JP2550574B2 - Radar device - Google Patents

Description

The present invention relates to a radar device, and more particularly to an FM-CW radar device for detecting the distance and speed of a target.

[Prior Art] An FM-CW radar device emits a frequency-modulated continuous wave toward a target, and accurately determines the distance and speed of the target from the reflected wave reflected from the target and the beat signal of the continuous wave. It is known, and in recent years, it has been attempted to apply it to a vehicle for forward monitoring of an auto drive device (for example, SANE82).
-36, SAE770267).

The above radar device normally obtains an oscillation wave that repeats rising and falling of frequency at a constant rate periodically by triangular wave modulation, emits this to the target, and outputs the beat signal at the rising frequency portion and the beat signal at the falling frequency portion. The beat signal is detected, and the distance and speed are calculated from these beat signals.

[Problems to be Solved by the Invention] In the above-described conventional radar device, since both beat signals are obtained in the first half and the second half of the modulation period, there is a time lag of a half period, and the target is in between. There was a problem that a measurement error occurred when was moved.

Further, it is necessary to accurately match the frequency rising rate and the frequency falling rate, but for this purpose, for example, a complicated circuit for correcting the distortion of the voltage-frequency characteristic of the voltage controlled oscillator in the modulated wave oscillating unit is required (special feature). (Kaisho 60-93977).

The present invention is intended to solve such a problem, and it is possible to obtain the beat signals of the frequency rising portion and the falling portion at the same time without causing a time shift, and it is possible to measure a high-speed target with high accuracy. Another object of the present invention is to provide a radar device that does not require a complicated correction circuit.

[Means for Solving Problems] The configuration of the present invention will be described with reference to FIG.
Oscillation means 1 for issuing a reference oscillation signal that oscillates at a reference frequency
And the reference oscillation signal is frequency-modulated by the same modulation wave, and the upper sideband signal in which the frequency repeats rising in a constant cycle in the region higher than the reference frequency, and the frequency in the region lower than the reference frequency in the constant period. Modulating means 2 that simultaneously emits a lower sideband signal that repeats falling, transmitting antenna 3 that transmits each of the signals of the upper sideband and the lower sideband toward a target, and the upper side reflected from the target. A receiving antenna 4 for receiving the waveband reflected signal and the lower sideband reflected signal,
The frequency difference between the upper sideband signal and the upper sideband reflection signal is detected and the frequency difference between the lower sideband signal and the lower sideband reflection signal is detected, and the distance and speed of the target are determined from these frequency differences. And a signal processing signal 5 to be calculated.

[Operations and Effects] In the radar device of the present invention, the reference oscillation signal is modulated with the same modulated wave, and the upper sideband signal that repeats rising at a constant cycle and the lower sideband signal that repeats falling at the same cycle are modulated. At the same time, the upper sideband signal and the lower sideband signal are emitted to the target as the transmitted waves, and the distance and speed of the target are calculated from the frequency difference between each signal and the reflection signal from the target, that is, the beat frequency. ing.

Thus, according to the present invention, since the transmitted wave includes the frequency rising portion and the falling portion at the same time with no time lag, it is highly accurate without error even when the target is moving at high speed. It is possible to measure.

Further, since the frequency rising part and the falling part are the upper sideband signal and the lower sideband signal which are obtained at the same time by the same modulated wave, the frequency rising and falling frequencies are completely symmetrically equal and the complicated correction as in the conventional No circuit required.

[Embodiment] FIG. 1 shows a block diagram of a radar apparatus. In FIG, 1 is a local oscillator, and outputs a reference oscillation signal S0 of the reference frequency f ₀ of the microwave range. The modulation means 2 includes a modulated wave transmitter 21 and two single sideband up converters 22A, 2
It is composed of 2B. Modulation wave oscillator 21 is modulated
And the modulated signal S1 has a constant period based on the frequency fm.
The frequency changes in a sawtooth pattern with tm (Fig. 2 (1)).
The frequency deviation of the signal S1 is Δf.

Both the reference oscillation signal S0 and the modulation signal S1 are input to the up-converters 22A and 22B, and the up-converter 22A emits the upper sideband signal S2 having the sum frequency of the both signals S0 and S1. On the other hand, in the up converter 22B, both signals S0 and S1
Emits a lower sideband signal S3 having a difference frequency of. Each of these signals S
As shown in FIG. 2 (2), the frequencies of 2 and S3 repeatedly rise and fall in a sawtooth wave at a constant period tm above and below the reference frequency f ₀ .

The signals S2 and S3 of the upper sideband and the lower sideband are input to the power combiner 6, are combined, and are emitted as a transmitted wave from the transmitting antenna 3 toward a target (not shown). Incidentally, the signals S2 and S3 are partially taken out by the directional couplers 7A and 7B on the way.

The transmitted wave is reflected by the target and returns, and the receiving antenna 4
Is received at. The received reflected wave is the power divider 7
Input into the mixer and divided to form the signal processing means 5.
Input to 51A and 51B.

Here, the upper sideband reflected signal S2 'and the lower sideband reflected signal S3' in the reflected wave are shown by broken lines in FIG. 2 (2). As is known from the figure, each of the reflection signals S2 'and S3' undergoes a time delay Δt proportional to the distance to the target and a frequency deviation fD proportional to the relative speed of the target.

The mixer 51A inputs the reflected wave and the upper sideband signal S2 from the directional coupler 7A. Above signal S2
The signals S2 'and S3' are down-converted by the mixer 51A to become the signal S4. In the signal S4, the down-converted components of the signals S2 and S3 'have a frequency of (2fm-fD) or more.

By the way, if the frequency fm is set to be sufficiently larger than the frequency fD, the above component can be cut by an appropriate low-pass filter. A filter 52A is provided for this purpose. Thus, the signal S6 that has passed through the filter 52A contains only the down-converted components of the signals S2 and S2 '. This is shown in FIG. 2 (3).

As shown in the figure, this down-converted component has a frequency that is the difference between the difference frequency fR and the frequency deviation fD due to the time delay Δt. The unnecessary beat shown by the broken line in the figure is cut by the filter 52A.

The mixer 51B inputs the reflected wave and the lower sideband signal S3, down-converts and outputs the signal S5. The signal S5 is input to the filter 52B and output as the signal S7. The process of obtaining the signal S7 is similar to the process of obtaining the signal S6, and the signal S7 includes only the down-converted components of the signal S3 and the signal S3 '. This is shown in FIG. 2 (4).

This down-converted component has a frequency that is the sum of the difference frequency fR and the frequency deviation fD as shown in the figure.

The signals S6 and S7 are input to the signal processing circuit 53. The configuration of the circuit 53 is shown in FIG. 3, and a pair of AD converters 531A and 531B for inputting signals S6 and S7, respectively, and a fast Fourier transform (FF
T) Processors 532A and 532B, and an arithmetic unit 533.

AD converters 531A and 531B convert the above signals from time to + Δt to to tm, and then FFT processors 532A and 532B.
Then, the frequencies fR−fD and fR + fD of these signals are calculated.
The calculator 533 obtains the frequencies fR and fD, and from these, the distance to the target and the relative speed are obtained, respectively. The obtained distance and relative speed are displayed on the display 9.

As described above, in the above radar device, the modulation waveform is a sawtooth wave, the rising slope portion is generated in the upper sideband, and the falling slope portion is generated in the lower sideband. Signal sampling is possible. Further, since the modulation waves input to the two up-converters are the same, the symmetry of the slope of the modulation output waveform is extremely good.

FIG. 4 shows another embodiment of the present invention. In this embodiment, one up-converter 22 simultaneously generates an upper sideband signal S2 and a lower sideband signal S3, and part of them is generated by the directional coupler 7.
After taking out with and dividing with the power divider 71, filter
The upper sideband signal S2 and the lower sideband signal S3 are separated through 72A and 72B, respectively. Separate the separated signals S2 and S3 with mixers 51A and 5A.
Supply to 1B.

According to this structure, since only one up converter needs to be provided, the radar device is simple and inexpensive.

[Brief description of drawings]

1 to 3 show an embodiment of the present invention, FIG. 1 is a block diagram of a radar device, FIG. 2 is a signal time chart, FIG. 3 is a block diagram of a signal processing circuit, and FIG.
FIG. 6 is a block diagram of a radar device showing another embodiment of the present invention. 1 ... Local oscillator (oscillating means) 2 ... Modulating means 21 ... Modulated wave oscillator 22, 22A, 22B ... Up converter 3 ... Transmitting antenna 4 ... Receiving antenna 5 ... Signal processing means 51A, 51B. Mixer 52A, 52B ... Filter 53 ... Signal processing circuit

Claims (1)

(57) [Claims] 1. An upper side wave which oscillates a reference oscillating signal oscillating at a reference frequency and frequency-modulates the reference oscillating signal with the same modulation wave so that the frequency repeatedly rises at a constant cycle in a region higher than the reference frequency. A band signal, and a modulation means for simultaneously emitting a lower sideband signal whose frequency repeats falling at the constant cycle in a region lower than the reference frequency, and each signal of the upper sideband and the lower sideband toward the target. A transmitting antenna that simultaneously transmits, a receiving antenna that receives the upper sideband reflected signal and the lower sideband reflected signal reflected from the target, and the frequency difference between the upper sideband signal and the upper sideband reflected signal is detected. In addition, the radar device is provided with signal processing means for detecting a frequency difference between the lower sideband signal and the lower sideband reflected signal and calculating the distance and speed of the target from the frequency difference.