JPH0231834B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a synthetic aperture radar that is mounted on an aircraft or a flying object and maps the ground.

First, the configuration of a conventional synthetic aperture radar of this type shown in FIG. 1 will be described.

Now, in FIG. 1, the IF (Intermediate
The CW signal in the frequency band is input to the pulse expansion device 2 and becomes a chirp signal (chiab bandwidth = B) whose frequency changes with time.

At this time, it is assumed that the chiave signal is generated in synchronization with the trigger signal from the trigger signal generator 15. The output of the pulse stretcher 2 is converted into an RF (Radio) from a stabilized local oscillator 4 by a mixer 3.
After being mixed with a frequency (frequency) signal and increased in output by a high-output amplifier 5, the signal passes through a transmitter/receiver switch 6 and an antenna 7, and is radiated into space as a radio wave. The radio waves reflected by the target are inputted again to the mixer 3 via the antenna 7 and the transmitter/receiver switch 6, where they are input to the stabilized local oscillator 4.
It is mixed with the RF signal from the IF band and becomes an IF band signal.

The IF band signal is amplified by an IF amplifier 8 and then compressed by a pulse compressor 9 to approximately 1/B in the range direction. Above, the compressed signal is passed through the phase detector 1
Phase detection is performed using the signal from the coherent signal generator 1 at 0.a. At the same time, the signal from the coherent signal generator 1 passes through a 90° phase shifter 11 and is input to a phase detector 10.b. The compressed signal input to the phase detector 10.b is subjected to phase detection using the output from the 90° phase shifter. Phase detector 10・a
The outputs of gate circuits 12.a and 10.b are respectively connected to gate circuits 12.a and 10.b.
After being input to 12.b and gated, these outputs 16.a and 16.b are input to an azimuth compression device 13. The azimuth compression device uses the fact that the Doppler frequencies of radar echoes from targets existing in various azimuth directions are different to separate targets in the azimuth direction and improve azimuth resolution. The signal 17 thus obtained is input to the display device 14 to obtain a high resolution image in both the range direction and the azimuth direction. In order to observe the image obtained at this time with even higher azimuth resolution, it is necessary to emit radio waves to the same target again and observe the target with a longer synthetic aperture time than the previous time.

Transmission wavelength λ, moving speed v of the radar device, speed v
In general, the azimuth resolution δθ is approximately given by δθ=λ/2vTsinθ (1) where θ is the angle formed between the direction of the radar device and the direction connecting the radar device and the target, that is, the squint angle, and T is the synthetic aperture time. The pulse repetition period of the pulse expansion device 2 is τ, and the number of points of the spectrum analysis means used in the azimuth compression device 13, such as FFT, is N.
Then, since the synthetic aperture time T is given by T=Nτ (2), equation (1) becomes δθ=λ/2vNτsinθ (3). Therefore, the transmission wavelength λ, moving speed v, squint angle θ, and pulse repetition period τ are constant,
If the number N of FFT points is fixed, the azimuth resolution δθ is constant. The synthetic aperture time for obtaining this azimuth resolution δθ is also constant, and cannot be quickly adjusted depending on the observation target. In other words, there are cases where you shorten the synthetic aperture time to quickly view a wide observation area with low resolution, and then extend the synthetic aperture time to view an area within that wide observation area that you want to observe in greater detail with high resolution. With conventional methods, it has not been possible to make the azimuth resolution variable in this way.

This invention solves these drawbacks by dividing the synthetic aperture length and combining the results of signal processing for each of the divided synthetic aperture lengths according to the required azimuth resolution to provide a zooming function. The drawings will be explained in detail below.

FIG. 2 shows an embodiment of the present invention, in which each output 16 of the gate circuits 12a and 12b shown in FIG.
a, 16b are compensated by the phase compensation device 118 by e×p(j4πr/λ) in phase with respect to the distance r from the radar device to the target. (Note: Outputs 16a and 16b are described as real signals, but to simplify the description, they will be treated as complex signals from now on without loss of generality.) Here, λ is the transmission wavelength, j is √-1, and the above phase compensation is performed for each transmission pulse. 1
The output of No. 8 is used to move the range bin by the range walk compensation device 19 so that the received echoes from the same target come to the same range bin regardless of the movement of the radar device. The output of 19 is transmitted to spectrum analysis means 1 (for example, FFT) 20 for each same range bin.
First, a spectrum is obtained for each small section obtained by dividing the synthetic aperture length. For example, as shown in FIG. 3, the spectrum analysis means 120 calculates N sets of spectra in each of N small sections l obtained by dividing the synthetic aperture length L into N. Or, for example, as shown in Fig. 4, the above subsection l may be overlapped to create 2N
- Spectral analysis means 12 for the echoes from the target obtained in each subsection by dividing into one subsection;
0, calculate 2N-1 sets of spectra.

Next, N sets in FIG. 3 and (2N-1) sets of spectra calculated by the spectrum analysis means 1 in FIG. 4 are stored in the memory device 21.

On the other _hand , the required azimuth resolution δ _R 〓24 is input to the constant calculator 25 in advance, and for FIG. For FIG. 4, M given by M=[λ/δ _R 〓l sinθ]-1 M=1, 2,..., (2N-1) (5) is calculated by the constant calculator 25. shall be taken as a thing. Here [ ] is a Gauss symbol. This M is input to the memory device 21 as the output of the constant calculator 25, and M sets of spectra are taken out from the memory device 21. For the same frequency components of these spectra, in the case of Fig. 3, e
×p(-j2πfl/vn), in the case of Fig. 4, e×p(
- j2πfl/2vn) is multiplied by the phase compensator 222 based on the calculation output M from the constant calculator 25. Here, n=1, 2,...,M. The spectrum analysis means 2 (for example, FFT) 23 is applied to the phase-compensated spectrum again.
Based on the calculation output M from the constant calculator 25, a spectrum at M points is determined.

The output of the spectrum analysis means 223 becomes 17 and is displayed on the display device shown in FIG. 1, and an image with a zooming effect on the same target can be obtained according to the required azimuth resolution 24 given from the outside. .

As described above, in the synthetic aperture radar according to the present invention, arbitrary azimuth resolution can be obtained by dividing the synthetic aperture length into small sections, obtaining spectra for each small section, and combining the required number of these spectra. It has the effect of

[Brief explanation of drawings]

Figure 1 is a configuration diagram of a conventional synthetic aperture radar, Figure 2
The figure is a block diagram of an azimuth compression device according to the present invention, and FIGS. 3 and 4 are diagrams showing divided synthetic aperture lengths used in the present invention. In the figure, 1 is a coherent signal generator, 2 is a pulse stretcher, and 3 is a coherent signal generator.
is mixer, 4 is stabilizing local oscillator, 5 is high output amplifier, 6 is transmitter/receiver switch, 7 is antenna, 8 is IF
amplifier, 9 is a pulse compression device, 10 is a phase detector, 11 is a 90° phase shifter, 12 is a gate circuit, 13
14 is an azimuth compression device, 14 is a display device, 15 is a trigger signal generator, 16 is an output of the gate circuit 12,
17 is the output of the azimuth compression device 13; 18 is the phase compensator 119; the range walk compensator; 20
is a spectrum analysis means 1, 21 is a memory device, 2
2 is a phase compensator 2; 23 is a spectrum analysis means 2; 24 is an input for commanding the required azimuth resolution;
25 is a constant calculator. It should be noted that the same or corresponding parts in the figures are indicated by the same reference numerals.

Claims (1)

[Claims] 1. In a radar device mounted on an aircraft or a flying object, a phase compensation means 1 for making multiple echo signals from a certain target in phase, and a range walk compensation means connected to the phase compensation means 1. and means 1 connected to the range walk compensation means and capable of determining a spectrum for the signal at each of the N divided synthetic aperture lengths, and connected to the means 1 capable of determining the spectrum, means capable of storing said N sets of spectra; and a phase corresponding to the delay time of each of said N divided synthetic aperture lengths, said means being connected to said means capable of storing said N sets of spectra. and a means 2 connected to the phase compensation means 2 and capable of determining a spectrum from the output obtained by the phase compensation means 2. A synthetic aperture radar characterized in that the spectrum of M points can be obtained for any externally given integer, for example, M (M≦N).