CN103135109A - 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 the ULTRA-WIDEBAND RADAR technical field of imaging, is a kind of ULTRA-WIDEBAND RADAR formation method based on multipath signal.

Background technology

In the ULTRA-WIDEBAND RADAR imaging, if there is comparatively ideal reflecting body to exist in scene, will produce stronger multipath signal, the radar imagery performance is impacted; Especially in the 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 and should be reflected back toward to the target echo of surrounding scattering the receiving antenna place, and these multipath signals from different directions are used, and can produce the effective aperture greater than actual receiver aperture, improves imaging resolution.

But utilize multipath signal, need the temporal resolution of radar enough high, each multipath signal can be separated, and the signal of ULTRA-WIDEBAND RADAR is with its ultrabroad band that has, relative Narrow-band Radar, can differentiate the multipath signal that receives 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.Be used to the multipath signal growth radar receiving antenna aperture from different directions in imaging process, reach the purpose that improves target imaging resolution.

Basic ideas of the present invention are: at first, in the situation that 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 phase place and Amplitude Compensation, and carry out imaging with any a pair of emitting antenna and receiving antenna; At last, the imaging results that each dual-mode antenna is right is carried out coherence stack, obtains 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 is determined virtual antenna position

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

Second step, multipath signal phase place and Amplitude Compensation

Amplitude and phase place that the signal that is reflected the body reflection is changed in reflection process compensate.When signal incided second medium by first medium, incident angle was θ _i, refraction angle θ _tCalculated by the Snell law:

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

ε wherein ₁The specific inductive capacity of first medium, ε ₂It is the specific inductive capacity of second medium; Calculate reflected field E by the Fresnel formula again _rWith incident electric field E _iThe ratio of complex amplitude:

$r_{\⊥}=\frac{E_r}{E_i}=\frac{{\mathrm{\η}}_2\cos {\mathrm{\θ}}_i-{\mathrm{\η}}_1\cos {\mathrm{\θ}}_t}{{\mathrm{\η}}_2\cos {\mathrm{\θ}}_i+{\mathrm{\η}}_1\cos {\mathrm{\θ}}_t}$ $\left(2\right)$

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

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 ₁Be the first medium wave impedance, first medium namely reflects the medium that front signal is propagated; η ₂Be the second medium wave impedance, second medium is the reflecting body medium.

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

In 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 the 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 and is 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.

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

The 4th step, the imaging results coherence stack

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

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

Description of drawings

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) expression is by virtual transmission antennas transmit, the multipath signal 1 that actual receiving antenna receives, (b) expression is by the 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 the actual transmission antenna transmission direct signal that actual receiving antenna receives.

The as a result figure of Fig. 4 for carrying out imaging according to four kinds of signals of Fig. 3 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 utilizes last high-resolution imaging that the present invention obtains figure as a result.

Embodiment

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

The imaging scene as shown in Figure 2, reflecting body is body of wall.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, represents with open circles; An emitting antenna is positioned in the middle of receiving array, represents with filled circles.Transmit and use the gaussian derivative pulse, pulse width is 1.2ns.Body of wall is positioned at the receiving array left end.Coordinate axis (long measure is as rice) take body of wall and receiving array place straight line as rectangular coordinate system, body of wall is positioned on the y axle, and receiving array is positioned on the x axle, from x=0 to x=2; Emitting antenna is positioned at (1,0).In the middle of scene, a target is arranged, be positioned at (0.7,1).

Implement by the following step:

The first step according to the travel path of signal, is determined 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 common property gives birth to three kinds of multipath signals, adds direct signal, determines altogether four kinds of different dual-mode antennas pair, as Fig. 3 (a) and (b), (c) with (d).(a) virtual emitting antenna and the actual receiving antenna for multipath signal 1 is carried out 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 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 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 imaging.

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

Be positioned at (u if three kinds of multipath signals are carried out the dual-mode antenna centering receiving antenna of imaging _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 calculate refraction angle by foregoing (1) formula, then calculated the ratio r (x, y) of refraction electric field and incident electric field complex amplitude by (2) formula.In this example, first medium is air, and second medium is body of wall.

Pulse signal as what use, need to signal carry out after Hilbert transform with

Multiply each other and get again real part; The complex signals such as linear frequency modulation or Step Frequency as what use, directly with

Multiply each other.With body of wall, two secondary reflections occuring need to carry out twice compensation.Multipath signal s after compensation _mn(t) be:

$s_{\mathrm{mn}}\left(t\right)$

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

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

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

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

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

$f_2(x,y)=\∫\∫s_{m2}\left(t\right)\mathrm{\δ}(t-\frac{\sqrt{{(x-u_{m2})}^2+y^2}+\sqrt{{(x-x_2)}^2+y^2}}{c})\mathrm{dtd}{u}_{m2}$ $\left(7\right)$

$f_3(x,y)=\∫\∫s_{m1}\left(t\right)\mathrm{\δ}(t-\frac{\sqrt{{(x-u_{m3})}^2+y^2}+\sqrt{{(x-x_3)}^2+y^2}}{c})\mathrm{dtd}{u}_{m3}$

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

Respectively as Fig. 4 (a) and (b), (c) with (d), wherein be the 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 with in the 3rd step obtains last composograph F:

F=f ₁+f ₂+f ₃+f (8)

The performance of the azimuth resolution 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/pair station ULTRA-WIDEBAND RADAR isotype, the imaging algorithm of use also can expand to other imaging algorithms.Should be pointed out that for those skilled in the art, under the prerequisite that does not break away from the principle 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 in the imaging scene, actual receiving antenna and reflecting body position, according to signal propagation path, the virtual emitting antenna of mirror image and the virtual receiving antenna of mirror image are set in the relevant position;

Second step, multipath signal phase place and Amplitude Compensation:

According to signal propagation path, when inciding second medium by first medium, incident angle is θ _i, refraction angle θ _tCalculated by the Snell law:

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

ε wherein ₁The specific inductive capacity of first medium, ε ₂It is the specific inductive capacity of second medium; Calculate reflected field E by the Fresnel formula again _rWith incident electric field E _iThe ratio of complex amplitude:

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

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

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 ₁Be the first medium wave impedance; η ₂Be the second medium wave impedance;

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

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

Calculate the imaging results f (x, y) between any a pair of emitting antenna and receiving antenna, computation process is as follows:

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

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

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, and utilizes following formula to obtain imaging results:

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

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

Calculate imaging results between any a pair of emitting antenna and receiving antenna by said process;

The 4th step, the imaging results coherence stack:

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

Images