TECHNICAL FIELD
The present invention relates to a vehicle antenna device which is to be mounted, for example, on a roof of a vehicle.
BACKGROUND ART
Recently, an antenna which is called a shark fin antenna has been developed. The height of the antenna is reduced, for example, to about 70 mm. On the other hand, the length of the antenna is increased in order to ensure the gain. Hence, the antenna base is larger as compared to a prior art one. From the viewpoints of the weight reduction and the cost reduction, therefore, a structure in which the antenna base is made of a resin is proposed. Patent Literature 1 below discloses a structure in which a metal-made base is assembled to a resin-made base from an inside of an antenna. In this structure, the size of the metal-made base is set in accordance with a size of the mounted antenna and the necessity/unnecessity of grounding depending on a antenna system, and the base of an antenna in which grounding is unnecessary is made of a resin, whereby the metal-made base can be miniaturized as far as possible.
CITATION LIST
Patent Literature
- Patent Literature 1: JP-A-2012-204996
SUMMARY OF INVENTION
Technical Problem
According to the structure in Patent Literature 1, in the case where the resin-made base enters between the metal-made base and the vehicle body (for example, the roof), and an antenna for a broadband such as the LTE is integrated, a phenomenon sometimes occurs in which the metal-made base has a resonance point according to a distance with respect to the vehicle body (ground), the unwanted resonance is occurred in a required frequency band, and then, the antenna gain is reduced.
The present invention has been conducted in view of such circumstances. It is an object of the present invention to provide a vehicle antenna device in which a reduction in the antenna gain can be avoided due to unwanted resonance between a metal-made base and a vehicle body.
Solution to Problem
An aspect of the present invention is a vehicle antenna device. The vehicle antenna device includes:
an antenna base;
an antenna case which is overlaid on the antenna base; and
an antenna element and an amplifier board which are disposed inside the antenna case,
the antenna base has a resin-made base which has an opening, and a metal-made base which is smaller in area than the resin-made base, is the metal-base being disposed on the resin-made base so as to close the opening, and having a cylindrical portion for attachment to a vehicle body, and
a conductor plate is attached to a surface of the resin-made base, the surface being opposite to a placement surface of the metal-made base.
The conductor plate may be electrically connected to the metal-made base.
In the conductor plate, as viewed in an axial direction of the cylindrical portion, an outer edge excluding a side facing a side of the cylindrical portion may approximately coincide with an outer edge of the metal-made base, or be outside the outer edge of the metal-made base.
The conductor plate may have at least one plate spring portion which extends so as to approach the vehicle body.
The conductor plate may be disposed respectively in front and rear of the cylindrical portion.
In the metal base, a resin-made part which prevents the metal base from being directly contacted with an inner circumferential portion of a mounting hole of the vehicle body may be disposed in a portion opposed to the inner circumferential portion of the mounting hole.
The resin-made part may be a holder for provisionally fixing the vehicle antenna device to the vehicle body.
A boss which is engaged with the inner circumferential portion of the mounting hole of the vehicle body may be disposed on a surface of the resin-made base, the surface being on a side of the vehicle body.
The antenna element may include a capacitive element, a coil element, and another antenna element for a frequency band which is different from a frequency band received by the capacitive element and the coil element.
A shape and a size of the metal-made base may be set so that, in a state where the conductor plate is absence, unwanted resonance is generated in a vicinity of a lowest frequency in a reception frequency band of the another antenna element.
A filter board may be disposed between the capacitive element and the coil element.
The coil element may be configured by forming a winding around a bobbin,
a first terminal to which one end of the coil element is electrically connected may be disposed on a side of one end of the bobbin, and
a lower surface of the filter board may be in contact with and electrically connected to the first terminal, and an upper surface of the filter board may be in contact with and electrically connected to the capacitive element.
Connecting portions of the first terminal, the filter board, and the capacitive element may be screwed to the antenna case in a state where the connecting portions overlap with one another, and electrically connected to one another at the screwed portions.
The vehicle antenna device may include an element holder which supports the capacitive element and the coil element, and
the element holder may have a placement portion on which the filter board is to be placed.
The placement portion may slidably support the filter board, and the filter board is latched by a latching claw at a predetermined slide position.
Arbitrary combinations of the above-described components, and expressions of the present invention which are converted in method and system are also effective as aspects of the present invention.
Advantageous Effects of Invention
According to the present invention, it is possible to provide a vehicle antenna device in which the reduction in the antenna gain can be avoided due to the unwanted resonance between the metal-made base and the vehicle body.
BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 is an exploded perspective view of a vehicle antenna device according to an embodiment of the present invention.
FIGS. 2(A), 2(B) and 2(C) are external views of the vehicle antenna device.
FIG. 3 is a side sectional view of the vehicle antenna device.
FIG. 4 is a perspective view of the vehicle antenna device in a state where conductor plates 90 are disassembled, as seen from the lower side.
FIG. 5 is a perspective view of the vehicle antenna device, as seen from the lower side.
FIG. 6 is an enlarged sectional view taken along A-A in FIG. 2(C).
FIGS. 7(A) to 7(D) are external views of a metal-made base 60 in FIG. 1.
FIGS. 8(A), 8(B) and 8(C) are external views of a resin base 70 in FIG. 1.
FIGS. 9(A), 9(B) and 9(C) are external views of the conductor plate 90 in FIG. 1.
FIG. 10 is a perspective view of a disassembled state of the metal-made base 60 and a provisional fixing holder 80 of the vehicle antenna device.
FIG. 11 is a perspective view of an assembled state of the metal-made base 60 and the provisional fixing holder 80 in FIG. 10.
FIGS. 12(A) and 12(B) are external views of the vehicle antenna device in a state where the device is attached to a through hole 111 of a vehicle body roof 110, as seen from the lower side.
FIG. 13 is a perspective view of a disassembled state of a bobbin 41, an upper terminal 45, and a lower terminal 47 of a coil element 40 in FIG. 1.
FIG. 14 is a perspective view of an assembled state of the bobbin 41, the upper terminal 45, and the lower terminal 47 in FIG. 13.
FIGS. 15(A) to 15(H) are views illustrating steps of producing the coil element 40.
FIG. 16 is a perspective view of an element holder 20 in FIG. 1.
FIG. 17 is a plan view of the element holder.
FIG. 18 is a side view of the element holder.
FIG. 19 is a front view of the element holder.
FIGS. 20(A), 20(B) and 20(C) are external views of a filter board 30 in FIG. 1.
FIGS. 21(A) and 21(B) are views illustrating processes of attaching the filter board 30 to the element holder 20.
FIG. 22 is a plan view of the element holder 20 which provisionally holds the filter board 30.
FIG. 23 is a sectional view taken along A-A in FIG. 22.
FIG. 24 is an enlarged sectional view taken along B-B in FIG. 22.
FIGS. 25(A) and 25(B) are perspective views of main portions of a vehicle antenna device according to a comparison example, as seen from the lower side.
FIG. 26 is a characteristic graph of VSWR versus frequency of vehicle antenna devices of an ideal state where unwanted resonance does not occur, the embodiment, and Comparison examples 1 and 2.
FIG. 27 is a characteristic graph in which the vicinity of 700 MHz in FIG. 26 is enlarged.
DESCRIPTION OF EMBODIMENTS
Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to the drawings. Identical or equivalent components, members, and the like shown in the drawings are denoted by the same reference numerals, and duplicated descriptions are appropriately omitted. The embodiment does not limit the invention, but only exemplifies the invention, and all features described in the embodiments, and their combinations are not necessarily essential in the invention.
FIG. 1 is an exploded perspective view of a vehicle antenna device according to the embodiment of the present invention. FIG. 2(A) is a front view of the vehicle antenna device. FIG. 2(B) is a side view of the vehicle antenna device, and FIG. 2(C) is a bottom view of the vehicle antenna device. FIG. 3 is a side sectional view of the vehicle antenna device. FIG. 4 is a perspective view of the vehicle antenna device in a state where conductor plates 90 are disassembled, as seen from the lower side. FIG. 5 is a perspective view of the vehicle antenna device, as seen from the lower side. FIG. 6 is an enlarged sectional view taken along A-A in FIG. 2(C). FIG. 7(A) is a bottom view of a metal-made base 60 in FIG. 1. FIG. 7(B) is a rear sectional view of the metal-made base, FIG. 7(C) is a side view of the metal-made base, and FIG. 7(D) is a side sectional view of the metal-made base. FIG. 8(A) is a side sectional view of a resin base 70 in FIG. 1. FIG. 8(B) is a side view of the resin base, and FIG. 8(C) is a bottom view of the resin base. FIG. 9(A) is a side view of the conductor plate 90 in FIG. 1. FIG. 9(B) is a bottom view of the conductor plate, and FIG. 9(C) is a rear view of the conductor plate.
An antenna case 1 is made of a radio wave transmissive synthetic resin (a molded product made of a resin such as PC or PET), and formed into a shark fin shape in which the side surfaces are inwardly curved. An antenna base is configured by combining the metal-made base 60 with the resin-made base 70. The resin-made base 70 has through holes 72a, 72b in a middle portion of a planar portion 71. A pair of bosses (projections) 71a which is engaged with an inner edge portion of a mounting hole of the vehicle body is disposed on the lower surface (the surface on the side of the vehicle body) of the planar portion 71. The metal-made base 60 is smaller in area than the resin-made base 70, and attached (fixed) by eight screws 103 onto the planar portion 71 of the resin-made base 70 so as to close the through holes 72a, 72b of the resin-made base 70. The metal-made base 60 has: a planar portion 61 which is to cover the through holes 72a, 72b; and a feeding cylindrical portion (hollow threaded shaft portion) 62 which is downwardly projected from the planar portion 61, and in which a male thread for attachment to the vehicle body (for example, the roof that is the panel to which attachment is to be made) is formed on the outer circumference. Convex portions 61a, 61b (FIG. 4) which are to be fitted into the through holes 72a, 72b of the resin base 70 are disposed on the lower surface of the planar portion 61. The feeding cylindrical portion 62 extends from the convex portion 61a toward the lower side of the resin-made base 70. An amplifier board 50 is attached (fixed) by screwing or the like onto the planar portion 61. A pair of conductor plate springs (terminals) 51 is disposed on the amplifier board 50. An output cable 52 downwardly elongates from the amplifier board 50, and passes through the inside of the feeding cylindrical portion 62 so as to be drawn out to the outside. An annular sealing member 5 is disposed between the planar portion 71 of the resin-made base 70 and the vehicle body. The sealing member 5 is disposed in the periphery of the through holes 72a, 72b of the resin-made base 70, and sandwiched and pressed between the planar portion 71 of the resin-made base 70 and the vehicle body, thereby preventing water from penetrating through a gap between the resin-made base 70 and the vehicle body.
A pad 3 is an elastic member made of elastomer, rubber, or the like, and disposed on the resin-made base 70 so as to make a circle along the periphery of the resin-made base 70 or the vicinity thereof. The pad 3 functions as a blinder for the gap between the lower end edge of the antenna case 1 and the vehicle body, and has also a simple waterproof function exerted between the resin-made base 70 and the vehicle body (the waterproof function is mainly exerted by the sealing member 5). The antenna case 1 is overlaid from the upper side on the resin-made base 70 while interposing the pad 3 between the antenna case 1 and the resin-made base 70, and attached (fixed) by nine screws 104 to the resin-made base 70. The antenna case 1 has a rib 1a (FIG. 3) for pressing the pad 3 against the whole circumference of the resin-made base 70. Therefore, penetration of water through a gap between the antenna case 1 and the resin-made base 70 can be avoided. Threaded-hole equipped bosses 1b, 1c (FIG. 3) are disposed on the ceiling portion of the antenna case 1. An LTE element 6, a satellite radio antenna 7, a capacitive element 10, and a coil element 40 which are antenna elements are disposed in a space between the antenna case 1 and the antenna base (the metal-made base 60 and the resin-made base 70). The capacitive element 10 and the coil element 40 are elements for an AM/FM antenna. The LTE element 6 and the satellite radio antenna 7 are examples of antenna elements other than elements for an AM/FM antenna.
The LTE element 6 is configured by a metal plate (conductor plate), and supported by a holder 6c which is erected from a board 6b. The board 6b is attached (fixed) by screwing or the like onto the planar portion 61 of the metal base 60. An output cable 6a elongates from the board 6b, and passes together with the output cable 52 of the amplifier board 50 through the inside of the feeding cylindrical portion 62 so as to be drawn out to the outside. The satellite radio antenna 7 is disposed on the planar portion 71 of the resin base 70. An output cable 7a of the satellite radio antenna 7 passes together with the output cable 6a of the LTE element 6 through the inside of the feeding cylindrical portion 62 so as to be drawn out to the outside.
The capacitive element 10 is configured by a metal plate (conductor plate), and bent in, for example, a squeezing process so as to have an umbrella-shaped curved surface portion 11 which is approximately parallel to an arcuate ceiling surface that is in the upper portion of the inside of the antenna case 1. In a state where the capacitive element 10 is fixed to the antenna case 1, the curved surface portion 11 is in proximity to the ceiling surface of the antenna case 1. A connecting portion 12 extends downwardly and rearwardly from a front end portion of the curved surface portion 11, to be formed into an L-like shape. The connecting portion 12 has a through hole 13 (FIG. 3) in a tip end portion. The upper surface of the periphery of the through hole 13 of the connecting portion 12 butts against the end surface of the threaded-hole equipped boss 1b (FIG. 3) in the antenna case 1. The lower surface of the periphery of the through hole 13 of the connecting portion 12 butts against the upper surface side of a conduction pattern 31a of a filter board 30 which will be described later. The lower surface side of the conduction pattern 31a of the filter board 30 butts against an upper terminal 45 of the coil element 40. In the curved surface portion 11, a through hole 14 (FIG. 1) is disposed in the rear side. The threaded-hole equipped boss 1c (FIG. 3) of the antenna case 1 is passed through the inside of the through hole 14.
An element holder 20 has a base portion 21, a cylindrical portion 22, a through hole 23, and a placement portion 24. The cylindrical portion 22 is raised from the base portion 21. The threaded-hole equipped boss 1c of the antenna case 1 is fitted into the inside of the cylindrical portion (FIG. 3). The element holder 20 is attached (fixed) to the antenna case 1 while interposing the capacitive element 10 between the element holder 20 and the antenna case 1, by a screw 102 which is screwed to the threaded-hole equipped boss 1c. Projections 22a are disposed in front and rear of the cylindrical portion 22, respectively. The projections 22a press the capacitive element 10 against the ceiling surface of the antenna case 1. The through hole 23 is disposed in the base portion 21, and located in front of the cylindrical portion 22. The element holder 20 has a space in which an upper portion of a bobbin 41 of the coil element 40 that will be described later is positioned and supported (fitted), below the through hole 23. The periphery and rear of the through hole 23 of the base portion 21 are formed as the placement portion 24 on which the filter board 30 is to be placed. The placement portion 24 will be described later. The filter board 30 is slid from the front side to be attached (provisionally fixed) to the placement portion 24.
As shown in FIG. 3, the coil element 40 is configured by forming a winding 42 around the bobbin 41 which is made of a resin. The upper terminal 45 is disposed (for example, pressingly inserted and fixed) in one end (upper end) of the bobbin 41. One end of the winding 42 is electrically connected to the upper terminal 45. A lower terminal 47 is disposed (for example, pressingly inserted and fixed) in the other end (lower end) of the bobbin 41. The other end of the winding 42 is electrically connected to the lower terminal 47. The upper terminal 45 is attached (fixed) to the threaded-hole equipped boss 1b of the antenna case 1 while interposing the filter board 30 (conduction pattern 31a) and the connecting portion 12 of the capacitive element 10 between the upper terminal 45 and the antenna case 1, by a screw 101. Namely, the screw 101 passes through a through hole 45d of the upper terminal 45, a through hole 31 of the filter board 30, and the through hole 13 of the connecting portion 12 of the capacitive element 10, and is screwed to the threaded-hole equipped boss 1b of the antenna case 1. Therefore, the coil element 40 and the capacitive element 10 are electrically connected to each other, and the filter board 30 is electrically connected between the coil element 40 and the capacitive element 10. Preferably, the screw 101 may have a spring washer so as to avoid a connection failure due to its loosening. A connection leg 47b of the lower terminal 47 is clamped by a pair of conductor plate springs 51 of the amplifier board 50. Therefore, the coil element 40 and the amplifier board 50 are electrically connected to each other.
In the planar portion 71 of the resin base 70, two conductor plates 90 are attached (fixed) to the surface (lower surface) opposite to a placement surface (upper surface) of the metal-made base 60, by eight screws 103. One of the conductor plates 90 is located in front of the feeding cylindrical portion 62, and the other conductor plate 90 is located in rear of the feeding cylindrical portion 62. The outer edge (three sides excluding a side facing the feeding cylindrical portion 62) of each of the conductor plates 90 is in proximity to the inner edge of the sealing member 5, and approximately coincides with the outer edge of the metal-made base 60 as seen in the axial direction (vertical direction) of the feeding cylindrical portion 62. As shown in FIG. 4, each of the conductor plates 90 has a screwed portion 93 in each of four corners of a corresponding planar portion 91. Each of the screwed portions 93 has a through hole 93a through which the corresponding screw 103 is passed, and is bent into an L-like shape so as to be raised to be higher than the planar portion 91 by one step. By contrast, eight concave portions 73 into which the screwed portions 93 of the conductor plates 90 enter respectively are disposed on the lower surface of the planar portion 71 of the resin base 70. A through hole 73a through which the screw 103 passes is disposed in each of the concave portions 73. The screws 103 cause the conductor plates 90 to be attached to the lower surface of the resin base 70, and the metal-made base 60 to be attached to the upper surface of the resin base 70. The metal-made base 60 and the conductor plates 90 are electrically connected to each other by the screws 103. Each of the conductor plates 90 has four plate spring portions 92 which are bent in an obliquely downward direction from the planar portion 91 so as to approach the side of the vehicle body. Tip end portions of the plate spring portions 92 face the side of the feeding cylindrical portion 62, and are contacted with the vehicle body roof (compressed by the vehicle body roof).
FIG. 10 is a perspective view of a disassembled state of the metal-made base 60 and the provisional fixing holder 80 of the vehicle antenna device. FIG. 11 is a perspective view of an assembled state of the metal-made base 60 and the provisional fixing holder 80 in FIG. 10. FIG. 12(A) is a perspective view of a state where the vehicle antenna device is attached to a through hole 111 of the vehicle body roof 110, as seen from the lower side. FIG. 12(B) is a bottom view of the state. The provisional fixing holder 80 which serves as the resin-made part has a U- or C-shaped external shape, and is engageable with (fittable into) the side surface of the feeding cylindrical portion 62 in a lateral direction perpendicular to the axial direction thereof. The provisional fixing holder 80 provisionally fixes the feeding cylindrical portion 62 in a state where the feeding cylindrical portion is inserted from the outside into the through hole 111 of the vehicle body roof 110 that serves as the panel to which attachment is to be made. The provisional fixing holder 80 is made of, for example, a flexible resin, and has: a pair of clamping portions 81 which clamps the feeding cylindrical portion 62; a liaison portion 82 through which the clamping portions 81 are connected to each other; and latching claws 83 which are formed in tip end portions of the clamping portions 81, respectively, so as to be outwardly projected. The feeding cylindrical portion 62 has on the side surface a pair of first groove portions 63 (FIGS. 7(B) and 10) which is engaged with the provisional fixing holder 80, and one second groove portion 64 which is at the midpoint between the first groove portions 63. The provisional fixing holder 80 is attached to the feeding cylindrical portion 62 by being engaged with the first groove portions 63 and the second groove portion 64. Namely, the pair of clamping portions 81 is engaged with the pair of first groove portions 63 so as to sandwich the feeding cylindrical portion 62, and the liaison portion 82 is engaged with the second groove portion 64. In the state where, after the provisional fixing holder 80 is attached to the feeding cylindrical portion 62, the feeding cylindrical portion 62 is inserted into the through hole 111 of the vehicle body roof 110, the latching claws 83 are caught by the inner surface of the roof, and can function as the provisionally fixation. As shown in FIGS. 12(A) and 12(B), the provisional fixing holder 80 which is made of a resin is interposed between the feeding cylindrical portion 62 and an inner edge portion (inner circumferential portion) of the through hole 111 of the vehicle body roof 110 to prevent the both members from being directly contacted with each other, i.e., from being electrically connected to each other.
FIG. 13 is a perspective view of a disassembled state of the bobbin 41, the upper terminal 45, and the lower terminal 47 of the coil element 40 in FIG. 1. FIG. 14 is a perspective view of an assembled state of the bobbin 41, the upper terminal 45, and the lower terminal 47 in FIG. 13. FIGS. 15(A) to 15(H) are views illustrating steps of producing the coil element 40.
The upper terminal 45 has a base portion 45a, a pair of attaching legs 45b, and a winding terminal connecting portion (tab) 45c. A through hole 45d is disposed in a middle portion of the base portion 45a. The pair of attaching legs 45b is bent into a U-like shape with respect to the base portion 45a, and located in the opposite sides across the center of the base portion 45a, respectively. The winding terminal connecting portion 45c is bent into an L-like shape with respect to the base portion 45a, and located in a different position which is rotated by 90 degrees in an axial direction from the attaching legs 45b.
The lower terminal 47 has an upper surface portion 47a, a connection leg 47b, a winding terminal connecting portion (tab) 47c, side surface portions 47e, and a lower surface portion 47f. A plate spring portion 47d which is bent in an obliquely downward direction is disposed in a middle portion of the upper surface portion 47a. The plate spring portion 47d has a function of preventing the bobbin 41 from rattling with respect to a lower terminal attaching portion 44 of the bobbin 41. The connection leg 47b is downwardly bent with respect to the base portion 45a. The winding terminal connecting portion 47c extends from the upper surface portion 47a to be projected toward the outside. The side surface portions 47e are downwardly bent with respect to the upper surface portion 47a at the both ends of the upper surface portion 47a, respectively. The lower surface portion 47f is a portion which is formed by bending the lower end of one of the side surface portions 47e, and extending the lower end approximately in parallel to the upper surface portion 47a. The lower terminal 47 is attached to the lower terminal attaching portion 44 in such a manner that the lower terminal attaching portion 44 is surrounded by the upper surface portion 47a, the side surface portions 47e, and the lower surface portion 47f.
The bobbin 41 has: upper terminal attaching portions 43 to which the upper terminal 45 is to be attached; the lower terminal attaching portion 44 to which the lower terminal 47 is to be attached; and a cylindrical winding barrel 48 in which the winding 42 is wound on the outer circumferential surface. The upper terminal attaching portions 43 are erected on the upper end surface of the winding barrel 48 while being distributed on the both sides of the center axis of the winding barrel 48. The upper terminal attaching portions 43 have a pair of convex portions 43a which is outwardly projected in the opposite directions to each other. The pair of convex portions 43a is engaged with the pair of attaching legs 45b of the upper terminal 45. The lower terminal attaching portion 44 is disposed so as to protrude toward the outside in the lower end portion of the winding barrel 48. A guide groove 48a which is the winding path of the winding 42, and a plurality of projections 48b which are in positions along the winding path of the winding 42 are disposed on the outer circumferential surface of the winding barrel 48. The guide groove 48a spirally extends around the outer circumferential surface of the winding barrel 48. At least one of the projections 48b is disposed in each of a plurality of circumferential positions (circumferential positions where the later-described winding terminal connecting portion 45c of the upper terminal 45 can exist) on the outer circumferential surface of the winding barrel 48. In the illustrated example, the projections 48b are disposed in two circumferential positions which are separated from each other by 180 degrees, and which are on the outer circumferential surface of the winding barrel 48, in plural numbers (ten in one of the positions, and eleven in the other position). One of the circumferential positions where the projections 48b are disposed coincides with the circumferential position of the winding terminal connecting portion 45c of the upper terminal 45. Each of the projections 48b functions as a hooking portion in the case where the winding end portion of the winding 42 is drawn out in the axial direction. From the viewpoint of ensuring of strength, the projections 48b are formed into a planer shape.
As shown in FIGS. 15(A) and 15(B), when the coil element 40 is to be assembled, first, the upper terminal 45 and the lower terminal 47 are slidingly attached to the upper terminal attaching portions 43 and the lower terminal attaching portion 44 of the bobbin 41, respectively. As shown in FIG. 15(C), then, a bent end portion of a wire 42′ which is to be configured as the winding 42 is hooked to the winding terminal connecting portion 47c of the lower terminal 47, and connected and fixed thereto by soldering, welding, or the like. As shown in FIGS. 15(D) and 15(E), then, the winding 42 is wound around the outer circumferential surface (guide groove 48a) of the winding barrel 48 of the bobbin 41, while rotating the bobbin 41. The winding pitch of the winding 42 is determined by the arrangement pitch of the guide groove 48a. As shown in FIGS. 15(F), 15(G), and 15(H), then, the winding end portion of the winding 42 is hooked on the predetermined projection 48b of the winding barrel 48, the terminal of the winding 42 is drawn out in the axial direction, the terminal of the winding 42 is connected and fixed to the winding terminal connecting portion 45c of the upper terminal 45 by soldering, welding, or the like, and an excess portion is cut away. The above-described series of operations can be conducted by an automatic winding machine. As a result, the coil element 40 is completed. The coil element 40 is installed into the antenna case 1 in following manner. First, the upper terminal 45 is fixed together with the capacitive element 10 to the threaded-hole equipped boss 1b of the antenna case 1 by the screw 101. Then, the connection leg 47b of the lower terminal 47, and the conductor plate springs 51 of the amplifier board 50 are positioned relative to each other, and an assembly of the amplifier board 50, the metal-made base 60, and the resin-made base 70 is attached to the antenna case 1 by, for example, screwing. Alternatively, the upper terminal 45 may be attached while being inverted by 180 degrees with respect the bobbin 41. When the projection 48b on which the winding end portion of the winding 42 is to be hooked is changed, and, as required, the upper terminal 45 is inverted by 180 degrees, the number of turns of the winding 42 can be changed in units of 0.5 turn.
FIG. 16 is a perspective view of the element holder 20 in FIG. 1. FIG. 17 is a plan view of the element holder 20. FIG. 18 is a side view of the element holder 20, and FIG. 19 is a front view of the element holder 20. FIG. 20(A) is a plan view of the filter board 30 in FIG. 1. FIG. 20(B) is a side view of the filter board 30, and FIG. 20(C) is a bottom view of the filter board 30. FIGS. 21(A) and 21(B) are views illustrating processes of attaching the filter board 30 to the element holder 20. FIG. 22 is a plan view of the element holder 20 which provisionally holds the filter board 30. FIG. 23 is a sectional view taken along A-A in FIG. 22. FIG. 24 is an enlarged sectional view taken along B-B in FIG. 22.
The element holder 20 has the placement portion 24 on which the filter board 30 is to be placed. Latching claws 24b are disposed on the both sides of the placement portion 24, respectively. A pair of projecting portions 24a is inwardly projected from the both upper sides of the through hole 23, respectively. The filter board 30 has a pair of cutouts 35 in the right and left sides. In the case where the filter board 30 is to be provisionally fixed to the placement portion 24 of the element holder 20, the filter board 30 is placed from the upper side on the placement portion 24 as shown in FIG. 21(A) while locating the cutouts 35 at the positions of the projecting portions 24a. The filter board 30 is rearwardly slid until butting occurs as shown in FIG. 21(B). Then, the pair of latching claws 24b is engaged with the edge portions of the cutouts 35 to latch (provisionally fix) the filter board 30. Moreover, the upper surface of the filter board 30, and the pair of projecting portions 24a and a pair of projecting portions 24c are engaged (face-to-face contacted) with each other, and the filter board 30 is prevented from upwardly slipping off. The filter board 30 has the conduction pattern 31a on the both surfaces of the periphery of the through hole 31, an inductive pattern 32a on the upper surface, and an inductive pattern 32b on the lower surface. The inductive patterns 32a, 32b extend from the conduction pattern 31a, and are connected to each other by a through hole 34. A chip capacitor 33 is disposed in the middle of the inductive pattern 32a.
FIG. 25(A) is a perspective view of main portions of a vehicle antenna device according to Comparison example 1, as seen from the lower side. FIG. 25(B) is a perspective view of main portions of a vehicle antenna device according to Comparison example 2, as seen from the lower side. Comparison example 1 shown in FIG. 25(A) is a device of the conventional type in which the conductor plates 90 in the embodiment are not disposed, and a holder 880 for provisional fixing to the vehicle body is attached from the upper side of a metal base 860, and which is not provided with a configuration for preventing the vehicle body roof and the metal-made base 860 from being directly contacted with each other. By contrast, Comparison example 2 shown in FIG. 25(B) has the conductor plates 90 in the embodiment, but, similarly with Comparison example 1, is not provided with a configuration for preventing the vehicle body roof and a metal-made base 960 from being directly contacted with each other.
FIG. 26 is a characteristic graph of VSWR versus frequency of vehicle antenna devices according to an ideal state where unwanted resonance does not occur, the embodiment, and Comparison examples 1 and 2. FIG. 27 is a characteristic graph in which the vicinity of 700 MHz in FIG. 26 is enlarged. The first and second frequency bands shown in these drawings are frequency bands used in the LTE. In the case of the second frequency band, in any configuration, characteristics which are close to the characteristic according to the ideal state are obtained. In the case of the first frequency band, in the configurations of Comparison examples 1 and 2, by contrast, the characteristics are largely deviated from the characteristic according to the ideal state as enlargedly shown in FIG. 27. In the configuration of the embodiment, on the other hand, the characteristic is relatively close to the characteristic according to the ideal state. The characteristic according to the embodiment which is close to the characteristic according to the ideal state is attained by the effect because of a phenomenon in which the capacitance is increased by the interposition of the conductor plate 90 between the metal-made base 60 and the vehicle body roof, and the resonance frequency is shifted to a frequency band that is lower than the first frequency band, and by the effect because of the configuration in which direct contact between the metal-made base 60 and the inner circumference of the mounting hole of the vehicle body roof is avoided by the provisional fixing holder 80 (the effect because of the fact that an unintended conduction path is not formed). In the configuration in the embodiment, characteristics in a band (300 MHz to 400 MHz) which is not in the first and second frequency bands are largely deviated from the characteristic according to the ideal state. However, this is no problem since this band is not used. In other words, according to the configuration in the embodiment, the frequency band in which deviation of the VSWR occurs due to unwanted resonance is shifted into an unused band, whereby the VSWR in the used frequency band can be made close to the VSWR in the ideal state (a reduction in the antenna gain is prevented).
The shape and the size of the metal-made base 60 in the embodiment is designed so that, in a state where a countermeasure against unwanted resonance is not taken as in Comparison example 1, unwanted resonance is generated in the vicinity of the lowest frequency in a frequency band which is used in the LTE as shown in FIG. 26. In an actual design, also the size of the board 50 to be placed on the metal-made base 60 is considered, the length of the metal-made base 60 which has a rectangular shape, in the short-side direction is first determined in accordance with the size of board, and then the length in the long-side direction is determined so that unwanted resonance is generated in the vicinity of the lowest frequency in the reception frequency band.
According to the embodiment, it is possible to attain the following effects.
- (1) The conductor plates 90 in the resin-made base 70 are disposed on the surface opposite to the placement surface of the metal-made base 60. Therefore, it is possible to avoid the reduction in the antenna gain since unwanted resonance due to an event that the metal-made base 60 has a resonance point according to the distance with respect to the vehicle body roof (ground) is occurred in a required frequency band.
- (2) Since the conductor plates 90 have the plate spring portions 92, and the plate spring portions 92 are compressed by the vehicle body roof, the plate spring portions 92 and the vehicle body roof can be surely contacted with each other even when the curvature of the vehicle body roof is changed, and therefore the reduction in the antenna gain is surely avoided.
- (3) Since each of the plate spring portions 92 is branched into a plurality of sections, many contacts can be ensured even when the curvature of the vehicle body roof is large.
- (4) Since the filter board 30 is disposed between the capacitive element 10 and the coil element 40, an adverse influence due to interferences between the antenna elements in the antenna case 1 can be reduced. Specifically, it is possible to avoid the reduction in the antenna gain of the LTE element 6 by a phenomenon that the second- or third-harmonics of the capacitive element 10 and the coil element 40 (AM/FM) enter the LTE element 6.
- (5) The filter board 30 has the configuration where the filter board 30 is fixed by the screw 101 in the state (stacked stated) where the filter board 30 is sandwiched between the upper terminal 45 of the coil element 40 and the connecting portion 12 of the capacitive element 10, and the filter board 30 is electrically connected between the capacitive element 10 and the coil element 40 by the screwing. Therefore, the mechanical fixation and the electrical connection of the filter board 30 can be performed in a lump and easily, and the assemblability is excellent.
- (6) Since the element holder 20 has the configuration where the element holder 20 has the placement portion 24 on which the filter board 30 is to be placed, and the filter board 30 is provisionally fixed to the predetermined position by the latching claws 24b and the projecting portions 24a, 24c, positioning of the filter board 30 is not required in the assembling process, and the assemblability is excellent.
- (7) The metal-made base 60 is formed into a size and shape in which, in a state where a countermeasure against unwanted resonance is not taken, unwanted resonance is generated in the vicinity of the lowest frequency in the reception frequency band. Therefore, the conductor plates 90 are disposed to cause unwanted resonance to be shifted into a lower frequency band, whereby the position of unwanted resonance can be surely deviated from the reception frequency band.
Although the present invention has been described with reference to the embodiment, it is obvious to those skilled in the art that the components and processing processes in the embodiment can be variously modified within the scope of the claims. Hereinafter, modifications will be described.
Even when each of the conductor plates 90 is configured by a flat plate having no plate spring portions 92, a certain level of effects can be attained in prevention of reduction of the antenna gain. Even when the conductor plates 90 are not conductive with the metal-made base 60, a certain level of effects can be attained in prevention of reduction of the antenna gain. The outer edge (three sides excluding the side facing the feeding cylindrical portion 62) of each of the conductor plates 90 may be outside the outer edge of the metal-made base 60 as seen in the axial direction (vertical direction) of the feeding cylindrical portion 62.
REFERENCE SIGNS LIST
1 antenna case, 1a rib, 1b, 1c threaded-hole equipped boss, 3 pad, 5 sealing member, 6 LTE element, 6a output cable, 6b board, 6c holder, 7 satellite radio antenna, 7a output cable, 10 capacitive element, 11 curved surface portion, 12 connecting portion, 13, 14 through hole, 20 element holder, 21 base portion, 22 cylindrical portion, 22a projection, 23 through hole, 24 placement portion, 24a projecting portion, 24b latching claw, 24c projecting portion, 30 filter board, 31 through hole, 31a conduction pattern, 32a, 32b inductive pattern, 33 chip capacitor, 34 through hole, 35 cutout, 40 coil element, bobbin, 42 winding, 42′ wire, 43 upper terminal attaching portion, 43a convex portion, 44 lower terminal attaching portion, 45 upper terminal (first terminal), 45a base portion, 45b attaching leg, 45c winding terminal connecting portion (tab), 45d through hole, 47 lower terminal (second terminal), 47a upper surface portion, 47b connection leg, 47c winding terminal connecting portion (tab), 47d plate spring portion, 47e side surface portion, 47f lower surface portion, 48 winding barrel, 48a guide groove, 48b projection, 50 amplifier board, 51 conductor plate spring (terminal), 52 output cable, 60 metal-made base (conductive base), 61 planar portion, 61a, 61b convex portion, 62 feeding cylindrical portion (hollow threaded shaft portion), 63 first groove portion, 64 second groove portion, 65 threaded hole, 70 resin-made base (insulative base), 71 planar portion, 71a boss (projection), 72a, 72b through hole, 73 concave portion, 73a through hole, 80 provisional fixing holder, 81 clamping portion, 82 liaison portion, 83 latching claw, conductor plate, 91 planar portion, 92 plate spring portion, 93 screwed portion, 93a through hole, 101, 102, 103, 104 screw
Patent Grant
10355335
