ARRAY ANTENNA

In this array antenna, if (a) a pair of antennas (130) are used and transmission signals having the same phase are fed in parallel via two secondary cables (33) branching off of a main cable (32), letting Z represent the impedance of the main cable (32), the impedance of each secondary cable (33) and the input impedance of each antenna (130) is set to 2Z; if (b) a set of three antennas (130) is used, the impedance of each secondary cable (33) and the input impedance of each antenna (130) is set to 3Z; and if (c) a set of N antennas (130) is used, the impedance of each secondary cable (33) and the input impedance of each antenna (130) is set to N×Z. In each case, the impedances match over a wide frequency band.

TECHNICAL FIELD

The present invention relates to an array antenna.

BACKGROUND ART

In a base station antenna for mobile communication (base station antenna), plural sector antennas, each of which radiates radio frequency for a sector being set corresponding to a direction of radiating radio frequency, are used in combination. As the sector antenna, an array antenna in which antenna elements, such as dipole antennas, are arranged in an array is used.

Patent Document 1 describes a 60° beam antenna apparatus that includes: first and second dipole antennas having lengths of about λ/2 (λ is the wavelength of the center frequency of the request frequency band) and arranged in parallel at a spacing of about λ/2; and a feeding unit having a main feeding line and first and second branched feeding lines which branched from the main feeding line and are connected to feeding points of dipole antennas, respectively, wherein the characteristic impedance of the main feeding line is set to about 50Ω, and the characteristic impedance of the first and second branched feeding lines is set to about 100Ω.

CITATION LIST

Patent Literature

SUMMARY OF INVENTION

Technical Problem

In the array antenna, plural antenna elements are fed in parallel in some cases. At this time, impedance matching is required between the antenna elements and the feeding lines.

An object of the present invention is to provide an array antenna capable of achieving impedance matching with ease in a wide band.

Solution to Problem

To achieve the above-described object, an array antenna to which the present invention is applied includes: a first feeding line having a first impedance; N second feeding lines branching off from the first feeding line; and N antennas, each of which has a second impedance that is set based on N times the first impedance, the N antennas being connected to the respective N second feeding lines, wherein N is an integer not less than 2.

According to this configuration, it is possible to achieve impedance matching with ease, as compared to a case in which impedance matching is carried out by a transformer or the like.

The antenna in the array antenna configured like this includes a pair of element sections, each of which is configured with a conductive material including a curved line at an edge thereof, the element sections being arranged at symmetrical positions with respect to a predetermined axis at a predetermined distance, and the second impedance is set by a shape thereof.

According to this configuration, the impedance can be set with ease, as compared to a case in which the present configuration is not provided.

Moreover, the antenna in the array antenna configured like this further includes another pair of element sections each configured with a conductive material including a curved line at an edge thereof, the element sections being arranged at symmetrical positions with respect to a predetermined axis at a predetermined distance, and the another pair of element sections is able to transmit and receive a polarization orthogonal to a polarization received and transmitted from and to the pair of element sections.

According to this configuration, it is possible to configure a downsized antenna for dual polarization, as compared to a case in which the present configuration is not provided.

Still further, the antenna in the array antenna configured like this includes a patch antenna having a first conductor, a second conductor and one of a dielectric or an air layer between the first conductor and the second conductor, and the second impedance is set by a position of feeding to the first conductor.

According to this configuration, the impedance can be set with ease, as compared to a case in which the present configuration is not provided.

Then, a radome that contains the array antenna is further included.

According to this configuration, it is possible to provide an array antenna capable of achieving impedance matching with ease and obtaining wide-band frequency characteristics.

Advantageous Effects of Invention

According to the present invention, it is possible to provide an array antenna capable of achieving impedance matching with ease in a wide band.

DESCRIPTION OF EMBODIMENTS

Hereinafter, exemplary embodiments according to the present invention will be described in detail with reference to attached drawings.

First Exemplary Embodiment

Base Station Antenna1

FIGS. 1A and 1Bare diagrams showing an example of an overall configuration of a base station antenna1for mobile communication, to which the first exemplary embodiment is applied.FIG. 1Ais a perspective view of the base station antenna1, andFIG. 1Bis a diagram illustrating an installation example of the base station antenna1.

The base station antenna1includes, as shown inFIG. 1A, plural array antennas10-1to10-6held by, for example, a tower20. Then, as shown inFIG. 1B, the base station antenna1causes the radio frequency to reach inside of a cell2. In other words, the cell2is a range in which the radio frequency transmitted by the base station antenna1reach, and a range in which the base station antenna1receives the radio frequency.

Each of the array antennas10-1to10-6has a cylindrical radome (refer to radome500inFIG. 2to be described later) on the outside thereof, and a center axis of the cylindrical radome500is provided vertical to the ground.

As shown inFIG. 1B, the cell2includes plural sectors3-1to3-6that are provided by angular division on the horizontal plane. The sectors3-1to3-6are provided corresponding to the six array antennas10-1to10-6of the base station antenna1, respectively. That is, in each of the array antennas10-1to10-6, a main lobe11with a large electric field of output radio frequency is in the direction of corresponding one of the sectors3-1to3-6.

Here, the array antennas10-1to10-6are collectively represented as an array antenna10, when not being distinguished from one another. Moreover, the sectors3-1to3-6are collectively represented as a sector3, when not being distinguished from one another.

Note that the base station antenna1shown as an example inFIGS. 1A and 1Bincludes the six array antennas10-1to10-6and the sectors3-1to3-6corresponding thereto. However, the array antenna10and the sector3may be of a number other than six predetermined in advance. Moreover, inFIG. 1A, the sector3is configured by dividing the cell2into 6 equal parts (center angle is 60°); however, the sector3may not be divided equally and any one sector3may be configured widely or narrowly as compared to another sector3.

Then, each array antenna10is connected to a transmission and reception cable31that transmits transmission signals and reception signals to a dipole antenna (refer to dipole antennas110-1to110-8inFIG. 2to be described later, represented as a dipole antenna110when not being distinguished from one another) included by the array antenna10.

The transmission and reception cable31is connected to a transceiver unit4(refer toFIG. 5to be described later) that is provided in the base station (not shown) to generate the transmission signals and receive the reception signals. The transmission and reception cable31is, for example, a coaxial cable.

InFIG. 1A, the transmission and reception cable31is illustrated with the array antenna10-1. Though, similar to the array antenna10-1, other array antennas10-2to10-6also include the transmission and reception cables31, illustration thereof is omitted.

Note that, hereinafter, description will be given based on the premise that the base station antenna1transmits the radio frequency; however, owing to reversibility of the antenna, the base station antenna1is able to receive the radio frequency. In the case of receiving the radio frequency, flow of the signals may be reversed by assuming, for example, the transmission signals as the reception signals.

Moreover, the array antenna10includes a phase shifter200(refer toFIG. 5to be described later) for feeding the plural dipole antennas110included by the array antenna10with the transmission signals having differentiated phases. By shifting the phases of the transmission signals to be fed to the plural dipole antennas110, the radiating angle of the radio frequency (beam) radiated from the array antenna10is tilted by the angle θ (assumed as a beam tilt angle θ) from the horizontal plane to the aboveground direction. This sets the radio frequency not to reach out of the cell2.

FIG. 2is a diagram showing an example of a configuration of the array antenna10in the first exemplary embodiment. InFIG. 2, the array antenna10is laid down, and shown in a perspective view as viewed laterally from an angle.

The array antenna10includes: a reflector120; the plural (here, as an example, 8) dipole antennas110-1to110-8arranged on the reflector120; and the phase shifter200that feeds each of the dipole antennas110-1to110-8with the transmission signals while shifting the phases thereof. Further, the array antenna10includes a radome500that contains the reflector120, the dipole antennas110-1to110-8and the phase shifter200so as to enclose thereof. InFIG. 2, the radome500is indicated by broken lines to let the reflector120and the dipole antennas110-1to110-8provided inside the radome500be seen. Note that, inFIG. 2, the phase shifter200is indicated by broken lines because the phase shifter200is provided on a side of the reflector120that is opposite to the side on which the dipole antennas110-1to110-8are provided.

Each of the odd-numbered dipole antennas110-1,110-3,110-5and110-7includes a pair of elliptic element sections111aand112a, in which the direction of the major axis is shifted 45° from the vertical direction. The odd-numbered dipole antennas110-1,110-3,110-5and110-7transmit and receive polarization shifted 45° from the vertical direction. Note that, as an example, the element sections111aand112aare provided so that the front surfaces thereof are parallel to a front reflection section120aof the reflector120, and arranged at a position symmetric with respect to the point O.

Each of the even-numbered dipole antennas110-2,110-4,110-6and110-8includes another pair of elliptic element sections111band112b, in which the direction of the major axis is shifted −45° from the vertical direction. The even-numbered dipole antennas110-2,110-4,110-6and110-8transmit and receive polarization shifted −45° from the vertical direction. As an example, the element sections111band112bare also provided so that the front surfaces thereof are parallel to a front reflection section120aof the reflector120, and arranged at a position symmetric with respect to the point O.

Then, the dipole antennas110-1and110-2are combined so that the point O on which the element sections111aand112aof the dipole antenna110-1are symmetrically arranged is in common with the point O on which the element sections111band112bof the dipole antenna110-2are symmetrically arranged, to thereby configure a pair. Further, the dipole antennas110-3,110-5and110-7are combined with the dipole antennas110-4,110-6and110-8, respectively, in a similar manner, to thereby configure pairs.

This allows the array antenna10to achieve dual polarization capable of transmitting and receiving ±45° polarization.

Note that the element sections111aand111bare collectively represented as an element section111when not being distinguished from each other, and the element sections112aand112bare collectively represented as an element section112when not being distinguished from each other.

Accordingly, hereinafter, description will be given by taking one of the dipole antennas110-1to110-8as the dipole antenna110.

Note that, inFIG. 2, it was assumed that the ±45° radio frequency are transmitted and received; however, it becomes possible to transmit and receive radio frequency of horizontal polarization and vertical polarization by rotating the two dipole antennas110having been paired 45° around the point O.

The reflector120reflects the radio frequency transmitted from the dipole antenna110, and also holds the dipole antenna110. InFIG. 2, the four pairs, each of which is configured with two dipole antennas110, are arranged on the reflector120with a distance of Dp, to thereby configure the array (array antenna10).

In the reflector120, the front reflection section120a, which the element sections111and112of the dipole antennas110face, is flat. Both end portions of the reflector120in the direction intersecting the array direction of the dipole antenna110are bent toward the dipole antenna110to become side reflection sections120b. The side reflection sections120bhaving been bent define a beam width within the horizontal plane of the array antenna10.

Note that, inFIG. 2, the side reflection sections120bare bent toward the dipole antenna110; however, the side reflection sections120bmay be bent toward the opposite side of the dipole antenna110. Moreover, inFIG. 2, one side reflection section120bis provided to each of the end portions of the reflector120; however, plural side reflection sections120bmay be provided.

Since the side reflection sections120bdefine the beam width within the horizontal plane of the array antenna10, setting may be carried out to obtain a predetermined beam width within the horizontal plane.

The reflector120is configured with a conductor, such as aluminum or copper.

InFIG. 2, the reflector120is provided in common to the eight dipole antennas110-1to110-8; however, it may be considered that the reflector120is divided for each and every dipole antenna110or each and every pair of two dipole antennas110.

Here, the dipole antenna110and the reflector120corresponding thereto are inclusively referred to as an antenna130. In the case of two dipole antennas110having been paired, the pair of dipole antennas110and the reflector120corresponding thereto are inclusively referred to as the antenna130.

The phase shifter200will be described later.

The radome500includes a cylinder501, an upper lid502that covers an end portion on the upper side of the cylinder501, and a lower lid503that covers an end portion on the lower side of the cylinder501. The radome500contains the antenna130inside thereof.

The lower lid503of the radome500is provided with a connector (not shown), and the transmission and reception cable31for receiving and transmitting the transmission signals and the reception signals from and to the dipole antenna110is connected thereto. Note that, inFIG. 2, illustration of connection between the transmission and reception cable31and the dipole antenna110is omitted.

The radome500is configured with an insulating resin, such as FRP (fiber reinforced plastics).

Note that the array antenna10shown inFIG. 2is configured with eight dipole antennas110; however, the number of dipole antennas110is not limited to eight, and may be any predetermined number.

Moreover, the array antenna10shown inFIG. 2is configured with a single array including eight dipole antennas110; however, the array antenna10may be configured by arranging multiple arrays.

Further, inFIG. 2, it was assumed that the radome500included by the array antenna10was the cylinder501provided with the upper lid502and the lower lid503; however, the cylinder501may be a tube with a rectangular cross section, and one side of the cross section may be an arc shape.

<Configuration of Array Antenna130>

FIGS. 3A and 3Bare diagrams illustrating a configuration of the antenna130in the first exemplary embodiment.FIG. 3Ais a plan view, andFIG. 3Bis a cross-sectional view at the IIIB-IIIB line inFIG. 3A. The antenna130includes the dipole antenna110and the reflector120.

The dipole antenna110includes: the above-described element sections111and112; a leg sections113and114extending from the element sections111and112, respectively; and a stage section115to which the leg sections113and114are fixed. Note that, though the leg sections113,114and the stage section115may not necessarily be provided, description will be given on the assumption that the dipole antenna110includes the leg sections113,114and the stage section115in the first exemplary embodiment.

Each of the element sections111and112of the dipole antenna110is, as shown inFIG. 3A, a member configured with a conductive material enclosed by an elliptical edge having a minor axis L1and a major axis L2. The element section111and the element section112are symmetrically arranged with respect to the point O, and face at a distance D so that the major axes L2thereof are arranged in line with each other.

Then, as shown inFIG. 3B, the element section111is provided with a circular opening at the side of the point O, and the leg section113in a cylindrical shape is connected to the opening. The element section112is also provided with a circular opening at the side of the point O, and the leg section114in a cylindrical shape is connected to the opening. Note that the opening may not be provided to the element section112, and the leg section114may have a cylindrical columnar shape.

The leg sections113and114of the dipole antenna110are connected to the stage section115having a circular front surface shape. Note that, in the stage section115, an opening is provided to face the cylindrical leg section113. In other words, a cylindrical hollow portion is provided from the opening in the element section111to the opening in the stage section115.

In the first exemplary embodiment, the element sections111and112, the leg sections113and114, and the stage section115are configured with a conductive material as a single piece. Note that each of the element sections111and112, the leg sections113and114, and the stage section115may be individually or partially configured as a single piece, and assembled by screws or the like.

The element sections111and112, the leg sections113and114, and the stage section115are configured with metal, such as copper or aluminum, or an alloy containing those metals.

The stage section115is fixed to the front reflection section120aof the reflector120by not-shown screws or the like. The surfaces of the element sections111and112of the dipole antenna110are configured to be parallel to the front reflection section120aof the reflector120.

Note that the distance from the surface of the reflector120on the dipole antenna110side to the center in the thickness direction of the element sections111and112is regarded as the height H.

In the cylindrical hollow portion running from the opening of the element section111to the opening of the stage section115, an insulator117including a conductor116at the center thereof is embedded. Note that the insulator117may be embedded in the entire hollow portion or in a part thereof.

Then, an end portion of the conductor116on the element section116side is bent 90° to be connected to an end portion of the element section112in proximity to the point O (the part indicated by arrow A). Note that the connection is conducted by soldering, for example.

An end portion of the conductor116on the stage section115side is connected to an inner conductor of a secondary cable33(a secondary cable33-1or a secondary cable33-2inFIG. 5to be described later, and represented as a secondary cable33) through an opening provided to the reflector120. Moreover, the reflector120is connected to an outer conductor of the secondary cable33.

The conductor116may be a conductor wire having a circular cross section; however, since such a wire is less likely to be bent 90°, the conductor116may be configured by cutting a metal plate into an L-shape. The conductor116is configured with metal, such as copper or aluminum, or an alloy containing those metals.

The insulator117is configured with, for example, polytetrafluoroethylene that is excellent in high frequency characteristics.

Note that, to prevent the conductor116that has been bent 90° from contacting the element section112, it is preferable to cut down an end portion of the element section112on the point O side (the part indicated by arrow B) toward the reflector120.

In the dipole antenna110, for example, the minor axis L1of the element sections111and112is 21 mm, the major axis L2thereof is 30 mm, and the distance D between the element sections111and112is 12 mm. The height H from the center in the thickness direction of the element sections111and112to the reflector120is 38.5 mm.

The height H is set to about ¼ wavelength in the case where the center frequency fc of the array antenna10is set to 2 GHz. Accordingly, in the case of being viewed from the element sections111and112, the element section111and the element section112are short-circuited on the stage section115, but a current does not flow.

Note that, though the leg sections113and114were supposed to have the cylindrical or cylindrical-columnar shape, the outer shape may not be limited to the cylindrical or cylindrical-columnar shape, and may be a rectangular-columnar shape, a tapered shape, and so forth.

In the case where the element sections111and112, the leg sections113and114, and the stage section115are integrally molded by a method such as die casting, the leg sections113and114may have a shape that is easily molded.

Then, the cylindrical hollow portion that extends from the element section111to the stage section115may be provided in the leg section113.

Moreover, in the case where two dipole antennas110are paired for dual polarization, the stage section115may be used in common. By configuring as a single piece, it is possible to produce the dipole antennas110in bulk, and provide excellent mass production ability.

However, the two dipole antennas110shown inFIGS. 3A and 3Bare paired to be combined, the conductors116are brought into contact with each other.

FIGS. 4A and 4Bare diagrams illustrating a configuration of the dipole antenna110, which is paired with the dipole antenna110inFIGS. 3A and 3Bfor dual polarization, in the first exemplary embodiment.FIG. 4Ais a plan view, andFIG. 4Bis a cross-sectional view at the IVB-IVB line inFIG. 4A.

FIGS. 4A and 4Bshow the dipole antenna110including the element sections111band112bwhen the dipole antenna110inFIGS. 3A and 3Bis assumed to include the element sections111aand112a(refer toFIG. 2). Accordingly, description will be given of the different portions, whereas description of the similar portions will be omitted.

In the dipole antenna110inFIGS. 4A and 4B, to prevent the conductor116of the dipole antenna110shown inFIGS. 4A and 4Bfrom contacting the conductor116of the dipole antenna110inFIGS. 3A and 3B, portions indicated by arrows A′ and B′ on the point O side are cut down deeper toward the reflector120as compared to the case of the dipole antenna110inFIGS. 3A and 3B. This causes the conductors116of the pair of dipole antennas110to intersect on spatially different levels, to thereby prevent the conductors116from contacting each other.

Note that, in the dipole antenna110, the element section112band the conductor116are connected at the portion indicated by arrow A′. The connection is conducted by soldering, for example.

As described above, inFIGS. 3A and 3B, the dipole antenna110does not necessarily include the stage section115. In this case, the leg sections113and114may be extended by the length corresponding to the thickness of the stage section115. Then, the leg sections113and114may be fixed to the front reflection section120aof the reflector120.

Note that, in the case where the stage section115is provided, since the dipole antenna110and the reflector120are able to be fixed by fixing the stage section115and the reflector120by screws or the like, assembly of the array antenna10is made easy.

So far, description has been given on the assumption that the surfaces of the element sections111and112are parallel to the front reflection section120aof the reflector120. However, the surfaces of the element sections111and112may not necessarily be parallel to the front reflection section120aof the reflector120. For example, the side of the element sections111and112closer to the point O may be approaching the front reflection section120aof the reflector120than the side of the element sections111and112farther from the point O. To the contrary, the closer side may be away from the front reflection section120aof the reflector120. In other words, as shown inFIGS. 3A and 3B, the element section111and the element section112may be symmetric with respect to an axis OO′ that connects the point O and a point O′, which is vertical projection of the point O onto the front reflection section120aof the reflector120.

Further, the axis OO′ may not necessarily be vertical to the front reflection section120aof the reflector120, but may be inclined.

<Method of Feeding to Array Antenna10>

Here, a supply method of the transmission signal (feeding method) in the array antenna10will be described.

FIG. 5is a diagram illustrating an example of the method of feeding to the antenna130in the array antenna10.

FIG. 5shows the method of feeding to the odd-numbered dipole antennas110in the array antenna10shown inFIG. 2. In other words, it is assumed that the array antenna10shown inFIG. 5includes only the odd-numbered dipole antennas110and does not include the even-numbered dipole antennas110.

Consequently, similar toFIG. 2, it is assumed that there are 4 odd-numbered dipole antennas110(the dipole antennas110-1,110-3,110-5and110-7) inFIG. 5, too. The antennas130corresponding to the dipole antennas110-1,110-3,110-5and110-7are represented as the antenna130-1,130-3,130-5and130-7, respectively.

Note that, in the antenna130for dual polarization configured by pairing the odd-numbered dipole antenna110with the even-numbered dipole antenna110, similar to the odd-numbered dipole antenna110, the even-numbered dipole antenna110is also fed.

The phase shifter200includes three input and output ports (Port0, Port1and Port2) for the array antenna10constituted by the odd-numbered antennas130(antennas130-1,130-3,130-5and130-7).

The Port0is connected to the transceiver unit4. When the array antenna10radiates the radio frequency, the transceiver unit4feeds the Port0with the transmission signal. The phase shifter200outputs the transmission signal, which has been inputted into the Port0, from the Port1and the Port2while shifting the phase thereof.

To the Port1, one end of the main cable32, as an example of the first feeding line, is connected. Then, to the other end of the main cable32, as if the main cable32is to be divided, one ends of the respective secondary cables33-1and33-2, as an example of two second feeding lines, are connected in parallel. The other end of the secondary cable33-1is connected to the antenna130-1, whereas the other end of the secondary cable33-2is connected to the antenna130-3.

For example, if it is assumed that the main cable32and the secondary cables33-1and33-2are coaxial cables, the inner conductor of the main cable32is connected to the inner conductor of each of the secondary cables33-1and33-2, and the outer conductor of the main cable32is connected to the outer conductor of each of the secondary cables33-1and33-2. Note that the two secondary cables33-1and33-2are collectively represented as a secondary cable33, when not being distinguished from each other.

Accordingly, as has been described inFIGS. 3A and 3B, the other end portion of the conductor116of the antenna130is connected to the internal conductor of the secondary cable33, and the reflector120is connected to the outer conductor of the secondary cable33.

The same is true for the Port2, and thereby description thereof will be omitted.

As described above, the antennas130-1and130-3are connected to the Port1of the phase shifter200, and the transmission signals of the same phase are fed thereto. Similarly, since the antennas130-5and130-7are connected to the Port2of the phase shifter200, the transmission signals of the same phase are also fed thereto.

However, the phase shifter200outputs the transmission signal, which has been inputted into the Port0, from the Port1and the Port2while shifting the phase thereof. For example, if a phase shift amount, which is deviation in phase, is φ (°), it is possible to calculate the beam tilt angle θ shown inFIG. 1A(sin θ=(φ×λ) (2×Dp×360)) from the distance Dp in arrangement of the antennas130shown inFIG. 2(here, since two antennas130are paired, 2×Dp). Note that, here, λ is a wavelength of the radio frequency which the antenna130radiates in a free space.

InFIG. 5, the antennas130-1and130-3were paired, and the transmission signals of the same phase were fed thereto in parallel. Similarly, the antennas130-5and130-7were paired, and the transmission signals of the same phase, which is different from the phase of the transmission signals fed to the pair of antennas130-1and130-3, were fed thereto in parallel.

Each antenna130may be fed with a transmission signals having different phases. This makes it possible to reduce disturbances in directivity, although the radiating angle (beam tilt angle θ) is changed. However, the phase shifter200having the input and output ports corresponding to the number of antennas130constituting the array antenna10is required.

Accordingly, the plural antennas130are formed into some sets, and the transmission signals having the same phase are fed in parallel to the antennas130belonging to the same set.

Note that, in the case where the plural antennas130are formed into a set and the transmission signals are fed in parallel thereto, impedance matching is required. If the impedance matching is not achieved, return loss of the antenna130is increased.

FIGS. 6A to 6care diagrams illustrating relation among impedances of the main cable32and the secondary cables33and input impedances of the antennas130in the case where the first exemplary embodiment is applied. InFIGS. 6A to 6C, the plural antennas130and the plural secondary cables33are illustrated, but without being distinguishing from one another, represented as the antennas130and the secondary cables33.

Moreover, the impedance of each of the main cable32and the secondary cables33and the input impedance of the antenna130are illustrated.

Here, it is assumed that the impedance of the main cable32from the phase shifter200shown inFIG. 5is Z (an example of a first impedance). Then, it is assumed that the impedance matching is achieved from the transceiver unit4to the main cable32of the phase shifter200.

Similar toFIG. 5,FIG. 6Ashows the case in which the two antennas130are paired and the transmission signals having the same phase are fed in parallel thereto. The input impedance of the antenna130is set to 2×Z.

Since the impedance of the main cable32is Z, by dividing thereof into two, the impedances of the secondary cables33become 2×Z.

The input impedance of the antenna130is also 2×Z, and accordingly, impedance matching is achieved.

In other words, as shown inFIG. 5, impedance matching is achieved by dividing the main cable32into a pair of secondary cables33and connecting each of the secondary cables33directly to the antenna130.

Unlike in the case ofFIG. 5,FIG. 6Bshows a case in which the three antennas130are formed into a set and the transmission signals having the same phase are fed in parallel thereto. The input impedance of the antenna130is set to 3×Z. Since the impedance of the main cable32is Z, by dividing thereof into three, the impedances of the secondary cables33become 3×Z.

The input impedance of the antenna130is also 3×Z, and accordingly, impedance matching is achieved.

In other words, impedance matching is achieved by dividing the main cable32into three secondary cables33and connecting each of the secondary cables33to the antenna130.

Unlike in the case ofFIG. 5,FIG. 6Cshows a case in which the N (N is an integer not less than 2) antennas130are formed into a set and the transmission signals having the same phase are fed in parallel thereto. The input impedance of the antenna130is set to N×Z (an example of a second impedance). Since the impedance of the main cable32is Z, by dividing thereof into N, the impedances of the secondary cables33become N×Z.

The input impedance of the antenna130is also N×Z, and accordingly, impedance matching is achieved.

In other words, impedance matching is achieved by dividing the main cable32into N secondary cables33and connecting each of the secondary cables33to the antenna130.

Note that, in the above description, it was assumed that the impedance of the antenna130was set to 2×Z, 3×Z and N×Z with respect to the impedance Z of the main cable32; however, the impedance of the antenna130may be values shifted around these values set based thereon.

FIG. 7is a diagram illustrating relation among impedances of the main cable32and the secondary cables33and input impedances of the antennas130in the case where the first exemplary embodiment is not applied. Even in the case, the two antennas130are paired and the transmission signals having the same phase are fed in parallel thereto. It is assumed that the input impedance of the antenna130is Z at this time. If the main cable32is divided into two, it is required to set the impedance of the secondary cable33to 2×Z, as described above. For this reason, impedance matching cannot be achieved by connecting the secondary cables33each having the impedance of 2×Z to the antennas130each having the impedance of Z. Accordingly, it is necessary to set the impedance of the secondary cable33to Z by providing a quarter-wavelength transformer300configured with a microstrip line or the like between the main cable32and the antennas130.

The quarter-wavelength transformer300constituted by the microstrip line or the like is configured to resonate with the wavelength λc of the center frequency fc of the radio wave radiated from the antenna130. Consequently, the quarter-wavelength transformer300has frequency dependence, and accordingly, has difficulty in adapting to wide-band frequency. Moreover, though the quarter-wavelength transformer300can be provided in a multistage configuration to widen the range of adaptable frequency, the quarter-wavelength transformer300still has characteristics dependent on frequency even in this case.

Accordingly, even though the antenna130has wide-band frequency characteristics, the range of frequency that can be used is limited by the frequency characteristics of the quarter-wavelength transformer300.

In contrast to this, in the first exemplary embodiment, since the input impedance of the antenna130is set corresponding to the impedance of the secondary cable33, the secondary cables33and the antennas130are able to be directly connected. For this reason, it is possible to transmit and receive the radio frequency in the frequency range of the wide-band antenna130.

Note that, in the above description, the main cable32and the secondary cable33were explained as the coaxial cables; however, the cables may be configured by other system, such as the microstrip line.

FIG. 8is a diagram illustrating a model used for performing simulation of characteristics of the antenna130. Six dipole antennas110-1to110-6are used, and the odd-numbered ones and the even-numbered ones are respectively paired for dual polarization. Note that the odd-numbered dipole antenna110is combined with the even-numbered dipole antenna110, to thereby configure the antenna130. Here, the dipole antenna110-1and the dipole antenna110-2configure the dual polarized antenna130-1, the dipole antenna110-3and the dipole antenna110-4configure the dual polarized antenna130-2, and the dipole antenna110-5and the dipole antenna110-6configure the dual polarized antenna130-3.

The transmission signal for transmitting the radio frequency was fed to the dipole antenna110-3of the dual polarized antenna130-2. The transmission signals were not fed to the other antennas130-1and130-3, and the dipole antenna110-4of the antenna130-2to use as dummy antennas.

FIG. 9is a diagram showing return loss (dB) characteristics of the antenna130in the first exemplary embodiment, which is obtained by the simulation model shown inFIG. 8. In the dipole antenna110of the antenna130, the minor axis L1of the element sections111and112is 21 mm, the major axis L2thereof is 30 mm, and the distance D between the element sections111and112is 12 mm. The height H from the center in the thickness direction of the element sections111and112to the reflector120is 38.5 mm.

In the frequency range in which the return loss is not more than −10 dB (VSWR≦2), the lower limit frequency fL is 1.6 GHz and the upper limit frequency fH is 3 GHz. The relative bandwidth is 61%.

In the antenna using the dipole antenna including the rod-shaped element sections111and112, the relative bandwidth is about 25%. Even though this dipole antenna is wide-banded by adding parasitic elements, the relative bandwidth thereof is about 40%.

Accordingly, the antenna130of the first exemplary embodiment is further wide-banded as compared to the antenna using the dipole antenna110including the rod-shaped element sections111and112added with the parasitic elements.

Moreover, the antenna130of the first exemplary embodiment has less components and is easy to be produced as compared to the antenna using the dipole antenna110having complex configuration added with the parasitic elements.

FIG. 10is a diagram showing a horizontal-plane beam width of the antenna130in the first exemplary embodiment, which is obtained by the simulation model shown inFIG. 8. Here, the figure shows the case in which the frequency f is 2 GHz. As the horizontal-plane beam width in the antenna130, 65° is obtained.

As described above, the horizontal-plane bean width is able to be defined by the side reflection section120b. Consequently, by adjusting the width of the reflector120, the shape of the side reflection section120b, the number thereof or the like, it is possible to adjust the horizontal-plane beam width of the antenna130.

Table 1 shows the input impedance (Ω) of the antenna130in the case where the minor axis L1of the element sections111and112shown inFIGS. 3A and 3Bis changed, which is a result obtained by simulation.

In the simulation, the impedance of the secondary cable33, which serves as the feeding line to the antenna130, was changed and the impedance of a portion constituted by the conductor116and the insulator117provided in the hollow part of the leg section113shown inFIGS. 3A and 3Bwas also changed, to thereby set the impedance in which the relative bandwidth of the return loss not more than −10 dB became widest as the input impedance of the antenna130. In other words, the setting is made so that impedance matching is achieved in the route from the secondary cable33, which serves as the feeding line, to the element sections111and112of the dipole antenna110.

Here, the major axis L2is 30 mm, the distance D between the element sections111and112is 12 mm, and the height H from the center in the thickness direction of the element sections111and112to the reflector120is 38.5 mm.

As shown in Table 1, the larger the minor axis L1of the element sections111and112of the dipole antenna110, the smaller the input impedance of the antenna130, and, for example, the input impedance is 1000 with the minor axis L1of 21 mm. To the contrary, the smaller the minor axis L1, the larger the input impedance, and, for example, the input impedance is 1750 with the minor axis L1of 15 mm.

In other words, in the first exemplary embodiment, it is possible to set the input impedance of the antenna130by the minor axis L1of the element sections111and112of the dipole antenna110.

Note that the result shown in Table 1 is merely an example, and the input impedance of the antenna130can further be changed by further changing the minor axis L1of the element sections111and112of the dipole antenna110.

Therefore, in the case where the main cable32shown inFIG. 6Ais divided into a pair of secondary cables33to be connected to a pair of antennas130, assuming that the impedance Z of the main cable32is 500, the impedance of the secondary cables33becomes 2×Z, namely, 1000. Accordingly, the antenna130in which the minor axis L1of the dipole antenna110is set to 21 mm may be used so that the input impedance thereof becomes 1000.

Moreover, in the case where the main cable32shown inFIG. 6Bis divided into three secondary cables33to be connected to three antennas130, assuming that the impedance Z of the main cable32is 500, the impedance of the secondary cables33becomes 3×Z, namely, 150Ω. Accordingly, the antenna130in which the minor axis L1of the dipole antenna110is set to 18 mm may be used so that the input impedance thereof becomes 1500.

In the antenna using the dipole antenna including the rod-shaped element sections111and112, unlike the antenna130of the first exemplary embodiment, the input impedance cannot be changed though the width of the rod is changed.

Table 2 shows the input impedance (Ω) of the antenna130in the case where the height H from the center in the thickness direction of the element sections111and112shown inFIGS. 3A and 3Bto the reflector120is changed, which is a result obtained by simulation.

In this simulation, also, the impedance of the transmission and reception cable31, which serves as the feeding line to the antenna130, was changed and the impedance of a portion constituted by the conductor116and the insulator117provided in the hollow part of the leg section113shown inFIGS. 3A and 3Bwas also changed, to thereby set the impedance in which the relative bandwidth of the return loss not more than −10 dB became widest as the input impedance of the antenna130. In other words, the setting is made so that impedance matching is achieved in the route from the feeding line to the element sections111and112of the dipole antenna110.

Here, the minor axis L1is 21 mm, the major axis L2is 30 mm, and the distance D between the element sections111and112is 12 mm.

As shown in Table 2, the smaller the height H from the center in the thickness direction of the element sections111and112of the dipole antenna110to the reflector120, the larger the input impedance of the antenna130, and, for example, the input impedance is 1500 with the height H of 32.5 mm. To the contrary, the smaller the height H, the larger the input impedance, and, for example, the input impedance is 750 with the height H of 42.5 mm.

In other words, in the first exemplary embodiment, it is also possible to set the input impedance of the antenna130by changing the height H from the center in the thickness direction of the element sections111and112of the dipole antenna110to the reflector120.

Note that the result shown in Table 2 is merely an example, and the input impedance of the antenna130can further be changed by further changing the height H from the center in the thickness direction of the element sections111and112of the dipole antenna110to the reflector120.

Therefore, in the case where the main cable32shown inFIG. 6Ais divided into a pair of secondary cables33to be connected to a pair of antennas130, assuming that the impedance Z of the main cable32is 50Ω, the impedance of the secondary cables33becomes 2×Z, namely, 100Ω. Accordingly, the antenna130in which the height H of the dipole antenna110is set to 37.5 mm may be used so that the input impedance thereof becomes 100Ω.

Moreover, in the case where the main cable32shown inFIG. 6Bis divided into three secondary cables33to be connected to three antennas130, assuming that the impedance Z of the main cable32is 50Ω, the impedance of the secondary cables33becomes 3×Z, namely, 150Ω. Accordingly, the antenna130in which the height H of the dipole antenna110is set to 32.5 mm may be used so that the input impedance thereof becomes 150Ω.

As described above, in the antenna130to which the first exemplary embodiment is applied, it is possible to set the input impedance of the antenna130by changing parameters for establishing the shape of the dipole antenna110, such as the minor axis L1of the element sections111and112, and the height H from the center in the thickness direction of the element sections111and112of the dipole antenna110to the reflector120in the antenna130.

Accordingly, in the case where the impedance of the main cable32is Z and the main cable32is divided into the N secondary cables33, the shape of the antenna130may be established to set the input impedance of the antenna130to N×Z.

Moreover, as shown inFIG. 9, the antenna130of the first exemplary embodiment shows two resonance frequencies. The resonance frequency on the lower frequency side exists in the vicinity of 1.8 GHz and the resonance frequency on the higher frequency side exists in the vicinity of 2.6 GHz.

Then, from the data of changing the shape of the element sections111and112, it was learned that the resonance frequency on the lower frequency side tends to depend on the length of the outer edge of the element sections111and112of the dipole antenna110, and the resonance frequency on the higher frequency side tends to depend on the minor axis L1of the element sections111and112of the dipole antenna110.

Therefore, by changing the length of the outer edge (perimeter) and the minor axis L1of the element sections111and112, it is possible to set the frequency range in which the return loss is not more than a predetermined value.

Further, by setting the same length of the outer edge (perimeter) and the same minor axis L1of the element sections111and112, it is possible to provide the antenna130using the dipole antenna110in which the frequency range not more than the return loss is set in a similar manner.

Second Exemplary Embodiment

In the first exemplary embodiment, the shape of the element sections111and112of the dipole antenna110in the antenna130was the ellipse. In the second exemplary embodiment, the shape of the element sections111and112of the dipole antenna110in the antenna130was made by connecting a pentagon to a semi-ellipse.

The configurations of other components are similar to the first exemplary embodiment, and thereby description of the similar components will be omitted and the configuration of the dipole antenna110, which is the different component, will be described.

FIG. 11is a plan view illustrating the configuration of the dipole antenna110in the second exemplary embodiment.

In the dipole antenna110inFIG. 11, the outer edge of the element sections111and112is elliptic at a portion closer to the point O (the boundary is indicated by broken lines), and at a portion away from the point O, the outer edge is pentagonal in which one of the vertexes protrudes in a direction away from the point O.

Even though the dipole antenna110has such a shape, the antenna130has wide-band frequency characteristics, and it is also possible to set the input impedance of the antenna130by changing the parameters for establishing the shape of the dipole antenna110.

FIG. 12is a diagram showing the return loss (dB) characteristics of the antenna130in the second exemplary embodiment. These characteristics were obtained, with respect to the antenna130configured by using the dipole antenna110shown inFIG. 11, by the simulation model shown inFIG. 8of the first exemplary embodiment.

In the frequency range in which the return loss is not more than −10 dB (VSWR≦2), the lower limit frequency fL is 1.6 GHz and the upper limit frequency fH (not shown) is not less than 3 GHz. The antenna130has wider-band characteristics than the antenna130in the first exemplary embodiment.

Third Exemplary Embodiment

In the third exemplary embodiment, similar to the second exemplary embodiment, the shape of the element sections111and112of the dipole antenna110in the antenna130of the first exemplary embodiment was changed.

The configurations of other components are similar to the first exemplary embodiment, and thereby description of the similar components will be omitted and the configuration of the dipole antenna110, which is the different component, will be described.

FIG. 13is a plan view illustrating the configuration of the dipole antenna110in the third exemplary embodiment.

In the dipole antenna110inFIG. 13, the outer edge of the element sections111and112is elliptic at a portion closer to the point O (the boundary is indicated by broken lines), and at a portion away from the point O, the outer edge is triangular in which one of the vertexes protrudes in a direction away from the point O.

Even though the dipole antenna110has such a shape, the antenna130has wide-band frequency characteristics, and it is also possible to set the input impedance of the antenna130by changing the parameters for establishing the shape of the dipole antenna110.

Fourth Exemplary Embodiment

In the fourth exemplary embodiment, similar to the second and third exemplary embodiments, the shape of the element sections111and112of the dipole antenna110in the antenna130of the first exemplary embodiment was changed.

The configurations of other components are similar to the first exemplary embodiment, and thereby description of the similar components will be omitted and the configuration of the dipole antenna110, which is the different component, will be described.

FIG. 14is a plan view illustrating the configuration of the dipole antenna110in the fourth exemplary embodiment.

In the dipole antenna110inFIG. 14, the outer edge of the element sections111and112is elliptic at a portion closer to the point O (the boundary is indicated by broken lines), and at a portion away from the point O, the outer edge is rectangular that protrudes in a direction away from the point O.

Even though the dipole antenna110has such a shape, the antenna130has wide-band frequency characteristics, and it is also possible to set the input impedance of the antenna130by changing the parameters for establishing the shape of the dipole antenna110.

As described in the first to fourth exemplary embodiments, the antenna130having a wide frequency range in which the return loss is not more than a predetermined value can be obtained by configuring the element sections111and112of the dipole antenna110with a conductive material and forming the outer edge thereof in a shape including a curved line, such as an ellipse.

Then, it is possible to set the input impedance of the antenna130by changing the parameters for establishing the shape of the above-described dipole antenna110, such as the minor axis L1of the element sections111and112, the height H from the center in the thickness direction of the element sections111and112to the reflector120, the major axis L2of the element sections111and112and the distance D between the element sections111and112of the dipole antenna110.

Moreover, by forming the portions in the vicinity of the point O in symmetrically arranging the element section111and the element section112of the dipole antenna110by curved lines such as the elliptical shape that is convex toward the point O, in the case where another dipole antenna110, which transmits and receives the polarization orthogonal to the polarization of the radio frequency transmitted and received by this dipole antenna110, is pared while sharing the point O for dual polarization, the two dipole antennas110having been paired can be easily combined without overlapping each other.

Further, by changing the length of the outer edge (perimeter) and the minor axis L1of the element sections111and112of the dipole antenna110, it is possible to set the frequency range in which the return loss is not more than a predetermined value. Consequently, it is possible to select the edge shape of the element sections111and112while setting the frequency range. This makes it easy, in the case where two dipole antennas110are paired for dual polarization, to establish the shape thereof not to overlap each other.

Note that, in the first to fourth exemplary embodiments, it was assumed that the element sections111and112, the leg sections113and114, and the stage section115were configured with a conductive material as a single piece or individually. However, the element sections111and112may be configured with metal foil or the like put on a dielectric substrate. In this case, the leg sections113and114are configured with metal rods or the like, and the element sections111and112configured with the metal foil or the like may be connected to the front reflection section120aof the reflector120. Then, the signal for transmitting the radio frequency to the element section112may be fed by the coaxial cable or the like.

Fifth Exemplary Embodiment

The array antenna10in the first to fourth exemplary embodiments was configured by arranging the antennas130for dual polarization in one direction.

The array antenna10in the fifth exemplary embodiment is configured by arranging plural antennas130in line so that directions of electric fields coincide with one another. The array antenna10is an omnidirectional antenna that radiates vertical polarization in the directions of 360°.

FIG. 15is a diagram showing an example of a configuration of the array antenna10capable of radiating vertical polarization in the fifth exemplary embodiment. InFIG. 15, four antennas130-1,130-2,130-3and130-4are linearly (in the vertical direction) arranged. Note that each of the four antennas130-1,130-2,130-3and130-4has a configuration such that, in the antenna130shown inFIGS. 3A and 3Bof the first exemplary embodiment, the dipole antenna110includes the element sections111and112, but does not include the leg sections113,114and the stage section115. Moreover, each of the four antennas does not include the reflector120. The conductor116is connected to the element section112via the opening of the element section111of the dipole antenna110. Then, each of the four antennas is fed in the same direction so that the radiating electric field oscillates in the vertical direction.

This makes it possible to provide the array antenna10that radiates (transmits) the vertical polarization. Note that the array antenna10is able to receive the vertical polarization in which the electric fields oscillate in the vertical direction, owing to the reversibility of the antenna.

In the array antenna10in the fifth exemplary embodiment shown inFIG. 15, the antennas130-1and130-2can be paired to be fed. In other words, the main cable32and the secondary cables33, which are the feeding lines, may be connected as shown inFIG. 6A. Note that the same may be true for the pair of antennas130-3and130-4.

Moreover, it may be possible to form a set of antennas130-1to130-4and carry out connection as shown inFIG. 6C. In this case, N=4.

Here, the array antenna10was configured with four antennas130; however, the number of antennas130is not limited to four and the number may be two, three, or may be more than four. In these cases, it may be possible to divide the plural antennas130into plural sets, provide the main cable33to each set and provide the secondary cables33branching off therefrom, to thereby carry out feeding. Note that the whole may be regarded as one set, without being divided into the plural sets.

Further, in the case of being divided into the plural sets, by feeding the transmission signals having different phases to each set, the radiating angle (beam tilt angle θ) of the radio frequency can be tilted from the horizontal plane toward the ground direction or the like.

As described in the first exemplary embodiment, the input impedance of the antenna130can be set by changing the parameter for establishing the shape of the dipole antenna110. Therefore, similar to the first exemplary embodiment, by setting the input impedance of the antenna130corresponding to the impedance of the secondary cable33and directly connecting the main cable32and the secondary cables33branching off therefrom, impedance matching is achieved. For this reason, it is possible to transmit and receive the radio frequency in the frequency range of the wide-band antenna130.

Note that the array antenna10here included the antennas130arranged in the vertical direction, but the antennas130may be arranged in the horizontal direction or in a direction tilted from the vertical direction. In this case, the polarization oscillating in the horizontal direction or the tilted direction are radiated.

Sixth Exemplary Embodiment

The array antenna10in the fifth exemplary embodiment was the omnidirectional antenna that radiated the vertical polarization.

The array antenna10in the sixth exemplary embodiment is the omnidirectional antenna that radiates horizontal polarization in the directions of 360°.

FIGS. 16A and 16Bare diagrams showing an example of a configuration of the array antenna10capable of radiating the horizontal-polarization in the sixth exemplary embodiment.FIG. 16Ais a plan view of the array antenna10, andFIG. 16Bis a cross-sectional view of the array antenna10at the XVIB-XVIB line inFIG. 16A. Note that the plan view inFIG. 16Ais a plan view of the array antenna10at the XVIA-XVIA line inFIG. 16B.

As shown inFIG. 16B, the array antenna10of the sixth exemplary embodiment is configured with, for example, three layers (layers P1to P3) overlapped in the vertical direction. When the layers P1to P3are not distinguished from one another, each of the layers is represented as a layer P. As shown inFIG. 16A, each layer P is configured with three antennas130(antennas130-1,130-2and130-3) on a horizontal plane. Note that each of the three antennas130-1,130-2and130-3has a configuration such that, in the antenna130shown inFIGS. 3A and 3Bof the first exemplary embodiment, the dipole antenna110includes the element sections111and112, but does not include the leg sections113,114and the stage section115. Moreover, each of the three antennas does not include the reflector120. The conductor116is connected to the element section112via the opening of the element section111.

The antennas130-1,130-2and130-3are arranged on sides of a triangle so that the lines connecting the element sections111and the element sections112of the dipole antennas110mutually cross at the angle of 60°.

This makes it possible to provide the array antenna10that transmits and receives the horizontal polarization in which the electric fields oscillate in a horizontal plane. Note that the array antenna10is able to receive the horizontally-polarized waves polarization in which the electric fields oscillate in the horizontal direction, owing to the reversibility of the antenna.

Note that, in the array antenna10here, the antennas130in each layer P are arranged on the horizontal plane; however, the antennas130may be arranged on a plane tilted from the horizontal plane. In this case, the polarization oscillating in the direction of the tilted plane are radiated.

In the array antenna10in the sixth exemplary embodiment shown inFIGS. 16A and 16B, the antennas130-1,130-2and130-3constituting the layer P1can be formed into a set to carry out feeding. In other words, the main cable32and the secondary cables33, which are the feeding lines, may be connected as shown inFIG. 6B. Note that the same may be for the sets of antennas130in the other layers P2and P3.

Moreover, it may be possible to form a set of antennas130-1in the respective layers P1to P3, and carry out connection as shown inFIG. 6B. The same may be for the other sets of antennas130-2and130-3.

Further, it may be possible to form a set of all of the antennas130-1,130-2and130-3in the respective layers P1to P3, and carry out connection as shown inFIG. 6C. In this case, N=9.

Moreover, the sets may be configured by other combinations.

Here, the array antenna10in each of the layers P1to P3was configured with three antennas130; however, the number of antennas130is not limited to three, and the number may be two, or more than three. However, in the case of two, as shown inFIG. 2, it is necessary to arrange the two antennas130at the positions rotated 90°, and carry out feeding with phase difference of 90° from each other.

In these cases, it may be possible to divide the plural antennas130into plural sets, provide the main cable33to each set and provide the secondary cables33branching off therefrom, to thereby carry out feeding. Note that the whole may be regarded as one set, without being divided into the plural sets.

Further, in the case of being divided into the plural sets, by supplying the transmission signals having different phases to each set, the radiating angle (beam tilt angle θ) of the radio frequency can be tilted from the horizontal plane toward the ground direction.

As described in the first exemplary embodiment, the input impedance of the antenna130can be set by changing the parameter for establishing the shape of the dipole antenna110. Therefore, similar to the first exemplary embodiment, by setting the input impedance of the antenna130corresponding to the impedance of the secondary cable33and directly connecting the main cable32and the secondary cables33branching off therefrom, impedance matching is achieved. For this reason, it is possible to transmit and receive the radio frequency in the frequency range of the wide-band antenna130.

Further, it is possible to provide a dual polarized omnidirectional antenna by combining the array antenna10in the fifth exemplary embodiment and the array antenna10in the sixth exemplary embodiment.

The combination of the array antenna10in the fifth exemplary embodiment and the array antenna10in the sixth exemplary embodiment can be achieved by, for example, inserting the antennas130of the array antenna10in the sixth exemplary embodiment between the respective antennas130of the array antenna10in the fifth exemplary embodiment.

Seventh Exemplary Embodiment

The array antenna10in the fifth exemplary embodiment was the omnidirectional antenna that transmitted and received the vertical polarization, and the array antenna10in the sixth exemplary embodiment was the omnidirectional antenna that transmitted and received the horizontal polarization.

The array antenna10in the seventh exemplary embodiment is an array antenna10that transmits and receives the radio frequency bi-directionally in the horizontal direction.

FIG. 17is a diagram showing an example of a configuration of the array antenna10capable of radiating bi-directionally in the seventh exemplary embodiment.

As shown inFIG. 17, the array antenna10of the seventh exemplary embodiment is configured with, for example, four antennas130. Of these, the two antennas130-1and130-2are arranged in the horizontal direction. In the same manner, the two antennas130-3and130-4are arranged in the horizontal direction. Then, the pair of antennas130-1,130-2and the pair of antennas130-3,130-4are arranged in the vertical direction.

Each of the four antennas130-1,130-2,130-3and130-4includes, in the antenna130shown inFIGS. 3A and 3Bof the first exemplary embodiment, the element sections111and112, but does not include the leg sections113,114, the stage section115and the reflector120. The conductor116is connected to the element section112via the opening of the element section111.

Then, the antenna130is arranged so that a straight line connecting the element section111and the element section112is in the vertical direction. However, in the pair of antennas130-1and130-2, positions of the element sections111and112are reversed, to thereby reverse the feeding directions. The same is true for the pair of antennas130-3and130-4. Note that the antennas130-1and130-3arranged in the vertical direction have the same positional relation between the element sections111and112. The same is true for the antennas130-2and130-4.

In the array antenna10in the seventh exemplary embodiment shown inFIG. 17, the antennas130-1,130-2,130-3and130-4are formed into a set to carry out feeding. In other words, the main cable32and the secondary cables33, which are the feeding lines, may be connected as shown inFIG. 6C. Note that N=4.

In the pair of antennas130arranged in the horizontal direction (for example, the antennas130-1and130-2), positions of the element sections111and112are reversed, to thereby reverse the feeding directions. Accordingly, it is possible to provide the array antenna10that radiates radio frequency to the + side in the horizontal direction (rightward inFIG. 17) and to the − side in the horizontal direction (leftward inFIG. 17). Note that the array antenna10is able to receive the radio frequency from the + side and the − side in the horizontal direction, owing to the reversibility of the antenna.

Here, the pairs of antennas130were laid in two tiers, but the number of tiers may be more than two, or may be only one. In the case of more than two, it may be possible to divide the plural antennas130into plural sets, provide the main cable32to each set and provide the secondary cables33branching off therefrom, to thereby carry out feeding. Note that the whole may be regarded as one set, without being divided into the plural sets.

Further, in the case of being divided into the plural sets, by supplying the transmission signals having different phases to each set, the radiating angle (beam tilt angle θ) of the radio frequency can be tilted from the horizontal plane toward the ground direction.

As described in the first exemplary embodiment, the input impedance of the antenna130can be set by changing the parameter for establishing the shape of the dipole antenna110. Therefore, similar to the first exemplary embodiment, by setting the input impedance of the antenna130corresponding to the impedance of the secondary cable33and directly connecting the main cable32and the secondary cables33branching off therefrom, impedance matching is achieved. For this reason, it is possible to transmit and receive the radio frequency in the frequency range of the wide-band antenna130.

Eighth Exemplary Embodiment

The array antenna10in the first to seventh exemplary embodiments included the dipole antenna110. The array antenna10in the eighth exemplary embodiment includes an antenna140, which is a patch antenna, in place of the antenna130including the dipole antenna110.

FIGS. 18A to 18Care diagrams illustrating a configuration of the antenna140in the eighth exemplary embodiment. InFIGS. 18A to 18C, how to feed the antenna140, which is the patch antenna, is different.

Any of the antennas140shown inFIGS. 18A to 18Cincludes a ground plate section141as an example of the first conductor, a patch section142as an example of the second conductor, and an dielectric layer143sandwiched between the ground plate section141and the patch section142. Note that both of the ground plate section141and the patch section142have rectangular planar shape, and are configured with metal having large electrical conductivity, such as copper or aluminum. The dielectric layer143is configured with, for example, polyimide or polytetrafluoroethylene. Note that an air layer may be provided instead of the dielectric layer143.

In the antenna140shown inFIG. 18A, a feeding point144, which is a position of feeding, is provided to a spot slightly deviated from the center of the patch section142. Then, a feeding line145is provided to penetrate through the dielectric layer143and the ground plate section141. The feeding line145in this case is configured with, for example, a rod of metal such as copper.

In the antenna140shown inFIG. 18B, the patch section142in the case ofFIG. 18Ais removed in a rectangular shape from a peripheral part of one side toward the center part. The feeding point144is provided to the removed part, and the feeding line145is provided from the feeding point. The feeding line145is provided on the dielectric layer143and constitutes a microstrip line together with the ground plate section141. Note that the air layer may be provided instead of the dielectric layer143.

In the antenna140shown inFIG. 18C, the feeding point144is provided to the center part of one side of the patch section142in the case ofFIG. 18A, and the feeding line145is provided from the feeding point. The feeding line145is provided on the dielectric layer143and constitutes a microstrip line together with the ground plate section141. Note that the air layer may be provided instead of the dielectric layer143.

The antenna140shown in each ofFIGS. 18A to 18Chas different input impedance because the position of feeding to the patch section142is different. OfFIGS. 18A to 18C, the antenna140shown inFIG. 18Ahas the lowest input impedance, whereas the antenna140shown inFIG. 18Chas the highest input impedance.

As described above, though the antenna140, which is the patch antenna, is used instead of the antenna130including the dipole antenna110, it is possible to set the input impedance by changing the shape of the antenna140, such as the position of the feeding point144in the patch section142.

Therefore, it may be possible to apply the antenna140in the eighth exemplary embodiment in place of the antenna130in the first exemplary embodiment.

REFERENCE SIGNS LIST