JP2000046932A - Fm-cw radar apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an FM-CW radar apparatus which can measure a desired distance range with a desired accuracy with using only one fixed filter. SOLUTION: The apparatus includes a VCO 15 controlled by a microcomputer 11, mixers 4a-4d for mixing an output of the VCO with echoes at an IF stage, and a BPF 16 as a fixed filter of a superior characteristic like a quartz filter. By selecting a desired signal frequency band, a desired distance range is measured with a necessary accuracy without increasing a process amount of data by the microcomputer 11. A linear FM modulated CW wave is irradiated to a target, the echo and a beat signal of a transmission signal are obtained, thereby generating an IF signal. The BPF 16 selects the echo from the target in a fixed distance range and generates a video signal. An A/D converter 10 converts the signal to digital data and the microcomputer 11 calculates a distance and a velocity. Moreover, the microcomputer 11 changes an oscillation frequency of the VCO 15, thereby adjusting the signal in the desired distance range to agree with a pass band of the BPF 16.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an FM-based radar for measuring a distance to a target object such as an on-vehicle radar or a radio altimeter.
The present invention relates to a CW radar device.

[0002]

2. Description of the Related Art Conventionally, there is an apparatus of this type shown in FIG. FIG. 3 shows a configuration diagram of an FM-CW radar device similar to that disclosed in JP-A-4-223286. In FIG. 3, 1 is a transmitting antenna, 2 is a receiving antenna, and 3 is directional. Coupler, 4 is a mixer, 5 is C
W oscillator, 6 is a triangular wave oscillator, 7 is an amplifier, 8 is a low-pass filter (LPF), 9 is a high-pass filter (HP
F), 10 is an A / D converter, and 11 is a microcomputer as control means. FIG. 4 is a diagram illustrating a transmission / reception signal frequency when a signal frequency-modulated by a triangular wave is transmitted.

Next, the operation will be described. In this type of radar, as shown in FIG. 4, a linear FM signal whose transmission frequency changes in a triangular waveform with time is transmitted, and beat signals (f and f) of transmission / reception signals (Tr and Rec) are respectively transmitted in up-chirp and down-chirp. _Up and f _dn ) are obtained, and the distance from the frequency to the target and its time change (speed) are measured.

In FIG. 3, a triangular wave oscillator 6 generates and outputs a triangular wave signal whose voltage periodically changes at a cycle designated by the microcomputer 11. The CW oscillator 5 generates a linear FM signal whose frequency changes according to the voltage of the triangular wave signal, and transmits the signal from the transmitting antenna 1 to the target via the directional coupler 3. The echo is received by the receiving antenna 2 and is mixed with the transmission signal distributed by the directional coupler 3 and the mixer 4 to generate a beat signal. The beat signal is output from the amplifier 7
, And after being filtered through a low-pass filter 8 and a high-pass filter 9, the A / D converter 10
Is converted into a digital signal and input to the microcomputer 11.

The following relationship exists between the frequency of the beat signal output from the mixer 4 and the target distance and speed. Here, f _up is the beat frequency in the up chirp, f _dn is the beat frequency in the down chirp, _fr
Is a beat frequency generated by a distance, f _d is a Doppler frequency generated by a speed, r is a distance, v is a speed, α is a frequency change rate of a linear FM, λ is a wavelength, and c is a radio wave propagation speed.

[0006]

(Equation 1)

Accordingly, the microcomputer 11 can obtain the distance r and the speed v by solving the above.

In this type of radar apparatus, the distance resolution Δr and the velocity resolution Δv are given by the following equations. Here, B is the transmission bandwidth, and T is a half of the period of the linear FM (duration of up-chirp or down-chirp).
It is.

[0009]

(Equation 2)

On the other hand, the width R of the observable distance and the width V of the velocity are
Is given by the following equation. However, b _w is a pass-band width of the BPF.

[0011]

(Equation 3)

That is, in order to increase the distance resolution Δr, the transmission bandwidth B is increased, and in order to increase the speed resolution Δv, the period 2T of the linear FM may be extended, and in order to increase the observation range of the distance r and the velocity v. it may should widen the pass band width b _w of the BPF. However, for that purpose, the A / D converter 1
Since it is necessary to increase the sampling frequency of 0 and extend the sampling time, there arises a problem that the number of data samples increases and the load on the microcomputer 11 increases.

Although not mentioned in Japanese Patent Application Laid-Open No. Hei 4-223286, this device can avoid such a problem by the following method. First, dropping the resolution by setting small the bandwidth B and the sample time T, instead by expanding the passband width b _w of BPF, it detects the rough observation to target a wide range of distance and speed range. Once you know the target distance and speed, by narrowing the pass bandwidth b _w of BPF, by increasing the transmission bandwidth B and sample time T, instead, to only accurately measure near the target distance and speed. By such a procedure, it is possible to realize a mode for observing a wide range with rough accuracy and a mode for observing a narrow range with high accuracy while keeping the number of data samples constant.

[0014]

Since INVENTION Problems to be Solved conventional FM-CW radar is constructed as this, implementing a variable settable filter or the like switched capacitor to the pass bandwidth b _w of the BPF variable There is a need to.
However, such a filter element has a narrow frequency variable range and is inferior in cutoff characteristics and pass characteristics as compared with a crystal filter, so that it has been difficult to realize a highly accurate FM-CW radar.

Further, it is conceivable to realize this by arranging a plurality of fixed filters having excellent characteristics such as a crystal filter, but there is a problem in that the weight and cost increase.

Alternatively, by changing the pass band of the filter, the conversion speed of the subsequent A / D converter must also be changed, resulting in a problem that the configuration becomes complicated.

Alternatively, there is a problem that the number of sample data to be A / D converted increases and the load on the microcomputer 11 increases.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and measures a desired distance range with a desired accuracy by using only one fixed filter having excellent characteristics such as a quartz filter. It is an object of the present invention to obtain an FM-CW radar device capable of performing the following.

[0019]

An FM-C according to the present invention.
The W radar device includes a triangular wave oscillator that generates a triangular wave signal, a CW oscillator that generates a linear FM signal whose frequency changes according to the voltage of the triangular wave output from the triangular wave oscillator, and a linear FM output from the CW oscillator. A transmitting antenna for transmitting a signal to a target, a directional coupler provided between the CW oscillator and the transmitting antenna, a receiving antenna for receiving an echo, and oscillating a signal having a constant frequency corresponding to an IF frequency. A coherent oscillator, a first mixer for mixing a transmission signal distributed by the directional coupler and a signal output from the coherent oscillator, a reception signal from the reception antenna, and a first mixer
A second mixer for generating an IF signal by mixing a signal mixed by the first mixer, an amplifier for amplifying the IF signal output from the second mixer, and a voltage for outputting a signal corresponding to the indicated frequency. A controlled oscillator, a third mixer for mixing the output of the amplifier and the output of the voltage controlled oscillator, a band-pass filter provided on the output side of the third mixer and having a pass frequency band set, A fourth mixer for obtaining a video signal by mixing an output from the coherent oscillator with an output via a pass filter, and an A / D converter for A / D converting and sampling the output from the fourth mixer And the video signal sampled by the A / D converter is input by variably controlling the oscillation frequency by giving the indicated frequency to the voltage controlled oscillator. The frequency spectrum obtained by, in which a control means for determining the distance of the target and the speed.

Further, the control means changes the band and the cycle of the linear FM signal output from the CW oscillator by giving an indicated cycle and an indicated amplitude to the triangular wave oscillator.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The FM-CW radar according to the present invention will be briefly described. The FM-CW radar according to the present invention is a voltage-controlled oscillator controlled by a microcomputer (hereinafter, referred to as a microcomputer) as control means. When,
A mixer for mixing the output with an echo in an IF stage,
A fixed filter having excellent characteristics such as a crystal filter is provided, and by selecting a desired signal frequency band, a desired distance range is measured with necessary accuracy without increasing the amount of processing data of the microcomputer.

That is, in the FM-CW radar according to the present invention, a target is irradiated with a linear FM-modulated CW wave, and its echo and a beat signal of a transmission signal are obtained to obtain an IF.
A signal is generated, and a bandpass filter selects echoes from a target within a certain distance range to generate a video signal.
The converter converts the data into digital data, and the microcomputer calculates the distance and speed. Further, the microcomputer changes the oscillation frequency of the voltage-controlled oscillator so that a signal in a desired distance range matches the pass band of the band-pass filter.

The bandwidth of the band-pass filter of the FM-CW radar and the oscillation frequency of the voltage-controlled oscillator are calculated in accordance with a desired distance range. Find the bandwidth of Further, the oscillation frequency of the voltage controlled oscillator is obtained from the desired distance range and the specifications of the linear FM signal.

Embodiment 1 (Distance Switching) Hereinafter, an FM-CW radar device according to Embodiment 1 of the present invention will be described with reference to the drawings. FIG. 1 is a configuration diagram showing an FM-CW radar device according to the first embodiment. 1, reference numerals 1 to 11 denote the same parts as in the conventional example shown in FIG. 3, and a description thereof will be omitted. As a new code, reference numeral 14 denotes a coherent oscillator (COHO: Coherent Oscillator) which oscillates a signal of a constant frequency corresponding to the IF frequency.
A voltage controlled oscillator (VCO: Volt) 15 outputs a signal corresponding to the indicated frequency.
age Controlled Oscllator (hereinafter referred to as VCO), 1
Reference numeral 6 denotes a band-pass filter (BPF) provided on the output side of the VCO 15 and having a set pass frequency band.
lter, hereinafter referred to as BPF).

Reference numeral 4a denotes a first mixer for mixing the transmission signal distributed by the directional coupler 3 and the signal output from the COHO 14, and 4b denotes a reception signal from the reception antenna 2 and a first mixer 4a. A second mixer that mixes the mixed signal with the mixed signal to generate an IF signal;
4c is a third mixer for mixing the output of the amplifier 7 and the output of the VCO 15, and 4d is the third mixer for mixing the output of the BPF 16 and COH.
Third to obtain a video signal by mixing with the output of O14
The microcomputer 11 gives an instruction frequency to the VCO 15 and variably controls the oscillation frequency, so that A
The video signal sampled by the / D converter 10 is input, its frequency spectrum is obtained, and the target distance and speed are obtained. Further, the triangular wave oscillator 6 is given an instruction period and an instruction amplitude to give the CW oscillator 5 Can change the band and cycle of the linear FM signal output from.

FIG. 2 shows the signal frequency of the IF stage, 17a and 17b are target echoes, and 18 is a BPF 16
Is the pass band of

Next, the operation will be described. The triangular wave oscillator 6 generates and outputs a triangular wave whose voltage periodically changes at a cycle specified by the microcomputer 11. The CW oscillator 5 performs a frequency modulation with the voltage to generate a linear FM modulation signal.
The directional coupler 3 distributes a part of the signal, and the transmission antenna 1
Emits radio waves towards the target. These operations are the same as those of the conventional FM-CW radar apparatus shown in FIG.

Further, the COHO 14 oscillates a signal having a constant frequency corresponding to the IF frequency, and the mixer 4a mixes the signal with the transmission signal. This signal is sent to mixer 4b
Is mixed with the reception signal received by the reception antenna 2 to generate an IF signal, and the amplifier 7 amplifies the IF signal. VCO15
Generates a signal of the frequency specified by the microcomputer 11,
Mixing with the IF signal is performed by the mixer 4c. The BPF 16 filters this output, and the mixer 4d mixes with the output of the COHO 14 to obtain a video signal. The A / D converter 10 samples the video signal, the microcomputer 11 obtains the frequency spectrum, and obtains the target distance and speed based on the equations (1) to (4).

When the BPF 16 is composed of a fixed frequency filter, the frequency passing therethrough is also determined.
As is clear from equations (1) to (4), the observable distance range (distance gate) is also fixed. Distance gate center r
_c and its width r _w are given by the following equation. However, f _FC is BPF
16 center frequency, f _IF is IF frequency, f _VCO is VCO
15 oscillation frequency.

[0030]

(Equation 4)

As can be seen from equation (9), the center of the distance gate is determined by the IF frequency f _IF , the center frequency f _{FC of} the BPF 16, and the oscillation frequency f _{VCO of the VCO} 15, and can be made variable by the _VCO 15. . This will be described with reference to FIG. If the frequency of the target signal 17a is out of the pass band 18 of the BPF 16, the frequency of the VCO 15 is changed to
8, the distance and speed of the target 17b can be determined.

As described above, according to the configuration of the present embodiment,
A target at an arbitrary distance can be observed using the fixed frequency filter, and an FM-CW radar device having higher distance, speed, and measurement accuracy than conventional devices can be obtained.

Embodiment 2 FIG. (Zooming) Hereinafter, F according to Embodiment 2 of the present invention will be described.
The M-CW radar will be described. The configuration of this device is the same as that of FIG. In the first embodiment, it has been described that a target at an arbitrary distance can be observed. However, in the second embodiment, it is described that an arbitrary resolution can be realized under a condition that the number of sample data is constant.

In order to change the distance resolution Δr, it is necessary to change the band B of the linear FM as shown in Expression (5). On the other hand, 1 sampled by the A / D converter 10
The number N of data points per cycle is given by the following equation.

[0035]

(Equation 5)

Here, bw is the bandwidth of the BPF 16 and is constant. Therefore, in order to keep the number of data points N constant, T _w
Needs to be constant. Therefore, when the resolution Δr is increased by increasing the transmission bandwidth B, if T is designed to be constant, the number of sample data can be kept constant.

In equation (7), α in the denominator is the frequency change rate of the linear FM, so that α = B / T. Therefore, the width R of the distance gate is designed so that T and _bw are fixed. Then, it can be seen that it is inversely proportional to the transmission bandwidth B. Equation (5) shows that the range resolution Δr is also inversely proportional to the transmission bandwidth B, so that the ratio between the range gate width R and the range resolution Δr is constant. Therefore, by changing the transmission bandwidth B after designing T and _bw constant, it is possible to switch between a mode in which a wide range is observed at a low resolution and a mode in which a narrow range is observed at a high resolution. Can be.

As described above, according to the configuration of the second embodiment, it is possible to realize a high resolution of the distance without increasing the load on the microcomputer 11, and a mode for searching for a wide distance gate with a low resolution is provided. It can be realized by switching the mode for precisely measuring a narrow distance range.

Embodiment 3 (VCO frequency, the design of b _w) will be described below a third embodiment of the present invention. In the third embodiment, in the apparatus having the configuration shown in FIG.
A method for calculating the oscillation frequency of the CO 15 will be described. First, the following equation is obtained by modifying equation (7).

[0040]

(Equation 6)

Therefore, the bandwidth b _{w of the} BPF 16 is
It can be seen that it can be determined by the period 2T of the linear FM and the range bin number R / レ ン ジ r. Next, the following equation is obtained by modifying equation (9).

[0042]

(Equation 7)

That is, the oscillation frequency f _vco of the VCO 15
It can be determined by equation (13) from the center distance r _c of the range gate.

As described above, according to the method of the present embodiment, it is possible to determine a design value necessary for observing an arbitrary distance at an arbitrary resolution with the FM-CW radar of FIG.

[0045]

As described above, according to the present invention, a desired distance range can be measured with a desired accuracy using a fixed frequency filter, and a target at an arbitrary distance can be observed. In addition, it is possible to obtain an FM-CW radar device having higher distance and speed measurement accuracy than the conventional device.
Further, high resolution of the distance can be realized without increasing the load on the control means. Further, the mode can be realized by switching between a mode for searching for a wide range gate with low resolution and a mode for precisely measuring a narrow range with high resolution.

Further, the control means gives an instruction cycle and an instruction amplitude to the upper angular wave oscillator to change the band and the cycle of the linear FM signal output from the CW oscillator.
Distance resolution and speed resolution can be increased.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an FM-CW radar according to a first embodiment of the present invention.

FIG. 2 is an explanatory diagram illustrating a power spectrum of a received signal of the FM-CW radar according to the first embodiment of the present invention.

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

FIG. 4 is an explanatory diagram showing transmission / reception signals of the FM-CW radar.

[Explanation of symbols]

1 transmitting antenna, 2 receiving antenna, 3 directional coupler, 4a, 4b, 4c, 4d mixer, 5 CW oscillator, 6 triangular wave oscillator, 7 amplifier, 10 A / D converter, 11 microcomputer, 14 COHO, 15 VCO,
16 BPF, 17 power spectrum of target echo,
18 BPF passband.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Takahiko Fujisaka 2-3-2 Marunouchi, Chiyoda-ku, Tokyo Mitsui Electric Co., Ltd. (72) Inventor Hirokazu Tanaka 2-3-2 Marunouchi, Chiyoda-ku, Tokyo 3 Inside Ryo Denki Co., Ltd. (72) Inventor Taikichi 2-1-1 Sengen, Tsukuba City, Ibaraki Pref. Space Development Corporation Tsukuba Space Center (72) Inventor Yasumasa Hisa 2-1-1 Sengen, Tsukuba City, Ibaraki Prefecture No. Space Development Corporation Tsukuba Space Center F term (reference) 5J070 AB19 AB21 AC02 AC03 AC06 AD02 AF03 AH25 AH31 AH42 AH50 AJ11 AJ20 AK22 AK27 BA01 BF02 BF03

Claims (2)

[Claims] 1. A triangular wave oscillator that generates a triangular wave signal, a CW oscillator that generates a linear FM signal whose frequency changes according to a voltage of a triangular wave output from the triangular wave oscillator, and a linear FM output from the CW oscillator A transmitting antenna for transmitting a signal to a target, a directional coupler provided between the CW oscillator and the transmitting antenna, a receiving antenna for receiving an echo, and oscillating a signal having a constant frequency corresponding to an IF frequency A first coherent oscillator for mixing a transmission signal distributed by the directional coupler with a signal output from the coherent oscillator;
A second mixer that mixes a signal received from the receiving antenna with a signal mixed by the first mixer to generate an IF signal; and an IF signal output from the second mixer. An amplifier for amplifying; a voltage-controlled oscillator for outputting a signal corresponding to an instruction frequency; a third mixer for mixing the output of the amplifier and the output of the voltage-controlled oscillator; and an output side of the third mixer A band-pass filter in which a pass frequency band is set, a fourth mixer that obtains a video signal by mixing an output through the band-pass filter and an output from the coherent oscillator, A / D converter for A / D converting and sampling the output, and variably controlling the oscillation frequency by giving an instruction frequency to the voltage controlled oscillator. Ri, Searching for the frequency spectrum by inputting a video signal sampled by the A / D converter, FM-CW radar apparatus provided with a control means for determining the distance of the target and the speed. 2. The FM-controller according to claim 1, wherein said control means changes a band and a cycle of a linear FM signal output from said CW oscillator by giving a designated period and a designated amplitude to said triangular wave oscillator. CW radar device.