JP3028166B2 - Underground radar - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an avalanche phenomenon caused by a trigger pulse in a transistor, and a monopulse or a monocycle pulse is transmitted by an output of the transistor to reflect a reflected object from a short distance such as in the ground. Regarding underground radar to detect.

[0002]

2. Description of the Related Art FIG. 3A shows a trigger pulse generating portion in a conventional underground radar. A period Tp as shown in FIG. 3B (a) and a square wave such as 5 μS are inputted to the differentiating circuit 12 from the terminal 11. The differentiating circuit 12 is, for example,
The input is sent to the AND circuit 1 through one inverter 13.
4 and supplied to an AND circuit through two inverters 15 and 16. That is, the output of the inverter 13 is delayed and inverted by the delay of one inverter as shown in FIG. 3B (b), and the output side of the inverter 16 is delayed by the delay of two inverters. An output as shown in FIG. 3B (c) is generated. Accordingly, as shown in FIG. 3B (d) is from the AND circuit 14, the pulse width T _W corresponding to the delay caused by one inverter 20 to 30nS trigger pulse Pt of the resulting.

This trigger pulse Pt is applied between the base and the emitter of a transistor 18 via a transformer 17. The collector of the transistor 18 is connected to a power supply terminal 21 through a resistor 19, and this collector is grounded through a capacitor 22. The transistor 18 has an emitter connected to the output terminal 23 and a load resistor 24.
Through the ground. When the trigger pulse is applied between the base and the emitter of the transistor 18 as described above, the transistor 18 causes an avalanche phenomenon, and has a very narrow pulse width of about 2 to 3 nS and a peak voltage of 2 nS.
A pulse of about 0 to 30 V is obtained at the output terminal 23, which is transmitted as, for example, a monopulse.

[0004]

In the conventional underground radar, fixed noise, that is, a state where a reflected target is always present at the same distance, is displayed on a display screen at a position corresponding to the reflected distance. Lines may occur. When such fixed noise occurs, even if a reflective target actually exists at that position, it cannot be found because it is hidden by the fixed noise. In addition, the appearance of such fixed noise on the display is unfavorable because it becomes obstructive to see other reflected targets.

[0005] As a result of exploring the cause of such a fixed noise, the following was found. That is, when the trigger pulse Pt is applied to the transistor 18, FIG.
As shown in (1), the transistor is turned on by the avalanche phenomenon, and a pulse Pe with a remarkably narrow width is generated. The peak voltage is about 30 V, and the pulse width (half width) of the pulse Pe is, for example, 3 nS. Subsequent to this pulse, an output of 150 to 300 mV is generated at the output terminal 23, which disappears continuously for about 60 to 150 nS from the rise of the pulse, that is, the start of the avalanche phenomenon. In other words, an avalanche occurs due to the avalanche phenomenon, and the transistor 18 is turned on for a while after the end of the avalanche. The part where the pulse Pe is generated is called an avalanche area,
The region where the transistor is in the ON state following this is called a running region. This running region continues even when the trigger pulse Pt applied to the base of the transistor 18 is lost. That is, in the related art, the pulse width Pw of the trigger pulse Pt is about 20 to 30 nS, but the running region is 60 to 150 nS from the rising of the trigger pulse Pt.
S Continue. Generally, the peak voltage in the avalanche region and the peak voltage in the running region are about 100: 1 to 200: 1,
The time width of the avalanche area and the time width of the traveling area are about 1:20 to 1:50. When the pulse width of the avalanche region is 3 nS and its peak voltage is 30 V, the voltage of the traveling region is 300 to 150 mV, and the time width is 60 to 150 nS.

At the end of the running region, the transistor 18 is suddenly turned off, and the output voltage suddenly falls, and it has been found that the falling waveform contains a power spectrum of 50 to 500 MHz. On the other hand, the receiving band of the underground radar is 50 to 500 MHz, and the observation time,
That is, the time from the rising of the trigger pulse Pt to the end of the observation, that is, the time width for checking whether or not there is a reflected wave is, for example, 200 nS. For this reason, the fall of the traveling area is located within the observation time of the underground radar, and the spectrum based on this fall is within the reception band of the underground radar,
It has been found that a spectrum based on the falling edge of the running area is received for each trigger pulse and becomes a fixed noise.

An object of the present invention is to provide an underground radar which is not affected by fixed noise based on the end of a traveling area.

[0008]

According to the present invention, the pulse width of the trigger pulse is selected to be longer than the observation time of the reflected wave.

[0009]

With this configuration, the trigger pulse is applied between the base and the emitter of the transistor even after the running time is over, so that the transistor is kept on. After the observation time is over, the transistor is turned off. Turn off. Therefore, no fixed noise is generated based on the falling edge of the running area.

[0010]

FIG. 1A shows a main portion of an embodiment of the present invention, and portions corresponding to those in FIG. 3A are denoted by the same reference numerals. In the present invention, the width of the trigger pulse Pt is made longer than the observation time of the reflected wave. Therefore, in this embodiment, a delay circuit 25 is inserted in series in the differentiating circuit 12 between the two paths input to the AND circuit 14 to provide a long delay. In this example, the delay circuit 25 is a CR integrating delay circuit including a series resistor 26 and a capacitor 27 connected between the output side and the ground. Time, for example 200 ns
To be selected. In this case, for example, the resistor 26 is desirably a variable resistor so that the delay amount can be changed as necessary.

With such a configuration, the output of the differentiating circuit 12 has a pulse width Tw as shown in FIG.
Becomes, for example, a trigger pulse Pt of 200 nS, that is, the pulse width is selected to be substantially equal to the observation time of the reflected wave. Thus, a trigger pulse having a wider width than the conventional one is applied between the base and the emitter of the transistor 18. Therefore, as shown in FIG. 1B (b), an avalanche phenomenon occurs at the rise of the trigger pulse Pt, a pulse Pe having a remarkably narrow width is generated, and a running area is subsequently generated. In this example, since the trigger pulse Pt of 200 nS is applied between the base and the emitter of the transistor 18, the running area is substantially extended until the end of the trigger pulse Pt. The running area falls at the fall of. Therefore, even if a power spectrum based on the fall of the running area is generated in the reception band of the underground radar, it is out of the observation time area, and fixed noise based on the fall of the running area does not appear on the display. .

Since the trigger pulse width is made longer than before, the period during which the transistor 18 is turned on is
The ratio of the trigger pulse Pt to the repetition period Tp becomes long, and if the capacitor 22 is not sufficiently charged, it may not be possible to generate a sharp pulse based on the avalanche phenomenon. In this case, it is necessary to reduce the resistance value of the resistor 19 so that the capacitor 22 is sufficiently charged before the next trigger pulse is generated. Further, since the width of the trigger pulse Pt is long, a pulse waveform having a width of, for example, 200 nS is applied to the transistor 18 without deteriorating. Therefore, it is necessary to couple the transformer 17 so that the trigger pulse Pt can sufficiently pass through.

In the above description, a positive pulse is obtained at the output terminal 23. To obtain a negative pulse, the emitter of the transistor 18 is directly grounded as shown in FIG. , The capacitor 22 is connected to the load resistor 2
4, and the output terminal is taken out from the connection point of the capacitor 22 and the resistor 24. In this case, the differentiation circuit 1
2 output directly to transistor 1 without going through a transformer
8 bases.

[0014]

As described above, according to the present invention, since the width of the trigger pulse is equal to or longer than the observation time of the reflected wave, it is turned on based on the avalanche phenomenon of the transistor 18 within the observation time. Later, the end point of the running area is apparently the end of the observation time point or later, and therefore, at the end of the running area, fixed noise due to the transistor being turned off does not appear on the display, and thus the fixed time There is no danger that the reflected wave from the true target will be hidden by the noise, and the display will be easier to see because there is no obstruction due to the fixed noise.

[Brief description of the drawings]

FIG. 1A is a connection diagram showing a main part of an embodiment of an underground radar according to the present invention, and FIG. 1B is a waveform diagram showing a trigger pulse and an output voltage when a transistor is triggered.

FIG. 2 is a connection diagram showing a main part of another embodiment of the present invention.

FIG. 3A is a connection diagram showing a portion that generates a narrow pulse in a conventional underground radar, FIG. 3B is an explanatory diagram of the operation of the differentiating circuit, and C is a trigger pulse and an output terminal generated by the trigger pulse. FIG.

────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Yu Isono 1177 Tanaka, Ichimachi, Yamanashi City, Yamanashi Prefecture (56) References JP-A-4-23610 (JP, A) JP-A-3-259768 (JP, A) 63-58279 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01S ⁷ /00-7/42 G01S 13/00-13/95 G01V 3/12 H03K 3/335

Claims (1)

(57) [Claims] 1. An underground radar that generates a transmission pulse by causing an avalanche phenomenon in a transistor by a trigger pulse, wherein the width of the trigger pulse is selected to be equal to or longer than the observation time of a reflected wave. Underground radar to do.