JPS6024478A - Synthetic-aperture radar - Google Patents

Abstract

PURPOSE:To make it possible to obtain arbitrary azimuth resolving power and zooming effect, by dividing a synthetic aperture length into small sections, and calculating a spectrum to each small section while combining a required number of spectra. CONSTITUTION:The movement of a hinge pin is performed so as to bring the received echo from a same object to the same range pin by a range walk compensating apparatus 19. The output of the apparatus 19 is applied to a spectrum analytical means 20 at every same range pin and a spectrum to each of small sections provided by dividing a synthetic aperture length is at first calculated. The spectrum calculated by the analytical means 20 is stored in a memory apparatus 21. The spectra are multiplied on the basis of the operation output due to a constant operator by a phase compensating apparatus 22 and the spectrum of an M-point is calculated. The output of a spectrum analytical means 23 is displayed by a display apparatus and an image having zooming effect to the same object corresponding to a desired azimuth resolving power 24 applied from the outside can be obtained.

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 coherent signal generator (1)
The IP output from
e-quency) band aW signal pulse expansion device (2
) and becomes a chirb signal (chirb bandwidth = B) whose frequency changes over time.

At this time, it is assumed that the chirb signal is generated in synchronization with the trigger signal from the trigger signal generator α field. The output of the pulse stretcher 1 (2) is converted to an RF (Radio Frequency) signal from a stabilized local oscillator (4) by a mixer (3).
After being mixed with a high-power amplifier (5) and increasing the output to a high output signal, the received signal passes through a transmitter/receiver switcher (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 the OR? It is mixed with the signal and becomes the signal of the engineering F band.

The IF band signal is amplified by an IP amplifier (8) and then compressed by a pulse compression device (9) to #Y1/E in the range direction. The above compressed signal is passed through a phase detector (10.
In a), phase detection is performed using the signal from the coherent signal generator 0). At the same time, the signal from the coherent signal generator (1) passes through a 90° phase shifter αυ to a phase detector (10・b).
is input. The compressed signal inputted to the phase detector (10.b) is phase-detected by the output from the 90° phase shifter. Phase detector (10・a) and (10・b
) outputs are gate circuits (12・a) and (12・b), respectively.
These outputs (16
・a) and (1t5・b) are input to the azimuth compression device member. 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 obtained in this way
n'+ is input to the display device a4 to obtain images with high resolution in both the range direction and the azimuth direction. If you try to observe the image obtained at this time with even higher azimuth resolution, you will emit radio waves to the same target again and use a longer synthetic aperture time than the previous time to reach the target f! : It is necessary to observe.

The angle between the transmission wavelength λ, the moving speed of the radar device, the direction of the speed V, and the direction connecting the radar device to the eye, that is, the squint angle, is θ2.When the synthetic aperture time is T, the azimuth resolution δθ is generally approximately λ θ− 2VT Si. It is given by θ (1). If the pulse repetition period of the pulse stretcher (2) is τ, and the number of points of the spectrum analysis means, such as FFT, used in the azimuth compression device 03 is N, then the synthetic aperture time T is given by T=Nτ (2). (11 is δθ=+3) 2VNT Sinθ. Therefore, if the transmission wavelength λ, moving speed V, squint angle θ, and pulse repetition period τ are constant, and the number N of FFT points is fixed, the γ-dimensional resolution δθ is constant. Therefore, it was not possible to observe the same target with variable azimuth resolution.

In order to solve these drawbacks, this invention has a zooming function by dividing the synthetic aperture length and synthesizing the results of signal processing for each divided synthetic aperture time according to the required azimuth resolution. The drawings will be explained in detail below.

FIG. 2 shows an embodiment of the present invention, in which the outputs (IS) of the gate circuits (12a) and (12b) shown in FIG.
&), (16b) is compensated by the phase compensation device 1 (In) by θx p (j-7-) for the distance 4πr Mlr from the radar device to the target. (Note: Output (16a)
, (16b) are written as real signals, but to simplify the description, they will be treated as complex signals from now on, but in particular, the membrane properties will not be lost). Here, λ is the transmission wavelength, j is t, and the above phase compensation is performed for each transmission pulse. The edge of αB is determined by the range walk compensation system ff1 (II), which moves the range bin so that the received echo from the same target comes to the same range bin regardless of the movement of the radar device.The output of αB is subjected to spectral analysis for each range bin. First, by means 1 (for example, FFT), a spectrum is obtained for each subsection into which the synthetic aperture length is divided.For example, as shown in FIG. The means 101 calculates N sets of spectra. Alternatively, as shown in FIG. The spectrum analysis means 1 calculates 2N-1 sets of spectra for the echoes.

Next, in Figure 3, there are N groups, and in Figure 4, (2N-
1) The spectrum calculated by the set of spectrum analysis means 1 is stored in the memory device Qυ.

- 10,000, the required azimuth resolution δR/ll is input into the constant calculator (c) in advance, and for Figure 3, the M given by is for Figure 4 is the constant calculator (c). Assume that it is calculated by Here [] is a Gauss symbol. This IA is input to the memory device c2I) as the output of the constant calculator (c), and M sets of spectra are taken out from the memory device Qchin. 1- for the same frequency components of these spectra
In the case of Fig. 3, eX p (-j 2πf'n
).

■ In the case of Figure 4, eXI) (-j2πf 2 , n
) is passed through the constant calculator (
The calculation output M obtained by c) is also multiplied by . Here n=1.2. ...9M. The spectrum analysis means 2 (
For example, in FFT)'fi, a spectrum of M points can be seen in the calculation output M of the constant calculation unit (c).

The output of the spectrum analysis means 2 (c) becomes Qη and the first
As described above, it is possible to obtain an image with a zooming effect on the same target, despite the required azimuth resolution (2) given from the outside, which is displayed on the display device shown in the figure. In aperture radar, an arbitrary azimuth resolution can be obtained by dividing the synthetic aperture length into small sections, taking a spectrum for each small section, and combining a required number of these spectra, which has a zooming effect.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of a conventional synthetic aperture radar, Fig. 2 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. It is. In the figure (1) is a coherent signal generator,
(2) is a pulse stretcher, (3) is a mixer, (4) is a stabilizing local oscillator, (5) is a high output amplifier, (6) is a transmitter/receiver switch, (7) is an antenna, and (8) is an IP Amplifier, (9
) is a pulse compression device, and the other is a phase detector. aυ is a 90' phase shifter, Q winter is a gate circuit, 0th floor is an azimuth compression device, 04 is a display device, and α is a trigger signal generator. σe is the output of the gate circuit 03, aη is the output of the azimuth compression device 01, and 08 is the output of the phase compensator t1. On is range walk compensation device, (E) is spectrum analysis means 1,0υ
(2) is a memory device, and (2) is a phase compensation device 2. (c) is spectrum analysis means 2. Q4 is an input that commands the required azimuthal resolution, c! ! 9 is a constant arithmetic unit. In addition, the same or corresponding parts in Figure 1 are indicated by the same reference numerals.

Claims (1)

[Claims] In a radar device mounted on an aircraft or a flying object, a phase compensation means 1 for making a plurality of echo signals from a certain target have the same phase, and a range walk compensation connected to the phase compensation means 1. means 1 connected to the range walk compensation means and capable of determining a spectrum for a signal at each of the N divided synthetic aperture lengths; and means 1 capable of determining the spectrum.
means connected to and capable of storing the N sets of spectra; and means connected to the means capable of storing the N sets of spectra to delay each of the N divided synthetic aperture lengths. A phase compensating means 2 capable of compensating a phase corresponding to time, and a means 2 connected to the phase compensating means 2 and capable of calculating a spectrum with respect to the output obtained by the phase compensating means 2. A synthetic aperture radar comprising means 2 for determining a spectrum, in which the f% sign is that the spectrum at M points can be determined for any externally given integer, for example, M (M≦N).