Abstract:
The invention comprises a mulli-wave radar system for obtaining first target position information of a flying object by capturing and tracking the flying object from a maximum detection distance, a stereo-camera system for taking over the tracking of the flying object in the vicinity of a landing point by acquiring the first target position information of the flying object from the milli-wave radar system, and obtaining second target position information having higher precision than the first target position information, and a controller for managing the first target position information of the milli-wave radar system and the second target position information of the stereo-camera system, controlling the milli-wave radar system to capture and track the flying object to the vicinity of the landing point, and controlling the stereo-camera system to capture and track the flying object at the time of landing of the flying object.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a target locating system and an approach guidance system which can be used to exactly guide a flying object to a narrow landing space, for example, in bad weather. 
     Systems for performing exact target locating include, for example, a radar system and an optical sensor such as a stereo-camera. These systems, however, have the following problems. 
     The optical sensor has high precision in target locating, but a distance for locating tends to be greatly shortened due to weather, e.g. rain or fog. 
     On the other hand, the radar system can perform target locating without great influence by weather. However, when target locating is performed with use of a radar system having a low frequency band, a large-sized antenna needs to be used in order to increase angular resolution, because of low frequencies used. In addition, in order to attain a good distance resolution, a method of decreasing a transmission pulse width or a frequency modulation transmission method such as chirp modulation needs to be used. In either method, however, it is necessary to increase the frequency band width. If the frequencies employed are low, it becomes difficult to maintain the frequency band width. 
     As stated above, the conventional target locating systems are inevitably influenced by weather and can hardly perform exact target locating. 
     A conical tracking radar system, for example, may be used as target locating system. An antenna apparatus used in the conical tracking radar system comprises a primary horn for radiating an antenna beam and a reflector, situated opposite to the radiation face of the primary horn, for reflecting the antenna beam and emitting it to the outside. The antenna beam radiated by the primary horn is rotated about the antenna visual line and scanned conically. In this case, the antenna apparatus is rotated, with the primary horn being angularly offset from the antenna visual line. 
     The primary horn of the antenna apparatus is provided with a rotary drive mechanism. This drive mechanism becomes an obstruction to block the antenna beam reflected from the reflector, resulting in a decrease in antenna efficiency. 
     Moreover, a structure such as a rotary joint for rotating the primary horn needs to be provided midway along a feed line. The use of the rotary joint causes mixing of noise in the antenna beam, variation in amplitude and phase, etc., thus considerably degrading the quality of the antenna beam. These drawbacks become conspicuous as the frequencies used become higher. Furthermore, if that portion of the feed line serving as electric wave propagation path, at which the rotary joint is provided, is mechanically rotated, the feed line, for example, may be broken. Thus, the reliability of the feed line itself, that is, the reliability of the system, may deteriorate. 
     BRIEF SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a target locating system and an approach guidance system capable of preventing the distance for locating from greatly decreasing due to weather, etc. and performing exact target locating in the vicinity of a landing point. 
     Another object of the invention is to provide a conical scan type antenna system capable of preventing the antenna efficiency and antenna beam quality from greatly decreasing, thus enhancing the reliability of the system. 
     According to an aspect of the invention, there is provided a target locating system comprising: 
     a milli-wave radar system for obtaining first target position information of a flying object being about to land, by capturing and tracking the flying object from a maximum detection distance; 
     a stereo-camera system for taking over the tracking of the flying object in the vicinity of a landing point by acquiring the first target position information of the flying object from the milli-wave radar system, and obtaining second target position information having higher precision than the first target position information; and 
     a controller for managing the first target position information of the milli-wave radar system and the second target position information of the stereo-camera system, controlling the milli-wave radar system to capture and track the flying object to the vicinity of the landing point, and controlling the stereo-camera system to capture and track the flying object at the time of landing of the flying object. 
     With the above structure, the flying object being about to land is captured and tracked by the milli-wave radar system, which is less susceptible to weather, etc., in a range between a maximum detection distance of the milli-wave radar system and the vicinity of the landing point, and the flying object is, in turn, captured and tracked by the stereo-camera system with high locating precision at the landing point. 
     Thus, the locating distance for the flying object being about to land is less decreased due to weather, etc., and exact target locating can be carried out in the vicinity of the landing point. 
     According to another aspect of the invention, there is provided an approach guidance system comprising: 
     a target locating system including a milli-wave radar system for obtaining first target position information of a flying object being about to land, by capturing and tracking the flying object from a maximum detection distance, a stereo-camera system for taking over the tracking of the flying object in the vicinity of a landing point by acquiring the first target position information of the flying object from the milli-wave radar system, and obtaining second target position information having higher precision than the first target position information, and a controller for managing the first target position information of the milli-wave radar system and the second target position information of the stereo-camera system, controlling the milli-wave radar system to capture and track the flying object to the vicinity of the landing point, and controlling the stereo-camera system to capture and track the flying object at the time of landing of the flying object; and 
     a control apparatus for guiding the flying object which is a target to the vicinity of the landing point on the basis of the first target position information output from the milli-wave radar system of the target locating system, and guiding the flying object to the landing point on the basis of the second target position information output from the stereo-camera system of the target locating system. 
     With this structure, the target position information of the flying object obtained by the milli-wave radar system and the target position information of the flying object obtained by the stereo-camera system is transmitted to the control apparatus. Thus, the control apparatus guides the flying object to the vicinity of the landing point, using the target position information from the milli-wave radar system which is less susceptible to weather, etc. In the vicinity of the landing point, the control apparatus guides the flying object to the landing point, using the target position information from the stereo-camera system with high location precision. 
     Accordingly, the flying object can be exactly guided to the landing point, without influence of weather, etc. 
     According to still another aspect of the invention, there is provided a conical scan type antenna system connected to a transmission/reception system and comprising a primary radiator for transmitting and receiving an antenna beam and a reflector, situated opposite to a radiation surface of the antenna beam of the primary radiator, for reflecting the antenna beam, 
     wherein the reflector is angularly offset from an antenna visual line to incline the antenna beam, and the reflector is rotated about the antenna visual line to conically scan the antenna beam. 
     In the above structure, it is preferable that the feed line from the transmission/reception system to the primary radiator does not pass through the rotary mechanism for the reflector. 
     According to the above structure, the reflector is rotated to conically scan the antenna beam, and the feed line from the transmission/reception system to the primary radiator does not pass through the rotary mechanism for the reflector. 
     As a result, there is no need to drive the primary radiator and feed line, and a degradation in quality of the antenna beam caused by this driving can be prevented. Therefore, stable transmission/reception of the beam is achieved. 
     Since the feed line is fixed between the transmission/reception system and primary radiator and is not driven or rotated. Thus, the reliability of the whole system is enhanced. 
     Only the primary radiator and feed line are disposed in front of the reflection surface of the reflector. Thus, the antenna beam reflected by the reflector is prevented from being blocked by an obstruction, and the antenna efficiency is less degraded. 
     Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
     The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate presently preferred embodiments of the invention, and together with the general description given above and the detailed description of the preferred embodiments give below, serve to explain the principles of the invention. 
     FIG. 1 is a system construction view showing a target locating system and an approach guidance system according to an embodiment of the present invention; 
     FIG.  2 A and FIG. 2B are cross-sectional views for describing the housing body in the embodiment in detail; 
     FIG. 3 shows a relationship between a target locating coverage of a milli-wave radar system and a stereo-camera system and an approach route of a flying object in the embodiment; 
     FIG. 4 shows a relationship between a target locating precision of the milli-wave radar system and stereo-camera system and a straight-line distance to the target; 
     FIG. 5 shows a state in which the milli-wave radar system and the stereo-camera system are mounted on a single gimbal in the embodiment; 
     FIG. 6 shows a state in which the milli-wave radar system is interposed between first and second cameras of a stereo-camera system according to a second embodiment of the invention; 
     FIG. 7 shows a third embodiment of the invention, wherein a conical tracking system is adopted as a target tracking system of the milli-wave radar system; 
     FIG. 8 is a cross-sectional view for describing the inclination of the antenna beam in the third embodiment; and 
     FIG. 9 shows a fourth embodiment of the invention, wherein a conical tracking system is adopted as a target tracking system of the milli-wave radar system. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Embodiments of the present invention will now be described in detail with reference to the accompanying drawings. 
     FIG. 1 is a system construction view showing a target locating system and an approach guidance system according to an embodiment of the present invention. 
     In FIG. 1, reference numeral  11  denotes a milli-wave radar system. The milli-wave radar system  11  captures and tracks a target or a flying object  21  (a helicopter in FIG. 1) being present within a maximum detection range (a location X 1  in FIG.  1 ). Reference numeral  12  denotes a stereo-camera system and captures and tracks the flying object  21  being present near a landing point (at a location X 2  in FIG.  1 ). The milli-wave radar system  11  and stereo-camera system  12  are disposed within, e.g. a housing body  1  having a gimbal structure. 
     The milli-wave radar system  11  receives a signal reflected from the target or flying object  21  and delivers it to a controller  13  as target position information. Similarly, the stereo-camera system  12  receives a signal reflected by the flying object  21  and delivers it to the controller  13  as target position information. The controller  13  manages target position information output from the milli-wave radar system  11  and stereo-camera system  12 . Based on the target position information, the controller  13  controls the milli-wave radar system  11  to capture and track the flying object  21  to the vicinity of landing point  0  and also controls the stereo-camera system  12  to capture and track the flying object  21  at the time of landing of flying object  21 . The target position information is transmitted to a control apparatus  32  from the controller  13  over a line  31 . 
     Based on the target position information from the milli-wave radar system  11 , the control apparatus  32  guides the flying object  21  to the vicinity of landing point O. In the vicinity of landing point O, the control apparatus  32  controls the flying object  21  on the basis of target position information from the stereo-camera system  12  so that the object  21  may land on the small-space landing point O. In this case, the control apparatus  32  delivers flight instructions of speech information, etc. to the flying object  21  over a line  33 , e.g. a wireless channel. 
     The milli-wave radar system  11 , stereo-camera system  12  and controller  13  constitute a target locating system of the present invention. Furthermore, the target locating system is combined with the control apparatus  32  to constitute an approach guidance system of the present invention. 
     As is shown in FIGS. 2A and 2B, the housing body  1  comprises a movable first housing portion  1   a  and an immovable second housing portion  1   b . The first housing portion  1   a  can be rotated by a rotary portion  1   c  in a direction of double-headed arrow Y 1 -Y 2 , as shown in FIG. 2A, and can be rotated by a rotary portion Id in a direction of double-headed arrow Z 1 -Z 2 , as shown in FIG.  2 B. Thus, the first housing portion  1   a  is rotated by the rotary portion  1   c ,  1   d  in the direction Yl-Y 2  or Zl-Z 2  in FIGS. 2A and 2B so that the milli-wave radar system  11  and stereo-camera system  12  may capture and track the flying object  21  which is moving. 
     FIG. 3 shows a relationship between a target locating coverage of the milli-wave radar system  11  and stereo-camera system  12  and an approach route of flying object  21 . FIG. 4 shows a relationship between a target location error of the milli-wave radar system  11  and stereo-camera system  12  and a straight-line distance to the target. 
     In FIG. 3, the vertical axis indicates the altitude of the target and the horizontal axis indicates a horizontal distance from, e.g. the landing point O to the target. In FIG. 3, symbol X indicates a flight path of the flying body  21  from point X 1  to point X 2 , as shown in FIG.  1 . 
     In FIG. 4, the vertical axis indicates a target location error and the horizontal axis indicates a straight-line distance from, e.g. the landing point  0  to the target. Symbol M indicates a target location error of the milli-wave radar system  11  in relation to the straight-line distance, and symbol S a target location error of the stereo-camera system  12  in relation to the straight-line distance. 
     Specifically, the target locating coverage of the milli-wave radar system  11 , as shown in FIG. 3, reaches farther than that of the stereo-camera system  12 . The locating coverage of the milli-wave radar system  11  is less influenced by rain, fog, etc. than that of the stereo-camera system  12 . 
     On the other hand, as shown in FIG. 4, the target location error of the stereo-camera system  12  is less than that of the milli-wave radar system  11  in a close range (near landing point O). Accordingly, the flying object  21  can be guided to exactly land on the smallspace landing point O. In addition, the stereo-camera system  12  is not greatly influenced by rain, fog, etc. in the close range. 
     Since the milli-wave radar system  11  has a transmission blind period (i.e. a reception halt period in a transmission pulse emission period), the minimum detection distance cannot be reduced to a level of the stereo-camera system  12 . 
     In the present invention, therefore, the milli-wave radar system  11 , which is less susceptible to rain, fog, etc., is used in a far range, and the stereo-camera system  12 , which has a less target location error, is used in the close range just before the landing. These systems  11  and  12  are switched so as to make use of their merits and compensate their demerits. 
     The operation of the embodiment including the milli-wave radar system  11  and stereo-camera system  12  will now be described with reference to FIG.  3 . 
     At the beginning of guidance, the controller  13  delivers position information of the flying object  21  to the milli-wave radar system  11  over the line  14 . Normally, the position information of the flying object  21  to be transmitted by the controller  13  is delivered to the controller  13  from the control apparatus  32 , which acquires over the line  33  the self-position information of the flying object  21  acquired by a navigation system (not shown), etc. Alternatively, the position information is acquired by another long-distance sensor (not shown). 
     If the flying object  21  has entered the target locating coverage C, the milli-wave radar system  11  captures the object  21  and starts to track it. The system  11  continuously locates the flying object  21  and transmits a locating result to the controller  13  over the line  14  as target position information. The target position information is then transmitted to the control apparatus  32  over the line  31 . 
     Based on the input target position information, the control apparatus  32  issues a flight instruction to the flying object  21  over the line  33 . At this time, the locating result of the milli-wave radar system  11  is transmitted to the stereo-camera  12 , too, over the line  15  as target position information. The stereo-camera system  12 , however, does not start tracking since the object  21  is out of the locating coverage. 
     If the flying object  21  has entered the locating coverage B, the stereo-camera system  12  starts detection. The target position information detected by the stereo-camera system  12  is transmitted to the controller  13  over the line  15 . The controller  13  correlates the target position information transmitted from the stereo-camera system  12  with the information of the flying object  21  which has been tracked by the milli-wave radar system  11  thus far. If a high correlation result is obtained, the locating result to be adopted is switched to that of the stereo-camera system  12  and this locating result is delivered to the control apparatus  32  as target position information. 
     The series of these operations (switching of locating result) are normally carried out while the flying object  21  is being present in the coverage B in which the locating coverage (B+C in FIG. 3) of the milli-wave radar system  11  overlaps the locating coverage (A+B in FIG. 3) of the stereo-camera system  12 . 
     Subsequently, using the target position information obtained by the stereo-camera system  12 , the control apparatus  32  guides the flying object  21  to the landing point  0 . Even if the tracking by the stereo-camera system  12  is locked off due to, e.g. temporary shut-off of the visual field of the camera, if the flying object  21  is being in the coverage B, the milli-wave radar system  11  continues the tracking. Thus, the target position information obtained by the milli-wave radar system  11  may be used for supplementation. Accordingly, after the temporary shut-off of the visual field has ended, the stereo-camera system  12  can track the object  21  once again, following the above procedures. 
     If the flying object  21  is present in the coverage A, latest target position information cannot be obtained by the milli-wave radar system  11 . However, the object  21  may be recaptured by continuing prediction of the target position on the basis of the target position information and movement information obtained at the time the tracking of the stereo-camera system  12  is locked off. In this case, since the flying object  21  is in the close range, the precision in prediction is very high. Needless to say, however, the minimum detection distance of the milli-wave radar system  11  should desirably be reduced as small as possible. Besides, if the flying object  21  has a hovering function, as in the case of a helicopter, it is one way to make the flying object  21  remain at the same position in the air until the temporary shut-off of the visual field of the stereo-camera system  12  will end. 
     In FIGS. 2A,  2 B and  5 , the milli-wave radar system  11  and stereo-camera system  12  are mounted on the single gimbal  41 . 
     In this case, the milli-wave radar system  11  and stereo-camera system  12  have a constant positional relationship and the same visual line direction. Thus, a displacement in angular reference axes of both systems  11  and  12  is small, and the precision in target tracking switching is high. Even if there is a positional error in disposition of the milli-wave radar system  11  and stereo-camera system  12 , such a positional error is invariable and may be geometrically corrected, and then the systems  11  and  12  may be used. 
     In the above embodiment, the milli-wave radar system  11  and stereo-camera system  12  may be mounted at different locations within the housing body  1 . In this case, however, the milli-wave radar system  11  and stereo-camera system  12  have respective angular references and an error will occur between the angular references. Consequently, it becomes difficult to find a good correlation in target position information at the time of target tracking switching. It is desirable, therefore, to mount the milli-wave radar system  11  and stereo-camera system  12  on the same gimbal  41 . 
     FIG. 6 shows a second embodiment of the invention. 
     In FIG. 6, the stereo-camera system  12  comprises at least a first camera  12   a  and a second camera  12   b . The distance between the first and second cameras  12   a  and  12   b  and the target can be calculated by using the theory of triangulation, if a separation distance between the first and second cameras  12   a  and  12   b  and the target directions (angles) to the same target are found. The target angles are found by the function of the camera itself. Based on these data, the stereo-camera  12  can perform target location. 
     The separation distance between the first and second cameras  12   a  and  12   b  in the stereo-camera system is sufficiently less than the target locating distance. It can be said from the theory of triangulation that the precision in measuring distance increases as the separation distance is larger. If the separation distance between the first and second cameras  12   a  and  12   b  is increased in order to enhance the precision in measuring distance, the size of the entire system including the milli-wave radar system increases. 
     Considering this problem, in the second embodiment, the first and second cameras  12   a  and  12   b  are arranged symmetrical with respect to the milli-wave radar system  11 . Thereby, the space for installation is reduced while the precision in measuring distance is maintained. Thus, the target locating system can be reduced in size and the precision in measuring distance can be enhanced. 
     Theoretically, if the visual line of the first camera  12   a  and that of the second camera  12   b  are made symmetrical with respect to the visual line of the milli-wave radar system  11  (r 1 =r 2 ), the visual line of the stereo-camera system  12  coincides with that of the milli-wave radar system  11 . Thus, an error in target locating results of the milli-wave radar system  11  and stereo-camera system  12  due to a displacement of visual lines of the milli-wave radar system  11  and stereo-camera system  12  is reduced. 
     A third embodiment of the present invention will now be described with reference to FIG.  7 . In the third embodiment, a conical tracking system is adopted in the milli-wave radar system  11 . In the preceding embodiments, the target locating system for the milli-wave radar system  11  is not specified. 
     In FIG. 7, reference numeral  111  is a primary horn serving as a primary radiator. The primary horn  111  is connected over a feed line  113  to a transmission/reception system  112  including a transmitter and a receiver. The primary horn  111  emits and receives an antenna beam. Reference numeral  114  denotes a reflector, e.g. a parabolic reflector. The reflector  114  is situated opposed to a radiation surface of an antenna beam radiated by the primary horn  111 , and reflects the antenna beam. The reflector  114  is selectively rotated in directions Z 1  and Z 2  by an antenna drive system  115  disposed in rear of the reflector  114 . The primary horn  111  and reflector  114  are arranged so that the centers of their mutually opposed faces may substantially coincide. 
     In operation a transmission signal produced by the transmitter (not shown) in the transmission/reception system  112  is supplied to the primary horn  111  over the feed line  113 . The primary horn  111  radiates the transmission signal to the reflector  114  as a beam  121 . An antenna beam  122  reflected by the reflector  114  is radiated to the space. 
     On the other hand, at the time of reception, a reception signal received by the primary horn  111  is supplied, in a reverse direction to the transmission mode, to the receiver (not shown) in the transmission/reception system  112  over the feed line  113 . 
     As is shown in FIG. 8, the reflector  114  is inclined such that the antenna beam  122  is offset by an angle φ with respect to the antenna visual line  123  (indicated by a two-dot-and-dash line in FIGS.  7  and  8 ). If the reflector  114  is rotated by the antenna drive system  115  about the antenna visual line  123 , the antenna beam  122  describes a conical locus at an angle φ with respect to the center axis or the antenna visual line  123 . In other words, the antenna beam  122  is scanned conically. 
     On the other hand, the feed line  113  from the transmission/reception system  112  to the primary horn  111  is extended from the outside of the reflector  114  to the reflection surface of the reflector  114  without passing through the antenna drive system  115 . Since the transmission/reception system  112  is disposed near the antenna drive system  115  on the rear side of the reflector  114 , the feed line  113  reaches the primary horn  111  from the transmission/reception system  112 , passing by the periphery of the reflector  114 . 
     According to the above embodiment, the conical scan of the antenna beam  122  is achieved by rotating the reflector  114 , and the feed line  113  is made to extend from the transmission/reception system  112  to the primary horn  111 , without passing through the antenna drive system  115 . The primary horn  111 , transmission/reception system  112  and feed line  113  are fixed as a beam generation source. As a result, unlike the prior art, the primary horn  111  and feed line  113  may not be provided with a rotary drive mechanism and a rotary joint etc. Thus, the factors of degrading the quality such as noise mixing, amplitude variation, or phase variation which are provided to antenna beam  122  by the rotary drive mechanism and rotary joint will be eliminated. Accordingly, stable transmission/reception of the beam can be achieved. 
     In addition, the feed line  113  can be used in a fixed state between the transmission/reception system  112  and primary horn  111 , for example, without rotating the feed line  113 . Thus, the feed line  113  itself may not be damaged, and the reliability of the entire system can be enhanced. 
     Furthermore, only the primary horn  111  and feed line  113  are disposed on the front side of the reflection surface of the reflector  114 . Thus, the antenna beam  122  reflected from the reflector  114  is less blocked by, e.g. an obstruction, and the antenna efficiency is less deteriorated. 
     FIG. 9 shows a fourth embodiment of the present invention. 
     In FIG. 9, the parts common to those in FIG. 7 are denoted by like reference numerals. The reflector  114  has a through-hole  131  at a central portion  114 a corresponding to its rotational axis. The through-hole  131  extends from the reflector  114  to the antenna drive system  115 . The feed line  113  extending from the transmission/reception system  112  to the primary horn  111  is passed through the through-hole  131 . 
     This structure is advantageous when the transmission/reception system  112  needs to be disposed behind the reflector  114  and antenna drive system  115  because of limitations to the disposition of the parts, or when the space for the feed line  113  cannot be provided around the reflector  114 . 
     According to the fourth embodiment, the through-hole  131  is formed at the rotational axis of the reflector  114 , and the feed line  113  extending from the transmission/reception system  112  to the primary horn  111  is passed through the through-hole  131 . Thus, the same advantage as with the preceding embodiments can be obtained without interference with the rotation of the reflector  114 . Moreover the size of the system can be reduced. 
     Even in a case where the length of the feed line  113  is limited, the feed line  113  may be passed through the through-hole  131  formed in the reflector  114  and antenna drive system  115 , thus same advantage can be obtained. 
     Needless to say, the driving system of the antenna drive system  115  in each of the above embodiments may be modified without departing from the spirit of the invention. 
     In the third embodiment, the milli-wave radar system  11  may be replaced with an electronic scan type antenna and the stereo-camera system  12  may be modified to have a wide field of view. As a result, the gimbal mechanism is dispensed with and the whole sensor can be fixed. Therefore, the precision in target locating can be enhanced. 
     In the third embodiment, the target tracking system for the milli-wave radar system  11  may be freely chosen, and different advantages may be obtained by the chosen system. The wavelength band used in the stereo-camera system  12  may be freely chosen, depending on the environment of use. 
     As has been described above, according to each of the embodiments, the flying object  21  being about to land is captured and tracked by the milli-wave radar system  11 , which is less susceptible to weather, etc., in a range between a maximum detection distance of the milli-wave radar system  11  and the vicinity of the landing point O, and the flying object  21  is, in turn, captured and tracked by the stereo-camera system  12  with high locating precision at the landing point O. 
     Accordingly, the locating distance for the flying object  21  being about to land is less decreased due to weather, etc., and exact target locating can be carried out in the vicinity of the landing point. 
     The target position information of the flying object  21  obtained by the milli-wave radar system  11  and the target position information of the flying object  21  obtained by the stereo-camera system  12  is transmitted to the control apparatus  32  via the controller  13 . Thus, the control apparatus  32  guides the flying object  21  to the vicinity of the landing point O, using the target position information from the milli-wave radar system  11  which is less susceptible to weather, etc. In the vicinity of the landing point O, the control apparatus  32  guides the flying object  21  to the landing point O, using the target position information from the stereo-camera system  12  with high location precision. 
     Accordingly, the flying object  21  can be exactly guided to the landing point, without influence of weather, etc. 
     The milli-wave radar system  11  and stereo-camera system  12  are mounted on the same gimbal  41 . Alternatively, making use of the structural feature that the stereo-camera system  12  comprises the first camera  12   a  and second camera  12   b , the first and second cameras  12   a  and  12   b  are arranged symmetrical with respect to the milli-wave radar system  11 . Thereby, the displacement in angular reference axes of both systems  11  and  12  is reduced, and the precision in switching the target tracking mode is enhanced. 
     The target tracking system of the milli-wave radar system  11  may be variously modified, for example, by adopting the conical tracking system. Thus, the transmission/reception system can be simplified, and the whole system can be reduced in size, weight and cost. If the milli-wave radar system  11  is replaced with the electronic scan type antenna and the stereo-camera system  12  is modified to have a wide field of view, a desired locating coverage can be achieved without using the gimbal mechanism. 
     In each of the above embodiments, the target detection probability or locating precision may be enhanced by providing the flying object  21  with a corner reflector for milli-wave radar or a marker for stereo-camera, which serves as a locating reference means. 
     The present invention is not limited to the above embodiments and, needless to say, various modifications may be made without departing from the spirit of the invention. 
     Additional advantages and modifications will readily occurs to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.