JPH01260387A - Synthetic aperture radar - Google Patents

Abstract

PURPOSE:To enable normal operation even in an invisible area or regardless of a change in height larger than expected, by detecting a reception timing at each action to generate a transmission pulse repetition frequency (PRF) corresponding to a change in height of a platform. CONSTITUTION:An synthetic aperture radar is provided with a reception timing detector 1, a PRF control section 2 and a transmitting section 3. A reception timing signal outputted from the reception timing detecting section 1 is inputted into a reception timing discriminator section 21 of the PRF control section 2 to be compared with a reception timing corresponding to a height at which a PRF must be changed. A PRF generating section 22 is controlled by the output thereof to output a transmission trigger corresponding to the height of the platform. A transmission pulse is outputted from a transmitter 3 by the transmission trigger.

Description

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

[Conventional technology]

Mobile vehicles using flying objects such as artificial satellites and aircraft.

emit radio waves from the toform to the side in the direction of travel,
Synthetic aperture radar, which obtains two-dimensional data for reconstructing images on the ground, has become well known in recent years.

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

A mobile platform of an aircraft moving at a speed V along a specific route or trajectory predetermined by a desired purpose is ho? At point A located at i7b degrees, a transmission pulse is emitted at fixed time intervals from the mounted side-looking radar antenna with a small aperture.

This transmission pulse is radiated in a direction perpendicular to the traveling direction with a widening beam width β, becomes a reflected wave from the area BCDE on the ground, and is received by the VEIDLE and KING radars.

This reflected wave is intermittently human-powered while the mobile platform is moving at a speed v, and is used as a received signal at each point in time while observing the ground between al and l' parallel to the direction of travel with a width of distance @SC. Shake/vomit information and phase information are recorded.

For example, the direction angle φ from the moving platform.

A point target P located at a distance L ends receiving the irradiation of the transmitted pulse at a point G on the travel line of the moving platform.

Reflected waves from point targets P are received while emitting transmit pulses, and the received signals contain distance information as well as phase information corresponding to constantly changing relative velocities.By processing this received signal, these point targets are output the set as image information.

The transmitted pulse is usually 1-LF to improve distance resolution.
It uses a linear FM pulse that modulates the frequency of radio waves at a constant rate of change. This linear FM is part of the pulse compression technology commonly used in synthetic aperture radars to improve distance resolution.This pulse compression technology increases the peak 1 direct output of the transmitted pulse, but The pulse width is changed and linearly applied to this Mf: In addition, the occupied bandwidth is widened to obtain a resolution equivalent to a short pulse.In image processing range compression, a distributed delay whose frequency vs. delay time characteristic is reversed is used. The signal is collected at one point via the wire and output as a sharp pulse.

The moving platform moves at a speed V along a preset line of advance, and receives information ft whose relative direction changes one after another.
``F Idle Looking Radar acquires the target, but at this time, the Voidle and King Radar emit a transmit pulse at a certain position in the direction of travel and receive the reflected wave from the target.The next transmit pulse is transmitted by the synthetic aperture radar system. The condition is the following (
Equation 1) and (2) as a condition that the transmitted pulse does not overlap with the received signal.

A transmission pulse is sent out using a PRF that satisfies equation (3).

PRFmin (PR, F (P 几Fmax...
. . . tllK: Constant V: Satellite speed θ: Antenna beam width in the direction of satellite travel λ: Wavelength Also, Rf, n is the distance from the platform to the target, as shown in FIG.

Here, n: Integer τ: Transmission pulse width C: The received signal containing distance and relative velocity, that is, azimuth information acquired at each position one after another, such as at or above the speed of light, is made to correspond to changes in the phase amount included in the phase information. By combining the antennas, the same effect as using an antenna with a long aperture can be obtained.

[Problem to be solved by the invention]

In general, in synthetic aperture radar devices, the above-mentioned (1) to (3)
), one PRF, e.g., P1-LF shown in Figure 4, cannot accommodate continuous altitude changes, but can only accommodate band 1, and therefore usually does not respond to altitude changes. For this purpose, we have prepared multiple PBFs.

In the conventional synthetic radar device, when the altitude of the platform changes more than can be covered by one i'RF, the 6i'kLF is changed by a command from the ground station. Moreover, when the platform is in an invisible area where it cannot be seen from the ground station, the ground station estimates the trajectory and sends the command to the platform side, and the command content becomes effective after a certain period of time using a delay command.F)PkL
I was changing F.

Therefore, if commands cannot be sent from the ground for some reason, or if the altitude changes more than expected, (1) to (
There is a drawback that the formula 3) cannot be satisfied, and the system cannot be operated as a normal synthetic aperture radar device.

[Failure to solve the problem]

The device of the present invention, in a synthetic aperture radar device mounted on a flying object such as an artificial satellite or an aircraft, includes a receiver 1Δ timing detection section that detects the reception start time of a received signal, and a receiver 1Δ timing detector that detects a reception start time of a received signal, and a transmitter that transmits signals in accordance with the reception typing. f' controlling the pulse repetition frequency to be variable in response to altitude fluctuations of the flying object;
f'l(,
F) Transmission 1 that outputs a transmission pulse signal using a trigger signal
g section.

〔Example〕

Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a 7' lock diagram of one embodiment of the present invention.

The embodiment shown in FIG. 1 is a reception timing detection section 1. P-F control section 2. It is configured to include a transmitter 3.

The reception timing detection section 1 includes an envelope detection section 11. which detects the envelope of the received signal. A counter unit 12 that outputs the time from the transmission time to the rise time of the output of the envelope detection unit 11
It is composed of:

The reception typing signal (To) outputted from the reception timing detection unit 1 is manually inputted to the reception timing determination unit 21 of the PRF control unit 2, and is inputted to the reception timing determination unit 21 of the PRF control unit 2, and is inputted to a preset T1°T, , T, .
..., Tn, that is, 1) To The transmission trigger is output in accordance with the size of the platform, that is, the altitude of the platform. The transmission trigger is manually applied to the transmitter 3 and outputs a transmission pulse corresponding to the magnitude of T.

〔Effect of the invention〕

As explained above, the present invention detects the reception timing for each reception and performs PR corresponding to changes in the altitude of the platform.
By generating F, there is an effect that the synthetic aperture radar can automatically operate normally even in the invisible area or when the altitude changes more than expected without using any other means.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing an embodiment of the present invention, Fig. 2 is an explanatory diagram of the principle of synthetic aperture radar, and Fig. 3 is a graph of the synthetic aperture radar, from Form 7J to the target observation width. An explanatory diagram of distance, Fig. 4 An explanatory diagram showing the relationship between Fip F and altitude.
F control unit, 3...transmission unit, 11...envelope detection unit, 12...counter unit, 21...
・Reception timing determination unit, 22... PRF generation unit. Agent Patent Attorney Uchihara Sweat, 7 to 7 ohm Figure 3

Claims (1)

[Claims] A synthetic aperture radar device mounted on a flying object such as an artificial satellite or an aircraft includes a reception timing detection section that detects the reception start time of a reception signal, and a transmission pulse repetition frequency (Pulse Repeat frequency) corresponding to the reception timing.
ion Frequency (hereinafter abbreviated as PRF)
a PRF control unit that controls P so as to be variable in response to altitude fluctuations of the flying object;
A synthetic aperture radar device comprising: a transmitter that outputs a transmission pulse signal in response to an RF trigger signal.