CN116684239A - Zero intermediate frequency receiving array IQ imbalance wave beam level compensation method - Google Patents
Zero intermediate frequency receiving array IQ imbalance wave beam level compensation method Download PDFInfo
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Abstract
The invention discloses a zero intermediate frequency receiving array IQ imbalance wave beam level compensation method, which comprises the following steps: acquiring radio frequency signals received by each array element; obtaining M intermediate frequency analog signals; obtaining M baseband analog in-phase signals and M baseband analog quadrature signals; the M baseband analog in-phase signals and the M baseband analog quadrature signals are respectively subjected to A/D sampling to obtain M baseband digital complex signals; obtaining M receiving channel amplitude-phase error compensation values; channel amplitude-phase error compensation and beam weighting compensation are carried out on M baseband digital complex signals of a digital array, and summation is carried out, so that a beam forming output complex signal is obtained; estimating and compensating an IQ imbalance error after beam forming by utilizing the round characteristic of the received baseband digital complex signal to obtain a final baseband digital complex signal of the digital array; the invention has the advantages that: a multi-channel IQ imbalance compensation method is provided that does not require channel-by-channel estimation and compensation of IQ imbalance errors and protects the circular nature of the communication signal from corruption.
Description
Technical Field
The invention relates to the field of IQ imbalance compensation, in particular to a zero intermediate frequency receiving array IQ imbalance wave beam level compensation method.
Background
With the continuous progress of digital signal processing technology and continuous improvement of corresponding processing capacity, digital arrays have gradually replaced analog array antennas due to the characteristics of multiple scanning beams, high design flexibility and the like, and become a main research direction in the technical field of electronic information such as communication, countermeasure, radar and the like. Digital arrays typically employ superheterodyne intermediate frequency sampling receivers (including multi-stage analog down-conversion and filtering, a/D intermediate frequency sampling, digital down-conversion, etc.) to convert the received rf analog signals from each array antenna to baseband digital signals.
Compared with a superheterodyne intermediate frequency sampling receiver, the zero intermediate frequency receiver has the advantages of simple circuit structure, low power consumption, easiness in integration, small volume, low cost and the like. The digital array constructed by multichannel zero intermediate frequency receiving has the characteristics of low cost, low power consumption, high integration and the like, and is an important direction of the current digital array development. In practical engineering, due to the limitation of the current device technology level, the quadrature local oscillation frequency sources used by the in-phase (I branch) and quadrature (Q branch) branches in the zero intermediate frequency receiving chip cannot guarantee absolute orthogonality, and the amplitude-frequency response of analog devices such as mixers, low-pass filters and the like of each branch cannot guarantee complete consistency, so that a certain amplitude-phase error (commonly called IQ imbalance error) exists between the in-phase and quadrature branches. When the IQ imbalance error is too large, the signals received by each channel of the digital array are severely distorted, and the overall performance index of the receiving array is greatly affected. Therefore, the research of the IQ imbalance error compensation method of the zero intermediate frequency receiving array has very high practical value.
Currently, there are many researches on IQ imbalance compensation methods of single-channel zero intermediate frequency receivers, for example, a method for correcting IQ imbalance of zero intermediate frequency receiver disclosed in chinese patent publication No. CN115833957 a. But IQ imbalance compensation methods using multichannel zero intermediate frequency receivers in digital arrays are discussed. If the single-channel IQ imbalance image suppression method is directly applied to the digital array, after the IQ imbalance errors of all channels are respectively estimated and compensated, the processing such as beam synthesis is carried out, and the system calibration complexity and the calculation amount are very large. In addition, in the field of cooperative communication, there are a class of communication signals of modulation types such as QPSK, 8PSK, etc., which have circular characteristics (the real part and the imaginary part of the complex envelope are equal in energy and statistically independent), and are widely used in various communication scenarios (such as satellite data transmission). Such communication signals having circular characteristics are received via digital arrays having IQ imbalance errors, which are destroyed.
In order to reduce the complexity of digital array channel calibration and avoid the distortion of communication signals with circular characteristics, it is necessary to find an IQ imbalance beam level compensation method capable of fully utilizing the circular characteristics of signals, so as to not only protect the circular characteristics of the communication signals from being damaged as much as possible, but also avoid estimating and compensating IQ imbalance errors channel by channel, and solve the problem of IQ imbalance compensation of zero intermediate frequency receiving arrays.
Disclosure of Invention
The technical problem to be solved by the invention is to provide a multichannel IQ imbalance compensation method without estimating and compensating IQ imbalance errors channel by channel, and fully utilize the signal circle characteristics to protect the circle characteristics of communication signals from being destroyed.
The invention solves the technical problems by the following technical means: a zero intermediate frequency receiving array IQ imbalance wave beam level compensation method comprises the following steps:
step 1: the digital array is provided with M array elements, and radio frequency signals received by each array element are obtained;
step 2: filtering and amplifying the radio frequency signals to obtain M intermediate frequency analog signals;
step 3: mixing and low-pass filtering are respectively carried out on the M intermediate frequency analog signals, the M in-phase local oscillator signals and the M quadrature local oscillator signals, and M baseband analog in-phase signals and M baseband analog quadrature signals are obtained;
step 4: the M baseband analog in-phase signals and the M baseband analog quadrature signals are respectively subjected to A/D sampling to obtain M baseband digital complex signals;
step 5: before beam synthesis is carried out on the digital array, amplitude-phase consistency of M receiving channels is calibrated, and M receiving channel amplitude-phase error compensation values are obtained;
step 6: channel amplitude-phase error compensation and beam weighting compensation are carried out on M baseband digital complex signals of a digital array, and summation is carried out, so that a beam forming output complex signal is obtained;
step 7: and estimating and compensating the IQ imbalance error after beam forming by utilizing the round characteristic of the received baseband digital complex signal to obtain the final baseband digital complex signal of the digital array.
Further, the step 1 includes:
the radio frequency signal received by the m-th array element is
x m (t)＝A(t)cos[Ω c (t-τ m )+φ(t)]m＝1,…,M
Wherein A (t) is amplitude modulation information, phi (t) is phase modulation information, omega c For the carrier analog angular frequency of the received signal, τ m The time delay difference is determined by the array element coordinates and the signal incidence direction, t is the current moment, and M is the total number of the array elements.
Still further, the step 2 includes:
the intermediate frequency analog signal obtained after the m-th array element is filtered and amplified is
wherein ,Acm Andthe amplitude and phase errors are brought about by the preselection filters and the low noise amplifiers of the channels, respectively.
Still further, the step 3 includes:
baseband analog in-phase signal I of mth channel m Baseband analog quadrature signals Q of (t) and mth channels m (t) are respectively
wherein , and />The low-pass filters of the in-phase branches in the mth channel are respectively +.>Induced amplitude and phase errors; /> and />Local oscillation frequency sources of in-phase branches in an mth channel are respectively adopted>Induced amplitude and phase errors; /> and />The low-pass filters of the quadrature branches in the mth channel are respectively +.>Induced amplitude and phase errors; /> and />Local oscillation frequency sources of orthogonal branches in an mth channel are respectively +.>The resulting amplitude and phase errors.
Still further, the step 4 includes:
baseband digital complex signal z of mth channel m (n) is
wherein , T s for A/D sampling period, n is nT s Index of time sample values.
Still further, the step 5 includes:
step 5-1, placing a single-frequency correction source in the normal direction of the digital array, calculating single-frequency signals radiated by the correction source, acquiring baseband digital complex signals of M channels through each channel of the zero intermediate frequency receiving array based on the influence of the single-frequency signals radiated by the correction source, and obtaining the baseband digital complex signals of M receiving channelsIs a sample of N samples;
step 5-2, for the mth channel, first calculate the fast Fourier transform of the N samples, then extract at frequency Ω d Spectral value Sp at m Corresponding amplitude value Ap m ；
Step 5-3, for M channel amplitude valuesSorting from small to large, selecting channel number r E [1, M corresponding to amplitude median after sorting]Selecting the r channel as a reference channel, and selecting the r channel amplitude value Ap r As the average value of normal channel decisions;
step 5-4, threshold A of given normal channel decision thr Calculating the upper amplitude limit Ap of the normal channel decision U And a lower limit Ap L Generating M channel normal identifiers CFg m ；
Step 5-5, using the spectral value Sp of the r-th channel r For reference, by the formulaCalculating the amplitude-phase error correction of each receiving channel relative to the r-th channel>Wherein, superscript is complex conjugate operation;
step 5-6, for the mth channel, the channel amplitude and phase error correction is rewritten as
Step 5-7, calculating M channels amplitude-phase error correction quantityAmplitude maximum of +.>And pass the formula +.>Normalizing the amplitude and phase error correction amounts of all channels to obtain a final channel amplitude and phase error compensation value +.>
Still further, the step 5-1 includes:
correcting the single frequency signal of source radiation to s c (t)＝A 0 cos[(Ω c +Ω d )t+φ 0 ]
wherein ,φ0 For initial phase, A 0 Is the amplitude of the single frequency signal, omega d Is the frequency offset of single frequency signal omega d ＝2πk 0 /(NT s )>0，k 0 Is a positive integer and 0<k 0 <N/2，N＝2 b B is a positive integer for collecting the number of samples;
baseband digital complex signals for M receive channelsIs of (1)
Still further, the step 5-4 includes:
threshold A for a given normal channel decision thr By the formulaCalculating the upper amplitude limit Ap of normal channel decision U And a lower limit Ap L Then ∈0 through the formula->M channel normal identifications are generated.
Still further, the step 6 includes:
the beam forming output complex signal z (n) is represented as
wherein ,beam weighting coefficient of mth array element, alpha m For the amplitude weighting value of the mth array element in the array, the maximum value thereof satisfies +.>s (n) is the target baseband digital complex signal and +.>λ 1 and λ2 Respectively a first coefficient and a second coefficient, respectively, expressed as
Still further, the step 7 includes:
step 7-1, through the formulaAnd formula->Calculating the autocorrelation function value gamma of the beam forming output complex signal z (n) s And complementary autocorrelation function c s Wherein L is the number of samples required to estimate the IQ imbalance error of the beamformed output;
step 7-2, utilizing the autocorrelation function value gamma s And complementary autocorrelation function c s Compensation coefficient w for IQ imbalance error opt Estimation is performed, i.e
Step 7-3, compensation coefficient w using IQ imbalance error opt Compensating the beam synthesis output data to obtain final baseband digital complex signalI.e. < ->
The invention has the advantages that:
(1) The invention provides a beam-level IQ imbalance estimation and compensation method, which does not need to estimate and compensate IQ imbalance errors channel by channel, only needs to estimate and compensate the channel-to-channel amplitude phase inconsistency and the IQ imbalance errors after beam forming, fully utilizes the round characteristics of a received baseband digital complex signal, and protects the round characteristics of a communication signal from being destroyed, thus being particularly suitable for occasions with round characteristics of communication signals processed by a digital array.
(2) The zero intermediate frequency receiving channel calibration algorithm and the IQ imbalance estimation and compensation algorithm provided by the invention have the advantages of simple principle, small operand and convenience for engineering realization.
(3) The method provided by the invention is not limited by the array structure, and is applicable to both planar digital arrays and conformal digital arrays. In addition, the method of the present invention is applicable not only to digital receiving arrays, but also to digital transmitting arrays.
Drawings
Fig. 1 is a flowchart of a method for compensating IQ imbalance beam levels of a zero intermediate frequency receiving array according to an embodiment of the present invention;
fig. 2 is a schematic diagram of estimation accuracy of channel amplitude error when a signal-to-noise ratio is 15dB in an IQ imbalance beam level compensation method of a zero intermediate frequency receiving array according to an embodiment of the present invention;
fig. 3 is a schematic diagram of estimation accuracy of channel phase error when the signal-to-noise ratio is 15dB in the IQ imbalance beam level compensation method of a zero intermediate frequency receiving array according to an embodiment of the present invention;
FIG. 4 is a diagram of uncompensated IQ imbalance error, target and mirror beam patterns when the beam direction is 20 degrees in an IQ imbalance beam level compensation method for a zero intermediate frequency receiving array according to an embodiment of the present invention;
FIG. 5 is a diagram of uncompensated IQ imbalance error, target and mirror beam patterns when the beam direction is 60 degrees in an IQ imbalance beam level compensation method for a zero intermediate frequency receiving array according to an embodiment of the present invention;
FIG. 6 is a diagram of IQ imbalance compensation method for zero intermediate frequency receiving array, wherein the IQ imbalance error is compensated when the beam direction is 20 degrees, and the target and mirror image beam patterns are shown in the embodiment of the invention;
FIG. 7 is a diagram of IQ imbalance compensation method for zero intermediate frequency receiving array, wherein the IQ imbalance error is compensated when the beam direction is 60 degrees, and the target and mirror image beam patterns are shown in the embodiment of the invention;
FIG. 8 is a graph showing the variation of the image rejection ratio with the number of sampling points when the signal-to-noise ratio is 15dB in the IQ imbalance beam level compensation method of the zero intermediate frequency receiving array according to the embodiment of the invention;
FIG. 9 is a graph showing the variation of the estimation accuracy of IQ imbalance amplitude error with the number of sampling points in an IQ imbalance beam level compensation method of a zero intermediate frequency receiving array according to an embodiment of the present invention;
fig. 10 is a graph showing the variation of the estimation accuracy of IQ-imbalance phase error with the number of sampling points in the IQ-imbalance beam level compensation method of the zero intermediate frequency receiving array according to the embodiment of the present invention.
Detailed Description
For the purpose of making the objects, technical solutions and advantages of the embodiments of the present invention more apparent, the technical solutions in the embodiments of the present invention will be clearly and completely described in the following in conjunction with the embodiments of the present invention, and it is apparent that the described embodiments are some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
As shown in fig. 1, the present invention provides a zero intermediate frequency receiving array IQ imbalance beam level compensation method, comprising the following steps:
step 1: the digital array has M array elements, and the radio frequency signal received by each array element is obtained by the specific process:
the radio frequency signal received by the m-th array element is
x m (t)＝A(t)cos[Ω c (t-τ m )+φ(t)]m＝1,…,M
Wherein A (t) is amplitude modulation information, phi (t) is phase modulation information, omega c For the carrier analog angular frequency of the received signal, τ m Is the time delay difference determined by the array element coordinates and the signal incidence direction.
Step 2: the method comprises the steps of filtering and amplifying radio frequency signals to obtain M intermediate frequency analog signals, wherein the specific process is as follows:
m radio frequency signals received by digital arrayAfter passing through a preselection filter and a low noise amplifier, M radio frequency signals amplified by filtering are obtained>I.e.
wherein ,Acm Andthe amplitude and phase errors are brought about by the preselection filters and the low noise amplifiers of the channels, respectively.
Step 3: mixing and low-pass filtering are respectively carried out on M intermediate frequency analog signals, M in-phase local oscillator signals and M quadrature local oscillator signals to obtain M baseband analog in-phase signals and M baseband analog quadrature signals, wherein the specific process is as follows:
m intermediate frequency analog signalsWith M in-phase local oscillator signals->And M orthogonal local oscillator signalsMixing and low-pass filtering are respectively carried out to obtain M baseband analog in-phase signals>And M baseband analog quadrature signals->I.e.
wherein , and />The low-pass filters of the in-phase branches in the mth channel are respectively +.>The resulting amplitude and phase errors. /> and />Local oscillation frequency sources of in-phase branches in an mth channel are respectively adopted>The resulting amplitude and phase errors. /> and />The low-pass filters of the quadrature branches in the mth channel are respectively +.>The resulting amplitude and phase errors. /> and />Local oscillation frequency sources of orthogonal branches in an mth channel are respectively +.>The resulting amplitude and phase errors.
Step 4: the M baseband analog in-phase signals and the M baseband analog quadrature signals are respectively subjected to A/D sampling to obtain M baseband digital complex signals, wherein the specific process is as follows:
m baseband analog in-phase signalsAnd M baseband analog quadrature signals->Respectively carrying out A/D sampling to obtain M baseband digital complex signals +.>I.e.
wherein , T s for the a/D sampling period.
Step 5: before beam forming is carried out on the digital array, the amplitude-phase consistency of M receiving channels is calibrated, and amplitude-phase error compensation values of the M receiving channels are obtained, wherein the specific process is as follows:
step 5-1: the single-frequency correction source is placed in the normal direction of the digital array, the far-field condition of the array is met, and the single-frequency signal radiated by the correction source is
s c (t)＝A 0 cos[(Ω c +Ω d )t+φ 0 ]
wherein ,φ0 For initial phase, A 0 Is the amplitude of the single frequency signal, omega d For frequency offset of single frequency signal, requiring Ω d ＝2πk 0 /(NT s )>0，k 0 Is a positive integer and 0<k 0 <N/2，N＝2 b For the number of samples collected, b is a positive integer greater than 0. Acquiring each channel of the zero intermediate frequency receiving array to obtain baseband digital complex signals of M receiving channelsHas N samples of
Step 5-2: correction samples in M channelsThe processing mode is the same. For the mth channel, a Fast Fourier Transform (FFT) of N corrected samples is first calculated, i.e
Then extracting at frequency Ω d Spectral value Sp at m Corresponding amplitude value Ap m I.e.
Ap m ＝20log 10 (|Z cm (k 0 )|)
Step 5-3: for M channel amplitude valuesSorting from small to large, selecting channel number r E [1, M corresponding to amplitude median after sorting]Selecting the r channel as a reference channel, and selecting the r channel amplitude value Ap r As the average of the normal channel decisions.
Step 5-4: threshold A for a given normal channel decision thr First, the upper amplitude limit Ap of the normal channel decision is calculated U And a lower limit Ap L I.e.
Ap U ＝Ap r +A thr
Ap L ＝Ap r -A thr
Then generating M channels normal marksI.e. the normal identification of the mth channel is
Step 5-5: with spectral value Sp of the r-th channel r For reference, the amplitude-phase error correction quantity of each receiving channel relative to the r-th channel is calculatedI.e.
Wherein, superscript is complex conjugate operation.
Step 5-6: normal identification according to channelCorrection of channel amplitude and phase errors +.>Processing to eliminate the influence of abnormal channel, i.e. for the mth channel, the channel amplitude-phase error correction is rewritten as
Step 5-7: calculating M-channel amplitude-phase error correctionAmplitude maximum of +.>I.e.
And normalizing the amplitude-phase error correction amounts of all channels by the maximum value to obtain the final channel amplitude-phase error compensation valueI.e.
Step 6: channel amplitude and phase error compensation and beam weighting compensation are carried out on M baseband digital complex signals of a digital array, and summation is carried out, so that beam forming output complex signals are obtained, and the specific process is as follows:
m baseband digital complex signals for a digital arrayChannel error compensation and beam weighting compensation are performed and summed to obtain a beam formed output complex signal z (n), i.e
wherein ,and the beam weighting coefficient of the m-th array element. Alpha m For the amplitude weighting value of the mth array element in the array, the maximum value thereof satisfies +.>The target baseband digital complex signal s (n) can be expressed as
Coefficient lambda 1 and λ2 Respectively denoted as
Step 7: estimating and compensating the IQ imbalance error after beam forming by utilizing the round characteristic of the received baseband digital complex signal to obtain the final baseband digital complex signal of the digital array, wherein the specific process comprises the following steps:
step 7-1: calculating the autocorrelation function value gamma of the beam-forming output signal z (n) s And complementary autocorrelation function c s I.e.
Where L is the number of samples required to estimate the IQ imbalance error of the beamformed output.
Step 7-2: using autocorrelation function values gamma s And complementary autocorrelation function c s Compensation coefficient w for IQ imbalance error opt Estimation is performed, i.e
Step 7-3: compensation coefficient w using IQ imbalance error opt Compensating the beam synthesis output data to obtain final baseband digital complex signalI.e.
Based on the detailed technical scheme of the invention, IQ imbalance error estimation and compensation can be performed by receiving the digital array beam synthesis output at zero intermediate frequency. Through three scenes of simulation experiments, the accuracy of the IQ imbalance beam level compensation method of the zero intermediate frequency receiving digital array is verified.
In the simulation experiment, the radio frequency of the system operation is 8GHz, the sampling rate of the system is 30MHz, the digital array is a uniform linear array, the array element spacing is 11mm, the number of the array elements is 64, and the uniform linear array adopts uniform weighting.
Scene 1: channel amplitude and phase error estimation precision
For zero intermediate frequency receive array, channel amplitude error A m The internal servo is uniformly distributed within 0 dB-1 dB, and the channel phase error is generatedIs uniformly distributed in + -45 degrees. During channel calibration, samples of baseband digital complex signals of all receiving channels of the array are collected, the signal-to-noise ratio of the samples is 15dB, and the number of the collected samples is 10 0 To 10 6 And takes a value. The estimation accuracy of the channel amplitude and phase error is shown in fig. 2 and 3 under different sample numbers through 1000 simulation experiments.
As can be seen from the figure, when the number of sampling points is 100, the mean +3 times standard deviation of the channel amplitude error estimation is equal to 0.7284dB, and the mean +3 times standard deviation of the channel phase error estimation is equal to 3.18 degrees. When the number of sampling points is 1024, the mean +3 times standard deviation of the channel amplitude error estimation is better than 0.1dB, and the mean +3 times standard deviation of the channel phase error estimation is better than 1 degree. When the signal-to-noise ratio of the channel acquisition samples is 15dB, the number N=1024 of the channel amplitude-phase error correction samples is selected, and the zero intermediate frequency receiving channel calibration algorithm has higher amplitude-phase error estimation precision.
Scene 2: directional diagram of array beam synthesis before and after IQ imbalance compensation
For zero intermediate frequency receive array, channel amplitude error A m The internal servo is uniformly distributed within 0 dB-1 dB, and the channel phase error is generatedIs uniformly distributed in + -45 degrees. Amplitude error g of IQ imbalance m Obeying uniform distribution between 0.5dB and 1.5dB, and phase error theta m Obeying uniform distribution between 0 degrees and 10 degrees, the image rejection ratio caused by the average value of the IQ imbalance amplitude and the phase error is 22.8dB. To obtain the beam pattern of the digital array, the target signal adopts a single-frequency signal with the radio frequency of 8.001GHz and the number of sampling points after beam synthesis of 3×10 6 And an integer number of single-frequency periods are ensured in the sampling duration time, and the condition with the circular characteristic is met. The beam-forming output signal-to-noise ratio is 30dB. The target signal is incident on the digital array from 20 degrees or 60 degrees.
When the beam forming output does not perform IQ imbalance error estimation and compensation, the beam is directed to the target and mirror array beam patterns of 20 degrees and 60 degrees, respectively, as shown in fig. 4 and 5. It can be seen from the figure that, compared with the IQ-imbalance image rejection level of the single channel, the beam synthesis of the digital array has a certain rejection capability for the image component caused by IQ-imbalance, and the image rejection ratio after the beam synthesis is about 32 dB. When the array scale is smaller, the image rejection level brought by array beam forming is limited, and IQ imbalance errors need to be further estimated and compensated after beam forming. After IQ imbalance beam level compensation, the target and mirror array beam patterns with beam directives of 20 degrees and 60 degrees, respectively, are shown in fig. 6 and 7. From the figure, the beam-level IQ imbalance error compensation improves the image rejection ratio from about 32dB before compensation to more than 64 dB. The provided beam-level IQ imbalance compensation method can further improve the image rejection ratio of the beam synthesis output.
Scene 3: beam-level IQ imbalance error compensation accuracy
For zero intermediate frequency receive array, channel amplitude error A m The internal servo is uniformly distributed within 0 dB-1 dB, and the channel phase error is generatedIs uniformly distributed in + -45 degrees. After channel amplitude and phase error compensation, a beam is formed at the normal position of the array surface. Amplitude error g of IQ imbalance of beam-formed output m 1dB, phase error θ m The image rejection ratio of IQ imbalance amplitude and phase error is 22.8dB, 5 degrees. The signal-to-noise ratio of the output of the array beam synthesis is 15dB, the sampling frequency is 30MHz, the target signal is a single-frequency signal, the radio frequency is 8.001GHz, and the number of sampling points after the beam synthesis is 3×10 2 Up to 3X 10 6 The variation ensures that the sampling duration has an integer number of single-frequency periods, and the condition with circular characteristics is satisfied. The image rejection ratio change curves corresponding to different sampling points after 1000 times of repeated experiments are shown in fig. 8. The Image Rejection Ratio (IRR) of the beam-formed output (before compensation) was 22.8dB when the number of sampling points was 3×10 6 The mean-3 times standard deviation of the image rejection ratio was 65.84dB. When the number of sampling points is small (for example, the number of sampling points is 3000), the mean-3 times standard deviation of the image rejection ratio is about 31dB.
Fig. 9 and 10 show the variation curves of the estimation accuracy of IQ imbalance amplitude error and phase error with the number of sampling points, respectively. When the sampling point number is 3×10 6 When the amplitude error estimation precision is 0.0012dB, the phase error estimation precision is 0.0080 degrees. When the number of sampling points is small (for example, the number of sampling points is 3000), the amplitude error estimation accuracy is 0.08dB, and the phase error estimation accuracy is 0.5 degrees. It can be seen that, to obtain an accurate estimate of the IQ-imbalance error, a large amount of sample data is acquired, which makes the IQ-imbalance error estimate more computationally intensive than the inter-channel amplitude-phase error estimate. If IQ imbalance error estimation is performed in each receiving channel of the digital array, the calculation amount is huge, which is not beneficial to practical application.
In summary, the IQ imbalance beam level compensation method of the zero intermediate frequency receiving array has the advantages of simple principle, small operand, easy engineering realization and verified performance through simulation experiments. The method of the invention does not need to estimate and compensate IQ imbalance error channel by channel, only needs to estimate and compensate IQ imbalance at the beam forming output, reduces the calculation amount of error estimation and compensation of the digital array, and is especially suitable for occasions where the digital array processes communication signals with circular characteristics.
The above embodiments are only for illustrating the technical solution of the present invention, and are not limiting; although the invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical scheme described in the foregoing embodiments can be modified or some technical features thereof can be replaced by equivalents; such modifications and substitutions do not depart from the spirit and scope of the technical solutions of the embodiments of the present invention.
Claims (10)
1. The IQ imbalance beam level compensation method for the zero intermediate frequency receiving array is characterized by comprising the following steps of:
step 1: the digital array is provided with M array elements, and radio frequency signals received by each array element are obtained;
step 2: filtering and amplifying the radio frequency signals to obtain M intermediate frequency analog signals;
step 3: mixing and low-pass filtering are respectively carried out on the M intermediate frequency analog signals, the M in-phase local oscillator signals and the M quadrature local oscillator signals, and M baseband analog in-phase signals and M baseband analog quadrature signals are obtained;
step 4: the M baseband analog in-phase signals and the M baseband analog quadrature signals are respectively subjected to A/D sampling to obtain M baseband digital complex signals;
step 5: before beam synthesis is carried out on the digital array, amplitude-phase consistency of M receiving channels is calibrated, and M receiving channel amplitude-phase error compensation values are obtained;
step 6: channel amplitude-phase error compensation and beam weighting compensation are carried out on M baseband digital complex signals of a digital array, and summation is carried out, so that a beam forming output complex signal is obtained;
step 7: and estimating and compensating the IQ imbalance error after beam forming by utilizing the round characteristic of the received baseband digital complex signal to obtain the final baseband digital complex signal of the digital array.
2. The method for IQ imbalance beam level compensation for a zero intermediate frequency receive array according to claim 1 wherein step 1 comprises:
the radio frequency signal received by the m-th array element is
x m (t)＝A(t)cos[Ω c (t-τ m )+φ(t)]m＝1,…,M
Wherein A (t) is amplitude modulation information, phi (t) is phase modulation information, omega c For the carrier analog angular frequency of the received signal, τ m The time delay difference is determined by the array element coordinates and the signal incidence direction, t is the current moment, and M is the total number of the array elements.
3. The method for IQ imbalance beam level compensation for a zero intermediate frequency receive array according to claim 2 wherein step 2 comprises:
the intermediate frequency analog signal obtained after the m-th array element is filtered and amplified is
wherein ,Acm Andthe amplitude and phase errors are brought about by the preselection filters and the low noise amplifiers of the channels, respectively.
4. The method for IQ imbalance beam level compensation for a zero intermediate frequency receive array according to claim 3 wherein step 3 comprises:
baseband analog in-phase signal I of mth channel m Baseband analog quadrature signals Q of (t) and mth channels m (t) are respectively
wherein , and />The low-pass filters of the in-phase branches in the mth channel are respectively +.>Induced amplitude and phase errors; /> and />Local oscillation frequency sources of in-phase branches in an mth channel are respectively adopted>Induced amplitude and phase errors; /> and />The low-pass filters of the quadrature branches in the mth channel are respectively +.>Induced amplitude and phase errors; and />Local oscillation frequency sources of orthogonal branches in an mth channel are respectively +.>The resulting amplitude and phase errors.
5. The method for IQ imbalance beam level compensation for a zero intermediate frequency receive array according to claim 4 wherein step 4 comprises:
baseband digital complex signal z of mth channel m (n) is
wherein , T s for A/D sampling period, n is nT s Index of time sample values.
6. The method for IQ imbalance beam level compensation for a zero intermediate frequency receive array according to claim 5 wherein step 5 comprises:
step 5-1, placing a single-frequency correction source in the normal direction of the digital array, calculating single-frequency signals radiated by the correction source, acquiring baseband digital complex signals of M channels through each channel of the zero intermediate frequency receiving array based on the influence of the single-frequency signals radiated by the correction source, and obtaining the baseband digital complex signals of M receiving channelsIs a sample of N samples;
step 5-2, for the mth channel, first calculate the fast Fourier transform of the N samples, then extract at frequency Ω d Spectral value Sp at m Corresponding amplitude value Ap m ；
Step 5-3, for M channel amplitude valuesSorting from small to large, selecting channel number r E [1, M corresponding to amplitude median after sorting]Selecting the r channel as a reference channel, and selecting the r channel amplitude value Ap r As the average value of normal channel decisions;
step 5-4, threshold A of given normal channel decision thr Calculating the upper amplitude limit Ap of the normal channel decision U And a lower limit Ap L Generating M channel normal identifiers CFg m ；
Step 5-5, using the spectral value Sp of the r-th channel r For reference, by the formulaCalculating the amplitude-phase error correction of each receiving channel relative to the r-th channel>Wherein, superscript is complex conjugate operation;
step 5-6, for the mth channel, the channel amplitude and phase error correction is rewritten as
Step 5-7, calculating M channels amplitude-phase error correction quantityAmplitude maximum of +.>And pass the formula +.>m=1, …, and M normalizes all channel amplitude and phase error correction amounts to obtain a final channel amplitude and phase error compensation value +.>
7. The IQ imbalance beam level compensation method according to claim 6 wherein step 5-1 comprises:
correcting the single frequency signal of source radiation to s c (t)＝A 0 cos[(Ω c +Ω d )t+φ 0 ]
wherein ,φ0 For initial phase, A 0 Is the amplitude of the single frequency signal, omega d Is the frequency offset of single frequency signal omega d ＝2πk 0 /(NT s )>0，k 0 Is a positive integer and 0<k 0 <N/2，N＝2 b B is a positive integer for collecting the number of samples;
baseband digital complex signals for M receive channelsIs of (1)
8. The IQ imbalance beam order compensation method according to claim 6 wherein steps 5-4 comprise:
threshold A for a given normal channel decision thr By the formulaCalculating the upper amplitude limit Ap of normal channel decision U And a lower limit Ap L Then ∈0 through the formula->M channel normal identifications are generated.
9. The method for IQ imbalance beam level compensation for a zero intermediate frequency receive array according to claim 6 wherein step 6 comprises:
the beam forming output complex signal z (n) is represented as
wherein ,beam weighting coefficient of mth array element, alpha m For the amplitude weighting value of the mth array element in the array, the maximum value thereof satisfies +.>s (n) is the target baseband digital complex signal and +.>λ 1 and λ2 Respectively a first coefficient and a second coefficient, respectively, expressed as
10. The method for IQ imbalance beam level compensation for a zero intermediate frequency receive array according to claim 9 wherein step 7 comprises:
step 7-1, through the formulaAnd formula->Calculating the autocorrelation function value gamma of the beam forming output complex signal z (n) s And complementary autocorrelation function c s Wherein L is the number of samples required to estimate the IQ imbalance error of the beamformed output;
step 7-2, utilizing the autocorrelation function value gamma s And complementary autocorrelation function c s Compensation coefficient w for IQ imbalance error opt Estimation is performed, i.e
Step 7-3, compensation coefficient w using IQ imbalance error opt Compensating the beam synthesis output data to obtain final baseband digital complex signalI.e. < ->
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