A digital multi-beamforming method for satellite-based ADS-B based on DDC calibration

Abstract

The present invention discloses a satellite-based ADS‑B digital multi-beam forming method based on DDC calibration, including: a radio frequency module completes calibration signal generation, down-conversion of ADS‑B radio frequency signals, quantizes analog intermediate frequency signals through analog-to-digital converter sampling, and obtains original digital intermediate frequency signals; a DDC amplitude and phase calibration module completes signal link calibration, and completes the generation of IQ signals before beamforming through the coordinated work of a calibrator and a calibration controller; a digital beamforming module uses a vector weighting method to complete the final digital beamforming, and outputs multiple required beams to achieve coverage of the monitoring area under multi-beams. The present invention uses a coherent calibration source, a local oscillator source, a sampling clock, etc. to ensure the stability of the signal chain, which is beneficial to the engineering realization of satellite-based ADS‑B equipment; the calculation process is simple and reliable, with low complexity, high stability, fast calibration and high precision.

Description

Technical Field

[0001] The present invention relates to the technical field of digital multi-beam forming, in particular to a satellite-based ADS-B digital multi-beam forming method based on DDC calibration. Background Art

[0002] At present, more than 70% of the world's airspace, including the ocean, polar regions, and deserts, still lacks real-time monitoring means. Due to the lack of effective aircraft monitoring means in the area involved, it is impossible to obtain the track information of the aircraft during flight and the accurate location of the final crash site. Therefore, it is impossible to organize effective rescue activities in a timely manner, and subsequent investigations into the cause of the accident are also difficult to carry out (see non-patent document 1). In order to further improve the level of aviation operation safety, combined with the development level and trend of aviation surveillance technology, the concept of satellite-based ADS-B (Automatic Dependent Surveillance-Broadcast) has been proposed in the field of aviation surveillance at home and abroad. Satellite-based ADS-B can use low-orbit satellites equipped with ADS-B receiving payloads to monitor aircraft in sea areas and remote areas, and further achieve real-time coverage of global airspace by establishing a satellite constellation with global coverage, which is of great significance for ensuring aviation flight safety.

[0003] Compared with traditional ground surveillance technology, satellite-based ADS-B has the characteristics of long surveillance distance and wide range, but there are also some factors that restrict the performance of the system, such as weak received signals and severe interleaving (see non-patent document 2). Since it is difficult to solve the problems of weak signal reception and interleaving using a single beam, digital multi-beam reception technology based on array antennas is the current mainstream solution at home and abroad. There are two main advantages of satellite-based ADS-B digital multi-beam reception: First, the digital synthesis technology of array antennas is used to obtain gain and improve weak signal detection capabilities. Secondly, regional coverage is achieved through reasonable beam arrangement or scheduling, reducing the probability of signal interleaving and improving aircraft detection rate. The schematic diagram of satellite-based ADS-B receiving payload coverage based on digital multi-beam reception technology is shown below. Figure 1 shown.

[0004] Digital multi-beamforming (DBF) processing technology also involves a key processing process before beamforming: amplitude and phase calibration of the signal link. There are two common methods for amplitude and phase calibration: one is to calibrate the analog channel by analog (phase shift attenuation) method. This method has complex circuit implementation, and its stability and accuracy are generally limited by device characteristics. The other is to compensate and calibrate the digital IQ signal, which has a large amount of calculation.

[0005] The existing satellite-based ADS-B multi-beam forming method has the following disadvantages: 1) It uses analog (phase shift attenuation) devices to complete amplitude and phase compensation, which has poor stability and accuracy; 2) It uses IQ processing to achieve compensation, and the amplitude and phase parameters are not independent, the calculation is complex, and it is difficult to implement on a single chip FPGA.

[0006] References:

[0007] Non-patent literature:

[0008] Non-patent literature 1: Ni Jiushun, Chen Lihu, et al. Research progress and prospects of satellite-borne ADS-B[J]. Chinese Space Science and Technology, 2022, 42(01): 30-37.

[0009] Non-patent literature 2: Yu Sunquan. Research on key technologies of satellite-borne ADS-B payload[D]. National University of Defense Technology, 2018. Summary of the invention

[0010] In view of this, the present invention provides a satellite-based ADS-B digital multi-beam forming method based on DDC calibration to solve the above technical problems.

[0011] The present invention discloses a satellite-based ADS-B digital multi-beam forming method based on DDC calibration, which comprises:

[0012] Step 1: Control the calibration source in the RF module through the calibration controller in the DDC amplitude and phase calibration module to obtain N RF signals;

[0013] Step 2: obtaining a coupling calibration signal based on the N RF signals; and after amplifying, filtering, mixing, and sampling the coupling calibration signal, the RF module outputs a digital intermediate frequency signal;

[0014] Step 3: digitally down-convert the digital intermediate frequency signal through the DDC amplitude and phase calibration module to obtain a baseband signal;

[0015] Step 4: The DDC amplitude and phase calibration module uses the baseband signal to perform amplitude and phase calibration to obtain amplitude control parameters and phase control parameters required for compensation calibration;

[0016] Step 5: Using N RF signals from the satellite-based ADS-B array antenna as the N RF signals, repeat steps 2 to 3, and use the amplitude control parameters and phase control parameters in step 4 to complete the amplitude and phase calibration, and finally form M digital beams that can effectively cover the target.

[0017] Furthermore, the step 1 comprises:

[0018] Step 11: The RF module is controlled to enter a calibration mode and start signal link calibration;

[0019] Step 12: The RF module receives a calibration control signal from the DDC amplitude and phase calibration module, the control signal adopts a long pulse TTL signal, and enables the calibration source;

[0020] Step 13: Use a power divider to divide the output signal of the calibration source into N signals with equal amplitude and phase, that is, N RF signals, namely jz1~jzN, where N is the total number of antenna arrays.

[0021] Furthermore, the step 2 comprises:

[0022] Step 21: The N radio frequency signals are coupled to the input end of the frequency converter by coupling, that is, coupling calibration signals are obtained, which are cp1 to cpN respectively;

[0023] Step 22: The coupled calibration signal enters the active link of the frequency converter to complete signal amplification, filtering and mixing. After mixing and filtering, the frequency converter outputs analog intermediate frequency signals, which are IF1 to IFN respectively. Among them, each frequency converter uses the same power division local oscillator for mixing, which are Lo1 to LoN respectively.

[0024] Step 23: Use the synchronous sampling ADC to complete the acquisition of the analog intermediate frequency signal to obtain digital intermediate frequency signals, which are s1~sN respectively. The digital intermediate frequency signals are sent to the DDC amplitude and phase calibration module. After the signal link is calibrated, the calibration mode is exited and the synthesis mode is started.

[0025] Furthermore, after step 23, the method further includes:

[0026] The calibration control signal of the DDC amplitude and phase calibration module acts on the calibration source and then turns off the output of the calibration source.

[0027] Furthermore, shutting down the output of the calibration source can be achieved by powering off the calibration source to avoid co-frequency interference caused by the calibration signal.

[0028] Furthermore, the step 3 comprises:

[0029] After multiplying the digital intermediate frequency signal and the local orthogonal carrier and filtering out the sum frequency ω+Ω component, the baseband signal is obtained as follows:

[0030]

[0031] Among them, b i (t) is the baseband signal, s i (t) is the digital intermediate frequency signal, l i (t) is the local orthogonal carrier, k is the scaling constant formed by the linear change process, t is time, A i is the signal amplitude, ω is the signal carrier frequency, is the initial phase of the signal, M i ,Ω,θ i are the local carrier amplitude, frequency, and phase, respectively, and M i and θ iThey are obtained after amplitude calibration and phase calibration respectively. Each calibration process regenerates M i and θ i , i=1,2…N.

[0032] Further, the DDC amplitude and phase calibration module is composed of a calibrator and a calibration controller;

[0033] In step 4:

[0034] The process of the calibrator to achieve amplitude and phase compensation calibration is:

[0035] Generate local carrier in-phase component and quadrature component signals by a digitally controlled oscillator;

[0036] The numerically controlled oscillator receives the phase control parameter cp i , to get θ i , thereby completing the phase offset compensation of each channel signal link without affecting the amplitude. The phase offset is recorded as PHA_deg, then x is cp i bit width, obtain the orthogonal carrier component cos of the phase offset i and sin i ;

[0037] The amplitude scale controller receives the amplitude control parameter ca i , to get M i , thereby completing the amplitude offset compensation of each channel signal link, the amplitude scale factor is recorded as ASF, then Y is the reference value bit width;

[0038] Orthogonal carrier component cos i and sin i In the amplitude scale controller, the i After multiplication and truncation, the orthogonal carrier component cos_cal is formed after amplitude and phase compensation i and sin_cal i , plural form is l i (t), is the local orthogonal carrier used for digital down-conversion;

[0039] Digital IF signal i (t) and cos_cal after calibration i and sin_cal i The multiplication is first completed in IQ_COV, and then the baseband signal b is obtained by passing it through the LPF low-pass filter. i (t).

[0040] Furthermore, the digitally controlled oscillator is obtained in the FPGA through DDS direct digital synthesis, or the digitally controlled oscillator is obtained in the FPGA through a table lookup method.

[0041] Furthermore, the calibration process of the calibration controller is:

[0042] Step 1) After power-on reset, the calibration controller outputs the default amplitude control parameter ca i o and phase control parameter cp i oTo the calibrator;

[0043] Step 2), in the default idle state machine, perform mode determination, if calibration is required, proceed to step 3), otherwise proceed to step 7);

[0044] Step 3) The calibration controller enables the calibration source in the RF module and controls the amplitude control parameter ca i o and phase control parameter cp i o is the reference value;

[0045] Step 4), the calibration controller calculates the amplitude and phase values ​​of each channel and forms a new amplitude control parameter, denoted as ca i and the phase control parameter, denoted as cp i to the calibrator;

[0046] Step 5) Latch ca i and cp i After that, determine the validity of this calibration, if it is valid, proceed to step 6), otherwise proceed to step 7);

[0047] Step 6) Complete this calibration and lock the ca i and cp i As the default amplitude control parameter and phase control parameter respectively, proceed to step 7);

[0048] Step 7), turn off the calibration source, enter the synthesis mode, and wait again for the next calibration control signal in the state machine. When the next calibration control signal arrives, re-execute steps 1) to 7).

[0049] Furthermore, in step 5:

[0050] The digital beamforming module includes M beamformers, each beamformer having N beamforming parameters;

[0051] For each beamformer, N baseband signals are multiplied one-to-one with the N beamforming parameters in the beamformer and summed, and finally M digital beams are obtained.

[0052] Due to the adoption of the above technical solution, the present invention has the following advantages:

[0053] 1) The RF module is highly integrated and uses a coherent calibration source, local oscillator source, sampling clock, etc. to ensure the stability of the signal chain, which is beneficial to the engineering implementation of satellite-based ADS-B equipment;

[0054] 2) Amplitude and phase calibration is realized in the DDC process. Due to the characteristics of independent linear control of amplitude and phase calibration parameters, the calculation process is simple and reliable, with low complexity, and is easy to implement on a single chip FPGA;

[0055] 3) The calibration and beamforming technology has high stability, fast calibration and high precision, which can ensure that the long-term performance indicators of the equipment do not deteriorate in the harsh environment of space. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the embodiments of the present invention. For ordinary technicians in this field, other drawings can also be obtained based on these drawings.

[0057] Figure 1 A schematic diagram of digital multi-beam satellite-based ADS-B receiving payload coverage according to an embodiment of the present invention;

[0058] Figure 2 It is a schematic diagram of the overall technical solution of a satellite-based ADS-B digital multi-beam forming method based on DDC calibration according to an embodiment of the present invention;

[0059] Figure 3 A principle block diagram of a calibrator according to an embodiment of the present invention;

[0060] Figure 4 The present invention is a flowchart of a calibration controller according to an embodiment of the present invention. DETAILED DESCRIPTION

[0061] The present invention is further described in conjunction with the accompanying drawings and embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by ordinary technicians in this field should fall within the scope of protection of the embodiments of the present invention.

[0062] In view of the following technical problems currently existing, the present invention provides a technical solution corresponding to a satellite-based ADS-B digital multi-beam forming method based on DDC calibration to solve the following technical problems.

[0063] (1) For satellite-based ADS-B applications, fully digital amplitude and phase calibration is achieved to solve the problem of pre-calibration of digital multi-beamforming;

[0064] (2) The signal link calibration is completed through the DDC (digital down conversion) process, which is easy to implement on a single FPGA and solves the problems of complex calibration, large amount of calculation and high resource consumption;

[0065] (3) NCO and ASC are used in the calibrator to achieve linear parameter compensation, and a new method is proposed to solve the problems of low amplitude and phase calibration accuracy and difficulty in independent control of parameters.

[0066] The overall technical solution of the embodiment of the present invention is functionally divided into three modules, including a radio frequency module, a digital down conversion (DDC) amplitude and phase calibration module, and a digital beamforming module. The overall technical solution block diagram of satellite-based ADS-B digital multi-beamforming based on DDC calibration is shown in the figure. Figure 2 shown.

[0067] The RF module completes the calibration signal generation and down-conversion of the ADS-B RF signal, and quantizes the analog intermediate frequency signal through ADC (analog-to-digital converter) sampling to obtain the original digital intermediate frequency signal.

[0068] The DDC amplitude and phase calibration module is a key module for realizing digital multi-beamforming. This module completes the calibration of the signal link and completes the generation of IQ signals before beamforming through the collaborative work of the calibrator and the calibration controller.

[0069] The digital beamforming module uses a vector weighting method to complete the final digital beamforming and outputs M required beams, which can achieve coverage of the monitoring area under multi-beams.

[0070] According to the working status, it can be divided into calibration mode and synthesis mode. In calibration mode, the signal link consistency compensation calibration is completed. In synthesis mode, the digital multi-beam signal output is completed. The synthesis mode can work normally only after the calibration is completed.

[0071] 1. RF module

[0072] This module realizes the functions of RF signal down-conversion, intermediate frequency sampling, and coupling calibration. The technical solution block diagram is as follows Figure 2 As shown, the main working steps are as follows:

[0073] 1) Before beamforming, the RF module is first controlled to enter the calibration mode, start signal link calibration, and enter step 2);

[0074] 2) The RF module receives the calibration control signal from the DDC amplitude and phase calibration module. The control signal uses a long pulse TTL signal to enable the calibration source and enter step 3);

[0075] 3) The calibration source works normally and outputs a continuous wave signal with a frequency of 1090MHz. Use a power divider to divide the calibration source output signal into N signals with equal amplitude and phase (N depends on the number of antenna arrays), namely jz1~jzN, and go to step 4);

[0076] 4) The calibration signal enters the inverter respectively through coupling. In order to ensure the consistency and stability of the analog link after calibration, the circuit and physical implementation of each inverter adopts a consistent design, and the microstrip line coupling design method is used to couple the signal to the front end of the inverter to obtain the coupled calibration signal, which is cp1~cpN respectively, and enter step 5);

[0077] 5) The coupled calibration signal enters the active link of the frequency converter to complete signal amplification, filtering and mixing. In order to achieve the coherent characteristics of each signal, each frequency converter uses the same power division local oscillator for mixing, which are Lo1~LoN respectively. After mixing and filtering, the frequency converter outputs analog intermediate frequency signals, which are IF1~IFN respectively, and enters step 6);

[0078] 6) Use synchronous sampling ADC to complete the acquisition of analog intermediate frequency signals and obtain quantized original digital intermediate frequency signals, which are s1~sN respectively. In particular, the bit width of the digital intermediate frequency signal acquired by ADC is 14 bits, which meets the signal-to-noise ratio and dynamic range requirements of satellites receiving ADS-B signals in orbit. The quantized digital intermediate frequency signal is sent to the DDC amplitude and phase calibration module. After the signal link is calibrated, the calibration mode is exited, the synthesis mode is started, and step 7 is entered;

[0079] 7) The calibration control signal of the DDC amplitude and phase calibration module acts on the calibration source. Preferably, the calibration source is powered off to avoid the calibration signal causing co-frequency interference, and then proceed to step 8);

[0080] 8) The frequency converter processes the RF signal from the satellite-based ADS-B array antenna, amplifies and selects the useful ADS-B signal through the frequency converter, and finally quantizes it into a digital intermediate frequency signal.

[0081] The calibration mode is carried out in a time scale cycle. Due to the use of coherent phase and synchronous sampling methods, the signal link has the advantages of long-term consistency and stability. Therefore, the calibration interval can be controlled to a large extent, so that the equipment can work in the synthesis mode for a long time, and the detection and monitoring of ADS-B targets can be achieved as much as possible. The working mode of the RF module is controlled by the DDC amplitude and phase calibration module, and the modules cooperate with each other to complete the calibration of the signal link.

[0082] 2. DDC amplitude and phase calibration module

[0083] DDC amplitude and phase calibration is to calibrate the amplitude and phase simultaneously during the DDC (digital down conversion) process, which has the advantages of flexible control and high precision. The technical points of the working principle of the DDC amplitude and phase calibration module are as follows:

[0084] The digital intermediate frequency signal is expressed as:

[0085]

[0086] Among them, s i (t) is the digital intermediate frequency signal, A i is the signal amplitude, ω is the signal carrier frequency, is the initial phase of the signal.

[0087] The local quadrature carrier used for down-conversion is:

[0088]

[0089] Among them, M i ,Ω,θ i are the local carrier amplitude, frequency, and phase, respectively, and M i and θ i All are designed as controllable parameters.

[0090] The down-conversion process multiplies the digital intermediate frequency signal and the local carrier and filters out the sum frequency (ω+Ω) component to obtain the baseband signal:

[0091]

[0092] Among them, b i (t) is the baseband signal, and k is the scaling constant formed by the linear change process.

[0093] For the signal from the satellite-based ADS-B payload array antenna, the baseband signal is expressed as:

[0094]

[0095] The compensation parameters are adjusted by different M i and θ i (i=1,2…N) are additionally injected into the signal chain to complete the consistency calibration. Each calibration process regenerates M i and θ i A new L(t) orthogonal carrier calibration matrix is ​​formed.

[0096] When the same (equal amplitude and same phase) signal is input to each converter port, the amplitude and phase inconsistency of the converter, local oscillator, and ADC circuits result in differences in the output amplitude and phase of the digital intermediate frequency signal S(t), which can ultimately be compensated through the L(t) orthogonal carrier calibration matrix.

[0097] The DDC amplitude and phase calibration module consists of a calibrator and a calibration controller, which is implemented in a fully digital manner in a single-chip FPGA. The calibrator completes the amplitude and phase compensation. The calibrator principle block diagram is shown in the figure. Figure 3 shown.

[0098] The working steps of the calibrator to achieve compensation calibration are as follows:

[0099] s1) Generate local carrier in-phase component and quadrature component signals through NCO (numerically controlled oscillator), preferably, NCO is implemented in FPGA through DDS direct digital synthesis, and enter step s2);

[0100] s2) Receive the phase control parameter cpi (i = 1, 2 ... N), complete the phase offset compensation of each channel signal link without affecting the amplitude, the offset is recorded as PHA_deg, then x is the cpi bit width. The phase parameter cpi bit width is selected as 10 bits, the data range is [0, 1023], the phase offset compensation degree range is [0, 360*1023 / 1024], and the control step accuracy degree is 360 / 1024, which has high phase control accuracy. The orthogonal carrier component cos after phase offset is obtained i and sin i (i=1,2…N) signal, go to step s3);

[0101] s3)cos i and sin i The signal enters the ASC (amplitude scale controller), which has the ability to transform the amplitude scale and can independently realize the cos i and sin i The signal amplitude is controlled and the process goes to step s4);

[0102] s4) Receive amplitude control parameter ca i (i=1,2…N), the amplitude of each channel signal link is offset compensated, and the amplitude scaling factor is recorded as ASF, then Y is the bit width of the reference value. Select the bit width Y as 13 and select the amplitude control parameter ca i The bit width is 14 bits and controls the ca i The data range is [4096, 16383], then the ASF range is [4096 / (2^13), 16383 / (2^13)], and the control step accuracy is 1 / (2^13), which has high amplitude control accuracy. Go to step s5);

[0103] s5) Orthogonal carrier component cos i and sin i Signaling within the ASC and cai After multiplication and truncation, the orthogonal carrier component cos_cal is formed after amplitude and phase compensation i and sin_cal i (i=1,2…N) signal, the complex form is denoted by l i (i=1, 2...N), for digital down-conversion, proceed to step s6);

[0104] s6) Original digital intermediate frequency signal s i (i=1,2…N) and calibrated cos_cal i and sin_cal i The signal is first multiplied in IQ_COV, and then passes through the LPF low-pass filter to obtain the baseband signal b i (i=1,2…N). According to the pulse width and frequency deviation characteristics of ADS-B signals (see RTCA / DO-260B《Minimum Operational Performance Standardsfor 1090MHz Extended Squitter Automatic Dependent Surveillance–Broadcast(ADS-B)and Traffic Information Services–Broadcast(TIS-B)》), the LPF filter bandwidth BW=3MHz is preferred. The filtered signal enters the beamforming module as a calibrated baseband signal for digital multi-beamforming.

[0105] The calibration controller controls the entire calibration process, completes data calculations and forms calibration parameters. The calibration controller workflow is as follows: Figure 4 shown.

[0106] The controller calibration workflow is as follows:

[0107] 1-1) After power-on reset, the calibration controller outputs the default parameters ca i o、cp i o(i=1,2…N) to the calibrator, go to step 2-1);

[0108] 2-1) In the default idle state machine, perform mode determination. If calibration is required, proceed to step 3), otherwise proceed to step 7-1);

[0109] 3-1) The calibration controller enables the calibration source in the RF module and controls the ca i o、cp i o is the reference value, go to step 4-1);

[0110] 4-1) The calibration controller calculates the amplitude and phase values ​​of each channel and forms new calibration parameters ca i 、cp i , proceed to step 5-1);

[0111] 5-1) Latch the new calibration parameters ca i 、cp i After that, determine the validity of this calibration, if it is valid, proceed to step 6-1), otherwise proceed to step 7-1);

[0112] 6-1) After completing this calibration, the latched ca i 、cp i The parameters are used as default calibration parameters and go to step 7-1);

[0113] 7-1) Turn off the calibration source, enter the synthesis mode, and wait again in the state machine for the next calibration control signal to be valid.

[0114] After the calibration controller has completed a complete calibration process, it will work in the synthesis mode most of the time. In the synthesis mode, the calibrator controller outputs the latest default calibration parameters ca i 、cp i To the calibrator, the amplitude and phase compensation calibration of the signal chain is realized in the DDC process.

[0115] 3. Digital beamforming module

[0116] After calibration is completed, the effective digital baseband b i =b i _I+j*b i _Q (i = 1, 2 ... N) signal enters the digital beamforming module. In the digital beamforming module, each beamforming parameter acts on the digital baseband signal to complete the amplitude and phase weighting. The specific formation process mainly uses complex multipliers and adders. In order to make the satellite-based ADS-B cover the target area as much as possible, according to the beam planning, M beams are formed at the same time to complete multi-beam coverage. The beam configuration parameters can also be reconfigured to facilitate coverage verification tests and on-orbit upgrades. The digital beamforming module outputs the synthesized IQ baseband signal, which can be used for ADS-B decoding and extraction of aircraft target information within the effective coverage of the beam pointing.

[0117] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents. Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A satellite-based ADS-B digital multi-beam forming method based on DDC calibration, characterized in that: include: Step 1: Controlling the calibration source in the RF module through the calibration controller in the digital down conversion (DDC) amplitude and phase calibration module to obtain N RF signals; Step 2: obtaining a coupling calibration signal based on the N RF signals; and after amplifying, filtering, mixing, and sampling the coupling calibration signal, the RF module outputs a digital intermediate frequency signal; Step 3: digitally down-convert the digital intermediate frequency signal through the DDC amplitude and phase calibration module to obtain a baseband signal; Step 4: The DDC amplitude and phase calibration module uses the baseband signal to perform amplitude and phase calibration to obtain amplitude control parameters and phase control parameters required for compensation calibration; Step 5: The digital beamforming module uses N radio frequency signals from the satellite-based automatic dependent surveillance-broadcast (ADS-B) array antenna as the N radio frequency signals, repeats steps 2 to 3, and uses the amplitude control parameters and phase control parameters in step 4 to complete the amplitude and phase calibration, and finally forms M digital beams that can effectively cover the target; The step 2 comprises: Step 21: The N radio frequency signals are coupled to the input end of the frequency converter by coupling, that is, coupling calibration signals are obtained, which are cp1 to cpN respectively; Step 22: The coupled calibration signal enters the active link of the frequency converter to complete signal amplification, filtering and mixing. After mixing and filtering, the frequency converter outputs analog intermediate frequency signals, which are IF1 to IFN respectively. Among them, each frequency converter uses the same power division local oscillator for mixing, which are Lo1 to LoN respectively. Step 23: Use the synchronous sampling ADC to complete the acquisition of the analog intermediate frequency signal to obtain digital intermediate frequency signals, which are s1 to sN. The digital intermediate frequency signals are sent to the DDC amplitude and phase calibration module. After the signal link is calibrated, the calibration mode is exited and the synthesis mode is started; The step 3 comprises: After multiplying the digital intermediate frequency signal and the local orthogonal carrier and filtering out the sum frequency ω+Ω component, the baseband signal is obtained as follows: Among them, b i (t) is the baseband signal, s i (t) is the digital intermediate frequency signal, l i (t) is the local orthogonal carrier, k is the scaling constant formed by the linear change process, t is time, A i is the signal amplitude, ω is the signal carrier frequency, is the initial phase of the signal, M i ,Ω,θ i are the local carrier amplitude, frequency, and phase, respectively, and M i and θ i They are obtained after amplitude calibration and phase calibration respectively. Each calibration process regenerates M i and θ i , i=1,2…N; The DDC amplitude and phase calibration module is composed of a calibrator and a calibration controller; In step 4: The process of the calibrator to achieve amplitude and phase compensation calibration is: Generate local carrier in-phase component and quadrature component signals by a digitally controlled oscillator; The numerically controlled oscillator receives the phase control parameter cp i , to get θ i , thereby completing the phase offset compensation of each channel signal link without affecting the amplitude. The phase offset is recorded as PHA_deg, then x is cp i bit width, obtain the orthogonal carrier component cos of the phase offset i and sin i ; The amplitude scale controller receives the amplitude control parameter ca i , to get M i , thereby completing the amplitude offset compensation of each channel signal link, the amplitude scale factor is recorded as ASF, then Y is the reference value bit width; Orthogonal carrier component cos i and sin i In the amplitude scale controller, the i After multiplication and truncation, the orthogonal carrier component cos_cal is formed after amplitude and phase compensation i and sin_cal i , plural form is l i (t), is the local orthogonal carrier used for digital down-conversion; Digital IF signal i (t) and cos_cal after calibration i and sin_cal i The multiplication is first completed in IQ_COV, and then the baseband signal b is obtained by passing it through the LPF low-pass filter. i (t); The calibration process of the calibration controller is: Step 1) After power-on reset, the calibration controller outputs the default amplitude control parameter ca i o and phase control parameter cp i oTo the calibrator; Step 2), in the default idle state machine, perform mode determination, if calibration is required, proceed to step 3), otherwise proceed to step 7); Step 3) The calibration controller enables the calibration source in the RF module and controls the amplitude control parameter ca i o and phase control parameter cp i o is the reference value; Step 4), the calibration controller calculates the amplitude and phase values ​​of each channel and forms a new amplitude control parameter, denoted as ca i and the phase control parameter, denoted as cp i to the calibrator; Step 5) Latch ca i and cp i After that, determine the validity of this calibration, if it is valid, proceed to step 6), otherwise proceed to step 7); Step 6) Complete this calibration and lock the ca i and cp i As the default amplitude control parameter and phase control parameter respectively, proceed to step 7); Step 7), turn off the calibration source, enter the synthesis mode, and wait again for the next calibration control signal in the state machine. When the next calibration control signal arrives, re-execute steps 1) to 7).

2. The method according to claim 1, characterized in that The step 1 comprises: Step 11: The RF module is controlled to enter a calibration mode and start signal link calibration; Step 12: The RF module receives a calibration control signal from the DDC amplitude and phase calibration module, the control signal adopts a long pulse TTL signal, and enables the calibration source; Step 13: Use a power divider to divide the output signal of the calibration source into N signals with equal amplitude and phase, that is, N RF signals, namely jz1~jzN, where N is the total number of antenna arrays.

3. The method according to claim 1, characterized in that After step 23, the method further includes: The calibration control signal of the DDC amplitude and phase calibration module acts on the calibration source and then turns off the output of the calibration source.

4. The method according to claim 3, characterized in that: The output of the calibration source may be turned off by powering off the calibration source, thereby preventing the calibration signal from causing co-frequency interference.

5. The method according to claim 1, characterized in that The digital controlled oscillator is obtained in the FPGA through DDS direct digital synthesis, or the digital controlled oscillator is obtained in the FPGA through a table lookup method.

6. The method according to claim 1, characterized in that In step 5: The digital beamforming module includes M beamformers, each beamformer having N beamforming parameters; For each beamformer, N baseband signals are multiplied one-to-one with the N beamforming parameters in the beamformer and summed, and finally M digital beams are obtained.

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