CN203909294U - Receiving/transmitting coaxial optical antenna of synthetic aperture laser imaging radar - Google Patents

Abstract

The utility model discloses a receiving/transmitting coaxial optical antenna of a synthetic aperture laser imaging radar, which comprises a transmitting optical antenna and a receiving optical antenna. A transmitting light beam of the transmitting optical antenna is coaxial with the receiving optical antenna through a reflector. A back focal surface of a telescope system is provided with an optical modulator. The receiving/transmitting coaxial optical antenna is based on synthetic aperture and heterodyne receiving technique. The transmitting antenna and the receiving antenna are designed to an integrated structure, thereby performing coaxial transmitting and receiving, simplifying structure, realizing more compact and firmer structure, facilitating matching between transmitting and receiving, reducing requirement for a displacement angle, eliminating quadratic phase effect of a received signal in real time through an optical modulator, ensuring higher received signal-to-noise ratio and larger receiving viewing field, and realizing synthetic aperture broad-width imaging.

Description

Synthetic aperture laser imaging radar is received and dispatched coaxial optical antenna

Technical field

The utility model belongs to synthetic aperture laser imaging radar technical field, relates in particular to a kind of synthetic aperture laser imaging radar and receives and dispatches coaxial optical antenna.

Background technology

Synthetic aperture laser imaging radar (SAIL) principle derives from microwave synthetic-aperture radar, is can be in the remote unique optical imagery means that realize centimetre magnitude resolution.But optical maser wavelength is than the little 3-6 of a microwave wavelength order of magnitude, and therefore its signal transmits and receives and had the new demand of optical field.Synthetic aperture laser imaging radar azimuth resolution depends primarily on the effective aperture of optical transmitting antenna, and is directly proportional to antenna aperture diameter, and therefore, in order to obtain large optics toes and high resolution, emitting antenna bore is generally less, in order to obtain higher echoed signal intensity and heterodyne signal signal to noise ratio (S/N ratio), require heterodyne reception visual field and Laser emission to disperse visual field identical, and heterodyne reception antenna aperture is the bigger the better (referring to [1] R.L.Lucke, L.J.Rickard, M.Bashkansky, J.Reintjes, E.E.Funk.Synthetic aperture ladar (SAL)-Fundamental theory, Design equations for a satellite system, and Laboratory demonstration 2002, Naval Research Laboratory report NRL/FR/7218-02-10, [2] Liu Liren. synthetic aperture laser imaging radar (III): bidirectional loop transmitting-receiving telescope for synthesis [J]. Acta Optica, 2008,28 (7), 1405-1410.).But due to the restriction of heavy caliber processing technology, Receiver aperture is always limited, the target echo signal that can receive is very little, large Receiver aperture brings again field of view of receiver to reduce simultaneously, this will have a strong impact on acquisition of signal difficulty and radar system performance (referring to [3] Steven M.Beck, Joseph R.Buck, Walter F.Buell etal..Synthetic-aperture imaging laser radar:laboratory demonstration and signal processing[J] .Appl.Opt., 2005,44 (35): 7621-7629.)

Prior art [4] (A.E.Siegman.The antenna properties of optical heterodyne receivers[J] .Pro.IEEE, 1966,54 (10): 1350-1356) once provided the antenna theory that optical heterodyne receives: the useful area product of antenna reception solid angle and Receiver aperture be approximately equal to wavelength square, therefore field of view of receiver and effectively always these those long relations that disappear of receiving aperture in theory.For synthetic aperture laser imaging radar, prior art [5] (Yan Aimin, Liu Li people, Zhou Yu, Sun Jianfeng. general optical antenna of synthetic aperture laser imaging radar, utility model patent, application number: 200920066851.0) proposed a kind of general optical antenna of synthetic aperture laser imaging radar structure, but this device transmitter-telescope and receiving telescope are fitted together by a public primary telescope collection, must launch reception timesharing carries out, and maximum field of view angle only determines by the diffraction limit of optical antenna bore, visual field is limited.Prior art [6] (Liu Liren. the lens focal plane array heterodyne reception optical antenna of synthetic aperture laser imaging radar, utility model patent, application number: 200910056646.0) propose to adopt lens focal plane place balanced array detector to realize wide cut multi channel signals and receive imaging, can break through the restriction of the described optical heterodyne receiving antenna theory of document [4], obtain larger field of view of receiver; But do not consider the impact of the quadratic phase of eliminating echoed signal, aperture of lens size still cannot be accomplished very large, and cannot adjust the relative area relation of local oscillator hot spot, flashlight hot spot and detector array unit, the signal light intensity utilization factor of reception is limited, final imaging signal to noise ratio (S/N ratio) is lower; The mentioned Cassegrain telescopic system of embodiment in scheme, secondary mirror is paraboloidal catoptron, and coma is very large, and available fields is less, can limit the apparent field of array detection in practical application, is not suitable for the synthetic aperture laser imaging radar application of large visual field.

Utility model content

Utility model object: the utility model aims to provide that a kind of real-time elimination receives signal quadratic term phase effect, the synthetic aperture laser imaging radar of realizing high-quality synthetic aperture imaging is received and dispatched coaxial optical antenna.

Technical scheme: a kind of synthetic aperture laser imaging radar is received and dispatched coaxial optical antenna, comprises transmitting optics antenna, the transmitter aperture diaphragm and the catoptron that comprise light source, arrange along light source optical path;

Receive optical antenna, the receiver aperture diaphragm that comprises target echo, is provided with successively along target echo incident direction, telescopic system, convergent lens, light combination mirror and balanced array detection system;

The transmitting light beam of transmitting optics antenna is via catoptron and the same optical axis of reception optical antenna, and telescopic system back focal plane place is provided with photomodulator.Close bundle through the local oscillator light reference light of ovennodulation and the converging light after photomodulator phase compensation in light combination mirror mixing, by the balanced array detection system heterodyne reception that is positioned at described convergent lens back focal plane place.

Described photomodulator is phase type LCD space light modulator.

The expression formula of the modulation signal of described phase type LCD space light modulator is:

$I_0\exp (-\mathrm{j\π}{M}^2\frac{x^2+y^2}{\mathrm{\λz}})$

I in formula ₀for corresponding constant term, z is the space length that target face arrives receiving telescope entrance pupil, is measured in real time or local oscillator light time delay conversion acquisition by altitude gauge.The modulation signal that phase type spatial light modulator sends can carry out the quadratic phase compensation to echoed signal.

The front focal plane place of described convergent lens is provided with convergent lens diaphragm, and convergent lens diaphragm is close on described photomodulator.

Described convergent lens diaphragm, transmitter aperture diaphragm and receiver aperture diaphragm are square aperture or circular aperture simultaneously.Described convergent lens diaphragm is provided with aperture size governor motion.

Described balanced array detection system comprises wave plate, polarization splitting prism, the first photoelectronic detecting array, the second photoelectronic detecting array, totalizer and balance receiving array circuit, wave plate is λ/2 or λ/4 wave plate, before wave plate is arranged on polarization splitting prism, the first photoelectronic detecting array and the second photoelectronic detecting array are positioned at the back focal plane place of described convergent lens; The input end of totalizer is connected with the output terminal of the second photoelectronic detecting array with the first described photoelectronic detecting array respectively; The output terminal of totalizer is connected with the input end of balance receiving array circuit.

Described telescopic system comprises receiving telescope object lens primary mirror, receiving telescope object lens secondary mirror, receiving telescope eyepiece, and described receiver aperture diaphragm is positioned at the front focal plane place of receiving telescope object lens primary mirror; The recessed reflecting surface of receiving telescope object lens primary mirror is relative with the recessed reflecting surface of receiving telescope object lens secondary mirror, the front focus of the focus of receiving telescope object lens primary mirror and receiving telescope object lens secondary mirror overlaps, and the back focus of the front focus of receiving telescope eyepiece and receiving telescope object lens secondary mirror overlaps.Receive the telescopic system that optical antenna adopts, processing technology is simple, can realize the many Receiver apertures larger than aperture of lens, receives more signal powers; And system differs that distortion is little, and the reflecting surface structure of concave-concave has the many available fields larger than concavo-convex reflecting surface structure, and the heavy caliber that is easy to realize synthetic aperture laser imaging radar is surveyed.Described receiving telescope object lens primary mirror is parabolic mirror, and described receiving telescope object lens secondary mirror is ellipsoidal mirror.

Described transmitting optics antenna also comprises the light shielding system of light source being disturbed for isolating target echo signal, before light shielding system is positioned at described transmitter aperture diaphragm.The light shielding system that adopts optical isolator or corresponding polaroid and wave plate to form has been eliminated the impact of echoed signal on lasing light emitter, has ensured the feasibility of system transmitting-receiving.

Principle of work: synthetic aperture laser imaging radar described in the utility model is received and dispatched coaxial optical antenna taking synthetic aperture and heterodyne reception technology as basis, utilize photomodulator to eliminate in real time and receive signal quadratic term phase effect, by balanced array Detection Techniques and adjustable convergent lens diaphragm, can realize the much bigger field of view of receiver in visual field than common Kepler telescope directly receives and optical antenna bore diffraction determines, and the impact of Background suppression noise and local oscillator optical noise greatly, obtain higher heterodyne efficiency, ensure the signal to noise ratio (S/N ratio) receiving.Because telescopic system does not have aberration, and easily realize heavy caliber processing, therefore can reduce the impact of the needed frequency chirp signal of radar, increase the flashlight energy receiving, in structure, easily form a coaxial synthetic aperture laser imaging radar with relatively small-bore transmitting optics antenna and receive and dispatch optical antenna, realize high-quality synthetic aperture imaging.

Beneficial effect: synthetic aperture laser imaging radar described in the utility model is received and dispatched coaxial optical antenna, wherein emitting antenna and receiving antenna are designed to integrative-structure, coaxial transmitting-receiving, it is firm that structure is tightlier urged simply, tightlier urged, transmit and receive more easily coupling, displacement angle requires step-down, adopts photomodulator can eliminate in real time the impact that receives the secondary phasic difference of signal corrugated, and corresponding modulation signal is simple and easy to control.Receiving antenna bore can be far longer than emitting antenna bore, has increased the signal power receiving.The use of convergent lens and balance detector array technology, the impact of Background suppression noise and local oscillator optical noise greatly, ensures to receive higher signal to noise ratio (S/N ratio) and larger field of view of receiver, realizes the imaging of synthetic aperture wide cut.

Brief description of the drawings

Fig. 1 is schematic diagram of the present utility model;

Fig. 2 is balanced array detection system schematic diagram in the utility model;

Fig. 3 is the contrast diagram of lens focal plane array heterodyne detection and traditional lens focal plane surface detector heterodyne detection in the utility model.

Embodiment

As shown in Figure 1, a kind of synthetic aperture laser imaging radar described in the utility model is received and dispatched coaxial optical antenna, comprise coaxial transmitting optics antenna and receive optical antenna, transmitting optics antenna formation is followed successively by light source 1, optical isolator 2, transmitter aperture diaphragm 3 and catoptron 4, receive optical antenna formation and be followed successively by target echo 5, receiver aperture diaphragm 6, receiving telescope object lens primary mirror 7, receiving telescope object lens secondary mirror 8, receiving telescope object lens prime focus 9, receiving telescope eyepiece 10, phase type LCD space light modulator 11, LCD space light modulator modulation signal 12, convergent lens diaphragm 13, convergent lens 14, local oscillator light reference light 16, light combination mirror 15 and balanced array detection system 17.Optical isolator 2 focus of interference 2 receiving telescope object lens primary mirrors 7 to light source and coincidence of the ellipsoid front focus of receiving telescope object lens secondary mirror 8 for separating echo signal 5 in described emitting antenna; The ellipsoid back focus of the front focus of described receiving telescope eyepiece 10 and receiving telescope object lens secondary mirror 8 overlaps, and together forms telescopic system with described receiving telescope object lens primary mirror 7.Described spatial light liquid crystal modulator modulation signal 12, for the PHASE DISTRIBUTION of control phase type LCD space light modulator 11, carries out the quadratic phase compensation to echoed signal.Described phase type LCD space light modulator 11 is positioned at the back focal plane place of receiving telescope eyepiece 10, and is positioned at the front focal plane place of convergent lens 14 simultaneously; Described convergent lens diaphragm 13 is positioned at the front focal plane place of convergent lens 14, is only pasting phase type LCD space light modulator 11; Within described light combination mirror 15 is positioned at one times of focal length after convergent lens 14, local oscillator light 16 through ovennodulation closes bundle with the converging light after 11 phase compensations of phase type LCD space light modulator in light combination mirror 15 mixing, by balanced array detection system 17 heterodyne receptions that are positioned at described convergent lens 14 back focal plane places.

As shown in Figure 2, balanced array detection system 17 is made up of wave plate 171, polarization splitting prism 172, the first photoelectronic detecting array 173, the second photoelectronic detecting array 174, totalizer 175 and balance receiving array circuit 176 successively.Described wave plate 171 is λ/2 and λ/4 wave plate; The first described photoelectronic detecting array 173 is identical with the second photoelectronic detecting array 174 structures and performance, is positioned at the back focal plane place of described convergent lens 13; The input end of described totalizer 175 is connected with the output terminal of the second photoelectronic detecting array 174 with the first described photoelectronic detecting array 173 respectively; The defeated place end of described totalizer 175 is connected with the input end of described balance receiving array circuit 176, balance receiving array circuit 176 output light paths 177.

Phase type LCD space light modulator 11 is carried out the quadratic phase compensation of echoed signal, and the expression formula of spatial light liquid crystal modulator modulation signal 12 can be reduced to:

$I_0\exp (-\mathrm{j\π}{M}^2\frac{x^2+y^2}{\mathrm{\λz}})$

I in formula ₀for corresponding constant term, z is the space length that target face arrives receiving telescope entrance pupil, in reality, is measured in real time or local oscillator light time delay conversion acquisition by altitude gauge.

For transmitter aperture diaphragm 3, the optics toes that square aperture has only limited target face are square, and circular aperture has determined circular optics toes.For receiver aperture diaphragm 6, when aperture is while being square, after telescopic system, the effective aperture function representation at emergent pupil place is:

$P_r^{\′}(x,y)=\mathrm{rect}(-\frac{\mathrm{Mx}}{L_{r,x}})\mathrm{rect}(-\frac{\mathrm{My}}{L_{r,y}})$

L in formula _r,x, L _r,yrepresent respectively the length of side of diaphragm both direction, M represents the enlargement factor of receiving telescope.

In the time that receiving telescope entrance pupil is circular aperture, establishing aperture diameter is D _r, after telescope, the effective aperture function representation at emergent pupil place is:

${\stackrel{\‾}{P}}_r^{\′}(x,y)=\mathrm{cyl}(-\frac{M\sqrt{x^2+y^2}}{D_r}),$

Therefore, for desirable telescope configuration, telescope only plays that corrugated expands or contracting Shu Zuoyong, itself can not bring phase differential and wavefront distortion, and square aperture is identical with circular aperture disposal route, and difference is that square aperture is to calculate in rectangular coordinate system, light field is square distribution, distance to the processing of Data in Azimuth Direction variables separation, circular aperture need transform in polar coordinate system and calculate, light field be circular light spot distribute.

The focal length of convergent lens 14 is f ₃balanced array detection system 17 is positioned at the back focal plane of this convergent lens 14, the light field at the light field on balanced array detection system 17 surfaces and convergent lens 14 front focal plane places is Fourier transform relation accurately, and in the time that convergent lens diaphragm 13 is square aperture, the length of side is respectively L _f,x, L _f,y, convergent lens 14 back focal plane optical pulse responses are:

$e_r(x,y)=\frac{L_{f,x}{L}_{f,y}}{\mathrm{j\λ}{f}_3}\·\frac{\sin \left(\mathrm{\π}\frac{L_{f,x}}{{\mathrm{\λf}}_3}x\right)}{\mathrm{\π}\frac{L_{f,x}}{{\mathrm{\λf}}_3}x}\·\frac{\sin \left(\mathrm{\π}\frac{L_{f,y}}{{\mathrm{\λf}}_3}y\right)}{\mathrm{\π}\frac{L_{f,y}}{{\mathrm{\λf}}_3}y}$

Corresponding spot width is:

${\mathrm{\Δl}}_{f,x}=\frac{{2\mathrm{\λf}}_3}{L_{f,x}},$

${\mathrm{\Δl}}_{f,y}=\frac{{2\mathrm{\λf}}_3}{L_{f,y}}.$

In the time that convergent lens diaphragm 13 is circular aperture, establishing its diameter is D _f,r, have optical pulse response to be:

${\stackrel{\‾}{e}}_r(x,y)=\frac{\mathrm{\π}{D}_{f,r}}{4\·\mathrm{j\λ}{f}_3}\·\frac{{2J}_1\left({\mathrm{\πD}}_{f,r}\frac{\sqrt{x^2+y^2}}{{\mathrm{\λf}}_3}\right)}{{\mathrm{\πD}}_{f,r}\frac{\sqrt{x^2+y^2}}{{\mathrm{\λf}}_3}},$

Corresponding spot width is:

${\mathrm{\Δd}}_{f,x}=2.44\frac{{\mathrm{\λf}}_3}{D_{f,x}}.$

Can see, the width of detector surface signal hot spot is inversely proportional to the aperture diameter of assembling lens stop 13, is directly proportional, by regulating convergent lens 14 aperture sizes to the focal length of convergent lens 14, get final product the width of control signal hot spot, ensure the coupling of signal hot spot and detector size.

In below analyzing, transmitter aperture diaphragm 3, receiver aperture diaphragm 6, convergent lens diaphragm 13 are all with square aperture analysis, and conclusion is equally applicable to circular aperture.

The focal length of described receiving telescope antenna object lens is f _r, the focal length of receiving telescope eyepiece 10 is f ₂, the enlargement factor of receiving telescope antenna is M=f _r/ f ₂.Suppose that n target resolution element centre coordinate is (x _n, y _n), the echoed signal of target reflection incides receiving telescope entrance pupil place through the propagation distance of space z, the light field e at emergent pupil place after telescope _n(x, y: be t):

In formula, P (x, y) is the aperture function at entrance pupil place, E _nfor the amplitude at telescope emergent pupil place, for corresponding item time phase.Second additive term that exponential term is light beam space diffraction in formula, it can affect the resolution of final imaging, cause diffusion of point image, for synthetic aperture laser imaging radar, distance z between radar and target is generally understood real-time transform, relies on before and adds phase-plate or the real-time impact of eliminating this quadratic phase of the very difficult realization of telescope out of focus scheme.Introduce phase type spatial light liquid crystal modulator herein at telescope emergent pupil place, by controlling the modulation signal of liquid crystal modulator, can eliminate in real time the impact of this quadratic phase item, corresponding liquid crystal modulator modulation signal is:

$I_0\exp (-\mathrm{j\π}{M}^2\frac{x^2+y^2}{\mathrm{\λz}}),$

Only need be according to altitude gauge or the time delay of local oscillator light convert the range information z of real-time update modulation signal in reality.After described phase type spatial light liquid crystal modulator compensation and lens convergence, be polarized two-way light path being distributed as on back focal plane after Amici prism beam splitting:

Now n target resolution element incides on array element corresponding to array photodetectors, the center of picture point in:

$x=\frac{f_3{x}_n}{z}$

$y=\frac{f_3{y}_n}{z}.$

Consider that the combination of balanced array probe unit receives, the corresponding centre coordinate of k receiving element combination is (x _k, y _k).If the local oscillation signal of optical heterodyne equivalence is light field on each corresponding detector is:

The general local oscillator light of synthetic aperture laser imaging radar is far better than flashlight, considers the light intensity individual features of balance detection technology and detector, and the intermediate-freuqncy signal that k corresponding balance receives probe unit output is:

Δ S in formula _kfor the photosensitive area of each detection array corresponding unit, S is each detector array total area, the responsiveness that α is array detection.

On balance detection array, the reception signal of all K combinations of detectors is:

If there is following corresponding relation hypothetical target point and array detection unit:

$\frac{f_3{x}_n}{z}={-x}_k,\frac{f_3{y}_n}{z}=-y_k,$

Final all signal powers of balance detection device array output are the stack of the echoed signal of all N object elements in synthetic aperture laser imaging radar optics toes:

Wherein optics toes are the field of view that emitting antenna and receiving antenna cover jointly in target face.

In heterodyne detection, it is generally acknowledged in the time that detector photosensitive area is less than or equal to the main lobe width that receives flashlight, just can have higher heterodyne mixing efficiency, no exception for array detection.While supposing that convergent lens diaphragm is square, the length of side is respectively L _{f, x}, L _{f, y}, main lobe width is and area is L _{d, x}× L _{d, y}, array element number is K _x× K _ydetector array photosurface in the maximum zero laps of flashlight main lobe number be , detector array number of arrays K minimum value is that array element only accounts for a flashlight main lobe, maximal value is target resolution element number, that is:

$\frac{L_{d,x}{L}_{f,x}}{2\mathrm{\λ}{f}_3}\left(\frac{L_{d,y}{L}_{f,y}}{2\mathrm{\λ}{f}_3}\right)\≤K_x\left(K_y\right)\≤N_x\left(N_y\right),$

N in formula _x, N _ybe respectively target face distance to orientation to target resolution element number.

As shown in Figure 3, visible signal light 21 and local oscillator light 24 close bundle in bundling device 25 mixing, and by detector 26 heterodyne receptions, detector 261 is detector array combination, and detector 262 is traditional surface detector.If adopt single surface detector 262 to receive signal, for flashlight energy is had compared with high usage, definition hot spot is the full duration that receives signal Airy disk main lobe, and generally the area of detector is always more than or equal to the spot size of echoed signal.Suppose that detector area is A _d, flashlight spot size is S _d, both area ratio coefficients are: K _d=A _d/ S _d.The signal light field and the local oscillator light field that receive are respectively E _rand E _1o, corresponding luminous power P _r=| E _r| ²s _d/ 2=|E _r| ²a _d/ 2K _dand P _lo=| E _lo| ²a _d/ 2; Because local oscillator light intensity is much larger than signal light intensity, the direct current signal of heterodyne reception is mainly local oscillator luminous power P _dC=P _lo, corresponding AC signal is expressed as $P_{\mathrm{AC}}=\left|E_{\mathrm{lo}}\right|\left|E_r\right|S_d=2\sqrt{P_{\mathrm{lo}}{P}_r}/\sqrt{K_d}.$

Johnson noise is mainly derived from the random fluctuation of direct current signal photon number, and root mean square Johnson noise power estimated value is P _σ=(h ν P _lo/ 2 τ _pul) ^1/2, τ in formula _pulfor the duration of pulse of laser signal.Suppose that echoed signal luminous power has signal to noise ratio (S/N ratio) S corresponding to root mean square Johnson noise power _shpt, P so _r=S _shotp _σ, therefore

$\sqrt{P_{\mathrm{lo}}}=\sqrt{{2\mathrm{\τ}}_{\mathrm{pul}}/\mathrm{hv}}{P}_r/S_{\mathrm{shot}}.$

Local oscillator luminous power expression formula is brought into, and corresponding AC signal can change into:

$P_{\mathrm{AC}}=2\sqrt{{2\mathrm{\τ}}_{\mathrm{pul}}/\mathrm{hv}}{P}_r\sqrt{P_r}/\left(S_{\mathrm{shot}}\sqrt{K_d}\right).$

In fact, in photoelectric conversion process, detector and follow-up amplifying circuit also can be introduced corresponding noise item, can unify to be equivalent to noise of detector P _n, due to the restriction of this noise item, minimum detectable power of definable carrys out the detectivity of characterization system to flashlight.Suppose that signal communication part is corresponding to noise of detector P _nthere is signal to noise ratio (S/N ratio) S _noise, so

P _AC＝S _noiseP _n。

Obtain the detectable echoed signal power of single surface detector by two formulas above

$P_r={\left(\frac{\mathrm{hv}}{2{\mathrm{\τ}}_{\mathrm{pul}}}\right)}^{1/3}{K}_d^{1/3}{\left(S_{\mathrm{noise}}{S}_{\mathrm{shot}}\right)}^{2/3}{\left(\frac{P_n}{2}\right)}^{2/3},$

Be transformed into receiving telescope entrance pupil face, desired receiving light power is expressed as:

$I_r={\left(\frac{\mathrm{hv}}{{2\mathrm{\τ}}_{\mathrm{pul}}}\right)}^{1/3}{K}_d^{1/3}{\left(S_{\mathrm{noise}}{S}_{\mathrm{shot}}\right)}^{2/3}{\left(\frac{P_n}{2}\right)}^{2/3}\frac{2}{D^2}.$

In formula, D is receiving telescope receiving aperture aperture stop size, can be by regulating convergent lens diaphragm size to change the value of Kd in reality, in controlled range, indirectly change the detectivity of receiving telescope, realize the coupling of signal hot spot, local oscillator hot spot and detector photosurface.

For 261 detector array combinations, if array element number is K, the detector total area is still A _d, single probe unit area and signal hot spot area ratio coefficient are K _d=A _d/ (KS _d).When in reality, detector array receives application, local oscillator light generally covers the whole photosurfaces of detector, the now noise equivalent power of whole detector completely therefore the detectable echoed signal light intensity of the single probe unit of detector array

$P_r^1={\left(\frac{\mathrm{hv}}{{2\mathrm{\τ}}_{\mathrm{pul}}}\right)}^{1/3}{K}_d^{1/3}{K}^{2/3}{\left(S_{\mathrm{noise}}{S}_{\mathrm{shot}}\right)}^{2/3}{\left(\frac{P_n^1}{2}\right)}^{2/3}.$

In like manner be transformed into receiving telescope entrance pupil face, desired receiving light power is expressed as:

$I_r^1=\frac{I_r}{K^{1/3}}.$

From upper surface analysis, for equal area detector and receiving telescope, detector array receives higher detectivity, lower to the expectation light intensity requirement of target face echo, only receives the 1/K of structure expectation light intensity for surface detector ^1/3doubly.

Consider that lens focal plane receives structure and the dwindle relation of receiving telescope antenna to field angle, the practical field of view angle that described two kinds of panel detector structures determine is:

${\mathrm{\θ}}_r=\frac{L_d}{{\mathrm{Mf}}_3},$

L in formula _dfor the length of side of square detector.

Consider that the AC power that the reception structure of single surface detector receives is P _aC, unified equivalent noise of detector is P _n, system signal noise ratio is

$S_{\mathrm{NR}}=\frac{P_{\mathrm{AC}}}{P_n}=\frac{2\sqrt{P_{\mathrm{lo}}{P}_r}}{\sqrt{K_d}{P}_n}.$

And the AC power that detector array reception structure receives is total equivalent noise of detector is actual is now system signal noise ratio is expressed as:

$S_{\mathrm{NR}}^1=\frac{P_{\mathrm{AC}}^1}{P_n^1}=\sqrt{K}{S}_{\mathrm{NR}}.$

Obviously see, array received structure has more high s/n ratio, and signal to noise ratio (S/N ratio) is in theory along with array element quantity increase and increase.Therefore the balanced array Detection Techniques that the utility model adopts have the detection performance better than traditional surface detector structure, are more suitable in this signal detection system of synthetic aperture laser imaging radar.

Verify the utility model taking specific design parameter below: a kind of resolution requirement of airborne synthetic aperture laser imaging radar is 20mm, imaging distance is 1000km, and laser signal wavelength is 1.55um.Systematic parameter is specially: transmitter aperture diaphragm is 50 × 50mm, and target is in Fraunhofer diffraction district, and corresponding synthetic aperture antenna length is 31m, and corresponding target resolution element number is minimum is 1550.In order to receive more echoed signal energy, 1m is even larger for receiving antenna telescope bore, design receiving telescope enlargement factor M=25, and convergent lens bore 10mm, focal length is 150mm, convergent lens back focal plane hot spot main lobe width is 46.5 × 46.5um; If detector array photosurface is square, the total area is 3 × 3mm, and detector array probe unit size is 46.5um to the maximum, and corresponding detector array array quantity minimum is K _x(K _y)=65, target resolution element hits is taken as N _x(N _y)=2000.Corresponding field of view of receiver angle is 0.80um, ideally improves 4 times than lens focal plane surface detector detectivity, and signal to noise ratio (S/N ratio) increases more than 8 times.The utility model is taking synthetic aperture and heterodyne reception technology as basis, utilize LCD space light modulator to eliminate in real time and receive signal quadratic term phase effect, by balanced array Detection Techniques and adjustable convergent lens diaphragm, can realize the much bigger field of view of receiver in visual field than common Kepler telescope directly receives and optical antenna bore diffraction determines, and the impact of Background suppression noise and local oscillator optical noise greatly, obtain higher heterodyne efficiency, ensure the signal to noise ratio (S/N ratio) receiving.Because mirror system does not have aberration, and easily realize heavy caliber processing, therefore can reduce the impact of the needed frequency chirp signal of radar, increase the flashlight energy receiving, in structure, easily form a coaxial synthetic aperture laser imaging radar with relatively small-bore transmitting optics antenna and receive and dispatch optical antenna, realize high-quality synthetic aperture imaging.In addition, Gregory receiving telescope antenna has formed a synthetic aperture laser imaging radar coaxial transmitting reception optical antenna with relatively small-bore transmitting optics antenna.

Claims (10)

1. synthetic aperture laser imaging radar is received and dispatched a coaxial optical antenna, comprising:

Transmitting optics antenna, the transmitter aperture diaphragm and the catoptron that comprise light source, arrange along light source optical path;

Receive optical antenna, the receiver aperture diaphragm that comprises target echo, is provided with successively along target echo incident direction, telescopic system, convergent lens, light combination mirror and balanced array detection system;

It is characterized in that, the transmitting light beam of transmitting optics antenna is via catoptron and the same optical axis of reception optical antenna, and telescopic system back focal plane place is provided with photomodulator.

2. synthetic aperture laser imaging radar according to claim 1 is received and dispatched coaxial optical antenna, it is characterized in that, described photomodulator is phase type LCD space light modulator.

3. synthetic aperture laser imaging radar according to claim 2 is received and dispatched coaxial optical antenna, it is characterized in that, the expression formula of the modulation signal of described phase type LCD space light modulator is:

I in formula ₀for corresponding constant term, z is the space length that target face arrives receiving telescope entrance pupil, is measured in real time or local oscillator light time delay conversion acquisition by altitude gauge, and M is the enlargement factor of receiving telescope antenna.

4. synthetic aperture laser imaging radar according to claim 1 is received and dispatched coaxial optical antenna, it is characterized in that, the front focal plane place of described convergent lens is provided with convergent lens diaphragm, and convergent lens diaphragm is close on described photomodulator.

5. synthetic aperture laser imaging radar according to claim 4 is received and dispatched coaxial optical antenna, it is characterized in that, described convergent lens diaphragm, transmitter aperture diaphragm and receiver aperture diaphragm are square aperture or circular aperture simultaneously.

6. synthetic aperture laser imaging radar according to claim 5 is received and dispatched coaxial optical antenna, it is characterized in that, described convergent lens diaphragm is provided with aperture size governor motion.

7. synthetic aperture laser imaging radar according to claim 1 is received and dispatched coaxial optical antenna, it is characterized in that, described balanced array detection system comprises wave plate, polarization splitting prism, the first photoelectronic detecting array, the second photoelectronic detecting array, totalizer and balance receiving array circuit, wave plate is λ/2 or λ/4 wave plate, before wave plate is arranged on polarization splitting prism, the first photoelectronic detecting array and the second photoelectronic detecting array are positioned at the back focal plane place of described convergent lens; The input end of totalizer is connected with the output terminal of the second photoelectronic detecting array with the first described photoelectronic detecting array respectively; The output terminal of totalizer is connected with the input end of balance receiving array circuit.

8. synthetic aperture laser imaging radar according to claim 1 is received and dispatched coaxial optical antenna, it is characterized in that, described telescopic system comprises receiving telescope object lens primary mirror, receiving telescope object lens secondary mirror, receiving telescope eyepiece, and described receiver aperture diaphragm is positioned at the front focal plane place of receiving telescope object lens primary mirror; The recessed reflecting surface of receiving telescope object lens primary mirror is relative with the recessed reflecting surface of receiving telescope object lens secondary mirror, the front focus of the focus of receiving telescope object lens primary mirror and receiving telescope object lens secondary mirror overlaps, and the back focus of the front focus of receiving telescope eyepiece and receiving telescope object lens secondary mirror overlaps.

9. synthetic aperture laser imaging radar according to claim 8 is received and dispatched coaxial optical antenna, it is characterized in that, described receiving telescope object lens primary mirror is parabolic mirror, and described receiving telescope object lens secondary mirror is ellipsoidal mirror.

10. synthetic aperture laser imaging radar according to claim 1 is received and dispatched coaxial optical antenna, it is characterized in that, described transmitting optics antenna also comprises the light shielding system of light source being disturbed for isolating target echo signal, before light shielding system is positioned at described transmitter aperture diaphragm.