JPS647341Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a radar signal processing device that automatically removes sea surface reflection interference in a pulse radar and detects only a target signal.

Sea surface reflections that occur during radar searches for maritime targets vary depending on the strength of waves, and can interfere with reflected signals from targets that should be detected (ship buoys, etc.).
This will greatly impede target detection. In order to remove this sea surface reflection disturbance, conventional methods were (a) STC (Sensitivity
(b)FTC
Method using (Fast Time Constant) circuit, (c)
Methods that use logarithmic amplifiers, CFAR circuits, and (d) correlation integration using an agility radar have been adopted.

By the way, in method (a) above, the STC circuit controls the sensitivity of the intermediate frequency amplifier of the radar receiver so that it is low for short-range radar echoes and high for long-range radar echoes. This prevents the large amplitude of near-field echoes from saturating the receiver and making it impossible to detect weak target signals. However, even if the STC circuit is set optimally, it is impossible to operate effectively in all 360-degree directions, and simply suppressing receiver sensitivity will not improve S/N. ,
The drawback was that it could not detect target signals smaller than waves reflected from the sea surface.

In addition, method (b) above uses images of radar echoes.
It attempts to find a specific target in a uniform reflected wave by differentiating it using an FTC circuit.
The circuit is a differential circuit with a short time constant and has poor response characteristics, which has the disadvantage of creating a region where sensitivity is reduced.

In addition, in the method (c) above, the intermediate frequency signal of the radar receiver is guided to the CFAR circuit and the DC component is removed by a low-pass filter. There was a limit to just doing that.

In addition, in the method (d) above, the frequency is varied for each transmitted pulse and the correlation is taken for each pulse or each scan, but since the correlation is taken while including the DC component, it is not necessarily possible to improve the S/N ratio. High expectations were not met.

This idea was made in view of the above circumstances.
Extract the fluctuation component of the radar echo signal input,
The present invention provides a radar signal processing device that can improve the S/N ratio and eliminate sea surface reflection interference by removing the DC component from the fluctuation component signal and then correlating it with a fixed target.

An embodiment of the present invention will be described in detail below with reference to the drawings.

In FIG. 1, a radar antenna 1 is connected to a radar transmitter 3 and a radar receiving system via a transmitter/receiver switch 2. In FIG. In this radar receiving system, 4 uses a mixer and 5 uses a logarithmic amplifier.
This is an IF (intermediate frequency) amplifier, and a fluctuation component (FLUCTUATION) detection circuit 6 and a signal level conversion circuit 7 are connected in sequence at the downstream stage of this amplifier 5.

On the other hand, 8 and 9 are first and second switching devices driven in conjunction with each other, and the first switching device 8 selects the output of the signal level conversion circuit 7 or the IF amplifier 5 to remove the DC component. Lead to circuit 10. A correlation integrator 11 is connected to the subsequent stage of this removal circuit 10,
The second switch 9 switches and selects the output of the correlation integrator 11 or the DC component removal circuit 10 and outputs the selected output to the video output terminal 12.

In the above configuration, the radar reception signal is converted into an IF signal by the mixer 4 and then logarithmically amplified by the IF amplifier 5. This amplified output includes a direct current component A obtained from sea surface reflection, a fluctuation component B, and a fixed target component C, as shown in FIG. 2 a to n, corresponding to radar pulses 1 to n, respectively. The fluctuation component B is generated by the logarithmic amplifier of the IF amplifier 5.
The near-field amplitude component and the long-range amplitude component are uniform. This amplified output is the fluctuation component detection circuit 6
As shown in FIGS. 3 a to 3 n, a signal is extracted in which the fluctuation component B includes a small amount of the fixed target component C.

Incidentally, the fluctuation component detection circuit 6 is configured as shown in FIG. 8, for example. That is, the input signal is guided to a PRF (pulse repetition frequency) delay circuit 81 and a delay correction circuit 82, and each delayed output is guided to a subtraction circuit 83 for subtraction processing. This PRF delay circuit 81 is variable so that any PRF delay from 1st to nth is possible. Further, the delay of the input signal flowing to the delay correction circuit 82 is compensated for the slight amount of delay caused by the input signal flowing through the PRF delay circuit 81.

Note that the waveform in FIG. 3 is generated by the PRF delay circuit 81.
Corresponding to the case of 1 PRF period delay, e.g. the signal received by the first transmitted pulse (Fig. 2a)
is delayed by one PRF cycle by the PRF delay circuit 81, and is obtained by subtracting it from the signal received by the second transmission pulse (Fig. 2b). The PRF delay of n is variably adjusted to an arbitrary value of 1PRF or more, 1 to nPRF, so as to effectively extract the fluctuation component B and the fixed target component C and obtain the optimum output.

The output signal of the fluctuation component detection circuit 6 described above is
The signal level conversion circuit 7 performs level conversion.
This level conversion is performed from a certain DC level to Figure 3a.
By subtracting signals such as .about.n, fluctuation component B and fixed target component C are extracted as the inverted signal levels as shown in FIG. 4 a to n. The signal extracted in this way is led to the DC component removal circuit 10 via the first switch 8, where the DC component is removed and the fluctuation component B and the fixed target component C are removed as shown in FIG. 5 a to n. is taken out.

FIG. 7 is shown to clearly explain the signal processing process from the fluctuation component detection circuit 6 to the DC component removal circuit 10, and A to C correspond to FIGS. 3 to 5. This is the waveform.

The output of the DC component removal circuit 10 is sent to the correlation integrator 1.
1, and here the uncorrelated signal (fluctuation component B in Fig. 5) and the correlated signal (fixed target component C in Fig. 5)
The uncorrelated signals are averaged and
By adding the highly correlated signals, a fluctuation component B and a fixed target component C with relatively improved S/N ratios are obtained as shown in FIG. derived through. In this case, by adding signals with strong correlation, the state of maximum sensitivity is automatically achieved from short distance to long distance.
The S/N ratio is significantly improved compared to the conventional method.

As shown in FIG. 9, the correlation integrator 11 includes an adder 91 that adds the input signal and the feedback signal of the integration factor K, and a 1PRF delay circuit 92 that delays the addition output of the adder 91 by 1PRF cycle.
A feedback circuit 9 that feeds back the output of this delay circuit 92
3 and more.

In addition, in Fig. 1, the switches 8 and 9 are switched to the opposite state from the one shown when there is little sea surface reflection, etc. (alternating current components with large fluctuations such as clutter). The best reception sensitivity can be obtained.

As described above, the present invention can provide a radar signal processing device that can remove sea surface reflected wave interference and improve the S/N of output video.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of a radar signal processing device according to the present invention, and FIGS. 2 to 6 are waveform diagrams showing each part of the signals in FIG. 1 for each radar pulse.
7 is a waveform diagram shown to explain the operation of FIG. 1, FIG. 8 is a block diagram showing an example of the fluctuation component detection circuit of FIG. 1, and FIG. 9 is an example of the correlation integrator of FIG. 1. FIG. 6... Fluctuation component detection circuit, 7... Signal level conversion circuit, 10... DC component removal circuit, 11... Correlation integrator.

Claims (1)

[Scope of utility model registration request] a transmitting means for transmitting a radar transmission repetition signal;
An antenna to which the output signal of the transmitting means is supplied via the transmitting/receiving switch and radiating electromagnetic waves into space and capturing reflected waves from the target; and a receiver to which the output signal of this antenna is supplied via the transmitting/receiving switch. a detection circuit that is supplied with the output signal of the receiving means and that detects uncorrelated signals by subtracting signals having a time difference of n transmission repetition periods (n is an integer of 1 or more); A level conversion circuit that subtracts the output signal level from a predetermined DC level, a DC component removal circuit that removes the DC component from the output signal of this level conversion circuit, and a signal that has a high correlation from the output signal of this DC component removal circuit. A radar signal processing device comprising an extraction means for extracting a signal.