JPS5828550B2 - radar - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a radar signal processing device, and particularly to an FM-CW radar signal processing device.

Unlike the commonly used pulse radar, unmodulated continuous wave (CW) radar is known as a type of special radar.

The principle of this CW radar is that when the radar transmission signal is reflected by a moving target, the received signal is subject to the Doppler effect.
By detecting this Doppler frequency component, the existence and velocity information of a moving target can be known.

Specifically, the received signal is mixed with a part of the transmitted signal and subjected to heterodyne detection or homodyne detection.6 A beat signal with a Doppler frequency component is detected, and this beat signal is amplified by an amplifier and the beat signal is detected. The fixed target signal component is removed by removing the DC component.

Therefore, the frequency characteristics of the beat signal amplifier mentioned above must be able to sufficiently remove DC components and extract signals with any expected small Doppler frequency components, so the low frequency cutoff characteristics must be quite sharp. It is normal.

The upper frequency cut-off characteristic is also chosen to pass the highest desired Doppler frequency.

However, the bandwidth of this frequency characteristic cannot be expanded indefinitely.

If the velocity component of the target you are trying to detect is unknown, you can widen the bandwidth enough to cover the expected Doppler frequency component, but widening the bandwidth increases noise and reduces sensitivity. Harmful effects will occur.

In order to solve this problem, narrowband filters are generally arranged in parallel in a comb shape to give them equivalently wide bandwidth characteristics.

This makes it possible to separate multiple targets, and the number of separable targets is equal to the number of filters mentioned above.However, the CW radar described above cannot measure the distance to a moving target, so it is necessary to have a measurement capability. For example, frequency modulation (FM) may be applied to the transmission signal to widen the frequency bandwidth of the transmission signal.

In this way, FM-
In a CW radar, if this FM is performed using, for example, a triangular wave, the relationship between the frequency of the transmitted signal and time is shown by the solid line in FIG. 1a.

If there is a fixed reflective target at a distance R, the reflected signal will return with a delay of a time proportional to R.

The dotted line in FIG. 1a represents the frequency versus time relationship of this reflected signal.

In this case, for example, the homodyne detection output (sea lion signal).

) frequency fo is not affected by Doppler frequency shift because the reflection target is a fixed target, and is based on the distance R, the FM modulation frequency fm,
FM maximum deviation is proportional to maximum f.

The relationship between frequency and time of the beat signal at this time is shown in FIG.

When the reflecting target is a moving target, the frequency versus time relationship between the transmitted signal and the received signal is as shown in Figure 1C, and the frequency of the beat signal is the beat signal frequency f in the case of the fixed target. , by a Doppler frequency fd, and the direction of the shift alternates every modulation cycle.

The relationship between frequency and time of the beat signal at this time is shown in Figure 1d.
It becomes as shown in .

Therefore, if the beat signal frequency is measured for each half cycle of FM modulation and the sum of the measured frequencies of both cycles is calculated by 1/2 to calculate the beat signal frequency fo for a fixed target, information on the distance to the target can be obtained. R can be found.

Similarly, by extracting only the Doppler frequency fd, the speed of the moving target can be determined.

By the way, according to the conventional FM-CW radar signal processing device as described above, a comb-shaped filter is required.
The disadvantage was that the configuration was complicated.

Furthermore, if there is a large unnecessary reflected signal ω) (so-called clutter) from a large fixed target such as the ground, and the moving target reflected signal is small, it is very difficult to extract only the small moving target signal from the large clutter. This method was difficult and had the disadvantage of limiting the maximum detection distance.

The present invention has been made to eliminate the above-mentioned drawbacks, and provides a radar signal processing device that has a simple configuration, has a high clutter suppression ratio, and can detect the speed of a moving target at a desired distance.

An embodiment of the present invention will be described in detail below with reference to the drawings.

In FIG. 2, a pigeon σ radar signal generator 11 generates an FM-CW radar signal that is FM-modulated using a linearly varying wave, such as a sawtooth modulated wave, supplied from a controller 12.

This radar signal is divided into two by a directional coupler 13, one of which is supplied to a circulator 14 and the other to a homodyne detector 15, for example.

Note that the detector 15 may be constituted by a heterodyne detector, which in principle belongs to the same type as homodyne detection.

The radar signal supplied to the circulator 14 is radiated from the antenna 16 toward the target.

This radiated signal is reflected by the target and received by the antenna 1.

This received signal has a frequency deviation corresponding to the distance from the antenna 16 to the target, and FM-CW if the target is a moving target.
It has a Doppler frequency shift that corresponds to its relative velocity to the radar.

Here, the relationship between the frequency and time of the transmitted radar signal is shown by a solid line in FIG. 3a, and the received signal is shown by a dotted line.

The received signal is supplied to a homodyne detector 15 through a circulator 14, where it is subjected to homodyne detection between it and the signal from the directional coupler 13.

The output signal of this detector 15 has frequency components close to a line spectrum corresponding to the target distance and Doppler frequency.

Here, the above detection output (beat signal).

) is shown in FIG. 3, and the frequency spectrum is shown in FIG. 3C.

Generally, the frequency spectrum of an FM modulated signal is
As is clear from FM modulation theory and Fourier transform theory, the frequency is given discretely for each FM modulation frequency interval with the carrier wave frequency as the center.

In the present invention, the transmitted signal is an FM modulated signal as shown in FIG. As C/b, there are only discrete components for each FM modulation frequency interval.Furthermore, the reflected signal from the target, that is, the received signal, as well as the transmitted signal, has F.
Since it is an M-modulated signal, if the target is a fixed target, its frequency spectrum will be a discrete frequency spectrum for each FM modulation frequency interval centering on the frequency of the carrier wave, similarly to the transmission signal.

On the other hand, if the target is a moving target, the received signal will undergo a frequency shift only by the Doppler frequency corresponding to the moving speed.
The frequency spectrum of the received signal becomes a discrete frequency spectrum separated by the Doppler frequency compared to the frequency spectrum in the case of a fixed target.

Therefore, the detection output of the homodyne detector 15, that is, the frequency spectrum of the beat signal obtained from the transmitted signal and the received signal, is the frequency spectrum of each discrete frequency component of the transmitted signal and each discrete frequency component of the received signal. This results in a discrete frequency spectrum with frequency components of the difference between .

Therefore, the frequency spectrum of this beat signal is
Even if the target is a fixed target, it exists only at an integer multiple of the cf1pM modulation frequency, and if the target is a moving target, it exists only at a Doppler frequency from the frequency spectrum for a fixed target, that is, a frequency value that is an integer multiple of the FM modulation frequency. exists in

In FIG. 3C, the solid line shows the frequency spectrum of the beat signal in the case of a fixed target, which is the radar repetition frequency (hereinafter abbreviated as PRF).

) (This is the FM modulation frequency, for example 5 kHz.

) has only components that are integral multiples of

The interval of this spectrum corresponds to the distance resolution, and the value of this distance resolution is the frequency band of the transmitted signal (maximum frequency deviation of FM modulation).

) is determined. For example, the distance resolution is about 15 m in a 10 MHz band.

In addition, in Figure 3C, the dotted lines indicate the frequency spectrum of the beat signal in the case of a moving target, and are spaced along the spectrum of the beat signal in the case of a fixed target with an interval of the Doppler frequency corresponding to the speed information. ing.

In this way, while the frequency spectrum of the beat signal described above becomes discrete, the amplitude (level) of each frequency component varies at a predetermined frequency corresponding to the distance to the target, as shown by the solid line in Figure 3C. By the way, it takes the maximum value, and the levels of other frequency components are small.

This is because the beat signal (detection output of the detector 15) obtained from the FM modulated transmission and reception signals shown in Fig. 3a is at a certain frequency proportional to the distance to the target.
This is because it becomes energetically concentrated.

Therefore, if the target is a fixed target, the target distance information is the same wave number spectrum that has the maximum level in the frequency spectrum of the beat signal (this is a frequency that is an integral multiple of PRF).

), and in the case of a moving target, it can be determined by detecting the same wave number that is an integral multiple of the PRF that is close to the same wave number spectrum when the maximum level value was detected.

In addition, the target speed information includes the frequency spectrum when the maximum level is detected and the nearest PR close to this.
This can be determined by detecting the same wave number deviation (that is, Doppler frequency) from the same wave number that is an integral multiple of F.

A specific example will be described below.

The homodyne detection output is amplified by an amplifier 11 and then guided to a synchronous detector 18, where it is connected to a phase synchronous oscillator 1.
Synchronous detection is performed with the distance gate signal supplied from 9.

This phase synchronized oscillator 19 is controlled based on the modulation signal supplied from the controller 12, and oscillates the distance gate signal, which is a highly stable coherent signal that is an integral multiple of the PRF.

In this case, in order to generate a gate signal corresponding to an arbitrary distance, for example, a phase-locked loop is used as the phase-locked oscillator 19, and the frequency division number of the variable divider in this loop is variably controlled. The frequency of the oscillator may be phase-synchronized to any integral multiple of the output frequency of the controller 12, which serves as a reference.

Therefore, the synchronous detector 18 outputs a distance gate signal representing the same distance information for the input signal having distance information and speed information, that is, a predetermined PRF corresponding to the distance.
The maximum detection output is obtained when the gate signal is guided over a distance that is an integer multiple of .

The relationship between the frequency and the level of this maximum detection output is shown in Figure 3d, where the fixed target reflection component, which is the zero beat frequency component, is shown as a solid line, and the moving component that is shifted by the same Doppler wave number from this zero beat frequency component is shown as a solid line. The target reflection component is indicated by a dotted line.

Therefore, as shown by the dashed line in FIG. band doppler filter 2
0 on the output side of the synchronous detector 18 (when a distance gate signal of a predetermined same wave number (integral multiple of PRF) corresponding to the ball movement target distance is supplied to the synchronous detector 18, during the synchronous detection output, Only the same wave number component, that is, the Doppler frequency component with the maximum level can be extracted, and the fixed target reflection component can be completely suppressed.

The output of this narrow band Doppler filter 20 is transmitted to the maximum value detector 2.
1, the maximum value of the filter output level is detected,
The distance of the moving target can be determined from the frequency of the distance gate signal (an integral multiple of PRF) when the maximum value is detected.

At the same time, the filter output is guided to the same wave number measuring device 22, and the same wave number of this filter output signal (this is the frequency of the difference between the solid line and the dotted line in FIG. 3d, ie, the Doppler frequency).

) is measured, and the speed of the moving target can be determined from this frequency.

The maximum value detector 21 is composed of, for example, a peak hold circuit with the same effect, and the output level of the narrowband filter 20 changes every time the distance gate signal frequency, that is, the output frequency of the phase synchronized oscillator 19 changes. This circuit is designed to detect the maximum level value.

Further, the wave number measuring device 22 can be configured by, for example, a simple counter.

As described above, in a device that receives and processes a target reflected signal of an FM-CW radar signal subjected to linear FM modulation, the received signal is subjected to homodyne detection or heterodyne detection, and this detection output is used as the modulated wave for FM modulation. Synchronous detection is performed with a range gate signal that is phase synchronized and has a frequency that is an integral multiple of the FM modulation frequency, and the output of this synchronized detection is extracted by a narrow band Doppler filter.

Therefore, since the comb-shaped filter required in the conventional device is not used, the configuration is simplified, and since only the moving target signal is extracted from the synchronous detection output by the narrow band Doppler filter, the clutter suppression ratio is high.

Moreover, the narrowband Doppler filter narrows the receiver bandwidth and increases the detection distance.

Furthermore, by setting the frequency of the distance gate signal to a predetermined frequency, a moving target at a desired distance can be detected.

As described above, the present invention can provide a radar signal processing device that has a simple configuration, has a high clutter suppression ratio, and can instantly detect the speed of a moving target at a desired distance.

[Brief explanation of drawings]

1A to 1D are timing diagrams shown to explain signals related to a conventional FM-CW radar, FIG. 2 is a block diagram showing an embodiment of a radar signal processing device according to the present invention, and FIG. 3A 2 to d are timing diagrams shown to explain the operation of FIG. 2. 11... FM-CW radar signal generator, 12... Controller, 13... Directional coupler, 14... Circulator, 15... Homodyne detector, 18... Synchronous detector, 19... Phase synchronized oscillator, 20... Narrow band Doppler filter, 21... Maximum value detector, 22... Frequency measuring device.

Claims (1)

[Claims] 1. A controller that outputs a modulated signal, a signal generator that is supplied with the modulated signal from this controller and generates a frequency-modulated FM-CW radar signal, and branching means that branches the output signal of this signal generator. , one of the signals branched by this branching means is supplied via a circulator to FM'-
An antenna that emits a CW radar transmission wave and receives a reflected wave from a target, a received signal from this antenna is supplied via the circulator, and the other signal branched by the branching means is supplied, and homodyne detection or a first detection means for performing heterodyne detection; and a phase synchronized oscillator that introduces a modulation signal from the controller, is controlled with the modulation signal as a reference, and generates a distance gate signal having a frequency corresponding to an arbitrary integral multiple of the modulation frequency. , a second detection means to which the distance gate signal from the phase synchronized oscillator and the output signal of the first detection means are supplied and performs synchronous detection; and an output of the second detection means having a band narrower than the modulation frequency. a narrowband Doppler filter that extracts only Doppler frequency components from a signal; a maximum value detector that is supplied with the output signal of the narrowband Doppler filter and detects a maximum level filter output signal; and a maximum value detector that detects the maximum level filter output signal; and a frequency measuring device that measures the supplied filter output signal frequency, detecting the distance of the target from the frequency of the distance gate signal at the time of detecting the maximum level, and detecting the speed of the target from the measurement frequency of the frequency measuring device. A radar signal processing device characterized by: