Abstract:
The present invention relates to a towed/surrogate decoy transmitter connectable via the tow cable to a platform or host aircraft using a wireless communicator link, the link providing useful performance and status information of the decoy transmitter to the host aircraft and providing the decoy with control and optimization information from the platform. The tow cable provides a mechanical connection to the host aircraft as well as a prime power connection and in some cases, a fiber optic (FO) interface. In order to optimize the protection provided by the towed/surrogate decoy transmitter, the host aircraft will use the wireless communication link to transmit operational status and control adjustment data back to the towed/surrogate decoy transmitter. The towed/surrogate decoy transmitter utilizes a wireless communicator link that can transmit data to any cooperative host aircraft and any other cooperative towed/surrogate decoy transmitters.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     (Not Applicable) 
     STATEMENT RE: FEDERALLY SPONSORED RESEARCH/DEVELOPMENT 
     (Not Applicable) 
     FIELD OF THE INVENTION 
     The present invention relates to a towed/surrogate decoy transmitter connected via a tow cable to a platform or host aircraft and in communication using a wireless communicator link, the wireless link providing useful performance and status information of the decoy transmitter to the host aircraft. The tow cable provides a mechanical connection to the host aircraft as well as a prime power connection and in some cases, a fiber optic (FO) interface. In order to optimize the protection provided by the towed/surrogate decoy transmitter, the host aircraft will use the wireless communication link to transmit operational status and control adjustment data back to the towed/surrogate decoy transmitter. The towed/surrogate decoy transmitter utilizes a wireless communicator link that can transmit data to any cooperative host aircraft and any other cooperative towed/surrogate decoy transmitters. 
     BACKGROUND OF THE INVENTION 
     Military aircraft operating in hostile airspace require protection against radio frequency (RF) based tracking missiles. One method of providing the needed protection is through the use of a towed/surrogate transmitter. This towed/surrogate transmitter may be dropped, fired, towed or otherwise deployed from the aircraft to be protected. The towed/surrogate transmitter acts as a decoy for the RF based tracking missile, resulting in the missile missing its target, the host aircraft, by a sufficient distance to result in survival of the host aircraft from the attack although the decoy may be sacrificed to save the aircraft. 
     It is important to ensure optimal performance of the decoy. However, without feedback on the operational status of the decoy, back to the host aircraft, the host aircraft is not warned of a failure and may not take the appropriate action to sever the decoy and deploy an operational replacement. Without any decoy operational status feedback, it is also difficult for several host aircraft to cooperate with one another for an optimal defense, where the transmitter assets of multiple aircraft can be shared to offer greater protection. 
     Towed/surrogate decoys presently communicate with the host aircraft in one of two ways. The first method is the use of fiber optic (FO) cable. For a two-way communication link using fiber optic cables, both the decoy and host aircraft must contain optical lasers and detectors. This method is expensive, because extensive modifications would be required in both the already existing decoy and host aircraft, and the complexity of a two-way link precludes it from being used in low cost, high volume decoy applications. For this reason, all current fiber optic towed decoys employ only a one-way fiber optic communications link from the host aircraft to the decoy, and optimization of the decoy operational performance is difficult. The FO interface between the host aircraft and the decoy is primarily used to relay the RF electronic countermeasure (ECM) information to the high power transmitter resident in the decoy. If the FO interface were to be used to relay decoy control information, the transmission of critical RF data, required to protect the aircraft from a missile attach, would be interrupted during the time that it takes to send the information to the decoy control circuitry. 
     The second method for a two-way communication link is through the use of a modem. The modem can be used in two ways. It can be used to superimpose the communication signals onto one of the prime power lines. This first modem realization requires that a modem and a means of coupling must be present on both the decoy and the host aircraft. The second modem realization requires that a modem must be present on both the decoy and host aircraft and a dedicated wire link must also be used. The wire link is typically at least two wires. This method is also expensive, because extensive modifications would be required in the already existing decoy, host aircraft, and the tow line (the adding of 2 wires). Some fiber optic towed decoys employ only a one-way modem communications link from either the host aircraft to the decoy, or from the decoy to the host aircraft. Lack of an easily implementable 2-way communication link to exchange operational status and control adjustment data between the decoy and host aircraft complicates the optimization of the ECM systems. 
     The decoy can also operate as a simple repeater. As a repeater, there is usually not any need for an aircraft communications interface. However, the optimization of decoy performance could benefit from such an interface. 
     SUMMARY OF THE INVENTION 
     An improved method of communications between a towed transmitter and the host aircraft to protect an aircraft against RF based tracking threats from a hostile source is disclosed. In order to deceive the RF based tracking radar, a towed/surrogate decoy transmitter is towed behind the platform or aircraft and the RF transmission is radiated by the decoy transmitter instead of the transmitters on board the aircraft. The RF based tracking missile will then lock on to the decoy transmitter instead of the aircraft. Depending on the type of tracking missile being defended against, the RF protection system can employ a variety of RF modulation schemes, called techniques, which prove effective against the particular threat. In order to be able to properly modulate the RF signal, the aircraft protection system needs to receive the operating status of the transmitter located in the towed decoy. This updated knowledge of the operating status will allow the protection system to optimize the transmitter RF drive signal from the aircraft or to command, via the control adjustment data, the decoy control circuitry to change. 
     In order to eliminate or minimize RF radiations/transmissions emanating from the host aircraft itself, the RF ECM signal, that is generated by the ECM system on-board the host aircraft, is transmitted by the towed/surrogate decoy transmitter. The signal generated by the host aircraft ECM system is transmitted through a FO cable within the tow line. Due to size and weight considerations of alternate means of transmission, fiber optics is normally used to transmit the RF signal to the towed/surrogate decoy transmitter. Due to size and cost constraints, associated with high quality lasers and detectors, the fiber optic path is typically a one-way communication link only from the host aircraft to the decoy. The only methods for the aircraft to monitor the RF transmission is to either receive the signal itself or be able to monitor transmitted signals through the use of detectors on the decoy. However, even if the host aircraft could monitor the RF transmission of the decoy using detectors on the decoy, there is no communication link, from the host aircraft to the decoy, to permit any operational parameters of the decoy transmitter to be adjusted. 
     It is important to ensure optimal performance of the decoy. However, without feedback on the status of the decoy back to the host aircraft, the host aircraft may not detect a failure or non-optimal operating performance in time to take appropriate action, from a simple parameter adjustment to severing the decoy and deploying a replacement. 
     The present invention has added a two-way RF communication link, for the purpose of sharing decoy status and operational performance of the decoy with the host aircraft. The transceivers of the two-way RF communication link can be separate circuits from the decoy transmitter circuitry. Using present cellular technology, the cost and miniaturization of the circuitry has already been achieved. The other advantage of separate circuitry, including radiating apertures/antennas, is that the operational parameters can be modified, while the towed/surrogate decoy transmitter is transmitting its RF ECM transmission to the RF based tracking radar/missile. However, it is also possible to inject the RF communication signals into the high power transmission path and utilize the existing transmitter assets and radiating aperture. 
     This communication link is used to monitor and potentially adjust the operational parameters of the towed/surrogate decoy transmitter. Built-In-Test (BIT) circuitry is utilized in the towed/surrogate decoy transmitter to monitor the operational parameters. As an example, power detectors that measure the radiated RF output power can be included in the radiating apertures of the transmitter. If the BIT circuitry on-board the decoy indicates that the decoy is not functioning properly, the host aircraft could be warned of the failure and appropriate action can be taken. The action taken may be to send operational adjust data to correct the operational performance or to sever the decoy and deploy an operational replacement. 
     In order to correct the operational performance, operational control circuitry in the decoy will process the operational adjust data from the host aircraft. The BIT circuit will monitor the modified performance and send this data to the transceivers for communication with the host aircraft. 
     If the towed/surrogate decoy transmitter is a simple repeater without a FO communication link to the host aircraft, the host aircraft could still receive the signal transmitted from the decoy and provide operational adjust data for the decoy operational control circuitry to process. 
     The host aircraft contains a host RF wireless transceiver to link with the decoy RF wireless transceiver. The performance information received by the host RF wireless transceiver is passed to the host aircraft operational control circuitry. This electronic circuitry on-board the host aircraft can process the performance data from the decoy, take appropriate corrective actions (i.e. sending control adjustment data, or severing the decoy and deploying another decoy). This information is transmitted from the host RF wireless transceiver for communication with the decoy RF wireless transceiver. For the purpose of optimizing the RF ECM signal effectiveness, the host aircraft operational control circuitry can adjust the RF input signal driving the towed decoy transmitter or any necessary adjustment, including, but not limited to modulation or signal strength. This RF input signal is transmitted through the FO tow line to the towed/surrogate decoy transmitter, where the signal is amplified for RF transmission. 
     The RF wireless communication signals can be transmitted to other aircraft, or towed/surrogate decoy transmitters for an optimized cooperative protection strategy. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a pictorial view of the preferred embodiment of the present invention of the host aircraft towing the towed/surrogate decoy transmitter. 
     FIG. 2 is a block diagram representation of the preferred embodiment of the host aircraft towing the towed/surrogate transmitter. 
     FIG. 3 is a pictorial view of an alternate embodiment utilizing shared RF transmitter and wireless communication assets. 
     FIG. 4 is a block diagram representation of the alternate embodiment illustrated in FIG.  3 . 
     FIG. 5 is a pictorial view of an alternate embodiment utilizing the towed/surrogate decoy as a repeater. 
     FIG. 6 is a block diagram representation of the alternate embodiment illustrated in FIG.  5 . 
     FIG. 7 is an pictorial view of multiple host aircraft and towed/surrogate decoy transmitters using wireless communication in a cooperative technique (sharing transmitter assets) to protect aircraft under hostile threats. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 illustrates the basic components, the preferred embodiment, for a defensive ECM system  10  against RF based tracking missiles using a towed/surrogate decoy transmitter  3 . The ECM system  10  is made up of a platform or host aircraft  1  connected to one end of a tow line  2 , and the other end connected to a towed/surrogate decoy transmitter  3 . By transmitting a RF ECM output transmission signal  4 A fore and  4 B aft from the decoy transmitter  3 , instead of from the host aircraft  1 , the RF based tracking missile will lock onto the decoy transmitter  3  instead of the host aircraft  1 . The decoy transmitter  3  is towed far enough behind the host plane, so that if any incoming missile destroys the decoy transmitter  3 , the host aircraft  1  will survive the explosion. The RF ECM signal  4 A is the fore RF ECM transmission from the towed decoy  3 .  5 A and  5 B are the two-way wireless communicator link ( 5 ) between the host aircraft  1  and the decoy transmitter  3 . If the decoy transmitter  3  is not functioning optimally, the host aircraft  1  can then use the communication link  5  to correct any operational problems, or if necessary, the defective/non-operation decoy can be severed and another decoy transmitter  3  can then be deployed. 
     FIG. 2 illustrates a block diagram of the preferred embodiment of a two-way wireless transmission link for the defensive ECM system  20  of the defensive protection system  10  in FIG.  1 . The wireless communication system  49  of the present invention is the portion depicted within the dashed lines. The host RF drive signal  27  is generated in the host aircraft  21  and rather than being transmitted from the host aircraft, the signal  27  is transmitted through the tow cable  22  to the decoy transmitter  23 . Methods of transmission though the tow cable  22  are well known in the industry and include the use of fiber optics, modems or coaxial cables to name a few. Decoy transmitter  23  will then transmit the RF ECM output transmission  24 A and  24 B, making the host aircraft  21  appear to be at a different location than it actually is. A two-way wireless link  25  is utilized by the host aircraft  21  to monitor the performance parameters of the towed decoy  23  and the host aircraft  21  will provide control signals to optimally adjust the parameters of the towed decoy  23 . 
     The host aircraft  21  contains the RF drive signal circuitry  26  to generate the host RF drive signal  27 . This signal  27  is then transmitted through the FO cable contained within the tow line  22  and is labeled as the tow line RF drive signal  41 . As the tow line RF drive signal  41 , is transmitted to the towed decoy  23 , the signal becomes the decoy RF input signal  32 . The decoy RF input signal  32 , received from the tow line  22 , is fed into the transmitter  33 . The transmitter  33  contains circuitry for amplification, modulation (if not already performed by the host aircraft) and transmission of the decoy RF input signal. The output of the transmitter  33  is the RF ECM output transmission  24 A and  24 B, which correspond to RF ECM outputs  4 A and  4 B in FIG.  1 . 
     The operational controller  28  on-board the host aircraft  21 , can also output data to adjust the operational controller  39  located in the towed decoy  23 . The output of the operational controller  28  utilizes the operational adjust lines  30 , which are an input to the wireless transceiver  31  of the host aircraft  21 . The host aircraft wireless transceiver  31  then transmits through the two-way wireless link  25  to the towed decoy wireless transceiver  37 . The decoy  23  wireless transceiver  37  then outputs this data onto the operational adjust lines  38 , for input to the operational control  39 . The operational control  39  then outputs transmission adjust signals  40  to the transmitter  33 , to modify the operational parameters desired. 
     The operational control  39  can also modify any adjustable decoy  23  performance parameter to the required specification. In this case, any signals outputted from the host aircraft operational control  28  and transmitted back to towed decoy operational control  39  through transceivers  31  and  37 , would be used to modify the operational performance of the decoy  23 . 
     BIT (Built-In-Test) circuitry  35  is used to monitor the performance specifications of transmitter  33 , through the monitored data lines  34 . The monitored data lines  34  can provide data on selected performance parameters, which include but are not limited to small signal gain, output power or modulation. One method to measure the radiated power from the transmitter is to include power detectors in the radiating apertures  45 A and  45 B. This data is then outputted by the BIT  35  as a BIT data signal  36  to the operational control circuitry  39 . Operational control circuitry  39  then outputs the BIT data on the operational adjust/BIT data lines  38  into the towed/surrogate decoy wireless transceiver  37 . The towed/surrogate decoy wireless transmitter  37 , then transmits through the two-way wireless link  25 , which corresponds to the two-way wireless communication link  5  ( 5 A and  5 B) in FIG. 1, to the host aircraft wireless transceiver  31 . The two-way wireless link  25  does not use any of the aircraft RF ECM signal generator circuitry  42  including the RF driver  26 , the tow line  22 , nor the towed decoy transmitter  33  circuitry. The transceivers  31  and  37  are not contained within the aircraft RF ECM signal generator  42  nor the decoy transmitter  33 , and therefore utilize an additional radiating aperture or antenna  46  and  47  in the two-way wireless communication link  49 . The host aircraft wireless transceiver  31  than outputs the data received through the two-way wireless link  25  as the operational adjust signal lines  30  to the RF drive signal circuitry  26 . The operational controller  28 , then determines what changes are necessary and can send commands, through the RF drive signal control lines  29 , to either adjust a performance parameter or check a performance parameter. This information can also be provided to the pilot display  43  through the control lines, pilot data  44 . The pilot can then override any potential commands from the operational control  28 . The pilot could then determine if the towed decoy performance was acceptable, needs modification, or if a new towed decoy  23  were required. The operational controller  28  can autonomously effect all operational performance adjustments or decided to deploy a new decoy. 
     FIG. 3 illustrates the second embodiment of the invention in which the wireless communications link of a defensive ECM system  110  between the host aircraft  101  and the decoy  103  can be accommodated by the sharing of the RF ECM transmitter circuitry (i.e., the amplifier and antenna assets)  107  and  106 A. The FO tow line  2  communicates the optically modulated RF ECM signal to the decoy transmitter  103 . If the communication link  107  is not available, then the wireless communication link  105  is required to realize this embodiment of the invention. 
     FIG.  4 . Illustrates a block diagram of a defensive ECM system  50 , wherein there need not be a stand alone two-way wireless transceivers  31  and  37  to transmit status of operational performance information  74  from the decoy  53  and operational adjust  30  from the host platform  51 . The two-way wireless link  49 , from the preferred embodiment shown in FIG. 2, would not be available. Instead the two-way wireless link  52  would utilize the on-board RF ECM antenna  57  on the host aircraft  51 , and a decoy antenna  45 A on the decoy  53 . The antenna  45 A would receive the host aircraft RF output  52  to the decoy transceiver  68 . The decoy transceiver  68  would provide the decoy receive output  69  to the decoy transmitter  73  for RF ECM output aft  24 B. A portion of the transmitted signal would also be transmitted towards the host aircraft  51  via antenna  45 A via line  78 . The decoy transceiver  68  is also in communication with the operational controller  72  through the operational adjust lines  77 . The operational controller  72  then uses the transmission adjust lines  75  to adjust the transmission of the decoy transmitter  73 . 
     The host aircraft  51  has a RF transmitter  55  that transmits the RF ECM input signal from the RF ECM generator/TG  42  to the antenna  57  and through the RF ECM Output (fore) and two-way wireless link  52 . The host aircraft still provides the decoy RF input signal  76  through the FO tow cable  22 . The host aircraft also has a host aircraft transceiver  56  connected to the same output path. This transceiver  56  provides the input to and receives output from the signal processing  58 . Signal processing  58  provides operational adjust input  63  to operational controller  28  and receives operational adjust input  63  back from the operational controller  28 . 
     FIG. 5 illustrates a third alternate embodiment of this invention in which the wireless communication link  117  includes the RF ECM signal including the RF decoy control and optimization signal. The reason for including the RF input signal is that the tow cable  118  does not include a FO connection between the host aircraft  111  and the decoy  113 . In other words, the decoy  113  acts as a repeater, receiving the radar signal and amplifying the signal before retransmitting. In fact, the cable line can be eliminated from the system if the decoy contains a self-contained prime power source (i.e., a battery), and is not to be towed, the towed decoy version  113  uses the host aircraft  111  for propulsion and prime power. Other embodiments would use a surrogate decoy transmitter  113 , that is either fired or released for a limited time deployment. Like the second alternate embodiment, if the on-board transmitter assets are available, the wireless communication link  119  is therefore not utilized. A communication link is critical to optimize the performance of the decoy transmitter  113 . 
     FIG. 6 shows the block diagram for the third alternate embodiment. The tow line  52  has no FO interface. The link to provide the operational adjust parameters can occur through either of two paths. If the host aircraft  82  does not have on-board ECM transmitter assets, then the two-way link  79  is used. If the host aircraft  82  has shared RF transmitter and wireless communication assets, then the link  90  is used. The difference between the link  90  in FIG.  6  and link  67  in FIG. 4 is due to the lack of FO interface in the tow line  52 . This requires the host aircraft RF ECM output (fore) and one-way wireless link  86  to provide the decoy control and optimization RF input signal through decoy receive path  88  to decoy receiver  85 . Decoy receiver  85  provides the decoy RF input signal to the decoy transmitter  73  through lines  69 . Link  87  provides the decoy RF ECM output and wireless one-way link (aft) to the host aircraft receiver  83 . The host receiver  83  then outputs this information to the signal processing  58 . 
     FIG. 7 illustrates the multiple communication paths among multiple host aircraft and decoys. Through the use of multiple paths, data from any host aircraft or decoy can be received and retransmitted by another host aircraft or decoy. This permits a master host aircraft, that is in overall control of the deployment strategy, to control any decoy RF ECM signal. The determination of the overall master host aircraft can be determined or changed as required. 
     In the illustration, host aircraft are labeled  151 ,  156  and  161 , each having a corresponding decoy labeled as  153 ,  158  and  163  respectively. A one-way communication from the host aircraft through the tow lines to the decoys are labeled as group set (host aircraft, tow line, decoy)  151 ,  152  and  153 , 156 ,  157  and  158 , and  161 ,  162  and  163 . In this illustration, host aircraft  151  is the master host aircraft. Each of the towed decoys  153 ,  158  and  163  have two-way wireless communication links,  154 ,  159  and  164 , respectively. Each of the host aircraft  151 ,  156  and  161  have two-way communication links,  155 ,  160  and  165 , respectively. Any of the aircraft or decoys can receive wireless data from and retransmit wireless data to the other towed decoys or any aircraft. The direction of the links is indicated by letters A , B and C which are added to the corresponding link number. A letter A indicates that the direction is to an aircraft or decoy above the transmitting decoy or aircraft. A letter B indicates that the direction is between an aircraft and the towed decoy. A letter C indicates that the direction is towards an aircraft or decoy that is below the transmitting aircraft or decoy. Master host aircraft  151  can communicate with decoy  163  directly through communication link  155 B, or through communication link  155 C to aircraft  156 , then aircraft  156  can retransmit through communication link  160 B to decoy  158  and then decoy  158  can retransmit though communication link  159 C to decoy  163 . The exact communication path is not critical to the control of the cooperative ECM transmitter assets. 
     Although preferred embodiments of the invention have been illustrated and described herein, it is intended to be understood by those skilled in the art that various modifications and omissions in form and detail may be made without departing from the spirit and scope of the invention as defined by the following claims.