CN109581299B - Ultra-wideband step-frequency continuous wave pulse compression sidelobe suppression method - Google Patents
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- CN109581299B CN109581299B CN201811511900.7A CN201811511900A CN109581299B CN 109581299 B CN109581299 B CN 109581299B CN 201811511900 A CN201811511900 A CN 201811511900A CN 109581299 B CN109581299 B CN 109581299B
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Abstract
The invention discloses a method for suppressing side lobes of ultra-wideband step-frequency continuous wave pulse compression, which comprises the following steps: s1: determining the number of discrete inverse Fourier transform points in pulse compression; s2: calculating discrete inverse Fourier transform of each frequency point of the step frequency continuous wave; s3: calculating the power sum of discrete inverse Fourier transform of each frequency point of the step frequency continuous wave; s4: all frequency points of the step frequency continuous wave are combined, and pulse compression is completed through discrete inverse Fourier transform; s5: calculating the power of the pulse compression of the step frequency continuous wave; dividing the power of pulse compression by the sum of the power of discrete inverse Fourier transform of each frequency point to construct a sidelobe suppression coefficient; and multiplying the sidelobe suppression coefficient by the step frequency continuous wave pulse compression to complete sidelobe suppression. The method has the advantages of small calculated amount, convenience, flexibility, good side lobe suppression effect, no main lobe broadening effect and the like.
Description
Technical Field
The invention mainly relates to the technical field of radar signal processing, in particular to an ultra wide band step frequency continuous wave pulse compression side lobe suppression method.
Background
The method includes the steps of gradually transmitting a single Frequency point signal by using a Stepped Frequency Continuous Wave (SFCW) according to fixed Frequency steps, obtaining a large bandwidth, and synthesizing an Ultra-Wideband (UWB) signal. The SFCW signal can be considered as a frequency domain signal, and usually an echo signal is transformed into a time domain by using Inverse Fast Fourier Transform (IFFT), so that pulse compression is performed and high range resolution is achieved.
Compared with frequency modulation continuous wave signals, the SFCW signals are more flexible in transmission, can effectively avoid interference frequency points, are discrete in frequency spectrum and are beneficial to digital signal processing. The SFCW signal achieves higher average transmit power and enables coherent processing relative to impulse UWB signals of very short duration.
However, the distance direction obtained by pulse compression of the SFCW signal is high-resolution (approximately represented by a sinc function), and the SFCW signal often has high side lobe level. The commonly used windowing sidelobe suppression method can expand a main lobe while suppressing sidelobes, so that the distance of the SFCW signal is reduced towards the resolution.
Disclosure of Invention
The technical problem to be solved by the invention is as follows: aiming at the technical problems in the prior art, the invention provides the ultra wide band step frequency continuous wave pulse compression side lobe suppression method which is small in calculated amount, convenient and flexible, good in side lobe suppression effect and free of main lobe broadening effect.
In order to solve the technical problems, the invention adopts the following technical scheme:
an ultra-wideband step-frequency continuous wave pulse compression sidelobe suppression method comprises the following steps:
step S1: determining the number of discrete inverse Fourier transform points in pulse compression;
step S2: calculating discrete inverse Fourier transform of each frequency point of the step frequency continuous wave;
step S3: calculating the power sum of discrete inverse Fourier transform of each frequency point of the step frequency continuous wave;
step S4: all frequency points of the step frequency continuous wave are combined, and pulse compression is completed through discrete inverse Fourier transform;
step S5: calculating the power of the pulse compression of the step frequency continuous wave; dividing the power of pulse compression by the sum of the power of discrete inverse Fourier transform of each frequency point to construct a sidelobe suppression coefficient; and multiplying the sidelobe suppression coefficient by the step frequency continuous wave pulse compression to complete sidelobe suppression.
As a further improvement of the invention: in step S1, the SFCW signal is composed of K frequency points, and the length of the discrete inverse fourier transform is set to N.
As a further improvement of the invention: in step S2, the discrete inverse fourier transform of each frequency point of the received SFCW signal is successively calculated, and the power sum of the discrete inverse fourier transform of each frequency point is calculated; for the k-th frequency point signal xkThe discrete inverse fourier transform calculation formula is as follows:
the power and calculation formula of all frequency point discrete inverse Fourier transform are as follows:
wherein XkRepresenting the k-th frequency point signal xkDiscrete inverse Fourier transform of (P)sAnd the power sum of all frequency point discrete inverse Fourier transform is shown.
As a further improvement of the invention: in step S3, all frequency points are combined together according to the following discrete inverse fourier transform formula:
realizing pulse compression of all frequency points, wherein RP represents pulse compression results of all frequency points, and j represents unit imaginary number; and calculating the power of the pulse compression according to the following formula:
P(i)＝|RP(i)|2,i＝1,2,…,N
wherein P represents the power of the pulse compression of all frequency bins.
As a further improvement of the invention: in step S4, the power of pulse compression is divided by the sum of the powers of discrete inverse fourier transform of each frequency point, and a sidelobe suppression coefficient is constructed, where the formula is as follows:
where w represents the sidelobe suppression coefficient.
As a further improvement of the invention: in step S5, the pulse compression result is multiplied by a suppression coefficient to complete the side lobe suppression with high resolution in the distance direction, and the formula is as follows:
S(i)＝w(i)RP(i),i＝1,2,…,N，
where S represents the pulse compression result after sidelobe suppression.
Compared with the prior art, the invention has the advantages that:
the ultra-wideband step frequency continuous wave pulse compression side lobe suppression method is suitable for side lobe suppression without broadening of a main lobe of an ultra-wideband SFCW signal, has the advantages of small calculated amount, convenience, flexibility and the like, and has good side lobe suppression effect and no main lobe broadening effect.
Drawings
FIG. 1 is a schematic flow diagram of the process of the present invention.
FIG. 2 is a diagram showing the results of a simulation comparison experiment in a specific application example of the present invention.
Fig. 3 is an enlarged schematic view of the main lobe region of the experimental result of fig. 2.
Detailed Description
The invention will be described in further detail below with reference to the drawings and specific examples.
As shown in fig. 1, the ultra-wideband step-frequency continuous wave pulse compression sidelobe suppression method of the present invention includes the steps of:
step S1: determining the number of discrete inverse Fourier transform points in pulse compression;
assuming that the SFCW signal consists of K frequency points, setting the length of discrete inverse Fourier transform to be N;
step S2: calculating discrete inverse Fourier transform of each frequency point of the step frequency continuous wave;
and successively calculating the discrete inverse Fourier transform of each frequency point of the received SFCW signal, and calculating the power sum of the discrete inverse Fourier transform of each frequency point. For the k-th frequency point signal xkThe discrete inverse fourier transform calculation formula is as follows:
the power and calculation formula of all frequency point discrete inverse Fourier transform are as follows:
wherein XkRepresenting the k-th frequency point signal xkDiscrete inverse Fourier transform of (P)sAnd the power sum of all frequency point discrete inverse Fourier transform is shown.
Step S3: calculating the power sum of discrete inverse Fourier transform of each frequency point of the step frequency continuous wave;
all frequency points are combined together according to the following discrete inverse Fourier transform formula:
and realizing the pulse compression of all frequency points, wherein RP represents the pulse compression result of all frequency points, and j represents unit imaginary number. And calculating the power of the pulse compression according to the following formula:
P(i)＝|RP(i)|2,i＝1,2,…,N (4)
wherein P represents the power of the pulse compression of all frequency bins.
Step S4: all frequency points of the step frequency continuous wave are combined, and pulse compression is completed through discrete inverse Fourier transform;
dividing the power of pulse compression by the power sum of discrete inverse Fourier transform of each frequency point to construct a sidelobe suppression coefficient, wherein the formula is as follows:
where w represents the sidelobe suppression coefficient.
Step S5: calculating the power of the pulse compression of the step frequency continuous wave; dividing the power of pulse compression by the sum of the power of discrete inverse Fourier transform of each frequency point to construct a sidelobe suppression coefficient; and multiplying the sidelobe suppression coefficient by the step frequency continuous wave pulse compression to complete sidelobe suppression.
And multiplying the pulse compression result by a suppression coefficient to complete the side lobe suppression in the distance direction with high resolution, wherein the formula is as follows:
S(i)＝w(i)RP(i),i＝1,2,…,N (6)
where S represents the pulse compression result after sidelobe suppression.
In a specific application example, the specific operation flow is as follows:
step S100: assuming that the SFCW signal consists of K frequency bins, the length of the discrete inverse fourier transform is set to N.
In the simulation experiment of the invention, the length of the discrete inverse Fourier transform is set to be N4096. Table 1 below gives the parameters of the SFCW signal in the simulation experiment.
TABLE 1 parameters of SFCW signals
| Starting frequency | Frequency stepping | Number of frequency points K | |
| 0.5 | 2MHz | 600 |
Step S200: and successively calculating the discrete inverse Fourier transform of each frequency point of the received SFCW signal, and calculating the power sum of the discrete inverse Fourier transform of each frequency point. For the k-th frequency point signal xkThe discrete inverse fourier transform calculation formula is as follows:
the IFFT power and the calculation formula of all frequency points are as follows;
wherein XkRepresenting the k-th frequency point signal xkDiscrete inverse Fourier transform of (P)sAnd the power sum of all frequency point discrete inverse Fourier transform is shown.
Step S300: all frequency points are combined together according to the following discrete inverse Fourier transform formula:
and realizing the pulse compression of all frequency points, wherein RP represents the pulse compression result of all frequency points, and j represents unit imaginary number. The power of the pulse compression is calculated according to the following formula:
P(i)＝|RP(i)|2,i＝1,2,…,N
as can be seen from the simulation experiment results of fig. 2 and fig. 3, the energy level of the side lobe is-13 dB, which is very high, in the original pulse compression result without side lobe suppression.
Step S400: dividing the power of pulse compression by the power sum of discrete inverse Fourier transform of each frequency point to construct a sidelobe suppression coefficient, wherein the formula is as follows:
where w represents the sidelobe suppression coefficient.
Step S500: and multiplying the pulse compression result by a suppression coefficient to complete the side lobe suppression in the distance direction with high resolution, wherein the formula is as follows:
S(i)＝w(i)RP(i),i＝1,2,…,N
where S represents the pulse compression result after sidelobe suppression.
As can be seen from the simulation experiment result of FIG. 2, after the Hamming window is added, the side lobe level of the pulse compression is reduced, but the main lobe is expanded. With the method of the present invention, the main lobe width is not widened but narrowed instead while the level of the side lobe is suppressed, which contributes to the improvement of the distance-to-resolution.
The above is only a preferred embodiment of the present invention, and the protection scope of the present invention is not limited to the above-mentioned embodiments, and all technical solutions belonging to the idea of the present invention belong to the protection scope of the present invention. It should be noted that modifications and embellishments within the scope of the invention may be made by those skilled in the art without departing from the principle of the invention.
Claims (5)
1. An ultra-wideband step frequency continuous wave pulse compression sidelobe suppression method is characterized by comprising the following steps:
step S1: determining the number of discrete inverse Fourier transform points in pulse compression;
step S2: calculating discrete inverse Fourier transform of each frequency point of the step frequency continuous wave;
step S3: calculating the power sum of discrete inverse Fourier transform of each frequency point of the step frequency continuous wave;
step S4: all frequency points of the step frequency continuous wave are combined, and pulse compression is completed through discrete inverse Fourier transform;
step S5: calculating the power of the pulse compression of the step frequency continuous wave; dividing the power of pulse compression by the sum of the power of discrete inverse Fourier transform of each frequency point to construct a sidelobe suppression coefficient; the formula is as follows:
wherein w represents a sidelobe suppression coefficient; p represents the power of all frequency point pulse compression; psThe power sum of all frequency point discrete inverse Fourier transform is represented; n is the length of discrete inverse Fourier transform; and multiplying the sidelobe suppression coefficient by the step frequency continuous wave pulse compression to complete sidelobe suppression.
2. The method for suppressing sidelobes of ultra-wideband step-frequency continuous wave pulse compression as claimed in claim 1, wherein the step-frequency continuous wave SFCW signal in step S1 is composed of K bins, and the length of the discrete inverse fourier transform is set to N.
3. The ultra-wideband step-frequency continuous wave pulse compression sidelobe suppression method according to claim 2, wherein in step S2, discrete inverse fourier transform of each frequency point of the received SFCW signal is successively calculated; for the signal x of the k-th frequency pointkThe discrete inverse fourier transform calculation formula is as follows:
and calculating the power sum of the discrete inverse Fourier transform of each frequency point, wherein the power sum calculation formula of the discrete inverse Fourier transform of all the frequency points is as follows:
wherein XkRepresenting the k-th frequency point signal xkDiscrete inverse Fourier transform of (P)sAnd the power sum of all frequency point discrete inverse Fourier transform is shown.
4. The ultra-wideband step-frequency continuous wave pulse compression sidelobe suppression method according to claim 3, wherein in step S4, all frequency points are combined together according to the following discrete inverse Fourier transform formula:
realizing pulse compression of all frequency points, wherein RP represents pulse compression results of all frequency points, and j represents unit imaginary number; and calculating the power of the pulse compression according to the following formula:
P(i)＝|RP(i)|2, i＝1,2,…,N
wherein P represents the power of the pulse compression of all frequency bins.
5. The ultra-wideband step-frequency continuous wave pulse compression sidelobe suppression method according to claim 4, wherein in step S5, the pulse compression result is multiplied by a suppression coefficient to complete sidelobe suppression in a distance direction with high resolution, and the formula is as follows:
S(i)＝w(i)RP(i), i＝1,2,…,N
where S represents the pulse compression result after sidelobe suppression.
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