Patent Publication Number: US-2017350963-A1

Title: Radar device and transmission power control method

Description:
BACKGROUND 
     1. Technical Field 
     The present disclosure relates to a radar device and transmission power control method. 
     2. Description of the Related Art 
     In recent years, with advance of microfabrication techniques in complementary metal oxide semiconductor (CMOS) process, integrated circuits for millimeter-wave radars using a millimeter-wave band in, for example, 77 GHz band, are being put into practical use. The operation frequency of an integrated circuit for a millimeter-wave radar is higher compared with the operation frequency of an integrated circuit for wireless communication in a microwave band. Therefore, a high cutoff frequency in the CMOS process, that is, a current gain becomes one fold, a difference between a frequency difficult for use as an amplifier element and the operation frequency is decreased, and these frequency values become close to each other. 
     Thus, variations occurring in the CMOS process and a temperature change cause great fluctuations of the gain of an amplifier for high-frequency signals (radio frequency signals). For example, in wireless communication in a millimeter-wave band, antenna gain variations tend to occur, and therefore an effective isotropic radiated power (EIRP) level of an antenna in a wireless communication device tends to become fluctuated. 
     Therefore, a wireless communication device which uses a non-volatile memory to correct a shift in transmission power due to variations occurring in the CMOS process has been disclosed in, for example, Japanese Unexamined Patent Application Publication No. 8-265210. 
     SUMMARY 
     However, in Japanese Unexamined Patent Application Publication No. 8-265210, correction of power of a high-frequency signal is not considered when antenna gain variations occur. Thus, in a wireless communication or radar device (for example, in a millimeter-wave band) where antenna gain variations tend to occur, it is difficult to make the EIRP level of the antenna in the wireless communication device constant. 
     One non-limiting and exemplary embodiment facilitates providing a radar device and a transmission power control method which make the EIRP level of the antenna constant even if antenna gain variations occur in wireless communication handling high-frequency signals. 
     In one general aspect, the techniques disclosed here feature a radar device including transmission signal generation circuitry that generates one or more transmission signals, a transmission amplifier that amplifies a power level of the one or more transmission signals, a transmission gain controller that adjusts a gain of the transmission amplifier, transmission antenna circuitry that converts each of the one or more amplified transmission signals into each of one or more radio signals and transmit the one or more radio signals to a measurement target space, reception antenna circuitry that receives the one or more radio signals from the measurement target space, and one or more receivers that detect a power level of a transmission/reception leakage signal using the one or more received radio signals. The transmission gain controller adjusts the gain of the transmission amplifier in accordance with a result of comparison between the detected power level and a power level of a transmission/reception leakage signal measured in advance. 
     It should be noted that general or specific embodiments may be implemented as a system, a method, an integrated circuit, a computer program, a storage medium, or any selective combination thereof. 
     According to the present disclosure, in the wireless communication using high-frequency signals, it is possible to make the EIRP level of the antenna constant even if antenna gain variations occur. 
     Additional benefits and advantages of the disclosed embodiments will become apparent from the specification and drawings. The benefits and/or advantages may be individually obtained by the various embodiments and features of the specification and drawings, which need not all be provided in order to obtain one or more of such benefits and/or advantages. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  depicts an example of structure of a radar device according to a first embodiment; 
         FIG. 2  is an example of results of a pulse detection process and a distance detection process at a received signal processing unit; 
         FIG. 3  is a flowchart for describing an operation procedure of AGC at the time of actual operation of the radar device according to the first embodiment and a second embodiment; 
         FIG. 4  depicts an example of structure of a radar device in the second embodiment; and 
         FIG. 5  depicts an example of transmission beams transmitted from a plurality of transmission antennas according to the second embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     In the following, embodiments of the present disclosure are described with reference to the drawings. Note that same reference characters represent a same or equivalent portion throughout the drawings. 
     First Embodiment 
       FIG. 1  depicts the structure of a radar device  100  according to a first embodiment of the present disclosure. The radar device  100  includes a transmitter unit  101 , a receiver unit  109 , and a gain control unit  118 . The transmitter unit  101  includes a transmission signal generator unit  102  (transmission signal generation circuitry), a transmission variable gain amplifier  103 , a frequency converting unit  104 , a local oscillator  105 , an amplifier  106 , and a transmission antenna  107 . 
     The receiver unit  109  functions as a detecting unit which receives a radio signal and detects a power level of a transmission/reception leakage signal in the received radio signal. Here, the transmission/reception leakage signal is a signal (leakage signal) among transmission signals generated by the transmitter unit  101 , the signal propagating via some medium and leaking into the receiver unit  109 . The medium is, for example, a substrate, a semiconductor substrate, or a medium between the transmission antenna  107  and a reception antenna  110  or between a transmitter IC and a receiver IC included in the radar device  100 . 
     The receiver unit  109  has the reception antenna  110 , an amplifier  111 , a frequency converter unit  112 , a local oscillator  113 , a reception variable gain amplifier  114 , and a received signal processing unit  115 . The gain control unit  118  includes a transmission gain control unit  108 , a reception gain control unit  116 , and a storage unit  117 . 
     The transmission signal generator unit  102  repeatedly generates a pulse signal (transmission pulse) having a predetermined pulse width as a transmission signal at constant time intervals for output to the transmission variable gain amplifier  103 . 
     When a pulse signal is used as a transmission signal, a distance measurable by the radar device  100  depends on a time interval for generating a transmission pulse. That is, a time period longer than a time period from a time when the radar device  100  transmits a pulse signal toward a measurement-target object positioned at an assumed maximum detection distance until the pulse signal reflected from the measurement-target object is received by the radar device  100  is set as a time interval (transmission-pulse transmission interval) for generating a transmission pulse. Also, the transmission pulse has a pulse width related to resolution at the time of measurement. As the pulse width is shorter, a distance at which reflected waves from a plurality of measurement-target objects are separable is shorter, thereby achieving high resolution. 
     In the first embodiment and a second embodiment, which will be described further below, a transmission signal with a single pulse waveform having a predetermined pulse width repeated in a predetermined cycle (at transmission-pulse transmission intervals) is used. However, the transmission signal is not restricted to this as long as the transmission signal is an intermittent signal (a signal repeatedly transmitted at transmission intervals) having a predetermined signal width and signal interval in accordance with the range of the distance for detection of the measurement-target object and resolution. For example, a pulse signal including a plurality of pulse strings or a modulated signal with a pulse signal including a single or plurality of pulse strings frequency-modulated or phase-modulated may be used as a transmission signal. 
     The transmission variable gain amplifier  103  amplifies an inputted pulse signal in accordance with an inputted gain control signal, and inputs the amplified pulse signal to the frequency converter unit  104 . The local oscillator  105  generates a local signal for modulation for use in the frequency converter unit  104 . 
     The frequency converter unit  104  includes a mixer and so forth, and mixes the amplified pulse signal inputted from the transmission variable gain amplifier  103  and the local signal outputted from the local oscillator  105  to upconvert the pulse signal of a baseband into a radio frequency (for example, a millimeter-wave band). Next, the frequency converter unit  104  inputs the pulse signal upconverted into the radio frequency to the amplifier  106 . 
     The amplifier  106  amplifies the pulse signal upconverted into the radio frequency to generate a transmission signal for output to the transmission antenna  107 . The transmission antenna  107  transmits the inputted transmission signal to a measurement target space. When a measurement-target object is present in the measurement target space, the signal transmitted from the transmission antenna  107  is reflected from the measurement-target object. 
     The reception antenna  110  receives a radio signal including a signal of the reflected wave reflected from the measurement-target object for output as a received signal of the radio frequency to the amplifier  111 . The disclosure is not limited to the transmission antenna  107  and the reception antenna  110  that are to be separately provided. A structure of sharing an antenna may be adopted. 
     The amplifier  111  amplifies the inputted received signal of the radio frequency, and outputs the amplified received signal of the radio frequency to the frequency converter unit  112 . 
     The local oscillator  113  generates a local signal for modulation for use in the frequency converting unit  112 . Note that while the present embodiment is configured so that the transmitter unit  101  and the receiver unit  109  each have an independent local oscillator, a structure may be adopted in which the transmitter unit  101  and the receiver unit  109  share one local oscillator. 
     The frequency converter unit  112  includes a mixer and so forth, and mixes the received signal of the radio frequency amplified by the amplifier  111  and the local signal outputted from the local oscillator  113  to down-convert the received signal of the radio frequency to a baseband. Next, the frequency converter unit  112  outputs the received signal down-converted to the baseband to the reception variable gain amplifier  114 . 
     The reception variable gain amplifier  114  amplifies the down-converted received signal in accordance with an inputted gain control signal, and outputs the amplified received signal to the received signal processing unit  115 . 
     The received signal processing unit  115  is an example of structure for achieving a function of detecting a measurement-target object. The received signal processing unit  115  receives an input of the received signal down-converted to the baseband. Then, on the inputted received signal, the received signal processing unit  115  performs, for example, wave detecting process, pulse detecting process, pulse power level detecting process, and process of detecting a distance to the measurement-target object, which are all known techniques and are not described herein in detail. 
     When a pulse of a reflected wave reflected from the measurement-target object is included in the received signal, the received signal processing unit  115  measures a time period from a time when the transmitter unit  101  transmits a transmission signal until the received signal processing unit  115  detects a pulse of a reflected wave, and calculates a distance to the measurement-target object based on the measured time period. 
     The reception gain control unit  116  uses, for example, a control method in which a total of thermal noise in an input unit of a receiver and inner thermal noise occurring inside the receiver is constant, to generate a gain control signal for controlling the gain of the reception variable gain amplifier  114  so that the gain of the receiver unit  109  falls within a range set in advance and to input the gain control signal to the reception variable gain amplifier  114 . The control method is a known technique, and is not described herein in detail. 
     The storage unit  117  stores a power level value of transmission/reception leakage signal when the EIRP level of the transmission signal transmitted from the transmission antenna  107  is equal to or higher than a desired power level. The storage unit  117  is, for example, a non-volatile memory. In one example, as will be described further below with reference to  FIG. 2 , the storage unit  117  stores information (a value or a value range) about the power level value of the transmission/reception leakage signal. Also, in one example, when a plurality of desired power levels are set, the storage unit  117  stores the power level values of the transmission/reception leakage signal for the respective desired power levels as a map. 
     For example, on inspection at the time of factory shipment, the gain of the transmission variable gain amplifier  103  is changed, and the EIRP level transmitted from the transmission antenna  107  is measured by using a power level measuring instrument  120  including an antenna  121 . Next, the received signal processing unit  115  calculates a power level of the transmission/reception leakage signal when the measured EIRP level is equal to or higher than the desired power level, and causes the calculated power level of the transmission/reception leakage signal to be stored in the storage unit  117 . 
     Also, in one example, the storage unit  117  stores an initial value of the gain of the transmission variable gain amplifier  103 . For example, at the time of factory shipment of the radar device  100 , when the measured EIRP level is equal to or higher than the desired power level, the storage unit  117  stores the gain of the transmission variable gain amplifier  103  as an initial value of the gain of the transmission variable gain amplifier  103 . Then, the transmission gain control unit  108  adjusts the gain of the transmission variable gain amplifier  103  in accordance with a difference between the power level of the transmission/reception leakage signal stored in the storage unit  117  and the power level of the transmission/reception leakage signal calculated by the received signal processing unit  115 . Adjustment of the gain of the transmission variable gain amplifier  103  will be described further below with reference to  FIG. 3 . 
     In one example, prior to adjusting the gain of the transmission variable gain amplifier  103 , the transmission gain control unit  108  initializes the gain of the transmission variable gain amplifier  103  by using the initial value of the gain of the transmission variable gain amplifier  103  stored in the storage unit  117 . Initialization of the gain can shorten the time taken to adjust the gain of the transmission variable gain amplifier  103 , as will be described further below with reference to  FIG. 3 . 
       FIG. 2  depicts an example of results of a pulse detection process and a distance detection process in the received signal processing unit  115 . The transmission/reception leakage signal is detected after a predetermined delay from a timing when the transmission signal is outputted. The detected distance can be regarded as zero. Then, after the transmission/reception leakage signal (power level P 0 ) is detected, a reflected wave (power level P 3 ) from the measurement-target object is detected. 
     When the EIRP level P 3  measured by using the power level measuring instrument  120  is equal to or higher than the desired power level and the detected power level of the transmission/reception leakage signal is P 0 , in one example, the storage unit  117  stores P 1  equivalent to P 0 −1 dB and P 2  equivalent to P 0 +1 dB as information about the power levels of the transmission/reception leakage signal. Instead, the storage unit  117  may store P 0  as information about the power level of the transmission/reception leakage signal. 
     Next, a transmission power control method in the radar device  100  according to the first embodiment is described with reference to  FIG. 3 .  FIG. 3  is a flowchart for describing an operation procedure of automatic gain control (AGC) at the time of actual operation of the radar device  100  according to the first embodiment of the present disclosure. 
     At step S 11 , the reception gain control unit  116  generates a gain control signal for controlling the gain of the reception variable gain amplifier  114  based on a difference between thermal noise of an input portion of the receiver unit  109  and inner thermal noise occurring inside the receiver unit  109  so that, for example, the gain of the reception variable gain amplifier  114  is in a desired range, and outputs the generated gain control signal to the reception variable gain amplifier  114 . 
     Next at step S 12 , the transmission gain control unit  108  reads the initial value of the gain of the transmission variable gain amplifier  103  stored in the storage unit  117 , generates a gain control signal for setting the gain of the transmission variable gain amplifier  103  at the initial value, and outputs the generated gain control signal to the transmission variable gain amplifier  103 . Note that step S 12  may be omitted in the first embodiment. 
     Next at step S 13 , the transmission antenna  107  transmits a transmission signal generated by the transmission signal generator unit  102  and amplified with the set gain by the transmission variable gain amplifier  103 . Next at step S 14 , from a reflected wave received by the reception antenna  110  and the received signal including a transmission/reception leakage signal, the received signal processing unit  115  calculates a received signal power level and a distance. 
     Next at step S 15 , from the results calculated by the received signal processing unit  115 , the transmission gain control unit  108  detects a peak value of the power level of the transmission/reception leakage signal. Next at step S 16 , the transmission gain control unit  108  compares the detected peak value of the power level of the transmission/reception leakage signal and the power level P 2  of the transmission/reception leakage signal stored in the storage unit  117 . 
     When the transmission gain control unit  108  determines at step S 16  that the detected peak value of the power level of the transmission/reception leakage signal is equal to or larger than the power level P 2  (NO at S 16 ), the process proceeds to step S 17 , decreasing the gain setting of the transmission variable gain amplifier  103  by 1 dB. After step S 17 , the operation of the radar device  100  returns to step S 14 . 
     On the other hand, when the transmission gain control unit  108  determines at step S 16  that the detected peak value of the power level of the transmission/reception leakage signal is smaller than the power level P 2  of the transmission/reception leakage signal (YES at S 16 ), the process proceeds to step S 18  without changing the gain setting of the transmission variable gain amplifier  103 . 
     At step S 18 , the transmission gain control unit  108  compares the detected peak value of the power level of the transmission/reception leakage signal and the power level P 1  of the transmission/reception leakage signal stored in the storage unit  117 . When the transmission gain control unit  108  determines at step S 18  that the detected transmission/reception leakage signal is equal to or smaller than the power level P 1  (NO at S 18 ), the process proceeds to step S 19 , increasing the gain setting of the transmission variable gain amplifier  103  by 1 dB. After step S 19 , the operation of the radar device  100  returns to step S 14 . 
     On the other hand, the transmission gain control unit  108  determines at step S 18  that the detected transmission/reception leakage signal is larger than the power level P 1  of the transmission/reception leakage signal (YES at S 18 ), the process proceeds to step S 20 , establishing the gain setting of the transmission variable gain amplifier  103  and ending the process. 
     From the above, for example, when the power level transmitted from the transmission antenna  107  on inspection at the time of factory shipment is equal to or higher than a desired power level, the radar device  100  of the first embodiment adjusts the gain of the transmission variable gain amplifier  103  by automatic gain control based on the result of comparison between the power level of the transmission/reception leakage signal and the detected transmission/reception leakage signal. With this, even if variations occurring in the CMOS process and fluctuations in conditions such as operation temperature occur, the EIRP of the radar device  100  can be kept constant. 
     Second Embodiment 
       FIG. 4  depicts the structure of a radar device  400  in the second embodiment.  FIG. 5  depicts an example of transmission beams transmitted from a plurality of transmission antennas  107   a , . . . ,  107   n  according to the second embodiment. In the second embodiment, a transmitter unit  401  is configured by using a phased array, and is a radar device configured of a plurality of transmission branches. The phased array is a known technique, and is not described herein in detail. 
     The radar device  400  includes the transmitter unit  401 , the receiver unit  109 , and a gain control unit  410 . The transmitter unit  401  includes the transmission signal generator unit  102 , a plurality of variable phase shifters  402   a , . . . ,  402   n , a plurality of transmission variable gain amplifiers  103   a , . . . ,  103   n , a plurality of frequency converting units  104   a , . . . ,  104   n , the local oscillator  105 , a plurality of amplifiers  106   a , . . . ,  106   n , and a plurality of transmission antennas  107   a , . . . ,  107   n . The receiver unit  109  includes the reception antenna  110 , the amplifier  111 , the frequency converter unit  112 , the local oscillator  113 , the reception variable gain amplifier  114 , and the received signal processing unit  115 . The gain control unit  410  includes a transmission gain control unit  403 , the reception gain control unit  116 , and a storage unit  404 . 
     In the second embodiment, compared with the first embodiment, the plurality of variable phase shifters  402   a , . . . ,  402   n  are added, and the transmission variable gain amplifier  103 , the frequency converter unit  104 , the amplifier  106 , and the transmission antenna  107  in the transmitter unit  101  are changed as the plurality of transmission variable gain amplifiers  103   a , . . . ,  103   n , the plurality of frequency converter units  104   a , . . . ,  104   n , the plurality of amplifiers  106   a , . . . ,  106   n , and the plurality of transmission antennas  107   a , . . . ,  107   n , respectively, in the transmitter unit  401 . Note that components used commonly in the first embodiment and the second embodiment are provided with a same reference numeral and these components are not described herein. 
     The plurality of variable phase shifters  402   a , . . . ,  402   n  each adjust the phase of the signal generated at the transmission signal generator unit  102  for output to each of the plurality of transmission variable gain amplifiers  103   a , . . . ,  103   n . By the plurality of variable phase shifters  402   a , . . . ,  402   n  each controlling the phase of each transmission branch, as depicted in  FIG. 5 , the directivity of a transmission beam transmitted from each of the plurality of transmission antennas  107   a , . . . ,  107   n  can be formed, that is, electronic scanning of the beams can be made. 
     The plurality of transmission variable gain amplifiers  103   a , . . . ,  103   n  each have a function similar to that of the transmission variable gain amplifier  103 . The plurality of frequency converter units  104   a , . . . ,  104   n  each have a function similar to that of the frequency converter unit  104 . The plurality of amplifiers  106   a , . . . ,  106   n  each have a function similar to that of the amplifier  106 . The plurality of transmission antennas  107   a , . . . ,  107   n  are arranged in an array, and each have a function similar to that of the transmission antenna  107 . 
     The storage unit  404  stores an initial value of a gain and a power level of a transmission/reception leakage signal of each of the plurality of transmission variable gain amplifiers  103   a , . . . ,  103   n . In one example, as with the storage unit  117 , the storage unit  404  stores information about the power level of the transmission/reception leakage signal. Here, note that the transmission/reception leakage signal in the radar device  400  is a signal among transmission signals generated by the transmitter unit  401 , the signal propagating through a substrate, through a semiconductor substrate, between the plurality of transmission antennas  107   a , . . . ,  107   n  and the reception antenna  110 , between the transmission IC and a reception IC, or the like included in the radar device  400  and leaking into the receiver unit  109 . 
     For example, on inspection at the time of factory shipment, the gain of the transmission variable gain amplifier  103   a  is changed, and the EIRP level transmitted from the transmission antenna  107   a  is measured by using the power level measuring instrument  120  including the antenna  121 . Next, when the measured EIRP level is equal to or higher than a desired power level, the storage unit  404  stores the gain of the transmission variable gain amplifier  103   a  as an initial value of the gain of the transmission variable gain amplifier  103   a.    
     Next, the gain of the transmission variable gain amplifier  103   b  is changed, and the EIRP level transmitted from the transmission antenna  107   b  is measured by using the power level measuring instrument  120  including the antenna  121 . Then, when the measured EIRP level is equal to or higher than the desired power level, the storage unit  404  stores the gain of the transmission variable gain amplifier  103   b  as an initial value of the gain of the transmission variable gain amplifier  103   b . As for the other transmission variable gain amplifiers  103   c , . . . ,  103   n , the storage unit  404  stores an initial value of the gain in a manner similar to that described above. 
     Next, the plurality of variable phase shifters  402   a , . . . ,  402   n  adjust the phase of the signal generated at the transmission signal generator unit  102  so that the azimuth of a transmission beam outputted from each of the plurality of transmission antennas  107   a , . . . ,  107   n  is set to be a predetermined azimuth (for example, a zero-degree direction). 
     Then, the gain of each of the plurality of transmission variable gain amplifiers  103   a , . . . ,  103   n  is changed by the same amount, and the EIRP level transmitted from each of the plurality of transmission antennas  107   a , . . . ,  107   n  is measured by using the power level measuring instrument  120  including the antenna  121 . Then, when the measured EIRP level is equal to or higher than a desired power level, the received signal processing unit  115  calculates a power level of a transmission/reception leakage signal, and causes the calculated power level of the transmission/reception leakage signal to be stored in the storage unit  404 . Note that when the measured EIRP level is equal to or higher than the desired power level, the storage unit  404  stores the value of the phase set in each of the plurality of variable phase shifters  402   a , . . . ,  402   n , the value of the gain set in each of the plurality of transmission variable gain amplifiers  103   a , . . . ,  103   n , and the measured EIRP level so as to establish a link thereamong. 
     The transmission gain control unit  403  causes the plurality of variable phase shifters  402   a , . . . ,  402   n  to each set an azimuth of an electron beam as an azimuth identical to the azimuth when the power level of the transmission/reception leakage signal is stored in the storage unit  404  (for example, zero-degree direction) to adjust the gain of each of the plurality of transmission variable gain amplifiers  103   a , . . . ,  103   n  in accordance with a difference between the power level of the transmission/reception leakage signal stored in the storage unit  404  and the power level of the transmission/reception leakage signal calculated by the received signal processing unit  115 . Adjustment of the gain of each of the plurality of transmission variable gain amplifiers  103   a , . . . ,  103   n  will be described further below. 
     Next, a transmission power control method in the radar device  400  according to the second embodiment is described by using  FIG. 3  again, which is referred to in the first embodiment. At step S 11 , the reception gain control unit  116  generates a gain control signal for controlling the gain of the reception variable gain amplifier  114  based on a difference between thermal noise of an input portion of the receiver unit  109  and inner thermal noise occurring inside the receiver unit  109  so that, for example, the gain of the reception variable gain amplifier  114  is in a desired range, and outputs the generated gain control signal to the reception variable gain amplifier  114 . 
     Next at step S 12 , the transmission gain control unit  403  reads the initial value of the gain of each of the plurality of transmission variable gain amplifiers  103   a , . . . ,  103   n  stored in the storage unit  404 , generates a gain control signal for setting the gain of each of the plurality of transmission variable gain amplifiers  103   a , . . . ,  103   n  at the initial value of the gain, and outputs the generated gain control signal to each of the plurality of transmission variable gain amplifiers  103   a , . . . ,  103   n.    
     Next at step S 13 , the transmission signal is transmitted from each of the plurality of transmission antenna  107   a , . . . ,  107   n , the transmission signal generated by the transmission signal generator unit  102 , with its azimuth set by each of the plurality of variable phase shifters  402   a , . . . ,  402   n  at an azimuth identical to that when the initial value of the gain is stored in the storage unit  404 , and amplified with the set gain by each of the plurality of transmission variable gain amplifiers  103   a , . . . ,  103   n.    
     Next at step S 14 , from a reflected wave received by the reception antenna  110  and the received signal including a transmission/reception leakage signal, the received signal processing unit  115  calculates a received signal power level and a distance. Next at step S 15 , from the results calculated by the received signal processing unit  115 , the transmission gain control unit  403  detects a peak value of the power level of the transmission/reception leakage signal. 
     Next at step S 16 , the transmission gain control unit  403  compares the detected peak value of the power level of the transmission/reception leakage signal and the power level P 2  of the transmission/reception leakage signal stored in the storage unit  404 . When the transmission gain control unit  403  determines at step S 16  that the detected peak value of the power level of the transmission/reception leakage signal is equal to or larger than the power level P 2  (NO at S 16 ), the process proceeds to step S 17 , decreasing the gain setting of each of the plurality of transmission variable gain amplifiers  103   a , . . . ,  103   n  by 1 dB. After step S 17 , the operation of the radar device  400  returns to step S 14 . 
     On the other hand, when the transmission gain control unit  403  determines at step S 16  that the detected peak value of the power level of the transmission/reception leakage signal is smaller than the power level P 2  of the transmission/reception leakage signal (YES at S 16 ), the process proceeds to step S 18  without changing the gain setting of each of the plurality of transmission variable gain amplifiers  103   a , . . . ,  103   n.    
     At step S 18 , the transmission gain control unit  403  compares the detected peak value of the power level of the transmission/reception leakage signal and the power level P 1  of the transmission/reception leakage signal stored in the storage unit  117 . When the transmission gain control unit  403  determines at step S 18  that the detected transmission/reception leakage signal is equal to or smaller than the power level P 1  of the transmission/reception leakage signal (NO at S 18 ), the process proceeds to step S 19 , increasing the gain setting of the plurality of transmission variable gain amplifiers  103   a , . . . ,  103   n  by 1 dB. After step S 19 , the operation of the radar device  400  returns to step S 14 . 
     On the other hand, the transmission gain control unit  403  determines at step S 18  that the detected transmission/reception leakage signal is larger than the power level P 1  of the transmission/reception leakage signal (YES at S 18 ), the process proceeds to step S 20 , establishing the gain setting of each of the plurality of transmission variable gain amplifiers  103   a , . . . ,  103   n  and ending the process. 
     From the above, for example, based on the power level of the transmission/reception leakage signal occurring when the EIRP level transmitted from each of the plurality of transmission antennas  107   a , . . . ,  107   n  on inspection at the time of factory shipment is equal to or higher than a desired power level and the initial value of the gain of each of the plurality of transmission variable gain amplifiers  103   a , . . . ,  103   n , the radar device  400  of the second embodiment adjusts the gain of each of the plurality of transmission variable gain amplifiers  103   a , . . . ,  103   n  by automatic gain control. 
     With this, even if variations occurring in the CMOS process and fluctuations in conditions such as operation temperature occur, the EIRP of the radar device  400  can be kept constant. Furthermore, in a structure including a plurality of branches such as a phased array, it is possible to inhibit fluctuations of directional transmission beams due to variations occurring in the CMOS process. 
     While various embodiments have been described with reference to the drawings, it goes without saying that the present disclosure is not restricted to the examples described herein. It is obvious for a person skilled in the art that various modification examples or corrected examples can be made within the range described in the claims and it is understood that these examples also naturally belong to the technical range of the present disclosure. 
     Note that the range of the power level of the transmission signal used in the first and second embodiments is merely an example and does not restrict the range of the power level. Similarly, the amount of adjustment of the transmission gain in the first and second embodiments is also merely an example, and does not restrict the amount of adjustment of the transmission gain. 
     While it has been described in the first and second embodiments that the reception antenna  110  of the receiver unit  109  is configured of one antenna, the reception antenna  110  is not restricted to this. For example, a plurality of array antennas arranged in an array may be used and, for example, a structure using a beam forming method may be adopted. 
     Also, while the pulse scheme is used as a radar scheme of the radar device in the first and second embodiments, the radar scheme of the radar device is not restricted to this. 
     Note that while a radar device is taken as an example for description in the first and second embodiments, the present disclosure is not restricted to the field of radars, and the present disclosure is an effective technique also in the field of wireless communications, for example, WiGig and so forth. 
     The radar device and transmission power control method according to the present disclosure are used for making an EIRP level of an antenna in a radar device using high-frequency signals (radio frequency signals) constant even if antenna gain variations occur.