JPH0511912B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to improving the target search and target tracking capabilities of a holographic radar.

[Conventional technology]

Figure 6 is from the international academic journal “Eascon-78”
(IEEE, EASCON-78) ABRAHAM E.RUVIN and LEONARD Weinberg (IEEE, EASCON-78)
WEINBERG)'s paper "Digital multi-beam forming technology for radar (DIGITAL MALTIPLE)"
BEAMFORMING TECHNIQUES FOR
1 is a diagram showing the configuration of a conventional holographic radar shown in ``RADAR''. In the figure, 1 is an element antenna, 2 is an antenna array consisting of N element antennas, 3 is connected to each element antenna 1, the element antenna 1 is an RF amplifier that amplifies the received high frequency signal, and 4 is an RF amplifier that amplifies the high frequency signal. A mixer for converting into an intermediate frequency signal, 5 an IF amplifier for amplifying the intermediate frequency signal output from the mixer 4, and 6 a mixer for converting the IF amplifier output into a baseband complex video signal while preserving the phase of the intermediate frequency signal. 7 is I (in phase) of the phase detector 6.
Low pass filter (LPF) connected to each output of channel and Q (quadrature) channel, 8
is an A/D converter that is connected to the LPF 7 and performs A/D conversion of the complex video signal converted to baseband; 9 is an output level adjuster that performs weighting to adjust the sidelobe level during beam forming; Reference numeral 10 denotes a receiver composed of the above-mentioned elements 3 to 9. Reference numeral 11 denotes a digital multi-beam former that performs digital calculations on the output of the receiver 10 connected to each element antenna 1 to form a number of multi-beams corresponding to the number of element antennas.

Next, the operation will be explained.

The high frequency signal received by the N element antennas 1 is amplified by the RF amplifier 3, converted to an intermediate frequency signal by the mixer 4, and amplified again by the IF amplifier 5. This intermediate frequency signal is phase detected by a phase detector 6 and converted into a complex video signal consisting of an I channel and a Q channel. After the complex video signal is band-limited by LPF 7, it is sent to A/D converter 8.
The signal is converted into a digital complex video signal by a weighted output level adjuster 9 for sidelobe reduction during beam forming, and then input to a digital multi-beam forming means 11. At this time, as shown in FIG. 7, the direction in which the N element antennas are lined up is the X axis, the angle between the arrival direction of the high frequency signal, that is, the radio wave, and the X axis is the arrival angle α of the radio wave, and the The spacing of antenna 1 is d, the wavelength is λ
Then, the phase difference between signals received by adjacent element antennas is 2π(d cosα)/λ, so
In the digital multi-beam beamformer 11,
Equation (1) below Br= _N/2-1 〓 〓 ^K=-N/2 Wk exp(j2πk d cos α/λ)・exp(−j(2
π/N)kr)...(1) r=-N/2,-N/2+1,...,0,...,
By calculating N/2-1, αr=cos ^-1 (rλ/Nd)
N beams with maximum gain (r=-N/
2,...,0,...,N/2-1) can be formed simultaneously. However, in Equation (1), Wk is a weighting coefficient for sidelobe suppression, and is given by the output level adjuster 9 in the receiver 10 connected to each antenna element.

At this time, the beam width δr of the r-th beam is given by the following equation (2) δr=wλ/Ndsin αr (2), and the interval Δαr between the r-th and r-1th beams is , is given by Equation (3) Δαr=αr−αr _-1 =λ/Ndsin αr ……(3). w in equation (2) is a constant determined by the weighting coefficient Wk, and is generally set to about 0.88 to 1.3.

[Problem that the invention seeks to solve]

By the way, the above-mentioned digital multi-beam former 1
1, Equation (1) is an equation indicating a discrete Fourier transform (DFT). In general, a Fast Fouriet Transform (FFT) algorithm is used to efficiently form multiple beams within the field of view, that is, the observation range determined by the beam width of the element antenna. Although FFT has very good computational efficiency, the direction of each beam formed is fixed, which makes it useful in search mode.
It is not suitable for a mode in which the beam is continuously scanned to track a target. In addition, although DFT allows the beam to be continuously scanned in any direction, the amount of calculation required is larger than that of FFT.
It is less practical for forming multi-beams.

As described above, in conventional holographic radars, if emphasis is placed on calculation efficiency in search mode, beam scanning in tracking mode becomes discontinuous, and if emphasis is placed on continuity of beam scanning in tracking mode, the beam scanning required for multi-beam formation in search mode becomes discontinuous. There was a problem that the amount of calculation was large and search and tracking could not be performed at the same time.

This invention was made to solve the above-mentioned problems, and aims to provide a holographic radar that can efficiently form multiple beams for search mode and beams for tracking mode at the same time. .

[Means for solving problems]

The holographic radar according to the invention is equipped with a buffer memory that stores the output of the receiver connected to each element antenna, and also has a digital multi-beam former using FFT for the search mode. a beam direction controller for controlling the directions of the two beams for use;
It is equipped with two beam formers that form two tracking beams using DFT according to this instruction, and an angle meter that measures the angle of the target being tracked using the two tracking beams. .

[Effect]

In this invention, digital video complex signals obtained by a plurality of receivers are stored in a buffer memory, and a multi-beam for search is efficiently formed using FFT to detect a target, and only the beam direction in which the target exists is detected. By reshaping the tracking beam using DFT, search and tracking can be performed efficiently at the same time.

〔Example〕

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
In FIG. 1, 1 is an element antenna, 10 is a receiver, 12 is a buffer memory for storing digital complex video signals output from each receiver 10, and 1
1 is a digital multi-beam former that performs FFT on the output of the buffer memory 12 to form a multi-beam for searching; 13 is a target detector that determines the presence or absence of a target for each of the formed multi-beams; 15 is a A beam direction controller 16 controls the direction of the tracking beam, and a beam former 16 performs DFT to form a tracking beam. 21 is a goniometer that measures the angle of the target using the outputs of the two beam formers 16; in this goniometer 21, 17 is a complex source calculator; 18 is a complex subtracter;
19 is a divider, and 20 is an angle converter.

Next, the operation will be explained. Since the operation of the receiver 10 is the same as that of the conventional device, the operation of the buffer memory 12 and below will be described in detail here.

The outputs of the N receivers 10, ie, digital complex video signals, are stored in a buffer memory 12. The digital multi-beamformer 11 reads out the digital complex video signal from the buffer memory 12 and uses the FFT algorithm to calculate αr=cor ^-1 (rλ/Nd) r=-N/2,...,0,...,N / _2-1 in ^the αr direction of
π/N)kr)... (1) Using r=-N/2,...,0,...,N/2-1, create N multi-beams as shown in Figure 2.
Br(r=-N/2,...,0,...,N/2-
1) Form. Each beam output Br formed by the digital multi-beam former 11 is input to the target detector 13, where the presence or absence of a target is determined for each beam, and the beam direction αr of the beam Br where the target exists is determined by the beam direction controller. Sent to 15.

In the beam direction controller 15, first, β=αr ...(4) Δβ=λ/(Nd sinβ) ...(5), and the directions of the two tracking beams β ₁ and β ₂ are set as β ₁ =β+Δβ/ 2 ...(6) β ₂ =β−Δβ/2 ...(7) Beam directions β ₁ and β ₂ are input to two beamformers 16 . Here, in order to distinguish between the two beamformers 16, the beamformer 16 to which β ₁ is input is called DFT1, and the beamformer 16 to which β ₂ is input is called DFT2.

In DFT1 and DFT2, N reception outputs, that is, digital complex video signals, are read out from the buffer memory 2, respectively, and the tracking beam _T1 is directed in the direction _β1 , and the tracking beam _T2 is directed in the direction _β2 according to equation (8) and ( 9) Formed by formula.

T ₁ = _N/2-1 〓 〓 ^K=-N/2 Wk exp(j2πk d cos α／λ)・exp(−j2πk
d cos β ₁ /λ)……(8) T ₂ = _N/2-1 〓 〓 ^K=-N/2 Wk exp(j2πk d cos α/λ)・exp(−j2πk
d cos β ₂ /λ)... (9) An example of T ₁ and T ₂ is shown in FIG.

Output of beamformer 16 of DFT1 and DFT2
T ₁ and T ₂ are input to the complex adder 17 and complex subtracter 18 in the goniometer 21, and the sum = T ₁
+T ₂ and the difference Δ=T ₁ −T ₂ are determined. At this time, the approximate expression cos β ₁ ≒cosβ−sinβ・Δβ/2 ...(10) cos β ₂ ≒cosβ+sinβ・Δβ/2 ...(11) holds, so 〓 and Δ are 〓= _{N/ 2-1} 〓 〓 ^K=-N/2 Wk exp(j2πkd(cosα−cosβ))・(2cos(π
kd sinβΔβ/λ))……(12) Δ= _N/2-1 〓 〓 ^K=-N/2 Wk exp(j2πkd(cosα−cosβ.))・(2j sin
(πkd sinβΔβ/λ))...(13) The relationship between Δ and β is shown in FIGS. 4a and 4b. As shown in the figure, when the target angle, that is, the arrival angles α and β of the radio waves match, the gain of 〓 takes the maximum value, and the gain of Δ takes the minimum value.

The sum 〓 and the difference Δ are input to the divider 19, and Δ/
〓 is output. At this time, there is a difference between the output Δ/〓 of the divider 19 and the angle β of the tracking beam.
Since the relationship shown in the figure holds, the angle converter 20 converts Δ/〓 into angle β, thereby making it possible to measure the arrival angle of the radio wave. This angle measurement result is fed back to the beam direction controller 15 again and is used to control the beam direction during the next beam formation.

As described above, the output of the receiver 10 is temporarily stored in the buffer memory 12, and is supplied to the digital multi-beam former 11 using FFT for forming multi-beams for search, and at the same time, it is used to form beams for tracking. By supplying the beam to the beamformer 16 using DFT, it becomes possible to perform search and tracking at the same time.

At this time, a search multi-beam is formed using computationally efficient FFT, the target is detected, and then beamforming is performed using DFT only for the detected target direction, thereby reducing the amount of calculation required for beamforming. It is possible to reduce the

Note that in the above embodiment, the case of a linear array antenna in which the element antennas are arranged in a straight line in the X-axis direction was explained, but in the case of a planar array antenna in which the element antennas are arranged in a two-dimensional array in the X and Y axes in a planar manner. Similar effects can be obtained by adopting the same configuration as in the above embodiment in both the X and Y axes.

〔Effect of the invention〕

As described above, according to the present invention, in addition to the digital multi-beam forming means for forming multi-beams for searching using FFT, a buffer memory is provided for storing digital complex video signals obtained from a plurality of receivers, Furthermore, since a beam forming means for forming a tracking beam using the signals stored in the buffer memory and an angle measuring means for measuring the angle of the target using the output of the beam forming means are provided, searching and tracking of the target can be performed easily. It has the effect of being efficient and being able to be executed simultaneously.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a holographic radar according to an embodiment of the present invention, and FIGS. 2, 3, 4 a, b, and 5 are diagrams for explaining the operation of the holographic radar. , FIG. 6 is a block diagram of a conventional holographic radar, and FIG. 7 is a diagram showing the operating principle of the conventional holographic radar. 1...Antenna, 10...Receiver, 11...Digital multi-beam former, 12...Buffer memory, 13...Target detector, 15...Beam direction controller, 16...Beam former, 17... Complex adder, 18... Complex subtractor, 19... Divider,
20... Angle converter, 21... Angle measuring instrument. Note that the same reference numerals in the figures indicate the same or equivalent parts.

Claims (1)

[Claims] 1. In a holographic radar that forms a multi-beam using digital complex video signals output from each receiver connected to each of a plurality of element antennas, the digital a buffer memory for storing a complex video signal; a digital multi-beam forming means for reading out the digital complex video signal from the buffer memory and forming a multi-beam with a fixed direction; and determining the presence or absence of a target for each of the formed multi-beams. a target detector connected to the buffer memory and forming two beams in any direction independently of the digital multi-beam forming means; A beam direction controller for controlling the directions of two beams formed by the beam forming means, and an angle measuring means for measuring the arrival angle of radio waves using the two beams formed by the beam forming means. A holographic radar featuring 2. The digital multi-beam forming means forms multiple beams by fast Fourier transform, and the beam forming means forms two beams by discrete Fourier transform. The holographic radar according to item 1.