JP3335778B2 - Radar equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radar device for detecting a moving target.

[0002]

2. Description of the Related Art As is well known, a radar apparatus for detecting a moving target basically utilizes the property that "reflected radio waves from a moving target are subject to a Doppler frequency shift", and the transmission frequency is kept constant. By repeatedly transmitting a single pulse while holding it, and performing phase detection on the received signal with a reference signal having the same phase as the transmitted signal, the Doppler frequency shift component due to reflection from a moving target such as a moving aircraft or vehicle ( (A target signal).

At this time, an unnecessary reflection signal from a fixed target called clutter (clutter on the ground or the sea surface which becomes unnecessary reflection, a building, clutter due to rain and snow, etc.) is mixed.
Processing called MTI (Mouving Target Indicator) is performed. In this MTI processing, a received signal is delayed by a delay circuit for a pulse repetition period, and a difference from a signal of the next period is taken, thereby canceling reflected signal components from a fixed target having the same phase with each other. By this processing, it is possible to detect only the signal component from the moving target that has undergone the Doppler frequency shift.

[0004] By adopting such a moving target detection method, unnecessary reflected signal components due to clutter are eliminated.
Although it is possible to detect only the moving target, as described above, since it is necessary to repeatedly transmit a single pulse while maintaining the transmission frequency constant, on the contrary, the target side, Alternatively, from the point of view of the radar apparatus that makes it difficult to collect a target echo, the transmission frequency of the radar can be easily measured, and it is easy to obstruct such radar processing by the radar apparatus.

As described above, although the radar apparatus employing the conventional moving target detection method can obtain the ability to detect only a desired moving target in an environment where there are many unnecessary reflection signals, it is possible to prevent the radar apparatus from interfering. I can't deny the weak side. If the frequency is changed for each pulse to avoid interference, there is an essential contradiction that the MTI does not hold.

[0006]

As described above, the radar apparatus adopting the conventional moving target detection method has a problem that it is susceptible to interference. SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems, and has as its object to provide a radar apparatus which does not easily receive interference while maintaining a moving target detection ability.

[0007]

[0008]

[MEANS FOR SOLVING THE PROBLEMS] To achieve the above object
According to the present invention, in a radar apparatus that performs target detection by repeatedly transmitting a pulse signal and receiving a reflected signal thereof, the frequencies are different from each other within a repetition cycle of the pulse signal, but one of them is one cycle before. A sub-pulse transmitting unit that generates and transmits a plurality of sub-pulses having the same frequency as any one of the sub-pulses, receives a reflected signal corresponding to each of the sub-pulses, and receives a received signal corresponding to a sub-pulse of the same frequency one cycle earlier and the same one cycle later. A receiving means for extracting a received signal corresponding to a sub-pulse of a frequency, and a receiving signal corresponding to a sub-pulse of the same frequency after one cycle taken out by this means is stored and corresponding to a stored sub-pulse of the same frequency one cycle earlier. Signal processing means for detecting a moving target by performing signal processing between received signals to be processed.

[0009]

[0010]

In the radar device having the above-described structure , a plurality of sub-pulses having different frequencies but one of which has the same frequency as one before one period are generated and transmitted within the repetition period of the pulse signal, and each sub-pulse is generated. Receiving the corresponding reflected signal, extracting the received signal corresponding to the sub-pulse of the same frequency one cycle earlier and the received signal corresponding to the sub-pulse of the same frequency one cycle later, and corresponding to the sub-pulse of the same frequency one cycle later The received signal is stored, and the moving target detection is performed by performing signal processing between the received signals corresponding to the sub-pulses of the same frequency one cycle before being stored, thereby maintaining the moving target detection capability.
The transmission frequency can be changed so as not to be easily disturbed.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below in detail with reference to the drawings. FIG. 1 shows a configuration of a radar apparatus according to the present invention. A timing generator 1 repeatedly generates a transmission trigger having a predetermined width at a predetermined cycle. Every time the frequency controller 2 receives a transmission trigger from the timing generator 1, it generates a control signal for changing the frequency of the transmission pulse in a fixed order or randomly.

The high-frequency oscillator 3 oscillates and outputs a high-stable high-frequency signal, and changes the oscillation frequency according to a control signal from the frequency controller 2. The reference signal generator 4 generates a reference signal for maintaining coherency of the same pulse. The high-frequency signal output from the high-frequency oscillator 3 is mixed with the reference signal from the reference signal generator 4 by the mixer 5 and supplied to the transmitter 6.

The transmitter 6 pulsates the input high-frequency signal every time a transmission trigger from the timing generator 1 is input, and amplifies the pulse to generate a transmission pulse signal. The transmission pulse signal is a circulator or the like. The antenna is radiated in a predetermined direction from the antenna 8 via the transmission / reception switch 7.
The antenna 8 is used for both transmission and reception, and captures a signal reflected by a radiated transmission pulse signal hitting a target. The captured signal is input to the receiver 9 via the transmission / reception switch 7.

The receiver 9 mixes the input signal with a high-frequency signal generated by the high-frequency oscillator 3 to convert the signal into an intermediate frequency signal, and then converts the intermediate frequency signal into a reference signal generated by the reference signal generator 4. A coherent video signal is generated by performing phase detection using the signal.

The coherent video signal generated by the receiver 9 is input to a signal processor 10. This signal processor 1
0 stores a video signal from the receiver 9 in the memory every time a transmission trigger from the timing generator 1 is input, and then inputs a coherent video signal of the same frequency as the signal from the transmission frequency information from the frequency controller 2 The Doppler frequency shift, that is, the moving target is detected by reading the video signal stored in the memory during the period, and obtaining the difference signal from the input video signal. Convert to a video signal suitable for display. After the detection of the moving target, the previous video signal stored in the memory is rewritten with a new video signal.

The indicator 11 is for displaying a video signal from the signal processor 10 on a screen. That is, in the radar device having the above configuration, the frequency of the transmission pulse signal is changed for each pulse in a fixed order or randomly. FIG. 2 shows an example of the transmission method.

In FIG. 2, (a) shows a transmission trigger,
(B) shows a transmission pulse signal. The number above the trigger signal indicates the number of the transmission pulse, and m and n are each m
And n-th transmission pulses. The figure shows that the first and mth pulses are transmitted at a frequency f1, and the second and nth pulses are transmitted at a frequency f2 different from f1. Each pulse is mixed with a reference signal for maintaining the same pulse coherency.

The pulse signal thus generated is transmitted to the antenna 8
When it radiates more into space and captures its reflected wave, the receiver 9
In the above, a coherent video signal is obtained by mixing an input signal with a high-frequency signal generated by the high-frequency oscillator 3 and converting the mixed signal into an intermediate frequency signal.

The signal processor 10 stores a video signal in a memory every time a transmission trigger is input, and then stores the video signal in the memory during a period when a video signal having the same frequency as the signal is input. To obtain a difference signal from the input video signal. Thereby, the clutter component is removed, and the Doppler frequency shift component, that is, the moving target can be detected.

Referring to the example of FIG. 2, a coherent video signal based on the first pulse is stored in a memory,
When a coherent video signal based on the m-th pulse is obtained, a subtraction process of both signals is performed for the first time to obtain a difference signal, whereby a Doppler frequency shift component can be detected. By performing the same processing between the second pulse and the n-th pulse, the Doppler frequency shift component can be detected.

Here, during the period from the transmission of the first pulse to the transmission of the m-th pulse of the same frequency, the desired maximum detection distance is Rmax, and the propagation speed of the radio wave =
Assuming that 3.0 × 10 ⁸ m / s is c, it is necessary not to fall below 2Rmax / c.

Therefore, the radar apparatus having the above configuration can detect a moving target while changing the frequency for each pulse, and can be less susceptible to interference. In the above embodiment, the case where the frequency of the transmission pulse signal is changed in the transmission repetition period has been described. However, the frequency of each sub-pulse is sequentially changed using a sub-pulse method in which a plurality of sub-pulses are transmitted within the transmission repetition period. Can further reduce the possibility of interference.

FIG. 3 shows another embodiment according to the present invention.
This shows a configuration when the above-described sub-pulse method is adopted. First, in the transmission system, the timing generator 21
Generates a plurality of sub-pulse transmission triggers at predetermined intervals within a predetermined transmission repetition period. Frequency controller 22
Generates a control signal for changing the frequency of a reference signal of a reference signal generator 24, which will be described later, in a fixed order or randomly each time a transmission trigger is received from the timing generator 21.
However, control is performed so that the frequency is always changed to the same frequency as one frequency one cycle before in the transmission repetition cycle. The number of sub-pulses depends on the transmission pulse width and the duty ratio.
The optimum value is determined for each radar system.

The high-frequency oscillator 23 oscillates and outputs a highly stable high-frequency signal. The reference signal generator 24 generates a reference signal for maintaining coherency of the same pulse, and changes the frequency according to a control signal from the frequency controller 22. The high-frequency signal output from the high-frequency oscillator 23 is mixed with a reference signal from a reference signal generator 24 by a mixer 25 and supplied to a transmitter 26.

The transmitter 26 pulsates the input high-frequency signal every time a transmission trigger from the timing generator 21 is input, and amplifies the power to generate a transmission pulse signal composed of a plurality of sub-pulses having different frequencies. so,
The transmission pulse signal is radiated in a predetermined direction from an antenna 28 via a transmission / reception switch 27 such as a circulator.
The antenna 28 is used for both transmission and reception, and captures the signal reflected by the emitted transmission pulse signal hitting the target. The captured signal is input to the receiver 29 via the transmission / reception switch 27.

The receiver 29 mixes the input signal with a high-frequency signal generated by the high-frequency oscillator 23 to convert the signal into an intermediate frequency signal, and then converts the intermediate frequency signal into a reference signal generated by the reference signal generator 24. Among the signals, phase detection is performed using a reference signal that matches one of the frequencies one cycle before, thereby generating a coherent video signal.

The coherent video signal generated by the receiver 29 is input to a signal processor 30. The signal processor 30 stores the video signal from the receiver 9 in the memory every time a transmission trigger of the transmission repetition period is input from the timing generator 21, and stores the video signal from the transmission frequency information from the frequency controller 2. A period during which a coherent video signal of the same frequency is input is determined.

Then, the video signal stored in the memory during the determined period is read out to obtain a difference signal from the input video signal, thereby detecting the Doppler frequency shift, that is, the moving target, and detecting the detected moving target signal. Convert to a video signal suitable for display. After the detection of the moving target, the previous video signal stored in the memory is rewritten with a new video signal.

The indicator 11 is for displaying a video signal from the signal processor 10 on a screen. FIG. 4 shows an example of the transmission method of the above embodiment. Here, for simplicity of description, a case where there are three sub-pulses will be described.

First, three sub-pulses P1, P2, P
3, in the first transmission repetition period, P1 transmits at frequency f1, P2 transmits at frequency f2, and P3 transmits at frequency f3. f1, f2, and f3 are generated by controlling the generation frequency of the reference signal generator 24 by the frequency controller 22 and mixing the reference signals of the respective frequencies with the high-stable high-frequency signal generated by the high-frequency oscillator 23. It was done. Further, P1, P2, and P3 are sequentially transmitted in a time division manner. Naturally, a reference signal mixed with f1, f2, and f3 is also generated in a time division manner under the control of the frequency controller 22.

In the second transmission repetition period, P1 is transmitted at frequency f4, P2 is transmitted at frequency f5, and P3 is transmitted at frequency f3. That is, P1 and P2 have their transmission frequencies changed independently, but only P3 is held at the same frequency as P3 one cycle before.

In the third transmission repetition period, P1 is transmitted at frequency f4, P2 is transmitted at frequency f6, and P3 is transmitted at frequency f7. That is, P2 and P3 have their transmission frequencies changed independently, but only P1 is held at the same frequency as P1 one cycle before.

As described above, only one of the sub-pulses is frequency-conserved only for the continuous transmission repetition period, and the other sub-pulses are changed to another frequency, so that the target side of the radar apparatus interferes. The power frequency cannot be easily determined. Further, by appropriately selecting the magnitude of the frequency change, it is possible to virtually eliminate the blind speed which is a problem in the detection of the moving target while keeping the transmission repetition period constant.

The received signal by the above three sub-pulses is
The following processing is performed in the receiver 30. First, after being amplified by the low noise amplifier, the frequency is converted by a high frequency signal from the high frequency oscillator 23 to become an intermediate frequency signal. This signal is split into two systems by a power splitter,
In one system, a signal having the same frequency as the frequency stored immediately before is extracted, and in the other system, a signal having a frequency to be stored next is extracted.

In the former process, a reference signal of a frequency stored in the transmission repetition cycle is input from the reference signal generator 24, and a frequency not stored from the received signal is output by a band-pass filter that passes only the frequency domain. Signal is removed. Here, the filter has a frequency bandwidth that can sufficiently cover the expected Doppler frequency shift amount in addition to the conserved frequency. Therefore, the transmission frequencies of the sub-pulses are set so that the pass bandwidths do not overlap each other. The extracted signal of the storage frequency is phase-detected by the reference signal of the reference frequency of the reference signal generator 24, and becomes a coherent video signal.

The latter processing is exactly the same, except that the extracted signal is a signal having a frequency to be stored next. The moving target detection process is performed on the coherent video signal obtained by the former process and the coherent video signal immediately before being delayed by one cycle in the signal processor 30. The coherent video signal obtained by the latter processing is retained by being delayed by one cycle to become a comparison signal in the next repetition cycle. The frequency selected in the latter processing is determined by the frequency controller 22, and the frequency changes in principle at random.

Therefore, the radar apparatus having the above configuration transmits a plurality of sub-pulses each having a frequency independently changed, and performs signal processing on the received signal of the same frequency sub-pulse before and after the transmission repetition period to detect a moving target. This makes it difficult for the target side to easily determine the frequency at which interference is to be applied. Thus, it is possible to maintain the moving target detection capability and not to be easily disturbed.

The present invention is not limited to the above embodiment. For example, when the moving target detection processing is not performed, normal radar processing is performed using all the pulses regardless of the transmission frequency. Can also. In addition, various modifications can be made without departing from the scope of the present invention.

[0039]

As described in detail above, according to the present invention,
It is possible to provide a radar device that does not easily receive interference while maintaining the moving target detection capability.

[Brief description of the drawings]

FIG. 1 is a block circuit diagram showing a configuration of an embodiment of a radar apparatus according to the present invention.

FIG. 2 is a timing chart illustrating an example of a transmission method according to the embodiment of FIG. 1;

FIG. 3 is a block circuit diagram showing a configuration of another embodiment of the radar apparatus according to the present invention.

FIG. 4 is a timing chart showing an example of a transmission method according to the embodiment of FIG. 2;

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Timing generator, 2 ... Frequency controller, 3 ... High frequency oscillator, 4 ... Reference signal generator, 5 ... Mixer, 6 ... Transmitter, 7 ... Transmission / reception switch, 8 ... Antenna, 9 ... Receiver, 10 …
Signal processor, 11 ... indicator, 21 ... timing generator,
Reference numeral 22: frequency controller, 23: high-frequency oscillator, 24: reference signal generator, 25: mixer, 26: transmitter, 27: transmission / reception switch, 28: antenna, 29: receiver, 30: signal processor, 31 ... indicator.

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-2-162285 (JP, A) JP-A-61-167891 (JP, A) JP-A-2-216489 (JP, A) JP-A-5-216489 126943 (JP, A) JP-A-2-11669 (JP, A) JP-A-3-81581 (JP, U) JP-A-5-4063 (JP, U) (58) Fields investigated (Int. Cl. G01S ^7/ 00-7/42 G01S 13/00-13/95

Claims (1)

(57) [Claims] 1. A method for transmitting a pulse signal repeatedly to obtain a reflected signal
The radar device that detects the target by receiving the
And the frequencies are different from each other within the repetition period of the pulse signal.
One has the same frequency as the previous one
Transmitting means for generating and transmitting two or more sub-pulses
And receiving the reflected signals corresponding to each of the sub-pulses.
Corresponding to the sub-pulse of the same frequency one cycle before
Corresponds to signal and sub-pulse of same frequency after one period
Receiving means for extracting a received signal; and a sub-path having the same frequency after one cycle extracted by the means.
Save the received signal corresponding to the
Between received signals corresponding to sub-pulses of the same frequency before
Signal processing means for detecting a moving target by performing signal processing;
A radar device comprising: