Vehicular glass antenna

Abstract

Provided is a vehicular glass antenna usable in an electric vehicle and constituting a diversity antenna less susceptible to electromagnetic noise. A vehicular glass antenna (A) for an electric vehicle (1) driven by a driving force from a motor receiving electric power from a battery includes: a glass sheet (2) separating inside and outside of the electric vehicle (1); and a first antenna element (10) fixed to a sheet surface(2a) of the glass sheet (2) and capable of receiving radio waves propagating through air outside the electric vehicle (1). The first antenna element (10) constitutes a diversity antenna in cooperation with a second antenna element (20) disposed on the outside of the electric vehicle (1) via a shielding section (7) capable of blocking electromagnetic noise emitted from a transformer disposed between the battery and a device receiving electric power from the battery, the second antenna element (20) being capable of receiving the radio waves.

Description

Technical Field

[0001] The present invention relates to a vehicular glass antenna.Background Art

[0002] Automobiles include antennas for reception of broadcast waves and for transmission and reception for various systems. Since the automobiles travel, the reception conditions of these radio waves also change constantly. Under such circumstances, in order to stabilize the reception conditions of radio waves, a diversity antenna for receiving radio waves with a plurality of antennas may be used.

[0003] Patent Literature 1 discloses a vehicular glass antenna including two antennas in a margin space present above a defogger on a rear window of an automobile. Even when the margin space is narrow, it is possible to achieve favorable diversity reception of FM broadcast waves. This vehicular glass antenna is constituted by two antennas for FM broadcast wave, disposed on the margin space above the defogger of the rear window of the automobile. Each of the antennas includes a power supply unit disposed on an upper end of the rear window, a vertical line connected to the power supply unit and extending downward, and a horizontal line connected to a lower end of the vertical line. The power supply units of the antennas are away from each other in the right-left direction. Each of the horizontal lines of the two antennas is disposed close to the uppermost heating horizontal line of the defogger and is capacitively coupled to the uppermost heating horizontal line. The vertical line or the power supply unit of at least one of the two antennas is connected to at least one auxiliary line for directional pattern adjustment.

[0004] Patent Literature 2 discloses a vehicular glass antenna including separate antennas for AM broadcast wave and for FM broadcast wave, disposed in a margin space of a defogger on a rear window of an automobile. The vehicular glass antenna can receive FM broadcast waves with high gain in particular and has an excellent directional characteristic. This antenna includes: an AM broadcast wave antenna including a plurality of horizontal lines spaced apart from each other, and at least two vertical lines perpendicular to the horizontal lines and spaced apart from each other, and having an AM feed point at a position set via a lead wire from the uppermost horizontal line; and an FM broadcast wave antenna having two FM feed points disposed on the right and left sides of the AM feed point and extending clockwise and counterclockwise from the two FM feed points along part of the outermost periphery of the AM broadcast wave antenna. The FM broadcast wave antenna includes a pair of right and left second vertical lines extended to have different lengths, so that the FM broadcast wave antenna can perform diversity reception effectively.

[0005] Patent Literature 3 describes a vehicular glass antenna (an automotive diversity glass antenna in Patent Literature 3) suitable for AM broadcast, FM broadcast, and TV broadcast reception.

[0006] The glass antenna includes a first antenna conductor capacitively coupled to a defogger on a rear window of an automobile, and a second antenna conductor not capacitively coupled to the defogger. The second antenna conductor is connected to the defogger by a capacitor selected to exhibit high impedance in the AM broadcast band, and diversity reception is performed by the first antenna conductor and the second antenna conductor.Citation ListPatent Literature

[0007] Patent Literature 1: Japanese Unexamined Patent Application Publication No. 2012-248981 Patent Literature 2: Japanese Unexamined Patent Application Publication No. 2010-109958 Patent Literature 3: Japanese Unexamined Patent Application Publication No. 9-130120 Summary of InventionTechnical Problem

[0008] These days, automobiles equipped with a motor as a travel drive source (a hybrid electric vehicle (HEV), a plug-in hybrid electric vehicle (PHEV), a battery electric vehicle (BEV), a fuel cell electric vehicle (FCEV), and the like, hereinafter also referred to as an "electric vehicle") are increasing in number. In an electric vehicle, a high-voltage battery is arranged inside the electric vehicle, and a voltage for operating various in-vehicle electronic devices is obtained by a DC-DC converter. However, electromagnetic noise generated during voltage conversion hinders signal reception by a diversity antenna. In the vehicular glass antennas described in Patent Literatures 1 to 3, two antennas for performing diversity reception are disposed on the rear window of the automobile.

[0009] From the viewpoint of processing a received signal, recent diversity antennas employ a phase diversity method in which an interference wave is derived from the difference between received signals of two antennas and subtracted from the received signals of the two antennas. Accordingly, the performance difference between the two antennas for diversity reception, namely the difference in received-signal strength, is preferably not excessively large. In the meantime, it is not preferable that the distance between the two antennas be too short. When the distance is too short, the difference between the received signal and the interfering wave at each of the antennas decreases, which may make the calculation of the interfering wave difficult.

[0010] In view of this, there is a need for vehicular glass antennas usable in electric vehicles and constituting diversity antennas less susceptible to electromagnetic noise.Solution to Problem

[0011] One aspect of a vehicular glass antenna according to the present invention is a vehicular glass antenna for an electric vehicle driven by a driving force from a motor receiving electric power from a battery. The vehicular glass antenna includes: a glass sheet separating inside and outside of the electric vehicle; and a first antenna element fixed to a sheet surface of the glass sheet and capable of receiving radio waves propagating through air outside the electric vehicle. The first antenna element constitutes a diversity antenna in cooperation with a second antenna element disposed on the outside of the electric vehicle via a shielding section capable of blocking electromagnetic noise emitted from a transformer disposed between the battery and a device receiving electric power from the battery, the second antenna element being capable of receiving the radio waves.

[0012] In the present aspect, the vehicular glass antenna includes: the glass sheet separating inside and outside of the electric vehicle; and the first antenna element capable of receiving radio waves propagating through the air outside the electric vehicle. Besides, the first antenna element constitutes a diversity antenna in cooperation with the second antenna element disposed on the outside of the electric vehicle via the shielding section capable of blocking electromagnetic noise emitted from the transformer disposed between the battery and the device receiving electric power from the battery, the second antenna element being capable of receiving the radio waves. Thus, the first antenna element fixed to the sheet surface of the glass sheet constitutes the diversity antenna in cooperation with the second antenna element that receives radio waves via the shielding section capable of blocking electromagnetic noise. As a result, it is possible to suppress the influence of electromagnetic noise from the transformer of the electric vehicle and to stably receive radio waves.

[0013] In another aspect of the vehicular glass antenna according to the present invention, the shielding section may be made of a metal plate.

[0014] In this aspect, since the shielding section is made of metal, the shielding section can surely block electromagnetic noise emitted from the transformer, thereby making it possible to suppress the influence of the electromagnetic noise on the second antenna element.

[0015] In another aspect of the vehicular glass antenna according to the present invention, the shielding section may be a metal exterior panel of the electric vehicle.

[0016] In this aspect, since the shielding section is a metal exterior panel of the electric vehicle, it is not necessary to provide an extra constituent for blocking electromagnetic noise, so that the electric vehicle can be manufactured at a low cost.

[0017] In another aspect of the vehicular glass antenna according to the present invention, the diversity antenna may be used for a phase diversity receiving method.

[0018] In this aspect, in a case where the diversity antenna employs the phase diversity receiving method, even in a place where multipath fading easily occurs, such as an urban canyon, for example, it is possible to stably receive radio waves.

[0019] In another aspect of the vehicular glass antenna according to the present invention, the radio waves may include a frequency band for use in FM radio broadcasting.

[0020] In this aspect, it is possible to stably receive FM radio broadcasting.

[0021] In another aspect of the vehicular glass antenna according to the present invention, the second antenna element may include a power supply unit and an element, and the power supply unit and the element may be disposed in this order in a direction away from the shielding section.

[0022] In this aspect, it is possible to improve the performance of the second antenna element and to stably receive radio waves.

[0023] In another aspect of the vehicular glass antenna according to the present invention, the first antenna element may be disposed at a position where the first antenna element is capacitively couplable to the metal exterior panel.

[0024] In this aspect, it is possible to change the reception performance of the first antenna element by changing the coupling capacitor between the first antenna element and the metal exterior panel.

[0025] In another aspect of the vehicular glass antenna according to the present invention, the first antenna element may have a reception gain equivalent to a reception gain of the second antenna element.

[0026] In this aspect, since the first antenna element and the second antenna element have equivalent reception gains, it is possible to exhibit the performance of the diversity antenna and to stably receive radio waves.

[0027] In another aspect of the vehicular glass antenna according to the present invention, the glass sheet may have an outer edge fixed to cover an open region in the metal exterior panel of the electric vehicle, and the first antenna element may include a horizontal element disposed within a separation distance of 20 mm from an opening edge of the open region in a direction perpendicular to a right-left direction of the electric vehicle and along the sheet surface of the glass sheet.

[0028] In this aspect, when the horizontal element is disposed at a position within the separation distance of 20 mm in a direction perpendicular to the right-left direction of the electric vehicle and along the sheet surface of the glass sheet, the first antenna element can have a reception gain equivalent to that of the second antenna element, thereby making it possible to stably receive radio waves.

[0029] In another aspect of the vehicular glass antenna according to the present invention, the horizontal element may be disposed closer to a center of the glass sheet than the opening edge of the open region.

[0030] In this aspect, when the horizontal element is disposed closer to the center of the glass sheet than the opening edge of the open region, the first antenna element can have a reception gain equivalent to that of the second antenna element, thereby making it possible to stably receive radio waves.

[0031] In another aspect of the vehicular glass antenna according to the present invention, the horizontal element may be disposed closer to the outer edge of the glass sheet than the opening edge of the open region.

[0032] In the present embodiment, when the horizontal element is disposed closer to the outer edge of the glass sheet than the opening edge of the open region, the first antenna element can have a reception gain equivalent to that of the second antenna element, thereby making it possible to stably receive radio waves.

[0033] In another aspect of the vehicular glass antenna according to the present invention, the glass sheet may be a rear window of the electric vehicle, and the shielding section may be a roof of the electric vehicle.

[0034] In this aspect, when the glass sheet is the rear window of the electric vehicle, and the shielding section is the roof of the electric vehicle, the first antenna element does not disturb the travel of the electric vehicle, and any special configuration is required for the shielding section to block electromagnetic noise. Hereby, it is possible to stably receive radio waves and to manufacture the electric vehicle at a low cost.

[0035] In another aspect of the vehicular glass antenna according to the present invention, the first antenna element may be disposed on a lower side of the rear window in an up-down direction of the rear window.

[0036] In this aspect, since the first antenna element and the second antenna element can be spaced apart from each other with an appropriate distance, it is possible to exhibit the performance of the diversity antenna and to stably receive radio waves.Brief Description of Drawings

[0037] Fig. 1 is a side view illustrating an electric vehicle using a vehicular glass antenna according to the present embodiment; Fig. 2 is a front view illustrating the vehicular glass antenna; Fig. 3 is a sectional view taken along a line III-III in Fig. 2; Fig. 4 is a front view illustrating another vehicular glass antenna; Fig. 5a is a front view illustrating a configuration of another vehicular glass antenna; Fig. 5b is a graph illustrating a reception gain difference between an antenna element and a shark-fin antenna in a domestic reception frequency band; Fig. 6a is a front view illustrating a configuration of another vehicular glass antenna; Fig. 6b is a front view illustrating a configuration of another vehicular glass antenna; Fig. 6c is a graph showing a reception gain difference between an antenna element and a shark-fin antenna in the domestic reception frequency band; Fig. 7a is a front view illustrating a configuration of another vehicular glass antenna; Fig. 7b is a graph showing a reception gain difference between an antenna element and a shark-fin antenna in the domestic reception frequency band; Fig. 8a is a front view illustrating a configuration of another vehicular glass antenna; and Fig. 8b is a graph showing a reception gain difference between an antenna element and a shark-fin antenna in the domestic reception frequency band. Description of Embodiments

[0038] The following describes embodiments of a vehicular glass antenna according to the present invention in detail with reference the drawings. Note that the following embodiments are just examples to describe the present invention and are not intended to limit the present invention to these embodiments. Accordingly, the present invention can be modified variously without deviating from the gist of the present invention.

[0039] As illustrated in Figs. 1, 2, a vehicular glass antenna A according to the present invention is used for automobiles equipped with a motor 3 as a travel drive source (a hybrid electric vehicle (HEV), a plug-in hybrid electric vehicle (PHEV), a battery electric vehicle (BEV), a fuel cell electric vehicle (FCEV), and the like). Hereinafter, these automobiles are generally referred to as an electric vehicle 1. In the following description, an up-down direction of the electric vehicle 1 is defined as an X-direction, and a right-left direction relative to an advancing direction is defined as a Y-direction. In the X-direction, an upper side of the electric vehicle 1 is defined as an X1-side, and a lower side thereof is defined as an X2-side. In the Y-direction, a right side relative to the advancing direction is defined as a Y1-side, and a light side relative to the advancing direction is defined as a Y2-side.

[0040] The electric vehicle 1 includes a battery 4 configured to supply electric power to the motor 3 as the travel drive source. The battery 4 has an output voltage of several hundreds volts DC. Accordingly, in order to supply electric power from the battery 4 to an in-vehicle electronic device 6 (an example of a device, e.g., a car navigation system, a radio, an audio system) that is provided for the electric vehicle 1 and operates at a low voltage, such as DC 12 V, it is necessary to step down the output of the battery 4 with the use of a DC-DC converter 5 (an example of a transformer). The DC-DC converter 5 emits electromagnetic noise due to switching required for the step-down. The electromagnetic noise may exert an adverse influence when radio waves propagating through the air outside the electric vehicle 1 are received by an antenna provided in the electric vehicle 1. The outside of the electric vehicle 1 indicates an external space opposite to a cabin 1a across a metal exterior panel 7 (a shielding section, an example of a metal plate) of the electric vehicle 1. In the meantime, an internal space including the cabin 1a, opposite to the outside of the electric vehicle 1 across the metal exterior panel 7, is referred to as the inside of the electric vehicle 1.

[0041] As the antenna in the present embodiment, a diversity antenna is used to stably receive radio waves in response to changes in reception conditions of radio waves during traveling of the electric vehicle 1. The diversity antenna of the present embodiment is configured such that the vehicular glass antenna A and a shark-fin antenna 20 (an example of a second antenna element) work together. The diversity antenna employs a phase diversity method that can combine desired waves and remove multipath fading by adjusting the amplitude and phase of radio waves (received signals) received by the vehicular glass antenna A and the shark-fin antenna 20. This can improve the quality of the received signals. The diversity antenna of the present embodiment can receive a frequency band used for FM radio broadcasting in particular. The principle of the diversity antenna employing the phase diversity method is well known, and therefore, its detailed description is omitted herein. Note that, in Figs. 1 to 4, except the shark-fin antenna 20 illustrated in Fig. 3, a transmission line 26 that connects an FM radio receiver included in the in-vehicle electronic device 6 to the vehicular glass antenna A and the shark-fin antenna 20 is not illustrated.

[0042] The vehicular glass antenna A includes a rear window 2 (an example of a glass sheet) of the electric vehicle 1, and an antenna element 10 (an example of a first antenna element) fixed to an inner surface 2a (an example of a sheet surface) of the rear window 2 (see Fig. 3). In order to reduce adverse effects from electromagnetic noise generated from the inside of the electric vehicle 1, the shark-fin antenna 20 is disposed on a roof 7c (a shielding section, an example of a metal plate) formed by a metal exterior panel 7 of the vehicle. This makes it possible to block electromagnetic noise emitted from the DC-DC converter 5, thereby allowing the shark-fin antenna 20 to stably receive radio waves propagating through the air outside the electric vehicle 1.

[0043] As illustrated in Fig. 2, the rear window 2 is attached to the metal exterior panel 7 of the electric vehicle 1 via an adhesive applied to an outer edge 2b of the inner surface 2a facing the inside of the electric vehicle 1. That is, in the rear window 2, light is transmitted through only an inner region 7b (an example of an open region) of a window frame 7a (an example of an opening edge) formed in the metal exterior panel 7. Here, the window frame 7a denotes an outer edge of the inner region 7b of the metal exterior panel 7. That is, in the metal exterior panel 7, the window frame 7a is defined as a boundary to the inner region 7b.

[0044] The antenna element 10 is formed by printing a conductive material such as silver paste printed on the inner surface 2a of the rear window 2. As illustrated in Figs. 2, 3, the antenna element 10 has a linear shape extending along the X-direction and includes a power supply unit 12 and a horizontal electric conductor 14 (an example of a horizontal element) along the X-direction. The power supply unit 12 of the antenna element 10 of the present embodiment is disposed outside a defogging region 2c on the inner surface 2a of the rear window 2 but inside the window frame 7a. The horizontal electric conductor 14 is disposed outside the defogging region 2c on the inner surface 2a of the rear window 2 and also outside the window frame 7a. That is, when the electric vehicle 1 is viewed from its rear side as illustrated in Fig. 2, the horizontal electric conductor 14 of the antenna element 10 is disposed to overlap the metal exterior panel 7. In other words, the horizontal electric conductor 14 of the antenna element 10 is disposed closer to the outer edge 2b of the rear window 2 than the window frame 7a as the outer edge of the inner region 7b.

[0045] In Fig. 3, the antenna element 10 formed on the inner surface 2a of the rear window 2 is spaced apart from the metal exterior panel 7. This is because the thickness of an adhesive layer 8 for bonding the rear window 2 to the metal exterior panel 7 is thicker than the thickness of the antenna element 10. In Fig. 3, the thickness of the antenna element 10 and the thickness of the adhesive layer 8 are illustrated in an exaggerated manner. The actual thickness of the antenna element 10 is approximately 3 µm to 30 µm, and the actual thickness of the adhesive layer 8 is approximately 1 mm to 15 mm.

[0046] The horizontal electric conductor 14 is divided into two. The horizontal electric conductor 14 disposed on the Y1-side is referred to as a first horizontal electric conductor 14a (an example of the horizontal element), and the horizontal electric conductor 14 disposed on the Y2-side is referred to as a second horizontal electric conductor 14b (an example of the horizontal element). The power supply unit 12 is connected to a Y1-side end portion of the first horizontal electric conductor 14a. The power supply unit 12 is not connected to the second horizontal electric conductor 14b. Both of the horizontal electric conductors 14 extend from the opposite end portions of the rear window 2 in the Y-direction to a central side of the rear window 2, but their distal ends disposed on the central side are spaced apart from each other. As described above, the horizontal electric conductor 14 of the antenna element 10 is spaced apart from the metal exterior panel 7, but the horizontal electric conductor 14 of the antenna element 10 is capacitively coupled to the metal exterior panel 7.

[0047] As another embodiment, the horizontal electric conductor 14 of the antenna element 10 may be disposed outside the defogging region 2c on the inner surface 2a of the rear window 2 but inside the window frame 7a, as illustrated in Fig. 4. In this case, when the electric vehicle 1 is viewed from its rear side, the horizontal electric conductor 14 of the antenna element 10 does not overlap the metal exterior panel 7. In other words, the horizontal electric conductor 14 of the antenna element 10 is disposed closer to a central side of the rear window 2 in the X-direction than the window frame 7a as the outer edge of the inner region 7b. Even in a case where the horizontal electric conductor 14 of the antenna element 10 is disposed in such a position, the horizontal electric conductor 14 of the antenna element 10 is capacitively coupled to the metal exterior panel 7.

[0048] The shark-fin antenna 20 is disposed on the outside of the electric vehicle 1 via the roof 7c of the metal exterior panel 7, as illustrated in Figs. 1 to 4. As illustrated in Fig. 3, the shark-fin antenna 20 includes a power supply unit 22, an antenna section 24 (an example of an element) connected to the power supply unit 22, and the transmission line 26 configured to transmit received radio waves to the in-vehicle electronic device 6. In the shark-fin antenna 20 of the present embodiment, the power supply unit 22 and the antenna section 24 are disposed on the outside of the electric vehicle 1 via the roof 7c (the metal exterior panel 7) to be arranged in this order in a direction away from the roof 7c. Since the shark-fin antenna 20 is disposed on the outside of the electric vehicle 1 via the roof 7c, electromagnetic noise generated from the inside (the DC-DC converter 5 in particular) of the electric vehicle 1 is blocked by the roof 7c, so that radio waves can be received stably. Note that the roof 7c may be a sunroof or may be made of only a metal plate. In a case where the roof 7c is a sunroof, it is desirable that the shark-fin antenna 20 be disposed on the metal exterior panel 7 other than a glass portion.

[0049] In order to stably receive radio waves by the diversity antenna employing the phase diversity method, it is necessary to reduce a difference (hereinafter also just referred to as a gain difference) in reception performance (reception gain) between the antenna element 10 of the vehicular glass antenna A and the shark-fin antenna 20, in a frequency band desired for reception (from 76 MHz to 108 MHz to be used in FM radio broadcasting in the present embodiment, hereinafter also referred to as a reception frequency band). More specifically, it is necessary to keep the gain difference between the antenna element 10 and the shark-fin antenna 20 within ± 15 dB over the entire reception frequency band, and the gain difference is preferably within ± 10dB, and more preferably within ± 5dB. When the gain difference between the antenna element 10 and the shark-fin antenna 20 is within ±5 dB over the entire reception frequency band, it can be said that the antenna element 10 and the shark-fin antenna 20 have equivalent reception gains.

[0050] It is difficult to actually change the reception performance of the shark-fin antenna 20 because of shape constraints. In the meantime, the antenna element 10 is capacitively coupled to the metal exterior panel 7 as described above. Therefore, the reception performance of the antenna element 10 can be changed by changing the coupling capacitance by changing a separation distance d between the horizontal electric conductor 14 of the antenna element 10 and the window frame 7a of the metal exterior panel 7 in a direction (hereinafter referred to as an inward direction) perpendicular to the Y-direction and along the inner surface 2a of the rear window 2. As illustrated in Fig. 3, the reference for the separation distance d (the location where d = 0) is where the normal of the rear window 2 intersects the window frame 7a. The separation distance d between the horizontal electric conductor 14 of the antenna element 10 and the window frame 7a to reduce the reception gain difference between the antenna element 10 and the shark-fin antenna 20 is preferably within ±20mm from the reference in the inward direction. When the separation distance d is within this range, it is possible to reduce the reception gain difference between the antenna element 10 and the shark-fin antenna 20. In the following description, in a case where the separation distance d is positive, the horizontal electric conductor 14 is disposed outside the defogging region 2c on the inner surface 2a of the rear window 2 but inside the window frame 7a, as illustrated in Fig. 4. In the meantime, in a case where the separation distance d is negative, the horizontal electric conductor 14 is disposed outside the defogging region 2c on the inner surface 2a of the rear window 2 and also outside the window frame 7a, as illustrated in Figs. 2, 3.

[0051] The reception frequency band from 76 MHz to 108 MHz is roughly divided into a domestic reception frequency band from 76 MHz to 96 MHz and an overseas reception frequency band from 88 MHz to 108 MHz. Figs. 5 to 8 exhibit gain differences between the antenna element 10 and the shark-fin antenna 20 in the reception frequency band, obtained by changing the separation distance d between the horizontal electric conductor 14 of the antenna element 10 in the vehicular glass antenna A and the window frame 7a.

[0052] Figs. 5a, 6a, 6b, 7a, 8a illustrate configurations of diversity antennas with different shapes of the horizontal electric conductor 14 of the antenna element 10 of the vehicular glass antenna A and different separation distances d between the horizontal electric conductor 14 and the window frame 7a. The antenna elements 10 illustrated in Figs. 5a, 6a, 6b, 7a are for the domestic reception frequency band, and the antenna element 10 illustrated in Fig. 8a is for the overseas reception frequency band. Figs. 5b, 6c, 7b, 8b show respective gain differences obtained with the use of the diversity antennas including respective antenna elements 10. Hereinafter, when these five antenna elements 10 are distinguished from each other, the antenna element 10 illustrated in Fig. 5a is referred to as an antenna element 10a. The antenna elements 10 illustrated in Figs. 6a, 6b are referred to as an antenna element 10b and an antenna element 10c, respectively. The antenna element 10 illustrated in Fig. 7a is referred to as an antenna element 10d. The antenna element 10 illustrated in Fig. 8a is referred to as an antenna element 10e. Note that, in any of the antenna elements 10a to 10e, the power supply unit 12 is disposed outside the defogging region 2c on the inner surface 2a of the rear window 2 but inside the window frame 7a.

[0053] Fig. 5a illustrates the antenna element 10a in which the separation distance d between the first horizontal electric conductor 14a disposed on the Y1-side and the window frame 7a is +45 mm, and part of a heating wire in the defogging region 2c is used as the horizontal electric conductor 14. Fig. 5b shows a gain difference obtained when the antenna element 10a is used. Hereinafter, the horizontal electric conductor 14 as the part of the heating wire in the defogging region 2c is referred to as a third horizontal electric conductor 14c (an example of the horizontal element). The third horizontal electric conductor 14c extends downward from the center of the defogging region 2c and horizontally extends toward both the right and left from an extended end. The separation distance d between the third horizontal electric conductor 14c and the window frame 7a is +25 mm.

[0054] A distal end of a portion of the third horizontal electric conductor 14c which portion extends rightward overlaps a distal end of the first horizontal electric conductor 14a in the up-down direction (the X-direction).

[0055] In terms of the antenna element 10a illustrated in Fig. 5a, the gain difference exceeds +15 dB in the range of 80 MHz to 84 MHz in the domestic reception frequency band from 76 MHz to 96 MHz, as shown in Fig. 5b. Accordingly, the antenna element 10a is unsuitable for use as a diversity antenna for domestic FM radio broadcasting.

[0056] Fig. 6a illustrates the antenna element 10b in which the separation distance d between the horizontal electric conductor 14 (the first horizontal electric conductor 14a) disposed on the Y1-side and the window frame 7a is +10 mm. Fig. 6b illustrates the antenna element 10c in which the separation distance d is -10 mm.

[0057] Fig. 6c shows gain differences obtained when the antenna element 10b and the antenna element 10c are used.

[0058] In terms of the antenna element 10b illustrated in Fig. 6a, the gain difference is within ±15 dB in the entire domestic reception frequency band of 76 MHz to 96 MHz, as shown in Fig. 6c. Accordingly, the antenna element 10b can be used as a diversity antenna for domestic FM radio broadcasting.

[0059] In terms of the antenna element 10c illustrated in Fig. 6b, the gain difference is within ±7 dB in the entire domestic reception frequency band, as shown in Fig. 6c. Accordingly, the antenna element 10c can be used as a diversity antenna for domestic FM radio broadcasting, having better reception performance than the antenna element 10b.

[0060] Fig. 7a illustrates the antenna element 10d in which the separation distance d between the horizontal electric conductor 14 (the first horizontal electric conductor 14a) disposed on the Y1-side and the window frame 7a is +17 mm and which includes the horizontal electric conductor 14 (the second horizontal electric conductor 14b) connected to a bus bar 2d on the Y2-side out of bus bars 2d disposed outside the defogging region 2c and configured to supply electric power to the heating wire of the defogging region 2c. Fig. 7b shows a gain difference obtained when the antenna element 10d is used. The second horizontal electric conductor 14b in Fig. 7a extends downward from the bus bar 2d on the Y2-side and extends in the Y-direction toward the center (the Y1-side) of the rear window 2 at a position where the separation distance d from the window frame 7a is -8 mm. The second horizontal electric conductor 14b is folded by 180 degrees around the center of the rear window 2 and extends toward the Y2-side. The separation distance d between this folded portion and the window frame 7a is +7 mm, and the folded portion extends inwardly by approximately one-third of the length of the second horizontal electric conductor 14b from a Y2-side end portion of the rear window 2 in a right-left direction of the rear window 2.

[0061] In terms of the antenna element 10d illustrated in Fig. 7a, the gain difference is within ±5 dB in the entire domestic reception frequency band, as shown in Fig. 7b. Accordingly, the antenna element 10d can be used as an optimal diversity antenna for domestic FM radio broadcasting, having better reception performance than the antenna elements 10b, 10c.

[0062] Fig. 8a illustrates the antenna element 10e in which the separation distance d between the horizontal electric conductor 14 (the first horizontal electric conductor 14a) disposed on the Y1-side and the window frame 7a is +8 mm and which includes the horizontal electric conductor 14 (the second horizontal electric conductor 14b) connected to the bus bar 2d on the Y2-side out of the bus bars 2d disposed outside the defogging region 2c. Fig. 8b shows a gain difference obtained when the antenna element 10e is used. The second horizontal electric conductor 14b in Fig. 8a extends downward from the bus bar 2d on the Y2-side and then extends in the Y-direction toward the center (the Y1-side) of the rear window 2 at a position where the separation distance d from the window frame 7a is -7 mm, so as to reach the vicinity of the center of the rear window 2. With this arrangement, the gain difference is adjusted to be small in the overseas reception frequency band of 88 MHz to 108 MHz.

[0063] In terms of the antenna element 10e illustrated in Fig. 8a, the gain difference is within ±5 dB in the entire overseas reception frequency band, as shown in Fig. 8b. Accordingly, the antenna element 10e can be used as an optimal diversity antenna for overseas FM radio broadcasting.[Other Embodiments]

[0064] Next will be described a configuration of an antenna and the like including the vehicular glass antenna A according to other embodiments of the present invention. Each of the other embodiments is different from the above embodiment in the configuration of the antenna and the like. The other configurations are the same as those in the above embodiment. Accordingly, in the description of the other embodiments, the reference sign of a constituent described in the above embodiment is assigned to a constituent having a configuration similar to the constituent described in the above embodiment, and a detailed description thereof is omitted. (1) The above embodiment has been described with reference to the shark-fin antenna 20 as one of the antennas constituting the diversity antenna employing the phase diversity method. However, the present invention is not limited to this. For example, antennas having any shape, such as a rod antenna, an antenna incorporated in a rear spoiler, and an antenna incorporated in a rear wing, can be used at any position in the electric vehicle 1, provided that the antennas can constitute a diversity antenna together with the vehicular glass antenna A. Note that it is preferable that the antennas be disposed at a position where electromagnetic noise generated from the inside (particularly, the DC-DC converter 5) of the electric vehicle 1 is blocked by the metal exterior panel 7. (2) In the above embodiment, the horizontal electric conductor 14 of the antenna element 10 extends in the X-direction but may extend to be inclined from the X-direction. In this case, the horizontal electric conductor 14 may intersect with the window frame 7a of the metal exterior panel 7 when the electric vehicle 1 is viewed from the rear side. (3) In the above embodiment, the antenna element 10 is disposed on the lower side (on the X2-side) of the rear window 2 in the X-direction but may be disposed on the upper side (on the X1-side) of the rear window 2. Industrial Applicability

[0065] The present invention is applicable to a vehicular glass antenna.Description of Reference Numerals

[0066] 1: electric vehicle 2: rear window (glass sheet) 2a: inner surface (sheet surface) 2b: outer edge 3: motor 4: battery 5: DC-DC converter (transformer) 6: in-vehicle electronic device (device) 7: metal exterior panel (shielding section, metal plate) 7a: window frame (opening edge) 7b: inner region (open region) 7c: roof (shielding section, metal plate) 10: antenna element (first antenna element) 10a: antenna element (first antenna element) 10b: antenna element (first antenna element) 10c: antenna element (first antenna element) 14: horizontal electric conductor (horizontal element) 14a: first horizontal electric conductor (horizontal element) 14b: second horizontal electric conductor (horizontal element) 14c: third horizontal electric conductor (horizontal element) 20: shark-fin antenna (second antenna element) 22: power supply unit 24: antenna section (element) A: vehicular glass antenna

Claims

1. A vehicular glass antenna for an electric vehicle driven by a driving force from a motor receiving electric power from a battery, the vehicular glass antenna comprising: a glass sheet separating inside and outside of the electric vehicle; and a first antenna element fixed to a sheet surface of the glass sheet and capable of receiving radio waves propagating through air outside the electric vehicle, the first antenna element constituting a diversity antenna in cooperation with a second antenna element disposed on the outside of the electric vehicle via a shielding section capable of blocking electromagnetic noise emitted from a transformer disposed between the battery and a device receiving electric power from the battery, the second antenna element being capable of receiving the radio waves.

2. The vehicular glass antenna according to claim 1, wherein the shielding section is made of a metal plate.

3. The vehicular glass antenna according to claim 2, wherein the shielding section is a metal exterior panel of the electric vehicle.

4. The vehicular glass antenna according to any one of claims 1 to 3, wherein the diversity antenna is used for a phase diversity receiving method.

5. The vehicular glass antenna according to any one of claims 1 to 4, wherein the radio waves include a frequency band for use in FM radio broadcasting.

6. The vehicular glass antenna according to any one of claims 1 to 5, wherein the second antenna element includes a power supply unit and an element, and the power supply unit and the element are disposed in this order in a direction away from the shielding section.

7. The vehicular glass antenna according to claim 3, wherein the first antenna element is disposed at a position where the first antenna element is capacitively couplable to the metal exterior panel.

8. The vehicular glass antenna according to claim 7, wherein the first antenna element has a reception gain equivalent to a reception gain of the second antenna element.

9. The vehicular glass antenna according to claim 8, wherein the glass sheet has an outer edge fixed to cover an open region in the metal exterior panel of the electric vehicle, and the first antenna element includes a horizontal element disposed within a separation distance of 20 mm from an opening edge of the open region in a direction perpendicular to a right-left direction of the electric vehicle and along the sheet surface of the glass sheet.

10. The vehicular glass antenna according to claim 9, wherein the horizontal element is disposed closer to a center of the glass sheet than the opening edge of the open region.

11. The vehicular glass antenna according to claim 9, wherein the horizontal element is disposed closer to the outer edge of the glass sheet than the opening edge of the open region.

12. The vehicular glass antenna according to claim 9, wherein the glass sheet is a rear window of the electric vehicle, and the shielding section is a roof of the electric vehicle.

13. The vehicular glass antenna according to claim 12, wherein the first antenna element is disposed on a lower side of the rear window in an up-down direction of the rear window.

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