Antenna device having patch antenna

An antenna device includes: a dielectric substrate formed with a ground plane; a patch antenna having a dominant polarization direction in a predetermined direction on the dielectric substrate; at least one patch radiating element for supplying electric power provided on the patch antenna, the at least one patch radiating element being formed on the dielectric substrate; a patch-shaped conductor pattern formed on a substrate front face of the dielectric substrate on which the patch radiating element is formed; a plurality of connection conductors formed to penetrate the dielectric substrate for electrically connecting the conductor pattern to the ground plane; and a conductive structure having the conductor pattern and a plurality of the connection conductors. A plurality of the conductive structures is provided.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based on and claims the benefit of priority from earlier Japanese Patent Application No. 2013-256083 filed Dec. 11, 2013, the description of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

Technical Field

The present disclosure relates to an antenna device having a patch antenna.

Background Art

A patch antenna formed on a dielectric substrate has been used for a radar apparatus, for example, on a mobile unit, including a vehicle and an airplane, for monitoring the surroundings of the mobile unit. Commonly, in the configuration of a patch antenna, a patch radiating element (a patch-shaped conductor) is formed on a dielectric substrate. Generally, a conductor part serving as a ground plane is formed on a face of the dielectric substrate (in the following, referred to as “a substrate rear face”) on the opposite side of a face on which the patch radiating element is formed (in the following, referred to as “a substrate front face”). Also on the substrate front face, a conductor part is sometimes widely formed to substrate end portions in addition to the patch radiating element.

In a patch antenna in this configuration, upon operating the patch antenna, electric current (surface current) flows through the surface of the ground plane due to an electric field formed across the patch radiating element and the ground plane. The surface current is propagated to the substrate end portions, and diffracted at the substrate end portions. Because of the influence of the diffracted waves, radiation (emission) occurs from the substrate end portions. In the case where a conductor part is formed on the substrate front face, the surface current also flows through the conductor part to cause radiation from the substrate end portions. Radiation from the substrate end portions due to this surface current is unnecessary radiation that adversely affects the performance of the patch antenna. In other words, radiation from the end portions disturbs the directivity of the patch antenna.

JP-T-2002-510886 discloses a technique to reduce surface current flowing through a ground plane. Specifically, a plurality of conductive patches is formed around a patch radiating element on the substrate front face of a dielectric substrate. The conductive patches are each electrically connected to a ground plane on the rear face of the substrate with a columnar connector (in the following, referred to as “a conducting via”). The structure configured of the conductive patch and the conducting via has a band gap (an electromagnetic band gap) that prevents the propagation of the surface current from flowing through the ground plane at a specified frequency. In the following, the structure configured of the conductive patch and the conducting via is referred to as “an EBG”.

In this manner, forming a large number of EBGs around the patch radiating element allows a reduction in the propagation of the surface current to the substrate end portions. Thus, the disturbance in the directivity of the patch antenna can be reduced.

CITATION LIST

Patent Literature

A tolerance with a predetermined margin is set to the outer diameter of the conducting via configuring the EBG (in the following, referred to as “a via diameter”). Thus, the via diameter of the conducting via is varied within a tolerance range. A variation in the via diameter causes the operating frequency band of the EBG, which is a band that can reduce the propagation of the surface current, to fluctuate from its designed operating frequency band. This is likely to cause disturbance (ripples) in the directivity of the patch antenna.

SUMMARY

Hence, it is desired to provide an antenna device is formed with a patch antenna and a conductive structure on a substrate. The conductive structure is a structure having a conductor pattern and a connection conductor for connecting the conductor pattern to a ground plane on the rear face of the substrate. In the antenna device, fluctuations in the operating frequency of the conductive structure due to the tolerance of the connection conductor are reduced, thereby reducing the disturbance in the directivity of the patch antenna due to the conductive structure, even though the dimensions of the connection conductor are varied.

An antenna device according to the present disclosure includes a dielectric substrate and a patch antenna. The dielectric substrate has a ground plane formed on one of plate faces. The patch antenna has at least one patch radiating element for supplying electric power formed on a plate face on the opposite side of the plate face of the dielectric substrate on which the ground plane is formed. The patch antenna has a dominant polarization direction in a predetermined direction of the plate faces of the dielectric substrate. The antenna device according to the present disclosure includes a plurality of conductive structures. The conductive structure includes a patch-shaped conductor pattern formed on a substrate front face that is the plate face of the dielectric substrate on which the patch radiating element is formed. The conductive structure includes a plurality of connection conductors formed across the conductor pattern and the ground plane to penetrate the dielectric substrate for electrically connecting the conductor pattern to the ground plane.

In accordance with the antenna device according to the present disclosure thus configured, a plurality of the conductive structures is formed around the patch radiating element. Thus, the propagation of the surface current from the patch radiating element to the substrate end portions is reduced. Additionally, the conductive structures each have a plurality of the connection conductors, in the configuration in which the plurality of the connection conductors connects the conductor pattern to the ground plane.

As described above, the conductive structure has a plurality of the connection conductors. Thus, even though the dimensions of the connection conductors are varied within a tolerance range, fluctuations in the operating frequency of the conductive structure (the frequency that can reduce the propagation of the surface current) are reduced. Consequently, even though the dimensions of the connection conductor are varied, the effect of reducing the disturbance in the directivity of the patch antenna due to the conductive structure can be maintained.

Note that, reference numerals and signs in parentheses in the claims are examples expressing correspondences with specific means, for example, described in embodiments, described later. The present disclosure is not limited to the specific means, for example, expressed by the reference numerals and signs in the parentheses.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In the following, referring to the drawings, preferred embodiments of the present disclosure will be described. Note that, the present disclosure is not limited to specific means, structures, and the like described in the embodiments below. The present disclosure can adopt various forms in the scope not deviating from the gist of the present disclosure. For example, a part of the configuration of the embodiment below may be replaced by a publicly known configuration having a similar function. A part of the configuration of the embodiment below may be added to or replaced by the configuration of another embodiment, for example, or may be omitted for solving the problems. Configurations may be provided by appropriately combining the embodiments below.

As illustrated inFIG. 1, in an antenna device1according to the present embodiment, a patch antenna7, a conductor plate6, and a plurality of EBGs4are formed on one face (a substrate front face) of a rectangular dielectric substrate2. A ground plane3formed of a conductor is formed on the other face (a substrate rear face). As illustrated inFIG. 1, the present embodiment will be appropriately described using x-, y-, and z-axes of a three dimensional coordinate system, in which the origin point is the center part of the patch antenna7(the center part of a patch radiating element5, described later), the x-axis is an axis passing the origin point and parallel with the short side of the dielectric substrate2, the y-axis is an axis passing the origin point and parallel with the long side of the dielectric substrate2, and the z-axis is an axis passing the origin point and perpendicular to the plate face of the dielectric substrate2.

Note that,FIG. 2is a detailed diagram (enlarged diagram) illustrating the end portion of the antenna device1in the y-axis direction, and the vicinity thereof.FIG. 3Ais a cross sectional view of the antenna device1taken along line A-A (seeFIG. 1).FIG. 3Bis a cross sectional view of the antenna device1taken along line B-B (seeFIG. 2).FIG. 3Cis a cross sectional view of the antenna device1taken along line C-C (seeFIG. 2).

The patch antenna7has the patch radiating element5having a square shape. The patch radiating element5is formed on the center part of the substrate front face. The ground plane3on the rear face of the substrate functions as a ground plane for the patch radiating element5. The patch radiating element5formed in a square shape is disposed in such a manner that a pair of opposing edges are parallel with each other in the x-axis direction and another pair of opposing edges are parallel with each other in the y-axis direction.

As apparent fromFIGS. 1 and 3A, the conductor plate6is formed around the patch radiating element5. However, a groove is formed between the conductor plate6and the patch radiating element5all around the edges of the patch radiating element5. The patch radiating element5is physically apart from the conductor plate6with the groove.

The length of one edge of the patch radiating element5is about λg/2. Note that, kg is a wavelength corresponding to the operating frequency of the patch antenna7, which is a wavelength in the inside of the dielectric. λg is expressed by λg=λ0/√∈r, where the free space wavelength is defined as λ0 and the relative dielectric constant of the dielectric substrate2is defined as ∈r. However, a length of about λg/2 is an example of length. For example, the optimum length is changed depending on various factors, such as the shape or size of the ground plane3.

For supplying electric power to the patch antenna7, electric power is supplied to the patch radiating element5. A configuration of power supply to the patch radiating element5is omitted in the drawings. Various methods for supplying power to a patch-shaped radiating element have been developed and practically used. Hence, the detailed description is omitted. In the present embodiment, a power supply configuration is provided, in which electric power is supplied from power supply microstrip lines by an electromagnetic coupling power supply method.

The patch antenna7operates as the y-axis direction is the dominant polarization direction. In other words, the patch antenna7is configured as an antenna to operate as the yz plane is the plane of polarization (the E-plane) and to allow excellent transmission and reception of polarized waves on the yz plane.

For example, the antenna device1is disposed in such a manner that on the front side of a vehicle, the substrate front face, on which the patch antenna7is formed, faces the front side of the vehicle and the long sides of the rectangular dielectric substrate2(the edges in the y-axis direction) are horizontally disposed with respect to the ground. The antenna device1is used for a millimeter wave radar apparatus to monitor the areas around the vehicle. In other words, when the antenna device1is mounted on the vehicle for use, the E-plane of the patch antenna7is horizontally disposed with respect to the ground. Thus, the patch antenna7is used as an antenna capable of favorably transmits and receives horizontally polarized waves. Note that, in the following description, the E-plane (the yz plane) of the patch antenna7is also referred to as a horizontal plane.

As illustrated inFIG. 1, in the present specification, the azimuth angle (sensing angle) on the horizontal plane (the E-plane) of the patch antenna7is treated in such a manner that based on the z-axis direction) (0°), angles on the left side of the patch antenna7are positive angles and angles on the right side are negative angles when the front side of the vehicle is viewed from the patch antenna7.

As also apparent fromFIGS. 2, 3B, and 3C, the EBG4has a patch-shaped metal pattern (in the following, referred to as “a patch-shaped pattern”)4aformed on the substrate front face of the dielectric substrate2and four conducting vias4bto electrically connect this patch-shaped pattern4ato the ground plane3. All of the patch-shaped pattern4aand the four conducting vias4bare conductors. A specific shape (the shape of a face in parallel with the substrate plate face) of the patch-shaped pattern4aaccording to the present embodiment is a square shape.

All of the four conducting vias4bare columnar conductors having an outer diameter (via diameter) φ. As illustrated in detail inFIGS. 3B and 3C, the conducting vias4bare provided so as to penetrate the dielectric substrate2in a thickness wd in a direction perpendicular to the plate face of the dielectric substrate2(in the z-axis direction). One end is connected to the patch-shaped pattern4a. The other end is connected to the ground plane3.

A plurality of the EBGs4is provided on the antenna device1. Specifically, throughout the region on the substrate front face other than an EBG absent region8(seeFIG. 1), a plurality of the patch-shaped patterns4ais arrayed with a predetermined pattern gap wg apart. The wavelength of the pattern gap wg is much shorter than a wavelength corresponding to the use frequency of the antenna device1. All the patch-shaped patterns4aare disposed in such a manner that a pair of opposing edges is in parallel with each other in the x-axis direction and another pair of opposing edges is in parallel with each other in the y-axis direction.

In the present embodiment, throughout the region on the substrate front face other than the EBG absent region8, a plurality of the patch-shaped patterns4ais disposed with the pattern gap wg therebetween. As illustrated inFIG. 1, on one end side of the dielectric substrate2in the y-axis direction when viewed from the patch radiating element5, the patch-shaped patterns4aare disposed in three rows in the x-axis direction and in nine rows in the y-axis direction. Also on the other end side of the dielectric substrate2in the y-axis direction when viewed from the patch radiating element5, the patch-shaped patterns4aare disposed in three rows in the x-axis direction and in nine rows in the y-axis direction similarly to the patch-shaped patterns4aon one end side.

One end of each of the four conducting vias4bof the EBGs4is connected to the center region of the patch-shaped pattern4a. Specifically, the conducting vias4bare connected in such a manner that the connecting portion of the conducting via4bis arranged in two rows in the x-axis direction and in two rows in the y-axis direction on the patch-shaped pattern4a. In other words, a group is formed of two conducting vias4barrayed in a row with a predetermined connection gap wv apart in the x-axis direction perpendicular to the E-plane. Two groups are arrayed side by side in the y-axis direction with the connection gap wv apart. The trace formed by connecting the connecting portions of the four conducting vias4bis a square. In the present embodiment, the center of the square is matched with the center of the patch-shaped pattern4a.

The EBG absent region8is a region in which the patch radiating element5is present in its center part and no patch-shaped pattern4ais present. The EBG absent region8is in a square shape as a whole. In the present embodiment, in the center of the EBG absent region8, the patch radiating element5is disposed. On nearly the entire region except the patch radiating element5, the conductor plate6is formed. Note that, the conductor plate6is indirectly electrically connected to the ground plane3on the rear face of the substrate, but the conductor plate6functions as the ground of the patch antenna7together with the ground plane3on the rear face of the substrate. However, the conductor plate6is not an essential component of the antenna device1. The conductor plate6may be omitted.

The EBGs4are capacitively coupled to adjacent EBGs4, and inductively and capacitively coupled to the ground plane3on the rear face of the substrate. Thus, the EBGs4function as a two-dimensional circuit network of a parallel resonant circuit as a whole, and reduce the propagation of a surface current to both ends of the substrate (to both ends in the dominant polarization direction). The surface current is produced by the operation (radiation) of the patch antenna7.

The equivalent circuit of the EBG4according to the present embodiment is as illustrated inFIG. 4B. Note that,FIG. 4Aalso illustrates the equivalent circuit of an EBG (comparative EBG)100having one conducting via for comparison.

As illustrated inFIG. 4A, the comparative EBG100has a patch-shaped pattern100aand a conducting via100b. In the comparative EBG100, a capacitive component (capacitance) CL1is provided by capacitively coupling the comparative EBG100to another adjacent comparative EBG100with the pattern gap wg apart. An inductive component (inductance) LR1is provided by the patch-shaped pattern100a. An inductive component LLis provided across the patch-shaped pattern100aand the ground plane3by the conducting via100b. In parallel with the inductive component LL, a capacitance component CR1is provided across the patch-shaped pattern100aand the ground plane3. Thus, the equivalent circuit of the comparative EBG100is a circuit as illustrated inFIG. 4A.

Unlike the comparative EBG100, the EBG4according to the present embodiment has four conducting vias4bin the same size and shape of the conducting via100bof the comparative EBG100. Thus, as illustrated in an equivalent circuit inFIG. 4B, inductive components LL1, LL2, LL3, and LL4by the conducting vias4bare present in parallel with one another across the patch-shaped pattern4aand the ground plane3. Therefore, the inductive components across the patch-shaped pattern4aand the ground plane3have the parallel combined values of these four inductive components LL1, LL2, LL3, and LL4.

Note that, the values (inductance values) of the four inductive components LL1, LL2, LL3, and LL4are the same. Each of these four inductance values is the same as the inductance value LLof the conducting via100bof the comparative EBG100. Thus, the four parallel combined inductances have values smaller than each of the inductance values.

In order to reduce the propagation of the surface current (the surface wave) at an operating frequency fc of the patch antenna7using the comparative EBG100and the EBG4according to the present embodiment, the resonance frequency of the LC parallel circuit formed across the patch-shaped pattern and the ground plane3is desirably set to the operating frequency fc of the patch antenna7.

In other words, in the comparative EBG100, the capacitance component CR1and the inductive component LLconfiguring the LC parallel circuit desirably satisfy Expression (1) below.

On the other hand, in the EBG4according to the present embodiment, a capacitance component CR2and the four inductive components LL1to LL4configuring the LC parallel circuit desirably satisfy Expression (2) below.

Note that, the parallel combined values of the four inductive components LL1, LL2, LL3, and LL4are basically expressed by Expression (3) below as known.

However, the operating frequency fc of the patch antenna7according to the present embodiment is in a high frequency band in the GHz band. Thus, coupling at high frequency range is produced among the four conducting vias4b. Because of this coupling, an actual parallel combined value LLPof the four inductive components LL1, LL2, LL3, and LL4is a value greater than a value obtained by the basic arithmetic expression expressed by Expression (3) above.

As already described, in the EBG4according to the present embodiment, the parallel combined inductance value LLPof the LC parallel circuit is a value of about ¼ (slightly greater than ¼) of the inductance value LLproduced by one conducting via4b. The parallel combined inductance value LLPis formed across the patch-shaped pattern4aand the ground plane3. Thus, the value of the capacitance component CR2is a value greater than the value of the capacitance component CR1of the comparative EBG100. Specifically, the value of the capacitance component CR2is a value slightly smaller than a value four times the value of the capacitance component CR1of the comparative EBG100.

Consequently, in the EBG4according to the present embodiment, the area of the patch-shaped pattern4ais formed slightly smaller than the area four times the area of the patch-shaped pattern100aof the comparative EBG100.

In other words, in the EBG4according to the present embodiment, the parallel combined inductance value LLPof the LC parallel circuit formed across the patch-shaped pattern4aand the ground plane3is a value smaller than the inductance value LLof the LC parallel circuit of the comparative EBG100(about ¼). Thus, the area of the patch-shaped pattern4ais formed greater than the area of the comparative EBG100, whereby the capacitance component CR2has a greater value. Consequently, the LC parallel circuit formed across the patch-shaped pattern4aand the ground plane3is designed in such a manner that the resonance frequency of the LC parallel circuit is matched with the operating frequency fc of the patch antenna7as a whole.

In summary, the design conditions of the EBG4according to the present embodiment can be expressed by Expression (2) above and Expression (4) below. Note that, in Expression (4) below, β is a phase constant.

In the antenna device1according to the present embodiment, taking into account of Expressions (2) and (4) above and the thickness wd and relative dielectric constant of the dielectric substrate2, for example, the dimensions and other parameters of the parts of the EBG4are designed. The dimensions and other parameters of the parts of the EBG4are the shape and dimensions of the patch-shaped pattern4a, the via diameter φ of the conducting via4b, the connection gap wv between the four conducting vias4b, and the pattern gap wg between the adjacent patch-shaped patterns4a, for example. The EBG4is designed in such a manner that Expressions (2) and (4) above are satisfied. Thus, the operating frequency (the surface current cutoff frequency) of the EBG can be matched with the operating frequency fc of the patch antenna7. Consequently, the propagation of the surface current to the substrate end portions can be favorably reduced.

A tolerance with a predetermined margin is set to the via diameter φ of the conducting via4bconfiguring the EBG4. This causes a variation in the via diameter φ of the conducting via4bwithin a tolerance range. A variation in the via diameter is likely to displace the operating frequency band of the EBG4from the designed operating frequency band (a predetermined band including the operating frequency fc of the patch antenna7as an approximate center frequency), resulting in the degradation of the performance of the EBG4. Specifically, because of the configuration, the EBG4has a high Q-value and a narrow cutoff band. Even a slight displacement from the design value of the via diameter φ is likely to relatively greatly affect the performance of the EBG4(even though a displacement is taken place within a tolerance range).

Therefore, in the present embodiment, the EBG4is provided with a plurality of the conducting vias4b, which are a principal factor to determine the operating frequency, to one patch-shaped pattern4a. In the present embodiment, four conducting vias4bare provided. One patch-shaped pattern4ais provided with a plurality of the conducting vias4b. Thus, the combined inductive component (LLP) in Expression (2) is smaller than the inductive component (LL) in Expression (1), and the capacitance component (CR2) becomes dominant. Consequently, a displacement in the conducting via gives a small influence, compared with Expression (1). The operating frequency fc is less affected. However, in Expression (2), the area of the patch shape forming the capacitance component is greater than in Expression (1).

FIG. 5Ashows three patterns of the transmission properties of a via diameter φo of the conducting via100bof the comparative EBG100, in which the via diameter φo has the designed reference value, which is 150 μm, the via diameter φo is shorter than the reference value, which is 130 μm, and the via diameter φo is longer than the reference value, which is 170 μm. Note that, the via diameters φo in these three patterns are all included within a tolerance range.

On the other hand,FIG. 5Bshows three patterns of the transmission properties of the four conducting vias4bof the EBG4according to the present embodiment, in which the via diameter φ of each of the four conducting vias4bhas the designed reference value, which is 150 μm, the via diameter φ of each of the four conducting vias4bis shorter than the reference value, which is 130 μm, and the via diameter φ of each of the four conducting vias4bis longer than the reference value, which is 170 μm.

As illustrated inFIG. 5A, in the comparative EBG100, when the via diameter φo of the conducting via100bis varied within a range of the reference value ±20 μm, the operating frequency (the cutoff frequency) is varied in a range of about 1.5 GHz as a whole. However, as illustrated inFIG. 5B, in the EBG4according to the present embodiment, when the via diameter φ of the conducting via4bis varied within a range of the reference value ±20 μm, fluctuations in the operating frequency (the cutoff frequency) are in a range of about 0.3 GHz. Thus, fluctuations in the operating frequency of the EBG4are greatly reduced, compared with fluctuations in the operating frequency of the comparative EBG100.

Referring toFIGS. 6A to 6C, differences in the directivity of the antenna device caused by the presence or absence of the EBG and the number of conducting vias configuring the EBG will be described.FIG. 6Ashows the directivity of an antenna device formed with no EBG (comparative example 1). In the antenna device according to comparative example 1, a patch radiating element5is formed in the center part of a dielectric substrate2, which is similar to the present embodiment. However, a conductor plate is formed around the patch radiating element5nearly throughout the surface.

FIG. 6Bshows the directivity of an antenna device formed with a plurality of EBGs, each having one conducting via (comparative example 2). The antenna device according to comparative example 2 has a configuration in which the comparative EBGs100(seeFIG. 4A) are formed throughout the region in which the EBGs4are formed in the antenna device1according to the present embodiment.

FIG. 6Cshows the directivity of the antenna device1according to the present embodiment formed with a plurality of the EBGs4, each having four conducting vias.

In the case of the antenna device with no EBG according to comparative example 1, the surface current is propagated to the substrate end portions, and radiation occurs from the substrate end portions. Thus, as illustrated inFIG. 6A, in the directivity of the antenna according to comparative example 1, the gain is decreased (ripples occur) in a specific direction (e.g. around a direction at an angle of ±45°).

On the other hand, in the case of the antenna device formed with the comparative EBGs100according to comparative example 2, an effect is obtained, in which the surface current is reduced by the comparative EBGs100. Thus, as illustrated inFIG. 6B, in the directivity of the antenna according to comparative example 2, a decrease in gain in a specific direction is reduced, compared with comparative example 1.

However, as apparent fromFIG. 6B, the displacement of the via diameter φo of the conducting via100bof the comparative EBG100from the designed reference value causes disturbance in directivity, compared with the case in which the via diameter φo has the reference value. When the conducting via100bis varied within a tolerance range, which is accepted in manufacture, the operating frequency of the comparative EBG100is also greatly varied, as described with reference toFIG. 5A. A great variation in the operating frequency causes disturbance in directivity as illustrated inFIG. 6B.

However, the antenna device1according to the present embodiment has the configuration in which a plurality of the conducting vias4b(four conducting vias4b) is connected to one patch-shaped pattern4a. As described with reference toFIG. 5B, in the EBG4in this configuration, even though the via diameter φ is varied, fluctuations in the operating frequency are small, compared with the comparative EBG100. Consequently, as illustrated inFIG. 6C, the directivity of the antenna device1is not disturbed so much when the via diameter φ is varied, and the effect of reducing ripples can be sufficiently obtained.

In accordance with the antenna device1according to the present embodiment described above, a plurality of the EBGs4is formed around the patch radiating element5. Thus, the propagation of the surface current from the patch radiating element5to the substrate end portions is reduced. Additionally, each of the EBGs4has a plurality of the conducting vias4bin the configuration in which the plurality of conducting vias4bconnects one patch-shaped pattern4ato the ground plane3.

The EBG4has a plurality of the conducting vias4bas described above. Thus, even though the via diameter φ of each of the conducting vias4bis varied within a tolerance range, fluctuations in the operating frequency of the EBG4are reduced. Consequently, even though the via diameter φ of the conducting via4bis varied, the effect of reducing the disturbance in the directivity of the patch antenna7caused by the EBGs4can be maintained.

Note that, the four conducting vias4bconfiguring the EBG4are disposed close to the center region of the patch-shaped pattern4a. Because of the characteristics of high frequency, the impedance characteristics of the conducting vias4bare changed depending on the locations at which the conducting vias4bare disposed (the locations, at which the conducting vias4bare disposed, depend on wavelengths). Thus, the plurality of conducting vias4bis densely disposed, allowing the impedance characteristics of the conducting vias4bto be made uniform. Therefore, densely disposing the plurality of conducting vias configuring the EBG is effective in reducing fluctuations in the operating frequency of the EBG caused by a variation in the via diameter φ, which in turn leads to effectiveness in reducing ripples in the directivity of the patch antenna more than in disposing the conducting vias apart from one another.

In the antenna device1, the EBGs4are not disposed all around the patch radiating element5on the substrate front face. The EBGs4are disposed on the outer side of the EBG absent region8including the patch radiating element5. As described above, the region in which the EBGs4are absent is provided around the patch radiating element5. Thus, an excess cutoff of the surface current is reduced, resulting in preventing the beam width of the directivity of the patch antenna7from being narrowed.

As illustrated inFIGS. 7A and 7B, in the present embodiment, two antenna devices30and50will be described. The two antenna devices30and50illustrated inFIGS. 7A and 7Bhave array structures of a plurality of conducting vias of an EBG different from that of the antenna device1according to the first embodiment illustrated inFIG. 1. The other configurations are the same as the configurations of the antenna device1according to the first embodiment.

First, the antenna device30illustrated inFIG. 7Awill be described. In the antenna device30illustrated inFIG. 7A, a plurality of EBGs31each includes one patch-shaped pattern31aand four conducting vias31b. The shape and dimensions of the patch-shaped pattern31aare the same as the shape and dimensions of the patch-shaped pattern4aof the EBG4according to the first embodiment. The shape and dimensions of each of the four conducting vias31bare the same as the shape and dimensions of the conducting via4bof the EBG4according to the first embodiment. However, the array form of these four vias is different from the array form in the EBG4according to the first embodiment. In the present embodiment, the four conducting vias31bare arrayed in a row. The array direction is the direction perpendicular to the plane of polarization (the E-plane) of the patch antenna7(i.e. the x-axis direction).

Next, the antenna device50illustrated inFIG. 7Bwill be described. In the antenna device50illustrated inFIG. 7B, a plurality of EBGs51each includes one patch-shaped pattern51aand four conducting vias51b. The shape and dimensions of the patch-shaped pattern51aare the same as the shape and dimensions of the patch-shaped pattern4aof the EBG4according to the first embodiment. The shape and dimensions of each of the four conducting vias51bare the same as the shape and dimensions of the conducting via4bof the EBG4according to the first embodiment. However, the array form of these four vias is different from the array form in the EBG4according to the first embodiment and the array form in the EBG31inFIG. 7A. In the antenna device50inFIG. 7B, the four conducting vias51bare arrayed in a row on the plane of polarization (the E-plane) of the patch antenna7. The array direction is the direction in parallel with the plane of polarization (the E-plane) of the patch antenna7(i.e. the y-axis direction).

In both of the antenna devices30and50inFIGS. 7A and 7Bthus configured, the EBG includes a plurality of conducting vias. Thus, similarly to the antenna device1according to the first embodiment, even though the via diameter of the conducting via is varied, fluctuations in the operating frequency of the EBG can be reduced, compared with the antenna device including the EBG with one conducting via.

On the other hand, in relative comparison among the antenna device1according to the first embodiment and the two antenna devices30and50illustrated inFIGS. 7A and 7B, the effect of reducing fluctuations in the operating frequency of the EBG caused by a variation in the via diameter is different among the antenna devices1,30, and50.

FIG. 8shows examples of the transmission properties of the EBGs of the antenna device1according to the first embodiment and the two antenna devices30and50according to the second embodiment. In the antenna device1according to the first embodiment, the four conducting vias4bare disposed in the center region of the patch-shaped pattern4aof each of the EBGs4. Specifically, as described above, two groups each formed of the two conducting vias4barrayed in a row in the x-axis direction with the connection gap wv apart are arrayed in the y-axis direction with the connection gap wv apart.

The transmission properties of the EBG4of the antenna device1thus configured are changed depending on a variation in the via diameter φ of each of the four conducting vias4bconfiguring the EBG4.FIG. 8shows three patterns of the transmission properties of the EBG4, in which the via diameter φ of each of the four conducting vias4bmatches a designed reference value of 150 μm, the via diameter φ of 130 μm is shorter than the reference value, and the via diameter φ is 170 μm which is longer than the reference value. Note that, the via diameters φo in these three patterns are all included within a tolerance range.

As illustrated inFIG. 8, in the EBG4of the antenna device1according to the first embodiment, when the via diameter φ of the conducting via4bis varied within a range of the reference value ±20 μm, the operating frequency (the cutoff frequency) is varied in a range of about 0.3 GHz as a whole.

On the other hand, in the antenna device30illustrated inFIG. 7A, the four conducting vias31bare arrayed perpendicularly to the plane of polarization on the EBGs31.

The transmission properties of the EBG31of the antenna device30thus configured are also changed depending on a variation in the via diameter φ of the four conducting vias31bconfiguring the EBG31.FIG. 8shows the transmission properties of the EBG31with the via diameters φ in the different three patterns similarly to the EBG4according to the first embodiment.

As illustrated inFIG. 8, in the EBG31of the antenna device30illustrated inFIG. 7A, when the via diameter φ of the conducting via31bis varied within a range of the reference value ±20 μm, the operating frequency (the cutoff frequency) is varied in a range of about 0.1 GHz as a whole. This variation is smaller than a variation in the EBG4according to the first embodiment.

In the antenna device50illustrated inFIG. 7B, the four conducting vias51bare arrayed parallel with the plane of polarization on the EBGs51.

The transmission properties of the EBG51of the antenna device50thus configured are also changed depending on a variation in the via diameters φ of the four conducting vias51bconfiguring the EBG51.FIG. 8shows the transmission properties of the EBG51with the via diameters φ in different three patterns similarly to the EBG4according to the first embodiment.

As illustrated inFIG. 8, in the EBG51of the antenna device50illustrated inFIG. 7B, when the via diameter φ of the conducting via51bis varied within a range of the reference value ±20 μm, the operating frequency (the cutoff frequency) is varied in a range of about 0.4 GHz as a whole. This variation is slightly greater than a variation in the EBG4according to the first embodiment.

The transmission properties inFIG. 8show the results on the array direction of a plurality of conducting vias configuring the EBG, in which the effect of reducing fluctuations in the operating frequency of the EBG is more enhanced in arraying the vias in the direction different from the plane of polarization than in arraying the vias in parallel with the plane of polarization. In order to more enhance the effect of reducing fluctuations in the operating frequency of the EBG, a plurality of conducting vias is preferably arrayed in the direction perpendicular to the plane of polarization.

(1) The region in which the EBGs are disposed on the substrate front face can be appropriately determined.

(2) The number of a plurality of conducting vias configuring one EBG can be appropriately determined. A specific shape (e.g. a cross sectional topology) of a plurality of conducting vias can be appropriately determined. The other conditions for a plurality of conducting vias can be appropriately determined, such as locations at which a plurality of conducting vias is connected to the patch-shaped pattern, and which direction vias are arrayed in the case in which a part or all of a plurality of conducting vias is arrayed in a row.

However, in order to enhance the effect of reducing fluctuations in the operating frequency of the EBG caused by a variation in the via diameter of the conducting via, a plurality of conducting vias is preferably disposed close to each other (vias are densely disposed).

FIGS. 9A and 9Billustrate other examples of the EBG. In an antenna device60illustrated inFIG. 9A, the array form of four conducting vias configuring an EBG is different from that in the antenna device1according to the first embodiment illustrated inFIG. 1. Specifically, as illustrated inFIG. 9A, a plurality of EBGs61each has four conducting vias61b. The four conducting vias61bare connected to one patch-shaped pattern61a. The direction in which the four conducting vias61bare arrayed is not in parallel with the x-axis or the y-axis.

In the antenna device70illustrated inFIG. 9B, the number of conducting vias configuring the EBG and the array form of the vias are different from those in the antenna device1according to the first embodiment illustrated inFIG. 1. Specifically, as illustrated inFIG. 9B, a plurality of EBGs71each has six conducting vias71b. The six conducting vias71bare connected to one patch-shaped pattern71a. The six conducting vias71bare disposed as three vias are arrayed in two rows. In other words, three conducting vias71barrayed in a row in the x-axis direction make a group. This group is disposed in two rows in the y-axis direction.

The forms of the EBGs61and71illustrated inFIGS. 9A and 9Bare merely examples. Any forms of the EBG can be variously adopted, other than these forms.

(3) For the specific shape of the patch-shaped pattern configuring the EBG, a square shape described in the embodiments is merely an example. The patch-shaped pattern can have any shapes. For example, as illustrated in an antenna device80inFIG. 9C, a plurality of EBGs81each having a hexagonal patch-shaped pattern81amay be formed on the dielectric substrate.

(4) The shape and number of the patch radiating element5configuring the patch antenna7can also be appropriately determined. For example, a configuration may be possible in which a plurality of patch radiating elements5is arrayed in the x-axis direction for forming an array antenna.

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