CN111736119B - Design method for anti-interference treatment of phased array radar - Google Patents
Design method for anti-interference treatment of phased array radar Download PDFInfo
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Abstract
The invention discloses a design method for anti-interference treatment of a phased array radar, which comprises the following steps: determining the number of array elements of the digital phased array radar, and forwarding and processing data by adopting multi-path optical fiber communication and two FPGA; aligning the multiple paths of optical fiber data; carrying out channel calibration before digital beam synthesis, and calculating an error compensation coefficient of each channel; performing digital beam synthesis according to the error compensation coefficient of each channel; selecting an optimal working frequency point in the current environment according to the application scene; and performing self-adaptive side lobe cancellation by adopting an open loop side lobe cancellation algorithm of a minimum mean square error criterion so as to cancel interference signals. The invention can realize the anti-interference processing of digital beam synthesis and self-adaptive side lobe cancellation on the digital phased array radar, has the characteristics of high speed, parallelism and large throughput, has the function of state monitoring and flexible beam weighting, and shortens the development and test period of the anti-interference processing of the radar.
Description
Technical Field
The invention relates to the technical field of digital phased array radars, in particular to a design method for anti-interference processing of a phased array radar, namely a design method for anti-interference processing of a light and high-maneuver search and tracking integrated radar platform, which can realize full airspace search of targets and accurately track appointed targets.
Background
Pulse phased arrays are the most important regime in modern radars. The antenna array is formed by arranging a plurality of array antennas according to a certain sequence and shape. Each array antenna is configured with its own control system. The radar finely adjusts the phase component of each array antenna to enable the whole array surface of the antenna to follow the interference principle to synthesize the wave beams meeting the functional requirements. Compared with other system radars, the pulse phased array has stronger anti-interference capability and longer detection distance. The data volume and the operation volume are generally larger, and more information can be provided for the back end in the same time.
Anti-interference is a necessary function of radar. Interference can be classified into active interference and passive interference according to energy sources. The squelch active interference generated by the enemy can enter from the side lobes of the antenna beam, inundating the target information in the main lobe. Modern phased array radars mostly employ adaptive sidelobe cancellation processing to reduce the effects of interference, also known as interference direction nulling. In different environments there is also more or less passive interference, typically caused by scattering, reflection and refraction of electromagnetic waves. When the environment changes, the operating frequency point with the smallest interference is generally selected again according to the interference power of different operating frequency points.
The phased array radar signal processing capability and the anti-interference capability are improved, the continuous pursuit of designing a radar processing method is realized, meanwhile, the requirements of engineering practice are also considered, and the development and test period is shortened.
Disclosure of Invention
Aiming at the problems existing in the prior art, the invention aims to provide a design method for anti-interference processing of a phased array radar, which can realize anti-interference processing of digital beam synthesis and self-adaptive side lobe cancellation on the digital phased array radar, has the characteristics of high speed, parallelism and large throughput, has complete state monitoring function and flexible beam weighting, and shortens development and test periods of the anti-interference processing of the radar.
In order to achieve the above purpose, the present invention is realized by the following technical scheme.
A design method for anti-interference treatment of a phased array radar comprises the following steps:
step 1, determining the number of array elements of a digital phased array radar, and forwarding and processing data by adopting multi-path optical fiber communication and two FPGA; aligning the multiple paths of optical fiber data before digital beam synthesis;
wherein, the two FPGAs are a master FPGA and a slave FPGA respectively;
step 2, carrying out channel calibration before digital beam synthesis, and calculating an error compensation coefficient of each channel;
step 3, digital wave beam synthesis is carried out according to the error compensation coefficient of each channel; selecting an optimal working frequency point in the current environment according to the application scene;
and 4, performing self-adaptive side lobe cancellation by adopting an open loop side lobe cancellation algorithm of a minimum mean square error criterion to eliminate interference signals and finish the anti-interference design of the radar.
Further, the number of array elements is 100-150, and the number of synthesized beams of each range gate is not more than 120.
Further, the alignment of the multiple paths of optical fiber data before the digital beam synthesis is specifically:
1.1, judging whether the physical connection of the optical fibers is normal, if so, turning to 1.2, otherwise, reconnecting;
wherein, the existence of continuous k data is the value within the code, and the physical connection of the optical fiber is judged, wherein, k is more than 240 and less than 260;
1.2, optical fiber forwarding: adopting fifo to perform data isolation of different clocks, forwarding fifo to reset in an idle period, so that abnormal data is not accumulated in fifo;
1.3, optical fiber synchronization: removing unconnected optical fibers, taking the associated clock of each path of data as a fifo write clock, and unifying all read clocks; each path of data enters fifo when valid, and after all data are written into at least 4 paths of data, the data are read out simultaneously, so that synchronization is completed. fifo is a first-in first-out queue, i.e., executed in order.
Further, step 2 comprises the sub-steps of:
2.1, carrying out channel calibration before the radar system starts to work, wherein one path of calibration signal simultaneously enters all channels, and the calibration signal is direct current after down-conversion and filtering;
2.2, calculating the average value of the received data at different moments for each channel, and further obtaining the phase and the amplitude of each channel;
2.3, selecting a certain channel as a reference channel, and calculating the phase difference between each channel in the rest channels and the reference channel; calculating the conjugate of the phase difference corresponding to each channel to obtain a corresponding phase compensation coefficient;
2.4, carrying out amplitude normalization on all channels according to the amplitudes of the reference channels to obtain normalized amplitudes of all channels, and taking the reciprocal of the normalized amplitudes of all channels as an amplitude compensation coefficient;
the error compensation coefficient is composed of a phase compensation coefficient and an amplitude compensation coefficient.
Further, the digital beam synthesis is performed according to the error compensation coefficient of each channel, specifically: and in the digital beam synthesis, the error compensation coefficient of each channel is adopted to weight the corresponding channel, and then the digital beam synthesis is carried out.
Further, according to the application scenario, selecting an optimal working frequency point under the current environment, specifically:
3.1, the data after the digital wave beam synthesis has a real part and an imaginary part, firstly, respectively squaring and summing the real part and the imaginary part of the data of each distance gate, and then, time-averaging the frequency point signals to be used as the power of the current frequency point;
3.2, repeating the step 3.1 for different working frequency points of the radar to obtain the power of all the working frequency points of the radar;
3.3, selecting frequency points with the maximum power and the minimum power from all working frequency points of the radar, and transmitting the frequency points to a frequency point switching device; the frequency point switching device selects a frequency point corresponding to the maximum or minimum power as the best working frequency point in the current environment according to the signal strength requirement in the current environment.
Furthermore, the open loop sidelobe cancellation algorithm adopting the minimum mean square error criterion performs adaptive sidelobe cancellation, specifically:
4.1, selecting N antenna array elements as auxiliary antennas, and synthesizing the rest (M-N) array elements into a main antenna after wave beams;
wherein M is the total number of array elements of the radar, N is an even number, and N is more than 2 and less than 10;
4.2, collecting side lobe cancellation data in the rest period of the radar, and canceling a main antenna signal by adopting the side lobe cancellation data of N auxiliary antennas so as to minimize the power output by the signal;
the specific process is as follows:
first, the output of the radar system isY is the data of the main channel,optimal weight w for the nth auxiliary channel n Conjugate of X n Data for the nth auxiliary channel, W H The transpose of the vector W formed by the optimal weight, and X is a vector formed by N auxiliary channel data;
secondly, calculating the mean square error of the radar system output:
wherein sigma (W) represents a mean square error with W as an argument, E { } represents a modulo operation,r is the conjugate transpose of the cross-correlation matrix of the main channel and the auxiliary channel XY Is the cross-correlation matrix of the main channel and the auxiliary channel, R XX An autocorrelation matrix for the auxiliary channel;
and finally, solving an auxiliary channel optimal weight which minimizes the mean square error, eliminating an interference signal by adopting the auxiliary channel optimal weight during normal operation of the radar, and reserving a target signal.
Further, gradient by mean square errorFor 0, calculate the optimum weight vector W of the auxiliary channel opt ：
Satisfy R XX W op t＝R XY The weight of (2) is the optimal weight vector.
Further, the data interaction process in the radar anti-interference processing process is as follows: in the digital beam forming process, the weight coefficient of each channel is transmitted to a master FPGA by a DSP chip, and then transmitted to a slave FPGA by the master FPGA, and the two FPGAs jointly complete beam forming in a range gate; and when the self-adaptive side lobes are eliminated, performing cross-correlation calculation on the main channel and the auxiliary channel from the FPGA, transmitting a calculation result to the main FPGA, performing data integration of auto-correlation and cross-correlation by the main FPGA, and transmitting the data integration to the DSP chip.
Further, the phased array radar system further comprises a pattern monitoring module and a channel monitoring module, wherein the pattern monitoring module is used for monitoring the effect of channel calibration and the beam forming coefficient, and the monitoring result can be used as a measurement basis of the actual tracking effect; the channel monitoring module is used for locating anomalies of the signal transmitting and signal receiving components.
Compared with the prior art, the invention has the beneficial effects that:
the invention realizes anti-interference treatment such as digital beam synthesis and self-adaptive side lobe cancellation on the digital phased array radar, and realizes the elimination of interference signals through the selection of the optimal working frequency point and the self-adaptive side lobe cancellation in the rest period; the hardware adopts two FPGA cooperative processing to realize the processing of large data rate, has the characteristics of high speed, parallelism and large throughput, has complete state monitoring function and flexible beam weighting, and shortens the development and test period.
Drawings
The invention will now be described in further detail with reference to the drawings and to specific examples.
FIG. 1 is a flow chart of a design method of a phased array radar anti-interference process of the present invention;
FIG. 2 is a data processing flow diagram of a phased array radar anti-interference process in accordance with an embodiment of the present invention;
FIG. 3 is a schematic diagram of a channel calibration structure according to an embodiment of the present invention;
fig. 4 is a block diagram of an adaptive sidelobe canceling system of an embodiment of the present invention;
FIG. 5 is a digital beam forming raw pattern of an embodiment of the present invention;
fig. 6 is a diagram of an adaptive sidelobe canceling pattern of an embodiment of the present invention.
Detailed Description
Embodiments of the present invention will be described in detail below with reference to examples, but it will be understood by those skilled in the art that the following examples are only for illustrating the present invention and should not be construed as limiting the scope of the present invention.
Referring to fig. 1, the design method for the anti-interference treatment of the phased array radar provided by the invention comprises the following steps:
step 1, determining the number of array elements of a digital phased array radar, and forwarding and processing data by adopting multi-path optical fiber communication and two FPGA; aligning the multiple paths of optical fiber data before digital beam synthesis;
wherein, the two FPGAs are a master FPGA and a slave FPGA respectively;
specifically, in order to obtain better digital beam forming direction, the number of array elements of the digital phased array radar is relatively large, and the number of the array elements is between one hundred and five. The data rate before beam forming is very high, and the combination of multipath optical fiber communication and an FPGA high-speed transceiver is generally adopted to meet the requirement of high data rate. To obtain high-precision angle information, 120 beams are proposed to be synthesized for each range gate. The operation resource requirement of the beam forming process is great, and two FPGAs are required to be completed together. Such a hardware platform adds functionality to the original data forwarding prior to beamforming. There is a delay in the multiplexed fiber data that needs to be aligned prior to beam synthesis.
As shown in fig. 2, the data processing flow in the present invention is: the data are transmitted by multiple paths of optical fibers and are connected with the main FPGA; the master FPGA receives optical fiber data and forwards the optical fiber data to the slave FPGA, and the master FPGA and the slave FPGA synchronously perform multipath data synchronization; and carrying out data analysis on the synchronous data and the self-checking data to obtain a related control signal.
When the channel is calibrated, the analyzed data is averaged and then transmitted to a DSP (digital signal processing) chip, the channel calibration coefficient is calculated in the DSP, and after being combined with a DBF (digital beam forming) coefficient, the channel calibration coefficient is transmitted back to the FPGA and stored in a DBF coefficient module through coefficient distribution and data interaction.
When the working frequency point is selected, the analyzed data are calculated in an AFT (automatic frequency tracking) module to obtain a maximum power frequency point and a minimum power frequency point. During normal operation, the analyzed data is buffered and converted into a clock, DBF operation is performed, and an operation result is output through the VPX bus. When the side lobes are eliminated, the analyzed auxiliary channel data and the main channel data of the DBF are integrated through data interaction, the data are transmitted to the DSP after the autocorrelation and the cross correlation are obtained, and the DBF coefficient is updated after the DSP obtains the optimal weight of the auxiliary channel. And (3) when the pattern is monitored, the DBF result is averaged and then output through a serial port.
Specific alignment procedures include fiber reception, forwarding, and synchronization.
First, the optical fiber physical connection is judged, the unconnected optical fiber is a messy code, and a value beyond the 8b/10b code can appear, and if 250 continuous data are all values within the code, the optical fiber can be considered to be physically connected.
Secondly, according to different clocks in forwarding, fifo is adopted for data isolation, and in order to increase the recovery capability of an abnormal state, the forwarding fifo resets in an idle period, so that abnormal data is ensured not to be accumulated in the fifo.
Finally, the physical unconnected optical fibers affect the synchronization of the normal optical fibers, so the unconnected optical fibers are excluded in the synchronization process according to the judgment result of the previous physical connection. When the optical fiber data are synchronized, the respective associated clocks of the data are used as fifo write clocks, and all read clocks are unified. Each path of data enters fifo when valid, and after all data are written into at least 4 paths of data, the data are read out simultaneously, so that synchronization is completed.
Step 2, carrying out channel calibration before digital beam synthesis, and calculating an error compensation coefficient of each channel;
after the airspace echo of the radar reaches the array surface, the airspace echo is received by the array element and reaches the acquisition port through the receiving channel. Because of the physical characteristics of the receive paths, the phase shift of the signal after each receive path is inconsistent, and digital beam synthesis precludes the effect of the receive path on the phase of the signal. Channel error compensation is performed prior to beam forming, and this error is measured in a specific time and is ultimately applied to the coefficients of beam forming.
The channel calibration structure is shown in fig. 3, and in normal operation, the space electromagnetic wave is received by the antenna and enters the receiving network. The phase delay and amplitude attenuation of each channel in a phased array radar receiving network are different, and the phase and amplitude of each channel need to be compensated. Therefore, channel calibration is required before receiving data, eliminating phase and amplitude differences between channels. When the channels are calibrated, the calibration signals enter the receiving network through the antenna coupling lines, all the channels receive the same signal, and the output of the channels can reflect the physical characteristics of the channels, namely the influence on the phase and the amplitude. Coefficients are used to compensate for these effects in subsequent digital beamforming.
Specifically, channel calibration is completed in a specific time, one path of calibration signal enters all receiving channels at the same time, in order to reduce resource occupation, the calibration signal is direct current after down-conversion and filtering, and a channel averaging method is adopted to obtain phase information of all channels. And selecting one of the channels as a reference channel to obtain phase differences of all the channels, calculating a phase compensation coefficient by taking conjugate of the phase differences, normalizing the amplitude of the reference channel, and taking the inverse of the amplitude of each channel as an amplitude compensation coefficient. The phase compensation and the amplitude compensation act together in the beam forming coefficients.
Taking three channels as an example, the average value of the first channel isWherein X is m Is the data of the first channel at time m. The second channel means +.>Wherein Y is m Is the data of the second channel at time m. The mean value of the third channel is +.>Wherein Z is m Is the data of the third channel at time m. Since the mean value of each channel is plural, it can also be written as + -> Wherein A is 1 ，A 2 ，A 3 The amplitudes of three channels respectively, theta 1 ，θ 2 ，θ 3 The phases of the three channels, respectively. Based on the first channel, C 0 C＝B，D 0 D=b, wherein C 0 ，D 0 The compensation coefficients of the second channel and the third channel, respectively. Thus get +.>
Step 3, digital wave beam synthesis is carried out according to the error compensation coefficient of each channel; selecting an optimal working frequency point in the current environment according to the application scene;
there are different interference backgrounds for different environments. The radar sequentially transmits specific signals of different frequency points, normal synthesis is carried out after the specific signals are received, and frequency points with the maximum power and the minimum power are selected. In practical application, certain environments have frequency control, and the maximum and minimum frequency points are selected according to control information.
And in the digital beam synthesis, the error compensation coefficient of each channel is adopted to weight the corresponding channel, and then the digital beam synthesis is carried out.
Further, according to the application scene, selecting an optimal working frequency point under the current environment, specifically:
3.1, the data after the digital wave beam synthesis has a real part and an imaginary part, firstly, respectively squaring and summing the real part and the imaginary part of the data of each distance gate, and then, time-averaging the frequency point signals to be used as the power of the current frequency point;
3.2, repeating the step 3.1 for different working frequency points of the radar to obtain the power of all the working frequency points of the radar;
3.3, selecting frequency points with the maximum power and the minimum power from all working frequency points of the radar, and transmitting the frequency points to a frequency point switching device; the frequency point switching device selects a frequency point corresponding to the maximum or minimum power as the best working frequency point in the current environment according to the signal strength requirement in the current environment. For example, in a new environment where various electromagnetic waves exist in a certain space, only signal reception is performed to obtain the power of the electromagnetic waves received in the environment at each frequency point, and at this time, it is desirable that the influence of the environment is minimum, and the frequency point with the minimum power is selected. Or if a determined target exists in the new environment, signal transmission and reception are carried out to obtain the power of the received determined target under each frequency point, and at the moment, the maximum echo power of the target is expected, and then the frequency point with the maximum power is selected.
And 4, performing self-adaptive side lobe cancellation by adopting an open loop side lobe cancellation algorithm of a minimum mean square error criterion to eliminate interference signals and finish the anti-interference design of the radar.
Specifically, to suppress interference coming in from the side lobes, an open-loop side lobe cancellation algorithm of minimum mean square error criterion is employed. And selecting 4 antennas from all the antenna array elements as auxiliary antennas, and synthesizing the rest array elements into a main antenna after beam synthesis. The goal of the algorithm is to cancel the main antenna signal with 4 degrees of freedom of the auxiliary antennas so that the power of the signal output is minimized. From the direction diagram, the direction diagram of the auxiliary antenna is very close to the gain of the main antenna direction diagram in the interference direction, and the specific approach degree reflects the cancellation effect. According to such criteria, it is desirable to obtain as much interference signal as possible while acquiring side lobe cancellation samples to avoid the target signal, the sampling time most meeting the requirements in this is in the radar rest period.
The open loop adaptive sidelobe canceling architecture under the minimum mean square error criterion is shown in fig. 4. During rest periods, interference enters the system through the primary and secondary antennas. And (3) carrying out optimal weight calculation on the sample Y of the main channel and the sample X of the auxiliary channel to obtain an optimal weight W, wherein the optimal weight at the moment enables the system output to be minimum, namely, inhibition is formed in the interference direction. During operation, the interference and target signals enter the system simultaneously. The auxiliary channel data is multiplied and accumulated with the optimal weight and then is differenced with the main channel, and the target signal is reserved and the interference is eliminated because the optimal weight forms inhibition in the interference direction.
The specific process is as follows: first, the output of the radar system isY is main channel data,>optimal weight w for the nth auxiliary channel n Conjugate of X n Data for the nth auxiliary channel, W H The transpose of the vector W formed by the optimal weight, and X is a vector formed by N auxiliary channel data;
secondly, calculating the mean square error of the radar system output:
wherein sigma (W) represents a mean square error with W as an argument, E { } represents a modulo operation,r is the conjugate transpose of the cross-correlation matrix of the main channel and the auxiliary channel XY Is the cross-correlation matrix of the main channel and the auxiliary channel, R XX An autocorrelation matrix for the auxiliary channel;
and finally, solving an auxiliary channel optimal weight which minimizes the mean square error, eliminating an interference signal by adopting the auxiliary channel optimal weight during normal operation of the radar, and reserving a target signal. I.e. the output mean square error is the smallest, i.e. the interference is the smallest through the system, and the auxiliary channel weights under this criterion are used during normal operation to cancel the interference and preserve the target signal.
Gradient by mean square errorFor 0, calculate the optimum weight vector W of the auxiliary channel opt ：
Satisfy R XX W opt ＝R XY The weight of (2) is the optimal weight vector.
Reporting the side lobe cancellation result to a terminal, wherein the terminal passes through a directional diagram monitoring module and a channel monitoring module, and the directional diagram monitoring module is used for adjusting a channel calibration coefficient and a beam synthesis coefficient at different working frequency points; the channel monitoring module is used for rapidly positioning the abnormal channel and can also assist in positioning links causing abnormal states so as to shorten debugging and testing periods.
Simulation experiment
The effect of the present invention can be further illustrated by the following simulation experiment.
The method of the invention is adopted to process and design radar signals, and the simulation conditions are as follows: the signal-to-noise ratio is 30dB, the signal-to-interference ratio is-40 dB, and the antenna array is 124 antennas which are linearly arranged, wherein 4 auxiliary antennas are arranged. The simulation of the number of different samples and the positions of the auxiliary antenna are respectively carried out, the number of the selected samples is 128 through the comprehensive consideration of the operand and the cancellation effect, and the auxiliary antenna is positioned in the middle of the array, namely 61, 62, 63 and 64 positions. The original pattern simulated by the algorithm is shown in fig. 5, wherein the solid line is a main channel pattern formed by 120 array elements, and the amplification of-10 degrees to 10 degrees is selected. The main lobe gain is 41.58dB, the first side lobe (-1.4 °) gain is 29.55dB, and if interference enters from the first side lobe, the target signal of the main lobe is basically submerged. The dashed line is the auxiliary channel pattern for which side lobe cancellation has not been performed.
The direction diagram after side lobe cancellation by the invention is shown in fig. 6, wherein the solid line is the main channel direction diagram, and the direction diagram is consistent with the upper diagram. The dashed line is the auxiliary channel pattern, and the dashed line coincides with the solid line at the first side lobe (-1.4 °) compared to fig. 5, meaning that the subtracted value in this direction is small. The solid line with asterisks is a cancelled pattern, and the gain of the first side lobe (-1.4 ℃) is 21.42dB, and the gain of the side lobe after cancellation is reduced by about 50 dB. The specific implementation flow is that after 128-point samples in the resting period are received, auxiliary channel autocorrelation operation is firstly carried out, operation results are stored, and then cross correlation operation is carried out on data of the auxiliary channel and a beam synthesis result. Because of the symmetry of the autocorrelation matrix, only the diagonal and upper triangular parts of the matrix are calculated, thereby reducing the calculation amount. The autocorrelation and cross-correlation data are transmitted to the DSP, and the autocorrelation matrix inversion is carried out first, and then the autocorrelation matrix inversion is multiplied with the cross-correlation matrix, so that the optimal weight vector is obtained.
In addition, the data interaction between the master FPGA and the slave FPGA is cooperatively processed. The weight coefficients required for digital beam forming are transmitted by the DSP chip to the main FPGA. And then the beam is transmitted to the slave FPGA by the master FPGA to jointly complete 120 beam synthesis. When the self-adaptive side lobe is eliminated, partial cross-correlation results of the main channel and the auxiliary channel are sent to the main FPGA by the slave FPGA, and then the main FPGA performs self-correlation and cross-correlation data integration and sends the data integration to the DSP chip. And the beam synthesis result of the slave FPGA in the monitoring mode is also transmitted to the master FPGA, and finally the master FPGA finishes the state reporting.
The invention also has a monitoring mode, which is mainly divided into pattern monitoring and channel monitoring; aiming at different working frequency points, the channel calibration coefficient and the beam synthesis coefficient need to be adjusted, and the adjusting effect is mainly observed through pattern monitoring. The pattern monitoring function can directly reflect the effect of channel calibration, the beam forming coefficient and other indexes. The tracking radar generally requires high precision, the direction is fine and dense during the monitoring of the directional diagram, and the monitoring result can be used as a measurement basis of the actual tracking effect. For monitoring of the channel, the abnormal channel can be rapidly positioned, the link causing the abnormal state can be positioned in an assisted manner, and the monitoring mode can shorten the debugging and testing period.
The method comprises the steps of firstly forwarding and synchronizing data received by an optical fiber, and then calculating a channel phase difference according to a channel calibration signal; the phase compensation value is obtained and is firstly applied to normal synthesis to obtain the most suitable working frequency point in the current environment; performing self-adaptive side lobe cancellation weight calculation in the rest period; and reporting the processing result after the side lobe cancellation through a monitoring mode.
While the invention has been described in detail in this specification with reference to the general description and the specific embodiments thereof, it will be apparent to one skilled in the art that modifications and improvements can be made thereto. Accordingly, such modifications or improvements may be made without departing from the spirit of the invention and are intended to be within the scope of the invention as claimed.
Claims (8)
1. The design method for the anti-interference treatment of the phased array radar is characterized by comprising the following steps of:
step 1, determining the number of array elements of a digital phased array radar, and forwarding and processing data by adopting multi-path optical fiber communication and two FPGA; aligning the multiple paths of optical fiber data before digital beam synthesis;
wherein, the two FPGAs are a master FPGA and a slave FPGA respectively;
step 2, carrying out channel calibration before digital beam synthesis, and calculating an error compensation coefficient of each channel;
step 3, digital wave beam synthesis is carried out according to the error compensation coefficient of each channel; selecting an optimal working frequency point in the current environment according to the application scene;
step 4, performing self-adaptive sidelobe cancellation by adopting an open loop sidelobe cancellation algorithm of a minimum mean square error criterion to cancel interference signals, and finishing radar anti-interference design;
the open loop sidelobe cancellation algorithm adopting the minimum mean square error criterion performs self-adaptive sidelobe cancellation, and specifically comprises the following steps:
4.1, selecting N antenna array elements as auxiliary antennas, and synthesizing the rest (M-N) array elements into a main antenna after wave beams;
m is the total number of array elements of the radar, N is an even number, and 2< N <10;
4.2, collecting side lobe cancellation data in the rest period of the radar, and canceling a main antenna signal by adopting the side lobe cancellation data of N auxiliary antennas so as to minimize the power output by the signal;
the specific process is as follows:
first, the output of the radar system isY is main channel data,>optimal weight w for the nth auxiliary channel n Conjugate of X n Data for the nth auxiliary channel, W H The transpose of the vector W formed by the optimal weight, and X is a vector formed by N auxiliary channel data;
secondly, calculating the mean square error of the radar system output:
where E { } represents the desire, i|is a modulo operation,r is the conjugate transpose of the cross-correlation matrix of the main channel and the auxiliary channel XY Is the cross-correlation matrix of the main channel and the auxiliary channel, R XX An autocorrelation matrix for the auxiliary channel;
finally, solving an auxiliary channel optimal weight which minimizes the mean square error, eliminating interference signals by adopting the auxiliary channel optimal weight during normal operation of the radar, and reserving target signals;
the method for solving the auxiliary channel optimal weight which minimizes the mean square error comprises the following specific processes: gradient by mean square errorFor 0, calculate the optimum weight vector W of the auxiliary channel opt ：
Satisfy R XX W opt ＝R XY The weight of (2) is the optimal weight vector.
2. The method for designing a phased array radar anti-interference process according to claim 1, wherein the number of the array elements is 100-150, and the number of the composite beams of each range gate is not more than 120.
3. The method for designing a phased array radar anti-interference process according to claim 1, wherein the aligning the multipath optical fiber data before the digital beam forming comprises the following specific steps:
1.1, judging whether the physical connection of the optical fibers is normal, if so, turning to 1.2, otherwise, reconnecting;
wherein, there are continuous k data which are all values within the code, judge that the optic fibre physics has been connected, 240< k <260;
1.2, optical fiber forwarding: adopting fifo to perform data isolation of different clocks, forwarding fifo to reset in an idle period, so that abnormal data is not accumulated in fifo;
1.3, optical fiber synchronization: removing unconnected optical fibers, taking the associated clock of each path of data as a fifo write clock, and unifying all read clocks; each path of data enters fifo when being effective, and after all data are written into at least 4 paths of data, the data are read out simultaneously to complete synchronization; wherein fifo is a first-in first-out queue, i.e. executed in order.
4. The method of designing a phased array radar anti-interference process according to claim 1, wherein step 2 comprises the sub-steps of:
2.1, carrying out channel calibration before the radar system starts to work, wherein one path of calibration signal simultaneously enters all channels, and the calibration signal is direct current after down-conversion and filtering;
2.2, calculating the average value of the received data at different moments for each channel, and further obtaining the phase and the amplitude of each channel;
2.3, selecting a certain channel as a reference channel, and calculating the phase difference between each channel in the rest channels and the reference channel; calculating the conjugate of the phase difference corresponding to each channel to obtain a corresponding phase compensation coefficient;
2.4, carrying out amplitude normalization on all channels according to the amplitudes of the reference channels to obtain normalized amplitudes of all channels, and taking the reciprocal of the normalized amplitudes of all channels as an amplitude compensation coefficient;
the error compensation coefficient is composed of a phase compensation coefficient and an amplitude compensation coefficient.
5. The method for designing a phased array radar anti-interference process according to claim 1, wherein in step 3, the digital beam synthesis is performed according to the error compensation coefficient of each channel, specifically: and in the digital beam synthesis, the error compensation coefficient of each channel is adopted to weight the corresponding channel, and then the digital beam synthesis is carried out.
6. The design method for anti-interference processing of the phased array radar according to claim 1, wherein the selecting an optimal working frequency point in a current environment according to an application scene is specifically as follows:
3.1, the data after the digital wave beam synthesis has a real part and an imaginary part, firstly, respectively squaring the real part and the imaginary part of the data of each distance gate, and then, time-averaging the frequency point signals to be used as the power of the current frequency point;
3.2, repeating the step 3.1 for different working frequency points of the radar to obtain the power of all the working frequency points of the radar;
3.3, selecting frequency points with the maximum power and the minimum power from all working frequency points of the radar, and transmitting the frequency points to a frequency point switching device; the frequency point switching device selects a frequency point corresponding to the maximum or minimum power as the best working frequency point in the current environment according to the signal strength requirement in the current environment.
7. The design method of anti-interference processing of a phased array radar according to claim 1, wherein the data interaction process in the anti-interference processing of the radar is: in the digital beam forming process, the weight coefficient of each channel is transmitted to a master FPGA by a DSP chip, and then transmitted to a slave FPGA by the master FPGA, and the two FPGAs jointly complete beam forming in a range gate; and when the self-adaptive side lobes are eliminated, performing cross-correlation calculation on the main channel and the auxiliary channel from the FPGA, transmitting a calculation result to the main FPGA, performing data integration of auto-correlation and cross-correlation by the main FPGA, and transmitting the data integration to the DSP chip.
8. The method for designing anti-interference treatment of a phased array radar according to any one of claims 1 to 6, wherein the phased array radar system further comprises a pattern monitoring module and a channel monitoring module, the pattern monitoring module is used for monitoring the effect of channel calibration and the beam synthesis coefficient, and the monitoring result is used as a measurement basis of the actual tracking effect; the channel monitoring module is used for locating anomalies of the signal transmitting and signal receiving components.
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