JP5634238B2 - Radar equipment - Google Patents

Description

  The present invention relates to a radar apparatus for separating high-resolution observation data by separating clutter (unnecessary reflected waves from the ground surface and the sea surface) and a target signal.

  In general, radar devices that detect stationary targets are mounted on platforms such as airplanes, send and receive radio waves from the sky, observe the ground surface and sea surface, detect targets located on the ground surface and sea surface, and classify them. To do.

  In the observation of the ground surface and the sea surface by this type of radar device, unnecessary reflected waves (ground clutter and sea clutter) from the ground surface and the sea surface are observed in addition to the reflected waves from the target. Hereinafter, these unnecessary reflected waves are collectively referred to as “clutter”.

FIG. 18 is an explanatory diagram schematically showing an operation mode of a conventionally known general radar apparatus.
In FIG. 18, the radar apparatus 10 is mounted on an aircraft (platform), has an antenna for transmission / reception (not shown), and observes a target M located on the ground surface E as a background. Here, a case where the radar apparatus 10 is mounted on an aircraft that performs ground monitoring or ocean monitoring will be described, but the present invention is not particularly limited thereto.

  As shown in FIG. 18, in the observation of the target M (stationary ground target) by the radar apparatus 10 mounted on the aircraft, a strong reflected wave (clutter) from the ground surface E is observed. There is a problem that separation of waves and clutter becomes difficult, and detection performance and classification performance of the target M are lowered.

  Here, the reception intensity Pclt of the clutter from the ground surface E depends on the irradiation area A of the radar beam Q irradiating the ground surface E (or the sea surface), and is given by the following equation (1).

  In Equation (1), Δmg is the ground range resolution and Δaz is the azimuth resolution. Pt is the transmission power of the radar apparatus 10, Gt is the antenna transmission gain, Gr is the antenna reception gain, λ is the observation wavelength, Rslt is the slant range (distance between the radar apparatus 10 and the target M), and σpq is Clutter backscatter coefficient.

As is clear from the equation (1), the clutter becomes stronger when the ground range resolution Δmg or the azimuth resolution Δaz is low, and conversely becomes smaller when the resolutions Δmg and Δaz are high.
The ground range resolution Δmg is determined by the transmission bandwidth Bw of the transmission signal and is expressed as the following equation (2).

However, in Formula (2), c is the speed of light.
On the other hand, the azimuth resolution Δaz obtained by observation with a radar beam Q from a normal transmission / reception antenna depends on the radar beam width Θw (where Θ is the incident angle of the radar beam Q with respect to the target M). It is expressed as follows.

  As is apparent from the equation (3), the azimuth resolution Δaz shows a large value when the slant range Rslt is large (observing the target M at a distant position), and therefore when observing the target M located at a long distance. It is known to be strongly influenced by clutter.

In the detection and classification of the target M in the environment as shown in FIG. 18, when the target M is moving, the clutter and the target signal are separated by noting that the Doppler frequencies of the clutter and the target signal are different. Is possible.
However, when the target M is stationary, since there is no difference in the Doppler frequency between the target M and the clutter, it is difficult to detect and classify the target M by the above method.

On the other hand, synthetic aperture processing is known as a technique for improving the detection performance and classification performance of the target M even in the above environment.
Synthetic aperture processing is a technique for improving the angle (azimuth) resolution of the radar apparatus 10 by creating an antenna with an equivalently large aperture by performing observations a plurality of times while the platform moves.

Synthetic aperture radar (SAR) is known as a known technique of this kind, and the Doppler frequency generated by the radar movement is subdivided with a filter to divide the beam into narrower beams than the actual beam. DBS (Doppler Beam Sharpening) for obtaining high resolution is known.
The azimuth resolution Δaz _synth obtained by the synthetic aperture processing is given by the following equation (4).

However, in Formula (4), L is a synthetic aperture length and (PHI) is a squint angle. The squint angle Φ is an angle formed between the direction in which the radar beam Q is directed and the traveling direction of the platform (the direction in which the radar beam Q is irradiated with respect to the traveling direction of the platform).
In general synthetic aperture processing, when applied to a fixed side antenna radar known as side-looking antenna radar (SLAR), the squint angle Φ is 90 °.

As apparent from the equation (4), in order to obtain a high azimuth resolution Δaz _synth by the synthetic aperture processing, it is necessary to set the synthetic aperture length L long.
In observation by a fixed side antenna radar, it is known that the synthetic aperture length L depends on the moving speed of the platform and the beam width Θw from the antenna.

On the other hand, when synthetic aperture processing is applied using data observed by a rotating radar device in which the radar beam Q rotates, it is difficult to continue irradiating the radar beam Q to the same position due to the rotation of the radar beam Q. Is likely to be.
Therefore, in the synthetic aperture processing by the rotary radar apparatus, the synthetic aperture length L also depends on the rotational speed of the radar beam Q.

Therefore, in order to obtain the desired azimuth resolution Δaz _synth by the synthetic aperture processing, the rotation speed of the radar beam Q is set to be slow during the observation of the target region of the synthetic aperture processing, and the beam irradiation time to the observation region (that is, A radar apparatus that obtains high-resolution observation data by increasing the synthetic aperture length L) has also been proposed (see, for example, Patent Document 1).

JP 2009-536329 A

  In the technique disclosed in Patent Document 1, a conventional radar apparatus obtains a synthetic aperture length necessary for synthetic aperture processing by reducing the rotation speed of a radar beam in order to obtain high-resolution observation data. Therefore, when the beam width of the radar beam is not sufficiently wide, it is necessary to make the rotation speed of the radar beam very slow, and there is a problem that it takes a lot of time to observe a wide area. .

  The present invention has been made to solve the above-described problems. By providing a processing means for obtaining a high-resolution image at the same time while realizing wide-area observation, the radar beam is scanned in the azimuth angle direction. An object of the present invention is to obtain a radar device that can be observed.

A radar apparatus according to the present invention is mounted on a moving platform, transmits and receives a radar beam composed of pulse signals while scanning in a azimuth angle direction, and receives a reflected signal from a target, and a received signal from the transmitting and receiving antenna Data processing means for processing the data as observation data, the data processing means includes a data division processing section for dividing the observation data into observation data in each angular direction, and a reception obtained by a plurality of observations. A synthetic aperture processing unit that improves the angular resolution of the signal, and a data output unit that stores high angular resolution data obtained by the synthetic aperture processing unit , wherein the data processing means includes an area for reproducing a high resolution image. It has a synthetic aperture block selector for selecting .

  According to the present invention, it is possible to obtain a radar apparatus capable of observing while scanning a radar beam in the azimuth angle direction by providing processing means for simultaneously acquiring a high resolution image while realizing wide-area observation.

1 is a block diagram showing a radar apparatus according to Embodiment 1 of the present invention. It is a block diagram which shows the function structure of the radar signal processing part in FIG. It is a block diagram which shows the function structure of the synthetic | combination opening process part in FIG. It is explanatory drawing which shows the observation form of the several range profile acquired by the radar signal processing part in FIG. It is explanatory drawing which shows the Doppler frequency of the both ends of the beam irradiation area | region in operation | movement of the radar signal processing part in FIG. It is explanatory drawing which shows operation | movement of the data division process part in FIG. It is explanatory drawing which shows the distance compensation process by the synthetic aperture process part in FIG. It is explanatory drawing which shows the phase compensation process by the synthetic aperture process part in FIG. It is a block diagram which shows the radar apparatus which concerns on Embodiment 2 of this invention. It is a block diagram which shows the radar apparatus which concerns on Embodiment 3 of this invention. It is explanatory drawing which shows the compensation process by Embodiment 3 of this invention. It is explanatory drawing which shows the beam reciprocating operation in Embodiment 4 of this invention. It is explanatory drawing which shows the observation timing of the squint angle direction in Embodiment 4 of this invention. It is a block diagram which shows the radar apparatus which concerns on Embodiment 4 of this invention. It is explanatory drawing which shows the decompression | restoration filter process by Embodiment 4 of this invention. It is a block diagram which shows the radar apparatus which concerns on Embodiment 5 of this invention. It is a block diagram which shows the function structure of the unequally spaced synthetic aperture process part in FIG. It is explanatory drawing which shows the operation | movement form of a general radar apparatus roughly.

Embodiment 1 FIG.
The first embodiment of the present invention will be described below with reference to FIGS.
The observation of the ground stationary target using the radar device according to the first embodiment of the present invention is performed while an aircraft equipped with the rotating antenna pulse radar device performs a plurality of observations while rotating the radar beam Q a plurality of times. In addition, the aircraft moves to obtain a high-resolution image of the observation area.

Here, an aircraft refers to a general airplane, a helicopter, an unmanned flight type automatic monitoring aircraft, or the like.
In addition, here, an antenna that scans the radar beam Q in the azimuth angle direction is used and described as a rotary antenna pulse radar device. However, the present invention is not limited to this, and for example, an electrical circuit such as a phased array antenna is used. Alternatively, an antenna that scans the radar beam Q may be used.

1 is a block diagram showing a radar apparatus according to Embodiment 1 of the present invention.
In FIG. 1, the radar device (rotary radar device) includes a radar signal acquisition unit 1, a data division processing unit 2, a synthetic aperture processing unit 5, and a data output unit 8.
The radar signal acquisition unit 1 performs observation with a rotary radar device mounted on an aircraft, and acquires a plurality of observation signals (hereinafter referred to as “range profiles”) that are observed a plurality of times at different positions.

The data division processing unit 2 divides the plurality of range profiles acquired by the radar signal acquisition unit 1 into blocks for the same squint angle.
The synthetic aperture processing unit 5 performs synthetic aperture processing for improving angular resolution using a plurality of range profiles.
The data output unit 8 stores the output result of the radar apparatus acquired by the radar signal acquisition unit 1, the data division processing unit 2, and the synthetic aperture processing unit 5.

FIG. 2 is a block diagram showing a functional configuration of the radar signal acquisition unit 1 in FIG.
In FIG. 2, the radar signal acquisition unit 1 includes a transmitter 11 that generates a pulse signal, a transmission / reception switch 12, a transmission / reception antenna 13, a receiver 14, and a reception signal storage unit 15.

The transmission / reception antenna 13 inputs the pulse signal from the transmitter 11 via the transmission / reception switch 12 and radiates it to the space, and receives the scattered wave scattered by the observation target.
The receiver 14 receives the reception signal of the scattered wave received by the transmission / reception antenna 13 via the transmission / reception switch 12.
The reception signal storage unit 15 temporarily stores the reception signal received by the receiver 14.

FIG. 3 is a block diagram showing a functional configuration of the synthetic aperture processing unit 5 in FIG.
In FIG. 3, the synthetic aperture processing unit 5 includes a distance compensation processing unit 51, a phase compensation processing unit 52, and a Fourier transform processing unit 53.

  The distance compensation processing unit 51 compensates for a change in the distance of the same point in a plurality of observations, arranges the same point at the same distance, and acquires a range hit image after the distance compensation. The range hit image after distance compensation consists of data in which range profiles are arranged at observation positions (time).

The phase compensation processing unit 52 compensates the phase change caused by the distance change for the range hit image after the distance compensation from the distance compensation processing unit 51. Note that the compensation amount by the phase compensation processing unit 52 is determined using the trajectory data of the radar apparatus 10 (platform) measured by a motion sensor (not shown).
The Fourier transform processing unit 53 obtains frequency data by performing Fourier transform on the data after phase change compensation from the phase compensation processing unit 52 in the observation hit direction.

Next, the operation according to the first embodiment of the present invention shown in FIGS. 1 to 3 will be described more specifically with reference to FIGS.
First, the operation of the radar signal acquisition unit 1 shown in FIG. 2 will be described with reference to FIGS. 4 and 5.

The pulse signal generated by the transmitter 11 is input to the transmission / reception antenna 13 via the transmission / reception switch 12 and radiated from the transmission / reception antenna 13 to the space.
The pulse signal radiated into the space is scattered by the observation target, and the scattered wave scattered by the observation target is received by the transmission / reception antenna 13.

A signal (scattered wave from the observation target) received by the transmission / reception antenna 13 is sent to the receiver 14 via the transmission / reception switch 12.
The receiver 14 performs a phase detection process and an A / D conversion process on the received signal, and outputs a digital received signal indicating the amplitude and phase of each received signal.

The reception signal processed by the receiver 14 is sent to the reception signal storage unit 15 and temporarily stored.
Thereafter, the above process is repeatedly executed by the number of observation points necessary for the synthetic aperture process while moving the aircraft. As a result, a plurality of range profiles observed at different positions are stored in the received signal storage unit 15.

FIG. 4 is an explanatory diagram showing an observation mode of a plurality of range profiles acquired by the rotary radar apparatus.
FIG. 5 is an explanatory diagram showing Doppler frequencies at both ends of the beam irradiation region for determining the Doppler band DB.

  In FIG. 4, the radar apparatus 10 (platform) moves at a speed Vplt from a broken line position to a one-dot chain line position via a solid line position, as indicated by a one-dot chain line, and is indicated by a broken-line circular arrow. The target M is observed while rotating the radar beam Q as described above.

  Here, a description is given assuming that a range profile in the same direction is obtained by one rotation of the rotary radar apparatus. Therefore, in order to obtain N range profiles, the radar beam Q needs to be rotated N times.

  However, since it is only necessary to observe N range profiles observed at different positions, for example, when an antenna that can simultaneously observe two or more radar beams Q with different azimuths is used, the radar beam Q is set to N. There is no need to rotate.

In a plurality of observations, it is necessary to determine the moving speed Vplt of the radar apparatus 10 (platform) from the observation interval determined by the rotation speed of the radar beam Q.
This is because when performing synthetic aperture processing, if the observation interval in a plurality of observations is not sufficient with respect to the Doppler band DB of the signal, the subsequent synthetic aperture processing unit 5 causes the signal in the azimuth direction to be folded back. This is because it is necessary to prevent this.

The Doppler band DB of the signal is determined by the Doppler frequencies (see FIG. 5) at both ends of the irradiation region of the radar beam Q.
In FIG. 5, the movement direction of the radar apparatus 10 (platform) is the x axis, the beam irradiation direction is the y axis (Squint angle Φ = 90 °), the right end relative velocity VR and the left end of the beam width Θw (irradiation area). The relative speed VL is indicated by an arrow.

  At this time, the Doppler band DB of the signal is given by the following equation (5) using the platform moving speed Vplt and the difference between the right end relative speed VR and the left end relative speed VL.

In order to prevent signal folding in the synthetic aperture processing, it is necessary to set the pulse repetition interval PRI (Pulse Repetition Interval) for multiple observations to be larger than the Doppler band DB calculated by Equation (5). There is.
Therefore, the relationship between the period Tpri of the pulse repetition interval and the Doppler band DB needs to satisfy the following formula (6).

  In the observation by the rotary radar apparatus, the pulse repetition interval PRI depends on the rotation period of the radar beam Q, so the rotation period Trot of the radar beam Q needs to be set to a required value or less. Further, the moving speed Vplt of the platform is set as shown in the following expression (7) from the expressions (5) and (6).

  Further, the received signal s (f, n, Φsq) at each observation position stored in the received signal storage unit 15 is expressed by the following equation (8).

In Equation (8), Φsq is a squint angle, and n (n = 1, 2,..., N) is an observation signal number (pulse hit number) obtained by a plurality of observations.
Further, fc is the transmission center frequency, Br is the transmission bandwidth, f (fc−Br / 2 ≦ f ≦ fc + Br / 2) is the transmission frequency, R (n) is the range, and c is the speed of light.
Note that, here, a description will be given using a received signal assuming pulse compression processing by the frequency chirp method, but the present invention is not particularly limited to this.

  Subsequently, the data division processing unit 2 divides the data acquired by the radar signal acquisition unit 1 into blocks for the same squint angle Φsq (hereinafter referred to as “squint angle block”).

FIG. 6 is an explanatory diagram showing a division image of a squint angle block in the data division processing unit 2.
In FIG. 6, the observation data So input to the data division processing unit 2 includes observation data S1 in which the radar beam Q is irradiated to the target M located at a certain squint angle, and observation data in which the radar beam Q is not irradiated. S2.

  For the synthetic aperture processing by the synthetic aperture processing unit 5, the data division processing unit 2 extracts the observation data S1 in which the radar beam Q is irradiated to the target M for each squint angle, and the observation data S1 is used as the observation data S1. The data is divided and further combined to obtain divided observation data S3.

The observation data So (radar signal) input to the data division processing unit 2 is in a state where the range profiles observed at each squint angle Φsq are arranged in the order of the squint angle Φsq of the rotary antenna.
Therefore, when the radar beam width Θw is equal to or smaller than the rotation angle of the rotary antenna, the observation data S2 to which the radar beam Q is not irradiated exists for the target M located at a certain arbitrary squint angle.

Next, the operation of the synthetic aperture processing unit 5 shown in FIG. 3 will be described with reference to FIGS.
FIG. 7 is an explanatory diagram showing the operation of the distance compensation processing unit 51 in the synthetic aperture processing unit 5, and FIG. 8 is an explanatory diagram showing the operation of the phase compensation processing unit 52 in the synthetic aperture processing unit 5.

  The synthetic aperture processing unit 5 performs synthetic aperture processing for improving angle (azimuth) resolution by using the N range profiles included in each squint angle block divided by the data division processing unit 2.

The synthetic aperture processing will be described using DBS processing of a known technique (for example, see “RADAR HANDBOOK, Third Edition” by Merrill Skolnik).
Further, since the synthetic aperture processing is performed in parallel in each squint angle block, here, the synthetic aperture processing of the squint angle block of Φsq = 90 ° will be described.

  In addition to the DBS process, an azimuth compression process generally used in a synthetic aperture radar (SAR) may be used. The azimuth compression processing used in the SAR is a well-known technique (for example, see “Basics of Synthetic Aperture Radar for Remote Sensing” written by Kazuo Ouchi), and is not described here.

As shown in FIG. 18, when the target M is observed from the radar apparatus 10 mounted on a moving aircraft, the acquired observation signal of the target M is caused by a distance change (range migration) caused by the movement of the aircraft. As in 7 (a), the observed position (range cell) of the target M may be different.
As a result, there is a possibility that a sufficient integration effect cannot be obtained in the subsequent Fourier transform processing unit 53.

  Therefore, first, the distance compensation processing unit 51 in the synthetic aperture processing unit 5 performs distance compensation for the range migration of FIG. 7A, and as shown in FIG. To be located in the same range cell.

  In FIG. 7, the horizontal axis is the hit direction, the vertical axis is the range (position), FIG. 7 (a) shows the trajectory of the reflected signal from the same point before distance compensation, and FIG. 7 (b) is the distance. The locus of the reflected signal after compensation is shown.

  The distance compensation processing unit 51 uses the fact that the range migration amount in the time domain is expressed as a linear phase shift in the spectral domain in the range direction, as shown in the following equation (9), in the frequency domain. The range migration Smig (f, n, 90 °) is compensated.

In Equation (9), Rsc (t) is the distance between the position of the aircraft at each observation time t and the scene center of the image. The scene center is a reference point for compensation in the distance compensation process and the phase compensation process.
The distance compensation process is not limited to the above-described method, and can be executed by shifting the range cell in accordance with the distance change on the time axis, and any of them may be used.

  As shown in the equation (9), by performing the range migration Smig (f, n, 90 °) compensation in the distance compensation processing unit 51, it becomes possible to compensate for the variation of the range cell due to observation from different positions. .

  However, even in the data after the distance compensation, as shown in FIG. 8A, a phase change may occur in the observation hit direction due to the influence of the fluctuation of the aircraft. In particular, the phase change of the second or higher order may cause the image to be blurred in the processing in the subsequent Fourier transform processing unit 53.

  Therefore, the phase compensation processing unit 52 in the synthetic aperture processing unit 5 performs phase compensation on the locus of FIG. 8A following the distance compensation by the distance compensation processing unit 51, as shown in FIG. 8B. , Remove the phase change.

In FIG. 8, the horizontal axis represents the hit direction, the vertical axis represents the phase, FIG. 8A shows the phase trajectory of the reflected signal from the same point before phase compensation, and FIG. 8B shows the phase compensation. The phase trajectory of the subsequent reflected signal is shown.
The phase compensation processing unit 52 performs compensation processing of the phase Dcmp (f, n, 90 °) as in the following formula (10).

  Finally, the Fourier transform processing unit 53 in the synthetic aperture processing unit 5 performs a Fourier transform in the observation hit direction on the signal compensated by the distance compensation processing unit 51 and the phase compensation processing unit 52, thereby producing a synthetic aperture. Process.

  As described above, the radar apparatus according to Embodiment 1 (FIGS. 1 to 8) of the present invention is mounted on a moving platform and transmits a radar beam Q composed of a pulse signal while scanning in the azimuth angle direction. A transmission / reception antenna for receiving a reflected signal from the target, and data processing means for processing the reception signal from the transmission / reception antenna as observation data are provided.

  The data processing means includes a data division processing unit 2 that divides observation data into observation data in each angle direction, a synthetic aperture processing unit 5 that improves the angular resolution of a received signal obtained by a plurality of observations, and synthetic aperture processing And a data output unit 8 for storing high-angle resolution data obtained by the unit.

  As a result, when using a rotating antenna pulse radar device as a radar device and observing while scanning the radar beam in the azimuth angle direction, a plurality of ranges observed at different observation positions obtained by a plurality of observations are obtained. Synthetic aperture processing can be performed using the profile. Therefore, it is possible to realize a radar apparatus that can acquire a high-resolution image at the same time while realizing wide-area observation.

Embodiment 2. FIG.
In the first embodiment, all the observation data S3 acquired by the data division processing unit 2 are input to the synthetic aperture processing unit 5. However, the SCR (Signal to Clutter Ratio) which is the intensity ratio between the target signal and the clutter signal is input. ) Is a synthetic aperture for the purpose of improving the detection performance and classification performance for all observed squint angles when the values necessary for realizing detection processing and classification processing with high accuracy are satisfied. There is no need to do any processing.

  Therefore, in consideration of the case where the SCR value satisfies the high-precision processing, in addition to the above-described configuration (see FIG. 1), the synthesis is performed between the data division processing unit 2 and the synthetic aperture processing unit 5 as shown in FIG. It is desirable to insert the opening block selector 3.

FIG. 9 is a block diagram showing a radar apparatus according to Embodiment 2 of the present invention.
The synthetic aperture block selection unit 3 according to Embodiment 2 (FIG. 9) of the present invention selects a squint angle block to which the synthetic aperture processing is applied, and the squint angle block is synthesized only when the SCR does not satisfy the required value. Input to the processing unit 5.
Hereinafter, when the SCR satisfies a required value by the synthetic aperture processing, the synthetic aperture block selection unit 3 stops the input of the squint angle block to the synthetic aperture processing unit 5.

  As described above, the data processing means according to the second embodiment (FIG. 9) of the present invention has the synthetic aperture block selection unit 3 for selecting a region for reproducing a high resolution image. It is possible to reduce the processing load and increase the speed of the synthetic aperture processing.

Embodiment 3 FIG.
Although not particularly mentioned in the first and second embodiments (FIGS. 1 to 9), the phase compensation processing unit 52 in the synthetic aperture processing unit 5 is the platform trajectory data measured by the motion sensor ( In order to acquire a higher resolution image, an autofocus processing unit 6 is inserted after the synthetic aperture processing unit 5 as shown in FIG. It is desirable.

10 is a block diagram showing a radar apparatus according to Embodiment 3 of the present invention.
In order to perform the phase compensation process with high accuracy, accurate trajectory information of the platform is required. However, since the actual trajectory of the platform is unknown and the actual trajectory needs to be estimated, the phase compensation processing unit 52 Uses orbit data estimation values including measurement errors.

FIG. 11 is an explanatory diagram showing compensation processing according to the third embodiment (FIG. 10) of the present invention.
11A shows a phase trajectory from the same point before phase compensation, FIG. 11B shows a phase trajectory after phase compensation using motion sensor data, and FIG. 11C shows autofocus. The locus | trajectory of the phase after the phase compensation by a process is shown.

FIG. 11D shows an image with blur before the autofocus process, and FIG. 11E shows an image with blur removed by the autofocus process.
In FIG. 11D and FIG. 11E, the horizontal axis represents the Doppler frequency and the vertical axis represents the signal intensity, which conceptually shows how images are formed.

As shown in FIGS. 11B and 11D, the phase error caused by the measurement error cannot be compensated only by the phase compensation using the trajectory data from the motion sensor.
That is, when the DBS process is applied without removing the phase error, the integration effect in the observation hit direction cannot be sufficiently obtained, and the peak level is lowered and the point image is reduced as shown in FIG. Is disturbed and a blurred image is generated.
On the other hand, after phase compensation by the autofocus processing unit 6, as shown in FIG. 11E, a high-resolution image in which blur is suppressed can be obtained by imaging with a high peak level.

  In addition, about an autofocus process, well-known technique (For example, DE Wahl, PH Echel, DG Giglia and CV Jakowatz, "Phase Gradient Autofocus-A robust tool high resolution AR solution"). correction, "IEEE Transactions on Aerospace and Electronic Systems, vol. 30, no. 3, July 1994.) and many other methods are not proposed here.

As described above, the data processing means according to the third embodiment (FIGS. 10 and 11) of the present invention performs autofocus for automatically compensating for blur on the high-resolution image caused by the estimation error of the platform observation position. The autofocus processing unit 6 estimates the phase error caused by the measurement error of the motion sensor, and automatically applies the phase error to the observed signal by applying autofocus processing. To compensate automatically.
Thus, as shown in FIG. 11E, a high-resolution image in which blur is suppressed or eliminated can be obtained.

Embodiment 4 FIG.
Although not particularly mentioned in the first to third embodiments (FIGS. 1 to 11), when the radar beam Q is observed while reciprocating (see the arrow in FIG. 12), as shown in FIG. It is desirable to insert the restoration filter processing unit 4 between the data division processing unit 2 and the synthetic aperture processing unit 5.
Hereinafter, a fourth embodiment of the present invention will be described with reference to FIGS.

FIG. 12 is an explanatory diagram showing the operation mode of the radar apparatus according to Embodiment 4 of the present invention, and FIG. 13 is an explanatory diagram showing the observation timing in each squint angle direction when the radar beam Q is reciprocated.
FIG. 14 is a block diagram showing a radar apparatus according to Embodiment 4 of the present invention, and FIG. 15 is an explanatory diagram showing the operation of the restoration filter processing unit 4 in FIG.

In FIG. 12, arrows that reverse alternately with the movement of the radar apparatus 10 (in the x-axis direction) indicate the reciprocation of the radar beam Q.
In this case, assuming that the rotation angle in the rotary antenna pulse radar apparatus is reduced to an arbitrary angle width, the radar apparatus 10 observes the angular width of the radar beam Q while reciprocating.

  In FIG. 13, the horizontal axis represents time, FIG. 13 (a) shows the observation timing in one direction of the rotation width of the radar beam Q, and FIG. 13 (b) shows the observation timing in the side direction (Φsq = 90 °). FIG. 13C shows the observation timing in the region of Φsq ≠ 90 °, and FIG. 13D shows the observation timing in the other end direction of the rotation width of the radar beam Q.

  For example, as is apparent from FIGS. 13 (a), 13 (c), and 13 (d), in a region other than the squint angle Φsq = 90 ° (FIG. 13 (b)), the rotary antenna pulse radar device is used. The observation interval PRI due to becomes unequal intervals.

  In general, the Fourier transform processing by the Fourier transform processing unit 53 in the synthetic aperture processing unit 5 is executed on the assumption that the data is observed at equal intervals. If synthetic aperture processing is performed directly, there is a possibility that an appropriate result cannot be obtained.

  Therefore, in the fourth embodiment (FIG. 14) of the present invention, the restoration filter processing unit 4 is provided in order to correctly perform synthetic aperture processing on the data observed in the operation mode in which the radar beam Q is reciprocated.

  As for the restoration filter processing, known techniques (for example, G. Krieger, N. Gebert, and A. Moreira, “SAR Signal Reconstruction from Non-Uniform Displaced Phase Center Sampling,” IEEE 04, AR'04). -24, pp. 1763-1766, 2004), and will not be described in detail here.

In FIG. 14, the same components as those described above (see FIGS. 1, 9, and 10) are denoted by the same reference numerals as those described above, and detailed description thereof is omitted.
Although not described in detail here, in addition to the configuration of FIG. 14, an extended form in which the synthetic aperture block selection unit 3 or the autofocus processing unit 6 in the second and third embodiments described above is added is applicable. Needless to say, in that case, the respective effects are also achieved.

The restoration filter processing unit 4 in FIG. 14 performs processing for equalizing signals observed at unequal intervals, and inputs the observation data after the restoration filter processing to the synthetic aperture processing unit 5.
FIG. 15 conceptually shows the restoration filter processing.

In FIG. 15, since the observation timing t0 and the observation timing t1 are shifted, the data acquisition timing is unequal.
The restoration filter processing unit 4 estimates data at the observation timing t2 (see the solid line frame) instead of the observation timing t1 (see the broken line frame) from the data at the observation timings t0 and t1, and the data acquisition timings are equally spaced. Set to be.

  As described above, according to the fourth embodiment of the present invention (FIGS. 12 to 15), the transmission / reception antenna 13 performs observation while reciprocating the radar beam Q, and the data processing means observes at unequal intervals. The restoration filter processing unit 4 restores the observed data at regular intervals.

  As described above, even when the observation data is acquired by reciprocating the radar beam Q in the observation by the rotating antenna pulse radar apparatus, the restoration filter processing is performed on the data observed at unequal intervals, thereby obtaining a high A resolution image can be acquired.

Embodiment 5 FIG.
In the fourth embodiment (FIG. 14), the restoration filter processing unit 4 is added between the data division processing unit 2 and the synthetic aperture processing unit 5. However, as shown in FIG. Instead, the restoration filter processing unit 4 may be unnecessary by providing the unequal interval synthetic aperture processing unit 7 that performs unequal interval Fourier transform.

16 is a block diagram showing a radar apparatus according to Embodiment 5 of the present invention, and FIG. 17 is a block diagram showing a functional configuration of the unequal interval synthetic aperture processing unit 7 in FIG.
In this case, the unequal-interval synthetic aperture processing unit 7 performs synthetic aperture processing using the unequal-interval Fourier transform processing as it is, instead of the above-described restoration filter processing.

In FIG. 16, the unequal interval synthetic aperture processing unit 7 performs synthetic aperture processing by unequal interval Fourier transform using a plurality of data observed at unequal intervals.
FIG. 17 is a block diagram showing a specific functional configuration of the unequal interval synthetic aperture processing unit 7.
In FIG. 17, the same components as those described above (see FIG. 3) are denoted by the same reference numerals as those described above, and detailed description thereof is omitted.

The unequal interval synthetic aperture processing unit 7 includes an unequal interval Fourier transform processing unit 74 in place of the Fourier transform processing unit 53 described above.
The unequal interval Fourier transform processing unit 74 performs synthetic aperture processing by performing unequal interval Fourier transform on the signals compensated by the distance compensation processing unit 51 and the phase compensation processing unit 52 in the observation hit direction.

  Note that the unequal interval Fourier transform processing is known in the art (for example, Fessler, JA and Sutton, BP, “Nonuniform fast Fourier transforming min-max interpolation,” Signal Processing, IEEE Transactions. 51, No. 2, pp. 560-574, Feb. 2003.), and will not be described in detail here.

  As described above, according to the fifth embodiment (FIGS. 16 and 17) of the present invention, the transmission / reception antenna 13 performs observation while reciprocating the radar beam Q, and the unequal interval synthetic aperture processing unit 7 Synthetic aperture processing is performed to improve the angular resolution of the received signal obtained by observation at a plurality of non-uniform intervals.

  As described above, even when the observation data is acquired by reciprocating the radar beam Q in the observation by the rotating antenna pulse radar apparatus, the unequal interval Fourier transform processing is used for the data observed at unequal intervals. Thus, a high resolution image can be acquired.

  In the first to fifth embodiments, the case where the radar apparatus 10 is mounted on the platform (aircraft) has been described. However, only the radar signal acquisition unit 1 is mounted on the platform, and other processing means (data division processing unit 2). The data output unit 8) may be installed on the ground and processed, for example, after the acquired signal is stored in the storage means.

  DESCRIPTION OF SYMBOLS 1 Radar signal acquisition part, 2 Data division | segmentation process part, 3 Synthetic aperture block selection part, 4 Restoration filter process part, 5 Synthetic aperture process part, 6 Auto focus process part, 7 Unequal interval synthetic aperture process part, 8 Data output part DESCRIPTION OF SYMBOLS 10 Radar apparatus 11 Transmitter 12 Transmission / reception switch 13 Transmission / reception antenna 14 Receiver 15 Receiving signal storage unit 51 Distance compensation processing unit 52 Phase compensation processing unit 53 Fourier transform processing unit 74 Unequal interval Fourier transform processing unit, Bw transmission bandwidth, E ground surface, M target, Q radar beam, t0 observation timing, t1 observation timing, t2 observation timing, Vplt moving speed, Θw beam width, Φsq squint angle.

Claims (4)

A transmitting / receiving antenna that is mounted on a moving platform, transmits a radar beam consisting of pulse signals while scanning in the azimuth angle direction, and receives a reflected signal from a target;
Data processing means for processing a received signal from the transmission / reception antenna as observation data;
In a radar apparatus equipped with
The data processing means includes
A data division processing unit for dividing the observation data into observation data in each angular direction;
A synthetic aperture processor that improves the angular resolution of the received signal obtained by multiple observations;
A data output unit for storing high angle resolution data obtained by the synthetic aperture processing unit ,
The radar apparatus according to claim 1, wherein the data processing means includes a synthetic aperture block selection unit for selecting a region for reproducing a high resolution image . The transmitting / receiving antenna performs observation while reciprocating a radar beam,
The radar apparatus according to claim 1, wherein the data processing unit includes a restoration filter processing unit that restores observation data observed at unequal intervals at equal intervals. The transmitting / receiving antenna performs observation while reciprocating a radar beam,
The radar apparatus according to claim 1, wherein the synthetic aperture processing unit performs synthetic aperture processing to improve an angular resolution of a received signal obtained by observation at a plurality of non-uniform intervals. Wherein the data processing means, of claims 1 to 3, characterized in that it comprises an autofocus processor for automatically compensating for the blur of the high resolution image generated by the estimation error of the observed position of the platform The radar device according to any one of the above.

Images