A method for calibrating errors of a terahertz multiple-input multiple-output array system

Abstract

The application provides a terahertz multi-transmitting and multi-receiving array system error calibration method, comprising the following steps: S1, redundancy compensation: array echo signals are rearranged according to equivalent element spacing in a terahertz multi-transmitting and multi-receiving detection subsystem, damaged channel information is removed by comparing and eliminating the echo of the redundant signal unit in the signal domain, and the phase error term generated by the wideband echo signal is analyzed; S2, system noise calibration: a background cancellation method is used to eliminate noise signals other than target signals; S3, dispersion and amplitude-phase inconsistency calibration: phase compensation is performed through a high-precision calibration piece; S4, system time delay calibration: the transmitting signal is introduced to the loudspeaker on the opposite side of the antenna as a delay calibration transmitting unit for transceiving and collecting, the single-element echo is pulse compressed, and the offset degree of the distance unit is compensated by judging the zero-frequency position of the signal. The application can improve the imaging quality of the terahertz array in engineering practice.

Description

Technical Field

[0001] This invention relates to the field of terahertz transceiver technology, and more specifically to an error calibration method for a terahertz multi-transmitter multi-receiver array system. Background Technology

[0002] In terahertz multiple-transmitter-multiple-receiver array systems, the terahertz transceiver front-end module is constrained by the physical characteristics of high-frequency bands, insufficient material properties, and manufacturing process limitations (high-frequency transceiver modules are extremely sensitive to circuit size and material uniformity). Terahertz MIMO array channels suffer from problems such as inconsistent standing waves, amplitude-phase inconsistencies, and dispersion inconsistencies, which change with the amplitude and phase of the feed signal, easily causing image defocusing and distortion. Simultaneously, its propagation loss is high, requiring power amplifiers to compensate for losses, and it is prone to component damage under prolonged high-load operation. Damage to some array elements affects the overall equivalent array element distribution, leading to non-uniform spatial sampling and image uniformity. Given current technology and processes, producing a terahertz array with ideal uniformity is extremely difficult and costly, with correspondingly high maintenance costs. Existing research often compensates for errors through data processing methods, proposing corresponding calibration methods for specific causes of amplitude-phase errors, such as array element position errors and mutual coupling between array elements. However, these research methods do not consider errors caused by changes in usage scenarios and loss factors during actual engineering applications. For high-bandwidth, multi-channel MIMO imaging systems, in addition to system noise, there are also problems such as inconsistency in dispersion caused by the linearity of high-bandwidth signals, inconsistency in amplitude and phase between channels, and deterioration of array uniformity caused by damage to array elements. These problems result in a series of issues such as beam widening, reduced gain, pointing offset, and increased sidelobes of the array antenna transmit and receive beams, leading to image defocusing and distortion.

[0003] Application number CN202411597394.3 discloses a contact-type terahertz characteristic parameter testing system and a testing error correction method, belonging to the field of testing technology. The testing system of this invention is based on a 110GHz vector network analyzer. For frequencies below 110GHz, a coaxial waveguide converter is used for easy system integration; for frequencies above 110GHz, a 110GHz signal is used as the excitation, greatly reducing the link size of the terahertz module and significantly improving signal quality. Combined with a material property testing device, it features high dynamic range and high stability, enabling high signal-to-noise ratio acquisition of the original signal. The testing method provided by this invention reduces the operational complexity of the testing system while ensuring testing accuracy, enabling automated testing of characteristic parameters with an accuracy of ±1%. The power-adjustable terahertz transceiver module can meet the testing requirements of samples with different attenuation characteristics by adjusting the signal power. The use of a terahertz detector reduces the complexity of traditional testing systems and improves the system's testing dynamics. Summary of the Invention

[0004] This invention aims to overcome the technical problems in existing high-bandwidth, multi-channel MIMO imaging systems, which, in addition to system noise, also suffer from problems such as inconsistent dispersion due to the linearity of the high-bandwidth signal, inconsistent amplitude and phase between channels, and deteriorated array uniformity caused by array element damage. These problems result in beamwidth, reduced gain, pointing offset, and increased sidelobes in the array antenna's transmit and receive beams. The invention provides a terahertz multi-transmit and multi-receive array system error calibration method that can improve the imaging quality of terahertz arrays in engineering practice.

[0005] This invention provides an error calibration method for a terahertz multi-transmitter multi-receiver array system, comprising the following steps: S1. Redundancy Compensation: In the terahertz multi-transmitter and multi-receiver detection subsystem, the array echo signals are rearranged according to the equivalent array element spacing. By comparing the echoes of redundant signal units in the signal domain and eliminating damaged channel information, the phase error term generated by the wideband echo signal is analyzed. S2. System noise calibration: The background cancellation method is used to eliminate noise signals other than the target signal; S3. Dispersion and Amplitude-Phase Inconsistency Calibration: Phase compensation is performed using a high-precision calibration device, including spectrum transformation of the echo signal of each channel of the high-precision calibration device to convert the time-domain signal into a frequency-domain signal, spectrum shifting to move the target to near zero frequency, extracting the phase information of the signal lamp and taking the conjugate, multiplying the spectrum of the test echo signal by the conjugate of the phase error to obtain the phase compensation function, and multiplying the received echo signal by the phase compensation function before performing distance pulse compression to obtain the calibration parameters; S4. System delay calibration: The transmitted signal is led out to the horn on the opposite side of the antenna as a delay calibration transmitting unit for transmission and reception acquisition. The echo of the single array element is pulse compressed. The offset of the distance element is judged by the zero frequency position of the signal and compensation is made accordingly.

[0006] The terahertz multi-transmitter multi-receiver array system error calibration method described in this invention, as a preferred embodiment, in step S1, the echo signal S(X) T The calculation method for (Y, Z) is as follows: ; Where, σ TR Let j be the target echo amplitude, j be the imaginary part, and f be the signal frequency. , The starting frequency of the signal. t is the frequency modulation slope; t is the current time; t0 is the distance from the target to the transceiver array element (X). T ,X R The time difference generated The product of the signal frequency f and (t-t0); φ(f) is the phase error caused by channel dispersion, φ(X) T ,X R S represents the error caused by the phase inconsistency between different channels, φ(∆t) represents the phase error caused by the time delay of the transceiver array antenna, and S represents the phase error caused by the phase inconsistency between different channels. noise (t) represents the system noise error caused by the antenna equipment.

[0007] The terahertz multi-transmitter multi-receiver array system error calibration method described in this invention, as a preferred method, targets the transceiver array element (X). T ,X R The calculation method for the resulting time difference t0 is as follows: ; Where: X TR Let X be the coordinates of the center position of the transceiver unit of a one-dimensional MIMO linear array. TR =(X T +X R ) / 2, (x,y,z) is the target R position, (X T (x, y, z) represents the position of the transmitting array element, .... R (Y,Z) represents the position of the receiving array element, and c represents the speed of light.

[0008] The terahertz multi-transmitter multi-receiver array system error calibration method described in this invention, as a preferred embodiment, involves the system noise error S generated by the antenna equipment. noise (t) includes thermal noise caused by temperature drift, interference noise caused by fluctuations in the antenna itself, and interference noise caused by manufacturing precision, etc. ; Among them, a n For random amplitude noise, φ(t) is random phase.

[0009] The terahertz multi-transmitter multi-receiver array system error calibration method of the present invention, as a preferred embodiment, includes the background cancellation method in step S2, which involves placing a piece of absorbing material with a cross-section of 1m×1m in front of the array to obtain an empty-sampling echo signal, and subtracting the empty-sampling echo signal from the target echo signal to obtain the echo signal after background calibration.

[0010] The terahertz multi-transmitter multi-receiver array system error calibration method of the present invention, as a preferred embodiment, in step S3, the calibration parameter S ref The calculation method is as follows: ; Among them, S real (X T ,X R S represents the actual echo signal of the calibration piece. idea (XT ,X R ) represents the theoretical echo signal of the calibration component, φ(f) represents the phase error caused by channel dispersion, and φ(X) represents the phase error caused by channel dispersion. T ,X R This refers to the error caused by the inconsistency in phase between different channels.

[0011] The terahertz multi-transmitter multi-receiver array system error calibration method described in this invention, as a preferred embodiment, uses the actual echo signal S of the calibration component. real (X T ,X R The calculation method for ) is as follows: ; Among them, X TR Let X be the coordinates of the center position of the transceiver unit of a one-dimensional MIMO linear array. TR =(X T +X R ) / 2, (x0,y0,z0) are the positions of the reflection points on the plane of the calibration piece, (X T (x, y, z) represents the position of the transmitting array element, .... R (x, y, z) represents the position of the receiving array element, φ(f) represents the phase error caused by channel dispersion, and φ(x, y, z) represents the phase error caused by channel dispersion. T ,X R ) represents the error caused by the phase inconsistency of different channels, and c is the speed of light.

[0012] The terahertz multi-transmitter multi-receiver array system error calibration method described in this invention, as a preferred embodiment, uses the theoretical echo signal S of the calibration component. idea (X T ,X R The calculation method for ) is as follows: ; Among them, X TR Let X be the coordinates of the center position of the transceiver unit of a one-dimensional MIMO linear array. TR =(X T +X R ) / 2, (x0,y0,z0) are the positions of the reflection points on the plane of the calibration piece, (X T (x, y, z) represents the position of the transmitting array element, .... R (Y,Z) represents the position of the receiving array element. The product of the signal frequency f and -t0; φ(f) is the phase error caused by channel dispersion, φ(X) T ,X R The error is caused by the phase inconsistency between different channels, and c is the speed of light; Theoretical echo signal S of the calibration piece idea (X T ,X R() represents the signal after down-conversion.

[0013] In the terahertz multi-transmitter multi-receiver array system error calibration method described in this invention, as a preferred embodiment, the zero-frequency position of the signal in step S4 is the system delay phase φ. Δ The calculation method is as follows: ; Where, φ real For the actual echo phase, φ idea This is the theoretical echo phase.

[0014] The terahertz multi-transmitter multi-receiver array system error calibration method described in this invention, as a preferred method, uses the actual echo phase φ real The calculation method is as follows: ; Where angle(*) is used to calculate the phase angle of the input target, S real (X T ,X R The actual echo signal of the calibration piece; Theoretical echo phase φ idea The calculation method is as follows: ; Among them, S idea (X T ,X R ) represents the theoretical echo signal of the calibration component.

[0015] The present invention has the following advantages: (1) By comparing the echoes of redundant signal elements in the signal domain and eliminating the information of damaged channels, the problem of poor uniformity of equivalent array elements caused by the damage of array element channels is effectively improved.

[0016] (2) Error compensation is performed on system noise, dispersion inconsistency caused by the linearity of large bandwidth signals, amplitude and phase inconsistency between channels, and array uniformity variation caused by array element damage, so as to improve the imaging quality of terahertz array. Attached Figure Description

[0017] Figure 1 Here is a flowchart of an error calibration method for a terahertz multi-transmitter multi-receiver array system; Figure 2 This is a schematic diagram of the sampling of the calibration piece in Example 1; Figure 3 This is a schematic diagram of delay calibration for the MIMO array receiver unit in Example 1; Figure 4 This is a schematic diagram of delay calibration for the MIMO array transmitter unit in Example 1; Figure 5This is a schematic diagram of the MIMO array layout for Example 1; Figure 6 The spectrum of the one-dimensional distance imaging echo signal before calibration in Example 1; Figure 7 This is a spectrum diagram of the two-dimensional imaging echo signal before calibration in Example 1; Figure 8 The spectrum of the one-dimensional distance imaging echo signal after calibration in Example 1; Figure 9 The image shows the spectrum of the two-dimensional imaging echo signal after calibration in Example 1. Detailed Implementation

[0018] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Example 1

[0019] like Figure 1 As shown, a method for error calibration of a terahertz multi-transmitter multi-receiver array system includes the following steps: First, redundancy compensation is applied to the terahertz multi-transmitter and multi-receiver detection subsystem to reduce the impact of array element damage.

[0020] In terahertz multiple-transmitter-multiple-receiver array systems, a large-scale uniform sparse array model and a multiple-transmitter-multiple-receiver operating mode are employed. Let the set of locations of the transmitting antenna array elements be denoted as . , dr represents the spacing between transmitting array elements; the set of positions for receiving antenna array elements is... , Let dt be the distance between the receiving array elements, then the equivalent position set of the transmitting and receiving array elements is: There are a total of M×N equivalent positions.

[0021] ; To increase the redundancy of the array elements, the array operating mode is changed without altering the array's physical design: each transmitting element... Corresponding to two sets of receiving array elements ,in Then the equivalent location set of the transmitting and receiving array elements. The equivalent array size is M*2N.

[0022] ; It can be observed that when k=j∈[1:N-1], The positions of most equivalent array elements are repeated, which increases the redundancy of radar system echo information.

[0023] Rearranging the array echo signals according to the equivalent element spacing represents the echo signal of n (n<2N) receiving elements of the m-th (m<M) transmitting array. By comparing redundant signal unit echoes in the signal domain and eliminating damaged channel information, the problem of poor uniformity of equivalent elements caused by element channel damage is effectively improved. The finally obtained effective large-bandwidth echo signal is: ; The possible phase error terms of the large-bandwidth echo signal are analyzed, and amplitude changes are ignored in the analysis.

[0024] Let the array transmit signal be: ; wherein , represents the starting frequency of the signal, is the frequency modulation slope; let the target be at position R the transmitting element is at position , and the receiving element is at position , the echo signal can be expressed as: ; wherein is the amplitude of the target echo; is the time difference generated between the target and the transmitting and receiving element : ; are the center position coordinates of the transmitting and receiving units of the one-dimensional MIMO linear array.

[0025] represents the phase error caused by channel dispersion. Dispersion is the phase change generated in the antenna channel by the frequency range span of the large-bandwidth signal, which is related to the signal frequency; represents the error caused by inconsistent phases of different channels; represents the phase error caused by the time delay of the transmitting and receiving array antennas. The time delay includes the internal time delay of different channels and the error time delay caused by path difference error (such as structural deformation, etc.); represents the system noise error generated by antenna equipment, which is a non-linear error. The purpose of system calibration is to eliminate error terms and retain only the phase change caused by path difference, so as to determine the position information of the target.

[0026] S2, system noise calibration adopts a background cancellation method to eliminate all noise signals other than the target signal , including thermal noise caused by temperature drift, interference noise generated by antenna fluctuation and processing accuracy, etc., which is represented by random phase .

[0027] ; A 1m x 1m absorbing material is placed 1m in front of the array to obtain the echo signal, i.e., the no-load echo. The system has high stability. The target echo signal is subtracted from the no-load echo signal to obtain the target echo signal after background calibration.

[0028] S3. Phase error caused by dispersion and channel inconsistency and Phase compensation is performed using high-precision calibration components. These components are metal planar plates that cover the array scanning range and are parallel to the transceiver array plane. All MIMO virtual array elements fall within the projection of the metal plate's reflective surface, meaning that each element maintains an equal distance from the target.

[0029] Place the high-precision calibration component in the imaging area in front of the terahertz transceiver array, such as... Figure 2 As shown, ignoring the residual video phase term and signal amplitude, the echo after down-conversion can be expressed as: ; in, This indicates the position of a reflection point on the plane of the calibration piece; for a terahertz multiple transmitter and receiver system, the same position... different directions Theoretically, the echoes from calibrated components have the same amplitude and phase information. However, when acquiring the echo signals from actual calibrated components, the phase errors and dispersion of the channels introduce additional phase information.

[0030] ; In practical processing, based on the phase compensation principle, the redundant phase terms in the actual echo signal are extracted, which are the calibration parameters we need. .

[0031] ; The specific execution steps are as follows: perform spectrum transformation on the echo signal of each channel of the calibration component, convert the time domain signal into a frequency domain signal, and shift the spectrum to move the target to near zero frequency.

[0032] ; The phase information of the extracted signal is taken as its conjugate, and the spectrum of the test echo signal is multiplied by the conjugate of the phase error to obtain the phase compensation function. During radar operation, the received echo signal is multiplied by the phase compensation function before range pulse compression to correct the influence of the error, resulting in better focusing of the one-dimensional range image.

[0033] Step 4: System delay calibration, i.e., antenna range element calibration. The transmitted signal is routed to the horn on the opposite side of the antenna as a delay calibration transmitting unit. Transmit and receive data, and pulse compression processing is performed on the single-element echo. The degree of range element offset is determined by the signal zero-frequency position, and compensation is performed. The theoretical echo of the transmitting channel is... The actual echo from the transmission channel is in , Where angle(*) is used to calculate the phase angle of the input target; The actual measured zero offset value is the system delay phase. .

[0034] like Figures 3-5 As shown, the terahertz multiple transmitter-receiver array system has a center frequency of 220 GHz, a bandwidth of 75 GHz, and a total of 64 transmitters and 64 receivers (MIMO) arrays. The calibration method described above is used to calibrate various errors, and the one-dimensional range image and two-dimensional imaging are as follows: Figures 6-9 As shown.

[0035] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for error calibration of a terahertz multi-transmitter multi-receiver array system, characterized in that: Includes the following steps: S1. Redundancy Compensation: In the terahertz multi-transmitter and multi-receiver detection subsystem, the array echo signals are rearranged according to the equivalent array element spacing. By comparing the echoes of redundant signal units in the signal domain and eliminating damaged channel information, the phase error term generated by the wideband echo signal is analyzed. S2. System noise calibration: The background cancellation method is used to eliminate noise signals other than the target signal; S3. Dispersion and Amplitude-Phase Inconsistency Calibration: Phase compensation is performed using a high-precision calibration device, including spectrum transformation of the echo signal of each channel of the high-precision calibration device to convert the time-domain signal into a frequency-domain signal, spectrum shifting to move the target to near zero frequency, extracting the phase information of the signal lamp and taking the conjugate, multiplying the spectrum of the test echo signal by the conjugate of the phase error to obtain the phase compensation function, and multiplying the received echo signal by the phase compensation function before performing distance pulse compression to obtain the calibration parameters; S4. System delay calibration: The transmitted signal is led out to the horn on the opposite side of the antenna as a delay calibration transmitting unit for transmission and reception acquisition. The echo of the single array element is pulse compressed. The offset of the distance element is judged by the zero frequency position of the signal and compensation is made accordingly.

2. The terahertz multiple transmitter / receiver array system error calibration method according to claim 1, characterized in that: The method for calculating the echo signal in step S1 is as follows: ； Where, σ TR Let j be the target echo amplitude, j be the imaginary part, and f be the signal frequency. , The starting frequency of the signal. t is the frequency modulation slope; t is the current time; t0 is the distance from the target to the transceiver array element (X). T ,X R The time difference generated The product of the signal frequency f and (t-t0); φ(f) is the phase error caused by channel dispersion, φ(X) T ,X R S represents the error caused by the phase inconsistency between different channels, φ(∆t) represents the phase error caused by the time delay of the transceiver array antenna, and S represents the phase error caused by the phase inconsistency between different channels. noise (t) represents the system noise error caused by the antenna equipment.

3. The terahertz multiple transmitter / receiver array system error calibration method according to claim 2, characterized in that: The target to the transceiver array element (X) T ,X R The calculation method for the resulting time difference t0 is as follows: ； Where: X TR Let X be the coordinates of the center position of the transceiver unit of a one-dimensional MIMO linear array. TR =(X T +X R ) / 2, (x,y,z) is the target R position, (X T (x, y, z) represents the position of the transmitting array element, .... R (Y,Z) represents the position of the receiving array element, and c represents the speed of light.

4. The terahertz multiple transmitter / receiver array system error calibration method according to claim 2, characterized in that: The system noise error S generated by the antenna device noise (t) includes thermal noise caused by temperature drift, interference noise caused by fluctuations in the antenna itself, and interference noise caused by manufacturing precision, etc. ； Among them, a n For random amplitude noise, φ(t) is random phase.

5. The terahertz multiple transmitter / receiver array system error calibration method according to claim 4, characterized in that: The background cancellation method described in step S2 includes placing a piece of absorbing material with a cross-section of 1m×1m in front of the array to obtain an empty echo signal, and subtracting the empty echo signal from the target echo signal to obtain the echo signal after background calibration.

6. The terahertz multiple transmitter / receiver array system error calibration method according to claim 4, characterized in that: The calibration parameter S in step S3 ref The calculation method is as follows: ； Among them, S real (X T ,X R S represents the actual echo signal of the calibration piece. idea (X T ,X R ) represents the theoretical echo signal of the calibration component.

7. The terahertz multiple transmitter / receiver array system error calibration method according to claim 6, characterized in that: The actual echo signal S of the calibration device real (X T ,X R The calculation method for ) is as follows: ； Among them, X TR Let X be the coordinates of the center position of the transceiver unit of a one-dimensional MIMO linear array. TR =(X T +X R ) / 2, (x0,y0,z0) are the positions of the reflection points on the plane of the calibration piece, (X T (x, y, z) represents the position of the transmitting array element, .... R (x, y, z) represents the position of the receiving array element, φ(f) represents the phase error caused by channel dispersion, and φ(x, y, z) represents the phase error caused by channel dispersion. T ,X R ) represents the error caused by the phase inconsistency of different channels, and c is the speed of light.

8. The terahertz multiple transmitter / receiver array system error calibration method according to claim 6, characterized in that: The theoretical echo signal S of the calibration component idea (X T ,X R The calculation method for ) is as follows: ； in, It is the product of the signal frequency f and -t0; The theoretical echo signal S of the calibration component idea (X T ,X R () represents the signal after down-conversion.

9. The terahertz multiple transmitter / receiver array system error calibration method according to claim 8, characterized in that: The zero-frequency position of the signal in step S4 is the system delay phase φ. Δ The calculation method is as follows: ； Where, φ real For the actual echo phase, φ idea This is the theoretical echo phase.

10. The terahertz multiple transmitter / receiver array system error calibration method according to claim 9, characterized in that: The actual echo phase φ real The calculation method is as follows: ； Here, angle(*) is used to calculate the phase angle of the input target; The theoretical echo phase φ idea The calculation method is as follows: 。

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