a ground portion. Wherein the height of the conductive shielding wall is an integral multiple of 1/2 of the transmission wavelength. 2. The shield case includes a case body and a conductive case cover, and the case body has the grounding portion in a pattern corresponding to a mounting state of a high frequency circuit to be electromagnetically separated. The high-frequency circuit unit according to claim 1, wherein a conductive shielding wall having a shape corresponding to a pattern of a ground portion is formed integrally with the case cover. 3. The high-frequency circuit unit according to claim 1, wherein a plurality of types of high-frequency circuits to be shielded and a transmission line for connecting these are mounted on the same plane. 4. The plurality of types of high-frequency circuits and a transmission line for connecting them are mounted on a single substrate, and through holes are formed in the substrate along the pattern of the ground portion. The high-frequency circuit unit according to claim 3, wherein: 5. The high-frequency circuit unit according to claim 4, wherein said transmission line is a microstrip line formed on said substrate. 6. The high-frequency circuit unit according to claim 4, wherein said transmission line is a coplanar line formed on said substrate. 7. The conductive shield according to claim 1, wherein the conductive shielding wall is formed integrally with the case cover and the surface thereof is made of a polymerized metal material. High frequency circuit unit.