CN107132511B

CN107132511B - Accurate radar linear frequency modulation source predistortion method

Info

Publication number: CN107132511B
Application number: CN201710330140.9A
Authority: CN
Inventors: 罗运华; 喻忠军; 徐正; 刘霖
Original assignee: Institute of Electronics of CAS
Current assignee: Institute of Electronics of CAS
Priority date: 2017-05-11
Filing date: 2017-05-11
Publication date: 2020-01-21
Anticipated expiration: 2037-05-11
Also published as: CN107132511A

Abstract

The invention provides an accurate radar linear frequency modulation source predistortion method, which comprises the following steps: s1, calculating the position of a phase zero point according to the provided calibration signal and the characteristic parameters of the frequency modulation source signal; s2, constructing an ideal reference linear frequency modulation signal based on the phase zero position, and obtaining the nonlinear phase error of the calibration signal after phase unwrapping and phase subtraction of the calibration signal; s3, detecting and compensating a phase jump point of the nonlinear phase error; s4, obtaining a fitting coefficient of the nonlinear phase error through polynomial fitting according to the nonlinear phase error corrected in the step S3, and reconstructing a phase error curve of the frequency modulation source end through polynomial fitting; s5, constructing a new transmitting chirp signal based on the characteristic parameters of the chirp source signal and the phase error curve reconstructed in the step S4, wherein the new transmitting chirp signal is the predistorted chirp source signal.

Description

Accurate radar linear frequency modulation source predistortion method

Technical Field

The invention relates to the field of radar system integration test and imaging processing, in particular to an accurate radar linear frequency modulation source predistortion method.

Background

In designing a radar system, in order to comprehensively compensate for the influence of a time-varying phase error caused by a system transceiving channel on imaging processing, a calibration signal is generally acquired for analysis, then the phase error of the calibration signal is extracted and is reversely compensated to a transmitting signal at a frequency modulation source end, so that a basically ideal signal waveform can be obtained at a receiving end, the processed compression index is greatly improved, and the process is generally called predistortion.

In a high-resolution (emission bandwidth is more than 400 MHz) radar, because the time-width bandwidth product of a linear frequency modulation signal is generally very large, symbol jump of data real part and imaginary part positions is easy to occur in a high-frequency part signal, a large number of phase jump points are introduced on an existing quadratic phase curve, after phase unwrapping, the points cause the phase curve to be completely deviated from the existing quadratic parabola shape, and huge phase errors are brought when phase errors are solved by predistortion, so that the accuracy of phase curve fitting is influenced.

The existing method realizes predistortion by performing piecewise fitting on phase errors and then piecewise compensation. However, the method has low compensation precision on a high frequency band (generally, a high frequency spectrum band which is 30% of the rearmost of the positive and negative frequency parts of a frequency modulation signal), poor effect, complex operation and difficulty in realizing automatic processing, which brings huge workload in the currently emerging multi-mode and multi-resolution radar system, and no suitable pre-distortion method exists at present for linear frequency modulation source signals under the large time-bandwidth product of a high-resolution radar.

Disclosure of Invention

Technical problem to be solved

In view of the above technical problems, the present invention provides an accurate radar linear frequency modulation source predistortion method, which is not only suitable for low resolution radar linear frequency modulation source predistortion, but also can meet the requirements of high precision and automation of signal predistortion under the large time-bandwidth product of a high resolution radar.

(II) technical scheme

According to one aspect of the invention, an accurate radar linear frequency modulation source predistortion method is provided, which comprises the following steps: s1, calculating the position of a phase zero point according to the provided calibration signal and the characteristic parameters of the frequency modulation source signal; s2, constructing an ideal reference linear frequency modulation signal based on the phase zero position, and obtaining the nonlinear phase error of the calibration signal after phase unwrapping and phase subtraction of the calibration signal; s3, detecting and compensating a phase jump point of the nonlinear phase error; s4, obtaining a fitting coefficient of the nonlinear phase error through polynomial fitting according to the nonlinear phase error corrected in the step S3, and reconstructing a phase error curve of the frequency modulation source end through polynomial fitting; s5, constructing a new transmitting chirp signal based on the characteristic parameters of the chirp source signal and the phase error curve reconstructed in the step S4, wherein the new transmitting chirp signal is the predistorted chirp source signal.

(III) advantageous effects

According to the technical scheme, the accurate radar linear frequency modulation source predistortion method has at least one of the following beneficial effects:

(1) the radar linear frequency modulation source predistortion method can obtain a compression result with good index even if the linear frequency modulation signal under the high resolution and large hour-width bandwidth product;

(2) the radar linear frequency modulation source predistortion method has good automatic processing capability and can meet the predistortion requirement of a multi-mode and high-resolution radar.

Drawings

Fig. 1 shows a high-frequency phase jump phenomenon of a chirp signal in a high-resolution radar.

Fig. 2 is a schematic flow chart of a high-resolution radar accurate linear frequency modulation source predistortion method according to an embodiment of the present invention.

Fig. 3(a) and (b) are respectively a phase curve and a phase error curve of the unwrapped scaled signal and the ideal reference chirp signal in the first embodiment of the present invention.

Fig. 4(a) and (b) are respectively the phase jump point automatically extracted and the compensated non-linear error curve in the first embodiment of the present invention.

Fig. 5 shows the compression result of the scaled signal before predistortion according to the first embodiment of the present invention.

Fig. 6 shows the result of compressing the scaled signal after the predistortion according to the first embodiment of the present invention.

Fig. 7(a), (b) are phase curves and phase error curves of unwrapped scaled signal and ideal reference chirp signal, respectively, in a second embodiment of the present invention.

Fig. 8(a) and (b) are respectively the phase jump point automatically extracted and the compensated non-linear error curve in the second embodiment of the present invention.

Fig. 9 shows the compression result of the scaled signal before predistortion according to the second embodiment of the present invention.

Fig. 10 shows the result of compressing the scaled signal after the predistortion according to the second embodiment of the present invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to specific embodiments and the accompanying drawings.

In an exemplary embodiment of the present invention, a high-resolution radar accurate linearly-modulated source predistortion method is provided. Fig. 1 is a high-frequency phase jump phenomenon of a chirp signal in a high-resolution radar, and fig. 2 is a schematic flow chart of a precise chirp source predistortion method for a high-resolution radar according to an embodiment of the present invention. As shown in fig. 2, the accurate linear frequency modulation source predistortion method for the high-resolution radar of the invention comprises the following steps: s1, calculating the position of a phase zero point according to the provided calibration signal and the characteristic parameters (bandwidth, pulse width and sampling rate) of the frequency modulation source signal; s2, constructing an ideal reference linear frequency modulation signal based on the phase zero point, and obtaining the nonlinear phase error of the calibration signal after phase unwrapping and phase subtraction of the calibration signal; s3, detecting and compensating a high-frequency phase jump point of the nonlinear phase error; s4, obtaining a fitting coefficient of the nonlinear phase error through polynomial fitting, and reconstructing a phase error curve of the frequency modulation source end through polynomial fitting; s5, constructing a new transmitting chirp signal based on the characteristic parameters of the chirp source signal and the phase error curve reconstructed in the step S4.

In step S1, the phase zero position of the compressed scaled signal is obtained by matched filtering. The method comprises the following specific steps: based on the supplied scaling signal S_dB(t) and the frequency modulation source signal characteristic parameters thereof to construct a frequency domain matched filter S_match(f_r) Will S_dB(t) and S_match(f_r) Multiplying (matched filtering) in frequency domain to obtain time domain compressed signal S_comp(t) taking S_compAnd (t) the position of the amplitude peak point is the position of the phase zero point.

S_dB(t)＝exp{j·π·K_r·t²+j·φ_err(t)}

S_comp(t)＝ifft{fft{S_dB(t)·S_match(f_r)}}

c＝max{ABS(S_comp(t)),index_max}

Wherein K_rIn order to adjust the frequency of the frequency,

wherein B is_rFor frequency-modulated source signal bandwidth, T_rIs the pulse width, t is the fast time of the scaled signal, phi_err(t) is the phase error associated with the fast time, where f_rIn order to be the distance-wise frequency,

in step S2, the specific steps are as follows: establishing a fast time axis t' by taking the extracted phase zero point as the fast time axis zero point, establishing an ideal reference linear frequency modulation signal through the provided calibration signal and the characteristic parameter of the frequency modulation source signal thereof, respectively performing phase unwrapping on the calibration signal and the reference linear frequency modulation signal, and acquiring the phase difference phi between the calibration signal and the reference linear frequency modulation signal_err(t'), i.e., the nonlinear phase error of the scaled signal.

φ_err(t')＝UN(S_dB(t))-UN(exp{j·π·K_r·t'²})

Where UN (-) is the phase unwrapping function.

In step S3, since the real part and the imaginary part of the data in the high frequency part of the chirp signal are prone to error, a large number of phase jump points, defined as Φ, often appear in the high frequency phase part_{jp_err}(t_n') which will affect the accuracy of the subsequent phase error fit, as shown in figure 1. The invention designs a differential phase detector according to the phase difference characteristic of the phase jump point.

The method comprises the following specific steps: s31: the nonlinear phase error is subtracted differentially, a reasonable phase jump threshold (the theoretical value is 360 degrees, generally more than 150 degrees to 300 degrees) is set, when the extracted nonlinear phase error passes through the differential phase detector, the position of a phase jump point can be automatically extracted, and then the first point phi of a phase error curve is used for phase difference of the jump point_err(t₁') as reference phase, for each phase the trip point (phi)_{jp_err}(t_n') to phi_{jp_err}(t_n+1'))) by a phase compensation amount of

Thereby obtaining a compensated phase error phi_{comp_err}(t')。

Wherein t is_n',t_n+1' current and next phase jump points, respectively, round (-) is an approximation function. S32: if the compensated phase error curve still has a phase jump point, the step S31 is repeated once.

In step S4, fitting is performed by using a polynomial fitting method according to the phase error corrected in step S3, where an eighth-order polynomial is generally used to meet the fitting accuracy requirement, and a polynomial fitting coefficient is obtained by phase fitting. Establishing a new time axis t' according to the sampling rate of the frequency modulation source signal, reconstructing the phase error curve of the linear frequency modulation source end by polynomial fitting

In step S5, the specific steps are as follows: and establishing an ideal linear frequency modulation signal by using the provided characteristic parameters (bandwidth, pulse width and sampling rate) of the frequency modulation source end emission signal, and then subtracting the extracted phase error from the phase item, wherein the signal is the linear frequency modulation signal after predistortion.

The predistortion verification is performed in the following specific example.

The first embodiment:

the transmission bandwidth is 740MHz, the pulse width is 60us, the output frequency of the frequency modulation source is 1700MHz, and the sampling rate of the AD sampling end of the receiver is 880 MHz.

Fig. 3(a) shows the provided calibration signal and the reference frequency modulation signal, and it can be seen that the two curves are greatly separated due to the large phase error of the high frequency end. Fig. 3(b) shows a phase error curve between them, and a large number of step-like phase jump points appear in the high frequency parts on both sides of the signal, in which case the conventional predistortion method cannot perform accurate phase fitting and compensation. Fig. 4(a) shows the detection result of the automatic phase jump point detection method provided by the present invention, it can be seen that the phase jump values are all greater than 250 °, and fig. 4(b) shows the nonlinear error compensated by the jump point compensation method provided by the present invention, and at this time, fitting can be performed accurately by polynomial fitting. Fig. 5 and fig. 6 show the compression results of the calibration signal without predistortion and after predistortion respectively, and it can be seen that the compression index is greatly improved, which illustrates the effectiveness of the present invention.

Second embodiment:

the transmission bandwidth is 1460MHz, the pulse width is 28us, the output frequency of the frequency modulation source is 1700MHz, and the sampling rate of the AD sampling end of the receiver is 1680 MHz.

Fig. 7(a) shows the scaled signal and the reference frequency modulated signal provided, and it can be seen that the two phase curves are close due to the relatively small phase error at the high frequency end. Fig. 7(b) shows the phase error curve between them, and the high frequency part on the left side of the signal shows a part of the step-like phase jump point, in which case the traditional predistortion method cannot perform accurate phase fitting and compensation, and needs to perform discarding or segment fitting. Fig. 8(a) shows the detection result of the automatic phase jump point detection method provided by the present invention, it can be seen that the phase jump values are all larger than 300 °, and fig. 8(b) shows the nonlinear error compensated by the jump point compensation method provided by the present invention, and at this time, fitting can be performed accurately by polynomial fitting. Fig. 9 and fig. 10 show the compression results of the calibration signal without predistortion and after predistortion, respectively, and it can be seen that the compression index is greatly improved, thus illustrating the effectiveness of the present invention.

Up to this point, the present embodiment has been described in detail with reference to the accompanying drawings. From the above description, those skilled in the art should clearly understand that the accurate radar linear frequency modulation source predistortion method of the present invention. The invention discloses an accurate linear frequency modulation source predistortion method applicable to a high-resolution radar (the transmission bandwidth is more than 400 MHz), which can introduce a phase compensation method aiming at the phenomenon that the phase of a high-frequency band (generally a high-frequency spectrum band which is positioned at the rearmost 30% of the positive and negative frequency parts of a frequency modulation signal) of a linear frequency modulation signal of the high-resolution radar under a large time-width bandwidth product is violently jumped, as shown in figure 1, the phase jump of the high-frequency band is effectively compensated, and then the extraction of an error phase is carried out by adopting a traditional polynomial fitting method. The actual measurement data experiment shows that the method can effectively compensate the phase distortion problem of the frequency-modulated signal caused by the channel under the large-time wide-bandwidth integration of the radar, the corrected signal index meets the application requirement, and the signal predistortion automatic processing requirement of the airborne and spaceborne high-resolution radar can be met.

It is to be noted that, in the attached drawings or in the description, the implementation modes not shown or described are all the modes known by the ordinary skilled person in the field of technology, and are not described in detail. Furthermore, the above definitions of the various elements and methods are not limited to the particular structures, shapes or arrangements of parts mentioned in the examples, which may be easily modified or substituted by one of ordinary skill in the art, for example:

the polynomial fitting order may vary depending on the actual error phase form.

The algorithms and displays presented herein are not inherently related to any particular computer, virtual machine, or other apparatus. Various general purpose systems may also be used with the teachings herein. The required structure for constructing such a system will be apparent from the description above. Moreover, the present invention is not directed to any particular programming language. It is appreciated that a variety of programming languages may be used to implement the teachings of the present invention as described herein, and any descriptions of specific languages are provided above to disclose the best mode of the invention.

In the description provided herein, numerous specific details are set forth. It is understood, however, that embodiments of the invention may be practiced without these specific details. In some instances, well-known methods, structures and techniques have not been shown in detail in order not to obscure an understanding of this description.

Similarly, it should be appreciated that in the foregoing description of exemplary embodiments of the invention, various features of the invention are sometimes grouped together in a single embodiment, figure, or description thereof for the purpose of streamlining the disclosure and aiding in the understanding of one or more of the various inventive aspects. However, the disclosed method should not be interpreted as reflecting an intention that: that the invention as claimed requires more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive aspects lie in less than all features of a single foregoing disclosed embodiment. Thus, the claims following the detailed description are hereby expressly incorporated into this detailed description, with each claim standing on its own as a separate embodiment of this invention.

The above-mentioned embodiments are intended to illustrate the objects, technical solutions and advantages of the present invention in further detail, and it should be understood that the above-mentioned embodiments are only exemplary embodiments of the present invention, and are not intended to limit the present invention, and any modifications, equivalents, improvements and the like made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. An accurate radar chirp source predistortion method, comprising the following steps:

S1. Calculate the phase zero position according to the provided calibration signal and its characteristic parameters of the FM source signal;

S2. Construct an ideal reference chirp signal based on the phase zero position, and obtain the nonlinear phase error of the calibration signal by subtracting the phase of the calibration signal after phase unwrapping;

S3, detecting and compensating the phase jump point of the nonlinear phase error;

S4. According to the nonlinear phase error corrected in step S3, the fitting coefficient of the nonlinear phase error is obtained through polynomial fitting, and the phase error curve of the FM source terminal is reconstructed through polynomial fitting;

S5. Construct a new transmit chirp signal based on the characteristic parameters of the FM source signal and the phase error curve reconstructed in step S4, that is, the predistorted chirp source signal; wherein,

In step S3, the phase jump point of the nonlinear phase error is detected and compensated by setting a differential phase detector, which specifically includes:

S31: Perform differential subtraction of the nonlinear phase error, and set a reasonable phase jump threshold. When the extracted nonlinear phase error passes through the differential phase detector, the position of the phase jump point can be automatically extracted, and then according to the jump point Taking the first point φ _err (t ₁ ') of the phase error curve as the reference phase, phase compensation is performed on the phase between each phase jump point, so as to obtain the compensated phase error;

S32: If it is found that the phase error curve after compensation still has a phase jump point, repeat step S31 once.

2. The radar chirp source predistortion method according to claim 1, wherein,

In step S1, the phase zero position of the compressed calibration signal is obtained through matched filtering.

3. The radar chirp source predistortion method according to claim 2, wherein the specific step of obtaining the phase zero position of the compressed calibration signal through matched filtering comprises:

According to the provided calibration signal S _dB (t) and its FM source signal characteristic parameters, construct a frequency domain matched filter S _match (f _r );

Multiply S _dB (t) and S _match (f _r ) in the frequency domain to obtain the time-domain compressed signal S _comp (t);

The position of the amplitude peak point of S _comp (t) is taken as the phase zero position.

4. The radar chirp source predistortion method according to claim 1, wherein step S2 specifically comprises:

Use the extracted phase zero point as the fast time axis zero point to establish the fast time axis t';

Establish an ideal reference chirp signal by providing the calibration signal and its FM source signal characteristic parameters;

The calibration signal and the reference chirp signal are phase unwrapped respectively, and the phase difference φ _err (t') of the two is obtained, which is the nonlinear phase error of the calibration signal.

5. The radar chirp source predistortion method according to claim 1, wherein the differential phase detector is a second-order differential phase detector.

6 . The radar chirp source predistortion method according to claim 1 , wherein the phase jump threshold is any value between 150° and 300°. 7 .

7. The radar chirp source predistortion method according to claim 1, wherein step S5 specifically comprises:

Using the provided characteristic parameters of the FM source signal, an ideal chirp signal is established, and then the extracted phase error is subtracted from the phase term, and the signal is the predistorted chirp signal.

8. The radar chirp source predistortion method according to any one of claims 1-7, wherein the characteristic parameters include: bandwidth, pulse width, and sampling rate.