JPH0129274B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an FM-CW radar that is capable of detecting nearby objects at a distance shorter than the relative distance measurement range.

The FM-CW radar is capable of measuring relative speed and distance, and can be applied to a collision prevention radar system for an automobile, and conventionally had the configuration shown in FIG. 1, for example. In the figure, 1 is a transmitting antenna, 2 is a transmitter, 3 is a modulator that performs modulation of frequency deviation ΔF with a modulation period of 1/Fm, and 4 is a synchronization signal that generates a synchronization signal with a modulation period of 1/Fm. a generating circuit, 5 a receiving antenna that receives reflected radio waves, 6 a mixer that mixes the received signal and a part of the transmitted signal and outputs a beat signal, 7
8 is a band pass filter that cuts out up to the third harmonic component of the modulation frequency Fm included in the beat signal, 8 is a counter that starts counting the beat signal for each synchronization signal, and 9 is the distance information of the count contents of counter 8. This is a display section that converts and displays the image.

The frequency Fr of the beat signal formed by the mixer 6 is defined as follows: When the relative speed is zero, that is, the traveling speed of the vehicle in front and the radar-equipped vehicle are the same, the relative distance to the vehicle in front is R, and the speed of light is C. Then, it is expressed as Fr=4・R・Fm・ΔF/C (1). Therefore, the relative distance R can be measured by measuring the beat frequency Fr.

In reality, a signal with a modulation frequency Fm leaks into the beat signal obtained by the mixer 6, and measuring this modulation frequency component will result in a large distance measurement error. It cuts frequencies up to about the third harmonic of frequency Fm. Therefore, the minimum detection distance Rmin
is expressed as Rmin=3・Fm・C/4・Fm・ΔF =3・C/4・ΔF (2) If ΔF=45MHz, Rmin=3m
becomes. Therefore, even if there is a vehicle or obstacle in front at a distance of 3 meters or less, it cannot be detected, and when an FM-CW radar is applied to a collision prevention radar system,
Minimum detection distance because it cannot detect nearby objects
There was a drawback that when approaching below Rmin, it was determined that there were no obstacles.

The present invention improves the above-mentioned drawbacks, and
The purpose of this invention is to enable detection of nearby objects that are less than the minimum detection distance by adding a small number of configurations. Examples will be described in detail below.

FIG. 2 is a block diagram of an embodiment of the present invention, in which the same symbols as in FIG. 1 indicate the same parts, 10 is a proximity detection circuit, 11 is a low pass filter, 12 is a detection circuit, 13 is an integration circuit, is the integration circuit 13
This is a level detection circuit that detects whether the output level of the output level is higher than or equal to a reference level. Since the time difference between the transmitted radio wave and the received radio wave for a nearby object is very small, the frequency of the beat signal output from the mixer 6 is low and can pass through the low-pass filter 11. The output of this low-pass filter 11 is detected by a detection circuit 12, integrated by an integration circuit 13, and converted into a DC level. When the level detection circuit 14 detects that this DC level is higher than a predetermined reference level, it is displayed on the display section 9 that there is an object nearby.

If the relative distance to an object such as a vehicle ahead is large to a certain extent, the frequency of the beat signal output from the mixer 6 will increase, making it impossible to pass through the low-pass filter 11, and the DC level of the output from the integrating circuit 13 will become low. , the level detection circuit 14 can determine that there is no nearby object. In this case, the normal
Similar to the FM-CW radar, the relative distance and relative speed are displayed on the display section 9.

As explained above, in conventional FM-CW radars, in order to eliminate relative distance measurement errors due to harmonic components, the bandpass filter 7 cuts the modulation frequency to, for example, the third harmonic, and then Therefore, it has been impossible to detect objects with a distance less than the minimum detection distance Rmin. However, according to the present invention, by detecting the level of the low frequency component of the output of the mixer 6 using the proximity detection circuit 10, it is possible to detect nearby objects. becomes possible. In other words, even if it is not possible to measure the distance to a nearby object, it is possible to detect the presence or absence of a nearby object.
When applied to a collision prevention radar system, reliable collision prevention control can be performed.
Reliability can be improved.

It should be noted that the present invention is not limited to the above-described embodiments; for example, it is also possible to adopt a configuration in which the transmitting antenna 1 and the receiving antenna 5 are shared.
It is also possible to generate a warning sound upon detection of a nearby object.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a conventional FM-CW radar, and FIG. 2 is a block diagram of an embodiment of the present invention. 1 is a transmitting antenna, 2 is a transmitter, 3 is a modulator,
4 is a synchronization signal generation circuit, 5 is a receiving antenna, 6 is a mixer, 7 is a band pass filter, 8 is a counter, 9 is a display section, 10 is a proximity detection circuit, 11 is a low pass filter, 12 is a detection circuit, 13 is an integrator The circuit 14 is a level detection circuit.

Claims (1)

[Claims] 1. Mixing a part of the transmission signal frequency-modulated with a modulation signal with a constant period and a constant frequency shift and the reception signal, and forming a beat signal by removing the frequency component of the modulation signal from the mixed signal. , an FM-CW radar that measures the frequency of the beat signal and measures the relative velocity and relative distance to an object, a low-pass filter that adds the beat signal, and a detection means that detects the output of the low-pass filter. , a proximity detection circuit comprising a determination means for determining that an object is present when the output level of the detection means is equal to or higher than a predetermined level.
FM-CW radar.