JPH05240945A - Frequency-modulated continuous-wave radar - Google Patents

Abstract

PURPOSE:To extend the frequency part of demodulated signals which are proportional to the distance to a target and to improve the detecting performance and distance resolution of the title radar near the limit of its measuring extent by generating two kinds of demodulated signals and respectively mixing the demodulated signals with received signals divided into two parts. CONSTITUTION:Continuous waves transmitted to a modulator 2 for transmission from an oscillator 1 are modulated into triangle waves which repeat a linear increase and decrease at every period of time T corresponding to a measuring extent and radiated from a transmission antenna 3. Then the reflected waves of the triangle waves from a target are inputted to demodulators 71 and 72 as delayed received signals. On the other hand, another continuous waves transmitted to a modulator 21 (22) from the oscillator 1 are modulated to signals for demodulation which repeat a saw tooth linear frequency change at every period of time 2T corresponding to the double of the measuring extent at the same frequency changing rate as that of transmitting signals synchronously to the increase (decrease) of the transmitted signals. By mixing the signals for demodulation with received signals divided into two parts by means of the demodulators 71 and 72, the frequency part of the demodulated signals proportional to the distance to a target is extended and the resolution is improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention transmits a continuous wave by frequency-modulating it so that its frequency changes linearly, and based on the frequency difference between this transmitted signal and the received signal reflected by a target. The present invention relates to a frequency modulation continuous wave radar that obtains the distance to a target by using

[0002]

2. Description of the Related Art FIG. 5 shows, for example, No. 16 of "Radar Handbook" edited by Merrill I Skolnik (issued in 1970 by McGraw-Hill).
Chapter "CW and FM Radar" (CW
and FM Radar) is a block diagram showing a conventional frequency modulation continuous wave radar.

In the figure, 1 is an oscillator which oscillates a continuous wave of a predetermined frequency, and 2 is a frequency modulation of the continuous wave which this oscillator 1 oscillates, and is linear at every time corresponding to the measurement range. It is a transmission modulator that generates a transmission signal in which the frequency is repeatedly increased and decreased. 3 is a transmitter for power-amplifying the transmission signal from this transmission modulator 2, and 4 is this transmitter 3
It is a transmission antenna that radiates the power-amplified transmission signal in space. Reference numeral 5 is a receiving antenna for receiving the reflected wave of the transmission signal from the target, and 6 is a high frequency amplifier for amplifying the receiving signal received by the receiving antenna 5. Reference numeral 7 is a demodulator that mixes the transmission signal from the transmission modulator 2 with the reception signal amplified by the high-frequency amplifier 6 to generate a demodulation signal, and 8 processes the demodulation signal from the demodulator 7. It is a filter bank that calculates the distance to the target.

Next, the operation will be described. Here, FIG.
FIG. 4 is an explanatory diagram showing frequency changes in each part of the frequency modulation continuous wave radar. The oscillator 1 constantly generates a continuous wave of a predetermined frequency, and this continuous wave is sent to the modulator for transmission 2 and undergoes modulation for transmission, and its frequency is measured in the measurement range as shown in FIG. 6 (a). Is transmitted to the transmitter 3 as a transmission signal that repeats linear increase / decrease every time “T” corresponding to. In the transmitter 3, the transmission signal received from the transmission modulator 2 is power-amplified and sent to the transmission antenna 4, which radiates it into space.

The transmission signal radiated into space from the transmission antenna 4 is reflected by the target, and the reflected wave is received by the reception antenna. The reception signal received by the reception antenna 5 is delayed by the time corresponding to the distance to the target. Therefore, if the distance from the frequency-modulated continuous wave radar to the target is short, the received signal is "d ₁ " as shown by the solid line in FIG. 6B, and if it is far, it is "d ₂ " as shown by the broken line. Be delayed. The received signal thus received is sent from the receiving antenna 5 to the high frequency amplifier 6 and then to the demodulator 7.

The demodulator 7 mixes the transmission signal generated by the transmission modulator 2 with the reception signal from the high frequency amplifier 6 to generate a demodulation signal. Therefore, this demodulated signal is the frequency output of the difference between the frequency of the transmission signal and the frequency of the reception signal, and is proportional to the distance to the target in the range where the frequency changes of the transmission signal and the reception signal are in the same direction. It becomes a predetermined frequency. FIG. 6 (c) shows the demodulated signal of the received signal shown by the solid line in FIG. 6 (b) until the frequency of the received signal starts to increase until that of the transmitted signal starts to decrease or the received signal Time t from when the frequency of the signal starts decreasing to when it increases in the transmitted signal
Only ₁ "has a frequency proportional to the distance to the target. Also, FIG. 6 (d) shows the demodulated signal of the received signal shown by the broken line in FIG. 6 (b). "T
_The frequency is only ₂ ”in proportion to the distance to the target.

The demodulated signal thus demodulated by the demodulator 7 is sent to the filter bank 8 where it is processed and the distance to the target is obtained. Here, in this filter bank 8, a large number of filters having different center frequencies are arranged in parallel by, for example, fast Fourier transform, and the distance to the target is obtained from the center frequency of the signal output through them.

[0008]

Since the conventional frequency-modulated continuous wave radar is constructed as described above, when the target is at a distance near the limit of the measurement range, as shown in FIG. 6 (d), The part of the demodulated signal, which has a frequency proportional to the distance to the target, has a short time of “t ₂ ”,
There was a problem that the target detection performance and range resolution deteriorated.

The present invention has been made to solve the above problems, and an object thereof is to obtain a frequency-modulated continuous wave radar in which the detection performance and range resolution of the target do not deteriorate to the limit of the measurement range. And

[0010]

A frequency-modulated continuous wave radar according to a first aspect of the present invention is a transmission that generates a transmission signal by linearly increasing or decreasing the frequency of a continuous wave at each time corresponding to a measurement range. Separately from the credit modulator, the modulation start is shifted by the time corresponding to the measurement range, and the frequency change rate is the same as that of the transmission signal, and linearly increases or decreases in a sawtooth shape at each time corresponding to twice the measurement range. Is provided with two demodulation modulators that generate two types of demodulation signals that repeat, and two demodulators that mix the respective demodulation signals with the reception signal and demodulate each.

Further, in the frequency-modulated continuous wave radar according to a second aspect of the present invention, the transmission signal generated by the transmission modulator is a sawtooth wave that repeats for a time corresponding to the measurement range.
The types of demodulation signals are shifted in the start of modulation for a time corresponding to the measurement range, and are changed in the same direction at the same frequency change rate as the transmission signal in a sawtooth shape at a time corresponding to twice the measurement range. It was done.

Further, the frequency-modulated continuous wave radar according to the third aspect of the invention is such that the transmission signal and the reception signal are transmitted and received by the super-heterodyne system.

[0013]

In the frequency-modulated continuous wave radar according to the first aspect of the invention, the received signal, which is the reflected wave of the transmitted signal due to the triangular wave, is divided into two parts, and the modulation start is shifted by the time corresponding to the measurement range. Proportional to the distance to the target in the demodulated signal by mixing and demodulating two types of demodulation signals that repeat increasing or decreasing in a sawtooth shape at each time corresponding to twice the measurement range with the same frequency change rate. A frequency-modulated continuous wave radar is realized in which the target frequency detection performance and range resolution are not deteriorated by sufficiently increasing the frequency range.

In the frequency-modulated continuous wave radar according to the second aspect of the invention, the received signal, which is the reflected wave of the transmitted signal due to the sawtooth wave, is divided into two parts, and the modulation start is shifted by a time corresponding to the measurement range. , By mixing and demodulating two kinds of demodulation signals, which have the same frequency change rate in the same direction as the transmission signal and repeat the change in a sawtooth shape at each time corresponding to twice the measurement range, To realize a frequency-modulated continuous wave radar in which the frequency of the frequency proportional to the distance to the target is made sufficiently long and the detection performance of the target and the range resolution do not deteriorate.

Furthermore, the frequency-modulated continuous-wave radar according to the third aspect of the present invention adopts the super-heterodyne system to realize the frequency-modulated continuous-wave radar in which good frequency selectivity can be easily obtained.

[0016]

【Example】

Example 1. An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of the invention of claim 1. In the figure, 1 is an oscillator, 2 is a modulator for transmission, 3 is a transmitter, 4 is a transmitting antenna, 5 is a receiving antenna, and 6 is a high-frequency amplifier. Alternatively, since it is a considerable portion, detailed description thereof will be omitted.

Reference numeral 21 denotes the same frequency change rate as that of the transmission signal generated by the transmission modulator 2, and the frequency increases linearly in a sawtooth shape at intervals of "2T" corresponding to twice the measurement range. , A first demodulation modulator for generating a first demodulation signal synchronized with the transmission signal, and 22 is the same as that of the measurement range with the same frequency change rate as the transmission signal.
The frequency is linearly reduced in a sawtooth shape every time "2T", which is twice as long, and a second demodulation signal that is deviated from the first demodulation signal by a time "T" corresponding to the measurement range is generated. It is a second demodulation modulator to be generated.

Reference numeral 71 is a first demodulator for mixing the reception signal amplified by the high frequency amplifier 6 with the first demodulation signal generated by the first demodulation modulator 21 to demodulate into a first demodulation signal. And 72 represents the received signal in the second demodulation modulator 22.
It is a second demodulator that mixes with the second demodulation signal generated by and demodulates it into a second demodulation signal. Reference numeral 81 is a first filter bank that processes the first demodulated signal demodulated by the first demodulator 71, and 82 is a second filter that processes the second demodulated signal demodulated by the second demodulator 72. It is a bank.

Next, the operation will be described. Here, FIG.
FIG. 4 is an explanatory diagram showing a frequency change of each part in the frequency modulation continuous wave radar according to the embodiment. The continuous wave generated by the oscillator 1 is sent to the transmission modulator 2 and the first and second demodulation modulators 21 and 22. The continuous wave sent to the transmission modulator 2 is subjected to the same transmission modulation as in the conventional case, and its frequency is linear every time "T" corresponding to the measurement range as shown in FIG. 2 (a). The signal is sent to the transmitter 3 as a triangular wave transmission signal that repeatedly increases and decreases, is amplified in power, and then radiated into space from the transmission antenna 4. This transmission signal is reflected by the target and received by the reception antenna 5, is sent to the high frequency amplifier 6 as a reception signal delayed by "d ₃ " as shown in FIG. It is input to the second demodulators 71 and 72.

On the other hand, the first demodulation modulator 21 is shown in FIG.
As shown by the solid line in (c), in synchronization with the increase of the transmission signal generated by the transmission modulator 2, the sawtooth shape is generated at the same frequency change rate every time “2T” corresponding to twice the measurement range. The first demodulation signal is repeatedly generated by linearly increasing the frequency and is supplied to the first demodulator 71. The second demodulation modulator 22 is synchronized with the decrease of the transmission signal, At the same frequency change rate, the time "2
A second sawtooth linear frequency decrease is repeated every T "
And supplies the second demodulator 72.

The first demodulator 71 mixes the first demodulation signal with the reception signal from the high frequency amplifier 6 to generate a first demodulation signal. Therefore, the difference between the frequency of the transmission signal and the frequency of the reception signal is output as the frequency of the first demodulation signal, and as shown in FIG. 2D, after the frequency of the reception signal starts to increase. up starts to decrease, the frequency proportional to the distance to the target by the time indicated by the "t _3" in FIG. In addition, the second demodulated signal is similarly processed as shown in FIG.
The frequency indicated by “t ₃ ” in (e) is a frequency proportional to the distance to the target only for the time from when the frequency of the received signal starts to decrease to when it increases.

In this way, the first and second demodulators 7 are
The first and second demodulated signals demodulated at 1, 72 are sent to the first or second filter banks 81, 82 for processing, and the distance to the target is obtained in the same manner as in the conventional case.

Example 2. In the first embodiment, the case where the continuous wave oscillated by the oscillator 1 is frequency-modulated by the triangular wave has been described. However, the continuous wave may be modulated by a sawtooth wave, and the same effect as that of the first embodiment is obtained. FIG. 3 is an explanatory view showing the frequency change of each part in such an embodiment of the invention described in claim 2, and the constitution of the device is the same as that shown in FIG. 3A is a transmission signal, FIG. 3B is a reception signal, FIG. 3C is the first and second demodulation signals, FIG. 3D is the first demodulation signal, and FIG. 3E is the second demodulation signal. The signals are shown respectively.

In this case, in synchronization with the increase of the transmission signal generated by the transmission modulator 2 shown in FIG. 3A, the same frequency change rate as shown by the solid line in FIG. The first demodulation signal is generated in the first demodulation modulator 21 by repeating the sawtooth linear frequency increase every "2T" corresponding to twice the measurement range. Do not show
A second demodulation signal, which is deviated from the first demodulation signal by a time “T” corresponding to the measurement range, is generated by the second demodulation modulator 22.

When such first and second demodulation signals are mixed with the reception signal shown in FIG. 3B by the first and second demodulators 71 and 72, the signals shown in FIGS. The first and second demodulated signals shown in are obtained. In this case, even if the delay of the received signal is as large as “d ₄ ”, as shown in FIG. 3B, the frequency is proportional to the distance to the target in these first and second demodulated signals. The period during which the frequency of the received signal is linearly increasing becomes equal to the period during which the frequency of the received signal is increased, and a sufficiently large time of "t ₄ " is obtained.

Example 3. Next, a third embodiment of the present invention will be described with reference to the drawings. FIG. 4 is a block diagram showing an embodiment of the invention of claim 3, and the same parts as those in FIG. 1 are designated by the same reference numerals to avoid redundant description. In the figure, 91 is a transmission mixer that performs frequency conversion of the transmission signal generated by the transmission modulator 2, 92 is a reception mixer that performs frequency conversion of the reception signal amplified by the high-frequency amplifier 6, and 10 is The local oscillator supplies a local oscillation frequency to the transmitting mixer 91 and the receiving mixer 92.

In this embodiment, the frequency selectivity is improved by transmitting and receiving the transmission signal and the reception signal by the super-heterodyne system, and the basic operation is the same as in the case of the first or second embodiment. It is the same.

[0028]

As described above, according to the first and second aspects of the present invention, the frequency change rate is the same as that of the transmission signal, and linearly changes in a sawtooth shape at intervals corresponding to twice the measurement range. Since two types of demodulation signals are generated and mixed with each of the two divided reception signals, it is possible to sufficiently lengthen the portion of the demodulation signal having a frequency proportional to the distance to the target. This makes it possible to obtain a frequency-modulated continuous wave radar that does not reduce the target detection performance and range resolution.

Further, according to the invention described in claim 3, since the transmission signal and the reception signal are transmitted and received by the super-heterodyne system, good frequency selectivity can be realized.

[Brief description of drawings]

FIG. 1 is a block diagram showing a first embodiment of the present invention.

FIG. 2 is an explanatory diagram showing a frequency change in each part of the above embodiment.

FIG. 3 is an explanatory diagram showing a frequency change in each part of the second embodiment of the present invention.

FIG. 4 is a block diagram showing a third embodiment of the present invention.

FIG. 5 is a block diagram showing a conventional frequency modulation continuous wave radar.

FIG. 6 is an explanatory diagram showing a frequency change in each part thereof.

[Explanation of symbols]

 1 Oscillator 2 Transmitter modulator 21 1st demodulator modulator 22 2nd demodulator modulator 4 Transmit antenna 5 Receive antenna 71 1st demodulator 72 2nd demodulator 91 Transmit mixer 92 Receive mixer 10 Local oscillator

Claims (3)

[Claims] 1. An oscillator that oscillates a continuous wave of a predetermined frequency, and frequency-modulates the continuous wave that the oscillator oscillates to generate a transmission signal that repeats a linear increase / decrease in frequency at intervals corresponding to a measurement range. And the same frequency change rate as that of the transmission signal, and the sawtooth linear frequency increase is repeated at intervals corresponding to twice the measurement range.
A first demodulation modulator that generates a first demodulation signal that is synchronized with the transmission signal, and a sawtooth shape at the same frequency change rate as the transmission signal, at intervals corresponding to twice the measurement range. A second demodulation modulator that generates a second demodulation signal that is deviated from the first demodulation signal by a time corresponding to the measurement range by repeating a linear frequency decrease, and the transmission signal in space. A transmitting antenna which radiates to the antenna, a receiving antenna which receives a reflected wave from the target of the transmitting signal, and a receiving signal of the receiving antenna which is mixed with the first demodulation signal and demodulated into a first demodulation signal. A frequency modulation continuous wave radar comprising a first demodulator and a second demodulator that mixes a reception signal of the reception antenna with the second demodulation signal to demodulate into a second demodulation signal. 2. An oscillator that oscillates a continuous wave of a predetermined frequency, and frequency-modulates the continuous wave that the oscillator oscillates to increase or decrease the frequency linearly in a sawtooth shape at intervals corresponding to the measurement range. A transmission modulator for generating a transmission signal to be repeated, and at the same rate of frequency change as that of the transmission signal, a sawtooth linear frequency increase or decrease is repeated at intervals corresponding to twice the measurement range. A first demodulation modulator that generates a first demodulation signal that is synchronized with a transmission signal, and a second demodulation signal that is shifted from the first demodulation signal by a time corresponding to the measurement range. A second demodulation modulator, a transmission antenna for radiating the transmission signal into space, a reception antenna for receiving a reflected wave from the target of the transmission signal, and a reception signal of the reception antenna for the first demodulation. Mixed with the signal, A first demodulator for demodulating into a first demodulated signal; and a second demodulator for mixing the received signal of the receiving antenna with the second demodulation signal and demodulating into a second demodulated signal. Frequency modulated continuous wave radar. 3. A transmission mixer for converting the frequency of the transmission signal, a reception mixer for converting the frequency of the reception signal, and a local oscillator for supplying a local oscillation frequency to the transmission mixer and the reception mixer. The frequency modulation continuous wave radar according to claim 1 or 2, further comprising: