Vehicle antenna device

Abstract

In a vehicle-mounted antenna device having a plurality of antenna units, proximal placement of the antenna units to each other within a limited space is enabled, while suppressing deterioration in characteristics of each other.　A vehicle-mounted antenna device 30 has an antenna case 11 that forms an accommodation space along with an antenna base 18. A first antenna unit 12 and a second antenna unit 13, which correspond to different frequencies from each other, are accommodated within the accommodation space. The antenna units 12 and 13 each include one or more elements, and part of the elements of the first antenna unit 12 overlaps part of the elements of the second antenna unit 13 in at least one of side view and plan view. Also, connected to a power feed unit of at least one antenna unit of the first antenna unit 12 and the second antenna unit 13 is a limiter circuit 31 that limits passage of signals of frequencies other than the frequency band that the antenna unit corresponds to.

Description

Technical Field

[0001] The present invention relates to an in-vehicle antenna device in which a plurality of antenna parts corresponding to different frequency bands are arranged in proximity to each other in a limited space.

Background Art

[0002] As an in-vehicle antenna device, an antenna device described in Patent Document 1 is known. This antenna device is used for receiving AM / FM broadcasts, and in order to reduce the height and improve the gain and the like, it includes an umbrella-shaped element that forms an antenna assembly together with a coil. The umbrella-shaped element is a plate-shaped conductor that is umbrella-shaped at the front and rear viewpoints, and is integrally formed with a top portion and an inclined portion that extends toward the skirt from the top portion as the center.

[0003] In recent years, in-vehicle antenna devices that receive not only AM / FM broadcasts but also terrestrial digital television broadcasts (sometimes called DTTV (Digital Terrestrial Television) or DTTB (Digital Terrestrial Television Broadcasting)) have been increasingly popular. FIG. 31A is a schematic cross-sectional view of a typical antenna device 200 of this type. This antenna device 200 mounts, on an antenna base 18 sealed with an antenna case 11, a first antenna part 12 corresponding to the DTTV band, a second antenna part 13 corresponding to the AM / FM band, a first circuit input part 14 for the DTTV band, a second circuit input part 15 for the AM / FM band, and circuit boards 16A and 16B on which electronic circuits (such as tuning circuits) for each frequency band are mounted. The antenna base 18 is provided with a mounting part 17 for attaching the antenna device 200 to a vehicle. The first antenna part 12 and the second antenna part 13 are separated by a certain distance or more, thereby suppressing the coupling between the antenna parts.

Prior Art Documents

Patent Documents

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-204996 Summary of the Invention [Problem to be solved by the invention]

[0005] In the antenna device disclosed in Patent Document 1, the umbrella-shaped element is plate-shaped and has an inclined portion, so if an antenna unit for the DTTV band is present nearby, mutual interference may occur, affecting characteristics (gain, directivity, etc.). Furthermore, while it is desirable for vehicle-mounted antenna devices to be small and low-profile, making antenna device 200 with the configuration shown in Fig. 31A small and low-profile requires reducing the physical length of first antenna unit 12, as shown in antenna device 201 in Fig. 31B. This not only makes impedance matching difficult, but also reduces gain, etc., by the amount the physical length is reduced.

[0006] An example of an object of the present invention is to enable an in-vehicle antenna device having multiple antenna units for different frequency bands to be arranged close to each other in a limited space while suppressing degradation of the characteristics of the antenna units. Other objects of the present invention will become apparent from the description of this specification. [Means for solving the problem]

[0007] One aspect of the present invention is an in-vehicle antenna device comprising an antenna base attached to a predetermined location on a vehicle, an antenna case forming a storage space together with the antenna base, a first antenna unit housed in the storage space and corresponding to a first frequency band, and a second antenna unit housed in the storage space and corresponding to a second frequency band lower than the first frequency band, wherein at least a portion of the area of the first antenna unit overlaps with at least a portion of the area of the second antenna unit, and a limiting circuit is connected to the power supply portion of at least one of the first and second antenna units to limit the passage of signals of frequencies other than the frequency band supported by that antenna unit. [Effects of the Invention]

[0008] According to the above configuration of the present invention, in an in-vehicle antenna device having a plurality of antenna units corresponding to different frequency bands, it becomes possible to arrange them in close proximity in a limited space while suppressing deterioration of the characteristics of the respective antenna units.

Brief Description of the Drawings

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[0010] Hereinafter, embodiments will be described in detail with reference to the drawings. Here, an example in the case of implementing as an in-vehicle antenna device attached to a vehicle roof or the like will be given. In this specification, the forward direction of the vehicle is referred to as "front" or "forward", the opposite direction is referred to as "rear" or "rearward", and when there is no need to distinguish between the two, it is referred to as "longitudinal direction". Also, the right side in the forward direction of the vehicle is referred to as "right" or "right direction", the left side in the forward direction is referred to as "left" or "left direction", and when there is no need to distinguish between the two, it is referred to as "width direction". Further, the gravitational direction of the vehicle is referred to as "down" or "downward", the opposite direction is referred to as "up" or "upward", and when there is no need to distinguish between the two, it is referred to as "vertical direction".

[0011] [First Embodiment] FIG. 1 is a schematic diagram of an antenna device 10 for explaining the first characteristic part of the present invention. For convenience, components that are functionally equivalent to the antenna devices 200 and 201 in FIGS. 31A and 31B showing conventional examples are denoted by the same reference numerals. The antenna device 10 is arranged such that when assuming orthogonal three-dimensional axes of the X-axis, Y-axis, and Z-axis, the forward direction of the vehicle is the positive direction of the X-axis (arrow direction), the left direction is the positive direction of the Y-axis (arrow direction), and the upward direction is the positive direction of the Z-axis (arrow direction). Therefore, the longitudinal direction (the X-axis direction in FIG. 1) of the antenna device 10 and the component parts described later coincides with the longitudinal direction of the vehicle.

[0012] The in-vehicle antenna device 10 in FIG. 1 includes an antenna base 18 that is attached to a predetermined part of a vehicle, for example, a vehicle roof, and an antenna case 11 that forms an accommodation space together with the antenna base 18. The accommodation space is a space in which a first antenna unit 12, a second antenna unit 13, a first circuit input unit 14, a second circuit input unit 15, and circuit boards 16A and 16B are accommodated. The first antenna unit 12 functions as an antenna corresponding to a first frequency band, and in this example, as an antenna for the DTTV band. The second antenna unit 13 functions as an antenna corresponding to a second frequency band, and in this example, as a part of an antenna for the AM / FM band. Each of the antenna units 12 and 13 is configured to include one or more elements having a predetermined shape, and is arranged so as to extend in the longitudinal direction as a whole antenna unit.

[0013] The circuit board 16A has an impedance matching circuit, a tuning circuit, an amplification circuit, etc. designed for the DTTV band mounted thereon. The circuit board 16B has an impedance matching circuit, a tuning circuit, an amplification circuit, etc. designed for the AM / FM band mounted thereon. The first circuit input unit 14 is an input interface (such as a feeder) with the circuit board 16A. The second circuit input unit 15 is an input interface (such as a feeder) with the circuit board 16B. The antenna base 18 is provided with an attachment portion 17 for attaching to the vehicle.

[0014] The rearmost rear end portion of the elements of the first antenna unit 12 and the foremost front end portion of the elements of the second antenna unit 13 are installed at positions that overlap when viewed from the side, that is, from the viewpoint in the Y-axis direction, while being non-contact with each other (in FIG. 1, the portion indicated by the dotted line represents the portion that overlaps in the longitudinal direction). Therefore, the distance between the front end portion of the first antenna unit 12 and the rear end portion of the second antenna unit 13, that is, the length in the longitudinal direction (physical length), is shorter than the sum value of the lengths in the longitudinal direction (physical length) when the elements of the first antenna unit 12 and the second antenna unit 13 do not overlap when viewed from the side. The configuration is not limited to one in which the rear end of the first antenna unit 12 overlaps with the front end of the second antenna unit 13, but may be one in which the rear portion of the first antenna unit 12 overlaps with the front portion of the second antenna unit 13. Furthermore, the configuration may be one in which the top of the first antenna unit 12 overlaps with the top of the second antenna unit.

[0015] 1, the first antenna unit 12 is depicted as having a streamlined shape with two right-angled portions at the rear and an arc portion at the front in a side view, and the second antenna unit 13 is depicted as having a rectangular shape, but these shapes are merely schematic for the sake of convenience. The actual shapes of the first antenna unit 12 and the second antenna unit 13 may differ from those shown in the drawings depending on the required antenna characteristics. For example, the first antenna unit 12 and the second antenna unit may each include elements that are linear, planar, or have a shape that is a combination of these.

[0016] Figure 2 is an explanatory diagram showing a schematic cross-sectional view from the side showing the shape and structure of the vehicle-mounted antenna device 10 in more detail, a rear view of the antenna device 10 (i.e., a view from the perspective of the -X axis direction), and a plan view of the antenna device 10, i.e., a view from the perspective of the -Z axis direction (top view). 2, area 211 represents the area of first antenna unit 12, and area 212 represents the area of second antenna unit 13. More specifically, area 211 is a solid body in three-dimensional space that includes each element of first antenna unit 12 and circuit board 16A, and is represented as a rectangular parallelepiped in the illustrated example.

[0017] The length of region 211 in the X-axis direction is the maximum length including first antenna unit 12 and circuit board 16A. In the drawing, the length is determined by the left end of circuit board 16A in the X-axis direction and the right end of first antenna unit 12 in the X-axis direction (the right end of fourth element 124 in the X-axis direction) in the schematic cross-sectional view. The length of region 211 in the Y-axis direction is the maximum length including first antenna unit 12 and circuit board 16A, and is defined by the upper and lower ends of circuit board 16A in the Y-axis direction in the schematic plan view of the figure. The length of the region 211 in the Z-axis direction is the maximum length including the first antenna section 12 and the circuit board 16A. In the figure, it is defined by the lower end of the circuit board 16A and the upper end of the first antenna section 12 (the upper end of the fourth element) in its schematic rear view.

[0018] Thus, the region 211 of the first antenna section is defined as a rectangular parallelepiped with the maximum dimensions determined by the maximum length including the first antenna section 12 and the circuit board 16A in the X-axis, Y-axis, and Z-axis directions. Also, the circuit board 16A itself is included in this region 211. Similarly, the region 212 of the second antenna section is defined as a rectangular parallelepiped with the maximum dimensions including the circuit board 16B, determined by the maximum length including the second antenna section 13 and the circuit board 16B in the X-axis, Y-axis, and Z-axis. Also, the circuit board 16B itself is included in this region 211.

[0019] In the schematic cross-sectional view of FIG. 2, a part of the region 211 and a part of the region 212 overlap in a side view, and this overlapping region is shown as the region α. Also, in the rear view, a part of the region 211 and a part of the region 212 overlap in a rear view, and this overlapping region is shown as the region β. Also, in the rear view, when viewed from the front side of the antenna 10, that is, from the viewpoint in the +X-axis direction, the relationship that a part of the region 211 and a part of the region 212 overlap in the region β remains unchanged. Therefore, it can be seen that a part of the region 211 and a part of the region 212 also overlap in a front view. In the plan view, the region 211 and the region 212 overlap in a top view, and this overlapping region is shown as the region γ. From the relationship between the region 211 and the region 212 shown in FIG. 2, it is shown that a part of the region of the first antenna section 12 and a part of the region of the second antenna section 13 overlap in any of the top view, side view, and front view.

[0020] In the example of FIG. 2, the first antenna section 12 is configured to include the first element 121, the second element 122, the third element 123, and the fourth element 124. These elements 121 to 124 are each manufactured by processing and forming a metal plate. The first element 121 is an element that is conductively connected to an input interface (such as a feeder) that extends vertically from the antenna base 18 (or circuit board 16A), and functions as a power feed section for the first antenna section 12. The vertically extending input interface also functions as an antenna, and the first circuit input section 14 functions as a power feed section. The second element 122 is an element that extends upward at a predetermined angle with respect to the X-axis from one end of the first element 121. The third element 123 is an element that is bent in the width direction from the end of the second element 122 that is opposite to the first element 121. The fourth element 124 is an element that extends further upward at a predetermined angle with respect to the X-axis from the end of the third element 123 that is opposite to the second element 122. The third element 123 is formed to shorten the length (physical length) in the longitudinal direction from the tip end of the first element 121 to the rear end of the fourth element 124 compared to when the third element 123 is not present, while maintaining the conductor area and electrical length of the entire elements of the first antenna unit 12. The third element 123 may be an element that forms a curved portion that curves in the width direction from the end of the second element 122 opposite to the first element 121.

[0021] The second antenna unit 13 includes inclined elements 131 and 132, each made of a pair of metal plates whose opposing distance decreases toward their upper ends (top ends), and a connecting element 133, which is a thin metal plate that connects the inclined elements 131 and 132 at their lower ends. An input interface extending vertically from the antenna base 18 (or circuit board 16B) to the connecting element 133 also functions as an antenna. The connecting element 133, together with the second circuit input unit 15 of the second antenna unit 13, functions as a power supply unit. In the vehicle-mounted antenna device 10 configured in this manner, a portion (rear end) of the fourth element 124 of the first antenna section 12 overlaps a portion (front end) of the pair of inclined elements 131, 132 of the second antenna section 13 in the longitudinal direction.

[0022] Note that the shapes and structures of the first antenna unit 12 and the second antenna unit 13 are not limited to the examples shown in FIG. 2. For example, the first element 121, the second element 122, the third element 123, and the fourth element 124 of the first antenna unit 12 may be fixed so as to cover the upper end portion of the insulating substrate having front and back surfaces, or in the vicinity of the upper end portion. In this case, the first element 121 and the second element 122 are formed on the front surface side of the insulating substrate, the fourth element 124 is formed on the back surface side of the insulating substrate, and the third element 123 can be formed as a conductive chip or a conductive plate that electrically connects the front surface side and the back surface side of the insulating substrate.

[0023] In addition, by increasing the number of elements of the first antenna unit 12 and increasing the number of bent portions, the length in the longitudinal direction of the first antenna unit 12, and thus the length (physical length) in the longitudinal direction including the second antenna unit 13 as well, can be further shortened. Configurations for increasing the number of bent portions include, for example, a bellows shape, a meander shape, a helical shape, etc. In other words, even when the length in the longitudinal direction of the antenna base 18 is shorter than that of the conventional in-vehicle antenna device 200 shown in FIG. 31A, the electrical length is ensured to be the same as that of the conventional in-vehicle antenna device 200, so the radiation efficiency can be increased.

[0024] The DTTV signal received by the first antenna unit 12 is transmitted to the electronic circuit of the circuit board 16A via the first circuit input unit 14. Also, the AM / FM signal received by the second antenna unit 13 is transmitted to the electronic circuit of the circuit board 16B via the second circuit input unit 15. Note that in the schematic cross-sectional view of FIG. 2 as well, a part of the first antenna unit 12 is shown by a dotted line. This represents, as in the schematic diagram of FIG. 1, the portion of the elements that overlap in side view while being separated from each other in top view with respect to the second antenna unit 13.

[0025] In this way, in the in-vehicle antenna device 10, a part of the elements of the first antenna unit 12 and a part of the elements of the second antenna unit 13 overlap each other in the longitudinal direction in a side view, and further, the first antenna unit 12 has a third element 123 bent in the width direction. Therefore, when the total length of the first antenna unit 12 is the same, by providing the third element 123 which is the bent part, the length in the longitudinal direction (physical length) can be made shorter than the case where there is no bent part. On the other hand, when the first antenna unit 12 is composed of a first element 121, a second element 122, and a fourth element 124 without a bent part, the total length becomes shorter compared to the case where there is the third element 123, so the antenna characteristics deteriorate. Therefore, by providing the third element 123 which is the bent part, the in-vehicle antenna device 10 can be made smaller without causing deterioration of the antenna characteristics.

[0026] The in-vehicle antenna device 20 of the first reference example shown in FIG. 3A and the in-vehicle antenna device 20' of the second reference example shown in FIG. 3B will be described respectively. The antenna characteristics of the in-vehicle antenna device 20 of the first reference example and the in-vehicle antenna device 20' of the second reference example will be compared and described. As shown in FIG. 3A, the in-vehicle antenna device 20 has a configuration in which the second antenna unit 13 is excluded from the in-vehicle antenna device 10 and the first antenna unit 12 has no bent third element 123 and is planar. The components other than the first antenna unit 12 and the second antenna unit 13 in the in-vehicle antenna device 20 of the first reference example are the same as those in the in-vehicle antenna device 10. That is, the in-vehicle antenna device 20 of the reference example has only the first antenna unit 12 corresponding to the DTTV band and is not affected by the AM / FM band or harmonics of the FM band.

[0027] 3B, the in-vehicle antenna device 20' of the second reference example is the same as the in-vehicle antenna device 20 in that the first antenna section 12 does not have the bent third element 123. However, the in-vehicle antenna device 20' differs from the in-vehicle antenna device 20 in that it has a second antenna section 13', and furthermore, it has a configuration that differs from the in-vehicle antenna device 10 in that the second antenna section 13' is not connected to the circuit board 16B. The components of the in-vehicle antenna device 20' of the second reference example are the same as those of the in-vehicle antenna device 20, except for the second antenna section 13' that is not connected to the circuit board 16B. That is, the in-vehicle antenna device 20' of the second reference example has a first antenna section 12 that corresponds to the DTTV band, and also has a second antenna section 13', but because the second antenna section 13' is not connected to the circuit board 16B, it is not affected by harmonics of the AM / FM band or the FM band. On the other hand, the in-vehicle antenna device 20' is affected by the second antenna section 13' as a capacitive plate.

[0028] FIG. 4 is a diagram showing frequency-gain characteristics in the DTTV band. The vertical axis represents gain (DTTV Gain [dBi]) and the horizontal axis represents frequency (Frequency [MHz]). In FIG. 4, the gain characteristics of the in-vehicle antenna device 20 are shown by a solid line, and the gain characteristics of the in-vehicle antenna device 20′ are shown by a dashed line. Referring to FIG. 4, the in-vehicle antenna device 20′ of FIG. 3B, in which part of the elements of the first antenna section 12 overlaps part of the elements of the second antenna section 13′ in a side view, has a gain approximately equal to that of the in-vehicle antenna device 20 near the center of the DTTV band, i.e., at frequencies around approximately 580 MHz to approximately 660 MHz. However, the gain of the in-vehicle antenna device 20′ is greater than that of the in-vehicle antenna device 20 in the frequency range of approximately 470 MHz to approximately 580 MHz, which is on the lower side of the DTTV band, and in the frequency range of approximately 660 MHz to approximately 720 MHz, which is on the higher side of the DTTV band. That is, the effect of the second antenna section 13' as a capacitance loading plate increases the gain, and it is shown that a wider bandwidth is achieved.

[0029] This is because, in the in-vehicle antenna device 10, some elements of the first antenna section 12 are close to elements of the second antenna section 13, so that the nearest elements are capacitively coupled and the capacitive impedance of the other element is added in parallel, resulting in an increase in the apparent antenna size (electrical length).In other words, this is because the second antenna section 13 for the AM / FM bands acts as a capacitance loading element that loads capacitance onto the first antenna section 12 for the DTTV band.

[0030] The positional relationship between the first antenna unit 12 and the second antenna unit 13 and the resulting effect of widening the bandwidth in the DTTV band are as described above, but it is also necessary to consider the electrical characteristics of the second antenna unit 13 in the AM / FM band and DTTV band. In the first embodiment, as shown in the schematic diagram of Figure 5, an in-vehicle antenna device 30 is provided in which a restriction circuit 31 is interposed between the second antenna section 13 and the second circuit input section 15, which allows AM / FM band signals to pass through while restricting the passage of signals of frequencies other than the AM / FM wave bands. The components of the in-vehicle antenna device 30 other than the limiting circuit 31 are the same as those of the in-vehicle antenna device 10.

[0031] As a simple example, limiting circuit 31 can be a band elimination filter (BEF) in which an inductive element (inductor) 311 and a capacitive element (capacitor, etc.) 312 are connected in parallel, as shown in Fig. 6. The electrical constants of the BEF are set to a high impedance value (parallel resonance state) that blocks signals from passing in the DTTV band, for example, but do not resonate at frequencies other than the DTTV band, allowing signals to pass. In particular, in the AM / FM band, the BEF acts as an inductor, so its effect on the antenna characteristics in the AM / FM band, such as gain, is minimized.

[0032] The in-vehicle antenna device 30 having such a limiting circuit 31 can suppress a decrease in the gain of the first antenna unit 12 due to connection to the circuit board 16B while maintaining the effect of broadbanding the operating frequency in the DTTV band. Note that the BEF can be configured using the self-resonance of an inductor. "Self-resonance" refers to a resonance phenomenon caused by minute distributed capacitance generated between winding conductors or terminals where the inductor has a coil structure. Since the distributed capacitance is not manifested during design, its existence often becomes a problem. However, in this embodiment, by positively using this distributed capacitance to configure the BEF, the number of components can be reduced, contributing to the miniaturization and weight reduction of the in-vehicle antenna device 30. Alternatively, instead of the BEF, a high-pass filter that blocks the passage of signals having a frequency higher than the FM band may be used.

[0033] FIG. 7 is an explanatory diagram showing a schematic view in a side view, a rear view of the in-vehicle antenna device 30, that is, a plan view from the viewpoint in the -X axis direction, and a top view of the in-vehicle antenna device 30, that is, a plan view from the viewpoint in the -Z axis direction, which more specifically shows the shape and structure of the in-vehicle antenna device 30. A helical element, which is an example of a dielectric element, is used for the limiting circuit 31. In FIG. 7, the first antenna unit 12, the second antenna unit 13, etc. have the same configuration as in FIG. 2. The helical element has its contact point P connected to the connection element 133 that serves as the feeding portion of the second antenna unit 13, and its central axis is arranged relatively forward or backward away from the connection element 133. This is to prevent the magnetic field lines generated from the helical element from causing electromagnetic induction in the inclined elements 131 and 132 of the second antenna unit 13.

[0034] FIG. 8 is a frequency-gain characteristic diagram in the DTTV band. The vertical axis represents the gain (DTTV Gain [dBi]), and the horizontal axis represents the frequency (Frequency). In FIG. 8, the gain characteristic of the in-vehicle antenna device 10 is indicated by a broken line, the gain characteristic of the in-vehicle antenna device 20 of the first reference example is indicated by a solid line, and the gain characteristic of the in-vehicle antenna device 30 having the limiting circuit 31 is indicated by a dashed-dotted line.

[0035] The gain characteristics of the in-vehicle antenna device 20 in the DTTV band are the same as those shown in Fig. 4. The gain of the in-vehicle antenna device 30 including the limiting circuit 31 at frequencies near the center of the DTTV band is a maximum of 1.9 dBi, which is equivalent to the maximum gain of the in-vehicle antenna device 20, 1.9 dBi. In other words, the limiting circuit 31 suppresses the reduction in gain in the DTTV band much more than that of the in-vehicle antenna device 10. On the other hand, in the range of approximately 470 MHz to approximately 580 MHz, which is the lower frequency range of the DTTV band, and approximately 620 MHz to approximately 720 MHz, which is the upper frequency range of the DTTV band, the gain in the DTTV band is greater than that of the in-vehicle antenna device 10 and the in-vehicle antenna device 20 of the first reference example. In other words, the difference between the maximum and minimum gain values in the DTTV band is smaller, achieving a wider usable frequency band. In this way, it has been found that by inserting the limiting circuit 31 between the second antenna section 13 and the second circuit input section 15, not only is the gain reduction in the DTTV band suppressed, but a wider bandwidth is also possible, even if the elements of the first antenna section 12 and the second antenna section 13 are brought close enough to each other that they partially overlap without changing the physical length of the elements.

[0036] In the first embodiment, an example in which the inclined elements 131, 132 of the second antenna unit 13 are metal plates has been described. However, multiple voids may be formed in each of the inclined elements 131, 132. By providing the voids, the second antenna unit 13 can be attached by simply fitting protrusions of a resin or insulating holder (not shown) fixed to the antenna case 11 or the antenna base 18 into the voids. The voids can also be used as a means for fine-tuning the electrical length of the second antenna unit 13. Part or all of each of the inclined elements 131, 132 may be a conductor plate having a fractal shape, a meander shape, or a shape that partially includes these shapes, with voids. This allows fine adjustment of the antenna characteristics of the second antenna unit 13. The same applies to the elements of the first antenna unit 12. In the first embodiment, an example in which the restriction circuit 31 is inserted between the second antenna unit 13 and the second circuit input unit 15 has been described. However, even if the restriction circuit 31 is arranged between the second circuit input unit 15 of the circuit board 16B and the subsequent-stage circuit, the same effects as those of the in-vehicle antenna device 30 can be obtained.

[0037] [Second Embodiment] Next, an in-vehicle antenna device according to the second embodiment will be described. In the AM / FM band, as in the antenna device disclosed in Patent Document 1, a coil may be used as a part of the elements of the antenna unit. The coil is adjusted to resonate in the FM band when combined with other elements (the umbrella-type element in the example of Patent Document 1). However, when the harmonic component of this resonance frequency becomes the frequency of the DTTV band, it becomes a factor for reducing the gain of the DTTV band. In the second embodiment, an example of an in-vehicle antenna device configured to eliminate such a factor will be described.

[0038] FIG. 9 is a cross-sectional view of an in-vehicle antenna device 40 of a third reference example. Components having the same functions as those of the in-vehicle antenna devices 10, 20, and 30 described in the first embodiment are given the same reference numerals for convenience. The in-vehicle antenna device 40 of the third reference example is used for a comparative description of the antenna characteristics with the in-vehicle antenna device 50 of the second embodiment to be described later. In a configuration similar to that of the in-vehicle antenna device 10 of the first embodiment, a helical element 41 is arranged between the second antenna unit 13 and the second circuit input unit 15. The helical element 41 is designed to resonate in the FM band together with the second antenna unit 13.

[0039] 10A shows a graph representing the measurement results of the reflection characteristics from second circuit input unit 15 to second antenna unit 13 in in-vehicle antenna device 40 of the third reference example. The vertical axis of FIG. 10A represents return loss (dB), and the horizontal axis represents frequency (MHz). Referring to FIG. 10A, in addition to the resonance frequency (f1: near 90 MHz) due to helical element 41 and second antenna unit 13, in-vehicle antenna device 40 also generates a first harmonic component (f2: 380 MHz) and a third harmonic component (f3: near 655 MHz) caused by helical element 41. Third harmonic component f3 is a frequency belonging to the DTTV band, and this third harmonic component f3 has an undesirable effect on the antenna characteristics of first antenna unit 12.

[0040] 10B shows a graph representing the measurement results of the reflection characteristics from the first circuit input unit 14 to the first antenna unit 12 side in the in-vehicle antenna device 40 of the third reference example. The vertical axis of Fig. 10B represents the return loss (dB) and the horizontal axis represents the frequency (MHz). 10B, in the DTTV band, the return loss increases to approximately -5 dB due to the influence of the third harmonic component f3 of the FM band. This is thought to be because the third harmonic component f3 generated on the second antenna unit 13 side interferes with the element of the first antenna unit 12, causing unwanted resonance in the DTTV band. If unwanted resonance occurs, the gain in the DTTV band will decrease, and signal regeneration may become impossible regardless of the vehicle's attitude.

[0041] There is isolation as a parameter representing the degree of signal separation between the first antenna unit 12 and the second antenna unit 13. Isolation can be expressed by the passing characteristics (dB) between the antenna units. FIG. 11 is a graph showing the measurement results of the gain in the DTTV band in the in-vehicle antenna device 40 of the third reference example. The vertical axis represents the gain (dB) in the DTTV band, and the horizontal axis represents the frequency (MHz). As shown in the figure, unnecessary resonance occurs due to the influence of the harmonic wave in the FM band near the frequency of 655 MHz, indicating that the gain in the DTTV band has decreased. Therefore, the distance between the rear end portion of the first antenna unit 12 and the front end portion of the second antenna unit 13 was increased from the state shown in FIG. 9 to change the isolation. FIG. 12 shows a graph representing the relationship between the change amount of the isolation (passing characteristics: dB) and the gain (dB) at this time. Note that the gain (dB) on the vertical axis is shown as the change amount from the reference, with the reference being the gain when the helical element 41, which is an inductive element, is not provided and the harmonic wave in the FM band does not occur in the DTTV band.

[0042] Referring to FIG. 12, when the isolation is -10.5 dB, the change amount of the gain is -0.4 dB. When the change amount of the gain is suppressed to a small value of -0.4 dB in this way, the first antenna unit 12 and the second antenna unit 13 are located at positions 12.5 mm apart in the antenna longitudinal direction, and the combined length of the first antenna unit 12 and the second antenna unit 13 is 115.5 mm. Also, when the isolation deteriorates more than -10.5 dB, the decrease amount of the gain becomes larger. In particular, it can be seen that when the isolation becomes -4 dB or more, the gain decreases rapidly.

[0043] Furthermore, because harmonics are generated by a resonance phenomenon between second antenna unit 13 and helical element 41, the impedance of second antenna unit 13 and helical element 41, which is an inductive element, decreases at the frequency of the resonance phenomenon. As a result, the isolation from first circuit input unit 14 to second circuit input unit 15 decreases, which may cause malfunctions in the electronic circuits of circuit boards 16A and 16B and downstream systems of in-vehicle antenna device 40 of the third reference example. Therefore, in the second embodiment, a configuration example for avoiding the phenomenon of unwanted resonance occurring in the DTTV band will be described.

[0044] 13 is a schematic diagram of an in-vehicle antenna device 50 of the second embodiment. As with the first embodiment, the shape and structure are shown in a schematic manner. In the in-vehicle antenna device 50, a limiting circuit 51 is interposed between the second antenna unit 13 and the helical element 41, which is an inductive element, of the in-vehicle antenna device 40 of the third reference example shown in FIG. 9.

[0045] The limiting circuit 51 can be a BEF in which an inductive element 311 and a capacitive element 312 are arranged in parallel, or a filter using a self-resonant coil-structure inductor, similar to the limiting circuit 31 of the first embodiment shown in FIG. 6 . In the second embodiment, any other filter can be used as long as it provides high impedance in the DTTV band and low impedance in the AM / FM band. Because the limiting circuit 51 ensures sufficient isolation, even if the first antenna unit 12 and the second antenna unit 13 are arranged so close that they partially overlap, gain reduction due to harmonics in the FM band is suppressed. In the second embodiment, the combined physical length of the first antenna unit 12 and the second antenna unit 13 in the longitudinal direction is 55.5 mm, which is 60 mm smaller than the in-vehicle antenna device 40 of the third reference example shown in FIG. 9 .

[0046] 14 is a graph showing the measurement results of the reflection characteristics of the first circuit input section 14 in the in-vehicle antenna device 50. In the in-vehicle antenna device 40 of the third reference example, the third harmonic component f3 was generated in the DTTV band, but in the in-vehicle antenna device 50 of the second embodiment, the generation of the third harmonic component f3 is suppressed. FIG. 15 is a graph showing the measurement results of the gain in the DTTV band in each of the in-vehicle antenna device 40 of the third reference example and the in-vehicle antenna device 50 according to the second embodiment. Note that the gain characteristics of the in-vehicle antenna device 40 of the third reference example are the same as the gain characteristics shown in FIG. 11. As shown in FIG. 15, in the in-vehicle antenna device 40 of the third reference example, the gain rapidly decreases and increases around 655 MHz, and a rapid gain variation due to the third harmonic component f3 occurs. However, in the in-vehicle antenna device 50 of the second embodiment, such a gain variation does not occur. That is, the interference due to the third harmonic component f3 is suppressed. Since the limiting circuit 51 functions as an inductor in the AM / FM band, it has almost no influence on the gain in the second antenna unit 13.

[0047] FIG. 16 is a graph showing the relationship between frequency and isolation. In the in-vehicle antenna device 40 of the third reference example, it is shown that the isolation between the first antenna unit 12 and the second antenna unit 13 deteriorates in the vicinity of 655 MHz, which is the frequency at which harmonics are generated. On the other hand, in the in-vehicle antenna device 50, due to the provision of the limiting circuit 51, the isolation is - 10.5 dB or less. As described above, when the isolation exceeds - 10.5 dB, the amount of gain reduction increases. However, in the second embodiment, due to the provision of the limiting circuit 51, the reduction of the gain is suppressed.

[0048] Here, the limiting circuit 51 used in the in-vehicle antenna device 50 will be described in more detail. FIGS. 17A to 17C are explanatory diagrams of a BEF as an example of the limiting circuit 51. FIG. 17A is an example using the self-resonance phenomenon of an inductive element alone, FIG. 17B is an example in which an inductive element and a capacitive element are connected in series, and FIG. 17C can be parallel-resonated by using a semiconductor such as a diode as a capacitive element with the inductive element. Also, when configured using the self-resonance of a coil, the limiting circuit 51 (BEF) and the helical element can be integrated.

[0049] FIG. 18 is a graph showing the measurement results of the gain characteristics in the DTTV band for each of the in-vehicle antenna device 20 of the first reference example shown in FIG. 3A and the in-vehicle antenna device 50 according to the second embodiment shown in FIG. 13. The in-vehicle antenna device 50 has a gain improvement of 1.3 dB near 470 MHz and a gain improvement of 0.8 dB near 720 MHz compared to the in-vehicle antenna device 20 of the first reference example, achieving a wider bandwidth of the operating frequency.

[0050] When a filter having a BEF or equivalent function is configured using self-resonance, the limiting circuit 51 and the helical element 41 can be realized by a coil structure using a single linear conductor. Hereinafter, a configuration example of a coil structure body in which the first inductor L1 and the second inductor L2 are connected will be described.

[0051] FIG. 19A is a front view of the first configuration example, and FIG. 19B is a top view thereof (a plan view seen from the -Z direction, the same applies hereinafter). In the first configuration example, the coil diameter φ1 of the first inductor L1, the coil diameter φ2 of the second inductor L2, and the coil pitches (pitches between conductors, the same applies hereinafter) p1, p2 and the transition turn pitch (coil pitch for distinguishing the first inductor L1 and the second inductor L2, the same applies hereinafter) p3 are different from each other. This is to reduce the influence of the magnetic flux of the first inductor L1 on the second inductor L2.

[0052] As shown in FIG. 19B, the second inductor L2 and the first inductor L1 are each circular in the top view, but their coil axes (the central axis of the coil; the same applies below) do not coincide. That is, the coil axes of the inductors L1 and L2 are parallel but spaced a certain distance apart in the X-axis direction. Also, in the top view, the second inductor L2 is inscribed within the first inductor L1. For example, the first inductor L1 has a coil diameter φ1 of 12.0 mm, a coil pitch p1 of 1.6 mm, and 5.5 turns, with the transition portion from the first inductor L1 to the second inductor L2 being one turn. The second inductor L2 has a coil diameter φ2 of 8.0 mm, a coil pitch p2 of 0.53 mm, and 7 turns. While the coil axes are not coincident in this example, they may coincide.

[0053] FIG. 20A is a front view of the second configuration example, and FIG. 20B is its top view. In the second configuration example, the first inductor L1 and the second inductor L2 have the same coil diameter φ1 but different coil pitches p1 and p2. The transition turn pitch p3 is the same as in FIG. 19A. As shown in FIG. 20B, the second inductor L2 and the first inductor L1 are each circular in the top view, have the same coil axis, and have the same coil diameter φ1. Therefore, the two inductors L1 and L2 overlap when viewed from above. As an example of size, the coil diameter φ1 is 12.0 mm, the coil pitch p1 is 2.57 mm, the number of turns is 3.5, and the transition portion from the first inductor L1 to the second inductor L2 is one turn. The second inductor L2 has a coil diameter φ2 of 12.0 mm, a coil pitch p2 of 0.70 mm, and six turns.

[0054] FIG. 21A is a front view of the third configuration example, and FIG. 21B is a top view thereof. In the third configuration example, the coil diameters φ1 of the first inductor L1 and the second inductor L2, the coil pitches p1 and p2 are the same, and the coil axes coincide. The transition turn pitch p3 is different from the coil pitches p1 and p2 and is the same as in FIG. 19A. As shown in FIG. 21B, the first inductor L1 and the second inductor L2 are each circular in the top view and have the same coil axis and coil diameter, so the two inductors L1 and L2 overlap in the top view.

[0055] As an example of the size, both the first inductor L1 and the second inductor L2 have a coil diameter φ1 of 12.0 mm and a coil pitch p1 of 1.0 mm. The number of turns of the first inductor L1 is 5 turns, the number of turns of the second inductor L2 is 5.5 turns, and the transition portion from the first inductor L1 to the second inductor L2 is 1 turn. The transition turn pitch p3 is the same as in the cases of FIGS. 19A and 20A. Also, the number of turns of the BEF according to the third configuration example is 10.5 turns, the inductance value of the first inductor is 306 nH, and the inductance value of the second inductor is 448 nH, for a total of 754 nH.

[0056] In the third configuration example, if the transition portion is not provided, harmonics in the FM band are generated within the band of the DTTV band, resulting in a gain reduction. In this case, for example, if isolation can be achieved in the desired band with another antenna or the like, it is also possible to shorten the transition portion or configure the antenna without the transition portion in the third configuration example. Also, as a characteristic required for the second inductor L2, by making the isolation between the first antenna section 12 and the second antenna section 13 - 10.5 dB or less, the gain reduction due to harmonics in the FM wave band can be suppressed within 0.4 dB. That is, if the isolation of the second inductor L2 alone can be made - 10.5 dB or less, even if the AM / FM antenna and the DTV antenna are placed close to each other, the gain reduction in the DTTV band can be suppressed.

[0057] Next, a specific example of the coil structure will be described. FIG. 22 is an explanatory diagram showing a front view of a coil structure 140 as an example, a left side view of the coil structure 140, a right side view of the coil structure 140, a top view of the coil structure 140, a bottom view of the coil structure 140, a perspective view of the coil structure 140 viewed from the right rear direction, a perspective view of the coil structure 140 viewed from the right rear direction in the state before winding the coil, a perspective view of the coil structure 140 viewed from the left front direction, and a perspective view of the coil structure 140 viewed from the left front direction in the state before winding the coil.

[0058] In the coil structure 140 illustrated in FIG. 22, a helical element 141 serving as a first inductor L1 and a BEF142 (inductive element) serving as a second inductor L2 are wound around a bobbin 143 which is an insulator. The coil structure 140 is provided below the second antenna unit 13. As the bobbin 143, for example, a resin bobbin may be used, but instead, a resin holder for supporting the entire second antenna unit 13 may be used as the bobbin 143. In order to avoid complication of the drawing, reference signs are omitted except for the front view of FIG. 22. In this example, the BEF142 is a single coil formed by winding a linear conductor integrated with the helical element 141 around a resin bobbin. In the FM band, the first inductor L1 functions as a tuning coil, so that resonance occurs in the FM band, but the second inductor L2 may be used as a part of the tuning coil.

[0059] Note that, in the front view of FIG. 22, the major axis B1 of the portion of the bobbin 143 around which the helical element 141 is wound is 24.2 mm, and the minor axis B2 of the portion around which the BEF142 is wound is 2.75 mm. In the left side view of FIG. 22, the minor axis B3 of the portion of the bobbin 143 around which the helical element 141 is wound is 9.8 mm, and in the top view of FIG. 22, the major axis B4 of the portion around which the BEF142 is wound is 8.8 mm.

[0060] In this way, by configuring the limiting circuit 51 with a single coil, the number of components can be reduced, and the cost can be further reduced. Also, since this single coil can be manufactured using an automatic winding machine or the like, productivity is improved compared to creating the limiting circuit 51 by combining separate components. In the resin bobbin, a depression is provided in the portion where the linear conductor is wound, so that the pitch between adjacent conductor lines (the coil pitch in this example) is uniform, the diameter of the helical element 141 (the coil diameter in this example) is the same, and the conductor lines can be wound a determined number of times. Therefore, stable electrical characteristics can be ensured.

[0061] In the example shown in FIG. 22, the central axes (the coil axes in this example) of the first inductor L1 and the second inductor L2 are orthogonal to each other. Therefore, the coil axes intersect each other. By making the coil axes orthogonal to each other, the coupling between the first inductor L1 and the second inductor L2 is suppressed. Therefore, the size in the Z direction can be made smaller than when the second inductor L2 is arranged above the first inductor L1 in the same winding direction, and the profile can be made lower. Also, such a coil structure has the advantage that the management in terms of design and manufacturing can be simplified.

[0062] In the example shown in FIG. 22, the coil structure in which the first inductor L1 and the second inductor L2 are arranged such that their coil axes are orthogonal to each other has been described. However, the first inductor L1 and the second inductor L2 may be stacked in the coil axis direction (Z direction) and connected in series. The coil structure in this case, compared to the coil structure shown in FIG. 22, is somewhat longer in the Z direction, but the physical lengths in the X direction and the Y direction can be shortened, and the degree of freedom in design on the antenna base 18 can be increased.

[0063] FIG. 23 is an exploded perspective view of an example of an in-vehicle antenna device equipped with the coil structure 140 shown in FIG. 22. This in-vehicle antenna device includes a first antenna unit 12, a second antenna unit 13, a helical element 141, a BEF 142, and a coil structure 140 including a bobbin 143 on an antenna base 18 that is hermetically and watertightly sealed by an antenna case 11, and circuit boards 16A, 16B, etc. are accommodated, and an attachment portion 17 is provided on the bottom surface of the antenna base 18.

[0064] Also, in this example, the second antenna unit 13 has a meander shape having one or more bent portions bent in a predetermined direction. As another form, the second antenna unit 13 may have a shape having one or more curved portions curved in a predetermined direction.

[0065] Also, the second antenna unit 13 is not limited to a meander shape and may have other shapes. FIG. 24 is a diagram showing a structural example of an umbrella-shaped second antenna unit 13'' as an example of other shapes. As shown in the drawing, the second antenna unit 13'' in this example has a top portion T. It is shown that this top portion T overlaps with the first antenna unit 12 in a top view. Thus, the first antenna unit 12 and the second antenna unit 13'' may overlap in a top view, or may overlap in both a top view and a side view.

[0066] Thus, according to the second embodiment, by providing the limiting circuits 31, 51, the generation of harmonics of the FM band in the DTTV band (the third harmonic component f3 in this example) can be suppressed, and the gain of the DTTV band can be increased. Other effects are the same as those of the first embodiment. Note that the limiting circuits 31, 51 may be configured to limit the passage of noise components emitted from elements (components, wirings, etc.) other than the limiting circuits 31, 51 in addition to the harmonics of the FM band. Since the noise components have various frequency components, by also limiting the passage of such noise components, a decrease in the gain of the DTTV band can be suppressed.

[0067] In the above description, an example in which the restriction circuits 31 and 51 are inserted only in the second antenna section 13 has been shown. However, a restriction circuit for restricting the passage of signals of frequencies other than the DTTV band may also be provided on the first antenna section 12 side. Such a restriction circuit may be, for example, a restriction circuit (not limited to a BEF, but may be a low-pass filter, a band-pass filter, etc.) that has a high impedance at the harmonics of the AM / FM band and / or the FM band, or the above noise components, and has a low impedance in the DTTV band. With such a configuration, it becomes possible to more significantly suppress the gain reduction in the DTTV band and the AM / FM band.

[0068] Also, the above description is based on the premise that the second antenna section 13 exists above the circuit board 16B. However, the circuit board 16B may be arranged in front of the front end of the second antenna section 13 or behind the rear end of the second antenna section 13, so that no metal member exists directly below the capacitive loading element that is the second antenna section 13. For example, the entire second antenna section 13 may exist on the circuit board 16B, and the second antenna section 13 may not exist on the ground conductor or other metal plate. At that time, the circuit board 16A and the circuit board 16B can be integrated into one circuit board. According to this configuration, no capacitance (stray capacitance) is generated between the second antenna section 13 and the metal member, so the gain in the AM / FM band can be improved. Furthermore, in the above description, the first antenna section 12 has been described as an antenna for DTTV. However, the present invention is applicable not only to an antenna for DTTV but also to antennas for SXM, GNSS, V2X (Vehicle to Everything), telematics, Wi-Fi, Bluetooth, etc., which are antennas for higher frequency bands than the FM / AM frequency. The same applies to the following Modification Examples 1 to 4.

[0069] [Modification Example] Next, the first to fourth modified examples of the in-vehicle antenna device 10 will be described. FIG. 25 shows an in-vehicle antenna device 60 as the first modified example. As shown in the figure, the in-vehicle antenna device 60 has a configuration in which a first antenna unit region 2401 and a second antenna unit region 2402 are provided on a resin base 2418. The resin base 2418 is attached to a predetermined part of the vehicle via an attachment part 2417. Further, the in-vehicle antenna device 60 has an antenna case (not shown) that forms an accommodation space together with the resin base 2418. Since the antenna case of the first modified example has the same configuration as the antenna case 11 in the first embodiment, the description thereof will be omitted. The antenna unit region 2401 and the antenna unit region 2402 are located within the accommodation space.

[0070] The first antenna unit region 2401 is composed of a first antenna part 2412 as an antenna element, a first circuit board 2416A, a cylindrical conductive base 2419A, and a flat conductive base 2420A. The second antenna unit region 2402 is composed of a second antenna part 2413 as an antenna element, a second circuit board 2416B, a cylindrical conductive base 2419B, and a flat conductive base 2420B. In the first modified example, the first circuit board 2416A is of the four-point type, four cylindrical conductive bases 2419A are provided on the flat conductive base 2420A, and the first circuit board 2416A is provided on these four cylindrical conductive bases 2419A. This is the same for the second, third, and fourth modified examples described later. The cylindrical conductive bases 2419A and 2419B only need to be conductive. For example, they may be conductors in the shape of a screw or a pin, or may be conductors in the shape of a rod, a column, or a weight.

[0071] The first antenna part 2412 is composed of a planar antenna and functions as an antenna for SXM composed of a patch antenna in the illustrated example. The second antenna part 2413 is an antenna corresponding to the second frequency band in the same manner as the first antenna part 12 of the in-vehicle antenna device 10 and functions as a part of an antenna for the AM / FM band in this example. Note that the first antenna unit 2412 may be not only an antenna for SXM, but also an antenna for DTTV band, an antenna for GNSS, or an antenna for V2X. Also, the planar antenna means an antenna having a planar portion, and includes, for example, a planar antenna, an antenna formed by a microstrip line, a patch antenna, etc., and the antenna types such as a dipole and a monopole are not limited. With such a configuration, the first antenna unit region 2401 functions as a planar antenna unit corresponding to the first frequency band, and the second antenna unit region 2402 functions as an antenna unit corresponding to AM / FM which is the second frequency band.

[0072] As shown in the figure, the length of the first antenna unit region 2401 in a side view is the length in the left-right direction in the figure, that is, the X-axis direction. Specifically, this length is the maximum length including the first antenna unit 2412, the first circuit board 2416A, the cylindrical conductive base 2419A, and the flat conductive base 2420A that constitute the first antenna unit region 2401. As shown in the figure, this length is determined by the left end and the right end of the conductive base 2420A. The length of the first antenna unit region 2401 in the up-down direction, that is, the Z-axis direction, is the maximum length including the first antenna unit 2412 and the like that constitute the first antenna unit region 2401, and is determined by the lower end of the conductive base 2420A and the upper end of the first antenna unit 2412 as shown in the figure. The length of the first antenna unit region 2401 in the depth direction of the paper surface, that is, the Y-axis direction, is the maximum length including the first antenna unit 2412 and the like that constitute the first antenna unit region 2401. In this example, although not shown in the figure, it is determined by the maximum length of the first circuit board 2416A in the Y-axis direction.

[0073] The length of the second antenna unit region 2402 in a side view is the length in the left - right direction in the figure, that is, the X - axis direction. Specifically, this length is the maximum length including the second antenna part 2413, the second circuit board 2416B, the cylindrical conductive base 2419B, and the flat - plate - shaped conductive base 2420B that constitute the second antenna unit region 2402, and is defined by the left end and the right end of the second antenna part 2413 as shown in the figure. The length of the second antenna unit region 2402 in the up - down direction, that is, the Z - axis direction, is the maximum length including the second antenna part 2413 and the like that constitute the second antenna unit region 2402, and is defined by the lower end of the conductive base 2420B and the upper end of the second antenna part 2413 as shown in the figure. The length of the second antenna unit region 2402 in the depth direction of the paper surface, that is, the Y - axis direction, is the maximum length including the second antenna part 2413 and the like that constitute the second antenna unit region 2402. In this example, although not shown in the figure, it is defined by the maximum length of the second circuit board 2416B in the Y - axis direction.

[0074] In the first antenna unit region 2401 and the second antenna unit region 2402 shown in FIG. 25, a part of the region of the first antenna unit region 2401 and a part of the region of the second antenna unit region 2402 overlap in any of the top view, side view, and front view. The same applies to FIGS. 26 - 28 below. Note that neither the resin base 2418 nor the attachment part 2417 is included in either the first antenna unit region 2401 or the second antenna unit region 2402.

[0075] FIG. 26 shows an in - vehicle antenna device 70 as a second modification. The in - vehicle antenna device 70 does not have a resin base. Also, in the in - vehicle antenna device 60, separate conductive bases such as the conductive base 2420A and the conductive base 2420B were used, but in the in - vehicle antenna device 70, instead of these, a common flat - plate - shaped conductive base 2420 for the first circuit board 2416A and the second circuit board 2416B is used. Other configurations are the same as those of the in - vehicle antenna device 60.

[0076] As shown in the figure, mounting portion 2417 is provided so that its left end substantially coincides with the left end of second circuit board 2416B in side view. The length of first antenna unit area 2401 in side view is the length in the left-right direction in the figure, i.e., the length in the X-axis direction. More specifically, this length is the maximum length including the first antenna unit 2412, first circuit board 2416A, cylindrical conductive base 2419A, and the portion of flat conductive base 2420 that contacts mounting portion 2417, which constitute first antenna unit area 2401. As shown in the figure, this length is determined by the left end of conductive base 2420 and the right end of mounting portion 2417.

[0077] The reason why the length of first antenna unit region 2401 in side view includes the portion that contacts mounting portion 2417 of flat conductive base 2420 will be explained. When the antenna and circuit are operating, high-frequency current also flows in the ground portion of the circuit board (e.g., the ground pattern) and the earth portion of the conductive base. If the earth portion of the conductive base is connected to the vehicle roof or the like via a mounting portion, high-frequency current also flows between the conductive base and the mounting portion, affecting other antenna units. For this reason, the antenna unit area is defined as the length of the first antenna unit area 2401 in a side view, including the portion that contacts the mounting portion 2417 of the flat conductive base 2420. For example, if the ground portion of the conductive base 2420 is connected to the vehicle roof or the like via the mounting portion 2417, the high-frequency current flows from the first antenna unit area 2401 toward the mounting portion 2417 and reaches the vehicle roof. The mounting portion 2417 is electrically coupled to the vehicle roof and is sufficiently grounded. Therefore, the high-frequency current in the first antenna unit area 2401 does not flow rearward of the mounting portion 2417.

[0078] The length of the first antenna unit area 2401 in the vertical direction, i.e., in the Z-axis direction, is the maximum length including the first antenna section 2412, first circuit board 2416A, cylindrical conductive base 2419A, and the portion of flat conductive base 2420 that contacts mounting section 2417, which constitute the first antenna unit area 2401, and is determined by the lower end of conductive base 2420 and the upper end of first antenna section 2412 as shown in the figure. The length of the first antenna unit area 2401 in the depth direction of the paper, i.e., in the Y-axis direction, is the maximum length including the first antenna part 2412, first circuit board 2416A, cylindrical conductive base 2419A, and the part of flat conductive base 2420 that contacts mounting part 2417, which constitute the first antenna unit area 2401, and in this example, although not shown, is determined by the maximum length of first circuit board 2416A in the Y-axis direction.

[0079] Similarly, the length of the second antenna unit region 2402 in a side view is determined by the left and right ends of the second antenna portion 2413 in the left-right direction (X-axis direction) in the figure, and by the lower end of the conductive base 2420 and the upper end of the second antenna portion 2413 in the up-down direction (Z-axis direction). Furthermore, the length of second antenna unit area 2402 in the depth direction of the paper, that is, in the Y-axis direction, is determined by the maximum length of second circuit board 2416B in the Y-axis direction, although this is not shown. The attachment portion 2417 is not included in either the first antenna unit area 2401 or the second antenna unit area 2402.

[0080] FIG. 27 shows an in-vehicle antenna device 80 as a third modified example. In the in-vehicle antenna device 80, the right end of the mounting portion 2417 is aligned with the right end of the conductive base 2420 in a side view, and the other configurations are the same as those of the in-vehicle antenna device 70. As shown in the figure, the length of the first antenna unit area 2401 in a side view is the length in the left-right direction in the figure, i.e., the length in the X-axis direction. More specifically, this length is the maximum length including the first antenna section 2412, first circuit board 2416A, cylindrical conductive base 2419A, and the portion of the flat conductive base 2420 that contacts the mounting portion 2417, which constitute the first antenna unit area 2401. As shown in the figure, this length is determined by the left end of the conductive base 2420 and the right end of the mounting portion 2417.

[0081] The length of the first antenna unit area 2401 in the vertical direction, i.e., in the Z-axis direction, is the maximum length including the first antenna section 2412 and other components that make up the first antenna unit area 2401, and is determined by the lower end of the conductive base 2420 and the upper end of the first antenna section 2412 as shown in the figure. The length of the first antenna unit area 2401 in the depth direction of the paper, i.e., in the Y-axis direction, is the maximum length including the first antenna section 2412 and the like that make up the first antenna unit area 2401. In this example, although not shown, this is determined by the maximum length of the first circuit board 2416A in the Y-axis direction.

[0082] The length of second antenna unit area 2402 in a side view is the length in the left-right direction in the figure, i.e., the length in the X-axis direction. In detail, this length is the maximum length including second antenna section 2413, second circuit board 2416B, cylindrical conductive base 2419B, and flat conductive base 2420B that make up second antenna unit area 2402, and is determined by the left and right ends of second antenna section 2413 as shown in the figure. The length of the second antenna unit region 2402 in the vertical direction, that is, the Z-axis direction, is the maximum length including the second antenna part 2413 and the like that constitute the second antenna unit region 2402, and is defined by the lower end of the conductive base 2420 and the upper end of the second antenna part 2413 as shown in the figure. Note that the attachment part 2417 is not included in either the first antenna unit region 2401 or the second antenna unit region 2402.

[0083] FIG. 28 shows an in-vehicle antenna device 90 as a fourth modification. Compared with the in-vehicle antenna device 70 of the second modification, the in-vehicle antenna device 90 is different in that the first antenna part 2412 and the second antenna part 2413 are provided on a common circuit board 2416. Further, the circuit board 2416 is disposed in a cylindrical conductive base 2419. The cylindrical conductive base 2419 is provided on a flat conductive base 2420. Other configurations are the same as those of the in-vehicle antenna device 70. Similar to the in-vehicle antenna device 70, in the in-vehicle antenna device 90, the length of the first antenna unit region 2401 in a side view is the length in the horizontal direction in the figure, that is, the X-axis direction. Specifically, this length is the maximum length including the portion of the first antenna part 2412 that constitutes the first antenna unit region 2401 and contacts the attachment part 2417 of the flat conductive base 2420. As shown in the figure, this length is defined by the left end of the conductive base 2420 and the right end of the attachment part 2417.

[0084] The length of the first antenna unit region 2401 in the vertical direction, that is, the Z-axis direction, is the maximum length including the first antenna part 2412 and the like that constitute the first antenna unit region 2401, and is defined by the lower end of the conductive base 2420 and the upper end of the first antenna part 2412 as shown in the figure. The length of the first antenna unit region 2401 in the depth direction of the paper surface, that is, the Y-axis direction, is the maximum length including the first antenna part 2412 and the circuit board 2416 that constitute the first antenna unit region 2401. In this example, although not shown in the figure, it is determined by the maximum length of the circuit board 2416 in the Y-axis direction. In the side view of the second antenna unit area 2402, the left - right direction (X - axis direction) in the figure is defined by the left end and the right end of the second antenna part 2413, and the up - down direction (Z - axis direction) is defined by the lower end of the conductive base 2420 and the upper end of the second antenna part 2413. Although not shown in the figure, the length of the first antenna unit area 2401 in the depth direction (Y - axis direction) of the paper surface is determined by the maximum length of the circuit board 2416 in the Y - axis direction. Note that the attachment part 2417 is not included in either the first antenna unit area 2401 or the second antenna unit area 2402.

[0085] Hereinafter, the characteristics common to the first to fourth modified examples will be described. In these modified examples, in any case, the first antenna part 2412 and the second antenna part 2413 have a positional relationship where they do not overlap with each other. That is, the antenna elements do not overlap. However, a part of the area of the first antenna unit area 2401 and a part of the area of the second antenna unit area 2402 overlap in any of the top view, side view, and front view. By configuring such that a part of the area of the first antenna unit area 2401 and a part of the second antenna unit area 2402 overlap in the top view, side view, and front view, the exclusive area of these areas can be reduced, the design of the in - vehicle antenna device 60 can be miniaturized, and the internal area of the case design can be effectively utilized.

[0086] Note that a portion of the first antenna unit region 2401 and a portion of the second antenna unit region 2402 do not need to overlap in all of the top, side, and front views, and may overlap in at least one of these views. Both the first antenna unit region 2401 and the second antenna unit region 2402 may be triangular or trapezoidal in top view. In particular, in the case of a shark fin antenna (SF antenna), its shape becomes thinner toward the tip when viewed from above. Therefore, by making the components of at least one of the first antenna unit region 2401 and the second antenna unit, such as a circuit board, triangular or trapezoidal and tapering the tip side to match the shape of the SF antenna, the internal region can be effectively utilized. In this case, the first antenna unit region 2401 is located further forward in the vehicle-mounted antenna device than the second antenna unit region 2402 and is located in a tapered position, so by making the components of the first antenna unit region 2401 triangular or trapezoidal, the internal region can be effectively utilized.

[0087] FIG. 29 shows in-vehicle antenna device 70-1 in which first circuit board 2416A is a three-point type in the second modified example shown in FIG. 26. As described above, in the first to fourth modified examples, circuit board 2416A is a four-point type. However, first circuit board 2416A may also be a three-point type. In the example of FIG. 29, three cylindrical conductive bases 2419A are provided on flat conductive base 2420A, and first circuit board 2416A is provided on these three cylindrical conductive bases 2419A. This figure shows that by making the tapered front side of first circuit board 2416A one point in accordance with the shape of the SF antenna, the front area inside the case can be reduced, thereby improving design. In addition, the first antenna unit region 2401 and the second antenna unit region 2402 in the schematic plan view and schematic side view of FIG. 29 correspond to the first antenna unit region 2401 and the second antenna unit region 2402 which are rectangular parallelepipeds with the maximum dimensions in FIG. 26, and their regions are similarly defined. Although not shown in FIG. 26, in the plan view of FIG. 29, it is shown that the length of the first antenna unit region 2401 in the Y-axis direction is defined by the maximum length of the first circuit board 2416A in the Y-axis direction. Also, in FIG. 29, it is shown that a part of the region of the first antenna unit region 2401 and a part of the region of the second antenna unit region 2402 overlap in any of the top view, side view, and front view.

[0088] FIG. 30 shows an in-vehicle antenna device 70-2 in which a non-powered element 2430 is arranged on the first antenna unit 2412 in the second modification. Thus, a configuration in which a non-powered element is provided on the first antenna unit 2412 may be adopted. Similarly, a configuration in which a non-powered element is provided on the second antenna unit 2413 may be adopted. In addition, the first antenna unit region 2401 and the second antenna unit region 2402 in the schematic plan view and schematic side view of FIG. 30 correspond to the first antenna unit region 2401 and the second antenna unit region 2402 which are rectangular parallelepipeds with the maximum dimensions in FIG. 26, and their regions are similarly defined. In the plan view of FIG. 30 as well, it is shown that the length of the first antenna unit region 2401 in the Y-axis direction is defined by the maximum length of the first circuit board 2416A in the Y-axis direction. Also, in FIG. 30, it is shown that a part of the region of the first antenna unit region 2401 and a part of the region of the second antenna unit region 2402 overlap in any of the top view, side view, and front view.

[0089] The characteristics of the first modification example will be described below. The conductive base is a component electrically connected to the ground portion of the circuit board, and when the antenna operates, current flows through the ground portion of the circuit board to the conductive base. Currents are flowing through the respective conductive bases 2416A, etc. in the first antenna unit region 2401 and the second antenna unit region 2402 in FIG. 25. Here, in order to reduce the influence on other media, it is desirable that the first antenna unit region 2401 and the second antenna unit region 2402 have separate conductive bases. Also, usually, using two conductive bases each having an area approximately half of the area of the large conductive base has an advantage in terms of cost compared to using one large conductive base.

[0090] As described above, in the first modification example, the conductive bases 2419A and 2420A in the first antenna unit region 2401 and the conductive bases 2419B and 2420B in the second antenna unit region 2402 are separate from each other. Therefore, the above-described merits such as reduced influence on other media and being advantageous in terms of cost can be obtained. Note that either die-cast or a plate may be used for the conductive base. Also, when the first antenna unit region 2401 is an antenna unit for SXM or for the DTTV band, the conductive base does not have to be directly connected to the vehicle roof.

[0091] On the other hand, in the second to fourth modification examples, the first antenna unit region 2401 and the second antenna unit region 2402 are configured as a common base connected by a common conductive base 2420. In these cases, since current flows to the vehicle roof, the region up to the attachment portion 2417 becomes the region constituting the antenna.

[0092] Next, the characteristics common to the first modification example, the second modification example, and the third modification example will be described. In these modification examples, the first antenna unit area 2401 and the second antenna unit area 2402 are configured to use separate circuit boards, namely, the first circuit board 2416A and the second circuit board 2416B. Generally, using two circuit boards each having an area approximately half of that of a single large circuit board has cost advantages over using one large circuit board. Therefore, the cost of the substrate can be reduced by using separate substrates. Also, in the first circuit board 2416A and the second circuit board 2416B, their respective heights can be freely set. In this case, it is also possible to suppress mechanical and electrical interference by individually adjusting the heights of the circuit boards.

[0093] Note that in the fourth modification example, a common circuit board 2416 is used for the first antenna unit area 2401 and the second antenna unit area 2402. In the case of using one substrate in this way, the number of components can be reduced, the substrate assembly work can be completed in one go, and the advantage of simplifying the manufacturing process can be obtained. Also, it is preferable to bring the planar antenna closer to the vehicle roof so that it has directivity upward from the horizontal plane. Here, in the first modification example, the second modification example, and the third modification example, the first circuit board 2416A is arranged at a lower position than the second circuit board 2416B. That is, the substrate on the planar antenna side is arranged lower than the substrate on the non-planar antenna side, which is also advantageous in terms of directivity.

[0094] <Operational effects according to the embodiment> The in-vehicle antenna device described in the above embodiment includes an antenna base 18, an antenna case 11 that forms an accommodation space together with this antenna base 18, a first antenna unit 12 accommodated in the accommodation space and corresponding to a first frequency band, and a second antenna unit 13 accommodated in the accommodation space and corresponding to a second frequency band lower than the first frequency band. By further adopting the following configuration, various operational effects can be achieved. (1) The first antenna section 12 and the second antenna section 13 each include one or more elements. A part of the elements of the first antenna section 12 overlaps with a part of the elements of the second antenna section 13 in side view and / or top view. A limiting circuit that restricts the passage of signals of frequencies other than the frequency band corresponding to the antenna section is connected to the power feeding section of at least one of the first antenna section 12 and the second antenna section 13. That is, at least a part of the region (for example, region 211) of the first antenna section 12 and at least a part of the region (for example, region 212) of the second antenna section 13 overlap, and a limiting circuit (for example, limiting circuit 31) that restricts the passage of signals of frequencies other than the frequency band corresponding to the antenna section is connected to the power feeding section of at least one of the first antenna section 12 and the second antenna section 13. According to this configuration, the difference between the maximum value and the minimum value of the gain in the first frequency band becomes smaller, and the bandwidth of the usable frequencies can be broadened. Also, these antenna sections 12, 13 can be arranged close to each other in a limited space while suppressing a decrease in the antenna characteristics of the first antenna section 12 and the second antenna section 13. Therefore, miniaturization of the antenna device becomes easy.

[0095] (2) A configuration including an element having one or more bent portions that bend the first antenna section 12 in the width direction in top view, for example, the third element 123. According to this configuration, without changing the electrical length of the elements of the first antenna section 12, the total value of the lengths in the longitudinal direction can be made even shorter. (3) A configuration in which the elements of the second antenna section 13 act as capacitive loading elements that capacitively load the elements of the first antenna section 12. It is well known that the elements of the second antenna section 13 act as capacitive loading elements for an AM / FM band coil, but it is not common for the elements of the second antenna section 13 to capacitively load the elements of the first antenna section 12. According to this configuration, the electrical antenna size can be increased without changing the physical length of the elements of the first antenna section 12. (4) A configuration in which a plurality of gaps are formed in the elements of the second antenna unit 13. According to this configuration, for example, by simply fitting a protrusion or the like of an insulator holder (not shown) fixed to the antenna case 11 or the antenna base 18 into the gap, the second antenna unit 13 can be attached, and in addition, the electrical length of the elements of the second antenna unit 13 can be easily adjusted. (5) A configuration in which part or all of the elements of the second antenna unit 13 are a plate-shaped conductor having a fractal shape, a meander shape, or a shape including a part of these and having a gap. According to this configuration, the fine adjustment of the electrical length and antenna characteristics becomes even easier.

[0096] (6) A configuration in which a limiting circuit (for example, the limiting circuit 31) that limits the passage of the other antenna unit in the corresponding frequency band is connected to the power supply unit of the first antenna unit 12 (for example, the first element 121) or the second antenna unit 13 (for example, the connection element 133). According to this configuration, even if the elements of the two antenna units for different frequency bands are arranged close to each other so that a part of them overlaps, interference is prevented and a decrease in gain is suppressed. (7) A configuration in which the limiting circuit is a filter that limits the passage of at least one of the signal in the second frequency band, the signal of the harmonic component of the second frequency band, and the noise component emitted from elements other than the limiting circuit at the power supply unit of the first antenna unit 12. In this configuration, a decrease in gain in the first frequency band and the second frequency band is suppressed. (8) A configuration in which the limiting circuit is a filter that limits the passage of at least one of the signal in the first frequency band, the signal of the harmonic component of the second frequency band, and the noise component emitted from elements other than the limiting circuit at the power supply unit of the second antenna unit 13. In this configuration, a decrease in gain in the first frequency band and the second frequency band is suppressed.

[0097] (9) The first inductor L1 is connected to the power supply section of the second antenna section 13, and a configuration in which a limiting circuit 31 or the like is the second inductor L2 connected in series with the first inductor L1. According to this configuration, for example, a limiting circuit can be realized by utilizing the self-resonance of an inductive element having a coil structure, so that the number of components of the in-vehicle antenna device 10 or the like can be reduced. (10) A configuration in which the first inductor L1 includes a first helical element, and the second inductor L2 includes a second helical element formed of a linear conductor integral with the first helical element. According to this configuration, a helical element that cooperates with the second antenna section 13 and a limiting circuit 31 or the like can be realized with only one linear conductor, so that the manufacturing process of the in-vehicle antenna device 10 or the like is simplified. (11) A configuration in which the diameter of the first helical element and the diameter of the second helical element are different from each other. According to this configuration, the first helical element that cooperates with the second antenna section 13 and the second helical element that operates as a limiting circuit 31 or the like can be distinguished, so that the antenna design work is simplified compared to the case where the diameters are the same. (12) A configuration in which the pitch between conductors of the first helical element and the pitch between conductors of the second helical element are different from each other. According to this configuration, the first helical element that cooperates with the second antenna section 13 and the second helical element that operates as a limiting circuit 31 or the like can be distinguished, so that the antenna design work is simplified compared to the case where the pitch between conductors is the same. (13) A configuration in which the coil axes, which are the central axes of the first helical element and the second helical element respectively, intersect. According to this configuration, in addition to avoiding the coupling between the helical elements, the height in the Z direction can be made lower than in the case where the coil axes are the same.

[0098] (14) A configuration in which the first helical element and the second helical element are wound around the same insulator. According to this configuration, the manufacturing process of the in-vehicle antenna device 10 or the like is simplified, and it is possible to save the installation space of each antenna section 12, 13 on the antenna base 18. Also, the degree of freedom in the installation position of the insulator can be increased. Furthermore, the number of components of the in-vehicle antenna device can be reduced, and it is also possible to reduce the length in the front-rear direction and the space in the height direction. (15) The circuit board 16B is arranged further forward than the front end of the second antenna portion 13, and there is no metal member directly below the capacitive loading element which is the second antenna portion 13. For example, the entire second antenna portion 13 exists on the circuit board 16B, and the second antenna portion 13 does not exist on the ground conductor or other metal plate. According to this configuration, stray capacitance does not occur in the second antenna portion 13, so the gain in the AM / FM band can be improved. (16) A configuration in which the circuit board 16A for the DTTV band and the circuit board 16B for the AM / FM band are provided on a single board. According to this configuration, by using a single circuit board, it is possible to reduce the number of components such as the in-vehicle antenna device 10. (17) A configuration in which the first inductor L1 and the second inductor L2 are configured separately. According to this configuration, the first inductor L1 and the second inductor L2 can be retrofitted respectively, added appropriately according to the installation environment, or the inductance of each inductor L1, L2 can be changed appropriately. (18) A configuration in which the second inductor L2 is wound tightly. According to this configuration, it is possible to adjust the second inductor L2 to the self-resonant frequency of the DTTV band. The second inductor L2 can ensure better isolation in a tightly wound configuration than in a loosely wound configuration.

[0099] (19) A configuration in which at least a part of the region of the first antenna portion and at least a part of the region of the second antenna portion overlap in any of the top view, side view, and front view. According to this configuration, the difference between the maximum value and the minimum value of the gain in the first frequency band is reduced, and the usable frequency can be broadened. Also, while suppressing a decrease in the antenna characteristics of the first antenna portion 12 and the second antenna portion 13, these antenna portions 12, 13 can be arranged close to each other in a limited space. Therefore, miniaturization of the antenna device becomes easy. (20) A configuration in which at least one of the first antenna section and the second antenna section includes an element having one or more bent portions bent in a predetermined direction or a curved portion curved in a predetermined direction. According to this configuration, without changing the electrical length of the element of at least one of the first antenna section and the second antenna section, the total value of the longitudinal length can be further shortened.

[0100] In the first embodiment and the second embodiment, the in-vehicle antenna device can be mounted not only on a vehicle but also on a moving body equivalent to a vehicle, such as a ship or a train, excluding those carried by a person like a mobile terminal.

Claims

1. An antenna base attached to a predetermined part of a vehicle, an antenna case that forms an accommodation space together with the antenna base, a first antenna part accommodated in the accommodation space and corresponding to a first frequency band, a second antenna part accommodated in the accommodation space and corresponding to a second frequency band lower than the first frequency band, and at least a part of the region of the first antenna part and at least a part of the region of the second antenna part overlap each other, a limiting circuit that restricts the passage of signals of frequencies other than the frequency band corresponding to the antenna part is connected to the power supply part of at least one of the first antenna part and the second antenna part, a first inductor is connected to the power supply part, the limiting circuit is a second inductor connected in series to the first inductor, the first inductor includes a first helical element, and the second inductor includes a second helical element formed of a linear conductor integral with the first helical element, the central axes of the first helical element and the second helical element intersect each other, an in-vehicle antenna device.

2. In any one of a top view, a side view, and a front view, at least a part of the region of the first antenna part and at least a part of the region of the second antenna part overlap each other, The in-vehicle antenna device according to claim 1.

3. At least one of the first antenna part and the second antenna part includes an element having one or more bent portions bent in a predetermined direction or a curved portion curved in a predetermined direction, The in-vehicle antenna device according to claim 1 or 2.

4. The limiting circuit is a filter that restricts the passage of at least one of a signal in the second frequency band, a signal of a harmonic component of the second frequency band, and a noise component emitted from elements other than the limiting circuit in the power supply part of the first antenna part, The in-vehicle antenna device according to any one of claims 1 to 3.

5. The limiting circuit is a filter that restricts the passage of at least one of a signal in the first frequency band, a signal of a harmonic component of the second frequency band, and a noise component emitted from elements other than the limiting circuit in the power supply part of the second antenna part, The in-vehicle antenna device according to any one of claims 1 to 4.

6. The diameter of the first helical element and the diameter of the second helical element are different from each other, The in-vehicle antenna device according to any one of claims 1 to 5.

7. The pitch between the conducting wires of the first helical element and the pitch between the conducting wires of the second helical element are different from each other. The in-vehicle antenna device according to any one of claims 1 to 6. **Claim 8** The first helical element and the second helical element are wound around the same insulator. The in-vehicle antenna device according to any one of claims 1 to 7. **Claim 9** A first inductor is connected to the power supply section of the second antenna section. The limiting circuit is one or more reactance elements connected in series with the first inductor. The in-vehicle antenna device according to any one of claims 1 to 8.

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