Patent Grant
10355364
The present invention relates to a waveguide tube slot antenna and a method of manufacturing the waveguide tube slot antenna.
As is well known, in a variety of electrical or electronic devices (systems) having a radio communication function, the waveguide tube slot antenna is used as an antenna for transmitting or receiving a radio wave having a high-frequency bandwidth (for example, radio wave having a millimeter wave band) and a radio wave having a low-frequency bandwidth (for example, radio wave having a centimeter wave band). The radio wave having a millimeter wave band is used, for example, for an on-vehicle radar system, and the radio wave having a centimeter wave band is used, for example, for a satellite broadcasting system using a broadcasting satellite (BS), a communication satellite (CS), or the like, a data transmission system such as a wireless LAN or Bluetooth (trademark), and an electronic toll collection system which is abbreviated to ETC (trademark). The radio wave having a millimeter wave band represents a radio wave having a wavelength of from to 10 mm and a frequency of from 30 GHz to 300 GHz, and the radio wave having a centimeter wave band represents a radio wave having a wavelength of from 10 mm to 100 mm and a frequency of 3 GHz to 30 GEL.
The need has arisen for reducing the cost of the waveguide tube slot antenna so as to promote lower prices for the variety of systems having the radio communication function. Accordingly, the applicant of the present application has proposed a waveguide tube slot antenna made of a resin in Patent Literature 1 described below. More specifically, the applicant has proposed a waveguide tube slot antenna that includes: a waveguide tube that is made of a resin and includes a waveguide extending in a tube axis direction, with a defining surface of the waveguide covered with a conductive coating film; and a plurality of radiating slots provided at predetermined intervals along the tube axis direction of the wave guide, the waveguide tube including a first waveguide tube forming member and a second waveguide tube forming member each having a transverse section having a shape with an end (a cross section orthogonal to the tube axis direction) and being configured to define the waveguide by being coupled to each other.
Patent Literature 1: JP 2014-60700 A
Incidentally, particularly in an application for transmitting and receiving radio waves at a low frequency band, the antenna needs to be increased in size (the antenna needs to be lengthened) in the relationship with a wavelength. However, in the waveguide tube slot antenna described in Patent Literature 1, when the size of the antenna is increased, undesirable deformation, such as warpage or bending in the tube axis direction, is liable to occur in the waveguide tube (both or any one of the two waveguide tube forming members) due to a temperature change or other factors. The occurrence of the deformation as described above is liable to cause, for example, the following failures.
The shape accuracy of the waveguide is adversely affected to decrease the efficiency in propagation of the radio waves.
A gap is formed in a coupled part of the two waveguide tube forming members, and the radio waves propagated in the waveguide are liable to leak to the outside through this gap.
Therefore, desired antenna characteristics cannot be exerted.
In view of the actual circumstances described above, it is an object of the present invention to achieve a waveguide tube slot antenna capable of stably exerting desired antenna characteristics.
In order to solve the above-mentioned problem, according to a first aspect of the present invention, there is provided a waveguide tube slot antenna, comprising: a waveguide tube that is made of a resin and includes a waveguide extending in a tube axis direction, with a defining surface of the waveguide coated with a conductive coating film; and a plurality of radiating slots provided at predetermined intervals along the tube axis direction of the waveguide tube, the waveguide tube including a first waveguide tube forming member and a second waveguide tube forming member each having a transverse section having a shape with an end at each part in an extending direction of the waveguide, and being configured to define the waveguide by being coupled each other, the waveguide tube slot antenna including a metal core disposed along the tube axis direction, and the metal core being held by both the first waveguide tube forming member and second waveguide tube forming member.
As described above, when the metal core disposed along the tube axis direction (metal core extending in the tube axis direction) is held by both the first waveguide tube forming member and the second waveguide tube forming member, bending rigidity and twisting rigidity of the waveguide tube including the coupled body of the two waveguide tube forming members can be enhanced, and hence deformation (in particular, warpage or bending along the tube axis direction) of the waveguide tube due to a temperature change or other factors is less liable to occur, With this configuration, the likelihood of occurrence of such failures as described above can be reduced as much as possible, and hence a waveguide tube slot antenna capable of stably exerting desired antenna characteristics can be achieved.
At least one of the first waveguide tube forming member acid second waveguide tube forming member may be an injection-molded article of a resin integrally including the metal core (an injection-molded article of a resin with the metal core taken as an insertion component). In this manner, the deformation of at least one of the waveguide tube forming members due to the molding shrinkage thereof can be prevented as much as possible. Thus, a decrease in coupling accuracy between the waveguide tube forming members caused by the deformation due to the molding shrinkage, or some other failures can be prevented as much as possible, thereby being capable of stably obtaining a waveguide tube slot antenna excellent in antenna characteristics.
The metal core includes a coupled body of a first metal core and a second metal core, and the first waveguide tube forming member may include an injection-molded article of a resin (an injection-molded article of a resin with the first metal core taken as an insertion component) integrally including the first metal core, and the second waveguide tube forming member may include an injection-molded article of a resin (an injection-molded article of a resin with the second metal core taken as an insertion component) integrally including the second metal core. In this manner, the deformation of each of the first and second waveguide tube forming members due to the molding shrinkage thereof can be prevented as much as possible, thereby being capable of stably obtaining a waveguide tube slot antenna more excellent in antenna characteristics.
The metal core may be buried in a wall part of the waveguide tube, or may be partially exposed to the outer surface of the waveguide tube.
Both the first waveguide tube forming member and second waveguide tube forming member can have the traverse section having a recessed shape.
In order to solve the above-mentioned problem, according to a second aspect of the present invention, there is provided a waveguide tube slot antenna, comprising: a waveguide tube that includes a waveguide extending in a tube axis direction; and a plurality of radiating slots provided at predetermined intervals along the tube axis direction of the waveguide tube, the waveguide tube including a coupled body of a first waveguide tube forming member and a second waveguide tube forming member each having a traverse section having a shape with an end at each part in an extending direction of the waveguide, the first waveguide tube forming member being formed of a flat metal member having the plurality of radiating slots, the second waveguide tube forming member being formed of a resin member integrally holding the first waveguide tube forming member, and at least a defining surface of the waveguide in the waveguide tube being coated with a continuous conductive coating film.
The waveguide tube slot antenna having the above-mentioned configuration can be manufactured by inserting the first waveguide tube forming member formed of a flat metal member having a plurality of radiating slots to injection-mold the second waveguide tube forming member with a resin so as to obtain the waveguide tube, and then performing a process of forming a conductive coating film on the waveguide tube so that at least the defining surface of the waveguide is coated with the conductive coating film.
As described above, through insertion of the first waveguide tube forming member formed of the flat metal member to injection-mold the second waveguide tube forming member with a resin so as to obtain the waveguide tube, the first waveguide tube forming member can function as a reinforcing member, and hence the waveguide tube which is less liable to be deformed due to a temperature change or other factors can be obtained at low cost while the deformation (in particular, warpage or bending in the tube axis direction) of the second waveguide tube forming member due to the molding shrinkage thereof is prevented as much as possible. Further, the second waveguide tube forming member integrally holds the first waveguide tube forming member, and at least the defining surface of the waveguide in the waveguide tube including the coupled body of the two waveguide tube forming members is coated with a continuous conductive coating film (seamless conductive coating film), and hence such a gap, through which radio waves propagated in the waveguide tube leak to the outside, is effectively prevented from being formed in the coupled part of the two waveguide tube forming members. From the above, it is possible to achieve at low cost a waveguide tube slot antenna capable of stably exerting desired antenna characteristics.
In the configuration of the second aspect of the present invention, the first waveguide tube forming member further has a hole, which is provided on a front side in a radiation direction of radio waves radiated to the outside through the radiating slot, and on an inner periphery of which the radiating slot is disposed. Through formation of such a hole in advance, it is possible to eliminate extraneous emission referred to also as grating lobes, thereby being capable of enhancing the antenna characteristics of the waveguide tube slot antenna.
In this case, the first waveguide tube forming member can include a laminate of a first metal plate having the radiating slot and a second metal plate having the hole. In this manner, each of the first metal plate having the radiating slot and the second metal plate having the hole can be taken as a press molded article which is obtained by performing pressing (punching) on the metal plate, so that the first waveguide tube forming member having the radiating slot and the hole can be manufactured at low cost.
The conductive coating film can also be formed continuously along the outer surface of the waveguide tube. Such a conductive coating film (waveguide tube) can be obtained by performing a processing for forming a conductive coating film on the waveguide tube without performing masking processing. This enables omission of a mask forming process on the waveguide tube, which is advantageous in reducing the cost of the waveguide tube slot antenna.
As described above, according to the first and second aspects of the present invention, it is possible to achieve the waveguide tube slot antenna capable of stably exerting desired antenna characteristics.
Now embodiments of the present invention are described with reference to the drawings.
Next, a detailed structure of each waveguide tube slot antenna 1 is described. As also illustrated in
As illustrated in
The top wall 10a comprises a plurality of recess parts 4 opened in an outer surface of the top wall 10a along the tube axis direction, and one radiating slot 3 is opened in an inner bottom surface of each recess part 4. In this embodiment, the recess part 4 is formed so as to have a perfect circle shape in plan view, but the recess part 4 may be formed so as to have a rectangle shape, an ellipse shape, or the like in plan view. Through formation of such recess parts 4, it is possible to suppress extraneous emission referred to also as grating lobes.
The waveguide tube 10 is formed by coupling a first waveguide tube forming member 11 and a second waveguide tube forming member 12 to each other whose transverse sections in each part of the waveguide 2 in the extending direction thereof each have a shape with an end. Specifically, as illustrated in
The first waveguide tube forming member 11 is an injection-molded article of a resin, and the radiating slot 3 and the recess part 4 are formed by molding simultaneously with the injection molding. Further, the second waveguide tube forming member 12 is also an injection-molded article of a resin, and the power supply slot 5 is formed by molding simultaneously with the injection molding. As a molding resin for the waveguide tube forming members 11 and 12, a resin having, for example, at least one kind of thermoplastic resin selected from the group consisting of a liquid crystal polymer (LCP), a polyphenylene sulfide (PPS), and a polyacetal (POM) as a base resin thereof is used. One or a plurality of types of fillers such as glass fibers (GF) or carbon fibers (CF) is added to the base resin as necessary. Among the resins exemplified above, the LCP is preferred because the LCP is excellent in form stability compared to a PPS or the like and may preferably suppress an occurrence amount of burrs caused by the molding.
The surface of the first waveguide tube forming member 11 which defines the waveguide 2 and the surface of the second waveguide tube forming member 12 which defines the waveguide 2 are covered with a conductive coating film 6 illustrated in an enlarged view in
The conductive coating film 6 may be formed of a single-layer metal plated coating film, but in this embodiment, the conductive coating film 6 is formed of a first coating film 6a obtained by precipitation formation on the surfaces of the waveguide tube forming members 11 and 12 and a second coating film 6b obtained by precipitation formation on the first coating film 6a. The first coating film 6a may be a plated coating film of a metal that is particularly excellent in conductivity (propagation property of the radio wave) such as copper, silver, or gold. Further, the second coating film 6b may be a plated coating film of a metal that is excellent in resistance (corrosion resistance) such as nickel. With the conductive coating film 6 having such a stacked structure, the conductive coating film 6 may have high conductivity and high resistance simultaneously, and in addition, a usage amount of an expensive metal such as copper and silver may be suppressed to obtain the conductive coating film 6 at low cost.
The conductive coating film 6 (6a and 6b) can be formed by, for example, an electrolytic plating method or an electroless plating method, but the electroless plating method is preferred. This is because the electroless plating method is more likely to obtain the conductive coating film 6 (6a and 6b) having a uniform thickness than the electrolytic plating method, which is advantageous in ensuring desired antenna performance. The film thickness of the conductive coating film 6 becomes lower in resistance when being too thin, and when being too thick to the contrary, requires an excessive amount of time for coating film formation, which leads to increased cost. From such a viewpoint, it is preferred that the film thickness of the conductive coating film 6 be set to 0.2 μm or more and 1.5 μm or less. When the conductive coating film 6 has a laminate structure of the first coating film 6a and the second coating film 6b as in this embodiment, the respective film thicknesses of the first coating film 6a and the second coating film 6b can be set to about 0.1 μm to about 1.0 μm and about 0.1 μm to 0.5 μm, for example.
The waveguide tube 10 is disposed along the tube axis direction and further includes metal cores 20 that are held by both the first waveguide tube forming member 11 and the second waveguide tube forming member 12. As also illustrated in
The pair of metal cores 20 and 20 can be held by both the first waveguide tube forming member 11 and the second waveguide tube forming member 12 by, for example, adopting any of means (procedures) described in (1) to (3) below.
(1) The upper portions of the metal cores 20 and 20 are fitted into holders 11a provided in (portions constructing the side walls 10c and 10d of) the first waveguide tube forming member 11, and the lower portions of the metal cores 20 and 20 are fitted into holders 12a provided in (portions constructing the side walls 10c and 10d of) the second waveguide tube forming member 12 (see
(2) In order to integrally hold the lower portions of the metal cores 20 and 20 by the second waveguide tube forming member 12, the second waveguide tube forming member 12 is injection-molded with resin by taking the metal cores 20 and 20 as insertion components, and the upper portions (portions protruding from the second waveguide tube forming member 12) of the metal cores 20 and 20 are fitted into the holders 11a respectively provided in portions constructing the side walls 10c and 10d of the first waveguide tube forming member 11 (see
(3) In order to integrally hold the upper portions of the metal cores 20 and 20 by the first waveguide tube forming member 11, the first waveguide tube forming member 11 is injection-molded with resin by taking the metal cores 20 and 20 as insertion components, and the lower portions (portions protruding from the first waveguide tube forming member 11) of the metal cores 20 and 20 are fitted into the holders 12a respectively provided in portions constructing the side walls 10c and 10d of the second waveguide tube forming member 12 (see
In this embodiment, the means of (2) described above is adopted to hold the pair of metal cores 20 and 20 by the two waveguide tube forming members 11 and 12. In the case of adopting the means of (2) described above, when the vertical dimension of the holder 11a provided in the first waveguide tube forming member 11 is smaller than the vertical dimension of the upper portion of the metal core 20 to be held by this holder 11a, the opposed two surfaces of the first waveguide tube forming member 11 and the second waveguide tube forming member 12 cannot be brought into contact with each other (a gap is formed between the two waveguide tube forming members 11 and 12), which may adversely affect the antenna characteristics. Thus, the vertical dimension of the holder 11a is previously set slightly larger than the vertical dimension of the upper portion of the metal core 20 to be held by this holder 11a, Also in the case of adopting the means (1) or (3) described above, the vertical dimensions of the holders 11a and 12a are set for the similar reason.
From the above, the waveguide tube slot antenna 1 (waveguide tube 10) according to this embodiment is completed by: injection-molding the first waveguide tube forming member 11 with resin, while injection-molding the second waveguide tube forming member 12 with resin by taking the metal cores 20 and 20 as insertion components forming the conductive coating film 6 on the surfaces of the two waveguide tube forming members 11 and 12 which define the waveguide 2, and then coupling the two waveguide tube forming members 11 and 12 to each other. The method of coupling the first waveguide tube forming member 11 and the second waveguide tube forming member 12 to each other can be suitably selected, and it is possible to adopt, for example, adhesion performed by curing an adhesive applied to an abutting part of the two waveguide tube forming members 11 and 12, welding performed by welding the waveguide tube forming members 11 and 12 to each other on the abutting part of the two waveguide tube forming members 11 and 12, or some other methods. Besides these methods, through fitting (press-fitting) of a protrusion provided on one of the two waveguide tube forming members 11 and 12 into a recess provided on another thereof the two waveguide tube forming members 11 and 12 can be coupled to each other. Further, the two waveguide tube forming members 11 and 12 can also be coupled to each other by using the metal core 20. Specifically, it is possible to adopt, for example, a method of press-fitting (fitting in an interference state) the upper portion of the metal core 20 into the holder 11a provided in the first waveguide tube forming member 11, a method of fitting the upper portion of the metal core 20 into the holder 11a filled with an adhesive and then curing the adhesive, or some other methods.
When adhesion is used for coupling both the waveguide tube forming members 11 and 12 to each other, for example, a thermosetting adhesive, an ultraviolet-curable adhesive, or an anaerobic adhesive may be used as an adhesive therefor, but with the thermosetting adhesive that requires heat processing when the adhesive is cured, the waveguide tube forming members 11 and 12 made of a resin may be, for example, deformed while being subjected to the heat processing. Therefore, the ultraviolet-curable adhesive or the anaerobic adhesive is preferred as the adhesive. The adhesive is generally an isolator, and hence when the adhesive adheres to a defining surface of the waveguide 2, there is a fear that a propagation property of the radio wave may be adversely affected. Therefore, when the adhesion is used for coupling both the waveguide tube forming members 11 and 12 to each other, it is important to pay attention so as to prevent the adhesive from adhering to the defining surface of the waveguide 2.
In the waveguide tube slot antenna 1 described above, the metal cores 20 disposed along the tube axis direction are held by bath the first and second waveguide tube forming members 11 and 12. This enhances the bending rigidity and the twisting rigidity of the waveguide tube 10 so that, even when both or any one of the two waveguide tube forming members 11 and 12 are to be deformed due to a temperature change or other factors, the deformation can be controlled by the metal core 20. This can reduce as much as possible the likelihood of occurrence of such failures as that the shape accuracy of the waveguide 2 decreases caused by the deformation of the waveguide tube forming members 11 and 12, and that a gap is formed in the coupled part of the two waveguide tube forming member 11 and 12 and radio waves propagated in the waveguide 2 leak to the outside through this gap. Thus, it is possible to achieve at low cost the waveguide tube slot antenna 1 capable of stably exerting desired antenna characteristics.
Particularly in this embodiment, the second waveguide tube forming member 12 is the injection-molded article of a resin integrally including the metal core 20 (the resin injection-molded article with the metal core 20 taken as the insertion component), so that the deformation of the second waveguide tube forming member 12 due to the molding shrinkage thereof can be prevented as much as possible. Thus, a decrease in coupling accuracy between the waveguide tube forming members 11 and 12 caused by the deformation of the second waveguide tube forming member 12 due to the molding shrinkage thereof, or some other failures, can be prevented as much as possible, thereby being capable of stably mass-producing the waveguide tube slot antenna 1 excellent in antenna characteristics.
The waveguide tube slot antenna 1 according to the first embodiment of the first aspect of the present invention is described above, but appropriate changes can be made to the waveguide tube slot antenna 1. Now, other embodiments are described below with reference to the drawings, but the components equivalent to those of the first embodiment described above are denoted by common reference symbols, and duplicate descriptions thereof are omitted as much as possible.
In each of
In this manner, the deformation of each of the first and second waveguide tube forming members 11 and 12 due to the molding shrinkage thereof can be prevented as much as possible, thereby being capable of further enhancing the coupling accuracy between the two waveguide tube forming members 11 and 12. Thus, it is possible to achieve the waveguide tube slot antenna 1 with more excellent antenna characteristics. In this embodiment, as illustrated in
As illustrated in
As described above, when the inner wall 13 for reducing the cross sectional area of the waveguide 2 is provided in the formation position for the radiating slot 3 in advance, it is possible to enhance radiation efficiency of radio waves propagated in the waveguide 2. In particular, assuming that, of two inner walls 13 and 13 adjacent in the tube axis direction, h1 represents the height dimension of the inner wall 13 on a side relatively close to the power supply slot 5, and h2 represents the height dimension of the inner wall 13 on a side relatively far from the power supply slot 5, when a relational expression of h1≤h2 is satisfied, an amount of radio waves radiated to the outside of the antenna 1 through each radiating slot 3 is less liable to vary among the radiating slots 3, so that radio waves in almost equal amount can be radiated from each radiating slot 3. Thus, the occurrence of variations in antenna performance among the parts in the tube axis direction can be avoided as much as possible, thereby improving the reliability of the waveguide tube slot antenna 1.
The waveguide tube 10 that forms the waveguide tube slot antenna 1 according to this embodiment is also formed by coupling the first waveguide tube forming member 11 and the second waveguide tube forming member 12 made of the resin to each other whose transverse sections each have a shape with an end in each part of the waveguide 2 in the extending direction thereof and in which at least the defining surface of the waveguide 2 is coated with the conductive coating film 6. Specifically, the first waveguide tube forming member 11, which integrally has the top wall 10a provided with the radiating slots 3 and the recess parts 4 and a part (the upper portion) of each of the side walls 10c and 10d, the termination walls 10e and 10f, and the branching wall 10g, is coupled to the second waveguide tube forming member 12, which integrally has the bottom wall 10b provided with the power supply slot 5 and the remaining part (the lower portion) of each of the side walls 10c and 10d, the termination walls 10e and 10f, and the branching wall 10g, thereby forming the waveguide tube 10.
The waveguide tube slot antenna 1 of the third embodiment is also disposed along the tube axis direction and further includes metal cores 20 that are held by both the first and second waveguide tube forming members 11 and 12. The metal cores 20 are each formed of a plate-like member having a rectangular shape extending in the tube axis direction, and are buried in an upright posture inside the side walls 10c and 10d, and a branching wall 10g. With the metal cores 20 provided in the above-mentioned form, the waveguide tube slot antenna 1 of this embodiment can also obtain a similar effect to that of the waveguide tube slot antenna 1 illustrated in
Although a detailed illustration is omitted, in this embodiment, in order to integrally hold all of the three metal cores 20 by any one of the two waveguide tube forming members 11 and 12, the first waveguide tube forming member 11 or the second waveguide tube forming member 12 can be injection-molded with resin by taking the three metal cores 20 as insertion components. Besides that, any one of the two waveguide tube forming members 11 and 12 can be injection-molded with resin by taking the metal cores 20 and 20, respectively held by the side walls 10c and 10d, as insertion components while another of the two waveguide tube forming members 11 and 12 is injection-molded with resin by taking the metal core 20, which is held by the branching wall 10g, as an insertion component.
The waveguide tube slot antenna 1 according to the embodiments of the first aspect of the present invention, which is described above, has the characteristic of being capable of preventing deformation due to a temperature change or other factors as much as possible, as described above. Thus, in particular, among the waveguide tube slot antennas, the first aspect of the present invention is preferably applicable to a waveguide tube slot antenna required to increase in antenna size (increase in dimension in the tube axis direction) in the relationship with a wavelength and configured to transmit and receive radio waves at a low frequency band where deformation due to a temperature change or other factors is liable to occur.
Next, a detailed structure of the waveguide tube slot antenna 31 is described. As illustrated in
As illustrated in
The top wall 40a has a hole 34 which is provided on a front side in a radiation direction of radio waves radiated to the outside through the radiating slot 33, and on the inner periphery of which the radiating slot 33 is disposed. That is, a plurality of opened holes 34 are provided along the tube axis direction on the outer surface (top surface) of the top wall 40a, and one radiating slot 33 is opened in the inner bottom surface of each hole 34. In this embodiment, the hole 34 is formed so as to have a perfect circle shape in plan view, but the hole 34 may be formed so as to have a rectangular shape, an ellipse shape, or the like in plan view. Through formation of such a hole 34, it is possible to suppress extraneous emission referred to also as grating lobes, thereby being capable of enhancing the antenna characteristics.
The waveguide tube 40 includes a coupled body of first and second waveguide tube forming members 41 and 42 whose transverse sections in each part of the waveguide 32 in the extending direction thereof each have a shape with an ends. Specifically, as illustrated in
The first waveguide tube forming member 41 includes, for example, a laminate of a first metal plate 41A formed into a predetermined shape by performing pressing (punching) on the metal plate and a second metal plate 41B formed into a predetermined shape by performing pressing (punching) on the metal plate. The radiating slot 33 is formed simultaneously with formation of the first metal plate 41A by pressing, and the hole 34 is formed simultaneously with formation of the second metal plate 41B by pressing.
Meanwhile, the second waveguide tube forming member 42 is a resin member integrally holding the first waveguide tube forming member 41, that is, an injection-molded article of a resin obtained by insertion of the first waveguide tube forming member 41 and injection molding with resin, and the power supply slot 35 is molded simultaneously with the injection-molding. As a resin material for use in molding of the second waveguide tube forming member 42, for example, there is used a material obtained by taking as a base resin at least one kind of thermoplastic resin selected from the group consisting of a liquid crystal polymer (LCP), a polyphenylene sulfide (PPS), and a polyacetal (POM), and adding one or a plurality of fillers such as glass fibers (GF) and carbon fibers (CF) to the base resin as necessary. Among the base resins exemplified above, the LCP is preferred because the LCP is excellent in form stability compared to a PPS or the like and may preferably suppress an occurrence amount of burrs caused by the molding.
As illustrated in an enlarged manner in
The above-mentioned holder 42a can also be obtained by a method other than the above-mentioned method, for example, a method of coupling and integrating the two metal plates 41A and 41B by appropriate means such as adhesion or welding, disposing this integrated article (first waveguide tube forming member 41) as an insertion component in a molding die, and then filling a plurality of filling parts 37 provided only in the first metal plate 41A with the above-mentioned resin material, to injection-mold the second waveguide tube forming member 42 (see
In the waveguide tube 40, at least the defining surface of the waveguide 32 is coated with a conductive coating film 36 as illustrated in an enlarged view of
The conductive coating film 36 may be formed of a single-layer metal plated coating film, but in this embodiment, the conductive coating film 36 is formed of a first coating film 36a obtained by precipitation formation on the waveguide tube 40 and a second coating film 36b obtained by precipitation formation on the first coating film 36a. The first coating film 36a can be a plated coating film of a metal that is particularly excellent in conductivity (propagation property of the radio wave) such as copper, silver, or gold. Further, the second coating film 36b can be a plated coating film of a metal that is excellent in resistance (corrosion resistance) such as nickel. With the conductive coating film 36 having such a stacked structure, the conductive coating film 36 can have high conductivity and high resistance simultaneously, and in addition, a usage amount of an expensive metal such as copper and silver can be suppressed to suppress the increase in cost.
The conductive coating film 36 is poor in durability when the film thickness thereof is excessively small, and on the contrary, when the film thickness is excessively large, it takes a great deal of time to form the conductive coating film 36, with the result that the cost increases. From such a viewpoint, it is preferred that the film thickness of the conductive coating film 36 be set to 0.2 μm or more and 1.5 μm or less. When the conductive coating film 36 has a laminate structure of the first coating film 36a and the second coating film 36b as in the this embodiment, the respective film thicknesses of the first coating film 36a and the second coating film 36b can be set to from about 0.1 μm to about 1.0 μm and from about 0.1 μm to about 0.5 μm, for example.
In the waveguide tube slot antenna 31 described above, the waveguide tube 40 includes a coupled body of the first waveguide tube forming member 41 formed of a flat metal member having a plurality of radiating slots 33 and the second waveguide tube forming member 42 formed of a resin member integrally holding the first waveguide tube forming member 41, and at least the defining surface of the waveguide 32 in the waveguide tube 40 is coated with the continuous conductive coating film 36. As described above, the waveguide tube slot antenna 31 having such a configuration can be manufactured by inserting the first waveguide tube forming member 41 formed of the flat metal member to injection-mold the second waveguide tube forming member 42 with resin so as to obtain the waveguide tube 40, and then performing the processing for forming the conductive coating film 36 on the waveguide tube 40.
As described above, through insertion of the first waveguide tube forming member 41 made of metal to injection-mold the second waveguide tube forming member 42 with resin so as to obtain the waveguide tube 40, the first waveguide tube forming member 41 can function as a reinforcing member, so that the waveguide tube 40 which is less liable to be deformed due to a temperature change or other factors can be obtained at low cost while the deformation of the second waveguide tube forming member 42 due to the molding shrinkage thereof is prevented as much as possible.
Further, the second waveguide tube forming member 42, which is injection-molded with resin by insertion of the first waveguide tube forming member 41, includes the holder 42a integrally holding the first waveguide tube forming member 41, and in the waveguide tube 40 formed of the coupled body of the two waveguide tube forming members 41 and 42, at least the defining surface of the waveguide 32 is coated with the continuous conductive coating film (seamless conductive coating film) 36, thereby being capable of effectively preventing formation of such a gap, through which radio waves propagated in the waveguide 32 leak to the outside, in the abutting part of the two waveguide tube forming members 41 and 42. From the above, it is possible to reduce as much as possible the likelihood of occurrence of such failures that cause deterioration in antenna characteristics, the failures being a decrease in propagation efficiency of radio waves caused by decreased shape accuracy of the waveguide tube 40 (waveguide 32), external leakage of radio waves through a gap formed in the abutting part of the two waveguide tube forming members 41 and 42, and some other failures. Thus, it is possible to achieve at low cost the waveguide tube slot antenna 31 capable of stably exerting desired antenna characteristics.
The waveguide tube slot antenna 31 according to the first embodiment of the second aspect of the present invention is described above, but appropriate changes can be made to the waveguide tube slot antenna 31 within a scope that does not depart from the gist of the present invention. Now, other embodiments of the second aspect of the present invention are described with reference to the drawings, but the components equivalent to those of the first embodiment described above are denoted by common reference symbols, and duplicate descriptions thereof are omitted.
Further, as illustrated in
As described above, when the inner wall 43 for reducing the cross sectional area of the waveguide 32 is provided in the formation position for the radiating slot 33 in advance, it is possible to enhance the radiation efficiency of radio waves propagated in the waveguide 32. In particular, assuming that, of two inner walls 43 and 43 adjacent in the tube axis direction, h10 represents the height dimension of the inner wall 43 on a side relatively close to the power supply slot 35, and h20 represents the height dimension of the inner wall 43 on a side relatively far from the power supply slot 35, when the relational expression of h10≤h20 is satisfied, the amount of radio waves radiated to the outside through each radiating slot 33 is less liable to vary among the radiating slots 33, so that almost an equal amount of radio waves can be radiated from each radiating slot 33. Thus, it is possible to avoid as much as possible the occurrence of variations in antenna performance among the parts in the tube axis direction and achieve the waveguide tube slot antenna 31 having excellent reliability.
The waveguide tube 40 constructing the waveguide tube slot antenna 31 of this embodiment also includes the first waveguide tube forming member 41 formed of a flat metal member and the second waveguide tube forming member 42 made of a resin, which integrally holds the first waveguide tube forming member 41 (injection-molded by inserting the first waveguide tube forming member 41), and at least a defining surface of the waveguide 32 is coated with the continuous conductive coating film 36.
As a matter of course, the second aspect of the present invention described above can be applied to a waveguide tube slot antenna for transmitting and receiving radio waves at a centimeter waveband (low-frequency band), other than being applied to the waveguide tube slot antenna 31 for transmitting and receiving radio waves at a millimeter waveband (high-frequency band).
The above-mentioned first and second aspects of the present invention are by no means limited to the embodiments described above. As a matter of course, those aspects of the present invention may be carried out in further various modes without departing from the spirit of this invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2015-185040 | Sep 2015 | JP | national |
| 2015-185042 | Sep 2015 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2016/075405 | 8/31/2016 | WO | 00 |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO2017/047381 | 3/23/2017 | WO | A |
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