KR101190731B1 - Multiple input multiple outputMIMO synthetic aperture radarSAR system for high resolution and wide swath width imaging and System thereof - Google Patents

Abstract

Disclosed are a method of using a multiple input multiple output image radar and a system using the same. The multi-input multiple-output image radar method includes a first step of providing a plurality of antennas to which different channels are respectively allocated, and a distance direction compression through a 1: N splitter for each of the different low-frequency signals of each channel to a transmission signal. A second step of performing a linear frequency modulation through the process, each linear frequency modulated signal is transmitted in a pulse form to the observation region through a corresponding antenna continuously and received by the first signal processing unit, which is output from the first signal processing unit Receiving a compressed signal and receiving a signal output from the third step and the second signal processor to sequentially perform a phase compensation process, a range cell migration correction (RCMC) process, an interleaving process, and an azimuth direction compression, and convert the signal into a 2D video signal. And outputting a fourth step.

Description

Multiple input multiple output (MIMO) synthetic aperture radar (SAR) system for high resolution and wide swath width imaging and System approximately}

The present invention relates to an image radar, and more particularly, a method of using a multi-input multiple output image radar for improving the azimuth resolution and widening the observation range, which is one of the most important requirements for satellite and aerial image radar, and a system using the same. It is about.

The range resolution of a typical radar depends on the width of the transmission pulse or the compression pulse and the azimuth resolution is determined by the antenna beam width. In order to obtain a high resolution terrain image, the antenna beam width must be small, so that a sufficiently large antenna is required, but since the size of the payload mounted on the aircraft is limited, it is difficult to obtain a high resolution image using a physically large antenna.

In order to solve this problem, Carl Wiley's first image radar method was first proposed in 1951 by moving a radar equipped with an antenna and synthesizing the received signal using a signal processing technique to obtain a high resolution image as if using a large antenna. synthetic aperture radar (SAR). This has the advantage of obtaining a constant azimuth resolution irrespective of the detection distance by forming a focal point by phase compensation, and it is possible to obtain high resolution image information regardless of weather conditions such as clouds and fog and the amount of sunshine.

FIG. 1 is an exemplary view showing a strip-map mode of a general image radar (SAR), FIG. 2 is an exemplary view showing a high resolution mode (spotlight mode) of a general image radar (SAR), and FIG. It is an exemplary view showing a wide-scan mode of a general image radar (SAR).

1 to 3, the basic operation modes of the image radar system can be classified into three types: a standard image mode (strip-map mode), a high resolution mode (spotlight mode), and a wide-scan mode. have.

The standard image mode (strip-map mode) described in FIG. 1 is the most basic image mode, which continuously obtains a terrain image observed in a flight direction at regular intervals and guarantees a normal resolution.

Equation 1 below represents an azimuth resolution of the standard image mode, and Equation 2 may be an equation for obtaining an observation region.

[Equation 1]

: 방위 방향 해상도,

: 안테나 길이,

:비행체 속도

: Azimuth resolution,

= Antenna length,

Flight speed

: 도플러 밴드위스(banwidth), PRF: 펄스 반복 주파수(Pulse repetition frequency)

: Doppler bandwidth, PRF: Pulse repetition frequency

&Quot; (2) "

: 관측영역,

: 광속,

: 입사각

: Observation area,

: Luminous flux,

: Angle of incidence

 If Equation 1 and Equation 2 shown above are summarized with respect to PRF, Equation 3 can be derived as follows.

Looking at Equation 3 in detail, it can be seen that the lower limit of the PRF is determined by the azimuth resolution, and the upper limit of the PRF is determined by the observation width.

That is, high PRF is required for high resolution (high resolution mode), but low PRF is required for wide viewing width (wide monitoring mode).

&Quot; (3) "

: 안테나 길이,

:비행체 속도

: 광속,

: 입사각

= Antenna length,

Flight speed

: Luminous flux,

: Angle of incidence

In addition, the high-resolution mode (spotlight mode) described in Figure 2 is a mode for forming a precise image of the scene area (Scene area) is a mode method for outputting the beam mechanically and electronically at different azimuth angles in the scene area (Scene area) By increasing the antenna beam irradiation time and obtaining a large amount of Doppler information of a target, a higher resolution image can be obtained. However, there is a disadvantage that the narrow reconnaissance range and the continuity of the image are not guaranteed.

The wide-scan mode described in FIG. 3 has the widest reconnaissance range by sequentially irradiating antenna beams in an elevation direction, but has a shorter irradiation time of beams allocated to one region, compared to other modes. It has a significant disadvantage, and because of the additional operation and processing techniques required for image formation, the complexity is less than the standard image mode (strip-map mode) and high-resolution mode (spotlight).

The above-mentioned azimuth resolution and the observation area of the above-described standard image mode (strip-map mode) may be represented by Equation 1 and Equation 2.

Accordingly, many studies have been conducted to increase the viewing range while increasing the azimuth resolution of satellite image radar.

One of them uses mostly one transmitter to emit a signal, and then has a large number of receivers to receive a low repetitive pulse frequency (hereinafter referred to as PRF) signal and then use signal processing techniques such as interleaving and sampling. By using this method, a high resolution image obtained by using a high PRF is obtained and the view width is extended by a lower PRF.

4 is an exemplary view showing a squinted multi beam method of a general image radar (SAR), FIG. 5 is an exemplary view showing a single phase center (SPC) mode of a general image radar (SAR), and FIG. FIG. 7 is an exemplary diagram illustrating a displaced phase center (DPC) mode of the SAR, FIG. 7 is a diagram illustrating a quad element array method of a general image radar (SAR), and FIG. 8 is a diagram of a general image radar (SAR). An illustration showing the high resolution wide swath (HRWS) method.

 Referring to FIG. 4, the squinted multi beam method is a technique of rotating an antenna in a vertical axis direction so that multiple beams of the antenna are radiated over a large area. It has the advantage of being comfortable.

However, the time emitted per observation area is short and does not guarantee high resolution.

The single phase center (SPC) method illustrated in FIG. 5 illustrates a method of transmitting with a single transmit antenna using a wide beam pattern in a wide viewing area and receiving with multiple narrow receive beam antennas.

The important point is that several narrow reception beams should cover all of the wide transmission beams without overlapping sections. Since each narrow receive beam already knows the angle of inclination relative to the center beam, it is possible to estimate the Doppler center frequency.

Receiving beams receiving a narrow area have a reduced Doppler frequency required for signal processing. For example, in the case of FIG. 5, a Doppler frequency of about 1/3 is required.

Therefore, the entire Doppler frequency band obtained in the standard video mode shown in FIG. 5 can be obtained using only 1/3 of the frequency bands in the SPC mode.

That is, the repetition pulse frequency (PRF) reduced by 1/3 increases the observation width correspondingly. However, since the single phase center (SPC) method has a disadvantage of acting as a very large noise because the side lobe of each reception beam affects the adjacent main lobe, a method of suppressing it is necessary.

The displaced phase center (DPC) method of FIG. 6 has a single transmit antenna irradiated over a wide area like the single phase center (SPC) method.

However, instead of using several narrow reception beams, several reception antennas having a beam as wide as a transmission beam are used. This can prevent the side lobe of the antenna from acting as noise on the signal of the side antenna main lobe.

In the case of FIG. 6, the DPC method obtains the same Doppler history as in the standard video mode using 1/3 PRF like the SPC method, but does not use the inclined Doppler center frequency of each channel but interleaves the received signal. ) It is used as a signal processing method.

In other words, by properly arranging the sampled signal in the middle, it is possible to obtain an effect as if sampling at a high PRF.

At this time, the required condition is that signal processing must be performed with a very accurate PRF.

If an error occurs in the PRF, a large error occurs in the process of overlapping signals, and thus it is difficult to accurately obtain an image having a desired resolution. Nevertheless, the DPC method is very useful as it is the basis for the other methods that follow because it largely eliminates the trade-off relationship between azimuth resolution and observation width.

The quad element array method shown in FIG. 7 is an extension of the DPC method and uses one transmitting antenna and four receiving antennas. Antennas separated by the vertical axis have different viewing areas and the horizontal axis The antenna located in the same direction as the DPC method guarantees the high resolution azimuth resolution.

In other words, it can be seen that the configuration of the DPC antenna further up the vertical axis. This method also requires a rigorous PRF, and the operation of the receiving antenna separated by the vertical axis has to be stopped during the transmission time, resulting in a discontinuous image between the two viewing areas.

The method proposed by further extending the DPC method is a high resolution wide swath (hereinafter referred to as HRWS) method. It has a bi-static structure by separating the transmitting and receiving antennas, and emits a beam in a wide viewing area with a small transmitting antenna, and compensates the gain of the small transmitting antenna by using the large receiving antenna.

Therefore, referring to FIG. 8, a resolution corresponding to half of the length of a transmission antenna is obtained in the azimuth direction in the same manner as a DPC, and in the distance direction, the beam is closely observed according to a reception time through digital beamforming. You can observe a wide range of areas by scanning from the area to the far field. In this manner, the viewing area can be widened in proportion to the size of the receiving antenna which is larger than that of the transmitting antenna.

However, the need for a very large memory and an increase in the size and weight of the physical receive antenna due to the increase of the reception channel are disadvantages of the HRWS method.

The method using one transmitting antenna and a plurality of receiving antennas increases the azimuth image by N (number of receiving antennas) or decreases the PRF by N times compared to a general image radar system that transmits and receives with a single antenna. It has the potential to widen the corresponding observation range.

The problem to be solved by the present invention is to solve the low azimuth resolution of the observation terrain and the narrow view width of the radar measured by the existing image radar structure with the method and system using the multi-input multiple output image radar of the present invention. .

According to an aspect of the present invention, there is provided a multi-input multiple output video radar system including an antenna unit having a plurality of antennas each having different channels assigned thereto, and each channel of each channel to a transmission signal output from the antenna unit. Each of the other low frequency signals performs linear frequency modulation through a 1: N splitter through a distance-wise compression process, and each linear frequency modulated signal is transmitted in a pulse form to the observation region continuously through the corresponding antenna. A second signal processor for receiving a compressed signal output from the first signal processor, the first signal processor, and sequentially performing a phase compensation process, a range cell migration correction (RCMC) process, an interleaving process, and an azimuth direction compression; It includes an image processing unit for receiving a signal output from the 2 signal processing unit to output a 2D image signal The.

Each of the antennas includes a transmitter for continuously radiating a transmission pulse including a channel allocated to the observation area and a receiver for receiving a signal through the corresponding channel, in which the transmission pulse is reflected from the observation area. do.

The first signal processor may include a filter for detecting low frequency signals of respective channels from a transmission signal received from an observation region, a divider for separating the low frequency signals output from the filter into a plurality of signals, and a signal output from the divider. And a distance direction compression unit configured to output a compressed signal N ² by performing a distance direction compression process.

The second signal processor receives a plurality of compressed signals output from the first signal processor and compensates the phase of each of the plurality of compressed signals, and receives a compensation signal output from the phase compensator. RCMC performing a distance movement adjustment process, an interleaving unit performing an interleaving process of data output from the RCMC, and an azimuth compression unit receiving a signal output from the interleaving unit and performing azimuth compression.

The first signal processor may use a slop varying shirp signal to maintain orthogonality of the transmission signal.

The first signal processor performs a signal distribution process by the plurality of transmissions received from the receiver, and the signal distribution process uses a matching filtering scheme to ensure orthogonality between the plurality of transmission signals.

&Quot; (4) "

[Equation 5]

Here, the i-th transmission signal S _txi is represented, and the baseband signal S _txb can be derived using Equation 5, Equation 4 and Equation 5. ].

는 시스템의 중심 주파수를,

는 신호의 크기,

는 펄스폭,

는 chirp 펄스의 선형 주파수 변조율(linear frequency modulation(LFM) rate)를 나타낸다.
here

Is the center frequency of the system,

Is the size of the signal,

Is the pulse width,

Denotes a linear frequency modulation (LFM) rate of chirp pulses.

The image radar system is characterized in that to obtain a sample position of N ² during one PRI interval.

According to an aspect of the present invention, there is provided a method of using a multiple input multiple output image radar, the method comprising: providing a plurality of antennas to which different channels are allocated, respectively, different low frequency signals of each channel to a transmission signal A linear frequency modulation is performed through a 1: N splitter through a distance direction compression process, and each linear frequency modulated signal is continuously transmitted to a viewing area through a corresponding antenna in a pulse form and received by a first signal processor. In the step, the second step of receiving a compressed signal output from the first signal processor to sequentially perform a phase compensation process, a range cell migration correction (RCMC) process, an interleaving process, and azimuth compression, and from the second signal processor And receiving the output signal and outputting the 2D video signal.

The first step is (a) modulating each channel to have an independent baseband from the transmission signal received from the observation region, a plurality of modulated signals using a 1: N splitter (N, N is a natural number) (B) distributing each signal into a signal and outputting a plurality of compressed signals (N ² and N are natural numbers) by performing a compression process according to the distance direction.

The second step includes receiving a plurality of compressed signals outputted from the first step and compensating a phase of each of the plurality of compressed signals using a phase compensator (d), which is output from the phase compensator. (E) performing a distance direction adjustment process by receiving a compensation signal, performing an interleaving process based on a result value output by performing the distance direction adjustment process, and a signal output from the interleaving unit (G) receiving a and performing azimuth compression.

The first step further includes using a slop varying shirp signal to maintain orthogonality of the transmitted signal.

The first step,

A signal distribution process is performed by the plurality of transmissions received from the receiving unit, and the signal distribution process is a step of using a matching filtering method to ensure orthogonality between the plurality of transmission signals.

&Quot; (4) "

[Equation 5]

Here, the i-th transmission signal S _txi is represented, and at this time, the baseband signal S _txb can be derived using Equation 5 above.

 Orthogonality between the plurality of signals using the equation (4) and the equation (5).

는 시스템의 중심 주파수를,

는 신호의 크기,

는 펄스폭,

는 chirp 펄스의 선형 주파수 변조율(linear frequency modulation(LFM) rate)를 나타낸다.
here

Is the center frequency of the system,

Is the size of the signal,

Is the pulse width,

Denotes a linear frequency modulation (LFM) rate of chirp pulses.

As described above, according to the present invention, by using a multi-input multiple-output image radar system, a sample position in N ² is obtained during one PRI, which increases the azimuth resolution by N times or repeats pulses compared to a DPC-based system. By reducing the frequency by N times, the corresponding coverage can be widened.

FIG. 1 is an exemplary view illustrating a standard image mode (strip-map mode) of a general image radar (SAR).
2 is a diagram illustrating a high resolution mode (spotlight mode) of a general image radar (SAR).
3 is an exemplary view showing a wide-scan mode of a general image radar (SAR).
4 is an exemplary diagram illustrating a squinted multi beam method of a general image radar (SAR).
5 is an exemplary diagram illustrating a single phase center (SPC) mode of a general image radar (SAR).
6 is an exemplary diagram illustrating a displaced phase center (DPC) mode of a general image radar (SAR).
7 is an exemplary diagram illustrating a quad element array method of a general image radar (SAR).
8 is an exemplary view illustrating a high resolution wide swath (HRWS) method of a general image radar (SAR).
9 is a block diagram schematically illustrating a multiple input multiple output video radar system according to an exemplary embodiment of the present invention.
FIG. 10 is a block diagram illustrating in detail the first signal processor illustrated in FIG. 9.
FIG. 11 is a block diagram illustrating in detail the second signal processor illustrated in FIG. 9.
FIG. 12 is a timing diagram illustrating timing of signals shown in FIG. 10.
FIG. 13 is a graph for measuring a change in frequency with time of each signal by applying various parameter values shown in Table 1. FIG.
14 is an exemplary view showing a signal acquisition position of a multiple input multiple output image radar system according to an embodiment of the present invention.
15 is an exemplary diagram illustrating a point target impulse response comparison between a DPC-based image radar system and a multi-input multiple output image radar system according to the present invention.
FIG. 16 is an exemplary diagram illustrating an observation width comparison between a DPC based image radar system and a multiple input multiple output image radar system according to the present invention.
17 is a flowchart illustrating a method of using a multiple input multiple output image radar according to an exemplary embodiment of the present invention.
FIG. 18 is a flow chart illustrating in detail the second step described in FIG. 17.
FIG. 19 is a flow chart showing in detail the third step described in FIG. 17.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art can easily carry out the present invention. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention. In the drawings, parts irrelevant to the description are omitted in order to clearly describe the present invention, and like reference numerals designate like parts throughout the specification.

Throughout the specification, when an element is referred to as "comprising ", it means that it can include other elements as well, without excluding other elements unless specifically stated otherwise. In addition, the terms "~", "~" described in the specification means a unit for processing at least one function or operation, which may be implemented in hardware or software or a combination of hardware and software.

DETAILED DESCRIPTION In order to fully understand the present invention, the operational advantages of the present invention, and the objects achieved by the practice of the present invention, reference should be made to the accompanying drawings that illustrate preferred embodiments of the present invention.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. Like reference symbols in the drawings denote like elements.

9 is a block diagram schematically illustrating a multiple input multiple output video radar system according to an exemplary embodiment of the present invention.

As shown in FIG. 9, the multi-input multiple-output image radar system includes an antenna unit 100 having a plurality of antennas, each of which is assigned a different channel. The first signal processor 200 performs linear frequency modulation through a distance-direction compression process through an N divider, and transmits each linear frequency modulated signal to the observation region continuously through a corresponding antenna in a pulse form. A second receiving the plurality of compressed signals MRx1 to MRxn output from the first signal processor 200 to sequentially perform a phase compensation process, a range cell migration correction (RCMC) process, an interleaving process, and an azimuth direction compression It includes a signal processor 300 and an image processor 400 for receiving a signal output from the second signal processor 300 to output a 2D image signal.

Each of the plurality of antennas (eg, the first antenna to the nth antenna) corresponds to a transmitter for continuously radiating a transmission pulse including a channel allocated from the observation region and a signal from which the transmission pulse is reflected and returned from the observation region. It may be configured as a receiver for receiving through a channel.

FIG. 10 is a block diagram illustrating in detail the first signal processor illustrated in FIG. 9.

Referring to FIG. 10, the first signal processor 200 may include a filter 210, a distributor 220, and a compressor 230. The filter unit 210 functions to detect a low frequency signal of each channel from the transmission signals SRx1 to SRxn received from the observation region.

The distribution unit 220 may be configured of a plurality of distributors, and performs a function of distributing each of the plurality of low frequency signals transmitted from the filter unit 210 into a plurality of signals (N and N are natural numbers).

The compression unit 230 generates a compressed signal N ² by performing a distance direction compression process on each of the plurality of low frequency signals transmitted from the distribution unit 220, and outputs the compressed signal N ² to the second signal processing unit 300. .

FIG. 11 is a block diagram illustrating in detail the second signal processor illustrated in FIG. 9.

Referring to FIG. 11, the second signal processor 300 may include a phase compensator 310, an RCMC 320, and an azimuth compression unit 330. In addition, the second signal processing unit 300 may further include an interleaving unit.

The phase compensator 310 receives a plurality of compressed signals N ² output from the first signal processor 200 and compensates phases of each of the plurality of compressed signals N ² . do.

The RCMC 320 receives a compensation signal output from the phase compensator 310, and then performs a distance direction adjustment process to output a corresponding result.

The interleaving unit interleaves a result value output from the RCMC.

The azimuth compression unit 330 receives a signal output from the interleaving unit and performs azimuth compression.

More specifically, the plurality of antennas in the antenna unit may be composed of a plurality of transmitters and a plurality of receivers, and the output signals output from the respective transmitters are transmitted to the observation area and each of the plurality of transmitted signals reflected by each of the first 1 is received by the signal processor.

Each of the plurality of received signals received by the first signal processor is modulated to include an independent baseband (eg, a lowband) through a matching filtering scheme.

Thereafter, the first signal processor 200 generates a compressed signal N ² according to a distance direction by using a 1: N splitter to measure the distance from the observation region to the received signal transmitted from the observation region. . Here, the reference signal used for each matching filtering may be a signal emitted from each of the plurality of transmitters.

The filter unit 210 may be composed of a plurality of low pass filters, and the number of the low pass filters may be the same as the number of the plurality of transmitters and receivers.

Here, the antenna unit may be composed of a plurality of transmit and receive antennas, and the lengths of the plurality of transmit antennas are formed to have a length that is at least equal to or twice the length of the receive antenna. At this time, a plurality of individual antennas constituting the transmission antenna can be independently on / off can be configured to easily adjust the length and position of the transmission antenna.

For reference, the interleaving represents a technique of distributing intensive bit errors in a wireless channel environment where intensive bit errors are likely to occur due to fading or the like.

In other words, by rearranging the order of the data strings in a certain unit, even if the bits in the middle of the data strings are lost due to instantaneous noise, the influences appear locally so that a plurality of the data strings can be localized. This means that when a signal is received with information lost due to interference at some point, the signal is rearranged again in the original order so that the lost information is distributed and only partially lost.

12 is a timing diagram illustrating timing of each of the signals illustrated in FIG. 9.

9 to 12, each of the plurality of transmission signals (Tx1 to TxN) is transmitted to each of the plurality of receivers in the receiver in pulse units having a first interval τ. Each of the plurality of transmission signals Tx1 to Txn is activated with a guide time at a time interval of Δτ.

In this case, the orthogonality between the transmission signals received from the observation region must be guaranteed to restore the correct image.

&Quot; (4) "

[Equation 5]

Equation 4 represents the i-th transmission signal S _txi , and the baseband signal S _txb can be derived using Equation 5 above.

는 시스템의 중심 주파수를,

는 신호의 크기,

는 펄스폭,

는 첩(chirp) 펄스의 선형 주파수 변조율(linear frequency modulation(LFM) rate)를 나타낸다.
here

Is the center frequency of the system,

Is the size of the signal,

Is the pulse width,

Denotes a linear frequency modulation (LFM) rate of chirp pulses.

Here, by using various linear frequency modulation rates (LFM rates), it is possible to ensure orthogonality between transmission signals.

&Quot; (6) "

In this case, in order to obtain the same resolution in the distance direction, each of the plurality of transmission signals must have the same bandwidth. Therefore, in order for each of the plurality of transmission signals having a different linear frequency modulation rate (LFM rate) to obtain the same bandwidth, the bandwidth of each transmission signal must be inversely proportional to the linear frequency modulation rate. The size of the bandwidth can be derived.

Here, it is assumed that the pulse width of the first transmission signal is the longest and the linear frequency modulation rate (LFM rate) is the smallest.

This process reduces the transmission signal width. As a result, the average power transmitted is reduced, which reduces the detection distance of the image radar. To compensate for this problem, Equation 7 below is used to compensate.

[Equation 7]

는 신호의 크기, i는 임의수,

는 펄스폭을 나타낸다.
here,

Is the magnitude of the signal, i is any number,

Represents the pulse width.

FIG. 13 is an exemplary diagram for measuring a change in frequency with time of each signal by applying various parameter values shown in Table 1, and Table 1 is an exemplary diagram showing four types of various parameter values.

1st Tx

2nd Tx

3rd Tx
4th Tx

9.7 (GHz)
9.7 (GHz)
9.7 (GHz)
9.7 (GHz)

300 (MHz)
300 (MHz)
300 (MHz)
300 (MHz)

1.5? 1013
-1.5? 1013
1.67? 1013
-1.67? 1013

20 (μs)
20 (μs)
18 (μs)
18 (μs)

One
One
1.11
1.11

13 and Table 1, the parameter values described in Table 1, for example, the first transmission unit (1st Tx) to the fourth transmission signal (4th Tx) should include the same frequency, the same baseband, linear frequency modulation rate Set only the pulse width and the signal size.

Signals to which the matched filtering is applied using the four types of parameter values described in Table 1 may have excellent auto-correlation characteristics and low cross-correlation characteristics.

When using the above-described four kinds of parameter values as the transmission signal of the present invention, an independent signal of N ² may be obtained after distance compression.

14 is an exemplary view showing a signal acquisition position of a multiple input multiple output image radar system according to an embodiment of the present invention.

As shown in FIG. 14, it can be seen that the multi-input multiple-output image radar system (b) of the present invention acquires samples of N ² during one PRI period. This can acquire N times more samples than obtaining N samples in a general DPC-based image radar (a).

At this time, in order to maintain the same spacing between samples to be obtained, first, the movement of the satellite equipped with the antenna must be considered. The distance of the satellite traveling during the previous transmission time when the kth (k = natural number) transmission pulse is emitted can be derived from Equation 8 described below.

[Equation 8]

Δm _k Is the distance of the satellite during the previous transmission time when the kth transmit pulse is emitted, k is the natural number, τ is the pulse width of the transmitted signal, Δτ is the pulse interval between the transmitted signals, and V _p is the average velocity of the satellite. Indicates.

Δm _k It is important to calculate the position of the transmitting antenna that emits the transmission signal in consideration of the position of the satellite. This can be expressed as Equation 9 described below, and it can be seen that the sample positions of the compressed signal N ² obtained through the same are maintained at the same interval.

&Quot; (9) "

&Quot; (10) "

Here, ΔS _k stands for the position (movement distance) of the transmitting antenna, N represents the sample position, can be represented by the equation (11), Δm _k interval represents the position (movement distance) of the satellite.

The moving distance of the transmitting antenna calculated in Equation 10 should always be greater than '0', and thus the maximum number of antennas of the multi-input multiple-output image radar system of the present invention can be calculated.

In addition, in order to accurately compensate the phase of the received signal, it is necessary to compensate for the delay of the transmission signal and the movement of the transmission antenna. Compensation for the delay of the transmission signal and the movement of the transmission antenna is compensated through the phase compensation interval of [Equation 12] described below, and by performing the phase compensation unit described in FIG. Will be.

&Quot; (11) "

[Equation 12]

General parameter
value
Carrier frequency
9.7 (GHz)
Platform height
580 (km)
Platform velocity
7560 (m / s)
Incidednt angle
20 ° -55 °
Chirp signal bandwidth
300 (MHz)
Total azimuth antenna length
12 (m)
Interval between pulses
5 (μS)

DPCA based SAR system
Proposed MIMO SAR system
Δx (m)
NO. of TX
NO. of Rx
Δx (m)
NO. of TX
NO, of Rx
case 1
4
One
3
4
3
4
case 2
3
One
4
3
4
4

Table 2 and Table 3 show the system parameter values of the present invention and the case where the DPCA image radar system simulation is compared with the MIMO image radar system simulation (Case1, Case2).

Referring to Table 2, through Equation 11, it can be seen that the maximum number of antennas in case 1 is 10, and in case 2, it is 7. It can be seen that this is sufficient for the operation of the multiple input multiple output image radar system.

15 is an exemplary view showing a point target impulse response comparison between a DPC-based image radar system and a multi-input multiple output image radar system of the present invention, and FIG. 16 is a DPC-based image radar system and a multi-input multiple output image of the present invention It is an example figure which showed the observation width comparison of a radar system.

DPCA
based SAR system
Proposed
MIMO SAR system
Case 1 & 2
Case 1
Case 2
PRF (Hz)
1116
372
279


Swath width (km)

Sw1
90
311
617
Sw2
47
160

Sw3
102


Sw4
54


Sw5
83


Sw6
34

Table 3 shows a comparison between the simulation PRF and the observation width.

Referring to FIGS. 15, 16 and Table 3, when comparing the impulse response to a point target with a DPC-based system and a multi-input multi-output system, when the same PRF is used, the system of the present invention is three times the case of Case 1, In case 2, the 4x resolution is improved.

It can be seen that the resolution is further improved as the number of transmitting and receiving antennas increases. In addition, referring to FIG. 15, when the same azimuth resolution (aperture) is obtained, in case 1, the PRF is reduced by 3 times, and in case 2, it is reduced by 4 times.

FIG. 17 is a flowchart illustrating a method of using a multiple input multiple output image radar according to an exemplary embodiment of the present invention, FIG. 18 is a flowchart illustrating the second step in FIG. 17 in more detail, and FIG. 19 is described in FIG. This is a flowchart showing the third step in more detail.

9 to 19, a method of using a multiple input multiple output image radar is

In a first step (S10) of providing a plurality of antennas to which different channels are respectively allocated, linear frequency modulation is performed through a distance-wise compression process through a 1: N splitter on different low-frequency signals of each channel to a transmission signal. In operation S20, each linear frequency-modulated signal is continuously transmitted to the observation region through a corresponding antenna in the form of a pulse and received by the first signal processing unit 200, and the compression is output from the first signal processing unit. Receiving a signal and receiving a signal output from the third step (S30) and the second signal processor 300 to sequentially perform a phase compensation process, a range cell migration correction (RCMC) process, an interleaving process, and azimuth compression And outputting the 2D video signal as a fourth step (S40).

The second step (S20) is a step (a) of modulating each channel to have an independent baseband from the transmission signal received from the observation region (S21), a plurality of modulated signals using a 1: N splitter ( (B) step S22 of distributing N and N as natural numbers and compressing each of the plurality of signals according to a distance direction to output a plurality of compressed signals (N ² and N are natural numbers) (C) step S23.

In the third step S30, receiving a plurality of compressed signals output from the second step S20 and compensating a phase of each of the plurality of compressed signals using a phase compensator (S31). (E) step S32 of receiving a compensation signal output from the phase compensator 310 to perform a distance direction adjustment process, and an interleaving process based on a result value output by performing the distance direction adjustment process. (F) step (S33) to perform the step and (g) step (S34) for receiving the signal output from the interleaving unit to perform azimuth compression.

The second step S20 may further include using various slope varying shirp signals to maintain orthogonality of the transmission signal.

The second step S20 performs a signal distribution process by each of the plurality of transmission signals SRx1 to SRxn received by the antenna unit 100, and the signal distribution process is orthogonality between the plurality of transmission signals. This may be a step of using a matching filtering scheme to ensure this.

Accordingly, the present invention provides a multi-input multiple-output image radar system having a plurality of transmitters and receivers, and obtains a high resolution image image by changing the positions of the plurality of transceivers by changing various parameter values and positions of the transmitters.

Therefore, according to the present invention, according to the present invention, as described above, by using a multiple input multiple output image radar system, a sample position in N ² is obtained during one PRI, which results in N azimuth resolution compared to a DPC based system. By increasing the number of times, or by reducing the repetitive pulse frequency by N times, the corresponding observation can be widened.

While the above has been shown and described with respect to preferred embodiments of the invention, the invention is not limited to the specific embodiments described above, in the technical field to which the invention belongs without departing from the spirit of the invention claimed in the claims Various modifications can be made by those skilled in the art, and of course, these modifications should not be understood individually from the technical idea or the prospect of the present invention.

200: first signal processor 300: second signal processor
400: image processing unit

Claims (12)

An antenna unit having a plurality of antennas to which different channels are respectively allocated;
Each of the different low frequency signals of each channel is subjected to a linear frequency modulation through a distance-wise compression process through a 1: N splitter on the transmission signal output from the antenna unit, and each linear frequency modulated signal corresponds to a pulse form. A first signal processor configured to continuously transmit and receive an observation region through an antenna;
A second signal processor which sequentially receives a compressed signal output from the first signal processor and sequentially performs a phase compensation process, a range cell migration correction (RCMC) process, an interleaving process, and an azimuth direction compression; And
And a video processor for receiving a signal output from the second signal processor and outputting the signal as a 2D video signal.
The method of claim 1,
Each antenna includes: a transmitter for continuously radiating a transmission pulse including a channel allocated to the observation region; And
And a receiver configured to receive signals transmitted from the observation region by the transmission pulses through the corresponding channel, respectively.
The method of claim 1,
The first signal processor,
A filter unit for detecting a low frequency signal of each channel from the transmission signal received from the observation region;
A divider for separating the low frequency signal output from the filter unit into a plurality of signals; And
And a distance direction compression unit configured to output a compressed signal (N ² ) by performing a distance direction compression process of signals output from the distributor.
The method of claim 1,
The second signal processor,
A phase compensator for receiving a plurality of compressed signals output from the first signal processor and compensating a phase of each of the plurality of compressed signals;
RCMC receiving a compensation signal output from the phase compensator and performing a movement adjustment process according to a distance direction;
An interleaving unit performing an interleaving process on the data output from the RCMC;
And azimuth compression unit configured to receive a signal output from the interleaving unit and perform azimuth compression.
The method of claim 1,
The first signal processor,
And a multiple input multiple output video radar system using various shirp signals to maintain orthogonality of the transmitted signal.
The method of claim 2,
The first signal processor,
A signal distribution process is performed by a plurality of transmissions received from the receiving unit, and the signal distribution process uses a matching filtering scheme to ensure orthogonality between the plurality of transmission signals.
&Quot; (4) "

&Quot; (5) "

Here, the i-th transmission signal S _txi is represented, and at this time, the baseband signal S _txb can be derived using Equation 5 above.
A multiple input multiple output image radar system using Equations 4 and 5 below.
here

Is the center frequency of the system,

Is the size of the signal,

Is the pulse width,

Denotes a linear frequency modulation (LFM) rate of chirp pulses.
The method of claim 1,
The video radar system,
It is characterized in that to obtain a sample position of N ² during one PRI interval,
The N is a natural number and is equal to the number of the plurality of transmission signals.
A first step of providing a plurality of antennas to which different channels are respectively allocated;
The first signal processor performs a linear frequency modulation on the transmission signal output from the antenna through a 1: N splitter for each of the different low frequency signals of each channel through a distance direction compression process, and each linear frequency modulated signal is A second step of transmitting to the observation region continuously through a corresponding antenna in the form of a pulse;
A third step of receiving, by a second signal processor, the compressed signal output from the first signal processor, sequentially performing a phase compensation process, a range cell migration correction (RCMC) process, an interleaving process, and an azimuth direction compression; And
And a fourth step of receiving, by the image processor, the signal output from the second signal processor and outputting the signal as a 2D image signal.
9. The method of claim 8,
In the first step,
(A) modulating each channel from the transmission signal received from the observation region so that each channel has an independent baseband;
(B) distributing the modulated signal into a plurality of signals (N, N is a natural number) using a 1: N splitter; And
And (c) outputting a plurality of compressed signals (N ² , N is a natural number) by performing a compression process along each of the plurality of distributed signals according to a distance direction.
9. The method of claim 8,
The second step comprises:
(D) receiving a plurality of compressed signals outputted from the first step and compensating a phase of each of the plurality of compressed signals using a phase compensator;
(E) receiving a compensation signal output from the phase compensator and performing a distance direction movement adjustment process;
(F) performing an interleaving process in an interleaving unit based on a result value output by performing the distance movement adjustment process; And
And (g) receiving a signal output from the interleaving unit and performing azimuth compression.
The method of claim 10,
The (e) step,
And using a variety of chirp signals to maintain the same resolution along the same distance direction of the transmitted signals.
9. The method of claim 8,
In the first step,
A signal distribution process is performed on each of the plurality of transmission signals received from the receiver of the antenna, and the signal distribution process is a step of using a matching filtering method to ensure orthogonality between the plurality of transmission signals.
&Quot; (4) "

&Quot; (5) "

Here, i represents the i-th transmission signal S _txi (i is a natural number), and at this time, the baseband signal S _txb can be derived using Equation 5,
Method of using a multiple input multiple output image radar using the equation (4) and the equation (5).
here

Is the center frequency of the system,

Is the size of the signal,

Is the pulse width,

Denotes the linear frequency modulation (LFM) rate of the chirp pulse signal.

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