Directional backtracking array for cross-eye interference

Abstract

The invention belongs to the technical field of radar interference, and particularly discloses a retrodirective array for cross-eye interference, which comprises at least two antennas, the antennas are configured to receive input signals and forward interference signals based on the input signals, and each antenna is provided with a transponder assembly coupled with the antenna. The transponder assembly can modify the phase of a forwarding signal thereof according to a reference signal, that is, all transponder assembly configurations except at least one transponder assembly can invert the phase of the forwarding signal of an input signal of a coupled antenna thereof according to the reference signal, so as to ensure that all signals are in phase at the source of the input signal. At least one transponder component is configured to introduce at least one phase adjustment to a forwarded signal such that the signal forwarded from the antenna has a phase difference of 170 DEG to 190 DEG and an amplitude difference of less than 3 dB at an input signal source, eliminate inherent delays in a Van Atta cross-eye jammer, introduce angle errors in a threat radar, and achieve conditions required for cross-eye jamming.

Description

Technical Field

[0001] The present invention belongs to the technical field of radar jamming, and specifically discloses a direction backtracking array for cross-eye jamming. Background Art

[0002] Advanced cross-eye jamming techniques can be implemented by various types of backtracking arrays described below. The backtracking array transmits in the direction of the input signal. As Figure 1 shown, this backtracking characteristic is achieved by ensuring that the signals forwarded by the antenna array are in-phase superimposed in the direction of the input signal. Figures 2 - 3 An example of a Van Atta backtracking array is shown. The antenna elements in the Van Atta array are connected in pairs. The signal received by one antenna element is retransmitted by the other antenna element in the pair. All antenna pairs share the same midpoint, and the feed networks of all antenna pairs have equal phase shifts. The importance of a common center point required between all antenna pairs in the Van Atta array is as Figure 4 shown. When rotating around the midpoint between antennas L1 = L2, the distance that one antenna element moves closer to the incident plane wave is equal to the distance that the other antenna element in a pair of antenna elements moves farther away from the incident plane wave L3 = L4. It can be seen therefrom that the total distance for the plane wave to propagate to and from each pair of antenna elements is constant because the signal received by one antenna element is transmitted by the other antenna element. As long as all antenna pairs share the same center point, the incident plane wave will propagate the same distance between all antenna pairs. In this way, from the perspective of propagation, the requirement that all signals transmitted by the backtracking array are in-phase is satisfied.

[0003] Assuming that the propagation distances of all antenna pairs sharing a common center position are equal, it is obvious that the phase shifts of the forwarded signals must also be equal to meet the conditions of the backtracking array. As Figure 3 shown, all connections have the same length. Simply connecting the antenna pairs with equal-length transmission lines is the simplest implementation of the Van Atta array. However, additional processing and gain are usually required, and Figure 3 the cylinders in represent the forwarding devices that receive the signals and retransmit them. In this case, it is necessary to match the total phase shift through all antenna pairs, i.e., antennas, transmission lines, repeaters, etc.

[0004] There is no explicit requirement that the antenna pairs be bidirectional, or that all reception and transmission occur on the same side of the array. As long as the requirements of a Van Atta array are met, namely that all antenna pairs share a common center point and the phase shift through all antenna pairs, their repeater systems, and any additional components is equal, the Van Atta array will still operate correctly regardless of which antenna in each pair receives, and whether some antenna pairs have bidirectional repeaters while some have unidirectional repeaters.

[0005] When used as a radar target, the echo of a Van Atta array appears to originate from the location at the center of all antenna pairs, but the distance behind this location corresponds to half of the delay through each antenna pair, its repeater, and any additional components. Therefore, the location where the echo appears to originate depends on the direction of the incident wave. More importantly, from the perspective of electronic warfare (EW), the apparent echo is behind the physical location of the Van Atta array and may even appear behind the platform on which the Van Atta array is installed, as Figure 5 shown. This distance separation makes it overly clear and easy for a radar to distinguish between the repeater echo and the echo of the platform on which it is installed. Since the electromagnetic (EM) wave propagates more slowly in the connecting components than in air, an improved design is required.

[0006] As Figures 6 - 7 shown, a phase conjugate array uses a common reference signal to compensate for the phase of the antenna elements. Figure 7 The squares in

[0007] Figure 8 represent repeaters that ensure that the phase of the transmitted signal is the negative phase relative to the reference signal, thereby compensating for the phase shift caused by the difference in position relative to the phase front. and at antennas 1 and 2, respectively. Transmitting signals with the negative values of these phases from the antennas will result in the transmitted signals having the phase at the plane wave reference point because the phase shift to this plane is compensated by the phase of the signals transmitted by the repeaters on each antenna element. The position of the phase reference plane is not important because the signals transmitted by the repeaters on all antenna elements will add in phase on any plane perpendicular to the direction of the incident signal. The signal received at one of the antenna elements can be used as a reference for the other repeaters, but this may be more challenging than implementing an independent reference signal. By replacing the common phase reference with a common phase reference plane and using a common phase reference for the signals transmitted from all antenna elements in the phase conjugate array, the situation depicted in Figure 8 is effectively achieved.

[0008] The fact that the phase is affected by an ambiguity of integer multiples of 2π does not affect the backscattering behavior of the phase conjugate array because these ambiguities do not affect the way the signals are superimposed. However, these ambiguities may cause the transmitted signals to be superimposed in the direction of the incident signal and in other directions. This effect is not limited to phase conjugate arrays and occurs in all antenna arrays, including Van Atta arrays. Techniques for reducing these sidelobes and grating lobes in a retro-directive array are similar to those in conventional antenna arrays.

[0009] Phase conjugate arrays were initially implemented by mixing the input signal with twice the carrier frequency because this allows the necessary phase reversal to be achieved. The frequency and phase of the retransmitted signal at each antenna element satisfy the following relationship:

[0010]

[0011] where ω c is the carrier frequency, t is time, is the phase of the received signal.

[0012] The second term in Equation (1) can be easily filtered out by a filter.

[0013] Depending on the implementation of the transponder, there may be many other phase conjugate implementations, including two-stage mixing with the carrier frequency, phase conjugate phase-locked loops (PLLs), and digital implementations.

[0014] Flicker analysis has shown that radar systems receiving two signals with approximately equal amplitudes and a phase difference of about 180° produce large angular errors. Cross-eye jamming aims to achieve the worst-case angular error due to flicker to mislead the radar system's judgment of the true position of the target.

[0015] The main drawback of cross-eye jamming is that the range of the jammer's rotation angle is extremely small, within which significant errors can be induced in the threat radar. Therefore, the implementation of reverse cross-eye jamming is adopted to ensure that the jammed signal can be automatically transmitted along the direction of the incident radar signal. The implementation of reverse cross-eye jamming is so important that some authors specifically use the term "cross-eye jamming" to describe this implementation, while "two-source coherent jamming" and its variants are usually used to describe non-reverse cases.

[0016] Typically, only a single cross-eye jamming loop like Figure 9 is considered. The use of multiple reverse cross-eye jamming loops has been evaluated, but despite the promising prospects, this multi-loop reverse cross-eye array faces implementation challenges. These challenges stem from the fact that the radar to be jammed should be located in the near field of the cross-eye jammer, so the far-field plane wave assumption inherent in the Van Atta array is invalid, i.e., Figure 4The incident and outgoing rays are not parallel, and the wavefront is arcuate.

[0017] The main drawback of using Van Atta retro-directive operation for cross-eye jamming is that the signal must propagate from one antenna to another before retransmission, which results in a delay. As the spacing between the jammer antennas increases, the cross-eye jammer will produce a larger angular error, and the typical antenna spacing ranges from 10 to 20 meters. Even in the best case, this delay will make the echo of the retro-directive cross-eye jammer appear 5 to 10 meters behind the position of its antenna.

[0018] However, the speed of signal propagation in transmission lines and waveguides is slower than the speed of light in air, and practical considerations increase the lengths required for transmission lines and waveguides, as Figure 5 shown, and any processing required in the transponder can further increase the delay, thereby increasing the apparent range of the jamming echo. This apparent range shift is the motivation for using pulse-front tracking as a countermeasure against cross-eye jamming, even though pulse-front tracking does not directly affect the angular error caused by the cross-eye jammer. Summary of the Invention

[0019] To solve the problems in the background art, the present invention discloses a direction backtracking array for cross-eye jamming, including at least two antennas, the antennas being configured to receive an input signal and forward a jamming signal based on the input signal, and each of the antennas having a transponder component coupled thereto, eliminating the delay inherent in a Van Atta cross-eye jammer and introducing an angular error in a threat radar.

[0020] To achieve the above invention object, the present invention adopts the following technical solutions:

[0021] A direction backtracking array for cross-eye jamming includes at least two antennas, the antennas being configured to receive an input signal and forward a jamming signal based on the input signal, each of the antennas having a transponder component coupled thereto, the corresponding transponder components being coupled to only one of the corresponding antennas, forming a one-to-one relationship, the transponder components being configured to use the same reference signal, the transponder components being capable of modifying the phase of their forwarded signals according to the reference signal, that is, all transponder components except at least one transponder component are configured to at least invert the phase of the forwarded signal of the input signal of its coupled antenna according to the reference signal to ensure that all signals are in phase at the source of the input signal, and at least one transponder component is configured to introduce at least one phase adjustment to the forwarded signal, so that the signals forwarded from the antennas have a phase difference of 170° to 190° and an amplitude difference of less than 3 dB at the source of the input signal.

[0022] Further, for the direction backtracking array for cross-eye jamming, in the case where the antenna array has two antennas and two phase conjugate components, only one transponder component may be configured to introduce a phase adjustment, and the phase adjustment is 170° to 190°, that is, the signal may have a phase difference of 170° to 190° at the source of the input signal. Alternatively, two or all transponder components may introduce a phase adjustment, and the phase adjustment may be configured such that the transmitted signal has a phase difference of 170° to 190° at the source of the input signal.

[0023] Further, for the direction backtracking array for cross-eye jamming, at least one transponder component is further configured to introduce an amplitude adjustment to the retransmitted signal, and the amplitude adjustment is configured such that the retransmitted signals from each antenna have an amplitude difference of up to 3 dm at the source of the input signal.

[0024] Further, for the direction backtracking array for cross-eye jamming, the bit adjustment and / or amplitude adjustment is to change the operation of the transponder beacon to make it a transponder cross-eye jammer, in a way that ensures the signal has a phase difference of 170° to 180° and an amplitude difference of less than 3 dB at the source of the input signal.

[0025] Further, for the direction backtracking array for cross-eye jamming, the transponder component is configured to invert the phase of the retransmitted signal according to an offset or phase shift, that is, to conjugate the signal.

[0026] Further, for the direction backtracking array for cross-eye jamming, the offset or phase shift is relative to a reference signal. Since each transponder component utilizes a common or identical reference signal, the offset or phase shift of one transponder component is relative to the offset or phase shift of other transponder components, and the offset or phase shift may be 180°.

[0027] Further, for the direction backtracking array for cross-eye jamming, the reference signal is provided by a signal network interconnecting the transponder components, and the signal network is phase-matched; that is, the network portion between the signal source and each transponder component is phase-matched.

[0028] Further, for the direction backtracking array for cross-eye jamming, the signal network is symmetric or approximately symmetric, that is, the lengths of the network between the reference signal source and the corresponding transponder components are equal or approximately equal. In contrast, there may be an asymmetric or unequal signal network, and this asymmetry or inequality can be compensated.

[0029] Further, for the direction backtracking array for cross-eye jamming, the common reference signal may be generated by one source of all transponder components, or may be generated by multiple sources, such as miniaturized and synchronized atomic clocks.

[0030] Due to the adoption of the above technical solution, the present invention has the following beneficial effects:

[0031] The direction-backtracking array for cross-eye jamming of the present invention includes at least two antennas. The antennas are configured to receive an input signal and forward a jamming signal based on the input signal. Each of the antennas is coupled to a corresponding repeater component, and the corresponding repeater components are coupled to only one of the corresponding antennas, forming a one-to-one relationship. All the repeater components are configured to use the same reference signal. The repeater components can modify the phase of their forwarded signals according to the reference signal, that is, all the repeater components except at least one repeater component can at least invert the phase of the forwarded signal of the input signal of its coupled antenna according to the reference signal to ensure that all signals are in phase at the source of the input signal, and at least one repeater component is configured to introduce at least one phase adjustment to the forwarded signal, so that the signals forwarded from the antennas have a phase difference of 170° to 190° and an amplitude difference of less than 3 dB at the input signal source, eliminating the inherent delay in the Van Atta cross-eye jammer, introducing an angular error in the threat radar, and realizing the conditions required for cross-eye jamming. Description of the Drawings

[0032] Figure 1 Schematically shows the situation where the reverse array in the prior art emits a signal in the direction of the received signal;

[0033] Figure 2 Schematically shows a front view of the Van Atta array in the prior art, showing the common center of all antenna pairs;

[0034] Figure 3 Schematically shows Figure 2 the back view of the Van Atta array in

[0035] Figure 4 Schematically shows the situation where a pair of antennas in the prior art rotate around their center, and this rotation does not change the total propagation distance of the retransmitted wave;

[0036] Figure 5 Schematically shows the delay situation of the Van Atta reverse array in the prior art, and this delay makes the radar target echo located behind the position of the reverse array (△r), especially when the antenna element spacing is large;

[0037] Figure 6 Schematically shows a front view of the phase conjugate array in the prior art, showing an arbitrary antenna layout;

[0038] Figure 7 Schematically showsFigure 6 Rear view of the phase conjugate array, showing the transponder assembly as the control box and common reference;

[0039] Figure 8 Schematically shows the prior art operation of the phase conjugate array, showing how the transmitted signals add in phase on the reference plane;

[0040] Figure 9 Schematically shows the Van Atta inverse crossed-eye jamming implementation in the prior art;

[0041] Figure 10 Schematically shows the antenna array according to the present invention;

[0042] Figure 11 Schematically shows Figure 10 the geometry of the antenna array in the near field of the array;

[0043] Figure 12 Schematically shows Figure 10 the interaction geometry of the antenna array in with a monopulse radar antenna element;

[0044] Figure 13 Shows the simulation of the prior art Van Atta crossed-eye jammer when the radar is pointed at the jammer (θc = 0°) and the jammer is rotated. Specific embodiments

[0045] To better understand the present invention, the content of the present invention will be further clearly elaborated below in conjunction with embodiments, but the protected content of the present invention is not limited to the following embodiments. In the following description, a large number of specific details are given to provide a more thorough understanding of the present invention. However, it will be obvious to those skilled in the art that the present invention can be implemented without one or more of these details.

[0046] Figures 1 - 9 Mainly relates to the antenna implementation of the prior art and has been described in the background of the invention section. Below, in conjunction with the attached Figures 10 - 13 , the direction backtracking array for crossed-eye jamming of the present invention is elaborated in detail.

[0047] Figure 10 Shows the antenna array 100 according to the present invention. The antenna array 100 can be regarded as a phase conjugate inverse crossed-eye radar jamming device, which will become obvious from the following description.

[0048] As Figure 10As shown, the antenna array 100 includes a pair of antennas, namely antenna A 110 and antenna B 111, which is the simplest implementation. According to the guidance of the present invention, an antenna array with more than two antennas can also be implemented; compared with the simplest two-antenna implementation, a version with more than two antennas may even be more advantageous or more desirable. Antenna A 110 and antenna B 111 are both configured to receive an input signal and transmit a reverse retransmission signal at least partially based on the input signal.

[0049] Antenna A 110 is connected to a transponder circuit component A 120, and antenna B 111 is connected to a transponder circuit component B 121, which are coupled one-to-one. In other words, antenna A 110 and antenna B 111 each have only one associated transponder circuit component A 120 and transponder circuit component B 121, and transponder circuit component A 120 and transponder circuit component B 121 are the only ones associated with transponder circuit component A 120 and transponder circuit component B 121. Transponder circuit component A 120 and transponder circuit component B 121 are configured to make the phase of the retransmission signal conjugate with respect to the input signal of the coupled antenna A 110 or antenna B 111; the antenna array 100 has a signal network 132 configured to provide a reference signal 130 to transponder circuit component A 120 and transponder circuit component B 121. Transponder circuit component A 120 and transponder circuit component B 121 both receive the same reference signal 130, so it is a common reference signal 130. A signal source, such as an oscillator, is phase-matched with a portion of the signal network 132 between transponder circuit component A 120 and transponder circuit component B 121 to provide the same reference signal 130 to each transponder component.

[0050] In this exemplary embodiment, transponder circuit component A 120 and transponder circuit component B 121 are configured to generate a retransmission signal based on the input signal and two additional factors: the reference signal 130 and an internal phase standard specific to each transponder component. For example, the phase standard specifies that the phases of the retransmission signals generated by transponder circuit component A 120 and transponder circuit component B 121 are different. For example, they are out of phase, for example, by 180°, and the amplitude may also change.

[0051] Since the antenna array 100 as a transponder reverse cross-eye jammer is new, there is no mathematical analysis for this situation. Therefore, the inventors of the present application have conducted an in-depth mathematical analysis of this antenna array 100. Although it is assumed that the far-field analysis of the above reverse array can be reused, in fact, this is not the case because the antenna array 100 must operate in its near field to be effective, so the far-field analysis cannot be reused. Therefore, the following provides a mathematical analysis when the phase conjugate array does not operate in its far-field region.

[0052] Starting from the analysis of the reverse phase conjugate array and then turning to the cross-eye jammer, relative to the radar phase reference from multiple transponders in the far field of the radar The electric field E t is given by:

[0053]

[0054] where: β is the free space propagation constant, N is the number of transponders, the subscript n represents the nth transponder, and the parameters of each transponder are Figure 11 the shown angles θ rn and θ cn the radar and transponder antenna gains P r (θ rn ) and P c (θ cn ), the electric field E rn gain, the phase shift a n and and Figure 11 the shown distance r n .

[0055] If it is necessary to ensure that the signals from multiple transponders add in phase at the radar (the goal of the reverse array), then it is necessary to ensure that all signals are received in phase. However, achieving this goal may be impractical because the distances to each transponder are not precisely known.

[0056] Explicitly considering the 2π periodic ambiguity of the phase, it can be obtained that

[0057]

[0058] where m n is an integer.

[0059] The three factors in the summation in formula (8) respectively correspond to the influence of the path from the radar to the nth transponder relative to the phase reference, the influence of the transponder, and the influence of the path from the transponder back to the radar.

[0060] Conjugating the signal at the transponder means that the signal E sn emitted by each transponder must have the following form

[0061]

[0062] This result corresponds to setting the transponder phase shift in formula (8) to

[0063]

[0064] Thus obtaining

[0065]

[0066] In this way, all repeater phases are equal, as required for a reverse array.

[0067] From an implementation perspective, an important observation is that the phase reference is arbitrary, so the only requirement is that it be the same for all repeaters. Figure 10 The implementation of the common phase is achieved by sharing the reference signal 130 from a common oscillator to all interfering channels via a phase-matching cable of the signal network 132. However, synchronization by other means or using a micro atomic clock is also possible, and it opens up the possibility of using multiple platforms to implement cross-eye interference.

[0068] Consider two repeaters and modify Equation (12) to

[0069]

[0070] where is the phase offset, and modify Equation (16) to

[0071]

[0072] where and

[0073] Let A→1 and result in two signals with approximately equal amplitudes and a phase difference of 180°, thus achieving the conditions required for cross-eye interference.

[0074] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Other modifications or equivalent replacements made by those of ordinary skill in the art to the technical solutions of the present invention should be covered within the scope of the claims of the present invention as long as they do not depart from the spirit and scope of the technical solutions of the present invention.

Claims

1. A direction backtracking array for cross-eye jamming, characterized in that: Comprising at least two antennas, the antennas being configured to receive an input signal and forward an interference signal based on the input signal, each of the antennas having a repeater component coupled thereto, the repeater components being configured to use the same reference signal, the repeater components being able to modify the phase of their forwarded signals according to the reference signal, and at least one of the repeater components being configured to introduce at least one phase adjustment to the forwarded signal such that the signal forwarded from the antenna has a phase difference of 170° to 190° and an amplitude difference of less than 3 dB at the input signal source.

2. The direction backtracking array for cross-eye jamming according to claim 1, characterized in that: The phase adjustment causes the retransmitted signal to have a phase difference of 170° to 190° at the source of the input signal.

3. The direction backtracking array for cross-eye jamming according to claim 1 or 2, characterized in that: At least one of the repeater components is further configured to introduce an amplitude adjustment to the retransmitted signal.

4. The direction backtracking array for cross-eye jamming according to claim 3, characterized in that: The amplitude adjustment causes the retransmitted signal from each antenna to have an amplitude difference of up to 3 dB at the source of the input signal.

5. The direction backtracking array for cross-eye jamming according to claim 3, wherein: The repeater components are configured to also invert the phase of the retransmitted signal according to an offset or a phase shift.

6. The direction backtracking array for cross-eye jamming according to claim 3, characterized in that: The reference signal is generated by one source or multiple synchronized sources, the reference signal is provided by a signal network interconnecting the repeater components, and the signal network is phase-matched.

7. The direction backtracking array for cross-eye jamming according to claim 3, characterized in that: The phase adjustment is configured to change the operation of the repeater beacon to make it a repeater cross-eye jammer by ensuring that the signal has a phase difference of 170° to 180° and an amplitude difference of less than 3 dB at the source of the input signal.

8. The direction backtracking array for cross-eye jamming according to claim 5, characterized in that: The offset or phase shift is relative to the reference signal.

9. The direction backtracking array for cross-eye jamming according to claim 5, characterized in that: The offset or phase shift of one repeater component is relative to the offset or phase shift of other repeater components because all repeater components utilize the same reference signal.

10. The direction backtracking array for cross-eye jamming according to claim 6, characterized in that: The signal network is symmetric, i.e., the lengths of the network are equal between the source of the reference signal and the respective repeater components.

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