JPH05297124A - Fm-cw distance measuring device - Google Patents

Abstract

PURPOSE:To remove the error in distance measuring due to false signal and establish accurate measurement of the distance by increasing or decreasing the frequency modulation rate, converting the spectrum into distance distribution from time to time, and determining correlation of distance distributions having different modulation rates. CONSTITUTION:Beat signals of the transmitted and received waves obtained by a mixer 8 are passed through an amplifier 9, LPF 10, and A/D converter 11, subjected to a high speed Fourier transform by an FFT processor 12, and converted into spectrum. A CPU 1 calculates the distance distribution from the data of frequency modulation rate obtained bar controlling this with a D/A converter 2. The distance distribution when the modulation rate is increased and decreased indicates that the distance information is diffused, when the time-based correlation of the distance is strong, and the true distance information remains unchanged. In the case where multiplication of the distance distributions having different modulation rates is conducted, therefore, the level of the true distance information rises while the level of the distance information diffused by the false signal sinks. The peak of the distance distribution shows the true distance, and errorless measurement is ensured even when the level of the false signal is large.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a frequency-modulated continuous wave (Fr) capable of accurately measuring a distance even in the presence of deceptive signals.
equency Modulation Continuous Wave, FM-CW
Abbreviated. ) Regarding a distance measuring device.

[0002]

2. Description of the Related Art The distance H is given by the following equation in the FM-CW distance measuring system by linear frequency modulation.

H = (C / 2) × (T / ΔF) × f _b (1) C: speed of light T: modulation period ΔF: frequency modulation width f _b : beat signal frequency τ = C / 2: delay time As shown in FIG. 2, when two spectrum components having a frequency difference of fbj are incident on the transmission / reception signal band, the beat signal spectrum has two beat signals f _b1 and f _bj proportional to the delay time τ. Will exist.

[0004]

However, in the conventional FM-CW range finder, as shown in FIG. 2A, when the level of f _bj is higher than the level of f _b1 , the beat converted into the distance is calculated. As for the frequency, f _bj became dominant, which adversely affected distance measurement.

This is because of the deception signal for the FM-CW range finding method. Conventionally, the existence of the deception signal is determined by determining the presence or absence of the signal obtained during the period during which the frequency modulation is stopped. If they did, they took measures such as issuing an alarm.

Therefore, it was impossible to measure the distance in the presence of the deceptive signal.

Therefore, in view of the above-mentioned drawbacks, a technical object of the present invention is to provide an FM-CW distance measuring device capable of eliminating an error in distance measuring caused by a deception signal and performing accurate distance measuring.

[0008]

According to the present invention, spectrum measuring means for measuring spectra of a plurality of beat signals, and the measured plurality of spectra are converted from different frequency modulation rates into a plurality of distance distributions. An FM-CW range finding device is obtained, which comprises: a distance distribution conversion unit that performs the above-described distance distribution and a correlation unit that correlates the plurality of distance distributions.

That is, according to the present invention, in order to obtain an accurate distance even in the presence of a deception signal, the frequency modulation rate is increased or decreased within a certain range, and the individual spectrum at that time is converted into a distance distribution to obtain the frequency modulation rate. FM- characterized by correlating multiple distance distributions with different
It is a CW range finder.

[0010]

Embodiments of the present invention will now be described with reference to the drawings.

FIG. 1 shows an embodiment of the present invention, 1 is a CPU (central processing unit), 2 is a D / A (digital / analog).
Converter, 3 saw-tooth generator, 4 VCO (voltage controlled oscillator), 5 directional coupler, 6 transmitting antenna, 7 receiving antenna, 8 mixer, 9 amplifier, 10 LPF
(Low-pass filter), 11 is an A / D (analog / digital) converter, and 12 is an FFT (fast Fourier transform) processor.

The digital signal generated by the CPU 1 is D / A
The converter 2 produces an analog signal and the sawtooth generator 4 produces a sawtooth signal. The voltage of the sawtooth wave signal causes the VCO 4 to oscillate a frequency modulation wave. Then, the directional coupler 5 supplies a part of the frequency-modulated wave to the mixer 8 and causes the rest to be radiated via the transmission antenna 6.

The reflected wave from the target surface is delayed in proportion to the distance and supplied to the mixer 8 through the receiving antenna 7. The beat signal obtained by the mixer 8 is amplified by the amplifier 9 to a predetermined level, and the LPF 1 for preventing aliasing distortion.
After being band-limited by 0, it is converted into a digital signal by the A / D converter 11. In addition, the digital signal is FFT
It is converted into a spectrum by the processor 12.

In the CPU 1, the spectrum of the beat signal, that is, the frequency component is converted into the distance distribution by the above-mentioned equation (1) from the data of the frequency modulation rate ΔF / T obtained by controlling the D / A converter 2. Convert.

At this time, as shown in FIG. 2 (a), the beat signal frequency f _bj due to the deception signal and the beat signal frequency f _b1 due to the delay amount τ are converted as H ₁ and H _j , respectively, and are converted into the conventional ones. According to the processing, H _j is set as the detection distance.

Here, when the next modulation rate is increased,
Assuming that there is almost no change in the distance, the obtained distance distribution is such that H _j shifts to a short distance and H ₂ becomes almost equal to H ₁ , as shown in FIG.

On the contrary, if the modulation rate is lowered, as shown in FIG.
As shown in (c), H _j moves to a long distance and H ₃ becomes almost equal to H ₁ .

As described above, when the modulation rate is increased / decreased and the distance distribution at that time is examined, when the distance has a strong temporal correlation,
The distance information by the deception signal is diffused, and the true distance information hardly changes.

Therefore, when the distance distributions having different modulation rates are multiplied, the level of H ₁ = H ₂ = H ₃ which is the true distance information rises as shown in FIG. 3 and is spread by H _j . The peak level of distance information will be reduced. The peak of this distance distribution indicates the true distance, and even when the level of the deception signal is large, the distance can be measured without error.

The above processing is performed by the CPU 1 and the distance information is output.

Since the above processing must be performed within the band of the LPF 10, control is performed with the center value of the modulation rate when the spectrum at the true distance comes to the center of the band. Further, when the distance is changing, the distance distribution is dispersed, and thus the obtained distance information is averaged and the real responsiveness is deteriorated. Therefore, if the spectrum above a certain level exists at the time when it is converted into a spectrum and there is a possibility of a deception signal, if the above process is performed and the distance for one modulation rate is normally calculated, The same responsiveness as in the past can be obtained.

[0022]

As described above, according to the present invention,
Even if there is a deception signal, the fact that the distance has a strong temporal correlation can be used to eliminate the error in distance measurement due to deception and to perform accurate distance measurement. Further, the modulation rate is not constant depending on the distance and changes randomly, so that a synchronous deception signal cannot be produced. Therefore, the anti-jamming property is improved as compared with the conventional case.

[Brief description of drawings]

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

FIG. 2 is a diagram showing a beat frequency distribution and a distance distribution when the modulation rate is changed.

FIG. 3 is a diagram showing a result of correlation of distance distributions of different modulation rates.

[Explanation of symbols]

 1 CPU 2 D / A converter 3 Sawtooth generator 4 VCO 5 Directional coupler 6 Transmission antenna 7 Reception antenna 8 Mixer 9 Amplifier 10 LPF 11 A / D converter 12 FFT processor

Claims (1)

[Claims] 1. A spectrum measuring unit for measuring spectra of a plurality of beat signals, a distance distribution converting unit for converting the measured plurality of spectra into a plurality of distance distributions from different frequency modulation rates, and the plurality of distance distribution converting units. An FM-CW distance measuring device, comprising: a correlating unit that correlates a distance distribution.