CN110940956A - Clutter suppression method for radar motion platform based on continuous wave system - Google Patents

Abstract

The invention discloses a clutter suppression method for a radar motion platform based on a continuous wave system, and relates to clutter suppression for the radar motion platform based on the continuous wave system in the field of radio measurement. The method mainly comprises the processing steps of space-distance radar echo data distance dimension demodulation processing, space-time echo data conversion to angle-Doppler data, optimal auxiliary channel selection, space-time two-dimensional filter coefficient calculation, space-time two-dimensional filter processing and the like. The method inhibits the extremely strong ground clutter received by the radar when the platform works during advancing, and solves the problem that the low-altitude weak target on the ground or near ground is submerged in the ground clutter and cannot be effectively detected. The method has the characteristics of small real-time calculation amount, good signal-to-noise-ratio improvement effect after space-time two-dimensional filtering output, good algorithm adaptation in a non-uniform clutter environment and simple engineering realization, and solves the problem that the performance of the radar is sharply reduced when the radar works during the advancing of the platform.

Description

Clutter suppression method for radar motion platform based on continuous wave system

Technical Field

The invention relates to the field of radar, in particular to a clutter suppression method for a continuous wave system radar motion platform.

Background

When the continuous wave body radar is arranged on a moving platform and is used for detecting moving targets on the ground and at low altitudes, strong ground clutter with wide distribution range has serious influence on the detection performance of a radar system. In a modern battlefield, a radar works during platform traveling, so that a static ground clutter block moves relative to the radar, and relative speeds of clutter blocks at different angles and a moving platform are different, so that Doppler frequencies corresponding to the clutter blocks at different angles are different when the platform moves. A clutter suppression method for a radar motion platform based on a continuous wave system is an important research direction.

When the radar works during the platform traveling, the radar receiver can receive extremely strong ground clutter, the ground clutter is high in power, and even fatal, due to the fact that the ground clutter from different directions are different in speed relative to the radar, the clutter spectrum is expanded seriously, and low-altitude weak targets on the ground or near the ground are usually submerged in the ground clutter and cannot be detected effectively. Therefore, the clutter suppression method for the radar motion platform based on the continuous wave system has important engineering value.

At present, continuous wave body radar generally does not have the capability of suppressing the motion clutter during the motion of a platform or has a very simple algorithm for suppressing the motion clutter.

Disclosure of Invention

The invention aims to solve the main technical problem of avoiding the defects in the background technology and provides a clutter suppression method for a continuous wave system radar motion platform. The traditional dimension-reducing space-time clutter suppression algorithm does not depend on echo data and has a fixed auxiliary channel selection method. The method for selecting the auxiliary channel of the algorithm designed by the invention is dependent on the current clutter environment, and the method for selecting the auxiliary channel is dynamically adjusted along with the dynamic change of the clutter environment.

The technical scheme adopted by the invention is as follows:

a clutter suppression method for a continuous wave system radar motion platform comprises the following steps:

step 1, delaying and demodulating a target echo signal of each receiving array element in a radar receiving antenna array to obtain a target baseband signal of each receiving array element, accumulating the target baseband signals of all the receiving array elements and forming a space-time target echo data matrix of the current period;

step 2, projecting the space-time target echo data matrix of the current period to an angle-Doppler domain, selecting the angular frequency of the expected target direction and a channel corresponding to the Doppler frequency in the angle-Doppler domain as a main channel, and taking the rest channels as auxiliary channels to be selected;

step 3, in the angle-Doppler domain, selecting an optimal channel from the auxiliary channels to be selected each time by adopting a step-by-step selection method according to the current clutter environment, removing clutter components in the main channel corresponding to the optimal channel until a set number of auxiliary channels are selected, and taking the selected auxiliary channels as the auxiliary channels of the next period; simultaneously, calculating a space-time two-bit filter coefficient of the angular frequency and the Doppler frequency of the current period aiming at the expected direction according to the auxiliary channel selected in the last period;

and 4, acting the space-time two-dimensional filtering coefficient w of the current period on the space-time target echo data matrix of the current period, and performing space-time two-dimensional filtering processing to obtain an output signal after the motion clutter of the current period is suppressed.

The specific way of calculating the spatial-temporal two-bit filter coefficient w of the current period in step 3 is as follows:

x_T＝I^Hx

i is a linear transformation matrix representing the selection of auxiliary channels from the space-time domain to the angle-Doppler domain, x represents a space-time target echo data matrix, x_TData representing the angle-Doppler domain, μ being a normalization constant, s being a vector corresponding to the desired direction in the space-time domain, s_TIs a vector corresponding to angular frequency and Doppler frequency of a desired direction in an angular-Doppler domain, R is a space-time domain clutter covariance matrix, R_TIs a clutter covariance matrix in the transform domain.

Compared with the background technology, the invention has the advantages and effects that:

(1) the invention aims at the problems that the traditional space-time two-dimensional filter coefficient has large calculation workload and does not depend on clutter environment data, and the like. The method for selecting the optimal channel is designed, namely, only one optimal channel is selected from the rest two-dimensional channels according to the selected channel in each step, then the influence of the current selected channel on the main channel is eliminated, namely, the clutter component in the main channel corresponding to the selected channel is removed, and then the next optimal channel is selected until the required number of auxiliary channels are selected. Whereas the method of the background art does not take this into account.

(2) Research shows that the conventional technology selects an auxiliary channel near a main channel or on a clutter ridge not to be the channel capable of eliminating clutter optimally, and the optimal auxiliary channel selected through iteration can improve the output SCNR (signal-to-noise-and-noise ratio) by more than 3dB compared with the conventional technology.

(3) In order to cope with the situation that only a single sample is available in an extreme non-uniform clutter environment, only a direct data domain processing method can be adopted, but the SCNR (signal to noise ratio) loss is large. For classical dimension-reduced space-time adaptive processing or rank-reduced space-time adaptive processing, it is not possible to work properly when only a single sample is available. In an extreme inhomogeneous clutter environment when only a single sample is available, by analyzing the clutter environment and adopting an optimal auxiliary channel calculation space-time two-dimensional adaptive filtering processing method of iterative screening, the invention realizes the great improvement of output SCNR (signal-to-noise-plus-noise ratio) which can reach more than 15 dB.

Drawings

FIG. 1 is a schematic diagram of a two-dimensional filtering of a spatio-temporal target echo data matrix according to the present invention;

FIG. 2 is a schematic diagram of a space-time target echo data matrix projection to the angle-Doppler domain according to the present invention;

fig. 3 is a schematic diagram of the present invention.

Detailed Description

The present invention will be described in further detail with reference to specific embodiments.

A clutter suppression method for a continuous wave system radar motion platform, as shown in fig. 3, the method includes the following steps:

step 1, delaying and demodulating a target echo signal of each receiving array element in a radar receiving antenna array to obtain a target baseband signal of each receiving array element, wherein the demodulation mode is that the echo signals in each group of transmission periods are subjected to FFT (fast Fourier transform) processing to obtain one-dimensional distance dimensional sample points, and the demodulation data of all the receiving array elements are accumulated to form a space-time target echo data matrix of the current period; the two-dimensional filtering process of the space-time target echo data matrix is shown in FIG. 1;

step 2, projecting the space-time target echo data matrix of the current period to an angle-Doppler domain, operating as shown in fig. 2, converting from the space-time domain to the angle-Doppler domain, which can be directly obtained through two-dimensional FFT conversion, and can also be realized through time domain beam forming and space domain beam forming, selecting the angular frequency of the expected target direction and the channel corresponding to the Doppler frequency in the formed conversion domain as the main channel, and using the rest channels as the auxiliary channels to be selected;

step 3, determining the number of the auxiliary channels selected in the next period in the angle-Doppler domain; introducing a channel selection matrix V for the formed auxiliary channels to be selected, wherein if all the rest channels are selected as auxiliary channels, the V becomes a unit matrix, and if only part of the two-dimensional channels are selected as auxiliary channels, the processing dimension can be reduced;

the auxiliary channel selection method is dependent on the current clutter environment, the auxiliary channel is dynamically adjusted along with the dynamic change of the clutter environment, the auxiliary channel with the maximum output SCNR (signal-to-noise-ratio) is the auxiliary channel selected by the algorithm, so the basis for selecting the auxiliary channel can be converted from maximizing the output SCNR into maximizing epsilon^HThe minimization of R epsilon adopts a step selection method, wherein epsilon is used for representing the deviation between the optimal weight vector without dimension reduction and the optimal weight vector after dimension reduction, R is a clutter covariance matrix, the step means that each step selects an optimal channel from the rest two-dimensional channels, then the influence of the selected optimal channel on a main channel is eliminated, namely, the clutter component in the main channel corresponding to the selected optimal channel is removed, and then the next optimal channel is selected until the auxiliary channel with the required quantity is selected;

meanwhile, if the filter is initial, calculating a space-time two-bit filter coefficient of the current period by using a set auxiliary channel; in the later period, calculating a space-time two-bit filter coefficient of the current period according to the auxiliary channel selected in the previous period;

step 4, performing space-time two-dimensional filter coefficient solving processing on angular frequency and Doppler frequency in an expected direction among a plurality of receiving array elements, calculating space-time two-dimensional filter coefficient w of the current period, representing a space-time target echo data matrix by using x, selecting an auxiliary channel converted from a space-time domain to an angle-Doppler domain, and representing the auxiliary channel by using a linear transformation matrix I, wherein the data of the angle-Doppler domain is represented by using x_TIs represented by x_T＝I^Hx, clutter covariance matrix R in transform domain_TIs composed of

The computation of the spatio-temporal two-dimensional filter coefficients w in the transform domain is given by:

where μ is a normalization constant, s is a vector corresponding to the desired direction in the space-time domain, s_TApplying a space-time two-dimensional filter coefficient w to a space-time data matrix accumulated before for a vector corresponding to an angular frequency and a Doppler frequency in a desired direction in an angle-Doppler domain, and performing two-dimensional adaptive filtering processing to obtain an output y-w after the dynamic clutter suppression^Hx。

According to the method, each CPI (phased array continuous wave radar beam dwell time) is regarded as a period, and the optimal channel which is applied only by the next CPI can be obtained through time-consuming iterative operation in the current CPI period. During the calculation of the spatial-temporal two-dimensional filter coefficients, the required best channel is already obtained in the last CPI. Assuming that the clutter is uniform or slowly varying, the statistical properties of the clutter within the previous CPI and the current CPI may be assumed to be the same.

Claims (2)

1. A clutter suppression method for a continuous wave system radar motion platform is characterized by comprising the following steps:

step 1, delaying and demodulating a target echo signal of each receiving array element in a radar receiving antenna array to obtain a target baseband signal of each receiving array element, accumulating the target baseband signals of all the receiving array elements and forming a space-time target echo data matrix of the current period;

step 2, projecting the space-time target echo data matrix of the current period to an angle-Doppler domain, selecting the angular frequency of the expected target direction and a channel corresponding to the Doppler frequency in the angle-Doppler domain as a main channel, and taking the rest channels as auxiliary channels to be selected;

step 3, in the angle-Doppler domain, selecting an optimal channel from the auxiliary channels to be selected each time by adopting a step-by-step selection method according to the current clutter environment, removing clutter components in the main channel corresponding to the optimal channel until a set number of auxiliary channels are selected, and taking the selected auxiliary channels as the auxiliary channels of the next period; simultaneously, calculating a space-time two-bit filter coefficient of the angular frequency and the Doppler frequency of the current period aiming at the expected direction according to the auxiliary channel selected in the last period;

and 4, acting the space-time two-dimensional filtering coefficient of the current period on the space-time target echo data matrix of the current period, and performing space-time two-dimensional filtering processing to obtain an output signal after the motion clutter suppression of the current period.

2. The method for suppressing clutter of a moving platform of a continuous wave system radar according to claim 1, wherein the specific way of calculating the spatio-temporal two-bit filter coefficient w of the current period in step 3 is as follows:

x_T＝I^Hx

i is a linear transformation matrix representing the selection of auxiliary channels from the space-time domain to the angle-Doppler domain, x represents a space-time target echo data matrix, x_TData representing the angle-Doppler domain, μ being a normalization constant, s being a vector corresponding to the desired direction in the space-time domain, s_TIs a vector corresponding to angular frequency and Doppler frequency of a desired direction in an angular-Doppler domain, R is a space-time domain clutter covariance matrix, R_TIs a clutter covariance matrix in the transform domain.

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