JPH0137710B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a radar device that accurately detects and tracks targets flying at low altitude.

Conventionally, this type of device is a monopulse radar (M
NPULSE RADAR). Figure 1a is a block diagram showing the principle of monopulse radar, in which 1 is a monopulse antenna, 2 is a hybrid circuit, 3 is an amplifier, 4 is an automatic gain control device, 5 is a phase detector, and 6 is a monopulse antenna. 1 central axis, 7 is the target, 8 is the image of target 7, 9 is the reflected wave (direct wave) from target 7,
10 is the reflected wave from the image 8, that is, the reflected wave from the target 7 due to the multipath effect (indirect wave); 1
1 is the sea level. FIG. 1b is an antenna pattern diagram of the monopulse antenna 1. As shown in FIG. Monopulse radar simultaneously receives reflected waves from a target using two partially overlapping antenna patterns as shown in Figure 1b, and calculates the sum signal Σ and difference signal of the two received signals obtained from each antenna pattern. Δ is obtained by the hybrid circuit 2. As a result, the output signal of the hybrid circuit becomes completely equivalent to the signal received by the two antenna patterns as shown in FIG. In the figure, the horizontal axis is the reception angle θ (antenna center axis 6
and the received reflected wave), and the vertical axis is the received voltage V
, 12 is the sum pattern, 13 is the difference pattern, 14 is the received voltage Σ _d due to the pattern 12 of the sum of the reflected waves 9, 15 is the received voltage Δ _d due to the pattern 3 of the difference of the reflected waves 9, 16 is the reflected wave The received voltage Σ _i due to the pattern 12 of the sum of the waves 10 and 17 is the received voltage Δ _i due to the pattern 13 of the difference of the reflected waves 10 . However, Σ, Δ, Σ _d , Δ _d , Σ _i , and Δ _i are complex signal voltages including amplitude and phase.

First, consider the case where image 8 does not exist. At this time, the monopulse antenna 1 receives only the reflected wave 9 from the target 7, so the received signal voltage Σ due to the sum pattern 12 and the received signal voltage △ due to the difference pattern are respectively Σ=Σ _d = Σ(θ _d ) (1) △=△ _d = △(θ _d ) (2). Here, θ _d is the receiving angle of the reflected wave 9.
The gain A of the amplifier 3 is controlled by the automatic gain control device 4 as shown in the following equation.

A=V _s /|Σ| (3) Here, V _s is a constant determined by the feedback amount of the automatic gain control device.

Therefore, the received signal voltage after passing through the amplifier 3 is Σ′=V _s Σ _d / |Σ _d |=V _s Σ(θ _d )/|Σ(θ _d )| (4) △′= V _s △ _d / |Σ _d | = V _s △(θ _d ) / |Σ(θ _d ) | (5). The phase detector 4 is a detector that maintains the amplitude and phase difference of two input signals, and when the two complex input signals are I and Q, its output voltage E is as follows: E=|I| ² Re[Q/I ] (6) becomes. Here, Re [ ] represents the real part. Therefore, the two signals expressed by equations (4) and (5) are detected by the phase detector 5.
, the output voltage E becomes E=V _s ² Re [Δ _d /Σ _d ] = V _s ² Re [Δ(θ _d )/Σ(θ _d )] (7).

FIG. 3 is a diagram in which the relationship between the reception angle θ _d and the phase detector output voltage E is calculated based on equation (7) and the antenna pattern shown in FIG. As shown in FIG. 3, the output voltage _E and the receiving angle θ _d have a proportional relationship in the range where the angle θ _d is not very large. The direction θ _d can be known accurately. Furthermore, by feeding back the output voltage E given by equation (7) to the drive section of the monopulse antenna 1 as an angular error signal, the target can be tracked with high accuracy.

On the other hand, when the image 8 exists, that is, when the reflected wave 10 due to the multipath effect and the reflected wave 9 from the target are simultaneously received by the monopulse antenna 1, the voltage Σ received in the sum pattern 12 and the difference pattern The radio wave Δ received by 11 is a composite value of two voltages as shown below.

Σ=Σ _d + Σ _i = Σ (θ _d ) + Σ (θ _i ) (8) △=△ _d + △ _i = △ (θ _d ) + △ (θ _i ) (9) Here, θ _i is the reflected wave 10 is the receiving angle.

By substituting equations (8) and (9) into equation (7), the phase detection output voltage E when there is a multipath effect is similarly given by the following equation.

E=V _s ² Re [△ _d + △ _i / Σ _d + Σ _i ] = V _s ² Re [△
(θ _d )/Σ(θ _d )・1+△(θ _i )/△(θ _d )/1+
Σ(θ _i )/Σ(θ _d )] (10) In the absence of multipath effects, the phase detection output voltage E is determined only by the reception angle of the reflected wave from the target if the antenna pattern is determined. However, in this case, due to the influence of the reflected waves from the image, as shown in equation (10), in addition to the above parameters, the above two
It is also affected by the amplitude ratio and phase difference of the two reflected waves. This means that the reception angle of the reflected wave from the target cannot be determined from the phase detection output voltage alone, and essentially monopulse radar cannot accurately detect and track the target due to the influence of multipath effects. It becomes possible.

However, conventional radar equipment uses a monopulse radar to detect and track a target flying at low altitude. As a result, the target detection and tracking accuracy is very poor, and in extreme cases, the target may be lost.

In order to solve these drawbacks, this invention removes the multipath effect by arranging multiple antennas vertically in a straight line and processing the received signals obtained simultaneously from each antenna in a predetermined manner. The aim is to improve target detection and tracking accuracy, and the drawings will be explained in detail below.

FIG. 4 shows an embodiment of the present invention.
8 is a transmitting/receiving antenna, 19 is a receiving antenna,
20 is a receiver, 21 is a transmitter, 22 is a transmission/reception switch, 23 is a ranging device, 24 is a signal processing device, 25
is the transmitted wave.

The radio waves generated by the transmitter 21 are sent to the transmitter/receiver switch 22,
It is radiated to the outside space as a transmission wave 25 via the antenna 18. Of the transmitted waves 25, the radio waves reflected by the target 7 and the image 8 are transmitted to the antenna 18,
19 and input to the signal processing device via the receiver 20. Here, the total number of antennas 18 and 19 is N, and for convenience of explanation, each antenna is numbered #1, #2, #2, etc. from the one closest to the sea surface 11.
Let's call it #N antenna. The reflected waves received by the antennas #1 to #N are a composite value of the reflected wave 9 from the target 7 and the reflected wave 10 from the image 8, which are phase-detected by the receiver 20 and input to the signal processing device 24. The complex signal S _i to be calculated is expressed as S _i =a _i +b _i (i=1, 2, . . . , N) (11). Here, i indicates the antenna number, and ai and bi are complex received signals corresponding to reflected waves 9 and 10, respectively. In addition, the distance to the target 7 of the reflected wave received by the #1 antenna is calculated by a known ranging device 23, and the distance measurement data R _p
is input to the signal processing device 24. R _p measured here includes an error due to the influence of the reflected wave 10, but
This error can be ignored if the altitude of target 7 is low enough to cause multipath effects.

FIG. 5 is a diagram showing the principle of the processing method performed by the signal processing device 24. In the figure, 26 is a virtual target for signal processing, 27 is a surface where the target 7 and image 8 exist, 28 is the antenna 18, 19 is an array axis, and 29 is an axis indicating the center of antennas #1 to #N.

The signal processing device 24 performs arithmetic processing as shown in the following equation on the received signal given by equation (11).

V = | _N 〓 ⁱ⁼¹ S _i t _i | (12) Here, t _i (i=1, 2,..., N) is a phase correction coefficient, which is calculated by the signal processing device 24 as follows. . First, the tentative phase target 26 is set at an elevation angle θ _p (θ _p is the central axis 2
7 and the virtual target 26 direction). Here, θ _p is set to a value at which target 7 is considered to exist. At this time, the phase correction coefficient t _i is calculated by the following equation.

t _i =K・eXP [−j2π/λR _i (13) Here, λ is the transmission wavelength, K is an arbitrary constant that is not zero, and R _i (i=1, 2, ..., N) is the virtual target 24 and the distance between the antennas #1 to #N, which is given by the following equation.

R _i = {(h _M + R _p tanθ _p −h _i ) ² + R _p ² } ^1/2 (14) (i = 1, 2,..., N) where h _i is the height of each antenna from the sea surface 11 and h _M is given by h _M = (h _N + h ₁ )/2 (15). The signal processing device 24 performs the arithmetic processing of equation (12) while sequentially changing the position of the virtual target 26, that is, the elevation angle θ _p . At this time, let the elevation angles for target 7 and image 8 be θ _t and θ _i , respectively, and the elevation angle θ _p is |θ _p −θ _t |<△θ (16) or |θ _p −θ _i |△θ (17) The calculation result V _IN of equation (12) when satisfying , and the elevation angle θ _p
When V OUT satisfies neither Equation (16) nor (17), the following relationship V _IN #V _OUT (18) holds true between the calculation result V _OUT of Equation (12).

Here, Δθ is an equivalent antenna beam width obtained by performing the above-described signal processing on the received signals obtained by antennas #1 to #N.

The phase correction coefficient shown by equation (13) is calculated based on the relationship between the virtual target 26 and #1 to #N when it is assumed that the reflected waves from the virtual target 26 are received by the antennas #1 to #N.
This is to correct the phase difference of the received signal due to the difference in distance with each antenna #N so that the received signal has the same phase. The situation is shown in FIG. In the figure, 30 is a virtual target 26
This is the equidistant plane from the virtual target, that is, the equiphase plane of the reflected wave from the virtual target. Now, assuming that the position of the virtual target 26 coincides with the position of the target 7, the calculation expressed by equation (12) is performed by arranging the antennas #1 to #N on 30 planes and Since the reflected waves are integrated, the calculation result is completely equivalent to receiving the reflected waves from the target 7 using a real aperture antenna with 30 mirror surfaces. Therefore, performing the arithmetic processing shown in equation (12) with the elevation angle θ _p on the signals received by the antennas #1 to #N means directing the real aperture antenna in the direction of the elevation angle θ _p and detecting the reflection from the target or image. If Equations (16) and (17) hold, it corresponds to receiving the reflected wave from the target or image with the main beam of the real aperture antenna, and conversely, Equation (16) and (17) hold. 16) and (17) do not hold, this corresponds to receiving the reflected waves from the target and the image as side lobes, and as a result, the relationship shown in equation (18) holds. Also, the beam width Δθ can be considered in the same way as in the case of a real aperture antenna, and is given by the following equation from a known formula that gives the beam width of a real aperture antenna.

Δθ=λ/(h _N −h ₁ ) (19) As described above, in the radar device according to the present invention, when receiving radio waves from a target with a radar device having a real aperture antenna with a large aperture length in the vertical direction, The phase correction coefficient given by Equation (13) can obtain the same angular resolution as the obtained angular resolution, and the beam scanning requires a large-scale driving device in radar equipment with a real aperture antenna. This can be done easily and quickly by changing the . Also, the beam width given by equation (19) is
With a real aperture antenna, this is obtained when the target is sufficiently far away, but in the device of the present invention, the phase correction coefficient in equation (13) is determined in consideration of the distance to the target. The beam width of equation (19) can be obtained regardless of .

Therefore, if the range of change in the elevation angle θ _p is made sufficiently small and the calculation of equation (12) is carried out, the calculation result shown in FIG. 7 can be obtained.

FIG. 7 is a diagram showing the effect of the present invention, and 3
1 and 32 are calculation results corresponding to target 7 and image 8, respectively. As shown in FIG. 7, the target and image can be separated by subjecting the received signals received by a plurality of antennas to signal processing as described above. By detecting the peak value of the calculation result V, the presence of the target can be detected accurately by removing the influence of multipath, and by extracting the angle information of the peak position of the calculation result V, the target can be detected accurately. You can also track.

Now, in the above explanation, it was assumed that the ranging data R _p gives the horizontal distance between the target 7 and the antenna element 18 as shown _in FIG. A slant range between antenna elements 18 is provided. Even if R _p is not a horizontal distance but a slant range, such an error in R _p will be Things that do not affect the effects of the present invention will be explained below.

First, the error occurring in the phase correction coefficient t _i calculated using equations (13) and (14) will be explained.

In equation (14), h _M + R _p tanθ _p is the virtual target 2
3 shows the altitude from sea level 11, and let this be h _p , h _p = h _M + R _p tanθ _p (20) Rewriting equation (14) using equation (20), the following equation is obtained. It will be done.

R _i = {(h _p −h _i ) ² + R _p ² } ^1/2 (21) When the radar device according to the present invention observes a target flying at a low altitude where the multiplier effect is a problem, the following equation is generally used. holds true.

R _p ≫ (h _p −h _i ) ² (22) Using equation (22), equation (21) can be approximated by the following equation.

R _i = R _p + 1/2R _p (h _p −h _i ) ² (23) On the right side of equation (23), the first term R _p is a constant with respect to the change in i, and R _p is the horizontal distance Even in the slant range, there is no phase correction error at all. Here, the horizontal distance is expressed as R _H , and the slant range R _p is expressed as the following equation.

R _p =R _H +ΔR (24) ΔR is the difference between the slant range R _p and the horizontal distance R _H , and when the altitude of the target 7 from the sea surface 11 is expressed by h _t , it is expressed by the following equation.

△R=√ _H ² + _t ² −R _H (25) R _H = 10 Km, h _t = 100 m with the radar device of the present invention
Since the purpose is to search and track low-altitude flying targets, equation (25) can be approximated by the following equation.

△Rh _t ² /2R _H (26) From equation (26), it is clear that △R/R _H ≪1 (27). Using equation (27), the second term on the right side of equation (23) can be expressed as the following equation.

The second term on the right side of equation (23) = 1/2R _H (h _p − h ₁ ) ² − △R/2R _H ² (h _p − h ₁ ) ² (28) The second term on the right side of equation (28) is This provides phase correction because the distance data is not a horizontal distance but a slant range. The magnitude of the phase correction error depends on the transmission wavelength. That is, if the second term on the right side of equation (28) is sufficiently small with respect to λ, it does not matter that the distance data is in the slant range. In the radar device according to the present invention, a transmission wavelength of about λ = 0.3 m is often used, and since the purpose is to search and track low-altitude flying targets,
At most R _H = 10 Km, h _t = 100 m, and h _p - _{h 1} = 200 m. At this time, it is clear that the following equation holds true.

△R/2R _H ² (h _p −h _i ) ² ≪λ (29) Next, the altitude of the target measured in this way
The error when the target elevation angle θ _t is derived from h _t will be explained. Given the target altitude h _t , the fifth
From the geometrical relationship shown in the figure, the target elevation angle θ _t is expressed by the following equation.

θ _t = tan ^-1 h _t −h _M /R _p (30) By substituting equation (24) into equation 30 and using equations (26) and (27), equation (30) becomes It is expressed by the following formula.

θ _t = tan ^-1 ((h _t −h _M )/R _H −h _t 2(h _t −h _M )/2R _H ³
) Equation (31) is expressed as Equation (32) using h _t <<R _H and h _M <<R _H.

θ _t h _t −h _M ／R _t −h _t ² (h _t −h _M )／2R _H3 The second term in equation (32) indicates that the distance measurement data R _p is not the horizontal distance but the slant range. It is clear that the second term is sufficiently smaller than the first term.

In this way, the radar device according to the present invention can generate the phase correction coefficient with sufficient accuracy even when using the slant range instead of the horizontal distance, and can measure the target elevation angle, achieving the effects shown in FIG. be able to.

FIG. 8 shows an embodiment in which the device of the present invention is used in a search radar, and in the figure, 33 is the radar device according to the present invention, and 34 is a known peak detection device. The calculation result V shown in FIG. 7 is transmitted from the signal processing device 24, and the peak 31 of the calculation result is detected by a known peak detection device 34, so that the target can be detected.
Utilizing this effect, the device of the present invention can be used in a search radar.

FIG. 9 shows an embodiment in which the device of the present invention is used in a tracking radar, and in the figure, 35 is a known device for extracting peak angle information. Signal processing device 2
4 to transmit the calculation result V shown in FIG. 7, and the device 35 extracts the angle information _θt of the peak 31
This is fed back to the signal processing device 24.
Since the signal processing device 24 can calculate an appropriate phase correction coefficient using the feedback angle information _θt , it can accurately track the target.

As described above, according to the present invention, the influence of multipath effects on targets flying at low altitude is removed,
Since it is possible to accurately know the existence and location of a target, it is extremely effective when used in radar equipment that detects and tracks targets at low elevation angles.

[Brief explanation of drawings]

Figure 1a is a block diagram showing the principle of monopulse radar, Figure 1b is a diagram showing the monopulse antenna pattern, Figure 2 is a diagram showing the sum and difference monopulse antenna patterns, and Figure 3 is the reception angle. FIG. 4 is a block diagram showing an embodiment of the inventive device, and FIG.
Figure 6 is a diagram showing the principle of the signal processing method, Figure 6 is a diagram showing the equivalence between this invention device and a real aperture antenna,
Fig. 7 is a diagram showing the effects of this inventive device, Fig. 8 is a block diagram of the configuration when this inventive device is used for a search radar, and Fig. 9 is a block diagram of the configuration when this inventive device is used for a tracking radar. It is a diagram. In the figure, 1 is a monopulse antenna, 2 is a hybrid circuit, 3 is an amplifier, 4 is an automatic gain control device,
5 is a phase detector, 6 is the central axis of the antenna, 7 is a target, 8 is an image, 9 and 10 are reflected waves, 11 is a sea surface, 12 is a sum pattern, 13 is a difference pattern,
14, 15, 16, 17 are reception voltages, 18 is a transmission/reception antenna, 19 is a reception-only antenna, 20 is a receiver, 21 is a transmitter, 22 is a transmission/reception switch, 23 is a ranging device, 24 is a signal processing device, 25 is a transmission wave,
26 is a virtual target, 27 is a plane where the target and image exist, 28 is an antenna array plane, 29 is an antenna central axis, 30 is an equal phase plane, 31 and 32 are calculation results,
33 is this invention device, 34 is a peak detection device, 3
5 is a peak position extraction device. In the drawings, the same or corresponding parts are indicated by the same reference numerals.

Claims (1)

[Scope of Claims] 1. An antenna in which a plurality of antenna elements, each consisting of a transmitting antenna element for transmitting radio waves and a reception-only antenna element for receiving radio waves, are arranged vertically in a row at predetermined intervals, and the antenna is directed toward a target. a transmitter that sends out radio waves to the transmitting antenna; a plurality of receivers each receiving a received signal from the receive-only antenna element; and a receiver of any one of the plurality of receivers. a ranging device that measures the slant range between the antenna and the target using the received signal obtained from the aircraft; i is the number that distinguishes the antenna element; C is the speed of light; N is the number of antenna elements; f _i
(i = 1, 2, 3, ..., N) is the transmission frequency, h _i (i
= 1, 2, 3, ..., N) is the height at which the antenna elements are arranged, R _p is the slant range measured by the above distance measuring device, θ _p is a variable for signal processing, and K is any non-zero value. When set as _{a constant} , _the correction coefficient _{t i expressed} ^{as 1/2 is} _{set for each} Calculate for each antenna element, and further calculate V = | _N 〓 ⁱ⁼¹ S _i t _i | when the signal obtained from each antenna element is S _i (i = 1, 2, ..., N), and use the above a signal processing device that outputs the peak value of the calculation result V by changing the signal processing variable θ _p , and the signal processing variable θ _p that gives the peak value of the calculation result V is set to the angle of the target position. A radar device characterized by detecting a target as information.