JP2000206233A - Echo eliminating method of radar - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable ensuring a long reduced distance when a radar wave of short pulse width which realizes high resolution is used by suppressing influence of a second period echo in a pulse radar. SOLUTION: A reflected wave shown in (1) is decomposed into a component of short pulse shown in (2) and a component of long pulse shown in (3), and logic product of them is obtained. As the result, the component of a second period echo is eliminated and an output waveform shown in (4) is obtained. Based on the output waveform, a video signal to be inputted in a display unit is formed. Thereby the influence of the second period echo is effectively suppressed, and compatibility of the resolution of a radar and the reduced distance which shows the observation range of the radar can be easily realized.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radar for measuring an azimuth of an object and a distance to the object by using reflection of radio waves and the like. The present invention relates to a technique for clearly capturing a target in a radar in which radio waves and the like intermittently reflected on the target surface return.

[0002]

2. Description of the Related Art In general, when considering the performance of a radar, it is extremely important to capture objects more clearly in a farther range. Of these points, the longer the distance, the longer the conversion distance,
It turns out that. This conversion distance is

Rmax (m) = T (μs) × 150
(M) T: radar repetition period

[0004] The following equation uniquely determines the radar repetition period. This conversion distance is the distance that the radio wave reciprocates in the repetition cycle. The radio wave is emitted from the radar, reflected by the target, and reaches the radar again.
Since only a shorter time than the repetition period is required, the maximum value of the possible distance is shown. If the target exists far beyond this conversion distance, the radio wave emitted from the radar cannot reach the radar again within a time within the repetition period. The radar repetition period refers to the time from the emission of a radio wave in a specific direction, the change of the emission direction of the radio wave with the passage of time, and the next emission of the radio wave in the same direction.

[0005] The converted distance indicates a distance range in which generation of a so-called second period echo can be avoided. Second
The periodic echo indicates that a radio wave emitted from a radar is reflected by an object and reaches the radar again after a repetition of a period. When such a phenomenon occurs, the radar cannot determine whether the arriving radio wave was emitted before the repetition period or was re-emitted after the repetition period, and erroneously measured the distance from the radar to the target become. In order to prevent such errors, by suppressing the reduced distance covered by the radar to the extent that the radio waves emitted from the object reach the radar again in a shorter period of the repetition period, the radio waves reflected by the object are reduced. This is to prevent a second-cycle echo from occurring.

On the other hand, the point that the target is more clearly captured means that the number of radar hits is increased.
The number of radar hits is the number of times that a radio wave emitted from a radar in a specific direction is reflected on a target surface and reaches the radar. That is, how many times the radio wave emitted at each repetition period is reflected by the target and reaches the radar again while the radar is facing the target is repeated. As the number of repetitions increases, the amount of information on the object can be collected more, and the object can be complemented more clearly.

In order to increase the number of radar hits,
The first is to reduce the change in the direction of emission of radio waves with the passage of time by reducing the number of revolutions of the radar. The second is to increase the beam width so that the direction of emission of the radio waves still changes in a specific direction. The radio wave to reach the target of the third,
In this case, the repetition period is lengthened so that the radio wave reflected on the target surface reaches the radar before the repetition period elapses. Increasing the third repetition period among these three measures is also effective for increasing the conversion distance.

[0008]

Here, as described at the beginning, if the performance of capturing the object more clearly in a farther range is to be improved, the setting of the repetition period is inconsistent. Therefore, there is a problem that it is difficult to balance these two performances. That is, firstly, to a farther range is nothing less than increasing the above-mentioned conversion distance, and for this purpose, the radio wave reciprocates between the radar and the target with a long repetition period. Therefore, it is necessary to allow a long time.

However, in order to more clearly capture the target, it is necessary to increase the number of radar hits described above. To this end, while the radar emission direction is the target direction, It is necessary to emit radio waves many times, in other words, to increase the repetition frequency. This means that it is necessary to shorten the repetition period without correcting it. As described above, in order to improve the performance of the radar more clearly and farther, there is a problem that the setting of the repetition period is inconsistent, and it is difficult to improve the performance.

[0010]

As means for solving the above-mentioned problems, in the present invention, means for generating two kinds of long and short pulses synchronized with each other, means for transmitting these pulses, and means for reflecting the reflected light from an object are provided. There are provided means for receiving two types of long and short pulses, means for calculating the logical product of these pulses, and means for generating a video signal based on the obtained logical product signal.

[0011]

Embodiments of the present invention will be described below in detail. FIG. 1 illustrates an outline of a configuration suitable for carrying out the present invention.

In FIG. 1, reference numeral 1 denotes a radar antenna.
The radar antenna 1 in this example is responsible for both transmission and reception of radar waves. 2 is a duplexer. The duplexer 2 is connected to the radar antenna 1 and arranges signals for performing both transmission and reception with one radar antenna 1. That is, a signal transmitted from a transmission side circuit of the radar transceiver described later is transmitted to the radar antenna 1
And, on the contrary, plays a role of sending a radar wave signal incident on the radar antenna 1 to a receiver side circuit of the radar transceiver which will also be described later.

Hereinafter, the transmitting side circuit will be described first.
A transmitter 3 modulates a pulse wave to generate a radar wave, that is, an electric signal that can be transmitted as a radio wave from the radar antenna 1. Drive circuit A4a and drive circuit B
The pulse waves generated in 4b are respectively input to the transmitter 3. The drive circuit 4a and the drive circuit B4b are both drive circuits, and each generate a pulse wave. This drive circuit A4
a and the pulse widths of the pulse waves generated by the drive circuit B4b are different. This pulse width will be described later in detail. Reference numeral 5 denotes a synchronization circuit that generates a synchronization signal. This synchronization signal is input to each of the driving circuits A4a and B4b. Drive circuit A4a and drive circuit B4b
Then, a pulse wave is generated based on the synchronization signal from the synchronization circuit 5. Here, the synchronization signals input to the driving circuits A4a and B4b are exactly the same, and as a result, the pulse wave generated by the driving circuit A4a and the pulse wave generated by the driving circuit B4b are synchronized. The details of the configuration of each circuit are considered to be in a range well known to those skilled in the art, and a description thereof will be omitted.

Next, the receiving circuit will be described. Reference numeral 6 denotes a reception selection circuit which decomposes a reception signal input from the radar antenna 1 via the duplexer 2 according to the pulse width. The received signal referred to here is a signal received by the radar antenna 1 from a radar wave reflected by the target. The reception selection circuit 6 receives the output signal of the synchronization circuit 5 described above, and distributes the reception signal to reception circuits 7a and 7b described below according to the signal from the synchronization circuit 5. The signal from the synchronizing circuit 5 here is the driving circuit A4
a, These are exactly the same signals as those sent to the drive circuit B4b. While the synchronization signal sent to the transmission side and the synchronization signal sent to the reception side are exactly the same, the reception signal is transmitted for the time required for a radar wave to reciprocate between the radar antenna 1 and a target (not shown). You will be late from the signal. However, actually, the delay is negligibly small compared to the pulse width of the signal. Therefore, even if the same synchronization signal is used in the transmitting circuit and the receiving circuit, no problem actually occurs.

Each of the receiving circuits 7a and 7b has a receiving characteristic suitable for signals having different pulse widths. The different pulse widths here are the pulse widths of the pulses generated by the drive circuits A4a and B4b. In addition, a signal having a pulse width corresponding to each reception characteristic is input to the reception circuits 7a and 7b by the reception selection circuit 6. Here, the reception selection circuit 6 sorts the reception signal according to the synchronization signal from the synchronization circuit 5 as described above. As a result, the drive circuits A4a and B4b and the reception circuits 7a and 7b are connected to one specific The signal generated by the driving circuit is reflected on the target surface and then to one specific receiving circuit, and the signal generated by the other driving circuit is also reflected on the target surface and then to the other receiving circuit. , And so on.

Reference numeral 8 denotes a binarizing circuit for binarizing the output signal of the receiving circuit 7b, and digitizes the output signal of the receiving circuit 7b. Reference numeral 9 denotes a memory that stores an output signal of the binarization circuit, and stores a binarized signal. Here, the binarizing circuit 8 and the memory 9 are connected to only one of the receiving circuits 7a and 7b. These binarization circuits 8
In addition, the memory 9 is connected to a receiving circuit that handles a signal having a long pulse width. In FIG. 1, the receiving circuit 7b is a receiving circuit that handles a signal having a long pulse width. on the other hand,
The receiving circuit 7a is a receiving circuit that handles a signal having a short pulse width. The reason why the binarizing circuit 8 and the memory 9 are connected to only one receiving circuit that handles a signal having a long pulse width will be clarified in the description of the operation of the circuit described later.

Reference numeral 10 denotes a selection circuit.
Calculates the logical product of the output signal of the receiving circuit 7a and the signal digitized by the binarizing circuit 8 and temporarily stored in the memory 9, and displays an image on a screen (not shown) based on the logical product. To generate a video signal.

Hereinafter, the operation of the circuit having the configuration of FIG. 1 described above will be described with reference to FIGS. 2 and 3 in addition to FIG.

When the synchronizing circuit 5 of FIG. 1 generates and outputs a synchronizing signal, the driving circuits A4a and B4b convert a signal having a long pulse width and a signal having a short pulse width based on the synchronizing signal. Generate each. The waveforms of these signals are shown in FIG. In FIG. 2, (1) shows a long pulse waveform, and (2) shows a short pulse waveform. The long pulse width signal and the short pulse width signal are synchronized based on the synchronization signal of the synchronization circuit 5. The long pulse and the short pulse are combined and transmitted as a radar wave having the waveform shown in FIG.

The transmitted radar wave is reflected on the surface of the object and reenters the radar as a reflected wave. However, at this time, the waveform is not exactly the same as when transmitted,
As shown in the waveform in FIG. 2D, the waveform is disturbed including the second pulse echo of the short pulse. The component of the second-period echo is reflected at a position different from the target to be captured by the transmitted radar wave, and the distance to the target to be captured and the distance to the reflection position at which the second-period echo is generated, The echoes of the short pulses of the radar wave transmitted at different timings are the true echo reflected on the surface of the target to be captured, and the second echo reflected at a different position from the target to be captured. As a result, the light enters the radar again almost at the same time.

However, the second-period echo does not always enter at exactly the same timing as the true echo, but rather often actually enters at a timing slightly shifted from the true echo. As a result, the incident waveform is disturbed. In particular, since the timing of the peak of the incident wave is deviated, it is very difficult for the radar to accurately measure the distance to the target.

Therefore, the reflected wave shown in FIG. 3A is first separated into a long pulse component and a short pulse component by the reception selecting circuit shown in FIG. Input to machine B. Here, the waveform shown in FIG. 3A is exactly the same as the waveform shown in FIG. The receiver A and the receiver B are circuits having reception characteristics suitable for a short pulse and a long pulse, respectively.

At this time, the waveform input to the receiver A is as shown in FIG. 3 (2), while the waveform input to the receiver B is as shown in FIG. 3 (3). Here, regarding the long pulse, the second wave echo does not occur even in the reflected wave. The reason lies in the pulse width of the long pulse. This is because the pulse of the second period can be absorbed by the true echo by setting the pulse width to a certain extent in a long pulse, that is, by setting the duration of each pulse to a certain extent. By the way, it is not to take such a wide pulse width in short pulse,
This is because the aim is to increase the measurement resolution by narrowing the pulse width of the short pulse.

Next, the long pulse component shown in the receiver B is
It is converted into a value, temporarily stored in a memory, and then output. The logical product of the output of the long pulse component and the output of the receiver A is obtained. The output waveform obtained by this logical product is shown in FIG.
This is shown in (4). Looking at the output waveform of FIG. 3 (4), the disturbance due to the second periodic echo seen in the waveform of FIG. 3 (1) has disappeared. The reason that the second-period echo disappears in this way is that the short-pulse true echo and the long-pulse echo are originally emitted from the radar as synchronized pulse signals, and both reflect off the surface of the target to be captured and are the same. Because it is a signal that follows the path and enters the radar again,
While both have substantially the same timing, the short-period second-period echo is a signal shifted from the short-pulse true echo so that the incident waveform is disturbed.
Naturally, the echo of the long pulse is also shifted. Therefore, if the logical product of the second cycle echo of the short pulse and the echo of the long pulse is obtained, the result becomes zero.

It should be noted here that the pulse width of a long pulse is not extended indefinitely. If the pulse width of the long pulse is unduly expanded, the long pulse will include the short-period second-period echo, so that the effect of removing the second-period echo aimed at by the present invention is sufficiently enjoyed. It may not be possible. Conversely, if the pulse width of the long pulse is excessively narrowed, the true echo component of the short pulse may not be output for a sufficient time when calculating the logical product of the long pulse and the binarized short pulse. Therefore, it is desirable to set the pulse width of the long pulse to an appropriate width in consideration of these conditions.

It is conceivable to increase the number of long pulses with the same configuration as in the above embodiment. The process in such a case will be described with reference to FIGS. In this case, since the circuit configuration is basically the same as that of the above-described embodiment, FIG. 1 will be used again for the circuit configuration.

When the synchronizing circuit 5 of FIG. 1 generates and outputs a synchronizing signal, the driving circuits A4a and B4b convert a signal having a long pulse width and a signal having a short pulse width based on the synchronizing signal. Generate each. The waveforms of these signals are shown in FIG. In FIG. 4, (1) shows a long pulse waveform, and (2) shows a short pulse waveform. 4 (1) and 4 (2), the only difference from the first embodiment is the long pulse interval. The signal having the long pulse width and the signal having the short pulse width are synchronized based on the synchronization signal of the synchronization circuit 5, as in the case of the first embodiment shown in FIG. The long pulse and the short pulse are combined and transmitted as a radar wave having the waveform shown in FIG.

When the radar wave is reflected on the surface of the object and reenters the radar, the short pulse contains the component of the second periodic echo, and has a waveform as shown in FIG.

Then, the reflected wave shown in FIG. 5A is first separated into a long pulse component and a short pulse component by the reception selection circuit shown in FIG. 1 and the receiver A7a shown in FIG.
And input to the receiver B7b. Here, the waveform shown in FIG. 5A is exactly the same as the waveform shown in FIG. The receivers A7a and B7b are circuits having reception characteristics suitable for short pulses and long pulses, respectively. At this time, the waveform input to the receiver A7a becomes the waveform shown in FIG. 5 (2), while the waveform input to the receiver B7b becomes the waveform shown in FIG. 5 (3). Here, as for the long pulse, the second wave echo does not occur in the reflected wave as in the first embodiment. The reason is the same as that already described in the description of the first embodiment.

Next, the long pulse component input to the receiver B 7 b is binarized, temporarily stored in the memory 9 and output, and the logical product of the output of the long pulse component and the output of the receiver A is calculated. Ask. FIG. 5D shows an output waveform obtained by the logical product. Looking at the output waveform of FIG. 5 (4), the disturbance due to the second period echo seen in the waveform of FIG. 5 (1) has disappeared. The reason for the disappearance of the second-period echo is that the short-period second-period echo deviates from the short-pulse true echo so that the incident waveform is disturbed, as in the first embodiment. Signal
Naturally, the echo of the long pulse is also shifted. Therefore, if the logical product of the second cycle echo of the short pulse and the echo of the long pulse is obtained, the result becomes zero.

However, in the second embodiment, as will be apparent from a comparison between FIG. 3 (4) and FIG. 5 (4), the second embodiment is used for generating a video signal in comparison with the first embodiment. The amount of information of the final output is large. Therefore, there is an additional advantage that higher-precision and real-time processing can be performed as compared with the first embodiment.

The basic configuration and operation of the present invention are as described above.
Various configurations other than those described with reference to FIG. 1 are conceivable. The following supplements the description of examples of such various configurations.

FIG. 6 is an example in which the configuration on the transmitting side is changed from the configuration in FIG. 6, two transmission systems are provided in place of the transmitter 3 in FIG. That is, the radar antennas 1a and 1b, the duplexers 2a and 2b,
Transmitters 3a and 3b. These transmitters 3a and 3b are independently connected to a drive circuit A4a and a drive circuit B4b, respectively, and are respectively connected to the independent radar antennas 1a and 1b via separate duplexers 2a and 2b. I have. This makes it possible to optimize the characteristics of the transmitter to those that match the signal characteristics such as the respective pulse widths.
Further, for example, when the frequency is changed between the long pulse and the short pulse, the long pulse and the short pulse are transmitted or reflected completely independently, so that loss of information can be suppressed. Further, since the receiving side is independent of the individual duplexers, the processing speed can be further improved and information can be obtained in real time.

FIG. 7 shows an example in which the configuration on the transmitting side is also changed from the configuration in FIG. 1. Unlike the configuration in FIG. 6, only one transmitter is used. The transmission frequency of the transmitter 3 is controlled via the circuit 11 provided. By controlling the transmission frequency in this manner, different frequencies can be realized by one transmitter, such as when the frequency is changed between a long pulse and a short pulse as shown in the first embodiment. The configuration can be simplified. As a circuit having a frequency conversion function, a gun oscillator, a klystron, or the like can be used.

FIG. 8 shows an example in which the configuration on the transmission side is also changed, in which a phase shifter 12 is inserted between the transmitter 3 and the duplexer 2. Here, a magnetron is used as the transmitter, and a transmitter whose frequency changes according to the load condition is adopted. In addition, the pulse width is set to be wider than a time corresponding to an angle of spread of the main spectrum of the radar wave, in which half of the frequency change amount is equal.

The gate circuit may have a configuration as shown in FIG. The output signals of the receiver A and the receiver B are respectively A / D converted to generate digital signals, which are input to the correlation circuit. This correlation circuit temporarily stores the digital signal on the long pulse side and compares the stored digital signal with the digital signal on the short pulse side. If the timings of both signals match, the digital signal on the short pulse side is D / A converted and output as it is. At this time, the amplitude on the long pulse side is used. If the timings of both signals do not match,
It outputs no signal or outputs a signal indicating that there is no signal to be D / A converted.

[0037]

As described above, according to the present invention, the effect of the second-period echo of the radar is effectively suppressed, and both the resolution of the radar and the reduced distance indicating the observation range of the radar are compatible. Can be easily realized. As reference data,
Take the following example. Radar antenna rotation speed: 10 (rpm) Detection probability: 0.9 False alarm rate 1 / 100,000,000 Noise figure: 8 (dB) 0.1 μs 0.1 μs 0.25 μs 3 kHz 1.5 kHz Equivalent distance (km) 50 50 100 Number of hits 12.58 8-9 6.3 Bandwidth (MHz) 14 144 Noise level (dBm) -94 -94 -100 Detection level (dBm) -81- 80-84 0.25 μs 0.25 μs 0.6 μs 1 kHz 500 Hz 1 kHz Conversion distance (km) 150 300 150 Number of hits 4.2 2 4.2 Bandwidth (MHz) 4 42 Noise level (dBm) -100 -100 −103 Detection level (dBm) −81 −80 −86, which is lower than the condition of 0.1 μs and 3 kHz that provides high resolution. Thus, the influence of the second-period echo can be effectively suppressed without impairing the information of the short pulse.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating an outline of a circuit configuration according to an embodiment of the present invention.

FIG. 2 is a conceptual diagram showing transmission / reception waveforms in the first embodiment.

FIG. 3 is a conceptual diagram showing processing of a reflected wave in the first embodiment by using a waveform.

FIG. 4 is a conceptual diagram showing transmission / reception waveforms in the second embodiment.

FIG. 5 is a conceptual diagram showing processing of a reflected wave in the second embodiment by using a waveform.

FIG. 6 is a block diagram showing an outline of a circuit configuration of still another embodiment of the present invention.

FIG. 7 is a block diagram showing an outline of a circuit configuration of still another embodiment of the present invention.

FIG. 8 is a block diagram showing an outline of a circuit configuration of still another embodiment of the present invention.

FIG. 9 is a block diagram illustrating a configuration example of still another signal processing unit according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Radar antenna 2 Duplexer 3 Transmitter 4 Drive circuit 5 Synchronization circuit 6 Reception selection circuit 7 Receiver 8 Binarization circuit 9 Memory 10 Gate circuit

Claims (1)

[Claims] 1. A pulse wave having a long pulse width and a pulse wave having a short pulse width are respectively generated, the long and short pulse waves are emitted, and the emitted pulse wave receives a reflected wave reflected by an object. A radar echo elimination method that separates a long pulse width component and a short pulse width component into a logical product of the long pulse width component and the short pulse width component, and outputs the logical product as an output.