JPS61241683A - Synthetic aperture radar equipment - Google Patents

Abstract

PURPOSE:To enable a zooming function by making the time of integration of an integrating device, for instance, the number of points of Fourier transform variable, and making the time length of reference function generated in a reference function computer variable. CONSTITUTION:Variable reference functions are generated by a reference function computer 8 by indicating required azimuth resolution from the outside. By making integration by integrating device 11.1-11.n at the integrating time corresponding to various time lengths of the reference function, azimuth angle resolution is made variable, and zooming becomes possible.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a synthetic aperture radar device that is mounted on an aircraft or a flying object and can map the ground.

[Conventional technology]

Figure 2 shows, for example, an IEEI transformer.

Aerospace and Electronic Systems Ainis 7.11 Volume N13. P338-348
, May 1975 (IEEE!rrans, Ae
roapace, pndElectronic S
yatema, vQl, AES-11, t4[L3,
338-348, May, 1975). In the figure, 1 is a stable oscillator, 2 is a transmitter, 3 is a transmitter/receiver switch, and 4 is a Antenna, 5 is an antenna servo mechanism,
6 is a receiver, 7 is an aircraft motion sensor, 8 is a reference function calculator, 9 is a clutter tracker, 10 is a mixer, 11
is an integrator, and 12 is an indicator.

Next, the operation will be explained. The radio frequency band generated by the stable oscillator 1, that is, RF (Radio Freque
Continuous wave signals in the CW (Continued Cy) band
The US Wave) signal is pulsed and amplified by a transmitter 2 and then passed through a circulator 3 to an antenna 4.
Emitted towards multiple targets. The signal reflected at the target is sent back to antenna 4. After passing through the circulator 3, the signal is extracted at the receiver 6 as a beat signal, that is, a Doppler signal, with the output of the stable oscillator 1. Also, the movement of the aircraft obtained by the aircraft motion sensor 7.

Information regarding the oscillation is sequentially input to the reference function calculator 8, and based on this information, a reference function identical to the beat signal that would be obtained for the reference point in the map area is generated in the reference function calculator 8. and input to mixer 10. On the other hand, the reference function calculator 8 outputs a control signal for stabilizing the antenna beam according to the output of the aircraft motion sensor 7, and drives the antenna 4 by the antenna servo mechanism 5. mixer 10
Then, the reference function that is the output of the reference function calculator 8 and the beat signal that is the output of the receiver 6 are mixed, and the integrator 1
1, coherent integration, such as Fourier transformation, is performed for each range gate. At this time, the signal in the short time domain is obtained as a spectrum in the frequency domain by Fourier transform, but
Since this frequency corresponds to the azimuth direction of the map area, a high-resolution image can be obtained in the azimuth direction. Note that a part of the output of the mixer 10 is input to the clutter tracker 9, and fed back to the reference function calculator 8 so that the center frequency of clutter becomes zero.

[Problem that the invention seeks to solve]

The conventional synthetic aperture radar device is configured as described above, and the integrator 11 performs a Fourier transform, for example, a fast Fourier transform (FFT).
The number of points in the Transform (Transform) is fixed, and the time length of the reference function generated by the reference function calculator 8 is also fixed, so the resolution in the azimuth direction is constant (), and the zoom function has variable resolution. There were problems such as not having

The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to obtain a synthetic aperture radar device capable of a zooming function.

[Means for solving problems]

The synthetic aperture radar device according to the present invention is one in which the integration time of the integrating device, for example, the number of FFT points, is made variable, and the time length of the reference function generated by the reference function calculator is made variable.

[Effect]

In the synthetic aperture radar device of the present invention, when a required azimuth resolution is specified from the outside, a reference function calculator generates a variable reference function, and an integrator performs integration at an integration time corresponding to various time lengths of the reference function. In particular, the azimuth angular resolution is made variable and zooming is possible.

〔Example〕

Hereinafter, one embodiment of the present invention will be described with reference to the drawings. In FIG. 1, the same or corresponding parts as in FIG. 2 described above are designated by the same reference numerals. 11・1.11・2
. . . 11.n are a plurality of integrators having different integration times, and these integrators constitute the integrating device 11. The integrator 11.1 has an integration time T, the integrator 11.2 has an integration time T, and the integrator 11.n has an integration time <T.
n coherent integrator, for example F F T (
Fast Fouriei Transform) processor.

Therefore, the number of FFT points is proportional to the integration time when the pulse repetition frequency of the radar is constant.

13 is a resolution switch, and A is an azimuth angle resolution instructed from the outside.

In such a synthetic aperture radar device, assuming that a predetermined azimuth angular resolution Δθ1 is specified from the outside, the resolution switch 13 calculates an integration time T1 given by: Here, λ is the transmission wavelength of the radar, V is the speed of the aircraft or flying object, and θ is the angle between the traveling direction of the aircraft or flying object and the reference point in the map area. When the integration time T1 obtained by equation (1) is input from the resolution switch 13 to the reference function calculator 8, the reference function calculator 8 generates a reference function according to the integration time T1.

Furthermore, when the integration time is T1, the integrator 11.1 whose integration time is TI is selected by the resolution switch 13, the output of the mixer 10 is input to the integrator 11.1, and the integrator 11.1 is inputted to the integrator 11.1.
1 is input to the indicator 12. Other integration time Tt
, T, . . . The same applies to Tn. In this way, by inputting the required azimuth angular resolution a from the outside, an arbitrary azimuth angular resolution can be obtained by selecting an integrator with an integration time corresponding to the input, and zooming becomes possible.

In the above embodiment, the integration device is composed of a plurality of integrators with different integration times, but if this integration device is created using software, there is no need to line up a plurality of integrators with different integration times.

〔Effect of the invention〕

As mentioned above, this F! According to A, when the required azimuth resolution is specified externally, a reference function calculator generates a variable reference function, and the integrator is configured to perform integration at integration times corresponding to various time lengths of the reference function. , the azimuthal angular resolution can be made variable, thus allowing zooming.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a synthetic aperture radar device according to an embodiment of the present invention, and FIG. 2 is a block diagram of a conventional synthetic aperture radar device. In the figure, 1 is a stable oscillator, 2 is a transmitter, 3 is a circulator, 4 is an antenna, 5 is an antenna servo mechanism, 6
is a receiver, 7 is an aircraft motion sensor, 8 is a reference function calculator, 9 is a clutter tracker, 10 is a mixer, 11 is an integrator, 11-1.11Φ2...11・n is an integral with different integration times 12 is an indicator, 13 is a resolution switch, and A is an externally given required angular resolution instruction. In addition, in the figures, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] In a synthetic aperture radar device mounted on an aircraft or flying object, a stable oscillator that outputs a continuous wave signal, and a transmitter that pulses and amplifies the continuous signal and transmits it from an antenna to a target via a circulator. and a receiver that receives an echo signal reflected by the target via the antenna and the circulator to extract a beat signal from the continuous wave signal, and obtains information regarding the movement and oscillation of the aircraft or flying object. An aircraft motion sensor, a resolution switch that calculates an integration time according to a required azimuth resolution specified from the outside, and information provided from the aircraft motion sensor that will be obtained for a reference point within the map area. a reference function calculator that generates the same reference function as the beat signal and varies the time length of the reference function according to the integral time signal from the resolution switch; and the beat signal from the receiver and the reference function calculator. a mixer that mixes the reference function from the above, and a variable integration time type that selects the integration time given from the resolution switch and obtains the output signal of the mixer by coherent integration T2, and obtains the signal in the time domain as a spectrum in the frequency domain. A synthetic aperture radar device comprising: an integrating device; and an indicator that indicates an output of the integrating device.