Antenna apparatus

According to an embodiment, an antenna apparatus include a ground plate; a first element disposed along the ground plate; a second element disposed along the first element at an opposing side of the ground plate; a connecting part to connect first and second terminal parts of the first element with first and second terminal parts of the second element, respectively, or to connect the first and second terminal parts of the first element with the ground plate; a first power feeding portion to feed power at a midpoint of the first or second element in a longitudinal direction when the first and second elements are connected together by the connecting part; and a second power feeding portion to feed power to the first element or the ground plate when the first element and the ground plate are connected together by the connecting part.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority of the prior Japanese Priority Application No. 2012-243795 filed on Nov. 5, 2012, the entire contents of which are hereby incorporated by reference.

FIELD

The disclosures herein relate to an antenna apparatus.

BACKGROUND

To improve radio signal quality, a technology has been developed that makes it possible to receive multiple radio waves having polarization planes different from each other by providing antennae for the respective polarization planes, and to prioritize a radio wave having higher strength to be used among the received radio waves. Such a technology is called polarization diversity.

An antenna that combines a dipole antenna and a slot antenna can be found, for example, in Patent Document 1.

This circular polarized antenna includes one antenna providing an antenna element extended in a predetermined direction, as well as another antenna that is configured as an aperture antenna to which a frame-shaped conductor is disposed.

Patent Documents

Incidentally, with a conventional antenna apparatus such as a circular polarized antenna, it is difficult to make the antenna apparatus smaller because the one antenna and the other antenna are arranged in series in the longitudinal direction.

SUMMARY

According to an embodiment, an antenna apparatus includes: a ground plate; a first element disposed along an edge line of the ground plate; a second element disposed along the first element at an opposing side of the ground plate, the opposing side being determined with respect to a plane view; a connecting part to connect a first terminal part and a second terminal part of the first element with the first terminal part and the second terminal part of the second element, respectively, or to connect the first terminal part and the second terminal part of the first element with the ground plate; a first power feeding portion to feed power at a midpoint of the first element or the second element in a longitudinal direction when the first element and the second element are connected with each other by the connecting part; and a second power feeding portion to feed power to the first element or the ground plate when the first element and the ground plate are connected with each other by the connecting part.

DESCRIPTION OF EMBODIMENTS

In the following, antenna apparatuses will be described according to preferred embodiments of the disclosures. The preferred embodiments relate to, for example, an antenna apparatus used in a wireless sensor network that combines a folded dipole antenna and a slot antenna, which can selectively utilize multiple radio waves having polarization planes different from each other.

First Embodiment

FIG. 1is a schematic view illustrating an antenna apparatus100according to the first embodiment.

According to the first embodiment, the antenna apparatus100includes a circuit board1, two antenna elements10-20, and a ground element30. Here, an X-Y-Z coordinate system is defined as an orthogonal coordinate system whose origin is set at the center of the surface (the illustrated side inFIG. 1) of the circuit board1. The X-axis extends in the downward direction from the center O inFIG. 1, the Y-axis extends in the right direction from the center O, and the Z-axis extends vertically upward from the center O.

The antenna elements10-20form a diversity antenna. According to the first embodiment, the antenna apparatus100is a device for communications using a diversity antenna that may serve a wireless sensor network, for example, using an area where communication can be done with the antenna elements10-20to receive information to be detected by a node (wireless terminal).

The circuit board1has a rectangular plate-shaped form in plane view, and its lateral direction is along the X-axis direction and its longitudinal direction is along the Y-axis direction. The thickness of the circuit board1is the length in the Z-axis direction. The circuit board1is, for example, an insulated circuit board compliant with FR-4 (Flame Retardant type 4) standards.

The antenna elements10-20and ground element30are formed on the surface of the circuit board1. The antenna elements10-20and ground element30are formed, for example, with generating patterns by applying etching or the like to copper foil formed on the surface of the circuit board1.

The antenna element10is a dipole antenna that has elements10A-10B, and fed with power at one terminal10A1of the element10A and one terminal10B1of the element10B. Power is fed, for example, using a balun supplying high-frequency signals having opposite phases to each other at the elements10A-10B from a coaxial cable.

The elements10A-10B are line-shaped conductors with the same length, disposed in the vicinity of an edge line1A that extends in parallel with the Y-axis, and located in the X-axis negative direction of the circuit board1.

Namely, the element10A extends from the one terminal10A1to another terminal10A2in the Y-axis negative direction. The element10B extends from the one terminal10B1to another terminal10B2in the Y-axis positive direction. The length between the other terminal10A2and the other terminal10B2is set to half of the wavelength (λ) of the operational frequency of the antenna element10.

The polarization direction of the above antenna element10is in the Y-axis direction. Wireless communication using the antenna element10is executed while wireless communication using the antenna element20is not executed. Namely, power is fed to the antenna element10while power is not fed to the antenna element20.

The antenna element20is a dipole antenna folded in a meandering shape including elements20A-20B. The antenna element20is fed with power at one terminal20A1of the element20A and one terminal20B1of the element20B. Power is fed, for example, using a balun supplying high-frequency signals having opposite phases to each other at the elements element20A-20B from a coaxial cable.

The elements element20A-20B are meander-shaped conductors with the same length, formed in the vicinity of and along an edge line1B that is parallel to the X-axis, and located in the Y-axis negative direction of the circuit board1.

The one terminal20A1of the element20A is positioned in the vicinity of the midpoint of the edge line1B. Another terminal20A2of the element20A is positioned in the vicinity of the element10A, and the final segment of the folded meander-shaped form from the one terminal20A1to the other terminal20A2is formed in the vicinity of and parallel to the element10A.

The one terminal20B1of the element20B is positioned adjacent to the one terminal20A1of the element20A in the vicinity of the midpoint of the edge line1B. The element20B is folded in a meander shape from the one terminal20B1to another terminal20B2, and has a nearly line-symmetric form with the element20A across the Y-axis.

The final segment of the element20B that is folded in the meandering-shaped form from the one terminal20B1to the other terminal20B2is formed in the vicinity of and along the edge line1C of the circuit board1. The edge line1C is an edge line of the circuit board1located on the opposite side of the edge line1A across the X-axis.

The polarization direction of the above antenna element20is in the X-axis direction, which is different by 90 degrees from the polarization direction of the antenna element10(Y-axis direction). The reason for having 90-degree difference between the polarization directions of the antenna elements10-20is to reduce a correlation between the antenna elements10-20so that a diversity effect by the antenna elements10-20is improved.

Wireless communication using the antenna element20is executed while wireless communication using the antenna element10is not executed. Namely, power is fed to the antenna element20while power is not fed to the antenna element10.

The ground element30is formed on an area of the surface of the circuit board1where the antenna elements10-20are not formed. The ground element30functions as a ground plate for the antenna elements10-20, and is also used as an area to mount various electronic parts, for example, a CPU (Central Processing Unit) chip, a memory chip, and the like. The ground element30occupies most of the surface of the circuit board1.

The reason the ground element30is formed occupying most of the surface of the circuit board1and the antenna elements10-20are formed in the remaining area is to make the antenna apparatus100smaller.

For example, if the antenna apparatus100according to the first embodiment is used for configuring a wireless sensor network, the antenna apparatus100is required to be made small to make a receiver device that includes the antenna apparatus100smaller.

To make it a suitable device for such usage, the antenna apparatus100is made small according to the first embodiment. Also, to improve transmitting/receiving sensitivity for wireless communications with nodes (wireless terminals) included in such a wireless sensor network, the antenna apparatus100adopts a diversity method realized by the antenna elements10-20.

Here, with reference toFIG. 2, directivity patterns of the antenna elements10-20will be described.

FIGS. 2A-2Bare schematic views illustrating directivity patterns of the antenna apparatus100according to the first embodiment.FIG. 2Aillustrates a directivity pattern on the Y-Z plane when feeding power to the antenna element10, andFIG. 2Billustrates a directivity pattern on the Y-Z plane when feeding power to the antenna element20.

InFIGS. 2A-2B, results of an electromagnetic field simulation are illustrated that are obtained with setting the operational frequency of the antenna apparatus100to 1 GHz. InFIGS. 2A-2B, gain in φ component is designated with a solid line, and gain in θ component is illustrated with dashed lines.

As illustrated inFIG. 2A, in the directivity pattern on the Y-Z plane when power is fed to the antenna element10, φ component designated with the solid line can be confirmed in addition to θ component designated with the dashed line.

When power is fed to the antenna element10, the antenna element20is not fed with power; hence, ideally, no radiation is generated from the antenna element20, and only θ component is supposed to be observed.

However, φ component is confirmed with the solid line as illustrated inFIG. 2A, which indicates that the antenna element20generates radiation when power is fed to the antenna element10in the antenna apparatus100.

Also, as illustrated inFIG. 2B, in the directivity pattern on the Y-Z plane when power is fed to the antenna element20, θ component designated with the dashed lines can be confirmed in addition to φ component designated with the solid line.

When power is fed to the antenna element20, the antenna element10is not fed with power; hence, ideally, no radiation is generated from the antenna element10, and only φ component is supposed to be observed.

However, θ component is confirmed with the dashed line as illustrated inFIG. 2B, which indicates that the antenna element10generates radiation when power is fed to the antenna element20in the antenna apparatus100.

As above, in the antenna apparatus100according to the first embodiment, the correlation between the antenna elements10-20is not sufficiently low, which suggests that mutual coupling between the antenna elements10-20is generated.

FIG. 3is a schematic view illustrating current distribution at the antenna elements10-20obtained by an electromagnetic field simulation. The current distribution illustrated inFIG. 3is obtained with a simulation in a state where power is fed to the antenna element10in the antenna apparatus100according to the first embodiment.

As illustrated inFIG. 3, current distribution is observed in the antenna element20even if power is fed only to the antenna element10.

Especially, the element20A that is closer to the antenna element10has greater current distribution than the element20B.

As above, the antenna apparatus100can be made smaller according to the first embodiment.

Second Embodiment

FIG. 4is a perspective view illustrating an antenna apparatus200according to the second embodiment.FIG. 5is a plane view illustrating the antenna apparatus200according to the second embodiment.FIG. 6is a bottom view illustrating the antenna apparatus200according to the second embodiment.

According to the second embodiment, the antenna apparatus200includes a circuit board201, antenna elements210-220, and a ground element230.

According to the second embodiment, similar to the first embodiment, the antenna apparatus200is a device for communication using a diversity antenna that may be used to configure a wireless sensor network and receive information to be detected by a node (wireless terminal).

Here, the X-Y-Z coordinate system in the second embodiment is set differently from the one in the first embodiment. In the second embodiment, the X-Y-Z coordinate system is defined as an orthogonal coordinate system whose origin is set at a point on the surface (the illustrated sides inFIGS. 4-5) of the circuit board201.

The X-axis extends in the longitudinal direction from the center O of the antenna apparatus200, the Y-axis extends towards the back side of the circuit board201from the center O, and the Z-axis extends vertically upward from the center O. In the second embodiment, the origin is positioned at the center of an area between the antenna elements210-220.

The antenna elements210-220and ground element230have line symmetrical forms (patterns) across the Z-axis.

Also, for the sake of simplicity for explanation, configuration elements on the back (bottom) side of the circuit board201inFIG. 4are not illustrated although the configuration elements on the back (bottom) side of the circuit board201are designated with dashed lines inFIG. 5. The configuration elements on the back (bottom) side of the circuit board201are illustrated inFIG. 6.

The circuit board201has a rectangular plate-shaped form in plane view, whose longitudinal direction is along the X-axis direction, and its lateral direction is along the Z-axis direction. The thickness of the circuit board201is the length in the Y-axis direction. The circuit board201is, for example, an insulated circuit board compliant with FR-4 (Flame Retardant type 4) standards.

The antenna elements210-220and ground element230are formed on the surface of the circuit board201. The antenna elements210-220and ground element230are formed, for example, with generating patterns by applying etching or the like to copper foil formed on the surface of the circuit board201.

The ground element230extends on the surface of the circuit board201in the Z-axis negative direction, between edge lines of the circuit board201crossing the X-axis, namely, one edge line201A (an edge line in the X-axis negative direction, extending in the Z-axis direction), and another edge line201B (an edge line in the X-axis positive direction, extending in the Z-axis direction). The ground element230is an example of a ground plate.

Here, one of the four edge lines of the ground element230is referred to as an edge line231that extends in the X-axis direction in the vicinity of and along the antenna element210.

The antenna element210(elements211-215) and the antenna element220are used to configure a slot antenna and a folded dipole antenna, to which a connection is turned over from the one to the other by switches, which will be described later.

The slot antenna is configured with the elements211-215of the antenna element210and the ground element230. Also, the folded dipole antenna is configured with the elements212and214of the antenna element210and the antenna element220. Connection switching between the slot antenna and the folded dipole antenna by switches will be described later with reference toFIG. 7.

Here, the configuration of the antenna element210will be described. As described above, the antenna element210includes the elements211-215. The antenna element210is an example of a first element.

The element211is a conductor with an L-shaped form in plane view, whose one terminal211A is connected to a corner part230A of the ground element230and whose other terminal211B is disposed in the vicinity of one terminal212A of the element212in the X-axis negative direction. The element211is folded at a folded part211C positioned between the one terminal211A and the other terminal211B.

Also, a via250is connected with the element211at a bit more negative position in the X-axis than the position of the other terminal211B (closer to the one terminal211A) for feeding power to the antenna element210. The via250is produced by plating a through hole that penetrates the circuit board201from the surface to the back with copper to form a film or the like. The via250is formed to connect the element211with an RF (Radio Frequency) module260disposed on the back of the circuit board201. The point where the element211is connect with the via250is an example of a second power feeding portion.

The one terminal212A of the element212is disposed in the vicinity of the other terminal211B of the element211in the X-axis positive direction, and another terminal212B is disposed in the vicinity of one terminal213A of the element213. The element212is a line-shaped conductor extending along the X-axis. The other terminal212B of the element212is positioned at a negative position in the X-axis direction from the origin O. A pad241is disposed in the Z-axis negative direction relative to the other terminal212B of the element212.

The one terminal213A of the element213is disposed in the vicinity of the other terminal212B of the element212in the X-axis positive direction, and another terminal213B is disposed in the vicinity of one terminal214A of the element214in the X-axis negative direction.

The element213is a very short line-shaped conductor extending along the X-axis direction. The midpoint of the element213in the X-axis direction coincides with the origin O in the X-axis direction. Namely, the X-axis coordinate value of the midpoint of the element213is X=0.

The one terminal214A of the element214is disposed in the vicinity of the other terminal213B of the element213in the X-axis positive direction, and another terminal214B is disposed in the vicinity of one terminal215A of the element215in the X-axis negative direction. The element214is a line-shaped conductor extending along the X-axis. The element214is disposed at the line-symmetric position with the element212across the Z-axis. A pad242is disposed at a position in the Z-axis negative direction relative to the one terminal214A of the element214.

The one terminal215A of the element215is disposed in the vicinity of the other terminal214B of the element214in the X-axis positive direction, and another terminal215B is connected with a corner part230B of the ground element230. The element215is an L-shaped conductor disposed at the line-symmetric position with the element211across the Z-axis. The element215is folded at a folded part215C positioned between the one terminal215A and the other terminal215B. Here, the element215does not have a power feeding portion, which is different from the element211.

In the antenna element210described above, the length between the folded part211C of the element211and the folded part215C of the element215in the X-axis direction is set to half of the wavelength (λ) of the operational frequency of the antenna apparatus200according to the second embodiment.

The antenna element220includes one terminal220A, a folded part220B, a straight line part220C, a folded part220D, and another terminal220E. The antenna element220is an example of a second element, which is disposed along the antenna element210on the opposite side of the ground element230relative to the antenna element210in plane view.

The antenna element220has a form that extends a bit in the Z-axis positive direction from the one terminal220A, turns by 90 degrees in the X-axis positive direction at the folded part220B, extends with the straight line part220C, turns by 90 degrees in the Z-axis negative direction at the folded part220D, extends a bit in the Z-axis negative direction, and reaches the other terminal220E.

The one terminal220A is disposed in the vicinity of the one terminal212A of the element212in the Z-axis positive direction, and the other terminal220E is disposed in the vicinity of the other terminal214B of the element214in the Z-axis positive direction. The midpoint of the straight line part220C in the X-axis direction coincides with the origin O in the X-axis direction. Namely, the X-axis coordinate value of the midpoint of the straight line part220C is X=0.

In the antenna element220described above, the length between the folded part220B and the folded part220D in the X-axis direction is set to half of the wavelength (λ) of the operational frequency of the antenna apparatus200according to the second embodiment.

Here, according to the second embodiment, although the length between the folded part220B and the folded part220D in the X-axis direction is a bit shorter than the length between the folded part211C of the element211and the folded part215C of the element215in the X-axis direction, both of the lengths are set to about λ/2. Both of the lengths may be set to an appropriate length using λ/2 as a reference, depending on characteristics of the folded dipole antenna and the slot antenna or the like, which will be described later.

The pads241-242are disposed in the Z-axis negative direction relative to the other terminal212B of the element212, and in the Z-axis negative direction relative to the one terminal214A of the element214, respectively. The pads241-242have line-symmetric forms and positions with each other across the Z-axis.

The pads241-242are connected with vias251-252, respectively. The vias251-252are produced by plating through holes that penetrate the circuit board201from the surface to the back with copper to form films or the like. The vias251-252are formed to connect the pads241-242with the RF module260disposed on the back of the circuit board201via a balun261.

Here, the pads241-242are connected with the other terminal212B of the element212and the one terminal214A of the element214via distinct switches, respectively. The other terminal212B of the element212and the one terminal214A of the element214are fed with power from the RF module260via the pads241-242, respectively.

As illustrated inFIG. 6, the RF module260, the balun261, the pad262, a coaxial cable263, pads264-265, and a coaxial cable266are formed on the back of the circuit board201.

The RF module260is a device for feeding power to the antenna elements210-220, and connected with a power source (not illustrated). It is desirable for the RF module260to be disposed in an area overlapped with the ground element230in plane view from a standpoint of suppressing noise or the like.

The RF module260is connected with the pad262via the coaxial cable263, and also connected with the balun261via the coaxial cable266. More specifically, the pad262is connect with the core wire of the coaxial cable263, and the shielding wire of the coaxial cable263is connected with the ground element230in the vicinity of the pad262, for example, by forming a via or the like in the vicinity of the pad262. Also, the core wire and shielding wire of the coaxial cable266are connected with the balun261.

Here, the balun261is disposed between the elements211-215(or212and214) of the antenna element210and the RF module260, which is a kind of converter to convert an equilibrium state of the antenna element210into a non-equilibrium state of the RF module260.

The pads262,264, and265are formed, for example, with generating patterns by applying etching or the like to copper foil or the like formed on the back of the circuit board201.

The pad262is connected with the element211through the via250. The pad264is connected with the pad241(seeFIG. 5) through the via251. The pad265is connected with the pad242(seeFIG. 5) through the via252.

Next, with reference toFIGS. 7-8, switches connected with the antenna element210-220and ground element230, and a slot antenna and a folded dipole antenna configured with the antenna element210-220and ground element230will be described.

FIG. 7is a schematic view illustrating switches used for configuring a slot antenna and a folded dipole antenna in the antenna apparatus200according to the second embodiment.

FIGS. 8A-8Bare schematic views illustrating states in which the switches are turned over in the antenna apparatus200according to the second embodiment.FIG. 8Aillustrates a state in which a folded dipole antenna is configured, andFIG. 8Billustrates a state in which a slot antenna is configured.

As illustrated inFIG. 7, the antenna apparatus200includes the switches271,272,273, and274and a CPU chip275according to the second embodiment. The switches271-274are three-terminal switches, respectively. For the switches271-274, for example, SPDT (Single Pole Double Throw) switches may be used, or alternatively, PIN (p-intrinsic-n Diode) diodes or mechanical switches may be used.

The switch271connects the one terminal212A of the element212with one of the other terminal211B of the element211and the one terminal220A of the antenna element220.

The switch272connects the other terminal212B of the element212with one of the one terminal213A of the element213and the pad241.

The switch273connects the one terminal214A of the element214with one of the other terminal213B of the element213and the pad242.

The switch274connects the other terminal214B of the element214with one of the one terminal215A of the element215and the other terminal220E of the antenna element220.

Here, the switches271-274are examples of connecting parts. Among these, the switches272and273are examples of first connecting parts, and the switches271and274are examples of second connecting parts.

The CPU chip275is disposed on the back of the circuit board201, connected with the switches271-274via a signal line designated by a dashed arrow, and also connected with the RF module260. The CPU chip275executes open/close control of the switches271-274for selecting one of the folded dipole antenna and the slot antenna depending on a communication state. The CPU chip275is an example of a control section to control connection states of the switches271-274.

Here, a signal line connecting the CPU chip275with the switches271-274may be wired in a way that does not have an influence on the impedance of the folded dipole antenna and the slot antenna. Also, although it is described here that the CPU chip275controls the switches271-274in the present embodiment, the CPU chip275may control the switches271-274via the RF module260, or the RF module260may control the switches271-274.

Next, with reference toFIGS. 8A-8B, turning over of the switches271-274will be described. InFIGS. 8A-8B, only a neighboring part of the edge line231of the ground element230is illustrated due to space limitation.

When configuring the folded dipole antenna as illustrated inFIG. 8A, the switch271connects the one terminal212A of the element212with the one terminal220A of the antenna element220. The switch272connects the other terminal212B of the element212with the pad241. The switch273connects the one terminal214A of the element214with the pad242. Also, the switch274connects the other terminal214B of the element214with the other terminal220E of the antenna element220.

In this way, the folded dipole antenna is configured that includes the elements212and214of the antenna element210and the antenna element220, and has the other terminal212B of the element212and the one terminal214A of the element214as power feeding portions (first power feeding portions). The other terminal212B and the one terminal214A are fed with power via the pads241-242, respectively.

The folded dipole antenna is configured by connecting the first terminal part (the one terminal212A of the element212) and the second terminal part (the other terminal214B of the element214) of the antenna element210as an example of the first element, with the first terminal part (one terminal220A) and the second terminal part (other terminal220E) of the antenna element220as an example of the second element, respectively.

Also, the folded dipole antenna is fed with power by supplying high-frequency signals in reversed phases to each other to the elements212and214from the RF module260via the switches272-273, pads241-242, vias251-252, balun261, and coaxial cable266(seeFIGS. 5-6).

The folded dipole antenna has its polarization directed for the horizontally polarized wave (X-axis direction) to obtain a polarized wave in the direction parallel to the longitudinal direction of the folded dipole antenna. The longitudinal direction of the folded dipole antenna is in the X-axis direction. In other words, the longitudinal direction of the folded dipole antenna is the direction coming from the one terminal212A of the element212towards the other terminal214B of the element214, or the direction opposite to it. Also, the longitudinal direction of the folded dipole antenna is the direction in which the straight line part220C of the antenna element220extends.

Also, when configuring the slot antenna as illustrated inFIG. 8B, the switch271connects the one terminal212A of the element212with the other terminal211B of the element211. The switch272connects the other terminal212B of the element212with the one terminal213A of the element213. The switch273connects the one terminal214A of the element214with the other terminal213B of the element213. Also, the switch274connects the other terminal214B of the element214with the one terminal215A of the element215.

In this way, the slot antenna is configured that includes the elements211-215of the antenna element210and a part of the ground element230on the side of the edge line231, and is fed with power through the via250.

The slot antenna is configured by connecting the first terminal part (the one terminal211A of the element211) and the second terminal part (the other terminal215B of the element215) of the antenna element210as an example of the first element, with the ground element230as an example of the ground plate.

Also, the slot antenna is fed with power by supplying high-frequency signals to the antenna element210from the RF module260through the via250, pad262, and coaxial cable263. The antenna element210of the slot antenna and a part of the ground element230on the side of the edge line231are supplied with high-frequency signals in reversed phases to each other from the RF module260because the shielding wire of the coaxial cable263is connected with the ground element230.

The slot antenna has its polarization directed for the vertically polarized wave (Z-axis direction) to obtain a polarized wave in the direction orthogonal to the longitudinal direction of the slot antenna. In other words, with the slot antenna, a polarization is generated in the direction between a part of the antenna element210mainly around the elements212,213, and214(a part extending in the X-axis direction), and the edge line231of the ground element230.

As above, in the antenna apparatus200according to the second embodiment, the polarization direction (horizontal polarized wave) obtained by the folded dipole antenna configured with the antenna elements210-220and ground element230differs from the polarization direction (vertical polarized wave) obtained with the slot antenna by 90 degrees.

Here, when configuring the folded dipole antenna, the first terminal part of the antenna element210as an example of the first element is the one terminal212A of the element212, and the second terminal part of the antenna element210as an example of the first element is the other terminal214B of the element214.

Also, when configuring the slot antenna, the first terminal part of the antenna element210as an example of the first element is the one terminal211A of the element211, and the second terminal part of the antenna element210as an example of the first element is the other terminal215B of the element215.

As above, the first terminal part of the antenna element210as an example of the first element is not limited to the one terminal211A at the edge of the antenna element210in the X-axis negative direction, but also includes the one terminal212A of the element212.

This is because characteristics of the folded dipole antenna are hardly influenced when treating the one terminal212A of the element212as the first terminal part because the length of the element211is miniscule in the total length of the antenna element210.

Also, the second terminal part of the antenna element210as an example of the first element is not limited to the other terminal215B at the edge of the antenna element215in the X-axis negative direction, but also includes the other terminal214B of the element214.

This is because characteristics of the folded dipole antenna are hardly influenced when treating the other terminal214B of the element214as the second terminal part because the length of the element215is miniscule in the total length of the antenna element210.

Next, with reference toFIG. 9, current distribution in the folded dipole antenna and the slot antenna in the antenna apparatus200will be described according to the second embodiment.

FIGS. 9A-9Bare schematic views illustrating current distribution of the folded dipole antenna and the slot antenna in the antenna apparatus200according to the second embodiment.

InFIGS. 9A-9B, to make current distribution easy to view, only the outline forms of the antenna element210(the elements211-215), the antenna element220, and the ground element230are illustrated. Also, only main numerical codes (the antenna element210, the antenna element220, and the ground element230) are designated, and the other numerical codes are omitted. For the other numerical codes, seeFIGS. 5,6, and7.

FIG. 9Ais a schematic view illustrating current distribution obtained when the antenna apparatus200operates as the folded dipole antenna according to the second embodiment. The current distribution is obtained with an electromagnetic field simulation.

The current distribution is obtained by feeding power to the folded dipole antenna by supplying high-frequency signals in reversed phases to each other to the elements212and214from the RF module260via the switches272-273, pads241-242, vias251-252, balun261, and coaxial cable266(seeFIGS. 5-6).

InFIG. 9A, a dark part indicates a part where the current density is high, whereas a bright part indicates a part where the current density is low. As illustrated inFIG. 9A, the current densities are high at a part of the element212of the antenna element210closer to the other terminal212B in the longitudinal direction relative to the center of the element212, a part of the element214closer to the one terminal214A in the longitudinal direction relative to the center of the element214, and the middle part of the straight line part220C of the antenna element220in the longitudinal direction.

Also, the current densities are low at a part of the element212of the antenna element210closer to the one terminal212A in the longitudinal direction relative to the center of the element212, a part of the element214closer to the other terminal214B in the longitudinal direction relative to the center of the element214, and both of the ends of the straight line part220C of the antenna element220in the longitudinal direction.

As above, when the antenna apparatus200operates as the folded dipole antenna according to the second embodiment, it is understood that the current density becomes high at the center part of the folded dipole antenna in the X-axis direction (longitudinal direction), and the current density becomes low at both of the terminal parts.

Therefore, it is confirmed that horizontal polarization (X-axis direction) is obtained with the folded dipole antenna.

Also,FIG. 9Bis a schematic view illustrating current distribution obtained when the antenna apparatus200operates as the slot antenna according to the second embodiment. The current distribution is obtained with an electromagnetic field simulation.

The current distribution is obtained by feeding power to the slot antenna by supplying high-frequency signals in reversed phases to each other to the element211and the ground element230from the RF module260through the via250, pad262, and coaxial cable263(seeFIG. 5andFIG. 6).

InFIG. 9B, a dark part indicates a part where the current density is high, whereas a bright part indicates a part where the current density is low. As illustrated inFIG. 9B, the current densities are high at a part of the element212of the antenna element210closer to the one terminal212A in the longitudinal direction relative to the center of the element212, a part of the element214closer to the other terminal214B in the longitudinal direction relative to the center of the element214, and both of the terminal parts of the edge line231of the ground element230.

Also, the current densities are low at a part of the element212of the antenna element210closer to the other terminal212B in the longitudinal direction relative to the center of the element212, a part of the element214closer to the one terminal214A in the longitudinal direction relative to the center of the element214, and the middle part of the edge line231of the ground element230.

As above, when the antenna apparatus200operates as the slot antenna according to the second embodiment, it is understood that the current density becomes low at the center part of the folded dipole antenna in the X-axis direction (longitudinal direction), and the current density becomes high at both of the terminal parts.

Therefore, it is confirmed that vertical polarization (Z-axis direction) is obtained with the slot antenna.

Next, with reference toFIGS. 10A-10Band11A-11B, directivity patterns and VSWR (Voltage Standing Wave Ratio) characteristics will be described that are obtained with the antenna apparatus200according to the second embodiment.

FIGS. 10A-10Bare schematic views illustrating a directivity pattern and a VSWR characteristic on the X-Y plane obtained when the antenna apparatus200operates as the folded dipole antenna according to the second embodiment.

FIGS. 10A-10Billustrate results obtained with an electromagnetic field simulation in which the operational frequency of the folded dipole antenna in the antenna apparatus200is set to 1 GHz. InFIG. 10A, gain of φ component is designated with a solid line, and gain in θ component is designated with a dashed line.

As illustrated inFIG. 10A, the directivity pattern of the folded dipole antenna on the X-Y plane indicates high gain in φ component designated with the solid lines, whose value is about 0 dBi. Also, the gain in θ component designated with the dashed line is low at about −20 dBi.

Therefore, it is confirmed that when operating the antenna apparatus200as the folded dipole antenna, only the folded dipole antenna operates, and almost no radiation is generated from the slot antenna.

Also, as for the VSWR characteristic illustrated inFIG. 10B, a very favorable value of about 1.2 is obtained as a minimal value at the operational frequency of 1 GHz.

As above, when operating the antenna apparatus200as the folded dipole antenna, it is understood that the correlation between the folded dipole antenna and the slot antenna is very low.

FIGS. 11A-11Bare schematic views illustrating a directivity pattern and a VSWR characteristic on the X-Y plane obtained when the antenna apparatus200operates as the slot antenna according to the second embodiment.

FIGS. 11A-11Billustrate results obtained with an electromagnetic field simulation in which the operational frequency of the folded dipole antenna in the antenna apparatus200is set to 1 GHz. InFIG. 11A, gain in φ component is designated with a solid line, and gain in θ component is designated with a dashed line.

As illustrated inFIG. 11A, the directivity pattern of the slot antenna on the X-Y plane indicates high gain in θ component designated with the dashed line, whose values is about 0 dBi to +5 dBi. Also, the gain in φ component designated with the solid line is low at about −23 dBi.

Therefore, it is confirmed that when operating the antenna apparatus200as the slot antenna, only the slot antenna operates, and almost no radiation is generated from the folded dipole antenna.

Also, as for the VSWR characteristic illustrated inFIG. 11B, a very favorable value of about 1.2 is obtained as a minimal value at the operational frequency of 1 GHz.

As above, when operating the antenna apparatus200as the slot antenna, it is understood that the correlation between the slot antenna and the folded dipole antenna is very low.

With the antenna apparatus200described above according to the second embodiment, it is possible to configure the folded dipole antenna and the slot antenna with a low correlation by turning over the switches271-274.

As illustrated inFIG. 5, the folded dipole antenna is an antenna that includes the elements212and214of the antenna element210and the antenna element220, and has the other terminal212B of the element212and the one terminal214A of the element214as power feeding portions (first power feeding portions).

Also as illustrated inFIG. 5, the slot antenna is an antenna that includes the elements211-215of the antenna element210and a part of the ground element230on the side of the edge line231, and is fed with power through the via250.

As above, the folded dipole antenna and the slot antenna implemented in the antenna apparatus200share the antenna element210(at least the elements212and214) according to the second embodiment.

Namely, according to the second embodiment, the antenna apparatus200is obtained by sharing parts between the folded dipole antenna that has its longitudinal direction in the X-axis direction and the slot antenna that also has its longitudinal direction in the X-axis direction, and placing them adjacent to each other in the Z-axis direction.

In other words, the antenna apparatus200is obtained by combining (or uniting) parts of the folded dipole antenna that has its longitudinal direction in the X-axis direction and the slot antenna that also has its longitudinal direction in the X-axis direction, and placing them adjacent to each other in the Z-axis direction.

Thus, the antenna apparatus200realizes to be made small in which the folded dipole antenna and the slot antenna are interchangeably implemented.

Therefore, according to the second embodiment, it is possible to provide the antenna apparatus200that is intended to be made small. In other words, according to the second embodiment, it is possible to provide the antenna apparatus200that is intended to be made small, as well as able to operate interchangeably as the folded dipole antenna or the slot antenna.

Therefore, by turning over the switches271-274in the antenna apparatus200, it is possible to execute a diversity-based wireless communication with the folded dipole antenna and the slot antenna according to the second embodiment.

With the antenna apparatus200according to the second embodiment, it is possible to execute very preferable communications and to contribute to save space because it is small and has a low correlation between the two antennae (folded dipole antenna and slot antenna) for diversity.

Therefore, it is suitable for usage, for example, in configuring a wireless sensor network in which information is received that is to be detected by a node (wireless terminal). Here, the antenna apparatus200according to the second embodiment is very suitable for such usage as configuring a wireless sensor network or the like because it has a lower correlation between the two antennae (folded dipole antenna and slot antenna) for diversity than the antenna apparatus100according to the first embodiment.

Here, as for downsizing of the antenna apparatus200, one of the contributing factors is to arrange the center position of the folded dipole antenna in the longitudinal direction coincident with the center position of the slot antenna in the longitudinal direction. However, these center positions do not necessarily need to be coincident with each other.

It is noted that, in the present embodiment, the folded dipole antenna is configured so that it has the other terminal212B of the element212and the one terminal214A of the element214as power feeding portions (first power feeding portions). The other terminal212B of the element212and the one terminal214A of the element214are at line-symmetric positions to each other across the Z-axis, positioned at the center of the folded dipole antenna in the longitudinal direction (X-axis direction).

However, the power feeding point of the folded dipole antenna may be disposed at an offset position from the center in the longitudinal direction shifted towards the X-axis positive direction or the X-axis negative direction. This may be implemented, for example, by shifting positions of the vias251-252without changing the forms of the elements211-215, or by making the forms of the elements211-215non-symmetric across the X-axis.

Also, the power feeding portion (first power feeding portion) of the folded dipole antenna may be disposed at the antenna element220. This will be described in the third embodiment.

Also in the present embodiment, although the power feeding portion (second power feeding portion) of the slot antenna is disposed at the element211of the antenna element210described, the power feeding portion (second power feeding portion) of the slot antenna may be disposed at any position in the X-axis direction.

Namely, the power feeding portion (second power feeding portion) of the slot antenna may be disposed at any position of the elements211-215. This may be implemented, for example, by changing the position of the via250.

Also, the power feeding portion (second power feeding portion) of the slot antenna may be disposed in the edge line231of the ground element230or in the vicinity of the edge line231.

Also in the present embodiment, although a switch is not disposed between the power feeding portion (second power feeding portion) of the slot antenna and the RF module260, a switch may be disposed between the power feeding portion (second power feeding portion) of the slot antenna and the RF module260.

Also in the present embodiment, the length between the folded part220B and the folded part220D in the X-axis direction is shorter than the length between the folded part211C of the element211and the folded part215C of the element215in the X-axis direction.

However, by appropriately changing the forms of the antenna element210(elements211-215) and the antenna element220, the length between the folded part220B and the folded part220D in the X-axis direction may be set longer than the length between the folded part211C of the element211and the folded part215C of the element215in the X-axis direction. Also, the lengths may be set equivalent to each other.

Also in the present embodiment, the antenna element210-220and ground element230have the forms (patterns) as illustrated inFIG. 5.

However, as described above, the forms (patterns) of the antenna element210-220and ground element230are not limited to the ones described above, but may take other forms as long as the folded dipole antenna and the slot antenna have the same longitudinal direction, and the folded dipole antenna and the slot antenna are configured with shared parts in the direction.

Third Embodiment

FIG. 12is a schematic view illustrating an antenna apparatus300according to the third embodiment.

According to the third embodiment, the antenna apparatus300has the power feeding portion (first power feeding portion) of the folded dipole antenna in the antenna apparatus200according to the second embodiment disposed at the side of the antenna element220.

In the following, differences from the antenna apparatus200according to the second embodiment will be mainly described. Also, substantially the same configuration elements as those in the antenna apparatus200according to the second embodiment are assigned the same numerical codes, and their description may be omitted.

The antenna apparatus300includes a circuit board201, antenna elements310-320, a ground element230, and switches371-372according to the third embodiment.

The antenna element310(elements311-313) and the antenna element320are used to configure a slot antenna and a folded dipole antenna, to which a connection is turned over by switches, which will be described later.

The slot antenna is configured with the elements311-313of the antenna element310and ground element230. Also, the folded dipole antenna is configured with the element312of the antenna element310and antenna element320.

Here, a configuration of the antenna element310will be described. As described above, the antenna element310includes the elements311-313. The antenna element310is an example of the first element.

The element311is a conductor with an L-shape form in plane view, and substantially the same as the element211of the antenna apparatus200according to the second embodiment. The element311has one terminal311A connected with the corner part230A of the ground element230and another terminal311B is disposed in the vicinity of one terminal312A of the element312in the X-axis negative region. The element311is folded at a folded part311C positioned between the one terminal311A and the other terminal311B.

Also, a via250is connected with the element311at a bit more negative position in the X-axis than the other terminal311B (closer to the one terminal311A) for feeding power to the antenna element310. The point where the element311is connected with the via250is an example of the second power feeding portion.

The one terminal312A of the element312is disposed in the vicinity of the other terminal311B at X-axis positive direction of the element311, and another terminal312B is disposed in the vicinity of one terminal313A of the element313.

The element312is a line-shaped conductor extending along the X-axis. The element312has a configuration in which the elements212,213, and214according to the second embodiment are united. Therefore, the position of the one terminal312A of the element312is the same as the position of the one terminal212A of the element212(seeFIG. 5) according to the second embodiment. Also, the position of the other terminal312B of the element312is the same as the other terminal214B of the element214(seeFIG. 5) according to the second embodiment.

The one terminal313A of the element313is disposed in the vicinity of the other terminal312B of the element312in the X-axis positive direction, and another terminal313B is connected with the corner part230B of the ground element230. The element313is an L-shaped conductor, and disposed at the line-symmetric position with the element311across the Z-axis. Namely, the element313is substantially the same as the element215according to the second embodiment (seeFIG. 5).

The element313is folded at a folded part313C positioned between the one terminal313A and the other terminal313B. Here, the element313is not provided with a power feeding portion, which is different from the element311.

In the antenna element310described above, the length between the folded part311C of the element311and the folded part313C in the X-axis direction is set to half of the wavelength (λ) of the operational frequency of the antenna apparatus300according to the third embodiment.

The antenna element320includes elements321-322. The antenna element320has a form that is obtained by dividing the form of the antenna element220according to the second embodiment (seeFIG. 5) at the center in the X-axis direction into two parts (into the elements321-322).

The antenna element320is an example of the second element, which is disposed along the antenna element310on the opposite side of the ground element230relative to the antenna element310in plane view.

The element321is an L-shaped conductor that extends a bit from the one terminal321A in the Z-axis positive direction, turns by 90 degrees in the X-axis positive direction at the folded part321C, and reaches the other terminal321B. The other terminal321B is positioned closer in the X-axis negative direction than the Z-axis, in the vicinity of the one terminal322A of the element322in the X-axis negative direction.

The one terminal322A of the element322is positioned in the vicinity of the other terminal321B of the element321in the X-axis positive direction. The element322is an L-shaped conductor that extends from the one terminal322A in the X-axis positive direction, turns by 90 degrees in the Z-axis negative direction at the folded part322C, and reaches the other terminal322B.

The elements321-322have line-symmetric forms (patterns) with each other across the Z-axis.

In the antenna element320described above, the length between the folded part321C of the element321and the folded part322C in the X-axis direction is set to half of the wavelength (λ) of the operational frequency of the antenna apparatus300according to the third embodiment.

In the antenna apparatus300according to the third embodiment, the other terminal321B of the element321and the one terminal322A of the element322are connected to the balun261via wiring parts364-365disposed on the back of the circuit board201and vias351-352, respectively.

The wiring parts364-365and the vias351-352correspond to the pads264-265and the vias251-252according to the second embodiment (seeFIG. 5), respectively, that are moved in the Z-axis positive direction to be connected with the elements321-322of the antenna element320.

Namely, in the antenna apparatus300according to the third embodiment, the other terminal321B of the element321of the antenna element320and the one terminal322A of the element322are the first power feeding portions.

Here, the antenna apparatus300according to the third embodiment does not include pads that correspond to the pads241-242in the antenna apparatus200according to the second embodiment.

The antenna apparatus300includes two switches371-372according to the third embodiment. For the switches371-372, similarly to the switches271-274according to the second embodiment, for example, SPDT switches may be used. The switches371-372are examples of the connecting parts.

The switch371connects the one terminal312A of the element312with one of the other terminal311B of the element311and the one terminal321A of the element321.

The switch372connects the other terminal312B of the element312with one of the one terminal313A of the element313and the other terminal322B of the element322.

When configuring the folded dipole antenna, the switch371connects the one terminal312A of the element312with the one terminal321A of the antenna element321. Also, the switch372connects the other terminal312B of the element312with the other terminal322B of the element322.

In this way, the folded dipole antenna is configured to include the element312of the antenna element310and the elements321-322of the antenna element320, and has the other terminal321B of the element321and the one terminal322A of the element322as power feeding portions (first power feeding portions). The other terminal321B and the one terminal322A are fed with power from the RF module260through the vias351-352, wiring parts364-365, balun261, and coaxial cable266, respectively.

The folded dipole antenna is configured by connecting the first terminal part (the one terminal312A of the element312) and the second terminal part (the other terminal312B of the element312) of the antenna element310as an example of the first element, with the first terminal part (the one terminal321A of the element321) and the second terminal part (the other terminal322C of the element322) of the antenna element320as an example of the second element, respectively.

Also, the folded dipole antenna is fed with power by supplying high-frequency signals in reversed phases to each other to the elements321-322from the RF module260through the vias351-352, wiring parts364-365, balun261, and coaxial cable266.

The folded dipole antenna has its polarization directed for the horizontally polarized wave (X-axis direction) to obtain a polarized wave in the direction parallel to the longitudinal direction of the folded dipole antenna. The longitudinal direction of the folded dipole antenna is in the X-axis direction. In other words, the longitudinal direction of the folded dipole antenna is the direction coming from the folded part321C of the element321towards the folded part322C of the element322, or the direction opposite to it. Also, the longitudinal direction of the folded dipole antenna is the direction in which the element312of the antenna element310extends.

Also, when configuring the slot antenna, the switch371connects the one terminal312A of the element312with the other terminal211B of the element311. Also, the switch372connects the other terminal312B of the element312with the one terminal313A of the element313.

In this way, the slot antenna is configured to include the elements311-313of the antenna element310and a part of the ground element230on the side of the edge line231, and is fed with power through the via250.

The slot antenna is configured by connecting the first terminal part (the one terminal311A of the element311) and the second terminal part (the other terminal313B of the element313) of the antenna element310as an example of the first element, with the ground element230as an example of the ground plate.

Also, the slot antenna is fed with power by supplying high-frequency signals to the antenna element310from the RF module260through the via250, pad262, and coaxial cable263. The antenna element310of the slot antenna and a part of the ground element230on the side of the edge line231are supplied with high-frequency signals in reversed phases to each other from the RF module260because the shielding wire of the coaxial cable263is connected with the ground element230.

The slot antenna has its polarization directed for the vertically polarized wave (Z-axis direction) to obtain a polarized wave in the direction orthogonal to the longitudinal direction of the slot antenna. In other words, with the slot antenna, a polarization is generated in the direction between a part (a part extending in the X-axis direction) of the antenna element310mainly around the elements311,312, and313, and the edge line231of the ground element230.

As above, in the antenna apparatus300according to the third embodiment, the polarization direction (horizontal polarized wave) obtained by the folded dipole antenna configured with the antenna elements310-320and ground element230differs from the polarization direction (vertical polarized wave) obtained with the slot antenna by 90 degrees.

As above, the folded dipole antenna and the slot antenna implemented in the antenna apparatus300share the antenna element310(at least the element312) according to the third embodiment.

Namely, according to the third embodiment, the antenna apparatus300is obtained by sharing parts between the folded dipole antenna that has its longitudinal direction in the X-axis direction and the slot antenna that also has its longitudinal direction in the X-axis direction, and placing them adjacent to each other in the Z-axis direction.

In other words, the antenna apparatus300is obtained by combining (or uniting) parts of the folded dipole antenna that has its longitudinal direction in the X-axis direction and the slot antenna that also has its longitudinal direction in the X-axis direction, and placing them adjacent to each other in the Z-axis direction.

Thus, the antenna apparatus300may be made small and may have the folded dipole antenna and the slot antenna interchangeably implemented.

Therefore, according to the third embodiment, it is possible to provide the antenna apparatus300that is intended to be made small. In other words, according to the third embodiment, it is possible to provide the antenna apparatus300that is intended to be made small, as well as able to operate interchangeably as the folded dipole antenna or the slot antenna.

Therefore, by turning over the switches371-372in the antenna apparatus300, it is possible to execute diversity-based wireless communications with the folded dipole antenna and the slot antenna according to the second embodiment.

As above, the folded dipole antenna and the slot antenna included in the antenna apparatus300according to the third embodiment are similar to the folded dipole antenna and the slot antenna included in the antenna apparatus200according to the second embodiment.

Therefore, the folded dipole antenna and the slot antenna included in the antenna apparatus300according to the third embodiment have a low correlation and favorable communication characteristics.

With the antenna apparatus300according to the third embodiment, it is possible to execute very preferable communications and to contribute to saving space because it is small and has a low correlation between the two antennae (folded dipole antenna and slot antenna) for diversity.

Therefore, it is suitable for usage, for example, in configuring a wireless sensor network in which information is received that is to be detected by a node (wireless terminal). Here, the antenna apparatus300according to the third embodiment is very suitable for such usage in configuring a wireless sensor network or the like because it has a lower correlation between the two antennae (folded dipole antenna and slot antenna) for diversity than the antenna apparatus100according to the first embodiment.

Here, various modifications can be applied to the antenna apparatus300according to the third embodiment similarly to the antenna apparatus200according to the second embodiment.