CN101236298A - Synthetic aperture laser image-forming radar space phase bias emission telescope - Google Patents

Abstract

The present invention discloses a spatial phase offset transmitter-telescope for a synthetic aperture laser imaging radar, namely a telescope having optical out-of-focus and an additional phase plate is used as an optical sending antenna in the synthetic aperture laser imaging radar so as to control the defocusing amount and the phase function of the phase adjusting plate; an additional spatial phase quadratic term can be generated in an illumination region of the laser transmitter-telescope for, before the laser illumination wave is changed, realizing target aperture synthetic imaging at the movement direction of the radar by generating a required quadric term phase course at the movement direction of the radar in a target echo receiving signal.

Description

The space phase bias emission telescope of synthetic aperture laser imaging radar

Technical field

The present invention relates to radar, particularly a kind of space phase bias emission telescope of synthetic aperture laser imaging radar is used as the optical transmitting antenna in the synthetic aperture laser imaging radar.In telescope, place the phase modulation (PM) flat board, control telescopical defocusing amount and modulate dull and stereotyped phase function mutually with the position, can produce additional space phase place quadratic term in the surround of laserscope, be used to change the laser lighting wavefront, in the target echo received signal, to produce the required quadratic term phase history on the radar direction of motion, realize the target aperture compound imaging on the radar direction of motion.

Background technology

The principle of synthetic aperture laser imaging radar is taken from the theory of SAR of RF application, is to obtain unique optical imagery Observations Means of centimetre magnitude resolution at a distance.Laser emission adopts optical telescope, because the yardstick of optical emitting telescope primary mirror is greater than a wavelength 3-6 order of magnitude, its emission characteristics and radio-frequency transmissions antenna have very big difference.

In the phase place quadratic term course that produces target on the synthetic aperture laser imaging radar direction of motion is the necessary condition that guarantees the aperture compound imaging of the target on the radar direction of motion.Therefore producing certain space quadratic term PHASE DISTRIBUTION on telescope emitted laser illumination hot spot is the key condition that guarantees to produce suitable phase place quadratic term course in optical receive signal.

The bore diameter laser imaging at first realizes checking in the laboratory, but these experiments belong to the closely simulation of tiny light beam, do not adopt true optical telescope emitting antenna.U.S. Raytheon Co. in 2006 and Nuo Ge company have realized airborne Synthetic Aperture Laser Radar test respectively under U.S. national defense Advanced Research Project Agency Net supports, but consider to utilize the characteristic before optical telescope changes transmitted wave.See also:

(1)M.Bashkansky，R.L.Lucke，F.Funk，L.J.Rickard，and?J.Reintjes，“Two-dimensional?synthetic?aperture?imaging?in?the?optical?domain，”Optics?Letters，Vol.27，pp1983-1985(2002).

(2)W.Buell，N.Marechal，J.Buck，R.Dickinson，D.Kozlowski，T.Wright，and?S.Beck，“Demonstrationof?synthetic?aperture?imaging?ladar，”Proc.of?SPIE，Vol.5791，pp.152-166(2005).

(3)J.Ricklin，M.Dierking，S.Fuhrer，B.Schumm，and?D.Tomlison，“Synthetic?apertureladar?for?tactical?imaging，”DARPA?Strategic?Technology?Office.

How to guarantee the target aperture compound imaging on the radar direction of motion, this is the gordian technique with optical characteristics that realizes the bore diameter laser imaging.

Summary of the invention

The technical problem to be solved in the present invention is in order to guarantee the target aperture compound imaging on the radar direction of motion, a kind of space phase bias emission telescope of synthetic aperture laser imaging radar is proposed, by in telescope, placing the phase modulation (PM) flat board, the defocusing amount of control telescope ocular back focal plane is modulated dull and stereotyped phase function mutually with the position, can produce additional space phase place quadratic term in the surround of laser transmitting telescope, be used to change the laser lighting wavefront, in the target echo received signal, to produce the required quadratic term phase history on the radar direction of motion, realize the target aperture compound imaging on the radar direction of motion.

Technical solution of the present invention is as follows:

A kind of space phase bias emission telescope of synthetic aperture laser imaging radar, be characterised in that its formation comprises that the focal length of described telescope ocular is f from emission laser beam telescope entrance pupil, eyepiece, eyepiece back focal plane, phase modulation (PM) flat board, object lens and telescope emergent pupil successively ₁With the focal length of object lens be f ₂, then telescopical enlargement factor is $M=\frac{f_2}{f_1},$ The plane of described telescope entrance pupil is positioned at the front focal plane of described eyepiece, and described telescope emergent pupil is positioned at the back focal plane of object lens, and the distance between the back focal plane of eyepiece and the front focal plane of object lens is telescopical defocusing amount:

$\mathrm{\Δl}=-\frac{f_2^2}{z+R},$

Place described phase modulation (PM) flat board on the front focal plane of described object lens, the equivalent focal length of the space phase quadratic term biasing that the phase modulation function of this phase modulation (PM) flat board produces is:

$F=\frac{{\mathrm{<figure-callout\; id="2"\; label="f"\; filenames="S2008100342408E00011.png"\; state="\{\{state\}\}">f</figure-callout>}}_2^2}{2z},$

In the formula: z is the synthetic aperture laser imaging radar range-to-go, and R is the radius-of-curvature of emission beam wave surface on distance Z.

A kind of space phase bias emission telescope of synthetic aperture laser imaging radar, be characterised in that its formation comprises that the focal length of described telescope ocular is f from emission laser beam telescope entrance pupil, eyepiece, eyepiece back focal plane, phase modulation (PM) flat board, object lens and telescope emergent pupil successively ₁With the focal length of object lens be f ₂, then telescopical enlargement factor is $M=\frac{f_2}{f_1},$ The plane of described telescope entrance pupil is positioned at the front focal plane of described eyepiece, and described telescope emergent pupil is positioned at the back focal plane of object lens, and the distance between the back focal plane of eyepiece and the front focal plane of object lens is telescopical defocusing amount:

Δl＝0，

Place described phase modulation (PM) flat board on the front focal plane of described object lens, the equivalent focal length of the space phase quadratic term biasing that the phase modulation function of this phase modulation (PM) flat board produces is:

$F=\frac{{\mathrm{<figure-callout\; id="2"\; label="f"\; filenames="S2008100342408E00011.png"\; state="\{\{state\}\}">f</figure-callout>}}_2^2}{z^2}R,$

In the formula: z is the synthetic aperture laser imaging radar range-to-go, and R is the radius-of-curvature of emission beam wave surface on distance Z.

A kind of space phase bias emission telescope of synthetic aperture laser imaging radar is characterised in that its formation comprises that the focal length of described telescope ocular is f from emission laser beam telescope entrance pupil, eyepiece, eyepiece back focal plane, object lens and telescope emergent pupil successively ₁With the focal length of object lens be f ₂, then telescopical enlargement factor is $M=\frac{f_2}{f_1},$ The plane of described telescope entrance pupil is positioned at the front focal plane of described eyepiece, described telescope emergent pupil is positioned at the back focal plane of object lens, distance between the back focal plane of eyepiece and the front focal plane of object lens is 0, connect a 4-f image rotation optical system at described telescope emergent pupil, carry out the biasing of out of focus and space phase quadratic term on the middle focal plane of this 4-f image rotation optical system, the defocusing amount of middle focal plane is:

${\mathrm{\&Delta;<figure-callout\; id="3"\; label="l"\; filenames="S2008100342408E00011.png"\; state="\{\{state\}\}">l</figure-callout>}}_3=-\frac{f_3^2}{Z+R},$

The equivalent focal length of space phase quadratic term biasing should be:

${\mathrm{<figure-callout\; id="3"\; label="R"\; filenames="S2008100342408E00011.png"\; state="\{\{state\}\}">R</figure-callout>}}_3=\frac{{\mathrm{<figure-callout\; id="3"\; label="f"\; filenames="S2008100342408E00011.png"\; state="\{\{state\}\}">f</figure-callout>}}_3^2}{2Z},$

In the formula: f ₃Be the focal length of described 4-f image rotation optical system, z is the synthetic aperture laser imaging radar range-to-go, and R is the radius-of-curvature of emission beam wave surface on distance Z.

Described telescope emergent pupil is positioned at the back focal plane of object lens, and this telescope emergent pupil is the aperture diaphragm of a reality, or only represents a planimetric position.

Technique effect of the present invention:

The present invention is by placing the phase modulation (PM) flat board in telescope, the defocusing amount of control telescope ocular back focal plane is modulated dull and stereotyped phase function mutually with the position, can produce additional space phase place quadratic term in the surround of laser transmitting telescope, be used to change the laser lighting wavefront, in the target echo received signal, to produce the required quadratic term phase history on the radar direction of motion, realize the target aperture compound imaging on the radar direction of motion.

Description of drawings

Fig. 1 is the system schematic of an embodiment of space phase bias emission telescope of synthetic aperture laser imaging radar of the present invention.

Embodiment

The invention will be further described below in conjunction with embodiment and accompanying drawing, but should not limit protection scope of the present invention with this.

See also Fig. 1 earlier, Fig. 1 is the system schematic of an embodiment of space phase bias emission telescope of synthetic aperture laser imaging radar of the present invention.As seen from the figure, the space phase bias emission telescope of synthetic aperture laser imaging radar of the present invention, its formation comprises that the focal length of described telescope ocular 3 is f from emission laser beam 1 telescope entrance pupil 2, eyepiece 3, eyepiece back focal plane 4, phase modulation (PM) flat board 5, object lens 6 and telescope emergent pupil 7 successively ₁With the focal length of object lens 6 be f ₂, then telescopical enlargement factor is $M=\frac{f_2}{f_1},$ The plane of described telescope entrance pupil 2 is positioned at the front focal plane of described eyepiece 3, and described telescope emergent pupil 7 is positioned at the back focal plane of object lens 6, and the distance between the back focal plane 4 of eyepiece 3 and the front focal plane of object lens 6 is telescopical defocusing amount:

$\mathrm{\&Delta;l}=-\frac{f_2^2}{z+R},$

Place described phase modulation (PM) flat board 5 on the front focal plane of described object lens 6, the equivalent focal length of the space phase quadratic term biasing that the phase modulation function of this phase modulation (PM) flat board 5 produces is:

$F=\frac{{\mathrm{<figure-callout\; id="2"\; label="f"\; filenames="S2008100342408E00011.png"\; state="\{\{state\}\}">f</figure-callout>}}_2^2}{2z},$

In the formula: z is the synthetic aperture laser imaging radar range-to-go, and R is the radius-of-curvature of emission beam wave surface on distance Z.

First principles analysis of the present invention is as follows:

The structure of the space phase bias emission telescope of synthetic aperture laser imaging radar of the present invention comprises, is telescope entrance pupil 2, eyepiece 3, eyepiece back focal plane 4, phase modulation (PM) flat board 5, object lens 6 and telescope emergent pupil 7 successively from 1 beginning of emission laser beam.

If the focal length of telescope ocular 3 is f ₁With the focal length of object lens 6 be f ₂, then telescopical enlargement factor is $M=\frac{f_2}{f_1}.$ The plane of telescope entrance pupil 2 is positioned at the front focal plane of eyepiece 3, can be the aperture diaphragm of a reality, also can not have diaphragm and represents a planimetric position.Telescope emergent pupil 7 is positioned at the back focal plane of object lens 6, can be the aperture diaphragm of a reality, also can not have diaphragm and represents a planimetric position.Distance between eyepiece back focal plane 4 and the object lens front focal plane is Δ l, represents telescopical defocusing amount, and telescope does not have out of focus and is in focusing state when Δ l=0.Place phase modulation (PM) flat board 5 on the object lens front focal plane, its phase modulation function is:

$\exp \left(\mathrm{j\&pi;}\frac{x^2+{\mathrm{<figure-callout\; id="2"\; label="y"\; filenames="S2008100342408E00011.png"\; state="\{\{state\}\}">y</figure-callout>}}^2}{\mathrm{\&lambda;F}}\right),$

Wherein F is an equivalent sphere ground roll curvature.

Suppose that the synthetic aperture laser imaging radar range-to-go is z, the diameter of telescope emergent pupil 2 or telescope objective 6 is D, and the target out to out is L, and the optical maser wavelength of using is λ, satisfies:

${\left|z\right|}^3>>\frac{\mathrm{\&pi;}{(D+L)}^4}{4\mathrm{\&lambda;}}$

The time, then radar is positioned at the Fei Nieer diffraction region of target.

The wavefront of telescopical emission laser beam 1 on the entrance pupil face is e ₀(x, y), then the target illumination wavefront is the Fei Nieer diffraction:

$e_z(x,y)=A[e_0(-\frac{x}{M},-\frac{y}{M})\&CircleTimes;\exp \left(\mathrm{j\&pi;}\frac{x^2+y^2}{\mathrm{\&lambda;z}}\right)].$

Require space phase quadratic term of diffraction illumination light field biasing $\exp \left(\mathrm{j\&pi;}\frac{x^2+{\mathrm{<figure-callout\; id="2"\; label="y"\; filenames="S2008100342408E00011.png"\; state="\{\{state\}\}">y</figure-callout>}}^2}{\mathrm{\&lambda;R}}\right),$ Then with respect to telescope emergent pupil wavefront then require be:

$e_3(x,y)=B\left\{\right[e_0(-\frac{x}{M},-\frac{y}{M})\&CircleTimes;\exp \left(\mathrm{j\&pi;}\frac{x^2+{\mathrm{<figure-callout\; id="2"\; label="y"\; filenames="S2008100342408E00011.png"\; state="\{\{state\}\}">y</figure-callout>}}^2}{\mathrm{\&lambda;z}}\right)]\&times;\exp \left(\mathrm{j\&pi;}\frac{x^2+y^2}{\mathrm{\&lambda;R}}\right)\}$

$\&CircleTimes;\exp (-\mathrm{j\&pi;}\frac{x^2+{\mathrm{<figure-callout\; id="2"\; label="y"\; filenames="S2008100342408E00011.png"\; state="\{\{state\}\}">y</figure-callout>}}^2}{\mathrm{\&lambda;z}}).$

In order to realize this wavefront biasing, telescopical defocusing amount should be:

$\mathrm{\&Delta;l}=-\frac{f_2^2}{z+R}.$

And the equivalent focal length of space phase quadratic term biasing should be:

$F=\frac{{\mathrm{<figure-callout\; id="2"\; label="f"\; filenames="S2008100342408E00011.png"\; state="\{\{state\}\}">f</figure-callout>}}_2^2}{2z}.$

Further satisfy

$\left|z_{12}\right|>>\frac{\mathrm{\&pi;}({\mathrm{<figure-callout\; id="2"\; label="D"\; filenames="S2008100342408E00011.png"\; state="\{\{state\}\}">D</figure-callout>}}^2+L^2)}{\mathrm{\&lambda;}},$

Then target is in the territory, Fraunhofer diffraction region.Reach the space phase quadratic term $\exp \left(\mathrm{j\&pi;}\frac{{\mathrm{<figure-callout\; id="2"\; label="x"\; filenames="S2008100342408E00011.png"\; state="\{\{state\}\}">x</figure-callout>}}^2+{\mathrm{<figure-callout\; id="2"\; label="y"\; filenames="S2008100342408E00011.png"\; state="\{\{state\}\}">y</figure-callout>}}^2}{\mathrm{\&lambda;R}}\right)$ Biasing requires defocusing amount to be:

Δl＝0

And the equivalent focal length of space phase quadratic term biasing should be:

$F=\frac{{\mathrm{<figure-callout\; id="2"\; label="f"\; filenames="S2008100342408E00011.png"\; state="\{\{state\}\}">f</figure-callout>}}_2^2}{z^2}R.$

At this moment before the illumination light field wave be:

$e_z(x,y)=C\underset{z}{\mathrm{FF}}\left\{e_0(-\frac{x}{M},-\frac{y}{M})\right\}\exp \left(\mathrm{j\&pi;}\frac{x^2+{\mathrm{<figure-callout\; id="2"\; label="y"\; filenames="S2008100342408E00011.png"\; state="\{\{state\}\}">y</figure-callout>}}^2}{\mathrm{\&lambda;z}}\right)\exp \left(\mathrm{j\&pi;}\frac{x^2+{\mathrm{<figure-callout\; id="2"\; label="y"\; filenames="S2008100342408E00011.png"\; state="\{\{state\}\}">y</figure-callout>}}^2}{\mathrm{\&lambda;R}}\right),$

Wherein

The Fourier transform of representative on distance z.

A in the above-mentioned expression formula, B and C are complex constant.

The general requirement: the object lens diameter is greater than telescope emergent pupil face footpath diaphragm diameter, and the eyepiece diameter is greater than telescope entrance pupil face footpath diaphragm diameter.

Telescope is in out of focus not and also can not adopt optical accessory to reach equivalent out of focus and phase bias outside telescope under the dull and stereotyped state of additive phase modulation.Its method is to connect a 4-f image rotation optical system, carries out out of focus and phase bias therebetween on the focal plane.The focal length of supposing 4-f image rotation optical system is f ₃, the defocusing amount of middle focal plane is:

${\mathrm{\&Delta;<figure-callout\; id="3"\; label="l"\; filenames="S2008100342408E00011.png"\; state="\{\{state\}\}">l</figure-callout>}}_3=-\frac{{\mathrm{<figure-callout\; id="3"\; label="f"\; filenames="S2008100342408E00011.png"\; state="\{\{state\}\}">f</figure-callout>}}_3^2}{Z+R},$

The equivalent focal length of space phase quadratic term biasing should be:

${\mathrm{<figure-callout\; id="3"\; label="R"\; filenames="S2008100342408E00011.png"\; state="\{\{state\}\}">R</figure-callout>}}_3=\frac{{\mathrm{<figure-callout\; id="3"\; label="f"\; filenames="S2008100342408E00011.png"\; state="\{\{state\}\}">f</figure-callout>}}_3^2}{2Z}.$

When the Laser emission light source is fiber laser or fiber amplifier, except collimation uses, laser fiber emission port or be equipped with the lens focus point again and can be placed directly on the position of eyepiece back focal plane 4.

The light beam of emission LASER Light Source is a Gaussian beam, is Gaussian beam ripple waist w on the control transmitter-telescope emergent pupil ₀, then the wavefront of light beam on distance z is quadratic term:

$R\left(z\right)=z[1+{\left(\frac{{\mathrm{kw}}_0^2}{2z}\right)}^2].$

When $z>>\frac{{\mathrm{\&pi;w}}_0^2}{\mathrm{\&lambda;}}$ When the far field, have:

$R\left(z\right)\&cong;z.$

Specific design is as follows:

The aperture compound imaging resolution requirement 25mm of a synthetic aperture laser imaging radar, the imaging viewing distance is 5km.

Setting the diameter that equivalent aperture light is blocked on the telescope emergent pupil 7 is 50mm, and the Gaussian beam ripple waist of emission laser on the emergent pupil face is w ₀=12.5mm.Design: the telescope enlargement factor is M=10, and the bore of object lens 6 is that φ 60mm (＞φ 50mm) and focal length are 1000mm, and the bore of eyepiece 3 is that φ 7mm (＞φ 5mm) and focal length are 100mm.

Gaussian beam wavefront at the 5km place is 5km, the high number of half-wave of the wavefront of its illumination radius is 4.47, can require the high number of half-wave for the ease of correct sampling and inverting is 20, at this moment need quadratic term that equivalent curvature is 1.437km of additional biasing, promptly the equivalent focal length of the dull and stereotyped quadratic term of phase modulation (PM) should be 0.05748mm.

The space phase bias emission telescope of synthetic aperture laser imaging radar of the present invention, by in telescope, placing the phase modulation (PM) flat board, the defocusing amount of control telescope ocular back focal plane is modulated dull and stereotyped phase function mutually with the position, can produce additional space phase place quadratic term in the surround of laser transmitting telescope, be used to change the laser lighting wavefront, in the target echo received signal, to produce the required quadratic term phase history on the radar direction of motion, realize the target aperture compound imaging on the radar direction of motion.

Claims (4)

1, a kind of space phase bias emission telescope of synthetic aperture laser imaging radar, be characterised in that its formation comprises that the focal length of described telescope ocular (3) is f from emission laser beam (1) telescope entrance pupil (2), eyepiece (3), eyepiece back focal plane (4), phase modulation (PM) flat board (5), object lens (6) and telescope emergent pupil (7) successively ₁And the focal length of object lens (6) is f ₂The plane of described telescope entrance pupil (2) is positioned at the front focal plane of described eyepiece (3), described telescope emergent pupil (7) is positioned at the back focal plane of object lens (6), and the distance between the back focal plane (4) of eyepiece (3) and the front focal plane of object lens (6) is telescopical defocusing amount:

$\mathrm{\&Delta;l}=-\frac{f_2^2}{z+R},$

Place described phase modulation (PM) flat board (5) on the front focal plane of described object lens (6), the equivalent focal length of the space phase quadratic term biasing that the phase modulation function of this phase modulation (PM) flat board (5) produces is:

$F=\frac{f_2^2}{2z},$

In the formula: z is the synthetic aperture laser imaging radar range-to-go, and R is the radius-of-curvature of emission beam wave surface on distance Z.

2, a kind of space phase bias emission telescope of synthetic aperture laser imaging radar, be characterised in that its formation comprises that the focal length of described telescope ocular (3) is f from emission laser beam (1) telescope entrance pupil (2), eyepiece (3), eyepiece back focal plane (4), phase modulation (PM) flat board (5), object lens (6) and telescope emergent pupil (7) successively ₁And the focal length of object lens (6) is f ₂The plane of described telescope entrance pupil (2) is positioned at the front focal plane of described eyepiece (3), described telescope emergent pupil (7) is positioned at the back focal plane of object lens (6), and the distance between the back focal plane (4) of eyepiece (3) and the front focal plane of object lens (6) is telescopical defocusing amount:

Δl＝0，

Place described phase modulation (PM) flat board (5) on the front focal plane of described object lens (6), the equivalent focal length of the space phase quadratic term biasing that the phase modulation function of this phase modulation (PM) flat board (5) produces is:

$F=\frac{f_2^2}{z^2}R,$

In the formula: z is the synthetic aperture laser imaging radar range-to-go, and R is the radius-of-curvature of emission beam wave surface on distance Z.

3, a kind of space phase bias emission telescope of synthetic aperture laser imaging radar, be characterised in that its formation comprises that the focal length of described telescope ocular 3 is f from emission laser beam (1) telescope entrance pupil (2), eyepiece (3), eyepiece back focal plane (4), object lens (6) and telescope emergent pupil (7) successively ₁And the focal length of object lens (6) is f ₂The plane of described telescope entrance pupil (2) is positioned at the front focal plane of described eyepiece (3), described telescope emergent pupil (7) is positioned at the back focal plane of object lens (6), distance between the back focal plane (4) of eyepiece (3) and the front focal plane of object lens (6) is 0, connect a 4-f image rotation optical system at described telescope emergent pupil (7), carry out the biasing of out of focus and space phase quadratic term on the middle focal plane of this 4-f image rotation optical system, the defocusing amount of middle focal plane is:

${\mathrm{\&Delta;l}}_3=-\frac{f_3^2}{Z+R},$

The equivalent focal length of space phase quadratic term biasing should be:

$R_3=\frac{f_3^2}{2Z},$

In the formula: f ₃Be the focal length of described 4-f image rotation optical system, z is the synthetic aperture laser imaging radar range-to-go, and R is the radius-of-curvature of emission beam wave surface on distance Z.

4, according to the space phase bias emission telescope of claim 1 or 2 or 3 described synthetic aperture laser imaging radars, it is characterized in that described telescope emergent pupil (7) is positioned at the back focal plane of object lens (6), this telescope emergent pupil (7) is the aperture diaphragm of a reality, or only represents a planimetric position.

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