A Phase Calibration Method for Spaceborne Phased Array SAR

Abstract

The present invention relates to a spaceborne phased array SAR phase calibration method, which belongs to the field of space microwave remote sensing technology. The method comprises designing the composition of the SAR phased array antenna; obtaining the amplitude #imgabs0# and phase value #imgabs1# of each TR component; and calculating the total phase shift value Δψ corresponding to the nth channel. n ; Perform phase assignment on the first-order delay TD1 and the second-order delay TD2 to obtain the delay code of the delay component; take the total phase of the TR component modulo 360°, and the residual value after modulo is the phase shift value α of the TR component n ; Calculate the phase shift code of the TR component; Calculate the attenuation code of the TR component; Complete phase calibration based on the delay code of the delay component, the phase shift code of the TR component, and the attenuation code of the TR component; The present invention adopts the phase residual method to solve the problem of fast calculation of the received delay code and phase shift code. The algorithm can be extended to the directions of receiving phase matching of spaceborne phased array SAR and fast calibration of spaceborne phased array radar.

Description

Technical Field

[0001] The invention belongs to the technical field of space microwave remote sensing and relates to a spaceborne phased array SAR phase calibration method. Background Art

[0002] The spaceborne phased array SAR payload consists of a data processor, transceiver channels, and phased array antennas. For spaceborne phased array antennas, inter-channel errors directly affect the antenna's radiation pattern performance, such as gain and sidelobes, and thus affect the sensitivity and ambiguity of the SAR system. Therefore, channel error correction is essential.

[0003] Currently, the vast majority of spaceborne SAR systems in orbit calibrate channel errors wirelessly on the ground, then compensate and test the antenna's radiation pattern at each beam position to verify that it meets system requirements. Once in orbit, as the various channels of the antenna's TR assembly age due to aging components, amplitude and phase errors between different channels can occur, impacting antenna performance. Existing correction schemes use calibration data to correct errors in each channel. First, the calibration data is transmitted to the ground. The amplitude and phase errors between each channel are then extracted based on the calibration data. Finally, a new TR assembly beam control code table is generated and uploaded to the satellite for update. However, this scheme involves multiple interactions between the satellite and the ground, resulting in a long calibration cycle and failing to meet the requirements for rapid in-orbit verification. Summary of the Invention

[0004] The technical problem solved by the present invention is: to overcome the shortcomings of the existing technology, propose a phase calibration method for spaceborne phased array SAR, and use the phase residual method to solve the problem of fast calculation of received delay code and phase shift code. The algorithm can be extended and applied to the directions of spaceborne phased array SAR receiving phase matching, spaceborne phased array radar fast calibration, etc.

[0005] The solution of the present invention is:

[0006] A spaceborne phased array SAR phase calibration method, comprising:

[0007] Design the components of a SAR phased array antenna, including a delay component and a TR component. The TR component consists of 96 channels. The TR channels are numbered sequentially: 1, ..., n, ..., 96. There are two types of delay components: a first-order delay (TD1) with a 1-bit delay and a second-order delay (TD2) with a 2-bit delay.

[0008] Each TR component channel is calibrated separately to obtain the amplitude of each TR component. and phase value

[0009] Set the beam pointing angle of the nth channel to (θ, φ) and calculate the total phase shift value Δψ corresponding to the nth channel n ; Divide the 96 channels of the TR component into 24 small groups; Divide the 96 channels of the TR component into 4 large groups;

[0010] The 24 small groups correspond to the first-level delay TD1 in the delay component; the 4 large groups correspond to the second-level delay TD2 in the delay component;

[0011] Performing phase assignment on the first-stage delay TD1 and the second-stage delay TD2 to obtain a delay code of the delay component;

[0012] The total phase of the TR component is modulo 360°, and the residual value after modulo is the phase shift value α of the TR component. n ;

[0013] Calculate the phase shift code of the TR component;

[0014] Calculate the attenuation code of the TR component;

[0015] Phase calibration is completed according to the delay code of the delay component, the phase shift code of the TR component, and the attenuation code of the TR component.

[0016] In the above-mentioned spaceborne phased array SAR phase calibration method, the SAR phased array antenna includes a total of 3 sub-arrays, each sub-array includes 32 TR component channels; each TR component has phase shifting and attenuation functions; each TR component is equipped with a 6-bit phase shifter with a corresponding phase shift step of 5.625°; and a 5-bit attenuator with a corresponding attenuation step of 0.5dB; the delay step of the delay component is 1 wavelength.

[0017] In the above-mentioned spaceborne phased array SAR phase calibration method, the specific method for obtaining the amplitude and phase values ​​of each TR component is as follows:

[0018] Assume that the signal s0(t) transmitted by the radar processor is:

[0019]

[0020] Where, T p is the width of the LFM pulse;

[0021] rect() is a rectangular window;

[0022] f c is the center frequency of the signal;

[0023] K is the modulation frequency of the LFM signal;

[0024] t is time;

[0025] Assume that the echo signal received by the nth channel is srn(t), n=1,2N p , N p is the total number of channels of the TR component, which is 96;

[0026] Then the echo signal received by the nth channel is s rn (t) is:

[0027]

[0028] Where A n The amplitude of each acquisition pulse;

[0029] t n is the time delay of each acquisition pulse;

[0030] is the phase of each acquisition pulse;

[0031] Extract the channel amplitude of the nth channel and phase value

[0032] In the above-mentioned spaceborne phased array SAR phase calibration method, the channel amplitude of the nth channel is extracted and phase value The method is:

[0033] The echo signal received for the nth channel is s rn (t) Perform matched filtering to obtain the pulse matched filter output s on (t);

[0034] Find s on Peak position of (t) And save its amplitude

[0035] Calculate the phase of the nth pulse output peak point angle() is a four-quadrant inverse tangent phase angle operation.

[0036] In the above-mentioned spaceborne phased array SAR phase calibration method, the total phase shift value Δψ corresponding to the nth channel n The calculation method is:

[0037]

[0038] Where, d xn The distance value of the nth channel in the X direction relative to the origin of the coordinate system;

[0039] d yn The Y-axis distance of the nth channel relative to the origin of the coordinate system;

[0040] The origin is defined as the center position of the first TR component channel of the entire phased array antenna;

[0041] is the initial phase error value of the nth channel.

[0042] In the above-mentioned spaceborne phased array SAR phase calibration method, when the 96 channels of the TR component are divided into 24 small groups, each small group includes 4 channels; when the 96 channels of the TR component are divided into 4 large groups, each large group includes 24 channels.

[0043] In the above-mentioned spaceborne phased array SAR phase calibration method, the specific method for phase allocation of the first-order delay TD1 is as follows:

[0044] According to the second channel among the four channels corresponding to each group, the phase of the first-stage delay TD1 is determined to be 0° or 360°, which is the delay code of the first-stage delay TD1.

[0045] In the above-mentioned spaceborne phased array SAR phase calibration method, the specific method of performing phase allocation by the second-stage delay TD2 is as follows:

[0046] According to the 12th channel in each large group of 24 channels, the phase of the second-level delay TD2 is determined to be 0°, 360°, 720° or 1080°, which is the delay code of the second-level delay TD2.

[0047] In the above-mentioned spaceborne phased array SAR phase calibration method, the phase shift code of the TR component is:

[0048] Since the phase step is 5.625°, the phase is converted into a binary code, which is the phase shift code of the TR component.

[0049] In the above-mentioned spaceborne phased array SAR phase calibration method, the attenuation code of the TR component is:

[0050] Since the attenuation step is 0.5 dB, the attenuation is converted into a binary code, which is the attenuation code of the TR component.

[0051] The beneficial effects of the present invention compared with the prior art are:

[0052] (1) The SAR phased array antenna of the present invention includes a delay component, a TR component, a power splitter network, and a calibration network, primarily forming the antenna pattern required by the SAR payload. The system can extract channel amplitude and phase errors and adjust the amplitude and phase codes of the TR component and the delay code of the extension component using wave control codes, thereby ensuring the electrical performance of the antenna.

[0053] (2) The present invention can extract the amplitude and phase errors of the phased array antenna TR component channel and convert them into beam control codes based on the system's amplitude and phase errors. Finally, corresponding beam control codes are generated based on different pointing requirements. This beam control code can be directly sent to the antenna to complete the antenna's beam pointing control. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Figure 1 This is a system block diagram of the amplitude and phase calibration of the spaceborne phased array SAR of the present invention;

[0055] Figure 2 This is a schematic diagram of the relationship between the delay component and the TR component of a daughter board of the SAR antenna of the present invention;

[0056] Figure 3 Schematic diagram of the relationship between a set of delay components and 16 TR component channels of the present invention. DETAILED DESCRIPTION

[0057] The present invention will be further described below in conjunction with the embodiments.

[0058] The present invention proposes a phase calibration system for spaceborne phased array SAR, which adopts the phase residual method to solve the problem of fast calculation of received delay code and phase shift code. The algorithm can be extended and applied to the receiving phase matching of spaceborne phased array SAR and fast calibration of spaceborne phased array radar.

[0059] The spaceborne phased array SAR amplitude and phase calibration system includes a data processor, a transceiver channel and a SAR phased array antenna. Figure 1 As shown in the figure, the data processor primarily extracts channel amplitude and phase errors and calculates the beam control code in real time. The transceiver channel primarily converts intermediate frequency (IF) signals into RF signals. The SAR phased array antenna, consisting of a delay element, a transmission element (TR) component, a power splitter network, and a calibration network, primarily forms the antenna pattern required by the SAR payload. The system extracts channel amplitude and phase errors and uses the beam control code to adjust the amplitude and phase codes of the TR component and the delay code of the extension element, thereby ensuring antenna electrical performance.

[0060] The implementation of amplitude and phase error calibration is divided into three steps: 1) Calculate the amplitude and phase errors of each channel of the antenna; 2) Determine the system delay based on the amplitude and phase errors and beam pointing, and convert it into the delay code of the extension component; 3) Determine the attenuation and phase shift values ​​of each channel of the TR component based on the amplitude and phase errors and beam pointing, and convert them into phase shift codes and attenuation codes.

[0061] The SAR phased array antenna consists of a delay component (TD) and a TR component (PS). The TR component contains 96 channels in total. There are two types of delay components: TD1 component, which corresponds to a 1-bit delay component, and TD2 component, which corresponds to a 2-bit delay component. Figure 2As shown in the figure, this phased array antenna consists of three subarrays, each containing 32 TR component channels. Each TR component has phase shifting and attenuation functions, requiring system input of phase shift and attenuation codes for control. Each TR component is equipped with a 6-bit phase shifter, corresponding to a phase shift step of 5.625°, and a 5-bit attenuator, corresponding to an attenuation step of 0.5dB. The delay component has a delay step of 1 wavelength.

[0062] The phase calibration method of spaceborne phased array SAR specifically includes the following steps:

[0063] Design the components of a SAR phased array antenna, including a delay component and a TR component. The TR component consists of 96 channels, and the channels of the TR component are numbered sequentially: 1, ..., n, ..., 96. There are two types of delay components: a first-stage delay TD1 with a bit number, and a second-stage delay TD2 component with a bit number.

[0064] The SAR phased array antenna consists of three sub-arrays, each of which includes 32 TR component channels. Each TR component has phase shifting and attenuation functions. Each TR component is equipped with a 6-bit phase shifter with a phase shift step of 5.625° and a 5-bit attenuator with an attenuation step of 0.5dB. The delay step of the delay component is 1 wavelength.

[0065] Each TR component channel is calibrated separately to obtain the amplitude of each TR component. and phase value The specific method for obtaining the amplitude and phase values ​​of each TR component is:

[0066] Assume that the signal s0(t) transmitted by the radar processor is:

[0067]

[0068] Where, T p is the width of the LFM pulse;

[0069] rect() is a rectangular window;

[0070] f c is the center frequency of the signal;

[0071] K is the modulation frequency of the LFM signal;

[0072] t is time;

[0073] Assume that the echo signal received by the nth channel is srn(t), n=1,2N p , N p is the total number of channels of the TR component, which is 96;

[0074] Then the echo signal received by the nth channel is s rn (t) is:

[0075]

[0076] Where A n The amplitude of each acquisition pulse;

[0077] t n is the time delay of each acquisition pulse;

[0078] is the phase of each acquisition pulse;

[0079] Extract the channel amplitude of the nth channel and phase value

[0080] Extract the channel amplitude of the nth channel and phase value The method is:

[0081] The echo signal received for the nth channel is s rn (t) Perform matched filtering to obtain the pulse matched filter output s on (t);

[0082] Find s on Peak position of (t) And save its amplitude

[0083] Calculate the phase of the nth pulse output peak point angle() is a four-quadrant inverse tangent phase angle operation.

[0084] Set the beam pointing angle of the nth channel to (θ, φ) and calculate the total phase shift value Δψ corresponding to the nth channel n ; The total phase shift value Δψ corresponding to the nth channel n The calculation method is:

[0085]

[0086] Where, d xn The distance value of the X-axis relative to the origin of the coordinate of the nth channel;

[0087] d yn The Y-axis distance of the nth channel relative to the origin of the coordinate system;

[0088] The origin is defined as the center position of the first TR component channel of the entire phased array antenna;

[0089] is the initial phase error value of the nth channel.

[0090] The 96 channels of the TR component are divided into 24 small groups; the 96 channels of the TR component are divided into 4 large groups; when the 96 channels of the TR component are divided into 24 small groups, each small group includes 4 channels; when the 96 channels of the TR component are divided into 4 large groups, each large group includes 24 channels.

[0091] The 24 small groups correspond to the first-order delay TD1 in the delay component; the 4 large groups correspond to the second-order delay TD2 in the delay component, such as Figure 3 shown.

[0092] Phase allocation is performed on the first-stage delay TD1 and the second-stage delay TD2 to obtain the delay code of the delay component. The specific method of phase allocation for the first-stage delay TD1 is:

[0093] According to the second channel among the four channels corresponding to each group, the phase of the first-stage delay TD1 is determined to be 0° or 360°, which is the delay code of the first-stage delay TD1.

[0094] The specific method of phase allocation by the second-level delay TD2 is:

[0095] According to the 12th channel in each large group of 24 channels, the phase of the second-level delay TD2 is determined to be 0°, 360°, 720° or 1080°, which is the delay code of the second-level delay TD2.

[0096] The Matlab implementation language of TD1 delay is as follows:

[0097] YF_TD1=floor( / 360)*(floor( / 360)<=1)

[0098] The MATLAB implementation language of TD2 delay is as follows:

[0099] YF_TD2=(floor( / 360)-YF_TD1)*(floor( / 360-YF_TD1)<=2)

[0100] The MATLAB implementation language for converting TD1 delay into binary code is as follows:

[0101] dec2bin(YF_TD1, 1)

[0102] The MATLAB implementation language for converting TD2 delay into binary code is as follows:

[0103] dec2bin(YF_TD2, 2)

[0104] The total phase of the TR component is modulo 360°, and the residual value after modulo is the phase shift value α of the TR component. n .

[0105] α n =mod(Δψ n / 360)

[0106] Calculate the phase shift code of the TR component; the phase shift code of the TR component is:

[0107] Since the phase step is 5.625°, the phase is converted into binary code, which is the phase shift code of the TR component. Its MATLAB implementation language is as follows:

[0108] dec2bin(α n 5.625, 6)

[0109] Calculate the attenuation code of the TR component; the attenuation code of the TR component is:

[0110] Since the attenuation step is 0.5dB, the attenuation is converted into binary code, which is the attenuation code of the TR component. Its MATLAB implementation language is as follows:

[0111]

[0112] Phase calibration is completed according to the delay code of the delay component, the phase shift code of the TR component, and the attenuation code of the TR component.

[0113] The present invention proposes a phase calibration system for spaceborne phased array SAR, which adopts the phase residual method to solve the problem of fast calculation of received delay code and phase shift code. The algorithm can be extended and applied to the receiving phase matching of spaceborne phased array SAR and fast calibration of spaceborne phased array radar.

[0114] During the specific implementation of the algorithm, the following process is followed:

[0115] Calculate the amplitude and phase errors of each tracking channel. For a phased array antenna SAR system, each TR component channel is calibrated individually to obtain the amplitude and phase values ​​of each TR component.

[0116] Delay code calculation: First, the total channel phase value is calculated based on the antenna beam pointing and the phase value of each TR component. Then, based on the arrangement of the delay components, the delay code of the first-stage delay component and the delay code of the second-stage delay component are calculated separately.

[0117] Calculate the TR component attenuation code and phase shift code. The total phase value is modulo 360°. The residual value after modulo 360° is the decimal phase shift value in the TR component, which is converted into a binary phase shift code. The TR component's binary attenuation code is calculated based on the TR component's amplitude value.

[0118] Although the present invention has been disclosed above in terms of preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art may make possible changes and modifications to the technical solutions of the present invention by using the methods and technical contents disclosed above without departing from the spirit and scope of the present invention. Therefore, any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solutions of the present invention shall fall within the scope of protection of the technical solutions of the present invention.

Claims

1. A method for phase calibration of spaceborne phased array SAR, characterized by: include: Design the components of a SAR phased array antenna, including a delay component and a TR component. The TR component consists of 96 channels. The TR channels are numbered sequentially: 1, ..., n, ..., 96. There are two types of delay components: a first-order delay (TD1) with a 1-bit delay and a second-order delay (TD2) with a 2-bit delay. Each TR component channel is calibrated separately to obtain the amplitude of each TR component. and phase value Set the beam pointing angle of the nth channel to (θ, φ) and calculate the total phase shift value Δψ corresponding to the nth channel n ; Divide the 96 channels of the TR component into 24 small groups; Divide the 96 channels of the TR component into 4 large groups; The 24 small groups correspond to the first-level delay TD1 in the delay component; the 4 large groups correspond to the second-level delay TD2 in the delay component; Performing phase assignment on the first-stage delay TD1 and the second-stage delay TD2 to obtain a delay code of the delay component; The total phase of the TR component is modulo 360°, and the residual value after modulo is the phase shift value α of the TR component. n ; Calculate the phase shift code of the TR component; Calculate the attenuation code of the TR component; Phase calibration is completed according to the delay code of the delay component, the phase shift code of the TR component, and the attenuation code of the TR component.

2. The method for phase calibration of a spaceborne phased array SAR according to claim 1, wherein: The SAR phased array antenna consists of three sub-arrays, each of which includes 32 TR component channels. Each TR component has phase shifting and attenuation functions. Each TR component is equipped with a 6-bit phase shifter with a phase shift step of 5.625° and a 5-bit attenuator with an attenuation step of 0.5dB. The delay step of the delay component is 1 wavelength.

3. The method for phase calibration of a spaceborne phased array SAR according to claim 1, wherein: The specific method for obtaining the amplitude and phase values ​​of each TR component is: Assume that the signal s0(t) transmitted by the radar processor is: Where, T p is the width of the LFM pulse; rect(·) is a rectangular window; f c is the center frequency of the signal; K is the modulation frequency of the LFM signal; t is time; Assume that the echo signal received by the nth channel is s rn (t), n=1,2…N p , N p is the total number of channels of the TR component, which is 96; Then the echo signal received by the nth channel is s rn (t) is: Where A n The amplitude of each acquisition pulse; t n is the time delay of each acquisition pulse; is the phase of each acquisition pulse; Extract the channel amplitude of the nth channel and phase value 4. The method for phase calibration of a spaceborne phased array SAR according to claim 3, wherein: Extract the channel amplitude of the nth channel and phase value The method is: The echo signal received for the nth channel is s rn (t) Perform matched filtering to obtain the pulse matched filter output s on (t); Find s on Peak position of (t) And save its amplitude Calculate the phase of the nth pulse output peak point angle(·) is the four-quadrant inverse tangent phase angle operation.

5. The method for phase calibration of a spaceborne phased array SAR according to claim 1, wherein: The total phase shift value Δψ corresponding to the nth channel n The calculation method is: Where, d xn The distance value of the X-axis relative to the origin of the coordinate of the nth channel; d yn The Y-axis distance of the nth channel relative to the origin of the coordinate system; The origin is defined as the center position of the first TR component channel of the entire phased array antenna; is the initial phase error value of the nth channel.

6. The method for phase calibration of a spaceborne phased array SAR according to claim 1, wherein: When the 96 channels of the TR component are divided into 24 small groups, each small group includes 4 channels; when the 96 channels of the TR component are divided into 4 large groups, each large group includes 24 channels.

7. The method for phase calibration of a spaceborne phased array SAR according to claim 6, wherein: The specific method for phase allocation of the first-level delay TD1 is: According to the second channel among the four channels corresponding to each group, the phase of the first-stage delay TD1 is determined to be 0° or 360°, which is the delay code of the first-stage delay TD1.

8. The method for phase calibration of a spaceborne phased array SAR according to claim 7, wherein: The specific method of phase allocation by the second-level delay TD2 is: According to the 12th channel in each large group of 24 channels, the phase of the second-level delay TD2 is determined to be 0°, 360°, 720° or 1080°, which is the delay code of the second-level delay TD2.

9. The method for phase calibration of a spaceborne phased array SAR according to claim 1, wherein: The phase shift code of the TR component is: Since the phase step is 5.625°, the phase is converted into a binary code, which is the phase shift code of the TR component.

10. The method for phase calibration of a spaceborne phased array SAR according to claim 1, wherein: The attenuation code of the TR component is: Since the attenuation step is 0.5 dB, the attenuation is converted into a binary code, which is the attenuation code of the TR component.

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