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 a vehicle roof and can receive radio waves for a plurality of media.

Background Art

[0002] As conventional antenna devices attached to a vehicle roof or the like, those disclosed in Patent Documents 1 to 3 are known. These antenna devices house an antenna unit in an antenna case that protrudes 70 mm or less from the vehicle roof. The antenna unit is provided with an antenna element that receives radio waves in the FM band and a metal plate provided in an umbrella shape near the top of the antenna element to increase the gain in the AM band.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0004] In recent years, in addition to AM and FM broadcasts, there has been a tendency to mix a large number of antennas for media such as a telephone antenna and a GPS antenna in an antenna case. For this reason, when the antenna element is provided as one large metal plate for miniaturization and low profile as in the antenna devices disclosed in Patent Documents 1 to 3, other antennas for media are arranged in close proximity, and the stray capacitance increases due to the adjacent antennas. The stray capacitance is an ineffective capacitance component unintended by the designer and is caused by the physical structure. The gain decreases as the stray capacitance increases. Also, antennas that are not adjacent are also more susceptible to the influence of each other.

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

Means for Solving the Problems

[0006] The antenna device provided by the present invention is an antenna device attached to a vehicle roof, and includes a radio wave transmissive case portion having a storage space formed therein, and an antenna portion stored in the storage space. The antenna portion includes a pair of capacitive loading elements facing each other at a predetermined interval and a predetermined angle around a plane orthogonal to the vehicle roof, a connecting portion provided at a position lower than the upper edges of the respective capacitive loading elements for electrically connecting the respective capacitive loading elements to each other, and a helical element electrically connected to the connecting portion.

Effects of the Invention

[0007] Since the edges (upper edge, side edge, lower edge) of the capacitive loading elements are separated from each other, a plane parallel to the vehicle roof is opened. Therefore, the capacitance to the ground of the helical element is increased by the capacitive loading elements, while the floating capacitance is reduced. Therefore, the gains of AM and FM broadcasts are improved. In addition, since the edges of the opposing capacitive loading elements are discontinuous, interference with radio waves received by antennas for other media can be suppressed.

Brief Description of the Drawings

[0008]

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Mode for Carrying Out the Invention

[0009] Hereinafter, an embodiment example in the case where the present invention is applied to a low-profile antenna device attached to a vehicle roof will be described. This antenna device includes a plurality of types of antennas for receiving or transmitting radio waves for a plurality of media. In the following, for convenience, the vehicle roof side is referred to as the downward direction, the vertically upward direction from the vehicle roof is referred to as the upward direction, the longitudinal direction of the present invention is the front-rear direction (the front is the front and the back is the rear), and the direction perpendicular to the longitudinal direction is referred to as the left-right direction. Also, the up-down direction may be expressed as the front-back or use similar expressions.

[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 the present embodiment includes a case portion made of a synthetic resin having radio wave permeability in which a storage space is formed inside, and an antenna portion stored in the storage space. The case portion is composed of an antenna case 10 having an opening surface portion on the lower surface side and an inner case (not shown). The antenna device 1 further includes a base portion 20 that closes the opening surface portion of the antenna case 10, and a capture portion 30 that attaches the antenna device 1 to the vehicle roof and takes the ground. The antenna case 10 is shaped in a streamlined shape that becomes thinner and lower toward the front (toward the tip), and the side surface is also a curved surface that curves inward (toward the central axis in the longitudinal direction). The lower surface portion of the antenna case 10 is formed in a shape that conforms to the shape of an attachment surface of a vehicle roof (the bottom surface of a portion on the vehicle roof side to which the antenna device 1 is attached, the same applies hereinafter) (not shown). The length of the antenna case 10 in the longitudinal direction is about 230 mm, the width is about 75 mm, and the height is about 70 mm.

[0011] <Component Arrangement Structure> Fig. 2 is an explanatory diagram of the component arrangement of the antenna device 1. The antenna device 1 includes 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 synthetic resin having radio wave permeability, and its lower surface side is open. Further, a groove portion and a plurality of bosses for screwing and fixing to the base portion 20 are formed on the flange outside the lower surface portion. The above storage space is formed inside the inner case 11 and is used to protect the antenna. Further, when the inner case 11 is screwed to the base portion 20, the 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, so that the dustproof and waterproof properties inside the antenna device 1 can be ensured. Align the resin engaging piece provided at the inner rear of the antenna case 10 with the engaging piece fitting portion of the insulating base 23. With this as a fulcrum, the engaging claws provided in front of and on the left and right of the antenna case 10 and the insulating base 23 engage with each other, thereby fixing the antenna case 10 to the insulating base 23. In addition, fixing pieces are provided on the left and right portions of the antenna case 10 in addition to the locking claws. The fixing pieces are inserted into the holes for the fixing pieces provided in the insulating base 23 and assembled. By providing the fixing pieces, it is possible to prevent the antenna case 10 from deforming due to an external force applied to the antenna case 10. In addition, in order to disperse the external force to the fixing pieces, the external force transmitted to the locking claws can be reduced, and the engagement between the locking claws can be prevented from coming off.

[0012] A pad 12 made of soft insulation is attached between the outer edge of the lower surface portion of the inner case 11 and the opening end portion of the antenna case 10. The pad 12 is sandwiched and fixed when the antenna case 10 is fixed to the base portion 20. Since the pad 12 closes the gap between the vehicle roof and the antenna case 10 and the inner case 11, it can improve the aesthetics and also improve the dustproof and waterproof properties. In particular, it plays a role in improving the waterproof property of the sealing material 34 by preventing water from being directly sprayed onto the sealing material 34 by the water discharge of a car wash machine or the like.

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

[0014] The AM / FM antenna 13 is screwed and fixed to the inner wall boss of the inner case 11 and is elastically held by an M-shaped connection piece 191, which is an elastic conductive member formed on the substrate 19. The SDARS antenna 14 is screwed and held to 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 each of the antennas 13 to 17 are sent to the vehicle-side electronic circuit through the signal cables C1, C2, and C3.

[0015] The AM / FM antenna 13 is composed of a pair of capacitive loading elements 131 and 132, a synthetic resin holder 133 having radio wave permeability, and a helical element 134. The capacitive loading elements 131 and 132 are elements each having an electrical delay portion, for example, a composite shape formed in a meander shape, at a substantially central portion, and do not resonate in the AM / FM band by themselves. However, they function as capacitive loading plates for adding (loading) capacitance to the helical element 134, improving the function as a voltage receiving element in the AM band, and causing the AM / FM antenna 13 to resonate in the FM band. Further, 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 capacitive loading elements 131 and 132 and operates as a helical antenna that resonates in the FM band in cooperation with the capacitive loading elements 131 and 132. This helical element 134 is formed by winding a linear conductor around a hollow bobbin, and terminal terminals (lower terminal terminal 1341 in the example shown in FIG. 2) that are electrically connected to the ends of the linear conductor are formed at the upper and lower ends, respectively. This lower terminal terminal 1341 is elastically held by the above-described M-shaped connection piece 191. The structure of the AM / FM antenna 13 will be described in detail later.

[0016] The SDARS antenna 14 is composed of a passive element 141, a holder 142 for the passive element, a planar antenna 143, an amplifier board 144 for SDARS, a shield cover 145, and a ground plate 146. The planar antenna 143 is the main antenna for SDARS, and the metal thin plate-shaped passive element 141 is provided above the planar antenna 143 at a predetermined interval to improve the antenna gain of the planar antenna 143. The shield cover 145 formed by configuring a metal thin plate in a box shape is a conductive member that electrically shields the amplifier board 144 for SDARS. The ground plate 146 is a conductive member that serves as the ground (grounding part, the same hereinafter) of the planar antenna 143. Note that the shield cover 145 and the ground plate 146 may be integrated. Such an SDARS antenna 14 is disposed in the recess of the insulating base 23 existing in front of the conductive base 21. The ground plate 146 is separated from the vehicle roof by a predetermined distance. Also, it is electrically separated from the ground of other antennas other than the SDARS antenna. The reason for this will be described later.

[0017] The LTE antenna 15 is erected on the substrate 18. The GNSS antenna 16 is a planar antenna and is attached to the surface of the substrate 18. On the back surface of the substrate 18, a GNSS amplification circuit, an LTE antenna matching circuit, and a diplexer circuit that combines the outputs of both antennas 15 and 16, which are not shown in the figure, are mounted. The GNSS antenna 16 is electrically connected to the input part of the GNSS amplification circuit. Also, the LTE antenna 15 is electrically connected to the input part of the LTE antenna matching circuit. The electrical connection is performed by soldering or the like. The above-mentioned telephone antenna 17 is erected on the surface of the substrate 19. On the back surface of the substrate 19, a matching circuit for the telephone antenna 17 and an AM / FM amplification circuit, etc., which are not shown in the figure, are mounted.

[0018] The base part 20 includes a conductive base 21 made of metal that becomes at the same potential as the vehicle roof after being attached to the vehicle roof, an O-ring 22 that is a flexible insulator, and an insulating base 23 made of resin whose outer periphery conforms to the shape of the lower surface part of the antenna case 10. The insulating base 23 is made of resin and has strength for holding the conductive base 21, the antenna case 10, the inner case 11, and the SDARS antenna 14. The conductive base 21 is a member having a predetermined strength formed by die casting, becomes at the same potential as the vehicle roof during attachment, and functions as a ground (earthing).

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

[0020] Around the recesses 211, 212, screw holes for screwing and fixing the substrates 18, 19, etc. are also formed. However, the interval between the screw holes is desirably set to be 1 / 2 or less of the wavelength of the radio wave in order to prevent leakage of the radio wave in the desired frequency band. Note that parts such as the signal output patterns of the substrates 18, 19 may be open. On the other hand, on the back side of the conductive base 21, bosses for screwing and fixing the above capture part 30 project downward.

[0021] The insulating base 23 has an outer peripheral portion with a shape corresponding to the shape of the opening surface portion of the antenna case 10. 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. Inside the guide groove and the engaging mechanism, a flat component mounting surface 231 is formed. A hole 232 is formed at a substantially central portion 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. The pre-lock holder 33 is provided with locking claws. When the antenna mounting boss portion is inserted and fitted into the mounting hole on the vehicle roof side, these locking claws fit around the mounting hole on the vehicle roof side. Thereby, the antenna device 1 can be temporarily fixed before tightening the bolt 31, improving the workability of mounting the antenna on the vehicle roof. 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 electrically and are 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 because it has elasticity. Thereby, it is possible to prevent dust from entering the vehicle through the vehicle roof and to achieve waterproofing. Also, rust prevention and waterproofness of the conductive base 21 and the metal spring 35 can be ensured. 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 deforms to follow the shape (curvature) of the vehicle roof. Its operational effects 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 holder 133 having a three-dimensional shape 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 that is long in the front-rear direction and short in the left-right direction, and the upper bottom surface 1331 is a substantially flat surface. In addition, a groove portion 1332 having a flat bottom surface of a predetermined width is formed in the upper bottom surface 1331 slightly forward from the long center portion. A screw hole 1333 is formed in a predetermined portion of the groove portion 1332. The screw hole 1333 is for fastening the capacitance loading elements 131, 132 and the helical element 134 to the inner wall boss of the inner case 11 together with a screw. A plurality of ribs 1334 having various widths are present 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, 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, 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, 132. As shown in these figures, the capacitance loading elements 131, 132 are elements made of composite elements that connect a front surface portion that is the front when installed and a rear surface portion that is the rear by a strip-shaped meander portion. The "meander portion" refers to a surface formed of a thin conductor element formed to have at least one meandering shape. Both elements are almost symmetrical in shape, and one of them faces the other at a predetermined interval and a predetermined angle with respect to a plane perpendicular to the vehicle roof. This interval and angle are determined according to the shape of the internal space of the inner case 11. In addition, the rear surface portion has a high structure.

[0025] The capacity loading elements 131 and 132 also have connecting portions 1312 and 1322 formed at positions lower than the uppermost part (hereinafter referred to as the "zenith part") when they are respectively mounted, and they are electrically connected to each other through these connecting portions 1312 and 1322. Each of the connecting portions 1312 and 1322 can be realized by forming a slit in a part of the capacity loading elements 131 and 132 respectively and then bending. The lengths of the connecting portions 1312 and 1322 are different in order to clarify the mounting directions of one capacity loading element 131 and the other capacity loading element 132 which are substantially symmetrical, but it is not always necessary to do so.

[0026] Fixing holes 1311 and 1321 are formed in the front and rear surface portions of these capacity loading elements 131 and 132. These fixing holes 1311 and 1321 are used for fitting with the locking claws 1335 of the holder 133. Thereby, the capacity loading elements 131 and 132 can be locked to the holder 133 without using an adhesive or the like, which not only simplifies the assembly process but also suppresses fluctuations in electrical characteristics caused by using an adhesive or the like. Also, instead of fixing with the locking claws, it is also possible to temporarily fix with the locking claws and then heat with heat or the like to weld and fix with the holder.

[0027] In the example of this embodiment, the height a1 of the front surface portion shown in FIG. 4(d) is about 26 mm, the lateral length a2 is about 23 mm, the lateral length a3 of the meander portion is about 14 mm, and the lateral length a4 of the rear surface portion is 23 mm. However, for the meander portion, a path length also occurs in the height direction.

[0028] The wavelength λ1 of the SDARS is approximately 120 mm, and the heights a1, and lengths a2, a4 are approximately 1 / 4 or less with respect to the wavelength λ1 of the SDARS, and the path length of the meander portion is approximately 1 / 2. Therefore, when looking at the meander portion (starting end) from the front face portion, the impedance becomes high at the frequency of the SDARS and is electrically separated. That is, the capacitive loading elements 131, 132 function as impedance converters, for example, in the frequency band used by the SDARS. The impedance when looking at the meander portion (rear end) from the rear face portion is the same. Therefore, for the SDARS antenna 14, the capacitive loading elements 131, 132 are conductors of a size that does not affect its own operation (including directivity). Also, for the capacitive loading elements 131, 132, since the impedance in the direction of the meander portion from the rear end and in the direction of the meander portion from the front end becomes high in the frequency band of the SDARS, they are not affected by the radio waves of the SDARS. That is, they do not interfere with each other. Further, the wavelength λ2 of the GNSS is approximately 190 mm, and since the electrical length of the capacitive loading elements 131, 132 is set to a non-resonant length so as not to become 1 / 2 of the wavelength λ2 of the GNSS, the capacitive loading elements 131, 132 do not interfere with the GNSS antenna 16.

[0029] On the other hand, in the case of a single-sided element without a meander portion as in Patent Documents 1 to 3 described above, when attempting to load the required capacitance to the ground, the lateral length becomes approximately 60 mm, which is 1 / 2 of the wavelength λ1. Therefore, at least for the SDARS antenna 14, problems such as a decrease in gain and distortion of directivity are likely to occur. Also, the height becomes approximately twice the above height a1, and again, it is approximately 1 / 2 of the wavelength λ1, and for the SDARS antenna 14, problems such as a decrease in gain and distortion of directivity are likely to occur.

[0030] According to the experiments of the inventors of the present application, for wavelengths λ1 and λ2, the plate thicknesses of the capacitive loading elements 131 and 132 are 1 to 2 mm or less (a thickness sufficiently small for wavelengths λ1 and λ2), the height a2 is a wavelength of about 1 / 4 or less of the wavelength λ1 of the radio wave received by the planar antenna 143, and if the path length of the meander portion is about 1 / 2 plus or minus 1 / 8 with respect to the wavelength λ1, no interference was observed between the AM / FM antenna 13 and the SDARS antenna 14. Also, if the capacitive loading elements 131 and 132 are not resonant lengths with respect to the radio wave received by the GNSS antenna 16, no interference was observed between the AM / FM antenna 13 and the GNSS antenna 16. Note that the lengths of the front surface portion and the rear surface portion electrically separated by the meander portion are desirably approximately 1 / 4 or less of the wavelength λ1.

[0031] As shown in FIGS. 4(a) to 4(d), the capacitive loading elements 131 and 132 having a structure with an open top also exhibit excellent effects in relation to the helical element 134. That is, since the top of the capacitive loading elements 131 and 132 is open, the projected area between the helical element 134 and the top is reduced compared to the case where capacitive loading is performed on a single plane. Therefore, in the capacitive loading elements 131 and 132, the eddy current that works to cancel the high-frequency current generated by the helical element 134 is reduced. As a result, the efficiency degradation of the AM / FM antenna 13 is reduced. Also, due to such an effect, the degree of freedom in the arrangement position of the helical element 134 with respect to the top is improved. For example, it is not necessary to always arrange the helical element 134 at the center of the top of the capacitive loading elements 131 and 132.

[0032] In the structure according to this embodiment, where the top portions of the capacitance loading elements 131 and 132 are open, there is no need to bend or draw the capacitance loading elements 131 and 132, so the processing steps are simplified, contributing to a reduction in manufacturing costs. Such a structure also has the effect that the parasitic capacitance generated between adjacent conductors, in this example, between the telephone antenna 17, is reduced compared to the case where a single-sided capacitance loading plate is used. Parasitic capacitance is an ineffective capacitance component unintended by the designer and is caused by the physical structure. As described above, the greater the parasitic capacitance, the lower the gain. The telephone antenna 17 is disposed substantially at the center between the side edges of the front surface portions of the opposing capacitance loading elements 131 and 132. This can also reduce the parasitic capacitance, so the opposing distance between the telephone antenna 17 and the capacitance loading elements 131 and 132 can be shortened as shown in FIGS. 7 and 8. In addition, in order to further reduce the parasitic capacitance with the telephone antenna 17, one or more additional holes or slits may be formed in the capacitance loading elements 131 and 132. By doing so, the parasitic capacitance mainly with the ground on the lower surface side of the capacitance loading elements 131 and 132 can be further reduced, so that sufficient performance can be obtained even if the lower surface side is configured with a conductive base.

[0033] Next, the helical element 134 will be described. FIG. 5(a) is a top view of the helical element 134, FIG. 5(b) is a front view thereof, and FIG. 5(c) is a rear view thereof. The helical element 134 is formed by winding a conducting wire around a cylindrical bobbin made of a radio wave-transmissive synthetic resin. Grooves with a determined diameter and pitch are formed on the surface of the bobbin so that a desired shape of the helical antenna can be configured. By winding a linear conductor around the bobbin a required number of turns, it becomes operable as a helical antenna. A lower terminal terminal 1341 electrically connected to one end of the conducting wire is formed at the lower part of the bobbin. This lower terminal terminal 1341 is elastically held by the above-described M-shaped connection piece 191 and conducts with the input terminal of the AM / FM amplification circuit mounted on the back surface of the substrate 19. The upper terminal terminal 1342 is electrically connected to the other end of the conducting wire. A metal screw is inserted upward from inside the bobbin, and the legs of this metal screw are inserted into the screw holes 1333 of the holder 133 and the circular holes formed by the connecting parts 1312 and 1322 of the capacitive loading elements 131 and 132, and these are fastened together to the inner wall bosses of the inner case 11, whereby the upper terminal terminal 1342 and the capacitive loading elements 131 and 132 are electrically connected. The metal screw may be a screw with a spring washer to strengthen mechanical holding. Also, the upper terminal 1342 has a structure that can be attached to the bobbin in a 180-degree inverted manner, and has a structure in which the number of turns of the helical element 134 can be adjusted every half turn while sharing parts. As a result, the reception frequency can be adjusted, and the degree of freedom in design can be improved.

[0034] The state in which the capacitance loading elements 131 and 132 are fixed to the holder 133 and further the helical element 134 is attached to the holder 133 is shown in FIG. 6. 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 arrangement position of the helical element 134 is improved as compared with the case of using a single-sided capacitance loading plate with the top portion blocked. In the present embodiment, the lower terminal terminal 1341 is positioned substantially in the middle of the capacitance loading elements 131 and 132, and the helical element 134 itself is somewhat eccentric toward the capacitance loading element 132 side. By making such an eccentricity, the capacitance loading element close to the helical element 134 becomes the capacitance loading element 132. Therefore, electrical interference can occur only with the capacitance loading element 132, and the interference can be reduced and the performance degradation can be suppressed as compared with the case where electrical interference occurs with both of the capacitance loading elements 131 and 132. The helical element 134 may be somewhat eccentric toward the capacitance loading element 131 side.

[0035] Also, the state of the antenna unit housed in the storage space of the inner case 11 is shown in FIG. 7. FIG. 7 is an external perspective view showing a state in which only the antenna case 10, the inner case 11, and the O-ring 22 are removed from the antenna device 1 assembled according to the arrangement shown in FIG. 2. FIG. 8 is an explanatory view showing a state in which the storage space is seen through with the antenna case 10, the inner case 11, and the O-ring 22 assembled. As shown in these figures, in the antenna device 1 of the present embodiment, the mutual edges of the capacitance loading elements 131 and 132 are separated from each other, and a surface parallel to the vehicle roof is opened. Therefore, the capacitance to ground is added to the helical element 134 by the capacitance loading elements 131 and 132, but the stray capacitance is reduced. Therefore, the gains of AM broadcast and FM broadcast are improved. Also, since 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, the antenna device 1 has a low-profile and narrow storage space with a length in the longitudinal direction of about 230 mm, a width of about 75 mm, and a height of about 70 mm. However, 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 in this order from the front without interfering with each other.

[0037] As shown in FIGS. 7 and 8, the AM / FM antenna 13 and the telephone antenna 17 are arranged close to each other. Therefore, the AM / FM antenna 13, which receives at a lower frequency than the telephone antenna 17, is more likely to be affected by the telephone antenna 17. Thus, in this embodiment, among the matching circuits mounted on the back surface of the substrate 19, after a capacitor of preferably about 20 pF is connected in series to the power supply point of the telephone antenna 17, the received signals of each frequency are impedance-matched. 20 pF results in an impedance of about 80 kΩ at 1 MHz in the AM band, for example, and about 80 Ω at 100 MHz in the FM band. On the other hand, in the frequency band received by the telephone antenna 17, for example, it becomes 10 Ω or less at 800 MHz or higher, and the impedance becomes significantly lower. Also, in order to match the impedance with the telephone antenna 17 in the matching circuit, the loss is smaller in the reception band of the telephone antenna 17. Considering the reception bandwidth of the telephone antenna 17, preferably about 2 pF to 20 pF is desirable. This has the effect of ensuring the gains of both the telephone antenna 17 and the AM / FM antenna 13. Alternatively, it is also possible to configure a BEF (Band Elimination Filter) composed of a parallel resonance circuit using an inductor and a capacitor to increase the impedance near the AM band or the FM band and obtain 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 as to prevent further interference with each other. 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 parallel resonance of an inductor and a capacitor or using 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 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 also 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 disposed in front of the insulating base 23 and is fitted so as to be positioned in a recess 233 provided inside the ribs of the insulating base 23. The thickness of the insulating base 233 at 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 partly 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. Also, the ground plate 146 is not connected to the conductive base 21 so as to be electrically separated from the conductive base 21. This is to prevent the influence on the electrical characteristics of the LTE antenna 15 and / or the telephone antenna 17 and to prevent the influence on the directivity of the SDARS antenna 14.

[0039] That is, the conductive base 21 also functions as the ground for the LTE antenna 15, the GNSS antenna 16, the telephone antenna 17, and the AM / FM antenna 13. However, depending on the distance between the vehicle roof and the conductive base 21 and the size of the conductive base 21, it may also cause unnecessary resonance (resonance phenomenon). The unnecessary resonance is more likely to occur as the conductive base 21 becomes larger. When unnecessary resonance occurs, the gain of the antenna that receives radio waves in the band including that frequency decreases. Also, 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 changes, and the gain of each of the antennas 13 to 17 may decrease or change due to unnecessary resonance.

[0040] Here, the unnecessary resonance will be briefly described. If the inductance of the part from the conductive base 21 to the vehicle fixing claw member 32 of the capture part 30 is L, and the capacitance between the conductive base 21 and the space of the vehicle roof is C, the frequency f of the unnecessary resonance is represented by 1 / [2π√(LC)]. Also, 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 above space is ε, the capacitance C is ε·S / d. Further, if the conductor loss is R, the Q value representing the sharpness of the unnecessary resonance is obtained by [√(L / C)] / R = 1 / (ωCR). Here, ω is the angular frequency of the unnecessary resonance, and ω = 2πf. Note that the smaller the Q value of the unnecessary resonance, the smaller the influence on the gain. When the conductive base 21 becomes larger and the area S becomes larger, the capacitance C becomes larger and the frequency f of the unnecessary resonance becomes lower. As a result, the frequency f of the unnecessary resonance becomes a frequency included in the frequency band (within the specification band) used for transmission or reception, and the gain of the antenna that receives the radio wave in the band including that frequency may decrease. Also, there are various types of vehicle roofs, and each curvature is different. When the metal spring 35 does not exist, if the curvature of the vehicle roof is large, the capacitance C becomes smaller. Then, as the frequency f of the unnecessary resonance becomes higher and the Q value becomes larger, the gains of the antennas 13 to 17 decrease. On the other hand, if the curvature of the vehicle roof is small, the capacitance C becomes larger, the frequency f of the unnecessary resonance becomes lower, and the Q value becomes smaller. Thus, due to the curvature of the vehicle roof, the capacitance C fluctuates greatly, and the frequency f of the unnecessary resonance also fluctuates greatly.

[0041] Therefore, in the present embodiment, by bringing the convex portion of the metal spring 35 into contact with the vehicle roof, first, the amount of variation in the frequency f of the unnecessary resonance is suppressed, and the antenna device 5 can be attached to vehicle roofs with various curvatures. When the metal spring 35 exists, since the metal spring 35 has slidability, the convex portion in contact deforms following the curvature of the vehicle roof. Therefore, the amount of variation in the capacitance C becomes smaller, and the amount of variation in the frequency f of the unnecessary resonance also becomes smaller, so that it can be attached to vehicle roofs with various curvatures.

[0042] Also, in the present embodiment, by bringing the convex portion of the metal spring 35 into contact with the vehicle roof, secondly, the capacitance C is increased so that the frequency f of unnecessary resonance shifts to the low frequency band. Therefore, the frequency of unnecessary resonance can be shifted outside the specification band.

[0043] In the present embodiment, also, in order to reduce the conductive base 21 to a size where unnecessary resonance does not enter, the SDARS antenna 14 is arranged not on the conductive base 21 but on the insulating base 23. And, for the ground of the planar antenna 143 of the SDARS, it was decided to use a ground plate 146 that is electrically separated from the conductive base 21. Since the reception band of the planar antenna 143 is a high frequency band such as the 2.3 GHz band, even with a separate ground plate 146, it is only necessary to make it slightly larger than the planar antenna 143, and a ground size sufficient to ensure antenna gain can be obtained.

[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 arrangement structure of the conductive base 21 are determined to some extent according to the required specifications of the antenna device 1. 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 the present embodiment, since the ground plate 146 is separate from the conductive base 21, the shape and size of the ground plate 146 can be arbitrarily set so that the desired electrical characteristics of the SDARS antenna 14 can be obtained. The directivity can be improved and the degree of freedom in design can be increased.

[0045] FIG. 9 is a diagram showing 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 facilitates the positioning of the ground plate 146 during assembly and improves workability. In addition, the depth (thickness) of the recess 233 is a factor that determines the distance between the ground plate 146 and the vehicle roof. As described above, the ground plate 146 is slightly larger in size than the planar antenna 143. Now, 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 (e). The distortion of the 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, so that sufficient electrical characteristics of the SDARS can be realized while maintaining a low profile of 70 mm or less.

[0046] The shielding property of the amplifier substrate 144 for SDARS ensures a shielding effect by soldering or welding the periphery of the shield cover 145 to the amplifier substrate 144 for SDARS. Since the shield cover 145 is electrically connected to the ground plate 146, it has the same potential as the ground plate 146.

[0047] In this embodiment, when connecting the connecting portions 1312 and 1322 of the capacitive loading elements 131 and 132, an example is shown in which the portion corresponding to the screw hole 1333 is formed as a circular hole. Such a circular hole can be easily formed by notching the opposing ends in a semicircular shape when forming each of the connecting portions 1312 and 1322, as shown in FIG. 10(a). Alternatively, as shown in FIGS. 10(b) and (c), the opposing ends of each of the connecting portions 1312 and 1322 may be made R-shaped or rectangular, and circular holes may be formed near their tip portions. In either case, since these circular holes serve as a positioning role, the effect of facilitating the work when fixing to the holder 133 is obtained. Also, although the meander shape is in the vertical direction, the same effect can be obtained when it is in the front - rear direction.

[0048] [Second Embodiment] Next, the second embodiment of the present invention will be described. The antenna device of the second embodiment has the same basic components such as an antenna case, an inner case, a base portion, a plurality of antennas, a substrate, a capture portion, and their arrangements as those of the antenna device 1 of the first embodiment, but the shape of the capacitive 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 capacitive loading element of the antenna device according to the second embodiment, Fig. 11(b) is a top view, and Fig. 11(c) is an assembly explanatory view showing a part of the inner case cut away for convenience. The antenna device 2 of this embodiment includes a pair of capacitive loading elements 131b and 132b, and the fact that a part of them is used as connecting portions 1312b and 1322b is the same as that of the capacitive loading elements 131 and 132 of the first embodiment, but the meander shape and the attachment structure to the holder 133b are different. The tips of the connecting portions 1312b and 1322b extend downward, and they are electrically connected by a metal screw via a conductive relay member.

[0049] Also in the antenna device 2 of the second embodiment, the upper edges and the lower edges of the capacitive loading elements 131b and 132b are separated from each other, and a surface parallel to the vehicle roof is opened. Therefore, the capacitance to the ground of the helical element is added by the capacitive loading elements 131b and 132b, while the stray capacitance is reduced. Since the connecting portions 1312b and 1322b extend downward, the generation of stray capacitance can also be suppressed in the connecting portions 1312b and 1322b. Therefore, the gains of AM and FM broadcasts are improved. Also, since the edges of the opposing capacitive loading elements are discontinuous, interference with the radio waves received by antennas for other media can be suppressed.

[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 such as an antenna case, an inner case, a base portion, a plurality of antennas, a substrate, and a capture portion and their arrangements as those of the antenna device 1 of the first embodiment, but the shape of the capacitive 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. 12(a) is an exploded perspective view of the capacitive loading element included in the antenna device according to the second embodiment, and FIG. 12(b) is an external perspective view of the assembled antenna device. The antenna device 3 of this embodiment includes a pair of capacitive loading elements 131c and 132c, and the point that a part of these is used as a connecting portion is the same as that of the capacitive loading elements 131b and 132b of the second embodiment, but the difference is that the shape is a meander shape and there are two connecting portions.

[0051] Also in the antenna device 3 of the third embodiment, the upper edges and the lower edges of the capacitive loading elements 131c and 132c are separated from each other, and a surface parallel to the vehicle roof opens. Therefore, the capacitance to the ground of the helical element is added by the capacitive loading elements 131c and 132c, but the parasitic capacitance is reduced. Therefore, the gains of AM broadcast and FM broadcast are improved. In addition, since the edges of the opposing capacitive loading elements are discontinuous, interference with the radio waves received by the 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 an antenna case, an inner case, a base portion, a plurality of antennas, a substrate, and a capture portion and their arrangements as those of the antenna device 1 of the first embodiment, but the configuration of the AM / FM antenna is different from that of the antenna device 1 of the first embodiment. FIG. 13 is an explanatory diagram of the arrangement of the antenna portion of the antenna device 4 according to the fourth embodiment. FIG. 14 is an explanatory diagram of the structure of the AM / FM antenna in the fourth embodiment, where (a) is a top view, (b) is a front view, and (c) is a side view.

[0053] The antenna device 4 of the fourth embodiment includes a pair of capacitive loading elements 131d and 132d, and a part of these is used as a connecting portion. The fact that it is fixed to the holder 133d through the fixing hole 1321d is the same as that of the capacitive loading elements 131 and 132 of the first embodiment, but the meander shape is different. In the capacitive loading elements 131d and 132d of the fourth embodiment, the remaining part of the portion that bends to form the connecting portion becomes a wide surface portion, the front becomes the first meander portion, and the rear becomes the second meander portion. Also, the helical element 134 has the same component parts as the helical element 134 described in the first embodiment, but is different 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 capacitive loading element 131d.

[0054] Also in the antenna device 4 of the fourth embodiment, the upper edges and the lower edges of the capacitive loading elements 131d and 132d are separated from each other, and a surface parallel to the vehicle roof opens. Therefore, the capacitance to the ground is added to the helical element 134 by the capacitive loading elements 131d and 132d, but the stray capacitance is reduced. Therefore, the gains of AM broadcast and FM broadcast are improved. Also, since the edges of the opposing capacitive loading elements are discontinuous, interference with the radio waves received by the antennas for other media can be suppressed.

[0055] As described above, the first to fourth embodiments have been described, but the embodiments of the present invention are not limited to these exemplary forms. For example, the pair of capacitive loading elements 131 (131b to 131d), 132 (132b to 132d) (hereinafter abbreviated as "131 etc.") and the helical element 134 may be electrically connected through a connecting piece having spring properties. Also, in order that the resonance frequencies of the capacitive loading elements 131 etc. and the helical element 134 do not become near the desired frequency, those in which the capacitive loading elements 131 etc. are connected by an LC element (inductor and capacitor) or a filter of a conductive pattern formed on the substrate may be used. In addition, the capacitive loading element 131 or the like may have any shape as long as it functions as an electrical delay section, such as a meander shape, at least one fold-back, zigzag, ninety-fold, fractal shape, etc. Also, in each embodiment, the upper and lower edges of the capacitive loading element 131 or the like are made discontinuous, but a configuration in which the front and rear edges are discontinuous may also be used. Further, the pair of capacitive loading elements 131 or the like do not necessarily have a symmetric shape.

[0056] Also, the arrangement of the planar antenna 143 of the SDARS and the GNSS antenna 16 may be reversed. Further, a structure in which the planar antenna 143 of the SDARS and the GNSS antenna 16 are stacked vertically may be used. Also, when the required performance requirements are not strict, if it is sufficient with the ground size of the SDARS amplifier board 144 or the shield cover 145 without setting the ground plate 146, similarly, by making a recess with a shape similar to its shape, an improvement in electrical performance can be expected.

[0057] Although the conductive base 21 is described as an integral one such as die-cast and a separate ground plate 146 is provided, the conductive base 21 includes those in which the conductive base 21 and the metal thin plate are electrically configured at the same potential by screwing or welding.

[0058] [Fifth Embodiment] Next, a fifth embodiment of the present invention will be described. FIG. 15(a) is an external perspective view of the antenna device according to the fifth embodiment, and FIG. 15(b) is a partial cutaway view seen from the A-A' direction of FIG. 15(a). FIG. 16 is an explanatory diagram of the arrangement of the components constituting the antenna device according to the fifth embodiment. The antenna device 5 of the fifth embodiment is an antenna device attached to the vehicle roof, similar to the previous embodiments, and includes a radio wave transmissive case portion in which a storage space is formed and an antenna portion stored in the storage space.

[0059] The case part includes an antenna case 50 having an opening surface on the lower surface side, and a base part 60 that closes the opening surface of the antenna case 50 via a pad 52 made of a soft resin. The antenna case 50 is shaped in a streamlined form that becomes thinner and lower toward the front (toward the tip), and the side surfaces are also curved surfaces that curve inward (toward the central axis in the longitudinal direction). The material and size of the antenna case 50 are substantially the same as those of the antenna case 10 in the first embodiment.

[0060] The base part 60 is configured to include a conductive base 61 and an insulating base 63 for fixing the conductive base 61. Holes 611 and 612 for passing cables C51, C53, C54, and C57 are formed in the front and rear of the conductive base 61. On the other hand, the insulating base 63 is formed with a mounting hole 631 for screwing and fixing the conductive base 61 from the vehicle roof side, and holes 632 and 633 for passing cables C51, C53, C54, and C57. Grooves for accommodating a metal spring 64 and a soft sealing material 65 are formed on the back surface of the insulating base 63, respectively. The metal spring 64 deforms so as to follow the shape (curvature) of the vehicle roof. That is, similar to the first embodiment, the metal spring 64, firstly, suppresses the variation amount of the capacitance C (the variation amount of the frequency f of unnecessary resonance), so that the antenna device 5 can be attached to vehicle roofs with various curvatures, and secondly, can shift the frequency f of unnecessary resonance outside the specification band. Therefore, the applicable range of vehicle roofs where sufficient antenna gain can be obtained can be expanded. The base part 60 is tightened with bolts from the vehicle roof side (not shown) and locked with a nut 66.

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

[0062] In front of the capacitively loaded elements 531 and 532, the telephone antenna 57 is arranged at a predetermined interval so as to be electrically discontinuous from each of the capacitively loaded elements 531 and 532. The telephone antenna 17 of the first embodiment is an antenna for transmitting and receiving signals at a frequency in the 800 MHz band. However, the telephone antenna 57 of the fifth embodiment is a planar conductor plate having a substantially ρ-shaped cross section with the upper part folded along the inner wall of the antenna case 50, and has a larger element width than the telephone antenna 17. Therefore, broadband operation is possible, and transmission and reception are also possible at a frequency in the 700 MHz band. The telephone antenna 57 is fixed to the inner wall of the antenna case 50 by screws 571. In front of the telephone antenna 57, a passive element 55 for SDARS having a substantially rectangular shape is arranged. The passive element 55 is fixed to the inner wall of the antenna case 50 by screws 551.

[0063] On the conductive base 61, a keyless entry substrate 510, an AM / FM substrate 530, and a telephone substrate 570, each having electronic circuit components mounted on an insulating member, are fixed by screwing. The other end (power supply portion) of the helical element 535 is electrically connected to the circuit contact of the AM / FM substrate 530 in an elastically held state. The circuit contact is electrically connected to electronic circuit components such as an amplifier mounted on the AM / FM substrate 530. The electronic circuit components of the AM / FM substrate 530 are electrically connected to vehicle-side electronic devices through the cable C53. The power supply portion of the telephone antenna 57 is electrically connected to the circuit contact of the telephone substrate 570 in an elastically held state. The circuit contact is electrically connected to the electronic circuit components mounted on the telephone substrate 570, and the electronic circuit components are electrically connected to vehicle-side electronic devices through the cable C57.

[0064] On the keyless entry substrate 510, a keyless entry antenna 51 is erected. 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 a signal with a frequency in the 900 MHz band. The power supply portion of the keyless entry antenna 51 is electrically connected to the electronic circuit components of the keyless entry substrate 510. The electronic circuit components of the keyless entry substrate 510 are electrically connected to vehicle-side electronic devices through the cable C51. The keyless entry antenna 51 is positioned behind the helical element 535 of the AM / FM antenna 53 in the longitudinal direction so as to be electrically discontinuous from the pair of capacitive loading elements 531, 532. Since it is arranged at the rearmost position among the antenna portions of the antenna device 5, for example, on the rear side of the vehicle roof, not only vertical polarization waves but also horizontal polarization waves can be received well, and the gain in the horizontal direction can be improved.

[0065] Note that the area of the conductive base 61 is larger than the areas of the capacitance loading elements 531 and 532 when viewed from above. That is, the area of the conductive base 61 is larger than the projected areas of the capacitance loading elements 531 and 532. Further, since the keyless entry antenna 51 is disposed below the capacitance loading elements 531 and 532, the grounding of the keyless entry antenna 51 can be surely achieved. Furthermore, since the gap between the capacitance loading elements 531 and 532 and the conductive base 61 is constant, the reception performance in the AM / FM band is not affected by the curvature of the vehicle roof.

[0066] In front of the insulating base 63, a ground plate 56 that serves as the ground for the SDARS antenna 54 is fixed. The SDARS antenna 54 is electrically connected to the vehicle-side electronic device through a cable C54. Details of the shapes and the positional relationships of the passive element 55, the SDARS antenna 54, and the ground plate 56 will be described later.

[0067] As described above, the operating frequencies of the telephone antenna 57 and the keyless entry antenna 51 are close to each other. Therefore, by interposing the AM / FM antenna 53 between the two and physically separating 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 is physically brought close to the telephone antenna 57 and the keyless entry antenna 51, they can operate with almost no problem in their respective frequency bands. The keyless entry antenna 51 is disposed behind and below the capacitance loading elements 531 and 532, but this is not the limit.

[0068] Next, the capacitive 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 capacitive loading elements 531 and 532. Further, FIG. 18 is an explanatory view of the shape of the capacitive loading elements 531 and 532, where (a) is its front view, (b) is its top view, (c) is its left side view, (d) is its right side view, and (e) is its bottom view. The capacitive loading elements 531 and 532 are formed integrally with the upper edges of a pair being separated from each other and including the connecting portion 530 at the lower edge. That is, the connecting portion 530 also has an electrical delay portion. A locking portion 5321 is formed at a part of the capacitive loading elements 531 and 532, for example, at the lower part of the capacitive loading element 532. The locking portion 5321 is formed to lock the capacitive loading elements 531 and 532 to the element holder 533.

[0069] The capacitive loading elements 531 and 532, including the connecting portion 530, are mostly formed in a meander shape. That is, the meander-shaped portions of the capacitive loading elements 531 and 532 are more than those of the capacitive loading elements 131 and 132 in the first embodiment, and thus the electrical length of the capacitive loading elements 531 and 532 is different from the electrical length of the capacitive loading elements 131 and 132 in the first embodiment. The electrical length of the capacitive loading elements 531 and 532 in the fifth embodiment is a length that does not resonate in the frequency band used by the telephone antenna 57 (about 700 MHz to 800 MHz) and the keyless entry antenna 51, and is longer than the wavelength in the frequency band used by the SDARS antenna 54. That is, the electrical length of the capacitive loading elements 531 and 532 is a length that does not resonate in the frequency band used by the SDARS antenna 54. Thereby, interference between the capacitive loading elements 531 and 532 and the telephone antenna 57 and the keyless entry antenna 51 can be reduced. Also, the drop (Ripple) in the horizontal directivity of the SDARS antenna 54 can be suppressed.

[0070] Fig. 19 shows an example of the result of verifying the difference 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 the frequency (700 MHz to 800 MHz) and the 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 than the telephone antenna 17 from 700 MHz to nearly 780 MHz. From this, it can be seen that according to the capacitive loading elements 531 and 532 of the fifth embodiment, the interference given to the telephone antenna 57 is reduced compared to the capacitive 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 indicates the average gain G12 of the keyless entry antenna 51 when the capacitive loading elements 131 and 132 of the first embodiment are used instead of the capacitive loading elements 531 and 532, and the solid line indicates the average gain G52 of the keyless entry antenna 51 when the capacitive loading elements 531 and 532 are used. As shown in the figure, by using the capacitive loading elements 531 and 532, the average gain of the keyless entry antenna 51 has increased. That is, the keyless entry antenna 51 is less susceptible to interference from the capacitive loading elements 531 and 532. Since the operating frequency band of the keyless entry antenna 51 is narrow, there is no problem even if it is made low-profile. Therefore, in the fifth embodiment, by arranging the keyless entry antenna 51 below the capacitive loading elements 531 and 532, even though the number of media (antennas) has increased, the length of the antenna device 5 in the front-rear direction is not much 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 the components constituting the SDARS antenna 54. Fig. 23 is a cross-sectional view taken along the line A - A' of Fig. 21. The SDARS antenna 54 has a planar antenna 540 as its main antenna. The planar antenna 540 is fixed to the surface of the SDARS substrate 542 by a double-sided tape 541. Electronic circuit components such as an amplifier are mounted on the back surface of the SDARS substrate 542 and shielded by a shield cover 543. The shield cover 543 is screwed and fixed to a ground plate 56 having a hole 561 formed in its central portion. The ground of the SDARS antenna 54 is separated from the vehicle roof by a predetermined distance and is electrically separated from the ground of other antennas that receive radio waves outside the frequency band of the SDARS antenna 54, which is the same as the antenna device 1 of the first embodiment.

[0073] Fig. 24 shows the positional relationship between the passive element 55 for SDARS and the SDARS antenna 54 (antenna body 540) when the antenna case 50 is placed on the base portion 60. In Fig. 24, the direction away from the paper surface (Z) is the zenith direction of the antenna device 5, the direction downward in the paper surface (X) is the rear of the antenna device 5, and the direction to the left in the paper surface (Y) is the width direction of the antenna device 5. As shown in Fig. 24, the passive element 55 is arranged to be displaced rearward (in the X direction) with respect to the SDARS antenna 54. Therefore, the influence on the antenna characteristics caused by the presence of the telephone antenna 57 or the like behind the SDARS antenna 54 can be suppressed.

[0074] Fig. 25 is a simulation diagram showing the gain change according to the direction of the SDARS antenna 54. In Fig. 25, the dashed line indicates the gain when the passive element 55 is not displaced, and the solid line indicates the gain when it is displaced. As shown in Fig. 25, the directivity Gx of the SDARS antenna 54 when the passive element is displaced rearward (in the X direction) does not change significantly compared to the directivity Go when it is not displaced, but it can be seen that the gain in the rearward (X direction) becomes higher in the displaced direction (X direction).

[0075] The SDARS antenna 54 of the fifth embodiment is different from the SDARS antenna 14 of the first embodiment in that the passive element 55 is shifted rearward (in the X direction), and a hole 561 is formed in the central portion of the ground plate 56. That is, in the SDARS antenna 54, it is difficult to couple the shield cover 543 and the ground plate 56, and the distance between the planar antenna 540 and the vehicle roof can be made shorter than that of the planar antenna 143 of the first embodiment.

[0076] FIG. 26 is a measured diagram showing the relationship between the frequency and gain in the 2.3 GHz band of the SDARS antenna 14 in the first embodiment and the SDARS antenna 54 in the fifth embodiment. In FIG. 26, the broken line is the gain G13 of the SDARS antenna 14, and the solid line is the gain G53 of the SDARS antenna 54. The average of the gain G13 of the SDARS antenna 14 at a frequency of 2320 MHz to 2345 MHz (for SDARS) was 28.7 dBi, and the average of the gain G53 of the SDARS antenna 54 was 31.0 dBi. Thus, it can be seen that the SDARS antenna 54 has a higher average gain at a frequency 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. The sixth embodiment shows a modified example of the mounting structure of the AM / FM antenna. FIG. 27 is an external perspective view of the antenna portion of the antenna device 6 according to the sixth embodiment. FIGS. 28(a) and (b) are explanatory diagrams of the structure of the capacitive loading element in the antenna device 6. FIG. 29 is an explanatory diagram of the mounting procedure of the element holder and the helical coil, where (a) shows the state before assembly and (b) shows the state after assembly. In the antenna device 6 of the sixth embodiment, among the pair of capacitive loading elements 631 and 632, a buffer 6321 is provided at one or a plurality of parts in the gap between the capacitive loading element and the inner wall of the antenna case to fill the gap. The buffer 6321 may be, for example, a protrusion formed by pushing out the capacitive loading element 632 from the inside, or may be provided on the inner wall of the antenna case. Further, the connecting portions 6313 and 6323 extending from the capacitive loading elements 631 and 632 are formed so as to overlap in the vertical direction when attached to the element holder 630, respectively. Further, a protrusion 6325 is provided on the connecting portion that overlaps above among the connecting portions 6313 and 6323, in this example, the connecting portion 6323.

[0078] In FIG. 27, only the buffer 6321 of one capacitive loading element 632 is shown, but a buffer similar to the buffer 6321 is also formed on the other capacitive loading element 631 that is not visible in FIG. 27. These buffers 6321 fill the gap between the inner wall of the antenna case at the time of assembly completion. That is, it contacts the inner wall of the antenna case. Therefore, it is possible to prevent the capacitive loading elements 631 and 632 from vibrating due to the vibration of the vehicle after the antenna device 6 is attached to the vehicle and generating abnormal sounds.

[0079] The reason for overlapping the connecting portions 6313 and 6323 in the vertical direction is to ensure electrical connection between the pair of capacitive loading elements 631 and 632 and one helical element 634. The protrusion 6325 is provided to prevent an error in the overlapping direction. That is, if the connecting portion 6323 is accidentally overlapped below the connecting portion 6313, the shapes of the capacitive loading elements 631 and 632 may be distorted, or the distances from one end of the helical element 634 to the ends of the respective capacitive loading elements 631 and 632 may be different. The protrusion 6325 is provided to prevent such a situation from occurring.

[0080] The element holder 630 has a guide with a predetermined thickness and having both sides formed at a predetermined front portion, and a protrusion 6301 is provided on one side surface (left direction in this example) of the guide. The guide with a predetermined thickness and having both sides is also provided at the upper end of the cylindrical holder of the helical element 634, and a groove 6341 sized to fit the protrusion 6301 is formed on one side surface (left direction in this example) of the guide. Before assembly, as shown in Fig. 29(a), the protrusion 6301 of the element holder 630 is positioned above the groove 6341 of the helical element 634. Then, as shown in Fig. 29(b), the protrusion 6301 is fitted into the groove 6341. By adopting such an attachment structure, it becomes impossible to assemble the helical element 134 in the wrong front-rear direction. Also, the helical element 634 becomes difficult to rotate with respect to the element holder 630, and the other end (power supply portion) of the helical element is surely held at the circuit contact of the AM / FM substrate 530.

Claims

1. An antenna device attached to a vehicle, comprising: a base portion; a case portion that forms a storage space together with the base portion; an antenna stored in the storage space, wherein the base portion has a conductive base and a ground plate is disposed thereon, the conductive base and the ground plate are separated from each other, and the antenna has a first antenna positioned above the conductive base and a second antenna positioned above the ground plate.

2. The conductive base and the ground plate are formed of different members from each other. The antenna device according to Claim 1.

3. The conductive base is electrically connected to the vehicle. The antenna device according to Claim 1 or 2.

4. The distance between the vehicle and the ground plate is 10 mm or less. The antenna device according to any one of Claims 1 to 3.

5. The distance between the vehicle and the ground plate is 2 mm or more and 10 mm or less. The antenna device according to any one of Claims 1 to 3.

6. The base portion has an insulating base, and the ground plate is positioned inside the ribs of the insulating base. The antenna device according to any one of Claims 1 to 5.

7. The insulating base has a recess inside the ribs, and at least a part of the recess has a shape conforming to the shape of the ground plate. The antenna device according to Claim 6.

8. Holes are formed in the ground plate. The antenna device according to any one of Claims 1 to 7.

9. Further comprising a shield cover fixed to the holes. The antenna device according to Claim 8.

10. The first antenna receives at least terrestrial waves, and the second antenna receives at least satellite waves. The antenna device according to any one of Claims 1 to 9.

11. The second antenna is a planar antenna corresponding to circularly polarized waves. The antenna device according to any one of Claims 1 to 10.

12. The ground plate is larger than the size of the second antenna and has a function of improving the gain of the second antenna. The antenna device according to any one of Claims 1 to 11.

13. The second antenna has a shield cover. The ground plate and the shield cover are integrated. The antenna device according to any one of claims 1 to 12.

14. The second antenna is a planar antenna corresponding to circularly polarized waves, further comprising a non-powered element positioned at a predetermined interval above the planar antenna, wherein the non-powered element is displaced and arranged on the side where the first antenna is located with respect to the planar antenna. The antenna device according to any one of claims 1 to 13.

15. The first antenna is at least one of an AM antenna, an FM antenna, an LTE antenna, a telephone antenna, and a keyless entry antenna. The antenna device according to any one of claims 1 to 14.

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