JPH06152455A - Receiver - Google Patents

Abstract

PURPOSE:To prevent the adverse influence of a reflected signal and to exactly amplify a small signal by consuming the signal reflected by a limiter in heat at an impedance matched terminal element through an isolator. CONSTITUTION:An isolator 19 is provided between a reception antenna 9 and a limiter 15. The isolator 19 introduces a signal from the antenna 9 through a line 20 to a line 16 and introduces the signal reflected at the limiter 15 from the line 16 through the isolator 19 to an output terminal 21. A terminal resistor 22 of the terminal impedance element matched with this output impedance is connected to the terminal 21. Thus, the signal reflected by the limiter 15 to the isolator 19, namely, to the side of the antenna 9 is consumed in heat by the resistor 22, therefore, the signal reflected by the limiter 15 is applied through the line 16 to the limiter 15 again, and the adverse influence caused by the reflected signal can be prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a receiver, which can be advantageously used in an underground exploration radar for detecting the position of a buried object buried in a hidden place such as the ground. Regarding the device.

[0002]

2. Description of the Related Art An underground exploration radar for detecting a pipe buried in the ground that transports gas etc. on the ground emits a pulsed electromagnetic wave into the ground and reflects the reflected wave from the underground pipe. It is possible to obtain the image of the cross section of the soil including the underground buried pipe based on the time difference between the electromagnetic wave radiated by the receiving antenna and the radiated wave and the reflected wave, thereby knowing the depth of the underground buried pipe and hence its position. be able to.

In such an underground survey radar, among the reflected waves received by the receiving antenna, the intensity of the reflected wave reflected on the ground surface is particularly large, and the reflected wave reflected by the underground pipe or the like. The strength is weak. The high-frequency amplifier circuit that amplifies the output from the receiving antenna is configured to have a high gain so as to amplify the weak reflected wave, and therefore the amplified circuit is saturated by the large-amplitude reflected wave from the ground surface, and the amplified signal is amplified. During the time from the end of reception of the large-amplitude reflected wave that depends on the time constant of the circuit, it becomes impossible to accurately amplify the weak reflected wave.

In order to solve such a problem, it is easily conceivable to interpose a limiter between the receiving antenna and the amplifying circuit so as to limit the amplitude of a large-amplitude signal. When configured, the impedance of the receiving antenna is, for example, 50Ω, and the input impedance of the limiter is zero when the limiter is conducting and limiting a large amplitude signal, and thus the impedance between such receiving antenna and the limiter is zero. The output of the receiving antenna is reflected by the limiter due to the mismatch of the, and then reflected by the receiving antenna and input to the limiter again.Therefore, even if the limiter is simply used, a clear image of the cross section of the soil can be obtained. It is impossible to get.

One prior art technique for solving this problem is disclosed in Japanese Patent Laid-Open No. 61-296286. In this prior art, a signal delay line is interposed between the receiving antenna and the limiter, the signal reflected by the limiter returns to the antenna via the signal delay line, and is again input to the amplifier circuit from the limiter via the signal delay line. Make the time to measure large enough,
For example, the delay time is set to several tens of nanoseconds to prevent the limiter from adversely affecting the reflected signal.

[0006]

In such a prior art, if the delay time of several tens of nanoseconds and the maintenance of the wide band property of the transmission signal are to be maintained by the signal delay line, as described above, for example, the coaxial cable may be 5 to 5. There is a problem that it requires 10 m, and therefore the configuration becomes large.

An object of the present invention is to enable a weak signal to be accurately amplified and detected even when a large-amplitude signal for a short time may be mixed, and the structure thereof can be downsized. It is to provide a receiver capable of performing the above.

[0008]

SUMMARY OF THE INVENTION The present invention includes a receiving antenna for receiving electromagnetic waves, an amplifier circuit, and a limiter provided in the preceding stage of the amplifier circuit for limiting an input signal to an amplitude within a range in which the amplifier circuit is not saturated. An isolator interposed between the receiving antenna and the limiter, inputting an output from the receiving antenna to the limiter, and deriving a reflected signal by the limiter,
A receiving device, comprising: a terminating impedance element that receives the reflected signal and matches an impedance from which the reflected signal of the isolator is derived.

Further, according to the present invention, a receiving antenna for receiving an electromagnetic wave, a buffer for deriving an output from the receiving antenna without saturating, an amplifier circuit having a gain larger than that of the buffer, and a buffer and an amplifier circuit are provided. And a limiter that intervenes and limits the output of the buffer with an amplitude within a range in which the amplifier circuit does not saturate.

Furthermore, the present invention further comprises a receiving antenna for receiving electromagnetic waves, a multi-stage amplifying circuit to which the output from the receiving antenna is given, and a multi-stage amplifying circuit which is connected immediately after each amplifying circuit and which outputs the output from the pre-stage amplifying circuit. And a limiter for limiting the amplitude within a range in which is not saturated.

[0011]

According to the present invention, an electromagnetic wave is received by the receiving antenna, and its output can be amplified with a high gain by an amplifier circuit. The output is given to the amplifier circuit through a limiter in the preceding stage of this amplifier circuit. The signal is limited to an amplitude within the range where the amplifier circuit does not saturate, and an isolator is interposed between the receiving antenna and the limiter, and the signal reflected by the limiter is impedance-matched to the isolator. Heat is consumed by a terminating impedance element such as a terminating resistor. As a result, the adverse effect of the reflected signal due to the limiter can be prevented, and thus a large-amplitude signal that saturates the amplifier circuit will not be given to the amplifier circuit. Such signals can be accurately amplified by an amplifier circuit.

According to the invention, the output of the receiving antenna is applied to a buffer, which has a low gain, eg 1.
Therefore, even if a large-amplitude signal is applied to the buffer from the receiving antenna, the buffer does not saturate, and the output of this buffer is amplitude-limited by the limiter and applied to the high-gain amplifier circuit. As a result, the signal reflected by the limiter does not return to the receiving antenna via the buffer. Therefore, the adverse effect of the reflected signal by the buffer can be prevented, and the weak signal can always be accurately amplified by the amplifier circuit.

Further, according to the present invention, the output from the receiving antenna is amplified by the first-stage amplifier circuit of the following multi-stage amplifier circuits, and the output of the front-stage amplifier circuit including the first stage is amplitude-limited by the limiter, Immediately after that, the limiter output is given to the latter-stage amplifier circuit with an amplitude within a range where the latter-stage amplifier circuit is not saturated. The pre-stage amplification circuit may have (a) a low gain so that a large-amplitude signal is not saturated even when given from the receiving antenna, or (b) the pre-stage amplification circuit is set to have a high gain. May be saturated. The subsequent limiter does not saturate the latter-stage amplifier circuit, and thus the latter-stage amplifier circuit can always accurately amplify a minute signal. The front-stage amplifier circuit and the rear-stage amplifier circuit are connected in series via a limiter. Therefore, the total gain of the front-stage amplifier circuit and the rear-stage amplifier circuit can be increased, and a weak signal can be accurately amplified with a large amplification factor. . If one of the amplifier circuits tries to obtain a desired high gain, undesired oscillation may occur, but the present invention avoids such a problem.

[0014]

1 is a block diagram of a receiver 1 according to an embodiment of the present invention. The receiver 1 is used in an underground search radar 2 shown in FIG. A pipe 4, which is an embedded object such as a steel pipe for transporting a fluid such as gas, is buried in the soil 3. On the ground, to search for this pipe 2,
For example, 100 MH is transmitted from the transmission circuit 6 to the transmission antenna 5.
A pulse having a frequency band of z to 1000 MHz is given, and an electromagnetic wave is radiated from the transmitting antenna 5 toward the soil 3 by this. The electromagnetic wave radiated from the transmitting antenna 5 travels as indicated by reference numeral 7 and is reflected by the tube 4, and the reflected wave by the tube 4 travels as indicated by reference numeral 8 and is received by the receiving antenna 9. . The receiving antenna 9 and the electric circuit 10 constitute the receiving device 1. Time difference ΔT between the emission of the electromagnetic wave from the transmitting antenna 5 and the reception of the reflected wave by the receiving antenna 9.
Corresponds to the distance between the surface of the soil 3 and the pipe 4. By fixing the transmitting antenna 5 and the receiving antenna 9 integrally and moving them across the underground buried pipe 2 as shown by the arrow 11, the cross section of the soil 1 including the pipe 2 in the vertical plane Images can be obtained.

In the receiving antenna 9, the electromagnetic wave radiated from the transmitting antenna 5 is reflected on the ground surface 12 of the soil 3, whereby an excessive large-amplitude reflection signal is given to the receiving antenna 9 and radiated from the transmitting antenna 5. The weak reflected signal of the generated electromagnetic wave reflected in the soil 3 is also received by the receiving antenna 9 following the large amplitude reflected wave. The large-amplitude signal due to the reflected wave of the ground surface 12 by the receiving antenna 9 is, for example, 2 to 3V, and the output of the reflected wave in the soil 3 is, for example, several μV and is weak.
If the output of the receiving antenna 9 is directly input to the high-gain high-frequency amplifier circuit 13, the input signal on the line 14 of the amplifier circuit 13 is saturated at several 100 mV. Therefore, immediately after the input of such a large amplitude signal, the amplifier circuit 1
With No. 3, it becomes impossible to accurately amplify a weak signal. In the present invention, in order to solve such a problem,
A limiter 15 is provided in front of the amplifier circuit 13, and the limiter 1
5 serves to limit the amplitude of the input signal given from the line 16 in the amplifier circuit 13 via the line 14 to an amplitude within a range in which the amplifier circuit 13 does not saturate.

The limiter 15 has a pair of mutually oppositely connected diodes 17, 18 connected between the line 16 and ground. These diodes 17 and 18 have the same characteristics.

FIG. 3 is a graph showing the characteristics of the diode 17. A predetermined voltage V1 in the forward direction applied to the diode 17.
Diode 17 conducts when a voltage having an amplitude greater than is applied. The other diode 18 also has the same characteristics as the diode 17. Therefore, the characteristic of the limiter 15 having such diodes 17 and 18 is as follows.
As shown in FIG. When the amplitude of the input signal given to the line 16 is weak in the range of −V1 to + V1, the diodes 17 and 18 are cut off, and such a weak signal does not saturate the amplifier circuit 13. , And is accurately amplified by the amplifier circuit 13.
The absolute value of the amplitude of the input signal given to the line 16 is V1
Limiter 17, 18 becomes conductive, and the line 1
The output voltage to 4 is limited to the maximum value V1. The amplifier circuit 13 does not saturate when the amplitude voltage of the signal input via the line 14 is V2 or less. In this way, the amplifier circuit 13 does not saturate even when a large amplitude signal is given to the line 16, and therefore it is possible to always accurately and accurately amplify a weak signal.

An isolator 19 is interposed between the receiving antenna 9 and the limiter 15. This isolator 19
Outputs a signal from the receiving antenna 9 via the line 20 to the line 16 and a reflected signal reflected by the limiter 15 and given to the isolator 19 from the line 16 to the output terminal 21. To the output terminal 21, a terminating resistor 22 which is a terminating impedance element matched with the output impedance of the output terminal 21 is connected. The output impedance of the connection terminal 21 is, for example, 50Ω, and the terminating resistor 22 is set to 50Ω at this time. In this way, the reflected signal to the isolator 19 and thus the receiving antenna 9 side by the limiter 15 is consumed by the terminating resistor 22, so that the reflected signal from the limiter 15 is again given to the limiter 15 via the line 16 and the reflected signal is adversely affected. Can be prevented.

FIG. 5 (1) shows the output waveform of the amplifier circuit 13 showing the experimental result of the present inventor. The waveform of the large amplitude reflected wave by the ground surface 12 is not saturated in the amplifier circuit 13, as indicated by the reference numeral 23. Further, as indicated by the reference numeral 24, the large amplitude waveform in the soil 3 is also amplified by the amplifier circuit 13.
Does not saturate at. Therefore, the weak signals 25 and 26 immediately after such large-amplitude waveforms 23 and 24 can be accurately detected, and thus the soil 3 can be accurately searched.

FIG. 5B shows a limiter 15 and an isolator 1.
9 shows the output waveform of the amplifier circuit 13 obtained when the line 20 of the receiving antenna 9 is directly connected to the amplifier circuit 13 because the amplifier 9 and the terminating resistor 22 are not provided.
The waveform 27 corresponding to the ground surface 12 and the large-amplitude signal 28 in the soil 3 are saturated in the amplifier circuit 13, so that the weak signals 29 and 30 thereafter are the same.
Due to the time constant of, the waveform is significantly distorted as compared with the accurate waveforms 25 and 26 of FIG. Therefore, it is understood that the prior art cannot accurately search the soil 3.

The output of the amplifier circuit 13 is given to a processing circuit 31 realized by a microcomputer or the like. A memory 32 is connected to the processing circuit 31. A signal as shown in FIG. 5 (1) when the transmitting antenna 5 and the receiving antenna 9 are made to travel in the direction of arrow 11 in FIG. 2 is stored in the memory 32. An image stored in the memory 32 of the soil 3 is displayed on the visual display means 33 which is realized by a cathode ray tube and liquid crystal, and the position of the underground buried pipe 4 can be clearly known.

FIG. 6 shows a receiver 3 according to another embodiment of the present invention.
4 is a block diagram of FIG. This embodiment is similar to the embodiment of FIG. 1 described above, and corresponding parts bear the same reference numerals. In this embodiment, the limiter 35 includes a pair of diodes 36 and 37 connected in series with opposite polarities and in series, and choke coils 38, 39 and 4 for cutting off pulse signals for underground exploration.
0 and a DC power supply 41. Diodes 36 and 37
Has the same characteristics as the diodes 17 and 18 described above. The voltage of the input signal applied to the line 16 and the voltage of the output signal derived to the line 14 are as shown in FIG. The characteristic of the limiter 35 shown in FIG. 7 is the same as that of FIG. 4 showing the characteristic of the limiter 15 described above.
Due to the characteristics shown in FIG. 7, in the limiter 35, when a large amplitude signal is input to the line 16, the diodes 36 and 37 respectively conduct in the forward direction and flow to the ground. Weak signals are sent from line 16 to choke coil 3
It flows through line 8 to line 14 and thus always prevents saturation of the amplifier circuit 13.

FIG. 8 shows a receiver 4 according to another embodiment of the present invention.
2 is a block diagram of FIG. This embodiment is similar to the previous embodiment, and corresponding parts bear the same reference numerals. In this embodiment, a buffer 43 for deriving the output from the receiving antenna 9 without saturating is provided.
The limiter 15 is interposed between the amplifier circuit 13 and the amplifier circuit 13 having a gain larger than that of the buffer 43.

The concrete structure of the buffer 43 is shown in FIG. In this buffer 43, a signal via line 20 is applied to the base of transistor 44, its emitter is grounded via resistor 45 having a resistance value of, for example, about 50 to 100 Ω, and this emitter is connected to line 16. A resistor 46 is connected between the base and collector of the transistor 44. Power supply voltage + VB is, for example, 15V. A large amplitude signal of maximum 2 to 3 V may be input to the line 20 for a short time, and the weak signal as described above for underground exploration is also given. The gain of such a buffer 43 is, for example, 1, which is a low value, and its input / output characteristic is as indicated by reference numeral 47 in FIG. Due to the low gain of the buffer 43,
Even if the large-amplitude signal reflected by the ground surface 12 is received by the receiving antenna 9 and the large-amplitude signal is input from the line 20, the buffer 43 is not saturated and is supplied to the limiter 15. The limiter 15 is indicated by reference numeral 4 in FIG.
The limiter 15 has a high gain as shown by 8 and prevents the high gain amplifier circuit 13 from being saturated.
Although the reflected wave from the limiter 15 is given to the buffer 43 via the line 16, it does not reach the receiving antenna 9 by the action of the buffer 43 and is consumed by the emitter resistor 45 of the buffer 43 shown in FIG. . In this way, the adverse effect of the reflected signal by the limiter 15 can be prevented. If the buffer 43 derives the large-amplitude signal 49 shown in FIG. 11 on the line 16 to the line 16 and directly supplies such a large-amplitude signal 49 to the amplifier circuit 13, the amplifier circuit 13 is saturated. However, the limiter 15 works to limit its amplitude to the range of ΔV,
This prevents the amplifier circuit 13 from being saturated. ΔV is, for example, a value of several hundred mV or less.

FIG. 12 is an electric circuit diagram of a buffer 50 according to another embodiment of the present invention which can be used in place of the buffer 43. The buffer 50 has a transistor 51 whose base is grounded, a resistor 52 is connected to the emitter on the input side, and a power supply voltage + VB is applied to the collector on the output side via the resistor 53. Such a buffer 5
0 has a little more gain than 1
The receiver of the present invention can be preferably implemented.

FIG. 13 is a block diagram of a receiver 54 according to still another embodiment of the present invention. The output of the receiving antenna 9 is given from the line 20 to the amplifier circuit 54, the line 55 to the limiter 56, and the line 57 to the amplifier circuit 5.
8 and then to another limiter 60 via a line 59, the output of which is given to an amplifier circuit 62 from a line 61, and a weak signal of the underground exploration is amplified and derived from a line 63. . Amplifier circuits 54, 58, 62
May have the same configuration and have a high gain. Even if saturation occurs due to the large-amplitude signal from the receiving antenna 9 in the amplifier circuit 54, the subsequent limiters 56 and 60 are
Saturation of the amplifier circuits 58 and 62 is prevented, so that the amplifier circuits 58 and 62 can accurately amplify a weak signal without causing saturation due to the input signal. Amplifier circuit 5
By connecting 4, 58, 62 in series via the limiters 56, 60 as described above, the total gain can be improved, and a weak signal can be sufficiently amplified. By providing a plurality of amplifier circuits 54, 58, and 62, it is possible to prevent undesired oscillation from occurring.

As another embodiment of the present invention, the amplifier circuit 54 shown in FIG. 13 is configured to have a low gain, for example, a gain of 1, so that the amplifier circuit 54 is not saturated even when a large amplitude signal is input. May be.

Lines 55 and 59 by limiters 56 and 60
The reflected signal of the signal from is not further propagated to the preceding stage side (that is, the left side of FIG. 13) by the action of the amplifier circuits 54 and 58, and is consumed as heat, for example, and is therefore reflected by the limiters 56 and 60. It is possible to prevent the bad influence of the signal. The limiter 15 of FIG. 8 and the limiter 5 of FIG.
6, 60 may have the same configuration as the limiter 35 in FIG.

The present invention is not only carried out in connection with the underground exploration radar, but it is also necessary to always accurately and accurately amplify a weak signal when a large amplitude signal for a short time may be input. It can be widely implemented in the field.

[0030]

As described above, according to the present invention, the output from the receiving antenna is given to the amplifier circuit through the limiter to limit the amplitude of the input signal of the amplifier circuit so that the amplifier circuit is not saturated, and the limiter is provided. The reflection signal from the limiter via the isolator is used in the preceding stage to be consumed by the termination impedance element whose impedance is matched via the isolator, so that the adverse effect of the reflection signal due to the limiter is prevented and a large amplitude signal is received by the receiving antenna. Even if it is output from, the minute signal immediately after that can be accurately amplified by the amplifier circuit.

Further, according to the present invention, the output of the receiving antenna is given to the limiter via the buffer and input to the amplifier circuit,
The buffer gain should be kept low to prevent it from saturating, and the limiter's amplitude limiting effect should not saturate the amplifier circuit, thus allowing the buffer and amplifier to output large amplitude signals to the receiving antenna. Circuit saturation can be prevented and weak signals can be amplified accurately, and the reflected signal from the limiter does not return to the receiving antenna via the buffer, which prevents the adverse effect of the reflected signal from the limiter. Be done.

Further, according to the present invention, in order to amplify the output from the receiving antenna with a high gain, amplifier circuits connected in cascade are provided, and a limiter is provided immediately after each amplifier circuit. Limits the output from the amplifier circuit at the stage prior to the limiter to an amplitude within a range in which the amplifier circuit at the stage immediately after the limiter does not saturate, and in this way the preceding stage amplifier circuit has a low gain and does not saturate. Of course,
Even if the gain is high and is saturated by a large-amplitude signal, the latter-stage amplifier circuit is prevented from being saturated by the limiter as described above. The signal can be amplified and detected as accurately as possible.

[Brief description of drawings]

FIG. 1 is a block diagram of a receiving device 1 according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration of an underground exploration radar in which the receiving device 1 is used.

FIG. 3 is a graph showing characteristics of a diode 17.

FIG. 4 is a graph for explaining the operation of the limiter 15.

5 is a waveform diagram for explaining the operation of the underground exploration radar shown in FIG.

FIG. 6 is a block diagram of a receiving device 34 according to another embodiment of the present invention.

FIG. 7 is a graph for explaining the operation of the limiter 35 shown in FIG.

FIG. 8 is a block diagram of a receiving device 42 according to another embodiment of the present invention.

9 is an electric circuit diagram showing a specific configuration of a buffer 43 shown in FIG.

FIG. 10 is a diagram for explaining operations of the buffer 43 and the amplifier circuit 13.

FIG. 11 is a diagram for explaining the operation of the receiving device 42 shown in FIG.

FIG. 12 is an electric circuit diagram showing a specific configuration of a buffer 50 according to another embodiment of the present invention.

FIG. 13 is a block diagram of another embodiment of the present invention.

[Explanation of Codes] 1,34,42,54 Receiver 2 Underground exploration radar 3 Soil 4 Underground pipe 5 Transmission antenna 6 Transmission circuit 9 Reception antenna 10 Electric circuit 13,54,58,62 Amplification circuit 15,35 , 56, 60 Limiter 19 Isolator 22 Termination resistor 31 Processing circuit 32 Memory 33 Visual display means 43 Buffer

Claims (3)

[Claims] 1. A receiving antenna for receiving an electromagnetic wave, an amplifier circuit, and a limiter provided in a preceding stage of the amplifier circuit for limiting an input signal to an amplitude within a range where the amplifier circuit is not saturated, and the receiver antenna and the limiter. An isolator, which is interposed between, inputs the output from the receiving antenna to the limiter and derives a reflected signal by the limiter, and a terminating impedance element that is provided with the reflected signal and matches the impedance from which the reflected signal of the isolator is derived. A receiving device including. 2. A receiving antenna for receiving an electromagnetic wave, a buffer for deriving an output from the receiving antenna without saturating, an amplifier circuit having a gain larger than that of the buffer, and a buffer interposed between the buffer circuit and the amplifier circuit. And a limiter for limiting the output of the buffer by an amplitude within a range in which the amplifier circuit does not saturate. 3. A receiving antenna for receiving electromagnetic waves, a multi-stage amplifying circuit to which an output from the receiving antenna is given, and a range connected to immediately after each amplifying circuit so that the output from the preceding amplifying circuit is not saturated by the following amplifying circuit. And a limiter for limiting the amplitude within the receiver.