General Midfield Calibration Method for Asymmetric Conformal Wideband Digital Phased Array Antennas

Abstract

The present invention discloses a general mid-field calibration method for an asymmetric conformal broadband digital phased array antenna. After the phased array system is powered on, according to the calibration control sequence, calibration signals at each discrete frequency point are sent out through the built-in calibration network, received by each array element after spatial coupling, and the self-calibration reception result data at different frequency points output by each array element is collected; the pre-calculated reception error data is compensated into the self-calibration reception result data to obtain the corrected self-calibration reception result data. The reception error data includes the relative internal and external calibration time delays and the relative frequency responses at different frequency points of each array element calculated from the calibration signals sent through the built-in calibration network and the mid-field calibration antenna; taking a certain array element channel in the corrected self-calibration reception result data as the reference channel, calculating the relative frequency response of the reference channel relative to other channels and compensating the relative frequency response to the corresponding channels to complete the mid-field calibration.

Description

Technical Field

[0001] The present invention relates to the technical field of phased array antenna calibration, and particularly to a general mid-field calibration method for an asymmetric conformal broadband digital phased array antenna. Background Art

[0002] The phased array antenna technology is very superior. Compared with traditional reflector antennas, it has obvious technical advantages in many aspects such as radio beam scanning, multi-beam pointing, and anti-interference ability. At present, the application scenarios of phased array antennas are very extensive, such as aerospace, radar, communication and other fields. With the rapid development of its application fields, naturally higher requirements are also put forward for phased array antenna technology: on the one hand, the phased array antenna not only needs to meet complex application requirements such as ultra-wideband, large-angle scanning, and multi-beams, on the other hand, it also needs to meet installation requirements such as miniaturization, light weight, and low profile. In this case, "conforming" the antenna array surface to the carrier shape can greatly enhance the adaptability of the antenna platform. Especially for some carrier platforms moving at high speeds, conformal antennas can not change their aerodynamic characteristics.

[0003] For phased array antennas, due to problems in the manufacturing process, there will be differences in the passive and active parts of each antenna. Such differences will cause different amplitudes and phases for signals, thus affecting beam synthesis (the beam synthesis phases must be consistent). To solve such differences, it is necessary to calibrate the antenna before beam synthesis, and compensate the calibration results to the active parts of each antenna, so that the amplitude and phase responses of each antenna to the same signal are exactly the same, and thus beam synthesis can be carried out. This is the purpose of phased array calibration. However, since the conformal antenna array configuration is generally irregular, there may be cases of multiple planes or curved surfaces. The conventional planar scanning probe used in planar near-field calibration can only move two-dimensionally and cannot meet the calibration requirements of conformal antennas. Because for the planar phased array calibration process, the antenna normal angle and the wave path difference of the antenna are relatively small and can be ignored, while for curved surfaces, these factors must obviously be considered. Therefore, the calibration of conformal antennas is more complex.

[0004] In addition, the bandwidth of a phased array antenna generally includes the signal bandwidth and the operating bandwidth. Phased arrays with a wide operating bandwidth or a wide signal bandwidth are usually referred to as broadband phased arrays. Among them, the number of phased arrays with a wide signal bandwidth is generally small and is usually used for information confrontation and measurement and control communication. The number of phased arrays with a narrow signal bandwidth is large and is generally used for radar detection. Compared with a digital phased array with a narrow signal bandwidth, for a digital phased array with a wide signal bandwidth, there are differences in the amplitude and phase at other frequencies in the channel compared with those at its center frequency. The time delay of a narrowband phased array can be converted into phase and then processed uniformly without changing its time-domain waveform. The relevant parameters to be considered are phase and amplitude. However, the calibration of a broadband conformal phased array is more complex because, in the calibration process of a digital phased array with a wide signal bandwidth, in addition to compensating for the frequency domain part, the time domain part also needs to be compensated. The relevant parameters to be considered are phase, amplitude, and time delay.

[0005] In the related art, a phased array calibration method proposed in a patent application document with publication number CN117491956A realizes the channel calibration of the phased array surface and the calculation of the channel response under different operating environment temperature conditions. This solution actually considers the influence of temperature on the passive part of the antenna based on antenna calibration, rather than the entire calibration process of the phased array antenna. A multi-beam phased array antenna control method is proposed in a patent application document with publication number CN116916339A. This solution takes differential compensation as a step in antenna control, but does not mention the test calculation process of the differences. The calibration of the antenna includes two parts: the first part is how to determine the differences between antenna elements, and the second part is to perform differential compensation so that the amplitude and phase responses of each antenna element to the same signal are exactly the same. Obviously, the process of determining the differences is very complex, while differential compensation is relatively simple.

[0006] A spatial multi-angle calibration method for a broadband phased array is proposed in a patent application document with publication number CN117459160A. This solution corrects once at three different angles and then reduces the calibration error through fitting calculation. It belongs to an optimization item of antenna calibration rather than antenna calibration.

[0007] The literature "A New Method for Mid-Field Phase Difference Calibration of a Phased Array Antenna Network, Radar Science and Technology, Wei Peng et al." proposes to use an auxiliary antenna to achieve mid-field phase difference calibration. This method first constructs a horn, then makes precise displacement or reconstructs the same horn again. By using two horns with different positions to calibrate an antenna array surface, but a necessary condition for this method is that the antenna is symmetric and regular, otherwise this method cannot be used. In addition, this method cannot achieve the calibration of the antenna frame elements.

[0008] Therefore, there is an urgent need for a general calibration method applicable to irregular array configurations to solve the calibration problem of such signals with a wide bandwidth for conformal antennas. Summary of the Invention

[0009] The technical problem to be solved by the present invention is how to provide a general calibration method for a wideband digital phased array antenna applicable to an irregular array configuration.

[0010] The present invention solves the above technical problems by the following technical means:

[0011] The present invention proposes a general mid-field calibration method for an asymmetric conformal wideband digital phased array antenna, and the method includes:

[0012] After the phased array system is powered on, according to the calibration control sequence, the calibration signals at each discrete frequency point are sent out through the built-in calibration network, and after being spatially coupled, they are respectively received by each array element, and the self-calibration result data of each array element at different frequency points is collected;

[0013] Compensate the pre-calculated reception error data into the self-calibration result data to obtain the self-calibration result data after removing the time delay error and frequency response error as the corrected self-calibration result data, wherein the reception error data includes the relative time delay values of internal and external calibrations and the relative frequency responses of internal and external calibrations corresponding to each array element at different frequency points;

[0014] Taking a certain array element channel in the corrected self-calibration result data as a reference channel, calculate the relative frequency response of the reference channel relative to other channels and compensate the relative frequency response to the corresponding channels to complete the mid-field calibration.

[0015] Further, the calculation process of the reception error data includes:

[0016] According to the calibration control sequence, the calibration signals at each discrete frequency point are respectively sent out through the built-in calibration network and the mid-field calibration antenna to respectively obtain the internal calibration reception result data and the external calibration reception result data of each array element at different frequency points;

[0017] Using the coordinates of the mid-field calibration antenna, perform compensation calculation on the external calibration reception result data to obtain the corrected external calibration reception result data;

[0018] Based on the internal calibration reception result data and the corrected external calibration reception result data corresponding to each frequency point, calculate the relative time delay values of internal and external calibrations at each frequency point and the relative frequency responses of internal and external calibrations at different frequency points and use them as the reception error data.

[0019] Further, according to the calibration control sequence, transmitting the calibration signals of each discrete frequency point through the built-in calibration network and the mid-field calibration antenna respectively to obtain the internal calibration reception result data and the external calibration reception result data of each array element at different frequency points, including:

[0020] According to the calibration control sequence, transmitting the calibration signals of each discrete frequency point through the built-in calibration network at different times, and after being spatially coupled to each array element structure, collecting the amplitude-frequency responses of each array element at different frequency points as the internal calibration reception result data;

[0021] According to the calibration control sequence, transmitting the calibration signals of each discrete frequency point through the mid-field calibration antenna, and after passing through each array element structure, collecting the amplitude-frequency responses of each array element at different frequency points as the external calibration reception result data.

[0022] Further, the built-in calibration network is composed of several microstrip antennas laid between each array element of the phased array antenna.

[0023] Further, before transmitting the calibration signals of each discrete frequency point through the built-in calibration network and the mid-field calibration antenna respectively according to the calibration control sequence to obtain the internal calibration reception result data and the external calibration reception result data of each array element at different frequency points, the method further includes:

[0024] Installing the mid-field calibration antenna and calibrating the position coordinates of the mid-field calibration antenna relative to the phased array antenna to be measured.

[0025] Further, the distance R between the mid-field calibration antenna and the phased array antenna to be measured satisfies: R≥max{R m ,R n}, where R m is the mid-field distance from the mid-field calibration antenna to the phased array antenna to be measured, and R n is the normal tolerance distance from the mid-field calibration antenna to the phased array antenna to be measured.

[0026] Further, using the coordinates of the mid-field calibration antenna to perform compensation calculation on the external calibration reception result data to obtain the corrected external calibration reception result data, including:

[0027] Based on the coordinates of the mid-field calibration antenna, performing compensation calculation on the external calibration reception result data by using a compensation coefficient and a multipath correction factor to obtain the corrected external calibration reception result data;

[0028] wherein, the compensation coefficient is used to compensate for the differences in wave path and normal direction caused by the mid-field effect between the mid-field calibration antenna and the phased array antenna to be measured, and the formula of the compensation coefficient is expressed as:

[0029]

[0030] In the formula, F represents the compensation coefficient, θ 1i represents the included angle between the connection line of the mid-field correction antenna and the i-th antenna element in the phased array antenna and the radiation direction of the mid-field correction antenna, θ 2i represents the included angle between the connection line of the mid-field correction antenna and the i-th antenna element in the phased array antenna and the radiation direction of the phased array antenna, R i represents the distance from the mid-field correction antenna to the i-th antenna element to be measured in the phased array antenna to be measured, R i , k represents the free space wave number corresponding to the operating frequency, and j represents a complex number;

[0031] It should be noted that the radiation direction of the phased array antenna is unique for the entire antenna, and the included angle between each element and this direction varies with the position.

[0032] The multipath correction factor is used to eliminate the multipath components in the external correction received result data, and the formula of the multipath correction factor is expressed as:

[0033]

[0034] In the formula, F mp represents the multipath correction factor, R ip represents the length of the maximum reflection path of the multipath effect in the correction scenario, and ρ represents the electromagnetic wave reflection coefficient of the reflecting surface in the maximum reflection path of the multipath effect in the correction scenario.

[0035] Furthermore, calculating the relative time delay value of the internal and external corrections at each frequency point and the relative frequency response of the internal and external corrections at different frequency points based on the internal correction received result data and the corrected external correction received result data corresponding to each frequency point, and using them as the received error data, includes:

[0036] Performing a ratio calculation on the internal correction received result data and the corrected external correction received result data corresponding to each frequency point to obtain the internal and external correction error signals at different frequency points of each element;

[0037] Calculating the relative time delay value of the internal and external corrections at each frequency point according to the internal and external correction error signals corresponding to two discrete frequency points within the broadband;

[0038] Constructing the phase difference value at each frequency point according to the relative time delay value of the internal and external corrections at each frequency point;

[0039] Compensating the phase difference value at each frequency point to the internal and external correction error signals at each frequency point to obtain the relative frequency response of the internal and external corrections at each frequency point;

[0040] Take the relative delay values of internal and external calibration at each frequency point and the relative frequency responses of internal and external calibration at each frequency point as the received error data.

[0041] Further, compensating the pre-calculated received error data into the self-calibration result data to obtain the self-calibration result data after removing the delay error and frequency response error as the corrected self-calibration result data includes:

[0042] Use the relative delay values of internal and external calibration at each frequency point to supplement the self-calibration delay in the self-calibration result data to obtain the compensated self-calibration delay;

[0043] Use the relative frequency responses of internal and external calibration at each frequency point to compensate the self-calibration frequency response after compensating the delay to obtain the frequency response result after deducting the delay;

[0044] Take the compensated self-calibration delay and the frequency response result after deducting the delay as the corrected self-calibration result data.

[0045] Further, taking a certain element channel in the corrected self-calibration result data as the reference channel, calculating the relative frequency response of the reference channel relative to other channels and compensating the relative frequency response to the corresponding channels to complete the mid-field calibration, includes:

[0046] Taking a certain element channel in the corrected self-calibration result data as the reference channel, calculating the relative delay value of the reference channel relative to other channels;

[0047] Based on the relative delay value of the reference channel relative to other channels, construct the phase difference at each frequency point;

[0048] According to the phase difference at each frequency point, compensate and calculate the relative frequency response between each element channel.

[0049] In addition, the present invention also proposes a general mid-field calibration method for an asymmetric conformal broadband digital phased array antenna, the method includes:

[0050] After the phased array system is powered on, according to the calibration control sequence, each element sends calibration signals in a time-sharing manner, which are received by the built-in calibration network after spatial coupling, and collect the self-calibration transmission result data of different frequency points output by the calibration network;

[0051] Compensate the pre-calculated transmission error data into the self-calibration transmission result data to obtain the self-calibration transmission result data after removing the delay error and frequency response error as the corrected self-calibration transmission result data, wherein the transmission error data includes the relative delay values of internal and external calibration corresponding to each element at different frequency points and the relative frequency responses of internal and external calibration calculated from the calibration signals received by the built-in calibration network and the mid-field calibration antenna;

[0052] A certain array element channel in the corrected self-correction transmission result data is used as a reference channel, the relative frequency response of the reference channel relative to other channels is calculated, and the relative frequency response is compensated to the corresponding channel to complete the mid-field correction.

[0053] The advantages of the present invention are:

[0054] (1) After each power-on of the phased array antenna, the present invention performs self-calibration through a built-in calibration network. The calibration does not require any external conditions. It only needs to collect the calibration signal of each channel after each power-on as the self-calibration result data through the built-in calibration network, and then compensate the self-calibration reception result data in combination with the pre-stored error signal to eliminate the delay error and frequency response error in the self-calibration reception result data to obtain the corrected self-calibration reception result. Then, a certain array element channel is selected from the corrected self-calibration reception result data as the reference channel, and the data of other channels are channel compensated to complete the mid-field calibration. By adopting the mid-field method, the present invention can reduce the limitation of environmental factors as much as possible without greatly affecting the calibration result, and reduce the footprint of the entire calibration project, so that some embodiments can be completed outside the microwave darkroom. It is applicable to the calibration of phased array antennas such as digital broadband phased arrays with irregular curved surfaces, planar digital arrays, narrowband digital arrays, and large digital arrays that cannot enter the microwave darkroom.

[0055] (2) The present invention constructs a built-in correction network and performs joint calculation processing through three different correction methods to compensate for the different positions and gains of array elements, the different responses of nodes on the correction network, the different responses of active components in each channel after each power-on, and the different responses of each frequency point in the channel.

[0056] (3) If the phased array system can ensure that the delay differences of each active channel remain consistent after each power-on, the inter-channel error results obtained by the mid-field calibration can be used for a one-time compensation, without the need for a built-in calibration network and subsequent calibration after each power-on.

[0057] (4) This method is different from the moving horn method used in the traditional planar near-field method. Instead, a correction horn, namely a mid-field correction antenna, is used. The amplitude-frequency differences caused by the different positions of other array elements are processed through compensation calculations, so it can be applied to antennas of various shapes.

[0058] Additional aspects and advantages of the present invention will be given in part in the following description and in part will be obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] Figure 1It is a schematic flow chart of a general mid-field calibration method for an asymmetric conformal broadband digital phased array antenna proposed in an embodiment of the present invention;

[0060] Figure 2 It is an example diagram of the application of a general receiving digital phased array structure to a curved array surface;

[0061] Figure 3 It is a schematic diagram of the microstrip line laying in an embodiment of the present invention;

[0062] Figure 4 It is a schematic diagram of channel calibration in an embodiment of the present invention;

[0063] Figure 5 It is a schematic flow chart of a general mid-field calibration method for an asymmetric conformal broadband digital phased array antenna proposed in an embodiment of the present invention for receiving calibration;

[0064] Figure 6 It is a schematic flow chart of another general mid-field calibration method for an asymmetric conformal broadband digital phased array antenna proposed in an embodiment of the present invention;

[0065] Figure 7 It is a schematic flow chart of a general mid-field calibration method for an asymmetric conformal broadband digital phased array antenna proposed in an embodiment of the present invention for transmitting calibration. Specific embodiments

[0066] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0067] As Figure 1 shown, a first embodiment of the present invention proposes a general mid-field calibration method for an asymmetric conformal broadband digital phased array antenna, which is used for receiving calibration and includes the following steps:

[0068] S101. After the phased array system is powered on, according to the calibration control sequence, calibration signals at each discrete frequency point are sent out through the built-in calibration network, received by each array element after spatial coupling, and self-calibration receiving result data at different frequency points output by each array element is collected;

[0069] S102. Compensate the pre-calculated received error data into the self-calibration received result data to obtain the self-calibration received result data after removing the time delay error and frequency response error as the corrected self-calibration received result data. Wherein, the received error data includes the relative internal and external calibration time delays and relative frequency responses corresponding to different frequency points of each array element calculated by the calibration signals transmitted through the built-in calibration network and the mid-field calibration antenna.

[0070] S103. Take a certain array element channel in the corrected self-calibration received result data as the reference channel, calculate the relative frequency response of this reference channel relative to other channels, and compensate the relative frequency response to the corresponding channels to complete the mid-field calibration.

[0071] As described in the background art, the complexity of the calibration process of the broadband conformal phased array makes the conformal antenna technology only stay at the theoretical level, and the actual usage scenarios are very rare. Especially in the fields of broadband communication and electronic countermeasures, it further increases the difficulty of the research on the calibration of the broadband conformal phased array. The present invention provides a brand-new method for calibration aiming at the combination of the curved surface conformal array and the broadband digital array, and breakthroughly solves the problem of the difficulty in calibrating the broadband digital phased array antenna with an irregular array surface configuration, making it possible to widely apply the conformal antenna technology in terms of technology and engineering. The specific solution idea is as follows: Taking the receiving beamforming as an example, Figure 2 An embodiment of applying a general digital phased array structure to a curved array surface is given, which is composed of antenna array elements, analog front ends, analog-to-digital converters A / D, digital downconverters DDC, and digital beamformers. Since the differences in the frequency responses of each channel of the phased array antenna are divided into passive parts and active parts, the passive parts are mainly caused by the differences of passive components such as array elements, calibration networks, and cables; the active parts are mainly jointly affected by each active component (mainly components such as A / D). Due to problems in the manufacturing process, the passive parts and active parts of each antenna cannot be exactly the same. Such differences will cause different amplitudes and phases for the signals, thus affecting the beam synthesis.

[0072] Therefore, for a digital phased array, the frequency response and time delay characteristics of the same active component may not be consistent each time it is powered on. Therefore, it is necessary to construct a built-in calibration network. After the phased array antenna is powered on each time, self-calibration is performed through the built-in calibration network. The calibration requires no external conditions. Only through the built-in calibration network, the calibration signals of each channel after each power-on are collected as the self-calibration result data. Then, the self-calibration received result data is compensated by combining the received error signals calculated from the calibration signals pre-stored and sent by the built-in calibration network and the mid-field calibration antenna, so as to eliminate the time delay error and frequency response error in the self-calibration result data, and obtain the corrected self-calibration received result data. Then, a certain element channel is selected from the corrected self-calibration received result data as the reference channel, and the data of other channels is compensated to complete the mid-field calibration.

[0073] In this embodiment, by adopting the mid-field method, on the basis of having little influence on the calibration result, the limitation of environmental factors is reduced as much as possible, the floor area of the entire calibration project is reduced, so that some embodiments can be completed outside the anechoic chamber. Compared with the commonly used planar near-field method for phased array calibration: specifically, after the calibration position is determined, the horn can move precisely, perpendicular to each element in turn (when moving, the distance from the horn to each element does not change), and calibration data is collected. Since the antenna is planar, the movement trajectory of the horn is also planar, which is easy to implement in engineering. However, when the antenna is curved, such as spherical, the horn obviously cannot complete the action of being perpendicular to each element. At this time, the planar near-field method is no longer applicable.

[0074] In the present invention, instead of moving the horn, a calibration horn is used, and the amplitude-frequency differences caused by different positions of other elements are all processed through compensation calculation, so it can be applied to various shapes. Moreover, different from the very high environmental requirements of the planar near-field method, a microwave anechoic chamber environment must be used, and the movement range of the calibration horn must also match the size of the antenna. When the antenna size is very large, a huge calibration horn support needs to be provided for the calibration horn to move. The present invention can perform calibration by setting a calibration horn in the mid-field range, with low environmental requirements.

[0075] It should be noted that the planar array is a simple special case of the curved surface or polyhedral array, and the narrowband phased array is a simple special case of the broadband phased array. The present invention is directed to the most complex situation among them, and its method can obviously be applied to these simpler special cases. Therefore, the present invention can be applied but not limited to the digital broadband phased array of irregular curved surfaces, and planar digital arrays, narrowband digital arrays, and large digital arrays that cannot enter the anechoic chamber can all use the calibration method proposed in this embodiment for calibration. For example, if the phased array system can ensure that the time delay differences of each active channel remain consistent after each power-on, the channel error results obtained from the mid-field calibration can be used for one-time compensation, and there is no need for a built-in calibration network and subsequent calibration after each power-on.

[0076] As a further preferred technical solution, the calculation process of the received error data includes:

[0077] a) According to the calibration control sequence, the calibration signals of each discrete frequency point are respectively sent out through the built-in calibration network and the mid-field calibration antenna, so as to obtain the internal calibration received result data and the external calibration received result data of each array element at different frequency points respectively;

[0078] Specifically, in this embodiment, according to the calibration control sequence sent by the calibration source emission channel, the calibration signals of each discrete frequency point are sent out through the built-in calibration network. After being spatially coupled to each array element structure, the signals are collected after passing through the antenna element → RF front end → analog-to-digital conversion → digital down-conversion. The amplitude-frequency responses of each array element at different frequency points are collected as the internal calibration received result data, and the internal calibration received result data is stored.

[0079] Specifically, in this embodiment, according to the calibration control sequence sent by the calibration source emission channel and according to the coordinate position of the mid-field calibration antenna, the receiving beam is directed to the mid-field calibration antenna, and the calibration signals of each discrete frequency point are sent out through the mid-field calibration antenna. The signals are collected after passing through spatial attenuation → antenna element → RF front end → analog-to-digital conversion → digital down-conversion, and the amplitude-frequency responses of each array element at different frequency points are obtained as the external calibration received result data, and the external calibration received result data is stored.

[0080] b) Using the coordinates of the mid-field calibration antenna, perform compensation calculation on the external calibration received result data to obtain the corrected external calibration received result data;

[0081] In this embodiment, according to the measured coordinates of the mid-field calibration antenna, compensation calculation is performed on the external calibration received result data to eliminate the conversion difference of the antenna projection area caused by the non-parallel normal directions of each antenna element, the signal amplitude difference caused by the wave path difference, and the phase difference caused by the wave path difference.

[0082] c) Based on the internal calibration received result data corresponding to each frequency point and the corrected external calibration received result data, calculate the relative time delay values of internal and external calibrations at each frequency point and the relative frequency responses of internal and external calibrations at different frequency points, and use them as the received error data.

[0083] As a further preferred technical solution, the built-in calibration network is composed of several microstrip antennas laid between the elements of the phased array antenna.

[0084] As Figure 3 shown, in this embodiment, by laying microstrip calibration antennas between the elements, a built-in calibration network of the phased array system is constructed for subsequent self-calibration and internal calibration. The signal is transmitted between the microstrip line and each element through spatial coupling, and the microstrip antenna is connected to the calibration processing module through a switch power divider device.

[0085] It should be noted that the specific laying method of the microstrip antenna can be determined according to the different situations of the antenna system. In engineering, it should be as close as possible to the antenna elements. Considering the possible situation of surface conformal of the elements, the structure of the microstrip line should also be bent accordingly. However, due to the physical properties of the microstrip antenna in a complex curved surface, complex bending is impossible, which may lead to the result that the microstrip line may be closer to one of the two elements between certain two elements during actual laying, resulting in errors in the calibration signals received or emitted by the microstrip line. The internal calibration and self-calibration both contain the same calibration network (i.e., microstrip line) error. Therefore, in the subsequent process, the error is deducted by using the cancellation calculation method, and the frequency response errors of different nodes of the microstrip line will be compensated and processed. Therefore, a slight position difference will not cause a difference in the calibration result.

[0086] During the self-calibration and internal calibration processes in receiving calibration, the calibration signal is emitted by each microstrip antenna and received by each element through spatial coupling in a time-sharing manner to complete the data acquisition work. During the self-calibration and internal calibration processes in transmitting calibration, the calibration signal is emitted by each element in a time-sharing manner and received by each microstrip antenna in a time-sharing manner to complete the data acquisition.

[0087] As a further preferred technical solution, in step a), the mid-field calibration antenna is pre-erected according to the actual situation of the calibration site, and the accurate coordinates of the mid-field calibration antenna relative to the entire antenna array to be measured are obtained through a position calibration device. Since the antenna array surface is an asymmetric curved surface, three aspects need to be considered in this process, namely the mid-field distance range, the radiation direction angle between the antenna to be measured and the calibration antenna, and the multipath effect.

[0088] Specifically, regarding the mid-field distance range, the distance R between the mid-field calibration antenna and the phased array antenna to be measured satisfies:

[0089] R≥max{R m ,Rn}

[0090] In the formula, R m is the mid-field distance from the mid-field correction antenna to the phased array antenna to be measured, and R n is the normal tolerance distance from the mid-field correction antenna to the phased array antenna to be measured.

[0091] Among them, for the mid-field distance R from the correction antenna to the antenna under test m , the following definition is given:

[0092]

[0093] In the formula: R m represents the mid-field distance from the correction antenna to the antenna under test; D represents the maximum linear dimension of the aperture (equivalent aperture) of the antenna under test; d represents the maximum linear dimension of the aperture (equivalent aperture) of the correction antenna; λ represents the operating wavelength.

[0094] Among them, for the normal tolerance distance R from the correction antenna to the antenna under test n , the following definition is given:

[0095]

[0096] In the formula: R n represents the normal tolerance distance from the correction antenna to the antenna under test; ρ represents the radius of curvature of the antenna array surface of the antenna under test at the element to be corrected; D represents the maximum linear dimension of the aperture (equivalent aperture) of the antenna under test; θ represents the angular tolerance range of the normal deflection of the antenna under test during calibration. In actual calibration, θ is determined according to the calibration accuracy requirements of the antenna under test, and the preferred value is 30°.

[0097] The above principle gives the lower limit requirement for the distance from the mid-field correction antenna to the antenna under test. According to the actual situation such as the calibration site and the length of the calibration cable, a reasonable distance from the mid-field correction antenna to the antenna under test is determined. At this distance in the normal direction of the part of the antenna under test to be corrected, the mid-field correction antenna is erected, and through the calibration equipment, the accurate coordinates of the mid-field correction antenna relative to the entire antenna elements to be measured are obtained.

[0098] Specifically, regarding the radiation angle between the antenna to be measured and the mid-field correction antenna, according to the coordinates of the correction antenna, calculate the distance R i from the correction antenna to each antenna element to be measured in the part of the antenna under test to be corrected, and calculate the angles θ 1 and θ 2 between the connection line of the correction antenna and the antenna under test and the radiation directions of the correction antenna and the antenna under test respectively. Thus, calculate the compensation coefficient F for compensating the wave path and normal direction differences caused by the mid-field effect between the correction antenna and the antenna under test:

[0099]

[0100] It should be noted that in this embodiment, the difference in the passive position is compensated by calculating the compensation coefficient.

[0101] In the formula: F represents the wave path and azimuth difference compensation coefficient from the calibration antenna to the antenna under test; θ 1i represents the angle between the connection line of the mid-field calibration antenna and the i-th antenna element in the phased array antenna and the radiation direction of the mid-field calibration antenna, θ 2i represents the angle between the connection line of the mid-field calibration antenna and the i-th antenna element in the phased array antenna and the radiation direction of the phased array antenna, R i represents the distance from the mid-field calibration antenna to the i-th antenna element to be measured in the phased array antenna to be measured, k represents the free space wave number corresponding to the operating frequency, and j represents a complex number.

[0102] Specifically, regarding the multipath effect, the electromagnetic reflection situation in the mid-field calibration environment is usually relatively complex, and there may be a large degree of electromagnetic reflection, making it difficult to achieve the perfect absorption state with extremely low electromagnetic signal reflection in a microwave anechoic chamber. This will generate a multipath effect on the calibration signal, affecting the transmission, reception, and processing of the signal, and thus affecting the calibration effect. Therefore, in order to improve the calibration result and enhance the calibration accuracy, it is necessary to correct the multipath effect and eliminate the multipath component in the received calibration signal. To eliminate the influence of the multipath effect, the received signal (i.e., the amplitude-frequency response result of the signal) needs to be multiplied by the multipath correction factor F mp so that the compensation can be directly calculated after calibrating the antenna coordinates. The multipath correction factor F mp is shown as follows:

[0103]

[0104] In the formula: F mp represents the multipath correction factor; R i represents the distance between the calibration antenna and the antenna element under test; ρ represents the electromagnetic wave reflection coefficient of the reflecting surface in the maximum reflection path of the multipath effect in the calibration scenario; R ip represents the length of the maximum reflection path of the multipath effect in the calibration scenario; k represents the free space wave number corresponding to the operating frequency.

[0105] Generally, the radiation direction of the calibration antenna should not be perpendicular or approximately perpendicular to the normal of a certain antenna element. Considering that there may be extreme cases for an asymmetric surface, the receiving channel of this element cannot receive the calibration signal sent by the calibration antenna or the signal is extremely small, affecting the calibration result. If there are indeed such contradictory situations for the antenna surface element, the method of using multiple mid-field calibration antennas can be adopted, and calibration antennas are installed at multiple different positions to solve the problem.

[0106] As a further preferred technical solution, in the step c), based on the internal calibration received result data and the corrected external calibration received result data corresponding to each frequency point, calculate the relative delay value of internal and external calibration at each frequency point and the relative frequency response of internal and external calibration at different frequency points as the received error data, including the following steps:

[0107] c1) Calculate the ratio of the internal calibration received result data corresponding to each frequency point and the corrected external calibration received result data to obtain the internal and external calibration error signals at different frequency points of each array element;

[0108] c2) Calculate the relative delay value of internal and external calibration at each frequency point according to the internal and external calibration error signals corresponding to two discrete frequency points within the broadband;

[0109] c3) Construct the phase difference at each frequency point according to the relative delay value of internal and external calibration at each frequency point;

[0110] c4) Compensate the phase difference at each frequency point to the internal and external calibration error signals at each frequency point to obtain the relative frequency response of internal and external calibration at each frequency point;

[0111] c5) Take the relative delay value of internal and external calibration at each frequency point and the relative frequency response of internal and external calibration at each frequency point as the received error data.

[0112] Specifically, in this embodiment, using the internal and external calibration error signals corresponding to two discrete frequency points within the broadband, the relative delay value Δτ of internal and external calibration can be calculated i1 , and then construct the phase difference exp(jωΔτ i1 ) at each frequency point, and compensate it to the internal and external calibration error signals corresponding to each discrete frequency point. After compensation, calculate the relative frequency response G 1 Δ(ω) of internal and external calibration. Store the relative delay value Δτ i1 of internal and external calibration at different frequency points of each array element and the relative frequency response G 1 Δ(ω) of internal and external calibration in a file as the received error data for subsequent self-calibration of the phased array antenna every time it is powered on.

[0113] As a further preferred technical solution, in the step S102: Compensate the pre-calculated received error data into the self-calibration result data to obtain the self-calibration result data after eliminating the delay error and frequency response error as the corrected self-calibration result data, including the following steps:

[0114] S121. Use the relative delay value of internal and external calibration at each frequency point to supplement the self-calibration delay in the self-calibration result data to obtain the compensated self-calibration delay;

[0115] S122. Compensate the self-calibration frequency response after compensating the time delay by using the relative frequency responses of the internal and external calibrations at each frequency point to obtain the frequency response result after deducting the time delay;

[0116] S123. Use the compensated self-calibration time delay and the frequency response result after deducting the time delay as the corrected self-calibration result data.

[0117] It should be noted that each time the phased array system is powered on, self-calibration is carried out: according to the calibration control sequence of the calibration processing module, the calibration signals of each discrete frequency point are sent out by the microstrip antenna, and after being spatially coupled, they are respectively received by each array element. The amplitude-frequency responses of the self-calibration of each array element at different frequency points are collected as self-calibration result data and stored. Then, the Δτ i1 and G 1 Δ(ω) of each array element at different frequency points in the received error data are compensated into the self-calibration result data, and the frequency response differences caused by different responses of each node on the calibration network are eliminated.

[0118] As a further preferred technical solution, in step S103: taking a certain array element channel in the corrected self-calibration result data as a reference channel, calculating the relative frequency response of the reference channel relative to other channels and compensating the relative frequency response to the corresponding channels to complete the mid-field calibration, including the following steps:

[0119] S131. Taking a certain array element channel in the corrected self-calibration result data as a reference channel, calculating the relative time delay value of the reference channel relative to other channels;

[0120] S132. Based on the relative time delay value of the reference channel relative to other channels, constructing the phase difference values at each frequency point;

[0121] S133. According to the phase difference values at each frequency point, compensating and calculating the relative frequency responses between each array element channel.

[0122] It should be noted that in this embodiment, taking a certain channel as a reference, using two discrete frequency points near the center frequency of the frequency band, calculating the relative time delay value Δτ i2 between channels, then constructing the phase difference values at each frequency point for compensation, and after compensation, calculating the relative frequency response G 2 Δ(ω) of each channel, and compensating this result to each channel to complete the calibration.

[0123] Combined with the general phased array system structure shown above Figure 2 When the frequency response characteristics of two receiving channels are exactly the same, these two channels simultaneously receive the incident signal x(t). D is the path difference, which can be calculated from the speed of light c, the coordinates of the antenna array elements, and the incident angle. Then the signals entering the analog receiving front end are respectively:

[0124] x 1x(t) = a(t)cos[ω RF t + θ(t)]

[0125] x 2 (t) = s·x(t - τ 0 ) = s·a(t - τ 0 )cos[ω RF (t - τ 0 ) + θ(t - τ 0 )]

[0126] where s is the conversion of the antenna projection area caused by the non - parallel normal directions of the antenna elements in Channel 1 and Channel 2 and the signal attenuation caused by the path difference, which can be calculated from information such as the element position coordinates and the incident angle; τ 0 is the inter - channel time delay difference caused by the difference in antenna coordinate positions, τ 0 = D / c; a(t) is the amplitude, ω RF is the radio frequency, ω IF is the intermediate frequency, θ(t) is the initial phase, and θ(t - τ 0 ) represents the time delay of τ 0 for x(t).

[0127] After frequency conversion by adding the intermediate frequency signal IF in the analog receiving front - end, the output is:

[0128] x 1 (t) = a(t)cos[ω IF t + θ(t)]

[0129] x 2 (t) = s·a(t - τ 0 )cos[ω IF t - ω RF τ 0 + θ(t - τ 0 )]

[0130] After sampling by the analog - to - digital converter A / D, the output is:

[0131] x 1 (n) = a(n)cos[ω I ′ F n + θ(n)]

[0132] x 2 (n) = s·a(n - τ 0 )cos[ω I ′ F n - ω RF τ 0 + θ(n - τ 0 )]

[0133] where a(n) is the sampling result of a(t), and ω I ′ F is the intermediate frequency after sampling.

[0134] Finally, through digital downconversion DDC, we can obtain:

[0135] x 1 (n) = a(n) exp[jθ(n)] exp(jω′ Δ n)

[0136] x 2 (n) = s·a(n - τ 0 ) exp[jθ(n - τ 0 )] exp(jω′ Δ n) exp(-jω RF τ 0 )

[0137] where ω′ Δ is the remaining frequency residual after the signal passes through analog and digital downconversion.

[0138] From the above calculations, the following conclusions can be drawn: 1) When the frequency response characteristics of the receiving channels are the same, the calibration needs to compensate for the time delay difference τ 0 caused by the antenna position, the inter-channel phase difference exp(-jω RF τ 0 ) caused by the signal carrier frequency and the antenna position, and the signal attenuation s caused by the projection conversion due to the antenna position and the path difference. Then, the signal output results of the two channels can be in-phase superimposed to complete digital beamforming. 2) Before digital beamforming, it is necessary to measure the frequency response between the two receiving channels first and compensate for the frequency response difference between the channels. This is the purpose of digital phased array channel calibration.

[0139] Taking the receiving beamforming as an example, preferably, a schematic diagram of channel calibration is given as Figure 4 shown, Figure 4 where τ A , G A (ω) are the time delay value at the center frequency and the frequency response after removing the time delay of the transmitting channel of the calibration signal source, respectively. τ B , G B (ω) are the time delay value at the center frequency and the frequency response after removing the time delay between the output end A of the calibration signal and the common feeder end B of the microstrip line, respectively. τ C , G C (ω) are the time delay value at the center frequency and the frequency response after removing the time delay from the output end A of the calibration signal to the probe (including the probe), respectively. τ Bi , G Bi($\omega$), $i = 1, 2, \ldots, M$ are the time delay values at the center frequency after removing the common feeder of the microstrip line of the $i$-th receiving channel, and the frequency response after deducting the time delay, where $M$ is the number of receiving channels. $\tau$ Di , $G$ Di ($\omega$), $i = 1, 2, \ldots, M$ are the time delay values at the center frequency from the mid-field calibration antenna to the antenna element to be measured of the $i$-th receiving channel, and the frequency response after deducting the time delay, $\tau$ Ei , $G$ Ei ($\omega$), $i = 1, 2, \ldots, M$ are the time delay values at the center frequency between the antenna element and the feeding point at the receiving backend within the $i$-th receiving channel, and the frequency response after deducting the time delay.

[0140] The calibration process of the received signal is as Figure 5 shown:

[0141] S1. According to the actual situation of the phased array antenna elements, a calibration network is formed by laying microstrip line antennas between the elements, and signals are transmitted between the microstrip lines and the elements through spatial coupling.

[0142] S2. Set up a mid-field calibration antenna at an appropriate position and calibrate the precise coordinates of the mid-field calibration antenna relative to the antenna to be measured.

[0143] S3. Perform internal calibration: According to the calibration control sequence of the calibration processing module, the calibration signals at each discrete frequency point are sent out through the microstrip line antenna in a time-sharing manner, and are respectively received by each element after spatial coupling. The signals are collected after passing through the antenna element → RF front end → analog-to-digital conversion → digital down-conversion, and the amplitude-frequency responses of the internal calibration at different frequency points of each element are obtained as the internal calibration reception result data and stored. Among them, the phase-frequency response obtained by internal calibration is:

[0144]

[0145] In the formula, is the frequency residue.

[0146] S4. Perform external calibration: According to the calibration control sequence of the calibration processing module, the calibration signals at each discrete frequency point are sent out by the mid-field calibration antenna. According to the coordinate position of the mid-field calibration antenna measured in step S2, the receiving beam is directed to the mid-field calibration antenna. The signals are collected after passing through spatial attenuation → antenna element → RF front end → analog-to-digital conversion → digital down-conversion, and the amplitude-frequency responses of the external calibration at different frequency points of each element are obtained as the external calibration reception result data and stored.

[0147] S5. According to the mid-field calibration antenna coordinates measured in step S2, perform compensation calculation on the external calibration received result data to obtain the corrected external calibration received result data, and eliminate the conversion differences in the antenna projection area caused by the non-parallel normal directions of each antenna element, the signal amplitude differences caused by the wave path difference, and the phase differences caused by the wave path difference.

[0148] Specifically, after eliminating the phase difference and amplitude difference brought by the antenna position information, the phase-frequency response obtained by external calibration is which is the frequency residue.

[0149] After the external calibration received result data is compensated by the accurate coordinates in step S2, it can be considered that the incident signals of the two channels are the same. Then, when taking channel 1 as the reference channel, the frequency response difference of channel 2 relative to the first channel can be expressed as:

[0150]

[0151] In practical applications, the frequency response is usually expressed as the amplitude-frequency response and the phase-frequency response, that is:

[0152]

[0153] where n 0 is the integer multiple time delay value brought by the A / D sampling of the receiving channel to the digital down-conversion output, is the phase-frequency response after deducting the integer multiple time delay value, which mainly depends on the phase-frequency characteristics of the analog channel from the antenna to before the A / D sampling.

[0154] S6. Calculate the ratio of the data of each element at different frequency points in the internal calibration received result data to the internal and external calibration results of each element at different frequency points in the corrected external calibration received result data to obtain the internal and external calibration error signals at different frequency points of each element; using the internal and external calibration error signals corresponding to two discrete frequency points within the broadband, the internal and external calibration relative time delay value Δτ i1 can be calculated, and then construct the phase difference exp(jωΔτ i1 ) of each frequency point, and compensate it to the internal and external calibration error signals corresponding to each discrete frequency point. After compensation, calculate the relative frequency response G 1 Δ(ω) of the internal and external calibration, and store the Δτ i1 and G 1 Δ(ω) of each element at different frequency points as the received error data in the file for subsequent use.

[0155] As can be seen from the above calculations, the true channel delay cannot be separated from the calibration signals collected in steps S3 and S4. Therefore, it is only necessary to pre-estimate the relative delay value between channels from the calibration signals and introduce the estimated delay value as the true delay value into the system calibration. The introduction of this error will not affect the system calibration because frequency response calibration must be performed after delay compensation. The following calculates the channel delay estimation:

[0156] Let the calibration data collected at frequency point i for channels 1 and 2 be respectively:

[0157]

[0158] Wherein, and are the amplitude-phase errors of channels 1 and 2 respectively, τ 0 is the delay of the calibration source in the transmitting channel, τ 1r , τ 2r are the delays of the calibration source in the two receiving channels respectively, T s is the sampling interval.

[0159] First, calculate the cross-correlation between channels at frequency point i, that is:

[0160]

[0161] In the formula, A 1i is the amplitude of channel 1, A 2i is the amplitude of channel 2, is the cross-correlation value between channels 1 and 2 at frequency point i, and * represents conjugation.

[0162] Then, for frequency points i and k, the cross-correlation between different frequencies of channels is:

[0163]

[0164] Finally, find the phase of the above cross-correlation, and there is:

[0165]

[0166] Wherein, f i , f k are the known RF frequencies, r ik is the known measured result, τ 1r -τ 2r is the true channel delay, unknown. It can be assumed that the estimated delay value between channels is Introduce it as the delay between channels into the system calibration, and its error can be corrected by the frequency response calibration after compensating the delay.

[0167] Furthermore, the selected frequency points i and k must satisfy angle(rik ) ≤ ±π, otherwise it will cause phase folding. At this time, it satisfies From the above calculations, it can be seen that it is particularly important to select an appropriate frequency difference within the bandwidth. The frequency difference f k - f i affects the estimation accuracy of the delay. The smaller the frequency difference, the worse the delay measurement accuracy. As the frequency difference increases, the delay measurement accuracy increases, but it will cause phase ambiguity. It also affects the maximum allowable relative time delay between channels, and the actual relative time delay between channels is related to the entire phased array system.

[0168] Specifically, in the preferred embodiment, f k - f i can be selected as 1 MHz. Then the maximum allowable relative delay between channels is 500 ns. If the difference in the active component part is considered to be small, the optical cable length corresponding to 500 ns is 150 meters. The optical cable difference between array elements generally does not exceed this magnitude. Different phased array systems can be selected according to actual needs. For example, some preferred implementation schemes can adopt the long and short baseline method, select 3 frequency points, construct 2 frequency differences, use the long frequency difference to increase the measurement accuracy, and the short frequency difference to increase the maximum allowable range.

[0169] Furthermore, combining the results of step S3 and step S5, select two appropriate frequency points within the working bandwidth, and calculate the internal and external calibration error time delay τ Δi1 through the above inter-channel time delay estimation, which satisfies:

[0170] τ Δi1 = (τ C + τ Di ) - (τ B + τ Bi )

[0171] Then construct the phase value exp(jωτ Δi1 ) at each frequency point and compensate it to the internal and external calibration error signals corresponding to each discrete frequency point.

[0172] After compensation, calculate the internal and external calibration relative frequency response G Δi1 (ω):

[0173]

[0174] After storing τ Δi1 , G Δi1 (ω) in a file, the first stage of the phased array calibration work is completed. The subsequent self-calibration work does not require the cooperation of the mid-field calibration antenna and only needs to be carried out by the microstrip line antenna laid after each power-on of the phased array channel.

[0175] S7. This step is carried out after each power-on of the phased array system and is a self-calibration step: according to the calibration control sequence of the calibration processing module, the calibration signals at each discrete frequency point are sent out by the microstrip antenna and received by each array element after spatial coupling. The amplitude-frequency response of the self-calibration at different frequency points of each array element is collected as the self-calibration result data and stored.

[0176] Specifically, the phase-frequency response obtained by self-calibration is where τ′ Ei is the time delay value at the center frequency between the antenna element and the input point of the receiving backend in the i-th receiving channel after a certain power-on for self-calibration.

[0177] S8. Compensate the Δτ i1 and G 1 Δ(ω) at different frequency points of each array element obtained in step S6 into the self-calibration result data, and eliminate the frequency response differences caused by different responses of each node on the calibration network.

[0178] Specifically, read τ Δi1 from step S6, and supplement the internal and external calibration error time delays at each frequency point into the self-calibration time delay. The compensated result can be obtained

[0179]

[0180] where τ A +τ C +τ Di is a fixed constant for a single array element, and τ′ Ei can be replaced by a new value after each self-calibration startup.

[0181] The frequency response after deducting the above time delay is

[0182]

[0183] where G 自 (ω) is the self-calibration frequency response after compensating the time delay, and G′ Ei (ω) is the frequency response result after deducting the time delay after a certain power-on for self-calibration, and can be replaced by a new value after each startup.

[0184] It can be calculated from the above formula that through the calibration method provided by the present invention, through three different calibration methods, the time delay error τ B +τ Bi and the frequency response error G B (ω)·G Bi after deducting the time delay can be eliminated. That is, in the self-calibration result of each startup, compensate the internal and external calibration error results and eliminate the influence of the calibration network.

[0185] S9. Taking a certain channel as a reference, using two discrete frequency points near the center frequency point of the frequency band, calculate the relative time delay value Δτ between channels i2 , then construct the phase difference of each frequency point and perform compensation. After compensation, calculate the relative frequency response G 2 Δ(ω) of each channel, and compensate this result to each channel to complete the reception correction.

[0186] Specifically, taking a certain channel as a reference, using the calibration signals corresponding to two discrete frequency points near the center frequency point, calculate the relative time delay between channels through the above-mentioned relative time delay value estimation between channels. For example, taking channel 1 as a reference, the time delay τ of it relative to other channels can be obtained R1,i as:

[0187] τ R1,i =(τ D1 +τ E1 )-(τ Di +τ Ei )

[0188] τ R1,i is the time delay of the analog signal, then construct the phase value exp(jωτ R1,i ) at each frequency point, and compensate it into the calibration signals corresponding to each discrete frequency point. After compensation, calculate the relative frequency response G′ DE1,i (ω) between each channel, which satisfies:

[0189]

[0190] In the formula, k R1,i is the channel time delay of the digital signal, and G′ DEi (ω) is the relative frequency response between each channel.

[0191] It should be particularly noted that the above embodiments are for the case where the signal bandwidth of the broadband phased array system is broadband. When the signal bandwidth of the broadband phased array system is narrowband or the antenna system is a narrowband phased array system, the amplitude and phase at other frequencies between the working channels are very close to the amplitude and phase at the center frequency. Therefore, there is no need to estimate the time delay between channels. For each discrete frequency point i within the broadband / narrowband, the relative frequency response of each channel can be directly obtained and then compensated to each channel. (The influence of the calibration network must be eliminated according to the internal and external calibration difference method proposed by the present invention). When the signal bandwidth of the system is broadband, the time delays of the frequency points i and k within the signal bandwidth are obviously not equal and cannot be directly compensated.

[0192] In addition, as Figure 6 shown, the second embodiment of the present invention also proposes a general mid-field calibration method for an asymmetric conformal broadband digital phased array antenna. The method is used for transmission calibration and includes the following steps:

[0193] After the phased array system is powered on, according to the calibration control sequence, each array element sends calibration signals at different times. After being spatially coupled, the signals are received by the built-in calibration network, and the self-calibration transmission result data at different frequency points output by the calibration network is collected.

[0194] S202. Compensate the pre-calculated transmission error data into the self-calibration transmission result data to obtain the self-calibration transmission result data after removing the delay error and frequency response error as the corrected self-calibration transmission result data. Among them, the transmission error data includes the relative internal and external calibration delay values and the relative frequency responses at different frequency points of each array element calculated from the calibration signals received by the built-in calibration network and the mid-field calibration antenna.

[0195] S203. Taking a certain array element channel in the corrected self-calibration transmission result data as the reference channel, calculate the relative frequency response of this reference channel relative to other channels and compensate the relative frequency response to the corresponding channels to complete the mid-field calibration.

[0196] It should be noted that the transmission calibration is similar to the reception calibration. The differences are as follows:

[0197] In the reception calibration, the transmission direction of the calibration signal is: calibration processing module → microstrip line / mid-field calibration antenna → antenna array → acquisition.

[0198] In the transmission calibration, the transmission direction of the calibration signal is: antenna array → microstrip line / mid-field calibration antenna → calibration processing module → acquisition.

[0199] The specific process of the transmission calibration is as Figure 7 shown and includes:

[0200] S1’. According to the actual situation of the phased array antenna elements, microstrip antennas are laid between the elements, and signals are transmitted between the microstrip lines and each element through spatial coupling.

[0201] S2’. Install a mid-field calibration antenna at a suitable position and calibrate the precise coordinates of the mid-field calibration antenna relative to the antenna under test.

[0202] S3’. Perform internal calibration: According to the calibration control sequence of the calibration processing module, each array element sends calibration signals at different times for each discrete frequency point. The signals pass through the antenna array → microstrip line → calibration processing module → acquisition to obtain the calibration signals at different frequency points output by each microstrip antenna as the internal calibration transmission result data and store it.

[0203] S4’. Perform external calibration: According to the calibration control sequence of the calibration processing module, calibration signals of each discrete frequency point are sent out by each transmitting channel at different times, received by the mid-field calibration antenna, and calibration signals of different discrete frequency points of each transmitting channel are collected and stored as external calibration transmission result data.

[0204] S5’. According to the coordinates of the mid-field calibration antenna measured in step S2’, perform compensation calculation on the external calibration transmission result data to eliminate the phase difference and amplitude difference caused by the probe position.

[0205] S6’. Calculate the ratio of the internal and external calibration transmission results of each discrete frequency point after correction to obtain the internal and external calibration error signals at different frequency points of each array element. Using the internal and external calibration error signals corresponding to two discrete frequency points within the broadband, the relative time delay value Δτ of internal and external calibration can be calculated. i1 , and then construct the phase difference of each frequency point exp(jωΔτ i1 ), and compensate it to the internal and external calibration error signals corresponding to each discrete frequency point. After compensation, calculate the relative frequency response G 1 Δ(ω) of internal and external calibration. Store the Δτ i1 and G 1 Δ(ω) of each array element at different frequency points in a file for subsequent use.

[0206] S7’. This step is carried out after each power-on of the phased array system and is self-calibration: According to the calibration control sequence of the calibration processing module, each array element sends calibration signals at different times, and calibration signals of each discrete frequency point output by each microstrip line are collected and stored as self-calibration transmission results.

[0207] S8’. Compensate the Δτ i1 and G 1 Δ(ω) of each array element at different frequency points obtained in step S6’ into the self-calibration transmission results to eliminate the frequency response differences caused by different responses of each node on the calibration network.

[0208] S9’. Taking a certain channel as a reference, use two discrete frequency points near the center frequency of the frequency band to calculate the relative time delay value Δτ i2 of channels, and then construct the phase difference of each frequency point and perform compensation. After compensation, calculate the relative frequency response G 2 Δ(ω) of each channel, and compensate this result to each channel to complete the calibration.

[0209] Its method and idea are exactly the same and will not be elaborated here.

[0210] It should be noted that the method and idea of the general mid-field calibration method for the asymmetric conformal broadband digital phased array antenna of the present invention for performing transmission calibration are exactly the same as those for performing reception calibration. Other embodiments or implementation methods can refer to Embodiment 1 of the above method, and will not be repeated here.

[0211] It should be specifically noted that, due to its extremely wide application range and numerous applicable scenarios, the present invention can be used to correct all or part of the correction methods proposed in the present invention for narrowband phased arrays, wideband phased arrays with narrowband signal bandwidths, planar phased arrays, phased arrays with controllable time delays in antenna active components, etc. The embodiments of the present invention are described and implemented for the most complex situations among the above various phased array systems. All embodiments implemented by using all or part of the correction methods proposed in the present invention for other relatively simple phased array systems fall within the scope of protection of the present invention.

[0212] In the description of this specification, the description with reference to terms such as "one embodiment", "some embodiments", "example", "specific example", or "some examples" means that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in a suitable manner in any one or more embodiments or examples.

[0213] In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include at least one of the features. In the description of the present invention, the meaning of "a plurality" is at least two, such as two, three, etc., unless otherwise specifically and clearly defined.

[0214] Although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those of ordinary skill in the art can make changes, modifications, substitutions, and variations to the above embodiments within the scope of the present invention.

Claims

1. A universal mid-field correction method for an asymmetric conformal broadband digital phased array antenna, characterized in that: The method comprises: After the phased array system is powered on, according to the correction control sequence, the calibration signals of each discrete frequency point are sent out through the built-in correction network, and are received by each array element after spatial coupling, and the self-correction reception result data of different frequency points output by each array element are collected. The correction network is composed of a number of microstrip line antennas laid between the array elements of the phased array antenna; The pre-calculated receiving error data is compensated to the self-correction receiving result data to obtain the self-correction receiving result data after the delay error and the frequency response error are eliminated as the corrected self-correction receiving result data, wherein the receiving error data includes the internal and external correction relative delay values ​​and the relative frequency responses of the internal and external correction corresponding to different frequency points of each array element calculated by the calibration signal sent by the built-in correction network and the mid-field correction antenna, and the calculation process of the receiving error data includes: according to the correction control sequence, the calibration signal of each discrete frequency point is respectively sent through the built-in correction network and the mid-field correction antenna to respectively obtain the internal correction receiving result data and the external correction receiving result data of different frequency points of each array element; using the coordinates of the mid-field correction antenna, the external correction receiving result data is compensated and calculated to obtain the corrected external correction receiving result data; based on the internal correction receiving result data corresponding to each frequency point and the corrected external correction receiving result data, the internal and external correction relative delay values ​​at each frequency point and the relative frequency responses of the internal and external correction at different frequency points are calculated and used as the receiving error data; Taking a certain array element channel in the corrected self-correction reception result data as a reference channel, the relative frequency response of the reference channel relative to other channels is calculated and the relative frequency response is compensated to the corresponding channel to complete the mid-field correction.

2. The universal mid-field correction method for an asymmetric conformal broadband digital phased array antenna according to claim 1, characterized in that: According to the correction control sequence, the calibration signals of each discrete frequency point are respectively sent through the built-in correction network and the mid-field correction antenna to obtain the internal correction reception result data and the external correction reception result data of different frequency points of each array element, including: According to the correction control sequence, the calibration signals of each discrete frequency point are sent out through the correction network in a time-sharing manner, and after being spatially coupled to each array element structure, the amplitude-frequency response of each array element at different frequency points is acquired as the internal correction reception result data; According to the correction control sequence, the calibration signal of each discrete frequency point is sent out through the mid-field correction antenna and then collected through each array element structure to obtain the amplitude-frequency response of each array element at different frequencies as the external correction reception result data.

3. The universal mid-field correction method for an asymmetric conformal broadband digital phased array antenna according to claim 1, characterized in that: Before the calibration signals of each discrete frequency point are respectively sent out through the built-in calibration network and the mid-field calibration antenna according to the calibration control sequence to respectively obtain the internal calibration reception result data and the external calibration reception result data of different frequency points of each array element, the method further includes: The mid-field correction antenna is set up, and the position coordinates of the mid-field correction antenna relative to the phased array antenna to be measured are calibrated.

4. The universal mid-field correction method for an asymmetric conformal broadband digital phased array antenna according to claim 3, characterized in that: The distance between the mid-field correction antenna and the phased array antenna to be measured satisfy: ,in, is the midfield distance from the midfield correction antenna to the phased array antenna to be measured, The normal tolerance distance from the mid-field correction antenna to the phased array antenna to be measured is defined as:

5. The universal mid-field correction method for an asymmetric conformal broadband digital phased array antenna according to claim 1, characterized in that: The method of using the coordinates of the mid-field correction antenna to perform compensation calculation on the external correction reception result data to obtain the corrected external correction reception result data includes: Based on the coordinates of the mid-field correction antenna, a compensation coefficient and a multipath correction factor are used to perform compensation calculation on the external correction reception result data to obtain corrected external correction reception result data; The compensation coefficient is used to compensate for the difference in wave path and normal direction between the mid-field correction antenna and the phased array antenna to be measured due to the mid-field effect. The formula of the compensation coefficient is expressed as follows: In the formula, represents the compensation coefficient, Indicates the mid-field correction antenna and the phased array antenna i The angle between the line connecting the antenna elements and the radiation direction of the mid-field correction antenna is Indicates the mid-field correction antenna and the phased array antenna i The angle between the line connecting the antenna elements and the radiation direction of the phased array antenna, Indicates the distance from the midfield correction antenna to the phased array antenna to be tested. i The distance between the antenna elements to be tested, represents the free space wave number corresponding to the operating frequency, Indicates plural; The multipath correction factor is used to eliminate the multipath component in the external correction reception result data. The formula of the multipath correction factor is expressed as: In the formula, represents the multipath correction factor, Indicates the length of the maximum reflection path of the multipath effect in the correction scenario, Indicates the electromagnetic wave reflection coefficient of the reflecting surface in the maximum reflection path of the multipath effect in the correction scene.

6. The universal mid-field correction method for an asymmetric conformal broadband digital phased array antenna according to claim 1, characterized in that: The internal correction receiving result data corresponding to each frequency point and the corrected external correction receiving result data are used to calculate the relative delay value of the internal and external correction at each frequency point and the relative frequency response of the internal and external correction at different frequency points as the receiving error data, including: Calculate the ratio of the internal correction reception result data corresponding to each frequency point to the corrected external correction reception result data to obtain the internal and external correction error signals at different frequency points of each array element; According to the internal and external correction error signals corresponding to two discrete frequency points in the broadband, the internal and external correction relative delay values ​​at each frequency point are calculated; Construct the phase difference value at each frequency point according to the relative delay value of the internal and external correction at each frequency point; Compensating the phase difference at each frequency point to the internal and external correction error signal at each frequency point to obtain the relative frequency response of the internal and external correction at each frequency point; The relative time delay value of the internal and external correction at each frequency point and the relative frequency response of the internal and external correction at each frequency point are used as the receiving error data.

7. The universal mid-field correction method for an asymmetric conformal broadband digital phased array antenna according to claim 1, characterized in that: The step of compensating the pre-calculated receiving error data to the self-correction result data to obtain the self-correction result data after eliminating the delay error and the frequency response error as the corrected self-correction result data includes: The internal and external correction relative delay values ​​at each frequency point are used to fill in the self-correction delay in the self-correction result data to obtain the compensated self-correction delay; Compensating the self-corrected frequency response after the delay compensation by using the relative frequency response of the internal and external corrections at each frequency point, to obtain a frequency response result after the delay is deducted; The compensated self-correction delay and the frequency response result after the delay is subtracted are used as the corrected self-correction result data.

8. The universal mid-field correction method for an asymmetric conformal broadband digital phased array antenna according to claim 1, characterized in that: The method of taking a certain array element channel in the corrected self-correction result data as a reference channel, calculating the relative frequency response of the reference channel relative to other channels and compensating the relative frequency response to the corresponding channel to complete the midfield correction includes: Taking a certain array element channel in the corrected self-calibration result data as a reference channel, calculating a relative delay value of the reference channel relative to other channels; Based on the relative delay value of the reference channel relative to other channels, the phase difference value at each frequency point is constructed; According to the phase difference at each frequency point, the relative frequency response between each array element channel is compensated and calculated.

9. A universal mid-field correction method for an asymmetric conformal broadband digital phased array antenna, characterized in that: The method comprises: After the phased array system is powered on, according to the correction control sequence, each array element sends a correction signal in time division, which is received by the built-in correction network after spatial coupling, and the self-correction transmission result data of different frequency points output by the correction network is collected. The correction network is composed of several microstrip line antennas laid between the array elements of the phased array antenna; The pre-calculated transmission error data is compensated to the self-correction transmission result data to obtain the self-correction transmission result data after the delay error and the frequency response error are eliminated as the corrected self-correction transmission result data, wherein the transmission error data includes the internal and external correction relative delay values ​​and the relative frequency responses of the internal and external correction corresponding to different frequency points of each array element calculated by the calibration signal received by the built-in correction network and the mid-field correction antenna, and the calculation process of the transmission error data includes: according to the correction control sequence, each array element sends out the correction signal of each discrete frequency point in a time-sharing manner, and receives it through the built-in correction network and the mid-field correction antenna respectively, so as to obtain the internal correction transmission result data and the external correction transmission result data of different frequency points of each array element respectively; using the coordinates of the mid-field correction antenna, the external correction transmission result data is compensated and calculated to obtain the corrected external correction transmission result data; based on the internal correction transmission result data corresponding to each frequency point and the corrected external correction transmission result data, the internal and external correction relative delay values ​​at each frequency point and the relative frequency responses of the internal and external correction at different frequency points are calculated and used as the transmission error data; Taking a certain array element channel in the corrected self-correction transmission result data as a reference channel, the relative frequency response of the reference channel relative to other channels is calculated and the relative frequency response is compensated to the corresponding channel to complete the mid-field correction.

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