JPH11183600A - Radar device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a radar device that can improve accuracy for measuring distance especially at a short-distance range and at the same time can be miniaturized with reduced weight, by providing a means for preventing routing of a transmission signal to a reception side. SOLUTION: A delay 200 and a DC component elimination circuit 300 are provided, a routing component is set to a DC component by obtaining difference between a frequency of a reception signal including routing and a frequency of a frequency modulation signal that is delayed by the delay 200 by routing delay time, and the DC component is eliminated by a DC component elimination circuit 300, thus eliminating a surplus signal due to routing from a signal being fed to a frequency analyzer 8. Also, a circulator 100 is provided and an electronic wave is transmitted/received by one transmission/reception antenna 6 via the circulator 100.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radar device used for measuring a distance to a target, and more particularly to a radar device suitably used for measuring a short distance.

[0002]

2. Description of the Related Art Conventionally, F has been used as a radar for distance measurement.
An M-CW radar is used. As shown in FIG. 2, the FM-CW radar has a frequency f
Is continuously transmitted (solid line in the figure), and the difference (beat) between the frequency of the reflected wave from the target (dotted line in the figure) and the transmission frequency at the time of receiving the reflected wave Frequency: arrow in the figure) is obtained, the beat frequency is associated with the time delay of the reflected wave, and the distance to the target is obtained based on this.

FIG. 3 shows a conventional configuration of an FM-CW radar. In the FM-CW radar, on the transmission side, a transmission IF signal generated by an FM signal generator 1 is split into two by a distributor 2, and one of the transmission IF signals is generated based on a local signal output from a local signal generator 3. The transmission RF signal obtained here is amplified by the transmission amplifier 5 and transmitted from the transmission antenna 61 to the space.

On the receiving side, a reflected wave from a target arriving at a receiving antenna 62 is amplified by a receiving amplifier 7 and then down-converted into a receiving IF signal by a mixer 42 based on the local signal. Then, the reception IF signal and the other transmission IF signal branched into two by the distributor 2 are mixed by the mixer 43, and the frequency analyzer 8 determines the beat frequency of the mixed signals. The distance to the target is measured based on this.

[0005] In a radar apparatus having a transmission system and a reception system, signal leakage from the transmission system to the reception system, that is, so-called "wraparound" occurs regardless of the magnitude of the degree. F
The situation is the same in the M-CW radar, and the route A in FIG.
As shown in (2), a part of the transmission wave radiated from the distributor 2 via the transmission antenna 61 goes directly to the mixer 43 via the reception antenna 62 without reaching the target.

Since this wraparound travels a shorter distance than the reflected wave, it appears at the position shown by the dashed line in FIG.
For this reason, in the distance observation, it is observed that there is another target at a position of several tens of centimeters to several meters.

Conventionally, the FM-CW radar has been used for finding the distance to a relatively long target in, for example, surveying, so that the appearance of the above-mentioned pseudo target does not pose a problem. Was. However, recently, FM-C
It has been considered that the W radar is mounted on, for example, a passenger car and is used for a purpose of finding a distance to a relatively short distance target such as another car, a passerby, or a wall. In such an application, the appearance of the above-mentioned pseudo target becomes a very serious problem.

In addition, the sneak power is usually large enough to cover the signal power of the received reflected wave.
For this reason, the wraparound has many adverse effects, such as insufficient receiving sensitivity, a very large dynamic range required for the receiving system (thereby increasing the price), and noise in the received signal.

[0009]

On the other hand, the conventional FM-CW radar does not have an active countermeasure against the sneaking of a transmission signal into a receiving system. Especially FM-CW
Radar, in principle, must transmit a transmitted wave and receive a reflected wave continuously in time. Therefore, the “transmission and reception performed in a time-division manner performed by a pulse radar, etc. In order to prevent the wraparound from being received. "

In the conventional FM-CW radar, the transmitting antenna 61 and the receiving antenna 62 are spatially separated from each other as shown in FIG. However, it is not possible to completely eliminate the problem, and furthermore, it is necessary to arrange two antennas, so that the size of the device becomes large. This is a serious problem in applications such as in-vehicles that require small size and light weight.

To summarize the above description, the conventional FM-C
Since the W radar does not have a countermeasure against the transmission signal sneaking into the receiving side, the appearance of a pseudo target, insufficient reception sensitivity, a very large dynamic range in the receiving system, It has various disadvantages when used for measuring particularly short distances, such as when noise is generated and when the device is large, or when it is used for applications where the size and weight of the device are limited. Was.

The present invention has been made in view of the above circumstances,
It is an object of the present invention to provide a radar apparatus which has means for preventing transmission signals from wrapping around to a receiving side, thereby improving the accuracy of distance measurement particularly in a short distance range and reducing the size and weight of the apparatus. It is in.

[0013]

(1) In order to achieve the above object, the present invention provides a frequency modulation signal generating means for generating and outputting a frequency modulation signal whose frequency changes with time; Branching means for branching, transmitting and receiving means for transmitting one of the frequency-modulated signals branched by the branching means to a space as a radar wave and receiving a reflected wave thereof, and the frequency-modulated signal branched by the branching means Delay means for delaying and outputting the other, frequency difference output means for outputting a difference between the frequency of the signal received by the transmission / reception means and the frequency of the frequency modulated signal delayed by the delay means, DC component removing means for removing a DC component included in the output of the output means, and a target countermeasure after the frequency modulation signal is transmitted based on the frequency of the output of the DC component removing means. Calculating means for obtaining a time until the signal is returned again to obtain a distance to a target based on the time.The delay means outputs the other frequency-modulated signal branched by the branching means to the branching means. One of the frequency-modulated signals branched by the means is delayed by a time from transmission and reception by the transmission / reception means to direct reception and input to the frequency difference output means.

With this configuration, the frequency modulation signal output from the frequency modulation signal generating means is branched into one and the other frequency modulation signals by the branching means. One of the frequency modulation signals is radiated into space as a radar wave by the transmission / reception means, and the reflected wave is received by the transmission / reception means together with the wraparound.

On the other hand, the other frequency-modulated signal that has been branched is delayed by the delay means for the delay time of the wraparound, and then supplied to the frequency difference output means together with the received reflected wave and the wraparound. Since the frequency of the wraparound and the frequency of the delayed frequency modulation signal are the same, both are canceled out to become a DC component, and from the frequency difference output means, the frequency of the frequency modulation signal transmitted and the frequency of the reflected wave are output. Is added to the difference to output a signal.

The output of the frequency difference output means is guided to a DC component removing means for removing the DC component. Based on the output of the DC component removing means, that is, the difference (beat frequency) between the frequency of the transmitted frequency modulated signal and the frequency of the reflected wave, the frequency modulated signal is reflected at the target after being sent out and returns again. And the distance to the target based on the time.

Therefore, at the stage of obtaining the distance to the target, an extra signal due to the wraparound is eliminated. Even if the transmission signal wraps around to the receiving side, for example, the appearance of a pseudo target, Problems such as insufficient reception sensitivity, an extremely large dynamic range in the reception system, and generation of noise in the reception signal can be solved. That is, it is possible to improve the accuracy of distance measurement not only in the long distance range but also particularly in the short distance range.

(2) Further, according to the present invention, the transmitting / receiving means comprises:
A transmitting / receiving shared antenna and a circulator connected to the shared transmitting / receiving antenna are provided, and one of the frequency modulation signals branched by the branching unit is transmitted as a radar wave from the shared transmitting / receiving antenna to the space via the circulator, and the reflected wave is transmitted. It is assumed that the signal is captured by the transmission / reception shared antenna and received through the circulator, and the other frequency-modulated signal branched by the branching unit is one of the frequency-modulated signals branched by the branching unit. It is characterized in that it is delayed by the time required to arrive at the frequency difference output means via a circulator.

With this configuration, the frequency modulation signal output from the frequency modulation signal generating means is branched into one and the other frequency modulation signals by the branching means. One of the frequency-modulated signals is radiated as a radar wave from a transmitting / receiving antenna via a circulator to a space by a transmitting / receiving means. Also, the reflected wave from the target is received by the transmission / reception means together with the wraparound.

Thereafter, in the same manner as in the above (1), at the stage of obtaining the distance to the target, an extra signal due to the wraparound is eliminated. This not only solves the problem caused by the transmission signal sneaking into the receiving side, but also transmits the radar wave and receives the reflected wave via one common transmitting and receiving antenna, so two antennas are arranged. This eliminates the need to perform the operation, and makes it possible to reduce the size and weight of the device. That is, it is possible to improve the accuracy of distance measurement not only in the long distance range but also in the short distance range, and to reduce the size and weight of the device.

[0021]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a functional block diagram showing a configuration of a radar device according to an embodiment of the present invention. In FIG. 1, the same parts as those in FIG. 3 are denoted by the same reference numerals, and only different parts will be described here.

The radar device shown in FIG.
0 and a transmitting / receiving antenna 6 connected to the circulator 100, and the output of the transmitting amplifier 5 is connected to the circulator 1
The transmission wave is transmitted from the transmission / reception antenna 6 to the space via the transmission antenna 00, and the reflected wave from the target arriving at the transmission / reception antenna 6 is guided to the reception amplifier 7 via the circulator 100.

The radar apparatus shown in FIG. 1 includes a delay device 200 between the distributor 2 and the mixer 43, and a DC component removing circuit 300 between the mixer 43 and the frequency analyzer 8. The delay device 200 is realized by, for example, a wound cable, a stretcher, a variable length cable, or the like. Further, the DC component removing circuit 300 is realized by, for example, a capacitor, a high-pass filter, a DC cut filter, or the like, or the output terminal of the mixer 43 or the input terminal of the frequency analyzer 8 is AC-coupled to remove a DC component by a capacitor. Is done.

The amount of delay in the delay unit 200 is determined by the time required for the transmission IF signal branched into two by the distributor 2 to follow the path A in the figure and reach the mixer 43 as a wraparound, and the time B in the figure.
Is set so that the time to reach the mixer 43 following the path is the same.

With this configuration, the mixer 43 includes:
The received reflected wave, the wraparound, and the delayed transmission IF signal are simultaneously provided. Here, delay device 2
Due to the operation of 00, the frequency of the wraparound becomes equal to the frequency of the delayed transmission IF signal. For this reason, both are canceled by the mixer 43 and become a DC component. Therefore,
The mixer 43 outputs a signal in which the DC component is added to the beat frequency of the frequency of the received reflected wave (down-converted) and the frequency of the delayed transmission IF signal.

The output of the mixer 43 is guided to a DC component removing circuit 300, where the DC component is removed.
That is, only the beat frequency from which the wraparound component has been removed is input to the frequency analyzer 8 connected next.

In the frequency analyzer 8, the input beat frequency is measured, and based on the measured beat frequency, the distance to the target is obtained by the frequency analyzer 8 itself or a computer (not shown) provided outside.

Thus, in the present embodiment, the delay device 200
And a DC component removing circuit 300, and the delay unit 2 is provided with the frequency of the received signal including the loop and the delay time of the loop.
By taking the difference from the frequency of the frequency-modulated signal delayed at 00, the wraparound component is converted to a DC component, and this DC component is removed by the DC component removing circuit 300, so that the frequency analyzer 8
Is removed from the signal given to the signal. This makes it possible to improve the accuracy of distance measurement particularly in the short distance range.

In this embodiment, the circulator 1
00 is provided so that one transmission / reception antenna 6 can transmit and receive radio waves via the circulator 100. As a result, the device can be reduced in size and weight, and a great advantage can be obtained particularly when the device is used for a vehicle or the like.

Further, as shown in the present embodiment, the DC component removing circuit 300 is realized by making the output terminal of the mixer 43 or the input terminal of the frequency analyzer 8 AC-coupled to remove the DC component by a capacitor. This also contributes to simplification of the configuration.

The present invention is not limited to the above embodiment. For example, in the above embodiment, the mixer 4
Although the transmission RF signal obtained by frequency conversion at 1 is amplified by the transmission amplifier 5, the transmission RF signal is directly introduced to the circulator 100 without the transmission amplifier 5 depending on the output level of the FM signal generator 1. You may do so.
Similarly, the receiving amplifier 7 may not be provided depending on the level of the reflected wave or the accuracy of the frequency analyzer 8, and the reflected wave from the circulator 100 may be directly guided to the mixer 42.

In the above embodiment, the circulator 100 and the transmission / reception antenna 6 are provided, and the transmission and reception of the radio wave are performed through one transmission / reception antenna 6, but the antenna for transmitting the radio wave, Of course, it is of course possible to separately provide an antenna for receiving radio waves.

In the above embodiment, the local signal generator 3 and the mixers 41 and 42 up-convert the IF signal generated by the FM signal generator 1 and down-convert the received reflected wave. If the signal generator 1 directly generates an RF signal, the local signal generator 3 and the mixers 41 and 42 need not be provided. In addition, various modifications can be made without departing from the spirit of the present invention.

[0034]

As described above in detail, according to the present invention, the delay means and the DC component removing means are provided, and the frequency of the received signal including the wraparound and the frequency modulation signal delayed by the delay means by the wraparound delay time are provided. By taking the difference between the frequency and the wraparound component as a DC component, and removing this DC component by DC component removal means, an extra signal due to the wraparound is eliminated at the stage of obtaining the distance to the target, In particular, it is possible to improve the accuracy of distance measurement in a short distance range.

According to the present invention, a circulator is provided, and the transmitting antenna and the receiving antenna are shared by the circulator, so that the device can be reduced in size and weight.

[Brief description of the drawings]

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

FIG. 2 is a diagram used to explain the principle of the FM-CW radar.

FIG. 3 is a functional block diagram showing a configuration of a conventional FM-CW radar.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... FM signal generator 2 ... Distributor 3 ... Local signal generator 41,42,43 ... Mixer 5 ... Transmitting amplifier 6 ... Transceiving antenna 7 ... Receiving amplifier 8 ... Frequency analyzer 100 ... Circulator 200 ... Delay device 300 ... DC Component removal circuit

Claims (4)

[Claims] A frequency-modulated signal generating means for generating and outputting a frequency-modulated signal whose frequency changes with time; a branching means for splitting the frequency-modulated signal into two; Transmitting / receiving means for transmitting one of them as a radar wave into space and receiving the reflected wave; delay means for delaying and outputting the other of the frequency modulated signals branched by the branching means; and Frequency difference output means for outputting a difference between the frequency of the received signal and the frequency of the frequency-modulated signal delayed by the delay means; and a DC component removal means for removing a DC component contained in the output of the frequency difference output means. Means, based on the frequency of the output of the DC component removing means, determine the time from when the frequency modulated signal is transmitted to when it is reflected at the target and returns again, Computing means for calculating a distance to a target based on the interval, wherein the delay means converts the other frequency-modulated signal branched by the branching means into one of the frequency-modulated signals branched by the branching means. A radar device for delaying by a time period from when the signal is transmitted and received directly by the transmission / reception means to when the signal is input to the frequency difference output means. 2. The transmission / reception means includes a transmission / reception shared antenna and a circulator connected to the transmission / reception shared antenna, and uses one of the frequency modulation signals branched by the branching means as a radar wave via the circulator for the transmission / reception shared. The antenna transmits to the space, the reflected wave is captured by the transmission / reception shared antenna, and is received via the circulator.The delay unit is configured to transmit the other frequency-modulated signal branched by the branching unit, 2. The radar apparatus according to claim 1, wherein one of the frequency modulation signals branched by the branching unit is delayed by a time required to arrive at the frequency difference output unit via the circulator. 3. The transmission / reception unit includes: a first frequency conversion unit configured to convert a frequency of one frequency-modulated signal branched by the branching unit into a frequency in a frequency band to be transmitted to a space; 2. The radar device according to claim 1, further comprising: a second frequency conversion unit that converts a frequency of the reflected wave into a frequency in a frequency range to be given to the frequency difference output unit. 4. The radar according to claim 1, wherein said DC component removing means has an AC coupling element interposed between an output terminal of said frequency difference output means and an input terminal of said calculating means. apparatus.