CN101697010B - Method for constructing multifunctional linear array three-dimensional synthetic aperture radar (SAR) system - Google Patents
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Abstract
The invention discloses a method for constructing a multifunctional linear array three-dimensional synthetic aperture radar (SAR) system. Aiming at the problems that severe vibration at the two ends of wings of a double-ended emission model more brings a large error, and simultaneously arrays cannot be densely distributed because feeder lines at the two ends are long, the center of gravity is far away and the like, a sparse-dense-sparse-dense-sparse type multifunctional linear array three-dimensional SAR system is constructed on the basis of a PCA principle. Such a system is closer to the body than dense main antenna array elements, so the error caused by the severe vibration of the two wings is reduced, the overall length of the feeder lines is shortened, and the center of gravity is close to an airframe, which contributes to stabilizing an overall system. Moreover, the method for constructing the multifunctional linear array three-dimensional synthetic aperture radar (SAR) system makes full use of resources of the system, saves cost, improves the comprehensive performance of the system, and realizes a radar imaging system with multi-working modes and a higher performance.
Description
The technical field is as follows:
the invention belongs to the technical field of radar, and particularly relates to the technical field of radar antennas and radar imaging.
Technical background:
radar imaging technology was developed in the 50's of the 20 th century, and is an important milestone in the development history of radar. From this point on, the radar functions not only to determine its position and motion parameters by regarding the observed object as a "point" target, but also to obtain images of the target and the scene with a high resolution unit. Meanwhile, the radar has the characteristics of all weather, all time, long distance, wide observation band and the like, so that the radar imaging technology obtains wide attention and research.
At present, radar imaging technology has been deeply researched at home and abroad, and a series of achievements have been applied to practical engineering. However, most radar systems are only suitable for a specific working scene to achieve a specific function, and in practical engineering, the radar is often required to be used in a rather complicated working environment, and a single radar type or a single radar system cannot meet the requirements, so that two or more than two radar types must be adopted to perform effective detection. Therefore, an imaging radar system with multiple functions and high performance is a hot spot of current research.
To the knowledge of the inventors and to published literature, for example: Jung-Hyo Kim, A.Ossowska, W.Wiesbeck "investment of MIMO SAR for interference" Radar Conference, 2007.EuRAD 2007. European. Klare "Digital Beamforming for a 3D MIMO SAR-Improvements through Frequency and wave form Diversity" Geosunce and RemoteSensing Symposium, 2008.IGARSS 2008.IEEE Intelligent. At present, the MIMO array antenna technology has been applied to the aspects of interferometric synthetic aperture radar (InSAR), linear array three-dimensional imaging synthetic aperture radar and the like, but most of the technologies have single functions and cannot fully utilize the resources of the system, and large errors are brought due to the unreasonable array model arrangement, so that the imaging quality is greatly influenced.
The invention content is as follows:
the invention mainly aims at the problems that the jitter of two ends of wings is severe and can bring larger errors, the feeder lines at two ends are longer, the gravity center is far and the like, which are not suitable for dense array and the like, which are generated in a foreign 'double-end transmitting' model.
For the convenience of describing the present invention, the following terms are first defined:
The pulse repetition frequency is the number of trigger pulses generated by the transmitter per second, denoted as PRF. The time interval between two adjacent pulses, called the pulse repetition period (also called slow time), is denoted by PRT, which is equal to the inverse of the pulse repetition frequency.
The two-dimensional synthetic aperture radar is a radar system which obtains high distance resolution by using a pulse compression technology and obtains high azimuth resolution by using the relative motion of a platform, and the main system indexes are the wavelength lambda of a working signal and the angular resolution rhoθAnd pulse repetition frequency PRF. See the document "radar imaging techniques", shines, cheng meng, wang tong editions, published by electronics industry publishers.
The interferometric synthetic aperture radar is a radar system which utilizes echo data obtained by observation of a plurality of receiving antennas to carry out interference processing so as to obtain high range information of an observation area and combines distance direction and azimuth direction information obtained by the synthetic aperture radar to realize three-dimensional imaging. See the document "radar imaging techniques", shines, cheng meng, wang tong editions, published by electronics industry publishers.
Definition 4, single baseline interferometric synthetic aperture radar and multi-baseline interferometric synthetic aperture radar
The connecting lines between the receiving antennas of the interferometric synthetic aperture radar are called base lines, the case of only one base line is called single-base-line interferometric synthetic aperture radar, and the case of two or more base lines is called multi-base-line interferometric synthetic aperture radar.
Definition 5, lower view line array three-dimensional imaging synthetic aperture radar
A downward-looking Linear Array three-dimensional imaging synthetic aperture radar (Linear Array3DSAR) is a synthetic aperture radar system which fixes a Linear Array antenna on a moving platform, combines the movement of the moving platform to synthesize a two-dimensional planar Array, and performs three-dimensional imaging on a target area right below the two-dimensional planar Array.
Define 6, multiple-input multiple-output (MIMO) array radar antenna
A multiple-input multiple-output (MIMO) array technology is a technology for synthesizing an equivalent array radar antenna by using a plurality of radar transmitting antennas and a plurality of radar receiving antennas, and details thereof may be found in fisher, e.haimovich, a.blum, r.cimini, r.chizhik, d.valenzuela, r. The advantages of organizational diversity ", signs, Systems and Computers, 2004.
Definitions 7, Primary antenna array and Secondary antenna array
The antenna array is a small antenna array formed by mounting small antennas with the function of transmitting or receiving radar electromagnetic waves on a fixing device according to a certain arrangement mode, and can be divided into a main antenna array and an auxiliary antenna array according to the importance of the small antennas. See the document "radar imaging techniques", shines, cheng meng, wang tong editions, published by electronics industry publishers.
The phase center approximation principle holds that: in far field conditions (i.e.
4r <, wherein LTRFor the spacing between the receiving and transmitting elements, r is the distance from the middle position of the transmitting and receiving elements to the scattering point, and λ is the signal wavelength), a pair of transmitting and receiving spaced antenna elements can be shared by a transceiver located at their center positionsInstead of the equivalent phase center. For details, reference may be made to BellettiniA, Pitto MA, "mechanical Access of Synthetic Aperture Source Micronavigation Using a displaced Phase Center Antenna". IEEE Journal of organic Engineering, 2002; vol.27, No.4, pp.780-789.
According to the phase center approximation principle, under the far field condition, a pair of antenna array elements with separated transmitting and receiving positions can be replaced by a transceiving shared equivalent phase center which is positioned at the center of the antenna array elements, and the transceiving shared equivalent phase center is a virtual array element; all the virtual array elements are arranged on a straight line according to a certain position relation to form a virtual linear array. For details, reference may be made to Ilya Bekkerman and Joseph Tabrijian. "TargetDetection and Localization Using MIMO Radars and Sonars". IEEE transactions on signal processing, 2006, 54 (10): 3873 to 3883.
Beamforming refers to a technique of directing a transmit (receive) beam in a certain spatial direction using a vector weighting technique of an antenna array. See the second edition of the document "adaptive filtering", Gong blaze atlas edition, electronic industry Press.
The size utilization rate of the linear MIMO array antenna is equal to the ratio of the length of the virtual linear array to the length of the real array, and is expressed by eta.
A multiplexer is a device that can connect a receiving (transmitting) system and a specific receiving (transmitting) radar antenna array element according to instructions, and its function is to selectively connect a loop, which is a common device in electronic technology. For example: a multi-channel automatic switching circuit implemented by a CMOS circuit or a TTL circuit is one example of the multiplexer used in the present invention. For details, the literature, "multichannel automatic switching circuit application" was first introduced in Journal of Shijiazhuang economic college (Journal of Shijiazhuang University of Economics), 1997, 03.
The synthetic aperture radar transmitter is a system for transmitting electromagnetic signals to an observation area, which is adopted by the existing synthetic aperture radar, and mainly comprises a signal generator, a mixer, an amplifier and other modules.
The synthetic aperture radar receiver is a system for receiving echoes in an observation area adopted by the existing synthetic aperture radar, and mainly comprises a mixer, an amplifier, an analog-to-digital converter, a storage device and the like.
The invention provides a construction method of a multifunctional linear array three-dimensional Synthetic Aperture Radar (SAR) system, which comprises the following steps:
step 1: linear MIMO array antenna parameter calculation
The support structure of the linear MIMO array antenna is a linear antenna mounting plate, the central position of the linear MIMO array antenna support structure is used as an original point, the right-hand direction is used as the positive direction of a direction axis, and a one-dimensional linear coordinate system is established at intervals by taking d as a basic array element, wherein d is lambda/2, and lambda is the carrier wavelength of the linear array three-dimensional SAR system. Distributing M main antenna elements and N auxiliary antenna elements on the antenna mounting plate, wherein M can be represented by formula
Obtaining of a symbol therein
Meaning the rounding operation, M should be even, if M is odd, then there is no physical significance, PRFallIs the pulse repetition frequency, PRF, of the systemeffIs the equivalent pulse repetition frequency of the virtual array element, wherein the pulse repetition frequency of the systemPRFallAnd equivalent pulse repetition frequency PRF of virtual array elementeffParameter indexes given for the system; n can be represented by the formula
Obtaining, wherein the symbol "[. ]]Doll"denotes the immediate even-out operation, LeqThe length of a virtual linear array equivalent to the linear MIMO array antenna, eta is the size utilization rate of the linear MIMO array antenna, LeqCan be represented by formula
Obtaining where pθFor the system angular resolution, η is taken to be 0.7.
Note that λ and ρθIs an index of a two-dimensional synthetic aperture radar system.
The main antenna array (main array) is divided into a left sub-main array and a right sub-main array by taking the origin as a boundary. Wherein the number of the auxiliary antenna elements between the two sub-main arrays is N1，N1Can be represented by formula
Obtaining, wherein eta is 0.7, and the number of the rest auxiliary antenna elements is N2，N2Can be represented by formula N2＝N-N1And (4) obtaining.
Step 2: main antenna array layout of linear MIMO array antenna
In the one-dimensional linear coordinate system established in the step 1, the number M of the main antenna array elements and the number N of the auxiliary antenna array elements obtained by calculation in the step 1 are utilized to distribute the 1 st array element of the main antenna array
Where, it is marked as x1(ii) a The 2 nd main antenna array element is arranged on
Where, it is marked as x2；
……
The ith main antenna array element is distributed on
Where, it is marked as xiWherein i is a natural number less than M/2;
the M/2 th main antenna array element is arranged on
Where, it is marked as xM/2；
The M/2+1 th main antenna array element is distributed on
Where, it is marked as xM/2+1(ii) a The M/2+2 th main antenna array element is distributed on
Where, it is marked as xM/2+2；
……
Arranging the M/2+ k main antenna array elements on
Where, it is marked as xM/2+kWherein k is a natural number less than M/2;
arranging the Mth main antenna array element onWhere, it is marked as xM；
The layout of the main antenna array of the linear MIMO array antenna is finished through the operation, and the position coordinate of each array element of the main antenna array is recorded as X ═ X1，x2，…，xM}。
And step 3: auxiliary antenna array layout of linear MIMO array antenna
In the one-dimensional linear coordinate system established in the step 1, the calculation is carried out by using the step 1The obtained number M of main antenna elements, the number N of auxiliary antenna elements and the number N of auxiliary elements between two sub-main arrays1The 1 st array element of the auxiliary antenna array is distributed on
Where, it is denoted as y1(ii) a Arranging the 2 nd auxiliary antenna array element on
Where, it is denoted as y2；
……
The ith auxiliary antenna array element is distributed onWhere, it is denoted as yiWherein i is a natural number less than N/2;
arranging the N/2 th auxiliary antenna array elements on
Where, it is denoted as yN/2；
The (N/2+1) th auxiliary antenna array element is distributed onWhere, it is denoted as yN/2+1(ii) a The (N/2+ 2) th auxiliary antenna array elements are distributed on
Where, it is denoted as yN/2+2；
……
Arranging the (N/2+ k) th auxiliary antenna array elements on
Where, it is denoted as yN/2+kWherein k is a natural number less than N/2;
arranging the Nth auxiliary antenna array element at
Where, it is denoted as yN；
The layout of the auxiliary antenna array of the linear MIMO array antenna is finished through the operation, and the position coordinate of each array element of the auxiliary antenna array is marked as Y ═ Y1，y2，…，yN}。
And 4, step 4: subject System construction
The main body system of the multifunctional linear array three-dimensional SAR system comprises: linear MIMO array antenna, two transmitters: a transmitter A and a transmitter B; the system comprises an N +2 receiver, two T/R change-over switches, two multiplexers: a multiplexer I and a multiplexer II; and a motion platform; the linear MIMO array antenna is composed of a main antenna array X of the linear MIMO array antenna constructed in the step 2 and an auxiliary antenna array Y of the linear MIMO array antenna constructed in the step 3, and the multi-path gate I is provided with two input ends, M output ends and a control end; the multi-path gate II is provided with N +2 input ends, N +2 output ends and a control end; the motion platform is a load platform of the radar system; the specific installation method of the main body system comprises the following steps:
fixing the linear MIMO array antenna with the motion platform along the direction which is parallel to the ground and vertical to the motion track of the motion platform;
connecting two input ends of a multi-path gate I with a transmitter A and a transmitter B respectively, wherein M-2 ports of M ports of the output end of the multi-path gate I are sequentially connected with M-2 main antenna array elements except M/2 and M/2+1 main antenna array elements in linear MIMO array antenna main antenna array elements through M-2 feeders, and the other 2 output ports of the multi-path gate I are respectively connected with radio frequency signal input ports 5a of two T/R conversion switches through 2 feeders; n ports in N +2 input ports of the multi-path gate II are sequentially connected with N auxiliary antenna array elements of the linear MIMO array antenna through N feeders, the other 2 input ports of the multi-path gate II are respectively connected with radio frequency signal output ports 5b of the two T/R conversion switches through 2 feeders, and N +2 ports at the output end of the multi-path gate II are sequentially connected with N +2 receivers; the antenna radio frequency output ports 6 of the two T/R change-over switches are respectively connected with the M/2 th and M/2+1 th main antenna array elements of the MIMO array antenna through 2 feeders; thereby forming a complete transmitting and receiving system together;
the main body system construction of the multifunctional linear array line three-dimensional SAR system is completed through the operation.
And 5: system operation mode design
The multifunctional linear array three-dimensional SAR system works according to a two-sided two-dimensional synthetic aperture radar (2-D SAR) mode or a two-sided single-baseline interferometric synthetic aperture radar (InSAR) mode or a two-sided Multi-baseline interferometric synthetic aperture radar (Multi-baseline InSAR) mode or a lower view line array three-dimensional imaging synthetic aperture radar (LinearRary 3DSAR) mode; the implementation method of the various working modes comprises the following steps:
1. the working mode of the bilateral two-dimensional synthetic aperture radar is realized by adopting the following steps
The method comprises the following steps: controlling a multi-channel gate I to respectively select a channel connected with an M/2 th main antenna array element and an M/2+1 th main antenna array element of the linear MIMO array antenna, starting the system to work, and entering a first pulse repetition period;
step two: the transmitter A transmits radar signals to a left observation scene through an M/2 th main antenna array element connected with the multi-path gate I;
step three: after delaying for half pulse repetition period, the transmitter B transmits radar signals to a right observation scene through an M/2+1 th main antenna array element connected with the multi-path gate I;
step IV: the (N +1) th receiver selects a path connected with the (M/2) th main antenna array element through a multi-way gate II, and receives T from the time of the time delay tau of a signal transmitted by the transmitter ArSecond echo, in which the delay τ is given by the formulaTo obtainWherein R isminThe distance from the center of the platform to the nearest point of the observation scene, R in practiceminCan be represented by formulaIs obtained approximately, where θminIs the angle between the inner edge of the beam and the vertical line, where H is the vertical height from the center of the platform to the ground, C is the speed of light, and the receiving time interval TrCan be represented by formula
Obtaining wherein T ispIn order to transmit the time width of the signal pulse envelope, the delta R is the difference value between the distance from the central position of the platform to the nearest point of an observation scene and the distance from the central position of the platform to the farthest point of the observation scene when the system works in a two-dimensional synthetic aperture radar working mode, and the delta R can be expressed by a formula in practiceIs obtained approximately, where θmaxIs the angle between the outer edge of the wave beam and the vertical line;
step five: the (N +2) th receiver selects a path connected with the (M/2 +1) th main antenna array element through a multi-way gate II, and receives T from the moment of time delay tau of a signal transmitted by a transmitter BrSecond echo;
repeating the steps from the second step to the fifth step in each pulse repetition period in the following period, and storing echo data received by the receiver until the observation is finished;
2. the working mode of the double-side single-baseline interference synthetic aperture radar is realized by adopting the following steps
The method comprises the following steps: controlling a multi-path gate I to respectively select paths related to the M/2 th main antenna array element and the M/2+1 th main antenna array element of the linear MIMO array antenna, starting the system to work, and entering a first pulse repetition period;
step two: the transmitter A transmits radar signals to a left observation scene through an M/2 th main antenna array element connected with the multi-path gate I;
step three: after delaying for half pulse repetition period, the transmitter B transmits radar signals to a right observation scene through an M/2+1 th main antenna array element connected with the multi-path gate I;
step IV: the N/2 th and the N/2-k th receivers respectively select the paths connected with the N/2 th and the N/2-k th auxiliary antenna array elements through the multi-way gating device II, and the two receivers receive T from the moment of time delay tau of the signal transmitted by the transmitter ArSecond echo, where k is a natural number less than N/2, k can be represented by the formula
Is obtained in which lsbThe length of the base line required by the system single base line interference synthetic aperture radar, wherein the time delay tau can be expressed by the formula
Obtaining wherein R isminThe distance from the center of the platform to the nearest point of the observation scene, R in practiceminCan be represented by formula
Approximately, where H is the vertical height from the center of the platform to the ground, C is the speed of light, and T is the receiving time periodrCan be represented by formula
Obtaining wherein T ispTo launch
The time width of signal pulse envelope, wherein Δ R is the difference between the distance from the center of the platform to the nearest point of the observation scene and the distance to the farthest point of the observation scene when the system works in the double-sided single-baseline interferometric synthetic aperture radar working mode, and in practice, Δ R may be represented by a formula
Obtaining an approximation;
step five: the N/2+1 th and (N/2+1) + k receivers are respectively selected by the multiplexer II from the N/2+1 th and the (N/2+1) + k auxiliary daysThe two receivers receive T from the time delay tau of the signal transmitted by the transmitter BrSecond echo;
repeating the steps from the second step to the fifth step in each pulse repetition period in the following period, and storing echo data received by the receiver until the observation is finished;
3. the working mode of the bilateral multi-baseline interferometric synthetic aperture radar is realized by adopting the following steps
The method comprises the following steps: firstly, the number n of baselines is given by a system, wherein n is a positive integer; controlling a multi-path gate I to respectively select paths related to the M/2 th main antenna array element and the M/2+1 th main antenna array element of the linear MIMO array antenna, starting the system to work, and entering a first pulse repetition period;
step two: the transmitter A transmits radar signals to a left observation scene through an M/2 th main antenna array element connected with the multi-path gate I;
step three: after delaying for half pulse repetition period, the transmitter B transmits radar signals to a right observation scene through an M/2+1 th main antenna array element connected with the multi-path gate I;
step IV: n/2, N/2-k1、N/2-k2、…、N/2-knThe receivers are respectively selected from N/2 th and N/2-k through a multiplexer II1、N/2-k2、…、N/2-knA path formed by connecting auxiliary antenna array elements, wherein the n +1 receivers receive T from the time delay tau of a signal transmitted by the transmitter ArSecond echo, where kiIs a natural number, kiCan be represented by formula
Obtaining i ═ 1, 2, …, n, where liThe base length required by the multi-base line interference synthetic aperture radar is given to the system; wherein the delay τ can be expressed by
Obtaining wherein R isminIn a platformDistance from the heart position to the closest point of the observed scene, R in practiceminCan be represented by formula
Approximately, where H is the vertical height from the center of the platform to the ground, C is the speed of light, and T is the receiving time periodrCan be represented by formula
Obtaining wherein T ispIn order to transmit the time width of signal pulse envelope, Δ R is the difference between the distance from the center of the platform to the nearest point of the observed scene and the distance to the farthest point of the observed scene when the system works in the double-sided multi-baseline interferometric synthetic aperture radar working mode, and in practice, Δ R may be represented by a formula <math>
<mrow>
<mi>ΔR</mi>
<mo>=</mo>
<mfrac>
<mi>H</mi>
<mrow>
<mi>cos</mi>
<msub>
<mi>θ</mi>
<mi>max</mi>
</msub>
</mrow>
</mfrac>
<mo>-</mo>
<mfrac>
<mi>H</mi>
<mrow>
<mi>sin</mi>
<msub>
<mi>θ</mi>
<mi>min</mi>
</msub>
</mrow>
</mfrac>
</mrow>
</math> Obtaining an approximation;
step five: n/2+1, (N/2+1) + k1、(N/2+1)+k2、…、(N/2+1)+knThe receivers are respectively selected by the multiplexer II to be the N/2+1, (N/2+1) + k1、(N/2+1)+k2、…、(N/2+1)+knThe n +1 receivers receive T from the time delay tau of the signal transmitted by the transmitter BrSecond echo;
repeating the steps from the second step to the fifth step in each pulse repetition period in the following period, and storing echo data received by the receiver until the observation is finished;
4. the working mode of the downward-looking linear array three-dimensional imaging synthetic aperture radar is realized by adopting the following steps
Step (ii) ofThe method comprises the following steps: controlling a multi-channel gate II, and sequentially connecting the 1 st, 2 nd, … th and N receivers with the 1 st, 2 nd, … th and N auxiliary antenna array elements after passing through the multi-channel gate II; setting the time delay tau from the signal transmission of each transmitter to the signal reception of the corresponding receiver3DThe delay τ can be represented by the formula
Obtaining H, wherein H is the vertical height from the center of the platform to the ground, and C is the light speed; let T be the time period from the beginning of echo reception to the end of echo reception in a pulse repetition period for a single receiver each time3DTime period T3DCan be represented by formulaObtaining wherein T ispFor the time width of the pulse envelope of the transmitted signal, the delta R is the difference value between the distance from the central position of the antenna supporting structure to the nearest point of an observation scene and the distance from the central position of the antenna supporting structure to the farthest point of the observation scene when the system works in the working mode of the lower sight line array three-dimensional imaging synthetic aperture radar, and the delta R can be represented by a formula
Obtaining a value delta theta, wherein the value delta theta is an observation angle range of a working mode of the lower view linear array three-dimensional imaging synthetic aperture radar, and the value delta theta is given by a system parameter index; taking M pulse repetition periods as a virtual linear array synthesis period, and entering a first virtual linear array synthesis period;
step two: one virtual linear array synthesis period comprises M pulse repetition periods;
in the 1 st pulse repetition period, namely slow time, controlling a multi-path gate I to select a path connected with the 1 st main antenna array element of the linear MIMO array antenna, transmitting radar signals to a scene observed right below by a transmitter A through the 1 st main antenna array element connected with the multi-path gate I, and transmitting signals by N receivers at a time delay tau from the 1 st main antenna array element by 1, 2, …3DReceiving T simultaneously from time to time3DSecond echo;
in the first placeControlling a multi-channel gate I to select a path connected with a 2 nd main antenna array element of the linear MIMO array antenna, wherein the transmitter A transmits radar signals to a downward observation scene through the 2 nd main antenna array element connected with the multi-channel gate I, and the N receivers transmit signals with a delay tau from the 2 nd main antenna array element at a 1 st, a 2 nd and a … st distance3DReceiving T simultaneously from time to time3DSecond echo;
……
controlling a multi-path gate I to select a passage connected with an Mth main antenna array element of the linear MIMO array antenna in the Mth pulse repetition period, namely slow time, and transmitting a radar signal to a directly lower observation scene by a transmitter A through the Mth main antenna array element connected with the multi-path gate I; 1, 2, …, N receivers transmit signal delay tau from Mth main antenna array element3DReceiving T simultaneously from time to time3DSecond echo;
step three: after a virtual line array synthesis period, M × N echo signals can be obtained, that is, a virtual line array composed of M × N virtual array elements can be approximately obtained, wherein the number of redundant virtual array elements isAnd (4) entering the next virtual linear array synthesis period from the M +1 pulse repetition period, circularly repeating the step (II) by taking the M pulse repetition periods as intervals, and storing echo data received by the receiver until the observation is finished.
It should be noted that the basic array element spacing d in the present invention can be any real number greater than 0 and smaller than 2 λ; the main antenna array element can also be a virtual transmitting array element which is formed by a plurality of small transmitting array elements by utilizing the beam forming technology; the size utilization rate eta of the linear MIMO array antenna can be any real number which is more than 0.67 and less than 0.75 when N1 is less than N/2, and when N is less than N1The size utilization rate eta of the linear MIMO array antenna can be any real number which is more than 0.75 and less than 1 when the number is N/2, and the distance between two main antenna elements which are farthest away in the two sub main arrays is L [1-2 (1-eta) ]]Determining where LThe total length of the real antenna array.
The essence of the invention is as follows: mainly aiming at the problems that the jitter of two ends of wings is severe and can bring larger errors, and simultaneously, the feeder lines at two ends are longer, the gravity center is far and the like which are not suitable for dense array distribution and the like, which are generated in a foreign 'double-end transmitting' model, a flexible linear array model, namely a 'sparse-dense-sparse' type linear array model, is provided on the basis of a PCA principle; a multifunctional linear array three-dimensional SAR system is constructed on the basis of the model, and the problems that large errors are caused by double-end emission, and feeders at two ends are long, the gravity center is far and the like, which are not suitable for dense array distribution, are solved; four working modes of the two-dimensional synthetic aperture radar at two sides, the single-baseline/multi-baseline interference synthetic aperture radar at two sides and the down-looking linear array three-dimensional imaging synthetic aperture radar can be realized through proper mode selection.
The invention has the innovation points that a more reasonable antenna array model, namely a sparse-dense-sparse type linear array model is constructed on the basis of a multiple-input multiple-output (MIMO) array antenna technology, a novel construction method of a multifunctional linear array three-dimensional SAR system is innovatively provided on the basis of the model, four different working modes of a 2-D SAR, an interference SAR, a multi-linear interference SAR and a look-down linear array three-dimensional imaging SAR are integrated, and the four modes can be freely switched according to requirements. The radar imaging system with multiple operation modes and high performance is realized by controlling the switching of the switch.
The method has the advantages that after the sparse-dense-sparse type linear array model is adopted, errors caused by unbalanced wing vibration distribution (mainly, the vibration at two ends of the wing is violent) are reduced, system resources are fully utilized, various SAR working modes are integrated, the cost is saved, and the comprehensive performance of the system is improved.
Drawings
Fig. 1 is a schematic diagram of a linear MIMO array antenna structure.
Wherein, 1 represents main antenna array element, 2 represents supplementary antenna array element, 3 represents antenna support structure, and 4 represent the bearing structure central point and put, and L represents the total length of real linear array.
FIG. 2 is a schematic diagram of a T/R switch.
Where 5a denotes an rf signal input port, 5b denotes an rf signal output port, and 6 denotes an antenna rf output port.
FIG. 3 is a schematic diagram of a multiplexer.
Wherein FIG. 3-a shows a multiplexer I having two input terminals, M output terminals and a control terminal; FIG. 3-b shows multiplexer II having N +2 inputs, N +2 outputs and a control terminal.
Fig. 4 is a schematic diagram of a transmitting and receiving system.
Where 7A denotes "transmitter a", 7B denotes "transmitter B", 8-1, 8-2, 8-3, and … 8- (N +2) denote 1 st, 2 nd, 3 th, … (N +2) th receivers, respectively, 9 denotes "multiplexer I", 10 denotes "multiplexer II", 11 denotes a feeder, 12 denotes a T/R switch, 13 denotes a main antenna element, 14 denotes an auxiliary antenna element, 15 denotes an antenna support structure, and 16 denotes a data stream.
Figure 5 is a schematic view of a motion stage.
Wherein, o represents a point of the platform center position vertically projected to the ground, a three-dimensional rectangular coordinate system is established by taking o as an origin, x represents the direction of a tangent track, y represents the direction along the track, z represents the direction of the height direction in the vertical direction, 17 represents a linear MIMO array antenna, 18 represents the motion track of the platform, and 19 represents the ground.
FIG. 6 is a schematic diagram of a position relationship between a system platform and an observation scene.
Wherein o represents a point where the center position of the platform is vertically projected on the ground, H represents a vertical height from the center position of the platform to the ground, and θminRepresenting the minimum observation angle, theta, of the radar beammaxRepresenting the maximum observation angle of the radar beam, ar representing the difference between the distance of the platform center position to the closest point of the observation scene and the distance to the farthest point of the observation scene, 20 representing the platform center position, 21 representing the beam range, and 22 representing the ground.
Figure 7 schematic diagram of a two-sided two-dimensional synthetic aperture radar mode.
Wherein,
the elements of the main antenna array are shown,
the auxiliary antenna element is shown, the M/2 th main antenna element is shown by 23-M/2, and the M/2+1 th main antenna element is shown by 23-M/2+ 1.
FIG. 8 schematic diagram of a two-sided single baseline interferometric synthetic aperture radar mode
Wherein,
the elements of the main antenna array are shown,the auxiliary antenna array element is shown, the M/2 th main antenna array element is shown by 24-M/2, and the M/2+1 th main antenna array element is shown by 24-M/2+ 1.
FIG. 9 is a schematic diagram of a double-sided multi-baseline interferometric synthetic aperture radar mode
Wherein,
the elements of the main antenna array are shown,
the auxiliary antenna array element is shown, the M/2 th main antenna array element is shown by 25-M/2, and the M/2+1 th main antenna array element is shown by 25-M/2+ 1.
Figure 10 is a schematic diagram of a view line array three-dimensional imaging synthetic aperture radar mode
Wherein,
the elements of the main antenna array are shown,
the auxiliary antenna element is shown, the 1 st main antenna element is shown as 26-1, the 2 nd main antenna element is shown as 26-2, and the Mth main antenna element is shown as 26-M.
FIG. 11 comparative block diagram for single-sided case between different modes
FIG. 12 flow chart of the present invention
The specific implementation mode is as follows:
firstly, parameter indexes of the system are given: motion platform is unmanned aerial vehicle, span 31(m), and the vertical height that the motion platform central point put ground during operation is 10000(m), and the emission signal is chirp (LFM) signal, and the carrier wave wavelength of system is 0.02(m) for lambda, and the time width T of emission signal pulse envelopep5 (m). The total length of the real antenna array is equal to 30(m), the size utilization rate of the antenna is equal to 0.7, and the angular resolution of the cutting track directionThe base line length of a given single base line interferometric synthetic aperture radar working mode is lsbThe number of base lines of the multi-base line interference synthetic aperture radar working mode is n-3, and the length of each base line is l1＝2(m)，l2＝3(m)，l35 (m). The pulse repetition frequency of the system and the observation angle of the radar beam have different settings for different working modes: (1) the pulse repetition frequency of the working modes of the two-sided two-dimensional synthetic aperture radar, the two-baseline-side single-interference synthetic aperture radar and the two-sided multi-baseline-interference synthetic aperture radar is PRF (2000 (Hz), and the minimum observation angle theta of radar wave beamsmin30 °, maximum observation angle θ of radar beammax60 °; (2) bottom view line array threeThe system pulse repetition frequency of the working mode of the dimensional imaging synthetic aperture radar is PRFall10000(Hz), equivalent pulse repetition frequency PRF of the virtual array elementeffThe maximum observation angle range of the radar beam is Δ θ, which is 200 (Hz).
Step 1: linear MIMO array antenna parameter calculation
The support structure of the linear MIMO array antenna is a linear antenna mounting plate, a one-dimensional linear coordinate system is established by taking the central position of the support structure as an origin, taking the right-hand direction as the positive direction of a direction axis and taking d as 0.01(m) as a basic array element interval. Co-laying on antenna mounting board
A main antenna element and
an auxiliary antenna element, wherein
Wherein the number of the auxiliary array elements positioned between the two sub-main arrays is
Step 2: main antenna array layout of linear MIMO array antenna
The 1 st array element of the main antenna array is distributed at the position of-5.99 (m) and is marked as x1(ii) a The 2 nd main antenna array element is distributed at the position of-5.97 (m) and is marked as x2；
……
The ith main antenna array element is distributed on the surface of the material- [550- (2i-1)]X0.01 (m) and is denoted as xiWherein i is a natural number less than 25;
the 25 th main antenna element is distributed at the position of-5.51 (m) and is marked as x25；
The 26 th main antenna element is arranged at 5.51(m), and is marked as x26(ii) a Will 2 nd7 main antenna elements are distributed at 5.53(m) and marked as x27；
……
The 25+ k th main antenna array element is distributed in [550+ (2k-1)]X0.01 (m) and is denoted as x25+kWherein k is a natural number less than 25;
the 50 th main antenna element is distributed at 5.99(m), and is marked as x50。
The layout of the main antenna array of the linear MIMO array antenna is finished through the operation, the array elements of the main antenna array are dense and are close to the machine body, and the position coordinates of the main antenna array are recorded as:
X＝{x1，x2，…，x50}＝{-5.99，-5.97，…，-5.51，5.51，5.53，…，5.59}
and step 3: auxiliary antenna array layout of linear MIMO array antenna
The 1 st array element of the auxiliary antenna array is distributed at the position of-15.00 (m) and is marked as y1(ii) a The 2 nd auxiliary antenna element is arranged at the position of-14.50 (m) and is marked as y2；
……
The ith auxiliary antenna array element is distributed at [1500- (i-1) M]X0.01 (m) and is denoted as yiWherein i is a natural number less than 23;
……
the 23 rd auxiliary antenna element is arranged at the position of-4.00 (m) and is marked as y23。
The 24 th auxiliary antenna element is arranged at 4.00(m), and is marked as y24(ii) a The 25 th auxiliary antenna element is laid at 4.50(m), denoted as y25；
……
The 23+ k auxiliary antenna elements are distributed in [400+50(k-1) ]]X0.01 (m) and is denoted as y23+kWherein k is a natural number less than 23;
the 46 th one is assistedThe antenna elements are arranged at 15.00(m) and are marked as y50。
The layout of the auxiliary antenna arrays of the linear MIMO array antenna is finished through the operation, the array elements of the auxiliary antenna arrays are sparse, and the position coordinates of the auxiliary antenna arrays are recorded as:
Y＝{y1，y2，…，y46}＝{-15.00，-14.50，…，-4.00，4.00，4.50…，15.00}
and 4, step 4: subject System construction
The following parts are prepared first: the linear MIMO array antenna (composed of a linear MIMO array antenna main antenna array X constructed in the second step and a linear MIMO array antenna auxiliary antenna array Y constructed in the third step), two transmitters, M +2 receivers, two T/R (time/frequency) change-over switches, two multi-way gates (a multi-way gate I and a multi-way gate II), and an unmanned aerial vehicle is used as a motion platform. The multiplexer I has two input ends, 50 output ends and a control end, and the multiplexer II has 48 input ends, 48 output ends and a control end.
Specifically, installation: the linear MIMO array antenna is fixed with the moving platform along the direction parallel to the ground and perpendicular to the moving track, namely the MIMO array antenna is installed on the wing of the unmanned aerial vehicle.
Two input ends of a multi-path gate I are respectively connected with a transmitter A and a transmitter B, 48 ports of 50 ports of the output end of the multi-path gate are sequentially connected with 48 main antenna array elements except 25 th and 26 th main antenna array elements in the main antenna array elements of the linear MIMO array antenna through 48 feeders, and the other 2 output ports of the multi-path gate are respectively connected with radio frequency signal input ports 5a of two T/R change-over switches through 2 feeders; 46 ports of 48 input ports of the multi-path gate II are sequentially connected with 46 auxiliary antenna array elements of the linear MIMO array antenna through 46 feeders, the other 2 input ports of the multi-path gate II are respectively connected with radio frequency signal output ports 5b of the two T/R conversion switches through 2 feeders, and 48 ports of the output end of the multi-path gate II are sequentially connected with 48 receivers; and the antenna radio frequency output ports 6 of the two T/R change-over switches are respectively connected with the 25 th main antenna array element and the 26 th main antenna array element of the MIMO array antenna through 2 feeders. Thus together forming a complete transmitting and receiving system.
The main body system construction of the multifunctional linear array line three-dimensional SAR system is completed through the operation.
And 5: system multi-working mode realization
The multifunctional linear array three-dimensional SAR system can realize four working modes of a two-dimensional synthetic aperture radar on two sides, a single-baseline interference synthetic aperture radar on two sides, a multi-baseline interference synthetic aperture radar on two sides and a lower sight linear array three-dimensional imaging synthetic aperture radar. The system can be controlled to be switched to the corresponding working mode through the mode switching operation.
1. The working mode of the bilateral two-dimensional synthetic aperture radar is realized by adopting the following steps
The method comprises the following steps: controlling a multi-channel gating device I to respectively select a channel related to a 25 th main antenna array element and a 26 th main antenna array element of the linear MIMO array antenna, starting the system to work, and entering a first pulse repetition period;
step two: the transmitter A transmits radar signals to a left observation scene through a 25 th main antenna array element connected with the multi-path gate I;
step three: after delaying for half pulse repetition period, the transmitter B transmits radar signals to a right observation scene through a 26 th main antenna array element connected with the multi-path gate I;
step IV: the 47 th receiver selects the path connected to the 25 th main antenna element via a multiplexer II, and the receiver transmits the signal with a delay τ of 7.6313 × 10 from the transmitter a-5Reception of T from time (second)r＝5.770×10-5(sec) echo;
step five: the 48 th receiver selects the path connected to the 26 th main antenna element via the multiplexer IIAt a time delay tau of 7.6313X 10 from the signal transmitted by the transmitter B-5Reception of T from time (second)r＝5.770×10-5(second) second echo.
Repeating the above steps from two to five at each pulse repetition period, and storing the echo data received by the receiver by corresponding storage equipment so as to carry out post imaging processing until the observation is finished.
2. The working mode of the double-side single-baseline interference synthetic aperture radar is realized by adopting the following steps
The method comprises the following steps: controlling a multi-channel gating device I to respectively select a channel connected with a 25 th main antenna array element and a 26 th main antenna array element of the linear MIMO array antenna, starting the system to work, and entering a first pulse repetition period;
step two: the transmitter A transmits radar signals to a left observation scene through a 25 th main antenna array element connected with the multi-path gate I;
step three: after delaying for half pulse repetition period, the transmitter B transmits radar signals to a right observation scene through a 26 th main antenna array element connected with the multi-path gate I;
step IV: the 23 rd and 13 th receivers select the path connected to the 23 rd and 13 th auxiliary antenna elements respectively via the multiplexer II, and the two receivers transmit signals with a delay tau 7.6313 × 10 from the transmitter a-5Reception of T from time (second)r＝5.770×10-5(sec) echo;
step five: the 24 th and 34 th receivers select the path connected to the 24 th and 34 th auxiliary antenna elements respectively via the multiplexer II, and the two receivers transmit signals with a delay tau of 7.6313 × 10 from the transmitter B-5Reception of T from time (second)r＝5.770×10-5(second) echo.
Repeating the above steps from two to five at each pulse repetition period, and storing the echo data received by the receiver by corresponding storage equipment so as to carry out post imaging processing until the observation is finished.
3. The working mode of the bilateral multi-baseline interferometric synthetic aperture radar is realized by adopting the following steps
The method comprises the following steps: controlling a multi-channel gating device I to respectively select a channel connected with a 25 th main antenna array element and a 26 th main antenna array element of the linear MIMO array antenna, starting the system to work, and entering a first pulse repetition period;
step two: the transmitter A transmits radar signals to a left observation scene through a 25 th main antenna array element connected with the multi-path gate I;
step three: after delaying for half pulse repetition period, the transmitter B transmits radar signals to a right observation scene through a 26 th main antenna array element connected with the multi-path gate I;
step IV: the 23 rd, 19 th, 17 th and 13 th receivers select the paths connected with the 23 rd, 19 th, 17 th and 13 th auxiliary antenna elements respectively through the multiplexer II, and the 4 th receivers transmit signals with the delay tau of 7.6313 multiplied by 10 from the transmitter A-5Reception of T from time (second)r＝5.770×10-5(sec) echo;
step five: the 24 th, 28 th, 30 th and 34 th receivers select the paths connected with the 24 th, 28 th, 30 th and 34 th auxiliary antenna elements respectively through the multiplexer II, and the 4 th receivers transmit signals with the delay tau of 7.6313 x 10 at the distance from the transmitter B-5Reception of T from time (second)r＝5.770×10-5(second) echo.
Repeating the above steps from two to five at each pulse repetition period, and storing the echo data received by the receiver by corresponding storage equipment so as to carry out post imaging processing until the observation is finished.
4. The working mode of the downward-looking linear array three-dimensional imaging synthetic aperture radar is realized by adopting the following steps
The method comprises the following steps: controlling the multiplexer II to make the 1 st, 2 nd, … th and 46 th receivers pass through the multiplexer II and then sequentially communicate with the 1 st, 2 nd, … th and 46 th auxiliary antenna elementsAre connected. Setting the time delay tau from the signal transmission of each transmitter to the signal reception of the corresponding receiver3D＝6.60×10-5(second), the time period from the beginning of receiving the echo to the end of receiving the echo in one pulse repetition period of a single receiver is set as T3D＝5.63×10-6And (second), taking 50 pulse repetition periods as a virtual line array synthesis period, and entering the first virtual line array synthesis period.
Step two: one virtual line array synthesis period contains 50 pulse repetition periods.
In the 1 st pulse repetition period (slow time), controlling a multi-channel gate I to select a path connected with the 1 st main antenna array element of the linear MIMO array antenna, transmitting a radar signal to a directly below observation scene by a transmitter A through the 1 st main antenna array element connected with the multi-channel gate I, and transmitting a signal delay tau from the 1 st main antenna array element by 1, 2, … and 46 receivers3D＝6.60×10-5Simultaneous reception of T from time (seconds)3D＝5.63×10-6(second) second echo.
In the 2 nd pulse repetition period (slow time), controlling a multi-channel gate I to select a path connected with the 2 nd main antenna array element of the linear MIMO array antenna, transmitting a radar signal to a directly lower observation scene by a transmitter A through the 2 nd main antenna array element connected with the multi-channel gate I, and transmitting a signal delay tau from the 1 st main antenna array element to the 2 nd receiver by the 1 st, 2 nd, … th and 46 th receivers3D＝6.60×10-5Simultaneous reception of T from time (seconds)3D＝5.63×10-6(second) second echo.
……
In the 50 th pulse repetition period (slow time), controlling a multi-path gate I to select a passage connected with the 50 th main antenna array element of the linear MIMO array antenna, and transmitting a radar signal to a directly lower observation scene by a transmitter A through the 50 th main antenna array element connected with the multi-path gate I; the 1, 2, …, 46 receivers transmit signal at the time delay tau from the 50 th main antenna array element3D＝6.60×10-5The time(s) startsTime receiving T3D＝5.63×10-6(second) echo.
Step three: after a virtual line array synthesis period, 2300 echo signals can be obtained, that is, a virtual line array composed of 2300 virtual array elements can be approximately obtained, wherein 200 virtual array elements are redundant. And (4) entering the next virtual linear array synthesis period from the 51 st pulse repetition period, circularly repeating the step (II) at intervals of 50 pulse repetition periods, and storing the echo data received by the receiver by corresponding storage equipment so as to perform post imaging processing until the observation is finished.
According to the multifunctional linear array three-dimensional SAR system constructed based on the sparse-dense-sparse type linear array model, the dense main antenna array elements are close to the body, so that errors caused by violent pulling at two ends of wings are reduced, the total length of a feeder line is reduced, and the gravity center is close to the body, so that the stability of the whole system is facilitated. The utilization rate eta of the antenna is approximately equal to 0.7, the utilization rate eta of the antenna is reasonable, the resources of the system are fully utilized, four SAR working modes are integrated, the cost is saved, and the comprehensive performance of the system is improved.
Claims (1)
1. A construction method of a multifunctional linear array three-dimensional SAR system is characterized by comprising the following steps:
step 1: linear MIMO array antenna parameter calculation
The support structure of the linear MIMO array antenna is a linear antenna mounting plate, the central position of the linear MIMO array antenna support structure is taken as an original point, the right-hand direction is taken as the positive direction of a direction axis, and a one-dimensional linear coordinate system is established at intervals by taking d as a basic array element, wherein d is lambda/2, and lambda is the carrier wavelength of the linear array three-dimensional SAR system; m main antennas are arranged on the antenna mounting plateA linear array element and N auxiliary antenna elements, wherein M can be represented by formula
Obtaining of a symbol therein
Meaning the rounding operation, M should be even, if M is odd, then there is no physical significance, PRFallIs the pulse repetition frequency, PRF, of the systemeffIs the equivalent pulse repetition frequency of the virtual array element, wherein the pulse repetition frequency PRF of the systemallAnd equivalent pulse repetition frequency PRF of virtual array elementeffParameter indexes given for the system; n can be represented by the formula
Obtaining, wherein the symbol "[. ]]Doll"denotes the immediate even-out operation, LeqThe length of a virtual linear array equivalent to the linear MIMO array antenna, eta is the size utilization rate of the linear MIMO array antenna, LeqCan be represented by formula
Obtaining where pθTaking eta equal to 0.7 for the angular resolution of the system; where λ and ρθIs an index of a two-dimensional synthetic aperture radar system;
the main antenna array (main array) is divided into a left sub-main array and a right sub-main array by taking an original point as a boundary; wherein the number of the auxiliary antenna elements between the two sub-main arrays is N1，N1Can be represented by formula
Obtaining, wherein eta is 0.7, and the number of the rest auxiliary antenna elements is N2，N2Can be represented by formula N2＝N-N1Obtaining;
step 2: main antenna array layout of linear MIMO array antenna
In the one-dimensional linear coordinate system established in the step 1, the main antenna array calculated in the step 1 is utilizedThe number of elements M and the number of auxiliary antenna elements N, and the 1 st array element of the main antenna array is distributed on
Where, it is marked as x1；
The 2 nd main antenna array element is arranged on
Where, it is marked as x2；
……
The ith main antenna array element is distributed onWhere, it is marked as xiWherein i is a natural number less than M/2;
the M/2 th main antenna array element is arranged on
Where, it is marked as xM/2；
The M/2+1 th main antenna array element is distributed onWhere, it is marked as xM/2+1(ii) a The M/2+2 th main antenna array element is distributed onWhere, it is marked as xM/2+2；
……
Arranging the M/2+ k main antenna array elements on
Where, it is marked as xM/2+kWherein k is a natural number less than M/2;
arranging the Mth main antenna array element on
Where, it is marked as xM；
The layout of the main antenna array of the linear MIMO array antenna is finished through the operation, and the position coordinate of each array element of the main antenna array is recorded as X ═ X1，x2，…，xM}；
And step 3: auxiliary antenna array layout of linear MIMO array antenna
In the one-dimensional linear coordinate system established in the step 1, the number M of the main antenna elements, the number N of the auxiliary antenna elements and the number N of the auxiliary antenna elements between the two sub-main arrays, which are obtained by calculation in the step 1, are utilized1The 1 st array element of the auxiliary antenna array is distributed on
Where, it is denoted as y1(ii) a Arranging the 2 nd auxiliary antenna array element on
Where, it is denoted as y2；
……
The ith auxiliary antenna array element is distributed on
Where, it is denoted as yiWherein i is a natural number less than N/2;
arranging the N/2 th auxiliary antenna array elements on
Where, it is denoted as yN/2；
The (N/2+1) th auxiliary antenna array element is distributed on
Where, it is denoted as yN/2+1(ii) a The (N/2+ 2) th auxiliary antenna array elements are distributed on
Where, it is denoted as yN/2+2；
……
Arranging the (N/2+ k) th auxiliary antenna array elements on
Where, it is denoted as yN/2+kWherein k is a natural number less than N/2;
arranging the Nth auxiliary antenna array element at
Where, it is denoted as yN；
The layout of the auxiliary antenna array of the linear MIMO array antenna is finished through the operation, and the position coordinate of each array element of the auxiliary antenna array is marked as Y ═ Y1，y2，…，yN}；
And 4, step 4: subject System construction
The main body system of the multifunctional linear array three-dimensional SAR system comprises: linear MIMO array antenna, two transmitters: a transmitter A and a transmitter B; the system comprises an N +2 receiver, two T/R change-over switches, two multiplexers: a multiplexer I and a multiplexer II; and a motion platform; the linear MIMO array antenna is composed of a main antenna array X of the linear MIMO array antenna constructed in the step 2 and an auxiliary antenna array Y of the linear MIMO array antenna constructed in the step 3, and the multi-path gate I is provided with two input ends, M output ends and a control end; the multi-path gate II is provided with N +2 input ends, N +2 output ends and a control end; the motion platform is a load platform of the radar system; the specific installation method of the main body system comprises the following steps:
fixing the linear MIMO array antenna with the motion platform along the direction which is parallel to the ground and vertical to the motion track of the motion platform;
connecting two input ends of a multi-path gate I with a transmitter A and a transmitter B respectively, wherein M-2 ports of M ports of the output end of the multi-path gate I are sequentially connected with M-2 main antenna array elements except M/2 and M/2+1 main antenna array elements in linear MIMO array antenna main antenna array elements through M-2 feeders, and the other 2 output ports of the multi-path gate I are respectively connected with radio frequency signal input ports 5a of two T/R conversion switches through 2 feeders; n ports in N +2 input ports of the multi-path gate II are sequentially connected with N auxiliary antenna array elements of the linear MIMO array antenna through N feeders, the other 2 input ports of the multi-path gate II are respectively connected with radio frequency signal output ports 5b of the two T/R conversion switches through 2 feeders, and N +2 ports at the output end of the multi-path gate II are sequentially connected with N +2 receivers; the antenna radio frequency output ports 6 of the two T/R change-over switches are respectively connected with the M/2 th and M/2+1 th main antenna array elements of the MIMO array antenna through 2 feeders; thereby forming a complete transmitting and receiving system together;
the main body system construction of the multifunctional linear array line three-dimensional SAR system is completed through the operation;
and 5: system operation mode design
The multifunctional Linear Array three-dimensional SAR system works according to a two-sided two-dimensional synthetic aperture radar (2-D SAR) mode or a two-sided single-baseline interferometric synthetic aperture radar (InSAR) mode or a two-sided Multi-baseline interferometric synthetic aperture radar (Multi-baseline InSAR) mode or a lower line Array three-dimensional imaging synthetic aperture radar (Linear Array3DSAR) mode; the implementation method of the various working modes comprises the following steps:
1. the working mode of the bilateral two-dimensional synthetic aperture radar is realized by adopting the following steps
The method comprises the following steps: controlling a multi-channel gate I to respectively select a channel connected with an M/2 th main antenna array element and an M/2+1 th main antenna array element of the linear MIMO array antenna, starting the system to work, and entering a first pulse repetition period;
step two: the transmitter A transmits radar signals to a left observation scene through an M/2 th main antenna array element connected with the multi-path gate I;
step three: after delaying for half pulse repetition period, the transmitter B transmits radar signals to a right observation scene through an M/2+1 th main antenna array element connected with the multi-path gate I;
step IV: the (N +1) th receiver selects a path connected with the (M/2) th main antenna array element through a multi-way gate II, and receives T from the time of the time delay tau of a signal transmitted by the transmitter ArSecond echo, in which the delay τ is given by the formula
The method comprises the steps of (1) obtaining,wherein R isminThe distance from the center of the platform to the nearest point of the observation scene, R in practiceminCan be represented by formula
Is obtained approximately, where θminIs the angle between the inner edge of the beam and the vertical line, where H is the vertical height from the center of the platform to the ground, C is the speed of light, and the receiving time interval TrCan be represented by formula
Obtaining wherein T ispIn order to transmit the time width of the signal pulse envelope, the delta R is the difference value between the distance from the central position of the platform to the nearest point of an observation scene and the distance from the central position of the platform to the farthest point of the observation scene when the system works in a two-dimensional synthetic aperture radar working mode, and the delta R can be expressed by a formula in practice
Is obtained approximately, where θmaxIs the angle between the outer edge of the wave beam and the vertical line;
step five: the (N +2) th receiver selects a path connected with the (M/2 +1) th main antenna array element through a multi-way gate II, and receives T from the moment of time delay tau of a signal transmitted by a transmitter BrSecond echo;
repeating the steps from the second step to the fifth step in each pulse repetition period in the following period, and storing echo data received by the receiver until the observation is finished;
2. the working mode of the double-side single-baseline interference synthetic aperture radar is realized by adopting the following steps
The method comprises the following steps: controlling a multi-path gate I to respectively select paths related to the M/2 th main antenna array element and the M/2+1 th main antenna array element of the linear MIMO array antenna, starting the system to work, and entering a first pulse repetition period;
step two: the transmitter A transmits radar signals to a left observation scene through an M/2 th main antenna array element connected with the multi-path gate I;
step three: after delaying for half pulse repetition period, the transmitter B transmits radar signals to a right observation scene through an M/2+1 th main antenna array element connected with the multi-path gate I;
step IV: the N/2 th and the N/2-k th receivers respectively select the paths connected with the N/2 th and the N/2-k th auxiliary antenna array elements through the multi-way gating device II, and the two receivers receive T from the moment of time delay tau of the signal transmitted by the transmitter ArSecond echo, where k is a natural number less than N/2, k can be represented by the formula
Is obtained in which lsbThe length of the base line required by the system single base line interference synthetic aperture radar, wherein the time delay tau can be expressed by the formula
Obtaining wherein R isminThe distance from the center of the platform to the nearest point of the observation scene, R in practiceminCan be represented by formula
Approximately, where H is the vertical height from the center of the platform to the ground, C is the speed of light, and T is the receiving time periodrCan be represented by formula
Obtaining wherein T ispIn order to transmit the time width of signal pulse envelope, the delta R is the difference value between the distance from the central position of the platform to the nearest point of an observation scene and the distance from the central position of the platform to the farthest point of the observation scene when the system works in the double-side single-baseline interferometric synthetic aperture radar working mode, and the delta R can be represented by a formula in practice <math>
<mrow>
<mi>ΔR</mi>
<mo>=</mo>
<mfrac>
<mi>H</mi>
<mrow>
<mi>cos</mi>
<msub>
<mi>θ</mi>
<mi>max</mi>
</msub>
</mrow>
</mfrac>
<mo>-</mo>
<mfrac>
<mi>H</mi>
<mrow>
<mi>sin</mi>
<msub>
<mi>θ</mi>
<mi>min</mi>
</msub>
</mrow>
</mfrac>
</mrow>
</math> Obtaining an approximation;
step five: the N/2+1 and (N/2+1) + k receivers respectively select a path connected with the N/2+1 and the (N/2+1) + k auxiliary antenna array elements through a multi-path gate II, and the two receivers receive T from the moment of time delay tau of a signal transmitted by a transmitter BrSecond echo;
repeating the steps from the second step to the fifth step in each pulse repetition period in the following period, and storing echo data received by the receiver until the observation is finished;
3. the working mode of the bilateral multi-baseline interferometric synthetic aperture radar is realized by adopting the following steps
The method comprises the following steps: firstly, the number n of baselines is given by a system, wherein n is a positive integer; controlling a multi-path gate I to respectively select paths related to the M/2 th main antenna array element and the M/2+1 th main antenna array element of the linear MIMO array antenna, starting the system to work, and entering a first pulse repetition period;
step two: the transmitter A transmits radar signals to a left observation scene through an M/2 th main antenna array element connected with the multi-path gate I;
step three: after delaying for half pulse repetition period, the transmitter B transmits radar signals to a right observation scene through an M/2+1 th main antenna array element connected with the multi-path gate I;
step IV: n/2, N/2-k1、N/2-k2、…、N/2-knThe receivers are respectively selected from N/2 th and N/2-k through a multiplexer II1、N/2-k2、…、N/2-knA path formed by connecting auxiliary antenna array elements, wherein the n +1 receivers receive T from the time delay tau of a signal transmitted by the transmitter ArSecond echo, where kiIs a natural number, kiCan be represented by formula
Obtaining i ═ 1, 2, …, n, where liThe base length required by the multi-base line interference synthetic aperture radar is given to the system; wherein the delay τ can be expressed byObtaining wherein R isminThe distance from the center of the platform to the nearest point of the observation scene, R in practiceminCan be represented by formula
Approximately, where H is the vertical height from the center of the platform to the ground, C is the speed of light, and T is the receiving time periodrCan be represented by formula
Obtaining wherein T ispIn order to transmit the time width of signal pulse envelope, Δ R is the difference between the distance from the center of the platform to the nearest point of the observed scene and the distance to the farthest point of the observed scene when the system works in the double-sided multi-baseline interferometric synthetic aperture radar working mode, and in practice, Δ R may be represented by a formula
Obtaining an approximation;
step five: n/2+1, (N/2+1) + k1、(N/2+1)+k2、…、(N/2+1)+knThe receivers are respectively selected by the multiplexer II to be the N/2+1, (N/2+1) + k1、(N/2+1)+k2、…、(N/2+1)+knThe n +1 receivers receive T from the time delay tau of the signal transmitted by the transmitter BrSecond echo;
repeating the steps from the second step to the fifth step in each pulse repetition period in the following period, and storing echo data received by the receiver until the observation is finished;
4. the working mode of the downward-looking linear array three-dimensional imaging synthetic aperture radar is realized by adopting the following steps
The method comprises the following steps: controlling a multi-channel gate II, and sequentially connecting the 1 st, 2 nd, … th and N receivers with the 1 st, 2 nd, … th and N auxiliary antenna array elements after passing through the multi-channel gate II; setting the time delay tau from the signal transmission of each transmitter to the signal reception of the corresponding receiver3DThe delay τ can be represented by the formula
Obtaining H, wherein H is the vertical height from the center of the platform to the ground, and C is the light speed; let T be the time period from the beginning of echo reception to the end of echo reception in a pulse repetition period for a single receiver each time3DTime period T3DCan be represented by formulaObtaining wherein T ispFor the time width of the pulse envelope of the transmitted signal, the delta R is the difference value between the distance from the central position of the antenna supporting structure to the nearest point of an observation scene and the distance from the central position of the antenna supporting structure to the farthest point of the observation scene when the system works in the working mode of the lower sight line array three-dimensional imaging synthetic aperture radar, and the delta R can be represented by a formula
Obtaining a value delta theta, wherein the value delta theta is an observation angle range of a working mode of the lower view linear array three-dimensional imaging synthetic aperture radar, and the value delta theta is given by a system parameter index; taking M pulse repetition periods as a virtual linear array synthesis period, and entering a first virtual linear array synthesis period;
step two: one virtual linear array synthesis period comprises M pulse repetition periods;
in the 1 st pulse repetition period, namely slow time, controlling a multi-path gate I to select a path connected with the 1 st main antenna array element of the linear MIMO array antenna, transmitting radar signals to a scene observed right below by a transmitter A through the 1 st main antenna array element connected with the multi-path gate I, and transmitting signals by N receivers at a time delay tau from the 1 st main antenna array element by 1, 2, …3DReceiving T simultaneously from time to time3DSecond echo;
in the 2 nd pulse repetition period, namely slow time, controlling a multi-path gate I to select a passage connected with the 2 nd main antenna array element of the linear MIMO array antenna, transmitting a radar signal to a directly lower observation scene by a transmitter A through the 2 nd main antenna array element connected with the multi-path gate I, and transmitting a signal delay tau from the 2 nd main antenna array element by N receivers at the 1 st, 2 nd, … st3DReceiving T simultaneously from time to time3DSecond echo;
……
controlling a multi-path gate I to select a passage connected with an Mth main antenna array element of the linear MIMO array antenna in the Mth pulse repetition period, namely slow time, and transmitting a radar signal to a directly lower observation scene by a transmitter A through the Mth main antenna array element connected with the multi-path gate I; 1, 2, …, N receivers transmit signal delay tau from Mth main antenna array element3DReceiving T simultaneously from time to time3DSecond echo;
step three: after a virtual line array synthesis period, M × N echo signals can be obtained, that is, a virtual line array composed of M × N virtual array elements can be approximately obtained, wherein the number of redundant virtual array elements isAnd (4) entering the next virtual linear array synthesis period from the M +1 pulse repetition period, circularly repeating the step (II) by taking the M pulse repetition periods as intervals, and storing echo data received by the receiver until the observation is finished.
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