Abstract:
A system for bistatic radar target detection employs an unmanned aerial vehicle (UAV) having a radar antenna for bistatic reception of reflected radar pulses. The UAV operates with a flight profile in contested airspace. A tactical fighter aircraft having a radar transmitter for transmitting radar pulses operates with a flight profile in uncontested airspace. A communications data link operably interconnects the UAV and the tactical fighter aircraft, the communications data link transmitting data produced by the bistatic reception of reflected radar pulses in the UAV radar antenna to the fighter aircraft.

Description:
BACKGROUND INFORMATION 
     Field 
       [0001]    Embodiments of the disclosure relate generally to tactical radar systems and more particularly to a system employing small unmanned air vehicles (UAV) deployed into contested airspace acting as bistatic radar receivers for tactical fighter jets providing the transmitting radar with data transmission from the UAV to the fighter jet for target information while allowing the fighter jet to remain out of potentially hostile airspace. 
       Background 
       [0002]    Aircraft reconnaissance and interdiction has been significantly complicated by the appearance highly accurate and often minimally detectable antiaircraft weapons. Consequently, most current tactical combat aircraft entering into contested or hostile airspace are placed at risk. The range of these weapons may be significant thus requiring a significant standoff distance to avoid the contested airspace, often beyond the effective range of radar systems employed in current tactical aircraft. The use of stealth aircraft to penetrate hostile airspace and accomplish such missions provides a certain level of increased survivability but such aircraft are highly expensive assets and are used only upon critical need. 
         [0003]    It is therefore desirable to provide a system whereby current inventory tactical aircraft may remain clear of contested airspace while being able to use radar surveillance for target identification. 
       SUMMARY 
       [0004]    Exemplary embodiments provide a system for bistatic radar target detection employing an unmanned aerial vehicle (UAV) having a radar antenna for bistatic reception of reflected radar pulses. The UAV operates with a flight profile in contested airspace. A tactical fighter aircraft having a radar transmitter for transmitting radar pulses operates with a flight profile in uncontested airspace. A communications data link operably interconnects the UAV and the tactical fighter aircraft, the communications data link transmitting data produced by the bistatic reception of reflected radar pulses in the UAV radar antenna to the fighter aircraft. 
         [0005]    The embodiments disclosed provide a method for bistatic radar target detection by launching a UAV and navigating the UAV into contested airspace while maintaining a fighter aircraft on a flight profile in uncontested airspace. A high power radar system on the fighter aircraft is employed to emit radar pulses and a radar antenna on the UAV is employed as a bistatic receiver to receive reflected radar pulses from targets. Target data is then transmitted from the UAV via a communications data link to the fighter aircraft. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]    The features, functions, and advantages that have been discussed can be achieved independently in various embodiments of the present disclosure or may be combined in yet other embodiments, further details of which can be seen with reference to the following description and drawings. 
           [0007]      FIG. 1A  is a pictorial representation of a current tactical combat aircraft with which the disclosed embodiments may be employed; 
           [0008]      FIG. 1B  is a detailed representation of external payload mounting of unmanned aerial vehicles (UAV) employed in the embodiments disclosed; 
           [0009]      FIG. 2  is a representation of the tactical aircraft and UAV after launch; 
           [0010]      FIG. 3  is a representation of the bistatic radar employed by the embodiment; 
           [0011]      FIG. 4  is a block diagram of the system elements in the UAV and aircraft; and, 
           [0012]      FIG. 5  is a flow chart of a method for implementing the disclosed embodiments. 
       
    
    
     DETAILED DESCRIPTION 
       [0013]    The system and methods described herein provide embodiments using small UAVs which are rack mountable/launchable from the air to be used as bistatic radar. The UAV is modified to carry a datalink and an appropriate radar receiver. The UAVs are launched and controlled from fighter jet such as a two-seat F-15 Eagle or F-18 Hornet. The bistatic radar combination of the UAV and fighter aircraft dramatically increases the detection range of the radar on board fighter aircraft. 
         [0014]    Referring to the drawings,  FIG. 1A  shows a tactical fighter aircraft  10  which may be employed with the system embodiments described herein. The aircraft depicted is an F-15 Eagle having multiple underwing or under fuselage pylons  12  which may support munitions or other external loads. While the aircraft  10  in the exemplary embodiment is disclosed with external load carrying capability, aircraft with internal or conformal weapons bays may also be employed.  FIG. 1B  shows a detailed view of exemplary mounting of multiple UAVs  14  on several pylons  12  to allow launch and monitoring of UAVs into multiple reconnaissance locations sequentially or simultaneously. The UAV will be launched with a launch rack  16  which adapts to the host aircraft&#39;s existing pylon. The rack  16  will may employ an Ethernet or fiber optic port, as will be described in greater detail subsequently, to load mission data from the aircraft&#39;s mission computer prior to launch. The UAV&#39;s wing is stored internal to the UAV and deployed shortly after launch of the UAV from the rack  16 . The UAV will free fall to clear out of the host fighter aircraft prior to deploying the wing or other control surfaces which may interfere with the rack  18 , pylon  12  or aircraft. Once the wing and/or control surfaces are deployed and the UAV is clear from the aircraft, then the engine of the UAV will be initiated. 
         [0015]    As represented in  FIG. 2 , after launch the UAV  14 , with wings  20 , vertical control surface  22  and horizontal control surfaces  24  deployed, is navigated, either autonomously with downloaded mission profile information or directly by aircrew in the fighter aircraft  10 , into the contested airspace  26 , represented as separated from uncontested or safe airspace  28  by boundary  30 . While UAV  14  is depicted in the exemplary embodiment as a propeller driven vehicle, turbojet or rocket powered vehicles may also be employed. 
         [0016]    In the contested airspace  26  UAV  14  provides a passive bistatic receiver for reflected radar pulses  32  from targets such as tank  34  by impinging radar pulses  36  emitted by the radar of the fighter aircraft  10 , which may remain in the uncontested airspace  28  as shown in  FIG. 3 . In the exemplary embodiments, the UAV  14  will be carrying receive only radar antenna and the host tactical fighter aircraft  10  will be carrying the transmit/receive radar. The fighter aircraft  10  has the capability to carry a radar system with power output of orders of magnitude of  10  or higher than that of the UAV  14  and thus is it possible for the fighter aircraft to stay in standoff range and radiate while remaining clear out of harm&#39;s way while UAV may need to stay “radio silence” to maintain its low observable nature. Passive operation enhances the ability of the location of the UAV  14  to be masked from hostile radar detection systems. Data characterizing target(s) such as tank  34  from the bistatically received radar data is then transmitted by the UAV  14  to the fighter aircraft  10  by datalink transmission  38 . 
         [0017]    The system components incorporated in the UAV  14  and fighter aircraft  10  are shown in  FIG. 4 . The fighter aircraft  10  incorporates a high power transmit and receive radar system  40  and a UAV controller  42 . A mission management system/pilot vehicle interface system  43  integral to the fighter aircraft and adapted for interface to a crewmember on the fighter aircraft provides interface control for the radar system  40  and the UAV controller  42 . The UAV controller may be operated by a crewmember on the fighter aircraft  10  for direct control of the UAV flight profile and UAV radar system. The UAV  14  incorporates a UAV flight control system  44  which controls the flight profile of the UAV. UAV radar system  46  is typically a passive radar antenna and data processing system for receiving and processing bistatic radar signals. However, in certain embodiments, the radar system may include transmitting capability to supplement the radar transmission from the fighter aircraft  10 . A communications data link  48  in the fighter aircraft  10  and a mating communications data link  50  in the UAV  14  are operably connected to provide communications between the fighter aircraft and the UAV. Data from the communications data link  48  to the mission management and pilot vehicle interface system  43  represented by arrow  45  provides bistatic radar information from the UAV radar system  46  and data regarding the UAV position and flight profile from the UAV control system  44  to the mission management and pilot vehicle interface system  43  for display. Radar commands  47  from the mission management and pilot vehicle interface system  43  to the aircraft radar system  40  provide commands to the radar to directionally control the radar beam to the intended target. UAV commands  49  from the mission management and pilot vehicle interface system  43  to the UAV controller  42  provide input through the communications data link  48  to command the UAV to fly/orbit/loiter in a desired flight profile. In the exemplary embodiment, an L-band (1.5 to 4 GHz) data link for line of sight bidirectional communication is employed. The UAV may remain primarily in a receive only mode. The data link will contain messages which will be used to direct and control the UAV&#39;s flight control system  44  as well as the radar system  46 , as needed. The UAV will use the data link to report its location and current air vehicle status back to the host fighter aircraft as well as transmission of data from the radar system  46 . The communications data links  48 ,  50  may employ data burst or beam agility capability for covert operation. As previously described, the communications data links  48 ,  50  may also employ pre-launch communications elements  52 ,  54  “hardwire” connected through Ethernet or fiber optic port  56  as previously described for pre-launch communication between the fighter aircraft  10  and UAV  14 . 
         [0018]    Accordingly, the UAV is not tethered, but rather the UAV is releasably coupled to a host aircraft&#39;s existing pylon (or other mounting structure) in a manner such that the UAV may be deployed from and guided by the UAV controller in the fighter aircraft towards a target in a contested airspace, to thereby increase the target detection range beyond the fighter aircraft such that the fighter aircraft can stay out of contested airspace while collecting radar data on a target within the contested airspace. 
         [0019]    The UAV  14  may be retrieved via conventional landing after a flight profile exiting the contested airspace or the UAV will carry a destruct system  58  with explosives for self-destruction purposes on vital communication and radar subsystems in the UAV. The destruct system  58  may be activated, either as a portion of the flight profile or upon loss of data link communications, through the UAV control system  44 , or upon instruction from mission management and pilot vehicle interface system  43  through the UAV controller  42  on the fighter aircraft  10  transmitted using communications data links  48 ,  50 . 
         [0020]    The embodiments disclosed herein allow a method of target detection as shown in  FIG. 5 . A UAV is mounted to a fighter aircraft, step  502 , and mission information, potentially including an autonomous flight profile, may be downloaded from the fighter aircraft to the UAV, step  504 . The UAV is launched and navigated into contested airspace, step  506 , while the fighter aircraft maintains a flight profile in uncontested airspace, step  508 . The fighter aircraft employs a high power radar system to emit radar pulses, step  510 , and the UAV employs a radar antenna as a bistatic receiver to receive reflected radar pulses from targets, step  512 . The UAV then transmits target data via a communications data link to the fighter aircraft, step  514 . The UAV may additionally receive flight control information from the fighter aircraft over the communications data link, step  516 , and may report its location and current status, step  518 . Upon completion of the mission profile, the UAV may fly to uncontested airspace and be recovered through conventional landing or other known recovery techniques, step  520 . Alternatively, the UAV may self-destruct either autonomously through commands from the UAV control system or upon direction from the UAV controller on the fighter aircraft, step  522 . While described herein as launched from the fighter aircraft, the UAV may be conventionally launched from other ground or airborne assets for the desired flight profile into contested airspace achieving data link communication with the fighter aircraft when both have established their respective flight profiles. 
         [0021]    Having now described various embodiments of the disclosure in detail as required by the patent statutes, those skilled in the art will recognize modifications and substitutions to the specific embodiments disclosed herein. Such modifications are within the scope and intent of the present disclosure as defined in the following claims.