Abstract:
Embodiments of the present invention relate to a chaff electronic countermeasure device for protecting mobile platforms against radio frequency threats. A device comprises an antenna that is in communication with a substrate. An integrated circuit is in electrical communication with the antenna. The device is configured to absorb from a source a first radio frequency having a first amplitude. In response to absorbing the first radio frequency, the device reradiates at least a portion of a second radio frequency having a second amplitude toward the radar source, which results in an increased radar cross section of the device as perceived by the radar source. The second amplitude is higher than the first amplitude.

Description:
[0001]    This application is a 371 application of International Application No. PCT/US15/55909, filed Oct. 16, 2015, which claims priority to Provisional Application No. 62/064,974 filed Oct. 16, 2014, which is hereby incorporated herein by reference. 
     
    
     BACKGROUND 
       [0002]    The present invention relates generally to electronic counter measures and specifically to electronic countermeasures for protecting mobile platforms against radio frequency threats. Radar systems, typically use electromagnetic waves to identify characteristics, such as range, altitude, direction, and/or speed, of moving objects, such as aircrafts and ships. Such radar systems may support surface-to-air missiles (“SAM”) and anti-aircraft armament (“AAA”). Radar system antennae typically transmit pulses of radio waves or microwaves. A portion of these pulsed waves can be reflected from objects that are in the wave&#39;s path (or sidelobes of the radar&#39;s antenna), and returned to the antenna, wherein the associated radar system detects and measures the reflected waves. Using the time it takes for the reflected waves to return to the antenna and additional signal processing techniques, a radar system computer can calculate how far away the object is, its radial velocity and other characteristics. Transmitters and receivers for such systems can be separate entities (“bistatic”) or may exist as co-located unified systems. 
         [0003]    Electronic counter measures (“ECM”) may include electrical devices that can be designed to nullify or reduce the effectiveness of radar systems. ECMs may be deployed defensively and/or offensively to deny and/or reduce the ability to generate targeting, tracking, identification, and/or positioning information. One form of radar countermeasures is the use of chaff. Chaff may be dispersed as clouds of resonant dipoles into the atmosphere to create a high radar return zone to mask the presence and/or location of an object. Chaff is typically a passive ECM that can be comprised of shredded aluminum foil and/or a glass substrate coated with aluminum. Chaff can have an average overall diameter of around 25 microns. Chaff can be deployed offensively and/or defensively. 
         [0004]    Chaff can be employed as a “decoy” or to disrupt the tracking radar lock-on function of, for example, a fire control anti-aircraft armament or missile system. The individual aluminized glass fibers can form electromagnetic dipoles. Effectively, chaff are passive reradiating antennae. The principles on which radar impairment is based are similar whether the radar system is monostatic or bistatic. The main idea is to cause a relatively large amount of energy, dispersed in both angle and range, to be reflected to the receiver with energetic energy sufficient to dominate (i.e. mask) the return signal from the object (i.e. the signal related to object scattering). 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0005]      FIG. 1  depicts a radio counter measure environment, in accordance with an embodiment of the present invention. 
           [0006]      FIG. 2  illustrates a return loss trace, in accordance with an embodiment of the present invention. 
           [0007]      FIG. 3  illustrates a step involved in a radio counter measure scheme, in accordance with an embodiment of the present invention. 
           [0008]      FIG. 4  illustrates an additional step involved in the radio counter measure scheme, in accordance with an embodiment of the present invention. 
           [0009]      FIG. 5  illustrates an additional step involved in the radio counter measure scheme, in accordance with an embodiment of the present invention. 
           [0010]      FIG. 6  illustrates an additional step involved in the radio counter measure scheme, in accordance with an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0011]    The descriptions of the various embodiments of the present invention have been presented for purposes of illustration but are not intended to be exhaustive or limited to the embodiments disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. The terminology used herein was chosen to best explain the principles of the embodiments, the practical application or technical improvement over technologies found in the marketplace, or to enable others of ordinary skill in the art to understand the embodiments disclosed herein. As used herein, the phrases “radio frequency energy” and “radio frequency signals” are used interchangeably. 
         [0012]    Radar systems, which may be associated with surface-to-air missiles (“SAM”) and anti-aircraft armament (“AAA”), can use electromagnetic waves to identify and/or track characteristics of mobile objects, such as range, altitude, direction, and/or speed. Applicable mobile objects include, for example, aerial and aquatic platforms. Radar system antennae typically transmit pulses of radio waves or microwaves. A portion of these pulsed waves can be reflected from the surface objects that are in the wave&#39;s path, and returned to the antenna, wherein the associated radar system detects and measures the direction of the reflected waves in azimuth and elevation. Using the time it takes for the reflected waves to return to the antenna, a radar system computer can calculate how far away the object is, its radial velocity and other characteristics. Transmitters and receivers for radar systems can be separate components or may exist as unified systems. 
         [0013]    Electronic counter measures (“ECM”) can include electrical devices that are designed to nullify or reduce the effectiveness of radar systems. ECMs may be deployed defensively and/or offensively to deny and/or reduce the ability to generate targeting information. One form of radar countermeasures is the use of chaff. Chaff is a passive ECM that is typically made of shredded aluminum foil and/or a glass substrate coated with aluminum. Chaff may be deployed as clouds of dipoles into the atmosphere to create a high radar return zone to mask the presence of true targets, such as mobile platform  300  (discussed below). 
         [0014]    Chaff may also be deployed as a “decoy” or to disrupt the tracking radar lock-on function of, for example, fire control anti-aircraft armament or missile systems. Individual aluminized glass fibers can form electromagnetic dipoles that effectively act as passively reradiating antennae. The principles on which radar impairment is based are similar whether the radar system is monostatic or bistatic. The main idea is to cause a relatively large amount of energy, dispersed in both angle and range, to be reflected to the receiver with energetic energy sufficient to dominate (i.e. mask) the return signal from the target (i.e. the signal related to target scattering). 
         [0015]    Embodiments of the present invention seek to provide electrical devices that protect mobile platforms, such as aerial and sea-based mobile platforms, against radio frequency (“RF”) threats. Other embodiments of the present invention seek to provide redirective active electronic countermeasures (“AECMs”). Additional embodiments of the present invention seek to provide AECMs that are comprised of printed components. Other aspects of the present invention seek to provide AECMs that reflect RF at a higher amplitude than received. Still other embodiments of the present invention seek to provide AECMs that having a finite life span. Additional embodiments seek to provide AECMs having electromagnetic wave scattering properties. Certain embodiments of the present invention seek to provide AECMs that transmit RF in a manner that compromises a radar system&#39;s resolution cells, in range and angle; Doppler sidelobes; and/or saturates the radar&#39;s processors. 
         [0016]      FIG. 1  depicts a RF counter measure environment (“RFCME”), generally  100 , in accordance with an embodiment of the present invention. RFCME environment  100  can include antenna  110  and active electronic counter measure (“AECM”)  140 . Antenna  110  is a radar antenna, such as a terrestrial, aerial, or aquatic platform. Antenna  110  can be stationary or included on a mobile platform. In an embodiment, antenna  110  is in communication with one or more SAM and/or AAA radar systems. AECM  140  is a radio-based electronic countermeasure having electromagnetic wave scattering properties, in accordance with an embodiment of the present invention. AECM  140  AECM  140  comprises integrated circuit (“IC”)  130  and antenna  120 . AECM  140  can reflect RF in a manner that increases the radar cross section of the device. AECM  140  may be included in a mobile platform (discussed below). AECM  140  can have a shape that is rectangular, multiangular, trapezoidal, round, or oblong. In certain embodiments, AECM  140  can have a shape that supports an atmospheric dwell time of about 1 minute to about 5 minutes. 
         [0017]    IC  130  can be an IC configured with a processing unit that modulates RF signals. Antenna  120  is an electrical device that converts electric power into radio waves and vice versa. Antenna  120  can be a dipole antenna. Antenna  120  can be a broadband antenna. Antenna  120  may be printed on to the surface of a substrate using an electrically conductive composition (“the composition”). The composition can include graphene, graphite, and/or conductive polymers. Applicable graphene can include graphene sheets. The graphene, composition, print substrates, and/or associated printing methods can be derived and/or accomplished utilizing a variety of methods, including, but not limited to, methods disclosed by, for example, U.S. Pat. No. 7,658,901 B2 by Prud&#39;Homme et al, United States patent application 2011/0189452 A1 by Lettow et al., McAllister et al. ( Chem. Mater.  2007, 19, 4396-4404), United States patent application 2014/0050903 A1 by Lettow et al., and U.S. Pat. No. 8,278,757 B2 by Crain et al, which are hereby incorporated by reference in their entirety. AECM  140   
         [0018]    In addition to the substrates disclosed in the aforementioned references, applicable substrates can include substrates that disintegrate in about 1 minutes to about 5 minutes, about 5 minutes to about 10 minutes, about 10 minutes to about 15 minutes, about 15 minutes to about 20 minutes, about 20 minutes to about 25 minutes, or about 25 minutes to about 30 minutes upon deployment, reaching a predetermined altitude, and/or exposure to air. Applicable substrates can be biodegradable. AECM  140  can comprise a substrate to which IC  130  and/or antenna  120  is applied and/or affixed. In certain embodiments, in response to a RF signal, such as carrier signal  160 , passing through antenna  120 , an AC voltage is generated across antenna  120 , which is rectified to result in DC voltage for the operation of IC  130 . IC  130  can operate similar to an active or passive RFID tag IC. 
         [0019]    IC  130  can become functional as a result of the DC voltage reaching a predetermined level at which time AECM  140 , via antenna  120 , reflects the RF signal (i.e. backscattering signal  150 ) in a near omnidirectional pattern, at least a portion of which is received by antenna  110 . AECM  140  can, via antenna  120 , transmit backscattering signal  150  at a higher amplitude compared to that of carrier signal  160 . For example, to achieve backscattering signal  150 , IC  130  can modulate the amplitude of carrier signal  160 . Alternatively, IC  130  can comprise an internal power source, such as a battery, to power the modulating function. In embodiments wherein IC  130  comprises an internal power source, the internal power source increases the gain and/or increases the amplitude of backscattering signal  150 . Antenna  120  can have a length that is about ¼ to about ½, about ½ to about ¾, or about a multiple of carrier signal  160 . 
         [0020]    The resonant frequency of a dipole antenna, such as antenna  120 , can be determined by its length. For example, the length of antenna  120  can be optimized for narrow band (specific radar threats) or changing the length to diameter ratio enabling larger bandwidth-frequency response to threat radar. The length of antenna  120  can be determined by equation [1]. 
         [0000]        l= 468/ f   MHz   [1]
 
         [0000]    wherein l is the dipole length in feet and f MHz  is the frequency in megahertz (MHz), which equals approximately the resonant half-wavelength of carrier signal  150 . For example, a cloud of AECM  140  requires the length of antenna  120  to be selected to provide dipole resonance that correspond to at least about the radar wavelength (i.e. carrier signal  150 ), and corresponding frequency, and for possible radar operation at adjacent frequencies in the radar band. In certain embodiments, the dipoles in an AECM  140  cloud can provide the broadband frequency coverage indicated by carrier signal  160 . For example, the broadband frequency coverage can be accomplished using dipoles of different lengths. 
         [0021]    Antenna  120  can have a length that is about ¼ to about ½, about ½ to about ¾, or about a multiple of carrier signal  160 . AECM  140  can be stored in an oxygen free enclosure. AECM  140  can be stored in an enclosure, such as a chaff launch tube. AECM  140  can function in a similar manner as chaff. Clouds of activated AECM  140  can act as decoys that mimic particular mobile platforms. Clouds of activated AECM  140  can confuse the aggressor missile threat by providing multiple false targets. Applicable shapes for AECM  140  can include, but are not limited to square trihedral corner retro-reflector, right dihedral corner reflector, flat plate, cylinder, sphere, straight edge normal incidence, curved edge normal incidence, apex, discontinuity of curvature along a straight line normal incidence, discontinuity of curvature of a curved edge, and discontinuity of curvature along an edge. 
         [0022]    The activated AECM  140  cloud can disrupt the tracking radar lock-on function of, for example, fire control anti-aircraft armaments or missile systems that are associated with antenna  110 . AECM  140  can transmit backscattering signal  160  to antenna  110  with an amplitude sufficient to dominate or mask energy due to target scattering. AECM  140  clouds can comprise randomly oriented copies of AECM  140  that contribute to the total radar cross section of the cloud. AECM  140  can transmit backscattering signal  160  in a continuous or discontinuous manner, for example, in a repeating manner. AECM  140  can transmit backscattering signal  160  in a delayed manner subsequent to activation, for example, to simulate different ranges. 
         [0023]    Antennas  120  can operate in one or more (multi-octave) North Atlantic Treaty Organization (“NATO”) frequency bands, such as A, B, C, D, E, F, G, H, I, J, K, L and M. In an embodiment, one or more copies of AECM  140  having differing operational frequencies are used to cover a plurality of bandwidths. Backscattering signal  160  can correspond to at least a portion of bandwidth  150 . 
         [0024]      FIGS. 2-4  illustrate data for an antenna, for example, antenna  120 , in accordance with an embodiment of the present invention.  FIG. 2  illustrates a gain versus frequency plot, generally  200 , in accordance with an embodiment of the present invention. Plot  200  depicts an antenna gain versus frequency plot, wherein measurements were taken while the antenna transmitted at frequencies corresponding to 800 MHz to 900 MHz.  FIG. 3  illustrates an antenna gain versus frequency plot, generally  302 , in accordance with an embodiment of the present invention. Plot  302  depicts an antenna gain versus frequency plot, wherein the measurements were taken while the antenna transmitted at frequencies corresponding to 650 MHz to 3000 MHz.  FIG. 4  illustrates an antenna return loss plot, in accordance with an embodiment of the present invention. Specifically,  FIG. 6  illustrates the S11 return loss for the antenna. Combined,  FIGS. 2-4  demonstrate that antennas of the present invention are capable of exhibiting broadband characteristics with high gain at 650 MHz to 3000 MHz, a relatively good match, and a return loss at or below about −10 dB. 
         [0025]      FIGS. 5-8  are presented herein to facilitate the discussion of the operation of AECM  140 , in accordance with an embodiment of the present invention. Antenna  110  transmits carrier signal  150  a portion of which irradiates mobile platform  300 , depicted here as an aircraft, as reflected in  FIG. 5 . For example, antenna  110  is associated with a radar having hostile, identification, and/or tracking intent towards mobile platform  300 , such as a radar system for a surface-to-air-missile or an anti-aircraft artillery system. In response to detecting carrier signal  150 , mobile platform  300  deploys multiple copies of AECM  140  in an expanding cloud, as reflected in  FIG. 6 . Subsequently, the AECM  140  cloud is activated by carrier signal  150 . 
         [0026]    The cloud of AECM  140  can expand in diameter upon dispersion through the air, which can thereby increases the radio cross section of the cloud. The AECM  140  cloud can be a diffuse object with a Gaussian distribution of dipole concentrations, wherein the separation of dipoles varies. For example, the central core, middle region, and diffuse regions can have a separation of 0.5, 1, and 4 meters, respectively. The cloud transmits backscattering signal  160  in a near (or quasi) omnidirectional manner one of which is in line with antenna  110 , as depicted in  FIG. 7 . The strength of backscattering signal  160  and the overall radio cross section of the cloud can result in the focus of the radar system associated with antenna  110  transferring to the cloud instead of mobile platform  300 , as depicted in  FIG. 8 .