JP6027872B2 - Inverted F antenna - Google Patents

Description

  The present invention relates to an inverted F antenna that can be used for receiving FM broadcasts.

  As an antenna device installed in a vehicle such as an automobile, an antenna device including a transparent dielectric sheet and a planar antenna formed on the dielectric sheet is widely used. Such an antenna device is usually used by being attached to a windshield.

  Patent Document 1 discloses an antenna device including a transparent dielectric sheet and a loop antenna formed on the dielectric sheet. Patent Document 1 describes that the total length (loop length) of a radiating element constituting a loop antenna is set to 60 cm in order to use this antenna device for reception of digital television broadcasting.

JP2007-158450 (released on June 21, 2007)

  However, when the antenna device described in Patent Literature 1 is used for FM broadcast reception, there is a problem that it is difficult to use the antenna device by attaching it to a windshield.

  In fact, as is well known, the total length of the radiating elements constituting the loop antenna is approximately the same as the resonance wavelength λ = c / f (where c is the speed of light and f is the resonance frequency). Therefore, in order to make the resonance frequency f coincide with the carrier frequency (about 100 MHz) of FM broadcast, the total length of the radiating elements constituting the loop antenna needs to be about 300 cm. On the other hand, the area on the windshield that can be used for attaching the antenna device is preferably 10 cm × 10 cm or less in order to ensure the visibility of the driver. The difficulty of forming a loop antenna having a radiating element length of 300 cm in a region having an area of 10 cm × 10 cm or less will be apparent without explanation.

  In order to solve such a problem, the planar antenna included in the antenna device may be changed from a loop antenna to an inverted F antenna. This is because the total length of the radiating element of the inverted F antenna capable of receiving FM broadcasting is about λ / 4 = 75 cm, as is well known.

  However, the inverted F antenna includes a ground plane constituted by a planar conductor in addition to a radiating element constituted by a linear conductor. For this reason, the antenna device provided with the inverted F antenna is not suitable for being attached to the windshield. This is because the driver's field of view may be blocked by the ground plane included in the inverted F antenna.

  Therefore, when installing the antenna device provided with the inverted F antenna in the vehicle, it is necessary to set the installation location other than the windshield. For example, a lid of a hood storage (storage for storing a hood) in an open top type vehicle is a good example of a portion other than a windshield on which an antenna device can be installed. However, the area other than the windshield on which the antenna device can be mounted generally has a smaller area than the windshield. For this reason, in order to realize an antenna device suitable for mounting on a vehicle and capable of receiving FM broadcasting, it is strongly required to shorten the length of the radiating element in the inverted F antenna.

  The present invention has been made in view of the above problems, and its purpose is to provide an inverted F antenna in which the total length of the radiating element is shortened, that is, an inverted F antenna in which the total length of the radiating element is shorter than λ / 4. It is to be realized.

  In order to solve the above problems, an inverted-F antenna according to the present invention includes a ground plane, a radiating element connected to the ground plane via a power feeding section, and a short-circuit section that short-circuits a point on the radiating element to the ground plane. And an inductor and a capacitor are inserted in series on the short-circuit portion.

  According to said structure, the full length of the said radiation element can be made shorter than (lambda) / 4 ((lambda) is the resonant wavelength of the said reverse F antenna).

  The inverted F antenna according to the present invention preferably further includes another radiating element connected to a point on the short-circuit portion, and further radiating element capacitively coupled to the radiating element.

  According to the above configuration, by adding the other radiating element, both the frequency f1 corresponding to the length of the radiating element and the frequency f2 corresponding to the length of the other radiating element are The resonance frequency of the inverted F antenna can be used. Further, by capacitively coupling the radiating element and the other radiating element, the VSWR value can be lowered over the entire band including these two resonance frequencies f1 and f2. That is, the entire band including these two resonance frequencies f1 and f2 can be set as the operating band of the inverted F antenna.

  In the inverted F antenna according to the present invention, the other radiating elements are preferably meandered in a region surrounded by the radiating elements.

  According to said structure, adding the said other radiating element which has sufficient length (for example, substantially the same length as the said radiating element), without increasing the area required for arrangement | positioning of the said reverse F antenna Can do.

  In the inverted F antenna according to the present invention, the radiating element includes a segment A1 extending from the feeding portion in substantially the same direction as the first direction, and a second orthogonal to the first direction from the end of the segment A1. A segment A2 extending in substantially the same direction as the direction, a segment A3 extending in a direction substantially opposite to the first direction from the end of the segment A2, and a direction substantially opposite to the second direction from the end of the segment A3. The segment A4 is extended, and the short-circuit portion is substantially opposite to the first direction from the segment B1 extending from the power feeding portion in substantially the same direction as the second direction and from the end of the segment B1. A segment B2 extending in the direction and a segment B3 extending in the direction substantially opposite to the second direction from the end of the segment B2 to reach the ground plane. The other radiating element includes a segment C1 extending in a direction substantially the same as the first direction from a point on the segment B1 of the short-circuit portion, and a second direction from the end of the segment C1. A segment C2 extending in substantially the same direction, a segment C3 extending in a direction substantially opposite to the first direction from the end of the segment C2, and a direction extending in a direction substantially opposite to the second direction from the end of the segment C3 A segment C4, a segment C5 extending from the end of the segment C4 in a direction substantially opposite to the first direction, a segment C6 extending from the end of the segment C5 in substantially the same direction as the second direction, and the segment Preferably, the segment C7 extends from the end of C6 in substantially the same direction as the first direction.

  According to said structure, the area required for arrangement | positioning of the said reverse F antenna can be made small, without reducing the receiving gain of the said reverse F antenna significantly.

  According to the present invention, it is possible to realize an inverted F antenna in which the overall length of the radiating element is shortened, that is, an inverted F antenna in which the overall length of the radiating element is shorter than λ / 4.

It is a circuit diagram which shows the topology of the inverted F antenna which concerns on one Embodiment of this invention. It is a circuit diagram which shows the modification of the inverted F antenna shown in FIG. It is a top view which shows the specific example of the inverted F antenna shown in FIG. Fig. 4 is a graph showing the direction dependence of reception gain in the inverted F antenna shown in Fig. 3.

  A configuration of the inverted F antenna 1 according to the present embodiment will be described with reference to FIGS. 1 and 2. 1 and 2 are circuit diagrams showing the topology of the inverted F antenna 1.

  As shown in FIG. 1, the inverted F antenna 1 includes (1) a ground plane 11, (2) a radiating element 13 connected to the ground plane 11 via a power feeding unit 12, and (3) a point P on the radiating element 13. And a short-circuit part 14 for short-circuiting the base plate 11 to the base plate 11.

  Note that the ground plane 11 and the radiating element 13 are connected via the power feeding unit 12. One conductor (for example, the outer conductor of the coaxial cable) constituting the power feeding line (for example, the coaxial cable) is connected to the ground plane 11. The other conductor (for example, the inner conductor of the coaxial cable) constituting the feeder line is connected to the radiating element 13.

  The ground plane 11 is composed of a plate-like conductor. On the other hand, the radiating element 13 and the short-circuit portion 14 are configured by linear or strip-shaped conductors. If the ground plane 11, the radiating element 13, and the short-circuit portion 14 are formed as a pattern on one main surface of the dielectric sheet, a thin planar antenna can be realized. In addition, when the dielectric sheet is regarded as a rectangular parallelepiped, the main surface of the dielectric sheet indicates two surfaces having the largest area among the six surfaces constituting the rectangular parallelepiped.

  A characteristic point of the inverted F antenna 1 is that an inductor 14 a and a capacitor 14 b are inserted in series on the short-circuit portion 14. In the conventional inverted F antenna, the radiating element and the ground plane are short-circuited in a direct current manner by the short-circuit portion, whereas in the inverted F antenna 1, the radiating element 13 and the ground plane 11 are alternatingly coupled by the short-circuit portion 14. It will be short-circuited.

  By inserting the inductor 14a and the capacitor 14b in series on the short-circuit portion 14, the resonance frequency of the inverted F antenna 1 can be shifted to the low frequency side. That is, in the conventional inverted-F antenna, if the total length of the radiating element is L, the resonance frequency f is f≈c / (4 × L) (c is the speed of light). On the other hand, in the inverted F antenna 1, the resonance frequency f is f <c / (4 × L), where L is the total length of the radiating element 13.

  In other words, the total length of the radiating element 13 can be shortened by inserting the inductor 14 a and the capacitor 14 b in series on the short-circuit portion 14. That is, in the conventional inverted-F antenna, when the resonance frequency is f, the total length L of the radiating element is L≈c / (4 × f). On the other hand, in the inverted F antenna 1, when the resonance frequency is f, the total length L of the radiating element 13 is L <c / (4 × f).

  For example, in the conventional inverted-F antenna, in order to include the resonance frequency in the frequency band of FM broadcasting (for example, 76 MHz or more and 108 MHz or less), the total length of the radiating element needs to be 69 cm or more. On the other hand, in the inverted F antenna 1, the resonance frequency can be included in the frequency band of FM broadcasting even when the total length of the radiating element 13 is shorter than this.

  In order to shorten the overall length of the radiating element 13, in addition to the technical significance that the inverted F antenna 1 can be reduced in size, the width of the radiating element 13 can be increased without increasing the size of the inverted F antenna 1. There is a technical significance that it is possible to widen or increase the interval between the mutually parallel portions of the meandering radiation element 13. By increasing the width of the radiating element 13, the band of the inverted F antenna 1 can be expanded. Further, the reception gain of the inverted F antenna 1 can be improved by widening the interval between the portions of the meandering radiating element 13 that run parallel to each other. That is, shortening the overall length of the radiating element 13 has a technical significance of improving the characteristics of the inverted F antenna 1 without increasing the size of the inverted F antenna 1.

  The inductor 14a and the capacitor 14b are not generated parasitically. That is, the inductor 14a and the capacitor 14b are loaded on the short-circuit portion 14 as electronic components and have a predetermined inductance and capacitance. Therefore, by appropriately setting the inductance of the inductor 14a and the capacitance of the capacitor 14b, the resonance frequency can be set to a desired value without changing the overall length of the radiating element 13. In other words, by appropriately setting the inductance of the inductor 14a and the capacitance of the capacitor 14b, the total length of the radiating element 13 can be set to a desired value without changing the resonance frequency.

  As shown in FIG. 2, the inverted F antenna 1 includes other radiating elements (hereinafter, “second radiating elements”) in addition to the radiating elements (hereinafter also referred to as “first radiating elements”) 13 described above. Description) 15 is preferably provided. The second radiating element 15 is connected to a point Q on the short-circuit portion 14 and is capacitively coupled to the first radiating element 13. In FIG. 2, the capacitance generated between the first radiating element 13 and the second radiating element 15 is expressed as a capacitor 16.

  By adding the second radiating element 15, both the frequency f1 corresponding to the length of the first radiating element 13 and the frequency f2 corresponding to the length of the second radiating element 15 are inverted F antennas. 1 resonance frequency. Further, by capacitively coupling the first radiating element 13 and the second radiating element 15, the VSWR value can be reduced over the entire band including these two resonance frequencies f1 and f2. That is, the entire band including these two resonance frequencies f1 and f2 can be used as the operating band of the inverted F antenna 1.

(Concrete example)
A specific example of the inverted F antenna 1 will be described with reference to FIG. FIG. 3 is a plan view showing a configuration example of the inverted-F antenna 1. The inverted-F antenna 1 shown in FIG. 3 is designed as a vehicle-mounted antenna that covers the frequency band (from 76 MHz to 108 MHz) of FM broadcasting.

  Since the topology of the inverted F antenna 1 has already been described with reference to FIG. 2, hereinafter, specific shapes of the ground plane 11, the first radiating element 13, the short-circuit portion 14, the second radiating element 15, and the like. Will be described. In the following description, a direction substantially the same as a certain direction refers to a direction in which an angle formed with the direction is 30 ° or less. Further, a direction substantially opposite to a certain direction refers to a direction in which an angle formed with the opposite direction of the direction is 30 ° or less.

  The ground plane 11 is composed of a rectangular conductor of 31 mm (long side) × 27 mm (short side), and is arranged so that the long side is parallel to the x-axis. What should be noted about the ground plane 11 is that its area is smaller than the area of the first radiating element 13. The reason why such a small-area conductor is used as the ground plane 11 is that it is assumed that the external conductor connected to the ground plane 11 functions together with the ground plane 11 as a ground. For example, when the inverted F antenna 1 is installed in an automobile, the ground plane 11 is connected to the body of the automobile. Thereby, the body of the automobile can be made to function as a ground together with the base plate 11.

  The first radiating element 13 is constituted by a strip-shaped conductor of 10 mm (average width) × 500 mm (full length). Moreover, the shape and arrangement | positioning of the 1st radiation | emission element 13 can be expressed as follows, for example. That is, the first radiating element 13 corresponds to the segment 13S1 (corresponding to the segment A1 in the claims) extending from the second feeding point 12b (described later) in substantially the same direction as the first direction (y-axis positive direction in FIG. 3). ), A segment 13S2 (corresponding to the segment A2 in the claims) extending in substantially the same direction as the second direction (the x-axis positive direction in FIG. 3) orthogonal to the first direction from the end of the segment 13S1, and a segment A segment 13S3 (corresponding to segment A3 in the claims) extending from the end of 13S2 in a direction substantially opposite to the first direction, and a segment 13S4 (corresponding to the second direction from the end of segment 13S3) (Corresponding to the segment A4 in the term) (in FIG. 3, the boundary between these segments is indicated by a dotted line) It shows). By adopting such a shape, the first radiating element 13 having a total length of 500 mm can be arranged in a rectangular area of about 258 mm × 131 mm.

  The first radiating element 13 faces the ground plane 11 at the start end of the segment 13S1. And in the area | region on the ground plane 11 facing the segment 13S1, the 1st feeding point 12a which is a point to which the outer conductor of a coaxial cable is connected is provided, and in the area on the segment 13S1 facing the ground plane 11, A second feeding point 12b, which is a point to which the inner conductor of the coaxial cable is connected, is provided. The power feeding unit 12 illustrated in FIG. 2 includes these power feeding points 12a and 12b.

  Note that the width of the first radiating element 13 is equal to or greater than 512 times the wavelength (69 cm) corresponding to the lower limit (76 MHz) of the frequency band of FM broadcasting, which contributes to the expansion of the band. ing. Thus, the width of the first radiating element 13 can be made sufficiently wide because the entire length of the first radiating element 13 can be sufficiently shortened by loading the inductor 14a and the capacitor 14b. Don't be.

  The short circuit part 14 is comprised by the strip | belt-shaped conductor of 5 mm (average width) * 155mm (full length). Moreover, the shape and arrangement | positioning of the short circuit part 14 can be expressed as follows, for example. That is, the short-circuit portion 14 is substantially the same as the second direction from the feeding point 12b (in this specific example, the point P on the first radiating element 13 shown in FIG. 2 coincides with the feeding point 12b). A segment 14S1 extending in the same direction (corresponding to the segment B1 in the claims), a segment 14S2 extending in the direction substantially opposite to the first direction from the end of the segment 14S1 (corresponding to the segment B2 in the claims), and a segment 14S2 The segment 14S3 (corresponding to the segment B3 in the claims) extending from the terminal end to the base plate 11 extending in a direction substantially opposite to the second direction is defined (in FIG. 3, a boundary between these segments is defined). (Shown as a dotted line). The short-circuit portion 14 is divided into three pieces of conductors by two gaps. The inductor 14a is loaded closer to the feeding point 12b among these two gaps, and the capacitor 14b is loaded farther from the feeding point 12b among these two gaps. In this specific example, an inductance element having an inductance of 86 nH is loaded as the inductor 14a, and a capacitor element having a capacitance of 47 pF is loaded as the capacitor 14b.

  The second radiating element 15 is configured by a strip-shaped conductor of 10 mm (average width) × 400 mm (full length). The shape and arrangement of the second radiating element 15 can be expressed as follows, for example. That is, the segment 15S1 (corresponding to the segment C1 in the claims) extending from the point Q on the segment 14S1 of the short-circuit portion 14 in substantially the same direction as the first direction, and the second direction from the end of the segment 15S1. A segment 15S2 extending in the same direction (corresponding to the segment C2 in the claims), a segment 15S3 extending in the direction substantially opposite to the first direction from the end of the segment 15S2 (corresponding to the segment C3 in the claims), and a segment 15S3 A segment 15S4 (corresponding to the segment C4 in the claims) extending from the end of the segment 15S4 in the direction substantially opposite to the second direction, and a segment 15S5 extending in the direction substantially opposite to the first direction from the end of the segment 15S4 (invention) Corresponding to segment C5) and the end of segment 15S5 15S6 (corresponding to the segment C6 in the claims) extending in the substantially same direction as the second direction from above, and a segment 15S7 extending in the same direction as the first direction from the end of the segment 15S6 (segment in the claims) (Corresponding to C7) (in FIG. 3, the boundaries between these segments are indicated by dotted lines). By adopting such a meander shape, the second radiating element 15 having a total length of 500 mm can be arranged in a rectangular area of approximately 206 mm × 45 mm surrounded by the first radiating element 13.

  The first radiating element 13 and the second radiating element 15 have a portion in which the outer edge on the inner peripheral side of the former and the outer edge on the outer peripheral side of the latter are close to each other. For this reason, the first radiating element 13 and the second radiating element 15 are capacitively coupled to each other. In the configuration example shown in FIG. 3, in the first radiating element 13, the outer edge on the inner peripheral side of the portion formed by the whole of the segment 13S3 and the vicinity of the start end of the segment 13S4 is the segment of the second radiating element 15. It is close to the outer edge on the outer peripheral side of the portion constituted by the vicinity of the terminal end of 15S6 and the entire segment 15S7. The capacitor 16 shown in FIG. 2 is constituted by these parts.

  The ground plane 11, the first radiating element 13, the short-circuit portion 14, and the second radiating element 15 are formed as a pattern on one main surface of the dielectric sheet 17. Thereby, a thin planar antenna suitable for in-vehicle use can be realized. As a preferable place for the installation of the inverted F antenna 1 in the open top type vehicle, for example, the back surface of a lid (contained by a dielectric such as a resin) of a hood storage (storage for storing the hood) can be cited. It is done. Of course, it will be clear that it may be installed in other places, without needing to add.

  Finally, it will be confirmed with reference to FIG. 4 that a sufficiently high reception gain can be obtained in the inverted-F antenna 1 shown in FIG. FIG. 4 is a graph showing the direction dependence of the reception gain in the inverted F antenna 1 shown in FIG.

  As shown in FIG. 4, the reception gain of the inverted F antenna 1 shown in FIG. 3 is −40 dB or more in the frequency band of FM broadcasting (specifically, 76 MHz and 84 MHz). That is, if the inverted F antenna 1 shown in FIG. 3 is used, FM broadcast waves coming from any direction can be received with high sensitivity.

[Additional Notes]
The present invention is not limited to the above-described embodiments, and various modifications can be made within the scope shown in the claims. That is, embodiments obtained by combining technical means appropriately modified within the scope of the claims are also included in the technical scope of the present invention.

  The inverted F antenna according to the present invention can be suitably used as, for example, a vehicle-mounted antenna, particularly a vehicle-mounted antenna for receiving FM broadcasting.

DESCRIPTION OF SYMBOLS 1 Reverse F antenna 11 Ground plate 12 Feed part 12a 1st feed point 12b 2nd feed point 13 Radiation element 13S1 Segment 13S2 Segment 13S3 Segment 13S4 Segment 14 Short-circuit part 14S1 Segment 14S2 Segment 14S3 Segment 14a Inductor 14b Capacitor 15 Radiation element 15S1 Segment 15S2 Segment 15S3 Segment 15S4 Segment 15S5 Segment 15S6 Segment 15S7 Segment 16 Capacitor 17 Dielectric Sheet

Claims (2)

A ground plane, a radiating element connected to the ground plane via a power feeding section, a short-circuit section that short-circuits a point on the radiating element to the ground plane, and another radiating element connected to a point on the short-circuit section. And another radiating element capacitively coupled to the radiating element ,
Inductor and a capacitor is inserted in series on the short circuit portion,
The other radiating element is meandered in a region surrounded by the radiating element.
An inverted-F antenna characterized by that. The radiating element includes a segment A1 extending from the power feeding unit in substantially the same direction as the first direction, and a segment extending from the terminal end of the segment A1 in substantially the same direction as the second direction orthogonal to the first direction. A2, a segment A3 extending in the direction substantially opposite to the first direction from the end of the segment A2, and a segment A4 extending in the direction substantially opposite to the second direction from the end of the segment A3. And
The short-circuit portion includes a segment B1 extending from the power supply portion in substantially the same direction as the second direction, a segment B2 extending from the end of the segment B1 in a direction substantially opposite to the first direction, and the segment B2 A segment B3 extending from the terminal end to the base plate extending in a direction substantially opposite to the second direction,
The other radiating element includes a segment C1 extending in a direction substantially the same as the first direction from a point on the segment B1 of the short-circuit portion, and a direction substantially the same as the second direction from the end of the segment C1. A segment C2 that extends, a segment C3 that extends in a direction substantially opposite to the first direction from the end of the segment C2, a segment C4 that extends in a direction substantially opposite to the second direction from the end of the segment C3, From the end of the segment C4, the segment C5 extending in the direction substantially opposite to the first direction, the segment C6 extending from the end of the segment C5 in substantially the same direction as the second direction, and the end of the segment C6 It is composed of a segment C7 extending in the same direction as the first direction.
The inverted F antenna according to claim 1 .

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