JPS5837010Y2 - Pulse reflected wave receiver - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to the field of reception technology for pulse waves in radars, echo sounders, and the like.

In particular, it is included in the received signal.

In the case of rain and snow, waves reflected from the sea surface, or sound waves, it relates to technology that removes reverberant waves from the bottom of a ship or the ocean floor.

Conventional similar techniques include a method of slicing received reflected waves at a constant level and then removing only irregularly periodic waves using a correlation technique.

However, as shown in FIG. 1a, there are many cases in which a sea surface reflected noise NA that has a large amplitude and lasts for a considerable period of time is present every time.

In such a case, slice at slice level L and
If you look at the waveform shaped like this, you will see that although the pulse width of NB may be long or short, it appears every time, so it is essentially treated on the circuit as if it were a signal, and it cannot be processed using normal correlation techniques alone. It cannot be removed.

Furthermore, there is a problem in that the effective small target shown as S4 in a is not picked up as a signal below the slice level.

Therefore, Utility Model Publication No. 50-112155 and Japanese Patent Application Publication No. 5121
As exemplified in Publication No. 796, a filter is used to extract an attenuation waveform similar to the envelope of the received reflected wave, and based on this, a slice level whose level changes continuously along the envelope is created; JP-A-49-5588 and JP-A-50
As exemplified in Japanese Patent No. 151495, it has been proposed to compress the amplitude of a received reflected wave and slice it.

However, since the former is a low-pass filter, the response at the rising position of the reflected wave is slow and a direct current component inevitably remains.
1-21796, the waveform shown in Figure 2 d is obtained, and this leaves the effect that the central part shines with high brightness on the cathode ray tube.

Also in the latter case, it is difficult to suppress the rise of the signal by compression.

The present invention significantly improves the above-mentioned drawbacks by combining the time constant control technology of the differentiating circuit and the limiter technology.

The case where the present invention is applied to a radar will be explained below according to the embodiment shown in the figure.

In FIG. 2, 1 is a transmitting/receiving circuit which emits a pulse wave in a target direction and receives the reflected wave.

A compression circuit 2 compresses the received output level.

3 is a slicing circuit that slices a signal of a predetermined level or higher from the received output and shapes it into a rectangular wave of the same amplitude.

4 is an oscillation circuit that oscillates high-frequency clock pulses in response to a transmission trigger signal applied from the transmission/reception circuit 1 during transmission;
5 is a gate circuit which gates the oscillation output with the output of the slice circuit 3.

Reference numeral 6 denotes a level regulating circuit, which will be described later, shown in FIG. 3, for example, and regulates the peak value of the human input signal.

A slicing circuit 7 slices the output of the level regulation circuit 6 at a predetermined level and shapes it.

8 is a correlation circuit that correlates the outputs of the slice circuit 7 several times and then correlates them with new received signals; 9 is a display circuit for the correlation output; in radars, this is usually a cathode ray tube display.

In the above device, the signal received by the transmitting/receiving circuit 1 in FIG.
The received waveform illustrated in FIG. 1 is compressed by the compression circuit 2 as shown in FIG.

Note that a-'C''NA is sea surface reflected noise, Sl, S2.
S3. S4 indicates reflected waves from effective targets such as ships and islands.

On the other hand, the output of this a is at the level L in the slice circuit 3.
The waveform is sliced and shaped into the waveform shown in the figure.

On the other hand, when a part of the transmission trigger signal is supplied from the transmission/reception circuit 1 to the oscillation circuit 4, the oscillation circuit 4 oscillates a clock pulse shown in C and supplies it to the gate circuit 5. The clock pulse of the oscillation circuit 4 is passed through the level regulation circuit 6 as shown in d only during the existence period of the output rectangular wave.

As shown in FIG. 3, the level regulating circuit 6 includes a differentiating circuit with a time constant CR1 and a diode D1. It consists of a series circuit of D2 and a series circuit of switch W and resistor R2, which are also connected in parallel.

The switch W is opened and closed by the output d of the gate circuit 5.

When the waveform shown in FIG. 1e is applied to the input terminal IN, its DC component is removed by a differentiating circuit consisting of C and R1, and only the change in peak value appears on the output side as shown in f.

Note that the reference potential of this waveform is at the starting level.

The time constant CR1 at this time is the wide effective signal S1. The length is set appropriately long so that no differential effect is exerted on S3 and the like.

However, if the time constant is long, the wavefront cannot be made discontinuous (sharpened) by the differential effect for continuous noise such as NE that is input at minute intervals.

For this reason, a series circuit of switch W and resistor R2 is provided, and when this is closed by clock pulse d, resistor R2 is connected in parallel to resistor R1, so the time constant of the differentiating circuit is instantaneously shortened. It becomes like this.

Therefore, the wavefront change in the short-time changing signal range NE shown in Figure 1e appears in the output as an intermittent pulse train NF (Figure 1f), and the wavefront change in the short-time changing signal range NE shown in Figure 1e appears in the output as an intermittent pulse train NF (Figure 1f). The pulses of S, f, and S3f do not cut off because the human power is constantly supplied even when the switch W is closed/opened.
will appear in the output as

Note that e is amplified and then supplied to the level regulation circuit.

Also, the diode D1. D2 regulates the wave front voltage of the output wave, and the level of the output wave is limited by the forward saturation voltage (2).

Therefore, the wave fronts of S, f and S3f are suppressed at level ■.

Due to such a level regulation circuit, the waveform of Fig. 1 e becomes f
As shown in , only the head portion of the waveform is changed to the selected one.

Note that at the rear ends of the large amplitude signals S1E and S3E, overshoot waveforms extend upward.

This waveform is sliced at level Lf in the slicing circuit 7 and shaped as shown in g.

This output waveform is temporarily stored in the correlation circuit 8 and correlated with the next output.

The second output (not shown) is also composed of the sea surface reflected wave group NG and the signal group SG, as in the first output, but while SG is periodic, NG is at the wavefront of the reflected noise wave. The selected one has irregular periodicity.

Therefore, the pulse appearance position in this section does not match every time, and hardly appears in the correlation output.

Note that the number of times of correlation is usually 3 to 4 times.

Finally, based on this correlation output, only the NG part is removed from the new input signal input from the transmitter/receiver circuit 1, and an image is displayed on the display circuit.

As explained above, in this case, the time constant of the differentiator circuit is small in the short distance section where the force of sea surface reflected waves is strong, and large in the medium speed distance section where the signal is scattered, and the amplitude of the signal is saturated. Even though it is noise, its rising part can be treated as an irregular periodic pulse, and correlation technology can be effectively utilized.

In particular, since there is almost no differential effect on the signal portion, there is an advantage that small signals can be displayed reliably without being degraded.

Further, the compression circuit 2 is used to ensure the operation of the level regulation circuit 6, and may be removed in principle.

[Brief explanation of drawings]

1 is an electrical waveform diagram of the main part of FIG. 2, FIG. 2 is a block diagram of an embodiment of the present invention, and FIG. 3 is a wiring diagram showing an example of a level regulating circuit.

Claims (1)

[Scope of utility model registration request] A first slice circuit that detects a signal of a predetermined level or higher among the detected reflected wave signals, and a differentiating circuit for the reflected wave signal and a differentiating circuit that reduces the time constant intermittently during the output existence period of the first slice circuit. a level regulating circuit consisting of an amplitude limiting circuit that limits the amplitude at a level higher than the diffuse reflection noise among the outputs of the level regulating circuit; A pulse reflected wave receiving device comprising a two-slice circuit and a correlation circuit that correlates the output of the second slice circuit with the received reflected wave and outputs it as a next-stage output.