JPH0332934B2 - - Google Patents

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a synthetic aperture radar device.

[Conventional technology]

By emitting radio waves from the Seideltzking radar mounted on the satellite to the ground on the side of the mobile platform, and receiving and synthesizing the reflected waves while moving, it is possible to effectively transmit radio waves using an antenna with a relatively small aperture. Synthetic aperture radars that can synthesize large aperture antennas are well known.

FIG. 2 is an operational perspective view showing the principle of operation for realizing a synthetic aperture radar using a side-lucking radar mounted on a mobile platform.

A specific route set in advance according to the desired purpose,
Alternatively, a mobile platform such as an artificial satellite or an aircraft that moves in an orbit L at a speed v transmits a transmission pulse at a fixed time interval from an on-board small-aperture Siderukking radar antenna at a point A located at an altitude h above the ground. radiate. This transmitted pulse is radiated in a direction perpendicular to the traveling trajectory L with a broadening beam width β, and is received by the Siderukking radar as a reflected wave from the area BCDE on the ground.

This reflected wave is transmitted by the moving platform at a speed v
are input one after another while moving, and the distance on the ground is
Amplitude information and phase information are recorded as a received signal at each point in time while observing between lines l and l' parallel to the traveling trajectory L with a width of BC. For example, a point target P located at a direction angle .phi. and a distance R from the moving platform begins receiving the transmitted pulses at a point F on the traveling trajectory L of the moving platform and ends at a point G.

The reflected wave from the point target P is received while the transmission pulse is being emitted, and the received signal contains distance information as well as phase information corresponding to the constantly changing relative velocity, and 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 RF radio waves at a constant rate of change to improve distance resolution. This linear
FM is part of a pulse compression technique commonly utilized in synthetic aperture radars to improve range resolution.This pulse compression technique reduces the pulse width instead of increasing the peak power of the transmitted pulse. By adding linear FM to this pulse, the occupied bandwidth is widened and the resolution equivalent to that of a short pulse is obtained.In range compression for image processing, a distributed delay line with opposite frequency vs. delay time characteristics is used. The signal is collected at one point and output as a sharp pulse.

While the moving platform is moving along a preset trajectory L at a speed v, the Siderutsuking radar acquires information about the relative orientation that changes one after another. It emits a transmission pulse and receives the reflected wave from the target. After a certain period of time, another pulse is transmitted at the next position, and the received signal containing the distance, relative velocity, or direction information acquired at each position one after another in this way is made to correspond to the change in the amount of phase included in the 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 diameter.

In the case of synthetic aperture radar, the resolution in the traveling direction (azimuthal direction) of the flying object, that is, the azimuth resolution δ _a , is
If the dimension in the antenna azimuth direction is D _a , it is expressed by the following equation.

δ _a = D _a /2 In addition, the resolution in the direction perpendicular to the traveling direction of the projectile (distance direction), that is, the distance resolution δ _r is calculated by the following formula, where Δf is the bandwidth of the radar signal and φ is the incident angle. It is indicated by.

δ _r =c/2・1/Δf・cosecφ Here, c is the speed of light.

[Problem that the invention seeks to solve]

Conventionally, in a synthetic aperture radar device, as shown in FIG. 3, a received signal obtained by a receiving section 100 is transferred to two switching sections 200 and 500, and two analog switches with the same configuration provided to ensure reliability. Transmission parts 300 and 400
The analog signal is then transmitted to the ground via an antenna 600, where it is converted into digital data and image processed. For this reason, there was a drawback that the received signal deteriorated due to the influence of noise etc. on the analog signal transmission path. Furthermore, since there is no high-density analog data recording tape, data in invisible areas cannot be obtained. Furthermore, in terms of reliability, conventional systems have had redundant systems (two analog transmission systems) of the same circuit, making them vulnerable to potential problems. That is, if a problem were to occur after installation, there was a possibility that both systems would become unusable and the synthetic aperture radar system would become unusable.

The purpose of the present invention is to eliminate the above-mentioned conventional drawbacks, prevent the received signal from deteriorating due to the effects on the transmission path when transmitting the received signal to the ground station, enable observation in invisible areas, and improve reliability. An object of the present invention is to provide an improved synthetic aperture radar device.

[Means for solving problems]

In the synthetic aperture radar device according to the present invention,
The received signal is input to a switching section, and the configuration is such that one of the following three methods can be selected using a control signal.

(1) Input the received signal only to the analog transmission section and transmit the analog signal to the ground station.

(2) Input the received signal only to the phase detection section, convert it to I and Q video signals in the phase detection section, convert it to a digital signal in the signal processing section, record the data, and send it from the digital transmission section to the ground station. Send digital data.

(3) Input the received signal to both the analog transmission section and the phase detection section, and transmit both the analog signal and digital signal to the ground station.

With this configuration, it is possible to reduce signal deterioration on the transmission path, make it possible to observe invisible areas using recording means, and improve reliability by having different redundant systems. .

〔Example〕

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

As shown in FIG. 1, the synthetic aperture radar device according to the present invention is composed of a switching section 1, an analog transmission section 2, a signal processing section 4 of a phase detection section 3, and a digital transmission section 5. It is designed to be driven by a control signal from a selection section (not shown).

The switching unit 1 includes a duplexer 11 and switches 12 and 13.
The switch 12,
13 to send the received signal to the analog transmission section 2 or the phase detection section 3. switch 12
When the switch 13 is set to ON and OFF, the received signal is input to the analog transmission unit 2, where it is converted into a transmission signal to the ground station, and then transmitted to the ground station via the antenna. switch 1
2 is set to OFF and switch 13 is set to ON, the received signal is input to the phase detection section 3, and the π/
A two-phase shifter 6 mixes the received LO signal with a phase difference of π/2, and converts it into I and Q video signals. The I and Q video signals are inputted to the signal processing section 4, and A/D converted by A/D converters 41 and 42 using an arbitrary number of bits. The I and Q data thus converted to digital data are recorded on a high-density magnetic tape 43 in the signal processing section 4, and are digitalized at any time when the artificial satellite carrying the synthetic aperture radar device is visible from the ground according to a control signal. The signal is input to the transmission unit 5 and transmitted to the ground station via the antenna. This allows observation of invisible areas.

Further, when both switches 12 and 13 of the switching section 1 are turned on, both analog signals and digital signals can be transmitted via the analog transmission section 2 and the digital transmission section 5.

Note that the control signals for the switches 12 and 13 of the switching section 1 are sent out from the selection section.

〔Effect of the invention〕

As explained above, the present invention enables both analog signal transmission and digital signal transmission by switching the received signal with a switching unit, which reduces signal deterioration on the transmission path and facilitates observation of invisible areas. This has the effect of increasing reliability by providing a redundant system of different circuits.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing an embodiment of the present invention, Fig. 2 is a diagram for explaining the principle of a general synthetic aperture radar, and Fig. 3 is a block diagram of a conventional synthetic aperture radar. be. 1...Switching section, 2...Analog transmission section, 3...
Phase detection section, 4... Signal processing section, 5... Digital transmission section, 6... π/2 phase shifter, 11... Branching filter, 12, 13... Switch, 41, 42...
A/D converter, 43...high-density magnetic tape.

Claims (1)

[Claims] 1 In a synthetic aperture radar device mounted on a satellite, there is a switching unit that switches connection circuits using control signals, an analog transmission unit that transmits the received analog signal to the ground, and a phase switch that converts the received analog signal into I and Q video signals. It is equipped with a detection section, a signal processing section that converts the I and Q video signals into digital signals with an arbitrary number of bits and records them on high-density magnetic tape, and a digital transmission section that transmits the digital signals to the ground. A synthetic aperture radar comprising a selection unit that selects one of three methods using a control signal: when transmitting only a signal, when transmitting only a digital signal, when transmitting both an analog signal and a digital signal. Device.