Patent Publication Number: US-2021167498-A1

Title: Method and device for detecting target

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority under 35 U.S.C. § 119 to Japanese Patent Application No. 2019-218838, which was filed on Dec. 3, 2019, the entire disclosure of which is hereby incorporated by reference. 
     TECHNICAL FIELD 
     The present disclosure relates to a target detection device and a target detecting method which transmit a transmission wave and detect a target object based on a corresponding reflection wave. 
     BACKGROUND 
     Conventionally, it is known that a target detection device transmits a transmission wave and detects a target object based on a reflection wave corresponding to the transmission wave. In order to detect the position of the target object within a target angle range, this type of target detection device needs to identify an incoming direction of the reflection wave within the angle range. For example, a transmission array where a plurality of transmission elements are disposed at a pitch more than half of the wave length of the transmission wave can be used. By adjusting the pitch of the transmission elements, grating lobes are generated. The grating lobes are inclined by given angles relative to the front direction of the transmission array. By adjusting the pitch of the transmission elements, the transmitting directions of the grating lobes can be adjusted. Therefore, if the grating lobes are used as the transmission wave, the transmitting direction of the transmission wave can be specified by the pitch of the transmission elements, and therefore, the incoming direction of the reflection wave can be specified. 
     As a method of covering the target angle range by the grating lobes, there is a method in which a plurality of transmission arrays having the above configuration are disposed with different angular orientations. According to such a configuration, for example, two transmission beams with different transmitting directions are generated by each transmission array. Each transmission array is disposed so that a gap between the two transmission beams transmitted from one transmission array is filled with the transmission beams transmitted from another transmission array. Thus, each transmission array is associated with the transmitting direction within the target angle range. Therefore, the receiving direction of the reflection wave may be specified depending on which transmission array transmits. 
     However, since such target detection method or device uses the plurality of transmission arrays, the configuration of the target detection is complicated and, thus, it is high cost. 
     SUMMARY 
     Therefore, the present disclosure is made in view of this problem, and one purpose thereof is to provide a target detection device and a target detecting method, capable of detecting a target object with a simple configuration. 
     According to an aspect of the present disclosure, a target detection device is provided, which includes a transmission array and a signal generator. The transmission array includes a plurality of transmission elements configured to convert an electric signal into a transmission wave. The signal generator generates a plurality of sets of electric signals including a first set of electric signals and a second set of electric signals different from the first set, each set being generated with different phase settings. The signal generator is configured to group the plurality of transmission elements according to a plurality of grouping configurations including a first grouping configuration and a second grouping configuration, in the first grouping configuration, the plurality of transmission elements being grouped into a plurality of groups each having p transmission elements, and, in the second grouping configuration, the plurality of transmission elements being grouped into a plurality of groups each having q transmission elements, the q being different from the p. The signal generator inputs the first set of electric signals to each group of the first grouping configuration, and inputs the second set of electric signals to each group of the second grouping configuration. 
     The target detection device may further include a reception array including at least one reception element configured to receive a reflection wave resulting from a reflection of the transmission wave on a target object and convert the reflection wave into a reception signal. In this case, the target detection device may further include processing circuitry configured to process the reception signal. The processing circuitry may extract, based on a frequency component of the reception signal, an equal frequency reception signal of the reflection wave corresponding to the frequency component. In the target detection device, the reception array may include a plurality of reception elements. The processing circuitry may perform beamforming based on a reception signal generated from each of the reception elements, and calculate an incoming direction of the reflection wave from the target based on the beamforming. 
     According to another aspect of the present disclosure, a method of detecting a target by transmitting a transmission wave from a transmission array having a plurality of transmission elements configured to convert an electric signal into a transmission wave, is provided. The method includes grouping the plurality of transmission elements according to a plurality of grouping configurations including a first grouping configuration and a second grouping configuration. In the first grouping configuration, the plurality of transmission elements are grouped into a plurality of groups each having p transmission elements, and, in the second grouping configuration, the plurality of transmission elements are grouped into a plurality of groups each having q transmission elements, the q being different from the p. The method includes generating a plurality of sets of electric signals including a first set of electric signals and a second set of electric signals different from the first set, each set being generated with different phase settings, inputting the first set of electric signals to each group of the first grouping configuration, and inputting the second set of electric signals to each group of the second grouping configuration. 
     According to this configuration, the grating lobe transmitted from the transmission elements grouped conforming to the first grouping configuration, and the grating lobe transmitted from the transmission elements grouped conforming to the second grouping configuration can be differentiated in the transmitting direction. Therefore, a plurality of the transmission beams (grating lobes) with different transmitting directions can be transmitted by the single transmission array. Therefore, the target object can be smoothly detected by the simple configuration. 
     The effects and the significance of the present disclosure will be clear from the embodiment described below. Note that the embodiment described below is to be interpreted only as illustration to implement the present disclosure, and not to limit the present disclosure. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The present disclosure is illustrated by way of example and not by way of limitation in the figures of the accompanying drawings, in which like reference numerals indicate like elements and in which: 
         FIG. 1  is a view illustrating a configuration of a transmission system according to a reference example; 
         FIG. 2  is a view illustrating a configuration of a transmission system according to one embodiment; 
         FIG. 3A  is a view illustrating a configuration of a phase adjusting circuit according to this embodiment; 
         FIG. 3B  is a view illustrating a configuration of a mixing circuit according to this embodiment; 
         FIG. 4A  is a simulation result of an appearing mode of a grating lobe when applying a first set of electric signals to each group of transmission elements conforming to a first grouping configuration according to this embodiment; 
         FIG. 4B  is a simulation result of the appearing mode of the grating lobe when applying the first set of electric signals to each group of transmission elements conforming to the first grouping configuration according to this embodiment; 
         FIG. 5A  is a simulation result of the appearing mode of the grating lobe when applying the first set of electric signals to each group of transmission elements conforming to the first grouping configuration according to this embodiment; 
         FIG. 5B  is a simulation result of the appearing mode of the grating lobe when applying the first set of electric signals to each group of transmission elements conforming to the first grouping configuration according to this embodiment; 
         FIG. 6A  is a simulation result of the appearing mode of the grating lobe when applying the first set of electric signals to each group of transmission elements conforming to the first grouping configuration according to this embodiment; 
         FIG. 6B  is a simulation result of the appearing mode of the grating lobe when applying the first set of electric signals to each group of transmission elements conforming to the first grouping configuration according to the embodiment; 
         FIG. 6C  is a simulation result of the appearing mode of the grating lobe when applying the first set of electric signals to each group of transmission elements conforming to the first grouping configuration according to this embodiment; 
         FIG. 7A  is a simulation result of the appearing mode of the grating lobe when applying a second set of electric signals to each group of transmission elements according to a second grouping configuration according to this embodiment; 
         FIG. 7B  is a simulation result of the appearing mode of the grating lobe when applying the second set of electric signals to each group of transmission elements conforming to the second grouping configuration according to this embodiment; 
         FIG. 8A  is a simulation result of the appearing mode of the grating lobe when applying the second set of electric signals to each group of transmission elements conforming to the second grouping configuration according to this embodiment; 
         FIG. 8B  is a simulation result of the appearing mode of the grating lobe when applying the second set of electric signals to each group of transmission elements conforming to the second grouping configuration according to this embodiment; 
         FIG. 9  is a view schematically illustrating a transmission mode of two transmission beams according to this embodiment; 
         FIG. 10  is a view schematically illustrating an example configuration of a transmission-and-reception system according to this embodiment; 
         FIG. 11  is a block diagram illustrating a concrete configuration of a target detection device according to this embodiment; 
         FIG. 12A  is a functional block diagram illustrating an example configuration of a reception signal processing module according to this embodiment; 
         FIG. 12B  is a functional block diagram illustrating another example configuration of the reception signal processing module according to this embodiment; 
         FIG. 13A  is a flowchart illustrating processing for transmitting transmission waves from the transmission elements which are grouped conforming to the first grouping configuration, according to this embodiment; 
         FIG. 13B  is a flowchart illustrating processing for transmitting transmission waves from the transmission elements which are grouped conforming to the second grouping configuration, according to this embodiment; 
         FIG. 14  is a flowchart illustrating processing for processing reception signals and displaying a detection image, according to this embodiment; 
         FIG. 15  is a view schematically illustrating a configuration of the target detection device according to this embodiment, when it is used as a sonar which detects an underwater target object; 
         FIG. 16  is a view illustrating a configuration of a transmission system according to Modification 1; 
         FIG. 17  is a view illustrating a configuration of a transmission system according to Modification 2; 
         FIG. 18A  is a simulation result of the appearing mode of the grating lobe when applying the first set of electric signals to each group of transmission elements conforming to the first grouping configuration according to Modification 2; 
         FIG. 18B  is a simulation result of the appearing mode of the grating lobe when applying the first set of electric signals to each group of transmission elements conforming to the first grouping configuration according to Modification 2; 
         FIG. 19A  is a simulation result of the appearing mode of the grating lobe when applying the first set of electric signals to each group of transmission elements conforming to the first grouping configuration according to Modification 2; 
         FIG. 19B  is a simulation result of the appearing mode of the grating lobe when applying the first set of electric signals to each group of transmission elements conforming to the first grouping configuration according to Modification 2; 
         FIG. 19C  is a simulation result of the appearing mode of the grating lobe when applying the first set of electric signals to each group of transmission elements conforming to the first grouping configuration according to Modification 2; 
         FIG. 20A  is a simulation result of the appearing mode of the grating lobe when applying the second set of electric signals to each group of transmission elements conforming to the second grouping configuration according to Modification 2; 
         FIG. 20B  is a simulation result of the appearing mode of the grating lobe when applying the second set of electric signals to each group of transmission elements conforming to the second grouping configuration according to Modification 2; 
         FIG. 21A  is a simulation result of the appearing mode of the grating lobe when applying the second set of electric signals to each group of transmission elements conforming to the second grouping configuration according to Modification 2; and 
         FIG. 21B  is a simulation result of the appearing mode of the grating lobe when applying the second set of electric signals to each group of transmission elements conforming to the second grouping configuration according to Modification 2. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, one embodiment of the present disclosure is described with reference to the accompanying drawings. 
     Basic Configuration 
     First, a basic configuration of a transmission-and-reception system of a target detection device according to this embodiment is described. 
       FIG. 1  is a view illustrating a configuration of a transmission system according to a reference example. 
     According to the configuration of  FIG. 1 , a transmission array  10  in which a plurality of transmission elements  10   a  are lined up in a single line is used. Here, although fourteen transmission elements  10   a  are illustrated for convenience, the number of transmission elements  10   a  is not limited to this number. In  FIG. 1 , the number is given for convenience to each transmission element  10   a  in an order from the top. 
     In this example configuration, four adjacent transmission elements  10   a  may be considered to be one set, and sine-wave electric signals are supplied from transmission circuits  20   a  and  20   b  to each set. Therefore, the four transmission elements  10   a  included in one set may function as one transmission area. A pitch between the sets may be more than half of the wave length of the electric signals outputted from the transmission circuits  20   a  and  20   b.  Therefore, the pitch of the transmission area may be more than half of the wave length of the electric signals. Thus, by setting the pitch of the transmission area (the pitch of each set) more than half of the wave length of the electric signals, a grating lobe can be transmitted from the transmission array  10 . 
     The transmission circuits  20   a  and  20   b  each may output the sine-wave electric signal. The transmission circuits  20   a  and  20   b  may output the electric signals at the same frequency. The electric signal outputted from the transmission circuit  20   b  may be advanced by 90° in the phase from the electric signal outputted from the transmission circuit  20   a.    
     The electric signal may be supplied from the transmission circuit  20   a  to the first and third transmission elements  10   a  among the four transmission elements  10   a  included in one set, and the electric signal may be supplied from the transmission circuit  20   b  to the second and fourth transmission elements  10   a.  The electric signals supplied from the transmission circuits  20   a  and  20   b  to the third and fourth transmission elements  10   a  may be inverted in the phase. The phase inversion is performed, for example, by inverting the polarities of the connections of the signal wires from the transmission circuits  20   a  and  20   b  relative to the transmission elements  10   a.  Note that a phase adjusting circuit for inverting the phase may be provided. 
     Thus, by supplying the electric signal to each transmission element  10   a,  the electric signals may be supplied to each set of four transmission elements  10   a  with the phase being shifted by 90° from each other. Therefore, the transmission waves may be outputted from the transmission array  10  so that the main lobe is eliminated and only one grating lobe appears on one side. In addition, by changing the frequency of the electric signals outputted from the transmission circuits  20   a  and  20   b,  the direction of the grating lobe can be changed to the arrayed direction of the transmission elements  10   a.  Therefore, an angle between the front direction of the transmission array  10  and the direction of the transmission waves can be changed so that the transmission wave can scan in the direction of this angle. 
     In this way, the transmitting direction of the transmission waves may be associated with the frequency of the electric signals. Therefore, the transmitting direction of the transmission wave can be identified based on the frequency of the reception signal generated by reception by a receiver of a reflection wave corresponding to the transmission wave. That is, a direction of a target object which caused the reflection wave may be identified with the frequency of the reception signal. 
     Note that, although in the above, the phase shift between the transmission elements  10   a  is set as 90°, the phase shift is not limited to this angle. For example, even if the phase shift between the transmission elements  10   a  is set as 60° or 45°, the main lobe can still be eliminated and only one grating lobe still appears on one side. For example, if the phase shift is set as 60°, six transmission elements  10   a  may be considered to be one set, and the electric signals at the phases of 0°, 60°, 120°, 180°, 240°, and 300° may be supplied to the six transmission elements  10   a  of each set. Moreover, if the phase shift is set as 45°, eight transmission elements  10   a  may be considered to be one set, and the electric signals at the phases of 0°, 45°, 90°, 135°, 180°, 225°, 270°, and 315° may be supplied to the eight transmission elements  10   a  of each set. Also in these cases, by changing the frequency of the electric signal, the direction of the grating lobe can be changed to the arrayed direction of the transmission elements  10   a,  and therefore the transmitting direction of the transmission wave can be changed. 
     Since only one grating lobe scans in the configuration of  FIG. 1 , a scan range of the transmission wave may be narrow. Therefore, in this embodiment, by supplying a plurality of sets of electric signals with different phase shifts to the plurality of transmission elements  10   a,  a plurality of grating lobes with different directions may be produced. In addition, by changing the frequency of the electric signals of each set, the transmitting direction may be changed for each grating lobe to allow the grating lobe to scan. Thereby, the entire scan range can be expanded. 
       FIG. 2  is a view illustrating a configuration of a transmission system according to this embodiment. Note that examples of a plurality of angles in  FIG. 2  illustrates phases of the electric signals supplied through the signal wires, when the phase of the electric signal (sine wave) outputted from a transmission circuit  21   a  is 0°. 
     In the example configuration of  FIG. 2 , a transmission array  11  in which 72 transmission elements  11   a  are lined up in a single line at equal interval is used. Note that the number of transmission elements  11   a  is not limited to 72. In  FIG. 2 , for convenience, the number is given to each transmission element  11   a  in an order from the top. 
     The 72 transmission elements  11   a  may be grouped conforming to a first grouping configuration and a second grouping configuration. In the first grouping configuration, the 72 transmission elements  11   a  may be grouped into a plurality of groups GR 1  each having four transmission elements  11   a.  Moreover, in the second grouping configuration, the 72 transmission elements  11   a  may be grouped into a plurality of groups GR 2  each having six transmission elements  11   a.  Therefore, the 72 transmission elements  11   a  used for the first grouping configuration may be the same as the 72 transmission elements  11   a  used for the second grouping configuration. That is, the common transmission elements  11   a  may be used for the first grouping configuration and the second grouping configuration. 
     Then, a first set of electric signals in which the phase shift is carried out by 90° may be inputted to each group GR 1  of the first grouping configuration, and a second set of electric signals in which the phase shift is carried out by 60° may be inputted to each group GR 2  of the second grouping configuration. That is, the plurality of electric signals included in the first group may have the equal phase shift between the electric signals (90° phase shift), and the plurality of electric signals included in the second group may have the equal phase shift between the electric signals (60° phase shift). 
     The electric signals outputted from transmission circuits  21   a  and  21   b  may be supplied to the transmission elements  11   a  of the group GR 1 . A pitch of the group GR 1  may be more than half of the wave length of the electric signals outputted from the transmission circuits  21   a  and  21   b.  The transmission circuits  21   a  and  21   b  may output the sine-wave electric signal with the 90° phase shift, similar to the transmission circuits  20   a  and  20   b  of  FIG. 1 . The electric signals outputted from the transmission circuits  21   a  and  21   b  may be converted into two routes of electric signals by a phase adjusting circuit  23 . The electric signal of the first route with “+” in  FIG. 2  among the electric signals of the two routes may be an electric signal at the same phase as the electric signals outputted from the transmission circuits  21   a  and  21   b,  and the electric signal of the second route with “−” may be an electric signal at the inverted phase of the electric signals outputted from the transmission circuits  21   a  and  21   b.  The electric signal of each route may be inputted into a corresponding mixing circuit  24 . 
     The electric signals outputted from transmission circuits  22   a - 22   c  may be supplied to the transmission elements  11   a  of the group GR 2 . A pitch of the group GR 2  may be more than half of the wave length of the electric signals outputted from the transmission circuits  22   a - 22   c.  The transmission circuits  22   a - 22   c  may output the sine-wave electric signals with 60° phase shift. The electric signals outputted from the transmission circuits  22   a - 22   c  may be converted into two routes of electric signals by the phase adjusting circuit  23  similarly to the above. The electric signal of the first route with “+” in  FIG. 2  among the electric signals of the two routes may be an electric signal at the same phase as the electric signals outputted from the transmission circuits  22   a - 22   c,  and the electric signal of the second route with “−” may be an electric signal at the inverted phase of the electric signals outputted from the transmission circuits  22   a - 22   c.  The electric signal of each route may be inputted into the corresponding mixing circuit  24 . 
       FIG. 3A  is a view illustrating a configuration of the phase adjusting circuit  23 . 
     The phase adjusting circuit  23  may be comprised of a transformer where one coil  23   a  is disposed at the input side and two coils  23   b  and  23   c  are disposed at the output side. The two coils  23   b  and  23   c  at the output side may be mutually reversed in the winding direction. The electric signal outputted from any of the transmission circuits  21   a,    21   b,  and  22   a - 22   c  may be inputted into the coil  23   a  at the input side. The electric signal at the same phase as the inputted electric signal may be outputted from one coil  23   b  at the output side by electromagnetic induction. This electric signal may be the electric signal of the first route. 
     The other coil  23   c  at the output side may be reversed in the winding direction from one coil  23   b.  Therefore, from the other coil  23   c,  the electric signal at the inverted phase of the electric signal inputted into the coil  23   a  may be outputted. This electric signal may be the electric signal of the second route. In this way, the two routes of electric signals with the mutually inverted phases may be outputted from the phase adjusting circuit  23 . 
     The phase adjusting circuit  23  is not limited to have the configuration of  FIG. 3A , and may have other configurations as long as it can generate the two routes of the electric signals comprised of the electric signal at the same phase as the electric signals outputted from the transmission circuits  21   a,    21   b,  and  22   a - 22   c,  and the electric signal at the inverted phase. 
     Returning to  FIG. 2 , the frequencies of the electric signals outputted from the transmission circuits  21   a  and  21   b  may be mutually the same. The transmission circuits  21   a  and  21   b  may switch the frequency of the electric signal according to a first frequency table. For example, frequencies of 95, 100, 105, 110, 120, 130, and 145 kHz are assigned to the first frequency table. The transmission circuits  21   a  and  21   b  may cyclically switch the frequency of the electric signal in the order of the frequencies assigned to the first frequency table. 
     Moreover, the frequencies of the electric signals outputted from the transmission circuits  22   a - 22   c  may be mutually the same. The transmission circuits  22   a - 22   c  may switch the frequency of the electric signal according to a second frequency table. The frequencies assigned to the second frequency table may be different from the frequencies assigned to the first frequency table. For example, frequencies of 115, 125, 135, and 150 kHz are assigned to the second frequency table. The transmission circuits  22   a - 22   c  may cyclically switch the frequency of the electric signal in the order of the frequencies assigned to the second frequency table. 
       FIG. 3B  is a view illustrating a configuration of the mixing circuit  24 . 
     The mixing circuit  24  may be comprised of a transformer where two coils  24   a  and  24   b  are disposed at the input side and one coil  24   c  is disposed at the output side. The two coils  24   a  and  24   b  at the input side may be the same in the winding direction. The electric signals of the first set and the second set may be inputted to the two coils  24   a  and  24   b  from the corresponding phase adjusting circuit  23 . The electric signals inputted into the coils  24   a  and  24   b  at the input side may be mixed with each other by electromagnetic induction, and may be outputted from the coil  24   c  at the output side. The outputted electric signal may include each frequency component of the two inputted electric signals. 
     Note that, although in the configuration of  FIG. 2  the phases of the electric signals outputted from the transmission circuits  21   a,    21   b,  and  22   a - 22   c  are inverted by the phase adjusting circuit  23 , the phases of the electric signals may be inverted by connecting the transmission circuits  21   a,    21   b,  and  22   a - 22   c  with the coils  24   a  and  24   b  so that currents flowing through the coils  24   a  and  24   b  normally become in the opposite direction to each other. That is, the output lines of the transmission circuits  21   a,    21   b,  and  22   a - 22   c  may be branched into two routes, one of the output lines may be connected to one of the coils  24   a  and  24   b  in the normal connecting form, and the other output line may be connected to the other coil in the form where current flows in the direction opposite from the normal connecting form. In this case, the phase adjusting circuit  23  may be omitted. 
     The mixing circuit  24  is not limited to have the configuration of  FIG. 3B , and it may have other configurations, as long as the two routes of electric signals are mixed on each other so that the frequency components of the two electric signals are included. 
     Returning to  FIG. 2 , the number of mixing circuits  24  (here, twelve) may be the least common multiple of the number of transmission elements  11   a  included in the group GR 1  (here, four) and the number of transmission elements  11   a  included in the group GR 2  (here, six). The electric signals outputted from the twelve mixing circuits  24  may be inputted into twelve transmission elements  11   a  which are continuously lined up, respectively. In  FIG. 2 , the electric signals outputted from the twelve mixing circuits  24  may be inputted into the 1st to 12th transmission elements  11   a,  the 13th to 24th transmission elements  11   a,  the 25th to 36th transmission elements  11   a,  the 37th to 48th transmission elements  11   a,  the 49th to 60th transmission elements  11   a,  and the 61th to 72nd transmission elements  11   a.    
     Here, different frequencies may be applied to the first set of electric signals inputted into the transmission elements  11   a  of the group GR 1  (i.e., the electric signals with the 90° phase shift outputted from the transmission circuits  21   a  and  21   b ) and the second set of electric signals inputted into the transmission elements  11   a  of the group GR 2  (i.e., the electric signals with the 60° phase shift outputted from the transmission circuits  22   a - 22   c ) based on the first frequency table and the second frequency table. Therefore, even if these electric signals are mixed and inputted into the transmission elements  11   a,  the grating lobe may be individually formed by the electric signals of each set. 
     Therefore, by inputting the electric signals into the 72 transmission elements  11   a  as described above, the grating lobe based on the first set of electric signals with the 90° phase shift may be formed based on the transmission elements  11   a  of the group GR 1 , and the grating lobe based on the second set of electric signals with the 60° phase shift may be formed based on the transmission elements  11   a  of the group GR 2 . Then, by changing the frequency of the electric signals of each set according to the corresponding frequency table, each grating lobe can be allowed to scan in the arrayed direction of the transmission elements  11   a.    
       FIGS. 4A to 8B  are graphs, each illustrating a simulation result of the direction in which the grating lobe occurs calculated by simulation. In  FIGS. 4A to 8B , the horizontal axis is an angle with the front direction of the transmission array  11 , and the vertical axis is an intensity of the transmission wave transmitted from the transmission array  11 . The arrayed direction of the transmission elements  11   a  may be ±90° in the horizontal axis. 
     In this simulation, the pitch of the transmission elements  11   a  may be set as 4.35 mm. The number of transmission elements  11   a  may be set as 72, similarly to the above. 
     Moreover, the first set and the second set of electric signals may be changed to the respective frequencies assigned to the first frequency table and the second frequency table. Moreover, the phase of the electric signal applied to each transmission element  11   a  may be set similar to  FIG. 2 . 
       FIGS. 4A to 6C  are simulation results when applying the first set of electric signals at the frequencies of 95, 100, 105, 110, 120, 130, and 145 kHz to the transmission elements  11   a  of the group GR 1 . Moreover,  FIGS. 7A to 8B  are simulation results when applying the second set of electric signals at the frequencies of 115, 125, 135, and 150 kHz to the transmission elements  11   a  of the group GR 2 . 
     As illustrated in  FIGS. 4A to 6C , when the electric signals at the frequencies of 95, 100, 105, 110, 120, 130, and 145 kHz are applied to the transmission elements  11   a  of the group GR 1 , the grating lobe may occur near different angles D 11 , D 12 , D 13 , D 14 , D 15 , D 16 , and D 17 . The six grating lobes may cover a range of −65° to −35° in general. Therefore, by changing the frequency of the electric signals applied to the transmission elements  11   a  of the group GR 1  as described above, the grating lobe occurring from the transmission elements  11   a  of the group GR 1  can be allowed to scan the range of −65° to −35°. 
     Moreover, as illustrated in  FIGS. 7A to 8B , when the electric signals at the frequencies of 115, 125, 135, and 150 kHz are applied to the transmission elements  11   a  of the group GR 2 , the grating lobe may occur near different angles D 21 , D 22 , D 23 , and D 24 . The four grating lobes may cover the range of −30° to −23° in general. Therefore, by changing the frequency of the electric signals applied to the transmission elements  11   a  of the group GR 2  as described above, the grating lobe occurring from the transmission elements  11   a  of the group GR 2  can be allowed to scan the range of −30° to −23°. 
     As described above, under the simulation condition described above, the grating lobe formed by the transmission elements  11   a  of the group GR 1  can cover the angle range of about 30° (−65° to −35°), the grating lobe formed by the transmission elements  11   a  of the group GR 2  can cover the angle range of about 7° (−30° to −23°). Therefore, adding up the angle ranges of the groups GR 1  and GR 2 , the two grating lobes can cover the angle range of about 42° (−65° to −23°). That is, an angle of visibility of 42° can be realized. 
       FIG. 9  is a view schematically illustrating a range covered by a transmission beam. 
     In  FIG. 9 , a transmission beam TB 1  may correspond to the grating lobe formed by the transmission elements  11   a  of the group GR 1 , and a transmission beam TB 2  may correspond to the grating lobe formed by the transmission elements  11   a  of the group GR 2 . By changing the frequency of the first set of electric signals supplied to the transmission elements  11   a  of the group GR 1  within a range of fa to fb, the transmission beam TB 1  may scan within a range of an angle θ 01 . Moreover, by changing the frequency of the second set of electric signals supplied to the transmission elements  11   a  of the group GR 2  within a range of fc to fd, the transmission beam TB 2  may scan within a range of an angle θ 02 . Therefore, the transmission beams TB 1  and TB 2  can scan the total range (an angle θ 0 ) of the angle θ 01  and the angle θ 02 . 
     In the above simulation, the varying range (fa-fb) of the frequency of the first set of electric signals and the varying range (fc-fd) of the frequency of the second set of electric signals are 95 to 145 kHz and 115 to 150 kHz, respectively, the angles θ 01  and θ 02  are 30° and 7°, respectively, and the angle θ 0  is 42°. 
     Note that although in the above configuration and simulation of  FIG. 2  the phase shift of the first set of electric signals is set as 90° and the phase shift of the second set of electric signals is set as 60°, the phase shift of the second set of electric signals may be set as 45°. In this case, the number of transmission elements  11   a  included in the group GR 2  may be changed according to the change in the number of combinations of the electric signals accompanying the change in the phase shift. 
     Alternatively, the phase shift of the first set of electric signals may be set as 45°. Also in this case, the number of transmission elements  11   a  included in the group GR 1  is changed according to the change in the number of combinations of the electric signals accompanying the change in the phase shift. 
     Moreover, the change in the frequencies of the first set and the second set of electric signals is not limited to the above example, and the frequencies may suitably be changed according to the ranges of the angles θ 01  and θ 02 . 
       FIG. 10  is a view schematically illustrating an example configuration of the transmission-and-reception system. 
     In this example configuration, a reception array  31  having a plurality of reception elements  31   a  may be provided as a reception system, in addition to the configuration of the transmission system illustrated in  FIG. 2 . The transmission system may be provided with the transmission array  11 , similar to  FIG. 2 . The transmission array  11  may be disposed along the X-axis. The reception array  31  may be disposed immediately above the transmission array  11 . In this example configuration, the arrayed direction of the reception elements  31   a  may be perpendicular to the arrayed direction of the transmission elements  11   a.    
     By driving the transmission elements  11   a  in the transmission array  11  by the method illustrated with reference to  FIG. 2 , a transmission beam TB 0  may be formed forward of the transmission array  11  (positive in the Z-axis). Here, the total range of the scan ranges of the transmission beams TB 1  and TB 2  illustrated in  FIG. 9  is illustrated as a scan range of the transmission beam TB 0 . 
     By performing a phase control (beamforming) to the reception signal outputted from each reception element  31   a,  a narrow reception beam RB 0  may be formed in the circumferential direction centering on the X-axis. Thus, the reception signals in an area where the reception beam RB 0  and the transmission beam TB 0  cross may be extracted. According to the phase control, by turning the reception beam RB 0  in a θ 1  direction centering on the X-axis, the reception signal at each turning position may be extracted. 
     The turning position of the reception beam RB 0  may define an incoming direction of the reflection wave in the horizontal direction (θ 1  direction), of which the transmission wave is reflected on a target object. Moreover, as described with reference to  FIG. 9 , an incoming direction of the reflection wave in a vertical direction (θ 0  direction) may be defined based on the frequency of the reception signal. 
     Therefore, among the reception signals extracted by the reception beam RB 0 , the reception signals at the frequencies of the first set and the second set of electric signals may be extracted. In a direction defined by the angle in the vertical direction (an angle in the θ 0  direction) corresponding to the extracted frequency and the angle in the horizontal direction (an angle in the θ 1  direction) based on the beamforming, by plotting data based on the intensity of the reception signal at a distance position based on a delay time of the reflection wave, a distribution of intensity data of the reception signals in the range where the reception beam RB 0  intersects with the transmission beam TB 0  may be acquired. Then, by turning the reception beam RB 0  within a detection range in the horizontal direction and acquiring the distribution of the intensity data at the respective turning positions, the intensity data (volume data) which distribute three-dimensionally in all the detection range in the horizontal direction and the vertical direction can be acquired. By imaging the intensity data (volume data), an image indicative of a state of target object(s) in the detection range can be obtained. 
     Concrete Configuration 
       FIG. 11  is a block diagram illustrating a concrete configuration of the target detection device  1 . 
     The target detection device  1  may be provided with the transmission array  11  as the transmission system. The transmission array  11  may have the same configuration as  FIG. 2 . The target detection device  1  may include a signal generator  111  and a transmission amplifier  112 , as a configuration for supplying a transmission signal S 1  to each transmission element  11   a  of the transmission array  11 . The signal generator  111  may have the same configuration as the circuitry illustrated in  FIG. 2 . According to the configuration of  FIG. 11 , the transmission amplifier  112  for amplifying the electric signal (transmission signal S 1 ) outputted from the mixing circuit  24  of  FIG. 2  and supplying it to each transmission element  11   a  may further be provided. Note that the transmission amplifier may be disposed between the transmission circuits  21   a,    21   b,  and  22   a - 22   c  of  FIG. 2 , and the phase adjusting circuit  23 . 
     The controller  101  may include an arithmetic processing circuit, such as a CPU (Central Processing Unit), and a storage media, such as a ROM (Read Only Memory), a RAM (Random Access Memory), and a hard disk drive. The controller  101  may be comprised of an integrated circuit, such as a FPGA (Field-Programmable Gate Array). 
     The controller  101  may cause the transmission circuits  21   a,    21   b,  and  22   a - 22   c  illustrated in  FIG. 2  to output the electric signals at the frequencies according to the first frequency table and the second frequency table. Thus, as illustrated with reference to  FIG. 9 , the transmission beams TB 1  and TB 2  may be transmitted from the transmission array  11 . As described above, the transmission beams TB 1  and TB 2  may scan the ranges of the angles θ 01  and θ 02  by sequentially changing the frequencies of the first set and the second set of electric signals according to the first frequency table and the second frequency table, respectively. Therefore, the transmission beam TB 0  of  FIG. 10  may be formed. 
     The target detection device  1  may be provided with the reception array  31  described above, as the reception system. The reception array  31  may have the same configuration as  FIG. 10 . In the reception array  31 , “m” reception elements  31   a  may be disposed. The reception signals may be outputted from the reception elements  31   a  to the corresponding channels CH 1 -CHm. 
     The target detection device  1  may include a plurality of reception processing modules  121 , a plurality of A/D conversion parts  122 , a reception signal processing module  123  (which may also be referred to as processing circuitry), and an image signal processing module  124 , as a configuration for processing the reception signal outputted from each reception element  31   a  of the reception array  31  and generating a detection image. 
     The plurality of reception processing modules  121  may be connected to the channels CH 1 -CHm, respectively. Each reception processing module  121  may perform processing for removing an unnecessary band from the inputted reception signal, processing for amplifying the reception signal to a level suitable for A/D conversion, and processing for removing a signal component at a band more than half of a sampling period of the A/D conversion. The plurality of A/D conversion parts  122  may be associated with the plurality of reception processing modules  121 , respectively. Each A/D conversion part  122  may convert the analog reception signal inputted from the corresponding reception processing module  121  into a digital signal at a given sampling period. 
     The reception signal processing module  123  may process the reception signals of the channels CH 1 -CHm inputted from the plurality of A/D conversion parts  122 , respectively, to calculate the intensity data of the reception signals distributed three-dimensionally over the detection range (volume data). The reception signal processing module  123  may be comprised of a single integrated circuit (FPGA etc.) together with the controller  101 . 
     The image signal processing module  124  may process the intensity data (volume data) inputted from the reception signal processing module  123  and generate the image data for imaging the state of the target object in the detection range. The image signal processing module  124  is comprised of a CPU, for example. A display unit  125  may be comprised of a monitor, and display the detection image according to the image data inputted from the image signal processing module  124 . 
       FIG. 12A  is a functional block diagram illustrating an example configuration of the reception signal processing module  123 . 
     The reception signal processing module  123  may include an arithmetic processing circuit and a storage medium. The reception signal processing module  123  may perform a function of each functional block illustrated in  FIG. 12A  according to a program stored in the storage medium. A part of the functions of  FIG. 12A  may be implemented by hardware instead of software. 
     The reception signal processing module  123  may include a plurality of digital filters  201 , a buffer  202 , a plurality of band-pass filters  203 , and a plurality of beam synthesizing parts  204 . 
     The plurality of digital filters  201  may be provided corresponding to the plurality of A/D conversion parts  122  of  FIG. 11 . The digital filter  201  may be a filter sharper than the filtering function of the reception processing module  121  of  FIG. 11 , and remove signals of unnecessary bands in the reception signal. 
     The buffer  202  may temporarily hold the reception signals of the channels CH 1 -CHm outputted from the plurality of digital filters  201 . The buffer  202  may hold the reception signals while the frequencies of the electric signals outputted from the transmission circuits  21   a,    21   b,  and  22   a - 22   c  are changed into all the frequencies assigned to the first frequency table and the second frequency table (hereinafter, “the reception signals for one scan”), chronologically for a plurality of scans. The buffer  202  may sequentially supply the reception signals for one scan to the plurality of band-pass filters  203 , respectively. The buffer  202  may eliminate the reception signals for one scan, when the reception signals for that one scan are supplied to the plurality of band-pass filters  203 . 
     The plurality of band-pass filters  203  may extract the frequency components (frequency reception signals) at frequencies F 1 -Fn from the reception signals for one scan of the inputted channels CH 1 -CHm, respectively. The frequencies F 1 -Fn may correspond to the frequencies assigned to the first frequency table and the second frequency table. The number of band-pass filter  203  provided may be the total number of frequencies assigned to the first frequency table and the second frequency table. The reception signal at each frequency assigned to the first frequency table and the second frequency table may be extracted by each band-pass filter  203 . Each band-pass filter  203  may extract the frequency component (frequency reception signal) at the frequency Fk set in itself from the reception signals for one scan of the channels CH 1 -CHm, and supply it to the beam synthesizing part  204 . 
     The plurality of beam synthesizing parts  204  may be provided corresponding to the plurality of band-pass filters  203 . The beam synthesizing part  204  may form the reception beam RB 0  by the beamforming based on the phase control, and separate the frequency reception signal in the θ 1  direction of  FIG. 10  at a given resolution. Thus, the frequency reception signal in the area where the reception beam RB 0  intersects with the transmission beam TB 1  or TB 2  of  FIG. 9  defined by the band-pass filter  203 , may be acquired. That is, from the top beam synthesizing part  204 , the frequency reception signal in the crossing area where the transmission beam (either the transmission beams TB 1  or TB 2 ) at the angle θ 0  direction (see  FIG. 9 ) corresponding to the frequency F 1  intersects with the reception beam RB 0  in each direction parallel to the horizontal surface (the θ 1  direction of  FIG. 10 ), may be acquired. 
     The acquired frequency reception signal may change in the intensity on the time axis according to the intensity of the reflection wave from the crossing area. This time axis may correspond to a distance from the reception array  31  in the crossing area. Therefore, by mapping each intensity on the time axis at the corresponding distance position from the reception array  31  in the crossing area, the distribution of the intensity data on the crossing area may be acquired. Thus, by integrating the distributions of the intensity data per direction, outputted from the beam synthesizing parts  204 , the volume data where the intensity data is distributed three-dimensionally over the detection range may be acquired. 
       FIG. 12B  is a functional block diagram illustrating another example configuration of the reception signal processing module  123 . 
     In this example configuration, the band-pass filter  203  in the example configuration of  FIG. 12A  may be replaced by an FFT (Fast Fourier Transform)  211  and a frequency extracting part  212 . The FFT  211  may calculate frequency spectrum from the reception signals for one scan of the channels CH 1 -CHm. The frequency extracting part  212  may extract the frequency components (frequency reception signals) at the frequencies F 1 -Fn from the frequency spectrum of each channel calculated by the FFT  211 , and supply them to the beam synthesizing part  204 . Processing of the beam synthesizing part  204  may be the same as  FIG. 12A . 
     Also according to this configuration, by integrating the distributions of the intensity data per direction, outputted from the beam synthesizing parts  204 , the volume data where the intensity data is distributed three-dimensionally over the detection range may be acquired, similar to the configuration of  FIG. 12A . Note that, in the example configuration of  FIG. 12B , the frequencies at which the frequency reception signals are extracted can be set more finely than the example configuration of  FIG. 12A . Therefore, when the number of the plurality of frequencies assigned to the first frequency table and the second frequency table is large, or when these frequencies are close to each other, it is advantageous to use the configuration of  FIG. 12B . 
       FIGS. 13A and 13B  are flowcharts illustrating the transmission processing performed by the controller  101  of  FIG. 11 . This processing may be continuously performed during the detection operation, and be ended according to a termination of the detection operation. The processings of  FIGS. 13A and 13B  may be performed in synchronization with each other. 
       FIG. 13A  is a flowchart illustrating the transmission processing to the transmission elements  11   a  of the group GR 1 . 
     The controller  101  may set the electric signals outputted from the transmission circuits  21   a  and  21   b  at the first frequency assigned to the first frequency table (S 111 ), and cause the transmission circuits  21   a  and  21   b  to output the electric signals for a given period (S 112 ). Thus, through the mixing circuit  24 , the first set of electric signals may be inputted into the transmission elements  11   a  of the group GR 1  (S 113 ), and the grating lobe (transmission beam TB 1 ) based on the first set of electric signals may be transmitted from the transmission array  11 . 
     Then, the controller  101  may wait for the lapse of the given period of the electric signal (S 114 : NO). When the given period passes and the next transmission timing comes (S 114 : YES), the controller  101  may return the processing to Step S 111 , set the electric signals outputted from the transmission circuits  21   a  and  21   b  at the second frequency assigned to the first frequency table, and perform similar processing. Thus, the transmitting direction of the grating lobe (transmission beam TB 1 ) may change in the angle  001  direction of  FIG. 9 . The controller  101  may repeat similar processing until the final frequency assigned to the first frequency table is applied to the transmission circuits  21   a  and  21   b  (S 115 : NO). Therefore, the transmitting direction of the grating lobe (transmission beam TB 1 ) may be changed within the range of the angle θ 01  of  FIG. 9 , and the range of the angle θ 01  may be scanned by the grating lobe (transmission beam TB 1 ). 
     Thus, when all the frequencies assigned to the first frequency table are applied to the transmission circuits  21   a  and  21   b  and the transmission beam TB 1  for one scan is transmitted (S 115 : YES), the controller  101  may end the processing. In this way, after the final transmission for one scan is performed, the controller  101  suspends the transmission until a reception period, corresponding to the transmission, ends. Then, when the reception period ends, the controller  101  may again perform the processing of  FIG. 13A  to perform the transmission for the next scan. In this way, the controller  101  may cause the transmission array  11  to transmit the grating lobe (transmission beam TB 1 ) while cyclically changing the frequency applied to the transmission circuits  21   a  and  21   b  based on the frequencies assigned to the first frequency table. Therefore, the range of the angle θ 01  of  FIG. 9  may be repeatedly scanned by the transmission beam TB 1 . 
       FIG. 13B  is a flowchart illustrating the transmission processing to the transmission elements  11   a  of the group GR 2 . 
     The controller  101  may set the electric signals outputted from the transmission circuits  22   a - 22   c  at the first frequency assigned to the second frequency table (S 121 ), and cause the transmission circuits  22   a - 22   c  to output the electric signals for a given period (S 122 ). Therefore, through the mixing circuit  24 , the second set of electric signals may be inputted into the transmission elements  11   a  of the group GR 2  (S 123 ), and the grating lobe (transmission beam TB 2 ) based on the second set of electric signals may be transmitted from the transmission array  11 . 
     Then, similar to  FIG. 13A , the controller  101  may repeatedly perform the processing at Steps S 121 -S 124  until the final frequency assigned to the second frequency table is applied to the transmission circuits  22   a - 22   c  (S 125 : NO). Moreover, when the reception period for the final transmission for one scan ends, the controller  101  may again perform the processing of  FIG. 13B  to repeat similar transmission processing. Thus, the grating lobe (transmission beam TB 2 ) may be transmitted from the transmission array  11 , while the frequency applied to the transmission circuits  22   a - 22   c  is cyclically changed based on the frequencies assigned to the second frequency table. In this way, the range of the angle θ 02  of  FIG. 9  may be scanned by the grating lobe (transmission beam TB 2 ). 
     Note that since in this embodiment the number of frequencies assigned to the second frequency table is less than the number of frequencies assigned to the first frequency table, the period during which all the frequencies are applied to each transmission circuit may become shorter in the processing of  FIG. 13B  than the processing of  FIG. 13A , if the switching timings at Steps S 114  and S 124  are the same. Therefore, the controller  101  may adjust the switching timings at Step S 114  and S 124  so that the period during which all the frequencies are applied to each transmission circuit is the same in the processing of  FIG. 13A  and the processing of  FIG. 13B . 
     Alternatively, after the processing of  FIG. 13B  for one scan ends, the controller  101  may suspend the processing of  FIG. 13B  until the processing of  FIG. 13A  is performed for one scan, and after the processing of  FIG. 13A  for one scan is finished, the controller  101  may start the processing for the next scan of  FIG. 13B  at the timing where the final reception period is ended. Therefore, the reception signals for one scan to each processing can be acquired for every fixed period. 
       FIG. 14  is a flowchart illustrating processing for processing the reception signals and displaying the detection image. This processing may be continuously performed during the detection operation, and be ended according to the termination of the detection operation. 
     The reception signals for one scan may be supplied to the plurality of band-pass filters  203  from the buffer  202  (S 201 ). Each band-pass filter  203  may extract the frequency component (frequency reception signal) at the frequency set in itself from the inputted reception signals of each channel, and supply it to the corresponding beam synthesizing part  204  (S 202 ). The beam synthesizing part  204  may extract the signal component in each horizontal direction (θ 1  direction) by beamforming from the inputted frequency components (frequency reception signals) (S 203 ). Thus, the distribution of the intensity data where the intensity data of the reception signal may be mapped in the range where the transmitting direction defined by each frequency intersects with each direction of the beamforming is acquired. The reception signal processing module  123  may integrate the intensity data from all the beam synthesizing parts  204 , and form the volume data where the intensity data is distributed three-dimensionally over the detection range (S 204 ). The reception signal processing module  123  may supply the volume data to the image signal processing module  124 . 
     The image signal processing module  124  may process the volume data to generate the image data for displaying the detecting situation of the target object(s) in the detection range, and supply the generated image data to the display unit  125  (S 205 ). The display unit  125  may display the image based on the inputted image data (S 206 ). Therefore, the detecting situation of the target object(s) for one scan in the detection range may be displayed. In this way, the processing for one scan may end. Then, the processing of  FIG. 14  may be repeated and the detection image for the subsequent scan may be displayed on the display unit  125 . 
       FIG. 15  is a view schematically illustrating a configuration of the target detection device  1  when it is used as a sonar which detects an underwater target object. 
     A transducer  300  may be installed on the bottom of a ship  2 . The transducer  300  may include the transmission array  11  and the reception array  31 . The transmission array  11  may transmit the transmission wave underwater by the processing described above. Here, an acoustic wave (e.g., an ultrasonic wave) may be transmitted as the transmission wave. Therefore, the transmission beams TB 1  and TB 2  may be scanned in the range of the angle θ 0  parallel to the vertical plane. 
     Configurations of  FIG. 11  other than the transmission array  11 , the reception array  31 , and the display unit  125  may be provided to a control device installed in a control room  2   a  of the ship  2 . The display unit  125  may be installed in the control room  2   a,  separately from the control device. The display unit  125  may also be integrally provided with the control device. 
     According to this configuration, the detection image indicative of a situation of a seabed  3  and a school of fish  4  may be displayed on the display unit  125 . Therefore, a user can grasp the underwater situation. Note that four transducers  300  which are directed forward, rearward, leftward, and rightward may be installed on the bottom of the ship. In this case, the configurations of the transmission system and the reception system of  FIG. 11  may be prepared for every transducer  300 . Thus, the detection image of all directions from the ship can be displayed on the display unit  125 . 
     Moreover, if the target detection device  1  is used as a radar which detects a target object in the air, the transducer  400  may be installed in an upper part of a control room  2   a,  for example. The transducer  400  may include the transmission array  11  and the reception array  31 . The transmission array  11  may transmit the transmission wave in the air by the processing described above. Here, a radio wave may be transmitted as the transmission wave. The configuration of the circuitry may be installed in the control room  2   a,  similar to the case of the sonar. 
     According to this configuration, the detection image indicative of a situation of an obstacle and a flock of birds may be displayed on the display unit  125 . Therefore, the user can grasp the situation in the air. Note that the transducer  400  may be installed on each of front, rear, right, and left side surfaces of the control room  2   a.  In this case, the configuration of the transmission system and the reception system of  FIG. 11  may be prepared for every transducer  400 . Therefore, the detection image of a space all around the ship can be displayed on the display unit  125 . 
     Effects of Embodiment 
     According to this embodiment, the following effects may be demonstrated. 
     The grating lobe transmitted from the transmission elements  11   a  grouped conforming to the first grouping configuration (group GR 1 ), and the grating lobe transmitted from the transmission elements  11   a  grouped conforming to the second grouping configuration (group GR 2 ) can be differentiated in the transmitting direction. Therefore, a plurality of the transmission beams (grating lobes) with different transmitting directions can be transmitted by the single transmission array  11 . Therefore, the target object can be smoothly detected by the simple configuration. 
     Moreover, since the common transmission elements  11   a  are used for the first grouping configuration and the second grouping configuration, it may not be necessary to separately prepare the transmission elements  11   a  for each of the first grouping configuration and the second grouping configuration. Therefore, the configuration of the transmission array  11  can be simplified, and the cost can be reduced. 
     Moreover, since the spacing or interval of the transmission elements  11   a  is constant, the grating lobes can appear smoothly in the given transmitting directions by adjusting the phases of the first set and the second set of electric signals. 
     Moreover, as illustrated in  FIG. 2 , since the mixing circuit  24 , which mixes the electric signal of the first set and the electric signal of the second set and inputs the mixed electric signal into the corresponding transmission element  11   a,  may be provided, the grating lobe (transmission beam TB 1 ) based on the first set of electric signals and the grating lobe (transmission beam TB 2 ) based on the second set of electric signals can be transmitted simultaneously, as illustrated in  FIG. 9 . Therefore, the target object over the detection range can be promptly detected. 
     Moreover, the frequencies of the first set of electric signals assigned to the first frequency table may differ from the frequencies of the second set of electric signals assigned to the second frequency table. Thus, the reception signal processing module  123  illustrated in  FIG. 11  can extract the reception signals based on the grating lobe of the first set of electric signals and the reception signals based on the grating lobe of the second set of electric signals according to the frequencies. Therefore, even if the two grating lobes are simultaneously transmitted by the mixing of the electric signals by the mixing circuit  24 , the reception signal processing module  123  can appropriately extract the reception signals based on each grating lobe, and can smoothly detect the target object which exists in the direction of each grating lobe. 
     As illustrated in  FIGS. 13A and 13B , the signal generator  111  may change the frequencies of the first set of electric signals according to the first frequency table, and change the frequencies of the second set of electric signals according to the second frequency table. Thus, by changing the frequencies in this way, the transmitting directions of the grating lobes based on the electric signals of the first set and the second set can be changed, as illustrated in the simulation results. Therefore, these grating lobes can each scan the given angle range and can extend the detection range of the target object. 
     As illustrated with reference to  FIGS. 12A and 12B , the reception signal processing module  123  may extract the reception signals based on the reflection waves of the grating lobe based on the frequency components of the reception signals. Therefore, the reception signals based on each grating lobe transmitted from the transmission array  11  can be acquired properly. Therefore, the target object can be detected properly based on the reception signals. 
     As illustrated in  FIG. 10 , the reception array  31  may be different than the transmission array  11 . The reception array  31  may include the plurality of reception elements  31   a,  and the reception beam generated based on the reception signal produced from each reception element  31   a  may intersect with the transmission beam generated by the transmission array  11 . According to this configuration, the distribution of the intensity data based on the intensities of the reflection waves can be calculated in the range where the reception beam RB 0  and the transmission beam TB 0  (grating lobe) cross. Therefore, by changing the orientation of the reception beam RB 0  by the beamforming within the detection range, the intensity data of the reflection waves distributed three-dimensionally over the detection range can be formed. 
     Modification 1 
     In the above embodiment, as illustrated in  FIG. 2 , the two routes of electric signals may be mixed by the mixing circuit  24  and inputted into the corresponding transmission elements  11   a.  However, as illustrated in  FIG. 16 , the electric signal inputted into the transmission element  11   a  may be switched in a time-divided manner between the two routes of electric signals. According to such a configuration, while one frequency is applied to the transmission circuits  21   a,    21   b,  and  22   a - 22   c,  a switching circuit  25  may be switched so that the first set of electric signals and the second set of electric signals at the frequency are supplied to the transmission element  11   a  in the time-divided manner. According to this configuration, the transmission beams TB 1  and TB 2  illustrated in  FIG. 9  are not transmitted simultaneously, but are alternately transmitted according to the switching of the switching circuit  25 . 
     Also according to this configuration, by changing the frequency applied to the transmission circuits  21   a,    21   b,  and  22   a - 22   c  according to the first frequency table and the second frequency table, the transmission beams TB 1  and TB 2  can scan the ranges of the angles θ 01  and θ 02 , similar to the above embodiment. Therefore, it is not necessary to provide a plurality of transmission arrays  11 , and the target object can be detected with the simple configuration. 
     However, according to this configuration, since the transmission beams TB 1  and TB 2  are not transmitted simultaneously but are alternately transmitted according to the switching of the switching circuit  25 , a period of the transmission beams TB 1  and TB 2  scanning the ranges of the angles θ 01  and θ 02  may become longer. Therefore, in order to scan more promptly, it is desirable to mix the two routes of electric signals by the mixing circuit  24  and supply it to the transmission element  11   a  similarly to the above embodiment. 
     Note that, in the configuration of  FIG. 16 , the switching circuit  25  may be comprised of a switching circuit using a multiplexer or a transistor. However, the configuration of the switching circuit  25  is not limited to this. For example, an electromagnetically driven mechanical switch may be used as the switching circuit  25 . 
     Note that, according to the configuration of Modification  1 , since the first set of electric signals and the second set of electric signals may be inputted in the time-divided manner to the transmission elements  11   a  of the group GR 1  and the transmission elements  11   a  of the group GR 2 , the transmission beams TB 1  and TB 2  (grating lobe) of  FIG. 9  may be transmitted in the time-divided manner. Therefore, the reception signal processing module  123  of  FIG. 11  may not need to be provided with the configuration for extracting the reception signals based on the first set of electric signals and the reception signals based on the second set of electric signals according to the frequency. The reception signal processing module  123  may identify the transmitting directions of the transmission beams TB 1  and TB 2  according to the transmission timings of the transmission beams TB 1  and TB 2 . 
     In this case, for example, the controller  101  may output the frequency of the transmission beam transmitted at each transmission timing to the reception signal processing module  123 , and the reception signal processing module  123  may identify the transmitting directions of the transmission beams TB 1  nd TB 2  based on the inputted frequencies. Alternatively, the controller  101  may transmit to the reception signal processing module  123  other information from which the transmitting directions of the transmitted transmission beams TB 1  and TB 2  can be identified, at each transmission timing, and the reception signal processing module  123  may identify the transmitting directions of the transmitted transmission beams TB 1  and TB 2  based on this information. 
     Modification 2 
     In the above embodiment, the electric signals at different phases may be inputted to the plurality of transmission elements  11   a  which constitute the group GR 1  and the group GR 2 . However, in Modification 2, the electric signals at the same phase may be inputted to a given number of transmission elements  11   a  among the plurality of transmission elements  11   a  which constitute the group GR 1  and the group GR 2 . 
       FIG. 17  is a view illustrating a configuration of a transmission system according to Modification 2. 
     As illustrated in  FIG. 17 , in the first grouping configuration, the group GR 1  may be comprised of six transmission elements  11   a,  and in the second grouping configuration, the group GR 2  may be comprised of eight transmission elements  11   a.  The electric signals of the first set at 0° phase may be inputted into three adjacent transmission elements  11   a  among the six transmission elements  11   a  which constitute the group GR 1 , and the first set of electric signals at 180° phase may be inputted into other three adjacent transmission elements  11   a.  Moreover, the second set of electric signals at 0° phase may be inputted into four adjacent transmission elements  11   a  among the eight transmission elements  11   a  which constitute the group GR 2 , and the second set of electric signals at 180° phase may be inputted into other four adjacent transmission elements  11   a.  The electric signals of the first set and the second set may be inputted into the 25th and subsequent transmission elements  11   a  so that similar phase pattern as the 1st to 24th transmission elements  11   a  is repeated. 
     According to the configuration of Modification 2, two kinds of electric signals with different phases may be inputted to the six transmission elements  11   a  included in the group GR 1 . That is, the number (six) of transmission elements  11   a  included in the group GR 1  may be a multiple (three times) of the number (two) of kinds of electric signals of the first set. Moreover, two kinds of electric signals with different phases may be inputted to the eight transmission elements  11   a  included in the group GR 2 . That is, the number (eight) of transmission elements  11   a  included in the group GR 2  may be a multiple (four times) of the number (two) of kinds of electric signals of the second set. Note that, also in the above embodiment, the numbers of transmission elements  11   a  included in the group GR 1  and the group GR 2  (four and six respectively) are multiple (1 time) of the numbers of kinds of electric signals of the first set and the second set (four and six respectively). Therefore, the number “p” of transmission elements  11   a  in the group GR 1  may be a multiple of the number of kinds of electric signals of the first set; and the number “q” of transmission elements  11   a  in the group GR 2  may be a multiple of the number of kinds of electric signals in the second set. 
     The electric signals of the first set may be generated by a transmission circuit  26  and a phase adjusting circuit  28  connected to the transmission circuit  26 . The electric signals of the second set may be generated by a transmission circuit  27  and a phase adjusting circuit  28  connected to the transmission circuit  27 . The phase adjusting circuit  28  may have the same configuration as the phase adjusting circuit  23  in the above embodiment. A mixing circuit  29  may mix and output the inputted electric signals of the two routes. The mixing circuit  29  may have the same configuration as the mixing circuit  24  in the above embodiment. 
     The transmission circuits  26  and  27  may each output the sine-wave electric signal at 0° phase. The transmission circuit  26  may change the frequency of the electric signal to be output, based on the frequencies assigned to the first frequency table. For example, frequencies of 130, 140, 150, 160, and 170 kHz are assigned to the first frequency table. The transmission circuit  27  may change the frequency of the electric signal to be output, based on the frequencies assigned to the second frequency table. For example, the frequencies of 135, 145, 155, and 165 kHz are assigned to the second frequency table. 
     In the configuration of  FIG. 17 , since the electric signals at the same phase are inputted to the three adjacent transmission elements  11   a  among the six transmission elements  11   a  of the group GR 1 , the three adjacent transmission elements  11   a  may function as a single transmission area. Therefore, as for the transmission elements  11   a  of the group GR 1 , the phase of the electric signals may be changed at a pitch between the transmission areas comprised of the three adjacent transmission elements  11   a.  For example, when the pitch between the transmission elements  11   a  is 2.5 mm, the pitch at which the phase of the electric signal changes is 7.5 mm. 
     Moreover, since the electric signals at the same phase are inputted to the four adjacent transmission elements  11   a  among the eight transmission elements  11   a  of the group GR 2 , the four adjacent transmission elements  11   a  may function as a single transmission area. Therefore, as for the transmission elements  11   a  of the group GR 2 , the phase of the electric signals may be changed at a pitch between the transmission areas comprised of the four adjacent transmission elements  11   a.  For example, when the pitch between the transmission elements  11   a  is 2.5 mm, the pitch at which the phase of the electric signal changes is 10 mm. 
     Thus, in Modification 2, the pitch at which the phase of the electric signals is changed may differ between the case where the first set of electric signals are inputted into the transmission elements  11   a  of the group GR 1  and the case where the second set of electric signals are inputted into the transmission elements  11   a  of the group GR 2 . Therefore, the transmitting direction of the grating lobe caused by the transmission elements  11   a  of the group GR 1  may differ from the transmitting direction of the grating lobe caused by the transmission elements  11   a  of the group GR 2 . Then, by changing the frequencies of the first set of electric signals and the second set of electric signals according to the first frequency table and the second frequency table, respectively, the transmitting direction of each grating lobe can be changed similarly to the above embodiment. Therefore, the two grating lobes (transmission beams) can scan in the given detection range. 
       FIGS. 18A to 21B  are views, each illustrating a simulation result of calculating the transmitting direction in which the grating lobe occurs in the configuration of Modification 2. 
     In the simulations, the pitch of the transmission elements  11   a  may be set as 2.5 mm. The number of transmission elements  11   a  may be set as 96. Moreover, the first set of electric signals and the second set of electric signals may be changed to each frequency assigned to the first frequency table and the second frequency table, respectively. Moreover, the phase of the electric signal applied to each transmission element  11   a  may be set similar to  FIG. 17 . 
       FIGS. 18A to 19C  are simulation results when applying the first set of electric signals at the frequencies of 130, 140, 150 160, and 170 kHz to the transmission elements  11   a  of the group GR 1 . Moreover,  FIGS. 20A to 21B  are simulation results when applying the second set of electric signals at the frequencies of 135, 145, 155, and 165 kHz to the transmission elements  11   a  of the group GR 2 . 
     As illustrated in  FIGS. 18A to 19C , when the electric signals at the frequencies of 130, 140, 150, 160, and 170 kHz are applied to the transmission elements  11   a  of the group GR 1 , the grating lobes may occur near different angles D 11 , D 12 , D 13 , D 14 , and D 15 . These five grating lobes may cover a range of −50° to −36° in general. Therefore, by changing the frequency of the electric signals applied to the transmission elements  11   a  of the group GR 1  as described above, the grating lobes occurring from the transmission elements  11   a  of the group GR 1  can scan the range of −50° to −36°. 
     Moreover, as illustrated in  FIGS. 20A to 21B , when the electric signals at the frequencies of 135, 145, 155, and 165 kHz are applied to the transmission elements  11   a  of the group GR 2 , the grating lobes may occur near different angles D 21 , D 22 , D 23 , and D 24 . These four grating lobes may cover a range of −34° to −27° in general. Therefore, by changing the frequency of the electric signals applied to the transmission elements  11   a  of the group GR 2  as described above, the grating lobes occurring from the transmission elements  11   a  of the group GR 2  can scan the range of −34° to −27°. 
     As described above, the grating lobes formed by the transmission elements  11   a  of the group GR 1  under the simulation condition described above can cover an angle range of 14° (−50° to −36°) in general, and the grating lobe formed by the transmission elements  11   a  of the group GR 2  can cover an angle range of 7° (−34° to −27°) in general. As the angle ranges of the groups GR 1  and GR 2  are integrated, the two grating lobes can cover an angle range of 23° (−50° to −27°) in general. That is, the angle of visibility of 23° can be realized. 
     Therefore, also according to the configuration of Modification 2, one of the grating lobes caused by the transmission elements  11   a  of the group GR 1  and one of the grating lobes caused by the transmission elements  11   a  of the group GR 2  can scan the angle range of about 23°. 
     Note that, according to the configuration of Modification 2, the two grating lobes may occur by the transmission elements  11   a  of the group GR 1  and the group GR 2  as illustrated in the respective simulation results. In this case, as for the detection of the target object, only one of the two grating lobes (e.g., the grating lobe at the minus side in the simulations of  FIGS. 18A to 21B ) is used, for example. For example, the angle range of the reception beam RB 0  is set so that the other grating lobe falls out from the range of the reception beam RB 0 . Therefore, by performing the processings of  FIGS. 13A to 14  using similar circuit configuration as  FIGS. 11 to 12B , the detection image of the given detection range can be displayed on the display unit  125 . 
     Other Modifications 
     In the above embodiment, as illustrated in  FIGS. 12A and 12B , after the frequency component at each frequency is extracted from the reception signal, the beamforming processing then performs a separation into the signal in each direction. However, the reception signal may be first separated into the signal in each direction by the beamforming processing, and then the frequency component of each frequency may be extracted from the separated signal in each direction. That is, the band-pass filter  203  and the beam synthesizing part  204  of  FIG. 12A  may be interchanged, or the FFT  211  and the frequency extracting part  212 , and the beam synthesizing part  204  of  FIG. 12B  may be interchanged. 
     Moreover, in the above embodiment, although the plurality of reception elements  31   a  are provided as illustrated in  FIG. 10 , the reflection wave may be received by a single reception element  31   a.  Note that, in this case, since the beamforming cannot be performed to the reception beam, the bearing of the reception beam (the direction θ 1  of  FIG. 10 ) is fixed. However, by extracting the frequency component of the reception signal from the reception beam of this bearing, the intensity data in each direction of the vertical direction can be acquired. Therefore, by mapping the intensity data in each direction of the vertical direction, the two-dimensional detection image can be displayed. 
     Moreover, the number of transmission elements  11   a  is not limited to the number illustrated in the above embodiment, and it may be other numbers as long as the plurality of kinds of grouping configurations are realizable. Moreover, three or more kinds of grouping configurations may be set for the plurality of transmission elements  11   a  included in the transmission array  11 , and therefore, the number of transmission elements  11   a  included in each group is not limited to the number described in the above embodiment and modifications. In any of the cases, the grating lobes are formed as the transmission waves so as to correspond to the number of grouping configurations. 
     Moreover, the grating lobes formed by the transmission elements  11   a  of each group may not necessarily be clearly separated, and may be partially overlapped. 
     Moreover, although in the above embodiment the transmission array and the reception array are disposed perpendicular to each other, the transmission array and the reception array may be disposed at an angle slightly offset from the perpendicular configuration. 
     Moreover, although in  FIG. 14  the target detection device  1  (sonar, radar) is disposed in the ship  2 , the target detection device  1  (sonar, radar) may be installed in a movable body other than the ship  2 , or the target detection device  1  (sonar, radar) may be installed in a structure, other than the movable body, such as a buoy. 
     Note that various modifications are suitably possible for the embodiment of the present disclosure within the scope of the appended claims. 
     Terminology 
     It is to be understood that not necessarily all objects or advantages may be achieved in accordance with any particular embodiment described herein. Thus, for example, those skilled in the art will recognize that certain embodiments may be configured to operate in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other objects or advantages as may be taught or suggested herein. 
     All of the processes described herein may be embodied in, and fully automated via, software code modules executed by a computing system that includes one or more computers or processors. The code modules may be stored in any type of non-transitory computer-readable medium or other computer storage device. Some or all the methods may be embodied in specialized computer hardware. 
     Many other variations than those described herein will be apparent from this disclosure. For example, depending on the embodiment, certain acts, events, or functions of any of the algorithms described herein can be performed in a different sequence, can be added, merged, or left out altogether (e.g., not all described acts or events are necessary for the practice of the algorithms). Moreover, in certain embodiments, acts or events can be performed concurrently, e.g., through multi-threaded processing, interrupt processing, or multiple processors or processor cores or on other parallel architectures, rather than sequentially. In addition, different tasks or processes can be performed by different machines and/or computing systems that can function together. 
     The various illustrative logical blocks and modules described in connection with the embodiments disclosed herein can be implemented or performed by a machine, such as a processor. A processor can be a microprocessor, but in the alternative, the processor can be a controller, microcontroller, or state machine, combinations of the same, or the like. A processor can include electrical circuitry configured to process computer-executable instructions. In another embodiment, a processor includes an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) or other programmable device that performs logic operations without processing computer-executable instructions. A processor can also be implemented as a combination of computing devices, e.g., a combination of a digital signal processor (DSP) and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration. Although described herein primarily with respect to digital technology, a processor may also include primarily analog components. For example, some or all of the signal processing algorithms described herein may be implemented in analog circuitry or mixed analog and digital circuitry. A computing environment can include any type of computer system, including, but not limited to, a computer system based on a microprocessor, a mainframe computer, a digital signal processor, a portable computing device, a device controller, or a computational engine within an appliance, to name a few. 
     Conditional language such as, among others, “can,” “could,” “might” or “may,” unless specifically stated otherwise, are otherwise understood within the context as used in general to convey that certain embodiments include, while other embodiments do not include, certain features, elements and/or steps. Thus, such conditional language is not generally intended to imply that features, elements and/or steps are in any way required for one or more embodiments or that one or more embodiments necessarily include logic for deciding, with or without user input or prompting, whether these features, elements and/or steps are included or are to be performed in any particular embodiment. 
     Disjunctive language such as the phrase “at least one of X, Y, or Z,” unless specifically stated otherwise, is otherwise understood with the context as used in general to present that an item, term, etc., may be either X, Y, or Z, or any combination thereof (e.g., X, Y, and/or Z). Thus, such disjunctive language is not generally intended to, and should not, imply that certain embodiments require at least one of X, at least one of Y, or at least one of Z to each be present. 
     Any process descriptions, elements or blocks in the flow diagrams described herein and/or depicted in the attached figures should be understood as potentially representing modules, segments, or portions of code which include one or more executable instructions for implementing specific logical functions or elements in the process. Alternate implementations are included within the scope of the embodiments described herein in which elements or functions may be deleted, executed out of order from that shown, or discussed, including substantially concurrently or in reverse order, depending on the functionality involved as would be understood by those skilled in the art. 
     Unless otherwise explicitly stated, articles such as “a” or “an” should generally be interpreted to include one or more described items. Accordingly, phrases such as “a device configured to” are intended to include one or more recited devices. Such one or more recited devices can also be collectively configured to carry out the stated recitations. For example, “a processor configured to carry out recitations A, B and C” can include a first processor configured to carry out recitation A working in conjunction with a second processor configured to carry out recitations B and C. The same holds true for the use of definite articles used to introduce embodiment recitations. In addition, even if a specific number of an introduced embodiment recitation is explicitly recited, those skilled in the art will recognize that such recitation should typically be interpreted to mean at least the recited number (e.g., the bare recitation of “two recitations,” without other modifiers, typically means at least two recitations, or two or more recitations). 
     It will be understood by those within the art that, in general, terms used herein, are generally intended as “open” terms (e.g., the term “including” should be interpreted as “including but not limited to,” the term “having” should be interpreted as “having at least,” the term “includes” should be interpreted as “includes but is not limited to,” etc.). 
     For expository purposes, the term “horizontal” as used herein is defined as a plane parallel to the plane or surface of the floor of the area in which the system being described is used or the method being described is performed, regardless of its orientation. The term “floor” can be interchanged with the term “ground” or “water surface.” The term “vertical” refers to a direction perpendicular to the horizontal as just defined. Terms such as “above,” “below,” “bottom,” “top,” “side,” “higher,” “lower,” “upper,” “over,” and “under,” are defined with respect to the horizontal plane. 
     As used herein, the terms “attached,” “connected,” “mated” and other such relational terms should be construed, unless otherwise noted, to include removable, moveable, fixed, adjustable, and/or releasable connections or attachments. The connections/attachments can include direct connections and/or connections having intermediate structure between the two components discussed. 
     Numbers preceded by a term such as “approximately,” “about,” and “substantially” as used herein include the recited numbers, and also represent an amount close to the stated amount that still performs a desired function or achieves a desired result. For example, the terms “approximately,” “about,” and “substantially” may refer to an amount that is within less than 10% of the stated amount. Features of embodiments disclosed herein preceded by a term such as “approximately,” “about,” and “substantially” as used herein represent the feature with some variability that still performs a desired function or achieves a desired result for that feature. 
     It should be emphasized that many variations and modifications may be made to the above-described embodiments, the elements of which are to be understood as being among other acceptable examples. All such modifications and variations are intended to be included herein within the scope of this disclosure and protected by the following claims.