JPS63249071A - Pulse compression circuit in searching apparatus - Google Patents

Abstract

PURPOSE:To enhance the resolving power of a receiving signal without requiring the wide band characteristic from a sensor and widening the band of an amplifying system, by compressing pulses by providing a frequency multiplier to a matched filter. CONSTITUTION:A chirp oscillator 2 sends out linear FM signals changing from frequency f1 to frequency f2 in a pulse like manner to operate a sensor 1 and the return reflected signal from a target to be searched received by the sensor 1 is amplified by an amplifier 3 and frequencies are multiplied by (n) by a PLL circuit 4 and a signal (b) changing to nf1-nf2 is sent to a correlation device 6 constituting a matched filter and a pulse width is compressed to 1/n to be sharpened while nf1-nf2 signals are applied to the correlation device 6 from a linear FM signal generator 7. By this constitution, all of phases coincide when the signal (b) is inputted and a peaked wave signal (c) is obtained without being accompanied by energy loss. This output is detected by a detector 8 and a signal (d) is outputted through a filter 9.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a pulse compression circuit for improving resolution in a device that detects a target object or distance by transmitting and receiving radio waves or ultrasonic pulses.

(Prior Art) Pulse compression technology is based on a pulse compression technique in which when a linear FM signal (see signal a in FIG. 2) whose carrier frequency changes to f, -f2 during a pulse width ta passes through a matched filter, the pulse width 1. The signal is compressed into a pulse-like signal.

At this time, t is becomes.

When the circuit design is optimal, the resolution of pulse compression using a linear FM signal is the value given by the above equation (1), and higher resolution cannot be expected.

In such a case, in order to increase the resolution, it is sufficient to increase the amount of change in the frequency of the linear FM signal.

(Problems to be Solved by the Invention) However, if the amount of change is increased, the occupied bandwidth of the signal becomes wider, resulting in the following drawbacks.

(1) Wideband characteristics are required for the ° sensor.

Ultrasonic transducers generally have a narrow band, so signals with a large amount of change cannot pass through them.In other words, the transducer limits the band, so it is not possible to obtain resolution greater than the band of the transducer.

(2) Broadband characteristics are required for the amplifier system.

Although it is not difficult to design an amplifier with a wide band, it is difficult to design an amplifier with a wide band because it increases noise.
/N ratio deteriorates.

(Means for Solving the Problems) The present invention does not require the sensor to have broadband characteristics;
It also achieves high resolution without widening the band of the 7-amp system, and provides a new pulse compression circuit with a frequency multiplier installed before the mated filter in detection equipment that uses conventional pulse compression technology. It is something.

(Function) According to the present invention, the linear FM signal that changes up to the frequency rt-12 can be converted into a change in the frequency nfl-nf2 by the multiplier, so the pulse width ts' due to the matched filter is as follows, and the pulse width is Sharpened to L.

(Embodiment) FIG. 1 is a circuit diagram showing an embodiment of the pulse compression technique according to the present invention. FIG. 2 is a waveform diagram thereof.

In Figure 1, 1 is a sensor that transmits and receives ultrasonic waves, and 2 is a linear FM whose frequency changes up to rt-f2.
This is a chirp oscillation circuit that sends out a pulsed signal to activate the sensor l. 3 amplifies the return reflection signal from the detection target received by sensor 1 (Figure 2a)
It's an amplifier.

4.5 is a PLI, a circuit, and an n frequency divider that constitute the PLL. The frequency of the PLL output signal is multiplied by n times, and n
The received pulse signal that changes from fr-nf2 is 0.6.7 is a correlator that constitutes a matched filter and 6 linear signals that send out a signal whose frequency changes from nf1 to nf2.
This is an FM signal generation circuit.

The correlator 6 is not shown, but is composed of, for example, a two-column shift register and a multiplier interposed between each stage of the shift register, and is already known. A signal with a frequency nf2 is taken into this shift register at a frequency that can be reproduced after sampling. Therefore, the capacity of the shift register is required to be equal to ta/fetching period.

A linear FM signal is previously taken in as a reference signal at the same timing as above and stored in the other shift register.

In this way, when the received signal is captured, all the phases match and the pulse width t is generated without energy loss.
A peak wave signal C of s' is obtained.

8 is a detection circuit for detecting the signal C, and 9 is a filter, from which a pulse wave d is obtained as an output as a detection signal.

(Effects of the Invention) As explained above, according to the present invention, the value of n can be freely selected by the frequency divider 5, so the resolution and accuracy in the time direction of the detection signal can be brought to the desired value and significantly improved. can be done.

Although the embodiment has been described using a shift register as the contents of the matched filter, it is also possible to use a general storage means, or to perform calculation processing on the entire matched filter using software.

Furthermore, it is also possible to achieve the same effect not only in a digital manner but also in an analog manner by configuring a surface acoustic wave filter or an LC delay line.

Further, the present invention is not limited to the case where a chirp signal is used as a transmission pulse, but can be similarly applied to a case where a constant frequency is transmitted and an FM signal is received at the time of reception.

That is, in a detection device such as a scanning sonar, 1. A large number of sensors are arranged in an annular shape on the cylindrical surface, and waves are transmitted simultaneously at a constant frequency, and waves are received by rotating the receiving beam at high speed. The received signal at each sensor shows a frequency change similar to that caused by the Doppler effect. In this case, the frequency change is quantitative due to the high-speed rotation of the received beam, so pulse compression technology is applied. It will be possible (Japanese Patent Application Laid-Open No. 58-12.71813)
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[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the pulse compression technique according to the present invention, and FIG. 2 is a waveform diagram thereof.

Claims (1)

[Claims] A device for transmitting and receiving pulse signals to detect targets and distances, comprising means for multiplying the frequency of the received signal by n times, and a matched filter for pulse-compressing the output of the multiplication means. A pulse compression circuit in a detection device comprising: