JPH02275381A - Radar apparatus airborne - Google Patents

Abstract

PURPOSE:To improve a detection capacity aimed to coexist with a clutter by varying a transmission pulse width on the basis of an airplane's own height signal and by obtaining a prescribed S/C ratio at all times. CONSTITUTION:In an exciter, a pulse width and a pulse repetition frequency are varied in proportion to an airplane's own height signal 13. On the occasion, a ratio between an echo and a reception power of a clutter, i.e. S/C, turns to be a prescribed value by varying the pulse width corresponding to a change in the height. On the other side, the alteration of the pulse width necessitates an alteration of a band width of a receiver, and this alteration causes a change in the noise of the receiver and further deterioration in an S/N ratio and lowering of reception sensitivity. In order to prevent this lowering, the pulse repetition frequency is varied to change a pulse integration frequency in a signal processing system, and thereby the S/N ratio can be improved by an integration effect.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] This invention relates to a search and tracking radar device mounted on an aircraft.

[Conventional technology]

Figure 2 is a block diagram showing part of a conventional pulse radar device. In Figure 1, (1) is a transmitter, (2) is an exciter, (3) is an antenna, and (4) is a receiver. , tilt is the radar controller, and συ is the radar display.

Conventionally, the pulse width, settings in the receiver band, and repetition frequency are either fixed or determined by a human operator while viewing the image of the radar reception video displayed on a 0 display device using a switching signal from the controller at 0. (13) The pulse width and PRF generation circuit in the exciter (2) and the filter circuit that determines the receiving bandwidth of the receiver (4) were changed by switching.

[The problem that the idea attempts to solve]

A radar mounted on an aircraft not only receives reflected waves from targets on the ground or on the sea, but also receives reflections (clutter) from the ground or sea surface. The received clutter power depends on the altitude of the own aircraft and the width of the transmitted pulse.

Since it is related to the beam width of the antenna and the number of reflections on the ground or sea surface, it is necessary to change the transmission pulse width and pulse repetition frequency to improve the received signal to clutter ratio depending on the aircraft situation (altitude, etc.) However, in the past, this was done by leaving it fixed or switching it manually.

This device automatically performs the manual changes described above using the aircraft's altitude signal, and adjusts the pulse width, pulse repetition frequency, and reception so that the probability of detection is always optimal in order to facilitate target detection. It is intended to be a radar device that changes the bandwidth and the number of pulse integrals.

[Means to solve the problem]

The airborne radar device according to this invention uses the altitude signal of the aircraft to determine the pulse width determined from the optimum signal-to-clutter ratio at that altitude and the detectable range of the target, and changes the pulse width by controlling the excitation circuit. At the same time, the filter that determines the receiver band of the receiver is controlled to change the band, and the pulse repetition frequency is also changed in order to comply with the duty ratio limit of the transmitting tube.

[Effect]

This idea utilizes the characteristic that the ratio (S/C ratio) of the received power of the target and clutter from the ground (sea surface) of the aircraft-mounted radar is inversely proportional to the altitude of the aircraft and proportional to the pulse width. An example of an increase in altitude will be explained. By narrowing the pulse width, it is possible to prevent the S/C ratio from deteriorating as the altitude increases.

On the other hand, by narrowing the pulse width, it is necessary to widen the receiving bandwidth of the receiver in order to prevent the passing loss of the received signal, and at the same time widen the receiver's bandwidth. Expansion in the receiver band increases the power of the receiver noise and increases the signal-to-signal noise power ratio (
However, if the duty ratio of the transmitting tube is kept constant, it is possible to increase the pulse repetition frequency by the amount by narrowing the pulse width, and the pulse repetition frequency is changed (increased). Changing the pulse repetition frequency can increase the number of integrations of the received signal because it increases the number of pulse hits from the target.

The S/N ratio can be improved by the integral effect, and it is possible to compensate for the deterioration in S/'N caused by the increase in the receiver band.

From the above, while minimizing the deterioration of the S/N ratio.

By changing the pulse width according to the altitude of the aircraft, the S/C ratio can be improved, and the ability to detect targets coexisting with clutter can be improved.

〔Example〕

FIG. 1 is a conceptual configuration diagram of a radar device showing an embodiment of this invention.

In the figure, (1) is a transmitter, (2) is an exciter, (3) is an antenna, (4) is a receiver, (5) is a radar signal processor,
(6) is an altimeter that measures the aircraft's own altitude.

The exciter (2) includes a high-frequency signal generation circuit (7) for transmission, a modulator (8) for pulse modulation, and a pulse generation circuit (9) (determining the pulse width and pulse repetition frequency). There is.

In FIG. 1, the own aircraft altitude signal a3 from the altimeter (6) is input to the exciter (2), and in the exciter, the own aircraft altitude signal a3 is input in proportion to the own aircraft altitude signal 0 to the pulse generating circuit (9).

The pulse width and pulse repetition frequency are varied.

Simultaneously, the aircraft altitude signal a3 is also input to the receiver of K(4), and the filter width that determines the reception band width is changed. Similarly, the radar signal processor (5) receives the aircraft altitude signal α and changes the number of pulse integrations.

Received power P8 from target in general pulse radar
And the clutter reception power Pa of the airborne radar device from the ground (or from the sea surface) is expressed by the first-order equations (11 and (2)).

Here, p=transmission power, a=antenna gain, λ=wavelength, R
= distance to target, σT = effective reflection area of target, C = speed of light, τ = pulse width, θ = beam width, φ = ground illumination angle, σ
0=reflection coefficient of ground or sea surface.

σ0 (reflection coefficient) in equation (2) is a function of the illumination angle φ, and can be approximated by σO=γOstnφ. Here, rO is the reflectance and Aφ=H/R. 86e when the beam angle is small
φ becomes approximately 1, and the equation (21) can be approximated to the following equation (3).

That’s it, huh? The ratio between Equation (1) and Equation (3) is the ratio of the received power of the signal from the target and the clutter, that is, the S/C ratio, and becomes Equation (4) of order 699.

According to equation (3), H1τ　φ is a variable parameter.

The other values are constants, and the 9s/c ratio is inversely proportional to the altitude H and the pulse width τ.

Therefore, by changing the pulse width in response to changes in altitude, a constant S/C ratio can be obtained regardless of the altitude.

On the other hand, the receiver noise generated by the receiver is proportional to the receiver band, and the receiver noise is set to an optimal value for the received pulse width in the receiver band. Therefore, changes in pulse width require changes in the receiver band, and this change changes the receiver noise and
This leads to deterioration of the S/N ratio and reception sensitivity. In order to prevent this decrease, the maximum duty of the transmitting system is adjusted within this allowable range as the pulse width is changed, the frequency is changed, and the number of pulse integrations in the signal processing system is changed to reduce the S
Implement measures to improve the /N ratio.

The above actions can prevent deterioration of the S/C due to changes in altitude.

[Effect of idea]

As described above, this invention maintains a constant S/C by changing the transmission pulse width according to the aircraft's own altitude.
There is no effect of obtaining the ratio, and S/ as the own aircraft altitude increases.
Deterioration of the C ratio can be prevented.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a radar device showing an embodiment of this invention, and FIG. 2 is a block diagram showing a part of a conventional radar device. In the figure, (1) is a transmitter. (2) is the exciter, (3) is the antenna, (4) is the receiver, (
5) is a radar signal processor, (6) is an altimeter, (7) is a high frequency signal generation circuit, (8) is a modulator, (9) is a pulse generation circuit, 1 is a controller, +lυ is a display device, c12 is the pulse width, PRF switching signal, and am is the own aircraft altitude signal. Note that the same reference numerals in each figure indicate the same or corresponding parts. Figure 1

Claims (1)

[Claims] A transmitter that amplifies a high-frequency pulse signal that constitutes a pulse radar, an antenna that radiates the amplified high-frequency pulse signal into space, and an exciter that generates the high-frequency pulse signal before being amplified. A receiver that amplifies and detects the reflected pulse signal received by the antenna, a signal processor that processes the reflected pulse signal obtained by the receiver for tracking or displaying the target, and a video of the obtained target. In an aircraft-mounted radar device equipped with a display device for displaying a signal,
The pulse width in the exciter, pulse repetition frequency, reception bandwidth in the receiver, and
An airborne radar device characterized by changing the number of pulse integrals in a signal processor.