Antenna device

Abstract

To provide an antenna device which is capable of reducing stray capacitance even if it is small in size and low in height and in which the other antenna for media can be mixed without trouble.SOLUTION: An AM / FM antenna 13 is configured by fixing a pair of capacitance loading elements 131 and 132 through a fixing hole 1321 to a holder 133 and fixing a helical antenna 134 to a lower part of the holder 134. The capacitance loading elements 131 and 132 are opposed at a predetermined interval and a predetermined angle with a face orthogonal with a vehicle roof defined as a center. Connection parts are provided at portions lower than upper edges, and the elements are conducted to each other via the connection parts. Edges of the capacitance loading elements 131 and 132 are sized so as not to interfere with e.g., an SDARS antenna 14 or a GNSS antenna 19. Between an M-shaped connection piece feeding power to the AM / FM antenna 13 and an AM / FM amplifier, a filter which brings a frequency of a phone antenna 17 into high impedance is connected in series.SELECTED DRAWING: Figure 7

Description

[Technical Field]

[0001] The present invention relates to a low-profile antenna device that is attached to the roof of a vehicle and is capable of receiving radio waves for a plurality of media. [Background technology]

[0002] Known conventional antenna devices that can be attached to the roof of a vehicle include those disclosed in Patent Documents 1 to 3. These antenna devices house an antenna unit in an antenna case that protrudes 70 mm or less from the vehicle roof. The antenna unit includes an antenna element that receives radio waves in the FM wave band and an umbrella-shaped metal plate near the top of the antenna element to increase the gain in the AM wave band. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-21856 [Patent Document 2] Japanese Patent Application Laid-Open No. 2015-84575 [Patent Document 3] Japanese Patent Application Laid-Open No. 2016-174368 Summary of the Invention [Problem to be solved by the invention]

[0004] In recent years, there has been a trend to combine antennas for multiple media, such as telephone antennas and GPS antennas, in addition to AM and FM broadcasts, in an antenna case. Therefore, when antenna elements are provided as a single large metal plate to achieve a small and low-profile design, as in the antenna devices disclosed in Patent Documents 1 to 3, antennas for other media are placed in close proximity, resulting in increased stray capacitance due to the proximity of the antennas. Stray capacitance is an ineffective capacitance component unintended by the designer and is caused by the physical structure. The larger this stray capacitance, the lower the gain. Furthermore, antennas that are not in close proximity are more susceptible to mutual influence.

[0005] An object of the present invention is to provide an antenna device that can reduce stray capacitance even if it is small and low-profile, and that can also be mounted with antennas for other media without any problems. [Means for solving the problem]

[0006] The antenna device provided by the present invention is an antenna device that is attached to the roof of a vehicle and comprises a radio wave transparent case portion having a storage space formed therein, and an antenna portion that is stored in the storage space, and is characterized in that the antenna portion has a pair of capacitance loading elements that face each other at a predetermined distance and a predetermined angle centered on a plane perpendicular to the vehicle roof, a connecting portion that is provided at a position lower than the upper edge of each capacitance loading element and that connects the capacitance loading elements to each other, and a helical element that is electrically connected to the connecting portion. [Effects of the Invention]

[0007] Because the edges of the capacitance loading element (top, side, and bottom edges) are spaced apart, the surface parallel to the vehicle roof is open. Therefore, the capacitance loading element adds capacitance to the ground to the helical element, but reduces stray capacitance. This improves the gain of AM and FM broadcasts. Furthermore, because the edges of opposing capacitance loading elements are discontinuous, interference with radio waves received by antennas for other media can be suppressed. [Brief explanation of the drawings]

[0008] [Figure 1] 3A to 3C are external views of the antenna device according to the first embodiment. [Figure 2] FIG. 2 is an explanatory diagram illustrating the arrangement of components that configure the antenna device according to the first embodiment. [Figure 3] (a) to (c) are explanatory diagrams of the holder structure. [Figure 4] (a) to (d) are explanatory diagrams of the structure of the capacity loading element. [Figure 5](a) to (c) are explanatory diagrams of the structure of the helical element. [Figure 6] (a) to (d) are diagrams explaining the structure of AM / FM antennas. [Figure 7] FIG. 10 is an external perspective view showing the antenna unit stored in the storage space. [Figure 8] 10 is a perspective view showing a structural example of an antenna device including an antenna portion in a storage space. FIG. [Figure 9] (a) to (e) are diagrams showing examples of changes in the electrical characteristics of a SDARS antenna. [Figure 10] 10(a) to 10(c) are diagrams illustrating the connection portions between the capacity loading elements. [Figure 11] 10(a) to 10(c) are explanatory diagrams of the structure of an antenna device according to a second embodiment. [Figure 12] 10A and 10B are explanatory diagrams illustrating the structure of an antenna device according to a third embodiment. [Figure 13] FIG. 10 is an explanatory diagram illustrating the arrangement of an antenna section of an antenna device according to a fourth embodiment. [Figure 14] 10(a) to 10(c) are explanatory diagrams of the structure of an AM / FM antenna according to a fourth embodiment. [Figure 15] 10A is a perspective view of the appearance of an antenna device according to a fifth embodiment, and FIG. 10B is a partially cutaway view of FIG. [Figure 16] FIG. 10 is an explanatory diagram illustrating the arrangement of components that configure the antenna device according to the fifth embodiment. [Figure 17] FIG. 11 is an external perspective view of a capacity loading element according to a fifth embodiment. [Figure 18] (a) to (e) are explanatory diagrams of the shape of the capacity loading element. [Figure 19] FIG. 10 is a graph showing the average gain-frequency characteristics of the telephone antennas according to the first and fifth embodiments. [Figure 20] Average gain vs. frequency characteristics of a keyless entry antenna. [Figure 21] FIG. 10 is an external perspective view of an SDARS antenna according to a fifth embodiment. [Figure 22] FIG. 22 is an explanatory diagram illustrating the arrangement of components constituting the SDARS antenna of FIG. 21. [Figure 23]22 is a cross-sectional view taken along line AA' in FIG. 21. [Figure 24] A diagram showing the positional relationship between the parasitic element for SDARS and the antenna body. [Figure 25] Simulation diagram showing gain change depending on the direction of the SDARS antenna. [Figure 26] SDARS antenna gain-frequency characteristics diagram. [Figure 27] FIG. 13 is an external perspective view of an antenna unit of an antenna device according to a sixth embodiment. [Figure 28] (a) and (b) are explanatory diagrams of the structure of the capacity loading element. [Figure 29] 1A and 1B are explanatory diagrams of the procedure for assembling a helical coil to an element holder, where (a) shows the state before assembly and (b) shows the state after assembly. DETAILED DESCRIPTION OF THE INVENTION

[0009] The following describes an embodiment in which the present invention is applied to a low-profile antenna device that can be attached to the roof of a vehicle. This antenna device is equipped with multiple types of antennas to receive or transmit radio waves for multiple media. In the following description, for convenience, the vehicle roof side will be referred to as the downward direction, the direction vertically upward from the vehicle roof as the upward direction, the longitudinal direction of the present invention as the front-to-rear direction (the front is the front, and the back is the rear), and the direction perpendicular to the longitudinal direction as the left-to-right direction. The up-and-down directions will also be referred to as the front and back, respectively, or similar expressions will be used.

[0010] [First embodiment] FIG. 1(a) is a plan view of the antenna device according to the first embodiment, FIG. 1(b) is a side view, and FIG. 1(c) is a rear view. The antenna device 1 according to this embodiment has a case made of a radio wave-transmitting synthetic resin with a storage space formed therein, and an antenna unit stored in the storage space. The case is composed of an antenna case 10 with an opening on the bottom side and an inner case (not shown). The antenna device 1 also has a base part 20 that closes the opening of the antenna case 10, and a capture part 30 that mounts the antenna device 1 to the vehicle roof and provides grounding. The antenna case 10 is tapered and lowered toward the front (toward the tip), and is formed into a streamlined shape with its sides curved inward (toward the longitudinal central axis). The underside of the antenna case 10 is formed to fit the shape of the mounting surface of the vehicle roof (not shown) (the bottom surface of the portion on the vehicle roof where the antenna device 1 is mounted; the same applies below). The length of the antenna case 10 in the longitudinal direction is approximately 230 mm, the width is approximately 75 mm, and the height is approximately 70 mm.

[0011] <Component layout structure> 2 is an explanatory diagram of the arrangement of components in the antenna device 1. The antenna device 1 has an inner case 11 whose outer wall has a shape corresponding to the shape of the inner wall of the antenna case 10. The inner case 11 is made of a radio wave-transmitting synthetic resin and has an opening on the bottom side. The outer flange of the bottom part has a groove and multiple bosses for screwing onto the base part 20. The storage space is formed inside this inner case 11 and is used to protect the antenna. Furthermore, when the inner case 11 is screwed to the base part 20, an O-ring 22 is sandwiched and fixed between the inner wall of the inner case 11 and the outer wall of the inner rib of the insulating wall of the insulating base 23, thereby ensuring dustproofness and waterproofness inside the antenna device 1. The resin engaging piece provided on the rear inside of the antenna case 10 is aligned with the engaging piece fitting portion of the insulating base 23, and the antenna case 10 is fixed to the insulating base 23 by engaging the locking claws provided on the front, left and right sides of the antenna case 10 and insulating base 23 with each other, using this as a fulcrum. In addition to the locking claws, fixing pieces are provided on the left and right sides of the antenna case 10, and the fixing pieces are assembled by being inserted into holes for the fixing pieces provided in the insulating base 23. By providing the fixing pieces, it is possible to prevent the antenna case 10 from being deformed by an external force applied to the antenna case 10, and also, because the external force is distributed to the fixing pieces, it is possible to reduce the external force transmitted to the locking claws and prevent the locking claws from disengaging from each other.

[0012] A soft insulating pad 12 is attached between the outer edge of the lower surface of the inner case 11 and the open end of the antenna case 10. The pad 12 is sandwiched and fixed when the antenna case 10 is fixed to the base part 20. The pad 12 seals the gap between the vehicle roof and the antenna case 10 and the inner case 11, improving the aesthetic appearance and also improving dustproofness and waterproofness. In particular, the pad 12 plays a role in improving the waterproofness of the sealant 34 by preventing water from being sprayed directly onto the sealant 34, such as by the water discharge from a car wash.

[0013] The storage space of the inner case 11 is fitted with an AM / FM antenna 13, a SDARS (Satellite Digital Audio Radio Service) antenna 14, an LTE antenna 15, a GNSS antenna 16, and a telephone antenna 17. The AM / FM antenna 13 receives AM broadcast signals from 522 kHz to 1710 kHz and FM broadcast signals from 76 MHz to 108 MHz. It can also receive LW broadcast signals from 153 kHz to 279 kHz. The SDARS antenna 14 receives circularly polarized waves in the 2.3 GHz band, which is used for satellite digital audio radio services. The LTE (Long Term Evolution) antenna 15 transmits and receives signals from the 700 MHz to 2.7 GHz band. The Global Navigation Satellite System (GNSS) is a collective term for satellite positioning systems such as GPS, GLONASS, Galileo, and Quasi-Zenith Satellite System (QZSS). The GNSS antenna 16 receives circularly polarized waves and receives GNSS signals in the 1.5 GHz band. The phone antenna 17 transmits and receives radio waves in the 700 MHz to 2.7 GHz bands and is actually a type of LTE antenna.

[0014] The AM / FM antenna 13 is fixed to a boss on the inner wall of the inner case 11 with a screw, and is elastically held by an M-shaped connecting piece 191, which is an elastic conductive member formed on the substrate 19. The SDARS antenna 14 is screwed and held in the insulating base 23. The LTE antenna 15 and the GNSS antenna 16 are fixed to the conductive base 21 via the substrate 18. The telephone antenna 17 is fixed to the conductive base 21 via the substrate 19. The signals received and amplified by the antennas 13 to 17 are sent to the electronic circuitry on the vehicle side through signal cables C1, C2, and C3.

[0015] The AM / FM antenna 13 includes a pair of capacitance-loading elements 131 and 132, a holder 133 made of radio-wave-transparent synthetic resin, and a helical element 134. The capacitance-loading elements 131 and 132 each have an electrical delay section (e.g., a meander-shaped composite) approximately in the center, and do not resonate in the AM / FM bands by themselves. However, they function as capacitance-loading plates that add (load) ground capacitance to the helical element 134, improving its function as a voltage-receiving element in the AM band and allowing the AM / FM antenna 13 to resonate in the FM band. Furthermore, at frequencies other than the AM and FM bands, they function as an impedance converter (described later). The helical element 134 is inserted between the capacitance-loading elements 131 and 132 and the AM / FM amplifier circuit, and works in conjunction with the capacitance-loading elements 131 and 132 to function as a helical antenna that resonates in the FM band. This helical element 134 is formed by winding a linear conductor around a hollow bobbin, and has terminals (lower terminal 1341 in the example shown in FIG. 2) formed at the upper and lower ends thereof that are electrically connected to the ends of the linear conductor, and this lower terminal 1341 is elastically held by the above-mentioned M-shaped connecting piece 191. The structure of the AM / FM antenna 13 will be described in detail later.

[0016] The SDARS antenna 14 includes a parasitic element 141, a parasitic element holder 142, a planar antenna 143, an SDARS amplifier board 144, a shield cover 145, and a ground plate 146. The planar antenna 143 is the main antenna for SDARS, and the parasitic element 141, which is a thin metal plate, is provided above the planar antenna 143 at a predetermined distance to improve the antenna gain of the planar antenna 143. The shield cover 145, which is a box-shaped thin metal plate, is a conductive member that electrically shields the SDARS amplifier board 144. The ground plate 146 is a conductive member that serves as the ground (grounding portion; the same applies hereinafter) for the planar antenna 143. The shield cover 145 and the ground plate 146 may be integrated. The SDARS antenna 14 is disposed in a recess in the insulating base 23 located in front of the conductive base 21. The ground plate 146 is spaced a predetermined distance from the vehicle roof. In addition, it is electrically isolated from the ground of other antennas other than the SDARS antenna, the reason for which will be explained later.

[0017] The LTE antenna 15 is provided on a substrate 18. The GNSS antenna 16 is a planar antenna and is attached to the surface of the substrate 18. A GNSS amplifier circuit, an LTE antenna matching circuit, and a diplexer circuit that combines the outputs of both antennas 15, 16 into one, which are not shown in the figure, are mounted on the back surface of the substrate 18. The GNSS antenna 16 is electrically connected to the input of the GNSS amplifier circuit. The LTE antenna 15 is also electrically connected to the input of the LTE antenna matching circuit. The electrical connection is made by soldering or the like. The telephone antenna 17 is provided on the surface of the substrate 19. A matching circuit for the telephone antenna 17 and an AM / FM amplifier circuit, which are not shown in the figure, are mounted on the back surface of the substrate 19.

[0018] The base part 20 is composed of a metal conductive base 21 that has the same potential as the vehicle roof after being attached to the vehicle roof, an O-ring 22 that is a soft insulator, and a resin insulating base 23 whose outer periphery fits the shape of the underside of the antenna case 10. The insulating base 23 is made of resin that has enough strength to hold the conductive base 21, the antenna case 10, the inner case 11, and the SDARS antenna 14. The conductive base 21 is a die-cast member that has a predetermined strength, and when attached, has the same potential as the vehicle roof and functions as ground (earth).

[0019] The front side of the conductive base 21 is formed with recesses 211 and 212 and a wall 213 that shields these recesses 211 and 212. The recess 211 houses electronic components such as an AM / FM amplifier circuit mounted on the back surface of the substrate 19. The recess 212 houses electronic components such as a GNSS amplifier circuit mounted on the back surface of the substrate 18. The wall 213 shields these storage spaces. In other words, the recesses 211 and 212 and the wall 213 position the substrates 18 and 19 and also form independent shield regions. In other words, the conductive base 21 also serves as a shielding member for the various electronic components.

[0020] Screw holes for screwing the substrates 18, 19, etc. are also formed around the recesses 211, 212. However, the spacing between the screw holes is preferably equal to or less than half the wavelength of the radio waves in the desired frequency band to prevent leakage of the radio waves. Note that portions of the substrates 18, 19, such as the signal output patterns, may be open. Meanwhile, bosses are formed on the back side of the conductive base 21 that protrude downward and are used to screw the capture unit 30.

[0021] The insulating base 23 has a shape corresponding to the shape of the opening surface portion of the antenna case 10 at its outer peripheral portion. A guide groove for fitting an O-ring 22 and an engaging mechanism for engaging the inner case 11 are formed slightly inside the outer peripheral portion. A flat component mounting surface 231 is formed inside the guide groove and the engaging mechanism. A hole portion 232 is formed at approximately the center of this component mounting surface 231 so that the conductive base 21 and the capture portion 30 are mechanically connected. Further, a recess 233 is formed in front of the insulating base 23. The SDARS antenna 14 is housed in this recess 233.

[0022] The capture portion 30 includes a bolt 31, a vehicle fixing claw member 32, a pre-lock holder 33, a sealing material 34, and a metal spring 35. The pre-lock holder 33 temporarily fixes the antenna device 1 to the vehicle roof. A locking claw is provided on the pre-lock holder 33. When the antenna mounting boss portion is inserted and fitted into the mounting hole on the vehicle roof side, the locking claw fits around the mounting hole on the vehicle roof side. Thereby, before tightening the bolt 31, the antenna device 1 can be temporarily fixed, and the workability of mounting the antenna on the vehicle roof is improved. After temporary fixing, when the bolt 31 is tightened, the claws of the vehicle fixing claw member 32 open. Thereafter, the tip of the fixing claw member 32 scrapes the painted surface of the vehicle roof, so that the vehicle roof and the conductive base 21 are connected so as to be substantially at the same electric potential and mechanically fixed. Also, when the bolt 31 is tightened, the sealing material 34 fixed to the back surface of the insulating base 23 with an adhesive or the like is compressed since it has elasticity. Thereby, it is possible to prevent dust from entering the vehicle through the vehicle roof and to achieve waterproofing. Also, it is possible to ensure rust prevention and waterproof properties of the conductive base 21 and the metal spring 35. The curvature of the vehicle roof on which the antenna device 1 is mounted may vary depending on the vehicle type. The metal spring 35 is a member having slidability with a convex portion in contact with the vehicle roof and is deformed so as to follow the shape (curvature) of the vehicle roof. Its action and effect will be described later.

[0023] <Structure of AM / FM Antenna> Next, the structure of the AM / FM antenna 13 will be described in detail. The AM / FM antenna 13 has a three-dimensional holder 133 with a trapezoidal cross section. FIG. 3(a) is a top view of the holder 133, FIG. 3(b) is a front view, and FIG. 3(c) is a side view. The holder 133 is made of radio wave-transmitting synthetic resin, long in the front-rear direction and short in the left-right direction, and its upper bottom surface 1331 is substantially flat. A groove 1332 with a flat bottom surface of a predetermined width is formed in the upper bottom surface 1331 slightly forward from the longitudinal center. A screw hole 1333 is formed in a predetermined position in this groove 1332. This screw hole 1333 is used to fasten the capacitance loading elements 131 and 132 and the helical element 134 together to the inner wall boss of the inner case 11 with a screw. Multiple ribs 1334 of various widths are formed on both sides of the holder 133. A locking claw 1335 is formed on one of the ribs 1334. The ribs 1334 and the locking claws 1335 not only regulate the angle and position of the capacitance loading elements 131 and 132, but also improve the strength of the holder.

[0024] FIG. 4 is an explanatory diagram showing an example of the shape and arrangement of the capacitance loading elements 131 and 132, where (a) is a top view, (b) is a front view, and (c) is a side view. Also, (d) is an explanatory diagram of the size of these capacitance loading elements 131 and 132. As shown in these figures, the capacitance loading elements 131 and 132 are composite elements that connect a front surface portion, which will be the front when installed, and a rear surface portion, which will be the rear, with a strip-shaped meander portion. The "meander portion" refers to a surface formed by a thin conductor element formed to have at least one meandering shape. The two elements are approximately symmetrical in shape, and one faces the other at a predetermined distance and a predetermined angle centered on a plane perpendicular to the vehicle roof. This distance and angle are determined according to the shape of the internal space of the inner case 11. The rear surface portion has a tall structure.

[0025] The capacitance loading elements 131, 132 also have connecting portions 1312, 1322 formed at a position lower than the portion that will be the uppermost end when installed (hereinafter referred to as the "zenith portion"), and are electrically connected to each other through these connecting portions 1312, 1322. Each connecting portion 1312, 1322 can be realized by forming a slit in a portion of each capacitance loading element 131, 132 and then bending it. The connecting portions 1312, 1322 have different lengths in order to clarify the installation direction of one capacitance loading element 131 and the other capacitance loading element 132, which are approximately symmetrical, but this does not always have to be the case.

[0026] Fixing holes 1311, 1321 are formed on the front and rear surfaces of these capacitance loading elements 131, 132. These fixing holes 1311, 1321 are used to fit into locking claws 1335 of the holder 133. This allows the capacitance loading elements 131, 132 to be locked to the holder 133 without using adhesive or the like, which not only simplifies the assembly process but also suppresses fluctuations in electrical characteristics caused by using adhesive or the like. Furthermore, instead of fixing with the locking claws, it is also possible to temporarily fix the holder with the locking claws, and then heat the holder to weld it to the holder for fixation.

[0027] In this embodiment, the height a1 of the front surface portion shown in Figure 4(d) is approximately 26 mm, the horizontal length a2 is approximately 23 mm, the horizontal length a3 of the meander portion is approximately 14 mm, and the horizontal length a4 of the rear surface portion is 23 mm. However, the meander portion also has a path length in the height direction.

[0028] The wavelength λ1 of the SDARS is approximately 120 mm, and the height a1 and lengths a2 and a4 are approximately 1 / 4 or less of the wavelength λ1 of the SDARS, and the path length of the meander section is approximately 1 / 2. Therefore, the impedance when looking at the meander section (starting end) from the front surface is high at the frequency of the SDARS, and they are electrically isolated. In other words, the capacitive loading elements 131 and 132 function as impedance converters, for example, in the frequency band used by the SDARS. The impedance when looking at the meander section (rear end) from the rear surface is also similar. Therefore, for the SDARS antenna 14, the capacitance loading elements 131 and 132 are conductors of a size that does not affect their own operation (including directivity). The impedance of the capacitance loading elements 131 and 132 from the rear end toward the meander portion and from the front end toward the meander portion is also high in the SDARS frequency band, so they are not affected by the SDARS radio waves. In other words, there is no mutual interference. Furthermore, the wavelength λ2 of the GNSS is approximately 190 mm, and the electrical lengths of the capacitance loading elements 131 and 132 are set to a length that does not resonate and is not half the wavelength λ2 of the GNSS. Therefore, the capacitance loading elements 131 and 132 do not interfere with the GNSS antenna 16.

[0029] In contrast, in the case of a single-plane element without a meandering portion as in Patent Documents 1 to 3, if a required capacitance to the ground is to be loaded, the horizontal length will be approximately 60 mm, which is half the wavelength λ1, and this will likely result in a decrease in gain and distortion of directivity, at least for the SDARS antenna 14. In addition, the height will be approximately twice the height a1, which is also approximately half the wavelength λ1, and this will likely result in a decrease in gain and distortion of directivity, at least for the SDARS antenna 14.

[0030] According to experiments by the inventors of the present application, when the plate thickness of the capacitance loading elements 131, 132 is 1 to 2 mm or less (a thickness sufficiently small compared to the wavelengths λ1, λ2) for the wavelengths λ1, λ2, the height a2 is approximately ¼ or less of the wavelength λ1 of the radio waves received by the planar antenna 143, and the path length of the meandering portion is approximately ½ ± ⅛ of the wavelength λ1, no interference is observed between the AM / FM antenna 13 and the SDARS antenna 14. Furthermore, when the capacitance loading elements 131, 132 have a length that does not resonate with the radio waves received by the GNSS antenna 16, no interference is observed between the AM / FM antenna 13 and the GNSS antenna 16. Note that the length of the front surface portion and the rear surface portion electrically separated by the meandering portion is preferably approximately ¼ or less of the wavelength λ1.

[0031] As shown in FIGS. 4(a) to 4(d), the capacitance-loading elements 131 and 132 with an open zenith structure also exhibit excellent effects in relation to the helical element 134. That is, because the zeniths of the capacitance-loading elements 131 and 132 are open, the projected area of ​​the helical element 134 and the zeniths is reduced compared to when capacitance loading is performed on a single surface. Therefore, in the capacitance-loading elements 131 and 132, eddy currents that act to cancel out the high-frequency current generated in the helical element 134 are reduced. This reduces the deterioration in efficiency of the AM / FM antenna 13. Furthermore, this effect improves the degree of freedom in the placement position of the helical element 134 relative to the zeniths. For example, it is no longer necessary to place the helical element 134 at the center of the zeniths of the capacitance-loading elements 131 and 132.

[0032] The structure of this embodiment, in which the apex portions of the capacitance loading elements 131 and 132 are open, does not require bending or drawing of the capacitance loading elements 131 and 132, simplifying the processing steps and contributing to reduced manufacturing costs. This structure also has the effect of reducing the stray capacitance generated between adjacent conductors, in this case, the telephone antenna 17, compared to when a single capacitance loading plate is used. Stray capacitance is an inactive capacitance component that is not intended by the designer and is caused by the physical structure. As mentioned above, the larger this stray capacitance, the lower the gain. The telephone antenna 17 is disposed approximately in the center between the side edges of the front surfaces of the opposing capacitance loading elements 131, 132. This also reduces the stray capacitance, so the opposing distance between the telephone antenna 17 and the capacitance loading elements 131, 132 can be shortened as shown in Figures 7 and 8. Note that, in order to further reduce the stray capacitance with the telephone antenna 17, one or more holes or slits may be formed in the capacitance loading elements 131, 132. This further reduces the stray capacitance, mainly with the ground, on the lower surface side of the capacitance loading elements 131, 132, so sufficient performance can be obtained even if the lower surface side is constructed with a conductive base.

[0033] Next, we will explain the helical element 134. Figure 5(a) is a top view of the helical element 134, (b) is a front view, and (c) is a rear view. The helical element 134 is formed by winding a conductor around a cylindrical bobbin made of radio wave-transmitting synthetic resin. Grooves with a predetermined diameter and pitch are formed on the surface of the bobbin so that the desired shape of the helical antenna can be formed. By winding a linear conductor around the bobbin the required number of turns, it can function as a helical antenna. A lower terminal 1341 is formed on the bottom of the bobbin and is electrically connected to one end of the conductor. This lower terminal 1341 is elastically held by the M-shaped connecting piece 191 described above and is electrically connected to the input terminal of the AM / FM amplifier circuit mounted on the back surface of the substrate 19. An upper terminal 1342 is electrically connected to the other end of the conductor. A metal screw is inserted upward from inside the bobbin, and the foot of this metal screw is inserted into the screw hole 1333 of the holder 133 and the circular hole formed by the connecting parts 1312, 1322 of the capacitance loading elements 131, 132, and these are then fastened together to the inner wall boss of the inner case 11, thereby electrically connecting the upper terminal 1342 and the capacitance loading elements 131, 132. The metal screw may be a screw with a spring washer to strengthen mechanical retention. Furthermore, the upper terminal 1342 has a structure that allows it to be attached to the bobbin by being rotated 180 degrees, and while sharing parts, the number of turns of the helical element 134 can be adjusted in half-turn increments, which makes it possible to adjust the receiving frequency and improves design freedom.

[0034] FIG. 6 shows the state in which the capacitance loading elements 131 and 132 are fixed to the holder 133 and the helical element 134 is attached to the holder 133. FIG. 6(a) is a top view, FIG. 6(b) is a front view, FIG. 6(c) is a side view, and FIG. 6(d) is a bottom view. As described above, the degree of freedom in the placement position of the helical element 134 is improved compared to when a single capacitance loading plate with the top portion closed is used. In this embodiment, the lower terminal 1341 is positioned approximately midway between the capacitance loading elements 131 and 132, and the helical element 134 itself is slightly eccentric toward the capacitance loading element 132. By eccentricity in this manner, the capacitance loading element adjacent to the helical element 134 becomes the capacitance loading element 132. Therefore, electrical interference can be prevented from occurring only with the capacitance loading element 132, which reduces interference and suppresses performance degradation compared to when electrical interference occurs with both the capacitance loading elements 131 and 132. The helical element 134 may be slightly eccentric toward the capacitance loading element 131.

[0035] 7 shows the state of the antenna section stored in the storage space of the inner case 11. Fig. 7 is an external perspective view showing the state in which only the antenna case 10, inner case 11, and O-ring 22 have been removed from the antenna device 1 assembled according to the arrangement shown in Fig. 2. Fig. 8 is an explanatory view showing a see-through state of the storage space in a state in which the antenna case 10, inner case 11, and O-ring 22 have also been assembled. As shown in these figures, in the antenna device 1 of this embodiment, the edges of the capacitance loading elements 131 and 132 are spaced apart, and the surfaces parallel to the vehicle roof are open. Therefore, the capacitance loading elements 131 and 132 add capacitance to the ground to the helical element 134, but reduce stray capacitance. This improves the gain of AM and FM broadcasts. Furthermore, because the edges of the opposing capacitance loading elements 131 and 132 are discontinuous, interference with radio waves received by antennas for other media can be suppressed.

[0036] That is, even though the antenna device 1 has a low profile and a narrow storage space, with a longitudinal length of approximately 230 mm, a width of approximately 75 mm, and a height of approximately 70 mm, the SDARS antenna 14, the LTE antenna 15, the GNSS antenna 16, the telephone antenna 17, and the AM / FM antenna 13 can be arranged side by side from the front in this order without interfering with each other.

[0037] 7 and 8, the AM / FM antenna 13 and the telephone antenna 17 are located close to each other. Therefore, the AM / FM antenna 13, which receives signals at lower frequencies than the telephone antenna 17, is more susceptible to the influence of the telephone antenna 17. Therefore, in this embodiment, a capacitor of preferably about 20 pF is connected in series to the feed point of the telephone antenna 17 in the matching circuit mounted on the back surface of the substrate 19, and then impedance matching of the received signals at each frequency is performed. 20 pF results in an impedance of about 80 kΩ at 1 MHz in the AM band, and about 80 Ω at 100 MHz in the FM band. In contrast, in the frequency band received by telephone antenna 17, for example, at 800 MHz or higher, the impedance drops to 10 Ω or less, significantly lower. Also, since impedance matching with telephone antenna 17 is achieved using a matching circuit, loss in the reception band of telephone antenna 17 is further reduced. Considering the reception bandwidth of telephone antenna 17, a capacitance of approximately 2 pF to 20 pF is desirable. This has the effect of ensuring the gain of both telephone antenna 17 and AM / FM antenna 13. Alternatively, a band elimination filter (BEF) consisting of a parallel resonant circuit using an inductor and capacitor can be configured to increase the impedance near the AM band or FM band, thereby achieving a similar effect. Also, a filter that makes the frequency of the telephone antenna 17 a high impedance is connected in series between the M-shaped connection piece 191 that supplies power to the AM / FM antenna 13 and the AM / FM amplifier, so that they do not interfere with each other further. The filter is configured such that chip capacitors are not arranged between the signal path and the ground, and the received signal in the AM band is not divided by the capacitor and attenuated. It is a filter configured by using parallel resonance of an inductor and a capacitor or an open stub to reflect or attenuate the desired frequency band of the telephone antenna 17.

[0038] <Mounting Structure of SDARS Antenna> In this embodiment, the SDARS amplifier substrate 144 is mounted on the back surface side of the substrate of the planar antenna 143 for SDARS, and the planar antenna 143 and the SDARS amplifier substrate 144 are sandwiched between the passive element holder 142 that houses the passive element 141 and the metal shield cover 145. At least two or more ribs are provided on the lower surface of the passive element holder 142 for positioning with the planar antenna 143 for SDARS. Also, the thickness of the passive element holder 142 is set to a thickness that makes the distance between the passive element 141 and the planar antenna 143 for SDARS constant. At least one or more positioning slits are provided in the conductive passive element 141, and the positioning is achieved by fitting the slits into the positioning ribs of the passive element holder 142. This may be a structure in which a protrusion is provided on the passive element 141 and a recessed shape is formed in the passive element holder 142. Then, these are fixed by screwing together the holes provided in the SDARS amplifier substrate 144 and the holes provided in the ground plate 146. The ground plate 146 is arranged in front of the insulating base 23 and is fitted so as to be positioned in the recess 233 provided inside the ribs of the insulating base 23. The thickness of the insulating base 233 in the portion where the recess 233 is formed is thinner than the thickness of the portion where the recess 233 is not formed, but since the recess 233 is provided in a shape that partially follows the shape of the ground plate 146 inside the ribs of the insulating base 23, the strength of the insulating base 23 is sufficiently maintained. Furthermore, the ground plate 146 is not connected to the conductive base 21 so as to be electrically isolated from the conductive base 21. This is to prevent the ground plate 146 from affecting the electrical characteristics of the LTE antenna 15 and / or the telephone antenna 17, and to prevent the ground plate 146 from affecting the directivity of the SDARS antenna 14.

[0039] That is, the conductive base 21 also functions as a ground for the LTE antenna 15, the GNSS antenna 16, the telephone antenna 17, and the AM / FM antenna 13, but it can also cause unwanted resonance (resonance phenomenon) depending on the distance between the vehicle roof and the conductive base 21 and the size of the conductive base 21. The larger the conductive base 21, the more likely it is that unwanted resonance will occur. When unwanted resonance occurs, the gain of the antenna that receives radio waves in the band that includes that frequency decreases. Furthermore, depending on the curvature of the vehicle roof on which the antenna device 1 is mounted, the capacitance component between the conductive base 21 and the vehicle roof may change, and the unwanted resonance may reduce or change the gain of each of the antennas 13 to 17.

[0040] Here, we briefly explain unwanted resonance. If the inductance of the conductive base 21 and the portion of the capture unit 30 up to the vehicle-fixing claw member 32 is L, and the capacitance of the space between the conductive base 21 and the vehicle roof is C, the frequency f of the unwanted resonance is expressed as 1 / [2π√(LC)]. If the area between the conductive base 21 and the vehicle roof is S, the distance between the conductive base 21 and the vehicle roof is d, and the relative permittivity of the space is ε, then the capacitance C is ε·S / d. If the conductor loss is R, the Q factor, which indicates the sharpness of the unwanted resonance, is calculated as [√(L / C)] / R=1 / (ωCR). Here, ω is the angular frequency of the unwanted resonance, expressed as ω=2πf. The smaller the Q factor of the unwanted resonance, the less impact it has on the gain. If the conductive base 21 becomes larger and the area S increases, the capacitance C increases, and the frequency f of the unwanted resonance decreases. As a result, the frequency f of the unwanted resonance falls within the frequency band used for transmission or reception (within the specified band), which can reduce the gain of the antenna receiving radio waves in the band that includes that frequency. There are various types of vehicle roofs, each with a different curvature. Without the metal spring 35, a large curvature of the vehicle roof reduces the capacitance C. As the frequency f of the unwanted resonance increases, the Q factor increases, and the gain of each antenna 13-17 decreases. On the other hand, a small curvature of the vehicle roof increases the capacitance C, lowering the frequency f of the unwanted resonance and reducing the Q factor. Thus, the curvature of the vehicle roof significantly varies the capacitance C, and the frequency f of the unwanted resonance also significantly varies.

[0041] Therefore, in this embodiment, by abutting the convex portion of the metal spring 35 against the vehicle roof, first, the amount of fluctuation in the frequency f of unwanted resonance is suppressed, and the antenna device 5 can be attached to vehicle roofs of various curvatures. When the metal spring 35 is present, the metal spring 35 has sliding properties, so the convex part that it comes into contact with deforms to follow the curvature of the vehicle roof. This reduces the amount of variation in capacitance C and the amount of variation in frequency f of unwanted resonance, making it possible to attach the sensor to vehicle roofs with various curvatures.

[0042] In addition, in this embodiment, the convex portion of the metal spring 35 is brought into contact with the vehicle roof, thereby secondly increasing the capacitance C and shifting the frequency f of the unwanted resonance to a lower frequency range. Therefore, the frequency of the unwanted resonance can be shifted out of the specified band.

[0043] In this embodiment, in order to reduce the size of the conductive base 21 to a size that does not allow unwanted resonance to enter, the SDARS antenna 14 is not placed on the conductive base 21 but is placed on the insulating base 23. The ground of the SDARS planar antenna 143 uses a ground plate 146 that is electrically isolated from the conductive base 21. Because the reception band of the planar antenna 143 is a high frequency band such as the 2.3 GHz band, even if the ground plate 146 is separate, it is only necessary to make it slightly larger than the planar antenna 143 to obtain a ground size sufficient to ensure antenna gain.

[0044] The structure in which the ground plate 146 is separate from the conductive base 21 also has the effect of increasing the degree of freedom in the size and structure of the ground plate 146. The size and layout of the conductive base 21 are determined to some extent depending on the required specifications of the antenna device 1, but for example, if the electrical length between the vehicle roof and the conductive base 21 is approximately 1 / 4 of the wavelength λ1 of the SDARS, the electrical characteristics of the SDARS may deteriorate. In this embodiment, because the ground plate 146 is separate from the conductive base 21, the shape and size of the ground plate 146 can be arbitrarily set to obtain the desired electrical characteristics of the SDARS antenna 14, thereby improving directivity and increasing the degree of freedom in design.

[0045] FIG. 9 shows an example of changes in electrical characteristics due to structural changes in the SDARS antenna 14. As described above, the SDARS antenna 14 is housed in the recess 233 of the insulating base 23. This recess 233 not only facilitates positioning of the ground plate 146 during assembly and improves workability, but also determines the distance between the ground plate 146 and the vehicle roof. As described above, the ground plate 146 is slightly larger than the planar antenna 143. As shown in FIG. 9(a), if the distance between the vehicle roof and the ground plate 146 (the depth of the recess 233) is t, the vertical directivity of the planar antenna 143 becomes more distorted as the distance t increases, as shown in FIGS. 9(b) to 9(e). This distortion in directivity leads to a decrease in the gain of the planar antenna 143. Therefore, this distance t is 10 mm or less, preferably 2 mm to 10 mm, which makes it possible to realize electrical characteristics of the SDARS that are sufficient for practical use, while maintaining a low profile of 70 mm or less.

[0046] The shielding effect of SDARS amplifier board 144 is ensured by soldering or welding the periphery of shield cover 145 to SDARS amplifier board 144. Shield cover 145 is electrically connected to ground plate 146, and therefore has the same potential as ground plate 146.

[0047] In this embodiment, when connecting the connecting portions 1312 and 1322 of the capacity loading elements 131 and 132, an example has been shown in which a circular hole is formed in the portion corresponding to the screw hole 1333. However, such a circular hole can be easily formed by cutting out a semicircular notch in each opposing end portion when molding each connecting portion 1312 and 1322, as shown in Figure 10(a). Alternatively, as shown in Figures 10(b) and 10(c), the opposing ends of each connecting portion 1312 and 1322 may be rounded or rectangular, and circular holes may be formed near their tips. In either case, these circular holes serve as positioning, which has the effect of facilitating the work of fixing to the holder 133. Also, although the meander shape is in the up-down direction, the same effect can be obtained if it is in the front-back direction.

[0048] [Second embodiment] Next, a second embodiment of the present invention will be described. The antenna device of the second embodiment has the same basic components, such as the antenna case, inner case, base, multiple antennas, circuit board, and capture unit, and their arrangement as the antenna device 1 of the first embodiment. However, the shape of the capacitance loading element constituting the AM / FM antenna and the structure of the holder are different from those of the antenna device 1 of the first embodiment. FIG. 11(a) is a side view of the capacitance loading element included in the antenna device of the second embodiment, FIG. 11(b) is a top view, and FIG. 11(c) is an assembly diagram showing a portion of the inner case cut away for convenience. The antenna device 2 of this embodiment includes a pair of capacitance loading elements 131b and 132b, some of which are connected to connecting portions 1312b and 1322b, similar to the capacitance loading elements 131 and 132 of the first embodiment. However, the meandering shape and the mounting structure to the holder 133b are different. The tips of the connecting portions 1312b and 1322b extend downward, and electrical continuity between them is established by metal screws via conductive relay members.

[0049] In the antenna device 2 of the second embodiment, the upper and lower edges of the capacitance-loading elements 131b and 132b are also spaced apart, leaving open surfaces parallel to the vehicle roof. Therefore, the capacitance-loading elements 131b and 132b add capacitance to the ground to the helical element, but reduce stray capacitance. Because the connecting portions 1312b and 1322b extend downward, the generation of stray capacitance at the connecting portions 1312b and 1322b is also reduced. This improves the gain of AM and FM broadcasts. Furthermore, because the edges of the opposing capacitance-loading elements are discontinuous, interference with radio waves received by antennas for other media is reduced.

[0050] [Third embodiment] Next, a third embodiment of the present invention will be described. The antenna device of the third embodiment also has the same basic components and arrangement as the antenna device 1 of the first embodiment, such as the antenna case, inner case, base, multiple antennas, board, and capture unit, but differs from the antenna device 1 of the first embodiment in the shape of the capacitance loading element constituting the AM / FM antenna and the structure of the holder. Fig. 12(a) is an exploded assembly diagram of the capacitance loading element included in the antenna device of the second embodiment, and Fig. 12(b) is an external perspective view of the antenna device after assembly. The antenna device 3 of this embodiment includes a pair of capacitance loading elements 131c and 132c, some of which are used as connecting parts, just like the capacitance loading elements 131b and 132b of the second embodiment, but differs in that it has a meandering shape and two connecting parts each.

[0051] In the antenna device 3 of the third embodiment, the upper and lower edges of the capacitance loading elements 131c and 132c are also spaced apart, leaving open surfaces parallel to the vehicle roof. Therefore, the capacitance loading elements 131c and 132c add capacitance to the ground to the helical element, but reduce stray capacitance. This improves the gain of AM and FM broadcasts. Furthermore, because the edges of the opposing capacitance loading elements are discontinuous, interference with radio waves received by antennas for other media can be suppressed.

[0052] [Fourth embodiment] Next, a fourth embodiment of the present invention will be described. The antenna device of the fourth embodiment also has the same basic components, such as the antenna case, inner case, base, multiple antennas, board, and capture unit, and their arrangement as the antenna device 1 of the first embodiment, but differs from the antenna device 1 of the first embodiment in the configuration of the AM / FM antenna. Fig. 13 is an explanatory diagram of the arrangement of the antenna unit of the antenna device 4 of the fourth embodiment. Fig. 14 is an explanatory diagram of the structure of the AM / FM antenna in the fourth embodiment, where Fig. 14(a) is a top view, Fig. 14(b) is a front view, and Fig. 14(c) is a side view.

[0053] The antenna device 4 of the fourth embodiment is similar to the capacitance loading elements 131 and 132 of the first embodiment in that it includes a pair of capacitance loading elements 131d and 132d, some of which are connected to a holder 133d through a fixing hole 1321d, but the meander shape is different. The remaining portions of the capacitance loading elements 131d and 132d of the fourth embodiment, which are bent to form the connecting portions, form wide surfaces, with the front portion forming a first meander portion and the rear portion forming a second meander portion. The helical element 134 has the same components as the helical element 134 described in the first embodiment, but differs from the first embodiment in that it is disposed on the conductive base 21 outside the substrate 19. Therefore, the helical element 134 is eccentric toward the capacitance loading element 131d.

[0054] In the antenna device 4 of the fourth embodiment, the upper and lower edges of the capacitance loading elements 131d and 132d are also spaced apart, leaving open surfaces parallel to the vehicle roof. Therefore, the capacitance loading elements 131d and 132d add capacitance to the ground to the helical element 134, but reduce stray capacitance. This improves the gain of AM and FM broadcasts. Furthermore, because the edges of the opposing capacitance loading elements are discontinuous, interference with radio waves received by antennas for other media can be suppressed.

[0055] Although the first to fourth embodiments have been described above, the embodiments of the present invention are not limited to these examples. For example, a pair of capacitance loading elements 131 (131b to 131d), 132 (132b to 132d) (hereinafter abbreviated as "131, etc.") and helical element 134 may be electrically connected through a connecting piece having spring properties. Furthermore, capacitance loading elements 131, etc. may be connected to each other using an LC element (inductor and capacitor) or a conductive pattern filter formed on a substrate so that the resonance frequency of capacitance loading element 131, etc. and helical element 134 is not close to a desired frequency. Furthermore, the capacitance loading elements 131, etc. may be any shape that functions as an electrical delay section, such as a meander shape, at least one fold, a zigzag shape, a zigzag shape, a fractal shape, etc. In each embodiment, the upper and lower edges of the capacitance loading elements 131, etc. are discontinuous, but the front and rear edges may also be discontinuous. Furthermore, a pair of capacitance loading elements 131, etc. do not necessarily have to have symmetrical shapes.

[0056] The arrangement of the SDARS planar antenna 143 and the GNSS antenna 16 may be reversed. The SDARS planar antenna 143 and the GNSS antenna 16 may also be stacked one above the other. If the required performance requirements are not strict, and the ground size of the SDARS amplifier board 144 or the shield cover 145 is sufficient without providing the ground plate 146, then similarly, by forming a recess in a shape similar to that of the SDARS amplifier board 144 or the shield cover 145, improved electrical performance can be expected.

[0057] In the above description, the conductive base 21 is made of one piece such as die-cast, and the ground plate 146 is provided separately, but the conductive base 21 may also be made of a thin metal plate that is screwed or welded together to have the same electrical potential.

[0058] [Fifth embodiment] Next, a fifth embodiment of the present invention will be described. Fig. 15(a) is an external perspective view of an antenna device according to the fifth embodiment, and Fig. 15(b) is a partially cutaway view of Fig. 15(a) as viewed from the A-A' direction. Fig. 16 is an explanatory diagram showing the arrangement of components constituting the antenna device according to the fifth embodiment. As with the previous embodiments, the antenna device 5 of the fifth embodiment is an antenna device that is attached to the roof of a vehicle, and includes a radio wave transparent case portion having a storage space formed therein, and an antenna portion that is stored in the storage space.

[0059] The case section comprises an antenna case 50 having an opening on the underside, and a base section 60 that closes the opening of the antenna case 50 via a soft resin pad 52. The antenna case 50 becomes thinner and lower towards the front (towards the tip), and is formed into a streamlined shape with its side surfaces curved inward (towards the central axis in the longitudinal direction). The material and size of the antenna case 50 are approximately the same as those of the antenna case 10 of the first embodiment.

[0060] The base portion 60 is configured to include a conductive base 61 and an insulating base 63 for fixing the conductive base 61. Holes 611, 612 are formed at the front and rear of the conductive base 61 for passing the cables C51, C53, C54, and C57 through. Meanwhile, the insulating base 63 is formed with a mounting hole 631 for screwing the conductive base 61 from the vehicle roof side, and holes 632, 633 for passing the cables C51, C53, C54, and C57 through. Grooves are formed on the back surface of the insulating base 63 for accommodating a metal spring 64 and a soft sealing material 65. The metal spring 64 deforms to follow the shape (curvature) of the vehicle roof. That is, as in the first embodiment, the metal spring 64, first, suppresses the amount of variation in capacitance C (the amount of variation in frequency f of unwanted resonance), allowing the antenna device 5 to be attached to vehicle roofs of various curvatures, and second, it can shift the frequency f of unwanted resonance outside the specified band. This makes it possible to expand the range of vehicle roofs for which sufficient antenna gain can be obtained. The base portion 60 is fastened with a bolt from the vehicle roof side (not shown) and locked with a nut 66.

[0061] The antenna section includes an SDARS antenna 54, a telephone antenna 57, an AM / FM antenna 53, and a keyless entry antenna 51, arranged in this order from the front. The AM / FM antenna 53 includes a pair of capacitance loading elements 531 and 532 electrically connected via a connecting portion 533, and a helical element 535, one end of which is electrically connected to the connecting portion 533 to enable reception of FM broadcasts. The pair of capacitance loading elements 531 and 532 and the connecting portion 533 are fixed to an element holder 534, which is a hard insulating member, and is fixed to the inner wall of the antenna case 50 by screws 5331. The helical element 535, together with the element holder 534, is fixed to the inner wall of the antenna case 50 by screws 5341.

[0062] A telephone antenna 57 is arranged in front of the capacitance loading elements 531 and 532 at a predetermined interval so as to be electrically discontinuous with the capacitance loading elements 531 and 532 . The telephone antenna 17 of the first embodiment is an antenna for transmitting and receiving signals in the 800 MHz band, but the telephone antenna 57 of the fifth embodiment is a planar conductor plate with a roughly p-shaped cross section whose upper portion is folded back along the inner wall of the antenna case 50, and has a larger element width than the telephone antenna 17. This allows for a wider bandwidth and enables transmission and reception even in the 700 MHz band. The telephone antenna 57 is fixed to the inner wall of the antenna case 50 with screws 571. A roughly rectangular parasitic element 55 for SDARS is disposed in front of the telephone antenna 57. The parasitic element 55 is fixed to the inner wall of the antenna case 50 with screws 551.

[0063] The keyless entry board 510, the AM / FM board 530, and the telephone board 570, each of which has electronic circuit components mounted on an insulating member, are fixed to the conductive base 61 with screws. The other end (power supply part) of the helical element 535 is elastically held and electrically connected to the circuit contacts of the AM / FM board 530. The circuit contacts are electrically connected to electronic circuit components such as an amplifier mounted on the AM / FM board 530. The electronic circuit components of the AM / FM board 530 are electrically connected to the vehicle-side electronic devices through cable C53. The power supply part of the telephone antenna 57 is elastically held and electrically connected to the circuit contacts of the telephone board 570. The circuit contacts are electrically connected to the electronic circuit components mounted on the telephone board 570, and the electronic circuit components are electrically connected to the vehicle-side electronic devices through cable C57.

[0064] A keyless entry antenna 51 is provided on the keyless entry board 510. The keyless entry antenna 51 is an antenna in which a linear conductor 512 is wound around a cylindrical holder 511 made of an insulator, and receives signals in the 900 MHz frequency band. A power supply unit of the keyless entry antenna 51 is electrically connected to electronic circuit components of the keyless entry board 510. The electronic circuit components of the keyless entry board 510 are electrically connected to vehicle-side electronic devices via a cable C51. The keyless entry antenna 51 is positioned so as to be electrically discontinuous with the pair of capacitance-loading elements 531, 532, longitudinally rearward of the helical element 535 of the AM / FM antenna 53. Because it is positioned at the rearmost of the antenna section of the antenna device 5, it can receive not only vertically polarized waves but also horizontally polarized waves well, for example, on the rear side of the vehicle roof, thereby improving horizontal gain.

[0065] The area of ​​the conductive base 61 is larger than the area of ​​the capacitance loading elements 531, 532 when viewed from above. In other words, the area of ​​the conductive base 61 is larger than the projected area of ​​the capacitance loading elements 531, 532. Furthermore, since the keyless entry antenna 51 is disposed below the capacitance loading elements 531, 532, the keyless entry antenna 51 can be reliably grounded. Furthermore, since the gap between the capacitance loading elements 531, 532 and the conductive base 61 is constant, reception performance in the AM / FM wavebands is no longer affected by the curvature of the vehicle roof.

[0066] A ground plate 56, which serves as the ground for the SDARS antenna 54, is fixed to the front of the insulating base 63. The SDARS antenna 54 is electrically connected to the vehicle-side electronic equipment through a cable C 54. The detailed shapes and positional relationships of the parasitic element 55, the SDARS antenna 54, and the ground plate 56 will be described later.

[0067] As described above, the telephone antenna 57 and the keyless entry antenna 51 operate at similar frequencies. Therefore, by physically separating them and placing the AM / FM antenna 53 between them, interference can be reduced. On the other hand, the frequency band of the AM / FM antenna 53 is far from the frequency bands of the telephone antenna 57 and the keyless entry antenna 51. Therefore, even if the AM / FM antenna 53 and the telephone antenna 57, and the AM / FM antenna 53 and the keyless entry antenna 51 are physically close to each other, they can operate with almost no interference in their respective frequency bands. The keyless entry antenna 51 is usually located behind and below the capacitance loading elements 531 and 532, but this is not a limitation.

[0068] Next, the capacitance loading elements 531 and 532 that make up the AM / FM antenna 53 will be described in detail. Fig. 17 is an external perspective view of the capacitance loading elements 531 and 532. Fig. 18 is an explanatory diagram of the shape of the capacitance loading elements 531 and 532, with (a) being a front view, (b) being a top view, (c) being a left side view, (d) being a right side view, and (e) being a bottom view. The capacitance loading elements 531 and 532 have a pair of upper edges that are separated from each other, and the rest are formed integrally, including the connecting portion 530 at the lower edge. In other words, the connecting portion 530 also has an electrical delay portion. A locking portion 5321 is formed on a part of the capacitance loading elements 531 and 532, for example, on the lower part of the capacitance loading element 532. The locking portion 5321 is formed to lock the capacitance loading elements 531 and 532 to the element holder 533.

[0069] The capacitance loading elements 531 and 532, including the connecting portion 530, are mostly formed in a meandering shape. That is, the meandering portion of the capacitance loading elements 53 and 532 is larger than that of the capacitance loading elements 131 and 132 of the first embodiment, and therefore the electrical lengths of the capacitance loading elements 53 and 532 are different from those of the capacitance loading elements 131 and 132 of the first embodiment. The electrical lengths of the capacitance loading elements 531 and 532 of the fifth embodiment are such that they do not resonate in the frequency bands used by the telephone antenna 57 (approximately 700 MHz to 800 MHz) and the keyless entry antenna 51, and are longer than the wavelength of the frequency band used by the SDARS antenna 54. That is, the electrical lengths of the capacitance loading elements 531 and 532 are such that they do not resonate in the frequency band used by the SDARS antenna 54. This reduces interference between the capacitance loading elements 531 and 532 and the telephone antenna 57 and the keyless entry antenna 51. In addition, the ripple in the horizontal directivity of the SDARS antenna 54 can be suppressed.

[0070] FIG. 19 shows an example of the results of verifying the differences in characteristics between the telephone antenna 17 of the first embodiment and the telephone antenna 57 of the fifth embodiment. FIG. 19 is a simulation diagram showing the relationship between frequency (700 MHz to 800 MHz) and average gain (dBi). In FIG. 19, the dashed line indicates the average gain G11 of the telephone antenna 17, and the solid line indicates the average gain G51 of the telephone antenna 57. As shown in the figure, the telephone antenna 57 has a higher average gain from 700 MHz to nearly 780 MHz compared to the telephone antenna 17. This shows that the capacitance loading elements 531 and 532 of the fifth embodiment reduce interference on the telephone antenna 57 more than the capacitance loading elements 131 and 132 of the first embodiment.

[0071] FIG. 20 is a simulation diagram showing the relationship between the frequency (915 MHz to 935 MHz) and the average gain (dBi) of the keyless entry antenna 51. In FIG. 20, the dashed line shows the average gain G12 of the keyless entry antenna 51 when the capacitance loading elements 131 and 132 of the first embodiment are used instead of the capacitance loading elements 531 and 532, and the solid line shows the average gain G52 of the keyless entry antenna 51 when the capacitance loading elements 531 and 532 are used. As shown in the figure, the use of the capacitance loading elements 531 and 532 increases the average gain of the keyless entry antenna 51. In other words, the keyless entry antenna 51 is less susceptible to interference from the capacitance loading elements 531 and 532. Since the keyless entry antenna 51 operates over a narrow frequency band, there is no problem with reducing its height. Therefore, in the fifth embodiment, by arranging the keyless entry antenna 51 below the capacitance loading elements 531, 532, even though the number of media (antennas) has increased, the length of the antenna device 5 in the front-to-rear direction is not significantly longer than that of the antenna device 1 of the first embodiment.

[0072] Next, the SDARS antenna 54 in the fifth embodiment will be described in detail. Fig. 21 is an external perspective view of the SDARS antenna 54. Fig. 22 is an explanatory diagram of the arrangement of components that make up the SDARS antenna 54. Fig. 23 is a cross-sectional view taken along line AA' in Fig. 21. The SDARS antenna 54 has a planar antenna 540 as its main antenna. Planar antenna 540 is fixed to the surface of an SDARS substrate 542 with double-sided tape 541. Electronic circuit components such as an amplifier are mounted on the back surface of the SDARS substrate 542 and are shielded by a shield cover 543. Shield cover 543 is fixed with screws to a ground plate 56 having a hole 561 formed in the center. Similar to the antenna device 1 of the first embodiment, the ground of SDARS antenna 54 is separated a predetermined distance from the vehicle roof and is electrically isolated from the grounds of other antennas that receive radio waves outside the frequency band of SDARS antenna 54.

[0073] Fig. 24 shows the positional relationship between the SDARS parasitic element 55 and the SDARS antenna 54 (antenna main body 540) when the antenna case 50 is placed over the base portion 60. In Fig. 24, the direction (Z) away from the paper surface is the zenith direction of the antenna device 5, the downward direction (X) on the paper surface is the rear of the antenna device 5, and the leftward direction (Y) on the paper surface is the width direction of the antenna device 5. As shown in Fig. 24, the parasitic element 55 is positioned so as to be shifted rearward (in the X direction) with respect to the SDARS antenna 54. This makes it possible to suppress the influence of the antenna characteristics caused by the presence of a telephone antenna 57 or the like behind the SDARS antenna 54.

[0074] Fig. 25 is a simulation diagram showing changes in gain depending on the direction of the SDARS antenna 54. In Fig. 25, the dashed line shows the gain when the parasitic element 55 is not misaligned, and the solid line shows the gain when it is misaligned. As shown in Fig. 25, the directivity Gx of the SDARS antenna 54 when the parasitic element is misaligned backward (X direction) does not change significantly compared to the directivity Go when there is no misalignment, but it can be seen that the gain in the backward direction (X direction) increases in the direction of misalignment (X direction).

[0075] The SDARS antenna 54 of the fifth embodiment differs from the SDARS antenna 14 of the first embodiment in that the parasitic element 55 is shifted rearward (in the X direction) and that a hole 561 is formed in the center of the ground plate 56. That is, in the SDARS antenna 54, the shield cover 543 and the ground plate 56 are less likely to be coupled together, and the distance between the planar antenna 540 and the vehicle roof can be made shorter than in the planar antenna 143 of the first embodiment.

[0076] Fig. 26 is a measured diagram showing the relationship between frequency and gain in the 2.3 GHz band for the SDARS antenna 14 of the first embodiment and the SDARS antenna 54 of the fifth embodiment. In Fig. 26, the dashed line indicates the gain G13 of the SDARS antenna 14, and the solid line indicates the gain G53 of the SDARS antenna 54. At frequencies of 2320 MHz to 2345 MHz (for SDARS), the average gain G13 of the SDARS antenna 14 was 28.7 dBi, and the average gain G53 of the SDARS antenna 54 was 31.0 dBi. As such, it can be seen that the SDARS antenna 54 has a higher average gain at frequencies in the 2.3 GHz band than the SDARS antenna 14.

[0077] [Sixth embodiment] Next, a sixth embodiment of the present invention will be described. In the sixth embodiment, a modified example of the mounting structure of an AM / FM antenna is shown. Fig. 27 is an external perspective view of the antenna section of an antenna device 6 according to the sixth embodiment. Figs. 28(a) and 28(b) are explanatory diagrams of the structure of a capacity loading element in the antenna device 6. Fig. 29 is an explanatory diagram of the mounting procedure of the element holder and helical coil, with (a) showing the state before assembly and (b) showing the state after assembly. In the antenna device 6 of the sixth embodiment, buffers 6321 are provided at one or more locations of the pair of capacitance loading elements 631, 632 to fill the gap between the pair and the inner wall of the antenna case. The buffers 6321 may be formed by, for example, protruding from the inside of the capacitance loading element 632, or may be provided on the inner wall of the antenna case. Furthermore, connecting portions 6313, 6323 extending from the capacitance loading elements 631, 632 are molded so as to overlap in the vertical direction when attached to the element holder 630. Furthermore, a protrusion 6325 is provided on the upper overlapping connecting portion of the connecting portions 6313, 6323, which in this example is connecting portion 6323.

[0078] 27 shows only the buffer 6321 of one of the capacitance loading elements 632, but a buffer similar to the buffer 6321 is also formed on the other capacitance loading element 631, which is not visible in FIG. 27. These buffers 6321 fill the gap with the inner wall of the antenna case when assembly is complete. In other words, they are in contact with the antenna case. Therefore, after the antenna device 6 is installed in a vehicle, it is possible to prevent the capacitance loading elements 631, 632 from vibrating due to vehicle vibrations and generating abnormal noise.

[0079] The connecting portions 6313, 6323 are stacked vertically to ensure reliable electrical connection between the pair of capacitance loading elements 631, 632 and one helical element 634, but the protrusion 6325 is provided to prevent the stacking direction from being incorrect. In other words, if the connecting portion 6323 is accidentally stacked below the connecting portion 6313, the shapes of the capacitance loading elements 631, 632 will be distorted, or the distances from one end of the helical element 634 to the ends of each capacitance loading element 631, 632 will differ. The protrusion 6325 is provided to prevent such a situation from occurring.

[0080] A guide having a predetermined thickness and double-sided portions is formed at a predetermined position on the front of element holder 630, and one surface (left side in this example) of the guide is provided with protrusion 6301. A guide having a predetermined thickness and double-sided portions is also provided at the upper end of the cylindrical holder of helical element 634, and a groove 6341 of a size into which protrusion 6301 fits is formed on one surface (left side in this example) of the guide. Before assembly, as shown in FIG. 29(a), protrusion 6301 of element holder 630 is positioned above groove 6341 of helical element 634. Thereafter, protrusion 6301 is fitted into groove 6341 as shown in FIG. 29(b). This mounting structure prevents helical element 134 from being assembled with the front-to-rear orientation incorrect. In addition, helical element 634 is less likely to rotate relative to element holder 630, and the other end of the helical element (power supply part) is reliably held by the circuit contact of AM / FM board 530.

Claims

1. An antenna device mounted on the roof of a vehicle, a radio wave transparent case portion having a storage space formed therein; an antenna unit that is stored in the storage space, the antenna unit includes an antenna having a capacitance loading element and two communication antennas operating at similar frequencies; An antenna device, wherein the two communication antennas are arranged at positions with the antenna having the capacitive loading element interposed therebetween.

2. 2. The antenna device according to claim 1, wherein at least one of the two communication antennas is disposed below the capacitive loading element.

3. 3. The antenna device according to claim 2, wherein the communication antenna disposed below the capacitance loading element has a frequency band used that is narrower than that of the other of the two communication antennas.

4. 4. The antenna device according to claim 1, wherein at least one of the two communication antennas is a telephone antenna.

5. The antenna device according to any one of claims 1 to 4, further comprising a satellite antenna.

6. 6. The antenna device according to claim 5, wherein the satellite antenna is disposed in the storage space and further forward of the vehicle than the antenna having the capacitive loading element and the two communication antennas.

7. The satellite antenna is located in front of the telephone antenna, 7. An antenna arrangement according to claim 5 or 6, wherein the antenna with the capacitive loading element is located behind the telephone antenna.

8. 8. The antenna device according to claim 5, wherein said capacitance loading element has a length that does not resonate with radio waves received by said satellite antenna.

9. 9. The antenna device according to claim 1, wherein one of the two communication antennas is disposed at the rearmost position of the vehicle within the storage space.

10. 10. The antenna device according to claim 1, wherein the two communication antennas are antennas for transmitting and receiving.

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