CN116930969A - Metamaterial tag target positioning and imaging method based on synthetic aperture radar - Google Patents

Abstract

The invention discloses a metamaterial tag target positioning and imaging method based on synthetic aperture radar, which belongs to the field of target imaging and detection. It uses a frequency modulated continuous wave synthetic aperture radar (SAR) system as the detection host to emit point frequency and linear frequency modulation signals. With the combined waveform, the tag design based on the metamaterial modulation coding method is equivalent to a point target with the function of modulating the radar detection signal. The echo signal in the point frequency band is used to calculate the modulation frequency of the metamaterial point target, and a compensation factor is constructed to perform two-dimensional modulation compensation in the range and azimuth directions for the wavenumber domain imaging algorithm to achieve focused imaging of the modulated target. The invention can realize imaging and perception of the surrounding environment of the tag while identifying and positioning the tag.

Description

Metamaterial tag target positioning and imaging method based on synthetic aperture radar

Technical field

The invention belongs to the field of target imaging and detection, and specifically relates to a metamaterial tag target positioning and imaging method based on synthetic aperture radar.

Background technique

Tag technology completes information interaction through information encoding on the tag side and signal detection on the host side. On the one hand, the unique identification of the tag is achieved through information encoding, and on the other hand, the discovery and positioning of the tag is achieved through signal detection and communication time delay. By carrying custom tags, people, objects or equipment can be identified and positioned, thereby providing better protection for human life, production, management, etc.

With traditional RFID tag technology, the host can accurately identify individuals by reading the coded information of the tag. This method is technically mature and the tags have the advantages of cheapness, low power consumption, and light weight. However, they have insufficient range and poor positioning accuracy. question. Another representative technology is ultra-wideband wireless communication technology (UWB). UWB completes the identification and positioning of tags through communication between the host and the tag. It has the advantages of low power consumption and low cost, but it suffers from disadvantages in terms of positioning accuracy and refresh rate. There are also shortcomings.

Synthetic aperture radar technology can achieve long-distance, high-resolution two-dimensional imaging. Combining synthetic aperture radar technology with tag technology is expected to achieve long-distance, high-precision, and high-refresh rate positioning of tags while also enabling asynchronous modulation of tags. Focused imaging. Compared with traditional tag technology, it can greatly improve the imaging and perception capabilities of the environment around the tag, which is of great significance for high-precision target positioning and environmental perception in complex scenes.

Contents of the invention

In order to solve the above technical problems, the present invention provides a metamaterial tag target positioning and imaging method based on synthetic aperture radar, which uses a frequency modulated continuous wave synthetic aperture radar (SAR) system as the detection host to emit a combined waveform of point frequency and linear frequency modulation signals. , the tag design based on the metamaterial modulation coding method is equivalent to a point target with the function of modulating the radar detection signal. The echo signal in the point frequency band is used to calculate the modulation frequency of the metamaterial point target, and a compensation factor is constructed to perform two-dimensional modulation compensation in the range and azimuth directions for the wavenumber domain imaging algorithm to achieve focused imaging of the modulated target.

In order to achieve the above objects, the present invention adopts the following technical solutions:

A metamaterial tag target positioning and imaging method based on synthetic aperture radar, including the following steps:

Step 1. Construct the joint waveform of the point frequency signal and the linear frequency modulation signal;

Step 2. After the linear frequency modulation band echo signal is coherently received, a metamaterial tag modulated echo signal model is constructed based on the de-FM reception principle;

Step 3. Transform the point frequency band echo signal into the two-dimensional frequency domain, and calculate the target azimuth modulation frequency based on the echo signal model modulated by the metamaterial tag;

Step 4: Use the modulation parameters of the metamaterial tag and the target azimuth modulation frequency calculated in step 3 to perform modulation compensation in the range and azimuth direction of the chirp band echo signal, and then construct a consistent compression reference function and Stolt Interpolation realizes global migration correction and azimuth compression, and finally the focused image result is obtained through two-dimensional inverse Fourier transformation.

Beneficial effects:

The method proposed by the present invention combines the characteristics of synthetic aperture radar technology and metamaterial tag modulation, and can realize the positioning and focused imaging of asynchronously modulated tags. Compared with traditional tag technology, it can realize tag identification and positioning at the same time as tag surroundings. Imaging and perception of the environment.

Description of the drawings

Figure 1 is a joint waveform diagram of point frequency signal and linear frequency modulation signal;

Figure 2 is a flow chart of the synthetic aperture radar-based metamaterial modulation tag target positioning and imaging method of the present invention.

Detailed ways

In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described here are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

As shown in Figure 2, the metamaterial tag target positioning and imaging method based on synthetic aperture radar of the present invention includes the following steps:

Step 1. Construct the joint waveform of the point frequency signal and the linear frequency modulation signal;

Step 2. After the linear frequency modulation band echo signal is coherently received, a metamaterial tag modulated echo signal model is constructed based on the de-FM reception principle;

Step 3. Transform the point frequency band echo signal into the two-dimensional frequency domain, and calculate the target azimuth modulation frequency based on the echo signal model modulated by the metamaterial tag;

Step 4: Use the modulation parameters of the metamaterial tag and the target azimuth modulation frequency calculated in step 3 to perform modulation compensation in the range and azimuth direction of the chirp band echo signal, and then construct a consistent compression reference function and Stolt Interpolation realizes global migration correction and azimuth compression, and finally the focused image result is obtained through two-dimensional inverse Fourier transformation.

Specifically, step 1 includes:

The metamaterial modulation tag will produce modulation effects in both the range and azimuth directions of the SAR echo, and the influence of the modulation effect needs to be eliminated before focusing imaging. The modulation effect in the range direction can be eliminated according to the modulation parameters of the metamaterial modulation tag, while the modulation effect in the azimuth direction requires special transmission waveform design to extract the azimuth modulation parameters. To this end, the present invention designs a joint waveform composed of point frequency and linear frequency modulation, as shown in Figure 1. The upper picture shows the relationship between amplitude and time, and the lower picture shows the relationship between frequency and time. The waveform repetition period is , in one cycle, the time length of the point frequency signal is/> , the time length of the chirp signal is/> ,/> for/> The frequency of the dot frequency signal within the time period also represents the starting frequency of the chirp segment,/> is the cutoff frequency of the chirp band,/> For the linear frequency modulation frequency, the point frequency signal echo is used to solve the azimuth modulation frequency, and the linear frequency modulation signal is used to achieve target imaging.

(1)

in, To transmit signals,/> ,/> are the amplitude of the point frequency signal and linear frequency modulation signal respectively,/> is the carrier frequency,/> is the propagation time of the transmitted signal,/> For the platform movement time,/> is the chirp frequency,/> is a natural number, exp[] represents the exponential power operation of e, j represents an imaginary number,/> is the range envelope function of the point frequency signal, is the range envelope function of the chirp signal, and rect() is the rectangular function (for any variable/> , if/> ,/> , if/> ,/> ), is the azimuth envelope function,/> is the target angle of view measured in the slant distance plane,/> is the beam width,/> is the pulse function,/> is any variable not equal to zero.

Specifically, the step 2 includes:

The present invention uses a modulation coding method to implement tags, which can be equivalent to a point target with the function of modulating radar detection signals. Suppose the modulation frequency is , the initial phase of the nth modulated signal is/> , n takes a positive integer, and the modulation method is phase modulation. According to the joint waveform in step 1 of this step, the chirp band echo signal/> Expressed as:

(2)

in, is the echo amplitude parameter,/> Represents the delay of the echo,

is the real-time slant distance between the radar and the target. The coordinates of the target in the scene are/> ,/> Indicates the minimum slope distance,/> is the target azimuth position,/> is the platform movement speed, full time ,/> For oblique angle,/> The propagation speed of electromagnetic waves in the air.

The transmitted signal is used as the local oscillator signal for deskewing reception. The deskewed intermediate frequency signal is , its expression is:

(3)

in, It is the amplitude parameter of the intermediate frequency signal received by deskewing.

Perform two-dimensional Fourier transform on the range and azimuth directions of equation (3) to obtain the two-dimensional frequency domain signal of the received intermediate frequency echo. , its expression is:

(4)

in, is the frequency value that represents the target distance,/> Represents the distance of a point target at zero Doppler time,/> is the distance-to-frequency axis variable,/> is the azimuth frequency axis variable,/> is the amplitude parameter of the two-dimensional frequency domain signal.

is the azimuth spectrum envelope,/> is the minimum slope distance,/> is the movement speed of the platform,/> is the azimuth spectrum offset caused by point target modulation, and mod is the remainder function. Equation (4) shows that the tag modulation signal causes the echo signal to be generated in the range frequency domain/> offset, generated in the azimuth frequency domain/> The offset will cause the imaging process to be unable to focus, and the offset needs to be calculated and compensated before imaging processing.

Specifically, step 3 includes:

According to the joint waveform in step 1, the point frequency signal segment echo signal obtained after deskewing reception is expressed as:

(5)

in, is the time domain form of the deskewed received point frequency signal,/> It is the amplitude parameter of the deskewed received point frequency signal;

Perform a two-dimensional Fourier transform on the echo signal of the deskewed received point frequency signal segment to obtain a two-dimensional spectrum signal theoretical model of the deskewed received point frequency signal. , its expression is:

(6)

in, is the distance spectrum envelope,/> is the amplitude parameter of the two-dimensional spectrum of the point frequency signal after deskewing reception.

It can be seen from formula (6) that the two-dimensional Fourier transform is performed on the echo signal of the actually received point frequency signal segment. The two-dimensional spectrum of the echo signal of the actually received point frequency signal segment and the point frequency obtained after deslope reception are Deviation of the two-dimensional spectrum signal theoretical model of the signal segment echo signal, and the azimuth spectrum offset caused by metamaterial tag modulation is solved . Specifically, step 4 includes:

based on what is known and solved/> , perform compensation imaging on the linear frequency modulation band.

First, construct the distance modulation compensation factor , perform distance modulation compensation on the linear frequency modulation band echo signal of formula (2), and obtain the range-compensated echo signal/> , its expression is:

(7)

Compensating the residual video phase factor for equation (7) , get the echo signal after removing the residual video phase/> , its expression is:

(8)

in, Represents the amplitude factor. Since signal phase processing is the most critical in focused imaging, this item will no longer be considered in subsequent imaging algorithm analysis.

The beam domain algorithm is used for focused imaging, and formula (8) is subjected to time-frequency transformation to obtain the time-frequency transformed signal. , its expression is:

(9)

in Represents the distance wavenumber parameter,/> is the azimuth position parameter.

Perform Fourier transform on equation (9) in the azimuth direction to obtain the two-dimensional spatial frequency domain signal. , its expression is:

(10)

in, Represents the azimuthal wave number, which is used in this formula/> The azimuth wavenumber is compensated to eliminate the modulation effect in the azimuth direction.

The last term in formula (10) The Doppler shift introduced for intrapulse motion can be multiplied by a compensation factor/> Cancel, and obtain the two-dimensional frequency domain signal after the Doppler frequency shift is compensated/> :

(11)

Build reference function , where the reference distance/> Taking the distance from the radar to the center of the scene, the reference function is multiplied by formula (12) to obtain the two-dimensional frequency domain signal focused at the reference distance. :

(12)

make Perform Stolt interpolation transformation on formula (12) to obtain the transformed signal/> , its expression is:

(13)

in, Represents the ordinate after Stolt interpolation transformation.

Finally, a two-dimensional inverse fast Fourier transform (2D-IFFT) is performed on the above equation to obtain a fully focused two-dimensional image.

It is easy for those skilled in the art to understand that the above descriptions are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions and improvements, etc., made within the spirit and principles of the present invention, All should be included in the protection scope of the present invention.

Claims (5)

1. The metamaterial tag target positioning and imaging method based on the synthetic aperture radar is characterized by comprising the following steps of:

step 1, constructing a joint waveform of a point frequency signal and a linear frequency modulation signal;

step 2, after coherent receiving of the echo signals in the linear frequency modulation band, constructing an echo signal model modulated by the metamaterial tag according to a frequency-removing receiving principle;

step 3, transforming the point frequency band echo signals into a two-dimensional frequency domain, and calculating target azimuth modulation frequency according to an echo signal model modulated by the metamaterial tag;

and 4, respectively carrying out distance and azimuth modulation compensation on the linear modulation band echo signals by using the modulation parameters of the metamaterial tag and the target azimuth modulation frequency calculated in the step 3, then realizing global migration correction and azimuth compression by constructing a consistency compressed reference function and Stolt interpolation conversion, and finally obtaining a focusing image result by two-dimensional inverse Fourier change.

2. The synthetic aperture radar-based metamaterial tag target positioning and imaging method according to claim 1, wherein the point frequency signal in the step 1 is used for solving a target azimuth modulation frequency, and the chirp signal is used for achieving target imaging.

3. The synthetic aperture radar-based metamaterial tag targeting and imaging method as claimed in claim 2, wherein said step 2 comprises:

a modulation coding method is adopted to realize a metamaterial tag, the metamaterial tag is equivalent to a point target with a function of realizing modulation on a radar detection signal, and the modulation mode is phase modulation;

and (3) solving the linear frequency modulation section echo signals by the combined waveform in the step (1), adopting the transmitting signals as local oscillation signals received by declivity, and carrying out two-dimensional Fourier transformation on the distance direction and the azimuth direction to obtain two-dimensional frequency domain signals of the received intermediate frequency echo.

4. A synthetic aperture radar-based metamaterial tag targeting and imaging method as defined in claim 3, wherein said step 3 comprises:

according to the combined waveform of the step 1, performing two-dimensional Fourier transform on the point frequency signal segment echo signals obtained after the deskewing reception to obtain a two-dimensional spectrum signal theoretical model of the point frequency signal segment echo signals after the deskewing reception; and carrying out two-dimensional Fourier transform on the actually received point frequency signal segment echo signals, and calculating azimuth spectrum offset caused by metamaterial tag modulation through the deviation of the two-dimensional spectrum of the actually received point frequency signal segment echo signals and a two-dimensional spectrum signal theoretical model of the point frequency signal segment echo signals obtained after deskewing.

5. The synthetic aperture radar-based metamaterial tag targeting and imaging method as defined in claim 4, wherein said step 4 includes:

firstly, constructing a distance modulation compensation factor, and performing distance modulation compensation on the linear frequency modulation band echo signals in the step 2 to obtain linear frequency modulation band echo signals after distance compensation;

compensating the residual video phase to obtain a linear tone segment echo signal after the residual video phase is removed;

focusing imaging is carried out by adopting a beam domain algorithm, time-frequency conversion is carried out, and a linear frequency modulation band echo signal after the time-frequency conversion is obtained;

performing Fourier transformation on the azimuth direction, performing azimuth beam frequency offset according to the azimuth spectrum offset calculated in the step 3, and completing azimuth modulation compensation of the metamaterial tag while acquiring a two-dimensional space frequency domain signal;

then, the Doppler frequency shift introduced by the motion in the pulse is offset by complex multiplication of the compensation factor, and a two-dimensional frequency domain signal of the linear frequency modulation band echo signal after the Doppler frequency shift is compensated is obtained;

constructing a reference function to obtain a two-dimensional frequency domain signal of a linear frequency modulation band echo signal focused at a reference distance;

global range migration correction and azimuth matched filtering are realized through Stolt interpolation transformation;

and finally, carrying out two-dimensional inverse fast Fourier transform to obtain a fully focused two-dimensional image.