JPS6173080A - Phase compensating device of synthetic aperture radar - Google Patents

Abstract

PURPOSE:To shorten considerably a calculation time required for phase compensation while maintaining necessary phase compensation precision by using a phase compensation error estimating device and an automatic setter for the number of divisions in combination. CONSTITUTION:The device is provided with a range calculating device 20, reference coordinate setter 21, phase calculating device 22, interpolator 25, phase compensation error estimating device 27, automatic setter 28 for the number of divisions, etc. Then the setter 28 sets L=2 and K=128, where N is an integral number, L is the number of divisions, and N/L is K; and the calculating device 20 calculates L+1=3 phases per gate at relative distance. The result is inputted to the estimating device 27 to estimate a phase compensa tion error. At this time, when the error is within a permissible range, the output of the calculating device 22 is inputted to the interpolator 25 and phase compen sation is completed. When, however, the error is not within the permissible range, L=4 and K=64; and the phase calculation is performed again. At this time, five distances and phases per gate are need not be calculated again. Here, a phase compensation error is estimated from the five phases.

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 a mass compression device, 8 is a display device, 9 is a phase 10 is a position calculation device, 11 is an inertial navigation device, 12 is a signal processing device, 13 is a compensation device;
is the flying body, 14 is the traveling direction of the flying body 13, 15
16 is the antenna 7 print, 16 is the observation cell, 17 is the range direction, 18 is the azimuth direction, A is the transmitted signal, and the mouth is the received signal. In addition, S is 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 toward the ground or sea surface via the circulator 2 and the antenna 1 as a transmission signal A. The emitted transmission signal A is reflected by a target on the ground or sea surface,
The signal is received again by the antenna 1 as a receiving signal port.

A reception signal port is input to a receiver 4 via a circulator 2. The receiver 4 amplifies and phase-detects the high frequency reception signal and converts it into a pace band video signal. This video signal is input to a pulse compression device 5 and subjected to pulse compression in order to improve the distance resolution. 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 follows. Here, C is the speed of light and is the pulse width after pulse compression.

The video signal S output from the range gate device 6 is input to the phase compensator 9, and irregular fluctuations in phase caused by air currents, maneuvers, etc., of the aircraft body are compensated for. At this time, the three axes (x, y, and z axes) of the radar platform, that is, the flying object 13, are controlled by the inertial navigation device 11.
The velocity in the direction is measured and the measurement result is sent to the position calculation device 10.
The instantaneous position of the flying object 13 is obtained by integrating the equation, and based on this, the phase compensation device 9 calculates the amount of phase compensation and performs phase compensation. 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 180 angular resolution in the azimuth direction. That is, due to the movement of the flying object 13, which is the radar platform, the squint angle θ is changed. The Doppler frequency fd generated at the reception signal port from the observation cell 16 located at is fd=
-T-cosθ.・・・・・・・・・・・・ (2
). Here, V is the flight speed of the flying object 13, and λ is the transmission wavelength. At this time, the synthetic opening time is T□
As, the minimum measurable Doppler frequency difference Δfd is Δfd=1/T□ ・・・・・・・・・・・・・・・
(3) becomes. The minimum observable angular difference (angular resolution) Δθ at this time is Δθ=λ/ (2vsinθo'r1) −−−−−
--(4), and the azimuth resolution can be improved. Is displayed. At this time, regarding the resolution of the radar image, that is, the size of the observation cell 16, the angular resolution Δθ is constant in the azimuth direction 18, and the distance resolution Δθ is constant in the range direction 17.

The azimuth resolution at this time depends on the phase compensation accuracy in the phase compensation device 9.

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.

The distance calculator 20 calculates the position coordinates A (ax(njt)) of the flying object 13 for each transmission pulse determined by the position calculation device 10 shown in FIG.

a, (njt), a2(nΔ1)) and the reference coordinates (piz*
The distance R1 (njt) between the flying object 13 and the phase compensation reference point for each transmission pulse is calculated using
t - Calculated from equation (1) below. However, n represents the transmission pulse number, Δt represents the pulse repetition period, and i represents the range gate number. Also, if the number of coherent integrals is N, then n =0. 1,...
, N -1, and the observation cell 16 in the range direction 17
When the number of is l, it becomes ""1, 29...,■. As a result, the above distance R1(njt) is + (1)iz-az(njt)...
-(I)n=Q, 1, 2. ---, N-1 1=1.2. ...becomes a work. The above calculation result is input to the phase calculator 22, and by calculating the following formula (II1), the phase φi(
njt) is calculated and input to the reference signal generator 23.

4" ・・・・・・・・・・・・(II)φ
i(njt)=Tn, (njt)n=o,
l, 2. -6. N-1i=1. 2.・
..., ■ The reference signal generator 23 calculates the reference signal Refi (njt) according to the following equation (1), and the multiplier 24 multiplies the video signal S and the reference signal Re (t (njt)). In this way, phase compensation is performed.

Refi(njt) = exp (-jφ1(njt
)) -------(1) n=Q, 1, 2. @-, N
-1 1=1'j2t ..., I In the above equation (11), j represents a purely imaginary number (r7x > 1) It is spent on calculating the distance of Eq.

Next, the phase compensation device 9 shown in FIG. 5 will be explained.

In the division number setter 26, the division number is set to a predetermined value, and the phase coordinate A (ax(njt)) of the flying object 13 between the transmission pulse and the transmission pulse is determined.

ay (nj t) t a z (nΔ'))”
From 20+1*2p '', L+1 coordinate values (ax(lKAt)) for every K=N/L.

ay(lKJt) t a (IKjt) ) 1=0
．． 1. ..., controls the distance calculator 20 to select Li. The distance calculator 20 calculates the position coordinates A of the L+1 flying objects 13 and the coordinates (piz t
piy, piz)i=x, 2. ..., I is used to calculate the relative distance R1 (IKjt) between two points using the following formula.

+(p・-a(IKΔ1)) ・・・・・・mouth lz
z 1=o, 1, 2. ..., L i=1.2. ..., I This allows the square root calculation to be reduced to about 1/K of the configuration shown in FIG.

The phase calculator 22 calculates the relative distance 1 (I
Kjt), the phase φi(&t
) and input the result to the interpolator 25.

4π φi (1 phantom t) =--pRl (IKjt) ・
...(g) 1=o, 1, 2. ..., L i=1. 2. ..., ■ In the interpolator 25, each phase φ1 (IKjt) and φi ((1
+1) KΔt), the phase φ1 (Δt for IKjt−1−) of each transmission pulse during this period is calculated by the following equation (4).

−φ1(IKΔ1)) ・・・・・・(capital)k=
1.2. ..., ni-1 1=o, 1. 2. Medium・φ, L−1i=
x, 2. ...,■ In this way, IxN phases φi(njt)n=Q.

1,...,N-1,i=1.2.3. ..., I are all determined, and using the results, the reference signal generator 23
The reference signal Refi ("Δt) is calculated by the above equation (I), and the product with the video signal S is calculated by the multiplier 24. The phase compensation accuracy at this time is determined by the interpolation accuracy of the above equation (4). Dependent.

[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 Ri(njt)i=1t 2t
1111+1. I% n=o, 1. 2.
Although the phase compensation accuracy is high because -*-, N -1 is calculated, there is a problem in that the time required to calculate the phase compensation is extremely long. On the other hand, in the phase compensation device 9 having the configuration shown in FIG. 5, the interpolation interval (KΔ
Since the movement of the flying object 13 during step t) is assumed to be a uniform linear motion, if the flying object 13 is shaken violently, the accuracy of calculating the phase by interpolation will be significantly degraded. In this way, the phase compensation device 9 having the configuration shown in FIG.
Compared to the phase compensation device 9 having the configuration shown in the figure, the time required for calculating phase compensation can be shortened, but there is a problem that the accuracy of the phase compensation is inferior.

This invention was made to solve this problem, and by using a phase compensation error estimator and an automatic division number setting device, the time required for calculating phase compensation can be reduced while maintaining the necessary phase compensation accuracy. The object of the present invention is to obtain a phase compensation device for a synthetic aperture radar that can shorten the time.

[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. and an automatic division number setting device for adjusting the number of distance calculation points based on this estimation result.
The phase compensation error is estimated using a phase compensation error estimator, and the automatic division number setting device is controlled so that this phase compensation error becomes less than a predetermined tolerance. The number of divisions is automatically set, thereby making it possible to reduce the time required to calculate phase compensation while maintaining the necessary phase compensation accuracy.

[Embodiment] FIG. 1 is a block diagram showing the configuration of a phase compensation device in a synthetic aperture radar that is an embodiment of the present invention. In the figure, 9 is a phase compensation device, 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, and 27 is a phase compensation error. The estimator 28 is an automatic division number setting device.

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, a power of 2 is usually selected as the coherent integral number=iN.

Here, to simplify the explanation, a case where N=256 will be described. The division number automatic setter 28 sets L=2. ni=N
/L=128 is set, and the distance calculator 20 calculates the above
Using the formula, the relative distance &4(lKjt), i.e. Ri(
0), Ri(128Δt), R,1(256Δt
) L+1=3 distance calculations are performed for each gate.

The phase calculator 22 calculates three phases φ1(0
).

φ1(128ΔDt φ1(256Δt) is the above (
G) is calculated by the formula. Then, this result is input to the phase compensation error estimator 27, and the phase compensation error Ci o is estimated by the following equation (2).

ei,. =-H(φ1(0)-2φ1(128Δt)+
φ1(256Δ1))...... At this time, if the phase compensation error ei o is within the allowable error range, the output of the phase calculator 22 is input to the interpolator 25,
Processing is performed 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 ei o is outside the allowable error range, L is doubled (L=2L)L, or L=4.
= 64 and redo the distance calculation and phase calculation. What is required at this time is 5 distances Ri(0) for each gate,
Ri(64Δ')t Ri(128Δt)t Ri(
192Δt).

Ri (256jt) (!:, 5 phases φ1(0)
tφ1(64Δt).

φ1 (128jt) t φ1 (192Δt), φ1
(256Δt), but the three distances and phases that have already been calculated are Ri(0), 几1(128, rt), Ri(2
56Δt), φ, (0), φ1(128Δt),
There is no need to recalculate φ1 (256Δt). Based on the five phases obtained here, the phase compensation error ei
1 is estimated using the following formula.

(1+1)Δ1)) ・・・・・・・・・
...hat 1=1. 2. 3. If all of the phase compensation errors ei 1 (1=1.2.3) are within the allowable error range, the output of the phase calculator 22 is input to the interpolator 25, and the phase compensation is completed as described above. Further, if any of the phase compensation errors e<, 1 (1==l, 2.3) 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 ei1 is estimated using the above equation (A).

+φ1 ((1+1)KΔ1)) ・・・・・・・・・
...■1=1.2. ...φL-1=N/L [Effects of the Invention] As explained above, the present invention provides a phase compensation device for a synthetic aperture radar by using a phase compensation error estimator and an automatic division number setting device in combination. , it is possible to automatically set the number of divisions according to the degree of oscillation of a flying object such as an aircraft, so compared to this type of conventional phase compensation device, it is possible to adjust the phase while maintaining the necessary phase compensation accuracy. This has the excellent effect of significantly shortening the calculation time required for compensation.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of a phase compensation device in a synthetic aperture radar that 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. A diagram to explain the principle of 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... multiplication vessel, 2
5... Interpolator, 27... Phase compensation error estimator, 28
...This is an automatic division number setting device. In each figure, the same reference numerals indicate the same or equivalent parts.

Claims (1)

[Claims] In a phase compensation device for compensating for the effects of aircraft oscillation in a synthetic aperture radar mounted on a flying object such as an aircraft and obtaining images of the ground or sea surface, the position coordinates of the flying object and the coordinates of a phase compensation reference point are used. A distance calculator and a phase calculator for calculating distance and phase, a phase compensation error estimator for estimating a phase compensation error from this phase calculation result, and for adjusting the number of distance calculation points based on this estimation result. A phase compensation device for a synthetic aperture radar, characterized in that it is equipped with an automatic division number setting device.