High-efficiency time reversal imaging method

Abstract

The invention discloses a high-efficiency time reversal imaging method. An ultra-wideband antenna array collects time-domain signals scattered by a non-cooperative object, the time-domain signals are converted into frequency-domain signals via Fourier transform, a frequency-domain space-frequency multi-mode response matrix is established, and the frequency-domain space-frequency multi-mode response matrix is decomposed by singular values to obtain signal subspace and noise subspace vectors; and selective focusing imaging of the object is realized by taking one selected from a position 1) where an inner product of the signal subspace vector and a background green function vector corresponding to an infield point of a detection area is maximal and a position 2) where a conjugate inner product where the noise subspace vector and the background green function vector corresponding to the infield point of the detection area is 0 as a focusing imaging position of the object. Via the method, it is required that the antenna array to collect scattering field data once to establish the space-frequency multi-mode response matrix. Focusing imaging of an active source object and a passive source object scattering other incident signals passively can be realized, focusing imaging of a rapid movement object can be also realized, and the imaging efficiency, accuracy, reliability and interference resistance are high.

Description

[0001] Technical field: [0002] The invention relates to an efficient time-reversal imaging technology, which belongs to the field of microwave imaging. [0003] Background technique: [0004] Microwave imaging refers to an imaging method that uses microwaves as information carriers. Its principle is to irradiate the measured object with microwaves, and then reconstruct the shape or (complex) dielectric constant distribution of the object through the measured value of the scattered field outside the object. There are many algorithms for microwave imaging, but due to the nonlinear relationship between the scattering field and the scatterer, and the non-uniqueness and instability of the solution to the electromagnetic inverse scattering problem, it is difficult for people to obtain an analytical solution to the electromagnetic inverse scattering problem; In most cases, it can only be solved by numerical methods, and only an optimal solution can be selected from many solutions as...

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Problems solved by technology

[0005] 1) Multi-station transmission and multi-station reception are necessary, and generally multi-stations surround the target, which makes imaging of unknown targets almost impossible, especially for moving unknown targets, the multi-station requirements can hardly be met

[0006] 2) The impact of the surrounding environment, multipath effects and other factors on target imaging is not considered, especially when the target is placed in the environment of multiple strong scatterers, even when the target is not within the line-of-sight range of the transmitting antenna

Therefore, the real-time performance of target focusing is difficult to be satisfied, and the focused imaging of active source targets and passive source targets that passively scatter other incident signals cannot be realized, and of course the focused imaging of fast-moving targets cannot be realized.

[0009] (2) At each frequency point, obtaining the return vector through singular value decomposition of the empty-empty polymorphic response matrix will generate a random phase that depends on the frequency, and the return signal waveform will change accordingly after inverse Fourier transform , the return signal transmitted by each antenna unit will not achieve coherent superposition at the target, which will affect the imaging accuracy

If the transmission medium is a random medium, the dielectric constant of the medium oscillates violently, causing the random phase to change drastically. This phenomenon becomes more prominent, and even the normal time-reversal signal cannot be extracted.

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