CN107290728B - Equivalent electromagnetic wave orbital angular momentum pulse radar detection method and system - Google Patents
Equivalent electromagnetic wave orbital angular momentum pulse radar detection method and system Download PDFInfo
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Abstract
An equivalent electromagnetic wave orbital angular momentum pulse radar detection method and system relate to the technical field of radar detection based on a rotating antenna. The radar detection system comprises a signal transmitting subsystem, an antenna subsystem and a signal receiving subsystem; the method comprises the steps that M array annular antenna arrays which are uniformly distributed rotate around the center, pulse signals are simultaneously transmitted in the rotating process, and coherent accumulation is carried out on the pulse signals, so that equivalent high-order mode number orbital angular momentum electromagnetic wave signals can be generated at a radar receiving end; the high-order mode number orbital angular momentum electromagnetic wave can generate obvious phase gradient at a target, and the orbital angular momentum electromagnetic waves with different mode numbers can realize waveform diversity for target detection. The diversity reception capability is utilized to further obtain the signal-to-noise ratio before high detection, so that the detection capability of the radar on weak and small targets is greatly improved.
Description
Technical Field
The invention relates to the technical field of radar detection, in particular to an equivalent electromagnetic wave orbital angular momentum pulse detection radar system of a rotating antenna.
Background
With the development of stealth technology, the traditional radar detection system is challenged more and more seriously, and the anti-stealth technology becomes a lasting research hotspot in radar detection. The stealth target can reduce the radar scattering cross section (RCS) of the future wave direction to 10-3m2The following. In order to prevent stealth, the radar generally adopts a signal processing method or improves the level of devices, so as to further improve the detection sensitivity, such as: the antenna power aperture product is increased, the radar working wave band is expanded, the polarization characteristic of the radar is changed, and the like. But is limited by the signal system and the manufacturing process, and the degree of improvement is limited.
In general, radar targets can be divided into point targets and extended targets, wherein a point target means that the size of the target is within one resolution unit. And the point targets can be further divided into simple targets and complex targets. A simple target means that the radar has only one scattering area, while a complex target has multiple scattering areas. In general, the point target detected by the radar is a complex target. Because the complex target is formed by superposing echoes of a plurality of scattering areas in one resolution unit, the coherence among signals is formed, so that RCS fluctuates along with factors such as a phase plane of a coming wave, the frequency of an electromagnetic wave and the like.
In recent years, electromagnetic wave Orbital Angular Momentum (OAM) has become a new means for utilizing electromagnetic waves as a new dimension of electromagnetic waves. The research in the field of OAM electromagnetic wave transmission lays a foundation for the application in the field of radar detection. In 2007, Thid e, B et al verified that low frequency electromagnetic waves (frequencies below 1GHz) can also produce orbital angular momentum through numerical simulation of antenna arrays. In 2010, Mohammadi S M discusses how to generate and detect different OAM electromagnetic waves with a circular antenna array. The influence of the radius, the number of elements, the frequency and the like of the antenna array on the OAM electromagnetic wave radiation pattern is analyzed in detail. In 2015, Liukang and the like in the department of defense propose that a circular antenna array is adopted to generate OAM waves, and FFT is adopted in an OAM domain to detect and image a target. In the same year, Niemiec studied the reflection of 2.45GHz OAM waves on spheres and cylinders. The mu sic algorithm is adopted by liumin group in the department of defense in 2016 to improve the angular resolution of OAM radar. Recently, research finds that the spiral wave front of OAM forms a special phase gradient, when a complex target is irradiated, the same-frequency electromagnetic waves with different OAM mode numbers have different RCS transmission signals, and the physical characteristic creates conditions for diversity reception.
Diversity reception is generally divided into combining diversity (maximum ratio combining and equal gain combining) and selection diversity. In any diversity mode, the system is required to generate more diversity branches. On the other hand, considering the significant phase gradient variation in the target size, a signal capable of generating higher-order OAM is also required. The current OAM electromagnetic wave generation method mainly includes: a spiral phase plate method, a spiral reflecting surface method, an antenna array method, a diffraction grating method, and the like. These several approaches have corresponding limitations in generating large OAM pattern counts. Among them, the spiral phase plate method, the spiral reflecting surface method and the grating method are limited by the processing precision and size of the equipment, and cannot generate large-scale OAM mode numbers. The antenna array method needs the number of antennas which is twice the number of the OAM modes, and in order to avoid the coupling between the antennas, the minimum distance needs to be kept between the antennas, so that the aperture of the antennas is very large. Therefore, none of the current methods is capable of generating the required OAM signal in the higher order mode.
Disclosure of Invention
Aiming at the problem of detecting weak and small targets such as stealth targets by radars, the invention aims to provide an equivalent electromagnetic wave orbital angular momentum pulse radar detection method and system based on a rotating antenna.
The technical scheme of the invention is as follows:
an equivalent electromagnetic wave orbital angular momentum pulse radar detection method is characterized by comprising the following steps:
1) the rotary antenna of the radar system is a ring-shaped antenna array formed by M antenna arrays which are uniformly distributed, wherein M is more than or equal to 1; the rotation period is defined as that the antenna array rotates counterclockwise or clockwise at a constant speed by taking the origin as the center
Radian, angular velocity of rotation omega, and period of rotation
2) The rotating device drives the rotating antenna to rotate, M antenna arrays simultaneously transmit pulse signals in the rotating process, and N pulses are transmitted in one period, namely each pulse is formed by overlapping the M signals; the signal transmitted by each antenna element has
A phase gradient which is increased linearly for increment, wherein l is the mode number of the needed electromagnetic wave orbital angular momentum;
3) during the rotation, the signal transmitted by each antenna at each transmitting point also has a linear phase shift with respect to the initial signal
Where k is 1,2, …, N, the phase of the signal transmitted by the ith antenna element is
M antenna elements in one rotation period
All M × N signals transmitted in the time interval of (1)
Is interval and has a phase gradient from 0 to
The signal sequence of (a);
4) during the time interval between adjacent transmitted pulses, the rotating antenna receives the echo signal at TrIs pulse repetition period, and synthesizes M × N signal sequences in the signal processor, wherein the signal synthesis process is that the echo time delay of the first pulse at the receiving end is (N-1) TrThe second is (N-2) Tr…, ith is (N-i) Tr…, the Nth has no time delay, and finally coherent accumulation is carried out, thereby forming an equivalent electromagnetic wave orbital angular momentum signal;
5) the electromagnetic wave orbital angular momentum waveform is integrated into Lall＝{l1,l2,...,lmaxIn the initial period, the subset of orbital angular momentum of the emitted electromagnetic wave is
The number of the electromagnetic wave orbital angular momentum signal paths allowed to be transmitted isPath K, whereinmaxThe number of the maximum electromagnetic wave orbital angular momentum modes,
represents the number of orbital angular momentum modes of the electromagnetic wave transmitted on the Kth path at the initial moment and has
6) Measuring the signal-to-noise ratio of each path of electromagnetic wave orbital angular momentum signal in a cognitive processor, wherein the signal-to-noise ratio of the ith path is βiThe maximum signal-to-noise ratio in all K paths is βmaxThe ith signal has
Change the number of orbital angular momentum modes of the electromagnetic wave to be transmitted next, i.e.
The next transmitted waveform, thereby maintaining the optimal state for target detection.
In the above technical solution, there are two methods for forming a phase gradient between all M × N signals transmitted by the M antennas in one rotation period, the first method is to arrange a phase shifter for the antennas, the second method is to arrange no phase shifter, and generate a required phase gradient by using a time delay generated by rotation, in which case the number of modes of orbital angular momentum of the generated electromagnetic wave is mM,
the angular velocity of rotation is omega and needs to satisfy
Omega is the electromagnetic wave angular frequency.
The invention provides an equivalent electromagnetic wave orbital angular momentum pulse radar detection system for realizing the method, which is characterized in that: the radar detection system includes:
1) the signal transmitting subsystem comprises a signal generator for generating a chirp signal and a transmitter for transmitting the signal after power amplification through an antenna;
2) the antenna subsystem comprises a duplexer for switching the transmitting state and the receiving state of the antenna, a rotating antenna, a beam-bunching device for collimating incident electromagnetic waves and a rotating device for realizing the rotation of the antenna;
3) a signal receiving subsystem comprising a receiver, a signal processor, a data processor, and a cognitive processor; the signal processor is used for carrying out coherent accumulation processing on the pulse to obtain a synthesized pulse signal; the data processor is used for detecting the synthesized signal;
a signal generator in the signal transmitting subsystem transmits a pulse signal to a transmitter, the transmitter feeds the pulse signal into an antenna subsystem, a rotating device drives a rotating antenna to perform uniform-speed circular motion, the pulse signal is transmitted in the rotating mode, the antenna subsystem receives an echo signal in a receiving state of a duplexer, the received echo signal is sampled by a receiver in a signal receiving subsystem and subjected to down-conversion and enters a signal processor for echo accumulation, and then the signals after echo accumulation are respectively transmitted to a data processor and a cognitive processor; the data processor detects the signals after the echo accumulation; and the cognitive processor adjusts the signal generator and the rotating device according to the signal-to-noise ratio of the current waveform by adopting an optimal signal-to-noise ratio principle, so that an optimal radar pulse signal to be transmitted next step is generated.
Preferably, the rotating antenna array of the present invention employs a horn antenna, a parabolic antenna, a cassegrain antenna, a patch antenna or an array antenna.
In the above technical solution, the rotating antenna is a mechanical rotating antenna or an electrical scanning rotating antenna, the electrical scanning rotating antenna is composed of a phased array antenna and a ring-shaped reflecting surface, the phased array antenna is located on a focal plane of the ring-shaped reflecting surface, a scanning azimuth angle of a beam or a beam cluster emitted by the phased array antenna is uniformly changed, the beam or the beam cluster is reflected by the reflecting surface to form an emergent beam or a beam cluster, and the emergent beams perform uniform circular motion around the center of the ring-shaped reflecting surface.
The invention has the following advantages and prominent technical effects: by adopting the equivalent electromagnetic wave orbital angular momentum radar detection method based on the rotating antenna, equivalent high-order mode number orbital angular momentum electromagnetic wave signals can be generated at a radar receiving end, and the mode number generated by the traditional method is small and limited by an antenna process. The high-order mode number orbital angular momentum electromagnetic wave can generate obvious phase gradient at a target, and the different mode number orbital angular momentum electromagnetic waves can realize waveform diversity of target detection. By utilizing the diversity gain, higher signal-to-noise ratio before detection can be obtained, so that the detection capability of the weak and small targets is greatly improved. The rotating antenna part of the present invention can be replaced by an electric scanning rotating antenna, and the same effect can be achieved. The phased array antenna is characterized in that the center of a wave beam of the phased array antenna is positioned on a focal plane of the annular reflecting surface, the scanning azimuth angle of the wave beam or the wave beam cluster emitted by the phased array antenna is uniformly changed, and the emitted wave beam or the wave beam cluster is formed after the wave beam or the wave beam cluster is reflected by the reflecting surface. The emergent beams do uniform circular motion around the center of the annular reflecting surface, and the method is equivalent to the method for generating the rotating beams in a mechanical rotating mode.
Drawings
Fig. 1 is a schematic structural diagram of an equivalent electromagnetic wave orbital angular momentum pulse detection radar system based on a rotating antenna.
FIG. 2 is a signal processing flow chart of the equivalent electromagnetic wave orbital angular momentum pulse detection radar of the rotating antenna.
Fig. 3 is a schematic diagram of a rotating antenna.
Fig. 4 is a schematic diagram of pulse accumulation in a signal processor.
Fig. 5 is a signal processing flow diagram of a cognitive processor.
FIG. 6 shows a simulation scenario in accordance with an embodiment of the present invention.
Fig. 7 shows simulation results in an embodiment of the present invention.
Figure 8 shows a schematic diagram of an electrically swept rotary antenna.
Detailed Description
The system architecture, principles and methods of the present invention are further described below in conjunction with the drawings and the examples to better explain and understand the technical solutions of the present invention. Wherein like or similar reference numerals refer to like or similar elements throughout, or to elements having like or similar functions.
Fig. 1 is a schematic structural diagram of an equivalent electromagnetic wave orbital angular momentum pulse detection radar system based on a rotating antenna, wherein the system comprises a signal transmitting subsystem 100, an antenna subsystem 200 and a signal receiving subsystem 300; wherein the signal transmitting subsystem comprises a signal generator 101 and a transmitter 102, the signal generator is used for generating a chirp signal; the transmitter up-converts the baseband pulse signal to a radio frequency signal of a required frequency point, and the signal is amplified by power and then sent to an antenna to be transmitted.
The antenna subsystem 200 stores, accumulates and detects echo signals, and improves the signal-to-noise ratio of a target before detection by using the difference of different OAM electromagnetic waves RCS and adopting a diversity technology, wherein the antenna subsystem specifically comprises a duplexer 201, a rotating antenna 202, a beam bunching device 203 and a rotating device 204; the rotating antenna is used for transmitting signals to convert guided waves in a transmission line into electromagnetic waves in free space, and the form of the rotating antenna can be various types, such as: horn antennas, parabolic antennas, cassegrain antennas, patch antennas, array antennas, and the like; the beam bunching device 203 is used for collimating the incident electromagnetic wave and reducing the beam divergence angle of the incident electromagnetic wave; the rotating device 204 is used to rotate the antenna, and may be a motor or any other type of mechanical rotation.
The signal receiving subsystem 300 comprises a receiver 301, a signal processor 302, a data processor 303 and a cognitive processor 304; the receiver 301 is configured to perform low-noise amplification on a received signal, perform matched filtering at an intermediate frequency, and perform digital IQ sampling on the signal; the signal processor 302 performs FFT and pulse compression on the signal to improve the signal-to-noise ratio of the signal, and then performs coherent accumulation processing on the pulse to obtain a synthesized pulse signal; the data processor 303 is mainly responsible for detecting the composite signal, and in this embodiment, performs a combining operation on each path of OAM signals, where an optional combining method includes selective combining, equal gain combining, and maximum ratio combining; the cognitive processor is used for carrying out cognitive processing on the target and feeding back an optimal radar signal to the signal generator and the rotating device according to a cognitive result.
The working process is as follows: a signal generator 101 in the signal transmitting subsystem 100 transmits a pulse signal to a transmitter 102, the transmitter feeds the pulse signal into an antenna subsystem 200, a rotating device 204 drives a rotating antenna 202 to perform uniform circular motion, the pulse signal is transmitted in the rotating mode, the antenna subsystem 200 receives an echo signal in a receiving state of a duplexer 201, the received echo signal is sampled and down-converted by a receiver 301 in a signal receiving subsystem 300 and enters a signal processor 302 for echo accumulation, and then the signals after echo accumulation are respectively transmitted to a data processor 303 and a cognitive processor 304; the data processor 303 detects the signal after the echo accumulation; the cognitive processor 304 adjusts the signal generator 101 and the rotating device 204 according to the signal-to-noise ratio of the current waveform by using the optimal signal-to-noise ratio principle, so as to generate the optimal radar pulse signal to be transmitted next.
The principle of the invention is described as follows: theoretically, OAM electromagnetic waves of any order can be generated by using the antenna array method, but this requires at least twice as many antenna sub-numbers as OAM modes, and thus is difficult to physically implement. The invention adopts the design of a rotary antenna, under the drive of a motor or other rotating devices, a single antenna array does uniform-speed circular motion around an original point, and when the antenna rotates, the array outwards transmits radar pulses (such as linear frequency modulation pulses) at uniform time intervals and receives echo signals at pulse transmitting intervals. Firstly, echo signals are stored and are not processed, and after the array rotates for a circle, coherent accumulation is carried out on the echo signals received in the cycle, so that a synthesized signal is formed. Since the composite signal has the same phase structure as the OAM signal in the radar irradiation direction, it is called an equivalent OAM pulse signal. Through theoretical calculation and numerical simulation, the OAM electromagnetic wave with any order can be generated by adopting the rotating antenna in the radar irradiation direction, which is equivalent to an antenna array method, and only a single antenna is needed, so that a large number of arrays are avoided. The equivalent OAM electromagnetic waves in the radar detection direction are obtained through pulse accumulation of the rotary antenna in the time domain, the signal-to-noise ratio of the radar before the detection of the weak and small targets is enhanced by using RCS diversity characteristics of different OAM waves, and the detection probability is improved.
Because RCS of different OAM electromagnetic waves are different, the invention adopts diversity reception technology at the receiving end, can send electromagnetic waves of different OAM mode numbers at the transmitting end, and adopts a combination diversity mode to directly receive at the receiving end; furthermore, a selection diversity technology can be adopted, the size of the RCS of the target under the irradiation of the electromagnetic waves with different OAM mode numbers is recognized, and the OAM electromagnetic waves corresponding to the optimal OAM mode number are selected to be transmitted by adopting a waveform recognition technology, so that the RCS of the irradiated target is improved.
Fig. 2 shows a signal processing flow chart of the equivalent electromagnetic wave orbital angular momentum pulse detection radar of the rotating antenna. The transmitting waveform is determined by the parameters of the antenna and the transmitter, the echo of the target is received after the target is reflected, and the target is processed by frequency conversion, sampling and the like in the receiver. If the antenna does not complete a transmission cycle, i.e. rotates a circle, the signal processor stores the echo signals, and after the transmission cycle is completed, the signals of one cycle are subjected to coherent accumulation, so that the synthesized pulse signals are obtained. And then constant false alarm detection is carried out on the pulse signals. The data processor can select the combination diversity or the selection diversity, if the combination diversity is selected, the maximum ratio combination or equal gain combination can be carried out on each path of OAM signals; and if the selection diversity is adopted, the detection result is further subjected to cognitive processing, the target RCS under the current OAM mode number is judged, the OAM electromagnetic wave capable of increasing the target RCS is selected, and parameters needing to be adjusted are fed back to the antenna and the transmitter for adjustment.
In one embodiment of the invention, the transmitting end sends a linear frequency modulation signal (L FM) to the rotating antenna, and since the radar adopts a duplex working mode, the antenna receives echo signals at the interval of adjacent pulses, the echo pulses are stored firstly, and after the antenna rotates for one circle, the echo signals are subjected to coherent accumulation to obtain a synthesized signal, and the synthesized signal is the equivalent OAM echo signal.
The rotary antenna is composed of M uniformly distributed circular antenna arrays. The rotation period is defined as that the antenna array rotates counterclockwise (clockwise) at a constant speed by taking the origin as the center
Radian, angular velocity of rotation is Ω, and rotation period is
In the rotation process, M antennas simultaneously transmit pulse signals, and N pulses are transmitted in one period, namely each pulse is formed by overlapping the M signals. The signals transmitted by the respective antennas have
The phase gradient is increased linearly for increment, wherein l is the mode number of the needed OAM electromagnetic wave. For example, the first antenna transmits at a phase of 0 and the second antenna transmits at a phase of
The phase of the i-th antenna transmission is
The phase of the Mth antenna is
As the antennas rotate, the transmitted signals from each antenna at each transmit point also have a linear phase shift relative to the original signal at
When the ith antenna transmits signals with the phase of
Thus ensuring that M antennas are in period
All M × N signals transmitted form a phase gradient from 0 to
And are provided with
Is a sequence of intervals. The superposition of the signal sequence can form an OAM signal with the number of modes l, and the generated OAM mode l needs to meet the limiting condition that
The phase gradient formed by all M × N signals transmitted by the M antennas in a rotation period has two methods, the first method is to configure a phase shifter for the antennas, so that when the antennas rotate to the position of a transmitted pulse, the phase shifter generates the required phase gradient, the generation mode is flexible, and if the precision of the phase shifter is high enough, any OAM mode number can be generated
Of the signal of (1).
The second method does not arrange phase shifters so that the signals transmitted by the M antennas have no phase difference or have a phase difference of an integer multiple of 2 pi, i.e.
Where m is a positive integer, a specific OAM pattern number may be generated
Of the signal of (1). The phase shift required during the antenna rotation is caused by the time delay of the antenna rotation, and the specific derivation process is as follows: at intervals of adjacent pulses
The phase difference of the antenna should satisfy
Where n is a positive integer for adjusting the number of periods of phase difference between adjacent pulses. Therefore, it is not only easy to use
Therefore, the rotation speed of the antenna needs to be satisfied
Then changing from l to mM
In order to solve the problem of divergence of the beam angle of the OAM wave, in the embodiment of the present invention, a beam focusing device such as a parabolic antenna or a lens may be used to focus the beam of the OAM wave generated by the rotating antenna.
Fig. 3 is a schematic diagram of a rotating antenna, and in an embodiment of the present invention, the rotating antenna 202 may be formed by a loop antenna array formed by one antenna or M antennas, and the antenna or the antenna array performs a uniform circular motion around a circular ring with a radius R under the driving of the rotating device 201. The normal direction of the antenna rotation plane coincides with the propagation direction of the antenna beam. The antenna element of the rotating antenna can be a horn antenna, a parabolic antenna, a patch antenna and other directional or omnidirectional antennas.
FIG. 4 shows the signal synthesis process, assuming that N pulses are emitted in one rotation period, the pulse width is τ and the pulse repetition period is TrIf the period of one rotation of the antenna is T ═ NTr. The echo time delay of the first pulse at the receiving end is (N-1) TrThe second is (N-2) TrThe ith is (N-i) TrThe Nth time delay-free, and finally the coherent accumulation in the synthesizer, thereby forming an equivalentOAM signals.
Fig. 5 is a signal processing flow diagram of a cognitive processor.
After the data processor of the system calculates the detection results of the electromagnetic waves with different OAM mode numbers, the results are sent to the cognitive processor. A preferred strategy is employed in the cognitive processor to analyze the RCS of electromagnetic waves of different OAM mode numbers and to select the OAM mode number that will produce the largest target RCS. After the optimization is completed, the selected strategy is changed into a control command to control a signal generator in the signal transmitting subsystem and a rotating device in the antenna subsystem to generate corresponding OAM electromagnetic waves.
In one embodiment of the present invention, the electromagnetic wave orbital angular momentum waveform is Lall＝{l1,l2,...,lmaxIn the initial period, the subset of orbital angular momentum of the emitted electromagnetic wave is
The number of the electromagnetic wave orbital angular momentum signal paths allowed to be transmitted is K, wherein lmaxThe number of the maximum electromagnetic wave orbital angular momentum modes,
represents the number of orbital angular momentum modes of the electromagnetic wave transmitted on the Kth path at the initial moment and has
Measuring the signal-to-noise ratio of each path of electromagnetic wave orbital angular momentum signal in a cognitive processor, wherein the signal-to-noise ratio of the ith path is βiThe maximum signal-to-noise ratio in all K paths is βmaxThe ith signal has
Change the number of orbital angular momentum modes of the electromagnetic wave to be transmitted next, i.e.
For the next transmitted waveform, thereby maintaining detection of the targetAnd (4) an optimal state.
FIG. 6 shows a simulation scenario in one embodiment of the present invention.
In one embodiment of the present invention, OAM electromagnetic waves are incident along the y-axis on a simple complex scatterer consisting of a first bead 1 and a second bead 2. The two small spheres can be regarded as point scatterers, the distance d is 1m, the frequency of the electromagnetic wave is 10GHz, and the distance r of the rotating antenna from the scatterers is 20000 m. The method adopts electromagnetic waves with the OAM mode number of l 10, l 100 and l 1000, and the pulse repetition period T is 9999999 at the free parameter mr＝10-3While the corresponding rotation speed is omegal＝10＝2π×100rad/s、Ωl＝100＝2π×10rad/s、Ω l＝10002 pi rad/s. In a far-field environment, electromagnetic waves of different OAM modes are incident on the scatterer. The angle between the line connecting 1 and 2 and the y-axis is theta, and the RCS of the scatterer in the y-axis direction changes along with the change of theta.
Fig. 7 shows simulation results in an embodiment of the present invention.
In fig. 7, to facilitate observing RCS differences between different OAM electromagnetic waves, θ ranges from 0 ° to 20 ° and normalized RCS, i.e., RCS at different angles divided by the maximum value of RCS, is used to measure the different OAM electromagnetic waves. It can be seen from the figure that the RCS fading positions of the electromagnetic wave and the plane wave when the OAM mode number is 100 have a significant difference. When the number of OAM modes is further increased to 1000, the frequency of RCS fading is significantly increased. And finally, the optimal OAM wave is selected through the optimization of the cognitive processor, so that deep fading of a corresponding position is avoided, the signal-to-noise ratio of a receiving end is improved, and the detection probability of a weak target is improved.
Figure 8 shows a schematic diagram of the present invention using phased array antenna electrical scanning instead of mechanical rotation.
The rotating antenna consists of a phased array antenna and a ring-shaped reflecting surface, the phased array antenna is positioned on a focal plane of the ring-shaped reflecting surface, and the center of a wave beam is positioned at the focal point. The reflected azimuth angle is uniformly changed along with the transmitted wave beams or wave beam clusters of the phased array antenna, and the wave beams reflected by the reflecting surface rotate at a constant speed along the center of the circular ring reflecting surface. The wave beam rotation is equivalent to the mode of mechanical rotation of the M antenna elements under the drive of the rotating device, so the electric scanning mode provides another mode of wave beam generation of the rotating antenna.
Claims (5)
1. An equivalent electromagnetic wave orbital angular momentum pulse radar detection method is characterized by comprising the following steps:
1) the rotary antenna of the radar system is a ring-shaped antenna array formed by M arrays which are uniformly distributed, wherein M is more than or equal to 1; the rotation period is defined as that the antenna array rotates counterclockwise or clockwise at a constant speed by taking the origin as the center
Radian, angular velocity of rotation omega, and period of rotation
2) The rotating device drives the rotating antenna to rotate, M antenna arrays simultaneously transmit pulse signals in the rotating process, and N pulses are transmitted in one period, namely each pulse is formed by overlapping the M signals; the signal transmitted by each antenna element has
A phase gradient which is increased linearly for increment, wherein l is the mode number of the needed electromagnetic wave orbital angular momentum;
3) during the rotation process, the signal transmitted by each antenna array at each transmitting point also has a linear phase shift relative to the initial signal
Where k is 1,2, …, N, the phase of the signal transmitted by the ith antenna element is
M antenna elements in one rotation period
All M × N signals transmitted in the time interval of (1)
Is interval and has a phase gradient from 0 to
The signal sequence of (a);
4) during the time interval between adjacent transmitted pulses, the rotating antenna receives the echo signal at TrIs pulse repetition period, and synthesizes M × N signal sequences in the signal processor, wherein the signal synthesis process is that the echo time delay of the first pulse at the receiving end is (N-1) TrThe second is (N-2) Tr…, ith is (N-i) Tr…, the Nth has no time delay, and finally coherent accumulation is carried out, thereby forming an equivalent electromagnetic wave orbital angular momentum signal;
5) the electromagnetic wave orbital angular momentum waveform is integrated into Lall＝{l1,l2,...,lmaxIn the initial period, the subset of orbital angular momentum of the emitted electromagnetic wave is
The number of the electromagnetic wave orbital angular momentum signal paths allowed to be transmitted is K, wherein lmaxThe number of the maximum electromagnetic wave orbital angular momentum modes,
represents the number of orbital angular momentum modes of the electromagnetic wave transmitted on the Kth path at the initial moment and has
6) Measuring the signal-to-noise ratio of each path of electromagnetic wave orbital angular momentum signal in a cognitive processor, wherein the signal-to-noise ratio of the ith path is βiMaximum signal-to-noise ratio in all K pathsIs βmaxThe ith signal has
Change the number of orbital angular momentum modes of the electromagnetic wave to be transmitted next, i.e.
The next transmitted waveform, thereby maintaining the optimal state for target detection.
2. The equivalent electromagnetic wave orbital angular momentum pulse radar detection method of claim 1, wherein the phase gradient formed by all M × N signals transmitted by M antennas in one rotation period is formed by two methods, the first method is to arrange a phase shifter for the antennas, the second method is to arrange no phase shifter, and the required phase gradient is generated by using the time delay generated by rotation, in this case, the number of modes of the generated electromagnetic wave orbital angular momentum is mM, M is a positive integer, and M is a positive integer
Rotational angular velocity Ω is required to satisfy
n is an integer, and ω is the electromagnetic angular frequency.
3. An equivalent electromagnetic wave orbital angular momentum pulse radar detection system for implementing the method of claim 1, wherein the radar detection system comprises:
1) a signal transmission subsystem (100) comprising a signal generator (101) for generating a chirp signal, and a transmitter (102) for power amplifying the signal and transmitting it through an antenna;
2) an antenna subsystem (200) comprising a duplexer (201) for switching the transmit and receive states of the antenna, a rotating antenna (202), a beamforming device (203) to collimate incident electromagnetic waves, and a rotating device (204) to effect rotation of the antenna;
3) a signal receiving subsystem (300), the signal receiving subsystem (300) comprising a receiver (301), a signal processor (302), a data processor (303), and a cognitive processor (304); wherein the signal processor (302) is used for carrying out coherent accumulation processing on the pulse to obtain a synthesized pulse signal; the data processor is used for detecting the synthesized signal;
a signal generator (101) in the signal transmitting subsystem (100) transmits a pulse signal to a transmitter (102), the transmitter (102) feeds the pulse signal into an antenna subsystem (200), a rotating device (204) drives a rotating antenna (202) to perform uniform-speed circular motion, the pulse signal is transmitted in the rotating mode, the antenna subsystem (200) receives an echo signal when a duplexer (201) is in a receiving state, the received echo signal is sampled and down-converted by a receiver (301) in a signal receiving subsystem (300) and enters a signal processor (302) for echo accumulation, and then the signals after echo accumulation are respectively transmitted to a data processor (303) and a cognitive processor (304); the data processor (303) detects the signals after the echo accumulation; and the cognitive processor (304) adjusts the signal generator (101) and the rotating device (204) according to the signal-to-noise ratio of the current waveform by adopting an optimal signal-to-noise ratio principle, so as to generate an optimal radar pulse signal to be transmitted next.
4. The equivalent electromagnetic wave orbital angular momentum pulse radar detection system of claim 3, wherein: the rotary antenna array adopts a horn antenna, a parabolic antenna, a Cassegrain antenna, a patch antenna or an array antenna.
5. The equivalent electromagnetic wave orbital angular momentum pulse radar detection system of claim 3, wherein: the rotating antenna (202) adopts a mechanical rotating antenna or an electric scanning rotating antenna, the electric scanning rotating antenna is composed of a phased array antenna and a ring-shaped reflecting surface, the phased array antenna is positioned on a focal plane of the ring-shaped reflecting surface, a beam or a beam cluster emitted by the phased array antenna uniformly changes a scanning azimuth angle, and is reflected by the reflecting surface to form emergent beams or a beam cluster, and the emergent beams do uniform circular motion around the center of the ring-shaped reflecting surface.
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| CN111740223B (en) * | 2020-07-06 | 2021-05-28 | 中国科学院成都生物研究所 | Method for synthesizing vortex electromagnetic field with high orbital angular momentum mode number |
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