JPH04357485A - Pulse doppler radar apparatus - Google Patents

Abstract

PURPOSE:To obtain a pulse compression means that is not affected by a Doppler shift even when a target has a relative speed in a pulse Doppler radar apparatus. CONSTITUTION:A transmitted pulse outputted by a transmitting means 1 is radiated to a target from an antenna 3 via a transmission/reception switch 4. A signal reflected on the target is inputted into a pulse compression means 5 containing a pulse Doppler processing means 6 passing through the antenna 3, the transmission/reception switch 4 and a receiving means 2. The signal inputted into the pulse compression means 5 undergoes a Fourier transform with N-point FFT arithmetic device 52 and M-point FFT arithmetic device 62 separately and then, is subjected to a complex multiplication with a reference signal corrected in Doppler effect generated by a reference signal generation means 10 with a complex multiplier 51. Thereafter, a reverse Fourier transform is performed with an N point IFFT arithmetic device 53 to produce a narrow pulse width signal.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pulse Doppler radar system for observing high-speed moving targets.

0002

2. Description of the Related Art Conventional pulse Doppler radar devices of this type are known, for example, from G.I. V. Morris: “
Airborne Pulsed Doppler
Radar”, Artech House, In
c. (1988), Donald R. Wehner: “High
Resolution Radar”, Artech
House, Inc. (1987), and Bern
ard L. Lewis et al.: “Aspect of
Radar Signal Processing
”, Artech House, Inc. (1986
) has been disclosed. FIG. 8 is a block diagram showing the configuration of a conventional chirp type pulse Doppler radar device, and FIG. 9 is a block diagram showing the configuration of a conventional code modulation type pulse Doppler radar device. 8 and 9, 1 is a transmitting means, 2 is a receiving means, 3 is an antenna, 4 is a transmitting/receiving switch, 5 is a pulse compression means, 6 is a pulse Doppler processing means, 7
8 is an amplitude detector, 8 is a display, and 10 is a reference signal generating means.

Next, an outline of the operation will be explained. 8, the transmission pulse generator 11 of the transmission means 1 generates a transmission pulse with a pulse width τ, and the pulse stretcher 12 generates the transmission pulse as shown in FIG.
As shown in 0(a), the pulse width T (T>>τ),
A chirp (linear FM modulation) pulse with a frequency bandwidth Δf (=1/τ) is generated. On the other hand, in FIG. 9, a transmission pulse with a pulse width τ is generated from the transmission pulse generator 11 of the transmission means 1, and in the example of encoded phase modulation using a 7-bit Barker code, the delay shown in FIG. Element 1
5 and an encoded phase modulator 14 with an adder 16,
An encoded phase modulation pulse with a pulse width T shown in FIG. 11(b) is generated. In both the chirp method and the code modulation method shown in FIGS. 8 and 9, the modulated transmission pulse is radiated to the target as a transmission radio wave via the transmitter/receiver switch 4 and the antenna 3, and the radio wave reflected from the target is transmitted to the antenna 3. The received signal passes through the transmitter/receiver switch 4 and is converted into a digital complex video signal by the receiving means 2.

In the receiving means 2 described above, as shown in FIG. 12, the received signal is multiplied by the output of the local oscillator 22 in the mixer 21 and converted into an intermediate frequency signal. The output of the mixer 21 is amplified by an IF (intermediate frequency) amplifier 23 and then divided into two parts, each of which is input to a phase detector 24. In the phase detector 24, the product with the output signal of the coherent oscillator 25 and the product with the signal obtained by delaying the phase of the output signal of the coherent oscillator 25 by 90 degrees in the 90 degrees phase shifter 26 are calculated, and the respective phases are detected. . The outputs of the respective phase detectors are held by the sample holder 27 as the real part (I) and imaginary part (Q) of the received complex video signal, and then the A/
A D converter 28 converts the signal into a digital complex video signal.

The output data of the receiving means 2 is two-dimensional range-pulse hit data. Here, the range is a unit of relative distance from the transceiver and represents half the distance that light travels during one sampling time, and the pulse hit is a unit of the number of transmitted pulses. Consider this range direction data for several pulse hits. Here, the number of data points in the range direction (total number of range bins) is N, and the number of data points in the pulse hit direction (
This is the number of Fourier transform points, and M is the total number of Doppler bins after Fourier transform. The output of the receiving means 2 is input to the pulse compressing means 5.

Pulse compression is a technology that converts a wide pulse width signal modulated during transmission into a narrow pulse width signal through correlation processing in the range direction during reception. tj and the received pulse signal is a function x (t-tj) of time t, then this and the reference signal x* (-t) (*: complex conjugate) are complex multiplied in the frequency domain to obtain the phase component of the spectrum. By making the signal constant over all frequencies and returning it to the time domain, the signal energy is concentrated in one place and converted into a narrow pulse width signal. (Figure 1 shows the compressed pulse waveform of the chirp method.
0(c). )

The output of the pulse compression means 5 is input to a pulse Doppler processing means 6 . Pulse Doppler processing decomposes the received signal into Doppler frequency components, which are the velocity components of the target, in order to detect the relative velocity of the target.The received signal in the time domain is Fourier transformed in the direction of the pulse hit, and then converted into the frequency domain. This is the process of converting it into a signal.

Next, the operations of the pulse compression means 5 and the pulse Doppler processing means 6 will be explained with reference to FIGS. 8, 9, and 13. First, the reference signal generated by the reference signal generating means 10 of FIGS. 8 and 9 and stored in the reference memory 50 of the pulse compressing means 5 in advance will be explained. This reference signal generating means 10 is
Reference signal generator 101 and N-point FFT calculator 10
The reference signal that has passed through the N-point FFT calculator 104 is input to the reference memory 50. Then, as long as the signal processing mode changes and the reference signal creation parameters (number of range bins N, transmission pulse width T, carrier frequency f0, sampling time ts) do not change, the same reference signal will be used.
Once the reference signal generating means 10 inputs the reference signal to the reference memory 50, it is disconnected. however,
When the signal processing mode is changed, the reference signal generating means 10 is connected again and the reference signal is inputted into the reference memory 50 again. The reference signal generator 101 generates a transmission pulse generated by the transmitting means 1 (in the case of the chirp method and the code modulation method, FIG. 10(a) and FIG. 11(), respectively).
b) is sampled at a sampling time TS and the signal is expressed as TR(r), a reference signal R(r) expressed by the following equation is generated. (In the case of chirp method and code modulation method, Fig. 10(b) and Fig. 11(
(shown in c)). Here, r represents the range bin, and the time is divided by the sampling time ts (r=
t/ts).

[0009]

[Math 1]

Next, in order to convert this R(r) into frequency domain data, it is Fourier transformed in the range direction by the N-point FFT calculator 104 to obtain the spectrum RR (fr) of the reference signal, which can be expressed by the following equation. It will be done. RR (fr)=FR [R(r)],

(2) (FR; Fourier transform in range direction, fr: frequency) Spectrum RR of the above reference signal (f
r) is generated by the reference signal generating means 10 and stored in the reference memory 50. Once stored, the reference signal generating means 10 is separated from the reference memory 50. Spectrum RR (f
The method for generating r) is the same for both the chirp method and the code modulation method.

Next, the flow of signal processing by the pulse compression means and pulse Doppler processing means will be explained with reference to FIG. In step 1, the output data S(r) of the receiving means 2 temporarily stored in the buffer memory 54 is Fourier transformed in the range direction by the N-point FFT calculator 52 in order to perform frequency analysis. The output of the N-point FFT calculator is converted to frequency domain data, and appears as a response for each frequency obtained by dividing the sampling frequency (1/ts) by N on the frequency axis, which can be expressed by the following equation. SR (fr)=FR [S(r)],

(3) (FR: Fourier transform in range direction, fr: frequency)

In step 2, the N-point FFT calculator 5
The output data SR (fr) of No. 2 is based on the spectrum RR (f
r) in a complex multiplier 51, and its output is temporarily stored in a buffer memory 55. The above complex multiplier 51
The output of can be expressed by the following equation. UR (fr)=SR (fr)×RR (fr)
(4)

In step 3, the output data UR (fr
) is subjected to inverse Fourier transform by the N-point IFFT calculator 53, and the signal energy returned to the time domain is concentrated at one location, resulting in a narrow pulse signal. The output of the N-point IFFT calculator 53 can be expressed by the following equation. U(r)=Ffr−1[UR(fr)],
(5
) (Ffr-1; inverse Fourier transform in frequency direction)

00
14] In step 4, step 1 to step 3 above
The process is repeated for the pulse hit p, and the N point IF
The output data U(r) of the FT calculator 53 is two-dimensional data U
It is stored in the two-dimensional memory 61 as (r,p). Then, data U(r,p) is read out from the two-dimensional memory 61 in the pulse hit direction, subjected to M-point Fourier transform in the pulse hit direction by the M-point FFT calculator 62, and subjected to pulse Doppler processing. Through this processing, each range bin is decomposed into Doppler frequency components, and the signal power is integrated into the Doppler bin corresponding to the relative velocity of the target, thereby making it possible to detect the relative velocity of the target. The output of the above M-point FFT calculator 62 can be expressed by the following equation. UP (r, fd)=Fp [U(r, p)],
(6) (Fp: Fourier transform in the pulse hit direction, fd: Doppler frequency) This Fourier transform in the pulse hit direction is repeated for the range bin r.

The output of the M-point FFT calculator 62 is subjected to envelope detection processing by the amplitude detector 7, and the target is displayed on the display 8 by displaying the range bin versus Doppler frequency.

[0016]

[Problems to be Solved by the Invention] A conventional pulse Doppler radar device of this type is constructed as described above, and a moving target within a certain range bin has a relative velocity V that produces a Doppler frequency fd. At the time, there were the following issues in pulse compression processing. In the case of the chirp method, the time versus frequency characteristics of the received pulse reflected by the moving target with the above relative velocity V (shown by the dotted line in Figure 14)
is shifted by the frequency fd with respect to the time versus frequency characteristic (shown by the solid line in FIG. 14) of the received pulse reflected by a target with a relative velocity of zero. Since the delay time vs. frequency characteristic of the pulse compression means of a conventional pulse Doppler radar device corresponds to the case where the relative velocity of the target is zero, the compression portion of the received pulse reflected by the moving target is shortened, and as shown in Fig. In the example of No. 14, the frequency f1 of the characteristic indicated by the dotted line
The pulse is compressed only in the region between and f2, resulting in a loss equal to the output of the pulse compression means x (Δtd/T). Further, in the pulse compression means, Δtd=(T/Δf
)fd delay, which corresponds to a reduction in the display range by (Δtd/τ) range bins.

In the case of the code modulation method, the Doppler frequency f
The frequency shift of d causes a phase rotation of the received pulse, causing the phase characteristics of the pulse before pulse compression and the reference signal to no longer match, resulting in an increase in range side lobes, a decrease in compression ratio, and misalignment or separation of the compressed pulse. Deterioration of pulse compression performance has been accompanied by distance measurement errors or inability to measure distances of high-speed moving targets. For example, if a Barker code is used for the code series, due to Doppler shift,
If a phase rotation of 2π occurs in the pulse of pulse width T before compression, the phase will not match with the reference signal at all. FIG. 15 shows an example of a pulse compression waveform when a 13-bit Barker code is used. In the figure, sample points represent range bins, and sample point 13 indicates the range bin where the target is located. The output is the value after pulse compression. When a phase rotation of 2π occurs in the pulse of pulse width T before compression, 2πf
d・T=2π[rad]
(7) becomes. Therefore, the relative speed V of the moving target, which is found by substituting fd=2V/λ, (λ: radar transmission wavelength) into the above equation, is V=
When λ/2T is reached, the output of the sample point 13 where the target is located becomes zero and becomes incompressible.

The present invention has been made to solve the above-mentioned problems, and uses pulse compression means that can achieve pulse compression without being affected by Doppler shift even if a high-speed moving target has a relative velocity V. An object of the present invention is to provide a pulse Doppler radar device with improved distance measurement performance for high-speed moving targets.

[0019]

[Means for Solving the Problems] In order to achieve the above object, the pulse Doppler radar device of the present invention includes a transmitter that generates and modulates a transmit pulse to widen the frequency band, and a target transmitter output. An antenna that emits toward the target and receives reflected signals from the target, a transmitter/receiver switch that switches the transmitter/receiver circuit, a receiver that processes the received signal to obtain a complex signal, and pulse Doppler processing that detects the relative velocity of the target. a pulse compression means that performs correlation processing on the modulated wide pulse width signal and converts it into a narrow pulse width signal using a reference signal corrected for the Doppler effect; and an envelope detection method for the output of the pulse compression means. It is equipped with an amplitude detector to detect the detected target, and a display to display the detected target.

[0020] Also, a transmitting means for generating and modulating a transmitting pulse to widen the frequency band, an antenna for radiating the output of the transmitting means toward a target and receiving a reflected signal from the target, and a transmitting/receiving switch for switching the transmitting/receiving circuit. Correlation processing is performed on the modulated wide pulse width received signal using a receiving means that processes the received signal to obtain a complex signal, and a reference signal that has corrected both the phase fluctuation due to the Doppler effect and the movement of the target range bin. and a pulse compression means for converting it into a narrow pulse width signal, an integration means for integrating the pulse compression signal during the observation time for each range bin and each Doppler bin, an amplitude detector for envelope detection of the output of the integration means, and a detected target. It is equipped with a display that displays the following information.

[0021]

[Operation] In a pulse Doppler radar device that uses a reference signal corrected for the Doppler effect, the pulse compression means performs pulse Doppler processing to detect the relative velocity of the target, and eliminates frequency shift (or phase shift) due to the Doppler effect. Using the corrected reference signal,
The modulated wide pulse width signal is correlated and converted into a narrow pulse width signal. In the case of the chirp method, even if the moving target has a relative velocity V that produces a Doppler frequency fd, the pulse compression means adjusts the Doppler frequency fd according to the relative velocity of the moving target from a conventional reference signal in which the relative velocity of the moving target is set to zero. Pulse compression over the entire frequency band of the received signal is performed using a reference signal with time versus frequency characteristics shifted by . In the case of the code modulation method, even if the moving target has a relative velocity V that produces a Doppler frequency fd, the pulse compression means generates a phase code with a phase shift of 2πfd·T over the pulse width T, depending on the relative velocity of the moving target. By using the modulated pulse as a reference signal, pulse compression is performed without being affected by phase errors due to Doppler frequency.

[0022] Furthermore, in a pulse Doppler radar system that uses a reference signal that corrects phase fluctuations due to the Doppler effect and target range bin movement from the start of observation,
The pulse compression means uses the reference signal to compress the signal to the range bin where the target is located at the start of observation, performs correlation processing on the modulated wide pulse width signal, and converts it into a narrow pulse width signal. Further, the integrating means performs an integral process on the signal compressed by the pulse compressing means for each range bin and each Doppler bin.

[0023]

【Example】

Example 1. Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a configuration block diagram showing an embodiment of the chirp method according to the present invention. FIG. 2 is a block diagram showing an embodiment of the code modulation method of the present invention. In the figure,
1 is a transmitting means that generates and modulates a transmission pulse to widen the frequency band; 2 is a receiving means; 3 is an antenna; 4 is a transmitting/receiving switch; 5 is a pulse compression means including a pulse Doppler processing means 6; 7 is an amplitude detector, 8 is a display, and 10 is a reference signal generating means. Since the above transmitting means 1, receiving means 2, antenna 3, transmitting/receiving switch 4, amplitude detector 7, and display 8, which have the same configuration as the conventional example, have already been explained, their explanation will be omitted here. The pulse compression means 5 including the pulse Doppler processing means 6 described above has the following configuration as shown in FIGS. 1 and 2. An N-point FFT calculator 52 performs N-point Fourier transform on the data in the buffer memory 54 that stores the output of the receiving means in the range direction and stores it in the two-dimensional memory 61, and an M-point Fourier transform on the two-dimensional memory data in the pulse hit direction. A pulse Doppler processing means 6 stores the output of the reference signal generating means 10 which generates a reference signal corresponding to the target relative velocity, and a reference memory 50 stores the output of the reference signal generating means 10 which generates a reference signal corresponding to the target relative velocity. A complex multiplier 5 that performs complex multiplication by the two-dimensional memory data output from the means and the reference memory data of the reference signal corresponding to the relative speed of the target.
1, and an N-point IFFT calculator 53 that stores the above complex multiplication result in a buffer memory 55 and performs inverse Fourier transform on the data in the range direction.

In the conventional example shown in FIGS. 8 and 9, a reference signal corresponding to a single Doppler frequency (Doppler frequency OHZ) is used for a received signal containing various Doppler components when the target has a relative velocity. Compression loss occurred because pulse compression was performed by complex multiplication using . Therefore, in this embodiment, a plurality of reference signals corresponding to respective Doppler frequencies are prepared so as to correspond to various Doppler-shifted signal components. Therefore, in the reference signal generation means 10, the Doppler corrector 1 is installed after the reference signal generator 101.
02 has been added. Furthermore, in the conventional example, the signal component was decomposed into Doppler frequency components by the pulse Doppler processing means 6 after pulse compression, but in this embodiment, the pulse Doppler processing means 6 is placed before the complex multiplier 51. By performing complex multiplication of each signal component whose Doppler frequency has been shifted by a reference signal that matches its characteristics, loss is prevented from occurring during pulse compression. Furthermore, in this embodiment, a two-dimensional memory 63 is provided after the M-point FFT calculator 62;
This is necessary in order to exchange data in the pulse hit direction and range direction so that pulse compression in the range direction can be performed after Fourier transform in the pulse hit direction by the T calculator 62. Further, the reference memory 50 uses a two-dimensional memory to store two-dimensional data obtained by Fourier-transforming the output of the Doppler corrector 102 by the N-point FFT calculator 104.

Next, an outline of the operation will be explained. Introduction, Figure 1
The reference signal generated by the reference signal generating means 10 of FIG. 2 and stored in the reference memory 50 of the pulse compressing means 5 in advance will be explained. The reference signal generator 101 generates a reference signal R(r) expressed by equation (1) as in the conventional case. Next, the reference signal R
(r) is input to the Doppler corrector 102 and corrected into a reference signal RP(r,fd) having time versus frequency characteristics shifted by the Doppler frequency fd. Here, since the relative velocity of the target is unknown, the Doppler frequency fd is
Assume multiple relative speeds of the target. For example, all types of Doppler frequencies used in Doppler decomposition in pulsed Doppler processing are used. This can be expressed by the following equation using a frequency obtained by dividing the repetition frequency of the transmission pulse by M.

[0026]

[Math 2]

Using the values obtained from this, the output RP (r, fd) of the Doppler corrector 102 can be expressed by the following equation. RP (r,fd)=R(r)×exp[2πfd
・r・ts ] (9) Next, in order to convert the output of the Doppler corrector 102 into frequency domain data, Fourier transform is performed in the range direction, and the spectrum RRP (fr, fd) of the reference signal, which can be expressed by the following equation, is obtained. can get. RRP (fr, fd) = FR [RP (r, fd
)], (10)(FR
; Fourier transform in the range direction) The spectrum RRP (fr, fd) of the above reference signal is stored in advance in the reference memory 5.
Store as 0. Once stored, the reference signal generating means 10 is separated from the reference memory 50 as in the prior art. Spectrum RRP (f
The method of generating r, fd) is the same for both the chirp method and the code modulation method.

Next, the operation of the pulse compression means 5 including the pulse Doppler processing means 6 will be explained with reference to FIG. 3, which shows the flow of pulse Doppler processing and signal processing of the pulse compression means. In step 1, data S of the output of the receiving means 2 temporarily stored in the buffer memory 54
(r), an N-point FFT calculator 5
2, the data is Fourier transformed in the range direction and converted to frequency domain data. The output of this N-point FFT calculator can be expressed by the following equation. SR (fr)=FR [S(r)],
(1
1) (FR: Fourier transform in the range direction, fr: frequency) Then, this process is repeated for the pulse hit p, and the output data SR (fr) of the N-point FFT calculator 52 is
is stored in the two-dimensional memory 61 based on the frequency fr and the pulse hit p. Let the data stored in the two-dimensional memory 61 be SR (fr,p).

In step 2, the M-point FFT calculator 62 retrieves data SR (fr,p) from the two-dimensional memory 61.
is read out and decomposed into Doppler frequency components for each frequency fr. In order to detect the relative velocity of the target, M-point Fourier transform is performed in the pulse hit direction, pulse Doppler processing is performed, and the components of all observed pulses are Integrate into Doppler bins. The results are stored in the two-dimensional memory 63. The output of this Doppler processing means 6 can be expressed by the following equation. SRP (fr, fd)=FP [SR (fr,
p)], (12)(FP
;Fourier transform of pulse hit direction, fd; Doppler frequency)

In step 3, the spectrum RRP (Fourier-transformed) of the reference signal corrected for the frequency shift (or phase shift) due to Doppler shift is calculated according to the relative speed of the moving target, which is stored in the two-dimensional reference memory 50 in advance. fr, fd) and the Doppler processing means 6
Data SRP(fr,
fd) is subjected to complex multiplication by a complex multiplier 51 for each corresponding frequency fr and Doppler frequency fd in order to make its phase component constant over all frequencies. This complex multiplier output can be expressed by the following equation. URP (fr, fd) = SRP (fr, fd) x R
RP (fr, fd) (13) This is repeated for the frequency fr and stored in the buffer memory 55. In the conventional example, the spectrum of one received pulse outputted from the N-point FFT calculator 52 was complex multiplied by one reference signal, but in the present invention, the signal of M pulses is multiplied by the pulse signal.
Doppler processing means 6 performs pulse Doppler processing, and 2
The signals stored in the dimensional memory 63 in the pulse hit direction are read out in the range direction, and complex multiplication is performed with the reference signal for each signal corresponding to each Doppler frequency.

In step 4, the output data URP (fr, f
d) is subjected to inverse Fourier transform in the frequency direction by the N-point IFFT calculator 53 and returned to the time domain, thereby concentrating the signal energy in one place and obtaining a narrow pulse signal. This N-point IFF
The T calculator output can be expressed by the following equation. UP (r, fd) = Ffr-1 [URP (fr,
fd)], (14)(Ffr-1
; inverse Fourier transform in frequency fr direction)

The processing in steps 3 and 4 above is repeated for the Doppler frequency fd corresponding to the assumed target relative velocity. Next, the amplitude detector 7 performs envelope detection on the output data of the N-point IFFT calculator, and the display 8 displays the signal output for each range bin versus Doppler frequency.

As described above, the pulse compression means includes pulse Doppler processing, and depending on the relative speed of the moving target, the Doppler shift frequency (or phase) is changed from the conventional reference signal with the relative speed of the target as zero. By using the corrected reference signal and compressing the pulse without being affected by the Doppler frequency, it is possible to improve the distance measurement performance of a high-speed moving target.

In the above embodiment, the buffer memories 54 and 55 may be either one-dimensional memories or two-dimensional memories, and the buffer memories 54 and 55 and the two-dimensional memories 61,
63 can also be used in common.

Example 2. 4 and 5 are block diagrams showing the configuration of other embodiments of the present invention. FIG. 4 shows the case of the chirp method, and FIG. 5 shows the case of the code modulation method. As will be described later, this invention can perform Doppler decomposition and signal processing of the target, which is similar to pulse compression and pulse Doppler processing, without being affected by the range bin movement of the target, even for high-speed moving targets that involve movement of the range bin during observation. This is a pulse Doppler radar device that can achieve the integral of In FIGS. 4 and 5, 1 is a transmitting means that generates and modulates a transmission pulse to widen the frequency band, 2 is a receiving means, 3 is an antenna, 4 is a transmitter/receiver switch, 5 is a pulse compression means, and 9 is a pulse integration process. 7 is an amplitude detector, 8 is a display, and 10 is a reference signal generating means. Since the above transmitting means 1, receiving means 2, antenna 3, transmitting/receiving switch 4, amplitude detector 7, and display 8, which have the same configuration as the conventional example, have already been explained, their explanation will be omitted here.

The above pulse compression means 5 is shown in FIGS. 4 and 5.
As shown in , it has the following configuration. an N-point FFT calculator 52 that performs N-point Fourier transform on the data in the buffer memory 54 that stores the output of the receiving means 2 in the range direction;
Two-dimensional memory 5 that stores the output of the N-point FFT calculator 52
6, a three-dimensional reference memory 50 that stores a reference signal corrected for the phase fluctuation due to the Doppler effect and the range bin movement of the target from the start of observation for each relative velocity of the target to be detected, and the output of the reference memory 50. and a complex multiplier 51 that performs complex multiplication on the output of the two-dimensional memory 56.
and an N-point IFFT calculator 53 that inversely Fourier transforms the complex multiplication result in the range direction via the buffer memory 55.
It is equipped with

In the second embodiment shown in FIGS. 4 and 5, in the same way as in the first embodiment, in order to eliminate the influence of Doppler shift in the conventional example, in the reference signal generating means 10,
A Doppler corrector 102 is added after the reference signal generator 101. Furthermore, in the conventional example and the first embodiment, when the relative speed of the target is large enough to cause range bin movement during the observation time, the pulses are compressed to the range where the target is located at each time point. Therefore, if we focus on the range bin in which the target is at one point in time during the observation time, the observation time will be shortened compared to the case where the target does not move in the range bin, and the integration efficiency will decrease in pulse Doppler processing. , a decrease in Doppler resolution occurs and the target velocity measurement performance deteriorates. Therefore, in this embodiment, regarding the relative velocity of each target that produces the Doppler frequency corrected by the Doppler corrector 102, the distance traveled by the target from the start of observation at the time of transmission of each pulse is calculated by the time it takes for the radio wave to propagate. We have prepared a reference signal that has been corrected accordingly. Therefore, a range bin corrector 103 is added after the Doppler corrector 102. In addition, in the first embodiment, by placing the pulse Doppler processing means 6 including an M-point FFT calculation unit in front of the complex multiplier 51, each observed pulse is decomposed into Doppler frequency components, and at the same time, all of the observed pulses are decomposed into Doppler frequency components. Pulse components were integrated into each Doppler bin, but in this example, a reference signal with range bin movement corrected corresponding to each pulse is used, so all pulse components are integrated before complex multiplication of the reference signal. I can't. Therefore, after complex multiplication of the reference signal corrected at each Doppler frequency and the received signal containing all Doppler frequency components, pulse compression and Doppler frequency decomposition are performed by inverse Fourier transform in the range bin direction. By placing an integrating means afterwards, the components of all the pulses are integrated into each Doppler bin.

Furthermore, in this embodiment, the N-point FFT calculator 5
2, a two-dimensional memory 56 is provided, which stores the Doppler frequency when performing complex multiplication with a reference signal of the output obtained by Fourier transforming each pulse during the observation time in the range bin direction by the N-point FFT calculator 52. This is necessary in order to repeatedly read signals from the two-dimensional memory 56 for the number of types. Further, the reference memory 50 stores the output (one-dimensional data) of the reference signal generator 101 subjected to Doppler correction by the Doppler corrector 102 (two-dimensional data), and the output (three-dimensional data) obtained by performing range bin correction with the range bin corrector 103. To do this, three-dimensional memory is used.

Next, an outline of the operation will be explained. First of all,
The reference signal generated by the reference signal generating means 10 of FIGS. 4 and 5 and stored in the reference memory 50 of the pulse compressing means 5 in advance will be explained. In the reference signal generating means 10, a reference signal generator 101 generates a reference signal R(r) expressed by equation (1) as in the conventional example and the first embodiment. Next, the Doppler corrector 102 generates a Doppler-corrected reference signal RP (r, fd) expressed by equation (9) as in the first embodiment.
It is corrected to Next, the output RP of the Doppler corrector 102
(r, fd) is input to the range bin corrector 103.

The range bin corrector 103 calculates the time required for a pulse to propagate the distance traveled by the target from the start of observation for each speed of the target assumed by the Doppler corrector 102, and converts the reference signal to that time. I'm just moving it. The relative velocity vd of the target with respect to the Doppler frequency fd used in the Doppler corrector 102 is vd=f
d×C/2f0
(15)
It is expressed as (f0: carrier frequency, C: speed of light). Then, when p pulses are hit from the start of observation, the time t(p) required for the pulse to propagate the distance traveled by the target is given by the following equation. Here, this time t(p) is sampled at sampling time ts, and the number of pulses to be observed is M.

[0041]

[Math 3]

In order to cancel this time t(p), a reference signal also shifted by t(p) on the time axis is used. This reference signal RPP (r, fd, p)
is expressed by the following equation. RPP(r,fd,p)=RP(r,fd)×u
(rt(p)) (17) However, u(r)=1
0≦r<T/tsu(r)=0 T/ts≦r<
N Next, the output RRP (r, fd, p) of the range corrector 103
In order to convert into frequency domain data as in the conventional example and the first embodiment, the N-point FFT calculator 104 performs Fourier transform in the range direction to obtain the reference signal spectrum RRPP (fr, fd , p). RRPP (fr, fd, p) = FR [RPP(
r, fd, P)] (18) (FR; Fourier transform in range direction) The spectrum RRPP (fr, fd, p) of the above reference signal is stored in the reference memory 50 in advance. Once stored, the reference signal generating means 10 stores the reference signal in the reference memory 5 as in the conventional example and the first embodiment.
It is separated from 0. The method for generating the spectrum RRPP (fr, fd, p) of the reference signal described above is the same for both the chirp method and the code modulation method.

Next, an overview of the operations of the pulse compression means 5 and the pulse integration processing means 9 will be explained with reference to FIG. In step 1, the data S(r) output from the receiving means 2 is Fourier-transformed in the range direction by the N-point FFT calculator 52 in order to convert it into frequency domain data. The output of this N-point FFT calculator can be expressed by the following equation. SR (fr)=FR [S(r)]
(
19) (fr: frequency, FR: Fourier transform in range direction) Repeat this for pulse hits to obtain SR (
fr, p) and input into the two-dimensional memory 56.

In step 2, the output SR of step 1
(fr, p) and reference signal RRPP (fr,
fd, p) to obtain spectral components whose phases are uniform over all frequencies. URPP this result
(fr, fd, p). URPP (fr, fd, p) = SR (fr, p) x RRPP (fr
, fd, p) (20) This is repeated for the frequency fr and stored in the buffer memory 55.

In step 3, the complex multiplication result URPP
In order to convert (fr, fd, p) into time domain data, inverse Fourier transform is performed in the frequency direction and UPP (
r, fd, p). UPP(r,fd,p)=Ffr-1[URPP
(fr, fd, p)]) (21) (Ffr-1: inverse Fourier transform in frequency direction)

In step 4, the processing of steps 2 and 3 is performed by pulse hit p.
are repeatedly stored in the two-dimensional memory 91. This inverse Fourier transform result UPP(r, fd, p) is read out from the two-dimensional memory 91, and integrated in the pulse direction for each r and fd to obtain W(r, fd). This has the same effect as in the conventional example and the pulse Doppler processing of Example 1, where the signal is decomposed into Doppler frequency components and the signal components are integrated at the Doppler frequency corresponding to the relative velocity of the target. . This is shown in the following equation.

[0047]

[Math 4]

This integration process is repeated for range bin r. The process in step 4 is repeated for the Doppler frequency fd corresponding to the assumed relative velocity of the target, and the integral result W(r, fd) is subjected to envelope detection by the amplitude detector 7 and displayed on the display 8.

The present embodiment differs from the first embodiment in operation and effect in the following points. This will be explained using FIG. 7. In Example 1, when the range bin containing the target does not move during the observation time, that is, the number of data points in the pulse hit direction is M, the pulse repetition period is Δt, and the range bin width is Δ.
When R is the speed of light and C is the speed of light, the following equation holds true. MΔt×V<ΔR=Cts/2
(2
3) At this time, in both the chirp method and code modulation method, as shown in FIG. 7(a), when pulse Doppler processing is performed to perform Fourier transform in the pulse hit direction,
In the Doppler bin for the observed relative velocity of the target, the signal is integrated into the range bin where the target is located. Here, since ΔR represents the distance resolution, the sampling time t
When s is increased and ΔR is increased, the distance resolution deteriorates.

However, if the range bin containing the target moves during the observation time, as shown in FIG. 7(b),
Since the pulse compression result is spread over multiple range bins, when pulse Doppler processing is performed, the output signal is dispersed to the range bin where the target has moved, and the integration effect of pulse Doppler processing cannot be obtained sufficiently. Distance measurement performance for fast-moving targets deteriorates. In addition, when Fourier transform is performed in pulse Doppler processing, the Doppler frequency band expands due to the effect of range bin movement, and the output signal is distributed over multiple Doppler bins, making it impossible to obtain the full integration effect of pulse Doppler processing. The speed measurement performance of moving targets deteriorates. Furthermore, if we focus on the range bin in which the target is located at a certain point in the observation time, the amount of information decreases in the same way that the observation time is shortened due to the movement of the range bin of the target, resulting in a decrease in Doppler resolution and the speed of the target. Measurement performance deteriorates.

On the other hand, in Example 2, by performing pulse compression using a reference signal corrected for range bin movement, as shown in FIG. All pulses inside are compressed. (The amount of range movement of the pulse at the start of observation is assumed to be zero.) Therefore, when performing integration processing, the signal power is integrated into one range bin, improving integration efficiency and improving distance measurement performance for high-speed moving targets. do. Also, regarding Doppler resolution, since range bin movement is removed, the amount of information is prevented from decreasing, so the same performance as Doppler resolution when no range bin movement occurs is obtained, and the speed measurement performance of high-speed moving targets is also improved.

[0052]

[Effects of the Invention] Since the present invention is constructed as described above, it produces the following effects. In the first embodiment, pulse Doppler processing is performed to detect the relative velocity of the target in the pulse compression means, and a reference signal corrected for the Doppler effect is used to perform correlation processing on the modulated wide pulse width signal. By providing a pulse compression means that converts into a narrow pulse width signal, even if a high-speed moving target has a relative velocity V, it is possible to compress the pulse without being affected by Doppler shift, improving the distance measurement performance of high-speed moving targets. A pulse Doppler radar device with improved performance can be obtained.

In addition, in the second embodiment, assuming the relative velocity V of the target, a narrow pulse is obtained by calculating the correlation between a reference signal corrected for phase fluctuation and range bin movement due to the Doppler effect, and a modulated wide pulse width received signal. Equipped with a pulse compression means for converting into a width signal and an integration means for integrating the received signal after pulse compression during the observation time for each range bin and each Doppler bin, it is possible to detect high-speed moving targets that move the range bins during observation. To obtain a pulse Doppler radar device that enables pulse compression and signal integration without being affected by phase fluctuations due to the Doppler effect and target range movement, and improves distance measurement performance and speed measurement performance for high-speed moving targets. be able to.

[Brief explanation of drawings]

FIG. 1 is a configuration block diagram showing an example of a chirp method according to Example 1 of the present invention.

FIG. 2 is a configuration block diagram showing an example of a code modulation method according to Example 1 of the present invention.

FIG. 3 is a diagram showing the flow of signal processing by pulse Doppler processing means and pulse compression means according to the first embodiment of the present invention.

FIG. 4 is a configuration block diagram showing an example of a chirp method according to a second embodiment of the present invention.

FIG. 5 is a configuration block diagram showing an example of a code modulation method according to Example 2 of the present invention.

FIG. 6 is a diagram showing the flow of signal processing by pulse compression means and integration means according to a second embodiment of the present invention.

FIG. 7 is a diagram showing the effect of correcting range bin movement according to Example 2 of the present invention.

FIG. 8 is a configuration block diagram of a conventional chirp method.

FIG. 9 is a configuration block diagram of a conventional code modulation method.

FIG. 10 is a diagram showing each signal waveform of the chirp method.

FIG. 11 is a diagram showing each signal waveform of the code modulation method.

FIG. 12 is a configuration block diagram of a receiving means.

FIG. 13 is a diagram showing the flow of signal processing by conventional pulse compression means and pulse Doppler processing means.

FIG. 14 is a diagram showing the influence of pulse compression due to Doppler shift in the conventional chirp method.

FIG. 15 is a diagram showing an example of a pulse compression waveform of a conventional code modulation method.

[Explanation of symbols]

1 Transmission means 2 Receiving means 3 Antenna 4 Transmission/reception switch 5 Pulse compression means 6 Pulse Doppler processing means 7 Amplitude detector 8. Display 9 Pulse integral processing means 10 Reference signal generation means

Claims (2)

[Claims] Claim 1: A transmitter that generates and modulates a transmission pulse to widen the frequency band; an antenna that radiates the output of the transmitter toward a target and receives reflected signals from the target; and a transmitter/receiver switch that switches the transmitter/receiver circuit. , receiving means for processing the received signal to obtain a complex signal, and pulse Doppler processing means for detecting the relative velocity of the target, and using a reference signal corrected for the Doppler effect, a modulated wide pulse is generated. A pulse Doppler radar device equipped with a pulse compression means for correlating a width signal and converting it into a narrow pulse width signal, an amplitude detector for envelope detection of the output of the pulse compression means, and a display for displaying a detected target. . [Claim 2] A transmitter that generates and modulates a transmission pulse to widen the frequency band, an antenna that radiates the output of the transmitter toward a target and receives a reflected signal from the target, and a transmitter/receiver switch that switches the transmitter/receiver circuit. A modulated wide pulse width signal is obtained using a receiving means that processes the received signal to obtain a complex signal, and a reference signal that has been corrected for phase fluctuations due to the Doppler effect of the target and range bin movement of the target from the start of observation. a pulse compression means that performs correlation processing and converts it into a narrow pulse width signal; an integration means that integrates the output of the pulse compression means for each range bin and each Doppler bin; an amplitude detector that performs envelope detection of the output of the integration means; A pulse Doppler radar device equipped with a display device.