CN103399301A - Device and method for receiving broadband synthetic aperture radar (SAR) signals - Google Patents

Abstract

The invention discloses a device and a method for receiving synthetic aperture radar (SAR) signals. The device comprises a receiving module, a difference frequency module and an acquisition module. The method comprises five steps. The device and the method disclosed by the invention carry out different frequency processing on received broadband SAR echo signals, enable the bandwidth of the radar echo signals to be reduced greatly, and simplify follow-up broadband SAR signal acquisition equipment, A/D conversion and the like. Radar direct wave signals are used as difference frequency signals required in carrying out difference frequency processing on the broadband SAR echo signals. Compared with traditional difference frequency processing, the method provided by the invention for receiving the broadband SAR signals can still carry out difference frequency processing on the received radar echo signals and complete acquisition of the SAR echo signals when specific parameters of the broadband SAR signals transmitted by radar can not be accurately determined, such as a non-cooperative SAR platform.

Description

Receiving trap and the method for reseptance of a kind of broadband SAR signal

Technical field

The present invention relates to the Radar Technology field, solve broadband SAR echoed signal Receiver Problem, be specifically related to receiving trap and the method for reseptance of a kind of broadband satellite-borne synthetic aperture radar (being called for short SAR) signal.

Background technology

Satellite-borne synthetic aperture radar (synthetic aperture radar SAR) is towards high resolving power, multipolarization, wide swath, multi-operation mode development.Along with improving constantly that the SAR system index requires, adopt advanced digital systems architecture to become the inevitable choice that improves the SAR system performance.Wherein, digitizing receiving system is the key link that realizes that SAR is system digitalized.Typical Spaceborne SAR System intermediate frequency digital received structure as shown in Figure 1, echoed signal is down-converted to intermediate frequency by frequency mixer after by antenna reception, by low noise amplifier, being amplified, intermediate-freuqncy signal utilizes A/D converter directly to sample and obtain digital intermediate frequency signal s (n) with the sample rate f s greater than the signal bandwidth twice after band-pass filter, and by digital quadrature demodulation, obtains I/Q two-way baseband signal and transfer to the follow-up data disposal system and process.

Conventional Spaceborne SAR System is the hardware store finite capacity often.But, in order to obtain high resolving power, broadband often or even the ultra-broadband signal of Spaceborne SAR System emission, in each pulse repetition time, sampled point is many.At this moment, conventional digital received system will face data acquisition difficulty, the excessive problem of data volume, thereby affect the accuracy of whole SAR system works.

Summary of the invention

The data acquisition difficulty problem excessive with data volume that faces when solving traditional SAR receiving system receiving wide-band signal, the present invention proposes receiving trap and the method for reseptance of a kind of broadband SAR signal, it can obtain the echoed signal in the interior anyon of broadband SAR signal irradiation area zone and with the sampling rate far below broadband SAR system transmitted signal bandwidth, echoed signal be gathered, and sampling rate only is proportional to the size of subregion.

The broadband SAR signal receiving device of the invention process form completes the adjustment of antenna direction by antenna element, make antenna point to respectively target area and SAR platform, by the two-way receiving cable, complete the reception to radar direct wave and echoed signal, and using direct-path signal, as the reference signal, the two-way radar signal is carried out to the difference frequency processing.After completing the difference frequency processing, by signal acquisition module, according to the bandwidth of difference frequency module output signal, complete the data acquisition of echoed signal.

The receiving trap of a kind of broadband SAR signal, comprise receiver module, difference frequency module and acquisition module;

Receiver module comprises the first antenna element, the first low noise amplifier unit, the second antenna element and the second low noise amplifier unit; The first antenna element receives the direct-path signal of broadband SAR signal by wireless mode, the first antenna element exports direct-path signal to first low noise amplifier unit with analog signal form by cable, the first low noise amplifier unit carries out limited range enlargement to direct-path signal, direct-path signal after amplifying by cable is with analog signal form, export the multiplier unit of difference frequency module to, direct-path signal is as the reference signal of multiplier unit; The second antenna element receives the echoed signal of broadband SAR signal by wireless mode, the second antenna element exports echoed signal to second low noise amplifier unit with analog signal form by cable, the second low noise amplifier unit carries out limited range enlargement to echoed signal, echoed signal after amplifying by cable, with analog signal form, exports the multiplier unit of difference frequency module to;

The difference frequency module comprises multiplier unit and low pass filter unit; Direct-path signal and the echoed signal of multiplier unit after to the limited range enlargement that receives multiplies each other, and the signal after multiplying each other exports low pass filter unit to analog signal form, the signal of low pass filter unit after to above-mentioned the multiplying each other that receives carries out low-pass filtering, the HFS of removing signal obtains the difference frequency output signal, and by cable, with analog signal form, exports the difference frequency output signal quadrature demodulation unit of acquisition module to;

Acquisition module comprises quadrature demodulation unit and A/D converting unit; The quadrature demodulation unit carries out the quadrature mixing to the above-mentioned difference frequency output signal that receives, and obtains the I/Q baseband signal, and by cable, with analog signal form, exports this I/Q baseband signal to the A/D converting unit; The A/D converting unit is sampled to described I/Q baseband signal, obtains the digital signal of I/Q baseband signal, and the digital signal that will obtain according to demand is stored as the SAR echo data of different data format.

Broadband SAR signal receiving device according to said structure, can obtain the echoed signal in anyon zone in the SAR signal irradiation area of broadband and with the sampling rate far below broadband SAR system transmitted signal bandwidth, echoed signal be gathered, sampling rate is proportional to the size of subregion.

The method of reseptance of a kind of broadband of the present invention SAR signal comprises following step:

Step 1: the linear FM signal of broadband SAR emission, the direct-path signal s of reception broadband SAR signal _DiWith echoed signal s _Re, to the direct-path signal s that receives _DiWith echoed signal s _ReCarry out limited range enlargement;

Step 2: direct-path signal s _DiAs the reference signal of difference frequency module, direct-path signal s _DiWith echoed signal s _ReBy multiplier unit, multiply each other, the signal after being multiplied each other;

Step 3: utilize low pass filter unit to remove the HFS of signal after the multiplier unit output multiplication, obtain the difference frequency output signal;

Step 4: utilize the signal s of quadrature demodulation unit to difference frequency output _outCarry out the quadrature mixing and obtain the I/Q baseband signal;

Step 5: utilize the A/D converting unit to sample and obtain digital signal the I/Q baseband signal, and be stored as the SAR echo data of different-format by different order according to the digital signal that different demands will obtain.

The invention has the advantages that:

(1) the broadband SAR echoed signal that receives is carried out to the difference frequency processing, the radar echo signal bandwidth is significantly reduced, follow-up broadband SAR signal collecting device (A/D conversion etc.) is simplified.

(2) use radar direct-path signal required difference frequency signal when broadband SAR echoed signal difference frequency is processed.Than traditional difference frequency, process, the broadband SAR signal acceptance method that the present invention proposes can not smart accurate timing (as the SAR platform of non-conformability) at the broadband of radar emission SAR signal design parameter, still can to the radar echo signal that receives, carry out the difference frequency processing and complete the collection of SAR echoed signal.

The accompanying drawing explanation

Fig. 1 is typical SAR intermediate frequency digital receiver structure in prior art;

Fig. 2 is the structural representation of broadband of the present invention SAR signal receiving device;

Fig. 3 is the processing flow chart of broadband of the present invention SAR signal acceptance method;

Fig. 4 is the invention process case geometric relationship schematic diagram;

In figure:

1-receiver module 2-difference frequency module 3-acquisition module

101-first antenna element 102-first low noise amplifier unit 103-the second antenna element

104-the second low noise amplifier unit 201-multiplier unit 202-low pass filter unit

301-quadrature demodulation unit 302-A/D converting unit

Embodiment

The present invention is described in further detail below in conjunction with drawings and Examples.

The receiving trap of a kind of broadband of the present invention SAR signal, as shown in Figure 2, comprise receiver module 1, difference frequency module 2 and acquisition module 3.

Receiver module 1 comprises the first antenna element 101, the first low noise amplifier unit 102, the second antenna element 103 and the second low noise amplifier unit 104, and receiver module 1 is be used to the direct-path signal of realizing broadband SAR signal and reception and the limited range enlargement of echoed signal.

The first antenna element 101 receives the direct-path signal of broadband SAR signal by wireless mode, the first antenna element 101 exports direct-path signal to first low noise amplifier unit 102 with analog signal form by cable, the first 102 pairs of low noise amplifier unit direct-path signal carries out limited range enlargement, direct-path signal after amplifying by cable is with analog signal form, export the multiplier unit 201 of difference frequency module 2 to, direct-path signal is as the reference signal of multiplier unit 201;

The second antenna element 103 receives the echoed signal of broadband SA R signal by wireless mode, the second antenna element 103 exports echoed signal to second low noise amplifier unit 103 with analog signal form by cable, the second 103 pairs of low noise amplifier unit echoed signal is carried out limited range enlargement, echoed signal after amplifying by cable, with analog signal form, exports the multiplier unit 201 of difference frequency module 2 to;

Difference frequency module 2 comprises multiplier unit 201 and low pass filter unit 202, and direct-path signal and the echoed signal of difference frequency module 2 after for the limited range enlargement to receiving carried out the difference frequency processing, obtains the difference frequency output signal.

Direct-path signal and echoed signal after 201 pairs of limited range enlargements that receive of multiplier unit multiply each other, and the signal after multiplying each other exports low pass filter unit 202 to analog signal form, signal after above-mentioned the multiplying each other that 202 pairs of low pass filter unit receive carries out low-pass filtering, the HFS of removing signal obtains the difference frequency output signal, and by cable, with analog signal form, exports the difference frequency output signal quadrature demodulation unit 301 of acquisition module 3 to;

Acquisition module 3 comprises quadrature demodulation unit 301 and A/D converting unit 302, and acquisition module 3 is for sampling to described difference frequency output signal and seeking survival into as required the SAR echo data of different data format.

The above-mentioned difference frequency output signal that 301 pairs of quadrature demodulation unit receive is carried out the quadrature mixing, obtains the I/Q baseband signal, and by cable, with analog signal form, exports this I/Q baseband signal to A/D converting unit 302.302 pairs of described I/Q baseband signals of A/D converting unit are sampled, and obtain the digital signal of I/Q baseband signal, and the digital signal that will obtain according to demand are stored as the SAR echo data of different data format.

The method of reseptance of a kind of broadband of the present invention SAR signal, flow process as shown in Figure 3, comprises following step:

Step 1: the linear FM signal of broadband SAR emission, the direct-path signal s of reception broadband SAR signal _DiWith echoed signal s _Re, to the direct-path signal s that receives _DiWith echoed signal s _ReCarry out limited range enlargement, the two paths of signals amplitude is consistent, to guarantee rear end difference frequency module 2, can work;

The linear FM signal of broadband SAR system emission is:

$s(\hat{t},t_m)=\mathrm{rect}\left(\frac{\hat{t}}{T_p}\right)\cos \left(2\mathrm{\π}(f_{c}t+\frac{1}{2}\mathrm{\γ}{\hat{t}}^2)\right)---\left(1\right)$

Wherein:

The linear FM signal of expression broadband SAR emission, f _cRepresent that the SAR carrier frequency is, T _pIndicating impulse width, γ represent the signal chirp rate, T indicating impulse repetition period, x time t _m=mT (m=0,1,2 ...), be the slow time, the time take x time as starting point as

For the fast time, slow time t _m, the fast time

And the pass of full-time t is

Wherein: $\mathrm{rect}\left(u\right)\left\{\begin{array}{cc}1& \left|u\right|\≤\frac{1}{2}\\ 0& \left|u\right|>\frac{1}{2}\end{array}\right.$

The signal of broadband SAR system emission is R through length ₁Travel path, after by the first antenna element 101, directly being received, the linear FM signal of its signal waveform and broadband SAR system emission is consistent, only exist on signal amplitude decay and Time delay.Therefore, as can be known by formula (1), the direct-path signal of direct-path signal after limited range enlargement that the first antenna element 101 receives can be expressed as:

$s_{\mathrm{di}}(\hat{t},t_m)=C\·\mathrm{rect}\left(\frac{\hat{t}-R_1/c}{T_p}\right)\cos \left(2\mathrm{\π}(f_c(t-R_1/c)+\frac{1}{2}\mathrm{\γ}{(\hat{t}-R_1/c)}^2)\right)---\left(2\right)$

Wherein:

The expression direct-path signal is R through length ₁Travel path, the signal time delay that causes after being received by the first antenna element 101, C represents the signal amplitude of signal after limiting amplifier, all the other each alphabetical physical significances are identical with formula (1);

The broadband SAR echoed signal that the present invention receives is the echoed signal of a certain subregion in the SAR signal irradiation area of broadband, remembers that this subregion is the echoed signal region of acceptance.In the echoed signal region of acceptance, the diffusion path length of the echoed signal process of each point is different.If in the echoed signal receiving area, the diffusion path length of certain any echoed signal process is R ₂, after the echoed signal of this point was received by the second antenna element 103, the linear FM signal of its signal waveform and the emission of broadband SAR system was consistent, and only exists the decay on signal amplitude to reach Time delay.Therefore, as can be known by formula (1), the echoed signal of echoed signal after limited range enlargement of this point that the second antenna element 103 receives can be expressed as:

$s_{\mathrm{re}}(\hat{t},t_m)=C\·\mathrm{rect}\left(\frac{\hat{t}-R_2/c}{T_p}\right)\cos \left(2\mathrm{\π}(f_c(t-R_2/c)+\frac{1}{2}\mathrm{\γ}{(\hat{t}-R_2/c)}^2)\right)---\left(3\right)$

Wherein:

The expression echoed signal is R through length ₂Travel path, the signal time delay that causes after being received by the second antenna element 103, C represents the signal amplitude of signal after limiting amplifier, all the other each alphabetical physical significances are identical with formula (1);

Step 2: direct-path signal s _DiAs the reference signal of difference frequency module 2, direct-path signal s _DiWith echoed signal s _ReBy multiplier unit 201, multiply each other, the signal after being multiplied each other;

Be specially:

Utilize direct-path signal s _DiAs reference signal and echoed signal s _ReMultiply each other, the signal after multiplying each other can be expressed as:

$s_{\mathrm{out}}(\hat{t},t_m)=s_{\mathrm{re}}(\hat{t},t_m)*s_{\mathrm{di}}(\hat{t},t_m)---\left(4\right)$

By formula (2), formula (3) substitution formula (4), as the R that satisfies condition ₂-R ₁≤ T _pDuring c,

$s_{\mathrm{out}}(\hat{t},t_m)=C^2\·\mathrm{rect}\left(\frac{\hat{t}-(R_1+R_2)/c}{T_{\mathrm{out}}}\right)\cos \left({\mathrm{\ω}}_1(\hat{t},t_m)\right)\·\cos \left({\mathrm{\ω}}_2(\hat{t},t_m)\right)---\left(5\right)$

In formula (5) $T_{\mathrm{out}}=T_p+R_1-R_2/c,{\mathrm{\ω}}_1(\hat{t},t_m)=2\mathrm{\π}(f_c(t-R_1/c)+\frac{1}{2}\mathrm{\γ}{(\hat{t}-R_1/c)}^2)$ For direct-path signal s _DiInstantaneous phase, ${\mathrm{\ω}}_2(\hat{t},t_m)=2\mathrm{\π}(f_c(t-R_2/c)+\frac{1}{2}\mathrm{\γ}{(\hat{t}-R_2/c)}^2)$ For echoed signal s _ReInstantaneous phase.

Formula (5) is carried out to conversion to be had

$s_{\mathrm{out}}(\hat{t},t_m)=\frac{1}{2}{C}^2\·\mathrm{rect}\left(\frac{\hat{t}-(R_1+R_2)/c}{T_{\mathrm{out}}}\right)\cos ({\mathrm{\ω}}_1(\hat{t},t_m)-{\mathrm{\ω}}_2(\hat{t},t_m))$

$+\frac{1}{2}{C}^2\·\mathrm{rect}\left(\frac{\hat{t}-(R_1+R_2)/c}{T_{\mathrm{out}}}\right)\cos ({\mathrm{\ω}}_1(\hat{t},t_m)+{\mathrm{\ω}}_2(\hat{t},t_m))---\left(6\right)$

In formula (6), the instantaneous phase of first is direct-path signal s _DiWith echoed signal s _ReInstantaneous phase instantaneous phase poor, second be direct-path signal s _DiWith echoed signal s _ReInstantaneous phase and.

Step 3: utilize low pass filter unit 202 to remove the HFS of signal after multiplier unit 201 output multiplications, obtain the difference frequency output signal;

The signal that utilizes low pass filter unit 202 to remove after multiplying each other HFS after, the difference frequency output signal can be expressed as:

$s_{\mathrm{out}}(\hat{t},t_m)=\frac{1}{2}{C}^2\·\mathrm{rect}\left(\frac{\hat{t}-(R_1+R_2)/c}{T_{\mathrm{out}}}\right)\cos ({\mathrm{\ω}}_1(\hat{t},t_m)-{\mathrm{\ω}}_2(\hat{t},t_m))---\left(7\right)$

Will

After expansion, show that the expression formula of difference frequency output signal is

In formula,

With the fast time

It is irrelevant,

R _Δ=R ₂-R ₁For direct-path signal and the echoed signal diffusion path length poor.

In the present invention, the bandwidth of difference frequency output signal is specially:

Within the same pulse repetition time, slow time t _m=mT (m=0,1,2 ...) remain unchanged, for certain any echoed signal in scene, R ₂, R ₁, R _ΔRemain unchanged.It is as can be known by formula (8),

With the fast time

Irrelevant.At this moment, the echoed signal of this point is that frequency equals

Simple signal.

Therefore, the echoed signal frequency range that comes from clawback signal receiving area is

R wherein _{Δ _ n}And R _{Δ _ f}The diffusion path length that is respectively the direct-path signal of proximal points in scene and remote point and echoed signal is poor, and the bandwidth of difference frequency output signal is

$B_{\mathrm{out}}=\frac{\mathrm{\γ}}{c}|R_{\mathrm{\Δ}\_n}-R_{\mathrm{\Δ}\_f}|---\left(9\right)$

Formula (9) is done to conversion, has:

$B_{\mathrm{out}}=\frac{|R_{\mathrm{\Δ}\_n}-R_{\mathrm{\Δ}\_f}|}{c{T}_p}{B}_w---\left(10\right)$

B in formula (10) _w=γ T _pThe linear FM signal bandwidth of expression broadband SAR emission.

R as shown in Figure 3 _{21_n}, R _{21_f}For echoed signal (reflection wave) the incident path length of echoed signal region of acceptance proximal points and remote point, R _{22_n}, R _{22_f}Echoed signal (reflection wave) reflection paths length for echoed signal region of acceptance proximal points and remote point.Therefore, R _{Δ _ n}And R _{Δ _ f}Can be represented as:

$\left\{\begin{array}{c}{R}_{\mathrm{\Δ}\_n}=R_{21\_n}+R_{22\_n}-R_1\\ R_{\mathrm{\Δ}\_f}=R_{21\_f}+R_{22\_f}-R_1\end{array}---\left(11\right)\right.$

Receiving trap of the present invention is when receiving signal, and the first antenna element and the second antenna element are in same position, and the orbit altitude H of SAR platform is much larger than the height H of receiving antenna _r, namely H>>H _r.At this moment,

|R _{Δ_n}-R _{Δ_f}≈R _{21_n}-R _{21_f}| （12）

By formula (12) substitution formula (10), obtain:

$B_{\mathrm{out}}\≈\frac{|R_{21\_n}-R_{21\_f}|}{c{T}_p}{B}_w---\left(13\right)$

Receiving trap of the present invention only obtains the echoed signal of a certain subregion in the SAR signal irradiation area of broadband, pulse width T when receiving signal _pGenerally more than tens microseconds, | R _{21_n}-R _{21_f}| generally only have hundreds of rice and be proportional to above-mentioned subregion scene domain size.Bandwidth B by formula (13) difference frequency output signal as can be known _outIt is only the linear FM signal bandwidth B of broadband SAR system emission _w1/tens and be proportional to above-mentioned subregion scene domain size.

Step 4: the signal s that utilizes the 301 pairs of difference frequency outputs in quadrature demodulation unit _outCarry out the quadrature mixing and obtain the I/Q baseband signal;

Step 5: utilize 302 pairs of I/Q baseband signals of A/D converting unit to sample and obtain digital signal, and be stored as the SAR echo data of different-format by different order according to the digital signal that different demands will obtain.

The present invention compares and has following advantage with typical broadband SAR receiving trap and method of reseptance:

1) by the echoed signal difference frequency is processed and made signal bandwidth significantly descend, follow-up broadband SAR signal collecting device (A/D conversion etc.) is simplified.

When 2) traditional SAR signal difference frequency is processed, need accurate linear frequency modulation ripple signal parameter (radar carrier frequency f _c, pulse repetition time T, pulse width T _p, signal chirp rate γ etc.) and so that being provided, difference frequency processes required reference signal.In the present invention, difference frequency method used is usingd direct-path signal that antenna reception arrives as the reference signal, even, when the linear frequency modulation ripple signal parameter of broadband SAR system emission can't accurately be known, still can complete difference frequency and process.

Case study on implementation 1:

Fig. 4 is the concrete example of the broadband SAR signal receiving device of the invention process form.In Fig. 4, broadband SAR system platform height H is 800km, scene center visual angle α _cBe 4.5 °, scene domain size 200m, it is outer apart from far-end 100m place that the first antenna element and the second antenna element are positioned at scene, receiving antenna height 100m, radar signal pulsewidth 30us.In figure: SAR satellite orbital altitude H is 800 kilometers, scene center visual angle α _cBe 4.5 °, scene size 200m, it is outer apart from far-end 100m place, receiving antenna height H that receiving antenna is positioned at scene _r100m, R ₁The received antenna reception of expression radar direct wave the travel path of process, R ₂₁Expression from the Texas tower to the scene in the diffusion path length of certain point, R ₂₂Represent the diffusion path length of this point to receiving antenna.

If the linear frequency modulation ripple signal of broadband SAR emission is:

$s(\hat{t},t_m)=\mathrm{rect}\left(\frac{\hat{t}}{T_p}\right)\cos \left(2\mathrm{\π}(f_{c}t+\frac{1}{2}\mathrm{\γ}{\hat{t}}^2)\right)---\left(14\right)$

The direct-path signal of broadband SAR is R through length ₁Travel path, after by the first antenna element 101, being received, the direct-path signal after limited range enlargement can be expressed as:

$s_{\mathrm{di}}(\hat{t},t_m)=C\·\mathrm{rect}\left(\frac{\hat{t}-R_1/c}{T_p}\right)\cos \left(2\mathrm{\π}(f_c(t-R_1/c)+\frac{1}{2}\mathrm{\γ}{(\hat{t}-R_1/c)}^2)\right)---\left(15\right)$

If in the echoed signal receiving area, the diffusion path length of certain any echoed signal process is R ₂, after the echoed signal of this point was received by the second antenna element 103, the echoed signal after limited range enlargement can be expressed as:

$s_{\mathrm{re}}(\hat{t},t_m)=C\·\mathrm{rect}\left(\frac{\hat{t}-R_2/c}{T_p}\right)\cos \left(2\mathrm{\π}(f_c(t-R_2/c)+\frac{1}{2}\mathrm{\γ}{(\hat{t}-R_2/c)}^2)\right)---\left(16\right)$

In Fig. 4, R ₂₁Expression from the Texas tower to the scene in the diffusion path length of certain point, R ₂₂Represent the diffusion path length of this point to receiving antenna:

R ₂＝R ₂₁+R ₂₂ （17）

Then, take direct-path signal as reference signal, by 2 pairs of direct-path signals of difference frequency module and echoed signal, carry out the difference frequency processing, the difference frequency output signal is

Signal bandwidth after difference frequency output is:

In the present embodiment:

|R _{Δ_n}-R _{Δ_f}|＝316.7m （19）

$\frac{|R_{\mathrm{\Δ}\_n}-R_{\mathrm{\Δ}\_f}|}{c{T}_p}=0.035---\left(20\right)$

Signal bandwidth after difference frequency output be only the linear frequency modulation wavestrip of radar emission wide 3.5%.

The difference frequency output signal obtains the I/Q baseband signal after via the quadrature mixing of quadrature demodulation unit, then utilizes the A/D converting unit with greater than B _outSampling rate the I/Q baseband signal is sampled and is obtained digital signal and according to different demands, by different order, be stored as the SAR echo data of different-format, thereby complete the reception collection of broadband SAR signal echo data.

By above-mentioned processing, as can be known by formula (20), the signal bandwidth that A/D converting unit 302 is processed be only radar emission signal bandwidth 3.5%.Compared to traditional traditional SAR receiving system, the sampling rate that broadband provided by the invention SAR signal receiving device adopts will decline to a great extent, solve conventional digital received systems face data acquisition difficulty, the excessive problem of data volume, realized the accurate collection of broadband SAR echoed signal.

Difference frequency treatment technology in tradition SAR signal process field is multiplex to be processed in the SAR echo data to after finishing receiving, and need to know accurate parameters (the SAR carrier frequency f that the SAR system transmits _c, signal chirp rate γ etc.) provide difference frequency to process required reference signal, the parameter that the carrier frequency of this reference signal, signal chirp rate should transmit with the SAR system is consistent, and just can complete difference frequency and process.In the present invention, adopt the direct-path signal that the first antenna element receives, as reference signal required in the difference frequency processing, the broadband SAR echoed signal that the second antenna element receives is carried out to the difference frequency processing.As can be known to the processing procedure of (20) by (14), at transmission signal parameters (the SAR carrier frequency f of broadband SAR system _c, signal chirp rate γ etc.) in the time of can't accurately knowing (for example SAR platform of non-conformability), adopt direct-path signal still can complete the difference frequency of echoed signal is processed as the reference signal, make the bandwidth of echoed signal decline to a great extent, reduce the difficulty that follow-up data gathers.

the data acquisition difficulty problem excessive with data volume that the present invention faces during mainly for conventional SAR receiving system receiving wide-band signal, utilize the radar direct-path signal to carry out the difference frequency processing to broadband SAR echoed signal, the radar echo signal bandwidth is significantly reduced, with the sampling rate much smaller than broadband SAR system transmitted signal bandwidth, the signal of difference frequency output is sampled on this basis, solved the data acquisition difficulty of conventional digital received systems face, the problem that data volume is excessive, realize a kind of device and method of reseptance that can accurately complete broadband SAR signal reception, and by instance analysis, described in further detail and utilized invention to complete the implementation process that broadband SAR signal receives.

Claims (2)

1. the receiving trap of a broadband SAR signal, comprise receiver module, difference frequency module and acquisition module;

Receiver module comprises the first antenna element, the first low noise amplifier unit, the second antenna element and the second low noise amplifier unit; The first antenna element receives the direct-path signal of broadband SAR signal by wireless mode, the first antenna element exports direct-path signal to first low noise amplifier unit with analog signal form by cable, the first low noise amplifier unit carries out limited range enlargement to direct-path signal, direct-path signal after amplifying by cable is with analog signal form, export the multiplier unit of difference frequency module to, direct-path signal is as the reference signal of multiplier unit; The second antenna element receives the echoed signal of broadband SAR signal by wireless mode, the second antenna element exports echoed signal to second low noise amplifier unit with analog signal form by cable, the second low noise amplifier unit carries out limited range enlargement to echoed signal, echoed signal after amplifying by cable, with analog signal form, exports the multiplier unit of difference frequency module to;

The difference frequency module comprises multiplier unit and low pass filter unit; Direct-path signal and the echoed signal of multiplier unit after to the limited range enlargement that receives multiplies each other, and the signal after multiplying each other exports low pass filter unit to analog signal form, the signal of low pass filter unit after to above-mentioned the multiplying each other that receives carries out low-pass filtering, the HFS of removing signal obtains the difference frequency output signal, and by cable, with analog signal form, exports the difference frequency output signal quadrature demodulation unit of acquisition module to;

Acquisition module comprises quadrature demodulation unit and A/D converting unit; The quadrature demodulation unit carries out the quadrature mixing to the above-mentioned difference frequency output signal that receives, and obtains the I/Q baseband signal, and by cable, with analog signal form, exports this I/Q baseband signal to the A/D converting unit; The A/D converting unit is sampled to described I/Q baseband signal, obtains the digital signal of I/Q baseband signal, and the digital signal that will obtain according to demand is stored as the SAR echo data of different data format.

2. the method for reseptance of a kind of broadband of the present invention SAR signal comprises following step:

Step 1: the linear FM signal of broadband SAR emission, the direct-path signal s of reception broadband SAR signal _DiWith echoed signal s _Re, to the direct-path signal s that receives _DiWith echoed signal s _ReCarry out limited range enlargement;

The linear FM signal of broadband SAR system emission is:

$s(\hat{t},t_m)=\mathrm{rect}\left(\frac{\hat{t}}{T_p}\right)\cos \left(2\mathrm{\π}(f_{c}t+\frac{1}{2}\mathrm{\γ}{\hat{t}}^2)\right)---\left(1\right)$

Wherein:

The linear FM signal of expression broadband SAR emission, f _cRepresent that the SAR carrier frequency is, T _pIndicating impulse width, γ represent the signal chirp rate, T indicating impulse repetition period, x time t _m=mT is the slow time, m=0, and 1,2 ..., the time take x time as starting point as

For the fast time, slow time t _m, the fast time

And the pass of full-time t is

Wherein: $\mathrm{rect}\left(u\right)\left\{\begin{array}{cc}1& \left|u\right|\≤\frac{1}{2}\\ 0& \left|u\right|>\frac{1}{2}\end{array}\right.$

The signal of broadband SAR system emission is R through length ₁Travel path, after by the first antenna element, directly being received, the linear FM signal of its signal waveform and broadband SAR system emission is consistent, only exist on signal amplitude decay and

Time delay; Therefore, as can be known by formula (1), the direct-path signal of direct-path signal after limited range enlargement that the first antenna element receives is expressed as:

$s_{\mathrm{di}}(\hat{t},t_m)=C\·\mathrm{rect}\left(\frac{\hat{t}-R_1/c}{T_p}\right)\cos \left(2\mathrm{\π}(f_c(t-R_1/c)+\frac{1}{2}\mathrm{\γ}{(\hat{t}-R_1/c)}^2)\right)---\left(2\right)$

Wherein:

The expression direct-path signal is R through length ₁Travel path, the signal time delay that causes after being received by the first antenna element 101, C represents the signal amplitude of signal after limiting amplifier;

The broadband SAR echoed signal that the present invention receives is the echoed signal of a certain subregion in the SAR signal irradiation area of broadband, remembers that this subregion is the echoed signal region of acceptance; In the echoed signal region of acceptance, the diffusion path length of the echoed signal process of each point is different; If in the echoed signal receiving area, the diffusion path length of certain any echoed signal process is R ₂, after the echoed signal of this point was received by the second antenna element, the linear FM signal of its signal waveform and the emission of broadband SAR system was consistent, and only existed the decay on signal amplitude to reach

Time delay; Therefore, as can be known by formula (1), the echoed signal of echoed signal after limited range enlargement of this point that the second antenna element receives is expressed as:

$s_{\mathrm{re}}(\hat{t},t_m)=C\·\mathrm{rect}\left(\frac{\hat{t}-R_2/c}{T_p}\right)\cos \left(2\mathrm{\π}(f_c(t-R_2/c)+\frac{1}{2}\mathrm{\γ}{(\hat{t}-R_2/c)}^2)\right)---\left(3\right)$

Wherein:

The expression echoed signal is R through length ₂Travel path, the signal time delay that causes after being received by the second antenna element, C represents the signal amplitude of signal after limiting amplifier;

Step 2: direct-path signal s _DiAs the reference signal of difference frequency module, direct-path signal s _DiWith echoed signal s _ReBy multiplier unit, multiply each other, the signal after being multiplied each other;

Be specially:

Utilize direct-path signal s _DiAs reference signal and echoed signal s _ReMultiply each other, the signal after multiplying each other can be expressed as:

$s_{\mathrm{out}}(\hat{t},t_m)=s_{\mathrm{re}}(\hat{t},t_m)*s_{\mathrm{di}}(\hat{t},t_m)---\left(4\right)$

By formula (2), formula (3) substitution formula (4), as the R that satisfies condition ₂-R ₁≤ T _pDuring c,

$s_{\mathrm{out}}(\hat{t},t_m)=C^2\·\mathrm{rect}\left(\frac{\hat{t}-(R_1+R_2)/c}{T_{\mathrm{out}}}\right)\cos \left({\mathrm{\ω}}_1(\hat{t},t_m)\right)\·\cos \left({\mathrm{\ω}}_2(\hat{t},t_m)\right)---\left(5\right)$

In formula (5) $T_{\mathrm{out}}=T_p+R_1-R_2/c,{\mathrm{\ω}}_1(\hat{t},t_m)=2\mathrm{\π}(f_c(t-R_1/c)+\frac{1}{2}\mathrm{\γ}{(\hat{t}-R_1/c)}^2)$ For direct-path signal s _DiInstantaneous phase, ${\mathrm{\ω}}_2(\hat{t},t_m)=2\mathrm{\π}(f_c(t-R_2/c)+\frac{1}{2}\mathrm{\γ}{(\hat{t}-R_2/c)}^2)$ For echoed signal s _ReInstantaneous phase;

Formula (5) is carried out to conversion to be had

$s_{\mathrm{out}}(\hat{t},t_m)=\frac{1}{2}{C}^2\·\mathrm{rect}\left(\frac{\hat{t}-(R_1+R_2)/c}{T_{\mathrm{out}}}\right)\cos ({\mathrm{\ω}}_1(\hat{t},t_m)-{\mathrm{\ω}}_2(\hat{t},t_m))$

$+\frac{1}{2}{C}^2\·\mathrm{rect}\left(\frac{\hat{t}-(R_1+R_2)/c}{T_{\mathrm{out}}}\right)\cos ({\mathrm{\ω}}_1(\hat{t},t_m)+{\mathrm{\ω}}_2(\hat{t},t_m))---\left(6\right)$

In formula (6), the instantaneous phase of first is direct-path signal s _DiWith echoed signal s _ReInstantaneous phase instantaneous phase poor, second be direct-path signal s _DiWith echoed signal s _ReInstantaneous phase and;

Step 3: utilize low pass filter unit to remove the HFS of signal after the multiplier unit output multiplication, obtain the difference frequency output signal;

Utilize low pass filter unit to remove the signal after multiplying each other

HFS after, the difference frequency output signal is expressed as:

$s_{\mathrm{out}}(\hat{t},t_m)=\frac{1}{2}{C}^2\·\mathrm{rect}\left(\frac{\hat{t}-(R_1+R_2)/c}{T_{\mathrm{out}}}\right)\cos ({\mathrm{\ω}}_1(\hat{t},t_m)-{\mathrm{\ω}}_2(\hat{t},t_m))---\left(7\right)$

Will

After expansion, show that the expression formula of difference frequency output signal is

In formula,

With the fast time

It is irrelevant,

R _Δ=R ₂-R ₁For direct-path signal and the echoed signal diffusion path length poor;

The bandwidth of difference frequency output signal is specially:

Within the same pulse repetition time, slow time t _m=mT remains unchanged, m=0, and 1,2 ..., for certain any echoed signal in scene, R ₂, R ₁, R _ΔRemain unchanged; It is as can be known by formula (8), With the fast time Irrelevant; At this moment, the echoed signal of this point is that frequency equals

Simple signal;

Therefore, the echoed signal frequency range that comes from clawback signal receiving area is

R wherein _{Δ _ n}And R _{Δ _ f}The diffusion path length that is respectively the direct-path signal of proximal points in scene and remote point and echoed signal is poor, and the bandwidth of difference frequency output signal is

$B_{\mathrm{out}}=\frac{\mathrm{\γ}}{c}|R_{\mathrm{\Δ}\_n}-R_{\mathrm{\Δ}\_f}|---\left(9\right)$

Formula (9) is done to conversion, has:

$B_{\mathrm{out}}=\frac{|R_{\mathrm{\Δ}\_n}-R_{\mathrm{\Δ}\_f}|}{c{T}_p}{B}_w---\left(10\right)$

B in formula (10) _w=γ T _pThe linear FM signal bandwidth of expression broadband SAR emission;

R _{Δ _ n}And R _{Δ _ f}Be expressed as:

$\left\{\begin{array}{c}{R}_{\mathrm{\Δ}\_n}=R_{21\_n}+R_{22\_n}-R_1\\ R_{\mathrm{\Δ}\_f}=R_{21\_f}+R_{22\_f}-R_1\end{array}---\left(11\right)\right.$

Wherein: R _{21_n}, R _{21_f}For the echoed signal incident path length of echoed signal region of acceptance proximal points and remote point, R _{22_n}, R _{22_f}Echoed signal reflection paths length for echoed signal region of acceptance proximal points and remote point;

Receiving trap of the present invention is when receiving signal, and the first antenna element and the second antenna element are in same position, and the orbit altitude H of SAR platform is much larger than the height H of receiving antenna _r, namely H>>H _rAt this moment,

|R _{Δ_n}-R _{Δ_f}|≈|R _{21_n}-R _{21_f}| （12）

By formula (12) substitution formula (10), obtain:

$B_{\mathrm{out}}\≈\frac{|R_{21\_n}-R_{21\_f}|}{c{T}_p}{B}_w---\left(13\right)$

Step 4: utilize the signal s of quadrature demodulation unit to difference frequency output _outCarry out the quadrature mixing and obtain the I/Q baseband signal;

Step 5: utilize the A/D converting unit to sample and obtain digital signal the I/Q baseband signal, and be stored as the SAR echo data of different-format by different order according to the digital signal that different demands will obtain.

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