JP2930740B2 - Servo slope type FM-CW radar - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a servo slope type FM.
The present invention relates to a CW radar, which limits a cycle of a modulation signal to improve a measurement cycle.

[0002]

2. Description of the Related Art Conventionally, a frequency-modulated continuous wave (a so-called FM
-CW) A radar of a type that performs sweep detection by a signal is used. A typical example of this system is a so-called servo-slope type FM-CW radar system, which is used, for example, in a radar system for berthing a ship.

FIG. 5 shows a configuration example of a radar system according to this system, that is, a servo slope FM-CW radar system.

[0004] To a modulator 10 that generates a modulation signal Fm (t) according to an input signal, a transmission / reception unit 12 that outputs a transmission signal frequency-modulated by the modulation signal Fm (t) is connected. The transmission / reception unit 12 includes a transmission circuit 14, a mixer 16, and a reception circuit 18, as shown in FIG.

[0005] That is, as shown in FIG.
The modulator 10 generates a modulated signal Fm (t) having a slope whose rise time Tm is determined by the input signal.
At this time, since the slope has a certain amplitude, the slope of the slope is determined by the rise time Tm. In the transmission circuit 14, the transmission signal is frequency-modulated by the modulated signal Fm (t) and output. At this time, the frequency of the transmission signal is the modulation signal Fm (t)
Is represented by a function f (t) of the sweep waveform of Therefore, the frequency f (t) of the transmission signal is equal to the fundamental frequency (for example, 13 GHz).
With respect to z), it changes linearly with a transition bandwidth ΔF (eg, 400 MHz) corresponding to the amplitude of the slope of the modulation signal Fm (t).

An antenna 22 for radiating a transmission signal to the target 20 and receiving a reflected wave from the target 20 is connected to the transmission circuit 14 via a mixer 16. The mixer 16 that mixes a part of the transmission signal with the reception signal of the antenna 22 is connected to a reception circuit 18 that amplifies the output of the mixer 16.

That is, the transmission signal is transmitted to the antenna 22
Is radiated as a radio wave, and a reflected wave of the radio wave by the target 20 is received by the antenna 22. The reflected wave received by the antenna 22 is mixed as a reception signal with a part of the transmission signal by the mixer 16, and the mixer 16 has a beat frequency f _b (for example, 100 kHz) corresponding to a frequency difference between the reception signal and the transmission signal. Outputs beat signal.

The beat frequency f _b is a value proportional to the distance D of the target 20. That is, as shown in FIG. 8B, the transmission signal and the reception signal have the rising time T
m, the ratio of the frequency f _b involved in mixing the transmission signal and the reception signal to the time difference τ between the transmission signal and the reception signal is equal to the slope of the slope. Match the slope. Here, the time difference tau between the transmitted and received signals, since radio wave transmission time according to the reflection route length 2D for target 20, in the case where the speed of light and C is, tau = relationship 2D / C To establish. On the other hand, since f _b / τ = ΔF / T as described above, f _b = (ΔF · 2D) / (TC) ∞D, and the beat frequency f _b is proportional to the distance D.

[0009] The reception circuit 18, the frequency f _b of the beat signal, is connected to the control discriminator 24 to determine the level and S / N, signal switching for opening and closing the servo loop to control discriminator 24 The vessel 26 is connected. The receiving circuit 18 is provided with a tracking discriminator 28 for generating an error signal.
And are connected in parallel.

[0010] That is, the reception beat signal amplified by the circuit 18 is input to the control discriminator 24, the control discriminator 24 frequency f _b, the received signal is the target by the level and S / N of the beat signal 20 It is determined whether or not the wave is a reflected wave. As a result of this determination, if the received signal is determined to be a reflected wave from the target 20, the control discriminator 24 issues a command to connect the tracking discriminator 28 and the modulator 10 to the signal switch 26. An error signal generated by the tracking discriminator 28 is input to the modulator 10 and the modulated signal F
Adjust the slope of the m (t) slope. Here, the error signal, the movement of the target 20, that is, a signal generated according to the amount of change in the beat frequency f _b associated with the change in the distance D. Thus, the modulation signal Fm (t) is servo-controlled.

A search voltage generating circuit 30 is further connected to the signal switch 26. That is, as a result of the determination by the control discriminator 24, if the received signal is not recognized as a reflected wave from the target 20, the control discriminator 24 sends the search voltage generation circuit 30 A connection command with modulator 10 is issued, and as a result, the search voltage generated in search voltage generation circuit 30 is input to modulator 10.
Here, the search voltage is a periodic signal for continuously changing the slope of the slope of the modulation signal Fm (t) within a predetermined range.
When the slope gradient of m (t) becomes larger, the presence / absence of a target at a shorter distance is detected, and when it becomes smaller, the presence / absence of a target at a longer distance is detected. Therefore, when the servo control is not being performed, the presence or absence of the target in the predetermined distance range is detected by the sweep according to the search voltage.

The modulator 10 has a beat frequency f
A distance output circuit 32 for outputting a distance D determined using _b to a display circuit (not shown) is connected. That is, the distance output circuit 32 calculates and outputs the distance D using the beat frequency f _b , the transition bandwidth ΔF, and the rise time Tm.

[0013] Such a conventional servo slope type FM-
According to the CW radar system, the distance D of the target 20 is measured and output using the reflection from the target 20, and the modulated signal F
The target object 20 is continuously captured by the servo control of (t), and when the target object 20 is not detected, sweep detection can be performed in a predetermined distance range.

The phase of the beat signal is an amount indicating the speed of the target. If the speed of the target has a speed component in the transmission direction of the radio wave, the speed component undergoes a phase change due to the Doppler phenomenon. Therefore, the speed of the target can be obtained by detecting the phase change of the beat signal and reproducing the Doppler frequency.

FIG. 7 shows a gate circuit 34 for taking in a beat signal of the frequency f _b , and a multiplier 36 is connected to a stage subsequent to the gate circuit 34. The gate circuit 34 samples the taken beat signal at a predetermined timing and outputs it. That is, a predetermined period of the beat signal is extracted and output to the multiplier 36.

On the other hand, the multiplier 36 includes the clock generator 3
8 are connected. The clock generator 38 has a frequency f
_{At b} , for example, a clock having a timing synchronized with the transmission signal is generated. Therefore, by multiplying the output of the gate circuit 34 by the clock by the multiplier 36, a phase change of the beat signal can be obtained in principle.

A low-pass filter 4 is provided downstream of the multiplier 36.
0 is connected, and the output of the multiplier 36 is filtered by the low-pass filter 40. Then, only the low frequency components related to the phase change of the beat signal are extracted from the output of the multiplier 36. The output of the low-pass filter 40 is counted by a counter 42. As a result, the Doppler frequency f _d of the target is obtained. The Doppler frequency f _d has a relationship of Vr = f _d · λ / 2 with respect to the speed Vr of the target. Here, λ is the center wavelength of the transmission signal of the gate circuit 34 at the same timing. Therefore, the speed Vr to be measured is obtained by the above operation.

[0018]

However, in the conventional servo-slope type FM-CW radar, the cycle of the modulation signal is proportional to the measurement distance, so that the measurement cycle at the time of long-distance measurement becomes long. In this case, the maximum speed that can be detected decreases. This is because the Doppler velocity cannot be detected by the sampling theorem when the target moves a distance of one wavelength or more of the transmission frequency for each measurement cycle.

SUMMARY OF THE INVENTION The present invention has been made to solve such a problem, and a servo slope type FM-CW radar capable of improving a measurement period without lowering a maximum detectable speed. The purpose is to provide.

[0020]

In order to achieve the above object, the present invention provides a means for sequentially outputting a plurality of types of transmission signals by sequentially switching at predetermined time intervals, and a first one of the plurality of types of transmission signals. And a comparator that outputs a predetermined signal when the period of the modulation signal related to the first transmission signal exceeds a set value in a first time domain in which the transmission signal is output. And a sample and hold circuit for storing the amplitude of the modulation signal immediately before the end of the cycle of the modulation signal, means for measuring a target distance, and the sample and hold circuit for storing the signal in the first time domain. Means for measuring a known distance in a second time domain according to the amplitude of the modulated signal, wherein the first time domain is determined based on the measurement result in the second time domain. And determining the distance of the target in.

[0021]

According to the present invention, the target distance in the first time domain is determined based on the known distance measured in the second time domain. The measurement in the first time domain is similar to the measurement in the conventional servo slope type FM-CW radar. The measurement in the second time domain is based on the amplitude stored by the sample and hold in the first time domain. The storage of the amplitude related to the sample hold is performed as follows. That is, in the first time domain, when the cycle of the modulation signal related to the first transmission signal exceeds the set value, the reset circuit operates by the output of the comparator, and the cycle of the modulation signal ends. At the end of the modulation signal, the amplitude of the modulation signal is stored in the sample and hold circuit. The amplitude stored in this way is used as the basis for the measurement of the known distance.

Therefore, in the present invention, the target distance in the first time domain is determined based on the measurement result of the known distance measured in the second time domain. Are performed at the same time, the period of the modulation signal can be set long without lowering the maximum detectable speed.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the drawings. The same components as those of the conventional example shown in FIGS. 5 to 8 are denoted by the same reference numerals, and description thereof will be omitted.

FIG. 1 shows the configuration of a servo slope type FM-CW radar according to one embodiment of the present invention. In this figure, a distance measuring unit 44 according to the features of the present invention is connected to the modulator 10, and the configuration of the distance measuring unit 44 is shown in FIG. As shown in this figure,
The modulator 10 is connected to a comparator 46 for comparing a period (hereinafter, referred to as Tm) of a modulated signal in a first time domain with a reference Tm. The output of the comparator 46 terminates the cycle of the modulation signal Fm (t) generated by the modulator 10 in the reset circuit 48. On the other hand, the output of the comparator 46 is connected to the sample and hold circuit 50, and stores the amplitude of the modulation signal Fm (t), which is the output of the modulator 10, immediately before the end of the cycle. The stored amplitude is modulated by the modulator 10 in the second time-domain modulated signal Fc (t).
Is used to determine the amplitude of

Here, the second time domain is a first time domain in which measurement serving as a reference for determining a target distance is performed.

That is, as shown in FIG.
In this embodiment, modulated signals Fm (t) having different periods in the first time domain and the second time domain are generated. In the first time domain related to the first cycle Tm, the distance measurement is performed using the modulation signal Fm (t). In the second time domain related to the cycle Tc,
Distance measurement is performed using the modulation signal Fc (t) having a gradient determined by the cycle Tc. As shown in FIG. 4B, the principle of the distance measurement is the same as that of the conventional example described above.

The measurement in the second time domain relates to measurement of a reference distance (measurement of a known distance) used for determining a distance in the first time domain. In this embodiment, a signal switch 52 and a delay circuit 54 are used in the transmitting and receiving unit 12 to perform such a measurement.

FIG. 3 shows the transmission / reception unit 12 in this embodiment.
Is shown.

As shown in this figure, the signal switch 52
Is disposed between the mixer 14 and the antenna 20;
The delay circuit 54 is connected to the signal switch 52.

The signal switch 52 is connected to the antenna 22 in a first time domain, and is connected to a delay circuit 54 in a second time domain. The delay circuit 54 has a fixed delay time and is used as a means for measuring a known distance.

The distance output circuit 32 determines a target distance in the first time domain based on the measurement result in the second time domain.

As described above, the measurement cycle can be improved by limiting the cycle of the modulation signal Fm (t) to an arbitrary value.

[0033]

As described above, according to the present invention, the second
Since the known distance is measured in the time domain and the target distance in the first time domain is determined using the measurement result, the measurement cycle is improved, and the maximum detectable speed is improved.

[Brief description of the drawings]

FIG. 1 shows a servo slope type FM according to an embodiment of the present invention.
It is a block diagram of a -CW radar.

FIG. 2 is a configuration diagram of a distance measurement unit in the present embodiment.

FIG. 3 is a configuration diagram of a transmission / reception unit in the present embodiment.

4A and 4B are operation diagrams of the present embodiment, in which FIG. 4A is a chart diagram of a modulation signal, and FIG. 4B is a chart diagram showing timings of a transmission signal and a reception signal.

FIG. 5 is a configuration diagram of a servo slope type FM-CW radar according to one conventional example.

FIG. 6 is a configuration diagram of a transmission / reception unit in the conventional example.

FIG. 7 is a configuration diagram of a speed output unit in this conventional example.

8A and 8B are operation diagrams of this conventional example, in which FIG. 8A is a chart showing a modulation signal, and FIG. 8B is a chart showing timings of a transmission signal and a reception signal.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Modulator 14 Transmission circuit 16 Mixer 18 Receiving circuit 46 Comparator 48 Reset circuit 50 Sample hold circuit 52 Signal switch 54 Delay circuit

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G01S 7/00-7/42 G01S 13/00-13/95

Claims (1)

(57) [Claims] 1. A transmission signal frequency-modulated by a continuous modulation signal having a linear slope is radiated as a radio wave, and a reception signal including a reflected wave from a target by the transmission signal and a part of the transmission signal are generated. By detecting the frequency difference between the transmission signal and the reflected wave from the target by mixing, the slope of the modulation signal and the slope of the modulation signal are servo-controlled so that the slope and the frequency difference become constant. A servo that tracks the object and opens the servo loop for performing the servo control when the reflected wave from the target is not detected and periodically changes the slope of the slope of the modulation signal to perform sweep detection from a short distance to a long distance. Slope type FM-CW
In the radar system, means for sequentially switching every predetermined time to output a plurality of types of transmission signals, and a first time domain in which a first transmission signal is output among the plurality of types of transmission signals, A comparator that outputs a predetermined signal when the cycle of the modulation signal related to the transmission signal exceeds a set value, a reset circuit that ends the cycle of the modulation signal by a change in the output of the comparator, and a reset circuit that ends the modulation signal immediately before the end of the cycle of the modulation signal. Means for measuring a target distance, including a sample and hold circuit for storing the amplitude, and measuring a known distance in a second time domain with the amplitude of the modulated signal stored in the sample and hold circuit in the first time domain Means for determining a target distance in the first time domain based on the measurement result in the second time domain. Bosuropu type FM-CW radar.