JPH0648292B2 - Servo slope type FM-CW radar method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a servo slope FM-CW radar method, and more particularly to a true target capturing method.

[Prior Art] Conventionally, for determining the distance of a target object within a predetermined radius,
2. Description of the Related Art A radar of a method of sweep detection using a frequency-modulated continuous wave (so-called FM-CW) signal is used. A typical example of this method is a so-called servo slope FM-CW radar method, which is used, for example, in a radar system for berthing a ship.

This system, that is, the servo slope FM is shown in FIG.
-A configuration example of a radar system related to the CW radar system is shown.

Modulator 10 for generating a modulation signal F (t) according to an input signal
A transmission circuit 12 that outputs a transmission signal frequency-modulated by the modulation signal F (t) is connected to the.

That is, as shown in FIG. 4 (a), the modulator 10 generates a modulation signal F (t) having a slope whose rise time T 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 rising time T. Further, in the transmission circuit 12, the transmission signal is frequency-modulated by this modulation signal F (t) and output. At this time, the frequency of the transmission signal is represented by a function f (t) of a similar waveform of the modulation signal F (t). Therefore, the frequency f (t) of the transmission signal has a transition bandwidth ΔF (eg, 40 GHz) corresponding to the amplitude of the slope of the modulation signal F (t) with respect to the fundamental frequency (eg, 13 GHz).
It changes linearly at 0 MHz).

An antenna 16 for radiating a transmission signal to the target object 14 and receiving a reflected wave from the target object 14 is connected to the transmission circuit 12 via a mixer 18, and a part of the transmission signal and a reception signal of the antenna 16 are connected. Mixer 1 for mixing
A receiving circuit 20 that amplifies the output of the mixer 18 is connected to 8.

That is, the transmission signal is radiated as a radio wave by the antenna 16, and the reflected wave of the radio wave from the target 14 is
It is received by the antenna 16. The reflected wave received by the antenna 16 is mixed as a reception signal with a part of the transmission signal by the mixer 18, and the mixer 18 produces a beat frequency f corresponding to the frequency difference between the reception signal and the transmission signal.
Output a beat signal having _b (for example, 100 kHz).

The beat frequency f _b is a value proportional to the distance D of the target object 14. That is, as shown in FIG. 4 (b),
Since the transmission signal and the reception signal have a slope having a slope that is the ratio of the transition bandwidth ΔF to the rise time T, the frequency relating to the mixing of the transmission signal and the reception signal with respect to the time difference τ between the transmission signal and the reception signal. The ratio of f _b corresponds to the slope of the slope. Here, the time difference τ between the transmission signal and the reception signal is determined by the reflection path length 2 with respect to the target 14.
Since it is a radio wave propagation time related to D, when the speed of light is C, the relationship of τ = 2D / C is established. On the other hand, since f _b / τ = ΔF / T as described above, therefore, f _b = (ΔF · 2D) / (T · C) ∝D, and the beat frequency f _b is proportional to the distance D.

The reception circuit 20 includes a frequency f _{b of the} beat signal,
A control discriminator 22 for determining the level and S / N is connected, and the control discriminator 22 is connected to a signal switch 24 for opening and closing a servo loop. Further, the reception signal circuit 20 includes a tracking discriminator 26 for generating an error signal.
Are connected in parallel with the control discriminator 22.

That is, the beat signal amplified in the reception circuit 20 is input to the control discriminator 22, and the control discriminator 22 reflects the received signal by the frequency f _b , level and S / N of the heat signal. Is determined. As a result of this determination, when the received signal is the reflected wave from the target 14, the control discriminator 22 instructs the signal switch 24 to connect the tracking discriminator 26 and the modulator 10. The error signal generated by the tracking discriminator 26 is input to the modulator 10 to adjust the slope of the slope of the modulation signal F (t). Here, this error signal is a signal generated according to the movement of the target object 14, that is, the amount of change of the beat frequency f _h accompanying the change of the distance D. In this way, the modulation signal F (t) is servo-controlled.

The signal switch 24 further includes a search voltage generating circuit 2
8 is connected.

That is, as a result of the determination by the control discriminator 22, when the received signal is not recognized as a reflected wave by the target object 14, the control discriminator 22 causes the signal switch 24 to include the search voltage generation circuit 28 and the above-mentioned. A connection command with the modulator 10 is issued, and as a result, the search voltage generated in the search voltage generation circuit 28 is input to the modulator 10. Here, the search voltage is a periodic signal for continuously changing the slope of the modulation signal F (t) within a predetermined range, and the search voltage causes the slope of the modulation signal F (t) to change. When the gradient becomes larger, the presence or absence of a target at a closer distance is detected, and when the gradient becomes smaller, the presence or absence of a target at a longer distance is detected. Therefore, when the servo control is not performed, the presence or absence of the target in the predetermined distance range is swept detected according to the search voltage.

Then, the modulator 10, the distance output circuit 30 for outputting the distance D is determined using the beat frequency f _b to the display circuit (not shown) is connected. That is, the distance output circuit 30 calculates and outputs the distance D using the beat frequency f _b , the transition bandwidth ΔF and the rising time T.

According to such a conventional servo slope type FM-CW radar system, the target object 1 using the reflection from the target object 14 is used.
The distance D of 4 is measured and output, the target object 14 is continuously captured by the servo control of the modulation signal F (t), and when the target object 14 is not detected, the predetermined distance range can be swept and detected.

[Problems to be Solved by the Invention] However, according to the conventional servo slope FM-CW radar system, there is a problem that the distance of the target is erroneously determined when multiple reflections occur. That is, when the radio wave radiated to the target object makes two round trips between the housing of the radar system according to this method and the target object, the path provided is twice the true reflection path by the antenna provided on the housing. Multiple reflected waves of length are received and the system outputs twice the true distance.

The present invention has been made to solve the above problems, and it is possible to prevent an erroneous determination of a distance due to multiple reflected waves and improve the accuracy of the distance determination. A servo slope FM-CW radar system The purpose is to provide.

[Means for Solving the Problems] In order to achieve the above-mentioned object, the present invention performs frequency modulation of a transmission signal alternately by a modulation signal and a double slope modulation signal at predetermined time intervals, and alternately performs the double slope modulation. The signal is a continuous signal having a slope having a gradient twice that of the modulation signal, and when the distance to the target is obtained by the one transmission signal, the transmission signal related to the double gradient modulation signal causes the distance of 1 The presence / absence of the target object at a distance of / 2 is determined, and when the target object is detected at the 1/2 distance, the servo loop for servo control is opened, and when the target object is detected at a certain distance, 1 It is characterized in that the presence / absence of a true target object at a distance of / 2 is determined, and only the true target object is tracked to determine the distance.

[Operation] In the present invention, when a target object and an object that is likely to be detected are detected at a certain distance, the target object and the target object are identified by a double-gradient modulation signal including a slope having a slope twice the slope of the modulation signal related to the detection. A transmission signal for detecting a distance half the distance at which the object is detected is radiated as a radio wave. Then, the presence or absence of the true target object at the distance of 1/2 is determined by the difference frequency signal between the transmission signal related to this double gradient modulation signal and the reception signal that is the reflected wave related to this transmission signal, and it is determined to be present. The servo loop is opened when this is done, and the target acquisition and the distance determination by the servo loop are continued when it is determined that there is nothing. Therefore, even when multiple reflected waves are generated, erroneous distance determination due to the multiple reflected waves is prevented, and the distance measurement angle is improved.

[Embodiment] An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows the configuration of a radar system using a servo slope type FM-CW radar system according to an embodiment of the present invention. The same components as those of the conventional example shown in FIG. 3 are designated by the same reference numerals and the description thereof will be omitted.

In this embodiment, the transmitter circuit 12 includes a modulator 10 and an additional modulator 32 for generating a double-slope modulation signal including a slope having a slope twice that of the modulation signal of the modulator 10. Signal switcher 3 with clock input
4 are connected in parallel.

That is, the modulation signal F (t) supplied to the transmission circuit 12
Is a slope due to the rise time T generated in the modulator 10, the additional modulator 32, as shown in FIG.
And the slope of the double slope due to the rise time T / 2 are signals which are switched by the clock in the signal switch 34 and appear alternately. Transmission circuit 12
In, the transmission signal frequency-modulated by the modulation signal F (t) is output as in the conventional example.

On the other hand, in the receiving circuit 22, the control discriminator 22 and the additional control discriminator 38 are connected in parallel via the signal switch 36. That is, regarding the beat signal output from the receiving circuit 20, a beat signal corresponding to the slope of the modulator 10 is supplied to the control discriminator 22 and the additional modulator 3
2 so that the beat signals corresponding to the slopes are respectively input to the additional control discriminator 38, the signal switch 36 that operates in synchronization with the signal switch 34 by the same clock input as the signal switch 34.
Is input by switching.

A control discriminator 22 and an additional control discriminator for judging whether or not the received signal of the transmitting / receiving antenna 16 is a reflected wave from the target 14 based on the frequency f _b , level and S / N of the beat signal input to each. 38 includes a control discriminator 22 and an additional control discriminator 3
The sample and hold circuit 40 and the additional sample and hold circuit 42 for holding the output signals of 8 are connected. That is, the control discriminator 22 and the additional control discriminator 38 are respectively provided with the modulator 10 and the additional modulator 32, as shown in FIG.
The presence / absence of a target at a distance corresponding to the slope of each modulation signal is detected by the beat signal corresponding to the modulation signal of 1, and a determination signal is input to the sample hold circuit 40 and the additional sample hold circuit 42, respectively. Then, the sample hold circuit 40 and the additional sample hold circuit 42 hold the determination signals of the control discriminator 22 and the additional control discriminator 38 in the time lag accompanying the signal switching by the clock of the signal switch 36.

The sample-hold circuit 40 and the additional sample-hold circuit 42 are connected to an effectiveness determination circuit 44 that gives a connection command to the signal switch 24 according to the respective determination signals input from the sample-hold circuit 40 and the additional sample-hold circuit 42. There is. That is, for example, when the determination signal of the control discriminator 22 is the rise time T
The target signal 14 is detected at a distance corresponding to the slope of the rising signal T / 2, which is a determination signal indicating that the target object 14 has been detected at a distance corresponding to the slope of the additional control discriminator 38. If it is a determination signal indicating that the signal has been changed, the validity determination circuit 44 includes the search voltage generation circuit 28 and the modulator 1 in the signal switch 24.
A connection command for connecting 0 and the additional modulator 32 is given. Further, the determination signal of the control disc liminator 22 is a determination signal indicating that the target object 14 is detected at a distance corresponding to the slope of the rising time T, and the determination signal of the additional control discriminator 38 is the rising time T.
If the determination signal indicates that the target object 14 is not detected at the distance corresponding to / 2, the validity determination circuit 4
Reference numeral 4 gives a connection command for connecting the tracking discriminator 26, the modulator 10 and the additional modulator 32 to the signal switch 24.

The tracking discriminator 26 and the search voltage generating circuit 28 are connected to the modulator 10 and the additional modulator 32 via the signal switch 24 and the signal switch 46 having a clock input. That is, in response to the connection command from the validity judging circuit 44, the signal switch 24
Supplies one of the error signal output from the tracking discriminator 26 and the search voltage output from the search voltage generation circuit 28 to the modulator 10 and the additional modulator 32 via the signal switch 46. To do. The signal switcher 46 includes the signal switcher 34 and the signal switcher 3.
The modulator 10, the control discriminator 22, the additional modulator 32, and the additional control discriminator 38 operate in synchronization with the clock 6 to generate the modulated signal and determine the beat signal, respectively.

Therefore, the servo slope type FM-CW according to this embodiment
According to the radar system using the radar method, even when an object that is supposed to be a target at a certain distance is detected, by detecting a distance that is 1/2 of this distance, the object and the supposed object are radiated by the transmitting and receiving antennas. It is determined whether or not the target is a false object that is twice as far as the actual target due to the multiple reflections of the radio waves, and only the actual target object 14 is tracked and captured to obtain an accurate distance D.
Can be measured. That is, when the beat signal due to the multiple reflection is read into the control discriminator 22, the beat signal related to the actual target 14 is read into the additional control discriminator 38, and the validity determining circuit 44 causes the modulator 10 and the additional modulation. The servo loop related to the servo control of the device 32 is opened, and the sweep detection is performed again by the search voltage which is the output of the search voltage generation circuit 28, so that the actual target 14 is captured and the actual distance D is measured.

[Effect of the Invention] As described above, according to the present invention, when the target object is detected, at the same time, the distance of 1/2 of the target object is also detected, and the erroneous measurement of the distance due to the multiple reflected waves is prevented. It is possible to improve.

[Brief description of drawings]

FIG. 1 is a servo slope type FM according to an embodiment of the present invention.
-Structure diagram of a radar system using the CW radar system, Fig. 2 is an operation diagram of the radar system shown in Fig. 1, and Fig. 2 (a) is a chart diagram of a modulated signal, Fig. 2
(b) is a chart showing timings of a transmission signal and a reception signal, FIG. 3 is a configuration diagram of a radar system using a conventional servo slope FM-CW radar system, and FIG. 4 is FIG. 4 (a) is an operation diagram of the radar system shown in FIG. 4, FIG. 4 (a) is a chart diagram showing modulated signals, and FIG. 4 (b) is a chart diagram showing timings of transmission signals and reception signals. 14 ... Target 32 ... Additional modulator 38 ... Additional control discriminator 44 ... Effectiveness judgment circuit D ... Distance ΔF …… Transition bandwidth T …… Rise time f _b …… Beat frequency τ …… Time lag

Claims (1)

[Claims] 1. A reception signal including a reflected wave from a target by the transmission signal and a transmission signal radiated as a radio wave, the transmission signal being frequency-modulated by a continuous modulation signal having a constant linear slope. The frequency difference between the transmission signal and the reflected wave from the target is detected by mixing with a part, and the distance of the target is obtained from the slope of the slope and the frequency difference so that the frequency difference becomes constant. Servo control the slope of the modulation signal to track the target object, and when a reflected wave from the target object is not detected, open a servo loop to perform the servo control, and periodically slope the slope of the modulation signal. In a servo slope type FM-CW radar method for varying and performing sweep detection from a short distance to a long distance, frequency modulation of the transmission signal is performed with the modulation signal and a double slope variation. The double gradient modulation signal is a continuous signal having a slope of a gradient twice that of the other, and the distance of the target object is changed by the one transmission signal. When determined, the presence or absence of the target object at a distance of 1/2 of the target object is determined by the transmission signal related to the double gradient modulation signal, and the true target object is detected at this 1/2 distance. Sometimes the servo loop is opened, and when a target object is detected at a certain distance,
A servo slope FM-CW radar method, characterized in that the presence or absence of a true target at a distance of 2 is determined and only the true target is tracked to determine the distance.