JP2558651B2 - Radar device - Google Patents

Description

Description: [Object of the Invention] (Field of Industrial Application) The present invention relates to a radar device, and more particularly to a device suitable for measuring a spatial shape of a target that performs a motion including a rotary motion.

(Prior Art) FIG. 3 shows a schematic configuration of a general radar device.

In this radar device, the highly stable oscillator 1 is a circuit that generates a stabilized signal of a predetermined frequency, and the generated signal is supplied to the transmitter 2 and the receiver 5, respectively. The transmitter 2 generates a pulse signal having a required repetition period based on the input signal, and supplies this to the antenna 4 via the transmission / reception switch 3. As a result, the same pulse signal is emitted from the antenna 4 as a transmission signal.
On the other hand, the reflected wave from the target is received by the antenna 4 and is supplied to the receiver 5 via the transmission / reception switch 3. As described above, the highly stable oscillator 1 is also included in the receiver 5.
Is supplied, and the received signal is mixed with the oscillated signal and demodulated. This demodulated signal is displayed on the display 6
Will be supplied to and displayed appropriately.

By the way, the microwave band radar is generally known to be less susceptible to weather conditions, but it has been said to be difficult to know the target shape by the microwave band loader. This is because the spatial resolution of the radar itself is coarser than the target size. Therefore, as a technique to overcome this, a synthetic aperture radar (hereinafter abbreviated as SAR) was proposed and put into practical use. As is well known, this SAR is to mount an antenna and a transmitter / receiver on a platform that moves at high speed, and collect target echo data at many places in the space associated with the movement of the antenna and the transmitter / receiver. By doing so, directivity equivalent to that of an antenna having a large aperture length is created, and the resolution of the radar device is enhanced.

However, in view of these functions of SAR, conversely, it can be inferred that even if the target object is moving, a normal fixed radar will be able to obtain the same high resolution as the above SAR. .

As an example of this, a method for obtaining high-resolution information about a rotating target will be described below with reference to FIG.

Now, assuming that the point P located at a position r away from the center of rotation on the target is two-dimensionally rotating in the manner as shown in FIG. Receives a signal with the Doppler frequency fd given by

Where λ is the wavelength of the radar transmission wave, x is the distance from the rotation center of the target to the point P on the x-axis taken in the direction perpendicular to the radar direction, and this observation is continued for time T. Then, frequency resolution can be performed for each 1 / T, so the resolution Δfd for the Doppler frequency fd is And the corresponding resolution Δx in the x-axis direction in FIG.
Is Will be expressed as

Thus, for a rotating target, high spatial resolution can be obtained by observing the target with an appropriate time width. However, the resolution obtained by the equation (3) is the resolution in the direction orthogonal to the distance direction (hereinafter, this direction is referred to as the cross range direction, and the resolution in this direction is referred to as the cross range resolution). It is assumed to be obtained by pulse compression such as modulation within a transmission pulse.

(Problems to be Solved by the Invention) As described above, with respect to a rotating target, a high spatial resolution can be obtained by observing the rotating target with an appropriate time width. Can be displayed, but as is clear from the above equation (3), a constant transmission frequency is a prerequisite for performing such an operation.

However, as a radar device, it is usually effective to change the radar transmission frequency for each pulse as a measure against interference and the like, and even if the transmission frequency is changed for each pulse in this way, the function as the radar device in question is obtained. If the desired measurement can be performed without degrading the above, it is best to use such a method.

The present invention is intended to provide a radar device capable of measuring the shape of a target without damaging the function as a radar even if the transmission frequency is changed for each pulse.

[Structure of the Invention] (Means for Solving the Problems) The present invention is directed to a high range capable of decomposing into a plurality of range cells a reflection signal of a signal applied to a target that performs at least a motion including rotary motion. In a radar device that has a resolution and outputs an image showing the physical shape of the target by performing distance tracking so that the reflected signal of the specific portion of the target remains in the same range cell, a specific portion of the reflected signal from the target Included in a specific portion of the reflection signal from the target including the predetermined complex signal, an extraction means for extracting the predetermined complex signal included in the above, a phase inversion means for inverting the sign of the phase information of the predetermined complex signal, The phase shift means and the phase shift means for shifting the phase information of the complex complex signal forming the complex signal by the amount of phase indicated by the inverted phase information. A plurality of complex signal phase-shifted Te characterized by comprising a Fourier transforming means for Fourier transform.

(Operation) As a result, even if the frequency of the signal transmitted to the target for irradiation, that is, the frequency of the signal reflected from the target corresponding to this signal irradiation changes sequentially, it can be obtained from the phase shift means.
The phase of the reflected signal for a specific portion (for example, the center of rotation) of the target is always constant. Therefore, even if the output signal from the phase shift means is Fourier transformed by the Fourier transform means, the above-mentioned high resolution is sufficiently maintained, and an image showing a target physical shape for performing a motion including at least a rotary motion can be output. .

(Example) First, the principle of the present invention will be described.

First, the reason why the above-mentioned transmission frequency cannot be changed will be considered again.

Generally, when the distance between the target rotation center that is supposed to be rotating and the radar is R, the echo of the rotation center is (4
It is known to be received by a radar with a phase of πR / λ).

Therefore, the reason why the transmission frequency cannot be changed is that when the transmission frequency is changed, the transmission wavelength λ also changes accordingly, so that the phase (4πR / λ) of the reception echo is random. It can be seen that this is due to the fact that the frequency of the received echo seems to change irregularly.

However, in a radar having a high range resolution capable of separating the target into a plurality of range cells, which is the object of the present invention, the Doppler frequency for obtaining such a high range resolution is different from the rotation center of the target and the other. It is caused by the frequency difference with each part of. Therefore, considering that the integral of these frequency differences is the instantaneous phase difference between the target rotation center and the other parts, as long as the phase difference between the target rotation center and the other parts is preserved, It can be seen that the high resolution image as described above can also be collected. That is, as long as the phase of the reflected echo with respect to the target rotation center can be made constant, the high resolution of the radar can be maintained even if the transmission frequency changes.

Below, the basic principle of the method for making the phase of the reflection echo constant with respect to the target rotation center will be shown.

First, the fact that the phase of the reflection echo with respect to the target rotation center is constant means that the Doppler frequency of the reflection echo is constant without rectification. here,
It is well known that the target echo of the reflected echo of constant Doppler frequency is expressed as Aexp (j2πfd t) where A: amplitude, fd: Doppler frequency t: time. Therefore, if the transmission is performed in pulses and the reflection echo (reception echo) from the target is obtained at intervals of T, which is the pulse period of the pulse, then xm = Aexp ( j2πfd T · m) (4) However, it can be said that the Doppler frequency is constant under the condition that the signal is received as the reception signal of the m: mth pulse. The received echo xm from this target is a formula on the assumption that the transmission frequency for each transmission pulse is the same,
The reception echo xm does not take into consideration the case where the transmission frequency of each transmission pulse changes.

By the way, a target echo, which is assumed to be at a distance R from the radar, is expressed as follows.

However, λ: radar communication wavelength Therefore, R (t) = R ₀ + vt However, considering V: the approach speed to the target radar,
The received signal has this as ym Becomes The received signal ym is an expression that takes into consideration the case where the transmission frequency differs for each transmission pulse.

Here, if the communication frequency at this time is changed, the wavelength λ of the above expression (5) changes, so that the phase of the received signal ym also changes, but the relationship of the following expression always holds. .

However, due to the conjugate complex number of ym ^* : ym, the Doppler frequency fd after frequency tracking is usually
In most cases, fd = 0 is set, and fd is set here for simplicity.
= 0, Becomes This does not impair generality.

In this equation (7), the first term is the received signal itself, and the second term is the phase correction term determined by this received signal. According to this equation (7), even if the received signal ym when the transmission frequency for each transmission pulse changes is used as it is, it can be treated equivalently to the reception echo xm on the assumption that the transmission frequency for each transmission pulse does not change. Becomes
That is, even if only the conversion of the equation (7) is performed, even if the transmission frequency is different for each transmission pulse, the phase of the Doppler frequency of each reception signal in the same cross range is the same as when the transmission frequency of the transmission pulse is the same. Therefore, the detection processing of the Doppler shift in the cross range direction can be easily performed.

As described above, if the phase of the reception signal from the target (center of rotation) is corrected or phase-shifted by the phase in which the sign of the signal phase is inverted, even if the transmission frequency changes. It can be seen that this can be made constant.

FIG. 1 shows an embodiment of a radar device according to the present invention constructed on the basis of the above-mentioned principle. However, in the apparatus of this embodiment, the portion shown in FIG. 1 is the portion arranged inside the receiver 5 of the radar apparatus shown in FIG. The illustration of other overlapping parts in FIG. 1 is omitted.

The functions and processing modes of the respective parts shown in FIG. 1 of the apparatus of this embodiment are listed below. Here, a case where the Doppler frequency fd is fixed to fd = 0 as described above will be described as an example.

Received echoes (received signals) y _{1 to} yn ( _{1 to} n) received by the receiver 5 (see FIG. 3) for a predetermined target.
Is the range cell number), first the sample circuit 51 and the delay circuit
Added in parallel to 53 and 53, respectively.

The sampling circuit 51, based on the sampling data Dsm corresponding to the range indicating the target rotation center designated by an appropriate range designating means (not shown), the sampling data Dsm of the received echoes received.
It is a circuit that samples the received echo in the range specified by. Received echo y sm sampled in this way
Are added to the phase calculation inverting circuit 52.

The phase calculation inverting circuit 52 calculates the phase of the sampled received echo y sm and inverts the sign of the calculated phase to form information corresponding to the phase correction term of the equation (7). Is. The information thus formed is added to the phase shifter 54, which will be described later, as corrected phase information (y sm ^* / A). The phase calculation / inversion circuit 52 can be configured by using a ROM (read only memory). That is, the correction phase information (y sm ^* / A) that can be obtained for the sample reception echo y sm is registered and stored in the ROM in advance in the form of a table, and the sample reception echo y
The correction phase information (y sm ^* / A) may be looked up by sm and the corresponding one of them may be read out at any time.

The delay circuit 53 receives the received echoes y ₁ to ... on the basis of the time required for the above-mentioned sampling of the sample circuit 51 and the time required for forming and outputting the above-mentioned corrected phase information (y sm ^* / A) of the phase calculation inverting circuit 52. It is a circuit that delays the transmission time of yn. This delayed received echo y ₁ -yn also has a phase shifter 54.
Is added to As a result, the phase shifter 54 includes the delay circuit
The reception echoes y _{1 to} yn delayed by 53 and the correction phase information (y sm ^* / A) formed based on a part of the reception echoes are added at the same time.

The phase shifter 54 calculates the phase of the delayed reception echoes y _{1 to} yn thus added on the basis of the equation (7), and the corrected phase information (y sm ^* / A for the sample reception echo y sm added at the same time). ) Is a circuit that changes, ie, shifts the phase by the phase indicated by. The received echoes (y ₁ · y sm ^* / A) to (yn · y sm ^* / A) thus phase-shifted are then added to the Fourier transformer 55 as received echoes after the completion of correction by the apparatus of this embodiment, Here, it is Fourier-transformed as required and is transmitted and displayed on the display 6 (see FIG. 3) as high-resolution image information indicating the shape of the rotation target.

As explained in the above principle, the output (y sm · y sm ^* / A) of the range (range corresponding to the center of rotation) of the received phase-shifted received echo is always constant in phase. (The Doppler frequency fd is fixed to fd = 0). Therefore, according to the apparatus of this embodiment, the frequency of the transmission pulse emitted from the transmitter 2 (see FIG. 3) changes from pulse to pulse. Even in this case, the target shape measurement with high resolution can be achieved as described above.

In the apparatus of the above embodiment, the target rotation center is treated as a known one, but this may be any one point as long as it is a point within the target that rotates. In short, the range cell for sampling for correction may be changed according to the selected point.

Further, in addition to the configuration of the above embodiment, a configuration as shown in FIG. 2 in consideration of the fact that the target extends over a plurality of range cells can be adopted.

That is, in the apparatus shown in FIG. 2, the target width detection circuit
56 is a circuit that receives the received echo and forms and outputs a gate TG that indicates the existing range of the target echo (or a desired portion of interest), and the data averaging circuit 57 is based on the formed and output gate TG. The received echoes y _{1 to} yn are circuits for accumulating those existing in the corresponding range and taking the average thereof, so that from the phase calculation inverting circuit 52, the corrected phase information corresponding to this average received echo y av (Y av ^*
/ A) is output and the received echo output from the phase shifter 54 as the corrected received echo is also the input received echo y ₁
~ (Yn ₁ ) corresponding to each range of (y ₁ · y av ^* / A) ~ (yn
・ Y av ^* / A) will be taken. However, in practice, it is desirable to limit the received echo to be the phase shift target so that it is included in the range of the formation gate TG by the target width detection circuit 56. By the way, this second
In the case of the device shown in the figure, the delay time of the delay circuit 53 is calculated based on the correction phase information (y av ^* /
It is set on the basis of the total time of the time required for the formation output of A) and the time required for the above-mentioned averaged reception echo by the data averaging circuit 57.

Further, in each of the above-described embodiments, the case where the Doppler frequency fd is fixed to fd = 0 has been shown for simplicity, but according to the principle described above (especially the expression (6)), the Doppler frequency fd is fixed. Obviously, the Doppler frequency can be arbitrarily selected.

By the way, in the explanation of the above principle and the explanation of the embodiment,
Although it is assumed that the target has a rotational motion, it is actually sufficient that the target has at least a rotational motion. According to the method described above, the phase change associated with the movement of the target is also corrected at the same time. However, even in this case, it is needless to say that the reflected echo of a specific portion of the same target (including an arbitrary point within the target or the entire target) remains in the same range cell by performing distance tracking.

[Effects of the Invention] As described above, according to the present invention, even if the transmission frequency is changed, it is possible to effectively measure the shape of a target performing a motion including a rotary motion.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an embodiment of a radar device according to the present invention, FIG. 2 is a block diagram showing a configuration of another embodiment of the radar device, and FIG. 3 is a schematic configuration of a general radar device. FIG. 4 is a schematic block diagram for explaining the principle of obtaining high resolution for a rotating target. 1 ... Highly stable oscillator, 2 ... Transmitter, 3 ... Transmission / reception switch, 4 ... Antenna, 5 ... Receiver, 6 ... Display, 51 ...
… Sample circuit, 52 …… Phase calculation inversion circuit, 53 …… Delay circuit, 54 …… Phase shifter, 55 …… Fourier transformer, 56 …… Target width detection circuit, 57 …… Data averaging circuit

Claims (2)

(57) [Claims] 1. A high-range resolution capable of resolving a reflection signal of a signal applied to a target performing a motion including at least a rotary motion into a plurality of range cells, and a reflection signal of a specific portion of the target is In a radar device that outputs an image showing the physical shape of the target by performing distance tracking so as to remain in the same range cell, an extraction unit that extracts a predetermined complex signal included in a specific portion of the reflected signal from the target, Phase inversion means for inverting the sign of the phase information of the predetermined complex signal, and phase information of a plurality of complex signals forming a complex signal included in a specific portion of the reflected signal from the target including the predetermined complex signal, , The phase shift means for shifting the phase by the phase amount indicated by the inverted phase information and the Fourier transform of the plurality of complex signals phase-shifted by the phase shift means. And a Fourier transforming means for transforming the radar device. 2. The predetermined complex signal included in the specific portion is an average signal obtained by averaging signals of a plurality of range cells in a part of the reflected signal from the target. The radar device according to the item 1).