Integrated antenna, and manufacturing method thereof

An integrated antenna (1) includes: a first loop antenna (11) having a first annular antenna element (11a); and a second loop antenna (13) having a second annular antenna element (13). The second annular antenna element (13) is arranged, on a surface identical to that where the first annular antenna element (13a) is arranged, so as to surround the first annular antenna element (13a).

TECHNICAL FIELD

The present invention relates to an integrated antenna into which a plurality of antennas are integrated. Specifically, the present invention relates to an integrated antenna into which at least two loop antennas are integrated. Further, the present invention relates to a method of manufacturing an integrated antenna.

BACKGROUND ART

In accordance with expansion of use application of wireless communications, an antenna which operates in various frequency bands has been desired. For example, as an on-vehicle antenna mounted on a vehicle such as a car, an antenna has been desired which operates in frequency bands of FM/AM broadcasting, SDARS (Satellite Digital Audio Radio Service), DAB (Digital Audio Broadcast), DTV (Digital Television), GPS (Global Positioning System), VICS (registered trademark) (Vehicle Information and Communication System), ETC (Electronic Toll Collection), and the like.

Conventionally, antennas which operate in respective different frequency bands have been often realized as individual antennas. For example, an antenna for FM/AM broadcasting has been realized as a whip antenna which is mounted on a rooftop, whereas an antenna for digital terrestrial broadcasting has been realized as a film antenna which is attached to a windshield.

However, a car has a limited space where an antenna device can be mounted. Furthermore, in a case where the number of antenna devices to be mounted on a car is increased, this causes problems such that a design of the car is spoiled or costs to mount the antenna devices are increased. In order to avoid such problems, it is effective to use an integrated antenna. Note here that an integrated antenna indicates an antenna device including a plurality of antennas which operate in respective different frequency bands.

As such an integrated antenna, for example, there is known an integrated antenna disclosed in Patent Literature 1. The integrated antenna disclosed in Patent Literature 1 is an integrated antenna into which an SDARS antenna and a GPS antenna are integrated. The integrated antenna disclosed in Patent Literature 1 employs a configuration such that the SDARS antenna and the GPS antenna, each of which is configured as a flat-panel antenna, are arranged side by side on an antenna base.

CITATION LIST

Patent Literature

The specification of U.S. patent application publication, No. 2008/0055171

SUMMARY OF INVENTION

Technical Problem

An integrated antenna into which at least two loop antennas are integrated has had the following problems.

That is, in a case where the loop antennas are arranged side by side on the basis of the integrated antenna disclosed in Patent Literature 1, there has been a problem that the integrated antenna is inevitably increased in size in a horizontal direction of the integrated antenna.

On the other hand, in a case where the loop antennas are arranged one above the other (in a case where the loop antennas are layered), there has been a problem that the integrated antenna is inevitably increased in size in a vertical direction of the integrated antenna. Moreover, in a case where two antennas, e.g., an SDARS antenna and a GPS antenna, are layered which receives respective electromagnetic waves coming from an identical direction (in this case, zenith direction), there has had concern that a characteristic of one of the antennas, which one is provided on a lower side, is deteriorated. This is because part of the electromagnetic wave which should be received by such a lower antenna is blocked by such an upper antenna.

The present invention has been made in view of the above problems, and an object of the present invention is to realize a small-sized integrated antenna into which at least two loop antennas are integrated, without causing a deterioration in characteristic of each of the loop antennas.

Solution to Problem

In order to attain the above object, an integrated antenna in accordance with the present invention includes: a first loop antenna having a first annular antenna element; and a second loop antenna having a second annular antenna element, the second loop antenna being lower in resonance frequency than the first loop antenna, the second annular antenna element being arranged, on an surface identical to that where the first annular antenna element is arranged, so as to surround the first annular antenna element.

Advantageous Effects of Invention

According to the present invention, it is possible to realize an integrated antenna which is smaller in size than a conventional integrated antenna, without causing a deterioration in characteristic of each loop antenna.

DESCRIPTION OF EMBODIMENTS

The following description will discuss, with reference to the drawings, an integrated antenna in accordance with the present embodiment.

A configuration of an integrated antenna1in accordance with the present embodiment will be described below with referent toFIG. 1.FIG. 1is a plan view illustrating a configuration of the integrated antenna1.

As illustrated inFIG. 1, the integrated antenna1includes a first loop antenna11, a first passive element12, a second loop antenna13, and a second passive element14. In the present embodiment, each of the first loop antenna11, the first passive element12, the second loop antenna13, and the second passive element14is made up of an electrically conductive foil (for example, copper foil) and is provided on a surface (identical surface) of a dielectric film (not illustrated).

The first loop antenna11has a first annular antenna element11a. In the present embodiment, a strip-shaped electric conductor which extends along a circle (can alternatively extend along an ellipse) is employed as the first annular antenna element11a. The first annular antenna element11aforms an open loop which is open in a direction of 9 o'clock (minus direction of an x axis) with respect to the center of the circle. That is, ends of the first annular antenna element11aface each other in the direction of 9 o'clock with respect to the center of the circle.

In the present embodiment, the first loop antenna11further has a first feed path11b, a second feed path11c, a first short-circuit part11d, and a second short-circuit part11e.

The first feed path11bis made up of a strip-shaped electric conductor which extends, substantially toward the center of the circle, from one of the ends of the first annular antenna element11a(which one is located on a plus direction side of a y axis relative to the other one of the ends). A first feed point11q, to which a coaxial cable (for example, an inner electric conductor of the coaxial cable) is connected, is provided at an end of the first feed path11bwhich end is located on a center side.

The second feed path11cis made up of a strip-shaped electric conductor which extends, substantially toward the center of the circle, from the other one of the ends of the first annular antenna element11a(which other one is located on a minus direction side of the y axis relative to the one of the ends). A second feed point11p, to which the coaxial cable (for example, an outer electric conductor of the coaxial cable) is connected, is provided at an end of the second feed path11cwhich end is located on the center side.

The first short-circuit part11dis made up of a straight stripe-shaped electric conductor, and is configured such that (i) a point on the first annular antenna element11a, particularly, a point located in a direction of 0 (zero) o'clock (plus direction of the y axis) with respect to the center of the circle and (ii) the end of the first feed path11b, which end is located on the center side, are short-circuited.

The second short-circuit part11eis made up of a straight stripe-shaped electric conductor, and is configured such that (i) a point on the first annular antenna element11a, particularly, a point located in a direction of 6 o'clock (minus direction of the y axis) with respect to the center of the circle and (ii) the end of the second feed path11c, which end is located on the center side, are short-circuited.

By providing the first short-circuit part11dand the second short-circuit part11e, a wide variety of current paths are formed on the first loop antenna11, so that a width of an operating band of the first loop antenna11is increased.

The first loop antenna11is provided so as to be adjacent to the first passive element12. In the present embodiment, the first passive element12is made up of a single electric conductor, and is arranged on an outer side of the first loop antenna11(inner side of the second loop antenna13). An inner circumference of the first passive element12faces (that is, the inner circumference of the first passive element12is capacitive-coupled with), in a direction between 0 (zero) o'clock and 3 o'clock and a direction between 6 o'clock and 9 o'clock with respect to the center of the circle, an outer circumference of the first annular antenna element11a.

The second loop antenna13has a second annular antenna element arranged, on a plane surface identical to that where the first annular antenna element11ais arranged, so as to surround the first annular antenna element11a(since the second loop antenna13has only the second annular antenna element as a component, the second annular antenna element will be also given a reference sign “13”). In the present embodiment, a strip-shaped electric conductor which extends along a square (can alternatively extend along a rectangle) is employed as the second annular antenna element13. The second annular antenna element13forms an open loop which is open in a direction of 0 (zero) o'clock with respect to the center of the square. That is, ends of the second annular antenna element13face each other in the direction of 0 (zero) o'clock with respect to the center of the square.

In other words, the second annular antenna element13is made up of (1) a first straight part13awhich extends in the minus direction of the x axis, (2) a second straight part13bwhich extends in the minus direction of the y axis from a terminal end of the first straight part13a, (3) a third straight part13cwhich extends in a plus direction of the x axis from a terminal end of the second straight part13b, (4) a fourth straight part13dwhich extends in the plus direction of the y axis from a terminal end of the third straight part13c, and (5) a fifth straight part13ewhich extends in the minus direction of the x axis from a terminal end of the fourth straight part13d. The first straight part13aand the fifth straight part13eare arranged on an identical straight line. A starting end of the first straight part13afaces a terminal end of the fifth straight part13e.

A first feed point13p, to which a coaxial cable (for example, an inner electric conductor of the coaxial cable) is connected, is provided at one of the ends of the second annular antenna element13(which one is located on a minus direction side of the x axis relative to the other one of the ends). Meanwhile, a second feed point13q, to which the coaxial cable (for example, an outer electric conductor of the coaxial cable) is connected, is provided at the other one of the ends of the second annular antenna element13(which other one is located on a plus direction side of the x axis relative to the one of the ends).

The second loop antenna13is provided so as to be adjacent to the second passive element14. In the present embodiment, the second passive element14is made up of a first electric conductor14aand a second electric conductor14beach of which is arranged an outer side of the second annular antenna element13. An inner circumference of the first electric conductor14afaces (that is, the inner circumference of the first electric conductor14ais capacitive-coupled with) outer circumferences of the first straight part13aand the second straight part13b, out of the straight parts constituting the second annular antenna element13. An inner circumference of the second electric conductor14bfaces (that is, the inner circumference of the second electric conductor14bis capacitive-coupled with) (i) an outer circumference of (part of) the third straight part13cand (ii) an outer circumference of the fourth straight part13d, out of the straight parts constituting the second annular antenna element13.

The first loop antenna11can be employed as an SDARS antenna which has a resonance frequency in an SDARS band (not less than 2320 MHz and not more than 2345 MHz). In this case, the first loop antenna11can be arranged in a square region of approximately 42 mm×42 mm.

The second loop antenna13can be employed as a GPS antenna which has a resonance frequency in a GPS band (1575.42±1 (one) MHz). In this case, the second loop antenna13can be arranged in a square region of approximately 54 mm×54 mm.

[Characteristics of Integrated Antenna]

Next, characteristics of the integrated antenna1, which characteristics have been revealed by the inventors carrying out simulations, will be described below with reference toFIGS. 2 and 3.

(a) ofFIG. 2is a perspective view illustrating current distribution formed in a case where a high-frequency current of 2.35 GHz is applied to the first and second feed points11pand11q.

In a case where the high-frequency current of 2.35 GHz is applied the first and second feed points11pand11q, strong current distribution is formed in the first loop antenna11(see (a) ofFIG. 2). It is understood from such distribution that the first loop antenna has a resonance frequency in the SDARS band, that is, functions as an SDARS antenna.

Note that, in a case where the high-frequency current of 2.35 GHz is applied to the first and second feed points11pand11q, current distribution formed in the second loop antenna13is sufficiently weak (see (a) ofFIG. 2). This means that, in causing the first loop antenna11to function as an SDARS antenna, the second loop antenna13has a sufficiently small effect.

(b) ofFIG. 2is a perspective view illustrating current distribution formed in a case where a high-frequency current of 1.575 GHz is applied to the first and second feed points13pand13q.

In a case where the high-frequency current of 1.575 GHz is applied to the first and second feed points13pand13q, strong current distribution is formed in the second loop antenna13(see (b) ofFIG. 2). It is understood from such distribution that the second loop antenna has a resonance frequency in the GPS band, that is, functions as a GPS antenna.

Note that, in a case where the high-frequency current of 1.575 GHz is applied to the first and second feed points13pand13q, current distribution formed in the first loop antenna11is sufficiently weak (see (b) ofFIG. 2). This means that, in causing the second loop antenna13to function as a GPS antenna, the first loop antenna11has a sufficiently small effect.

(a) ofFIG. 3is a graph illustrating a VSWR characteristic of the first loop antenna11. In the graph illustrated in (a) ofFIG. 3, a plot shown by block circles indicates the VSWR characteristic of the first loop antenna11which is integrated with the second loop antenna13. A plot shown by white triangles indicates the VSWR characteristic of the first loop antenna11which is not integrated with the second loop antenna13.

It is understood from (a) ofFIG. 3that a VSWR value of the first loop antenna11is not more than 4 in the SDARS band, irrespective of whether or not the first loop antenna11is integrated with the second loop antenna13. That is, it is understood from (a) ofFIG. 3that the operating band of the first loop antenna11corresponds to the SDARS band and that the first loop antenna11does not lose this characteristic even in a case where the first loop antenna11is integrated with the second loop antenna13.

(b) ofFIG. 3is a graph illustrating a VSWR characteristic of the second loop antenna13. In the graph illustrated in (b) ofFIG. 3, a plot shown by block circles indicates the VSWR characteristic of the second loop antenna13which is integrated with the first loop antenna11. A plot shown by white triangles indicates the VSWR characteristic of the second loop antenna13which is not integrated with the first loop antenna11.

It is understood from (b) ofFIG. 3that a VSWR value of the second loop antenna13is not more than 3 in the SDARS band, irrespective of whether or not the second loop antenna13is integrated with the first loop antenna11. That is, it is understood from (b) ofFIG. 3that an operating band of the second loop antenna13corresponds to the GPS band and that the second loop antenna13does not lose this characteristic even in a case where the second loop antenna13is integrated with the first loop antenna11.

Next, the characteristics of the integrated antenna1, which characteristics have been revealed by the inventors carrying out an experiment, will be described below with reference toFIGS. 4 and 5.

FIG. 4is a picture of an integrated antenna1used in the experiment. As illustrated inFIG. 4, the integrated antenna1used in the experiment is configured in the exactly same manner as the integrated antenna1illustrated inFIG. 1.

(a) ofFIG. 5is a graph illustrating (i) a VSWR characteristic of a first loop antenna11(shown as “SDARS” in (a) ofFIG. 5) and (ii) a VSWR characteristic of a second loop antenna13(shown as “GPS” in (a) ofFIG. 5). This graph is obtained by carrying out the experiment in a state where the first loop antenna1and the second loop antenna13are integrated with each other.

It is understood from (a) ofFIG. 5that (1) a VSWR value of the first loop antenna11is actually not more than 3 in the SDARS band and (2) a VSWR value of the second loop antenna13is actually not more than 4 in the GPS band.

(b) ofFIG. 5is a graph illustrating directional dependence of radiant gain, on a yz plane (seeFIG. 1), of a circularly polarized wave of the second loop antenna13. In (b) ofFIG. 5, θ indicates an angle formed with respect to a plus direction of a z axis (seeFIG. 1), and a unit of the radiant gain of the circularly polarized wave is dBic.

It is understood from (b) ofFIG. 5that the radiant gain of the circularly polarized wave of the second loop antenna13is sufficiently high in almost every direction (high enough to put the second loop antenna13to practical use).

(c) ofFIG. 5is a graph illustrating directional dependence of radiant gain, on the yz plane (seeFIG. 1), of a circularly polarized wave of the first loop antenna11. In (c) ofFIG. 5, θ indicates an angle formed with respect to the plus direction of the z axis (seeFIG. 1), and a unit of the radiant gain of the circularly polarized wave is dBic.

It is understood from (c) ofFIG. 5that the radiant gain of the circularly polarized wave of the first loop antenna11is sufficiently high in every direction (high enough to put the first loop antenna11to practical use).

As has been described, the operating band of the first loop antenna11corresponds to the SDARS band, and the first loop antenna11does not lose this characteristic even in a case where the first loop antenna11is integrated with the second loop antenna13. Meanwhile, the operating band of the second loop antenna13corresponds to the GPS band, and the second loop antenna13does not lose this characteristic even in a case where the second loop antenna13is integrated with the first loop antenna11.

However, this does not deny that (i) existence of the first loop antenna11affects the characteristic of the second loop antenna13and (ii) existence of the second loop antenna13affects the characteristic of the first loop antenna11. Indeed, an axial ratio of the first loop antenna11is improved by integrating the first loop antenna11with the second loop antenna13. That is, by combining the first loop antenna11with the second loop antenna13as illustrated inFIG. 1, a new effect is brought about such that the axial ratio of the first loop antenna11is improved.

This point will be described below with reference toFIG. 6.

(a) and (b) ofFIG. 6are graphs each illustrating directional dependence of radiant gain of a circularly polarized wave of the first loop antenna11at 2340 MHz which gain is obtained in a state where the first loop antenna11is integrated with the second loop antenna13. In particular, (a) ofFIG. 6illustrates gain, on a zx plane (seeFIG. 1), of a left-handed circularly polarized wave (LHCP) and of a right-handed circularly polarized wave (RHCP). (b) ofFIG. 6illustrates gain, on a yz plane (seeFIG. 1), of a left-handed circularly polarized wave (LHCP) and of a right-handed circularly polarized wave (RHCP).

On the other hand, (c) and (d) ofFIG. 6are graphs each illustrating the directional dependence of the radiant gain of the circularly polarized wave of the first loop antenna11at 2340 MHz which gain is obtained in a state where the first loop antenna11is not integrated with the second loop antenna13. In particular, (c) ofFIG. 6illustrates the gain, on the zx plane (seeFIG. 1), of the left-handed circularly polarized wave (LHCP) and of the right-handed circularly polarized wave (RHCP). (d) ofFIG. 6illustrates the gain, on the yz plane (seeFIG. 1), of the left-handed circularly polarized wave (LHCP) and of the right-handed circularly polarized wave (RHCP).

In regard to the radiant gain, on the zx plane, of the circularly polarized wave of the first loop antenna11, it is understood from comparison between the graph illustrated in (a) ofFIG. 6and the graph illustrated in (c) ofFIG. 6that, by integrating the first loop antenna11with the second loop antenna13, the radiant gain of the right-handed circularly polarized wave can be lowered while the radiant gain of the left-handed circularly polarized wave is kept substantially constant. That is, in regard to the radiant gain, on the zx plane, of the circularly polarized wave of the first loop antenna11, it is understood that the axial ratio of the first loop antenna11is improved by integrating the first loop antenna11with the second loop antenna13.

Meanwhile, in regard to the radiant gain, on the yz plane, of the circularly polarized wave of the first loop antenna11, it is understood from comparison between the graph illustrated in (b) ofFIG. 6and the graph illustrated in (d) ofFIG. 6that, by integrating the first loop antenna11with the second loop antenna13, the radiant gain of the right-handed circularly polarized wave can be lowered while the radiant gain of the left-handed circularly polarized wave is kept substantially constant. That is, in regard to the radiant gain, on the yz plane, of the circularly polarized wave of the first loop antenna11, it is understood that the axial ratio of the first loop antenna11is improved by integrating the first loop antenna11with the second loop antenna13.

It is considered that the reason why the axial ratio of the first loop antenna11is thus improved is that the second loop antenna13functions as a passive element for the first loop antenna11and, as a result, a phase difference between a longitudinal current and a lateral current in the first loop antenna11is adjusted.

According to the integrated antenna1, the first passive element12is provided between the antenna element of the first loop antenna11and the antenna element of the second loop antenna13. Therefore, even in a case where a shape, on an inner circumference side and/or an outer circumference side, of the antenna element of the first loop antenna11is changed so as to adjust the resonance frequency of the first loop antenna11, there is no concern that such a change in shape affects the resonance frequency of the second loop antenna13. Similarly, even in a case where a shape, on an outer circumference side, of the antenna element of the second loop antenna13is changed so as to adjust the resonance frequency of the second loop antenna13, there is no concern that such a change in shape affects the resonance frequency of the first loop antenna11. Therefore, the integrated antenna1brings about a merit in manufacturing such that it is possible to individually adjust the resonance frequency of the first loop antenna11and the resonance frequency of the second loop antenna13. This point will be described below with reference toFIG. 7.

FIG. 7is a plan view illustrating a configuration of an integrated antenna1in accordance with Example of the present invention. (a) ofFIG. 7illustrates the configuration of the integrated antenna1in which no change was made. According to the integrated antenna1illustrated in (a) ofFIG. 7, a resonance frequency of a first loop antenna11was 1.90 GHz, whereas a resonance frequency of a second loop antenna13was 1.96 GHz.

(b) ofFIG. 7illustrates the configuration of the integrated antenna1in which a shape, on an inner circumference side, of the first loop antenna11was changed. Specifically, as illustrated in (b) ofFIG. 7, a change was made in shape by adding an electric conductor11fto an inner circumference side of an antenna element of the first loop antenna11. According to the integrated antenna1illustrated in (b) ofFIG. 7, the resonance frequency of the first loop antenna11was 2.11 GHz, whereas the resonance frequency of the second loop antenna13was 1.96 GHz. That is, it was found that, even in a case where the resonance frequency of the first loop antenna11was changed by making such a change, the resonance frequency of the second loop antenna13did not change.

(c) ofFIG. 7illustrates the configuration of the integrated antenna1in which the shape, on the inner circumference side and an outer circumference side, of the first loop antenna11was changed. Specifically, as illustrated in (c) ofFIG. 7, a change was made in shape by adding the electric conductor11fto the antenna element of the first loop antenna11so that part of the electric conductor11fprojects out from an outer circumference side of the antenna element. According to the integrated antenna1illustrated in (c) ofFIG. 7, the resonance frequency of the first loop antenna11was 1.69 GHz, whereas the resonance frequency of the second loop antenna13was 1.96 GHz. That is, it was found that, even in a case where the resonance frequency of the first loop antenna11was changed by making such a change, the resonance frequency of the second loop antenna13did not change.

(d) ofFIG. 7illustrates the configuration of the integrated antenna1in which a shape, on an outer circumference side, of the second loop antenna13was changed. Specifically, as illustrated in (d) ofFIG. 7, a change was made in shape by adding electric conductors13fand13gto an outer circumference side of an antenna element of the second loop antenna13. According to the integrated antenna1illustrated in (d) ofFIG. 7, the resonance frequency of the second loop antenna13was 1.82 GHz, whereas the resonance frequency of the first loop antenna11was 1.90 GHz. That is, it was found that, even in a case where the resonance frequency of the second loop antenna13was changed by making such a change, the resonance frequency of the first loop antenna11did not change.

Even in a case where no first passive element12is provided between the antenna element of the first loop antenna11and the antenna element of the second loop antenna13, it is possible to achieve the following effect. That is, even in a case where the inner circumference side of the antenna element of the first loop antenna11is changed in shape so as to adjust the resonance frequency of the first loop antenna11, this does not affect the resonance frequency of the second loop antenna13. This point will be described below with reference toFIG. 8.

FIG. 8is a plan view illustrating a configuration of an integrated antenna1in accordance with Example of the present invention. (a) ofFIG. 8illustrates the configuration of the integrated antenna1in which no change was made. The integrated antenna1illustrated inFIG. 8was identical in configuration to the integrated antenna1illustrated inFIG. 7, except that the integrated antenna1illustrated inFIG. 8included no first passive element12and no second passive element14. According to the integrated antenna1illustrated in (a) ofFIG. 8, a resonance frequency of a first loop antenna11was 1.50 GHz, whereas a resonance frequency of a second loop antenna13was 1.30 GHz.

(b) ofFIG. 8illustrates the configuration of the integrated antenna1in which a shape, on an inner circumference side, of the first loop antenna11was changed. Specifically, as illustrated in (b) ofFIG. 8, a change was made in shape by adding electric conductors11f,11g, and11hto an inner circumference side of an antenna element of the first loop antenna11. According to the integrated antenna1illustrated in (b) ofFIG. 8, the resonance frequency of the first loop antenna11was 0.79 GHz, whereas the resonance frequency of the second loop antenna13was 1.30 GHz. That is, it was found that, even in a case where the resonance frequency of the first loop antenna11was changed by making such a change, the resonance frequency of the second loop antenna13did not change.

The integrated antenna1is suitably mounted on an on-vehicle antenna device. Such an antenna device2will be described below with reference toFIG. 9.FIG. 9is a perspective view schematically illustrating a configuration of the antenna device2.

As illustrated inFIG. 9, the antenna device2includes a base21, a spacer22, and a radome23. Note that, in order to clarify an inner structure of the antenna device2,FIG. 9illustrates the antenna device2in a state where the radome23is removed.

The base21is a plate member whose upper and lower surfaces each have a square shape, and is made of metal such as aluminum. In a case where the antenna device2is mounted on a vehicle, the base21is arranged on a roof of the vehicle so that a diagonal line of the base21is parallel to a travelling direction of the vehicle.

The spacer22is placed on the upper surface of the base21. The spacer22is, for example, a columnar member made of resin, and is configured to cause the base21to be apart from an antenna.

On an upper surface of the spacer22, three areas A1, A2, an A3are provided to each of which an antenna is attached. The integrated antenna1is attached to the area A1which has a square shape and which is provided in the center of the upper surface of the spacer22.

The radome23is, for example, a ship-bottom-shaped member made of resin, and is configured to cover the spacer22to whose upper surface an antenna is attached. The antenna, housed in an enclosed space formed by the base21and the radome23, is not exposed to rain water.

The area A of the antenna device2, to which area A the integrated antenna1is attached, is arranged so that a diagonal line of the area A is parallel to the travelling direction of the vehicle, that is, the diagonal line of the area A is parallel to the diagonal line of the upper surface of the base21. This allows the antenna device2to have a streamline-shape in which a front part of the antenna device2is sharp, without unnecessarily increasing a size of the antenna device2.

Note that an antenna, other than the integrated antenna1, such as an antenna for DAB or an antenna for LTE can be mounted on the antenna device2. Each of the areas A2and A3, each having an L-shape and provided on the upper surface of the spacer22, is an area to which such an antenna is attached. Examples of the antenna, other than the integrated antenna1, which is suitably mounted on the antenna device2encompass a monopole antenna and an inverted F antenna.

In this case, the antenna to be attached to the area A2can be attached, in part, to a side surface S1and/or a side surface S2of the spacer22. Similarly, the antenna to be attached to the area A3can be attached, in part, to a side surface S3and/or a side surface S4of the spacer22. Further, in a case where the base21is made of metal, the base21can be used as a ground plane.

The foregoing embodiment has described a configuration such that the first passive element12is arranged on the outer side of the first annular antenna element11a(between the first annular antenna element11aand the second annular antenna element13). However, the present invention is not limited to such a configuration. That is, the first passive element12can be alternatively arranged on an inner side of the first annular antenna element11a.

Furthermore, the foregoing embodiment has described a configuration such that the second passive element14is arranged on the outer side of the second annular antenna element13. However, the present invention is not limited to such a configuration. That is, the second passive element14can be alternatively arranged on the inner side of the second annular antenna element13(between the first annular antenna element11aand the second annular antenna element13).

As has been described, an integrated antenna in accordance with the present embodiment includes: a first loop antenna having a first annular antenna element; and a second loop antenna having a second annular antenna element, the second loop antenna being lower in resonance frequency than the first loop antenna, the second annular antenna element being arranged, on an surface identical to that where the first annular antenna element is arranged, so as to surround the first annular antenna element.

According to the above configuration, the second annular antenna element is arranged so as to surround the first annular antenna element. Therefore, it is possible to avoid a problem with a configuration in which two loop antennas are arranged side by side. That is, it is possible to avoid a problem that the integrated antenna is increased in side in a horizontal direction of the integrated antenna. Furthermore, according to the above configuration, the first annular antenna element and the second annular antenna element are arranged on an identical surface. Therefore, it is possible to avoid problems with a configuration in which two loop antennas are layered. That is, it is possible to avoid (i) a problem that the integrated antenna is increased in size in a vertical direction of the integrated antenna and (ii) a problem that a characteristic of one of the two loop antennas, which one is provided on a lower side, is deteriorated. Namely, according the above configuration, it is possible to realize an integrated antenna which is smaller in size than a conventional integrated antenna, without causing a deterioration in characteristic of each loop antenna.

Moreover, it has been revealed from the experiment carried out by the inventors that an axial ratio of the first loop antenna is improved by arranging the second annular antenna element so as to surround the first annular antenna element. That is, according to the above configuration, it is possible to achieve not only a passive effect that the characteristic of each loop antenna is not deteriorated, but also an active effect that the axial ratio of the first loop antenna is improved.

The integrated antenna in accordance with the present embodiment is preferably arranged so as to further include a first passive element arranged between the first annular antenna element and the second annular antenna element, at least part of an inner circumference of the first passive element facing at least part of an outer circumference of the first annular antenna element.

According to the above configuration, it is possible to cause the first loop antenna to function as an antenna suitable to receive a circularly polarized wave such as an SDARS wave, due to action of the first passive element. Besides, since the first passive element is arranged on an outer side of the first annular antenna element, it is possible to add, to an inner side of the first annular antenna element, a configuration such as a feed path and a short-circuit part.

Furthermore, according to the above configuration, the first passive element is provided between the second annular antenna element and the first annular antenna element. Therefore, even in a case where a shape of the first annular antenna element is changed so as to adjust the resonance frequency of the first loop antenna, the resonance frequency of the second loop antenna does not change considerably. Meanwhile, even in a case where a shape of the second annular antenna element is changed so as to adjust the resonance frequency of the second loop antenna, the resonance frequency of the first loop antenna does not change considerably. Therefore, according to the above configuration, it is possible to realize an integrated antenna which allows the resonance frequency of the first loop antenna and the resonance frequency of the second loop antenna to be individually (that is, easily) adjusted.

The integrated antenna in accordance with the present embodiment is preferably arranged such that the first loop antenna further has: first and second feed paths extending, toward a center of a region surrounded by the first annular antenna element, from respective ends of the first annular antenna element which ends face each other; a first short-circuit part configured such that (i) an end of the first feed path which end is located on a center side and (ii) a first point on the first annular antenna element are short-circuited; and a second short-circuit part configured such that an end of the second feed path which end is located on the center side and (ii) a second point on the first annular antenna element are short-circuited.

According to the above configuration, it is possible to connect a coaxial cable to the ends of the respective first and second feed paths which ends are each located on the center side. Therefore, it is possible to avoid a problem caused in a case where a coaxial cable is connected to the ends of the first annular antenna element. That is, it is possible to avoid a problem that a characteristic of the first loop antenna is deteriorated because the coaxial cable passes by the first annular antenna element.

Moreover, according to the above configuration, by providing the first and second short-circuit parts, a wide variety of current paths are formed on the first loop antenna. As a result, it is possible to increase a width of an operating band (band in which a VSRW value is not more than a predetermined threshold) of the first loop antenna.

The integrated antenna in accordance with the present embodiment is preferably arranged so as to further include a second passive element arranged on an outer side of the second annular antenna element, at least part of an inner circumference of the second passive element facing at least part of an outer circumference of the second annular antenna element.

According to the above configuration, it is possible to cause the second loop antenna to function as an antenna suitable to receive a circularly polarized wave such as a GPS wave, due to action of the second passive element.

As has been described, according to the integrated antenna in accordance with the present embodiment, it is possible to realize an integrated antenna which is smaller in size than a conventional integrated antenna, without causing a deterioration in characteristic of each loop antenna.

A method of manufacturing the integrated antenna in accordance with the present embodiment includes the step of: changing a shape of the first annular antenna element so as to adjust the resonance frequency of the first loop antenna.

According to the integrated antenna, the first passive element is provided between the second annular antenna element and the first annular antenna element. Therefore, even in a case where the step of changing the shape of the first annular antenna element is carried out so as to adjust the resonance frequency of the first loop antenna, the resonance frequency of the second loop antenna hardly changes. Thus, according to the above configuration, it is possible to individually (that is, easily) adjust the resonance frequency of the first loop antenna and the resonance of the second loop antenna.

A method of manufacturing the integrated antenna in accordance with the present embodiment includes the step of: changing a shape, on an inner circumference side, of the first annular antenna element so as to adjust the resonance frequency of the first loop antenna.

According to the integrated antenna, even in a case where the step of changing the shape, on the inner circumference side, of the first annular antenna element is carried out so as to adjust the resonance frequency of the first loop antenna, the resonance frequency of the second loop antenna hardly changes. Thus, according to the above configuration, it is possible to adjust the resonance frequency of the first loop antenna, separately from the resonance of the second loop antenna. That is, it is possible to easily adjust the resonance frequency of the first loop antenna.

Although the embodiments of the present invention have been described, the present invention is not limited to the embodiments, but may be altered by a skilled person in the art within the scope of the claims. An embodiment derived from a proper combination of technical means disclosed in different embodiments is also encompassed in the technical scope of the present invention.

INDUSTRIAL APPLICABILITY

The present invention is widely applicable to integrate antennas which operate in two or more different frequency bands. For example, the present invention is suitably employed as an on-vehicle antenna mounted on a vehicle such as a car.

REFERENCE SIGNS LIST