Antenna device

Included are: a coaxial line (10) provided so as to pass through a second ground conductor (6), a first dielectric substrate (8), and a second dielectric substrate (9), the coaxial line (10) including an outer conductor (11) allowing a first ground conductor (1), a second ground conductor (6), and a third ground conductor (7) to be conductive thereamong; and a conductive member (15) provided so as to pass through the first dielectric substrate (8), the conductive member (15) allowing the first ground conductor (1) and the second ground conductor (6) to be conductive therebetween. An interface circuit (18) combines a plurality of signals having mutually different phases output from each of plurality of element antennas (3a), (3b), (3c), and (3d) and outputs the combined signal to the coaxial line (10).

TECHNICAL FIELD

The present invention relates to an antenna device including a plurality of element antennas.

BACKGROUND ART

Some of terminals for receiving polarized waves transmitted from satellite telephone service or global positioning system (GPS) satellites use circularly polarized wave antennas in order to avoid a polarized wave loss from growing even when a terminal user moves.

Examples of circularly polarized wave antennas include spiral antennas and patch antennas. However, it is known that a circularly polarized wave antenna such as a spiral antenna is increased in size if an attempt is made to broaden the bandwidth of the antenna.

Moreover, for example when a polarized wave transmitted from a GPS satellite is reflected by the ground or a building, the polarized wave may be changed to reverse rotation.

In a case where the polarized wave transmitted from the GPS satellite is a right-handed circularly polarized wave (RHCP), the RHCP may change to a left-handed circularly polarized wave (LHCP).

It is known that when a circularly polarized wave antenna such as a spiral antenna is reduced in size, a back lobe, which is a cross polarized wave extending backward from the antenna, increases. In a case where the polarized wave transmitted from the GPS satellite is RHCP, a back lobe which is a cross polarized wave is LHCP.

For this reason, reducing the size of a circularly polarized wave antenna increases the possibility for the circularly polarized wave antenna to receive unwanted LHCPs, which may deteriorate the positioning performance based on polarized waves transmitted from the GPS satellites.

Since reducing the size of a circularly polarized wave antenna increases the possibility of receiving unnecessary back lobes, a large-sized circularly polarized wave antenna is generally used. In a case where it is highly desired to reducing the size of a circularly polarized wave antenna, however, reception of unnecessary back lobes may be suppressed by providing a large ground plate separately.

However, in a case where a large ground plate is provided separately, the entire antenna device including the circularly polarized wave antenna becomes larger.

Patent Literature 1 below discloses an antenna device in which reception of unnecessary back lobes is suppressed without separately providing a large ground plate.

The antenna device disclosed in Patent Literature 1 suppresses reception of unnecessary back lobes by providing a choke structure on the bottom surface of a radiation conductor.

The choke structure provided on the bottom surface of the radiation conductor has two conductor plates arranged in parallel, and the center portions of the two conductor plates are thicker than the edges of the two conductor plates.

By allowing the center portions of the two conductor plates and the edges of the two conductor plates to have different thicknesses, it becomes possible to adjust the electrical length of the choke structure depending on the frequency of an unnecessary back lobe.

CITATION LIST

Patent Literature

Patent Literature 1: JP 2014-135707 A

SUMMARY OF INVENTION

Technical Problem

Since a conventional antenna device is configured as described above, reception of unnecessary back lobes can be suppressed without providing a large ground plate separately.

However, since the choke structure provided instead of a large ground plate has a complicated structure in which the center portions of the two conductor plates and the edges of the two conductor plates have different thicknesses, producing the antenna devices is disadvantageously troublesome.

The present invention has been devised to solve the disadvantage as described above, and an object of the invention is to obtain an antenna device capable of adjusting the resonance frequency and suppressing reception of unnecessary back lobes without mounting a complicated choke structure.

Solution to Problem

An antenna device according to the present invention includes: a first ground conductor having a first plane and a second plane; a plurality of element antennas arranged on the first plane of the first ground conductor; a second ground conductor arranged on the second plane of the first ground conductor in parallel with the first ground conductor; a third ground conductor arranged in parallel to the second ground conductor on, of two planes of the second ground conductor, a plane opposite to the plane on which the first ground conductor is arranged; a first dielectric substrate arranged between the first ground conductor and the second ground conductor; a second dielectric substrate arranged between the second ground conductor and the third ground conductor; a coaxial line provided so as to pass through the second ground conductor and the first and second dielectric substrates, the coaxial line including an outer conductor allowing the first ground conductor, the second ground conductor, and the third ground conductor to be conductive thereamong; a conductive member provided so as to pass through the first dielectric substrate, the conductive member allowing the first ground conductor and the second ground conductor to be conductive therebetween; and an interface circuit for combining a plurality of signals having mutually different phases output from each of the plurality of element antennas and outputting the combined signal to the coaxial line.

Advantageous Effects of Invention

According to this invention, included are: a coaxial line provided so as to pass through a second ground conductor and first and second dielectric substrates, the coaxial line including an outer conductor allowing the first ground conductor, the second ground conductor, and the third ground conductor to be conductive thereamong; and a conductive member provided so as to pass through the first dielectric substrate, the conductive member allowing the first ground conductor and the second ground conductor to be conductive therebetween, and an interface circuit combines a plurality of signals having mutually different phases output from each of the plurality of element antennas and outputs the combined signal to the coaxial line. This allows the resonance frequency to be adjusted to suppress reception of unwanted back lobes without mounting a complicated choke structure.

DESCRIPTION OF EMBODIMENTS

To describe the present invention further in detail, embodiments for carrying out the present invention will be described below with reference to the accompanying drawings.

First Embodiment

FIG. 1is a perspective view illustrating an antenna device according to a first embodiment of the present invention.

FIG. 2is a cross-sectional side view of the antenna device ofFIG. 1as viewed from direction A.

FIG. 3is a plan view illustrating feeding points4a,4b,4c, and4dof element antennas3a,3b,3c, and3d, a coaxial line10, and an interface circuit18on a first plane1aof a first ground conductor1.

InFIGS. 1 to 3, the first ground conductor1has the first plane1aand a second plane1b.

The first ground conductor1is a flat plate having a square planar shape.

A circularly polarized wave transmitting/receiving unit2is arranged on the first plane1aof the first ground conductor1.

The circularly polarized wave transmitting/receiving unit2includes the element antennas3a,3b,3c, and3dthat can transmit and receive circularly polarized waves.

In this first embodiment, an example will be explained in which the circularly polarized wave transmitting/receiving unit2has four element antennas3a,3b,3c, and3das element antennas; however, the number of element antennas is only required to be plural, and is not limited to four.

The feeding points4a,4b,4c, and4dof the element antennas3a,3b,3c, and3dindicate, for example, positions where a signal output from the interface circuit18is input when a circularly polarized wave is transmitted. Although the feeding points4a,4b,4c, and4dare drawn inFIGS. 1 to 3; however, the feeding points4a,4b,4c, and4dare not formed as physical components of the antenna device.

The total length of each of the element antennas3a,3b,3c, and3dis about a quarter wavelength at the resonance frequency.

In the element antennas3a,3b,3c, and3d, each of the tip portions extending from the bended points3ab,3bb,3cb, and3dbto the tips5a,5b,5c, and5dis parallel to the first plane1aof the first ground conductor1.

Moreover, in the element antennas3a,3b,3c, and3d, directions from the bended points3ab,3bb,3cb, and3dbto the tips5a,5b,5c, and5dare different from each other by 90 degrees, and are parallel to one of the sides of the first ground conductor1.

InFIG. 1, the direction from the bended point3abto the tip5ais parallel to the lower side of the first ground conductor1on the paper, and the direction from the bended point3bbto the tip5bis parallel to the left side of the first ground conductor1on the paper.

The direction from the bended point3cbto the tip5cis parallel to the upper side of the first ground conductor1on the paper, and the direction from the bended point3dbto the tip5dis parallel to the right side of the first ground conductor1on the paper.

A second ground conductor6is arranged in parallel with the first ground conductor1on a second plane1bside of the first ground conductor1.

The second ground conductor6is a flat plate having a square planar shape, and the length of each side of the second ground conductor6is half a wavelength at the resonance frequency of the element antennas3a,3b,3c, and3d.

Note that the length of each side of the second ground conductor6may be the length that completely matches the length of the half wavelength at the resonance frequency and may also be a length that substantially matches the length of the half wavelength at the resonance frequency.

A third ground conductor7is arranged in parallel with the second ground conductor6on the plane opposite to the plane on which the first ground conductor1is arranged out of the two planes of the second ground conductor6.

The third ground conductor7is a flat plate having a square planar shape, and the length of each side of the third ground conductor7is longer than or equal to half a wavelength at the resonance frequency of the element antennas3a,3b,3c, and3d.

A first dielectric substrate8is arranged between the first ground conductor1and the second ground conductor6.

A second dielectric substrate9is arranged between the second ground conductor6and the third ground conductor7.

The length of each side of the second dielectric substrate9is longer than or equal to the length of each side of the third ground conductor7since the second ground conductor6and the third ground conductor7are copper foil patterns on the second dielectric substrate9.

The coaxial line10includes an outer conductor11and an inner conductor14. Although the coaxial line10is illustrated inFIGS. 2 and 3, the coaxial line10is not illustrated inFIG. 1to simplify the drawing.

The outer conductor11is provided so as to pass through the second ground conductor6, the first dielectric substrate8, and the second dielectric substrate9, and allows the first ground conductor1, the second ground conductor6, and the third ground conductor7to be conductive thereamong.

The outer conductor11includes a penetrating member12and a conductor13, and one end thereof is connected to the second plane1bof the first ground conductor1at a position surrounded by the feeding points4a,4b,4c, and4dof the element antennas3a,3b,3c, and3d.

InFIG. 3, an example is illustrated in which seven outer conductors11are arranged.

The penetrating member12is a through-hole member arranged at a position surrounded by the feeding points4a,4b,4c, and4din the element antennas3a,3b,3c, and3don the second plane1bof the first ground conductor1.

The conductor13is a metal member that is inserted in the penetrating member12to allow the first ground conductor1, the second ground conductor6, and the third ground conductor7to be conductive thereamong.

The inner conductor14is arranged at a position surrounded by the plurality of outer conductors11, and one end14aof the inner conductor14is connected to a 180-degree hybrid19of the interface circuit18.

The other end14bof the inner conductor14is connected to a circuit (not illustrated) for inputting and outputting signals.

A conductive member15includes a penetrating member16and a conductor17, and one end thereof is connected to the second plane1bof the first ground conductor1at a position surrounding the feeding points4a,4b,4c, and4dof the element antennas3a,3b,3c, and3d.

Although, inFIG. 2, an example is illustrated in which two conductive members15are arranged, tens or hundreds of conductive members15are often arranged in practice.

The conductive members15are provided so as to pass through the first dielectric substrate8and allow the first ground conductor1and the second ground conductor6to be conductive therebetween.

The penetrating members16are through-hole members arranged at positions surrounding the feeding points4a,4b,4c, and4din the element antennas3a,3b,3c, and3don the second plane1bof the first ground conductor1.

The conductor17is a metal member that is inserted in a penetrating member16to allow the first ground conductor1and the second ground conductor6to be conductive therebetween.

The interface circuit18includes the 180-degree hybrid19and 90-degree hybrids20and21, and is patterned on the first plane1aof the first ground conductor1by etching.

The interface circuit18combines four signals having mutually different phases output from each of the feeding points4a,4b,4c, and4dof the element antennas3a,3b,3c, and3dand outputs the combined signal to the coaxial line10when the element antennas3a,3b,3c, and3dare used as reception antennas.

The interface circuit18divides a signal transmitted by the coaxial line10into four signals having mutually different phases and outputs each of the divided four signals to one of the feeding points4a,4b,4c, and4dof the element antennas3a,3b,3c, and3dwhen the element antennas3a,3b,3c, and3dare used as transmission antennas.

Although the interface circuit18is illustrated inFIG. 3, the interface circuit18is not illustrated inFIG. 1nor2to simplify the drawings.

The 180-degree hybrid19combines, for example, a signal having a phase of 0 degrees output from the 90-degree hybrid20and, for example, a signal having a phase of 180 degrees output from the 90-degree hybrid21and outputs the combined signal to the coaxial line10when the element antennas3a,3b,3c, and3dare used as reception antennas.

The 180-degree hybrid19divides a signal transmitted by the coaxial line10into two signals having phases that are 180 degrees different from each other, and outputs one of the divided signals to the 90-degree hybrid20and the other divided signal to the 90-degree hybrid21when the element antennas3a,3b,3c, and3dare used as transmission antennas.

For example, in a case where the phase of one of the divided signals is 0 degrees, the phase of the signal output from the 180-degree hybrid19to the 90-degree hybrid20is 0 degrees, and the phase of the signal output from the 180-degree hybrid19to the 90-degree hybrid21is 180 degrees.

The 90-degree hybrid20combines, for example, a signal having a phase of 0 degrees output from the feeding point4aof the element antenna3aand, for example, a signal having a phase of 90 degrees output from the feeding point4bof the element antenna3band outputs a synthesized signal having a phase of 0 degrees to the 180-degree hybrid19when the element antennas3a,3b,3c, and3dare used as reception antennas.

The 90-degree hybrid20divides, for example, a signal having a phase of 0 degrees output from the 180-degree hybrid19into a signal having a phase of 0 degrees and a signal having a phase of 90 degrees, and outputs the divided signal having the phase of 0 degrees to the feeding point4aof the element antenna3aand the divided signal having the phase of 90 degrees to the feeding point4bof the element antenna3bwhen the element antennas3a,3b,3c, and3dare used as transmission antennas.

The 90-degree hybrid21combines a signal having, for example, a phase of 180 degrees output from the feeding point4cof the element antenna3cand a signal having, for example, a phase of 270 degrees output from the feeding point4dof the element antenna3dand outputs a synthesized signal having a phase of 180 degrees to the 180-degree hybrid19when the element antennas3a,3b,3c, and3dare used as reception antennas.

The 90-degree hybrid21divides, for example, a signal having a phase of 180 degrees output from the 180-degree hybrid19into a signal having a phase of 180 degrees and a signal having a phase of 270 degrees, and outputs the divided signal having the phase of 180 degrees to the feeding point4cof the element antenna3cand the divided signal having the phase of 270 degrees to the feeding point4dof the element antenna3dwhen the element antennas3a,3b,3c, and3dare used as transmission antennas.

In the first embodiment, the portion sandwiched between the second ground conductor6and the third ground conductor7operates as a microstrip resonator22.

Next, the operation will be described.

Since the operation when the element antennas3a,3b,3c, and3dare used as transmission antennas and the operation when the element antennas3a,3b,3c, and3dare used as reception antennas are reversible, here, the operation when the element antennas3a,3b,3c, and3dare used as transmission antennas will be described representatively.

When a signal is given from the circuit not illustrated to the other end14bof the inner conductor14in the coaxial line10, the signal given from the circuit not illustrated is transmitted to the one end14aof the coaxial line10and then is transmitted to the interface circuit18.

Here, for convenience of explanation, it is assumed that the phase of the signal output from the one end14aof the coaxial line10to the interface circuit18is 0 degrees.

The 180-degree hybrid19of the interface circuit18divides the signal having the phase of 0 degrees output from the one end14aof the coaxial line10into two signals having phases that are 180 degrees different from each other, and outputs a signal having a phase of 0 degrees to the 90-degree hybrid20and a signal having a phase of 180 degrees to the 90-degree hybrid21.

The 90-degree hybrid20divides the signal having the phase of 0 degrees output from the 180-degree hybrid19into two signals having phases that are 90 degrees different from each other, and outputs a signal having a phase of 0 degrees to the feeding point4aof the element antenna3aand a signal having a phase of 90 degrees to the feeding point4bof the element antenna3b.

The 90-degree hybrid21divides the signal having the phase of 180 degrees output from the 180-degree hybrid19into two signals having phases that are 90 degrees different from each other, and outputs a signal having a phase of 180 degrees to the feeding point4cof the element antenna3cand a signal having a phase of 270 degrees to the feeding point4dof the element antenna3d.

As a result, the element antennas3a,3b,3c, and3dof the circularly polarized wave transmitting/receiving unit2are provided with signals whose phases are different from each other by 90 degrees, and an electromagnetic wave corresponding to the signals is radiated into a space as a result of the resonance phenomenon generated when the signals are transmitted through the element antennas3a,3b,3c, and3d.

Since the phases of the signals transmitted through the element antennas3a,3b,3c, and3dare different from each other by 90 degrees, RHCP which is a desired electromagnetic wave is radiated in the zenith direction (0 deg) illustrated inFIG. 2and LHCP which is an unwanted electromagnetic wave is radiated in the ground direction (±90 deg).

The antenna device includes the third ground conductor7and the second dielectric substrate9in the first embodiment; however, a case is assumed as illustrated inFIGS. 4 and 5in which the antenna device does not include the third ground conductor7nor the second dielectric substrate9.

FIG. 4is a perspective view illustrating an antenna device not including the third ground conductor7nor the second dielectric substrate9.

FIG. 5is a cross-sectional side view of the antenna device ofFIG. 4as viewed from direction A.

In a case of an antenna device in which the length of each side of the first dielectric substrate8, the first ground conductor1, and the second ground conductor6is short, the values of the RHCP gain and the LHCP gain are substantially the same as illustrated inFIG. 6. As an example in which the length of each side of the second ground conductor6is short, the length of half a wavelength at the resonance frequency of the element antennas3a,3b,3c, and3dis conceivable.

FIG. 6is an explanatory graph illustrating the RHCP gain and the LHCP gain in an antenna device in which each side of the first dielectric substrate8, the first ground conductor1, and the second ground conductor6is short.

The horizontal axis inFIG. 6represents the zenith angles of RHCP and LHCP, and the vertical axis inFIG. 6represents the gains of the RHCP and the LHCP.

For example, when an RHCP signal is transmitted to the ground from a GPS satellite or a quasi-zenith satellite, the RHCP signal is reflected by the ground, a building, etc., and the RHCP signal is inverted to generate LHCP.

Since the antenna device, in which each side of the first dielectric substrate8, the first ground conductor1, and the second ground conductor6is short, has substantially the same value for the RHCP gain and the LHCP gain, there is a high possibility that an LHCP signal, which is an unwanted wave, is received erroneously when the antenna device is used for receiving an RHCP signal transmitted from the GPS satellite or the quasi-zenith satellite to the ground. Therefore, the possibility of incurring degradation of the positioning performance based on the RHCP increases.

In the first embodiment, the antenna device includes the third ground conductor7and the second dielectric substrate9in order to reduce the possibility of erroneously receiving an LHCP signal that is an unwanted wave even in the case where the length of each side of the first dielectric substrate8, the first ground conductor1, and the second ground conductor6is small.

In the first embodiment, the length of each side of the second ground conductor6equals the length of half a wavelength at the resonance frequency of the element antennas3a,3b,3c, and3d.

The length of each side of the third ground conductor7is longer than or equal to the length of the half wavelength at the resonance frequency of the element antennas3a,3b,3c, and3d.

Moreover, the length of each side of the second dielectric substrate9is longer than or equal to the length of each side of the third ground conductor7.

Therefore, a resonance phenomenon occurs in the microstrip resonator22due to electromagnetic waves transmitted and received by the element antennas3a,3b,3c, and3d.

Therefore, by adjusting the resonance frequency of the element antennas3a,3b,3c, and3dand the resonance frequency of the microstrip resonator22, a broadband impedance characteristic can be obtained. Moreover, not only that a broadband impedance characteristic can be obtained, but also the broadband impedance characteristic can be maintained even when the antenna device is installed on a large ground plate.

That is, although the resonance frequency of the microstrip resonator22slightly changes being affected by the fringing effect when the antenna device is installed on a large ground plate, but there is no significant difference from the case where the antenna device is not installed on a large ground plate. Therefore, even when the antenna device is installed on a large ground plate, a broadband impedance characteristic can be maintained.

Note that the wider the gap between the second ground conductor6and the third ground conductor7is, the wider the band of the microstrip resonator22becomes, and thus a broadband impedance characteristic can be obtained.

Furthermore, when the resonance frequency of the element antennas3a,3b,3c, and3dand the resonance frequency of the microstrip resonator22are adjusted to the same level, the radiation pattern of the antenna device is obtained by superimposing the radiation pattern of the circularly polarized wave transmitting/receiving unit2as a current source and the radiation pattern of the microstrip resonator22as a magnetic current source.

As illustrated inFIG. 7, the radiation pattern obtained by the antenna device can be expressed by a simple model including current sources (J1to J4) and magnetic current sources (M1to M4).

FIG. 7is an explanatory diagram illustrating a simple model including the current sources (J1to J4) and the magnetic current sources (M1to M4).

In this example, the phase differences between the current sources (J1to J4) are 90 degrees each and the phase differences between the magnetic current sources (M1to M4) are 90 degrees each so that RHCP is radiated in the zenith direction.

It is also assumed that the amplitudes of the current sources (J1to J4) and the amplitudes of the magnetic current sources (M1to M4) are all equal and that a phase difference between a current source (Jn: n=1, 2, 3, 4) and a magnetic current source (Mn: n=1, 2, 3, 4) is Δφ.

Although the positions of the current sources and the magnetic current sources appear to be different inFIG. 7, they are assumed to be in the same position.

By performing electromagnetic field analysis on the basis of the relationship illustrated inFIG. 7, the relationship between the phase difference Δφ between a current source (Jn) and a magnetic current source (Mn) and the peak value of the radiation pattern is simulated.

FIG. 8is an explanatory graph illustrating a simulation result of the correspondence relationship between the phase difference Δφ and the peak values of the radiation patterns.

The horizontal axis inFIG. 8represents the phase difference Δφ between the current source (Jn) and the magnetic current source (Mn), and the vertical axis inFIG. 8represents the peak value of the radiation patterns.

FIG. 8indicates that LHCP can be suppressed when the phase difference Δφ is positive and the phase of the magnetic current source (Mn) is delayed from the phase of the current source (Jn). When Δφ=90 degrees, LHCP is most suppressed.

The relationship between the phase difference Δφ and the peak values of the radiation patterns is dependent on the physical positions of the element antennas3a,3b,3c, and3dbut also contributes to the phase centers of the element antennas3a,3b,3c, and3d. Therefore, it becomes possible to adjust the suppression amount of LHCP by adopting inverted L antennas as the element antennas3a,3b,3c, and3dto allow the phase centers of the element antennas3a,3b,3c, and3dto move in the vertical direction that is the zenith direction (0 deg).

Specifically, the suppression amount of LHCP can be adjusted by changing the shapes of the element antennas3a,3b,3c, and3d. As a result, as illustrated inFIG. 9, a radiation pattern having a high gain and a low cross-polarization (LHCP) can be obtained.

FIG. 9is an explanatory diagram illustrating the RHCP gain and the LHCP gain in the antenna device.

The horizontal axis inFIG. 9represents the zenith angle of RHCP and LHCP, and the vertical axis inFIG. 9represents the RHCP and LHCP gains.

InFIG. 9, the phase difference Δφ is adjusted to 90 degrees, and the LHCP is most suppressed at a phase of 0 degrees.

As is apparent from the above, according to the first embodiment, included are: the coaxial line10provided so as to pass through the second ground conductor6and the first and second dielectric substrates8and9, the coaxial line10including the outer conductor11allowing the first ground conductor1, the second ground conductor6, and the third ground conductor7to be conductive thereamong; and the conductive member15provided so as to pass through the first dielectric substrate8, the conductive member15allowing the first ground conductor1and the second ground conductor6to be conductive therebetween, and the interface circuit18combines a plurality of signals having mutually different phases output from each of the plurality of element antennas3a,3b,3c, and3dand outputs the combined signal to the coaxial line10. This allows the resonance frequency to be adjusted to suppress reception of unnecessary back lobes without mounting a complex choke structure.

Although the example in which the element antennas3a,3b,3c, and3dare inverted L antennas is described in the first embodiment, the antennas are only required to have element shapes having directivity in the zenith direction, and the element antennas3a,3b,3c, and3dare not limited to inverted L antennas.

For example, the element antennas3a,3b,3c, and3dmay be inverted antennas as illustrated inFIG. 10A, or may be folded monopole antennas as illustrated inFIG. 10B.

FIG. 10Ais an explanatory diagram illustrating an example in which the element antennas are inverted F antennas, andFIG. 10Bis an explanatory diagram illustrating an example in which the element antennas are folded monopole antennas.

Like the inverted L antennas, the inverted antennas have feeding points4a,4b,4c, and4d, and also have connection points with the first plane1aof the first ground conductor1.

In the case where the element antennas3a,3b,3c, and3dare inverted antennas, the lengths from the feeding points4a,4b,4c, and4dto the tips5a,5b,5c, and5dare about a quarter wavelength at the resonance frequency.

In the inverted antennas, each of the tip portions extending from bended points3ab,3bb,3cb, and3dbto tips5a,5b,5c, and5dis parallel to the first plane1aof the first ground conductor1.

Moreover, in the inverted F typo antennas, directions from the bended points3ab,3bb,3cb, and3dbto the tips5a,5b,5c, and5dare different from each other by 90 degrees, and are parallel to one of the sides of the first ground conductor1.

Like the inverted L antennas, the folded monopole antennas have feeding points4a,4b,4c, and4d, and also have connection points with the first plane1aof the first ground conductor1.

In the case where the element antennas3a,3b,3c, and3dare folded monopole antennas, the lengths from the feeding points4a,4b,4c, and4dto the connection points are about half a wavelength at the resonance frequency.

In the folded monopole antennas, each of the portions extending from bended points3ab,3bb,3cb, and3dbto folded points is parallel to the first plane1aof the first ground conductor1.

Moreover, in the folded monopole antennas, directions from the bended points3ab,3bb,3cb, and3dbto the folded points are different from each other by 90 degrees, and are parallel to any one of the sides of the first ground conductor1.

Furthermore, since the element antennas3a,3b,3c, and3dare only required to be element-type antennas having directivity in the zenith direction, antennas such as loop antennas, helical antennas or meander antennas may be used.

In the first embodiment, the antenna device having four feeding points is illustrated; however, for example, an antenna device having two feeding points or one feeding point may be used.

In the first embodiment, the example in which the circularly polarized wave transmitting/receiving unit2includes the element antennas3a,3b,3c, and3dis illustrated; however, a passive element30corresponding to each of the element antennas3a,3b,3c, and3dmay be included as illustrated inFIG. 11.

FIG. 11Ais an explanatory diagram illustrating an example in which element antennas that are inverted L antennas and passive elements30are included,FIG. 11Bis an explanatory diagram illustrating an example in which element antennas that are inverted F antennas and passive elements30are included, andFIG. 11Cis an explanatory diagram illustrating an example in which element antennas that are folded monopole antennas and passive elements30are included.

With the circularly polarized wave transmitting/receiving unit2including the passive elements30in addition to the element antennas3a,3b,3c, and3d, the antenna device functions as a multiband antenna that resonates in a plurality of bands.

In the case of the multiband antenna using the passive elements30, it is possible to adjust the coupling amount of the element antennas3a,3b,3c, and3d. For this reason, for example, it is possible to suppress unwanted waves of long term evolution (LTE) of the 1.5 GHz band that is between multiple frequencies used in the quasi-zenith satellites.

In the case of using the passive elements30, there is an advantage that the cost can be reduced as compared with a case where a high-performance filter is used to suppress unwanted waves of the LTE.

Although the example is illustrated in the first embodiment in which a signal is given from the other end14bof the inner conductor14in the coaxial line10when the element antennas3a,3b,3c, and3dare used as transmission antennas, a signal may be given from a side surface of the first ground conductor1, for example.

InFIG. 2, the side surface of the first ground conductor1may be, for example, on the left side or the right side, on the paper, of the first ground conductor1.

In the case where a signal is given from the side surface of the first ground conductor1, the coaxial line10penetrating through the substrates becomes unnecessary. However, this results in asymmetry in the structure, thus deteriorating the axial ratio, and thus it is desirable that a signal is given from the other end14bof the inner conductor14in the coaxial line10.

In the first embodiment, the example is illustrated in which the interface circuit18is patterned on the first plane1aof the first ground conductor1by etching.

However, this is merely an example. For example, the interface circuit18may be formed using a chip component or the like.

In the first embodiment, the example is illustrated in which the coaxial line10capable of signal transmission is formed with the plurality of outer conductors11arranged at positions surrounding the inner conductor14.

In this case, although it is desirable that the intervals between the multiple outer conductors11be dense, if the intervals are too narrow, a line drawn from the inner conductor14in the coaxial line10to the interface circuit18cannot be formed.

For this reason, the plurality of outer conductors11is arranged in a C shape in the first embodiment as illustrated inFIG. 3. Specifically, an interval between two outer conductors11is widened only at a position where a line is drawn from the inner conductor14in the coaxial line10to the interface circuit18as compared to other positions.

Although the example is illustrated in the first embodiment in which the planar shapes of the first ground conductor1, the second ground conductor6, the third ground conductor7, the first dielectric substrate8, and the second dielectric substrate9is a square, the present embodiment is not limited to the example of square planar shapes. For example, as illustrated inFIG. 12, the planar shapes of the first ground conductor1, the second ground conductor6, the third ground conductor7, the first dielectric substrate8, and the second dielectric substrate9may be circular.

FIG. 12is a plan view illustrating a first ground conductor1and a first dielectric substrate8having circular planar shapes.

The example is illustrated in the first embodiment in which the first ground conductor1, the second ground conductor6, the third ground conductor7, the first dielectric substrate8, and the second dielectric substrate9are multilayered; however, a fourth ground conductor41and a third dielectric substrate42may be multilayered as illustrated inFIG. 13.

FIG. 13is a cross-sectional side view illustrating another antenna device according to the first embodiment of the invention.

InFIG. 13, the fourth ground conductor41is arranged in parallel with the third ground conductor7on, of the two planes of the third ground conductor7, a plane opposite to the plane on which the second ground conductor6is arranged.

The third dielectric substrate42is arranged between the third ground conductor7and the fourth ground conductor41.

In the antenna device illustrated inFIG. 13, the portion sandwiched between the second ground conductor6and the third ground conductor7operates as the microstrip resonator22, and in addition to this, the portion sandwiched by the third ground conductor7and the fourth ground conductor41operates as a microstrip resonator43.

Therefore, by adding the fourth ground conductor41having sides the length of which is about half a wavelength at a desired frequency, a radiation pattern characteristic having a low cross-polarization can be obtained in multiple frequency bands.

Second Embodiment

In the first embodiment, the example in which the planar shape of the second ground conductor6is a square is illustrated.

In a second embodiment, an example in which notches are formed in each of the four sides of a second ground conductor6as illustrated inFIG. 14will be described.

FIG. 14is a plan view illustrating the planar shape of the second ground conductor6in the antenna device according to the second embodiment of the present invention. InFIG. 14, the same symbol as that inFIGS. 1 to 3represents the same or a corresponding part.

In the example ofFIG. 14, a coaxial line10is arranged at the center of the second ground conductor6.

Symbols X1, X2, X3, and X4 represent the dimensions of the respective sides of the second ground conductor6, and X1=X2=X3=X4 holds.

Symbols Y1, Y2, Y3, and Y4 indicate the notch size of the sides of the second ground conductor6.

The second ground conductor6having a square planar shape is notched with the same notch size at the center of each of the four sides.

Specifically, inFIG. 14, the dimensions of the notches of the upper side on the paper (hereinafter referred to as the upper side), the lower side on the paper (hereinafter referred to as the lower side), the left side on the paper (hereinafter referred to as the left side), and the right side on the paper (hereinafter referred to as the right side), of the second ground conductor6, are all X2+X3.

Furthermore, the notch sizes on the upper side, the lower side, the left side, and the right side of the second ground conductor6are all Y (=Y1=Y2=Y3=Y4).

Therefore, even with the notches, the planar shape of the second ground conductor6maintains symmetry, and thus the axial ratio characteristic can be maintained.

Since the path of a signal flowing through the second ground conductor6becomes longer when a notch is formed in each of the four sides of the second ground conductor6, the operation frequency of the microstrip resonator22shifts to the lower frequency side.

The resonance frequency can be adjusted by adjusting the notch size Y on the upper side, the lower side, the left side, and the right side of the second ground conductor6. Therefore, the phase relationship can be adjusted not only by the arrangement and the shapes of the element antennas3a,3b,3c, and3dbut also by modifying the shape of the second ground conductor6by the notches when the phase relationship between the circularly polarized wave transmitting/receiving unit2that is a current source and the microstrip resonator22that is a magnetic current source is adjusted.

In the second embodiment, the example in which Y1=Y2=Y3=Y4 holds for the notch sizes is illustrated in order to maintain the axial ratio characteristic and to prevent cross polarized waves from increasing.

In a case where there is no particular problem even if some cross polarized waves increase due to asymmetry, the notch sizes may be, for example, Y1≠Y2≠Y3≠Y4. Moreover, (X2+X3)≠(X1+X4) may be satisfied.

Although the example is illustrated in the second embodiment in which each of the four sides of the second ground conductor6is notched; however, each of the four sides of the third ground conductor7may be notched.

Third Embodiment

In the first embodiment, the example is illustrated in which the element antennas3a,3b,3c, and3dare arranged on the first plane1aof the first ground conductor1.

In a third embodiment, an example will be described in which third dielectric substrates51arranged on a first plane1aof a first ground conductor1are further included, and element antennas3a,3b,3c, and3dare formed in the third dielectric substrates51.

FIG. 15is a cross-sectional side view illustrating an antenna device according to a third embodiment of the invention.

FIG. 16is a plan view illustrating a top surface of the antenna device according to the third embodiment of the present invention.

InFIGS. 15 and 16, the same symbol as that inFIGS. 1 to 3represents the same or a corresponding part and thus description thereof is omitted.

The third dielectric substrates51are dielectric substrates stacked on the first plane1aof the first ground conductor1so as to surround a coaxial line10.

Inside the third dielectric substrates51, the element antennas3a,3b,3c, and3dare formed.

Also, in the case where the element antennas3a,3b,3c, and3dare formed inside the third dielectric substrates51, an antenna device that operates in a similar manner to the first embodiment is obtained.

Fourth Embodiment

FIG. 13of the first embodiment illustrates the antenna device including the fourth ground conductor41.

In a fourth embodiment, an antenna device will be described in which communication component circuits62, including a filter used for suppressing unwanted waves, an amplifier for amplifying a signal or the like when satellite communication is performed for example, are mounted on a fourth ground conductor41as illustrated inFIG. 17.

FIG. 17is a cross-sectional side view illustrating an antenna device according to a fourth embodiment of the invention.

InFIG. 17, the same symbol as that inFIGS. 1 to 3 and 13represents the same or a corresponding part and thus description thereof is omitted.

Conductive members61are provided so as to pass through a third dielectric substrate42and allow the third ground conductor7and the fourth ground conductor41to be conductive therebetween.

The multiple conductive members61are arranged at positions surrounding a coaxial line10and communication component circuits62.

The communication component circuits62are attached to, out of the two planes of the fourth ground conductor41, the plane opposite to the plane on which the third ground conductor7is arranged, and includes communication components such as filters or amplifiers used for satellite communication, for example.

A first metal housing63is connected to the fourth ground conductor41so as to shield the communication component circuit62from the surroundings thereof.

In the antenna device illustrated inFIG. 17, conductive members61allow the third ground conductor7and the fourth ground conductor41to be conductive therebetween, and the first metal housing63protects the communication component circuit62.

Therefore, even when the antenna device is mounted with the communication component circuits62, the antenna device itself can operate in a similar manner to the first embodiment.

Fifth Embodiment

In the fourth embodiment, the antenna device including the first metal housing63is illustrated.

In a fifth embodiment, an antenna device further including a second metal housing64as illustrated inFIG. 18will be described.

FIG. 18is a cross-sectional side view illustrating the antenna device according to the fifth embodiment of the invention.

InFIG. 18, the same symbol as that inFIGS. 1 to 3 and 17represents the same or a corresponding part and thus description thereof is omitted.

The second metal housing64is arranged so as to surround a first metal housing63.

A resin member65is filled between the first metal housing63and the second metal housing64.

In the antenna device illustrated inFIG. 18, the second metal housing64is arranged so as to surround a first metal housing63, and the space between the first metal housing63and the second metal housing64is filled with a resin member65, and thus a microstrip resonator66is formed by the first metal housing63and the second metal housing64.

In this case, if the electrical length between the first metal housing63and the second metal housing64is about half a wavelength at the resonance frequency, the microstrip resonator66operates in a similar manner to the microstrip resonator22.

According to the fifth embodiment, cross polarized waves can be suppressed also by the microstrip resonator66formed by the first metal housing63and the second metal housing64.

Note that the present invention may include a flexible combination of the respective embodiments, a modification of any component of the embodiments, or an omission of any component in the embodiments within the scope of the present invention.

INDUSTRIAL APPLICABILITY

The present invention is suitable for an antenna device including a plurality of element antennas.

REFERENCE SIGNS LIST