JPH08122428A - Am radar - Google Patents

Abstract

PURPOSE: To obtain an AM radar in which interference is prevented among a plurality of radars operating on vehicles located closely each other. CONSTITUTION: The AM radar comprises a circuit 1 for generating a carrier (C), a circuit 2 for generating a modulation signal (a) having lower frequency than the carrier, a circuit 3 for amplitude modulating the carrier (C) with the modulation signal (a), antennas 4, 5 for transmitting the amplitude modulated signal and receiving the reflected wave thereof, a circuit 6 for detecting a modulation signal (b) included in the reflected wave being received, and a circuit 7 for detecting the phase difference between the modulation signals (a) and (b). The AM radar further comprises a circuit 10 for calculating the distance to the object on which the carrier is reflected from the phase difference thus detected, and means 10 for altering the frequency of the modulation signal being generated from the circuit 2 randomly over a predetermined range.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an AM radar device as a vehicle-mounted radar system, and more particularly to an AM radar device capable of effectively preventing interference between vehicles.

[0002]

2. Description of the Related Art An on-vehicle radar device mounted on a vehicle such as a passenger car is used in combination with a warning device or a display device for collision prevention. Such an on-vehicle radar device has a short-distance detection capability of several tens of centimeters because it is a warning target for a rear-end collision accident in a state where the inter-vehicle distance is small, such as during a traffic jam, or a contact accident when the vehicle is parked. In this respect, AM radar and F
The form of M radar is suitable. Further, in terms of downsizing of the radar module, it is desirable to use radio waves in the high-frequency millimeter wave band as a carrier wave. Such a millimeter-wave band FM radar device is disclosed in the specification of Japanese Patent Application No. 3-42979 related to the applicant's prior application.

In the AM radar device, a high frequency carrier wave is amplitude-modulated by a low frequency sine wave or rectangular wave modulation signal and sent out from the antenna. The reflected wave from the target is received by the antenna, and the phase difference between the modulated signal contained in the received reflected wave and the original modulated signal is detected. The distance to the target that caused the reflected wave is calculated.

[0004]

The above-described operation A is performed.
In the M radar device, A of a plurality of vehicles that are close to each other
If the M radar device uses a modulated signal of the same frequency,
There is a problem that interference between devices occurs and the function as a radar device is impaired. That is, if the AM radar device of each vehicle mistakenly recognizes the AM signal transmitted from the AM radar device of another vehicle as the reflected wave of the AM signal transmitted by the AM radar device of the own vehicle, a completely incorrect detection result regarding the target position is obtained. I will get it. Therefore, one object of the present invention is to provide an AM radar device in which interference between devices is less likely to occur.

[0004]

SUMMARY OF THE INVENTION An AM radar device of the present invention is a carrier generation circuit, a modulation signal generation circuit for generating a modulation signal of a frequency lower than this carrier, and an amplitude for amplitude-modulating the carrier signal with the modulation signal. A modulation circuit, an antenna that sends out an amplitude-modulated signal and receives the reflected wave, a modulation signal detection circuit that detects the modulation signal included in the received reflection wave, and a modulation signal that is detected by this modulation signal detection circuit And a phase difference detection circuit for detecting the phase difference between the modulation signals generated by the modulation signal generation circuit, and a calculation circuit for calculating the distance from the detected phase difference to the object that generated the received reflected wave. There is. And this AM radar device
And frequency changing means for randomly changing the frequency of the modulation signal generated by the modulation signal generation circuit over a predetermined range.

[0005]

The modulation signal generation circuit in each AM radar device is composed of a voltage controlled oscillation circuit (VCO) or the like, and the frequency of the generated modulation signal is randomly controlled by a processor using a random number table. Be changed. Along with this, the probability that the frequencies of the modulation signals of a plurality of AM radar devices operating on adjacent vehicles coincide with each other is significantly reduced, and the problem of mutual interference is improved to the extent that there is no practical problem. Hereinafter, the operation of the present invention will be described in more detail with reference to Examples.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in the block diagram of FIG. 1, an AM radar apparatus according to an embodiment of the present invention includes a carrier wave generation circuit 1, a modulation signal generation circuit 2, an amplitude modulation circuit 3, a transmission antenna 4, a reception antenna 5, Detection circuit 6, phase difference detection circuit 7, A / D
It includes a conversion circuit 8, a D / A conversion circuit 9, a processor 10 and a memory 11. This AM radar device is mounted on a vehicle.

The carrier wave generating circuit 1 includes a Gunn diode and an H
It is composed of a semiconductor device such as EMT and generates a carrier wave C (carrier) in the millimeter wave band of about 60 GHz. The modulation signal generation circuit 2 is composed of a voltage controlled oscillator (VCO) and generates a modulation signal a consisting of a sine wave having a frequency of several MHz which is determined according to the DC voltage value output from the A / D conversion circuit 9. To do. The amplitude modulation circuit 3 is composed of a PIN diode that multiplies the carrier wave C and the modulation signal a, and creates an amplitude modulation signal in the millimeter wave band whose amplitude changes in the cycle of the modulation signal. This amplitude modulation signal is radiated from the transmission antenna 4 toward the front of the vehicle or the like.

The amplitude-modulated signal reflected by the target outside the vehicle is
The reflected wave is received by the receiving antenna 5, and the detection signal is detected by the detection circuit 6. Detected modulation signal b
Is supplied to one input terminal of the phase difference detection circuit 7.
The modulation signal a generated by the modulation signal generation circuit 2 is supplied to the other input terminal of the phase difference detection circuit 7. The modulated signal b detected by the detection circuit 6 has a history of propagating from the transmitting antenna 4 to the object causing the reflection for a time τ and then returning to the receiving antenna 5 in the opposite direction for a time τ.

Therefore, compared with the modulation signal a supplied from the modulation signal generating circuit 2 to the phase difference detecting circuit 7, the detected modulation signal b is equal to the time 2τ required for round-trip propagation with the object. That is, the modulation signal is generated in advance by the modulation signal generation circuit 2, and the modulation signals a and b have a phase difference of a magnitude proportional to 2τ. The phase difference detection circuit 7 compares the phases of the signals supplied to the two input terminals and outputs a DC voltage having a magnitude proportional to the phase difference proportional to the required propagation time 2τ. The DC voltage indicating this phase difference is converted into a digital signal by the A / D conversion circuit 8 and read by the processor 10. The processor 10 calculates the distance to the object based on the read phase difference and the frequency of the modulation signal currently set.

In parallel with the above distance calculation processing, the processor 10 executes control for randomly changing the frequency of the modulation signal generated by the modulation signal generating circuit 2 in a predetermined cycle over a predetermined range. That is, the processor 10
If you accept a timer interrupt that occurs at regular intervals,
Only one number in the random number table registered in the memory 11 is read in the order of the array, and the read value is output to the D / A conversion circuit 9. The DC voltage V output from the D / A conversion circuit 9 is supplied as a control voltage to the voltage controlled oscillator forming the modulation signal generation circuit 2. As a result, the frequency of the modulation signal generated by the modulation signal generation circuit 2 is randomly changed at a constant cycle over a predetermined range.

FIG. 2 is a conceptual diagram exemplifying how the frequency of the modulation signal is randomly changed. The vertical axis represents the frequency of the modulation signal and the horizontal axis represents the elapsed time. As shown,
The frequency of the modulation signal is randomly changed at a constant period over a predetermined range exemplified by 1 MHz to 5 MHz. This fixed period is set to an appropriate value in consideration of the processing time required for transmission of the signal, reception of the reflected signal, and various detections.

The configuration in which the frequency of the modulation signal is randomly changed at a constant cycle has been described above. However, it is possible to have a plurality of adjacent units by changing the frequency of the modulation signal asynchronously with the completion of other processes related to various kinds of detection and control, or by randomly changing the frequency changing period itself. It is also possible to adopt a configuration that further enhances the non-correlation of the operations between the FM radar devices.

Further, a software configuration for randomly changing the frequency using the processor and the random number table has been illustrated. However, the frequency may be randomly changed by a hardware configuration including a pseudo random pulse generation circuit or the like.

Further, a configuration in which the transmitting antenna and the receiving antenna are separately installed is illustrated. However, by using a signal separation circuit such as a circulator together,
It is also possible to adopt a configuration of a transmission / reception shared antenna in which transmission and reception are performed by a single antenna.

[0015]

As described in detail above, the A of the present invention
Since the M radar device has a configuration in which the frequency of the modulation signal is randomly changed over a certain range, the probability that the frequencies of the modulation signals of a plurality of AM radar devices operating on adjacent vehicles coincide with each other is significantly reduced. The problem of mutual interference is improved to such an extent that there is no practical problem.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an AM radar device according to an embodiment of the present invention.

FIG. 2 is a conceptual diagram exemplifying how the frequency of the modulated signal is randomly changed over a predetermined range in a constant cycle in the above-described embodiment.

[Explanation of symbols]

 1 carrier wave generation circuit 2 modulation signal generation circuit composed of VCO 3 amplitude modulation circuit 4 transmission antenna 5 reception antenna 6 detection circuit 7 phase difference detection circuit 10 processor 11 memory for registering random number table

Claims (3)

[Claims] 1. A carrier wave generation circuit, a modulation signal generation circuit for generating a modulation signal having a frequency lower than that of the carrier wave, and an amplitude modulation circuit for amplitude-modulating the generated carrier wave signal with the generated modulation signal. An antenna for transmitting the amplitude-modulated signal and receiving a reflected wave thereof, a modulation signal detection circuit for detecting a modulation signal included in the received reflection wave, a modulation signal detected by the modulation signal detection circuit, and the modulation A phase difference detection circuit for detecting a phase difference between the modulated signal generated by the signal generation circuit, a calculation circuit for calculating the distance from the detected phase difference to the object that generated the received reflected wave, and the modulation An AM radar device comprising: frequency changing means for randomly changing a frequency of a modulation signal generated by a signal generating circuit over a predetermined range. 2. The processor according to claim 1, wherein the modulation signal generation circuit includes a voltage controlled oscillator, and the frequency changing unit sets a voltage of a value read from a random number table as a control voltage of the voltage controlled oscillator. An AM radar device comprising: 3. The AM radar device according to claim 1, wherein the frequency of the modulated signal is changed at a predetermined cycle.