JPH0656413B2 - Radar equipment - Google Patents

Description

TECHNICAL FIELD The present invention relates to a pulse Doppler radar device for measuring a distance to an aircraft target by frequency modulation.

[Prior Art] FIG. 4 is a configuration diagram showing a conventional radar device for measuring a distance to an aircraft target by a transmission wave that is frequency-modulated with a high pulse repetition frequency. In the figure, (1) is a straight line. Excitation / receiver that generates a pulse-frequency-modulated transmit wave, pulse-modulates it at a high pulse repetition frequency, sends it out, amplifies the received signal, and converts it to a digital signal after clutter removal. Antenna which amplifies and radiates to the space and receives the reflected wave from the target. (3) receives the digital signal from the excitation / receiver (1) and performs various signal processing to measure the distance to the target. Signal processor, (4) clutter removal filter, (5) Doppler filter,
(6) is a signal detector, (11) is a target number judging circuit, (8) is a distance measuring circuit, and (10) is a display for displaying the target distance and the like.

FIG. 5 is a conceptual diagram in which the radar device is mounted on a flying object or the like and scans the antenna beam while moving to search for a target. In the figure, (12) is the radar device and (13) is the main beam. , (14) is the side rope, (15) the target aircraft, and (16) is the ground.

FIG. 6 is a conceptual diagram for explaining that a plane electric wave is incident on the blade of the jet engine compressor and undergoes a Doppler shift in the negative direction. In the figure, (17) is the blade.

FIG. 7 is a frequency spectrum of the signal received by the radar device in the state shown in FIG. 5, where (18) is the main beam clutter, (19) is the sidelobe clutter, and (20) is the target Doppler signal. , (21) are Doppler signals due to jet engine modulation.

FIG. 8 is a diagram showing temporal frequency changes of the frequency-modulated transmission and reception signals when performing distance measurement. In the figure, (22) is the frequency change characteristic of the transmitted wave, and (23) is the target Doppler. The frequency change characteristic of the signal, (24) is the frequency change characteristic of the Doppler signal due to the jet engine modulation.

FIG. 9 is a diagram showing combinations when distances are calculated using a plurality of Doppler frequency signals obtained in both FM phases.

Next, the operation will be described. The transmission wave from the excitation / receiver (1) in which constant frequency and linear frequency modulation are alternately repeated is pulse-modulated at a high pulse repetition frequency
Sent to (2). The antenna (2) amplifies this transmitted wave to high power and forms an antenna beam. Then, it electronically scans the antenna beam to search for the target, and receives the received signal from the target together with unnecessary clutter. In FIG. 5, a flying body equipped with the radar device (12) is flying at its own speed V ₁ , and the radar device is in a down-look state.
When (12) searches for the target aircraft (15), the main beam (13) and the side lobes (14) irradiate the ground (16) to receive unnecessary clutter, and the main beam (13) receives the target aircraft. (15)
To receive the signal from. At this time, the signal from the target aircraft (15) is generated with a plurality of Doppler frequencies due to the modulation caused by the rotation of the blade of the jet engine of the target aircraft (15). As shown in FIG. 6, the blade (17)
Operates so that the Doppler shift becomes low because the radio wave irradiation surface rotates away from the moving direction. Then, a sub-harmonic modulated wave component having a complicated shape of the blade (17) and different in inclination and rotational speed is generated. The radio wave irradiating P ₁ point irradiates P ₂ point by slight rotation of the blade, so the blade acts so as to move away even if the target aircraft (15) is approaching, As a result, a plurality of Doppler frequencies lower than the Doppler frequency due to the relative velocity V _R with the target aircraft (15) are generated.

The Doppler frequency f ₁ of the target aircraft flying at the speed V _T is given by the following equation.

Where f ₀ is the transmission frequency, C ₀ is the speed of light, θ is the velocity vector V _I
And the antenna beam.

Next, assuming that the frequency shift amount due to jet engine modulation is f _JEM , a plurality of Doppler frequencies are shown by the following equation.

The frequency spectrum of the clutter and the signal shown above is shown in FIG.

The true Doppler frequency of the target given by Eq. (1), which is determined by the relative speed to the target (20), and lower frequencies.
The received signal includes the jet engine modulation signal (21) given by equations (2) to (5) and the main beam clutter (18) and sidelobe clutter (19). The excitation / receiver (1) receives this received signal from the antenna (2) and firstly amplifies it with low noise, converts it to an intermediate frequency by the local oscillator signal, removes clutter, and then performs phase detection on the video band. To obtain a Doppler signal and convert it to a digital signal.

Next, the digital signal is input to the signal processor (3), and the clutter is removed again by the clutter removal filter (4). After that, it becomes a narrow band Doppler signal by the Doppler filter (5) by the fast Fourier transform, and this output is detected as a signal by the signal detector (6) that compares the amplitude with the noise after amplitude detection. As shown in FIG.
A plurality of Doppler frequency signals are detected in each of the M phase C and the FM phase B of the linear frequency modulation. FM
In phase C, four Doppler frequency signals with frequencies f ₁ , f ₂ , f ₃ , and f ₄ are received. In FM phase B, frequency shifts g ₁ , g ₂ , by a value according to the target distance, Four Doppler frequency signals with frequencies g ₃ and g ₄ are received. The frequency variation characteristic (23) of the target Doppler signal is higher than the frequency variation characteristic (22) of the transmitted wave by f ₁ and is delayed by the time τ shown by the following equation.

However, R is a target distance.

Similarly, the frequency variation characteristic (24) of the Doppler signal due to jet engine modulation also has a frequency higher than the transmitted wave by f ₂ , f ₃ , and f _{4 and} delayed by time τ.

If there is only one signal, the target distance is obtained from the frequency f ₁ detected in FM phase C and the frequency g ₁ detected in FM phase B by the following equation.

However, F is the frequency modulation degree of FM phase B.

However, when there are two or more signals, FM phase C and FM
With the two combinations of phase B, the target distances of four combinations are obtained. Therefore, in the conventional radar device, it is possible to obtain the distances of two targets by adding another FM phase A and changing the frequency modulation degree to use. However, when there are three or more Doppler frequency signals as shown in FIG. 8, it is difficult to find the three target distances even if the three FM phases are used. For this reason, the target number determination circuit (11) uses the FM phase C and the FM phase B when the number of Doppler frequency signals is one.
In case of two, FM phase C, FM phase B, and FM phase A are used to send the frequency of the target signal to the distance measuring circuit (8) to execute the calculation by equation (8). It was When there are three or more, there are many combinations as shown in FIG. 9, and when there are N, there are N × N combinations.
However, the frequency of FM phase B is always smaller than that of FM phase C, so that R ₂₁ , R ₃₁ , R ₄₁ , R ₄₂ , and R ₄₃ are negative and are out of the calculation target. In reality, there are (N + 1) × N ÷ 2 distance calculation combinations. As described above, the distance cannot be measured because the true target distance cannot be obtained.

[Problems to be Solved by the Invention] In the conventional radar device, since the target distance is calculated by the above method, one target is provided and a plurality of Doppler frequency signals are detected by the jet engine modulation. In some cases, distance measurement was impossible. There is a problem that the performance of the radar device is significantly deteriorated when the signal is detected and the distance measurement is impossible even when only one target is present.

The present invention has been made to solve such a problem, and paying attention to the fact that the differences between a plurality of Doppler frequencies due to jet engine modulation are almost evenly spaced, even if three or more signals are detected. An object of the present invention is to obtain a radar device capable of obtaining a true target distance in a short time and easily by sequentially performing calculation from a higher frequency for a combination of a plurality of Doppler frequency differences in two frequency modulation phases. To do.

[Means for Solving the Problems] In order to achieve such an object, the radar apparatus according to the present invention selects a higher Doppler frequency from a higher Doppler frequency by a frequency determination circuit after signal detection in the signal processor.
The difference between the signal frequency of the M phase C and the frequency of the FM phase B is calculated, and only for the combination of the signal frequencies for which the difference is positive, the distance measurement circuit executes the distance calculation using the frequency difference, and then the distance determination circuit. It is determined whether the target distance calculation result is within the distance performance peculiar to the radar, and if it is more than this distance, the frequency judgment circuit selects a combination of two signal frequencies in descending order of frequency and executes the same calculation processing. . Then, when it is determined that the target distance calculation result is within the radar-specific distance performance, the true target distance is simply calculated in a short time by determining this as the true target distance.

[Operation] In the present invention, after detecting a plurality of Doppler frequency signals, the frequency judgment circuit selects one having a higher Doppler frequency, and the distance calculation is performed from the frequency difference between the two frequency modulation phases. By determining whether the target distance is a proper value, it is possible to easily obtain the true target distance in a short time and prevent the performance of the radar device from deteriorating.

[Embodiment] An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows the configuration of a radar device according to the present invention. In the figure, (1) to (6), (8), and (10) are the same devices or parts as the above-described conventional radar device. In this invention,
(7) is a frequency judgment circuit that selects multiple Doppler frequency signals from the one with the highest frequency, and (9) is a distance judgment circuit that judges whether the distance calculation result is valid by comparison with the radar detection performance. To work. FIG. 2 shows the result of calculating the distance for all combinations using four Doppler frequency signals detected in two frequency modulation phases. FIG. 3 shows a flow chart of distance calculation processing from the frequency judgment circuit to the distance judgment circuit of the signal processor in the present invention.

Next, the operation of the radar device according to the present invention will be described. After the transmitted wave from the excitation / receiver (1) is radiated into space from the antenna (2) and received again by the antenna (2), amplification, frequency conversion, clutter removal, and phase detection are performed at the excitation / receiver (1). Signal processor that is converted to a digital signal
It is input in (3). Then, the signal processor (3) removes clutter with the clutter removal filter (4), extracts as a narrowband Doppler frequency signal with the Doppler filter (5), and detects the amplitude and noise from the signal detector (6). It is the same as that of the conventional radar device until the above is performed and detected as a Doppler frequency signal. Multiple Doppler frequency signals due to jet engine modulation caused by the rotation of the jet engine blades (17) of the target aircraft (15) are received.
The frequency is lower than that of the signal determined by the relative speed to the target, and the frequency intervals f _JEM thereof are almost even. Further, the frequency difference between the FM phase C and the FM phase B of the Doppler frequency signal due to the jet engine modulation is determined by the distance, and its value is almost the same. FIG. 2 shows this in the figure, and f ₁ is the true Doppler frequency determined by the relative speed with the target. f ₂ , f ₃ , and f ₄ are jet engine
The Doppler frequency due to modulation. And
g ₁ is the true Doppler frequency received during linear frequency modulation and is given by (7) for f ₁ Only low frequency. Similarly g ₂ , g ₃ , g ₄ respectively
For f ₂ , f ₃ , and f ₄ Only low frequency. The frequency intervals of the signals f _{1 to} f ₄ and g _{1 to} g ₄ are equal to f _JEM . Therefore, considering that the combination of the distance calculations is always lower in the FM phase B than in the FM phase C, it can be excluded when the frequency difference is negative, and therefore there are 10 combinations of (4 + 3 + 2 + 1). The true target distance to be obtained in the present invention is R ₀ calculated by f ₁ and g ₁ .

Similar distances R ₁ , R ₂ and R ₃ other than R ₀ are expressed by the following equations.

The frequency deviation f _JEM due to jet engine modulation is determined by the rotational speed ω of the blade (17), the inclination angle φ of the blade (17) with respect to the rotation surface, and the distance L from the rotation center of the filter engine, (14) It is represented by a formula.

Here, L = 0.3m, ω = 10000rpm, φ = 45 °, f ₀ = 10GH
If z and C ₀ = 3 × 10 ⁸ m / S, then f _JEM = 3.3 KHz. Further, when the frequency modulation degree F = 4 MHz / S, the calculation distance R _JEM by FM ranging corresponding to f _JEM is calculated from the equation (13) and becomes R _JEM = 123.75 Km. On the other hand, the detection range performance of the radar is determined by the target radar cross section of the specifications of the radar device such as the gain of the antenna, the effective radiation power, and the noise figure of the receiving system. The radar cross section for a relatively small aircraft target is about 5 m ² , and the contribution of the jet engine blade to this radar cross section of 5 m ² depends on the size of the aircraft engine opening, but is 1/100. It is about 1/50. When the maximum detection distance is changed with a radar cross section of 5 m ² and the distance at which jet engine modulation occurs is obtained, equation (15) is obtained.

In the case of a radar device having R _m <R _JEM , for example, R _m = 100 Km, R _L = 31.6 to 37.6 Km, which is a value sufficiently smaller than R _JEM = 123.75 Km, so R ₁ , R ₂ , R ₃ ,… ＞ R _m (R _J ) …… (16) If the distance to be compared by the distance judgment circuit is R _m , it is possible to easily distinguish the false distance from the true distance, and R ₁ = R _JEM
+ R ₀ , R ₂ = 2R _JEM + R ₀ can be excluded as similar distances. Based on the above principle, a new frequency judgment circuit (7) is installed at the output of the signal detector (6), the distance calculation circuit (8) performs the same calculation as the conventional operation according to the frequency selected there, and the output is the distance judgment circuit. (9) distinguishes the true distance from the similar distance, outputs the true target distance, and displays it on the display (10). Figure 3 shows the frequency judgment circuit (7) to the distance judgment circuit (9)
First, the frequency judgment circuit (7) first selects signals from FM phase C in descending order of frequency in step (a), and then in step (a) FM
Also from phase B, signals are selected in descending order of frequency. Then, in step (c), the difference between the two is taken, and if the difference is positive, the frequency difference is sent to the distance measuring circuit (8). If the difference is negative, for example, in FM phase B in FIG.
When there is a frequency g ₀ greater than g _{1 and} greater than f ₁ f ₁ −
g ₀ <0, and again in step (a) in FM phase B
Since g ₁ is chosen next to g ₀ , f ₁ −g ₁ >
A result of 0 is obtained and distance measurement is possible. Next, when the frequency difference is positive, the distance measuring circuit (8) performs distance calculation based on equation (8) in step (d). As shown in FIG. 2, a true distance R ₀ is obtained as a result of calculation with f ₁ and g ₁ , and is input to the distance determination circuit (9). If the distance is smaller than R _JEM in step (e), the true target distance is determined in step (f), and if it is sent for display, it returns to the beginning as a similar distance. For example, if g ₁ is not detected in FIG. 2, and f ₁
Since the distances by g ₂ , g ₃ , and g ₄ are all larger than R _JEM ,
It is judged that the distance is similar. Then, in step (a), f ₂ having the next largest frequency after f ₁ is selected in FM phase C. However, if f ₂ and g ₂ , the combination is the same as f ₁ and g ₁ , so the jet engine The true distance will also be determined by the modulation signal. In this way, the distance R _J for detecting the jet engine modulation signal of the radar is set as the comparison distance in the distance determination circuit, and when two or more true target candidates are obtained, the FM phase C and the FM phase B are used. The true target distance can be easily obtained in a short time by further determining whether or not the target is the true target by using the number of signals of.

Although the above embodiment shows the radar device using the antenna that electronically performs the beam device, it is also possible to use the radar device using the antenna of the mechanical scanning antenna, and the signal processor is a hardware. Both the software configuration and the software configuration are practical.

[Effects of the Invention] As described above, the present invention utilizes the distance measurement calculation method of the conventional radar device, and simply adds the frequency judgment circuit and the distance judgment circuit before and after the distance measurement circuit of the signal processor. Even if a large number of Doppler frequency signals due to jet engine modulation caused by rotation of the jet engine blade of the aircraft target in the configuration are detected, the true target distance can be easily calculated in a short time and radar detection performance deteriorates. The effect is to prevent.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing a radar device according to an embodiment of the present invention, FIG. 2 is a diagram showing a combination for performing frequency modulation distance measurement in the present invention, and FIG. 3 is a distance calculation in the present invention. A flow chart, FIG. 4 is a schematic configuration diagram showing a conventional radar device, FIG. 5 is a conceptual diagram in which the radar device is searching for a target aircraft while flying, and FIG. 6 is a negative diagram due to rotation of a jet engine blade. 7 is a conceptual diagram for explaining the Doppler shift of the direction, FIG. 7 is a frequency spectrum of a signal received by the radar device shown in FIG. 5, and FIG. 8 is a diagram showing changes with time of a transmitted wave and a received wave, FIG. 9 is a diagram showing combinations when distance calculation is performed using a plurality of Doppler frequency signals. In the figure, (1) is the excitation / receiver,
(2) aerial, (3) signal processor, (4) clutter removal filter, (5) Doppler filter, (6) signal detector, (7) frequency decision circuit, (8) Is a distance measuring circuit, (9) is a distance determining circuit, (10) is an indicator, (11) is a target number determining circuit, and (1
2) radar device, (13) main beam, (14) side lobe, (15) target aircraft, (16) ground, (17) blade, (18) main beam clutter, (19) Sidelobe clutter, (20) target Doppler signal, (21) Doppler signal by jet engine modulation, (22) frequency change characteristic of transmitted wave, (23) frequency change characteristic of target Doppler signal, (24) ) Is the frequency change characteristic of the Doppler signal due to jet engine modulation, f ₁ , f ₂ , f ₃ ,
f ₄ , g ₁ , g ₂ , g ₃ , g ₄ are Doppler frequencies, f _JEM is the jet engine modulation frequency, R ₀ is the true target distance, R ₁ , R ₂ , R ₃ are similar distances, R _J is the distance at which jet engine modulation occurs, R is the target distance, R _m
Is the maximum radar detection distance, N is the number of signals detected in the FM phase, VT is the target speed, VI is the speed of the aircraft, θ is the angle between the speed vector and the antenna beam, and φ is the blade's surface relative to the rotating surface. Tilt angle, ω is blade rotation speed,
L is the length of the blade, C ₀ is the speed of light, τ is the time delay, F is the frequency modulation factor of linear frequency modulation, R _JEM is the distance calculated using f _JEM , PRF is the pulse repetition frequency, and f ₀ is the transmission frequency of the wave, R ₁₁ to R ₄₄ are each of a distance calculation flow distance computed by a combination of f ₁ ~f ₄ and g ₁ to g _4, a-Sa from the frequency determining circuit of the signal processing section to the distance determination circuit It is a step. The same reference numerals in the drawings indicate the same or corresponding parts.

 ─────────────────────────────────────────────────── ─── Continued front page (72) Inventor Shigeki Oshima 2718-1 Hakonegasaki, Mizuho-cho, Nishitama-gun, Tokyo (72) Inventor Noboru Kurihara 325 Kamimachiya, Kamakura-shi, Kanagawa Mitsubishi Electric Corporation Kamakura Factory

Claims (1)

[Claims] 1. A transmission wave having a constant frequency and a transmission wave having a linear frequency modulation are alternately generated for a predetermined period, and the transmission wave is pulse-modulated with a predetermined pulse width and a predetermined pulse repetition frequency and sent to an antenna. Along with the excitation that amplifies the received signal
Receiver, radiating the transmitted wave from the excitation / receiver in space, the antenna receiving the reflected signal from the target, and removing the clutter contained in the received signal from the excitation / receiver,
Signal processing that detects the Doppler frequency from the target by frequency analysis in the transmission period with a constant frequency and the transmission period with linear frequency modulation, and calculates the distance to the target from the difference between the Doppler frequencies obtained in both periods The signal processor further selects the Doppler frequency signals in the two FM phases detected by the frequency analysis in descending order of frequency, and determines whether the frequency difference between the Doppler frequency signals in the two FM phases is positive or negative. The frequency determination circuit that determines the frequency difference and the frequency determination circuit calculates the distance from the frequency difference when the frequency difference is determined to be positive, and the distance obtained by the distance measurement circuit causes the jet engine modulation. And a distance determining circuit that determines a true distance when the distance is smaller than the distance.