JP3243052B2 - Sampling receiver - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a sampling receiver used for detecting signals of an underground radar or the like.

[0002]

2. Description of the Related Art In general, in an underground radar for detecting an object buried in the ground, the electromagnetic wave used is greatly attenuated by a medium. The signal intensity of the reflected light becomes extremely large, which hinders the measurement. For this reason, a so-called STC is used, in which the receiving sensitivity is reduced at a short distance, and the receiving sensitivity is increased as the distance increases, that is, as time passes.

[0003] There are generally two types of STC methods. One is a measurement time zone for each transmission signal, for example, 200 ns.
There is a method in which the signal strength is adjusted by directly controlling the gain of the high-frequency amplifier. (First Prior Art) As another method, a sampling circuit is used to perform measurement. For example, a signal in a measurement time zone of 200 ns is extended by 100,000 times to obtain a signal in a time zone of 20 ms. There is a method of performing STC on the signal obtained. (Second
With respect to these methods, the present applicant inserts a voltage-controlled variable attenuator in the first stage in a sampling receiver,
Means for performing STC is disclosed in Japanese Patent Application Laid-Open No. 2-27285.

[0004]

In the first prior art, a gain control circuit is used in the first stage of the receiver, so that an STC with a large dynamic range can be applied. However, the gain control is performed within a short time of 200 ns for each measurement time zone. Therefore, there is a drawback that the adjustment of the STC signal is delicate and that a gain variable element having an ultra-high-speed response is required. In the second prior art, the period is 20 ms because the sampling is performed.
Although the STC is easy to control, it operates on a time-expanded signal, and the dynamic range of the signal is small. Therefore, there is a disadvantage that accurate STC cannot be performed in a signal saturation region.

On the other hand, the applicant of the present invention has disclosed in
In the sampling receiver, a voltage-controlled variable attenuator is inserted in the first stage to apply STC with a large dynamic range,
The period of time is extended to make the control of the STC easy, thereby solving the drawbacks of both the first prior art and the second prior art. However, in the latter half of the time expansion, since the gain is increased, a strong short-range signal is input to the high-frequency amplifier before sampling. Therefore, there is a disadvantage that a weak signal from a long distance is distorted. Due to this drawback, a limiting amplifier must be used before the high-frequency amplifier, or an amplifier with a large saturation level must be used, which complicates the circuit configuration. An object of the present invention is to provide a sampling circuit having a simple circuit configuration in which a weak signal from a long distance is not distorted.

[0006]

According to the present invention, in order to solve the above-mentioned problems, in a sampling receiver, a switch circuit is provided before a high-frequency amplifier, and a monostable multi-circuit is driven by a signal from a strobe signal generation circuit. do it,
At the same time when the switch circuit is turned on and off, a reception signal is sampled only during a time period when the switch circuit is turned on.

[0007]

FIG. 1 shows an embodiment in which the present invention is applied to an underground radar apparatus. The transmission timing output from the strobe signal generation circuit 1 is supplied to the pulser 11 after being given a fixed delay by the fixed delay circuit 2, whereby a high-output transmission pulse is generated, and the balun 12
A pulse electromagnetic wave is emitted from the transmission antenna 13 through the.

[0008] The reflected wave of the pulsed electromagnetic wave is received by the receiving antenna 14. This received signal is balun 15
Passes through the voltage-controlled variable attenuator 6 via the switch (S
W) is controlled by the circuit 7 and applied to the high frequency amplifier 8. The output of the high-frequency amplifier 8 is sampled by a signal obtained by delaying the strobe signal from the strobe signal generation circuit 1 by the delay circuit 2 '. The output of the sampler 9 is shaped by a low-pass filter 10 and extracted as a target signal.

FIG. 2 shows the time relationship of sampling in the present apparatus. a is the period of the time-expanded received signal, which is, for example, 20 ms. At the same time, the STC operation is shown, and an STC signal synchronized with the time-expanded reception signal is generated by the STC signal generator 5 by a signal from the strobe signal generation circuit 1. The voltage controlled attenuator 6 is controlled by the STC signal so as to minimize the gain at the beginning of sampling, gradually increase the gain with time, and maximize the gain at the end of sampling.

[0010] "b" indicates an output pulse of the transmitting antenna 13, and its cycle is set to, for example, 600 ns. The transmission signal generated by the strobe signal generation circuit 1 is supplied to the pulser 11 after being delayed for a predetermined time by the delay circuit 2. Pulsar 1
A high-output transmission pulse is generated by 1, and a pulse electromagnetic wave is emitted from the transmission antenna 13 through the balun 12. All received signals are within this 600 ns.

C is a signal which is time-controlled by the strobe signal generation circuit 1 so that the sampling time is sequentially shifted;
The signal is delayed by a delay circuit 2 ′ having the same delay time as the delay circuit 2, and becomes a strobe signal in the sampler 9. In the case of c, the transmission signal of b is delayed by the strobe signal generation circuit 1 for the first time and at the next time by the time Δt, and thereafter, by the third time, the time of the fourth time, the time delay of 2Δt, 3Δt... , Create a maximum delay time between 20 ms and repeat it. Therefore, the received signal in the transmission cycle of 600 ns is 20 ms / 600 ns.
, The time is extended.

D indicates an output signal of the monostable multi-circuit 4. The monostable multi-circuit 4 is triggered by a signal that is time-controlled so that the sampling time is sequentially shifted by the strobe signal generation circuit 1, and outputs a pulse r having a predetermined time width. The switch r is controlled to be turned on by the pulse r. Therefore, the received signal is input to the high frequency amplifier 8 only during the time width of the pulse r.

At the beginning of the sampling time, the gain is suppressed to the minimum by the function of the STC signal as described above, and the received signal is not distorted. We try to receive weak signals as much as possible. However, the transmission cycle of 600
Since a strong signal from a short distance always exists within the reception range of ns, a normal amplifier saturates the amplifier and distorts a received signal from a long distance.

Here, the pulse r is output earlier than the strobe signal indicated by c by the delay time of the delay circuit 2 '. Since only the received signal having the width of the pulse r is input to the high-frequency amplifier 8, signals other than signals necessary for sampling are not applied to the high-frequency amplifier 8. For this reason, a strong signal from a short distance is not applied to the high frequency amplifier 8, so that a received signal from a long distance is not distorted, and the original purpose of the STC can be achieved. The width of the pulse r should be as narrow as possible as long as a signal in a time zone necessary for sampling detection can be passed. However, an appropriate value may be determined depending on circuit characteristics and the like.

[0015]

In the STC conventionally used, the influence of a strong signal from a short distance is unavoidable in a portion corresponding to a long distance, and a limiting amplifier is used in front of a high frequency amplifier or a high saturation level is used. It was necessary to take measures such as using an amplifier. According to the present invention, the received signal is completely cut off except during the sampling period, so that the received signal from a long distance is not distorted despite the time-expanded STC, achieving the original purpose of the STC. can do.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a diagram showing a relationship between signals of main parts.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Strobe signal generation circuit 2 Delay circuit 2 'delay circuit 4 Monostable multi-circuit 5 STC signal generator 6 Voltage control variable attenuator 7 SW circuit 8 High frequency amplifier 9 Sampler 10 Low pass filter 11 Pulser 12 Balun 13 Transmission antenna 14 Reception Antenna 15 Balun a Time expansion cycle b Transmission cycle c Strobe signal d Monostable multi-circuit output signal

Continuation of the front page (56) References JP-A-2-27285 (JP, A) JP-A-62-104226 (JP, A) JP-A-64-479 (JP, A) JP-A-58-225370 (JP) , A) Fully open sho 61-112283 (JP, U) Fully open sho 63-55186 (JP, U) Full open hira 2-63482 (JP, U) Full open hei 5-11081 (JP, U) (58) Field surveyed (Int. Cl. ⁷ , DB name) G01S ⁷ /00-7/42 G01S 13/00-13/95

Claims (1)

(57) [Claims] 1. A sampling receiver which samples a received signal returned by reflection by using a strobe signal which is synchronized with the reflected signal but whose phase is sequentially shifted to obtain a signal having a received waveform which is time-expanded. A voltage-controlled variable attenuator inserted at the first stage of the device; and an STC for generating a sensitivity time control signal in synchronization with the time-expanded reception waveform and supplying the signal to the voltage-controlled variable attenuator.
A sampling receiver, comprising: a signal generator; and a switching circuit for controlling connection of a received signal only during a time period in which the strobe signal is sampling, and not for connection in other time periods.