JPS58223770A - Synthetic aperture radar device - Google Patents

Abstract

PURPOSE:To set optional directivity for an antenna beam and to perform wide- area observation by providing a transmitter with a switching function and varying the amount of phase shifting of a variable phase shifter. CONSTITUTION:A transmit signal is radiated from an antenna 7 through the variable phase shifter 6 whose phase-shifting amount is varied optionally. A receive signal reflected on the ground is inputted to a receiver 8. An SAR control part is equipped with a transmitter controller 9 which switches on and off state of (n) units of transmitters and sends out control signals and command signals to the transmitters, and a phase shifter controller 10 which calculates the amount of phase shifting of each variable phase shifter by using a computer 11 according to the command signal to obtain an optional antenna beam direction. Then, a receive output signal is recorded at a recording part 13 through a digital signal processing part 12 and the recording data is transmitted to an SAR picture processor 14 on the ground.

Description

[Detailed description of the invention] The present invention relates to a six-synthetic aperture radar device.

A side-looking radar mounted on a flying object (platform) such as an aircraft emits radio waves to the ground on the side of the mobile platform, and by receiving and synthesizing the reflected waves while moving, it is possible to use an antenna with a relatively small aperture. Synthetic aperture radars that can effectively synthesize large aperture antennas are well known.

FIG. 1 is an operational perspective view showing the principle of operation for realizing a synthetic open-route radar using a side-looking radar mounted on a mobile platform.

A specific route preset according to the desired purpose at a speed V
Transmission pulses are emitted at fixed time intervals from a sideking radar antenna with a small aperture mounted on a mobile platform such as an aircraft moving at a point A located at an altitude of h above the ground. This transmitted pulse is radiated in a direction perpendicular to the traveling direction with a beam width β, and is received by the side-looking radar as a reflected wave from the area BCL)E on the ground.

This reflected wave is input intermittently while the moving platform is moving at a speed of ■, and at each point in time while observing the ground between a line 1.1' parallel to the direction of travel with a width of distance @ BC. Amplitude information and phase information are recorded as the received signal. For example, a point target P located at an azimuth angle y and a distance l from the mobile platform receives the transmission pulse irradiation at a point q on the travel line of the mobile platform.

The reflected wave from the point target P is received while the transmission pulse is being emitted, and the received signal includes distance information.

contains phase information corresponding to the constantly changing relative velocity,
By processing this received signal, a set of these point targets is output as image information. The transmission pulse usually uses a linear FM pulse that modulates the frequency of a 1'tFt wave at a constant rate of change in order to improve distance resolution. This linear FM is part of a pulse compression technique commonly used in synthetic aperture radars to improve range resolution.

This pulse compression technology increases the total peak value output of the transmitted pulse, but instead lengthens the pulse width and adds linear FM to this to widen the occupied bandwidth and obtain resolution equivalent to a short pulse.One image processing In range compression, signals are collected at one point via a distributed delay line or the like with opposite frequency vs. delay time characteristics and output as a sharp pulse.

While the mobile platform moves along a preset line of travel at a speed of V, the side-looking radar acquires information that the relative orientation changes one after another. radiate and receive reflected waves from the target. - After a short period of time, another pulse is transmitted at the next position, and in this way, the received signal containing the distance, relative velocity, or direction information acquired at each position one after another is made to correspond to the change in the phase amount included in one phase information. By combining the two antennas, it is possible to provide a function as a synthetic aperture radar that can effectively achieve the same effect as using an antenna with a long aperture.

In the case of synthetic aperture radar, the traveling direction (azimuth direction) of the flying object
The resolution, that is, the azimuth resolution δa is.

When the dimension in the antenna azimuth direction is fDa, it is expressed by the following equation.

In addition, the resolution in the direction perpendicular to the traveling direction of the flying object (distance direction), that is, the distance resolution δr, is calculated by the following formula, %, where the bandwidth of the radar signal is Δf and the angle of incidence is Da. Here, C is the speed of light. It is.

Traditionally, synthetic aperture radars are mounted on flying objects.

Since the Brehner array antenna with equal phase feeding was used, the beam direction was limited. Therefore, the data obtained with synthetic aperture radar is limited by the trajectory of the flying object and the direction of the antenna beam direction, so it cannot be used in the same direction. 9Synthetic aperture radar had the disadvantage that only the same resolution could be obtained. Furthermore, even if Noculus compression technology was used, the synthetic aperture radar required extremely large transmission power, making it difficult to design a power amplifier. .

The present invention has been made in order to eliminate these drawbacks, and aims to provide a synthetic aperture radar device that can realize any resolution in any beam direction and make the transmission power variable. In the present invention, there is a transmitter including one power amplifier, one circulator, and one variable phase shifter for each antenna element of the play antenna. The transmission power of the transmitter is controlled by a transmitter control device having an on/off switching function, and the amount of phase shift of the variable phase shifter is set by the phase shifter control device.

Furthermore, the beam pointing direction can be arbitrarily set and the transmission power can also be changed by commands.

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 2 shows an example in which an aircraft is used.

The present invention can be roughly divided into two parts: an aircraft mounting part and a ground part.The navigation aircraft mounting part is composed of a transmitting part, an antenna part, a receiving part, a control part, a signal processing part, and a data recorder part. .

Transmitter i, 8Ai (synchronizer for synchronizing the system, 1
．． Dryno (-device 2. to improve the level of the transmitted signal)
3. A power distribution device that distributes power to the transmitter; 4. A transmitter consisting of a power amplifier, etc.; It is composed of nine circulators 5 that switch between transmitting signals and receiving signals. The transmitted signal is
The light is radiated from the antenna element 7 via a variable phase shifter 6 that can arbitrarily change the amount of phase shift. SAD, antenna part US
It consists of an array antenna with n antenna elements and n variable phase shifters. The received signal reflected and returned from the ground is input to the receiver 8 through the antenna section. Switching function for on/off status of n transmitters on the SAW control side and control signals for the transmitter.

A transmitter control device 9 that outputs a command signal, and a phase shifter control device that uses a computer 11 to calculate the amount of phase shift of each variable phase shifter so as to obtain an arbitrary antenna beam pointing direction according to commands from the transmitter control device. Consists of 10.

The output signal of the receiver is processed by the signal processing unit 12.)
The data is converted into data and recorded by a recording unit 13 such as a data recorder. The data stored in the recording unit 13 is processed by the SA processing image processing device 14 located on the ground.

According to the present invention, an arbitrary antenna beam pointing direction can be set by providing a transmitter with a switching function and changing the amount of phase shift of a variable phase shifter. It is possible to reproduce images of various 5A) l data with different incident angles, making it possible to observe over a wide range.In addition, since the power amplifier inside the transmitter is divided into n pieces, for example, a 400W power amplifier Using 16 pieces,
This is equivalent to a 5.4KW power amplifier, which has the effect of simplifying the design of the transmitter.

[Brief explanation of the drawing]

FIG. 1 is an operational perspective view showing the principle of operation of a synthetic aperture radar, and FIG. 2 is a block diagram showing an embodiment of the present invention. 1...Synchronization device, 2...Driver device, 3...
Power distribution device, 4...8A)? , transmitter, 5... circulator, 6... variable phase shifter, 7... antenna radiation element, 8... receiver, 9... transmitter control device,
10... Phase shifter control device, 11... 1 calculator, 12...
...Signal processing unit, 13...Recording unit, 14...SAR
A image processing device. Figure 1 ゛υ゛

Claims (1)

[Claims] A transmitter, a circuit resistor, and a variable phase shifter are mounted on a flying object in correspondence with each antenna element of the array antenna, and each of the transmitters is turned on and off, and each of the variable phase shifters is controlled. By controlling the amount of phase shift. 1. A synthetic aperture radar device comprising an adjustment means for arbitrarily adjusting the beam direction of an antenna.