Patent Publication Number: US-10326201-B2

Title: Antenna apparatus and antenna excitation method

Description:
TECHNICAL FIELD 
     This disclosure relates to antenna apparatuses and antenna excitation methods for controlling the amplitude and phase of carrier signals to be provided to a plurality of element antennas in an array antenna. 
     BACKGROUND ART 
     An antenna apparatus equipped with a phased array antenna can form a directional beam by controlling the amplitude and phase of carrier signals to be provided to a plurality of element antennas that form the phased array antenna. 
     In communication using a directional beam, a communication signal which is a signal to be communicated is transmitted not only in a main lobe direction of the directional beam but also in sidelobe directions. Hence, there is a case in which even a receiving station present in a direction different than a communication direction can receive a communication signal and demodulate the communication signal. 
     The following Non-Patent Literature 1 discloses an antenna apparatus that limits a communicable area by mounting an array antenna that transmits signals only to an area near a communication direction (hereinafter, referred to as “directional modulation array antenna”). 
     The antenna apparatus generates a baseband modulated signal, a signal to be communicated, by performing a quadrature phase shift keying (QPSK) modulation process on a transmission bit sequence, calculates an excitation distribution that associates the amplitude and phase of each constellation point of the baseband modulated signal with electric field amplitude and phase in a communication direction, and provides carrier signals to be provided to a plurality of element antennas forming the directional modulation array antenna with the calculated excitation distribution in a time division manner. 
     The following Patent Literature 1 discloses an antenna apparatus that achieves narrower coverage of a directional modulation array antenna. 
     The antenna apparatus limits a communicable area by obtaining a non-uniform excitation distribution for the directional modulation array antenna. For example, in a case in which the directional modulation array antenna is a linear array antenna, of carrier signals to be provided to a plurality of element antennas forming the array antenna, carrier signals to be provided to element antennas disposed at the edges are increased in excitation amplitude over a carrier signal to be provided to an element antenna disposed at the center, by which the communicable area is limited. 
     CITATION LIST 
     Patent Literatures 
     Patent Literature 1: JP 2015-65565 A 
     Non-Patent Literatures 
     Non-Patent Literature 1: M. P. Daly, “Directional Modulation Technique for Phased arrays”, IEEE Trans. Antennas Propagat., vol. 57, pp. 2633-2640, 2009. 
     SUMMARY OF INVENTION 
     Technical Problem 
     Since conventional antenna apparatuses are formed in the above-described manner, it is necessary to calculate an excitation distribution provided in a time division manner. Further, it is necessary to calculate an excitation distribution in which the excitation amplitudes of carrier signals to be provided to element antennas disposed at the edges are larger than that of a carrier signal to be provided to an element antenna disposed at the center. These excitation distributions can be obtained by solving an evaluation function obtained based on the bit error rate for each direction, etc., using an optimization technique such as a genetic algorithm (GA). However, when the optimization technique is used, the amount of computation is enormous and thus there is a problem that it may take a long time to obtain an excitation distribution. 
     An aspect of embodiments of this disclosure relates to solving the problem described above, and an object of the embodiments is to obtain an antenna apparatus and an antenna excitation method that are capable of reducing the amount of computation for an excitation distribution for an array antenna that is used to implement secure communication with a limited communicable area. 
     Solution to Problem 
     An antenna apparatus according to the present disclosure is provided with an array antenna including a plurality of element antennas for radiating carrier signals; a communication signal generating unit for generating a communication signal that is a signal to be communicated; an interference signal generating unit for generating an interference signal serving as a disturbing wave for the communication signal; a communication excitation distribution calculating unit for calculating an excitation distribution of a communication beam by using an excitation phase distribution that directs a main lobe of the communication beam toward a communication direction, the communication beam being a radio wave that transmits the communication signal; an interference excitation distribution calculating unit for calculating an excitation distribution of an interference beam by using an excitation phase distribution that forms a null of an antenna pattern in the communication direction, the interference beam being a radio wave that transmits the interference signal; an excitation distribution combining unit for combining the excitation distribution of the communication beam calculated by the communication excitation distribution calculating unit and the excitation distribution of the interference beam calculated by the interference excitation distribution calculating unit; and an amplitude/phase controlling unit for controlling amplitudes and phases of carrier signals to be provided to the plurality of element antennas in accordance with the combined excitation distribution obtained by the excitation distribution combining unit. 
     Advantageous Effects of Invention 
     According to an aspect of embodiments of the present disclosure, an antenna apparatus is configured such that it is equipped with the communication excitation distribution calculating unit that calculates an excitation distribution of a communication beam by using an excitation phase distribution that directs a main lobe of the communication beam toward a communication direction, and the interference excitation distribution calculating unit that calculates an excitation distribution of an interference beam by using an excitation phase distribution that forms a null of an antenna pattern in the communication direction, and that the excitation distribution combining unit combines the excitation distribution of the communication beam calculated by the communication excitation distribution calculating unit and the excitation distribution of the interference beam calculated by the interference excitation distribution calculating unit. Hence, there is an advantageous effect of being able to reduce the amount of computation for an excitation distribution for the array antenna that is used to implement secure communication with a limited communicable area. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a configuration diagram showing an antenna apparatus in accordance with Embodiment 1 of the disclosure. 
         FIG. 2  is a hardware configuration diagram of a signal processing unit  10  of the antenna apparatus in accordance with Embodiment 1 of the disclosure. 
         FIG. 3  is a hardware configuration diagram of a computer for a case in which the signal processing unit  10  is implemented by software, firmware, or the like. 
         FIG. 4  is a flowchart showing the operation of a carrier signal generating unit  1 , a divider  2 , an amplitude/phase controlling unit  30 , and element antennas  3 - 1  to  3 -K. 
         FIG. 5  is a flowchart showing the processing operations of a communication signal generating unit  4  and a communication excitation distribution calculating unit  11 . 
         FIG. 6  is a flowchart showing the processing operations of an interference signal generating unit  5  and an interference excitation distribution calculating unit  14 . 
         FIG. 7  is a flowchart showing the processing operations of a beam-scanning phase distribution setting unit  18 , a weight setting unit  19 , and an excitation distribution combining unit  20 . 
         FIG. 8  is an illustrative diagram showing an amplitude characteristic of a communication beam calculated from an excitation distribution W 1 ( t ) of the communication beam, and an amplitude characteristic of an interference beam calculated from an excitation distribution W 2 ( t ) of the interference beam. 
         FIG. 9  is an illustrative diagram showing a phase characteristic of an antenna pattern calculated from a combined excitation distribution E(t). 
         FIG. 10  is a configuration diagram showing an antenna apparatus in accordance with Embodiment 2 of the disclosure. 
         FIG. 11  is a hardware configuration diagram of a signal processing unit  10  of the antenna apparatus in accordance with Embodiment 2 of the disclosure. 
         FIG. 12  is a configuration diagram showing an antenna apparatus in accordance with Embodiment 3 of the disclosure. 
         FIG. 13  is a configuration diagram showing an antenna apparatus in accordance with Embodiment 4 of the disclosure. 
         FIG. 14  is a flowchart showing the operation of a carrier signal generating unit  61 , an amplitude/phase controlling unit  70 , and element antennas  3 - 1  to  3 -K. 
         FIG. 15  is a configuration diagram showing an antenna apparatus in accordance with Embodiment 5 of the disclosure. 
         FIG. 16  is a configuration diagram showing an interference signal generating unit  80  of the antenna apparatus in accordance with the Embodiment 5 of the disclosure. 
         FIG. 17  is a flowchart showing the processing operation of a phase adjuster  81  in the interference signal generating unit  80 . 
         FIG. 18  is an illustrative diagram showing an excitation amplitude distribution A of a communication beam which is the same as an excitation amplitude distribution A of an interference beam. 
         FIG. 19  is an illustrative diagram showing an excitation amplitude distribution A of a communication beam which is the same as an excitation amplitude distribution A of an interference beam. 
         FIG. 20A  is an illustrative diagram showing an example of a linear array antenna,  FIG. 20B  is an illustrative diagram showing an example of a planar array antenna, and  FIG. 20C  is an illustrative diagram showing an example of a conformal array antenna. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, to describe this application in more detail, embodiments in accordance with the disclosure will be described with reference to the accompanying drawings. 
     Embodiment 1 
       FIG. 1  is a configuration diagram showing an antenna apparatus in accordance with Embodiment 1 of the disclosure, and  FIG. 2  is a hardware configuration diagram of a signal processing unit  10  of the antenna apparatus in accordance with Embodiment 1 of the disclosure. 
     In  FIGS. 1 and 2 , a carrier signal generating unit  1  is, for example, a signal oscillator for generating a radio frequency carrier signal. 
     A divider  2  divides the carrier signal generated by the carrier signal generating unit  1  into K carrier signals (K is an integer equal to or more than two) and outputs the K carrier signals to an amplitude/phase controlling unit  30 . 
     An array antenna  3  includes K element antennas  3 - 1  to  3 -K, and the element antennas  3 - 1  to  3 -K radiate carrier signals whose amplitudes and phases are adjusted by amplitude/phase adjusters  31 - 1  to  31 -K in the amplitude/phase controlling unit  30  into space. 
     A communication signal generating unit  4  is implemented by, for example, a semiconductor integrated circuit having a central processing unit (CPU) mounted thereon, a single-chip microcomputer, or the like. 
     The communication signal generating unit  4  performs, for example, a process of generating a communication signal d(t) which is a signal to be communicated, by performing a baseband modulation process such as QPSK on a transmission bit sequence which is provided from an external source. 
     Although here an example in which the modulation scheme for the transmission bit sequence is QPSK is shown, the modulation scheme is not limited to QPSK and, for example, a modulation scheme such as binary phase shift keying (BPSK), 16 quadrature amplitude modulation (QAM), or 64QAM may be used. 
     An interference signal generating unit  5  is implemented by, for example, a semiconductor integrated circuit having a CPU mounted thereon, a single-chip microcomputer, or the like. 
     The interference signal generating unit  5  performs a process of generating an interference signal i(t) which serves as a disturbing wave for the communication signal d(t) generated by the communication signal generating unit  4 . 
     Note that the modulation scheme used when the interference signal generating unit  5  generates the interference signal i(t) may be the same as or different from the modulation scheme used when the communication signal generating unit  4  generates the communication signal d(t). Alternatively, the interference signal i(t) generated by the interference signal generating unit  5  may be a random-phase signal without depending on the modulation scheme. 
     The signal processing unit  10  includes a communication excitation distribution calculating unit  11 , an interference excitation distribution calculating unit  14 , a beam-scanning phase distribution setting unit  18 , a weight setting unit  19 , an excitation distribution combining unit  20 , and an antenna pattern displaying unit  21 . 
     The signal processing unit  10  performs a process of calculating an excitation distribution for the array antenna  3 , i.e., an excitation distribution for controlling the amplitudes and phases of carrier signals. 
     The communication excitation distribution calculating unit  11  in the signal processing unit  10  includes a sum-pattern excitation phase distribution setting unit  12  and a communication excitation distribution calculation processing unit  13 . 
     The sum-pattern excitation phase distribution setting unit  12  is implemented by, for example, a sum-pattern excitation phase distribution setting processing circuit  41  shown in  FIG. 2 . 
     The sum-pattern excitation phase distribution setting unit  12  performs a process of setting a sum-pattern excitation phase distribution S for the array antenna  3  as an excitation phase distribution that directs a main lobe of a communication beam which is a radio wave that transmits the communication signal d(t) toward a communication direction. 
     The communication excitation distribution calculation processing unit  13  is implemented by, for example, a communication excitation distribution calculation processing circuit  42  shown in  FIG. 2 . 
     The communication excitation distribution calculation processing unit  13  performs a process of calculating an excitation distribution W 1 ( t ) of the communication beam, using the excitation phase distribution S set by the sum-pattern excitation phase distribution setting unit  12 . 
     The interference excitation distribution calculating unit  14  includes a difference-pattern excitation phase distribution setting unit  15 , a difference-pattern excitation amplitude distribution setting unit  16 , and an interference excitation distribution calculation processing unit  17 . 
     The difference-pattern excitation phase distribution setting unit  15  is implemented by, for example, a difference-pattern excitation phase distribution setting processing circuit  43  shown in  FIG. 2 . 
     The difference-pattern excitation phase distribution setting unit  15  performs a process of setting a difference-pattern excitation phase distribution D for the array antenna  3  as an excitation phase distribution that forms a null in an antenna pattern toward the communication direction. 
     The difference-pattern excitation amplitude distribution setting unit  16  is implemented by, for example, a difference-pattern excitation amplitude distribution setting processing circuit  44  shown in  FIG. 2 . 
     The difference-pattern excitation amplitude distribution setting unit  16  performs a process of setting an excitation amplitude distribution A in which the gain of the interference beam which is a radio wave that transmits the interference signal i(t) is increased in the direction corresponding to a sidelobe direction of the communication beam. 
     The interference excitation distribution calculation processing unit  17  is implemented by, for example, an interference excitation distribution calculation processing circuit  45  shown in  FIG. 2 . 
     The interference excitation distribution calculation processing unit  17  performs a process of calculating an excitation distribution W 2 ( t ) of the interference beam by using the excitation phase distribution D set by the difference-pattern excitation phase distribution setting unit  15  and the excitation amplitude distribution A set by the difference-pattern excitation amplitude distribution setting unit  16 . 
     The beam-scanning phase distribution setting unit  18  is implemented by, for example, a beam-scanning phase distribution setting processing circuit  46  shown in  FIG. 2 . 
     The beam-scanning phase distribution setting unit  18  performs a process of setting a beam-scanning phase distribution P that determines the communication direction. 
     The weight setting unit  19  is implemented by, for example, a weight setting processing circuit  47  shown in  FIG. 2 . 
     The weight setting unit  19  performs a process of setting a weight m for the excitation distribution W 1 ( t ) of the communication beam calculated by the communication excitation distribution calculating unit  11  and a weight n for the excitation distribution W 2 ( t ) of the interference beam calculated by the interference excitation distribution calculating unit  14 . 
     The excitation distribution combining unit  20  is implemented by, for example, an excitation distribution combining processing circuit  48  shown in  FIG. 2 . 
     The excitation distribution combining unit  20  performs a process of combining the excitation distribution W 1 ( t ) of the communication beam calculated by the communication excitation distribution calculating unit and the excitation distribution W 2 ( t ) of the interference beam calculated by the interference excitation distribution calculating unit  14 , in accordance with the weights m and n set by the weight setting unit  19 . 
     In addition, the excitation distribution combining unit  20  performs a process of calculating a combined excitation distribution E(t) (combined excitation distribution) by multiplying the excitation distribution which is obtained by combining the excitation distribution W 1 ( t ) and the excitation distribution W 2 ( t ), by the beam-scanning phase distribution P set by the beam-scanning phase distribution setting unit  18 , and outputting the combined excitation distribution E(t). 
     The antenna pattern displaying unit  21  is implemented by, for example, an antenna pattern display processing circuit  49  shown in  FIG. 2 . 
     The antenna pattern displaying unit  21  performs a process of computing an antenna pattern from the combined excitation distribution E(t) outputted from the excitation distribution combining unit  20 , and outputting the antenna pattern to a display  6 . 
     The display  6  includes, for example, a liquid crystal display, etc., and displays the antenna pattern outputted from the antenna pattern displaying unit  21 . 
     The amplitude/phase controlling unit  30  includes the amplitude/phase adjusters  31 - 1  to  31 -K and a controller  32 , and controls the amplitudes and phases of carrier signals to be provided to the element antennas  3 - 1  to  3 -K, in accordance with the combined excitation distribution E(t) outputted from the excitation distribution combining unit  20 . 
     The amplitude/phase adjusters  31 - 1  to  31 -K each include a phase controlling device  31   a  and an amplitude controlling device  31   b.    
     The phase controlling device  31   a  includes, for example, a phase shifter and adjusts the phase of a carrier signal divide by the divider  2 , in accordance with the amount of phase adjustment indicated by a control signal outputted from the controller  32 . 
     The amplitude controlling device  31   b  includes, for example, a variable gain amplifier and adjusts the amplitude of the carrier signal whose phase has been adjusted by the phase controlling device  31   a , in accordance with the amount of amplitude adjustment indicated by a control signal outputted from the controller  32 . 
     The controller  32  controls the amounts of adjustment of amplitude and phase for the amplitude/phase adjusters  31 - 1  to  31 -K, in accordance with the combined excitation distribution E(t) outputted from the excitation distribution combining unit  20 . 
     In the example illustrated in  FIG. 1 , it is assumed that each of the communication excitation distribution calculating unit  11 , the interference excitation distribution calculating unit  14 , the beam-scanning phase distribution setting unit  18 , the weight setting unit  19 , the excitation distribution combining unit  20 , and the antenna pattern displaying unit  21  which are components of the signal processing unit  10  is implemented by dedicated hardware such as that shown in  FIG. 2 . 
     Namely, it is assumed that the signal processing unit  10  is implemented by the sum-pattern excitation phase distribution setting processing circuit  41 , the communication excitation distribution calculation processing circuit  42 , the difference-pattern excitation phase distribution setting processing circuit  43 , the difference-pattern excitation amplitude distribution setting processing circuit  44 , the interference excitation distribution calculation processing circuit  45 , the beam-scanning phase distribution setting processing circuit  46 , the weight setting processing circuit  47 , the excitation distribution combining processing circuit  48 , and the antenna pattern display processing circuit  49 . 
     Each of the sum-pattern excitation phase distribution setting processing circuit  41 , the communication excitation distribution calculation processing circuit  42 , the difference-pattern excitation phase distribution setting processing circuit  43 , the difference-pattern excitation amplitude distribution setting processing circuit  44 , the interference excitation distribution calculation processing circuit  45 , the beam-scanning phase distribution setting processing circuit  46 , the weight setting processing circuit  47 , the excitation distribution combining processing circuit  48 , and the antenna pattern display processing circuit  49  may be, for example, a single circuit, a combined circuit, a programmed processor, a parallel programmed processor, an application specific integrated circuit (ASIC), a field-programmable gate array (FPGA), or a combination thereof. 
     Note, however, that the components of the signal processing unit  10  in the antenna apparatus are not limited to those implemented by dedicated hardware, and the signal processing unit  10  may be implemented by software, firmware, or a combination of software and firmware. 
     The software or firmware is stored as a program in a memory of a computer. The computer refers to hardware that executes the program and may be, for example, a central processing unit (CPU), a processing device, a computing device, a microprocessor, a microcomputer, a processor, a digital signal processor (DSP), etc. 
       FIG. 3  is a hardware configuration diagram of a computer for a case in which the signal processing unit  10  is implemented by software, firmware, or the like. 
     In a case in which the signal processing unit  10  is implemented by software, firmware, or the like, a program for causing a computer to perform processing procedures of the communication excitation distribution calculating unit  11 , the interference excitation distribution calculating unit  14 , the beam-scanning phase distribution setting unit  18 , the weight setting unit  19 , the excitation distribution combining unit  20 , and the antenna pattern displaying unit  21  is stored in a memory  51 , and a processor  52  of the computer executes the program stored in the memory  51 . 
     The memory  51  of the computer may be, for example, a nonvolatile or volatile semiconductor memory such as a random access memory (RAM), a read only memory (ROM), a flash memory, an erasable programmable read only memory (EPROM), or an electrically erasable programmable read only memory (EEPROM), a magnetic disc, a flexible disc, an optical disc, a compact disc, a MiniDisc, a digital versatile disc (DVD), etc. 
     Note that in  FIG. 3  an input interface device  53  is, for example, an interface device having a signal input/output port such as a universal serial bus (USB) port or a serial port. 
     The input interface device  53  is connected to the communication signal generating unit  4  and the interference signal generating unit  5  and accepts, as input, the communication signal d(t) outputted from the communication signal generating unit  4  and the interference signal i(t) outputted from the interference signal generating unit  5 . 
     An output interface device  54  is, for example, an interface device having a signal input/output port such as a USB port or a serial port. 
     The output interface device  54  is connected to the amplitude/phase controlling unit  30  and outputs the combined excitation distribution E(t) outputted from the excitation distribution combining unit  20 , to the amplitude/phase controlling unit  30 . 
     A display interface device  55  is an interface device for establishing connection with the display  6  and outputs the antenna pattern outputted from the antenna pattern displaying unit  21 , to the display  6 . 
       FIG. 4  is a flowchart showing the operation of the carrier signal generating unit  1 , the divider  2 , the amplitude/phase controlling unit  30 , and the element antennas  3 - 1  to  3 -K. 
       FIG. 5  is a flowchart showing the processing operations of the communication signal generating unit  4  and the communication excitation distribution calculating unit  11 . 
       FIG. 6  is a flowchart showing the processing operations of the interference signal generating unit  5  and the interference excitation distribution calculating unit  14 . 
       FIG. 7  is a flowchart showing the processing operations of the beam-scanning phase distribution setting unit  18 , the weight setting unit  19 , and the excitation distribution combining unit  20 . 
       FIG. 8  is an illustrative diagram showing an amplitude characteristic of a communication beam calculated from an excitation distribution W 1 ( t ) of the communication beam, and an amplitude characteristic of an interference beam calculated from an excitation distribution W 2 ( t ) of the interference beam. 
     In  FIG. 8 , G 1  indicates the amplitude characteristic of the communication beam and G 2  indicates the amplitude characteristic of the interference beam. 
       FIG. 9  is an illustrative diagram showing a phase characteristic of an antenna pattern calculated from a combined excitation distribution E(t). 
     Next, the operations will be described. 
     The carrier signal generating unit  1  generates, for example, a radio frequency carrier signal and outputs the carrier signal to the divider  2  (step ST 1  in  FIG. 4 ). 
     When the divider  2  receives the carrier signal from the carrier signal generating unit  1 , the divider  2  divides the carrier signal into K carrier signals and outputs the K carrier signals to the amplitude/phase controlling unit  30  (step ST 2 ). 
     The communication signal generating unit  4  generates a communication signal d(t) which is a signal to be communicated, by, for example, performing a baseband modulation process such as QPSK on a transmission bit sequence which is provided from an external source, and outputs the communication signal d(t) to the communication excitation distribution calculating unit  11  in the signal processing unit  10  (step ST 11  in  FIG. 5 ). 
     Here, t represents the time, and when the modulation scheme is QPSK, the constellation points of the communication signal d(t) are exp(jπ/4), exp(j3π/4), exp(−j3π/4), and exp(−jπ/4). 
     The sum-pattern excitation phase distribution setting unit  12  in the communication excitation distribution calculating unit  11  sets a sum-pattern excitation phase distribution S for the array antenna  3  as an excitation phase distribution that directs a main lobe of a communication beam toward a communication direction (step ST 12 ). 
     The sum-pattern excitation phase distribution S is, though detailed description thereof is omitted as the sum-pattern excitation phase distribution S is a publicly known excitation phase distribution, represented by a matrix with K rows and one column, and each element of the matrix is a complex number. Since the sum-pattern excitation phase is 0 degrees, as shown in Equation (1) below, the excitation phase distribution S is a matrix having exp(j0) as elements: 
     
       
         
           
             
               
                 
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     It is known that by calculating an excitation distribution of the communication beam using the sum-pattern excitation phase distribution S, an amplitude characteristic like G 1  in  FIG. 8  can be obtained as an amplitude characteristic of the communication beam. 
     In the amplitude characteristic G 1  of the communication beam shown in  FIG. 8 , since a main lobe of the communication beam has its peak at 0 degrees, a 0-degree direction is a communication direction. 
     When the sum-pattern excitation phase distribution setting unit  12  sets the sum-pattern excitation phase distribution S, as shown in Equation (2) below, the communication excitation distribution calculation processing unit  13  calculates an excitation distribution W 1 ( t ) of the communication beam by multiplying the communication signal d(t) outputted from the communication signal generating unit  4  by the excitation phase distribution S (step ST 13 ):
 
 W 1( t )= d ( t )· S   (2)
 
     The interference signal generating unit  5  generates an interference signal i(t) which serves as a disturbing wave for the communication signal d(t) generated by the communication signal generating unit  4 , and outputs the interference signal i(t) to the interference excitation distribution calculating unit  14  in the signal processing unit  10  (step ST 21  in  FIG. 6 ). For example, as the interference signal i(t), a random-phase signal is generated. 
     The difference-pattern excitation phase distribution setting unit  15  in the interference excitation distribution calculating unit  14  sets a difference-pattern excitation phase distribution D for the array antenna  3  as an excitation phase distribution that forms a null of an antenna pattern in the communication direction in an interference beam which is a radio wave that transmits the interference signal i(t) (step ST 22 ). 
     The difference-pattern excitation phase distribution D is, though detailed description thereof is omitted as the difference-pattern excitation phase distribution D is a publicly known excitation phase distribution, represented by a matrix with K rows and one column. 
     For example, if the elements of the first row to (K/2)nd row of the matrix are exp(jπ) and the elements of the ((K/2)+1)st row to Kth row are exp(j0), then the difference-pattern excitation phase distribution D is represented as shown in Equation (3) below: 
     
       
         
           
             
               
                 
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     It is known that by calculating an excitation distribution of the interference beam using the difference-pattern excitation phase distribution D, an amplitude characteristic like G 2  in  FIG. 8  can be obtained as an amplitude characteristic of the interference beam. 
     In the amplitude characteristic G 2  of the interference beam shown in  FIG. 8 , a null of an antenna pattern is formed in a 0-degree direction. 
     In Embodiment 1, in view of the fact that the amount of computation is smaller for a process of combining excitation distributions of two beams having an orthogonal relationship than for a process of combining two beams having no orthogonal relationship, a communication beam and an interference beam that have an orthogonal relationship are generated. Hence, it is shown that the sum-pattern excitation phase distribution setting unit  12  sets a sum-pattern excitation phase distribution S and the difference-pattern excitation phase distribution setting unit  15  sets a difference-pattern excitation phase distribution D. 
     Note, however, that this is merely an example, and a communication beam and an interference beam that have an orthogonal relationship may be generated by setting excitation phase distributions other than sum-pattern and difference-pattern excitation phase distributions. 
     In addition, excitation phase distributions by which a communication beam and an interference beam that have no orthogonal relationship are generated may be set, though it is assumed that the amount of computation increases more or less. Even in a case of performing a process of combining excitation distributions of a communication beam and an interference beam that have no orthogonal relationship, the amount of computation is significantly reduced over a case of calculating an excitation distribution using an optimization technique. 
     The difference-pattern excitation amplitude distribution setting unit  16  sets a difference-pattern excitation amplitude distribution A in which the gain of the interference beam is increased in a direction corresponding to a sidelobe direction of the communication beam, to make it difficult to demodulate the communication signal d(t) in the sidelobe direction of the communication beam (step ST 23  in  FIG. 6 ). 
     As shown in  FIG. 8 , when the gains of the interference beam in the sidelobe directions of the communication beam are higher than the sidelobe gains of the communication beam, the interference signal i(t) is larger than the communication signal d(t). In this case, since the communication signal d(t) is buried in the interference signal i(t), it becomes difficult to demodulate the communication signal d(t) in the sidelobe directions of the communication beam. 
     Hence, in order to make the relationship between the amplitude characteristic of the communication beam and the amplitude characteristic of the interference beam like the relationship between the amplitude characteristics G 1  and G 2  shown in  FIG. 8 , the difference-pattern excitation amplitude distribution setting unit  16  sets a difference-pattern excitation amplitude distribution A in which gains of the interference beam are increased in the sidelobe directions of the communication beam. 
     The difference-pattern excitation amplitude distribution A is represented by a matrix with K rows and one column, and for example, each element of the matrix is a positive integer. The difference-pattern excitation amplitude distribution A can be obtained from, for example, Taylor distribution, etc. 
     The Taylor distribution is a distribution in which the sidelobe level decreases as it gets further away from the main beam, and thus, a distribution that is obtained by modifying the Taylor distribution in such a manner that the sidelobe level increases as it gets further away from the main beam may be used as the difference-pattern excitation amplitude distribution A. 
     Namely, although the Taylor distribution is known to be a distribution that decreases the sidelobe level, by using the Taylor distribution for the difference-pattern excitation amplitude distribution A, the sidelobe level can be increased and the gains of the interference beam can be increased in the sidelobe directions of the communication beam. 
     When the difference-pattern excitation phase distribution setting unit  15  sets the excitation phase distribution D and the difference-pattern excitation amplitude distribution setting unit  16  sets the excitation amplitude distribution A, as shown in Equation (4) below, the interference excitation distribution calculation processing unit  17  calculates an excitation distribution W 2 ( t ) of the interference beam by multiplying the interference signal i(t) outputted from the interference signal generating unit  5  by the excitation phase distribution D and a diagonal matrix of the excitation amplitude distribution A (step ST 24  in  FIG. 6 ):
 
 W 2( t )= i ( t )·diag( A )· D   (4)
 
     In Eq. (4), diag(A) is the diagonal matrix having A as diagonal elements. 
     The beam-scanning phase distribution setting unit  18  sets a beam-scanning phase distribution P that determines the communication direction (step ST 31  in  FIG. 7 ). 
     For example, there is a case in which the sum-pattern excitation phase distribution setting unit  12  sets an excitation phase distribution S that directs the main lobe of the communication beam in the 0-degree direction, and the difference-pattern excitation phase distribution setting unit  15  sets an excitation phase distribution D that forms a null of an antenna pattern in the 0-degree direction. In a case in which, when the excitation phase distribution S and the excitation phase distribution D are thus set, for example, the communication direction needs to be directed in a 30-degree direction, a 45-degree direction, etc., the beam-scanning phase distribution setting unit  18  sets a beam-scanning phase distribution P in which the communication direction indicates the 30-degree direction or 45-degree direction, by which the communication direction is changed to the 30-degree direction or 45-degree direction. 
     In this case, the main lobe of the communication beam is directed in the 30-degree direction or 45-degree direction, and for the interference beam the null of the antenna pattern is formed in the 30-degree direction or 45-degree direction. 
     The beam-scanning phase distribution P is represented by a matrix with K rows and one column, and each element of the matrix is a complex number.  FIG. 8  shows an example of setting a beam-scanning phase distribution P that sets the communication direction to the 0-degree direction. 
     When the communication direction needs to be switched as appropriate, the beam-scanning phase distribution setting unit  18  needs to be implemented; however, when the communication direction is fixed, e.g., when the communication direction is always a front direction of the array antenna  3 , the beam-scanning phase distribution setting unit  18  may not be implemented and the excitation distribution combining unit  20  may store a beam-scanning phase distribution P which is set beforehand. 
     The weight setting unit  19  sets weights m and n (m and n are positive integers) for the excitation distribution W 1 ( t ) of the communication beam calculated by the communication excitation distribution calculating unit and the excitation distribution W 2 ( t ) of the interference beam calculated by the interference excitation distribution calculating unit  14  (step ST 32 ). 
     The weights m and n are to set a combining ratio of the excitation distribution W 1 ( t ) of the communication beam and the excitation distribution W 2 ( t ) of the interference beam. For example, when m&lt;n, the degree of contribution of the excitation distribution W 2 ( t ) of the interference beam can be increased in a combined excitation distribution E(t) of the excitation distribution W 1 ( t ) and the excitation distribution W 2 ( t ). Namely, the interference signal i(t) which is transmitted by the interference beam is increased, by which a communicable area can be narrowed. 
     On the other hand, when m&gt;n, the degree of contribution of the excitation distribution W 2 ( t ) of the interference beam can be reduced in the combined excitation distribution E(t) of the excitation distribution W 1 ( t ) and the excitation distribution W 2 ( t ). Namely, the interference signal i(t) which is transmitted by the interference beam is reduced, by which the communicable area can be widened. 
     Note that when the excitation distribution W 1 ( t ) of the communication beam and the excitation distribution W 2 ( t ) of the interference beam are always combined at the same ratio without changing the combining ratio thereof, e.g., when the excitation distribution W 1 ( t ) of the communication beam and the excitation distribution W 2 ( t ) of the interference beam are always combined such that m=n=1, the weight setting unit  19  may not be implemented and the excitation distribution combining unit  20  may store weights m and n which are set beforehand. 
     When the beam-scanning phase distribution setting unit  18  sets the beam-scanning phase distribution P and the weight setting unit  19  sets the weights m and n, the excitation distribution combining unit  20  combines the excitation distribution W 1 ( t ) of the communication beam calculated by the communication excitation distribution calculating unit  11  and the excitation distribution W 2 ( t ) of the interference beam calculated by the interference excitation distribution calculating unit  14 , in accordance with the weights m and n. 
     Then, as shown in equation (5) below, the excitation distribution combining unit  20  calculates a combined excitation distribution E(t) by multiplying the excitation distribution which is obtained by combining the excitation distribution W 1 ( t ) and the excitation distribution W 2 ( t ), by a diagonal matrix of the beam-scanning phase distribution P (step ST 33 ):
 
 E ( t )=diag( P )·{ m·W 1( t )+ n·W 2( t )}  (5)
 
     The combined excitation distribution E(t) is obtained by combining the communication beam and the interference beam that have an orthogonal relationship, and as can also be seen from Eq. (5), only simple computation is performed in a process of combining the communication beam and the interference beam that have an orthogonal relationship. Namely, only by performing addition and multiplication of the matrix, the communication beam and the interference beam can be combined. Hence, comparing to a case of calculating a combined excitation distribution E(t) using an optimization technique, the amount of computation is about a few percent to a few tenths of a percent. 
     When the excitation distribution combining unit  20  calculates the combined excitation distribution E(t), the excitation distribution combining unit  20  outputs the combined excitation distribution E(t) as an excitation distribution for the array antenna  3  to the amplitude/phase controlling unit  30 . 
     When the controller  32  in the amplitude/phase controlling unit  30  receives the combined excitation distribution E(t) from the excitation distribution combining unit  20 , the controller  32  outputs control signals indicating amounts of adjustment of amplitude and phase for the amplitude/phase adjusters  31 - 1  to  31 -K to the amplitude/phase adjusters  31 - 1  to  31 -K, in accordance with the combined excitation distribution E(t). 
     A process of identifying the amounts of adjustment of amplitude and phase from the combined excitation distribution E(t) and outputting control signals indicating the amounts of adjustment of amplitude and phase itself is a publicly known technique and thus detailed description thereof is omitted. 
     When each of the phase controlling devices  31   a  in the amplitude/phase adjusters  31 - 1  to  31 -K receives a control signal from the controller  32 , the phase controlling device  31   a  adjusts the phase of the carrier signal divided by the divider  2 , in accordance with the amount of phase adjustment indicated by the control signal, and outputs the phase-adjusted carrier signal to a corresponding amplitude controlling device  31   b  (step ST 3  in  FIG. 4 ). 
     When each of the amplitude controlling devices  31   b  in the amplitude/phase adjusters  31 - 1  to  31 -K receives a control signal from the controller  32 , the amplitude controlling device  31   b  adjusts the amplitude of the carrier signal outputted from a corresponding phase controlling device  31   a , in accordance with the amount of amplitude adjustment indicated by the control signal, and outputs the amplitude-adjusted carrier signal to a corresponding one of the element antennas  3 - 1  to  3 -K (step ST 4 ). 
     By this, the amplitude- and phase-adjusted carrier signals are radiated into space from the element antennas  3 - 1  to  3 -K (step ST 5 ). 
     A communication beam and an interference beam that are formed by the carrier signals radiated from the element antennas  3 - 1  to  3 -K are, for example, those shown in  FIG. 8 . In the example illustrated in  FIG. 8 , since the amplitude characteristic of the communication beam is G 1 , a main lobe has its peak at 0 degrees. In addition, since the amplitude characteristic of the interference beam is G 2 , a null of an antenna pattern is formed in a 0-degree direction. Hence, a receiving station present in the 0-degree direction can receive the communication signal d(t) transmitted by the communication beam, but the interference signal i(t) is not transmitted thereto. Therefore, the communication signal d(t) can be demodulated without being influenced by the interference signal i(t). 
     In addition, in Embodiment 1, the communication signal d(t) is subjected to a QPSK modulation process and a constellation point is present at a location where the phase is π/4 (=45 degrees). As shown in  FIG. 9 , since the phase of the antenna pattern is π/4 (=45 degrees) in the 0-degree direction, the receiving station present in the 0-degree direction can demodulate the constellation point present at the location where the phase is π/4 (=45 degrees). 
     In the sidelobe directions of the communication beam, the gains of the interference beam are larger than the gains of the communication beam. 
     Hence, receiving stations present in the sidelobe directions of the communication beam are greatly influenced by the interference signal i(t) transmitted by the interference beam and thus even if the receiving stations can receive the communication signal d(t) transmitted by the communication beam, the receiving stations have difficulty in demodulating the communication signal d(t). 
     Thus, since demodulation of the communication signal d(t) is possible only at an angle at which a communication direction is 0 degrees or at angles near this direction, a communicable area is limited. 
     As is clear from the above, according to Embodiment 1, the configuration is such that there are provided the communication excitation distribution calculating unit  11  that calculates an excitation distribution W 1 ( t ) of a communication beam using an excitation phase distribution S that directs a main lobe of the communication beam in a communication direction; and the interference excitation distribution calculating unit  14  that calculates an excitation distribution W 2 ( t ) of an interference beam using an excitation phase distribution D that forms a null of an antenna pattern in the communication direction, and the excitation distribution combining unit  20  combines the excitation distribution W 1 ( t ) of the communication beam calculated by the communication excitation distribution calculating unit and the excitation distribution W 2 ( t ) of the interference beam calculated by the interference excitation distribution calculating unit  14 , and thus, an advantageous effect of being able to reduce the amount of computation for an excitation distribution for the array antenna  3  that is used to implement secure communication with a limited communicable area is provided. 
     In addition, according to Embodiment 1, the configuration is such that there is provided the weight setting unit  19  that sets weights m and n for the excitation distribution W 1 ( t ) of the communication beam calculated by the communication excitation distribution calculating unit  11  and the excitation distribution W 2 ( t ) of the interference beam calculated by the interference excitation distribution calculating unit  14 , and the excitation distribution combining unit  20  combines the excitation distribution W 1 ( t ) of the communication beam and the excitation distribution W 2 ( t ) of the interference beam, in accordance with the weights m and n set by the weight setting unit  19 , and thus, an advantageous effect of being able to change the range of a communicable area as appropriate is provided. 
     According to Embodiment 1, the configuration is such that there is provided the beam-scanning phase distribution setting unit  18  that sets a beam-scanning phase distribution P that determines the communication direction, and the excitation distribution combining unit combines the excitation distribution W 1 ( t ) of the communication beam and the excitation distribution W 2 ( t ) of the interference beam and calculates a combined excitation distribution E(t) by multiplying the combined excitation distribution by a diagonal matrix of the beam-scanning phase distribution P set by the beam-scanning phase distribution setting unit  18 , and thus, an advantageous effect of being able to change the communication direction as appropriate is provided. 
     In addition, according to Embodiment 1, the configuration is such that the interference excitation distribution calculating unit  14  sets an excitation amplitude distribution A in which gains of the interference beam are increased in directions corresponding to sidelobe directions of the communication beam, and multiplies an interference signal i(t) by a diagonal matrix of the excitation amplitude distribution A, and thus, the sidelobe gains of the communication beam can be relatively reduced compared to the gains of the interference beam. Hence, an advantageous effect of being able to improve secrecy by making it difficult for receiving stations present in the sidelobe directions of the communication beam to demodulate the communication signal d(t) is provided. 
     In Embodiment 1, an example is shown in which while a communication signal d(t) and an interference signal i(t) are generated, a combined excitation distribution E(t) is calculated as an excitation distribution for the array antenna  3 . 
     This is merely an example. The excitation distribution combining unit  20  may calculate beforehand a combined excitation distribution E(t) for a communication signal d(t) and an interference signal i(t), and store the combined excitation distribution E(t) in a storage device such as the memory  51 . Then, when a communication signal d(t) and an interference signal i(t) are received, a combined excitation distribution E(t) for the communication signal d(t) and the interference signal i(t) may be read from the memory  51 , and the combined excitation distribution E(t) may be outputted to the amplitude/phase controlling unit  30 . 
     In Embodiment 1, an example is shown in which the beam-scanning phase distribution setting unit  18  that sets a beam-scanning phase distribution P is provided, and the excitation distribution combining unit  20  multiplies an excitation distribution which is obtained by combining an excitation distribution W 1 ( t ) of a communication beam and an excitation distribution W 2 ( t ) of an interference beam, by a diagonal matrix of the beam-scanning phase distribution P. 
     This is merely an example. Alternatively, two beam-scanning phase distribution setting units  18  may be implemented, and an excitation distribution W 1 ( t ) of a communication beam may be multiplied by a diagonal matrix of a beam-scanning phase distribution P 1  set by one of the beam-scanning phase distribution setting units  18 , and an excitation distribution W 2 ( t ) of an interference beam may be multiplied by a diagonal matrix of a beam-scanning phase distribution P 2  set by the other beam-scanning phase distribution setting unit  18 . Then, the excitation distribution combining unit  20  may combine the excitation distribution W 1 ( t ) of the communication beam multiplied by the diagonal matrix of the beam-scanning phase distribution P 1  and the excitation distribution W 2 ( t ) of the interference beam multiplied by the diagonal matrix of the beam-scanning phase distribution P 2 . 
     Embodiment 2 
     In the above-described Embodiment 1, an example is shown in which in order to relatively reduce the sidelobe gains of a communication beam compared to the gains of an interference beam, the interference excitation distribution calculation processing unit  17  multiplies an interference signal i(t) by a diagonal matrix of an excitation amplitude distribution A set by the difference-pattern excitation amplitude distribution setting unit  16 . 
     In this Embodiment 2, an example will be described in which the communication excitation distribution calculation processing unit  13  multiplies a communication signal d(t) by a diagonal matrix of an excitation amplitude distribution in which a gain in a sidelobe direction of a communication beam is reduced. 
       FIG. 10  is a configuration diagram showing an antenna apparatus of Embodiment 2 of the invention, and  FIG. 11  is a hardware configuration diagram of a signal processing unit  10  of the antenna apparatus of Embodiment 2 of the invention. 
     In  FIGS. 10 and 11 , the same reference signs as those in  FIGS. 1 and 2  indicate the same or corresponding portions and thus description thereof is omitted. 
     A sum-pattern excitation amplitude distribution setting unit  22  is implemented by, for example, a sum-pattern excitation amplitude distribution setting processing circuit  50  shown in  FIG. 11 . 
     The sum-pattern excitation amplitude distribution setting unit  22  performs a process of setting an excitation amplitude distribution B in which a gain in a sidelobe direction of a communication beam is reduced. 
     A communication excitation distribution calculation processing unit  23  is implemented by, for example, a communication excitation distribution calculation processing circuit  42  shown in  FIG. 11 . 
     The communication excitation distribution calculation processing unit  23  performs a process of calculating an excitation distribution W 1 ( t ) of the communication beam using an excitation phase distribution S set by the sum-pattern excitation phase distribution setting unit  12  and the excitation amplitude distribution B set by the sum-pattern excitation amplitude distribution setting unit  22 . 
     Next, operation will be described. 
     Processing operations other than those of the communication excitation distribution calculating unit  11  and the interference excitation distribution calculating unit  14  are the same as those in the above-described Embodiment 1, and thus, here only the processing operations of the communication excitation distribution calculating unit  11  and the interference excitation distribution calculating unit  14  will be described. 
     The sum-pattern excitation amplitude distribution setting unit  22  in the communication excitation distribution calculating unit  11  sets a sum-pattern excitation amplitude distribution B in which a gain in a sidelobe direction of a communication beam is reduced, to make it difficult to demodulate a communication signal d(t) in the sidelobe direction of the communication beam. 
     The sum-pattern excitation amplitude distribution B is represented by a matrix with K rows and one column, and for example, each element of the matrix is a positive integer. For the sum-pattern excitation amplitude distribution B, for example, Taylor distribution, etc., can be used. 
     The sum-pattern excitation phase distribution setting unit  12  in the communication excitation distribution calculating unit  11  sets a sum-pattern excitation phase distribution S as in the above-described Embodiment 1. 
     As shown in Equation (6) below, the communication excitation distribution calculation processing unit  23  in the communication excitation distribution calculating unit calculates an excitation distribution W 1 ( t ) of the communication beam by multiplying the communication signal d(t) outputted from the communication signal generating unit  4  by the sum-pattern excitation phase distribution S and a diagonal matrix of the excitation amplitude distribution B:
 
 W 1( t )= d ( t )·diag( B )· S   (6)
 
     In Eq. (6), diag(B) is the diagonal matrix having B as diagonal elements. 
     When the difference-pattern excitation phase distribution setting unit  15  sets an excitation phase distribution D as in the above-described Embodiment 1, as shown in Equation (7) below, the interference excitation distribution calculation processing unit  17  calculates an excitation distribution W 2 ( t ) of an interference beam by multiplying an interference signal i(t) outputted from the interference signal generating unit  5  by the excitation phase distribution D:
 
 W 2( t )= i ( t )· D   (7)
 
     As is clear from the above, according to Embodiment 2, the configuration is such that the communication excitation distribution calculating unit  11  sets a sum-pattern excitation amplitude distribution B in which the gain in sidelobe direction of the communication beam is reduced, and multiplies a communication signal d(t) by a diagonal matrix of the excitation amplitude distribution B, and thus, the sidelobe gains of the communication beam can be relatively reduced compared to the gains of an interference beam. Hence, an advantageous effect of being able to improve secrecy by making it difficult for receiving stations present in the sidelobe directions of the communication beam to demodulate the communication signal d(t) is provided. 
     Embodiment 3 
     In the above-described Embodiment 1, an example is shown in which in order to relatively reduce the sidelobe gains of a communication beam compared to the gains of an interference beam, the interference excitation distribution calculation processing unit  17  multiplies an interference signal i(t) by a diagonal matrix of an excitation amplitude distribution A set by the difference-pattern excitation amplitude distribution setting unit  16 . 
     In this Embodiment 3, furthermore, the communication excitation distribution calculation processing unit  13  may multiply a communication signal d(t) by a diagonal matrix of an excitation amplitude distribution B in which the gain in sidelobe direction of the communication beam is reduced. 
       FIG. 12  is a configuration diagram showing an antenna apparatus of Embodiment 3 of the invention, and in  FIG. 12  the same reference signs as those in  FIGS. 1 and 10  indicate the same or corresponding portions and thus description thereof is omitted. 
     In Embodiment 3, the sum-pattern excitation amplitude distribution setting unit  22  is mounted on the communication excitation distribution calculating unit  11 , and the difference-pattern excitation amplitude distribution setting unit  16  is mounted on the interference excitation distribution calculating unit  14 . 
     Hence, when the sum-pattern excitation phase distribution setting unit  12  sets a sum-pattern excitation phase distribution S and the sum-pattern excitation amplitude distribution setting unit  22  sets a sum-pattern excitation amplitude distribution B, as in the above-described Embodiment 2, the communication excitation distribution calculation processing unit  23  in the communication excitation distribution calculating unit  11  calculates an excitation distribution W 1 ( t ) of a communication beam by multiplying a communication signal d(t) outputted from the communication signal generating unit  4  by the excitation phase distribution S and a diagonal matrix of the excitation amplitude distribution B. 
     In addition, when the difference-pattern excitation phase distribution setting unit  15  sets an excitation phase distribution D and the difference-pattern excitation amplitude distribution setting unit  16  sets an excitation amplitude distribution A, as in the above-described Embodiment 1, the interference excitation distribution calculation processing unit  17  in the interference excitation distribution calculating unit  14  calculates an excitation distribution W 2 ( t ) of an interference beam by multiplying an interference signal i(t) outputted from the interference signal generating unit  5  by the excitation phase distribution D and a diagonal matrix of the excitation amplitude distribution A. 
     By this, as in the above-described first and Embodiment 2s, the sidelobe gains of the communication beam can be relatively reduced compared to the gains of the interference beam. Hence, an advantageous effect of being able to improve secrecy by making it difficult for receiving stations present in sidelobe directions of the communication beam to demodulate the communication signal d(t) is provided. 
     In Embodiment 3, an example is shown in which in order to relatively reduce the sidelobe gains of the communication beam compared to the gains of the interference beam, the interference excitation distribution calculation processing unit  17  multiplies the interference signal i(t) by the diagonal matrix of the excitation amplitude distribution A set by the difference-pattern excitation amplitude distribution setting unit  16 . 
     This is merely an example, and the communication excitation distribution calculation processing unit  13  may multiply the communication signal d(t) by a diagonal matrix of an excitation amplitude distribution C in which a gain in sidelobe direction of the communication beam is increased within a range not exceeding the gain of the interference beam. 
     By this, the gains in the sidelobe directions of the communication beam increase within the range in which the gains in the sidelobe directions of the communication beam do not exceed the gains of the interference beam, and thus, the communication signal d(t) increases in the sidelobe directions; however, in this case, too, since the interference signal i(t) is larger than the communication signal d(t), it is difficult to demodulate the communication signal d(t) in the sidelobe directions of the communication beam. 
     Note that the sum-pattern excitation amplitude distribution C is represented by a matrix with K rows and one column, and for example, each element of the matrix is a positive integer. For the sum-pattern excitation amplitude distribution C, for example, a reverse-tapered excitation amplitude distribution can be used in which, of the element antennas  3 - 1  to  3 -K that form the array antenna  3 , element antennas disposed at the edges have a higher excitation amplitude distribution than an element antenna disposed at the center. By using such a reverse-tapered excitation amplitude distribution C, the beam width of the communication beam is narrowed, and thus, narrow coverage of a communication area can also be expected. 
     Embodiment 4 
     In the above-described first to Embodiment 3s, an example is shown in which each of the phase controlling devices  31   a  in the amplitude/phase adjusters  31 - 1  to  31 -K adjusts the phase of a carrier signal divide by the divider  2 , in accordance with the amount of phase adjustment indicated by a control signal outputted from the controller  32 , and each of the amplitude controlling devices  31   b  in the amplitude/phase adjusters  31 - 1  to  31 -K adjusts the amplitude of the carrier signal outputted from a corresponding phase controlling device  31   a , in accordance with the amount of amplitude adjustment indicated by a control signal outputted from the controller  32 . 
     In this Embodiment 4, the amplitude and phase of a carrier signal may be adjusted by digital signal processing. 
       FIG. 13  is a configuration diagram showing an antenna apparatus of the Embodiment 4 of the invention, and in  FIG. 13  the same reference signs as those in  FIGS. 1, 10, and 12  indicate the same or corresponding portions and thus description thereof is omitted. 
     A carrier signal generating unit  61  is a signal oscillator that generates a carrier signal which is a digital signal. 
     An amplitude/phase controlling unit  70  includes amplitude/phase adjusters  71 - 1  to  71 -K and a controller  72 , and controls the amplitudes and phases of carrier signals to be provided to the element antennas  3 - 1  to  3 -K, in accordance with a combined excitation distribution E(t) outputted from the excitation distribution combining unit  20 . 
     The amplitude/phase adjusters  71 - 1  to  71 -K each include a digital signal processor  71   a , a digital/analog converter (hereinafter, referred to as “D/A converter”)  71   b , and an amplifier  71   c.    
     The amplitude/phase adjusters  71 - 1  to  71 -K each adjust the phase of a carrier signal by digital signal processing according to the amount of phase adjustment indicated by a control signal outputted from the controller  72 , and adjust the amplitude of the carrier signal by digital signal processing in accordance with the amount of amplitude adjustment indicated by a control signal outputted from the controller  72 . 
     The controller  72  controls the amounts of adjustment of amplitude and phase for the amplitude/phase adjusters  71 - 1  to  71 -K, in accordance with the combined excitation distribution E(t) outputted from the excitation distribution combining unit  20 . 
     The digital signal processors  71   a  in the amplitude/phase adjusters  71 - 1  to  71 -K are implemented by, for example, a semiconductor integrated circuit having a CPU mounted thereon, a single-chip microcomputer, or the like. 
     Each digital signal processor  71   a  adjusts the amplitude and phase of a carrier signal by digital signal processing. 
     Each of the D/A converters  71   b  in the amplitude/phase adjusters  71 - 1  to  71 -K converts the carrier signal whose amplitude and phase have been adjusted by a corresponding digital signal processor  71   a  into an analog signal. 
     Each of the amplifiers  71   c  in the amplitude/phase adjusters  71 - 1  to  71 -K amplifies the carrier signal having been converted into the analog signal by a corresponding D/A converter  71   b , and outputs the amplified carrier signal to a corresponding one of the element antennas  3 - 1  to  3 -K. 
       FIG. 14  is a flowchart showing the operation of the carrier signal generating unit  61 , the amplitude/phase controlling unit  70 , and the element antennas  3 - 1  to  3 -K. 
     Next, operation will be described. 
     In the Embodiment 4, the processing operations of the signal processing unit  10  are the same as those of the above-described Embodiment 3, and thus, processing operations other than those of the signal processing unit  10  will be described. Note that the processing operations of the signal processing unit  10  may be the same as those of the above-described first and Embodiment 2s. 
     The carrier signal generating unit  61  generates a carrier signal which is a digital signal, and outputs the carrier signal to the amplitude/phase adjusters  71 - 1  to  71 -K in the amplitude/phase controlling unit  70  (step ST 41  in  FIG. 14 ). 
     When the excitation distribution combining unit  20  in the signal processing unit  10  calculates a combined excitation distribution E(t) as in the above-described Embodiment 3, the controller  72  in the amplitude/phase controlling unit  70  outputs control signals indicating the amounts of adjustment of amplitude and phase for the amplitude/phase adjusters  71 - 1  to  71 -K to the amplitude/phase adjusters  71 - 1  to  71 -K, in accordance with the combined excitation distribution E(t). 
     A process of identifying the amounts of adjustment of amplitude and phase from the combined excitation distribution E(t) and outputting control signals indicating the amounts of adjustment of amplitude and phase itself is a publicly known technique and thus detailed description thereof is omitted. 
     When each of the digital signal processors  71   a  in the amplitude/phase adjusters  71 - 1  to  71 -K receives the control signals from the controller  72 , the digital signal processor  71   a  adjusts the phase of the carrier signal outputted from the carrier signal generating unit  61  by digital signal processing in accordance with the amount of phase adjustment indicated by the control signal, and adjusts the amplitude of the carrier signal by digital signal processing in accordance with the amount of amplitude adjustment indicated by the control signal (step ST 42 ). 
     When each of the D/A converters  71   b  in the amplitude/phase adjusters  71 - 1  to  71 -K receives the amplitude- and phase-adjusted carrier signal from a corresponding digital signal processor  71   a , the D/A converter  71   b  converts the carrier signal into an analog signal and outputs the analog carrier signal to a corresponding amplifier  71   c  (step ST 43 ). 
     When each of the amplifiers  71   c  in the amplitude/phase adjusters  71 - 1  to  71 -K receives the analog carrier signal from a corresponding D/A converter  71   b , the amplifier  71   c  amplifies the carrier signal and outputs the amplified carrier signal to a corresponding one of the element antennas  3 - 1  to  3 -K (step ST 44 ). 
     By this, the amplitude- and phase-adjusted carrier signals are radiated into space from the element antennas  3 - 1  to  3 -K (step ST 45 ). 
     A communication beam and an interference beam that are formed by the carrier signals radiated from the element antennas  3 - 1  to  3 -K are, for example, those shown in  FIG. 8 . In the example illustrated in  FIG. 8 , since the amplitude characteristic of the communication beam is G 1 , a main lobe has its peak at 0 degrees. In addition, since the amplitude characteristic of the interference beam is G 2 , a null of an antenna pattern is formed in a 0-degree direction. Hence, a receiving station present in the 0-degree direction can receive a communication signal d(t) transmitted by the communication beam, but an interference signal i(t) is not transmitted thereto. Therefore, the communication signal d(t) can be demodulated without being influenced by the interference signal i(t). 
     In addition, in the Embodiment 4, the communication signal d(t) is subjected to a QPSK modulation process and a constellation point is present at a location where the phase is π/4 (=45 degrees). As shown in  FIG. 9 , since the phase of the antenna pattern is π/4 (=45 degrees) in the 0-degree direction, the receiving station present in the 0-degree direction can demodulate the constellation point present at the location where the phase is π/4 (=45 degrees). 
     In the sidelobe directions of the communication beam, the gains of the interference beam are larger than the gains of the communication beam. 
     Hence, receiving stations present in the sidelobe directions of the communication beam are greatly influenced by the interference signal i(t) transmitted by the interference beam and thus even if the receiving stations can receive the communication signal d(t) transmitted by the communication beam, the receiving stations have difficulty in demodulating the communication signal d(t). 
     Thus, since demodulation of the communication signal d(t) is possible only at angles near a communication direction of 0 degrees, a communicable area is limited. 
     As is clear from the above, according to the Embodiment 4, the configuration is such that there are provided the communication excitation distribution calculating unit  11  that calculates an excitation distribution W 1 ( t ) of a communication beam using an excitation phase distribution S that directs a main lobe of the communication beam in a communication direction; and the interference excitation distribution calculating unit  14  that calculates an excitation distribution W 2 ( t ) of an interference beam using an excitation phase distribution D that forms a null of an antenna pattern in the communication direction, and the excitation distribution combining unit  20  combines the excitation distribution W 1 ( t ) of the communication beam calculated by the communication excitation distribution calculating unit and the excitation distribution W 2 ( t ) of the interference beam calculated by the interference excitation distribution calculating unit  14 , and thus, an advantageous effect of being able to reduce the amount of computation for an excitation distribution for the array antenna that is used to implement secure communication with a limited communicable area is provided. 
     In addition, according to the Embodiment 4, the configuration is such that the amplitude/phase adjusters  71 - 1  to  71 -K each adjust the phase of a carrier signal by digital signal processing in accordance with the amount of phase adjustment indicated by a control signal outputted from the controller  72 , and adjusts the amplitude of the carrier signal by digital signal processing in accordance with the amount of amplitude adjustment indicated by a control signal outputted from the controller  72 , and thus, an advantageous effect of being able to increase the formation accuracy of an antenna pattern compared to the above-described first to Embodiment 3s is provided. 
     Embodiment 5 
     In the above-described first to Embodiment 4s, an example in which an interference signal i(t) and a communication signal d(t) are independently generated is shown. 
     In this Embodiment 5, an example in which an interference signal i(t) is generated from a communication signal d(t) generated by the communication signal generating unit  4  will be described. 
       FIG. 15  is a configuration diagram showing an antenna apparatus of the Embodiment 5 of the invention, and in  FIG. 15  the same reference signs as those in  FIGS. 1, 10, and 12  indicate the same or corresponding portions and thus description thereof is omitted. 
     An interference signal generating unit  80  includes a phase adjuster  81 , and performs a process of generating an interference signal i(t) which serves as a disturbing wave for a communication signal d(t) generated by the communication signal generating unit  4 , by adjusting the phase of the communication signal d(t), and outputting the interference signal i(t) to the interference excitation distribution calculation processing unit  17 . 
       FIG. 16  is a configuration diagram showing the interference signal generating unit  80  of the antenna apparatus of the Embodiment 5 of the invention. 
     In  FIG. 16 , the phase adjuster  81  is implemented by, for example, a semiconductor integrated circuit having a CPU mounted thereon, a single-chip microcomputer, or the like. Alternatively, the phase adjuster  81  is implemented by a phase shifter. 
     The phase adjuster  81  generates an interference signal i(t) by shifting the phase of a communication signal d(t) generated by the communication signal generating unit  4  by 90 degrees or −90 degrees. 
       FIG. 17  is a flowchart showing the processing operation of the phase adjuster  81  in the interference signal generating unit  80 . 
     Next, operation will be described. 
     When the phase adjuster  81  in the interference signal generating unit  80  receives a communication signal d(t) from the communication signal generating unit  4 , the phase adjuster  81  generates an interference signal i(t) which serves as a disturbing wave by adjusting the phase of the communication signal d(t), and outputs the interference signal i(t) to the interference excitation distribution calculation processing unit  17  (step ST 51  in  FIG. 17 ). 
     For example, the phase adjuster  81  generates an interference signal i(t) by shifting the phase of the communication signal d(t) by 90 degrees or −90 degrees. 
     Specifically, when a communication signal d(t) at time t which uses a QPSK modulation scheme is exp(jπ/4), if the communication signal d(t) has a phase difference of π/2 (=90 degrees), then an interference signal i(t) is exp(j3π/4). 
     Therefore, the interference signal i(t) is represented as shown in Equation (8) below:
 
 i ( t )= d ( t )·exp( jπ/ 2)= j·d ( t )  (8)
 
     Note that the sign of the phase difference of the interference signal i(t) from the communication signal d(t) may be fixed or may be randomly switched. 
     Note also that the sign of the phase difference may be switched for every modulation symbol of the communication signal d(t). 
     Specific description is as follows. 
     For example, when the phase of a communication signal d(t) at given time t is present in the first quadrant like when the communication signal d(t) is exp(jπ/4), the phase difference between the communication signal d(t) and the interference signal i(t) is a first phase difference. 
     When the phase of the communication signal d(t) at given time t is present in the second quadrant like when the communication signal d(t) is exp(−j3π/4), the phase difference between the communication signal d(t) and the interference signal i(t) is a second phase difference. 
     In addition, when the phase of the communication signal d(t) at given time t is present in the third quadrant like when the communication signal d(t) is exp(j3π/4), the phase difference between the communication signal d(t) and the interference signal i(t) is a third phase difference. 
     Furthermore, when the phase of the communication signal d(t) at given time t is present in the fourth quadrant like when the communication signal d(t) is exp(−jπ/4), the phase difference between the communication signal d(t) and the interference signal i(t) is a fourth phase difference. 
     At this time, the interference signal i(t) is generated such that the first phase difference and the third phase difference are of different signs. For example, the interference signal i(t) is generated such that the first phase difference is exp(jπ/2) and the third phase difference is exp(−jπ/2). 
     In addition, the interference signal i(t) is generated such that the second phase difference and the fourth phase difference are of different signs. For example, the interference signal i(t) is generated such that the second phase difference is exp(−jπ/2) and the fourth phase difference is exp(jπ/2). 
     As in the above-described Embodiment 1, the communication excitation distribution calculation processing unit  23  in the communication excitation distribution calculating unit  11  calculates an excitation distribution W 1 ( t ) of a communication beam by multiplying a communication signal d(t) outputted from the communication signal generating unit  4  by an excitation phase distribution S and a diagonal matrix of an excitation amplitude distribution A. 
     As in the above-described Embodiment 1, the interference excitation distribution calculation processing unit  17  in the interference excitation distribution calculating unit  14  calculates an excitation distribution W 2 ( t ) of an interference beam by multiplying an interference signal i(t) outputted from the interference signal generating unit  80  by an excitation phase distribution D and a diagonal matrix of an excitation amplitude distribution A. 
     Here, the excitation amplitude distribution A of the communication beam which is used by the communication excitation distribution calculation processing unit  23  to calculate the excitation distribution W 1 ( t ) of the communication beam and the excitation amplitude distribution A of the interference beam which is used by the interference excitation distribution calculation processing unit  17  to calculate the excitation distribution W 2 ( t ) of the interference beam are identical excitation amplitude distributions. 
       FIG. 18  is an illustrative diagram showing an excitation amplitude distribution A of a communication beam which is the same as an excitation amplitude distribution A of an interference beam. 
       FIG. 18  shows an example in which the number of element antennas included in the array antenna  3  is four. 
     The example illustrated in  FIG. 18  shows an excitation amplitude distribution A in which, of four element antennas  3 - 1  to  3 - 4 , the element antennas  3 - 1  and  3 - 4  at the edges have a smaller excitation amplitude of the communication beam than the element antennas  3 - 2  and  3 - 3  which are other than those at the edges. 
     Note, however, that this is an example and, as shown in  FIG. 19 , the excitation amplitude distribution A may be such that the element antennas  3 - 1  and  3 - 4  at the edges have a larger excitation amplitude of the communication beam than the element antennas  3 - 2  and  3 - 3  which are other than those at the edges. 
       FIG. 19  is an illustrative diagram showing an excitation amplitude distribution A of a communication beam which is the same as an excitation amplitude distribution A of an interference beam. 
     As in the above-described Embodiment 1, the excitation distribution combining unit  20  combines the excitation distribution W 1 ( t ) of the communication beam calculated by the communication excitation distribution calculation processing unit  23  and the excitation distribution W 2 ( t ) of the interference beam calculated by the interference excitation distribution calculation processing unit  17 , in accordance with weights m and n set by the weight setting unit  19 . 
     Then, as shown in Equation (9) below, the excitation distribution combining unit  20  calculates a combined excitation distribution E(t) by multiplying the excitation distribution which is obtained by combining the excitation distribution W 1 ( t ) and the excitation distribution W 2 ( t ), by a diagonal matrix of a beam-scanning phase distribution P set by the beam-scanning phase distribution setting unit  18 : 
     
       
         
           
             
               
                 
                   
                     
                       
                         
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     Here, since the amplitudes of the respective elements of a column vector in the fourth term on the right side of Eq. (9) are identical, an excitation amplitude distribution of the combined excitation distribution E(t) is represented by diag(A). 
     Therefore, even if the phase of the modulation symbol is changed, the same combined excitation distribution E(t) can be obtained. 
     As is clear from the above, according to the Embodiment 5, the configuration is such that there is provided the interference signal generating unit  80  that generates an interference signal i(t) which serves as a disturbing wave for a communication signal d(t) generated by the communication signal generating unit  4 , by adjusting the phase of the communication signal d(t), and an excitation amplitude distribution A of a communication beam and an excitation amplitude distribution A of an interference beam are identical excitation amplitude distributions, and thus, it is possible to eliminate the need for excitation amplitude control on a per symbol of a combined excitation distribution E(t) basis while secure communication with a limited communicable area is implemented. 
     In the antenna apparatuses in  FIGS. 1, 10, 12, 13, and 15  in Embodiments 1 to 5 described above, a linear array antenna in which the element antennas  3 - 1  to  3 -K of the array antenna  3  are linearly arranged is assumed. 
     However, the array antenna  3  is not limited to a linear array antenna and, for example, a planar array antenna in which the element antennas  3 - 1  to  3 -K of the array antenna  3  are two-dimensionally disposed in the same plane may be used. Alternatively, for example, a conformal array antenna in which the element antennas  3 - 1  to  3 -K of the array antenna  3  are disposed along a curved surface may be used. 
       FIG. 20  is an illustrative diagram showing examples of the array antenna  3 . 
       FIG. 20A  shows an example of a linear array antenna,  FIG. 20B  shows an example of a planar array antenna, and  FIG. 20C  shows an example of a conformal array antenna. 
     Note that, in the invention of the present application, a free combination of the embodiments, modifications to any component in the embodiments, or omissions of any component in the embodiments are possible within the scope of the invention. 
     INDUSTRIAL APPLICABILITY 
     Embodiments of the disclosure are suitable for use as antenna apparatuses and antenna excitation methods that control the amplitudes and phases of carrier signals to be provided to a plurality of element antennas included in an array antenna. 
     REFERENCE SIGNS LIST 
     
         
         
           
               1 : Carrier signal generating unit,  2 : Divider,  3 : Array antenna,  3 - 1  to  3 -K: Element antenna,  4 : Communication signal generating unit,  5 : Interference signal generating unit,  6 : Display,  10 : Signal processing unit,  11 : Communication excitation distribution calculating unit,  12 : Sum-pattern excitation phase distribution setting unit,  13  and  23 : Communication excitation distribution calculation processing unit,  14 : Interference excitation distribution calculating unit,  15 : Difference-pattern excitation phase distribution setting unit,  16 : Difference-pattern excitation amplitude distribution setting unit,  17 : Interference excitation distribution calculation processing unit,  18 : Beam-scanning phase distribution setting unit,  19 : Weight setting unit,  20 : Excitation distribution combining unit,  21 : Antenna pattern displaying unit,  22 : Sum-pattern excitation amplitude distribution setting unit,  30 : Amplitude/phase controlling unit,  31 - 1  to  31 -K: Amplitude/phase adjuster,  31   a : Phase controlling device,  31   b : Amplitude controlling device,  32 : Controller,  41 : Sum-pattern excitation phase distribution setting processing circuit,  42 : Communication excitation distribution calculation processing circuit,  43 : Difference-pattern excitation phase distribution setting processing circuit,  44 : Difference-pattern excitation amplitude distribution setting processing circuit,  45 : Interference excitation distribution calculation processing circuit,  46 : Beam-scanning phase distribution setting processing circuit,  47 : Weight setting processing circuit,  48 : Excitation distribution combining processing circuit,  49 : Antenna pattern display processing circuit,  50 : Sum-pattern excitation amplitude distribution setting processing circuit,  51 : Memory,  52 : Processor,  53 : Input interface device,  54 : Output interface device,  55 : Display interface device,  61 : Carrier signal generating unit,  70 : Amplitude/phase controlling unit,  71 - 1  to  71 -K: Amplitude/phase adjuster,  71   a : Digital signal processor,  71   b : D/A converter,  71   c : Amplifier,  72 : Controller,  80 : Interference signal generating unit, and  81 : Phase adjuster