Abstract:
A tactical electronic counter measure system comprising a first retro-directional transceiver sub-system, receiving signals at a first frequency band, and first retro-directional transceiver re-transmitting a signal at least substantially toward the direction from which the sources signal was received, and first retro-directional transceiver sub-system including a plurality of blade antennas and a controller, coupled with and first retro-directional transceiver, and controller controlling the activity of and first retro-directional transceiver sub-system, and controller further managing the missions of and first retro-directional transceiver sub-system.

Description:
CROSS REFERENCE 
       [0001]    This application is a continuation of, and claims priority to and the benefit of, U.S. patent application Ser. No. 13/387,171, which is a US national stage application of International Patent Application Number PCT/IL2011/000292 filed on Apr. 6, 2011. International Patent Application Number PCT/IL2011/000292 claims priority to and the benefit of Israeli Patent Application 204,908 filed on Apr. 8, 2010, and also Israeli Patent Application 204,909 filed on Apr. 8, 2010. The entirety of each of these applications is incorporated herein by reference. 
     
    
     FIELD OF THE DISCLOSED TECHNIQUE 
       [0002]    The disclosed technique relates to Electronic Counter Measure Systems in general, and to a dual band Electronic Counter Measure Systems, in particular. 
       BACKGROUND OF THE DISCLOSED TECHNIQUE 
       [0003]    Electronic Counter Measure (ECM) systems generally operate over a large range of frequencies, for example, between the VHF frequency band and K frequency band (i.e., according to the IEEE radio bands). These systems are typically divided into a plurality of sub-systems, each operating on a corresponding frequency range and packaged separately. For example, the ALQ-99 system is housed in five different pods. Furthermore, this multiplicity of sub-systems results in substantial power consumption. One of the sub-systems in an ECM system may be a signal re-transmitting system. Retransmitting signals toward the direction from which signals are received (i.e., either the same signals or other signals) may increase the Signal-to-Noise Ration (SNR) of the retransmitted signal. Another application of retransmitting signals toward the direction from which signals are received is in ECM systems. For example, interfering with signals transmitted by a RADAR allows a vehicle (e.g., aircrafts, vessels, land vehicles) to impair the detection of that vehicle and other vehicles by the RADAR. According to one known in the art method for interfering with RADAR signals the vehicle transmits a directional interfering signal, substantially similar to the RADAR signal, toward the RADAR. Since the directional interfering signal is substantially similar to the RADAR signal the RADAR cannot distinguish between the interfering signal and the RADAR signal reflected from the vehicle. Thus, the interfering signal ‘jams’ the RADAR signal. Transmitting a directional signal requires either using directional antennas (e.g., horn antennas) or using a phased antenna array, where the relative position of the antennas in the array is known. 
         [0004]    U.S. Pat. No. 7,248,203 to Gounalis, entitled “System and Method for Detecting and Jamming Emitter Signals”, describes a detection system which includes one or more antenna and a processing systems that receive and process signals received by the antenna. These signals are, for example, electromagnetic signals transmitted in any one of a number of frequencies, including radar, communication, and other types of signals. The received signals are passed to the processor. The processor implements a scan strategy detecting one or more threats by observing frequency bands defined by the scan strategy. The system determines the scan strategy. The scan strategy is determined to optimize signal intercept of an selected sets of emitter or emitters parameters. The scan strategy is also determined to minimize the “dwells” for each emitter. A dwell defines the scan resources such as frequency range, scan period and revisit time. The processor determines emitter parameters according to the received signals in the determined “dwells”. The processor determines a jamming signal and provides this jamming signal to a jammer transmitter which “jams” the emitter. 
         [0005]    U.S. Pat. No. 4,467,328 to Hacker, entitled “RADAR Jammer With an Antenna Array of Pseudo-Randomly Spaced Radiating Elements”, directs to a RADAR jammer which includes an antenna array with randomly spaced elements, a jammer transmitter, a power divider, and a plurality of phase shifting elements. The RADAR jammer further includes a directional finding system which includes four monopulse horn antennas, a monopulse receiver, a phase-shifter logic and phase-shifter drivers. The power divider is coupled with the jammer transmitter and with the phase shifting elements. The phase-shifter driver is coupled with the phase shifting elements and with the phase-shifter logic. The monopulse receiver is coupled with the four horn antennas and with the phase-shifter logic. The phase shifting elements are further coupled with the antenna array elements. 
         [0006]    The monopulse receiver receives signals from the horn antennas and determines the direction of the detected threat and generates a signal representative of the threat direction. The phase-shifter has values of the spacing of the antenna array elements stored thereat (i.e., the spacing dimensions of the randomly distributed antenna elements are known) and determines a set of phase shifting signals intended to alter the phase of the power signals of the radiation elements to render a single narrow high power beam of jamming radiation directed at the detected threat. Because of the spread-out nature of the radiating elements, it is proposed that the main beam will be much narrower and require much less energy to defeat the RADAR threat in the detected direction. As a result, the remaining energy associated with the spuriously produced beam is spread out over the entire threat volume dispersed everywhere. 
         [0007]    U.S. Pat. No. 4,472,719, to Hills, entitled “ECM Multiple-Target Retrodirective Antenna” directs to a receive and transmit linear antennas arrays each including a plurality of antenna elements. Each antenna element is mounted in a horizontal plane and connected via an equal length transmission line to a microwave. The microwave lens consists of two parallel conducting surfaces spaced less than half a wavelength apart. Each output port of the microwave lens corresponds to an individual beam pattern in azimuth. A logic processor converts the voltages from each receiver to binary voltage. The binary voltages are gated to a switching apparatus which receives ECM signals from an external source. The logic processor detects the signal and activates the switch to transmit the signal according to the desired beam. 
       SUMMARY OF THE PRESENT DISCLOSED TECHNIQUE 
       [0008]    It is an object of the disclosed technique to provide a novel system for electronic counter measures. 
         [0009]    In accordance with the disclosed technique, there is thus provided a tactical electronic counter measure system. The system includes a first retro-directional transceiver sub-system and a controller. The controller is coupled with the first retro-directional transceiver sub-system. The first retro-directional transceiver sub-system receives signals at a first frequency band. The first retro-directional transceiver sub-system re-transmits a signal, at least substantially toward the direction from which a sources signal was received. The first retro-directional transceiver sub-system includes a plurality of blade antennas. The controller controls the activity of first retro-directional transceiver sub-system. The controller further manages the missions of the first retro-directional transceiver sub-system. 
         [0010]    In accordance with another aspect of the disclosed technique, there is thus provided a dual band tactical electronic counter measure system. The dual band tactical electronic counter measure system includes a first band transceiver sub-system and a controller. The controller is coupled with the first band transceiver sub-system. The first band transceiver sub-system includes a communication and RADAR digital transceiver and a first communication transceiver. The controller controls the activity the first band transceiver sub-system. The controller further manages the missions of the first band transceiver sub-system. 
         [0011]    In accordance with a further aspect of the disclosed technique, there is thus provided a tactical electronic counter measure system. The tactical electronic counter measure system includes a first-band transceiving array, a second band transceiver module, a RADAR receiver, a communications receiver, a signal source generator, a switch and a controller. The first-band transceiving array includes a plurality of blade antennas and a plurality of first-band transceiver modules each coupled with a respective one of the antennas. The second band transceiver module is coupled with a respective antenna. The RADAR receiver is coupled, during a reception period, with each of the first-band transceiver modules and with the second band transceiver module. The communications receiver is coupled, during a reception period, with each of the first-band transceiver modules and with the second band transceiver module. The signal source generator is coupled, during a first transmission period with the first-band transceiver modules. The signal source generator is further coupled, during a second transmission period with the second-band transceiver module. The switch is coupled with the RADAR receiver, with the communications receiver, and with the signal source generator. The controller is coupled with the switch, with the RADAR receiver, with the communications receiver and with the signal source generator. 
         [0012]    Each of the first-band transceiver modules receives a source signal transmitted by an emitter during a reception period. Each of the first-band transceiver modules further shifts the phase of an intermediate signal by a respective relative phase-shift and transmits the phase shifted intermediate signal via the respective antenna thereof. The second-band transceiver module receives, during the reception period, a source signal transmitted by an emitter. The second-band transceiver module further transmitting an intermediate signal via the respective antenna thereof. The RADAR receiver determines a second received RADAR signal parameters corresponding to a first and a second frequency band. The RADAR receiver further determines a respective relative phase, for each of the received signals, relative to a reference phase, thereby determining the respective relative phase of the first-band transceiver module. The RADAR receiver further provides the respective relative phase to each of the first-band transceiver modules. The communications receiver determines second received communications signal parameters corresponding to a first and a second frequency band. The communications receiver further determines a respective relative phase for each of the received signals relative to a reference phase thereby determining the respective relative phase for each of the first-band transceiver modules. The communications receiver further provides the respective relative phase to each of the first-band transceiver modules. 
         [0013]    The signal source generator generates a first intermediate signal according to the first received signal parameters. The signal source generator generates a second intermediate signal according to the second received signal parameters. The signal source generator provides the first intermediate signal to the transceiver modules during the first transmission period. The signal source generator provides the second intermediate signal to the second-band transceiver module during the second transmission period. The controller directs the switch to couple the first-band transceiver modules and the second-band transceiver module with the RADAR receiver and with the communications receiver during a reception period. The controller further directs the switch to couple the signal source generator with the first-band transceiver modules during the first transmission period and with the second-band transceiver module during the second transmission period. The controller further controls the activity and manages the missions of the RADAR receiver, the communications receiver and the signal source generator. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    The disclosed technique will be understood and appreciated more fully from the following detailed description taken in conjunction with the drawings in which: 
           [0015]      FIG. 1  is a schematic illustration of a low frequencies tactical ECM system, constructed and operative in accordance with an embodiment of the disclosed technique; 
           [0016]      FIG. 2  is a schematic illustration of a first retro-directional transceiver sub-system, constructed and operative in accordance with another embodiment of the disclosed technique; 
           [0017]      FIG. 3  is a schematic illustration of a first retro-directional transceiver sub-system, constructed and operative in accordance with a further embodiment of the disclosed technique; 
           [0018]      FIG. 4A  is a representation of a signal received by one of the antennas in the antenna array; 
           [0019]      FIG. 4B  is a time reversed version with respect to the signal in  FIG. 4A ; 
           [0020]      FIG. 4C  is a representation of a discrete signal which includes impulses received by one of the antennas in the antenna array; 
           [0021]      FIG. 4D  is a time reversed with respect to in  FIG. 4C ; 
           [0022]      FIG. 4E  is a schematic illustration of a first retro-directional transceiver sub-system constructed and operative in accordance with another embodiment of the disclosed technique; 
           [0023]      FIG. 5  is a schematic illustration of a second transmitting sub-system constructed and operative in accordance with a further embodiment of the disclosed technique; 
           [0024]      FIG. 6  is a schematic illustration of a low frequency tactical ECM system constructed an operative in accordance with another embodiment of the disclosed technique; 
           [0025]      FIG. 7  is a schematic illustration of a low frequencies tactical ECM system housed within an aerodynamic container, in accordance with a further embodiment of the disclosed technique; and 
           [0026]      FIG. 8  is a schematic illustration of a low frequencies tactical ECM system, housed within an aerodynamic container in accordance with another embodiment of the disclosed technique. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0027]    The disclosed technique overcomes the disadvantages of the prior art by providing a low frequencies tactical ECM system which includes a first retro-directional transceiver sub-system and a second transceiver sub-system. The low frequencies dual tactical ECM system operates, in particular, between the VHF band and the C (i.e., according to the IEEE radio bands) frequency band. The first transceiver sub-system operates in a first frequency band, in particular between the UHF band and the C frequency band. The First transceiver sub-system re-transmits a signal toward the signal source, such as a communications device or a RADAR, using a phased antenna array where the relative positions of the antennas is unknown. The source signal is received by each antenna in the antenna array and recorded. Thereafter the sub-system re-transmits the received source signal, by the same antenna array that received the signal, such that the re-transmitted signal is transmitter at least substantially toward the direction from which the sources signal was received. The first retro-directional transceiver sub-system according to the disclosed technique may alter the relative phase of the re-transmitted signal (i.e., the relative phase between each pair of antennas in the antenna array) from the negative of the relative phase of the received source signal to introduce additional effects to the re-transmitted signal (e.g., de-focusing, multi-beam). The second transmitting sub-system operates in a second frequency band, in particular between the VHF band and the UHF band. The second transmitting sub-system includes a digital transmitter. 
         [0028]    In the system according to the disclosed technique, RADAR jamming and communication jamming are integrated into one system. Furthermore, the Effective Radiated Power (ERP) of the RADAR is lower at low frequencies. Therefore, the required ERP of the system is also lower resulting in reduced power consumption (e.g., up to three kilowatts). Furthermore, reduced power consumption results in substantially lower heat dissipation which needs to be evacuated (i.e., the system needs substantially less cooling) relative to other systems transmitting in high frequencies (e.g., in the X and K u  bands. Furthermore, the transmitter in the second transceiver sub-system is a frequency selective transmitter transmitting only in the frequencies of the received signal further reducing the power consumption of the system. Additionally, the system may be implemented with solid state technology resulting in the system occupying smaller volume (i.e., relative to systems operating in the high frequency bands) and further reduction in the power consumption of the system. The reduced volume of the system according to the disclosed technique simplifies housing the system within an aerodynamic container (e.g., pod, bomb shell). This makes the system particular useful for self protection and escort jamming applications. 
         [0029]    Reference is now made to  FIG. 1 , which is a schematic illustration of a low frequencies tactical ECM system, generally reference  100 , constructed and operative in accordance with an embodiment of the disclosed technique. System  100  includes a controller  102 , a first retro-directional transceiver sub-system  104  and a second transceiver sub-system  106 . First retro-directional transceiver sub-system  104  operates between the UHF band and the C frequency band. First retro-directional transceiver sub-system  104  further includes an antenna array, which includes a plurality of antennas  108   1 ,  108   2  and  108   3 . Antennas  108   1 ,  108   2  and  108   3  are embodied as ‘blade antennas’ (i.e., antennas that are located within a body exhibiting a blade like shape). Second transceiver sub-system  106  includes antenna  110 . Antenna  110  may also be embodied as a blade antenna. Both first retro-directional transceiver sub-system  104  and second transceiver sub-system  106  are coupled with controller  102 . 
         [0030]    First retro-directional transceiver sub-system  104  receives signals at the first frequency band and re-transmits a signal at least substantially toward the direction from which the sources signal was received. First retro-directional transceiver sub-system  104  is further explained below in conjunction with  FIGS. 2 ,  3  and  4 E. Second transceiver sub-system  106  includes a communication and RADAR digital transceiver and a second communication transceiver. Second transceiver sub-system  106  is further explained in conjunction with  FIG. 5 . Controller  102  controls the activity of both the first retro-directional transceiver sub-system  104  and second transceiver sub-system  106 . This includes resources (e.g., power) management and time sharing (e.g., when harmonic signals from one band interfere with the received signal in the other band). Controller  102  further manages the different missions of first retro-directional transceiver sub-system  104  and second transceiver sub-system  106 . These missions include, for example, emitter acquisition (i.e., recognizing the transmission of an emitter and determining the characteristics thereof) and emitter maintenance (i.e., updating the characteristics of an acquired emitter). It is noted that either one or both first retro-directional transceiver sub-system  104  and second transceiver sub-system  106  interfere with both RADAR and communication devices. For example, first retro-directional transceiver sub-system  104  interferes with both RADAR and communications while second transceiver sub-system  106  interferes only with communications. Thus, system  100  interferes with both RADAR and communications (i.e., RADAR jamming and communication jamming are integrated into one system). 
         [0031]    As mentioned above, the first retro-directional transceiver sub-system receives signals at a first frequency band and re-transmits a signal at least substantially toward the direction from which the source signal was received. Accordingly, the first retro-directional transceiver module includes a relative phase determinator determines the relative phase between the signal received at one of the antennas and the signals received at each one of the other antennas. The relative phase determinator determines a respective phase-shift associated with each one of the phase-shifters at least according to the respective detected relative phases between the received signals (e.g., the negative of the detected relative phases). The relative phase determinator provides these determined relative phases to the respective phase-shifters. Thus, the sub-system only stores the signal received at the one antenna. Reference is now made to  FIG. 2 , which is a schematic illustration of a first retro-directional transceiver sub-system, generally referenced  120 , constructed and operative in accordance with another embodiment of the disclosed technique. First retro-directional transceiver sub-system  120  corresponds to first retro-directional transceiver sub-system  104  in  FIG. 1 . Sub-system  120  includes a plurality of antennas  122   1 ,  122   2 , . . . ,  122   N , a signal source generator  126 , a relative phase determinator  128  and a plurality of transceiver modules  123   1 ,  123   2 , . . . ,  123   N  (abbreviated T X R X  in  FIG. 3 ). Each transceiver module includes a respective receiver, phase-shifter and amplifier. Transceiver module  123   1  includes receiver  124   1 , phase-shifter  130   1  and amplifier  132   1 . Transceiver module  123   2  includes receiver  124   2 , phase-shifter  130   2  and amplifier  132   2 . Transceiver module  123   N  includes receiver  124   N , phase-shifter  130   N  and amplifier  132   N . Each one of phase-shifters  130   1 ,  130   2 , . . . ,  130   N  may be a true phase shifter or a true time delay phase shifter. At least one of the transceiver modules is defined as a reference transceiver module. In  FIG. 1 , transceiver module  123   1  is defined as the reference transceiver module. It is noted the generally, the phase-shifter of the reference transceiver module is optional (i.e., the reference transceiver module does not have to have a phase shifter). Thus, in transceiver module  123   1 , phase-shifter  130   1  is optional. It is further noted that Signal source generator  128 , together with the phase-shifter and the amplifier respective of each transceiver module form the transmitter of that transceiver module. 
         [0032]    Each one of antennas  122   1 ,  122   2 , . . . ,  122   N  is coupled with a respective one of receivers  124   1 ,  124   2 , . . . ,  124   N  and with a respective one of amplifiers  132   1 ,  132   2 , . . . ,  132   N . Each one of amplifiers  132   1 ,  132   2 , . . . ,  132   N  is further coupled with a respective one of phase-shifters  130   1 ,  130   2 , . . . ,  130   N . Signal source  126  is coupled with receiver  124   1  and with each one of phase-shifters  130   2 ,  130   2 , . . . ,  130   N . Relative phase determinator  128  is coupled with each one of receivers  124   1 ,  124   2 , . . . ,  124   N  and with each one of phase-shifters  130   1 ,  130   2 , . . . ,  130   N . 
         [0033]    Each one of receivers  124   1 ,  124   2 , . . . ,  124   N  receives a source signal, transmitted by a source (not shown), via the respective antenna thereof. Receiver  124   1  receives the source signal via antenna  122   1 , receiver  124   2  receives the source signal via antenna  122   2  and receiver  124   N  receives the source signal via antenna  122   N . Each one of receivers  124   1 ,  124   2 , . . . ,  124   N  performs down conversion, filtering sampling and the like. Receivers  124   1 ,  124   2 , . . . ,  124   N  provide the received signal thereof to relative phase determinator  128 . Receiver  124   1  provides the received signal thereby to signal source generator  126  and to relative phase determinator  128 . Signal source generator  126  determines an intermediate signal according to the received signal. Signal source generator  126  determines this intermediate signal by determining first received signal parameters, and generates the intermediate signal according to these first received signal parameters (i.e., signal source generator synthesizes the intermediate signal). These first received signal parameters are, for example, the frequency, the phase and the amplitude of the received signal. These first received signal parameters may further be the pulse rise and fall time and the intra-pulse modulation scheme (e.g., linear and non-linear frequency modulation, phase modulations such as Phase Shift Keying and Amplitude Modulation). Signal source generator  126  determines the first received signal parameters according to signal processing techniques. For example, the frequency may be determined according to the Fourier Transform of the received signal. The frequency of the received signal may alternatively be determined according to the rate of change of the phase of the signal. The pulse width may be determined by determining the start time and the end time of the pulse. Alternatively, signal source generator  126  stores the received signal. Signal source generator  126  determines an intermediate signal according to stored received signal (i.e., either the stored signal is output from the signal source generator directly or the signal source generator re-produces the stored signal accordingly). According to yet another alternative, signal source generator  126  stores the received signal, determines first received signal parameters of the received signal and generates the intermediate signal accordingly. Signal source generator  126  may further modulate this intermediate signal (e.g., frequency modulation, phase modulation, amplitude modulation, pulse width modulation) delay or filter the intermediate signal. Signal source generator  126  may also modulate the signal according to information to be transmitted to the signal source (e.g., a message to a mobile device in a cellular network). 
         [0034]    Relative phase determinator  128  detects the relative phase, for example, between the signal received by receiver  124   1  respective of reference transceiver module  123   1  and the signal received by each one of receivers  124   2 , . . . ,  124   N  respective of transceiver modules  123   2 , . . . ,  123   N . Alternatively, relative phase determinator  128  detects the relative phase between the signals received by each adjacent pair of receivers (e.g., between receiver  124   1  and receiver  124   2 , between receiver  124   2  and receiver  124   3  etc.). In general, relative phase determinator  128  performs N−1 independent measurements of the relative phase between the receivers (i.e., N equals the number of receivers). 
         [0035]    Relative phase determinator  128  further determines a respective phase-shift associated with each one of phase-shifters  130   1 ,  130   2 , . . . ,  130   N  at least according to detected relative phases between the signals received by the receivers. Relative phase determinator  128  determines these respective phase shifts such that the re-transmitted signal will be transmitted at least, substantially towards the direction from which the source signal was received (e.g., according to the negative of the detected relative phases of the received signals). Relative phase determinator  128  may further determine the respective phase-shift associated with each one of phase-shifters  130   1 ,  130   2 , . . . ,  130   N  according to required additional transmission effects (e.g., multi-beam, de-focusing) to be introduced to the re-transmitted signal. Relative phase determinator  128  provides each determined phase-shift to the respective one of phase-shifters  130   1 ,  130   2 , . . . ,  130   N . 
         [0036]    Thereafter, signal source generator  126  provides the intermediate signal determined thereby to each one of phase-shifters  130   1 ,  130   2 , . . . ,  130   N . Each one of phase-shifters  130   1 ,  130   2 , . . . ,  130   N  shifts the phase of the intermediate signal by the respective phase shift associated with that phase-shifter. Each one of phase-shifters  130   1 ,  130   2 , . . . ,  130   N  may further shift the phase of the intermediate signal to introduce additional effects (e.g., de-focusing, multi-beam). Each one of phase-shifters  130   1 ,  130   2 , . . . ,  130   N  provides the respective phase shifted signal to the respective amplifier thereof. Phase-shifter  130   1  provides the respective phase shifted signal to amplifier  132   1 , Phase-shifter  130   2  provides the respective phase shifted signal to amplifier  132   2  and phase-shifter  130   N  provides the respective phase shifted signal to amplifier  132   N . Each one of amplifiers  132   1 ,  132   2 , . . . ,  132   N  amplifies the respective signal thereof and provides the respective amplified signal, to the respective antenna associated therewith. Amplifier  132   1  provides the respective amplified signal to the antenna  122   1 , amplifier  132   2  provides the respective amplified signal to the antenna  122   2  and amplifier  132   N  provides the respective amplified signal to the antenna  122   N . Each of antennas  122   1 ,  122   2 , . . . ,  122   N  transmits the respective signal thereof. Since the signal transmitted by each of antennas  122   1 ,  122   2 , . . . ,  122   N  includes a respective phase-shift (i.e., introduced by phase-shifters  130   1 ,  130   2 , . . . ,  130   N  respectively), the re-transmitted signal is transmitted at least substantially toward the direction from which the sources signal was received. Thus, the relative position between each pair of antennas need not be known to determine the direction of the re-transmitted signal. The re-transmitted signal may be transmitted to additional directions (e.g., due to grating lobes). 
         [0037]    It is noted that in general, the output signal of signal source generator  126  and phase-shifters  130   1 ,  130   2 , . . . ,  130   N  is a digital signal and a digital to analog converter (not shown in  FIG. 2 ) precedes each of amplifiers  132   1 ,  132   2 , . . . ,  132   N . However, the digital to analog converter may precede each of phase-shifters  130   2 , . . . ,  130   N . It is further noted that the change in the phase of the signal during the propagation thereof between reference receiver  124   1  and signal source generator  126  and between signal source generator  126  and each of phase-shifter  130   1 ,  130   2 , . . . ,  130   N  should at least be known, and thus compensated for by relative phase determinator  128 . Alternatively, the change in the phase of the signal during the propagation thereof between reference receiver  124   1  and signal source generator  126  and between signal source generator  126  and each of phase-shifter  130   1 ,  130   2 , . . . ,  130   N  should be substantially the same. 
         [0038]    According to a further embodiment of the disclosed technique, the first retro-directional transceiver sub-system includes relative phase determinator and a switch. The switch sequentially couples the relative phase determinator with a pair of receivers according to a switching scheme. This switching scheme includes, for example, coupling the reference receiver with the relative phase determinator and sequentially coupling each one of the other receivers with the relative phase determinator. The relative phase determinator detects the relative phase between the signal at the reference receiver and the signals received at each one of the other receivers. The relative phase determinator determines a respective phase-shift associated with each one of the phase-shifters at least according to the respective detected relative phases. Thereafter, the switch sequentially couples the relative phase determinator with each one of the phase-shifters and the relative phase determinator provides these determined phases to the respective phase-shifters. Reference is now made to  FIG. 3 , which is a schematic illustration of a first retro-directional transceiver sub-system generally referenced  150 , constructed and operative in accordance with a further embodiment of the disclosed technique. System  150  includes a plurality of antennas  152   1 ,  152   2 , . . . ,  152   N , a signal source generator  156 , a relative phase determinator  158 , a switch  160  and a plurality of transceiver modules  153   1 ,  153   2 , . . . ,  153   N  (abbreviated T X R X  in  FIG. 3 ). Each transceiver module includes a respective receiver, phase-shifter and amplifier. Transceiver module  153   1  includes receiver  154   1 , phase-shifter  162   1  and amplifier  164   1 . Transceiver module  153   2  includes receiver  154   2 , phase-shifter  162   2  and amplifier  164   2 . Transceiver module  153   N  includes receiver  154   N , phase-shifter  162   N  and amplifier  164   N . Each one of phase-shifters  162   1 ,  162   2 , . . . ,  162   N  may be a true phase shifter or a true time delay phase shifter. At least one of the transceiver modules is defined as a reference transceiver module. In  FIG. 3 , transceiver module  152   1  is defined as the reference transceiver module. As mentioned above, the phase-shifter of the reference transceiver module is optional (i.e., the reference transceiver module does not have to have a phase shifter). Thus, in transceiver module  152   1 , phase-shifter  164   1  is optional. It is noted that Signal source generator  156 , together with the phase-shifter and the amplifier of each transceiver module form the transmitter of that transceiver module. 
         [0039]    Each one of antennas  152   1 ,  152   2 , . . . ,  152   N  is coupled with a respective one of receivers  154   1 ,  154   2 , . . . ,  154   N  and with a respective one of amplifiers  164   1 ,  164   2 , . . . ,  164   N . Each one of antennas  152   1 ,  152   2 , . . . ,  152   N  is further coupled with a respective one of phase-shifters  162   1 ,  162   2 , . . . ,  162   N . Signal source generator  156  is coupled with receiver  154   1  and each one of phase-shifters  162   1 ,  162   2 , . . . ,  162   N . Relative phase determinator  158  is coupled with switch  160 . Switch  160  is further coupled with each one of receivers  154   1 ,  154   2 , . . . ,  154   N  and with each one of phase-shifters  162   1 ,  162   2 , . . . ,  162   N . 
         [0040]    Each one of receivers  154   1 ,  154   2 , . . . ,  154   N  receives a source signal, transmitted by a source, via the respective antenna thereof. Receiver  154   1  receives the source signal via antenna  152   1 , receiver  154   2  receives the source signal via antenna  152   2  and receiver  154   N  receives the source signal via antenna  152   N . Each one of receivers  154   1 ,  154   2 , . . . ,  154   N  performs down conversion, filtering sampling and the like. Receiver  154   1  provides the received signal thereby to signal source generator  156  and to relative phase determinator  158 . Signal source generator  156  determines an intermediate signal according to the received signal. Signal source generator  156  determines this intermediate signal by determining first received signal parameters, and generating the intermediate signal according to these first received signal parameters (i.e., signal source generator synthesizes the intermediate signal). These first received signal parameters are, for example, the frequency, the phase and the amplitude of the received signal. These first received signal parameters may further be the pulse rise and fall time and the intra-pulse modulation scheme (e.g., linear and non-linear frequency modulation, phase modulations such as Phase Shift Keying and Amplitude Modulation). Similarly to as mentioned above signal source generator  156  determines the first received signal parameters according to signal processing techniques. Alternatively, signal source generator  156  stores the received signal. Signal source generator  156  determines an intermediate signal according to stored received signal (i.e., either the stored signal is output from the signal source generator directly or the signal source generator re-produces the stored signal accordingly). According to yet another alternative, signal source generator  156  stores the received signal and determines first signal parameters of the received signal and generates the intermediate signal accordingly. Signal source generator  156  may further modulate this intermediate signal (e.g., frequency modulation, phase modulation, amplitude modulation, pulse width modulation) delay or filter the intermediate signal. Signal source generator  156  may also modulate the signal according to information to be transmitted to the signal source (e.g., a message to a mobile device in a cellular network). 
         [0041]    Switch  160  couples receivers  154   1 ,  154   2 , . . . ,  154   N  with relative phase determinator  158  according to a determined switching scheme. This switching scheme includes, for example, coupling reference receiver  154   1  with relative phase determinator  160  and sequentially coupling receivers  154   2 , . . . ,  154   N  with relative phase determinator  158 . This switching scheme may alternatively include coupling each adjacent pair of receivers  154   1 ,  154   2 , . . . ,  154   N . In general, the switching scheme is determined such that relative phase determinator  158  performs N−1 independent measurements of the relative phase between the receiver (i.e., N equals the number of receivers). 
         [0042]    Relative phase determinator  158  further determines a respective phase-shift associated with each one of phase-shifters  162   1 ,  162   2 , . . . ,  162   N  at least according detected relative phases between the signals received by the receivers. Relative phase determinator  158  determines these respective phase shifts such that the re-transmitted signal will be transmitted at least, substantially towards the direction from which the source signal was received (e.g., according to the negative of the detected relative phases of the received signals). Relative phase determinator  158  may further determine the respective phase-shift associated with each one of phase-shifters  162   1 ,  162   2 , . . . ,  162   N  according to required additional transmission effects (e.g., multi-beam, de-focusing) to be introduced to the re-transmitted signal. Switch  160  couples relative phase determinator  158  with each one of phase-shifters  162   1 ,  162   2 , . . . ,  162   N  (i.e., according to a switching scheme) and relative phase determinator  158  provides each determined phase-shift to the respective one of phase-shifters  162   1 ,  162   2 , . . . ,  162   N . Switch  160  couples relative phase determinator  158  with each one of phase-shifters  162   1 ,  162   2 , . . . ,  162   N , for example, sequentially after all the respective phase shifts associated with phase-shifters  162   1 ,  162   2 , . . . ,  162   N  are determined. Alternatively, switch  160  couples relative phase determinator  160  with each one of phase-shifters  162   1 ,  162   2 , . . . ,  162   N , for example, after relative phase determinator  158  determines the respective phase shift associated with the respective one of phase-shifters  162   1 ,  162   2 , . . . ,  162   N . 
         [0043]    Thereafter, signal source generator  156  provides the intermediate signal determined thereby to each one of phase-shifters  162   1 ,  162   2 , . . . ,  162   N . Each one of phase-shifters  162   1 ,  162   2 , . . . ,  162   N  shifts the intermediate signal by the respective phases shift associated with that phase-shifter. Each one of phase-shifters  162   1 ,  162   2 , . . . ,  162   N  shifts phase of the intermediate signal by the respective phases shift associated with that phase-shifter. Each one of phase-shifters  162   1 ,  162   2 , . . . ,  162   N  may further shift the phase of the intermediate signal to introduce additional effects (e.g., de-focusing, multi-beam). Each one of phase-shifters  162   1 ,  162   2 , . . . ,  162   N  provides the respective phase shifted signal thereof to the respective amplifier thereof. Phase-shifter  162   1  provides the respective phase shifted signal to amplifier  164   1 . Phase-shifter  162   2  provides the respective phase shifted signal to amplifier  164   2  and phase-shifter  162   N  provides the respective phase shifted signal to amplifier  164   N . Each one of amplifiers  164   1 ,  164   2 , . . . , 164   N  provides the respective amplified signal, to the respective antenna associated therewith. Amplifier  164   1  provides the respective amplified signal to the antenna  152   1 , amplifier  164   2  provides the respective amplified signal to the antenna  152   2  and amplifier  164   N  provides the respective amplified signal to the antenna  152   N . Each of antennas  152   1 ,  152   2  . . . ,  152   N  re-transmits the respective signal thereof. Since the signal transmitted by each of antennas  152   1 ,  152   2 , . . . ,  152   N  includes a respective phase-shift (i.e., introduced by phase-shifters  162   1 ,  162   2 , . . . ,  162   N  respectively), the re-transmitted signal is transmitted at least substantially toward the direction from which the source signal was received. Thus, the relative position between each pair of antennas need not be known to determine the direction of the re-transmitted signal. The re-transmitted signal may be transmitted to additional directions (e.g., due to grating lobes). 
         [0044]    It is noted that in general, the output signal of signal source generator  156  and phase-shifters  162   1 ,  162   2 , . . . ,  162   N  is a digital signal and a digital to analog converter (not shown in  FIG. 3 ) precedes each of amplifiers  164   1 ,  164   2 , . . . ,  164   N . However, the digital to analog converter may precede each of phase-shifters  162   1 ,  162   2 , . . . ,  162   N . It is further noted that the change in the phase of the signal during the propagation thereof between reference receiver  154   1  and signal source generator  156  and between signal source generator  156  and each of phase-shifter  162   1 ,  162   2 , . . . ,  162   N  should at least be known, and thus compensated for by relative phase determinator  158 . Alternatively the change in the phase of the signal during the propagation thereof between reference receiver  154   1  and signal source generator  156  and between signal source generator  156  and each of phase-shifter  162   1 ,  162   2 , . . . ,  162   N  should be substantially the same. 
         [0045]    According to another embodiment of the disclosed technique, the first retro-directional transceiver sub-system transmits, by each antenna in the antenna array, a reversed time version of the signal received by the same antenna. Thus, the relative phase of re-transmitted signals, between each pair of antennas, is substantially the negative of relative phase of the received source signal between the same pair of antennas. Reference is now made to  FIGS. 4A and 4B . In  FIG. 4A  signal  200  is a representation of a signal received by one of the antennas in the antenna array. In  FIG. 4B , signal  202  is time reversed version with respect to signal  200  ( FIG. 4A ). Signal  202  is transmitted by the same antenna that received signal  200 . 
         [0046]    Reference is now made to  FIGS. 4C and 4D . In  FIG. 4C  signal  204  is a representation of a discrete signal which includes impulses  204   1 ,  204   2 ,  204   3  (i.e., exhibiting a value of zero) and  204   4  received by one of the antennas in the antenna array. In  FIG. 4D , signal  206  is time reversed with respect to signal  204  ( FIG. 4C ). Signal  206  includes impulses  206   1  (i.e., corresponding to impulse  204   4  in  FIG. 4C ),  206   2  (i.e., corresponding to impulse  204   3  in  FIG. 4C ),  206   3  (i.e., corresponding to impulse  204   4  in  FIG. 4C) and 206   4  (i.e., corresponding to impulse  204   1  in  FIG. 4C ). Signal  206  is transmitted by the same antenna that received signal  204 . In general a discrete reversed signal is produced by placing the first impulse last, the second impulse second to last etc. 
         [0047]    Reference is now made to  FIG. 4E , which is a schematic illustration of a first retro-directional transceiver sub-system, generally referenced  250 , constructed and operative in accordance with another embodiment of the disclosed technique. System  250  includes a plurality of antennas  252   1 ,  252   2 , . . . ,  252   N , and a plurality of transceiver modules  253   1 ,  253   2 , . . . ,  253   N  (abbreviated T X R X  in  FIG. 2E ). Each transceiver module includes a respective receiver, source signal generator, phase-shifter and amplifier. Transceiver module  253   1  includes receiver  254   1 , source signal generator  256   1 , phase-shifter  258   1  and amplifier  260   1 . Transceiver module  253   2  includes receiver  254   2 , source signal generator  256   2 , phase-shifter  258   2  and amplifier  260   2 . Transceiver module  253   N  includes receiver  254   N , source signal generator  256   N , phase-shifter  258   N  and amplifier  260   N . The signal source generator, the phase-shifter and the amplifier of each transceiver module form the transmitter of that transceiver module. 
         [0048]    Each one of antennas  252   1 ,  252   2 , . . . ,  252   N  is coupled with a respective one of receivers  254   1 ,  254   2 , . . . ,  254   N  and with a respective one of amplifiers  260   1 ,  260   2 , . . . ,  260   N . Antenna  252   1  is coupled with receivers  254   1  and with amplifier  260   1 . Antenna  252   2  is coupled with receiver  254   2  and with a amplifier  260   2 . Antenna  252   N  is coupled with receiver  254   N  and with amplifier  260   N . Each one of signal source generators  256   1 ,  256   2 , . . . ,  256   N  is coupled with a corresponding one of receivers  254   1 ,  254   2 , . . . ,  254   N , and with a corresponding one of phase-shifters  258   1 ,  258   2 , . . . ,  258   N . Signal source generator  256   1  is coupled with receiver  254   1  and with phase-shifter  258   1 , signal source generator  256   2  is coupled with receiver  254   2  and with phase-shifter  258   2 , signal source generator  256   N  is coupled with receiver  254   N  and with phase-shifter  258   N . Each one of phase-shifters  258   1 ,  258   2 , . . . ,  258   N  is further coupled with a respective one of amplifiers  260   1 ,  260   2 , . . . , 260   N . Phase-shifters  258   1  is coupled with amplifier  260   1 . Phase-shifters  258   2  is coupled with amplifier  260   2 . Phase-shifters  258   N  is coupled with amplifier  260   N . 
         [0049]    Each one of receivers  254   1 ,  254   2 , . . . ,  254   N  receives a source signal, transmitted by a source, via the respective antenna thereof. Receiver  254   1  receives the source signal via antenna  252   1 , receiver  254   2  receives the source signal via antenna  252   2  and receiver  254   N  receives the source signal via antenna  252   N . Each one of receivers  254   1 ,  254   2 , . . . ,  254   N  performs down conversion, filtering sampling and the like and provides the received signal thereby to the respective signal source generator thereof. Receiver  254   1  provides the respective received signal thereof to signal source generator  256   1 , receiver  254   2  provides the respective received signal thereof to signal source generator  256   2  and receiver  254   N  provides the respective received signal thereof to signal source generator  256   N . Each one of signal source generators  256   1 ,  256   2 , . . . ,  256   N  determines a respective intermediate signal according to the respective received signal thereof. This intermediate signal is at least time reversed with respect to the received signal. Each one of signal source generators  256   1 ,  256   2 , . . . ,  256   N  determines the respective intermediate signal by determining first received signal parameters of the respective received signal thereof, and generates the respective intermediate signal thereof according to these first received signal parameters (i.e., each one of signal source generator  256   1 ,  256   2 , . . . ,  256   N  synthesizes the respective intermediate signal). These first received signal parameters are, for example, the frequency, the phase and the amplitude of the received signal. These first received signal parameters may further be the pulse rise and fall time and the intra-pulse modulation scheme (e.g., linear and non-linear frequency modulation, phase modulations such as Phase Shift Keying and Amplitude Modulation). Alternatively, each one signal source generator  256   1 ,  256   2 , . . . ,  256   N  stores the respective received signal thereof. Each one of signal source generators  256   1 ,  256   2 , . . . ,  256   N  determines the respective intermediate signal thereof according to the respective stored received signal (i.e., either the stored signal is output from the signal source generator directly or the signal source generator re-produces the stored signal accordingly). According to yet another alternative, each one of signal source generators  256   1 ,  256   2 , . . . ,  256   N  stores the respective received signal, determines received first signal parameters of the respective received signal and generates the intermediate signal accordingly. Each one of signal source generators  256   1 ,  256   2 , . . . ,  256   N  may further modulate the respective intermediate signal thereof (e.g., frequency modulation, phase modulation, amplitude modulation, pulse width modulation) delay or filter the respective intermediate signal. In general, the intermediate signal generated by each signal source generator  256   1 ,  256   2 , . . . ,  256   N  is at least the reversed time version of the respective received signal. 
         [0050]    Thereafter, each one of signal source generator  256   1 ,  256   2 , . . . ,  256   N  provide the respective intermediate signal thereof to the corresponding phase-shifter thereof. Signal source generator  256   1  provides the respective intermediate signal thereof to phase-shifter  258   1 . Signal source generator  256   2  provides the respective intermediate signal thereof to phase-shifter  258   2 . Signal source generator  256   N  provides the respective intermediate signal thereof to phase-shifter  258   N . Each one of phase-shifters  258   1 ,  258   2 , . . . ,  258   N  shifts the respective intermediate signal thereof by the respective phase shift associated with each of phase-shifters  258   1 ,  258   2 , . . . ,  258   N . The phase shift associated with each of phase-shifters  258   1 ,  258   2 , . . . ,  258   N  is determined according to required additional transmission effects (e.g., multi-beam, de-focusing) to be introduced to the re-transmitted signal. 
         [0051]    Each one of phase-shifters  258   1 ,  258   2 , . . . ,  258   N  provides the respective phase shifted signal thereof to the respective amplifier coupled therewith. Phase-shifter  258   1  provides the respective phase shifted signal thereof to amplifier  260   1 . Phase-shifter  258   2  provides the respective phase shifted signal thereof to amplifier  260   2 . Phase-shifter  258   N  provides the respective phase shifted signal thereof to amplifier  260   N . Each one of amplifiers  260   1 ,  260   2 , . . . ,  260   N  amplifies the respective signal thereof and provides the respective amplified signal, to the respective antenna associated therewith. Amplifier  260   1  provides the respective amplified signal to the antenna  252   1 , amplifier  260   2  provides the respective amplified signal to the antenna  252   2  and amplifier  260   N  provides the respective amplified signal to the antenna  252   N . Thus, each of antennas  252   1 ,  252   2  . . . ,  252   N  re-transmits the respective signal thereof. Since the signal transmitted by each of antennas  252   1 ,  252   2 , . . . ,  252   N  includes at least the time reversed version of the received signal the re-transmitted signal is transmitted at least substantially toward the direction from which the sources signal was received. Thus, the relative position between each pair of antennas need not be known to determine the direction of the re-transmitted signal. The re-transmitted signal may be transmitted to additional directions (e.g., due to grating lobes). 
         [0052]    It is noted that in general, the output signal of signal source generators  256   1 ,  256   2 , . . . ,  256   N  and phase-shifters  258   1 ,  258   2 , . . . ,  258   N  is a digital signal. A corresponding digital to analog converters (not shown in 
         [0053]      FIG. 3E ) precedes each of amplifiers  260   1 ,  260   2 , . . . ,  260   N . However, a digital to analog converters may precede each of phase-shifters  258   1 ,  258   2 , . . . ,  258   N . It is further noted that in  FIG. 3E , phase-shifters  258   1 ,  258   2 , . . . ,  258   N  are optional. When no additional effects are required then phase-shifters  258   1 ,  258   2 , . . . ,  258   N  may be omitted and each one of signal source generators  256   1 ,  256   2 , . . . ,  256   N  is directly coupled with a respective one of amplifiers  260   1 ,  260   2 , . . . ,  260   N . 
         [0054]    The systems described hereinabove in conjunction with  FIGS. 1 ,  2  and  3 E are similarly applicable to one two and three dimensional arrays. For example, in two dimensional arrays, the relative phase determinator detects the relative phase between the received signal by a reference receiver and the received signal in each one of the other receivers in the antenna array. 
         [0055]    As mentioned above, second transmitting sub-system transmits a signal between the VHF band and the UHF band. The signal may be, for example, a communication signal or a RADAR signal. Reference is now made to  FIG. 5 , which is a schematic illustration of a second transmitting sub-system, generally referenced  300 , constructed and operative in accordance with a further embodiment of the disclosed technique. Second transmitting sub-system  300  includes second RADAR and communication transceiver  304 , second communication transceiver  306  and antenna  302 . Second RADAR and communication transceiver  304  includes digital transceiver  308 . Second communication transceiver  306  includes second communication receiver  310  and second communication signal determinator  312 . Antenna  302  is coupled with digital transceiver  308 , with second communication receiver  310  and with amplifier  314 . Digital transceiver  308  is coupled with amplifier  314  and with second communication signal determinator  312 . Second communication receiver  310  is further coupled with second communication signal determinator  312 . 
         [0056]    Digital transceiver  308  receives a signal from antenna  302  and directly samples the received signal. Digital transceiver  308  determines second received signal parameters. These second received signal parameters are, for example, the frequency, the phase and the amplitude of the received signal. These second received signal parameters may further be the pulse rise and fall time and the intra-pulse modulation scheme (e.g., linear and non-linear frequency modulation, phase modulations such as Phase Shift Keying and Amplitude Modulation). Second communication receiver  310  receives a communication signal and performs down conversion, filtering, sampling and the like and provides the received signal thereby to second communication signal determinator  312 . Second communication signal determinator  312  determines received communication signal parameters of the received signal. Similarly to as mentioned above, digital transceiver  308  and second communication signal determinator  312  determine the communication signal parameters respective of the signals received thereby, according to signal processing techniques. Second communication signal determinator  312  provides the determined communication signal parameters to digital transceiver  308 . Digital transceiver  308  synthesizes a retransmitted signal according to the signal parameters determined thereby, and according to the signal parameters determined by second communication signal determinator  312 , and provides the determined retransmitted signal to amplifier  314 . Amplifier  314  amplifies the determined retransmitted signal and provides the amplified signal to antenna  302 . Antenna  302  re-transmits the amplified signal. Similar to antenna  100  ( FIG. 1 ) antenna  302  may be embodied as a blade antenna. 
         [0057]    The low frequencies tactical ECM system described above includes two sub-systems. However, according to the disclosed technique low frequencies tactical ECM system may be integrated into a dual function single system. Reference is now made to  FIG. 6 , which is a schematic illustration of a low frequency tactical ECM system, generally reference  350 , constructed an operative in accordance with another embodiment of the disclosed technique. System  350  includes a first band transceiving array  352 , a second band transceiving antenna  354 , a second-band transceiver module  356 , a switch  358 , a RADAR receiver  360 , a communications receiver  362 , a signal generator  364  and a controller  366 . Transceiving array  352  includes a plurality of antennas  368   1 ,  368   2 , . . . ,  368   N  and corresponding first-band transceiver modules  370   1 ,  370   2 , . . . ,  370   N . Each one of antennas  354 ,  368   1 ,  368   2 , . . . ,  368   N  may be embodied as a blade antenna. 
         [0058]    Signal source generator  364  is coupled with controller  366 , with RADAR receiver  360 , with communications receiver  362  and with switch  358 . RADAR receiver  360  is further coupled with switch  358  and with controller  366 . Communications receiver  362  is further coupled with switch  358  and with controller  366 . Each one of first-band transceiver modules  370   1 ,  370   2 , . . . ,  370   N  is coupled with a corresponding one of antennas  368   1 ,  368   2 , . . . ,  368   N  and with switch  358 . Second-band transceiver module  356  is coupled with second-band transceiving antenna  354  and with switch  358 . Controller  366  is further coupled with switch  358 . 
         [0059]    Controller  366  directs switch  358  to couple first-band transceiver modules  370   1 ,  370   2 , . . . ,  370   N  and second-band transceiver module  356  with RADAR receiver  360  and with communications receiver  362  during a reception period. Furthermore controller  366  directs switch  358  to alternately couple source signal generator  364  with first-band transceiver modules  370   1 ,  370   2 , . . . ,  370   N  and with second-band transceiver module  356  during a first and a second transmission periods. Similar to controller  103  ( FIG. 1 ), controller  366  controls the activity of system  350 . This includes resources (e.g., power) management and time sharing (e.g., when harmonic signals from one band interfere with the received signal in the other band, coupling of transceiver modules  370   1 ,  370   2 , . . . ,  370   N  and  356  with RADAR receiver  360 , with communications receiver  362  and signal source generator  364 ). Controller  366  further manages the different missions of system  350  such as emitter signal acquisition (i.e., recognizing the transmission of an emitter and determining the characteristics thereof) and emitter maintenance (i.e., updating the characteristics of an acquired emitter). 
         [0060]    During a reception period transceiver modules  370   1 ,  370   2 , . . . ,  370   N  and  356  receives a source signal, transmitted by a source (i.e., an emitter), via the respective one of antennas  368   1 ,  368   2 , . . . ,  368   N  and  354 . Each one of transceivers  370   1 ,  370   2 , . . . ,  370   N  and  356  performs down conversion, filtering sampling and the like. Each one of transceivers  370   1 ,  370   2 , . . . ,  370   N  and  356  provide the received signal thereof to RADAR receiver  360  and communications receiver  362 . RADAR receiver  360  determines first and second received RADAR signal parameters corresponding to the first and second frequency band. Communications receiver  362  determines first and second received communications signal parameters corresponding to the first and second frequency band. As mentioned above, these signal parameters are, for example, the frequency, the phase and the amplitude of the received signal. These first received signal parameters may further be the pulse rise and fall time and the intra-pulse modulation scheme. RADAR receiver  360  and communication receiver  362  further determine a respective relative phase for each of the signals received by antennas  368   1 ,  368   2 , . . . ,  368   N , relative to a reference phase (e.g., the phase of a selected one of the received signals) and provide each of the determined relative phases to the respective one of transceiver modules  370   1 ,  370   2 , . . . ,  370   N . It is noted that, similar to as mentioned above, RADAR receiver  360  and communications receiver  362  may alter the relative phase of the re-transmitted signal to introduce additional effects to the re-transmitted signal. Furthermore, RADAR receiver  360  and communications receiver  362  provide the determined received signals parameters to signal source generator  364 . 
         [0061]    Signal source generator  364  generates a first intermediate signal according to the first received signal parameters and a second intermediate signal according to the second received signal parameters. During transmission in the first frequency band (i.e., the first transmission period), signal source generator  364  provides the first intermediate signal to transceiver modules  370   1 ,  370   2 , . . . ,  370   N . Each one of transceiver modules  370   1 ,  370   2 , . . . ,  370   N  shifts the phase of the first intermediate signal by the corresponding relative phase shift thereof, amplifies the corresponding phase shifted signal and re-transmits the amplified signal via the corresponding one of antennas  368   1 ,  368   2 , . . . ,  368   N . Thus, the transmitted signal the re-transmitted signal is transmitted at least substantially toward the direction from which the sources signal was received. Accordingly, the relative position between each pair of antennas need not be known to determine the direction of the re-transmitted signal. During a transmission in the second frequency band (i.e., the second transmission period), signal source generator  364  provides the second intermediate signal to transceiver modules  356 . Transceiver module  356  amplifies the second intermediate signal and re-transmits the amplified signal by the corresponding antenna  354 . 
         [0062]    The low frequencies tactical ECM system according to the disclosed technique may be housed within an aerodynamic container attachable to an aircraft. Reference is now made to  FIG. 7 , which is a schematic illustration of a low frequencies tactical ECM system generally reference  400 , housed within an aerodynamic container  402 , in accordance with a further embodiment of the disclosed technique. Low frequencies tactical ECM system  400  corresponds to low frequencies tactical ECM system, generally reference  100  of  FIG. 1 . Aerodynamic container  402  is attachable to an aircraft. The transceiver system includes antennas  404   1 ,  404   2 , . . . ,  404   N  and antenna  406 . Antennas  404   1 ,  404   2 , . . . ,  404   N  are affixed on the exterior of aerodynamic container  402  and antenna  406  is located at one of the fins of aerodynamic container  402 . Thus, low frequencies tactical ECM system generally reference  400 , is may be used for self protection of air crafts or for escort jamming purposes. In  FIG. 6 , antennas  404   1 ,  404   2 , . . . ,  404   N  are ‘blade antennas’ (i.e., antennas that are located within a body exhibiting a blade like shape), thus, maintaining the aerodynamic structure of aerodynamic container  402 . Alternatively, antennas  404   1 ,  404   2 , . . . ,  404   N  may also be located on the fins of aerodynamic container  402 . As a further alternative, antenna  406  may be affixed on the exterior of aerodynamic container  402  and be embodied as a blade antenna. Aerodynamic container  402  may be for example a pod, a munitions shell such as a bomb shell, a munitions contour (i.e., having the shape of a munitions shell by made of a different material), fuel tanks or cargo tanks. It is noted that retro-directional transceiver system  400  may be any one of transceiver system  100  described in conjunction with  FIG. 1 . 
         [0063]    Reference is now made to  FIG. 8 , which is a schematic illustration of a low frequencies tactical ECM system generally reference  420 , housed within an aerodynamic container  422 , in accordance with another embodiment of the disclosed technique. Low frequencies tactical ECM system  420  corresponds to low frequencies tactical ECM system, generally reference  100  of  FIG. 1 . Aerodynamic container  422  is attachable to an aircraft. The retro-directional transceiver system includes antennas  424   1 ,  424   2 , . . . ,  424   N  and antenna  426 . Antennas  424   1 ,  424   2 , . . . ,  424   N  are located within aerodynamic container  422  and antenna  426  is located at the one of the fins if aerodynamic container  422 . Thus the exterior of aerodynamic container  422  remains unchanged. Aerodynamic container  422  may be for example a pod, a munitions shell such as a bomb shell, a munitions contour (i.e., having the shape of a munitions shell by made of a different material), fuel tanks or cargo tanks. Thus, low frequencies tactical ECM system generally reference  400 , is may be used for self protection of air crafts or for escort jamming purposes. It is noted that transceiver system  420  ( FIG. 7 ) may be any one of transceiver system  100  described in conjunction with  FIG. 1 . Is noted that each one of the antennas described hereinabove, may be any type of antenna (e.g., a monopole antenna, a dipole antenna, a slot antenna, a loop antenna, a spiral antenna) exhibiting any desired shape thus achieving desired properties such as bandwidth and directionality. 
         [0064]    It will be appreciated by persons skilled in the art that the disclosed technique is not limited to what has been particularly shown and described hereinabove. Rather the scope of the disclosed technique is defined only by the claims, which follow.