A method for compensating amplitude flatness of broadband radar signals

Abstract

The present invention discloses a method for compensating the amplitude flatness of broadband radar signals, which includes: obtaining the bandwidth and signal pulse width of the broadband radar signal, generating a chirp signal as the baseband signal, and outputting it as an intermediate frequency analog signal after carrier modulation; obtaining the amplitude of the intermediate frequency analog signal, evenly taking n frequency points, normalizing, taking the reciprocal, and quantizing to generate n compensation values, and generating a compensation value group C1; generating compensation values for all frequency points on the chirp signal according to the n compensation values, and pre-compensating them in the digital signal waveform to generate a new baseband signal and intermediate frequency signal, and obtaining a compensation value group C2; repeating the above steps to obtain the final compensation value. The present invention makes the curve formed by the compensation values closer to the reciprocal of the signal output spectrum by compensating multiple times and increasing the number of compensation values taken, ensuring the flatness within the signal band after compensation; collecting signals from ports such as the baseband, intermediate frequency, and radio frequency output to complete the compensation and correction of the flatness within the entire channel band.

Description

Technical Field

[0001] The invention belongs to the field of signal processing, and in particular relates to a method for compensating the amplitude flatness of a broadband radar signal, which is suitable for occasions such as software radar simulation systems that need to provide broadband radar signals. Background Art

[0002] Radar is an indispensable device in modern military or civilian fields. It not only needs to extract information such as target position and speed, but also needs to analyze and identify images. In order to improve the performance of the radar system, the radar signal needs to have a large product of time width, bandwidth and energy. Therefore, in the processing of radar signals, linear frequency modulation signals are usually emitted, and pulse compression is used to process the signals to improve the radar's range resolution, signal-to-noise ratio and other performance.

[0003] Due to the performance of the current DAC chip itself and other reasons, the amplitude of the output broadband signal will fluctuate greatly within the frequency band. This will cause the side lobes of the signal to be larger after pulse compression, resulting in a loss of signal-to-noise ratio. Therefore, it is usually necessary to compensate the signal within the frequency band to ensure the signal's in-band flatness requirements.

[0004] At present, the compensation method for broadband signals usually adopts the method of selecting a fixed number of frequency points, using a signal generator to generate a single frequency point signal, and measuring the output amplitude at each frequency point. This method is feasible when the bandwidth is narrow and the frequency points are few. However, it is difficult to implement when the bandwidth is wide and there are many frequency points. Measuring a small number of frequency points will result in insufficient compensation accuracy, affecting radar performance. Summary of the invention

[0005] Based on this, the present invention provides a method for compensating the amplitude flatness of a broadband radar signal. This method can effectively improve the compensation accuracy of the amplitude flatness within the frequency band of a broadband radar signal and improve the signal quality. At the same time, the operation is simple, the signals at different positions can be corrected, and the method has a wide range of applications.

[0006] The technical solution of the present invention is a method for compensating the amplitude flatness of a broadband radar signal, comprising the following steps:

[0007] Step 1: Obtain the bandwidth and signal pulse width of the broadband radar signal, generate a digital signal waveform of the corresponding linear frequency modulation signal, that is, a first baseband signal, and generate a carrier, mix the first baseband signal and the carrier signal to generate a first intermediate frequency digital signal, and convert the first intermediate frequency digital signal into a first intermediate frequency analog signal for output.

[0008] Knowing the bandwidth and pulse width of the broadband radar signal, according to the formula

[0009] s(t)=A cos(2πf0t+πkt 2 )

[0010] Generate the corresponding linear frequency modulation signal. s By sampling the signal, we can get:

[0011] s(t)=A cos[2πf0nT s +πk(nT s ) 2 ]

[0012] Where n∈[0,N],T s =1 / f s .

[0013] In actual use, the maximum clock frequency of FPGA is 300MHz, which may be much smaller than the bandwidth of the signal. Therefore, a multi-channel parallel method is used to generate linear frequency modulation signals.

[0014] According to the principle of DDS, to generate a linear frequency modulation (LFM) signal, the change value of the LFM phase is input into the phase accumulator of the DDS each time, so the phase value at time n+1 is as follows:

[0015] s(t)=A cos[2πf0(n+1)T s +πk(n+1) 2 T s 2 ]

[0016] Among them, T s It is the step value in the actual DDS design process. K=kT s / 2=k / 2f s .

[0017] Using the basic formula of LFM signal, take K = kT s / 2=k / 2f s , let n=mi+j,x(n)=x(mi+j)=x i,j =(f0+Kn)nT, where i∈[0,N / M],j∈[0,m]. By transforming the formula, we can get x i,j ,x i+1,j , ΔX k (n), and thus calculate the frequency control word and phase control word for generating the linear frequency modulation signal. i,j represents the phase value of channel j at time i; x i+1,j Indicates the phase value of channel j at time i+1; Indicates the part of the phase change from time i+1 to time i with a frequency of zero at time zero; ΔX k (n) represents the part of the phase change where the slope changes from time i+1 to time i.

[0018] Inputting the calculated frequency control word and phase control word into the DDS can generate an output of a linear frequency modulation signal with corresponding bandwidth and pulse width.

[0019] After the corresponding linear frequency modulation signal is generated by DDS, it is used as a baseband signal for carrier modulation and sent to a high-speed DAC chip to output the corresponding intermediate frequency signal.

[0020] Step 2: Obtain the first intermediate frequency analog signal in the frequency band range (f min ,f max ) amplitude, uniform

[0021] The intermediate frequency signal output by the DA intermediate frequency signal is sent to the spectrum analyzer to obtain the amplitude of all sampling points of the spectrum analyzer within the frequency band, and the amplitudes A1 to A1 of n frequency points are evenly taken. n . Get the maximum amplitude value A at that frequency point max , normalize all values ​​and take the inverse to get,

[0022] c 1,i =A max / A i , where i∈[0,n]

[0023] C 1,i Quantization is performed to obtain a first group of compensation values ​​C1. The first group of n compensation values ​​divides the signal into n-1 compensation intervals.

[0024] Step three: Generate compensation values ​​for all frequency points on the linear frequency modulation signal based on the n compensation values, and pre-compensate the compensation values ​​for all frequency points in the first baseband signal to generate a second baseband signal, and after carrier modulation, generate a second intermediate frequency digital signal and a second intermediate frequency analog signal; re-complete step S20 to generate compensation value group C2.

[0025] According to the n frequency points of the intermediate frequency output, determine the n frequency points f1, f2, ..., f on the baseband signal n ;

[0026] Calculate the number of points of each generated linear frequency modulation signal according to the pulse width of the linear frequency modulation signal and the clock of the FPGA;

[0027] Calculate the number of compensation points in each compensation interval according to the number of linear frequency modulation signal points in each route and the number n of compensation values;

[0028] Calculating compensation values ​​of all frequency points in each compensation interval according to the compensation interval, the compensation value of the compensation interval and the number of compensation points in the compensation interval based on a linear relationship;

[0029] Pre-compensating the compensation values ​​of all frequency points within the compensation interval in the original digital signal waveform in sequence, generating a new digital signal waveform, and outputting it as a new baseband signal and intermediate frequency signal;

[0030] The operation of step 2 is repeated on the new baseband signal and the intermediate frequency signal to obtain a compensation value group C2, and the compensation value group C2 is multiplied by the compensation value group C1 to obtain a compensation value C=C1C2 of the current digital signal.

[0031] Step 4: After repeating steps 2 and 3 several times, the final compensation value is C = C1C2...C m , and pre-compensate the final compensation value in the digital signal.

[0032] The beneficial effects of the present invention are:

[0033] (1) Using the technical method provided by the present invention, the frequency band range (f min ,f max ) can also visually see the effect of the compensated signal;

[0034] (2) The technical method provided by the present invention can achieve a good compensation effect. By performing multiple compensations and increasing the number of compensation values, the curve formed by the compensation values ​​can be made closer to the inverse of the spectrum of the signal output, thereby ensuring the flatness of the signal band after compensation;

[0035] (3) The technical method provided by the present invention is simple to operate and widely used. It can collect signals from baseband, intermediate frequency, radio frequency output and other ports, obtain corresponding compensation signals, and complete the compensation and correction of the in-band flatness of the entire channel. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 A schematic diagram of a flow chart of a method for compensating for amplitude flatness of a broadband radar signal in one embodiment;

[0037] Figure 2 A comparison diagram of the results of generating parallel linear frequency modulation signals in one embodiment, wherein (a) is the linear frequency modulation signal result directly generated by MATLAB, and (b) is the linear frequency modulation signal generated by FPGA and output by MATLAB;

[0038] Figure 31 is a comparison diagram of broadband radar signal amplitude before and after compensation in an embodiment, wherein (a) is the signal output result before compensation, and (b) is the signal output result after compensation. DETAILED DESCRIPTION

[0039] In order to make the purpose, technical solution and advantages of the present application more clearly understood, the present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0040] In this implementation example, Figure 1 As shown, a method for compensating the amplitude flatness of a broadband radar signal is provided, comprising the following steps:

[0041] Step S102, obtaining the bandwidth and signal pulse width of the broadband radar signal, generating a first baseband signal and a carrier, mixing the first baseband signal and the carrier signal to generate a first intermediate frequency digital signal, converting the first intermediate frequency digital signal into a first intermediate frequency analog signal for output.

[0042] In this embodiment, the bandwidth of the radar signal is 1300 MHz, the pulse width is 100 μs, and the sampling frequency f s The frequency band is 3200MHz, the carrier frequency is 2400MHz, and the flatness requirement is ±1dB within the bandwidth.

[0043] According to the formula of linear frequency modulation signal

[0044] s(t)=A cos(2πf0t+πkt 2 ) (Formula 1)

[0045] Generate the corresponding linear frequency modulation signal. Where t is the time variable, in seconds; f0 is the zero time frequency; k represents the frequency change rate, that is, the slope. When k>0, the frequency increases, and when k<0, the frequency decreases. Here B is the signal bandwidth and τ is the signal pulse width.

[0046] Using f s By sampling the signal, we can get:

[0047] s(t)=A cos[2πf0nT s +πk(nT s ) 2 ]

[0048] Where n∈[0,N],T s =1 / f s .

[0049] In this embodiment, the working clock of the FPGA is 200 MHz, which is much smaller than the bandwidth of the signal (the radar signal bandwidth is 1300 MHz), so 16 channels are used in parallel to generate the linear frequency modulation signal.

[0050] According to the principle of DDS (Direct Digital Synthesizer), to generate LFM signal, the change value of LFM phase is input into the phase accumulator of DDS each time, so the phase value at time n+1 is as follows:

[0051] s(t)=A cos[2πf0(n+1)T s +πk(n+1) 2 T s 2 ] (Formula 2)

[0052] Among them, T s is the step value in the actual DDS design process, K = kT s / 2=k / 2f s .

[0053] Let n = 16i + j, x(n) = x(16i + j) = x i,j =(f0+Kn)nT, where Then we can calculate ΔX f0 (n) = 16f0T s ,ΔX k (n) = (512i + 32j + 256) KT s , thus obtaining the accumulated value of the frequency control word and phase control word of DDS. The obtained frequency control word and phase control word can be directly used to generate the corresponding linear frequency modulation signal using the DDS IP core in FPGA.

[0054] In this implementation example, Figure 2 As shown in the figure, the results of the linear frequency modulation signal (a) directly generated by MATLAB and the 16-channel parallel linear frequency modulation signal (b) generated by FPGA are shown. It can be seen that the two are consistent. Using the technical method provided by the present invention, the frequency band range (f min ,f max ) can also visually show the effect of the compensated signal.

[0055] The calculated frequency control word and phase control word are input into the DDS to generate a linear frequency modulation signal with a corresponding bandwidth and pulse width, that is, a first baseband signal, and output it.

[0056] After the corresponding linear frequency modulation signal is generated by DDS, it is used as a baseband signal for carrier modulation, and then sent to the high-speed DAC chip to output the corresponding first intermediate frequency digital signal, and the first intermediate frequency digital signal is converted from digital to analog to be converted into a first intermediate frequency analog signal.

[0057] Step S104, obtaining the first intermediate frequency analog signal in the frequency band range (f min ,f max ), evenly take n frequency points, normalize, invert, and quantize to generate corresponding n compensation values, and generate a compensation value group C1.

[0058] In this embodiment, the first intermediate frequency analog signal output by the DA intermediate frequency signal is sent to the spectrum analyzer to obtain the amplitudes of all sampling points of the spectrum analyzer within the frequency band, and the amplitudes of n frequency points are uniformly taken. In this embodiment, n is 1024, and the amplitudes of the 1024 frequency points are A1~A 1024 . Get the maximum amplitude value A among 1024 frequency points max , normalize all values ​​and take the inverse to get,

[0059] c 1,i =A max / A i , where i∈[0,1024] (Formula 3)

[0060] C 1,i Quantization is performed to obtain a first group of compensation values ​​C1. The first group of 1024 compensation values ​​divides the signal into 1023 compensation intervals.

[0061] Step S106, based on the n compensation values, generate compensation values ​​for all frequency points on the linear frequency modulation signal, and pre-compensate the compensation values ​​for all frequency points in the first baseband signal to generate a second baseband signal, and after carrier modulation, generate a second intermediate frequency digital signal and a second intermediate frequency analog signal; re-complete step S104 to generate compensation value group C2.

[0062] The frequency point of the intermediate frequency signal output corresponds to the frequency point of the baseband signal. Since the output of the baseband signal is a linear frequency modulation signal, the corresponding frequency point is f b =f m -f c , f b is the baseband signal frequency, f m is the intermediate frequency signal frequency, f c is the carrier signal frequency.

[0063] According to the pulse width of the linear frequency modulation signal and the clock of the FPGA, the number of points of each linear frequency modulation signal generated is calculated as m = τ·f s=20000. According to the number of linear frequency modulation signal points in each line and the number of compensation values ​​1024, the number of compensation points in each compensation interval is calculated as m / n=20000 / 1023=l…r=19…563, where 19 is the number of compensation points and 544 is the remainder. Then the number of compensation points in the first 1022 intervals (NC i ) is 19, the number of compensation points in the 1023rd interval (NC 1023 ) is 582=19+563.

[0064] For each interval, the compensation value of each point is calculated linearly, that is:

[0065] C in the first 1022 compensation intervals 1,j =C 1,i +j·(C 1,i+1 -C 1,i ) / l;

[0066] Among them, i∈[1, 1022], j∈[1, 19].

[0067] C in the 1023rd compensation interval 1,1023 =C 1,1023 +j·(C 1,1024 -C 1,1023 ) / 582.

[0068] Among them, j∈[1,582].

[0069] The compensation value C of all frequency points in the compensation interval 1,j Pre-compensate the first baseband signal (B1) in sequence to generate a second baseband signal (B2), form a second intermediate frequency digital signal (MD2) after carrier modulation, and generate a second intermediate frequency analog signal (MA2) output through a DAC chip;

[0070] The second intermediate frequency analog signal (MA2) is subjected to the operation of step S104 again to obtain the compensation value group C2; the compensation value group C2 is multiplied by the compensation value group C1 to obtain the compensation value group C=C1C2 of the current baseband signal.

[0071] Step S108, repeating steps S104 and S106 for several times to generate several compensation value groups.

[0072] The second baseband signal, the second intermediate frequency digital signal and the second intermediate frequency analog signal of the linear frequency modulation signal generated in step S106 are used as the first baseband signal, the first intermediate frequency digital signal and the first intermediate frequency analog signal, and steps S104 and S106 are repeated several times until the result output on the spectrum analyzer meets the requirement of in-band flatness of ±1dB. The several compensation value groups generated are C1, C2, ..., C m .

[0073] Step S110, obtaining the final compensation value C=C1C2...C m , the final compensation value is pre-compensated in the baseband signal.

[0074] The compensation value group C1, C2, ..., C m Multiply to get the final compensation value C = C1C2...C m , and pre-compensate the obtained compensation value in the baseband signal.

[0075] In this embodiment, if Figure 3 As shown, the change in amplitude flatness before and after signal compensation with a bandwidth of 1.3 GHz is demonstrated. Figure 3 (a) is the amplitude flatness before compensation. From the figure, we can see that when one grid is 2dB, the amplitude fluctuation is about 12dB. Figure 3 (b) is the amplitude flatness after compensation. It can be seen from the figure that when one grid is 1dB, the amplitude fluctuation is about 2dB. Therefore, this method has a good compensation effect for broadband signals. It can be seen that the technical method provided by the present invention can achieve a good compensation effect. Through multiple compensations and increasing the number of compensation values, the curve composed of the compensation values ​​can be made closer to the inverse of the spectrum of the signal output, thereby ensuring the flatness of the signal band after compensation.

[0076] The beneficial effects of the present invention are:

[0077] (1) Using the technical method provided by the present invention, the frequency band range (f min ,f max ) can also visually see the effect of the compensated signal;

[0078] (2) The technical method provided by the present invention can achieve a good compensation effect. By performing multiple compensations and increasing the number of compensation values, the curve formed by the compensation values ​​can be made closer to the inverse of the spectrum of the signal output, thereby ensuring the flatness of the signal band after compensation;

[0079] (3) The technical method provided by the present invention is simple to operate and widely used. It can collect signals from baseband, intermediate frequency, radio frequency output and other ports, obtain corresponding compensation signals, and complete the compensation and correction of the in-band flatness of the entire channel.

[0080] The above are only preferred embodiments of the present invention, and are not intended to limit the present invention in any form. Although the present invention has been disclosed as above in terms of preferred embodiments, they are not intended to limit the present invention. Any technician familiar with the art can use the above disclosed technical content to make many possible changes and modifications to the technical solution of the present invention, or modify it into an equivalent embodiment of equivalent changes, without departing from the scope of the technical solution of the present invention. Therefore, any simple modification, equivalent change and modification made to the above embodiments based on the technical essence of the present invention, which does not depart from the content of the technical solution of the present invention, should fall within the scope of protection of the technical solution of the present invention.

Claims

1. A method for compensating wideband radar signal amplitude flatness, characterized in that: The method comprises: S10: acquiring the bandwidth and signal pulse width of the broadband radar signal, generating a digital signal waveform of a corresponding linear frequency modulation signal, namely, a first baseband signal, and generating a carrier, mixing the first baseband signal with the carrier signal to generate a first intermediate frequency digital signal, and converting the first intermediate frequency digital signal into a first intermediate frequency analog signal for output; S20: Obtain the first intermediate frequency analog signal in the frequency band range The amplitude is uniformly taken n frequency points, normalize, invert, and quantize to generate the corresponding n compensation values ​​and generate compensation value groups C 1; S30: According to the n a compensation value, generating compensation values ​​for all frequency points on the linear frequency modulation signal, and pre-compensating the compensation values ​​for all frequency points in the first baseband signal to generate a second baseband signal, and after carrier modulation, generating a second intermediate frequency digital signal and a second intermediate frequency analog signal, and using the second baseband signal, the second intermediate frequency digital signal and the second intermediate frequency analog signal of the linear frequency modulation signal as the first baseband signal, the first intermediate frequency digital signal and the first intermediate frequency analog signal; S40: Repeat steps S20 and S30 several times to obtain the corresponding compensation value group C1, C2, ..., Cm, and obtain the final compensation value C = C1C2 ... C m , the final compensation value is pre-compensated in the baseband signal.

2. The method for compensating the amplitude flatness of a broadband radar signal according to claim 1, characterized in that: The step of obtaining the bandwidth and the signal pulse width of the broadband radar signal, generating a digital signal waveform of a corresponding linear frequency modulation signal, namely, a first baseband signal, and generating a carrier wave comprises: According to the bandwidth and signal pulse width of the broadband radar signal, using FPGA to generate multiple parallel linear frequency modulation signals, namely the first baseband signal; The carrier is generated using a direct digital frequency synthesizer.

3. The method for compensating the amplitude flatness of a broadband radar signal according to claim 2, characterized in that: The step of obtaining the bandwidth and the signal pulse width of the broadband radar signal and generating a digital signal waveform of a corresponding linear frequency modulation signal, namely, a first baseband signal, includes: According to the bandwidth and signal pulse width of the broadband radar signal, multiple groups of frequency control words and phase control words are calculated and generated in the FPGA; According to the frequency control word and the phase control word, a DDS IP core in the FPGA is used to generate a multi-channel parallel linear frequency modulation signal digital signal waveform, namely the first baseband signal.

4. The method for compensating the amplitude flatness of a broadband radar signal according to claim 2, characterized in that: The mixing of the first baseband signal and the carrier signal to generate a first intermediate frequency digital signal, and converting the first intermediate frequency digital signal into a first intermediate frequency analog signal for output, comprises: Perform carrier modulation and mixing on the first baseband signal to generate the first intermediate frequency digital signal, and send the first intermediate frequency digital signal to the DAC chip; After receiving the first intermediate frequency digital signal, the DAC chip performs digital-to-analog conversion to generate the first intermediate frequency analog signal for output.

5. The method for compensating the amplitude flatness of a broadband radar signal according to claim 1, characterized in that: Obtain the first intermediate frequency analog signal in the frequency band range The amplitude is uniformly taken n frequency points, normalize, invert, and quantize to generate the corresponding n compensation values ​​and generate compensation value groups C 1, including: Inputting the first intermediate frequency analog signal into a spectrum analyzer to obtain the amplitudes of all frequency points output by the spectrum analyzer within a frequency band; The amplitudes of all the frequency points are uniformly taken n The amplitude of the frequency points is generated n -1 compensation interval; Take the n The maximum value of the frequency amplitude is used n The amplitude of the frequency point is divided by the maximum value, and normalized to obtain the n Compensation value c 1,i ,in ; The n Compensation value c 1,i Take the inverse and quantize to generate the compensation value group of the current digital signal C = C 1.

6. The method for compensating the amplitude flatness of a broadband radar signal according to claim 5, characterized in that: According to the n The method comprises: generating compensation values ​​of all frequency points on the first baseband signal, pre-compensating the compensation values ​​of all frequency points in the first baseband signal, generating a second baseband signal, a second intermediate frequency digital signal, and a second intermediate frequency analog signal, including: According to the first intermediate frequency analog signal n frequency points, determine the first baseband signal n Frequency points f 1, f 2,..., f n , generating the corresponding n-1 compensation interval; According to the pulse width of the linear frequency modulation signal and the clock of the FPGA, the number of points of each linear frequency modulation signal generated is calculated; According to the number of linear frequency modulation signal points and the number of compensation values ​​of each line n , calculate and obtain the number of compensation points in each compensation interval; According to the compensation interval , the number of compensation points in the compensation interval and the compensation values ​​at both ends of the compensation interval C 1,i and C 1,i+1 , based on the linear relationship, calculate the compensation interval i Compensation values ​​for all frequency points in the n-1 The compensation values ​​of all frequency points within a compensation interval; Pre-compensate the compensation values ​​of all frequency points in the compensation interval in the first baseband signal in sequence to generate a second baseband signal, form a second intermediate frequency digital signal after carrier modulation, and generate a second intermediate frequency analog signal output through a DAC chip; Repeat the operation of step S20 for the second intermediate frequency analog signal to obtain a compensation value group C2; multiply the compensation value group C2 by the compensation value group C1 to obtain a compensation value group C = C1C2 of the current baseband signal.

Images