JPH0449915B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a phase compensation device for a synthetic aperture radar mounted on a flying object such as an aircraft to obtain images of the ground or sea surface.

[Conventional technology]

FIG. 2 is a block diagram showing the configuration of a conventional synthetic aperture radar, and FIG. 3 is a diagram for explaining the principle of the synthetic aperture radar shown in FIG. In each figure,
1 is an antenna, 2 is a circulator, 3 is a transmitter, 4 is a receiver, 5 is a pulse compression device, 6 is a range gate device, 7 is an azimuth compression device, 8 is a display device, 9 is a phase compensation device, 10 is a position computing device,
11 is an inertial navigation device, 12 is a signal processing device, 13
14 is the traveling direction of the flying object 13, 15 is the antenna footprint, 16 is the observation cell, 17 is the range direction, 18 is the azimuth direction, A is the transmitted signal, and B is the received signal. Also,
s indicates the video signal before phase compensation, S indicates the video signal after phase compensation, and A indicates the position coordinates of the flying object 13.

Next, the operation of the conventional synthetic aperture radar shown in FIG. 2 will be explained. Transmission pulses generated by the transmitter 3 are radiated via the circulator 2 and the antenna 1 as a transmission signal A toward the ground or sea surface. The radiated transmission signal A is reflected by a target on the ground or sea surface and is received again by the antenna 1 as a receiving signal port. The reception signal port is input to the receiver 4 via the circulator 2. The receiver 4 amplifies and phase-detects the high-frequency reception signal, and converts it into a baseband video signal. This video signal is input to a pulse compression device 5 and subjected to pulse compression in order to enhance the distance field capability. This pulse-compressed video signal is input to the range gate device 6 and divided into range bins. At this time, the minimum resolvable distance difference ΔR is expressed as ΔR=Cτ/2 (1). Here, C is the speed of light and τ is the pulse width after pulse compression.

Video signal s output from range gate device 6
is input to the phase compensator 9, and irregular fluctuations in the phase caused by air currents, maneuvers, etc., are compensated for. At this time, the inertial navigation device 11 measures the velocity of the radar platform, that is, the flying object 13, in the three-axis (x, y, and z axes) directions, and the measurement results are transmitted to the position calculation device 10. By integrating, the instantaneous position of the flying object 13 is obtained, and based on this, the phase compensation amount is calculated by the phase compensation device 9, and phase compensation is performed.
The video signal S after phase compensation is input to the azimuth compression device 7, and the azimuth compression device 7 performs processing (azimuth compression) for increasing the angular resolution in the azimuth direction 18. In other words, radar
Due to the movement of the flying object 13, which is a platform, the Doppler frequency f _d generated at the receiving signal port from the observation cell 16 at the squint angle θ ₀ is expressed as f _d = 2v/λ cos θ ₀ (2) . Here, v is the flight speed of the flying object 13, and λ is the transmission wavelength. At this time, when the synthetic aperture time is _T1 , the minimum measurable Doppler frequency difference Δf _d is Δf _d =1/T _I (3). The minimum observable angular difference (angular resolution) Δθ at this time is Δθ=λ/(2vsinθ ₀ T _I ) (4), and the azimuth resolution can be improved.

The video signal whose resolution has been increased in both the range direction 17 and the azimuth direction 18 as described above is displayed on the display device 8 as a radar image. At this time, the resolution of the radar image, that is, the size of the observation cell 16 is 1 in the azimuth direction.
8, the angular resolution Δθ is constant, and for the range direction 17, the distance resolution ΔR is constant. The azimuth resolution at this time is the phase compensator 9
It depends on the phase compensation accuracy in .

4 and 5 are block diagrams showing the configuration of the phase compensation device in the synthetic aperture radar of FIG. 2, respectively. First, the phase compensation device 9 shown in FIG. 4 will be explained. In the distance calculator 20, the second
The position coordinates A (a _x
(nΔt)), a _y (nΔt), a _z (nΔt)) and the reference coordinates (p _ix , p _iy , p _iz ) set by the reference coordinate setter 21
Using , the distance R _i (nΔt) between the flying object 13 and the phase compensation reference point for each transmitted pulse is calculated as follows ().
Calculate from the formula. However, n represents the transmission pulse number, Δt represents the pulse repetition period, and i represents the range gate number. Further, if the number of coherent integrals is N, then n=0, 1, . As a result, the above distance R _i (nΔt) becomes R _i (nΔt)=√( _ix − _x ()) ² + ( _iy −
_y ()) ² + ( _iz − _z ()) ² ... (
) n=0,1,2,...,N-1 i=1,2,..., The above calculation result is input to the phase calculator 22, and the phase φ _i (nΔt) is calculated by calculating the following equation (), and the reference signal generator 23
is input to.

φ _i (nΔt)=4π/λR _i (nΔt)...() n=0, 1, 2,..., N-1 i=1, 2,..., In the reference signal generator 23, the following equation () is used. The reference signal R _efi (nΔt) is calculated by the multiplier 24, and the multiplier 24 multiplies the video signal s and the reference signal R _efi (nΔt), thereby performing phase compensation.

R _efi (nΔt)=exp(−jφ _i (nΔt) ...() n=0,1,2,...,N-1 i=1,2,..., In the above formula (), j is a pure imaginary number ( √−1)
represents. In this type of phase compensation calculation, most of the time required for the phase compensation calculation is spent in calculating the distance in equation () above.

Next, the phase compensation device 9 shown in FIG. 5 will be explained. In the division number setter 26, the division number L is set to a predetermined value, and the phase coordinates A (a _x (nΔt)), a _y of the flying object 13 for each transmission pulse are set.
(nΔt), a _z (nΔt)) from n=0, 1, 2,..., K
= L+1 coordinate values for every N/L pieces (a _x (lKΔt),
The distance calculator 20 is controlled to select a _y (lKΔt), a _z (lKΔt)1=0, 1, . . . , L. distance calculator 20
Then, the position coordinates A of the L+1 flying objects 13 and the coordinates (p _ix , p _iy , p _iz ) of the I phase compensation reference points set by the reference coordinate setter 21 i=1,
2,...,I, the relative distance R _i between two points
(lKΔt) is calculated using the following equation ().

R _i (lKΔt) = √( _ix − _x ()) ² + ( _i
y − _y (1)) ² + ( _iz − _z ()) ² …
...() l=0,1,2,...,L i=1,2,...,I This reduces the square root calculation to about 1/K of the configuration shown in Figure 4. I can do it. The phase calculator 22 calculates the phase φ _i (lKΔt) from the relative distance R _i (lKΔt) of the calculation result using the following equation (), and inputs the result to the interpolator 25 .

φ _i (lKΔt) = −4π/λR _i (lKΔt) ... () l=0, 1, 2, ..., Li = 1, 2, ..., I In the interpolator 25, each phase φ _i (lKΔt) and φ _i ((l+
1) Using KΔt), the phase φ _i (lKΔt+kΔt) of each transmission pulse during this period is calculated by the following equation ().

φ _i (lKΔt+kΔt)=φ _i (lKΔt)+k/K
{φ _i ((l+1)KΔt)−φ _i (lKΔt)}...() k=1,2,...,K-1 l=0,1,2,...,L-1 i=1,2, ...,I In this way, I×N phases φ _i (nΔt)n=0,
1,...,N-1, i=1,2,3...,I are all obtained, and using the results, the reference signal generator 2
3, the reference signal R _efi (nΔt) is calculated using the above equation (), and multiplier 24 multiplies it with the video signal s. The phase compensation accuracy at this time depends on the interpolation accuracy of the above equation ().

[Problems that the invention is expected to solve]

In the phase compensation device in the conventional synthetic aperture radar as described above, in the phase compensation device 9 having the configuration shown in FIG. 4, the distance R _i (nΔt)i
=1,2,...,I, n=0,1,2,...,N-1
Although the phase compensation accuracy is high because it calculates , there is a problem that the time required to calculate the phase compensation becomes very long. On the other hand, in the phase compensator 9 having the configuration shown in FIG. When the oscillation of 13 is severe, the accuracy of phase calculation by interpolation deteriorates significantly. As described above, the phase compensation device 9 having the configuration shown in FIG. There was a problem that the compensation accuracy was poor.

This invention was made to solve these problems, and by using a phase compensation error estimator and an automatic division number setter, the required phase compensation accuracy can be maintained while reducing the time required to calculate phase compensation. The object of the present invention is to obtain a phase compensation device for a synthetic aperture radar that can be shortened.

[Means for solving problems]

A phase compensation device for a synthetic aperture radar according to the present invention includes a distance calculator and a phase calculator for calculating the distance and phase of a flying object, and a phase compensation error estimator for estimating a phase compensation error from the result of the phase calculation. The system is equipped with an automatic division number setting device for adjusting the number of distance calculation points based on this estimation result.

[Effect]

In the phase compensation device for a synthetic aperture radar of the present invention, a phase compensation error estimator is used to estimate a phase compensation error, and an automatic division number setting device is installed so that this phase compensation error becomes less than a predetermined tolerance. The number of divisions is automatically set according to the degree of oscillation of the flying object, thereby making it possible to reduce the time required to calculate phase compensation while maintaining the necessary phase compensation accuracy.

〔Example〕

FIG. 1 is a block diagram showing the configuration of a phase compensation device in a synthetic aperture radar which is an embodiment of the present invention. In the figure, 9 is a phase compensator, 20
is a distance calculator, 21 is a reference coordinate setter, 22 is a phase calculator, 23 is a reference signal generator, 24 is a multiplier, 25 is an interpolator, 27 is a phase compensation error estimator,
28 is a division automatic setting device, and 29 is a switch.

Next, the operation of the phase compensation device 9, which is an embodiment of the present invention shown in FIG. 1, will be described. Generally, in this type of synthetic aperture radar, the number of coherent integrals is N, and a power of 2 is usually selected. Here, to simplify the explanation, a case where N=256 will be described. With the division number automatic setting device 28,
L=2, K=N/L=128 are set, and the distance calculator 20 calculates the relative distance R _i using the above equation ().
(lKΔt), i.e. R _i (0), R _i (128Δt), R _i
L+1=3 distance calculations are performed for each gate of (256Δt). The phase calculator 22 calculates three phases φ _i (0), φ _i (128Δt), φ _i (256Δt
) is calculated by the above equation (). Then, this result is input to the phase compensation error estimator 27, and the phase compensation error e _i,p is estimated using the following equation ().

e _i,p = 1/8 (φ _i (0) − 2φ _i (128Δt) +φ _i (256Δt)) ... () At this time, if the phase compensation error e _i,p is within the tolerance range, By switching the switch 29 by the phase compensation error estimator 27, the phase calculator 2
2 and an interpolator 25 are connected, and the output of the phase calculator 22 is inputted to the interpolator 25, where it is processed in the same manner as in the case of the phase compensation device 9 having the configuration shown in FIG. 5, and the phase compensation is completed. However, if the phase compensation error e _i,p is outside the tolerance range, the phase compensation error estimator 2
By switching the switch 29 at 7, the connection between the phase calculator 22 and the interpolator 25 is cut off, and the automatic division number setting device 28 performs re-division and re-calculation of the distance, phase, and phase compensation error. .
That is, double L (L=2L), that is, L=
4. Redo the distance calculation and phase calculation with K=64. At this time, we need 5 distances for each gate.
R _i (0), R _i (64Δt), R _i (128Δt), R _i (192Δt)
, R _i
(256Δt), five phases φ _i (0), φ _i (64Δt),
_φi
(128Δt), φ _i (192Δt), φ _i (256Δt),
Three distances and phases R _i (0), R _i that have already been calculated
(128Δt), R _i (256Δt), φ _i (0), φ _i (128Δt)
, φ _i
(256Δt), there is no need to recalculate.
The phase compensation error is determined by the five phases obtained here.
E _i , l are estimated using the following equation ().

e _i,l = 1/8(φ _i (64(l-1)Δt)−2
φ _i (64lΔt) + φ _i (64(l+1)Δt))...() l=1,2,3 Phase compensation error e _i,l (l=1,2,3) is all within the tolerance range If so, the output of the phase calculator 22 is input to the interpolator 25, and phase compensation is completed as described above. Also, the phase compensation error e _i,l (l=1, 2,
If any of 3) is outside the allowable error range, L is doubled again and the same process as above is repeated. Generally, when the number of divisions is L, the phase compensation error e _i,l is estimated by the following equation ().

e _i,l = 1/8(φ _i ((l-1)KΔt)−2φ _i (lKΔt)+φ _i ((l+1)KΔt)) ...() l=1,2,...L-1 K= N/L [Effects of the Invention] As explained above, the present invention uses a combination of a phase compensation error estimator and an automatic division number setting device in a phase compensation device for a synthetic aperture radar to improve the performance of flying objects such as aircraft. Since it is possible to automatically set the number of divisions according to the degree of fluctuation of the This has the excellent effect of being able to shorten the length.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of a phase compensation device in a synthetic aperture radar which is an embodiment of the present invention, FIG. 2 is a block diagram showing the configuration of a conventional synthetic aperture radar, and FIG. 3 is a block diagram showing the configuration of a conventional synthetic aperture radar. 4 and 5 are block diagrams showing the configuration of the phase compensation device in the synthetic aperture radar of FIG. 2, respectively. In the figure, 9... phase compensation device, 20... distance calculator, 21... reference coordinate setter, 22... phase calculator, 23... reference signal generator, 24... multiplier, 25... interpolation 27...phase compensation error estimator, 28...automatic division number setting device, 29...switch. In each figure, the same reference numerals indicate the same or equivalent parts.

Claims (1)

[Claims] 1 Mounted on a flying object such as an aircraft, a high-frequency pulse signal generated by a transmitter is emitted from an antenna toward an observation target, and the signal reflected by this observation target is received by the antenna again, and this is transmitted to a receiver. Amplification, phase detection, and A/D conversion are carried out by a signal processing device consisting of a pulse compression device, a range gate device, a phase compensation device, a position calculation device, and an azimuth compression device to achieve high resolution in both range and azimuth directions. In the phase compensation device for compensating for the influence of aircraft vibration in a synthetic aperture radar device that obtains radar images of the ground or sea surface, the position coordinates of the flying object and the coordinates of the phase reference point at both ends of the synthetic aperture length are determined. A distance calculator and a phase calculator that calculate these distances and phases, and estimate the phase compensation error from the output of this phase calculator, and if the estimated error exceeds a preset tolerance value, Instructs the automatic division number setting device connected to this to redivide the synthetic aperture length, and if the error is less than a tolerance value, sets the switch between the phase calculator and interpolator to the connected state. a phase compensation error estimator; an interpolator that interpolates the phase amount for each pulse hit from the phase amount determined by the phase calculator; and a reference signal for phase compensation is generated from the phase determined by the interpolator. 1. A phase compensation device for a synthetic aperture radar, comprising a reference signal generator and a multiplier for calculating the product of the reference signal and a signal output from the range gate device.