Signal coupling apparatus and transmitter including signal coupling apparatus

A signal coupling apparatus includes a coaxial type signal coupling element and a structure for fixing the element at a predetermined position on a circuit board. The structure includes a supporting member having a conductive cover part, longitudinal direction facing parts integrated with the cover part, and grounding parts integrated with both lateral sides of the cover part. The cover part is fitted on an external conductor of the element, and the grounding parts are in contact with grounding patterns on the board when the element is disposed at the predetermined position. Fixing elements fix the grounding parts to the board. The facing parts prevent an insulator surrounded by the external conductor from thermally expanding in the longitudinal direction of a central conductor surrounded by the insulator in the element while the element operates. A transmitter includes the above described circuit board and signal coupling apparatus.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority from prior Japanese Patent Application No. 2006-243110, filed Sep. 7, 2006, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a signal coupling apparatus and a transmitter including a signal coupling apparatus.

2. Description of the Related Art

For example, in a transmitter transmitting high-frequency signals such as a transmitter used in a television broadcasting system, a signal coupling apparatus such as a 3 dB coupler line is used for coupling a plurality of high-frequency signals to amplify them.

JP-A-2002-290101 (KOKAI) discloses a tri-plate type signal coupling apparatus. In the tri-plate type signal coupling apparatus, plates (three dielectric plates and a ground plate) used herein must be brought in close contact with one another. However, the mutual closely contact of these plates in the tri-plate type signal coupling apparatus is easy to loosen. As a result, the tri-plate type signal coupling apparatus can not assure sufficient grounding, so that it is difficult to obtain stable and precise high-frequency characteristic.

As another signal coupling apparatus, a coaxial type signal coupling apparatus is also known. The coaxial type signal coupling apparatus is provided with a coaxial type signal coupling element which includes a slender central electrical conductor having both end parts for providing input and output terminals and an intermediate part between the both end parts, an electrical insulator surrounding the intermediate part of the central conductor concentrically, and an external electrical conductor surrounding an outer peripheral surface of the insulator. The insulator is made of heat-resistant synthetic resin such as polyimide, PTFE (polytetrafluoroethylene), and the like.

After the coaxial type signal coupling element is disposed at a predetermined position on a circuit board, both end parts and a central part of the external conductor in a longitudinal direction of the central conductor are soldered to ground patterns on the circuit board, and the input and output terminals at the both end parts of the central conductor are soldered to predetermined input/output connection patterns on the circuit board.

The coaxial type signal coupling apparatus is further provided with a structure for fixing the coaxial type signal coupling element at the predetermined position on the circuit board securely after the coaxial type signal coupling element is disposed at the predetermined position on the circuit board and electrical connection of the signal coupling element to predetermined circuits on the circuit board is terminated as described above.

This fixing structure includes band members and fixing elements. The band members are made of high heat-conductive material such as copper or aluminum, and these are put on the both end parts and the central part on the outer peripheral surface of the external conductor while the coaxial type signal coupling element is disposed at the predetermined position on the circuit board. The fixing elements, for example screws, are made of high heat-conductive material such as metal and fix both end parts of each band member to the circuit board. Distal end parts of the fixing elements penetrate the circuit board and are connected to a chassis supporting the circuit board and made of high heat-conductive material such as metal.

The band members and the fixing elements fix the coaxial type signal coupling element at the predetermined position on the circuit board securely, and transfer heat generated by the coaxial type signal coupling element while it operates to the chassis made of high heat-conductive material to radiate heat from the chassis.

The thermal expansion of the heat-resistant synthetic resin for the insulator is small, but it is not zero. Accordingly, the insulator expands slightly due to heat generated by the coaxial type signal coupling element while it operates. The thermal expansion of the insulator becomes the maximum in a direction along the longitudinal direction of the central conductor because the insulator has the largest size in the above described direction.

The both end parts of the insulator expanded maximum in the longitudinal direction projects outwardly from the both end parts of the external conductor having heat conductance superior to that of the insulator and having thermal expansion smaller than that of the insulator.

When the operation of the coaxial type signal coupling element is stopped and heat generation by the signal coupling element is also stopped, the insulator contracts. At this time, when both end parts of the outer peripheral surface of the insulator are caught by roughly worked portions on inner peripheral edges of end surfaces of the both end parts of the external conductor being in contact with the both end parts of the outer peripheral surfaces of the insulator, the both end parts of the insulator can not return to their initial positions.

As a result, the both end parts of the insulator cause stresses at the soldered portions on the both end parts of the outer peripheral surface of the external conductor. Such stresses occur at the soldered portions each time when the coaxial type signal coupling element stops its operation, so that durability of the soldered portions is lowered. When cracks or fractures occur at the soldered portions, desired grounding of the coaxial type signal coupling element can not be achieved sufficiently so that performance (namely, stable precise high-frequency characteristic) of the coaxial type signal coupling element lowers.

BRIEF SUMMARY OF THE INVENTION

According to one aspect of the present invention, a signal coupling apparatus comprises: a signal coupling element which couples inputted signals and which outputs coupled signal; and a fixing structure which fixes the signal coupling element at a predetermined position on a circuit board including a signal input/output circuit in and from which a predetermined signal is inputted and outputted and signal input/output patterns and grounding patterns for the signal input/output circuit, while the signal coupling element is electrically connected to the signal input/output patterns and grounding patterns. The signal coupling element comprises: a slender central electrical conductor which has both end parts providing input and output terminals electrically connected to the signal input/output patterns on the circuit board and an intermediate part between the both end parts; an insulator surrounding the intermediate part of the central conductor concentrically; and an external electrical conductor surrounding an outer peripheral surface of the insulator. The signal coupling element couples signals inputted from the input terminals and outputs the coupled signal from the output terminal. The fixing structure comprises: a supporting member which includes an electrically conductive cover part, longitudinal direction facing parts provided integrally with the cover part, and electrically conductive grounding parts provided integrally with both sides of the cover part in a radial direction of the central conductor; and fixing elements which fix the grounding parts of the supporting member to the circuit board. The cover part is in contact with an outer peripheral surface of the external conductor of the signal coupling element and extends over a length of the outer peripheral surface in a longitudinal direction of the central conductor. Each facing part faces at least one portion of a peripheral edge of each end surface of the insulator of the signal coupling element in the longitudinal direction of the central conductor. And, each grounding part extends in the longitudinal direction of the central conductor and is in contact with each grounding pattern on the circuit board when the signal coupling element is disposed at the predetermined position on the circuit board. The facing parts prevent the insulator from thermally expanding in the longitudinal direction of the central conductor while the signal coupling element operates.

According to one aspect of the present invention, a transmitter which generates, amplifies, and outputs a desired signal, comprises: a circuit board which includes a signal input/output circuit in and from which a desired signal is inputted and outputted and signal input/output patterns and grounding patterns for the signal input/output circuit; a signal coupling element which is disposed at a predetermined position on the circuit board, which is electrically connected to the signal input/output patterns and grounding patterns, and which couples inputted signals and outputs the coupled signal; and a fixing structure which fixes the signal coupling element to the predetermined position on the circuit board, while the signal coupling element is disposed at the predetermined position on the circuit board and is electrically connected to the signal input/output patterns and grounding patterns. The signal coupling element comprises: a slender central electrical conductor which has both end parts providing input and output terminals electrically connected to the signal input/output patterns on the circuit board and an intermediate part between the both end parts; an insulator surrounding the intermediate part of the central conductor concentrically; and an external electrical conductor surrounding an outer peripheral surface of the insulator. The signal coupling element couples signals inputted from the input terminals and outputs the coupled signal from the output terminal. The fixing structure comprises: a supporting member which includes an electrically conductive cover part, longitudinal direction facing parts provided integrally with the cover part, and electrically conductive grounding parts provided integrally with both sides of the cover part in a radial direction of the central conductor; and fixing elements which fix the grounding parts of the supporting member to the circuit board. The cover part is in contact with an outer peripheral surface of the external conductor of the signal coupling element and extends over a length of the outer peripheral surface in a longitudinal direction of the central conductor. Each facing part faces at least one portion of a peripheral edge of each end surface of the insulator of the signal coupling element in the longitudinal direction of the central conductor. And, each grounding part extends in the longitudinal direction of the central conductor and is in contact with each grounding pattern on the circuit board when the signal coupling element is disposed at the predetermined position on the circuit board. The facing parts prevent the insulator from thermally expanding in the longitudinal direction of the central conductor while the signal coupling element operates.

DETAILED DESCRIPTION OF THE INVENTION

As schematically shown inFIG. 1, a transmitter12for generating a desired signal, amplifying the signal, and outputting the same includes a signal coupling apparatus10according to an embodiment of the present invention, and first and second circuit board parts18aand18b.

The first circuit board part18aincludes a signal input circuit16aon its one surface, and the signal input circuit16ais connected to a power source14. A desired signal is generated and inputted in the signal input circuit16a. The second circuit board part18bincludes a signal output circuit16bon its one surface, and the signal output circuit16boutputs a desired signal. The signal output circuit16bis connected with an antenna20.

A slender opening22(shown inFIGS. 4-6in detail) is formed at a predetermined position on the first circuit board part18a. The signal input circuit16aincludes two signal input patterns24aand24bdisposed near both ends of the opening22in its longitudinal direction, and further includes a dummy pattern24cdisposed near one end of the opening22in the longitudinal direction. The signal output circuit16bincludes a signal output pattern24ddisposed near the other end of the opening22in the longitudinal direction.

The signal input circuit16afurther includes two grounding patterns26aand26bdisposed along two edges of the opening22extending in the longitudinal direction.

That is, in this embodiment, a combination of the signal input circuit16aon the first circuit board part18aand the signal output circuit16bon the second circuit board part18bconfigures a signal input/output circuit in and from which a desired signal is inputted and outputted. Further, in this embodiment, a combination of the two signal input patterns24aand24band two grounding patterns26aand26bon the signal input circuit16aand the signal output pattern24don the signal output circuit16bconfigures signal input/output patterns and grounding patterns for the signal input/output circuit.

In this embodiment, through-holes28(shown inFIGS. 5 and 6in detail) penetrating through the first circuit board part18aare formed in each of the two grounding patterns26aand26bat plural positions spaced apart from one another in a longitudinal direction of each of the grounding patterns26aand26b. In this embodiment, three through-holes28are formed at both end parts and a central part between the both end parts on each of the two grounding patterns26aand26b.

A not shown grounding pattern is also provided on the other surface (back surface) of the first circuit board part18a, and each of the two grounding patterns26aand26bprovided on the one surface is connected to the other not shown grounding pattern on the back surface through not shown conductors provided on inner peripheral surfaces of the through-holes28.

The back surface of the first circuit board part18aopposed to its one surface on which the signal input circuit16ais provided and a back surface of the second circuit board part18bopposed to its one surface on which the signal output circuit16bis provided are supported by an external supporting structure (chassis)30made of electrically conductive material (for example, iron, aluminum, or the like), as shown inFIGS. 4-6. The not shown grounding pattern on the other surface (back surface) of the first circuit board section18ais electrically connected to the external supporting structure (chassis)30while the back surfaces of the first and second circuit board parts18aand18bare supported by the external supporting structure (chassis)30. The external supporting structure (chassis)30further has good heat conductivity.

In this embodiment, spacers32for height adjustment are sandwiched between the first circuit board part18aand the external supporting structure (chassis)30and between the second circuit board part18band the external supporting structure (chassis)30, as shown inFIGS. 4-6. The spacers32are made of electrically conductive material (for example, iron, aluminum, or the like), and these have good heat conductivity. Accordingly, the spacer32achieves electrical connection and thermal connection between the not shown grounding pattern on the other surface (back surface) of the first circuit board part18aand the external supporting structure (chassis)30.

The spacer32does not cover the opening22at the predetermined position on the first circuit board part18a, so that the opening22faces the external supporting structure (chassis)30.

The transmitter12is further provided with a coaxial type signal coupling element34disposed in the slender opening22at the predetermined position on the first circuit board part18a. In this embodiment, the signal coupling element34is electrically connected to the signal input patterns24aand24b, the dummy pattern24c, and the grounding patterns26aand26bon the first circuit board part18a, and the signal output pattern24don the second circuit board part18b. The signal coupling element34couples signals inputted from the signal input patterns24aand24band outputs the coupled signal to the signal output pattern24d.

Specifically, as well shown inFIGS. 2 and 3, the signal coupling element34includes a slender central conductor36having both end parts and an intermediate part between the both end parts, an insulator38surrounding the intermediate part of the central conductor36concentrically, and an external conductor40surrounding an outer peripheral surface of the insulator38. An outer peripheral surface of the external conductor40configures a circular surface having a predetermined diameter.

The insulator38is made of heat-resistant synthetic resin such as polyimide, PTFE (polytetrafluoroethylene), and the like.

The both end parts of the central conductor36provide a first input terminal36aand a second input terminal36b, and further provides a dummy terminal36cand an output terminal36d.

Such a coaxial type signal coupling element34is known and its internal structure is not described in detail.

Incidentally, in this embodiment, each of the first input terminal36a, the second input terminal36b, the dummy terminal36c, and the output terminal36dat the both end parts of the central conductor36has a length longer than a predetermined length.

The transmitter12is further provided with a fixing structure42for fixing the signal coupling element34at a predetermined position (that is, the opening22in the embodiment) on the first circuit board part18a.

The fixing structure42is provided with a supporting member44including a cover part44aof electrically conductive material (for example, copper, aluminum, and the like). The cover part44ais configured to be in contact with an outer peripheral surface of the external conductor40of the signal coupling element34, and extends over at least 50% of a length of the outer peripheral surface of the external conductor40in a direction along a longitudinal center line of the central conductor36.

The supporting member44further includes longitudinal direction facing parts44bprovided integrally with the cover part44a. Each of the longitudinal direction facing parts44bfaces at least one portion of a peripheral edge of each end surface of the insulator38of the signal coupling element34in the longitudinal direction of the central conductor36.

The supporting member44further includes a pair of grounding parts44cof electrically conductive material (for example, copper, aluminum, and the like) on both sides of the cover part44ain a radial direction of the central conductor38. The grounding parts44care integrated with the both sides of the cover part44aand extend in a direction along the longitudinal direction center line of the central conductor38.

Plural through-holes are formed in each of the grounding parts44cat the same arrangement intervals as those of the plural through-holes28formed in each of the two grounding patterns26aand26bof the first circuit board part18a.

In this embodiment, the cover part44aof the supporting member44is configured to cover a predetermined area of the outer peripheral surface of the external conductor40of the signal coupling element34and to make in close contact with the predetermined area. For example, the predetermined area of the outer peripheral surface of the external conductor40is defined by almost a half of a length in a circumferential direction of the outer peripheral surface and a full length in a longitudinal direction of the outer peripheral surface, and the cover part44ahas an approximately semi-circular cross-section with the same radius as that of the predetermined area of the outer peripheral surface of the external conductor40of the signal coupling element34.

Each longitudinal direction facing part44bis configured by an inward flange-shaped part projecting inward from each of the both longitudinal ends of the cover part44ain its radial direction.

The longitudinal direction facing parts44bat the both longitudinal ends of the cover part44aand the grounding parts44cat the both radial sides of the cover portion44aare formed integrally with the cover part44awith the same material as that of the cover part44a. And, the cover part44a, longitudinal direction facing parts44b, and grounding parts44cof the supporting member44has good heat conductivity.

In this embodiment, when the predetermined area of the outer peripheral surface of the external conductor40of the signal coupling element34comes in close contact with the inner peripheral surface of the cover part44aof the supporting member44, the pair of grounding parts44cof the supporting member44, and the first and second input terminals36aand36b, the dummy terminal36c, and the output terminal36dat the both end parts of the central conductor36of the signal coupling element34are disposed to have a predetermined relative positional relationship.

In this state, plural sites adjacent to the pair of grounding parts44cof the supporting member44in an area except for the predetermined area on the outer peripheral surface of the external conductor40of the signal coupling element34are fixed to the pair of grounding parts44cby fixing means having electrical conductivity, for example, soldering. In the embodiment, the plural sites corresponds to both end parts and a central part between the both end parts on the outer peripheral surface of the external conductor40of the signal coupling element34in the longitudinal direction thereof.

The fixing means ensures electrical connection between the external conductor40of the signal coupling element34and the pair of grounding parts44cof the supporting member44for a long term, and also assures the predetermined relative positional relationship described above for a long term.

The assembly of the supporting member44and the signal coupling element34after the cover part44aof the supporting member44is in contact with and fixed to the signal coupling element34as described above, is fixed to the predetermined position of the first circuit board part18ain the following manner.

First, the external conductor40of the signal coupling element34is positioned in the slender opening22at the predetermined position on the first circuit board part18a, and the two grounding parts44cof the supporting member44are placed on the two grounding patterns26aand26bon the both sides of the slender opening22in the first circuit board part18a. In this state, the first and second input terminals36aand36b, the dummy terminal36c, and the output terminal36dat the both end parts of the central conductor36of the signal coupling element34are placed on and brought in line-contact with the signal input patterns24a,24band dummy pattern24con the first circuit board part18aand the signal output pattern24don the second circuit board pattern18bover the length equal to or longer than the abovementioned predetermined length respectively.

These line contacts can be achieved owing to the abovementioned predetermined relative positional relationship among the pair of grounding parts44cof the supporting member44, the first and second input terminals36aand36b, the dummy terminal36c, and the output terminal36dat the both end parts of the central conductor36of the signal coupling element34; and owing to a proper setting of a predetermined thickness of each of the spacers32interposed between the first and second circuit board parts18aand18band the external supporting structure (chassis)30.

Next, plural fixing elements46, for example, fixing pins or fixing screws, are inserted into the through-holes (not shown) in the two grounding parts44cand fixed to the through-holes28in the two grounding patterns26aand26bon the first circuit board part18acorresponding to the through-holes (not shown) in the two grounding parts44c.

These fixing elements46are preferably fixing screws having electrical conductivity, more preferably fixing screws having electrical conductivity and good heat conductivity, and distal end parts of these fixing elements46are fixed to the external supporting structure (chassis)30in this embodiment.

Such a plurality of fixing elements46, together with the supporting member44, provides the fixing structure42for fixing the signal coupling element34at the predetermined position on the first circuit board part18a. That is, the fixing structure42includes the plurality of fixing elements46in addition to the supporting member44.

The first and second input terminals36aand36b, the dummy terminal36c, and the output terminal36dat the both end parts of the central conductor36of the signal coupling element34are surely and electrically connected to the signal input patterns24aand24band dummy pattern24con the first circuit board part18aand the signal output pattern24don the second circuit board part18bby known electrical connecting elements, for example, soldering.

Further, in this embodiment, a top end of an externally exposed area on the outer peripheral surface of the external conductor40of the signal coupling element34, received in the opening22at the predetermined position on the first circuit board section18a, is in line contact with a part of the surface of the external supporting structure (chassis)30exposed in the opening22.

In the signal coupling element34fixed at the predetermined position on the first circuit board part18aas described above, while the first and second input terminals36aand36b, dummy terminal36c, and output terminal36dat the both end parts of the central conductor36of the signal coupling element34are in line-contact with the signal input patterns24aand24band dummy pattern24con the first circuit board part18aand the signal output pattern24don the second circuit board part18brespectively over the length longer than the predetermine length, these terminals are electrically connected to these patterns by known electrical connecting elements, for example, soldering. Therefore, these electrical connections are reliable and their strengths are high.

The external conductor40of the signal coupling element34is reliably, firmly and electrically connected (namely, grounded) to the two grounding patterns26aand26b, since the plural sites of the outer peripheral surface of the external conductor40are fixed to the pair of grounding parts44cof the supporting member44by the fixing means having electrical conductivity and the grounding parts44care fixed to the two grounding patterns26aand26bon the first circuit board part18aby the plural fixing elements46having electrical conductivity.

In this embodiment, the two grounding patterns26aand26bare finally, reliably, firmly, and electrically connected (namely, grounded) to the external supporting structure (chassis)30having electrical conductivity through the abovementioned grounding pattern (not shown) on the other surface (back surface) of the first circuit board part18aelectrically connected to the two grounding patterns26aand26bby the conductors (not shown) on the inner peripheral surfaces of the plurality of through-holes28formed in the grounding patterns26aand26band through the spacers32having electrical conductivity.

Further, since the distal end parts of the plural fixing elements46having electrical conductivity are fixed to the external supporting structure (chassis)30having electrical conductivity and since the top end of the externally exposed area on the outer peripheral surface of the external conductor40of the signal coupling element34is in line contact with the part of the surface of the external supporting structure (chassis)30exposed in the opening22, grounding of the external conductor40of the signal coupling element34is achieved further reliably and firmly.

While the predetermined signals are inputted from the signal input patterns24aand24bof the first circuit board part18ainto the first and second input terminals36aand36bat the both end parts of the central conductor36and are coupled with each other, and the coupled signal is outputted from the output terminal36dto the signal output pattern24dof the second circuit board part18d(that is, during operation of the signal coupling element34), the signal coupling element34generates heat.

This heat is radiated efficiently through the cover part44aof the supporting member44having good heat conductivity and being in close contact with the outer peripheral surface of the external conductor40of the signal coupling element34.

This heat is also transferred to the two grounding patterns26aand26bfrom the pair of grounding parts44cof the supporting member44fixed to the external conductor40by the fixing means having heat conductivity. And, it is finally and reliably transferred to the external supporting structure (chassis)30having good heat conductivity through the above described conductors (not shown) on the inner peripheral surfaces of the through-holes28in the two grounding patterns26aand26b, the above described grounding pattern (not shown) on the other surface (back surface) on the first circuit board part18a, and the spacer32having good heat conductivity.

In this embodiment, the above described heat is also transferred to the external supporting structure (chassis)30having good heat conductivity by the fixing elements46having good heat conductivity and fixing the grounding parts44cof the supporting member44to the external supporting structure (chassis)30, and the heat is also transferred to the external supporting structure (chassis)30through the top end of the externally exposed area on the outer peripheral surface of the external conductor40being in line contact with the part of the surface of the external supporting structure (chassis)30exposed in the opening22.

Therefore, in this embodiment, the heat generated in the signal coupling element34is radiated reliably and efficiently.

The heat generated in the signal coupling element34acts to cause relatively large thermal expansion in the insulator38in the direction along the longitudinal center line of the central conductor36. However, this thermal expansion is prevented because the peripheral edges of the both end surfaces of the insulator38in the direction along the longitudinal center line abut on the pair of longitudinal direction facing parts44bof the supporting member44.

Therefore, the both end surfaces of the insulator38are prevented from projecting externally from the both end surfaces of the external conductor40in the direction along the longitudinal center line while the signal coupling element34operates and generates heat.

As a result, repeated stress to lower grounding performance of the supporting member44between the external conductor40of the signal coupling element34and the two grounding patterns26aand26bon the first circuit board part18adoes not occur between them. This means that the heat generated by the operation of the signal coupling element34does not lower the performance of the signal coupling element34.