Wireless communication device and wireless communication method

Abstract

A wireless communication device and a wireless communication method capable of improving the directivity of an antenna in a desired direction for a low cost are provided. According to one example embodiment, a wireless communication device (1) includes: a printed board (10) having a substrate surface (11); a ground plane (20) having a plate shape that is disposed on the substrate surface (11), connected to the ground potential, and is parallel to the substrate surface (11); an omnidirectional antenna (30) that is disposed alongside the ground plane (20) on the substrate surface (11) in one direction in a plane parallel to the substrate surface (11), and is caused to emit radio waves by being supplied with power; and a parasitic antenna (40) that is disposed away from the ground plane (20) in a direction perpendicular to the substrate surface (11) and resonates with the omnidirectional antenna (30) supplied with power. Figure 4

Description

Wireless communication device and wireless communication method

[0001] The present invention relates to a wireless communication device and a wireless communication method.

[0002] In recent years, with the increasing speed of wireless communication, there has been a demand for wireless communication devices with better wireless communication characteristics. As an example of such wireless communication devices, there is an increasing demand for home routers that comply with the WiMAX (Worldwide Interoperability for Microwave Access) standard and the LTE (Long Term Evolution) standard.

[0003] In order to achieve smooth wireless communication using an omnidirectional antenna in a home router that complies with such standards, it is necessary to install the home router in a location with as strong radio wave intensity as possible. In particular, the communication frequency band for the WiMAX standard is the GHz band, which is high and has large propagation loss. Therefore, if a WiMAX-compliant home router is installed in a location where radio waves have difficulty reaching, such as the center of a room, it may be difficult to achieve smooth wireless communication.

[0004] To prevent such a situation, current technology involves installing the home router near a window where radio waves are more likely to be emitted, or, as in Patent Document 1, attaching a reflector to orient the antenna in the direction in which the radio waves should arrive.

[0005] JP 2012-5146 A International Publication No. 2016 / 092801 JP 2009-130451 A

[0006] However, in current wireless communication devices configured using omnidirectional antennas such as inverted L antennas, there is a limit to how much improvement can be made in the radiation characteristics of radio waves. For example, even if we try to apply the countermeasures for the home router described above as an example of a current wireless communication device, the following problems arise.

[0007] For example, even if a home router is installed near a large window, if the antenna directionality is not directed outward from the window, it will not be very effective and comfortable wireless communication will not be possible.

[0008] Furthermore, with regard to the current technology described in Patent Document 1 and the like, which installs a reflector to give directionality to radio waves, a reflector larger than the size of the home router is required.

[0009] Furthermore, when a reflector such as that described in Patent Document 1 is used, there is a disadvantage in that the radio waves used for communication between the home router and the subordinate radio communication terminal (wireless LAN terminal) will have the same directionality as the radio waves of the WiMAX standard and the LTE standard.

[0010] For example, if a WiMAX-compliant home router is installed near a window, the WiMAX antenna must be oriented to direct radio waves toward the outside of the window. On the other hand, a wireless LAN antenna for wireless communication with a subordinate wireless communication terminal must be oriented toward the room where the subordinate wireless communication terminal is located, i.e., toward the inside of the window. Therefore, even if a reflector such as that described in Patent Document 1 is used, it is not possible to achieve the desired directivity.

[0011] In view of the above circumstances, the purpose of this development is to provide a wireless communication device and a wireless communication method that can improve the directivity of an antenna in a desired direction at low cost.

[0012] A wireless communication device according to one embodiment comprises a printed circuit board having a board surface, a plate-shaped ground plane arranged on the board surface, connected to a ground potential, and parallel to the board surface, an omnidirectional antenna arranged on the board surface alongside the ground plane in one direction within a plane parallel to the board surface, and radiating radio waves when fed with power, and a parasitic antenna arranged at a distance from the ground plane in a direction perpendicular to the board surface, and resonating with the fed omnidirectional antenna.

[0013] A wireless communication method according to one embodiment includes the steps of preparing a wireless communication device including a printed circuit board having a board surface, a plate-shaped ground plane arranged on the board surface and parallel to the board surface, an omnidirectional antenna arranged on the board surface alongside the ground plane in one direction within a plane parallel to the board surface, and a parasitic antenna arranged at a distance from the ground plane in a direction perpendicular to the board surface; connecting the ground plane to a ground potential; feeding power to the omnidirectional antenna and causing the omnidirectional antenna to radiate radio waves; resonating the parasitic antenna and the powered omnidirectional antenna; and reflecting the radio waves radiated from the resonated parasitic antenna off the ground plane and radiating them.

[0014] According to one embodiment, it is possible to provide a wireless communication device and a wireless communication method that can improve the directivity of an antenna in a desired direction at low cost.

[0015] 1 is a perspective view illustrating a configuration in which a parasitic antenna is omitted from a wireless communication device according to a first embodiment; FIG. 2 is a front view illustrating a configuration in which a parasitic antenna is omitted from a wireless communication device according to a first embodiment; FIG. 3 is a top view illustrating a configuration in which a parasitic antenna is omitted from a wireless communication device according to a first embodiment; FIG. 4 is a perspective view illustrating a wireless communication device according to a first embodiment; FIG. 5 is a front view illustrating a wireless communication device according to a first embodiment; FIG. 6 is a top view illustrating a wireless communication device according to a first embodiment; FIG. 7 is a diagram illustrating an operation of a wireless communication device according to a first embodiment; FIG. 8 is a characteristic diagram illustrating a radiation pattern of vertically polarized waves on the XY plane when power is fed to the omnidirectional antenna in a wireless communication device in which a parasitic antenna is omitted according to a first embodiment; FIG. 9 is a characteristic diagram illustrating a radiation pattern of vertically polarized waves on the XY plane when power is fed to the omnidirectional antenna in a wireless communication device according to a first embodiment; 1 is a perspective view illustrating a wireless communication device according to a second embodiment. FIG. 2 is a front view illustrating a wireless communication device according to the second embodiment. FIG. 3 is a top view illustrating a wireless communication device according to the second embodiment. FIG. 4 is a diagram illustrating the operation of the wireless communication device according to the second embodiment. FIG. 5 is a characteristic diagram illustrating radiation patterns of vertically polarized waves and horizontally polarized waves on the XY plane in the wireless communication device according to the second embodiment. FIG. 6 is a perspective view illustrating a wireless communication device according to a third embodiment. FIG. 7 is a front view illustrating a wireless communication device according to the third embodiment. FIG. 8 is a top view illustrating a wireless communication device according to the third embodiment. FIG. 9 is a characteristic diagram illustrating radiation patterns of vertically polarized waves and horizontally polarized waves on the XY plane in the wireless communication device according to the third embodiment. FIG. 10 is a perspective view illustrating a wireless communication device according to a fourth embodiment. FIG. 11 is a front view illustrating a wireless communication device according to the fourth embodiment. FIG. 12 is a side view illustrating a wireless communication device according to the fourth embodiment. FIG. 13 is a diagram illustrating the operation of the wireless communication device according to the fourth embodiment. FIG. 14 is a characteristic diagram illustrating the radiation pattern of horizontally polarized waves on the XZ plane in the wireless communication device according to the first embodiment, for comparison.10 is a characteristic diagram illustrating a radiation pattern of horizontally polarized waves on the XZ plane in a wireless communication device according to a fourth embodiment. FIG.

[0016] Hereinafter, a wireless communication device and a wireless communication method according to an embodiment will be described with reference to the drawings. Note that the reference numerals in the drawings are given for convenience to each element as an example to facilitate understanding, and needless to say, are not intended to limit the embodiments to those shown in the drawings.

[0017] (Embodiment 1) A wireless communication device according to embodiment 1 will be described. First, the configuration of the wireless communication device according to embodiment 1 will be described. Then, the operation of the wireless communication device according to embodiment 1 and a wireless communication method will be described.

[0018] FIG. 1 is a perspective view illustrating a configuration of a wireless communication device according to a first embodiment, omitting a parasitic antenna. FIG. 2 is a front view illustrating a configuration of a wireless communication device according to a first embodiment, omitting a parasitic antenna. FIG. 3 is a top view illustrating a configuration of a wireless communication device according to a first embodiment, omitting a parasitic antenna. As shown in FIGS. 1 to 3, the wireless communication device 1 includes a printed circuit board 10, a ground plane 20, and an omnidirectional antenna 30. The wireless communication device 1 emits or receives radio waves in, for example, the 2.4 GHz frequency band used in Wi-Fi and the 2.6 GHz frequency band used in WiMAX.

[0019] Here, for the sake of convenience in explaining the wireless communication device 1, an XYZ Cartesian coordinate system will be introduced. For example, one direction in a plane parallel to one surface of the printed circuit board 10 is defined as the Z-axis direction. A direction perpendicular to the Z-axis direction in a plane parallel to the one surface is defined as the X-axis direction. Therefore, the plane parallel to the one surface is defined as the XZ plane. The direction perpendicular to the one surface is defined as the Y-axis direction. Each component of the wireless communication device 1 will be described below.

[0020] <Printed Circuit Board> The printed circuit board 10 is plate-shaped or sheet-shaped and has one side and another side opposite to the one side. One side is called the board side 11, and the other side is called the back side 12. The printed circuit board 10 includes an insulating material. A circuit pattern is formed on the board side 11 of the printed circuit board 10 using, for example, a metal conductor.

[0021] <Ground Plane> The ground plane 20 is disposed on the board surface 11 of the printed circuit board 10. The ground plane 20 is a plate parallel to the board surface 11. The ground plane 20 includes, for example, a metal conductor. The ground plane 20 may be rectangular when viewed from the Y-axis direction. The edge of the ground plane 20 on the +Z-axis direction side is a side extending in the X-axis direction. The ground plane 20 is connected to the ground potential of the wireless communication device 1. The ground plane 20 covers, for example, a portion of the printed circuit board 10 other than the circuit pattern.

[0022] <Omnidirectional Antenna> The omnidirectional antenna 30 is arranged alongside the ground plane 20 in the Z-axis direction on the board surface 11. The omnidirectional antenna 30 is arranged on the +Z-axis direction side of the ground plane 20. The omnidirectional antenna 30 includes, for example, a metal conductor. The omnidirectional antenna 30 is, for example, inverted L-shaped. The shape of the omnidirectional antenna 30 is not limited to an inverted L-shape. The omnidirectional antenna 30 may be L-shaped or inverted F-shaped as long as the radio waves it radiates are omnidirectional. The omnidirectional antenna 30 may be drawn on the board surface 11 of the printed circuit board 10, or may be arranged using a chip antenna or the like. A plurality of omnidirectional antennas 30 may be arranged on the printed circuit board 10.

[0023] When the omnidirectional antenna 30 is in an inverted L-shape, the omnidirectional antenna 30 has an extension portion 31 extending in the Z-axis direction and an extension portion 32 extending in the X-axis direction. The length of the extension portion 31 in the Z-axis direction is greater than the width of the extension portion 31 in the X-axis direction. The length of the extension portion 32 in the X-axis direction is greater than the width of the extension portion 32 in the Z-axis direction. For example, the length of the extension portion 32 in the X-axis direction is greater than the length of the extension portion 31 in the Z-axis direction.

[0024] One end of the extension portion 31 in the Z-axis direction is connected to the power feed point 33. For example, the end of the extension portion 31 on the −Z-axis direction side is connected to the power feed point 33. The other end of the extension portion 31 in the Z-axis direction is connected to one end of the extension portion 32 in the X-axis direction. For example, the end of the extension portion 31 on the +Z-axis direction side is connected to the end of the extension portion 32 on the −X-axis direction side.

[0025] The omnidirectional antenna 30 emits radio waves when power is supplied from a power supply point 33. The radio waves are, for example, radio waves. The frequency of the radio waves emitted by the omnidirectional antenna 30 is, for example, in the 2.4 GHz band. However, the frequency of the radio waves emitted by the omnidirectional antenna 30 is not limited to the 2.4 GHz band.

[0026] <Passive Antenna> Fig. 4 is a perspective view illustrating a wireless communication device according to embodiment 1. Fig. 5 is a front view illustrating the wireless communication device according to embodiment 1. Fig. 6 is a top view illustrating the wireless communication device according to embodiment 1.

[0027] As shown in FIGS. 4 to 6 , the wireless communication device 1 further includes a parasitic antenna 40. The parasitic antenna 40 is, for example, a plate extending in the Z-axis direction. The plate surface of the parasitic antenna 40 is parallel to the XZ plane. The parasitic antenna 40 includes, for example, a metal conductor. The parasitic antenna 40 is spaced apart from the ground plane 20 in the Y-axis direction, which is perpendicular to the substrate surface 11. For example, if the frequency of the radio waves radiated by the omnidirectional antenna 30 is in the 2.4 GHz band, a distance of approximately 5 mm between the ground plane 20 and the parasitic antenna 40 is appropriate. If the distance is too small and the ground plane 20 and the parasitic antenna 40 are too close, the radiation characteristics tend to deteriorate. If the distance is too large and the ground plane 20 and the parasitic antenna 40 are too far apart, the directivity of the parasitic antenna 40 becomes weak. The distance between the ground plane 20 and the parasitic antenna 40 can be adjusted to match the directivity of the wireless communication device 1.

[0028] The parasitic antenna 40 is formed to resonate with the powered omnidirectional antenna 30. Specifically, the parasitic antenna 40 extends, for example, in the Z-axis direction. The length of the parasitic antenna 40 in the Z-axis direction is ½ of the wavelength λ of the radio waves radiated by the omnidirectional antenna 30, i.e., λ / 2. Therefore, when power is supplied to the omnidirectional antenna 30 and a high-frequency current flows through the omnidirectional antenna 30, the parasitic antenna 40 is excited. As a result, a high-frequency current also flows through the parasitic antenna 40. Then, the parasitic antenna 40 radiates radio waves.

[0029] The parasitic antenna 40 is disposed near the omnidirectional antenna 30. This allows the parasitic antenna 40 to resonate with the powered omnidirectional antenna 30. The end of the omnidirectional antenna 30 opposite the ground plane 20 in the Z-axis direction and the end of the parasitic antenna 40 in the Z-axis direction coincide with each other in the Z-axis direction. Specifically, the end of the omnidirectional antenna 30 on the +Z-axis direction side and the end of the parasitic antenna 40 on the +Z-axis direction side coincide with each other in the Z-axis direction. Furthermore, the parasitic antenna 40 and the extension portion 31 of the omnidirectional antenna 30 are parallel to each other. A portion of the extension portion 32 of the omnidirectional antenna 30 and a portion of the parasitic antenna 40 including the end on the +Z-axis direction side face each other in the Y-axis direction. In this way, the parasitic antenna 40 is disposed near the omnidirectional antenna 30, and the parasitic antenna 40 resonates with the powered omnidirectional antenna 30. Furthermore, the parasitic antenna 40 may be disposed on the tip side of the omnidirectional antenna 30, specifically, on the opposite side of the extension portion 32 from the extension portion 31 (on the +X-axis direction side of the center of the extension portion 32). This makes it easier for the parasitic antenna 40 to resonate with the powered omnidirectional antenna 30.

[0030] The parasitic antenna 40 is disposed within a range facing the board surface 11 of the printed circuit board 10. Therefore, radio waves radiated from the parasitic antenna 40 can be reflected by the printed circuit board 10 and the ground plane 20. The high-frequency current flowing through the parasitic antenna 40 is strongest at the center portion of the parasitic antenna 40 in the longitudinal direction. Therefore, the radio waves radiated from the parasitic antenna 40 are also strongest at this center portion. Therefore, this center portion is made to face the ground plane 20. This allows the radio waves radiated from this center portion to be reflected by the ground plane 20, increasing the strength of the radio waves radiated toward the +Y-axis direction.

[0031] <Operation> Next, the operation of the wireless communication device 1 will be described. Figures 7 and 8 are diagrams illustrating the operation of the wireless communication device according to the first embodiment. As shown in Figure 7, a high-frequency current I1 having a frequency of, for example, 2.4 GHz flows through the omnidirectional antenna 30. Specifically, the high-frequency current I1 is supplied from the feed point 33 to the extension portion 31 and the extension portion 32. As a result, an excited high-frequency current I2 having a frequency of 2.4 GHz also flows through the parasitic antenna 40 arranged near the omnidirectional antenna 30.

[0032] The parasitic antenna 40 has a length that is half the communication wavelength λ of the 2.4 GHz frequency. The parasitic antenna 40 is disposed near the omnidirectional antenna 30 and parallel to the extension part 31. Therefore, an excited high-frequency current I2 of the 2.4 GHz frequency flows through the parasitic antenna 40.

[0033] When high-frequency current I2 flows through parasitic antenna 40, radio waves are radiated radially from parasitic antenna 40. That is, radio waves are radiated radially from parasitic antenna 40, which extends in the Z-axis direction, in a direction perpendicular to the Z-axis direction. Parasitic antenna 40 is disposed on the +Y-axis direction side of ground plane 20 with a gap therebetween. Therefore, radio waves radiated from parasitic antenna 40 in the -Y-axis direction are reflected by ground plane 20 and printed circuit board 10.

[0034] As shown in Figure 8, radio waves W1 reflected by the ground plane 20 and the printed circuit board 10 are radiated in the +Y-axis direction. Therefore, stronger radio waves are radiated in the +Y-axis direction. As a result, the radio waves radiated from the parasitic antenna 40 have directivity in the +Y-axis direction. The radio waves radiated from the parasitic antenna 40 are vertically polarized in the XY plane.

[0035] Fig. 9 is a characteristic diagram illustrating a radiation pattern of vertically polarized waves on the XY plane when power is fed to the omnidirectional antenna in a wireless communication device that does not include a parasitic antenna according to embodiment 1. Fig. 10 is a characteristic diagram illustrating a radiation pattern of vertically polarized waves on the XY plane when power is fed to the omnidirectional antenna in the wireless communication device according to embodiment 1.

[0036] As shown in Figure 9, before the parasitic antenna 40 is mounted, the radiation pattern is oriented in all directions on the XY plane. The radiation pattern has approximately equal intensity in all directions on the XY plane. Before the parasitic antenna 40 is mounted, the wireless communication device 1 radiates radio waves only from the omnidirectional antenna 30. Therefore, a wireless communication device 1 that does not mount the parasitic antenna 40 does not have directionality.

[0037] 10, in the wireless communication device 1 equipped with the parasitic antenna 40, the radiation pattern has a greater intensity in the +Y-axis direction in the XY plane. After the parasitic antenna 40 is mounted, radio waves are radiated not only from the omnidirectional antenna 30 but also from the parasitic antenna 40 that has excited the omnidirectional antenna 30. The radio waves radiated from the parasitic antenna 40 are reflected in the +Y-axis direction by the ground plane 20 and the printed circuit board 10. As a result, the wireless communication device 1 has directivity in the +Y-axis direction.

[0038] (Wireless Communication Method) Next, a wireless communication method using the wireless communication device 1 of this embodiment will be described. Fig. 11 is a flowchart illustrating a wireless communication method using the wireless communication device according to the first embodiment.

[0039] As shown in step S11 of Fig. 11 , a wireless communication device 1 is prepared. Specifically, the wireless communication device 1 is prepared, and includes a printed circuit board 10, a ground plane 20, an omnidirectional antenna 30, and a parasitic antenna 40. The printed circuit board 10 has a board surface 11. The ground plane 20 is disposed on the board surface 11 and is a plate-like member parallel to the board surface 11. The omnidirectional antenna 30 is disposed on the board surface 11 alongside the ground plane 20 in the Z-axis direction. The parasitic antenna 40 is disposed at a distance from the ground plane 20 in the +Y-axis direction.

[0040] Next, as shown in step S12, the ground plane 20 is connected to the ground potential. Next, as shown in step S13, power is fed to the omnidirectional antenna 30, causing the omnidirectional antenna 30 to radiate radio waves. Next, as shown in step S14, the parasitic antenna 40 and the powered omnidirectional antenna 30 are resonated. Then, as shown in step S15, the radio waves radiated from the resonated parasitic antenna 40 are reflected by the ground plane 20 and the printed circuit board 10 and then radiated. In this manner, wireless communication can be performed using the wireless communication device 1.

[0041] Next, the effects of this embodiment will be described. The wireless communication device 1 of this embodiment includes a parasitic antenna 40 that is spaced apart from the ground plane 20 and resonates with the powered omnidirectional antenna 30. Radio waves excited by the omnidirectional antenna 30 and radiated from the parasitic antenna 40 are reflected by the ground plane 20 and the printed circuit board 10 and are radiated in the +Y-axis direction. This improves the directivity of the antenna in a desired direction.

[0042] The omnidirectional antenna 30 is, for example, inverted L-shaped, and the parasitic antenna 40 is, for example, a plate-like shape extending in one direction, so that the directivity of the antenna can be improved at low cost.

[0043] By setting the length of the parasitic antenna 40 in the Z-axis direction to half the wavelength λ of the radio waves radiated by the omnidirectional antenna 30, the parasitic antenna 40 can be made to resonate with the powered omnidirectional antenna 30. Furthermore, since the end of the omnidirectional antenna 30 on the +Z-axis direction and the end of the parasitic antenna 40 on the +Z-axis direction are aligned in the Z-axis direction, the radio waves radiated from the parasitic antenna 40 can be reflected by the ground plane 20 and the printed circuit board 10. This improves the directivity of the antenna.

[0044] By providing multiple omnidirectional antennas 30 and multiple parasitic antennas 40 corresponding to each omnidirectional antenna 30, it is possible to support various communication standards, such as 2x2 MIMO (Multiple-Input & Multiple-Output).

[0045] Furthermore, by arranging each parasitic antenna 40 corresponding to each omnidirectional antenna 30 in different positions, such as on the board surface 11 or back surface 12 of the printed circuit board 10, the wireless communication device 1 can be given multiple directivities. For example, if a home router conforming to the WiMAX standard is installed near a window, the WiMAX antenna can be given directivity for radio waves toward the outside of the window. At the same time, the wireless LAN antenna for wireless communication with a subordinate wireless communication terminal can be given directivity for radio waves toward the room where the subordinate wireless communication terminal is located, i.e., toward the inside of the window.

[0046] (Embodiment 2) Next, a wireless communication device according to embodiment 2 will be described, but before that, the problems with the wireless communication device 1 according to embodiment 1 will be described. Fig. 12 is a characteristic diagram illustrating radiation patterns of vertically polarized waves and horizontally polarized waves on the XY plane in the wireless communication device according to embodiment 1. As shown in Fig. 12, in the wireless communication device 1 according to embodiment 1, as described above, the vertically polarized waves have directionality. On the other hand, the horizontally polarized waves do not have sufficient directionality.

[0047] Next, a wireless communication device according to a second embodiment will be described. In the wireless communication device of this embodiment, a parasitic antenna is bent midway to generate a high-frequency current in the horizontal direction, thereby providing directionality to horizontally polarized waves as well.

[0048] Fig. 13 is a perspective view illustrating a wireless communication device according to embodiment 2. Fig. 14 is a front view illustrating a wireless communication device according to embodiment 2. Fig. 15 is a top view illustrating a wireless communication device according to embodiment 2.

[0049] 13 to 15, the parasitic antenna 40a of the wireless communication device 2 has an inverted L-shape when viewed in the Y-axis direction. The parasitic antenna 40a has an extension portion 41 that extends in the Z-axis direction and an extension portion 42 that extends in the X-axis direction. One end of the extension portion 41 in the Z-axis direction is connected to one end of the extension portion 42 in the X-axis direction. Specifically, the end of the extension portion 41 on the −Z-axis direction is connected to the end of the extension portion 42 on the −X-axis direction.

[0050] The length of the extension portion 41 in the Z-axis direction is 1 / 2 the wavelength λ, i.e., λ / 2, of the radio waves radiated by the omnidirectional antenna 30. The length of the extension portion 42 in the X-axis direction is 1 / 2 the wavelength λ, i.e., λ / 2, of the radio waves radiated by the omnidirectional antenna 30. Therefore, the total length of the parasitic antenna 40a is λ.

[0051] The parasitic antenna 40a is disposed at a distance in the Y-axis direction from the ground plane 20. That is, the extension portion 41 and the extension portion 42 are both disposed at a distance in the Y-axis direction from the ground plane 20. The width of the extension portion 41 in the X-axis direction and the width of the extension portion 42 in the Z-axis direction are the same length.

[0052] The end of the extension portion 41 of the parasitic antenna 40a on the +Z-axis direction side coincides in the Z-axis direction with the end of the omnidirectional antenna 30 on the +Z-axis direction side. The central portions of the extension portions 41 and 42 face the ground plane 20 in the Y-axis direction. Other than this, the configuration of the wireless communication device 2 is the same as the configuration of the wireless communication device 1 of the first embodiment described above.

[0053] Next, the operation of the wireless communication device 2 according to the second embodiment will be described. Fig. 16 is a diagram illustrating the operation of the wireless communication device according to the second embodiment. As shown in Fig. 16, a high-frequency current I1 having a frequency of, for example, 2.4 GHz flows through the omnidirectional antenna 30. Specifically, the high-frequency current I1 is supplied from the feed point 33 to the extension portion 31 and the extension portion 32. As a result, an excited high-frequency current I3 having a frequency of, for example, 2.4 GHz also flows through the parasitic antenna 40a arranged near the omnidirectional antenna 30.

[0054] The total length of the parasitic antenna 40a, including the extension portions 41 and 42, is the communication wavelength λ of a frequency of 2.4 GHz. Moreover, the parasitic antenna 40a is disposed near the omnidirectional antenna 30 and is parallel to the extension portions 31 and 32. Therefore, an excited high-frequency current I3 of a frequency of 2.4 GHz flows through the parasitic antenna 40a. Specifically, for example, the high-frequency current I3 flows from the +Z-axis direction side to the −Z-axis direction side of the extension portion 41, and also flows from the +X-axis direction side to the −X-axis direction side of the extension portion 42.

[0055] When high-frequency current I3 flows through parasitic antenna 40a, radio waves are radiated radially from parasitic antenna 40a as a center. That is, radio waves are radiated radially from extension portion 41 extending in the Z-axis direction in a direction perpendicular to the Z-axis direction. Also, radio waves are radiated radially from extension portion 42 extending in the X-axis direction in a direction perpendicular to the X-axis direction. Parasitic antenna 40a is disposed at a distance from ground plane 20 on the +Y-axis side. Therefore, radio waves radiated from parasitic antenna 40a in the -Y-axis direction are reflected by ground plane 20 and printed circuit board 10.

[0056] 17 is a characteristic diagram illustrating radiation patterns of vertically polarized waves and horizontally polarized waves on the XY plane in the wireless communication device 2 according to the second embodiment. As shown in FIG. 17, the radiation patterns of both vertically polarized waves and horizontally polarized waves have higher intensity on the +Y-axis direction on the XY plane. Radio waves radiated from the extension portions 41 and 42 of the parasitic antenna 40a are reflected by the ground plane 20 and the printed circuit board 10 toward the +Y-axis direction. As a result, the wireless communication device 2 has directivity in the +Y-axis direction for both vertically polarized waves and horizontally polarized waves.

[0057] According to the wireless communication device 2 of this embodiment, the shape of the parasitic antenna 40a can be changed to provide directionality for both horizontally polarized waves and vertically polarized waves, thereby improving the radiation and reception of radio waves of both horizontally polarized waves and vertically polarized waves.

[0058] The shape of the parasitic antenna 40a can be changed, for example, by adopting a bent structure. This allows for improved directivity at low cost. Furthermore, the bent structure allows for greater flexibility in the design. Other advantages are included in the description of the first embodiment.

[0059] (Embodiment 3) Next, a wireless communication device according to embodiment 3 will be described. The total length of the parasitic antenna 40a according to the above-described embodiment 2 is wavelength λ. In contrast, the total length of the parasitic antenna of the wireless communication device according to this embodiment is half the wavelength, i.e., (λ / 2).

[0060] Fig. 18 is a perspective view illustrating a wireless communication device according to embodiment 3. Fig. 19 is a front view illustrating a wireless communication device according to embodiment 3. Fig. 20 is a top view illustrating a wireless communication device according to embodiment 3.

[0061] As shown in FIGS. 18 to 20 , the parasitic antenna 40b of the wireless communication device 3 has an inverted L-shape. The parasitic antenna 40b has an extension portion 43 extending in the Z-axis direction and an extension portion 44 extending in the X-axis direction. The end of the extension portion 43 on the −Z-axis direction is connected to the end of the extension portion 44 on the −X-axis direction. The length of the extension portion 43 in the Z-axis direction is ¼ of the wavelength λ of the radio waves emitted by the omnidirectional antenna 30. The length of the extension portion 44 in the X-axis direction is ¼ of the wavelength λ of the radio waves emitted by the omnidirectional antenna 30. The parasitic antenna 40b is spaced apart from the ground plane 20 in the Y-axis direction, which is perpendicular to the substrate surface 11. That is, the extension portions 43 and 44 are spaced apart from the ground plane 20 in the Y-axis direction. For example, the width of the extension portion 43 in the X-axis direction and the width of the extension portion 44 in the Z-axis direction are the same length.

[0062] Next, a description will be given of the operation of the wireless communication device 3 according to the third embodiment. A high-frequency current having a frequency of, for example, 2.4 GHz flows through the omnidirectional antenna 30. Then, an excited high-frequency current having a frequency of 2.4 GHz also flows through the parasitic antenna 40b arranged near the omnidirectional antenna 30.

[0063] The total length of parasitic antenna 40b, including extensions 43 and 44, is half the communication wavelength λ of 2.4 GHz. Parasitic antenna 40b is disposed near omnidirectional antenna 30 and is parallel to extensions 31 and 32. Therefore, an excited high-frequency current of 2.4 GHz flows through parasitic antenna 40b.

[0064] When a high-frequency current flows through the parasitic antenna 40b, radio waves are radiated radially from the parasitic antenna 40b. That is, radio waves are radiated radially in a direction perpendicular to the Z-axis direction from the extension portion 43 extending in the Z-axis direction. Also, radio waves are radiated radially in a direction perpendicular to the X-axis direction from the extension portion 44 extending in the X-axis direction. The parasitic antenna 40b is disposed at a distance from the ground plane 20 on the +Y-axis side. Therefore, radio waves radiated from the parasitic antenna 40b in the -Y-axis direction are reflected by the ground plane 20 and the printed circuit board 10.

[0065] 21 is a characteristic diagram illustrating radiation patterns of vertically polarized waves and horizontally polarized waves on the XY plane in the wireless communication device according to embodiment 3. As shown in FIG. 21, the radiation patterns of both vertically polarized waves and horizontally polarized waves have greater intensity on the +Y-axis direction side on the XY plane. Radio waves radiated from the extension portions 43 and 44 of the parasitic antenna 40b are reflected by the ground plane 20 and the printed circuit board 10 toward the +Y-axis direction. As a result, the wireless communication device 3 has directivity in the +Y-axis direction for both vertically polarized waves and horizontally polarized waves.

[0066] According to the wireless communication device 3 of this embodiment, the size of the parasitic antenna 40b can be reduced. Therefore, the size of the wireless communication device 3 can also be reduced. In this case, the directivity can be improved at low cost. Other configurations, operations, and effects are included in the descriptions of the first and second embodiments.

[0067] (Embodiment 4) Next, a wireless communication device according to embodiment 4 will be described. In the wireless communication device described above, the parasitic antenna is arranged on the +Y-axis direction side of the ground plane 20 and the omnidirectional antenna 30. In contrast, in the wireless communication device of this embodiment, the parasitic antenna is arranged on the +Z-axis direction side of the ground plane 20 and the omnidirectional antenna 30.

[0068] Fig. 22 is a perspective view illustrating a wireless communication device according to embodiment 4. Fig. 23 is a front view illustrating a wireless communication device according to embodiment 4. Fig. 24 is a side view illustrating a wireless communication device according to embodiment 4.

[0069] 22 to 24 , the wireless communication device 4 of this embodiment includes, for example, a plate-shaped parasitic antenna 40c extending in the X-axis direction. The parasitic antenna 40c is arranged on the opposite side of the omnidirectional antenna 30 from the ground plane 20 in the Z-axis direction, with a gap therebetween. Specifically, the parasitic antenna 40 is arranged on the +Z-axis direction side of the omnidirectional antenna 30 with a gap therebetween. The parasitic antenna 40c is formed to resonate with the powered omnidirectional antenna 30. Specifically, the parasitic antenna 40c is arranged near the omnidirectional antenna 30. The length of the parasitic antenna 40c in the X-axis direction is ½ the wavelength λ of the radio waves emitted by the omnidirectional antenna 30, i.e., λ / 2.

[0070] The length of the parasitic antenna 40c in the X-axis direction is shorter than the length of the ground plane 20 in the X-axis direction. This allows the radio waves reflected by the ground plane 20 and radiated in the +Z-axis direction to be increased. This allows the wireless communication device 1 to improve its directivity.

[0071] Next, the operation of the wireless communication device 4 will be described. Fig. 25 is a diagram illustrating the operation of the wireless communication device according to the fourth embodiment. As shown in Fig. 25, a high-frequency current I1 having a frequency of, for example, 2.4 GHz flows through the omnidirectional antenna 30. As a result, an excited high-frequency current I4 having a frequency of 2.4 GHz also flows through the parasitic antenna 40c arranged near the omnidirectional antenna 30.

[0072] The parasitic antenna 40c has a length that is, for example, half the communication wavelength λ of a frequency of 2.4 GHz. The parasitic antenna 40c is disposed near the omnidirectional antenna 30 and parallel to the extension portion 32. Therefore, an excited high-frequency current I4 of a frequency of 2.4 GHz flows through the parasitic antenna 40c.

[0073] When high-frequency current I4 flows through the parasitic antenna 40c, radio waves are radiated radially from the parasitic antenna 40c. That is, radio waves are radiated radially from the parasitic antenna 40c, which extends in the X-axis direction, in a direction perpendicular to the X-axis direction. The parasitic antenna 40c is disposed on the +Z-axis direction side of the ground plane 20 and the printed circuit board 10 with a gap therebetween. Therefore, radio waves radiated from the parasitic antenna 40c in the -Z-axis direction are reflected by the ground plane 20 and the printed circuit board 10.

[0074] The radio waves W2 reflected by the ground plane 20 and the printed circuit board 10 are radiated in the +Z-axis direction. Therefore, stronger radio waves are radiated in the +Z-axis direction. As a result, the radio waves radiated from the parasitic antenna 40c have directivity in the +Z-axis direction.

[0075] For comparison, Fig. 26 is a characteristic diagram illustrating a radiation pattern of horizontally polarized waves on the XZ plane in the wireless communication device according to embodiment 1. Fig. 27 is a characteristic diagram illustrating a radiation pattern of horizontally polarized waves on the XZ plane in the wireless communication device according to embodiment 4.

[0076] As shown in Fig. 26, in the wireless communication device 1 according to the first embodiment, which is the subject of comparison, the radiation pattern of horizontally polarized waves is directed uniformly in all directions in the XZ plane. In contrast, as shown in Fig. 27, in the wireless communication device 4 according to this embodiment, the radiation pattern of horizontally polarized waves has greater intensity in the +Z-axis direction in the XZ plane. Radio waves radiated from the parasitic antenna 40c are reflected by the ground plane 20 and the printed circuit board 10 toward the +Z-axis direction. As a result, the wireless communication device 4 has directivity in the +Z-axis direction.

[0077] According to the wireless communication device 4 of this embodiment, the direction of directivity can be changed by changing the position of the parasitic antenna 40c. Specifically, it is possible to provide directivity in the Z-axis direction along the board surface 11 of the printed circuit board 10. This further improves the degree of freedom in directivity.

[0078] By arranging the parasitic antenna 40c near the omnidirectional antenna 30 and extending it in the X-axis direction, it can resonate with the omnidirectional antenna 30. Furthermore, by setting the length of the parasitic antenna 40c in the X-axis direction to half the wavelength λ of the radio waves emitted by the omnidirectional antenna 30, it can resonate with the omnidirectional antenna 30. Therefore, the directivity of the wireless communication device 4 can be improved.

[0079] By making the length of the parasitic antenna 40c in the X-axis direction shorter than the length of the ground plane 20 in the X-axis direction, the radio waves radiated from the parasitic antenna 40c can be sufficiently reflected in the +Z-axis direction, thereby improving the directivity of the wireless communication device 4. Other configurations, operations, and effects are included in the descriptions of the first to third embodiments.

[0080] The present invention is not limited to the above-described embodiments, and can be modified as appropriate without departing from the spirit of the invention. For example, a combination of the configurations of embodiments 1 to 4 is also included within the scope of the technical ideas of embodiments 1 to 4. Furthermore, some or all of the above-described embodiments can be described as follows, but are not limited to the following.

[0081] (Supplementary Note 1) A wireless communication method comprising the steps of: preparing a wireless communication device including: a printed circuit board having a board surface; a plate-shaped ground plane arranged on the board surface and parallel to the board surface; an omnidirectional antenna arranged on the board surface alongside the ground plane in one direction within a plane parallel to the board surface; and a parasitic antenna arranged at a distance from the ground plane in a direction perpendicular to the board surface; connecting the ground plane to a ground potential; feeding power to the omnidirectional antenna and causing the omnidirectional antenna to radiate radio waves; resonating the parasitic antenna and the powered omnidirectional antenna; and reflecting the radio waves radiated from the resonated parasitic antenna by the ground plane and radiating them.

[0082] (Supplementary Note 2) The wireless communication method described in Supplementary Note 1, wherein the omnidirectional antenna has an inverted L-shape and includes a first extension portion extending in the one direction and a second extension portion extending in another direction perpendicular to the one direction in a plane parallel to the substrate surface, wherein one end of the first extension portion in the one direction is connected to a feed point, and the other end of the first extension portion in the one direction is connected to one end of the second extension portion in the other direction.

[0083] (Supplementary Note 3) The wireless communication method according to Supplementary Note 1 or 2, wherein an end of the omnidirectional antenna opposite to the ground plane in the one direction and an end of the parasitic antenna in the one direction coincide with each other in the one direction.

[0084] (Supplementary Note 4) The wireless communication method according to any one of Supplementary Notes 1 to 3, wherein the parasitic antenna extends in the one direction, and the length of the parasitic antenna in the one direction is ½ of the wavelength of the radio wave radiated by the omnidirectional antenna.

[0085] (Supplementary Note 5) The wireless communication method described in any one of Supplementary Notes 1 to 3, wherein the parasitic antenna has an inverted L-shape and includes a third extension portion extending in the one direction and a fourth extension portion extending in another direction perpendicular to the one direction in a plane parallel to the substrate surface, and one end of the third extension portion in the one direction is connected to one end of the fourth extension portion in the other direction.

[0086] (Supplementary Note 6) The wireless communication method according to Supplementary Note 5, wherein the length of the third extension portion in one direction is ½ of the wavelength of the radio wave radiated by the omnidirectional antenna, and the length of the fourth extension portion in the other direction is ½ of the wavelength of the radio wave radiated by the omnidirectional antenna.

[0087] (Supplementary Note 7) The wireless communication method described in Supplementary Note 5, wherein the length of the third extension portion in one direction is ¼ of the wavelength of the radio wave radiated by the omnidirectional antenna, and the length of the fourth extension portion in the other direction is ¼ of the wavelength of the radio wave radiated by the omnidirectional antenna.

[0088] (Supplementary Note 8) The wireless communication method according to any one of Supplementary Notes 1 to 7, wherein the frequency of the radio wave is in the 2.4 GHz band, and the distance between the ground plane and the parasitic antenna is adjustable.

[0089] Although the present invention has been described above with reference to the embodiments, the present invention is not limited to the above. Various modifications that can be understood by those skilled in the art can be made to the configuration and details of the present invention within the scope of the invention.

[0090] This application claims priority based on Japanese Patent Application No. 2019-174873, filed on September 26, 2019, the disclosure of which is incorporated herein by reference in its entirety.

[0091] 1, 2, 3, 4 Wireless communication device 10 Printed circuit board 11 Board surface 12 Back surface 20 Ground plane 30 Omnidirectional antenna 31, 32 Extension portion 33 Feeding point 40, 40a, 40b, 40c Parasitic antenna 41, 42, 43, 44 Extension portion I1, I2, I3, I4 Current W1, W2 Radio wave

Claims

1. A wireless communication device comprising: a printed circuit board having a board surface; a plate-shaped ground plane arranged on said board surface, connected to ground potential, and parallel to said board surface; an omnidirectional antenna arranged on said board surface alongside said ground plane in one direction within a plane parallel to said board surface, and which radiates radio waves when fed with power; and a parasitic antenna arranged at a distance from said ground plane in a direction perpendicular to said board surface, and which resonates with the fed omnidirectional antenna.

2. The wireless communication device according to claim 1, wherein the omnidirectional antenna is in an inverted L-shape and has a first extending portion extending in the one direction and a second extending portion extending in another direction perpendicular to the one direction in a plane parallel to the substrate surface, one end of the first extending portion in the one direction is connected to a feed point, and the other end of the first extending portion in the one direction is connected to one end of the second extending portion in the other direction.

3. The wireless communication device according to claim 1 or 2, wherein an end of the omnidirectional antenna opposite to the ground plane in said one direction and an end of the parasitic antenna in said one direction coincide with each other in said one direction.

4. A wireless communication device according to any one of claims 1 to 3, wherein the parasitic antenna extends in the one direction, and the length of the parasitic antenna in the one direction is 1 / 2 the wavelength of the radio waves radiated by the omnidirectional antenna.

5. The wireless communication device according to any one of claims 1 to 3, wherein the parasitic antenna is in an inverted L shape and has a third extension portion extending in the one direction and a fourth extension portion extending in another direction perpendicular to the one direction in a plane parallel to the substrate surface, and one end of the third extension portion in the one direction is connected to one end of the fourth extension portion in the other direction.

6. The wireless communication device according to claim 5, wherein the length in one direction of the third extension portion is 1 / 2 the wavelength of the radio waves radiated by the omnidirectional antenna, and the length in the other direction of the fourth extension portion is 1 / 2 the wavelength of the radio waves radiated by the omnidirectional antenna.

7. The wireless communication device according to claim 5, wherein the length of the third extension portion in one direction is 1 / 4 of the wavelength of the radio waves radiated by the omnidirectional antenna, and the length of the fourth extension portion in the other direction is 1 / 4 of the wavelength of the radio waves radiated by the omnidirectional antenna.

8. A wireless communication device comprising: a printed circuit board having a board surface; a plate-shaped ground plane arranged on said board surface, connected to ground potential, and parallel to said board surface; an omnidirectional antenna arranged on said board surface alongside said ground plane in one direction within a plane parallel to said board surface, and radiating radio waves when fed; and a parasitic antenna arranged on the opposite side of said omnidirectional antenna from the ground plane in said one direction, with a gap therebetween, and resonating with the powered omnidirectional antenna, wherein said parasitic antenna extends in another direction orthogonal to said one direction within a plane parallel to said board surface, the length of said parasitic antenna in said other direction being 1 / 2 the wavelength of the radio waves radiated by said omnidirectional antenna, and the length of said parasitic antenna in said other direction being shorter than the length of said ground plane in said other direction.

9. The wireless communication device according to any one of claims 1 to 8, wherein the frequency of the radio waves is in the 2.4 GHz band, and the distance between the ground plane and the parasitic antenna is adjustable.

10. A wireless communication method comprising: preparing a wireless communication device comprising: a printed circuit board having a board surface; a plate-shaped ground plane arranged on said board surface and parallel to said board surface; an omnidirectional antenna arranged on said board surface alongside said ground plane in one direction within a plane parallel to said board surface; and a parasitic antenna arranged at a distance from said ground plane in a direction perpendicular to said board surface; connecting said ground plane to a ground potential; feeding power to said omnidirectional antenna and causing said omnidirectional antenna to radiate radio waves; resonating said parasitic antenna and the powered omnidirectional antenna; and reflecting the radio waves radiated from the resonated parasitic antenna off of said ground plane for radiation.

11. The wireless communication method described in claim 10, wherein the omnidirectional antenna has an inverted L-shape and comprises a first extending portion extending in the one direction and a second extending portion extending in another direction perpendicular to the one direction in a plane parallel to the substrate surface, one end of the first extending portion in the one direction being connected to a feed point, and the other end of the first extending portion in the one direction being connected to one end of the second extending portion in the other direction.

12. The wireless communication method according to claim 10 or 11, wherein an end of the omnidirectional antenna opposite to the ground plane in said one direction and an end of the parasitic antenna in said one direction coincide with each other in said one direction.

13. The wireless communication method according to any one of claims 10 to 12, wherein the parasitic antenna extends in the one direction, and the length of the parasitic antenna in the one direction is 1 / 2 the wavelength of the radio waves radiated by the omnidirectional antenna.

14. The wireless communication method according to any one of claims 10 to 12, wherein the parasitic antenna is in an inverted L-shape and has a third extension portion extending in the one direction and a fourth extension portion extending in another direction perpendicular to the one direction in a plane parallel to the substrate surface, and one end of the third extension portion in the one direction is connected to one end of the fourth extension portion in the other direction.

15. The wireless communication method described in claim 14, wherein the length of the third extension portion in one direction is 1 / 2 the wavelength of the radio waves radiated by the omnidirectional antenna, and the length of the fourth extension portion in the other direction is 1 / 2 the wavelength of the radio waves radiated by the omnidirectional antenna.

16. The wireless communication method described in claim 14, wherein the length of the third extension portion in one direction is 1 / 4 of the wavelength of the radio waves radiated by the omnidirectional antenna, and the length of the fourth extension portion in the other direction is 1 / 4 of the wavelength of the radio waves radiated by the omnidirectional antenna.

17. The wireless communication method according to any one of claims 10 to 16, wherein the frequency of the radio waves is in the 2.4 GHz band, and the distance between the ground plane and the parasitic antenna is adjustable.