CN103135109B - Ultra wide band radar imaging method based on multipath signals - Google Patents

Abstract

The invention provides an ultra wide band radar imaging method based on multipath signals. The method includes a first step of setting mirroring virtual transmitting antennas and mirroring virtual receiving antennas according to a signal propagation route on the condition that the position of a reflecting body is known, a second step of carrying out phase position and amplitude compensation on multipath signals according to imaging geometry and utilizing any pair of the transmitting antenna and the receiving antenna to carrying out imaging, and a third step of carrying out coherence stack on imaging results of each transmitting and receiving antenna pair to obtain the final imaging. In the imaging process, the multipath signals from different directions are utilized to increase the aperture of a radar receiving antenna in the ultra wide band radar imaging method, and consequently the purpose of improving imaging resolving rate of an objective is achieved.

Description

A kind of ULTRA-WIDEBAND RADAR formation method based on multipath signal

Technical field

The invention belongs to ULTRA-WIDEBAND RADAR technical field of imaging, is a kind of ULTRA-WIDEBAND RADAR formation method based on multipath signal.

Background technology

In ULTRA-WIDEBAND RADAR imaging, if there is comparatively ideal reflecting body to exist in scene, will produce stronger multipath signal, radar imagery performance is impacted; Especially in ultra-broadband wall-through imaging, due to the existence of the reflecting bodys such as body of wall, ceiling, ground, multipath signal is very abundant, if use traditional radar imagery technology, these multipath signals will form the virtual image on image.But the existence of reflecting body makes to be reflected back toward to the target echo of surrounding scattering receiving antenna place, the multipath signal to these from different directions is used, and can produce the effective aperture that is greater than actual receiver aperture, improves imaging resolution.

But utilize multipath signal, need the temporal resolution of radar enough high, can each multipath signal is separated, and the ultrabroad band that the signal of ULTRA-WIDEBAND RADAR has with it, relative Narrow-band Radar, can differentiate the multipath signal receiving at different time, thereby it is processed accordingly.

Summary of the invention

The present invention proposes a kind of ULTRA-WIDEBAND RADAR formation method based on multipath signal.In imaging process, utilize the multipath signal from different directions to increase radar receiving antenna aperture, reach the object that improves target imaging resolution.

Basic ideas of the present invention are: first, the in the situation that of known reflecting body position, the path of propagating according to signal arranges the virtual emitting antenna of mirror image and the virtual receiving antenna of mirror image; Then, according to imaging geometry, multipath signal is carried out to phase place and Amplitude Compensation, and carry out imaging with any a pair of emitting antenna and receiving antenna; Finally, the imaging results that each dual-mode antenna is right is carried out to coherence stack, obtain final image.The present invention only considers to be not more than with reflecting body the multipath signal of two secondary reflections, and more the multipath signal of multiple reflection number of times is due to intensity weak ignoring too.

Technical scheme of the present invention comprises following treatment step:

The first step, determines virtual antenna position

According to actual transmission antenna, actual receiving antenna and reflecting body position in imaging scene, according to signal propagation path, the virtual emitting antenna of mirror image and the virtual receiving antenna of mirror image are set in relevant position.

Second step, multipath signal phase place and Amplitude Compensation

To being reflected amplitude and the phase place that the signal of body reflection changes in reflection process, compensate.When signal incides second medium by first medium, incident angle is θ _i, refraction angle θ _tby Snell law, calculated:

$\frac{{\sin \mathrm{\θ}}_i}{{\sin \mathrm{\θ}}_t}=\sqrt{\frac{{\mathrm{\ϵ}}_2}{{\mathrm{\ϵ}}_1}}---\left(1\right)$

ε wherein ₁the specific inductive capacity of first medium, ε ₂it is the specific inductive capacity of second medium; By Fresnel formula, calculate reflected field E again _rwith incident electric field E _ithe ratio of complex amplitude:

$\begin{array}{c}{r}_{\⊥}=\frac{E_r}{E_i}=\frac{{\mathrm{\η}}_2{\cos \mathrm{\θ}}_i-{\mathrm{\η}}_1{\cos \mathrm{\θ}}_t}{{\mathrm{\η}}_2{\cos \mathrm{\θ}}_i+{\mathrm{\η}}_1{\cos \mathrm{\θ}}_t}\\ r_{//}=\frac{E_r}{E_i}=\frac{{\mathrm{\η}}_1{\cos \mathrm{\θ}}_i-{\mathrm{\η}}_2{\cos \mathrm{\θ}}_t}{{\mathrm{\η}}_1{\cos \mathrm{\θ}}_i+{\mathrm{\η}}_2{\cos \mathrm{\θ}}_t}\end{array}---\left(2\right)$

R _⊥reflected field E during for vertical polarization _rwith incident electric field E _ithe ratio of complex amplitude; r _//reflected field E during for horizontal polarization _rwith incident electric field E _ithe ratio of complex amplitude, wherein η ₁for first medium wave impedance, first medium reflects the medium that front signal is propagated; η ₂for second medium wave impedance, second medium is reflecting body medium.

The signal (being multipath signal) that utilizes the comparison of electric field complex amplitude to be reflected body reflection carries out phase place and Amplitude Compensation.

The 3rd step, each dual-mode antenna is to imaging

Calculate the imaging results f (x between any a pair of emitting antenna and receiving antenna, y), wherein emitting antenna can be both that actual transmission antenna can be also virtual emitting antenna, and receiving antenna can be both that actual receiving antenna can be also virtual receiving antenna, and computation process is as follows:

Suppose emitting antenna coordinate (x _t, 0), receiving antenna coordinate (u, 0); Order transmits as p (t), receives signal and is:

$s(t,u)=\∫\∫g(x,y)p(t-\frac{\sqrt{{(x-u)}^2+y^2}+\sqrt{{(x-x_t)}^2+y^2}}{c})\mathrm{dxdy}---\left(3\right)$

Wherein t is the fast time, and c is velocity of EM-waves, and g (x, y) is the scattering function that scene (x, y) is located;

Utilize following formula to obtain imaging results:

$f(x,y)=\∫\∫s(t,u)\mathrm{\δ}(t-\frac{\sqrt{{(x-u)}^2+y^2}+\sqrt{{(x-x_t)}^2+y^2}}{c})\mathrm{dtdu}---\left(4\right)$

Wherein f (x, y) is the image value that scene (x, y) is located, and δ () is impulse function.

By said process, calculate the imaging results between any a pair of emitting antenna and receiving antenna, comprise the imaging results of utilizing direct signal and the imaging results of utilizing multipath signal.

The 4th step, imaging results coherence stack

Resulting each imaging results in the 3rd step is superposeed, obtain high-resolution imaging effect.Owing to the phase place of multipath signal being compensated at second step, each image addition is coherence stack, and after stack, imaging effect is best.

Beneficial effect of the present invention: the present invention has obtained than Geng great effective aperture, actual antennas aperture by virtual dual-mode antenna is set, and has improved target imaging resolution; By the phase place of reflected signal and amplitude are compensated, become image to carry out coherence stack each simultaneously, reach the object that improves imaging resolution.

Accompanying drawing explanation

Fig. 1 is treatment scheme schematic diagram of the present invention;

Fig. 2 is imaging scene schematic diagram;

Fig. 3 is three kinds of multipath signals and direct signal schematic diagram, (a) represent by virtual transmission antennas transmit, the multipath signal 1 that actual receiving antenna receives, (b) represent by actual transmission antenna transmission, the multipath signal 2 that virtual receiving antenna receives, (c) represents by virtual transmission antennas transmit, the multipath signal 3 that virtual receiving antenna receives, (d) represent by actual transmission antenna transmission the direct signal that actual receiving antenna receives.

Fig. 4, for according to four of Fig. 3 kinds of result figure that signal carries out imaging, is (a) to multipath signal 1 imaging results figure; (b) be to multipath signal 2 imaging results figure; (c) be to multipath signal 3 imaging results figure; (d) be direct signal imaging results figure;

Fig. 5 is the last high-resolution imaging result figure that utilizes the present invention to obtain.

Embodiment

The ultra broadband formation method based on multipath signal that the present invention proposes is divided into four steps, as shown in Figure 1.Below in conjunction with an example, the present invention is further explained.

As shown in Figure 2, reflecting body is body of wall to imaging scene.Actual dual-mode antenna is mode of single illuminator and multiple receivers, and receiving antenna is the receiving array of long 2 meters, depending on as a whole, by open circles, represents; An emitting antenna is positioned in the middle of receiving array, by filled circles, represents.Transmit and use gaussian derivative pulse, pulse width is 1.2ns.Body of wall is positioned at receiving array left end.Take the coordinate axis that body of wall and receiving array place straight line be rectangular coordinate system (long measure is rice), body of wall is positioned on y axle, and receiving array is positioned on x axle, from x=0 to x=2; Emitting antenna is positioned at (1,0).In the middle of scene, there is a target, be positioned at (0.7,1).

Implement by the following step:

The first step, according to the travel path of signal, determines virtual emitting antenna and virtual receiving antenna position.The present invention only considers to be not more than reflection case twice with body of wall, so the raw three kinds of multipath signals of common property, adds direct signal, determines altogether four kinds of different dual-mode antennas pair, as Fig. 3 (a), (b), (c) with (d).(a) virtual emitting antenna and the actual receiving antenna for multipath signal 1 is carried out to imaging, wherein virtual emitting antenna is positioned at (1,0); (b) actual transmission antenna and the virtual receiving antenna for multipath signal 2 is carried out to imaging, wherein virtual receiving array is from x=-2 to x=0; (c) virtual emitting antenna and the virtual receiving antenna for multipath signal 3 is carried out to imaging, wherein virtual receiving array is from x=-2 to x=0, and virtual emitting antenna is positioned at (1,0); (d) actual transmission antenna and the actual receiving antenna for direct signal is carried out to imaging.

Second step, carries out phase place and Amplitude Compensation to multipath signal.

If three kinds of multipath signals are carried out to the dual-mode antenna centering receiving antenna of imaging, be positioned at (u _mn, 0), n=1,2,3,

Emitting antenna is positioned at (x _n, 0), wherein the different values of n represent different multipath signals, m represents m receiving antenna in receiving antenna array, according to signal propagation path, can calculate the angle that the multipath signal of locating through scene (x, y) incides body of wall by following formula:

${\mathrm{\θ}}_{\mathrm{in}}(x,y)=\arctan \left(\frac{y}{x-u_{\mathrm{mn}}}\right)---\left(5\right)$

Then by foregoing (1) formula, calculate refraction angle, then by (2) formula, calculated the ratio r (x, y) of refraction electric field and incident electric field complex amplitude.In this example, first medium is air, and second medium is body of wall.

As what use, be pulse signal, need to signal carry out after Hilbert transform with multiply each other and get again real part; As what use, be the complex signals such as linear frequency modulation or Step Frequency, directly with multiply each other.There are two secondary reflections with body of wall and need to carry out twice compensation.Multipath signal s after compensation _mn(t) be:

s _mn(t)

$=\∫\∫\mathrm{Re}\left\{\mathrm{HT}\right[g(x,y)p(t-\frac{\sqrt{{(x-u_{\mathrm{mn}})}^2+y^2}+\sqrt{{(x-x_n)}^2+y^2}}{c})\left]\frac{1}{r(x,y)}\right\}\mathrm{dxdy},n=\mathrm{1,2,3}---\left(6\right)$

HT[wherein] be Hilbert transform operator, Re{} is the number of winning the confidence real part.

The 3rd step, each dual-mode antenna is to imaging.

After multipath signal after being compensated by (6) formula, re-use foregoing (4) formula, by each dual-mode antenna in Fig. 3, to utilizing multipath signal and direct signal to carry out imaging, obtain the imaging results f of three kinds of multipath signals ₁, f ₁, f ₃with the imaging results f of direct signal, wherein s (t) is uncompensated direct signal:

$\begin{array}{c}{f}_1(x,y)=\∫\∫s_{m1}\left(t\right)\mathrm{\δ}(t-\frac{\sqrt{{(x-u_{m1})}^2+y^2}+\sqrt{{(x-x_1)}^2{+y}^2}}{c}){\mathrm{dtdu}}_{m1}\\ f_2(x,y)=\∫\∫s_{m2}\left(t\right)\mathrm{\δ}(t-\frac{\sqrt{{(x-u_{m2})}^2+y^2}+\sqrt{{(x-x_2)}^2+y^2}}{c}){\mathrm{dtdu}}_{m2}\\ f_3(x,y)={\∫\∫s}_{m3}\left(t\right)\mathrm{\δ}(t-\frac{\sqrt{{(x-u_{m3})}^2+y^2}+\sqrt{{(x-x_3)}^2+y^2}}{c}){\mathrm{dtdu}}_{m3}\\ f(x,y)=\∫\∫s\left(t\right)\mathrm{\δ}(t-\frac{\sqrt{{(x-u)}^2+y^2}+\sqrt{{(x-x_t)}^2+y^2}}{c})\mathrm{dtdu}\end{array}---\left(7\right)$

Respectively as Fig. 4 (a), (b), (c) with (d), be wherein orientation to be distance to, ordinate to, unit be meter horizontal ordinate.Fig. 4 (a) is the imaging results between dual-mode antenna in Fig. 3 (a), Fig. 4 (b) is the imaging results between dual-mode antenna in Fig. 3 (b), Fig. 4 (c) is the imaging results between dual-mode antenna in Fig. 3 (c), and Fig. 4 (d) is the imaging results between dual-mode antenna in Fig. 3 (d).

The 4th step, each imaging results coherence stack.

Each imaging results coherence stack by the 3rd step, obtains last composograph F:

F＝f ₁+f ₂+f ₃+f (8)

The azimuth resolution performance of F obviously improves, and brings up to 0.06 meter by original 0.10 meter, as shown in Figure 5.

The above is only a kind of preferred implementation of the present invention, in the present invention for single-shot multiple receive antenna configuration can also expand to MIMO (Multiple-Input Multiple-Out-put) and single station/bis-station ULTRA-WIDEBAND RADAR isotype, the imaging algorithm of use also can expand to other imaging algorithms.It should be pointed out that for those skilled in the art, under the premise without departing from the principles of the invention, can also make some improvements and modifications, these improvements and modifications also should be considered as protection scope of the present invention.

Claims (1)

1. the ULTRA-WIDEBAND RADAR formation method based on multipath signal, is characterized in that, comprises the steps:

The first step, determine virtual antenna position:

According to actual transmission antenna, actual receiving antenna and reflecting body position in imaging scene, according to signal propagation path, the virtual emitting antenna of mirror image and the virtual receiving antenna of mirror image are set in relevant position;

Second step, multipath signal phase place and Amplitude Compensation:

According to signal propagation path, while inciding second medium by first medium, incident angle is θ _i, refraction angle θ _tby Snell law, calculated:

$\frac{{\sin \mathrm{\θ}}_i}{\sin {\mathrm{\θ}}_t}=\sqrt{\frac{{\mathrm{\ϵ}}_2}{{\mathrm{\ϵ}}_1}}$

ε wherein ₁the specific inductive capacity of first medium, ε ₂it is the specific inductive capacity of second medium; By Fresnel formula, calculate reflected field E again _rwith incident electric field E _ithe ratio of complex amplitude:

$r_{\⊥}=\frac{E_r}{E_i}=\frac{{\mathrm{\η}}_2{\cos \mathrm{\θ}}_i-{\mathrm{\η}}_1\cos {\mathrm{\θ}}_t}{{\mathrm{\η}}_2\cos {\mathrm{\θ}}_i+{\mathrm{\η}}_1\cos {\mathrm{\θ}}_t}$

$r_{//}=\frac{E_r}{E_i}=\frac{{\mathrm{\η}}_1\cos {\mathrm{\θ}}_i-{\mathrm{\η}}_2\cos {\mathrm{\θ}}_t}{{\text{\η}}_1\cos {\mathrm{\θ}}_i+{\mathrm{\η}}_2\cos {\mathrm{\θ}}_t}$

R _⊥reflected field E during for vertical polarization _rwith incident electric field E _ithe ratio of complex amplitude; r _//reflected field E during for horizontal polarization _rwith incident electric field E _ithe ratio of complex amplitude, wherein η ₁for first medium wave impedance; η ₂for second medium wave impedance;

The signal that utilizes the comparison of electric field complex amplitude to be reflected body reflection carries out phase place and Amplitude Compensation, and the multipath signal after being compensated is;

$\begin{array}{c}{s}_{\mathrm{mn}}\left(t\right)\\ =\∫\∫\mathrm{Re}\left\{\mathrm{HT}\right[g(x,y)p(t-\frac{\sqrt{{(x-u_{\mathrm{mn}})}^2+y^2}+\sqrt{{(x-x_n)}^2+y^2}}{c})\left]\frac{1}{r(x,y)}\right\}\mathrm{dxdy},n=\mathrm{1,2,3}\end{array}$

HT[wherein] be Hilbert transform operator, Re{} is the number of winning the confidence real part; R (x, y), for the ratio of refraction electric field and incident electric field complex amplitude, is r when vertical polarization _⊥, when horizontal polarization, be r _//; The dual-mode antenna centering receiving antenna that three kinds of multipath signals is carried out to imaging is positioned at (u _mn, 0), emitting antenna is positioned at (x _n, 0), wherein the different values of n represent different multipath signals, m represents m receiving antenna in receiving antenna array; G (x, y) is the scattering function that scene (x, y) is located;

The 3rd step, each dual-mode antenna is to imaging:

Calculate multipath signal between any a pair of emitting antenna and receiving antenna and the imaging results of direct signal:

$f_1(x,y)=\∫\∫s_{m1}\left(t\right)\mathrm{\δ}(t-\frac{\sqrt{{(x-u_{m1})}^2+y^2}+\sqrt{{(x-x_1)}^2+y^2}}{c}){\mathrm{dtdu}}_{m1}$

$f_2(x,y)=\∫\∫s_{m2}\left(t\right)\mathrm{\δ}(t-\frac{\sqrt{{(x-u_{m2})}^2+y^2}+\sqrt{{(x-x_2)}^2+y^2}}{c}){\mathrm{dtdu}}_{m2}$

$f_3(x,y)=\∫\∫s_{m3}\left(t\right)\mathrm{\δ}(t-\frac{\sqrt{{(x-u_{m3})}^2+y^2}+\sqrt{{(x-x_3)}^2+y^2}}{c}){\mathrm{dtdu}}_{m3}$

$f(x,y)=\∫\∫s\left(t\right)\mathrm{\δ}(t-\frac{\sqrt{{(x-u)}^2+y^2}+\sqrt{{(x-x_t)}^2+y^2}}{c})\mathrm{dtdu}$

F wherein ₁(x, y), f ₂(x, y), f ₃(x, y) is the imaging results of multipath signal, the imaging results of f (x, y) direct signal, and δ () is impulse function, s (t) is uncompensated direct signal;

The 4th step, imaging results coherence stack:

Resulting each imaging results in the 3rd step is superposeed, obtain high-resolution imaging effect.