CN100526912C - Active externally coefficient potentiometer and scaling method of wideband synthetic aperture radar - Google Patents

Abstract

The invention discloses an external scaler and calibrating method of new broad-band synthetic aperture radar, which is characterized by the following: modulating the signal of the received synthetic aperture radar through sine amplitude; making two sides of the Doppler signal of synthetic aperture radar of scaler generate symmetrical mirror-image spectrum; utilizing positional filter to extract the mirror-image spectrum; separating the synthetic aperture radar signal from ground clutter. The scaler contains receiving and transmitting antenna, RF mode and modulating mode. The invention realizes external scaling signal separated from ground clutter completely to form loop testing circuit with radar transceiver system, antenna, transmitting path and external scaler without influencing by ground clutter, which improves the precision of external scaler greatly under complex and high-ground clutter condition.

Description

A kind of active externally coefficient potentiometer of wideband synthetic aperture radar and calibrating method thereof

Technical field

The invention belongs to the The radar exploration technique field, relate to a kind of new wideband synthetic aperture radar externally coefficient potentiometer particularly.

Background technology

Synthetic aperture radar (SAR) adopts the synthetic aperture principle to improve the orientation to resolution, distance is then sought help from pulse compression technique to the raising of resolution, but because synthetic-aperture radar round-the-clock, round-the-clock imaging over the ground and have the ability that necessarily penetrates vegetation and camouflage, therefore, be widely used in fields such as military affairs, ocean, agricultural, resource, disaster monitoring, topographic mapping, and be subjected to the attention of countries in the world especially.At present, resolution from hundred meters magnitudes at initial stage, is brought up to sub-meter grade as one of core technology index of synthetic-aperture radar, and for example De Guo PAMIR has reached 0.1 meter.Outer calibration technology is also demanded development urgently as the main means of check synthetic aperture radar image-forming resolution, calibration polarization sensitive synthetic aperture radar system error, adapts to the demand of high resolving power, the outer calibration of modern mode imaging radar.Generally speaking, require the physical size of externally coefficient potentiometer must be less than a resolution elements.Under such restrictive condition, along with the raising of resolution, the radar cross section of traditional passive corner reflector (RCS) is very low, is very easily covered by the scene clutter, is difficult to be applicable to the outer calibration test of high resolution synthetic aperture radar.Active by contrast calibration technology relies on reception and transmits the synthetic-aperture radar signal and simulate terrain object, therefore, just can obtain bigger RCS as long as improve the gain of receive-transmit system, and is irrelevant with physical size.Simultaneously, can increase redundant information to synthetic aperture radar signal additional modulation or coding before transmitting, the further signal to noise ratio (S/N ratio) that improves outer rate-aided signal reduces the externally requirement of calibration field, satisfies the outer calibration demand of modern high resolution synthetic aperture radar.

Summary of the invention

In order to satisfy the synthetic-aperture radar high-resolution imaging and such as to outer calibration technology requirements of clutter background imaging doughtily such as cities, the objective of the invention is to improve the gain of active calibration receive-transmit system, obtain bigger radar cross section (RCS), simultaneously, can be before transmitting to synthetic aperture radar signal additional modulation or coding, increase redundant information, further improve the signal to noise ratio (S/N ratio) of outer rate-aided signal, reduce the externally requirement of calibration field, satisfy the outer calibration demand of modern high resolution synthetic aperture radar, for this reason, the present invention will provide a kind of active externally coefficient potentiometer and calibrating method thereof of wideband synthetic aperture radar.

First aspect of the present invention, a kind of active outer calibrating method of wideband synthetic aperture radar, following steps:

Receive synthetic-aperture radar pulse linear FM signal, amplify then, filtering;

This synthetic-aperture radar pulse linear FM signal is carried out the sine amplitude modulation, make the Doppler frequency spectrum both sides, orientation of this scaler echoed signal produce the image spectra of symmetry;

This modulation signal quantitatively decayed is provided with the long-pending RCS of equivalent radar cross section, then power amplification and change and send back to synthetic-aperture radar;

The synthetic-aperture radar echo data that comprises this scaler modulation signal is carried out distance after compression, and azimuth filtering is extracted this mirror image Doppler frequency.

But described sine amplitude is modulated the device of available voltage controlled attenuator or other power attenuation stepless control and is realized, should satisfy following relational expression:

S _r(t)＝(1+A?cos(ωt))S _t(t)

S wherein _t(t) the synthetic-aperture radar pulse linear FM signal for receiving, S _r(t) for transmitting back the signal of synthetic-aperture radar after the scaler modulation, A is an amplitude-modulation index, and ω is the modulation angular frequency;

But amplitude-modulation index A is satisfied by the maximum attenuation degree of depth decision of voltage controlled attenuator or other power stepless control devices:

2log ((1+A)/(1-A))≤maximum attenuation degree of depth

The modulation angular frequency is by synthetic-aperture radar pulse repetition rate PRF and orientation doppler bandwidth Δ f _DopplerDecision, should satisfy:

2πΔf _doppler≤ω≤PRF/2

Second aspect of the present invention, a kind of active externally coefficient potentiometer of wideband synthetic aperture radar comprises: reception and transmission antenna device, radio-frequency module, modulation module; Receiving antenna, emitting antenna receive synthetic-aperture radar pulse linear FM signal and launch the outer signal of demarcating of output, and radio-frequency module amplifies, modulates and transmits synthetic-aperture radar pulse linear FM signal, and generates the outer demarcation signal of amplitude modulation(PAM); Modulation module produces voltage controlled attenuator and the numerical-control attenuator that voltage-controlled signal and digital control signal are controlled radio-frequency module respectively.

Beneficial effect of the present invention: the invention describes a kind of source scaler (source scaler: Amplitude Modulation Transponder) based on amplitude modulation(PAM), this scaler is simple and easy to realize, it carries out amplitude modulation(PAM) to the synthetic-aperture radar signal that receives, be transmitted to synthetic-aperture radar then, through the orientation after handling, because amplitude modulation, lower sideband produces mirror image respectively on original Doppler frequency spectrum, the outer rate-aided signal of separating fully with land clutter can be provided, accurately realize a radar transmit-receive system that not influenced by land clutter, antenna, transmission path and externally coefficient potentiometer closed loop test loop, even in complexity, under the situation of high ground clutter, also can improve the precision of outer calibration greatly.Utilize this mirror image Doppler frequency spectrum, can also estimate the unmodulated echoed signal of source scaler, the phase place of this signal has comprised the range information of source scaler to the carrier aircraft platform.Therefore, can also the high-precision movement locus that estimates the carrier aircraft platform in conjunction with differential Global Positioning System/strapdown inertial navitation system (SINS) DGPS/SINS with the method for Kalman filtering, improve the precision of motion compensation, this is very important for high resolution synthetic aperture radar.

Description of drawings

By the detailed description below in conjunction with accompanying drawing, above-mentioned and others, feature and advantage of the present invention will become more apparent.In the accompanying drawing:

Fig. 1 is the active externally coefficient potentiometer system architecture block scheme of wideband synthetic aperture radar of the present invention

Fig. 2 is the active externally coefficient potentiometer system construction drawing of wideband synthetic aperture radar of the present invention

Fig. 3 is a transmitter module structural drawing of the present invention

Fig. 4 is a modulation module structural drawing of the present invention

Fig. 5 is the unmodulated signal frequency spectrum of accepting, transmitting through source scaler of the present invention

Fig. 6 is the spectrum modulation signal of accepting, transmitting through source scaler of the present invention

Fig. 7 and Fig. 8 are the source scaler outward appearance photos of the embodiment of the invention

Embodiment

Below in conjunction with accompanying drawing the present invention is specified.Be noted that described embodiment only is considered as illustrative purposes, rather than limitation of the present invention.

According to the present invention, the active externally coefficient potentiometer system architecture block scheme of wideband synthetic aperture radar shown in Figure 1, Fig. 2 is the active externally coefficient potentiometer system construction drawing of wideband synthetic aperture radar of the present invention, comprises among the figure:

Receiving antenna 1, modulation module 2, radio-frequency module 3 and emitting antenna 4; Radio-frequency module is connected with emitting antenna input with the output of receiving antenna respectively, and another input of radio-frequency module is connected with modulation module output; Receiving antenna 1 receives the synthetic-aperture radar signal, and by the outer signal of demarcating of emitting antenna 2 emission outputs, modulation module 2 is used to produce voltage-controlled signal and digital control signal control radio-frequency module 3; Radio-frequency module 3 is used for amplifying, modulates and transmits synthetic-aperture radar pulse linear FM signal, generates the outer demarcation signal of amplitude modulation modulation, and this signal is amplified, and the gain of amplification is controlled by digital control signal.Modulation module produces voltage-controlled signal end and is connected with numerical-control attenuator with the voltage controlled attenuator of radio-frequency module respectively with the digital control signal end, the voltage controlled attenuator and the numerical-control attenuator of control radio-frequency module.

Fig. 3 according to the present invention is the transmitter module structural drawing, comprises among the figure:

Described radio-frequency module 3 main compositions are interconnected as low noise amplifier 21, bandpass filter 22, voltage controlled attenuator 23, numerical-control attenuator 24, power amplifier 25, isolator 26 successively, wherein the control end of voltage controlled attenuator 23 links to each other with the voltage-controlled signal end of modulation module 2, and the control end of numerical-control attenuator 24 links to each other with the digital control signal end of modulation module 2;

21 pairs of synthetic-aperture radar pulse linear FM signals from receiving antenna 1 of low noise amplifier are carried out the amplification of first order low noise and are exported bandpass filter 22 to;

Bandpass filter 22 suppresses the outer clutter of band of input signal, exports voltage controlled attenuator 23 rf inputs to;

Voltage controlled attenuator 23 is according to carrying out corresponding amplitude modulation(PAM) from the voltage-controlled signal of modulation module 2 to the signal of rf inputs, and exports numerical-control attenuator 24 rf inputs to;

Numerical-control attenuator 24 is according to carrying out corresponding quantitatively decay from the digital control signal of modulation module 2 to the signal of rf inputs, and exports power amplifier 25 to;

Power amplifier 25 carries out the final stage power amplification with the signal of input, exports isolator 26 to;

Isolator 26 exports the signal of input to emitting antenna 4, and isolates reflected signal and noise signal from emitting antenna 4.

Fig. 4 according to the present invention is the modulation module structural drawing, among the figure:

Described modulation module 2 main compositions comprise: computing machine 31, serial interface unit 32, FPGA waveform storage unit 33, clock unit 34, D/A D/A converting circuit 35, filter unit 36, level conversion unit 37;

Computing machine 31 input 4bit numerical control sign indicating numbers and modulating wave font code are given serial interface unit 32, and an output terminal of serial interface unit 32 outputs to 4bit numerical control sign indicating number an input end (generation digital control signal) of level conversion unit 37; Another output terminal of serial interface unit 32 outputs to the modulating wave font code input end of FPGA storage unit 33;

Another input end of FPGA storage unit 33 links to each other with the output terminal of clock unit 34, the reading speed output of control FPGA storage unit 33;

The output terminal of FPGA storage unit 33 is connected with D/A D/A converting circuit 35 input ends, finishes the conversion of modulation waveform yardage word to simulation; The output terminal of D/A D/A converting circuit 35 is connected with the input end of filter unit 36, by filter unit 36 filter away high frequency noise, is input to level conversion unit 37 then, produces voltage-controlled signal.

According to the present invention, the specific design of a kind of active externally coefficient potentiometer embodiment of wideband synthetic aperture radar is as follows:

I. source scaler system architecture

The design of source scaler working frequency range is at X-band, and centre frequency is 9.8GHz, and bandwidth is 1.6GHz, and its structured flowchart as shown in Figure 1.

Receiving antenna 1 and emitting antenna 4 selection 3dB beam angles are the X-band standard horn antenna of E face 24 degree H faces 30 degree among Fig. 1; The low noise amplifier 21 of Fig. 2 selects gain greater than 45dB, the noise figure broadband X-band LNA less than 2.5dB; Bandpass filter 22 is selected 9.8GHz, and bandwidth is the cavity band-pass filter of 1.6GHz; Voltage controlled attenuator 23 selects the maximum attenuation degree of depth greater than 40dB, and voltage-controlled range of signal is the X-band broadband voltage controlled attenuator of 0-5V; It is the X-band broadband numerical-control attenuator of 2dB that numerical-control attenuator 24 is selected 4 figure place control signals, decay stepping; Power amplifier 25 is selected the X-band wideband power amplifer of P1dB greater than 10dBm; Isolator 26 selects frequency of operation at X-band.

Before the work of the active externally coefficient potentiometer of a kind of wideband synthetic aperture radar of the present invention, give serial interface unit 32 by computing machine 31 input 4bit numerical control sign indicating numbers and modulating wave font code earlier, the level conversion unit 37 that 4bit numerical control sign indicating number is outputed to of serial interface unit 32 generates digital control signal, and the gain of radio-frequency module 3 is set; In the time of serial interface unit 32 the modulating wave font code is loaded into FPGA storage unit 33;

During source scaler work, FPGA storage unit 33 is with the clock frequency of clock unit 34, output modulating wave font code is to D/A D/A converting circuit 35, finish of the conversion of modulation waveform yardage word to simulation, output to filter unit 36 filter away high frequency noise then, be input to level conversion unit 37 then, produce voltage-controlled signal.

The synthetic-aperture radar signal is through receiving electromagnetic horn 1 by after the low noise bandpass filter 22, according to the voltage-controlled signal that modulation module 2 produces the synthetic aperture radar pulse signal is carried out amplitude modulation(PAM) by voltage controlled attenuator 23, after amplifying, be sent to the carrier aircraft platform of synthetic-aperture radar again by emission electromagnetic horn 4.

II. the design of source scaler equivalence radar cross section RCS:

According to the active outer calibrating method and the described active externally coefficient potentiometer of described wideband synthetic aperture radar, the step that the quantitative decay of described usefulness is provided with equivalent radar cross section RCS comprises:

The equivalent radar cross section RCS that at first determines source scaler is determined by following formula:

$\mathrm{\σ}=\frac{{\mathrm{\λ}}^2}{4\mathrm{\π}}{\mathrm{GG}}_{\mathrm{tr}}{G}_{\mathrm{tr}}$

Wherein σ represents equivalent radar cross section RCS, and λ represents the carrier wavelength of synthetic-aperture radar pulse linear FM signal, and G represents the gain of source scaler radio-frequency module, G _TrThe gain of expression source scaler dual-mode antenna;

Realize quantitatively decay with N figure place controlling attenuation device, the high-low level of its N position control end of numerical control deamplification can determine 2 ^NIndividual attenuation state, available Nbit numerical control representation has adopted 4 figure place controlling attenuation devices in embodiments of the present invention, so use 4bit numerical control sign indicating number;

By computing machine the Nbit numerical control sign indicating number of needs is sent to modulation module, produce and export corresponding numerical control deamplification and output to the control end of numerical-control attenuator, change the gain G of source scaler radio-frequency module, thereby change the equivalent radar cross section RCS of source scaler;

Nbit numerical control sign indicating number correspondence 2 ^NIndividual different equivalent radar cross section amasss RCS.

The concrete realization of equivalence radar cross section is: according to the running parameter of polarization sensitive synthetic aperture radar system, and utilization radar equation, the target radar cross-sectional area RCS that the derivation source scaler is simulated and the relation of source scaler system-gain.

The equivalent radar cross section of supposing source scaler is σ, and the gain of radio-frequency module 2 is G, can determine that according to the receiving antenna 1 of source scaler and the E face H face 3dB beam angle of emitting antenna 4 its gain is G _Tr=15dB.Know that the receiving antenna 1 terminal received power of source scaler is:

$P_{\mathrm{rf}\_\mathrm{in}}=\frac{P_t{G}_t{G}_{\mathrm{tr}}}{\left(4\mathrm{\π}{R}^2\right)}{\mathrm{\λ}}^2$

Wherein, P _tBe synthetic-aperture radar output power of transmitter, G _tBe 4 gains of synthetic-aperture radar emitting antenna, λ is the carrier wavelength of synthetic-aperture radar pulse linear FM signal, and R is the oblique distance of synthetic-aperture radar apart from mapping band central point, and then the emissive power of source scaler forwarding is:

P _{rf_out}＝GP _{rf_in}

The reception echo power of synthetic-aperture radar receiving antenna end is:

$P_r=\frac{P_{\mathrm{rf}\_\mathrm{out}}{G}_{\mathrm{tr}}{G}_r}{\left(4\mathrm{\π}{R}^2\right)}{\mathrm{\λ}}^2=\frac{P_{\mathrm{rf}\_\mathrm{in}}{\mathrm{GG}}_{\mathrm{tr}}{G}_r}{\left(4\mathrm{\π}{R}^2\right)}{\mathrm{\λ}}^2=\frac{P_t{G}_t{G}_r}{{\left(4\mathrm{\π}\right)}^3{R}^4}{\mathrm{\λ}}^2\left(\frac{{\mathrm{\λ}}^2}{4\mathrm{\π}}{\mathrm{GG}}_{\mathrm{tr}}{G}_{\mathrm{tr}}\right)$

G wherein _rBe the synthetic-aperture radar receiving antenna gain, G under the situation of single base station _rWith G _tEquate.For radar cross section RCS is σ _cPoint target, the reception echo power of synthetic-aperture radar receiving antenna end is:

$P_r=\frac{P_t{G}_t{G}_r}{{\left(4\mathrm{\π}\right)}^3{R}^4}{\mathrm{\λ}}^2{\mathrm{\σ}}_c$

Therefore, the relation of the equivalent radar cross section RCS of described source scaler and source scaler gain is as follows:

$\mathrm{\σ}={\mathrm{\σ}}_c=\frac{{\mathrm{\λ}}^2}{4\mathrm{\π}}{\mathrm{GG}}_{\mathrm{tr}}{G}_{\mathrm{tr}}=G-11.5\mathrm{dB}$

Described source scaler adopts the 4bit data to be sent in the modulation module 2 by control computer 31 by serial interface unit 2, after changing, level commentaries on classics logical block 35 forms the numerical-control attenuator control signal, reach the control system gain, realize the function of 16 different RCS point targets of simulation.

III. the design of source scaler amplitude modulation speed

Described source scaler modulation module 2 adopts the clock frequency of fixed clock unit 34, adjust different modulation waveform memory lengths by FPGA storage unit 33 and change amplitude modulation speed, the bandwidth and the synthetic-aperture radar pulse repetition rate of Doppler's history depended in the selection of this amplitude modulation speed.

In order to guarantee that the mirror image Doppler frequency spectrum that produces after source scaler is to synthetic aperture radar signal amplitude modulation(PAM) can be by undistorted sample record, do not produce aliasing,, the pulse repetition rate PRF value that must satisfy synthetic-aperture radar is the twice of modulation angular frequency at least, simultaneously ω/2 π

At least greater than synthetic-aperture radar orientation doppler bandwidth Δ f _Doppler, promptly satisfy following formula:

2πΔf _doppler≤ω≤PRF/2

The PRF value also should multiply by over-sampling coefficient Ga=1.2 on engineering.Is example with 0.5 meter orientation to resolution, and its doppler bandwidth is approximately 500Hz, supposes that modulation rate is set to 625Hz, and modulation back bandwidth is 875Hz, and then the minimum in theory 1750Hz that gets of PRF value should get 2100Hz on the engineering at least.

IV. source scaler antenna, structure and power supply design

Described source scaler receiving antenna 1, emitting antenna 4 all adopt the standard pyramidal horn antenna, H face, E face 3dB beam angle should guarantee to point to fully width, generally get corresponding synthetic aperture radar antenna H face, E face 3dB beam angle 5 times, E face and H face 3dB beam angle are designed to 30 °, 24 ° respectively in the present embodiment.Receiving antenna 1, emitting antenna 4 are fixed on the anistree rotatable platform, keep the H face parallel, and the polarization mode that anistree rotatable platform can change receiving antenna 1, emitting antenna 2 is rotated in the coupling of E face; The isolation of receiving antenna 1, emitting antenna 4 at least should be than radio-frequency module 3, receiving antenna 1, the big 10dB of emitting antenna 4 gain sums, (this description defines the spatial relation of receiving antenna 1, emitting antenna 4) spacing of receiving antenna 1, emitting antenna 4 in the design is got 30cm, to guarantee that isolation is greater than 60dB; Supporting structure has the function of adjusting level and angle sensing simultaneously, makes with bakelite, and the antenna pallet adopts aluminum alloy material, and slim x wave band absorbing material is sticked on the surface, can reduce supporting structure greatly to the radar wave reflection.Fig. 7 and Fig. 8 are the source scaler outward appearance photos of design example of the present invention.

The source scaler operating voltage is 19V---28V, total system power consumption≤500mA, DC voltage about 26 volts can be provided after Panasonic's lead-acid accumulator of power module employing two 12V, 40Ah, the parallel connection, service time is the longest to be 80 hours, in 8 hours duration of charging, can fully guarantee the outfield power demands.

The active outer calibrating method of a kind of wideband synthetic aperture radar of the present invention, principle design is as follows:

The principle of source scaler is to realize moving of Doppler frequency spectrum by amplitude modulation(PAM), suppose the reception synthetic-aperture radar transmit for

$S_t\left(t\right)=u\left(t\right)e^{{\mathrm{j\ω}}_{c}t}$

Wherein u (t) represents the wideband pulse linear FM signal of synthetic-aperture radar, ω _cRepresent the carrier frequency that transmits.After postponing α ' after a while, the source scaler received signal is

$S_{\mathrm{tr}}\left(t\right)=u(t-\mathrm{\α}\′)e^{{\mathrm{j\ω}}_c(t-\mathrm{\α}\′)}$

Butt joint folds into the sine amplitude of aperture radar signal and modulates, and is transmitted to synthetic-aperture radar carrier aircraft platform after the modulation, and received signal can be expressed from the next

$S_r=\{1+A\cos \left(\mathrm{\ω}(t-\mathrm{\α}\′\′)\right)\}u(t-\mathrm{\α}\′-\mathrm{\α}\′\′)e^{{\mathrm{j\ω}}_c(t-\mathrm{\α}\′-\mathrm{\α}\′\′)}$

$=u(t-\mathrm{\α})e^{{\mathrm{j\ω}}_c(t-\mathrm{\α})}+\frac{A}{2}u(t-\mathrm{\α})e^{j{\mathrm{\ω}}_c(t-\mathrm{\α})-\mathrm{j\ω}(t-\mathrm{\α}\′\′)}+\frac{A}{2}u(t-\mathrm{\α})e^{j{\mathrm{\ω}}_c(t-\mathrm{\α})+\mathrm{j\ω}(t-\mathrm{\α}\′\′)}$

$=u(t-\mathrm{\α})e^{j{\mathrm{\ω}}_c(t-\mathrm{\α})}+\frac{A}{2}u(t-\mathrm{\α})e^{j({\mathrm{\ω}}_c-\mathrm{\ω})t-j({\mathrm{\ω}}_c\mathrm{\α}-\mathrm{\ω\α}\′\′)}+\frac{A}{2}u(t-\mathrm{\α})e^{j({\mathrm{\ω}}_c+\mathrm{\ω})t-j({\mathrm{\ω}}_c\mathrm{\α}+\mathrm{\ω\α}\′\′)}$

Wherein α be the pulse linear FM signal from being transmitted into the overall delay of reception, ω is the modulation rate of amplitude modulation(PAM), ω is by synthetic-aperture radar pulse repetition rate PRF and orientation doppler bandwidth Δ f _DopplerDecision, should satisfy:

2πΔf _doppler≤ω≤PRF/2

But amplitude-modulation index A should be satisfied by the maximum attenuation degree of depth decision of voltage controlled attenuator or other power stepless control devices:

2log ((1+A)/(1-A))≤maximum attenuation degree of depth

α " be that modulation is forwarded to the time delay that synthetic-aperture radar receives, by following formula as can be known, Be the phase differential of fixing, it does not play an important role in our analysis, To produce a pair of mirror image in lower sideband ± ω place on Doppler frequency spectrum, even the Doppler signal both sides, synthetic-aperture radar orientation of scaler produce the image spectra of symmetry, this image spectra does not comprise any scene clutter.As long as the PRF value of polarization sensitive synthetic aperture radar system is enough high, satisfy the nyquist sampling law, just can extract the mirror image Doppler frequency spectrum that produces by amplitude modulation.

In the design embodiment, with the frequency is 9.8GHz, and power is-and the point-frequency signal of 40dBm is as the input signal of source scaler radio-frequency module 3, and modulation rate ω=625Hz is set, amplitude-modulation index A=0.9 has done testing authentication to the modulation function of source scaler.As Fig. 5 is the unmodulated signal frequency spectrum that source scaler of the present invention receives, transmits, and Fig. 6 illustrates through the spectrum modulation signal that source scaler of the present invention receives, transmits.Comparison diagram 5 and Fig. 6 are as can be seen, 9.8GHz has produced image frequency in both sides ± 625Hz place up and down in initial point frequency signal frequency, and the clutter of energy maximum than image frequency low 34dB, this explanation source scaler has well realized the acceptance point sine amplitude modulation of signal frequently.

Described mirror image Doppler frequency spectrum can also estimate the unmodulated echoed signal of source scaler, and the phase place of this signal has comprised the range information of source scaler to the carrier aircraft platform.Therefore, can also the high-precision movement locus that estimates the carrier aircraft platform in conjunction with differential Global Positioning System/strapdown inertial navitation system (SINS) (DGPS/SINS) with the method for Kalman filtering, improve the precision of motion compensation, this is very important for high resolution synthetic aperture radar.

Describing above is to be used to realize the present invention and embodiment, and each step is example, and therefore, scope of the present invention should not described by this and limit.It should be appreciated by those skilled in the art,, all belong to claim of the present invention and come restricted portion in any modification or partial replacement that does not depart from the scope of the present invention.

Claims (7)

1, a kind of active outer calibrating method of wideband synthetic aperture radar is characterized in that: comprise the steps:

Receive synthetic-aperture radar pulse linear FM signal, amplify then, filtering;

This synthetic-aperture radar pulse linear FM signal is carried out the sine amplitude modulation, make the Doppler frequency spectrum both sides, orientation of this scaler echoed signal produce the image spectra of symmetry;

This modulation signal quantitatively decayed is provided with the long-pending RCS of equivalent radar cross section, then power amplification and change and send back to synthetic-aperture radar;

The synthetic-aperture radar echo data that comprises this scaler modulation signal is carried out distance after compression, and azimuth filtering is extracted this mirror image Doppler frequency.

2, according to the active outer calibrating method of the described wideband synthetic aperture radar of claim 1, it is characterized in that: but described sine amplitude is modulated the device realization of available voltage controlled attenuator or other power attenuation stepless control, satisfies following relational expression:

S _r(t)＝(1+Acos(ωt))S _t(t)

S wherein _t(t) the synthetic-aperture radar pulse linear FM signal for receiving, S _r(t) for transmitting back the signal of synthetic-aperture radar after the scaler modulation, A is an amplitude-modulation index, and ω is the modulation angular frequency;

But amplitude-modulation index A is satisfied by the maximum attenuation degree of depth decision of voltage controlled attenuator or other power stepless control devices:

2log ((1+A)/(1-A))≤maximum attenuation degree of depth

The modulation angular frequency is by synthetic-aperture radar pulse repetition rate PRF and orientation doppler bandwidth Δ f _DopplerDecision, satisfy:

2πΔf _doppler≤ω≤PRF/2

3, a kind of active externally coefficient potentiometer of wideband synthetic aperture radar is characterized in that, this scaler comprises: receiving antenna and emitting antenna, radio-frequency module, modulation module; Receiving antenna, emitting antenna receive synthetic-aperture radar pulse linear FM signal and launch the outer signal of demarcating of output, and radio-frequency module amplifies, modulates and transmits synthetic-aperture radar pulse linear FM signal, and generates the outer demarcation signal of amplitude modulation(PAM); Modulation module produces voltage controlled attenuator and the numerical-control attenuator that voltage-controlled signal and digital control signal are controlled radio-frequency module respectively.

4, according to the active externally coefficient potentiometer of the described wideband synthetic aperture radar of claim 3, it is characterized in that: the radio-frequency module main composition comprises: be interconnected as low noise amplifier, bandpass filter, voltage controlled attenuator, numerical-control attenuator, power amplifier, isolator successively; Wherein: the control end of voltage controlled attenuator links to each other with the voltage-controlled signal end of modulation module, and the control end of numerical-control attenuator links to each other with the digital control signal end of modulation module; Low noise amplifier is to carrying out the amplification of first order low noise and exporting bandpass filter to from the synthetic-aperture radar pulse linear FM signal of receiving antenna; Bandpass filter, the outer clutter of the band of inhibition input signal exports the voltage controlled attenuator rf inputs to; Voltage controlled attenuator according to from the voltage-controlled signal of modulation module the signal of rf inputs being carried out corresponding amplitude modulation(PAM), exports the numerical-control attenuator rf inputs to; Numerical-control attenuator according to from the digital control signal of modulation module the signal of rf inputs being carried out corresponding quantitatively decay, exports power amplifier to; Power amplifier carries out the final stage power amplification with the signal of importing, and exports isolator to; Isolator exports the signal of importing to emitting antenna, and isolates reflected signal and noise signal from emitting antenna.

5, according to the active externally coefficient potentiometer of the described wideband synthetic aperture radar of claim 3, it is characterized in that: described modulation module main composition comprises: computing machine, serial interface unit, FPGA waveform storage unit, clock unit, D/A converting circuit D/A, filter unit, level conversion unit;

Give the serial interface unit by computing machine input numerical control sign indicating number and modulating wave font code, an output terminal of serial interface unit outputs to an input end of level conversion unit with the numerical control sign indicating number, generates digital control signal; Another output terminal of serial interface unit outputs to the modulating wave font code input end of FPGA storage unit;

Another input end of FPGA storage unit links to each other with the output terminal of clock unit, the reading speed output of control FPGA storage unit;

The output terminal of FPGA storage unit is connected with D/A converting circuit D/A input end, finishes the conversion of modulation waveform yardage word to simulation; The output terminal of D/A converting circuit D/A is connected with the input end of filter unit, by the filter unit filter away high frequency noise, is input to level conversion unit then, produces voltage-controlled signal.

6, according to the active externally coefficient potentiometer of the described wideband synthetic aperture radar of claim 3, it is characterized in that: described receiving antenna, emitting antenna adopt standard x wave band electromagnetic horn, H face E face 3dB beam angle guarantees to point to fully width, 5 times of getting corresponding synthetic aperture radar antenna H face, E face 3dB beam angle; Receiving antenna, emitting antenna are fixed on the anistree rotatable platform, make that the H face is parallel, the coupling of E face, and the isolation of receiving antenna, emitting antenna at least should be greater than radio-frequency module, receiving antenna, transmitter antenna gain (dBi) sum 10dB; Adjust the polarization mode of receiving antenna, emitting antenna by rotating anistree rotatable platform.

7, according to the active outer calibrating method of the described wideband synthetic aperture radar of claim 1, it is characterized in that: the step that the quantitative decay of described usefulness is provided with equivalent radar cross section RCS comprises:

The equivalent radar cross section RCS that at first determines source scaler is determined by following formula:

$\mathrm{\σ}=\frac{{\mathrm{\λ}}^2}{4\mathrm{\π}}{\mathrm{GG}}_{\mathrm{tr}}{G}_{\mathrm{tr}}$

Wherein σ represents equivalent radar cross section RCS, and λ represents the carrier wavelength of synthetic-aperture radar pulse linear FM signal, and G represents the gain of source scaler radio-frequency module, G _TrThe gain of expression source scaler dual-mode antenna;

Quantitatively decay with N figure place controlling attenuation device, the high-low level of its N position control end of numerical control deamplification determines 2 ^NIndividual attenuation state is with Nbit numerical control representation;

By computing machine the Nbit numerical control sign indicating number of needs is sent to modulation module, produce and export corresponding numerical control deamplification and output to the control end of numerical-control attenuator, change the gain G of source scaler radio-frequency module, thereby change the equivalent radar cross section RCS of source scaler;

Nbit numerical control sign indicating number correspondence 2 ^NIndividual different equivalent radar cross section amasss RCS.

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