Wireless communication apparatus

A wireless communication apparatus includes multiple antennas, a receiver for performing diversity reception using the antennas, a transmitter, a selector circuit connected to the antennas, a divider, and a phase shifter. The divider is located in a transmission line which connects the selector circuit to the transmitter and distributes a signal outputted from the transmitter among the antennas during transmission. The phase shifter is located in at least one of multiple transmission lines, each of which connects the divider to a corresponding one of the antennas.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a U.S. National Phase Application under 35 U.S.C. 371 of International Application No. PCT/JP2013/004992 filed on Aug. 23, 2013 and published in Japanese as WO 2014/034068 A1 on Mar. 6, 2014. This application is based on and claims the benefit of priority from Japanese Patent Application No. 2012-193248 filed on Sep. 3, 2012. The entire disclosures of all of the above applications are incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to wireless communication apparatus for wirelessly performing transmission and reception and, in particular, relates to a wireless communication apparatus capable of performing diversity reception.

BACKGROUND ART

A wireless communication apparatus capable of performing diversity reception is widely known (for example, a patent literature 1). The wireless communication apparatus disclosed in the patent literature 1 has two antenna elements and selects any one of the two antenna elements used for reception by a selector switch so that antenna directivity as a whole can be changed.

PRIOR ART LITERATURES

Patent Literature

SUMMARY OF INVENTION

However, although two antennas are included for performing diversity reception, transmission is performed by using only one of the antennas. Therefore, transmission performance is insufficient.

In view of the above, it is an object of the present disclosure to improve transmission performance of a wireless communication apparatus capable of performing diversity reception.

According to an aspect of the present disclosure, a wireless communication apparatus includes multiple antennas and performs diversity reception using the antennas. The wireless communication apparatus includes a receiver, a transmitter, a selector circuit connected to the antennas, a divider located in a transmission line which connects the selector circuit to the transmitter and configured to distribute a signal outputted from the transmitter among the antennas during transmission, and a phase shifter located in at least one of multiple transmission lines, each of which connects the divider to a corresponding one of the antennas.

As described above, according to the aspect of the present disclosure, the divider connects the transmitter to multiple antennas, and transmission is performed by using the antennas which are also used to perform diversity reception. Further, the phase shifter is located in at least one of the transmission lines, each of which connects the divider to a corresponding one of the antennas. Since a combined directivity can be changed by adjusting the phase shift amount caused by the phase shifter, directivity can be set appropriately, for example, according to an angle of a mount condition. Accordingly, transmission performance can be improved.

EMBODIMENTS FOR CARRYING OUT INVENTION

Below, embodiments of the present disclosure are described with reference to the drawings.

As shown inFIG. 1, a vehicular wireless communication apparatus1includes an antenna module100and an ECU200and performs at least one of vehicle-to-vehicle communication and vehicle-to-road-side communication. For example, a communication frequency of a 5.9 GHz band can be used for vehicle-to-vehicle communication and vehicle-to-road-side communication.

Firstly, a structure of the antenna module100is described. For vehicle-to-vehicle communication and vehicle-to-road-side communication, the antenna module100includes two antennas110A and110B, three selector circuits120A,120B, and120C, a divider130, a phase shifter140, and two low-noise amplifiers150A and150B, and a power amplifier160.

In addition, the antenna module100includes a GNSS (Global Navigation Satellite Systems) antenna170, a low-noise amplifier180, and a cellular phone antenna190. The GNSS antenna170is connected to the low-noise amplifier180, and the low-noise amplifier180is connected to a coaxial cable30. The cellular phone antenna190is connected to a coaxial cable40.

The two antennas110A and110B are used for both reception and transmission. During reception, the selector circuit120A connects the antenna110A and the low-noise amplifier150A. The low-noise amplifier150A is connected to the ECU200through a coaxial cable10.

Further, during reception, the selector circuit120B connects the antenna110B and the low-noise amplifier150B. Further, during reception, the selector circuit120C connects the low-noise amplifier150B and a coaxial cable20. Thus, during reception, the two antennas110A and110B are used. It is noted that a connection position of each of the selector circuits120A,120B, and120C is changed by an antenna selector switch240of the ECU200.

During transmission, the selector circuit120C connects the coaxial cable20and the power amplifier160. The power amplifier160is connected to the divider130. The divider130distributes an input signal from the power amplifier160between the antenna110A and the antenna110B.

The selector circuit120A is located between the divider130and the antenna110A. During transmission, the selector circuit120A connects the divider130and the antenna110A. The selector circuit120B is located between the divider130and the antenna110B. During transmission, the selector circuit120B connects the divider130and the antenna110B.

In addition to the selector circuit120B, the phase shifter140is also located between the divider130and the antenna110B and located closer to the divider130than the selector circuit120B. A signal which is phase-shifted by the phase shifter140is transmitted to the antenna110B. In contrast, there is no phase shifter between the antenna110A and the divider130. Thus, a phase of a radio wave transmitted by the antenna110A is different from a phase of a radio wave transmitted by the antenna110B.

Next, a structure of the ECU200is described. The ECU200includes a processor210, a communication chip220, a selector circuit230, the antenna selector switch240, a GNSS receiver250, a security access module (SAM)260, a cellular transceiver270, and a power source280.

The GNSS receiver250is connected through the coaxial cable30to the GNSS antenna170, generates reception data by filtering, amplifying, and demodulating a signal supplied from the GNSS antenna170, and supplies the reception data to the processor210. The SAM260encrypts and decrypts signals transmitted and received through vehicle-to-vehicle communication or vehicle-to-road-side communication. The cellular transceiver270is connected through the coaxial cable40to the cellular phone antenna190and capable of connecting to a cellular phone line. Transmission data to the cellular phone line is inputted from the processor210, and reception data from the cellular phone line is outputted to the processor210. The power source280supplies electric power to internal components of the ECU200and also supplies electric power to components of the antenna module100.

The processor210includes a CPU211, a memory212, and an interface (I/F)213. The memory212is nonvolatile and stores phase shift amount information which is described later. Although not shown in the drawings, a volatile memory is also included. The I/F213is connected to a CAN300which is an in-vehicle communication network. The processor210obtains various kinds of information of a vehicle through the I/F213and the CAN300and also supplies various kinds of information to devices mounted on the vehicle.

The communication chip220includes two receivers221and222, a transmitter, and a baseband section224. According to the present embodiment, vehicle-to-vehicle communication and vehicle-to-road-side communication are performed in accordance with a communication standard defined by IEEE802.11p.

The receiver221is connected to the coaxial cable10, and a signal received by the antenna110A is inputted to the receiver221through the coaxial cable10. The receiver221filters and amplifies the input signal and then sends it to the baseband section224. The receiver222has the same function as the receiver221. The receiver222is connected to the antenna110B through the selector circuit230and the coaxial cable20.

The transmitter223is also connected to the selector circuit230. The selector circuit230selects one of a state where the receiver222is connected to the coaxial cable20and a state where the transmitter223is connected to the coaxial cable20. The connection state selected by the selector circuit230is changed by the antenna selector switch240. The antenna selector switch240selects one of transmission and reception based on a communication condition of the communication chip220. The baseband section224performs modulation and demodulation. During reception, diversity reception is performed (maximum ratio combining diversity here).

The communication chip220is capable of communicating with the processor210. During both reception and transmission of radio waves, the communication chip220and the processor210communicate with each other.

FIG. 2shows a manner in which the vehicular wireless communication apparatus1is installed. This figure is intended to show a positional relationship among the antennas110A and110B and a roof2of the vehicle, and therefore leaves out the ECU200and the components of the antenna module100except for the antennas110A and110B.

As shown inFIG. 2, from an outer design perspective, the vehicular wireless communication apparatus1has a streamlined shape (what is called a shark fin shape) in a direction from the front to the rear of the vehicle.

A ground plane has an almost rectangular planar shape and is made of a metal plate. The ground plane4extends along a roof surface2aof the vehicle roof2under a condition where the vehicular wireless communication apparatus1is installed on the roof surface2aof the vehicle roof2. A planar board5made of resin is almost vertically (not limited to perfectly vertically) stood on a ground plane surface4awhich is a top surface of the ground plane4.

An antenna ground6is formed as a conductor pattern (conductor film) on a first surface5aof the board5. Further, a connector7for electrically connecting the antenna ground6and the ground plane4is formed as a conductor pattern on the first surface5aof the board5. That is, the antenna ground6is spaced by a predetermined distance from the ground plane surface4aof the ground plane4and has the same potential as the ground plane4because of the connector7. It is noted that the antenna ground6is rectangular and has predetermined widths in both vertical and horizontal directions.

The antenna110A is connected to a top end6aof the antenna ground6. The antenna110A is a linear monopole antenna for transmitting and receiving vertically polarized waves, and a base end110Aa is electrically connected.

The antenna110A is connected in such a manner that a distance between the antenna110A and the antenna ground6increases in an almost vertically direction from its base end110Aa to its tip end110Ab. A length (element length) of the antenna110A is electrically equal to a “¼” wavelength and can be determined by multiplying a wavelength of a radio wave of a frequency of, for example, 5.9 GHz band by “¼” and a wavelength shortening ratio depending on a relative permittivity of a material of which the board5is made.

The base end110Aa of the antenna110is provided with a feeding point9from which the antenna110A is supplied with electric power. The antenna110A is positioned so that a height of the base end110Aa from the ground plane surface4acan be about 40 [mm].

Likewise, the antenna110B is connected to a bottom end6bof the antenna ground6. The antenna110B is also a linear monopole antenna for transmitting and receiving vertically polarized waves, and a base end110Ba is electrically connected.

The antenna110B is connected in such a manner that a distance between the antenna110B and the antenna ground6increases in an almost vertically direction from its base end110Ba to its tip end110Bb. A length (element length) of the antenna110B is electrically equal to a “¼” wavelength and can be determined by multiplying a wavelength of a radio wave of a frequency of, for example, 5.9 GHz band by “¼” and a wavelength shortening ratio depending on a relative permittivity of a material of which the board5is made.

The base end110Ba of the antenna110B is provided with a feeding point12from which the antenna110B is supplied with electric power. The antenna110B is positioned so that a height of the base end110Ba from the ground plane surface4acan be about 20 [mm].

Each of axes of the antennas110A and110B is misaligned with a center portion6cof the antenna ground6in the horizontal direction. It is preferable that a width of the antenna ground6in the horizontal direction should be greater than a length which is calculated by multiplying a wavelength of a radio wave of a frequency of, for example, 5.9GHz band by “¼” and a wavelength shortening ratio depending on a relative permittivity of a material of which the board5is made. Further, in order to reduce correlation between the antennas110A and110B as space diversity, it is preferable that a distance between the feeding points9and12should be greater than a length which is calculated by multiplying a wavelength of a radio wave of a frequency of, for example, 5.9GHz band by “¼” and a wavelength shortening ratio depending on a relative permittivity of a material of which the board5is made.

FIGS. 3A and 3Bshows results of simulations conducted to assess horizontal plane directivities of the antennas110A and110B, respectively. As shown inFIG. 3A, the simulation result of the horizontal plane directivity of the antenna110A is that LIN.AVG=−2.7 dBi, AVG=−3.2 dBi, MAX=0.9 dBi, and MIN=−8.5 dBi. As shown inFIG. 3B, the simulation result of the horizontal plane directivity of the antenna110B is that LIN.AVG=−1.0 dBi, AVG=−1.2 dBi, MAX=1.3 dBi, and MIN=−5.1 dBi. However, according to the present embodiment, instead of selectively using one of the antennas110A and110B having the directivities respectively shown inFIGS. 3A and 3B, radio waves are emitted from the two antennas110A and110B while the phase shifter140causes their phases to differ from each other.

The phase shifter140adjusts the phase emitted from the antenna110B so that a combined emission characteristic (combined directivity) into which the emissions from the two antennas110A and110B are combined can be changed.

Further, as shown inFIG. 2, the two antennas110A and110B are located at different positions in the horizontal direction and also located at different positions in a front-rear direction of the vehicle. When the two antennas110A and110B are arranged in this manner, both horizontal plane directivity and vertical plane directivity can be changed by producing the phase difference using the phase shifter140.

FIG. 4shows a change in the horizontal plane directivity.FIG. 5shows a change in the vertical plane directivity. BothFIGS. 4 and 5show cases where the phase of the antenna110B, which is located on the lower side, is advanced. As can be seen fromFIG. 4, the horizontal plane directivity can be set to frontal directivity, no directivity, or rear directivity by adjusting the phase difference by using the phase shifter140. The no directivity is not limited to absolutely no directivity, but can include almost no directivity.

Further, as can be seen fromFIG. 5, the vertical plane directivity can be set to a small elevation angle or a large elevation angle.

As described above, according to the first embodiment, the vehicular wireless communication apparatus1includes the divider130and performs transmission by using both of the two antennas110A and110B which are also used to perform diversity reception. Further, the phase shifter140is located between the antenna110B and the divider130, and the combined directivity is changed by adjusting the phase shift amount of the phase shifter140. Thus, the directivity can be set appropriately, for example, according to an angle of the mount condition so that transmission performance can be improved.

Next, a second embodiment is described. In the description of the second embodiment, the same reference characters already used in the preceding embodiment indicate the same parts in the preceding embodiment unless otherwise stated.

As shown inFIG. 6, according to the second embodiment, an antenna module100-1includes the whole structure of the antenna module100of the first embodiment. The antenna module100-1further includes a DC coupling section112, a power source114, three bandpass filters (BPF)122,124, and126, a transmission power detector128, a carrier sensor132, and a selector controller134. The antenna110A (not shown inFIG. 6) is connected through a coaxial cable50to the selector circuit120A. The antenna110B (not shown inFIG. 6) is connected through a coaxial cable60to the selector circuit120B.

The DC coupling section112is connected to a signal line between the selector circuit120C and the coaxial cable20, and a signal of the signal line is inputted through the DC coupling section112to the power source114.

The bandpass filters122,124, and126are located between the amplifiers150A,150B, and160and the antennas110A and110B to reduce unnecessary emission or to reduce interference with out-of-band signals. The transmission power detector128outputs a transmission power monitor signal to the communication chip220of the ECU200. The communication chip220adjusts output power according to the transmission power monitor signal.

The selector controller134changes connection states of the selector circuits120A-120C. The carrier sensor132detects a transmission signal inputted from the coaxial cable20and makes a determination of whether transmission is now being performed. The selector controller134controls the connection states of the selector circuits120A-120C based on a result of the determination made by the carrier sensor132. According to the second embodiment, since the selector controller134changes the connection states of the selector circuits120A-120C, the ECU200does not have the antenna selector switch240.

In an antenna module100-2shown inFIG. 7, the phase shifter140is configured so that the phase shift amount can be electronically controlled. A control value indicative of the phase shift amount is inputted to the phase shifter140from the ECU200. The other structures are the same as those shown inFIG. 6.

According to a third embodiment, since the ECU200is capable of controlling the phase shift amount of the phase shifter140, radio waves can be transmitted with directivity appropriate for communication environment after installation on the vehicle.

FIG. 8shows a vehicular wireless communication apparatus1-1according to a fourth embodiment. As shown inFIG. 8, according to the fourth embodiment, the selector circuits120A and120B, the divider130, the phase shifter140, the low-noise amplifiers150A and150B, and the power amplifier160, which are included in the antenna module100in the first embodiment, are included in an ECU200-1.

Like in the fourth embodiment, the divider130, the phase shifter140, and the transmission amplifiers (the low-noise amplifiers150A and150B, and the power amplifier160) can be included in the ECU200-1.

According to a fifth embodiment shown inFIG. 9, the phase shifter140is configured so that the phase shift amount can be electronically controlled. A control value indicative of the phase shift amount is inputted to the phase shifter140from the processor210.

Like in the preceding embodiments, an antenna module100-2includes two antennas110A and110B. The antenna110A is provided with two selector circuits120D and120E, one low-noise amplifier150C, and one power amplifier161A, and the antenna110B is provided with two selector circuits120F and120G, one low-noise amplifier150D, and one power amplifier161B.

Although not shown inFIG. 9, connection states of the four selector circuits120D-120G are controlled by the antenna selector switch240of an ECU200-1.

During transmission, the antenna110A is connected to the power amplifier161A through the selector circuits120D and120E, and the antenna110B is connected to the power amplifier161B through the selector circuits120F and120G.

Since the two antennas110A and110B are respectively connected to the power amplifiers161A and161B during transmission, total transmission power can be increased easily. However, in this structure, the phase shift amount varies depending on a difference in length between the coaxial cables10and20and depending on a difference in characteristic between the power amplifiers161A and161B. Therefore, the processor210adjusts the phase shift amount of the phase shifter140.

An embodiment described below relates to a method of setting the phase shift amount of the phase shifter140. The embodiment described below can be applied to any of the preceding embodiments where the phase shift amount of the phase shifter140can be adjusted. The processor210of the ECU200executes each step of flowcharts explained below except a step of inputting the phase shift amount.

According to the sixth embodiment, a process shown inFIG. 10is performed before communication such as during manufacture and during installation, and a process shown inFIG. 11is performed during actual communication. InFIG. 1, at step S1, a worker inputs phase shift amount information using a predetermined input device. The inputted phase shift amount information is stored in the memory212(step S2).

During communication, as shown inFIG. 11, the inputted phase shift amount information is read from the memory212(step S11), and a control value used to control the shift amount control is set based on the read phase shift amount information (step S12). The control value is inputted to the phase shifter140.

According to a seventh embodiment, processes shown inFIGS. 12 and 13are performed instead of those shown inFIGS. 10 and 11. LikeFIG. 10,FIG. 12is performed in advance before communication. At step S21, phase shift amount information for vehicle-to-road-side communication is inputted. The inputted phase shift amount information for vehicle-to-road-side communication is stored in the memory212(step S22).

Then, phase shift amount information for vehicle-to-vehicle communication is inputted (step S23). The inputted phase shift amount information for vehicle-to-vehicle communication is also stored in the memory212(step S24). It is noted that appropriate values for the phase shift amount information for vehicle-to-road-side communication and the phase shift amount information for vehicle-to-vehicle communication are experimentally determined in advance.

During communication, as shown inFIG. 13, it is determined whether it is vehicle-to-road-side communication. For example, this determination is made based on kinds of a transmission signal. If the signal is directed to other vehicles, the determination is YES, and if the signal is directed to a roadside device, the determination is NO. This determination can be made based on various conditions (for example, a location or whether an in-vehicle device or a road-side device has a transmitter which transmits a reception signal) before the transmission signal is decided.

If it is vehicle-to-road-side communication (S31: YES), the phase shift amount information for vehicle-to-road-side communication is read from the memory212(step S32). In contrast, if it is vehicle-to-vehicle communication (S31: NO), the phase shift amount information for vehicle-to-road-side communication is read from the memory212(step S33).

After step S32or S33is executed, a control value used to control the phase shift amount is set based on the read phase shift amount information (step S34).

Thus, in the case of either vehicle-to-vehicle communication or vehicle-to-road-side communication, radio waves can be transmitted with transmission directivity appropriate for their communications by using the same antennas110A and110B.

According to a seventh embodiment, a process shown inFIG. 14is performed instead of those shown inFIGS. 10 and 12, and a process shown inFIG. 15is performed instead of those shown inFIGS. 11 and 13.

InFIG. 14, at step S41, phase shift amount information for large elevation angle communication is inputted. The inputted phase shift amount information for large elevation angle communication is stored in the memory212(step S42). At step S43, phase shift amount information for small elevation angle communication is inputted. The inputted phase shift amount information for small elevation angle communication is stored in the memory212(step S44). It is noted that the large elevation angle and the small elevation angle mean that one is larger or smaller in elevation angle than the other. For example, the phase shift amount information for large elevation angle communication and the phase shift amount information for small elevation angle communication can be phase differences 30° and 270° shown inFIG. 5.

During communication, as shown inFIG. 15, vehicle speed information is read firstly through the CAN300and the I/F213(step51). Then, it is determined whether the vehicle is moving at high speed greater than a predetermined speed (step S52).

If it is determined that the vehicle is moving at high speed (S52: YES), the process proceeds to step S53where the phase shift amount information for small elevation angle communication is read from the memory212. In contrast, it is determined that the vehicle is not running at high speed (S52: NO), the process proceeds to step S54where the phase shift amount information for large elevation angle communication is read from the memory212.

At step S55, a control value used to control the phase shift amount is set based on the phase shift amount information read at step S53or S54. A reason for determining whether the vehicle is moving at high speed is to determine whether the vehicle is moving inside a city area. A reason for selecting a large elevation angle when the vehicle is not moving at high speed (moving inside a city area) and selecting a small elevation angle when the vehicle is moving at high speed (moving outside a city area) is that it has been experimentally found that better communication can be achieved by selecting a large elevation angle when the vehicle is moving inside a city area.

The phase shift information is not limited to two kinds: the large elevation angle communication purpose and the small elevation angle communication purpose. Three or more kinds of phase shift information for different elevation angles can be stored in the memory212, and the three or more kinds of phase shift information can be set according to the vehicle speed.

According to a ninth embodiment, a process shown inFIG. 16is performed instead of that shown inFIG. 15of the eighth embodiment. The process shown inFIG. 14is also performed in the ninth embodiment.

During communication, as shown inFIG. 16, camera sensor information is read firstly through the CAN300and the I/F213(step61). Then, it is determined whether there is a large vehicle right ahead (whether a vehicle right ahead is a large vehicle) based on the camera sensor information (step S62).

If it is determined that there is a large vehicle ahead (S62: YES), the process proceeds to step S53where the phase shift amount information for large elevation angle communication is read from the memory212. In contrast, it is determined that there is no large vehicle ahead (S62: NO), the process proceeds to step S64where the phase shift amount information for small elevation angle communication is read from the memory212.

At step S65, a control value used to control the phase shift amount is set based on the phase shift amount information read at step S63or S64. In such an approach, even when there is a large vehicle ahead, better communication can be achieved by preventing the large vehicle from obstructing radio waves. Further, when there is no large vehicle ahead, a small elevation angle is selected. Thus, communication distance can be increased compared to when a large elevation angle is selected.

In the ninth embodiment too, three or more kinds of phase shift information for different elevation angles can be stored in the memory212. In this case, the three or more kinds of phase shift information can be set according to a height of a vehicle ahead. In addition to a height of a vehicle ahead, a distance to the vehicle ahead can be considered in such a manner that the phase shift information for a larger elevation angle can be used, as the height of the vehicle ahead is larger, and as the distance to the vehicle ahead is smaller.

According to a tenth embodiment, a process shown inFIG. 17is performed in advance before communication. InFIG. 17, at step S71, the phase shift amount information for no directivity is inputted. The inputted phase shift amount information for no directivity is stored in the memory212(step S72). At step S73, the phase shift amount information for frontal directivity is inputted. The inputted phase shift amount information for frontal directivity is also stored in the memory212(step S74). For example, the phase shift amount information for no directivity and the phase shift amount information for frontal directivity can be phase differences 90° and 180° shown inFIG. 4.

During communication, as shown inFIG. 18, vehicle speed information is read firstly through the CAN300and the I/F213(step81). Then, it is determined whether the vehicle is moving on an expressway (step S82). Instead of the vehicle speed information, map information and present location information can be used to determine whether the vehicle is moving on an expressway.

If it is determined that the vehicle is moving on an expressway (S82: YES), the process proceeds to step S83where the phase shift amount information for frontal directivity is read from the memory212. In contrast, it is determined that the vehicle is moving on an expressway (S82: NO), the process proceeds to step S84where the phase shift amount information for no directivity is read from the memory212.

At step S85, a control value used to control the phase shift amount is set based on the phase shift amount information read at step S83or S84. A reason for selecting frontal directivity when the vehicle is moving on an expressway is that since a transmission target (vehicle or road-side device) exists only in the front and rear direction when the vehicle is moving on an expressway, there is no need to transmit radio waves in a cross direction.

According to the tenth embodiment, since directivity in the horizontal direction is changed based on whether the vehicle is moving on an expressway, better transmission performance can be achieved either when the vehicle is moving on an expressway or when the vehicle is moving on a road other than an expressway.

According to an eleventh embodiment, a process shown inFIG. 19is performed during manufacture. InFIG. 19, at step S91, the phase shift amount information for a vehicle model X is inputted. The inputted phase shift amount information for the vehicle model X is stored in the memory212(step S92). At step S93, the phase shift amount information for a vehicle model Y is inputted. The phase shift amount information for the vehicle model Y is also stored in the memory212(step S94). Further, the phase shift amount information for a vehicle model Z is inputted (step S95). The phase shift amount information for the vehicle model Z is also stored in the memory212(step S96). InFIG. 19, the phase shift amount information for three vehicle models X, Y, and Z are inputted and stored. Alternatively, the phase shift amount information for two or more than three vehicle models can be stored.

According to the present embodiment, a process shown inFIG. 20is performed during actual communication. InFIG. 20, at step S101, vehicle model information is read through the CAN300and the I/F213.

Then, it is determined which vehicle model is read. If the vehicle model X is read, the process proceeds to step S103where the phase shift amount information for the vehicle model X is read from the memory212. If the vehicle model Y is read, the process proceeds to step S104where the phase shift amount information for the vehicle model Y is read from the memory212. If the vehicle model Z is read, the process proceeds to step S105where the phase shift amount information for the vehicle model Z is read from the memory212.

At step S106, a control value used to control the phase shift amount is set based on the phase shift amount information read at step S103, S104, or S105.

In such an approach, appropriate directivity for roof inclinations which vary depending on the vehicle models can be set.

While the present disclosure has been described with reference to the embodiments, it is to be understood that the disclosure is not limited to the embodiments. The present disclosure is intended to cover various modifications and equivalent arrangements inside the spirit and scope of the present disclosure.

For example, in the preceding embodiments, two antennas110A and110B are located at different positions in a front-rear direction of the vehicle and also located at different positions in a top-bottom direction of the vehicle. Alternatively, two antennas can be located at the same position in the top-bottom direction while being located at different positions in the front-rear direction (first modification). In addition, the relative positional relationship between two antennas can be changed in various ways. Further, the number of antennas can be three or more (second modification). Furthermore, although the preceding embodiments are for vehicles, application of the preset disclosure is not limited to vehicles.