JP6918607B2 - Antenna device - Google Patents

Description

The present invention relates to a small antenna device that receives signals in a plurality of frequency bands.

AM wave band (522 kHz to 1710 kHz) and FM wave band (76 MHz to 95 MHz or 87.5 MHz to 108 MHz) antenna and DTTB (Digital Terrestrial Television Broadcasting) DTTB wave band (470 MHz to 710 MHz) antenna. As an in-vehicle antenna device housed in one case, the antenna device disclosed in Patent Document 1 is known. This antenna device has an antenna case made of resin and an antenna base into which the antenna case is fitted. The antenna board is installed vertically on the antenna base. Two antennas (elements) are provided on the antenna board. That is, a first antenna having a rectangular pattern and a roof-shaped top capable of receiving AM broadcasts and FM broadcasts is provided above the rear portion, and an elongated strip-shaped second antenna for receiving DTTB broadcasts is provided above the front portion.

Japanese Unexamined Patent Publication No. 2012-199865

Patent Document 1 explains that when the distance between the two antennas on the antenna substrate becomes small, the rate of increase in stray capacitance increases, so that the distance between the two antennas needs to be longer than a certain distance. Therefore, it is not possible to shorten the length of the antenna substrate on which each antenna is provided in the front-rear direction. Patent Document 1 states that the length in the front-rear direction is about 150 mm. That is, the antenna device disclosed in Patent Document 1 has a limit in its miniaturization.

A main object of the present invention is to provide an antenna device capable of reducing the overall size of an antenna device capable of receiving signals of a plurality of frequency bands.

The antenna device to which the present invention is applied has, for example, a radio wave transmitting antenna case in which a storage space is formed, and an antenna portion stored in the storage space, and the antenna portion is the storage space of the storage space. A first element arranged in the direction from the front to the rear and a second element electrically separated from the first element are included, and a part or all of the second element is housed in the housing. It is characterized in that it overlaps with the first element in the front-rear direction of the space.

According to the present invention, it is possible to provide an antenna device capable of receiving signals in a plurality of frequency bands and reducing the overall size.

(A) is a top view of the antenna device according to the first embodiment, (b) is a side view, and (c) is a rear view. The exploded perspective view which shows the component arrangement example which concerns on the antenna device of 1st Embodiment. (A) to (c) are diagrams showing a configuration example of a trap circuit. (A) is a side view of the antenna device of the first embodiment with the antenna case removed, (b) is a rear view, and (c) is an external perspective view. The figure which shows the result example of the simulation about the maximum and minimum difference (range) of the gain in the vertical polarization horizontal plane of the DTTB wave band according to the degree (ratio) of overlap (ratio) of a capacitive loading element and a DTTB element. The figure which shows the result example of the simulation about the DTTB wave band directivity for each ratio. The figure which shows the result example of the simulation which shows the difference between the case where a trap circuit is provided and the case where it is not provided. The figure which shows the result example of the simulation which shows the change example of the FM wave band average gain for every ratio. (A) to (c) are diagrams showing a structural example of a simulated capacitive loading element. The figure which shows the result example of the simulation according to the structural difference of a capacitive loading element. The figure which shows the result example of the simulation according to the structural difference of a capacitive loading element. The figure which shows the result example of the simulation according to the composition difference of a trap circuit. (A) to (d) are diagrams showing other configuration examples of the trap circuit. (A) and (b) are schematic views showing an arrangement example of a DTTB element. The figure which shows the result example of the simulation according to the arrangement difference of the DTTB element. The schematic diagram which shows another position of the feeding part of a DTTB element. The figure which shows the result example of the simulation according to the difference of the position of the feeding part of a DTTB element. The figure which shows the result example of the simulation according to the shape difference of the DTTB element.

Hereinafter, examples of embodiments when the present invention is applied to an antenna device attached to a vehicle roof will be described. This antenna device includes a plurality of antennas used for receiving signals in different frequency bands.

[First Embodiment]
FIG. 1A is a top view of the antenna device according to the first embodiment, FIG. 1B is a side view, and FIG. 1C is a rear view. The antenna device 1 according to the present embodiment has a radio wave transmitting antenna case 10 and a resin antenna base 20 that closes the opening of the antenna case 10. The antenna case 10 becomes thinner and lower toward the tip, and the side surface is also formed into a streamlined shape having a curved surface curved inward. This is to prevent air resistance when the vehicle is running as much as possible. A capture unit 30 for attaching the antenna device 1 to the vehicle roof is provided at substantially the center of the antenna base 20. A storage space for storing the antenna parts is formed inside the antenna case 10 and the antenna base 20.

FIG. 2 shows an example of arrangement of antenna parts stored in the storage space. One of the antenna components is a three-dimensional first holder 11 whose outer wall extends from the front portion to the rear portion of the storage space according to the shape of the inner wall of the antenna case 10. The first holder 11 is made of a radio wave transmitting synthetic resin, and a plurality of flanges 111 are formed on a portion other than the lower surface portion thereof. These flanges 111 reduce the amount of synthetic resin used for molding the first holder 11, and are used for positioning and locking the element 121 of the capacitive loading element 12, which will be described later. An electrically separated capacitive loading element 12 and a DTTB element 13 are provided on the upper portion and the side portion of the first holder 11.

The capacitive loading element 12 is a metal element that loads a resistance component and a capacitance to ground on a helical element 15 that is one of the antennas, and is used together with the helical element 15 for signal reception in the AM wave band and the FM wave band. .. The capacitive loading element 12 includes two elements 121 facing each other at a predetermined interval and a predetermined angle via a virtual surface substantially orthogonal to the mounting surface of the vehicle roof. Each element 121 has an edge 122 whose electrical length is discontinuous. The edge 122 of the capacitive loading element 12 is arranged at a portion having a large distance from the mounting surface of the vehicle roof (not shown), and is formed into a shape corresponding to the inner wall in the height direction of the antenna case 10. In the present embodiment, the edge 122 is gradually increased from the front where the height of the antenna case 10 is the lowest to the rear where the height of the antenna case 10 is the highest.

The virtual surface is a virtual surface that does not actually exist, and is a surface located substantially at the center between the opposing edges 122. That is, the capacitive loading element 12 does not have a top parallel to the mounting surface of the vehicle roof. Since the mounting surface of the vehicle roof is metal, the absence of a top means that the stray capacitance generated between the mounting surface and the capacitive loading element 12 is smaller than when the top is present. The capacitive loading element 12 is also conducted by a metal connecting portion 123 at a portion lower than the edge 122. Further, the connecting portion 123 also conducts with the upper end of the helical element 15.

In the present embodiment, as an example of the capacitive loading element 12, a meander-shaped element having an element 121 having a width that fits in a gap between the side portions of the flange 111 at a predetermined portion in the first holder 11 is used. That is, the capacitive loading element 12 is arranged in the direction from the front portion to the rear portion of the storage space formed inside the antenna case 10. When parameters such as the width, length, and pitch of each of the meander-shaped elements 121 are changed, the antenna characteristics of the AM wave band and the FM wave band in the state where the helical element 15 is connected changes. This parameter can be arbitrarily set according to the desired antenna characteristics. A groove 112 for sandwiching and accommodating the DTTB element 13 is formed in the central portion (on the virtual surface) of the flange 111 of the portion corresponding to the top of the capacitive loading element 12.

The DTTB element 13 is a rod-shaped conductor used for receiving signals in the DTTB wave band. The DTTB element 13 has both ends, one end extending slightly forward from the foremost end of the capacitive loading element 12. The other end of the DTTB element 13 extends toward the rear end of the capacitive loading element 12 while being sandwiched between the grooves 112 of the first holder 11. That is, when viewed from the side surface direction of the antenna device 1, the DTTB element 13 overlaps with the capacitive loading element 12. One end of the DTTB element 13 is extended to a position in front of the capacitive loading element 12 in order to secure a longer length in order to increase the gain and to make the distance from the ground potential surface as large as possible. be. Further, the capacitive loading element 12 and the DTTB element 13 are made to overlap each other by shortening the length of the antenna device 1 in the front-rear direction and the range of gain in the vertically polarized horizontal plane in the DTTB wave band, that is, the maximum value. This is to reduce the difference between the minimum value and the minimum value.

The distance between the opposing edges 122 in the capacitive loading element 12 is widest at the front end of the capacitive loading element 12 and narrows toward the rear end, but the groove 112 is the edge from the front end to the rear end of the capacitive loading element 12. It is arranged at a substantially central position between 122. Therefore, a gap is formed between the DTTB element 13 and the edge 122 of the capacitive loading element 12, and the DTTB element 13 and the capacitive loading element 12 are electrically separated from each other. Further, since it is not necessary to separately provide a dedicated space for the DTTB element 13, the antenna device 1 can be made smaller.

In front of the first holder 11, a DTTB connection fitting 113 that conducts with one end of the DTTB element 13 is provided. A second holder 16 is arranged on the lower surface of the first holder 11. The second holder 16 has an elliptical hollow tubular portion made of synthetic resin whose major axis is in the front-rear direction of the antenna device 1, and an AM / FM connection fitting 161 is provided at the front end portion thereof. The helical element 15 is wound around the surface of the hollow tubular portion of the second holder 16. The second holder 16 is screwed and fixed to the lower surface portion of the first holder 11 through the hollow tubular portion. Since the hollow tubular portion of the second holder 16 has an elliptical shape, the overall height can be lowered as compared with the case where the second holder 16 has a perfect circular shape, and the antenna device 1 can be lowered by that amount. In this embodiment, an example in which the second holder 16 is a hollow tubular portion will be described, but the tubular portion may be filled with resin or the like.

The DTTB element 13 conducts with the terminal 171 of the printed circuit board 17 via the DTTB connection fitting 113. Further, the lower end of the helical element 15 is conductive with the AM / FM connection fitting 161 and the terminal 181 of the printed circuit board 18. Therefore, the DTTB connection fitting 113 serves as a feeding portion for the DTTB element 13, and the AM / FM connecting fitting 161 serves as a feeding portion for the helical element 15. The DTTB connection fitting 113 and the AM / FM connection fitting 161 are integrally formed with a plurality of protrusions pointing to the terminals 171 and 181 respectively. Therefore, the electrical connection between the DTTB element 13 and the helical element 15 and the terminals 171 and 181 can be more reliably performed as compared with the case where each protrusion is not provided.

The terminal 171 of the printed circuit board 17, the terminal 181 of the printed circuit board 18, and the mounting portion of the electronic circuit described later are each subjected to a solder leveler treatment. The solder leveler treatment protects the metal surfaces such as the metal terminals 171 and 181 formed on the printed circuit boards 17 and 18, which are insulating members, and the wiring portion of the electronic circuit, and enhances the wettability at the time of mounting. This is a process of performing solder coating for the purpose of this. As a result, only the metal surface portion excluding the insulating portion is coated with solder. By performing the solder leveler treatment, for example, it is less likely to rust than the case where the heat-resistant preflux treatment is performed, and the cost can be reduced as compared with the case where the gold flash treatment is performed.

Electronic circuits are mounted on the printed circuit boards 17 and 18, respectively. For example, on the printed circuit board 17, as one of the electronic circuits, a trap circuit connected to the terminal 171, a matching circuit of the DTTB wave band in the subsequent stage of the trap circuit, an amplifier circuit for amplifying a signal of the DTTB wave band passing through the matching circuit, An output circuit (not shown) for outputting the amplified signal to the vehicle side is provided. The matching circuit may be provided after the amplifier circuit.

The trap circuit is a circuit that cuts off (traps) the FM wave band. In this embodiment, for example, a trap circuit is configured by combining an inductor (L) and a capacitor (C). FIG. 3A is a principle diagram when the trap circuit is configured by the LC parallel circuit. In such a trap circuit, the impedance in the FM wave band is maximized by matching the resonance frequency with the FM wave band. Since the impedance is low in the DTTB wave band, it passes through the trap circuit. That is, the trap circuit in this case acts as a band elimination filter (band stop filter: BEF).

FIG. 3B is a principle diagram when the trap circuit is configured by the LC series circuit. In such a trap circuit, by bringing the resonance frequency closer to the DTTB wave band, the impedance becomes high in the FM wave band, so that the passage of the signal is blocked.

FIG. 3C is a principle diagram when the trap circuit is configured by the LC series-parallel circuit. The electrical constant of the LC in this case is determined to either maximize the impedance of the FM wave band or minimize the impedance of the DTTB wave band. In addition, in FIGS. 3A to 3C, at least one of the coil (L) and the capacitor (C) may be variable. By providing such a trap circuit, it is possible to prevent interference when the capacitive loading element 12 and the DTTB element 13 are superposed in the front-rear direction and a decrease in the average gain in the FM wave band. This will be explained in detail later.

The printed circuit board 18 has a filter that passes the FM wave band signal input through the terminal 181 and an amplifier circuit that amplifies the FM wave band signal that has passed through the filter, and outputs the amplified signal to the vehicle side. Output circuit (not shown) is provided. Further, a filter that passes the AM wave band signal input through the terminal 181, an amplifier circuit that amplifies the AM wave band signal that has passed through the filter, and an output circuit for outputting the amplified signal to the vehicle side ( (Not shown) is provided. The FM wave band output circuit and the AM wave band output circuit are combined and output to the vehicle side. The printed circuit boards 17 and 18 are fixed to predetermined portions of the metal plate 19 with solder, respectively. Further, the metal plate 19 is fitted into the recess on the upper surface of the antenna base 20. The metal plate 19 is a strength member having a predetermined strength, and is a member that firmly holds the capture unit 30 with the antenna base 20 interposed therebetween. A female screw 191 is engraved in the substantially central portion of the metal plate 19.

The capture unit 30 has a bolt 31 whose tip is crimped to a female screw 191 and a capture fastener 32 that fits into the vehicle roof to electrically connect the vehicle roof and the metal plate 19, and a tubular collar having a C-shaped cross section. 33. Includes a sealing material 34 for maintaining airtightness. The tubular collar 33 limits the amount of screw 31 screwed into the female screw 191. When the capture portion 30 is fitted to the vehicle roof side, the capture fastener 32 is fitted into the recess on the vehicle roof side. As a result, when the bolt 31 is inserted from the vehicle through the mounting surface of the vehicle roof, the vehicle roof and the metal plate 19 are connected and fixed so as to be electrically connected. Further, by tightening the bolt 31, the sealing material 34 fixed to the back surface of the antenna base 20 with an adhesive or the like has elasticity and is therefore compressed. As a result, dust entering the vehicle through the vehicle roof can be prevented and waterproofing can be achieved. In addition, rust prevention and waterproofness of the metal plate 19 can be ensured.

When the antenna component is stored in the storage space, an insulating pad 21 made of a soft material is set on the peripheral edge of the antenna base 20, and the antenna case 10 is placed on the insulating pad 21. After that, the antenna base 20, the insulating pad 21, and the antenna case 10 are positioned. Then, a plurality of screws are inserted from the lower surface of the antenna base 20 toward the insulating pad 21 and the female screw of the antenna case 10, and the antenna case 10 and the antenna base 20 are fixed. In this way, the assembly of the antenna device 1 is completed.

FIG. 4 shows an example of the arrangement structure of the antenna device 1 before the antenna case 10 is covered. FIG. 4A is a side view of such an antenna device 1, FIG. 4B is a rear view, and FIG. 4C is an external perspective view. As is clear from these figures, the capacitive loading element 12 is engaged with a part of the meander-shaped element 121 without being screwed into the gap between the flange 111 side portions of the first holder 11. Since the DTTB element 13 is sandwiched in the groove 112 at the center of the flange 111 and overlaps with the capacitive loading element 12 in the front-rear direction, the height and the length in the front-rear direction of the antenna device 1 are approximately the same as the capacitive loading element 12. It depends on the length and height of the anterior-posterior direction. The second holder 16 is fixed so as to be slightly displaced to the left from the above virtual surface. As a result, the helical element 15 is also offset to the left. Therefore, the DTTB element 13 is less susceptible to the interlinkage magnetic flux generated in the helical element 15. Since the offset amount is arbitrary, the degree of freedom of layout in the antenna case 10 can be increased.

<Antenna characteristic simulation>
Next, the structure of the antenna component of the antenna device 1, particularly the reason for adopting the shape, structure, and combination of the capacitive loading element 12 and the DTTB element 13 will be described in detail based on the simulation results. FIG. 5 shows the ratio (horizontal axis) of the length at which the capacitive loading element 12 and the DTTB element 13 overlap in the front-rear direction when the width, length, inclination, etc. of the DTTB element 13 are shared, and the DTTB element 13. It is a simulation observation diagram which showed the relationship with the range (vertical axis: dB) of the gain in the vertically polarized horizontal plane in the DTTB wave band of. The trap circuit is not connected to the DTTB element 13.

In FIG. 5, “ratio 1” is a state in which the DTTB element 13 completely overlaps the capacitive loading element 12 in the front-rear direction. In this case, the DTTB element 13 is located at the front end of the capacitive loading element 12, and the length of the DTTB element 13 is substantially the same as the length of the edge 122 of the capacitive loading element 12. “Ratio 0” is a state in which the DTTB element 13 does not overlap with the capacitive loading element 12 at all. In this case, the DTTB element 13 is separated from the capacitive loading element 12. That is, the higher the ratio, the longer the length of the capacitive loading element 12 and the DTTB element 13 overlapping in the front-rear direction. As shown in FIG. 5, the higher the ratio, the smaller the range of gain in the vertically polarized horizontal plane in the DTTB wave band of the DTTB element 13. The change of the range stops at around 0.6, and the range does not change when the ratio is 0.67 or more. That is, the DTTB element 13 approaches omnidirectionality.

FIG. 6 shows the relationship between the horizontal angle (horizontal axis: °) for each ratio and the gain (vertical axis: dB) in the vertically polarized horizontal plane of the DTTB element 13 in the DTTB wave band. An angle of 0 degrees (= 360 degrees) represents the front, and an angle of 180 degrees represents the rear. A trap circuit is not connected to the DTTB element 13. In FIG. 6, the solid line has a ratio of 1, the long dashed line has a ratio of 0.67, the middle dashed line has a ratio of 0.3, and the short dashed line has 0. In FIG. 6, the gain of the angle which is the minimum value for each ratio is set to 0 dB. As is clear from FIG. 6, when the ratio is 0, the degree of change in gain is the largest depending on the angle, and when the ratio is 0.6 or more, the degree of change is small.

Next, the influence on the antenna characteristics of the FM wave band when the trap circuit illustrated in FIGS. 3A to 3C is connected to the feeding portion of the DTTB element 13 and when the trap circuit is not connected will be described. FIG. 7 shows the relationship between the average gain (vertical axis: dBi) in the vertically polarized horizontal plane in the FM wave band and the ratio (horizontal axis). The broken line is when there is no trap circuit, and the solid line is when the trap circuit is connected.

As shown in FIG. 7, when the trap circuit is not connected to the DTTB element 13 (without the trap circuit), the larger the ratio, the smaller the average gain in the FM wave band. This trend continues up to around 0.6. On the other hand, when the trap circuit was connected to the DTTB element 13 (with the trap circuit), there was almost no decrease in the average gain in the vertically polarized horizontal plane in the FM wave band. That is, the trap circuit not only cuts off the FM wave band in the DTTB wave band, but also prevents a decrease in the average gain in the FM wave band. It is considered that the average gain when the trap circuit is connected at the ratio of 0 (with the trap circuit) is lower than when the trap circuit is not connected (without the trap circuit) due to the insertion loss of the trap circuit.

Based on the results shown in FIG. 7, the present inventor received the frequency including the FM wave band (horizontal axis: MHz) and the average gain in the FM wave band (vertical axis: dBi) when the trap circuit was connected to the DTTB element 13. The relationship with was simulated for each ratio. An example of the result is shown in FIG. The electric constants of the trap circuit and other electronic circuits are determined to show the highest gain around 86 MHz included in the FM wave band. In the figure, the solid line is the case where the ratio is 1, the long broken line is the ratio 0.67, and the short broken line is the case where the ratio is 0. As shown in FIG. 8, it is confirmed that by connecting the trap circuit to the DTTB element 13, even if the capacitive loading element 12 and the DTTB element 13 overlap each other, the average gain in the FM wave band is hardly affected. Was done.

As a result of the above simulation, the trap circuit is connected to the feeding portion (one end) of the DTTB element 13, and a part or all of the DTTB element up to the other end is overlapped with the capacitive loading element 12, so that the FM wave band and the FM wave band and the whole are overlapped. It has been found that the length of the antenna device 1 in the front-rear direction can be shortened while suppressing the decrease in gain in the DTTB wave band. As a result, for example, according to the present embodiment, the length of the antenna component (antenna substrate), which is said to require about 150 mm in the structure of the antenna device disclosed in Patent Document 1, is about 90 mm (from one end of the DTTB element 13). It could be shortened to the rear end of the capacitive loading element 12).

Next, the simulation result of the shape or structure of the capacitive loading element 12 used as a pair with the DTTB element 13 will be described. FIG. 9A is an example of a combination of an umbrella-shaped capacitive loading element 42 having a top and a plate-like side surface and a DTTB element 43. FIG. 9B is an example of a combination of a pair of plate-shaped capacitive loading elements 52 and a DTTB element 53 that do not have a top and are electrically connected to each other at the lowest portion from the mounting surface. FIG. 9C shows an example of a combination of a pair of meander-shaped capacitive loading elements 62 and a DTTB element 63 that do not have a top and are electrically connected to each other at the lowest portion from the mounting surface.
The set of the capacitive loading element and the DTTB element may be hereinafter referred to as an "antenna portion". The outer circumferences of the side surfaces of the capacitive loading elements 42, 52, and 62 are the same. Further, one end of each of the DTTB elements 43, 53, 63 protrudes slightly forward from the tip of each capacitance loading element 42, 52, 62, and the other end extends to the rear end of each capacitance loading element 42, 52, 62. It is extending.

FIG. 10 shows the relationship between the frequency (horizontal axis: MHz) and the average gain (vertical axis: dBi) at each frequency when the data relating to the arrangement of the antenna components including these antenna portions is input to the simulator. The electric constants of the trap circuit and other electronic circuits are determined to show the highest gain around 570 MHz included in the DTTB wave band. Further, the relationship between the gain (vertical axis: dBi) and the angle (horizontal axis: °) in the horizontal plane of the DTTB wave band at 570 MHz is shown in FIG. 11 (a), the average gain range (vertical axis: dB) and the capacitive loading element. The relationship with the structure (horizontal axis) of is shown in FIG. 11 (b).

As shown in FIG. 10, the average gain is the combination of the DTTB element 63 and the meander-shaped capacitive loading element 62, the combination of the DTTB element 53 and the plate-shaped capacitive loading element 52, and the DTTB element 43 and the umbrella-shaped capacitance. The value increased in the order of combination with the loading element 42. That is, it was found that the average gain of the DTTB wave band becomes high when there is no top, and the average gain becomes even higher when the DTTB wave band is made into a meander shape rather than a plate shape. It is considered that this is because the influence of the shielding by the capacitive loading element is reduced and the DTTB element is more likely to receive the signal in the DTTB wave band.

Further, as shown in FIG. 11A, it was found that the gain in the horizontal plane in the DTTB wave band is high and the change for each angle is small without the top. Further, as shown in FIG. 11B, the horizontal gain range of the umbrella-shaped capacitive loading element 42 is 0.48 dB, the horizontal gain range of the plate-shaped capacitive loading element 52 is 0.46 dB, and Mianda. The range of gain in the horizontal plane of the capacitive loading element 62 was 0.24 dB. From this, it was found that the gain in the horizontal plane in the DTTB wave band is high and almost omnidirectional is exhibited by using the capacitive loading element 62 having no top and having a meander shape.
From the above, in the present embodiment, an example of a combination of the meander-shaped capacitive loading element 62 and the DTTB element 62 shown in FIG. 9C is adopted.

As described above, in the first embodiment, the DTTB element 13, which is electrically separated from the capacitive loading element 12, overlaps with the capacitive loading element in the front-rear direction of the storage space. It is possible to reduce the size while suppressing a decrease in gain due to interference when the element 12, the helical element 15, and the DTTB element 13 are housed.

In particular, since the DTTB element 13 becomes omnidirectional in the DTTB wave band by overlapping 0.6 times or more the length of the capacitive loading element 12, the direction of the vehicle after being attached to the vehicle roof is taken into consideration. It becomes possible to receive the broadcast of the DTTB wave band without setting.

Further, since the capacitance loading element 12 has two elements 121 facing each other at a predetermined interval and a predetermined angle about the virtual surface and conducts at a portion lower than the upper edge, there is no top and stray capacitance is suppressed. You can . Therefore , the average gain in the FM wave band can be increased as compared with the structure in which the top is present. Further, since the capacitive loading element 12 is formed in a meander shape, not only the antenna characteristics can be finely adjusted, but also positioning and engagement with the flange 111 become easy.

Further, since the DTTB element 13 is composed of a rod-shaped conductor parallel to the virtual surface, it is not necessary to form a special shape, and an increase in manufacturing cost can be suppressed. Further, since the trap circuit that cuts off the FM wave band signal is connected to the feeding portion of the DTTB element 13, the electrical separation from the capacitive loading element 12 and the helical element 15 can be made more complete. , Mutual interference between adjacent antennas can be effectively prevented. Since this trap circuit can be configured only by a combination of a capacitor and an inductor, it is advantageous in terms of cost.

[Second Embodiment]
In the antenna device 1 according to the first embodiment, the trap circuit having the configuration exemplified in FIGS. 3A to 3C is used, but as shown in FIG. 13A, the trap circuit is formed only by the capacitor C. It may be configured. Further, as shown in the same (b), the capacitor C may be variable.
12 shows the frequencies when the trap circuit is configured by the LC parallel circuit shown in FIG. 3A and when the trap circuit is configured only by the capacitor C as shown in FIGS. 13A and 13B. It is a simulation result which showed the relationship between (horizontal axis: MHz) and average gain (vertical axis: dBi). The electric constants of the trap circuit and the like are determined so that the average gain is maximized at around 86 MHz. The broken line is the case where the trap circuit composed of the LC parallel circuit is connected, and the solid line is the case of the trap circuit composed of only the capacitor C.
As shown in FIG. 12, even if the trap circuit is configured only with the capacitor C, the DTTB wave band and the FM wave band are separated, so that the decrease in the average gain in the FM wave band is suppressed. The trap circuit may be configured only with the inductor L shown in FIG. 13 (c). Further, as shown in the same (d), the inductor L may be variable.
This can further contribute to the reduction of the manufacturing cost of the antenna device 1.

[Third Embodiment]
In the first embodiment, an example in which the DTTB element 13 is arranged between the edges 122 of the capacitive loading element 12 at the height of each edge has been described, but in the third embodiment, the DTTB element is placed on a virtual surface. An example of arranging the device above the capacitive loading element, that is, at a height higher than the edge will be described. The configurations other than the DTTB element and the capacitive element are the same as those in the first embodiment. FIG. 14A is an example of an antenna portion in which the DTTB element 73 is arranged above the umbrella-shaped capacitive loading element 72 having a top. Further, FIG. 14B is an example of an antenna portion in which the DTTB element 83 is arranged above the meander-shaped capacitive loading element 82 having no top. In each case, the DTTB elements 73 and 83 are on the virtual surface described in the first embodiment, and overlap with the capacitive loading elements 72 and 82 in the front-rear direction. Further, the trap circuit described in the first embodiment or the second embodiment is connected to the DTTB elements 73 and 83. The mounting of the DTTB elements 73, 83 is actually fixed along the inner wall of the antenna case 10.

FIG. 15 is a diagram showing an example of simulation results showing the relationship between the frequency of the DTTB wave band (horizontal axis: MHz) and the average gain of the DTTB wave band (vertical axis: dBi). For comparison, the case of the antenna portion shown in FIG. 9 (a) is shown by a thin broken line (umbrella shape), and the case of the antenna portion shown in FIG. 9 (c) is shown by a thick broken line (manda shape).
As is clear from FIG. 15, the average gain is highest in the case of the antenna portion of FIG. 14 (b) shown by the thick solid line (manda shape (high)), followed by the thin solid line (umbrella shape (high)). The case of the antenna portion of FIG. 14 (a) is higher. That is, as shown in FIGS. 14A and 14B, by arranging the DTTB elements 73 and 83 above the capacitive loading elements 72 and 82, the average gain of the DTTB wave band was improved. It is considered that this is because the heights of the DTTB elements 73 and 83 are higher than the mounting surface of the vehicle roof.
Thus, according to the third embodiment, the gain in the DTTB wave band can be further increased.

[Fourth Embodiment]
In the first embodiment, an example in which the DTTB connection fitting 113 serving as the DTTB power feeding unit is present in front of the capacitive loading element 12 has been described, but in the fourth embodiment, the DTTB feeding unit is located near the rear end of the capacitive loading element. It may be located at. FIG. 16 is a schematic view of the antenna portion according to the fourth embodiment. The capacitive loading element 92 is the same as the capacitive loading element 12 described in the first embodiment. The DTTB element 93 of the fourth embodiment extends from the same position as the front end portion of the capacitive loading element 92 to the rear end portion of the capacitive loading element 92 when viewed from the front-rear direction, and is then bent downward. A DTTB connection fitting (DTTB feeding portion) (not shown) is arranged at the bent tip.

FIG. 17 shows the result of a simulation showing the relationship between the frequency of the FM wave band (horizontal axis: MHz) and the average gain of the FM wave band (vertical axis: dBi) when the antenna portion is configured as shown in FIG. It is a figure which shows an example. The case of the antenna portion of the first embodiment in which the DTTB feeding portion is in front of the capacitive loading element is shown by a broken line (front), and the case of the antenna portion of the fourth embodiment is shown by a solid line (rear).
As shown in FIG. 17, there was no significant difference in the average gain of the FM wave band whether the DTTB feeding unit was in the front or the rear. This means that the degree of freedom of layout in the storage space of the antenna portion is increased.

[Fifth Embodiment]
In the first embodiment, an example in which the DTTB element 13 is composed of a rod-shaped conductor has been described, but in a fifth embodiment, an example in which the DTTB element 13 is composed of a plate-shaped conductor will be described. The DTTB element according to the fifth embodiment has the same width as the DTTB element 13 of the first embodiment, for example, a copper plate, but the shape, size, and material of the plate-shaped conductor are arbitrary. The capacitive loading element and other configurations are the same as those in the first embodiment.

FIG. 18A shows an example of a simulation result showing the relationship between the frequency (horizontal axis: MHz) and the average gain (vertical axis: dBi) of the DTTB wave band, and FIG. 18B shows the frequency (horizontal axis: MHz). It is a figure which shows the example of the result of the simulation which showed the relationship with the average gain (vertical axis: dBi) of FM wave band. In each case, the capacitive loading element is the capacitive loading element 12 described in the first embodiment. The case where the DTTB element is composed of a rod-shaped conductor is shown by a broken line (rod-shaped), and the case where the DTTB element is composed of a plate-shaped conductor is shown by a solid line (plate-shaped). As shown in FIG. 18B, the average gain in the practical band of the FM wave band did not differ significantly in the average gain regardless of whether the DTTB element was a rod-shaped conductor or a plate-shaped conductor. However, according to FIG. 18A, the average gain in the practical band of the DTTB wave band is -1.25 dBi in the case of a rod-shaped conductor and -1.13 dBi in the case of a plate-shaped conductor, and is composed of a plate-shaped conductor. The one who did it became higher.
Thus, according to the fifth embodiment, the average gain of the DTTB wave band can be further increased.

In the first to fifth embodiments, an example in which a plurality of antennas housed close to the storage space of the antenna case 10 are an FM wave band antenna and a DTTB element has been described, but each antenna receives. The combination of frequency bands to be used is not limited to the examples of each embodiment. For example, even if the frequency band is higher than the FM wave band, such as the frequency of a mobile phone, Wi-Fi, or other frequency bands, each embodiment can be similarly applied.
Further, each embodiment is not necessarily limited to an in-vehicle antenna device, and can be similarly applied to an antenna device mounted on another mobile body or a stationary antenna device.

Claims (13)

A radio wave transmitting antenna case having a storage space for accommodating antenna parts inside, and a first antenna part and a second antenna part composed of different antenna parts, respectively.
With
The first antenna portion includes a metal capacitive loading element extending in the front-rear direction of the storage space.
A part or all of the antenna parts of the second antenna portion overlap with the capacitive loading element in a side view.
Antenna equipment. The first antenna unit receives at least a signal in the first frequency band and receives at least a signal in the first frequency band.
The second antenna unit receives at least a signal in a second frequency band higher than the first frequency band.
The antenna device according to claim 1. The capacitive loading element is formed in a meander shape .
The antenna device according to claim 1 or 2. The second antenna portion includes a radiating element composed of any of a linear conductor , a rod-shaped conductor, and a plate-shaped conductor.
The antenna device according to any one of claims 1 to 3. The capacitive loading element comprises two elements having opposite edges at predetermined intervals.
A part or all of the radiating element is located between the edge of one of the elements and the edge of the other.
The antenna device according to claim 4. The front of the capacitive loading element is arranged so as to cover the rear of the radiating element, or the rear of the capacitive loading element is arranged so as to cover the front of the radiating element.
The antenna device according to claim 4. The radiating element overlaps 0.6 times or more the length of the capacitive loading element.
The antenna device according to claim 5 or 6. The feeding portion of the first antenna portion is located between the front end and the rear end of the capacitive loading element.
Feeding part of the second antenna unit is positioned in the vicinity of the rear end of the front or the capacitive loading element of a front end of the capacitive loading elements,
The antenna device according to any one of claims 1 to 7. A trap circuit that blocks signals in at least a frequency band that can be received by the first antenna unit is connected to the power feeding unit of the second antenna unit.
The antenna device according to any one of claims 1 to 8. The trap circuit is composed of a capacitor, an inductor, or a combination thereof .
The antenna device according to claim 9. The first antenna portion further includes a helical element, and the helical element is offset with respect to the second antenna portion.
The antenna device according to any one of claims 1 to 10. The first antenna unit receives at least a signal in the broadcast wave band of the FM wave band, and receives at least a signal in the broadcast wave band.
The second antenna unit receives at least a signal in a broadcast wave band higher than the FM wave band.
The antenna device according to any one of claims 1 to 11. An antenna base that closes the opening of the antenna case is further provided.
The antenna device according to any one of claims 1 to 12 .

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