Abstract:
Method of automatic target angle tracking by sum-and-difference monopulse radar covers radiolocation sphere and specifically monopulse direction finding systems. It can be used in order to increase guidance accuracy, for example, for anti aircraft missiles and of unmanned aerial vehicles to radar targets such as: radio beacons; aerial vehicles reflecting the radio signal that illuminates them; aerial vehicles and ground-based devices radiating radio signals and jamming signals. The aim of the method consists in the assurance of reliability and stability and in the enhancement of guidance accuracy of automatic target angle tracking due to elimination of automatic tracking losses and great errors arising during the influence of the signals of orthogonal polarization or polarization close to it. 
     The proposed method provides full protection from polarization jamming for all types of monopulse radars.

Description:
[0001]    The invention relates generally to radiolocation sphere, and particularly to monopulse direction finding systems. It can be used to increase guidance accuracy, for example, of unmanned aerial vehicles to radar targets such as: radio beacons; aerial vehicles reflecting the radio signal that illuminates them; aerial vehicles and ground-based devices radiating radio signals and jamming signals. 
         [0002]    It is commonly known that the presence of antenna cross-polarization radiation leads to reduction of direction finding accuracy; it can result in the complete failing of the monopulse direction finding system, i.e. automatic tracking loss /1/ (Chapters 6,8). The said phenomenon occurs during direction finding of the targets with marked depolarization effect which is the majority of real aerodynamic targets possess. But this problem is most important when so-called polarization interference is used as electronic countermeasures means See /1/, paragraph 8.5.2, see also /2/). 
         [0003]    A method of target angle tracking by the sum-and-difference monopulse radio direction-finder is known, in which reception of signals from the target in the sum and difference channels on two orthogonal (cross) polarizations is used to decrease tracking errors (see /1/, p. 249). The described direction-finders possess possibility to operate on the group of reception channels that have polarization most closely coinciding with the one of the reception channels. 
         [0004]    However, the drawback of the abovementioned method is the necessity of doubling in the number of monopulse direction-finder reception channels (six instead of three), that makes this method virtually unacceptable for usage in, for example, the air-borne equipment of aerial vehicles and the like due to weight and size restrictions. 
         [0005]    A method of target angle tracking is known, that is the closest to the claimed one herein, which is based on the use of polarization filtering of electromagnetic waves coming from the target in the sum-and-difference monopulse radio direction-finder (see /1/, p. 69-71, p. 168-169). In this case polarization filtering is performed with the help of the polarization array mounted in the monopulse antenna mouth that allows to weaken an adverse effect of signals on cross polarization on the target direction finding accuracy. 
         [0006]    However the presence of diffraction effect on the edges of the polarization array doesn&#39;t allow to get a cross polarization level less than minus 35 dB (see /1/, p. 165-169) with the help of polarization filtering which is insufficient to protect from modern polarization interference jammers that create interference exceeding the signal by 40 dB and more (see /1/, p. 224). Besides that this mode is often inefficient when the monopulse direction-finder antenna is located under the blister (for example, an airplane or an unmanned aerial vehicle). The blister owing to the curvilinearity of its surface considerably (up to minus 30-minus 15 dB) increases the cross polarization level of the receiving antenna with a polarization filter that heightens the susceptibility of the direction-finder to the influence of polarization interference and leads to the degradation of target tracking accuracy (See /1/, p. 158, see also /2/). 
         [0007]    The stability analysis of the angle tracking of the polarization interference source by the monopulse direction-finder is published in /3/. The tracking loss problem was brought to Lyapunov&#39;s problem about the solution stability of a differential equation system. In this work it was shown that the influence of polarization interference leads to negative definiteness of the first derivative of the direction-finding characteristic that results in the shift of the eigenvalue spectrum matrix of the differential equation system factors describing the automatic control system under study in the right half-plane that in its turn leads to the instability of the automatic tracking system and in general case—to the automatic angle tracking loss. In this work it was also shown that it is impossible to form the optimal control function according to Bellman during the operation of the angular gauge by the polarization interference source beyond the system. Furthermore, in /3/ in the state space of the automatic control system under study was carried out the synthesis of the solution which was optimal regarding the automatic tracking accuracy of the polarization interference jammer and it was shown the existence and uniqueness of the derived solution which corresponded to the inverse function from the function of error signal on the condition of the detection of the polarization interference influence on the monopulse direction-finder. 
         [0008]    The fact of the detection of the polarization interference influence on the monopulse direction-finder is established by the polarization interference detector /4/. The polarization interference detector in the case under consideration is an additional receiving channel of the signals on the orthogonal polarization, the output of which with the output of the sum channel is supplied through detectors to the comparator from the output of which, in the case of the detection of the polarization interference influence, the logical unit is removed. This is nothing other than a polarization interference detector with a single-bit analog-to-digital converter (See /3/). 
         [0009]    The solution derived in /3/ provides a good coincidence with the direction-finding characteristic of the monopulse direction-finder on the working polarization on the section approximately 0.4-0.5 of its half-width taken as a unit (See  FIG. 10 ) and a continuous tracking of the polarization interference source with minimum errors (See  FIG. 4 , line  43 ). 
       SUMMARY OF THE INVENTION 
       [0010]    Thus, the aim and the main technical result of the present invention is to ensure stability of automatic angle tracking on target. 
         [0011]    The set aim is achieved by the following special features:
       during angle tracking by the sum-and-difference direction-finder the reception of signals from the target is performed on the fixed polarization;   the difference signal amplitude and the phase difference between the sum and difference signals are calculated and the monopulse antenna is orientated in the direction of the target relying on the calculated values of the amplitude and the phase difference sign as an angular error value and its sign;   an additional reception of signal component from the target on the polarization, different from the working polarization of the monopulse antenna, is performed;   the amplitude values of the additional and sum signals are compared when the amplitude value of the additional channel signal exceeds the amplitude value of the sum signal;—   the monopulse antenna is oriented relying (depending) on the angular error, the sign of which corresponds to the measured value of the phase difference between the sum and difference signals,   the value is formed via the inverse transformation of the measured amplitude value of the difference signal.       
 
         [0018]    The essence of the invention consists in the assurance of reliability and stability and in the enhancement of guidance accuracy of automatic target angle tracking due to elimination of automatic tracking losses and great errors arising during the influence of the signals of orthogonal polarization or polarization close to it. 
         [0019]    The claimed method is illustrated via devices realizing thereof. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]      FIG. 1  gives the overview of the first variant of the flow diagram of the sum-and-difference monopulse radio direction-finder with the components which realize the claimed method. 
           [0021]      FIG. 2  shows the assumption diagrams of the directivity of the monopulse antenna, the antenna of the secondary channel and the system “monopulse antenna-antenna of the secondary channel” on the working and cross polarization. Besides this, in  FIG. 2  are shown time dependences of the voltages on the outputs of the sum and secondary channels during the ramp of angle α—the inclination angle of the signal polarization plane in the receiving basis of the monopulse antenna with a certain constant angular velocity Ω providing the unambiguous loss of the signal source (target) automatic angle tracking by the prior art device. 
           [0022]      FIG. 3  shows time diagrams of the calculated functions of the error signal for the prior art and the claimed method during the ramp of the inclination angle of the signal polarization plane in the receiving basis of the monopulse antenna with a certain constant angular velocity. 
           [0023]      FIG. 4  shows experimental time diagrams which illustrate the radio direction-finder principle of operation in the prior art mode and with application of the claimed method. 
           [0024]      FIG. 5  shows the direction-finding characteristic on the working polarization at the zero inclination angle of the signal polarization plane α. 
           [0025]      FIG. 6  depicts the direction-finding characteristics for inclination angles of the polarization plane (α=10; 60; 70; 80; 85; 87 degrees. 
           [0026]      FIG. 7  depicts the direction-finding characteristics for inclination angles of the polarization plane a=88; 89; 89.5; 89.9 degrees. 
           [0027]      FIG. 8  shows the direction-finding characteristic on the cross polarization at α=90 degrees. 
           [0028]      FIG. 9  depicts back unstandardized direction-finding characteristics for inclination angles of the polarization plane α=90; 89.5; 89; 88 degrees. 
           [0029]      FIG. 10  depicts standardized back direction-finding characteristics for inclination angles of the polarization plane α=90; 89.5; 89; 88 degrees and the direction-finding characteristic on the working polarization at the zero inclination angle of the signal polarization plane α. 
           [0030]      FIG. 11  depicts the first variant of the diagram of the devices which realize the claimed method and provide an experimental check (verification) of its proper performance. 
           [0031]      FIG. 12  depicts the second variant of the flow diagram of the sum-and-difference monopulse radio direction-finder with the components which realize the claimed method. 
           [0032]      FIG. 13  depicts the diagram of the devices which realize the claimed method according to the second variant. 
       
    
    
       [0033]    The diagrams of the directivity of the antennas were calculated in the azimuth plane in the range of angles φε[−90; +90] degrees at a zero tilt angle (θ=0 degrees). 
         [0034]    The following designations are used:
         1 —Monopulse antenna.     2 —Stripline ring.     3 —Mixer of the sum channel.     4 —Mixer of the difference channel.     5 —Heterodyne.     6 ,  7 —Intermediate-frequency amplifiers of the sum and difference channels.     8 —Automatic gain control system of the sum channel.     9 —Phase detector.     10 —Error-signal amplifier.     11 —Monopulse antenna drive (mechanism).     12 —Horn antenna of the secondary channel (waveguide aperture).     13 —Mixer of the secondary channel.     14 —Intermediate-frequency amplifier of the secondary channel.     15 , 16 —Detectors of the secondary and sum channels.     17 —Compare means (comparator).     18 —Switching device.     19 —Polarization filter.     20 —Radome.     21 —Analog-to-digital converter.     22 —Arithmetic unit.     23 —Digital-to-analog converter.     24 —F P   Σ (φ)—assumption diagram of the mirror antenna  1  directivity of the sum channel on the working polarization in the azimuth plane.     25 —F K   Σ (Σ)—assumption diagram of the mirror antenna  1  directivity of the sum channel on the cross polarization in the azimuth plane.     26 —F P   Aon (φ)—assumption diagram of the horn antenna  12  directivity of the secondary channel on the working polarization in the azimuth plane.     27 —F K   Aon (φ)—assumption diagram of the horn antenna  12  directivity of the secondary channel on the cross polarization in the azimuth plane.     28 ,  29 —F P   Σ (φ)         F K   add (φ)—assumption diagrams of the system “mirror antenna-horn antenna” at the outputs of devices  16  and  15  respectively during operation by the target signal on the working polarization of the mirror antenna in the azimuth plane.     30 ,  31 —F K   Σ (φ)         F P   add (φ)—assumption diagrams of the system “mirror antenna-horn antenna” at the outputs of devices  16  and  15  respectively during operation by the target signal on the cross polarization of the mirror antenna in the azimuth plane.     32 ,  33 —U Σ (φ,α,t)         U add (φ,α,t)—calculated functions of the signals at the outputs of devices  16  and  15  respectively during rotation of the target signal polarization plane with a certain constant angular velocity Ω in the basis of the receiving antenna  1  in the azimuth plane (         =Ω=const).     34 —U com (φ,α,t)—signal at the output of comparator  17  (output of comparator).     35 —U co (φ,α,t)—calculated function of the error signal at the output of error-signal amplifier  10  prior art.     36 —U m (φ,α,t)—calculated function of the error signal at the output of error-signal amplifier  10  during application of the claimed method.     37 —α(t)—rated dependence of the inclination angle of the target signal polarization plane relative to the vertical line in the receiving basis of the monopulse antenna  1 .     38 —α(t)—experimental dependence of the inclination angle of the target signal polarization plane relative to the vertical line in the receiving basis of the monopulse antenna  1 .     39 —U Σ (φ,α,t)—experimental dependence of the sum channel voltage amplitude at the output of device  16 .     40 —U add (φ,α,t)—voltage of the secondary channel at the output of device  15 .     41 —U com (φ,α,t)—voltage at the output of comparator  17 .     42 —U co (φ,α,t)—experimental time dependence of the prior art tracking error value.     43 —U m (φ,α,t)—experimental time dependence of the tracking error value for the claimed method.       
 
       DETAILED DESCRIPTION OF THE INVENTION 
     Example 1 
       [0073]    The radio direction-finder ( FIG. 1 ) comprises monopulse antenna (for example, a paraboloid of revolution with two-mode feed) in the mouth of which a polarization filter  19  is mounted. The working polarization for antenna  1  is a vertical one. The outputs of antenna  1  are connected to the sum-and-difference device in the form of stripline ring  2 , the sum output of which is connected to mixer  3  and the difference output—to mixer  4 . Mixers  3  and  4  are also connected to heterodyne  5  which is also connected to mixer  13 . The signal input of mixer  13  is connected to horn antenna  12  having the horizontal working polarization (orthogonal relative to the working polarization of monopulse antenna  1 ) and aperture (mouth) area 0.5 . . . 1.2λ 2 , which is mounted on the edge of antenna  1 . The outputs of mixers  3  and  4  are connected respectively to the inputs of intermediate-frequency amplifiers  6  and  7 , the outputs of which are connected to the appropriate inputs of phase detector  9 , the output of which through error-signal amplifier  10  is connected to drive mechanism  11  of antenna  1  with polarization filter  19  that is located under radome  20  and that has, for example, an ogival form. Intermediate-frequency amplifiers  6  and  14  are connected through detectors  15  and  16  to the appropriate inputs of comparator  17  (compare facility), the output of which is connected to the driving point of switching device  18 . The outputs of intermediate-frequency amplifiers  6  and  7  are also connected to the appropriate inputs of comparator  17  the output of which is connected through automatic gain control system  8  with intermediate-frequency amplifiers  6  and  7 . 
         [0074]    Realization of units  1 - 16 ,  19  is described in /1/ (chapters 2, 3, 7). 
         [0075]    Realization of devices  15 , 16 , 17 , 18  is shown in  FIG. 11 . Signal detection of the secondary and sum channels in devices  15  and  16  is carried out through diodes D 1  and D 2  respectively. Comparator  17  is assembled on microcircuit K140UD2A (CA3047T) with bipolar feed voltage U feed =±12.6+/−0.5V. Radio electronic relay  10  is used as switching device  18  with operating voltage in the range [9 V . . . 12 V], operating current 50 mA and operating time 11 ms. 
         [0076]    It is necessary to mention that in order to decrease operating time any type of electronic switches on the basis of transistors, thyristors, dynistors or microcircuits instead of the relay can be used. 
         [0077]    A device realizing the claimed method operates as follows. 
         [0078]    Let radio direction-finder track the target the signal polarization of which changes in time from the agreed polarization up to the orthogonal one in accordance with line  38  shown in  FIG. 4 , where α—is the inclination angle of the target signal polarization vector relative to the vertical line—the ordinate of the diagram, time is laid along the abscissa axis. The real changes of the signal polarization can be caused by the polarization interference jamming or by the fluctuations of the signal reflected from the target. This signal after passing through the radome  20  and polarization filter  19  is received by monopulse antenna  1  having the vertical working polarization. Polarization filter  19  can be in the form of a set of thin conductors located in the monopulse antenna  1  mouth and oriented orthogonally to its working polarization which provide the reception of vertical polarization signals without attenuation and the reception of orthogonally polarized signals with certain attenuation. The signals from the outputs of monopulse antenna  1  come to the inputs of stripline ring  2  providing at its outputs the shaping of microwave signals of the sum and difference channels the signals of which come to mixers  3  and  4  respectively where they are transformed with the help of heterodyne  5  into the signals of intermediate frequency, which then are amplified in intermediate-frequency amplifiers  6  and  7  up to the required value and come to the inputs of phase detector  9 . The difference signal amplitude determines the value of the angular error signal at the output of phase detector  9 , the phase difference at the input of phase detector  9  between the signals of the sum and difference channels determines the sign of the angular error signal U co (φ,α,t) at the output  9  where φ is the angular error (displacement angle between a true direction on target and radar boresight of the monopulse direction-finder), α is the inclination angle of the target signal polarization vector relative to the working polarization vector of the monopulse antenna, and t is a time. Automatic gain control system  8  excludes the dependence of the angular error signal amplitude at the output of phase detector  9  on the level of the received signals by the connection of the input of automatic gain control system  8  through normally closed contacts of switching device  18  to the output of intermediate-frequency amplifier  6  of the sum channel, in this case the signal at the output of automatic gain control system  8  makes a simultaneous adjustment of the amplification coefficients of intermediate-frequency amplifiers  6  and  7  providing the signal normalization of the difference channel with the help of the sum one. 
         [0079]    At the same time the reception of the signal component on the horizontal polarization by the secondary channel of the direction-finder is performed with the help of horn antenna  12 , mixer  13  and intermediate-frequency amplifier  14 . 
         [0080]    Time dependences of the voltages on the outputs of the sum channel U Σ (φ,α,t) and secondary channel U add (φ,α,t) are shown in  FIG. 2  with curves  32  and  33  respectively. Voltage of automatic gain control system in dB (sum channel) is shown in  FIG. 4  by curve  39  and the signal of the secondary channel—by line  40 . 
         [0081]    Voltage U com (φ,α,t) at the output of comparator  17  ( FIG. 4  line  41 ) will be equal to +U feed , when U Aon (φ,α,t)&gt;U Σ (φ,α,t) and will be equal to −U feed  when U add (φ,α,t)&lt;U Σ. (φ,α,t): 
         [0000]    
       
         
           
             
               
                 U 
                 com 
               
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                   ϕ 
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                   t 
                 
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             = 
             
               { 
               
                 
                   
                     
                       
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                       , 
                       
                         
                           when 
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                               ( 
                               
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                         &gt; 
                         
                           
                             U 
                             Σ 
                           
                            
                           
                             ( 
                             
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                             ) 
                           
                         
                       
                     
                   
                 
                 
                   
                     
                       
                         - 
                         
                           U 
                           feed 
                         
                       
                       , 
                       
                         
                           when 
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                               ( 
                               
                                 ϕ 
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                               ) 
                             
                           
                         
                         &lt; 
                         
                           
                             U 
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                            
                           
                             ( 
                             
                               ϕ 
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                             ) 
                           
                         
                       
                     
                   
                 
               
             
           
         
       
     
         [0082]    If the leg  1  of microcircuit K140UD2A is grounded the necessity in diode D 3  disappears. The voltage at the output of comparison (comparator) circuit  17  is shown in  FIG. 2  by line  34  and is written in the following form: 
         [0000]    
       
         
           
             
               
                 U 
                 com 
               
                
               
                 ( 
                 
                   ϕ 
                   , 
                   α 
                   , 
                   t 
                 
                 ) 
               
             
             = 
             
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                         + 
                         
                           U 
                           feed 
                         
                       
                       , 
                       
                         
                           when 
                            
                           
                               
                           
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                               U 
                               add 
                             
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                               ( 
                               
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                               ) 
                             
                           
                         
                         &gt; 
                         
                           
                             U 
                             Σ 
                           
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                       , 
                       
                         
                           when 
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                               ) 
                             
                           
                         
                         &lt; 
                         
                           
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         [0083]    Voltage of the automatic gain control system, curve  32 , and voltage of the secondary channel, curve  33 , is shown in dB in  FIG. 4 , and U com (φ,α,t)—in volts. Time is shown on the abscissa axis. 
         [0084]    Voltage U com (φ,α,t) comes to switching device  18  as a control signal. 
         [0085]      FIG. 4  shows the operation of the radio direction-finder in the prior art mode and in the mode of the claimed method. 
         [0086]    Operation of the Device.
       Conditions:—power supply to device  17  is switched off (microcircuit K140UD2A is disconnected);
           —relay R 1  contacts are normally closed. Operation order is shown in  FIG. 4 :   
               
 
         [0089]    Up to time point ti, the following condition is fulfilled: 
         [0000]        U   Σ (φ,α, t )&gt; U   add (φ,α, t )
 
         [0000]    a control signal at the input of switching device  18  is absent (line  41  in  FIG. 4 ) and the direction-finder works in the prior art mode—in the design mode of automatic target tracking /1/ (p.p. 69-71). The input of automatic gain control system  8  is connected through normally closed contacts of relay R 1  (switching device  18 ) to the output of intermediate-frequency amplifier  6  of the sum channel whereby the signal normalization of the difference channel is carried out with the help of the sum one. The error signal from the output of phase detector  9  through error-signal amplifier  10  comes to drive mechanism  11  of the monopulse antenna which turns the antenna in such a way that its radar boresight coincide with the direction on target and the error signal value is maintained close to zero. As the inclination angle of the target signal polarization plane of the input signal reaches the orthogonal position the voltage amplitude of automatic gain control system  8  decreases ( FIG. 4 , curve  39 ) and after a certain value starts the avalanche-like increase of the error signal ( FIG. 4 , curve  42 ). 
         [0090]    In time interval t 1 &lt;t&lt;t 2  the target signal polarization vector passes through the position close to the orthogonal position which is relative to the working polarization of antenna  1  (see  FIG. 4 , curve  38 ). In this case at the output of phase detector  9  abruptly increases the angle tracking error which leads to the loss of automatic angle tracking on target. The sum and difference channels change places, normalization condition is violated (See /1/ Sections 7.3, 8.5). The automatic tracking loss occurs because during the impact of the signal on the orthogonal polarization on the monopulse direction-finder the voltage of the sum channel reaches in a certain small ε-neighborhood of the radar boresight the values close to zero and, being in the denominator, turns the error signal into infinity. 
         [0091]    The Claimed Method Operation.
       Conditions:—power supply to device  17  is switched on (microcircuit K140UD2A is switched on);
           —contacts of switching device (relay R 1 ) are normally closed.   
               
 
         [0094]    Operation procedure is shown in  FIG. 4 : 
         [0095]    During application of the claimed method the monopulse direction-finder operates in the prior art mode (in the design mode) up to time point t 6  
       the following condition is met: U Σ (φ,α,t)&gt;U add (φ,α,t);   at the output of device  17  the control voltage is absent U com (φ,α,t)=0.   the input of automatic gain control system  8  is connected through normally closed contacts of relay R 1  (switching device  18 ) to the output of intermediate-frequency amplifier  6  of the sum channel whereby the signal normalization of the difference channel is carried out with the help of the sum one.       
 
         [0099]    At interval t 6 &lt;t&lt;t 7 :
       U Σ (φ,α,t)&lt;U add (φ,α,t);   at the output of device  17  the control voltage is generated U com (φ,α,t)   under the influence of the control voltage from comparator  17  U com  switching device  18  is actuated: it disconnects the input of automatic gain control system from the output of intermediate-frequency amplifier  6  of the sum channel and connects the input of automatic gain control system  8  to the output of intermediate-frequency amplifier  6  whereby the signal normalization of the sum channel is carried out with the help of the difference channel and the decision derived in /3/ is realized.       
 
         [0103]    In time interval t 6 &lt;t&lt;t 7  the loss of automatic angle tracking on target doesn&#39;t occur because at the time of the signal influence on cross polarization in time interval t 6 &lt;t&lt;t 7  due to application of devices  12 - 18  drive mechanism  11  carries out orientation of antenna  1  on target according to the direction-finding characteristic close to the direction-finding characteristic on the working polarization. In this case the voltage of the difference channel which can reach in a certain small ε-neighborhood of the radar boresight sufficiently big values appears in the denominator, and the values of the sum channel close to zero moves to the numerator. 
         [0104]    When the polarization plane passes the signal of the orthogonal position the voltage of the difference channel decreases due to the change of the directivity diagram, the amplification coefficient increases correspondingly (desensitization decreases) of the sum and difference channels respectively. During this process the amplitudes of the sum and secondary channels are permanently compared. After passing point t 7 :
       the following condition is met: U Σ (φ,α,t)&gt;U add (φ,α,t);   at the output of device  17  the control voltage is absent U com (φ,α,t).   switching device  18  is actuated: it disconnects the input of automatic gain control system from the output of intermediate-frequency amplifier  7  of the difference channel and returns the connection of the input of automatic gain control system  8  to the output of intermediate-frequency amplifier  6  of the sum channel whereby the standard normalization of the difference channel signal is carried out with the help of the sum channel.       
 
         [0108]    The circuit consisting of devices  12 - 17  can be characterized as a single-bit detector of the interference on the cross polarization, and device  18  connecting by the signal of the interference polarization detector the input of automatic gain control system  8  to the output of intermediate-frequency amplifier  6  of the sum channel or to the output of intermediate-frequency amplifier  7  of the difference channel as a protector of the monopulse direction-finder from the impact of cross-polarization signals and interferences. 
       Example 2 
       [0109]    The radio direction-finder ( FIG. 12 ) includes monopulse antenna (for example, a paraboloid of revolution with two-mode feed) in the mouth of which polarization filter  19  is mounted. The working polarization for antenna  1  is a vertical one. The outputs of antenna  1  are connected to the sum-and-difference device in the form of stripline ring  2 , the sum output of which is connected to mixer  3  and the difference output—to mixer  4 . Mixers  3  and  4  are also connected to heterodyne  5  which is also connected to mixer  13 . The signal input of mixer  13  is connected to horn antenna  12  having the horizontal working polarization (orthogonal relative to the working polarization of monopulse antenna  1 ) and aperture (mouth) area 0.5 . . . 1.2λ 2 , which is mounted on the edge of antenna  1 . The outputs of mixers  3  and  4  are connected respectively to the inputs of intermediate-frequency amplifiers  6  and  7 . The output of intermediate-frequency amplifier  6  is connected to the input of automatic gain control system  8  the output of which is connected to intermediate-frequency amplifiers  6  and  7 . The outputs of intermediate-frequency amplifiers  6  and  7  are connected to phase detector  9 , and the outputs of intermediate-frequency amplifiers  6  and  14  are connected through detectors  15  and  16  to the corresponding inputs of comparator  17  the output of which is connected to the control input of switching device  18 . The output of phase detector  9  is connected to the signal input of switching device  18 , one output of which is connected to drive mechanism  11  of antenna  1  through error-signal amplifier  10 , the other output of the switching device through analog-to-digital converter  21 , arithmetic unit  22 , digital-to-analog converter  23  and error-signal amplifier  10  is also connected to drive mechanism  11  of antenna  1  located under radome  20  and having, for example, an ogival form. 
         [0110]    Realization of units  1 - 16 , 19  is described in /1/ chapters 2, 3, 7. 
         [0111]    Realization of devices  15 , 16 , 17 , 18 ,  19 ,  20 ,  21  is shown in  FIG. 13 . Devices  15 , 16 , 17  and  18  are described above. As device an eight-digits analog-to-digital converter on microcircuit K1107PV4A (TDC 1025J) with the range of input voltage [−2.5 V . . . +2.5 V] was used, programmable read-only memory KR556RT5 was used as arithmetic unit  22 , as eight-digits digital-to-analog converter (device  23 )—microcircuit 1118 PA1 (MS 10318). 
         [0112]    A device realizing the claimed method operates in accordance with the following method. 
         [0113]    Let radio direction-finder track the target, the signal polarization of which changes in time from the agreed polarization up to the orthogonal one in accordance with line  37  shown in  FIG. 3 , where α is the inclination angle of the target signal polarization vector relative to the vertical line—the ordinate of the diagram, time is laid along the abscissa axis. The real changes of the signal polarization can be caused by the polarization interference jamming or by the fluctuations of the signal reflected from the target. This signal after passing through radome  20  and polarization filter  19  is received by monopulse antenna  1  having the vertical working polarization. The polarization filter can be in the form of a set of thin conductors located in the monopulse antenna  1  mouth and oriented orthogonally to its working polarization which provide the reception of vertical polarization signals without attenuation and the reception of orthogonally polarized signals with certain attenuation. The signals from the outputs of monopulse antenna  1  come to the inputs of stripline ring  2  providing at its outputs the shaping of microwave signals of the sum and difference channels the signals of which come to mixers  3  and  4  respectively where they are transformed with the help of heterodyne  5  into the signals of intermediate frequency, which then are amplified in intermediate-frequency amplifiers  6  and  7  up to the required value and come to the inputs of phase detector  9 . The difference signal amplitude determines the value of the angular error signal at the output of phase detector  9 , the phase difference at the input of phase detector  9  between the signals of the sum and difference channels determines the sign of the angular error signal at the output of phase detector  9 . Automatic gain control system  8  excludes the dependence of the angular error signal amplitude at the output of phase detector  9  on the level of the received signals by the connection of the input of automatic gain control system  8  to the output of intermediate-frequency amplifier  6  of the sum channel, in this case the signal at the output of automatic gain control system  8  makes a simultaneous adjustment of the amplification coefficients of intermediate-frequency amplifiers  6  and  7  providing the signal normalization of the difference channel with the help of the sum one. 
         [0114]    Simultaneously the reception of the signal component on the horizontal polarization by the secondary channel of the direction-finder is performed preferably with the help of horn antenna  12 , mixer  13  and intermediate-frequency amplifier  14 . 
         [0115]    Time dependences shown in  FIGS. 2 ,  3  and  4  are the same. 
         [0116]    Expressions are also true for U com —the voltage at the output of comparator  17 . 
       a) Preferred Embodiment Device Operation 
       [0000]    
       
         Conditions:—power supply to device  17  is switched off (microcircuit K140UD2A shown in  FIG. 13  is switched off);
       —contacts of switching device  18  (relay R 1  shown in  FIG. 13 ) are normally closed.
 
Operation procedure is shown in  FIG. 4 :
   
     
       
     
         [0119]    Up to time point ti, the following condition is fulfilled: 
         [0000]        U   Σ (φ,α, t )&gt; U   Aon (φ,α, t )
 
         [0000]    a control signal at the input of switching device  18  is absent (line  41  in  FIG. 4 ) and the direction-finder works in the prior art mode—in the design mode of automatic target tracking (/1/ p.p. 69-71). The error signal from the output of phase detector  9  through the normally closed contacts of switching device  18  comes to error-signal amplifier  10  and then to drive mechanism  11  of the monopulse antenna which turns antenna  1  in such a way that its radar boresight coincides with the direction on target and the error signal value is maintained close to zero. As the inclination angle of the target signal polarization plane of the input signal reaches the orthogonal position the voltage amplitude of automatic gain control system decreases and after a certain value starts the avalanche-like increase of the error signal. 
         [0120]    In time interval t 1 &lt;t&lt;t 2  the target signal polarization vector passes through the position close to the orthogonal position which is relative to the working polarization of antenna  1  (see  FIG. 3 , curve  41 ). In this case at the output of phase detector  9  abruptly increases the angle tracking error which leads to the loss of automatic angle tracking on target. (See /1/ Sections 7.3, 8.5). 
       b) Claimed Method Operation. 
       [0000]    
       
         Conditions:—power supply to device  17  is switched on (microcircuit L140UD2A is switched on);
       —contacts of switching device  18  (relay R 1  shown in  FIG. 13 ) are normally closed.
 
Operation procedure is shown in  FIG. 4 :
   
     
       
     
         [0123]    When the claimed method is used the loss of automatic angle tracking on target doesn&#39;t occur because at the time of the signal influence on cross polarization in time interval t 6 &lt;t&lt;t 7  due to application of devices  12 - 23  drive mechanism  11  carries out orientation of antenna  1  on target according to the direction-finding characteristic close to the direction-finding characteristic on the working polarization (See  FIG. 10 ). It is achieved by the use of the control function Ucontr(t) calculated with the help of arithmetic unit  22  realized on the programmable read-only memory which carries out a table functional transformation of the error signal function U co (φ,α,t) having the following form: 
         [0000]        U   m (φ,α, t )= U   contr ( t )=[ U   co (φ,α, t )] −1  
 
         [0000]    As it is seen from  FIG. 4  (curve  43 ) the angular error value U m (φ,α,t) in time interval t 6 &lt;t&lt;t 7  doesn&#39;t exceed the value. 
         [0124]    At time point t 7 , when the target signal polarization vector finishes to pass through a hazardous position ( FIG. 4 , curve  38 ), the control voltage at the input of switching device  18  turns into zero (curve  41 ) and switching device  18  disconnects phase detector  9  from the circuit of devices  19 - 21  and connects it directly to error-signal amplifier  10  and to drive mechanism of antenna  1 , the direction-finder returns to operation in the design mode of automatic tracking in which the error signal from the output of phase detector  9  is used to operate antenna  1  tracking the target. 
         [0125]    The circuit consisting of devices  12 - 17  can be characterized as a single-bit detector of the interference on the cross polarization, and the circuit of devices  18 ,  21 - 23  as a protector of the monopulse direction-finder from the impact of cross-polarization signals and interferences. 
         [0126]    Application of the invention will allow to:
       Reduce the direction-finding error caused by the depolarization of the signals reflected from the target to a minimum;   Exclude losses of automatic angle tracking on target of the polarization interference jammer;   Increase target tracking accuracy of the polarization interference jammer in 8-10 times.       
 
         [0130]    It should be mentioned that a positive effect is greater when the direction-finder antenna is mounted under the blister. 
         [0131]    A T  additional significant advantage of the method is the fact that its hardware implementation is based on cheap parabolic antennas and it doesn&#39;t require a great volume of additional equipment. When the claimed method is used it is unnecessary to mount on an aerial vehicle (including an unmanned aerial vehicle) expensive flat antenna arrays as monopulse antenna  1  which are used as the solution of the hazards of automatic angle tracking loss caused by the influence of the signals on cross polarization. 
         [0132]    Some additional useful remarks and applications of the disclosed method and devices are described in details in /5/. 
       CITED DOCUMENTS 
       [0000]    
       
         1. A. I. Leonov, K. I. Fomichev. Monopulse radiolocation. Moscow, Radio and communication, 1984. 
         2. Van Brunt L. B. Applied ECM N.Y., 1978, v.1, E. W. Engineering. Part 4. 
         3. E. I. Markin, On interference immunity of angle tracking systems under conditions of interference distorting location characteristic, Radar Conference IEEE 2009, May 4-8, 2009, Pasadena, USA. 
         4. Transactions of the European conference IEEE 2009 in St. Petersburg: E. Markin, Jamming detection in providing for radar jamming immunity, Eurocon 2009, May 18-23, 2009, Saint Petersburg, Russia. 
         5. E. Markin, Method of automatic target angle tracking by sum-and-difference monopulse radar invariant against the polarization jamming. Intellcom LLC, Moscow, Russian Federation. EUROPWEAN MICROWAVE WEEK 2010, CNIT La Defense, Paris, France, Sep. 26-Oct. 1 2010. Conference Program, page 75: Sep. 30, 2010, EuRAD Poster05-6.