Abstract:
A ranging seeker apparatus includes an RF antenna and a bistatic ranging detector operatively connected with the RF antenna. The RF antenna and bistatic ranging detector are operative for detecting one or more guidance objects in a RF band and providing angle and range data to the missile. Also, a missile including a missile body, a missile propulsion system disposed in or on the missile body, and the ranging bistatic RF seeker disposed in or on the missile body.

Description:
STATEMENT OF GOVERNMENT INTEREST 
     This invention was made with Government support under Contract N00024-03-C-6110 awarded by the Department of the Navy. The Government has certain rights in this invention. 
    
    
     FIELD OF THE INVENTION 
     The disclosure relates to target tracking devices. More particularly, the disclosure relates to a missile with a ranging bistatic RF seeker. 
     BACKGROUND 
     High-velocity guided missiles are used for intercepting very fast targets, such as ballistic rockets, or highly maneuverable targets. Such missiles use a seeker to detect and guide the missile to the intended target. 
     Seeker-missiles typically employ optical, infrared (IR), radio frequency (RF), or multi-mode seekers for detecting and guiding the missile toward the intended target. Multi-mode seekers, may employ both an IR and/or optical seeker, and a RF seeker for detecting and guiding the missile toward the intended target. 
     Existing multi-mode seekers employ either an active RF seeker providing range and angle information for terminal guidance only, or employ a bistatic RF seeker that is not cohered with an illuminator, and therefore provides angle information only. Consequently, existing multi-mode seekers fail to provide range information over most or all of the intercept path, which degrades their ability to detect and guide the missile toward the intended target. 
     Accordingly, a seeker that provides the missile with ranging information offers the ability to resolve objects in range that are close in angle, and the ability to measure object distance for improved detection and guidance of the missile to its intended target. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic side view of an exemplary embodiment of a missile with bistatic RF ranging capability. 
         FIG. 2  is a schematic front view of the missile of  FIG. 1 . 
         FIG. 3  is a schematic diagram of an exemplary embodiment of a system, in which the missile of  FIG. 1  may be used. 
         FIG. 4  is a block diagram detailing data flow in the system of  FIG. 3 . 
         FIG. 5A  schematically illustrates how the bistatic range detector computes the range (bistatic range) of each one of the objects of a cluster of moving, air-borne objects (the range between the missile and the object). 
         FIG. 5B  depicts an iso-delay surface for illustrating bistatic range calculations. 
     
    
    
     SUMMARY 
     A seeker apparatus for a missile is disclosed herein. The apparatus includes a an RF antenna; and a bistatic ranging detector operatively connected with the RF antenna. The RF antenna and bistatic ranging detector are operative for detecting one or more guidance objects in a RF band and providing angle and range data to the missile. 
     Further disclosed herein is a missile including a missile body; a missile propulsion system disposed in or on the missile body; and a ranging bistatic RF seeker disposed in or on the missile body. 
     Also disclosed herein is a method for detecting and guiding a missile to a targeted object. The method includes illuminating the target object with RF illumination produced by a source external to and cohered with the missile; detecting RF illumination scattered by the targeted object with an RF seeker of the missile; estimating a range between the missile and the targeted object with the RF seeker using illuminator position data, missile position data, missile attitude data, targeted object delay data and target object angle data; and guiding the missile to the targeted object using the estimated range data. 
     Still further disclosed herein is a method far detecting and guiding a missile to an object targeted in a cluster of objects. The method includes illuminating the objects with RF illumination produced by a source external to and cohered with the missile; detecting RF illumination scattered by each of the objects with an RF seeker of the missile; estimating a range between the missile and each of the objects with the RF seeker using illuminator position data, missile position data, missile attitude data, and target object angle data; and guiding the missile to a selected one of the objects in the cluster of objects based on the estimated ranges, angles, and rates, the selected one of the objects being the targeted object. 
     DETAILED DESCRIPTION 
       FIG. 1  shows an exemplary embodiment of a missile with bistatic RF ranging capability, designated by reference numeral  100 . The missile  100  includes a missile body  102  that contains a guidance and propulsion system  104 . The propulsion sub-system of the guidance and propulsion system  104  includes, for example, a rocket motor, a jet engine, or other thrust-producing device. The guidance and propulsion system provides missile guidance, control, and propulsion to enable the missile to intercept a targeted, moving, air-borne object (target object). 
     The missile  100  further includes a ranging bistatic RF seeker (RF seeker) formed by an RF seeker antenna  122 , a multi-channel receiver  114 , and a bistatic ranging detector  116 . The bistatic RF seeker detects the moving, air-borne targeted object or a cluster of moving, air-borne objects (one of which is the targeted object) in the RF band and provides angle and precision range data for object association and missile guidance. The RF seeker antenna  122  is located in a forward tip  103  of the missile  100  behind a dome  110  which is transparent to infrared and RF radiation. In other embodiments of the missile  100 , the dome  110  may be omitted. The multi-channel receiver  114  is located in the missile body  102  and has one or more inputs that are operatively coupled to one or more outputs of the RF seeker antenna  122 , and an output that is operatively coupled to an input of the bistatic ranging detector  116 . As shown in  FIG. 4 , the bistatic ranging detector  116 , in one embodiment, includes a multi-channel detector  408  and a bistatic range estimator  410  operatively coupled to an output of the multi-channel detector  408 . 
     An IR seeker  112  can also be located in the forward tip  103  of the missile  100  behind the dome  110 . The IR seeker  112  is operatively coupled to an input of the RF seeker&#39;s multi-channel receiver  114 . The IR seeker  112  detects the moving targeted object or the cluster of moving objects that includes the targeted object, in the IR band and provides precision angle data for object association and missile guidance in conjunction with the ranging bistatic RF seeker. In other embodiments of the missile, the IR seeker  112  may be omitted. 
     An illuminator-synched high-precision clock  120  or other coherent timing source can be included in the missile body  102  of the missile  100 , and is operatively coupled to the input of the multi-channel receiver  114 . The illuminator-synched clock  120  provides the multi-channel receiver  114  with precision time delay data relating to one or more RF radar illuminators located remotely from the missile  100 . In other embodiments, the clock  120  can be included in the RF seeker or be external to both the missile and RF seeker. 
     The missile  100  can further include a GPS/INS navigation system  118  (a global positioning system integrated with an inertial navigation system) operatively coupled to the bistatic ranging detector  116 . The navigation system  118 , in other embodiments, can be included in the RF seeker or be external to both the missile and the RF seeker. The GPS/INS navigation system  118  provides the bistatic ranging detector  116  with missile position and attitude data (seeker navigation data). The bistatic range detector  116  is constructed to generate RF seeker-observed target object angles and RF seeker-observed target object ranges. More specifically, the multi-channel detector  408  of the bistatic range detector  116  generates time synchronized detections, i.e., target object delays and target object angles. The target object angles at the output of the multi-channel detector  408  are available at the output of the bistatic range detector  116  for use in missile guidance and association. The bistatic range estimator of the bistatic range detector  116  uses the time synchronized detections (target delays and target angles) at the output of the multi-channel detector  408  and the missile or seeker navigation data (e.g., missile position, velocity, and/or attitude) at the output of the GPS/INS navigation system  118 , to estimate target object ranges. 
     An RF communications antenna  109  is located on or in the missile body  102  of the missile  100 . The RF communications antenna  109  is operatively coupled to an RF uplink  108  located in the missile body  102 . The RF communications antenna  109  receives target object map (TOM) data (pertaining to the moving targeted object or the cluster of moving objects which includes the targeted object) from a missile firing platform  304  ( FIG. 3 ) of the missile and/or a Radar Command and Control System  302  ( FIG. 3 ) and the RF uplink  108  uploads the object data (TOM data) to an operatively coupled association and selection logic (ASL) unit  106  located in the missile body  102  of the missile  100 . The ASL unit  106  is also operatively coupled to the input of the bistatic ranging detector  116  and an input of the guidance and propulsion system  104 . The ASL unit  106  processes the object data received from the RF uplink  108  and the estimated seeker angle and range data at the output of the bistatic ranging detector  116 , to associate by position and velocity, the moving targeted object or the cluster of moving objects that includes the targeted object observed or detected by the RF seeker (and the IR seeker if equipped), with targeted object guidance data provided by the missile firing platform  304  of the missile and/or the Radar Command and Control System  302  via the RF uplink, and in the case of the cluster of objects selects a “best” one of the objects in the cluster (i.e., the targeted object to intercept) for input to the guidance and propulsion system  104 . 
       FIG. 2  is a front view of the missile. As can be seen, the RF seeker antenna  122 , in one exemplary embodiment, is formed by a set of sub-arrays  122   a , each sub-array  112   a  being formed by one or more antenna elements. The sub-arrays  122   a  of the RF seeker antenna  122  conventionally sense and convert scattered RF radar illumination into a radar signal which is applied to the input of the multi-channel receiver  114 . 
       FIG. 3  is a schematic diagram of an exemplary embodiment of a system, designated by reference numeral  300 , in which the RF seeker-equipped missile  100  may be used. The system  300  includes, a Radar Command and Control System (RCCS)  302 , a missile firing platform  304  for firing the missile  100 , an RF illuminator  306  located at the firing platform  304 , and/or one or more RF illuminators  308  located remote from the firing platform. The missile  100 , the missile firing platform  304 , the RF illuminator  306 , and the remotely located RF illuminator(s)  308  are operatively coupled (using e.g., any suitable wireless method) with the RCCS  302 . The RCCS  302  coordinates the missile  100 , the missile firing platform  304  and the RF illuminators  306 ,  308  and provides command and control services between assets (not shown). The one or more remote RF illuminators  308  may be located on the ground, in the sky, at sea, in space or in or at any other remote location. In addition, the RF illuminators  306 ,  308  form an external RF radar illumination source for the missile  100 . 
     Although the RF seeker-equipped missile  100  uses bistatic ranging in conjunction with some type of association logic to associate with an external TOM, it should be understood that in other embodiments, the RF seeker-equipped missile  100  can operate with just course guidance (point and direction) and without any external information. 
     Referring still to  FIG. 3 , the RCCS  302  directs the RF illuminator(s) ( 306 ,  308 ) to illuminate one or more air-borne objects  310  with remote RF radar illumination. The RF illuminators  306 ,  308  sense the RF illumination scattered by one or more objects in object cluster  310  and communicate this radar data (illuminator sensed radar data) to the RCCS  302 . The RCCS  302  evaluates the illuminator sensed radar data and possibly data from other sensor assets (not shown), to produce targeted object guidance information for the missile  100 . The RCCS  302  communicates the targeted object guidance information to the RF seeker-equipped missile  100  and/or the missile platform  304  and then, the RCCS  302  and/or the platform  304  fires the missile  100 . As the missile  100  travels towards a targeted one of the objects in the cluster of objects  310 , the missile  100  is cohered with the external illumination provided by first and second RF illuminators  306 ,  308  because the RCCS  302  continuously sends updated targeted object guidance information to the missile  100 . The missile  100  receives and processes the targeted object guidance data and associates the cluster of objects  310  observed or sensed by the RF seeker and optionally, the IR seeker of the missile  100  with the target object guidance data provided by the missile firing platform  304  of the missile  100  and/or the Radar Command and Control System  302  to select the “best” one of the objects in the object cluster  310  (the targeted object to intercept) for input to the guidance and propulsion system  104  of the missile  100 . 
       FIG. 4  is a block diagram detailing data flow in the system  300  of  FIG. 3 . The RF illuminators  306 ,  308  each have a coherent timing source  403  (e.g., a high-precision clock) that generates timing data. As the RF illuminators  306 ,  308  illuminate the one or more objects in the object cluster  310  and then sense the RF radar illumination scattered by the one or more objects in the object cluster  310 , the timing data generated by the coherent timing sources  403  of the RF illuminators  306 ,  308  is time synchronize against a time-synched reference  402  (e.g., clock  120  of the missile  100  or an illuminator-synchronize clock). Accordingly, the RF illuminators  306 ,  308  form a coherent, external illumination source for the RF seeker-equipped missile  100  the RF illumination of which is cohered with the missile  100 . The time-synched reference  402  coheres the multi-channel detector  408  of the bistatic range detector  116  with one or more remote RF radar illuminators  306 ,  308 . Illuminator position data  404  provided by the RCCS  302 ,  308  and seeker position and attitude data  406  provided by the GPS/INS  118  of the missile  100 , are applied to the bistatic range estimator  410  of the bistatic range detector  116  of the missile  100 . The RF seeker antenna  122  of the missile  100  conventionally senses and converts the RF illuminator&#39;s radar illumination scattered by the objects in the cluster  310  into a radar signal (e.g., a voltage), which radar signal is communicated to the multi-channel receiver  114 . The multi-channel receiver  114  conventionally processes the radar signal and applies the processed radar signal to the input of the multi-channel detector  408 . The multi-channel detector  408  applies target object delay data  408 - m  and target object angle data  408   TA  to the input of the bistatic range estimator  410 . The multi-channel detector also applies the target object angle data  408   TA  to the input of the ASL unit  106 . The bistatic range estimator  410  uses the illuminator position data  404 , the seeker position and attitude data  406 , the target object delay data  408   TD  and the target object angle data  408   TA , to estimate target object range data  410   TR  for each object detected in the cluster  310 , which is applied to the input of the ASL unit  106 . The ASL unit  106  processes the target object angle data  408   TA  received from the multichannel detector  408 , the estimated target object range data  410   TR  received from the bistatic range estimator  410 , and the object data (TOM data)  108   O  received from the RF uplink  108 , to perform the earlier described association and guidance functions, i.e., associate the one or more target objects observed or detected by the RF seeker of the missile  100  with the guidance object data (e.g., object track and discrimination data) provided by the missile firing platform  304  of the missile and/or the Radar Command and Control System  302 , and select the best guidance object (the object in the cluster which best matches targeted object to hit) for input to the guidance and propulsion system  104  of the missile  200 . Any suitable matching method, such as a goodness-of-fit or closeness metric, can be used for selecting the best guidance object. 
       FIG. 5A  schematically illustrates how the bistatic ranging detector  116  of the RF seeker-equipped missile  100  calculates the range (bistatic range) of each one of the objects (the target object for that calculation) of the cluster (the range  506  between the RF seeker-equipped missile  100  and the target object  500 ). The RF seeker of the missile  100  senses or detects a response by each one of the target objects  500 , to a given one of the RF illuminators (either RF illuminator  306  or  308 ) along a surface  502  of constant time delay, i.e., an iso-delay surface. The iso-delay surface  502  can be determined by measuring the time delay difference between the received waveform and the on-missile waveform generated from the cohered clock. The iso-delay surface  502  forms an ellipsoid whose two foci are coincident with the RF illuminator  306  or  308  and the missile  100 . For each one of the target objects  500  of the cluster, the distance or range  504  from the missile  100  to the target object  500  is the point of intersection  510  between the ellipsoid surface  502  and a line  506  subtended in the seeker observed direction  508  defined by angles Φ, Θ. The angles Φ, Θ can be determined using a monopulse or phase difference of arrival technique. Because the RE seeker of the missile  100  and the RF illuminator  306  or  308  are cohered, i.e., the timing data generated by the coherent timing sources  403  of the RF illuminators  306 ,  308  is time synchronized against the time-synched reference  402 , the bistatic ranging detector  116  of the RF seeker of the missile  100  can estimate the range  506  between the missile  100  and the target object  500 . In one exemplary embodiment, the illuminator waveforms are time and/or phase coded to maximize range resolution, accuracy, and detection; and minimize range ambiguity. Time and/or phase coding is often employed in other digital communications systems, such as GPS, for instance for similar reasons stated. 
     The bistatic range calculations performed by the bistatic ranging detector  116  of the RF seeker-equipped missile  100  will now be described with reference to the iso-delay surface  502  (τ) illustrated in  FIG. 5B . Given the following expressions:
 
∥ P   Tgt   −P   Skr   ∥+∥P   Tgt   −P   III   ∥c·τ 
 
 P   Tgt   =P   Skr   +R·d  
 
             R   =             c   2     ·     τ   2       -         [       P   Skr     -     P     I   ⁢           ⁢   11         ]     T     ⁡     [       P   Skr     -     P     I   ⁢           ⁢   11         ]           2   ·     (       s   ·   τ     +       d   T     ⁡     [       P   Skr     -     P     I   ⁢           ⁢   11         ]         )         .           
where:
 
     P Tgt  is the location vector or point of the target object  500  on the iso-delay surface  502 ; 
     P Skr  is the location vector or point of the RF seeker-equipped missile  100  on the iso-delay surface  502 ; 
     P III  is the location vector or point of the RF illuminator  306  or  308  on the iso-delay surface  502 ;
         ∥P Tgt −P Skr ∥ is the norm of the distance on the iso-delay surface  502  between the point of the target object  500  and the point of the RF seeker-equipped missile  100 ;   ∥P Tgt −P III ∥ is the norm of the distance on the iso-delay surface  502  between the point of the target object  500  and the point of the RF illuminator  306  or  308 ;   c is the velocity constant for speed of light; and   d is the RF seeker-equipped missile-to-target object direction vector,
 
the bistatic range R, i.e., the range between the RF seeker-equipped missile  100  and the target object  500 , can be estimated using the following expression:
       

     
       
         
           
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     The bistatic range data (the estimated target object range data  410   TR ) can then be used by the ASL unit  106  along with the target object angle data  408   TH  and the object data (TOM data)  108   O , to perform the earlier described association and guidance functions and select the best guidance object (target object to hit) for input to the guidance and propulsion system  104  of the missile  200 . 
     While exemplary drawings and specific embodiments have been described and illustrated herein, it is to be understood that that the scope of the present disclosure is not to be limited to the particular embodiments discussed. Thus, the embodiments shall be regarded as illustrative rather than restrictive, and it should be understood that variations may be made in those embodiments by persons skilled in the art without departing from the scope of the present invention as set forth in the claims that follow and their structural and functional equivalents.