JPS63179273A - Holographic radar - Google Patents

Abstract

PURPOSE:To detect a target signal with good accuracy by detecting the arrival of a disturbing signal and forming a notch in the direction. CONSTITUTION:The target signal S1 and disturbing signal S2 are inputted to A/D converters 3 (3a-3c) through antenna elements 1a... and receivers 2a.... A switch 19 selects digital signals X (X1...) outputted by the converters 3 or signals (u) (u1...) transferred from a switch 18 and transfers them as signals W (W1...) to a zero data addition device 20. The addition device 20 adds mN zero data to the signals W and transfers the results to a 2nd fast Fourier transform processor 13. The processor 13 generates the spectra of the signals W and transfers them to a maximum value detector 15 through a detector 14. The detector 15 outputs the largest spectrum intensity and transfers its frequency number to a notch filter 16. The filter 16 performs arithmetic for the signals (u) for the 2nd and succeeding times to remove the signal S2 from the signals X, and the signals (u) are transferred to a 1st fast Fourier transform processor 4 through the switch 18.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a radar system that removes interference signals contained in received signals by digital signal processing of signals received by a plurality of antenna elements arranged in space. It is related to.

[Conventional technology]

As a conventional method for removing interference signals contained in signals received by radar, for example, the international academic journal [EMSCON'86J (EMSCON'86)], which was held in 1978,
6) Abraham Rupin
“Digital Multiple Beam Forming Technology for Radar (Digital Multiple Beam f
Orming Techniques for Radar
) A holographic radar disclosed in J.

FIG. 7 is a block diagram showing the configuration of a conventional holographic radar. In FIG. 7, la.

lb, lc are antenna elements, 2a, 2b, 'lc are receivers, 3a, 3b, 3c are A/D converters, 4 is a fast Fourier transform.
m; FFT) is an FFT processor as a calculation means.

31 and S2 are radio wave signals received by the holographic radar, and here, to simplify the explanation, the number of radio wave signals is assumed to be two. Sl is the target signal and S2 is the interference signal. The direction of arrival of each signal is set to θ1. It is also assumed that the total number of antenna elements, receivers, and A/D converters is N, represented by θ2.

For convenience of explanation below, antenna element 1 is shown in FIG.
a with the number #1, antenna element 1b with the number #2,
Give the antenna element IC a number #N.

A radio wave signal arriving from outside space is first captured by N antenna elements 1a to IC. The antenna elements 1a to IC transmit the captured radio signals to RF (Radio Frequency).
ency) is converted into an electric signal and transmitted to the receivers 2a to 2C. The receivers 28 to 2C internally amplify and single-phase detect the input RF multiplied signal, convert it into a baseband electrical signal, and transfer it to the A/D converters 3a to 3C. A/
Each of the D converters 3a to 3c samples and quantizes the input baseband signal internally, and generates digital signals x (1) to
x(N) and output. Digital signal x (1
) to x(N) hold the phase information of the radio signal received by the antenna elements 1a to IC, and are so-called I (in
-phase) signal and quadrature p
hase) the real part of each signal.

It is a complex signal with an imaginary part. The subscript numbers used to represent the digital signals here correspond to the numbers given to distinguish the antenna elements. For example, x(1) is the digital signal generated from the radio signal captured by the antenna element 1a. It shows that.

These digital signals are then transferred to the FFT processor 4. The FFT processor 4 internally performs a digital Fourier transform (Digital Fourier Transform).
sform ; D F T) operation to obtain the spectrum y (1) of the digital signal x (1) ~x(N)
), y (2) to y(N) are output. The subscript i used in the notation of these spectra is a numerical value representing the frequency of the spectrum, which will hereinafter be referred to as a frequency number. F
The DFT calculation performed by the FT processor 4 can align and integrate the phases of the radio wave signals individually received by the N antenna elements 1a to lc, and as a result, the power of the received radio wave signal can be calculated based on the direction of arrival of the radio wave signal. It is possible to concentrate and output the spectrum corresponding to . Arrival direction θ of radio signal
The correspondence relationship between and frequency number i is given by the following equation.

Nd5in θ i=□ (1) λ d: Antenna element spacing λ: Wavelength of the received signal Also, the spectrum intensity 1yo)12 is an amount proportional to the power of the radio signal arriving from the θ direction.

The holographic radar can spatially discriminate a plurality of radio wave signals simultaneously captured by the antenna elements 1a to IC through the above-described arithmetic processing. That is, as shown in FIG. 8, the holographic radar forms a plurality of pencil beams 5 toward the external space, and can discriminate a plurality of radio wave signals arriving at the same time according to the direction of arrival.

The number attached to the pencil beam 5 in FIG. 8 is a frequency number. For example, as shown in FIG. As shown in FIG. 9, the spectrum intensity 13F(1)12(l-1~N) output by 6.
7, the spectral peak l )F(i 1) +
26 is due to the target signal S1, and the spectral peak 1y(i2) 127 is due to the reception of the interfering signal S2.

From the above equation (1), frequency number 11 and frequency number i-
2 are given by the following equations.

In this way, the holographic radar can distinguish between simultaneously received radio signals, so here the spectrum y (
If only the spectrum y(it) is extracted while ignoring i2), it is possible to equivalently remove the interference signal S2 and detect the target signal S1.

[Problem that the invention seeks to solve]

Conventional holographic radars have attempted to remove interference signals using the methods described above, but they have had the following problems. The problem will be explained using FIGS. 10 and 11.

FIG. 10 is an enlarged view of the pencil beam 5 equivalently formed by the DFT operation performed by the FFT processor 4, where 10 is the main lobe of the spectrum and 11 is the side lobe of the spectrum.

Strictly speaking, the FFT processor 4 uses the antenna element 1a
The main lobe 10 of the spectrum can be formed by concentrating most of the power of the radio signal captured by the IC on the frequency number calculated by equation (1). However, since the number of antenna elements is limited, a part of the radio wave signal power captured by the antenna elements 1a to 1c leaks to other frequency numbers due to the well-known uncertainty principle, forming a spectral sidelobe 11. For example, in FIG. 9, 8 indicates the side lobe of the target signal S1, and 9 indicates the side lobe of the interference signal S2. As shown in FIG. 9, the sidelobes cause mutual spectral interference and can degrade the discrimination performance of radio signals.

Normally, the size of the sidelobe is about 1/100 smaller than the size of the main lobe, so unless there is a large difference between the power of the interfering signal S2 and the power of the target signal S1, interference caused by sidelobes will hardly be a problem. Therefore, the target signal can be detected accurately.

However, if the interference is intentional, the power of the interference signal S2 is 103 times the power of the target signal S1.

A device having 104 times as much power is used. In such a case, the spectrum intensity 1y(1)12 becomes as shown in FIG. 11, and the target signal S1 is buried in the side lobe of the interference signal S2, resulting in a problem that the target signal S1 cannot be detected.

As mentioned above, conventional holographic radars are configured to eliminate interference signals by forming multiple pencil beams and spatially discriminating simultaneously received radio signals. When the power of the signal is larger than that of the target signal, there is a problem that the target signal is buried under the side lobe, making it impossible to detect it.

The present invention was made to solve the above-mentioned problems, and it is an object of the present invention to provide a holographic radar that can remove interference signals and detect target signals even when the power of the interference signals is large.

[Means for solving problems]

The holographic radar according to the present invention detects the arrival direction of the interference signal using a zero data addition means, a spectrum calculation means, and a maximum value detector, and includes a notch filter that can form a notch in the detected direction in the front stage of the FFT processor. to remove interfering signal components contained in the digital signal. After repeating the above-mentioned operation several times using the switching means, the output signal of the notch filter is input to the FFT to equivalently form a multi-beam, and the target signal is detected.

[Effect]

In the holographic radar according to the present invention, before the FFT processor discriminates the radio wave signal by its internal calculation, the interference signal component is filtered several times through a digital filter having a notch in the direction of arrival of the interference signal. The sidelobes of the jamming signal are removed from interfering with the target signal.

〔Example〕

Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing one embodiment of the present invention.

In FIG. 1, 12 is a spectrum calculation means, 20 is a zero data adder, 13 is a second FFT processor, 14 is a detector, 15 is a maximum value detector, 16 is a notch filter,
18 and 19 are switching devices. Also, in Figure 1,
The symbols 1a to lc, 2a to 2c, and 3a to 3C14 are exactly the same as those used in FIG. 7. The difference between this embodiment device shown in FIG. 1 and the conventional device shown in FIG. 7 is that a notch filter 16 and a switch 18 are added in front of the first FFT processor 4, and digital signals w(1) to W(N), a spectrum calculation means 12 and a maximum value detector 15 are added. The spectrum calculation means 12 includes a zero data addition layer 20. Second FFT processor 13. and a detector 14, and calculates the spectra of the digital signals w(1) to W(N) by the periodogram method.

Switch a19. Zero data additional layer 20. Second OFFT processor 13. Detector 14. Maximum value detector 15. Notch filter 16. and the switch 18 receives the digital signal x
This is a means for repeatedly performing the operation of detecting and removing the arrival direction of the interference signal S2 from (1) to x(N), and these operations will be explained below.

FIG. 3 is a detailed block diagram of the switch 19. Third
In the figure, 22 is a counter and 23 is a switch changeover device. The switch 19 connects the A/D converters 3a to 3.
Digital signal x (1) to x(N) transferred from C
, or the signal u (1
) ~ u (N), and the signal w (1) ~
It is transferred to the zero data adder 20 as w(N). The counter 22 and switch changeover device 23 are used for this selection. The initial state of the counter 22 is zero, and the signal x
(When 11~x(N) is input to the switch 19
If the counter 22 is zero, the switch switching device 23 receives the signal x (1) w x (N) A(
Connect so that the signal w (1) ~ w (N), and if the counter is not zero, connect so that the signal u (1) ~ u (N) becomes the signal w (1) ~ W (N) do. FIG. 4 is a detailed block diagram of the zero data adder 20. In FIG. 4, 24 is a register that stores the signals W(1) to w(N) transferred from the switch 19, adds, for example, (mN) zero data to the signals W(+ ) ~w
(m N) to the second FFT processor 13.

The contents of the signals W(N+1) to w(mN) are zero.

Performing FFT using data with such zero data added corresponds to interpolating data on the frequency axis,
A more precise spectrum is calculated by performing FFT with zero data added than by performing FFT without adding zero data.

The calculations carried out internally by the second FFT processor 13 are completely equivalent to the calculations carried out by the first OFFT processor 4, and are based on the spectra y (1) - y ( m N) and transfer them to the detector 14. The detector 14 is y(1) to y
(mN) absolute square value 1 y(1) l 2~l y(
mN) l 2 and transfer these to the maximum value detector i5.

Now, as shown in FIG. 1, the holographic radar of this embodiment receives two radio signals: a target signal s1 (direction of arrival is θ1) and a jamming signal S2 (direction of arrival is θ2). Considering the case where the power of S2 is sufficiently larger than that of the target signal S1, the distribution of the spectrum intensity 13F(1)12 (i-1 to mN) output by the detector 14 is as shown in FIG. As is clear from Figure 1L, the maximum value of 13'(i)12 is I y(i 2) +
It is given by 2. Since 12 corresponds to the arrival angle of the interference signal according to equation (3), detecting 12, that is, 1
Detecting the maximum value of yoN2 is equivalent to detecting the arrival angle of the interfering signal. The maximum value detector 15 detects the arrival direction of the interference signal based on the principle described above, and detects the N spectrum intensities 1y(
1) Execute the magnitude comparison of 12 (n = 1 to N) and detect the maximum spectral intensity 1y (] November, +7 (+2)
Frequency number 12 giving +2 is transferred to the notch filter 16 as an output signal.

FIG. 5 is a detailed block diagram of the notch filter 16.

In FIG. 5, 25a, 25b, and 25C are complex multipliers, 26a, 26b, and 26c are complex subtracters, and 27 is a load calculation means. Notch filter 16 is A/D converter 3a
, 3b, 3c, the digital signals x(1)~
From the second time onwards, the calculation shown in equation (4) is performed on the signals u (1) to U-(N) transferred from the switch 18 to X(N), and the signal u (1) -1) generate.

u(1)=x(i-!-1)-W-x(1)i
-1 to N-1...(4) The subtraction appearing in equation (4) is performed by the ri prime subtractors 26a, 26
b, 26 c, and the multiplication is performed by complex multiplier 25
a, 25b, and 25c. For example, u
(1) is generated using a complex multiplier 25a and a complex subtracter 26a. Complex multiplier 26a.

The same load W is used for all the loads applied to 26b and 26c, and the load W is generated by the load calculation means 27.

The load calculation means 27 generates the load W by internally executing the calculation shown in equation (5) based on the frequency 12 which is the signal output by the maximum value detector 15.

By executing the above-mentioned operations internally, the notch filter 16 converts the digital signals x(1) to x(N)
The interference wave signal S2 included in the interference wave signal S2 is removed. Target signal s1.
Since the interference signal S2 is a plane wave, the digital signal x
(1) to x(N) can be expressed by the following formula.

X (1)x S, o-Jafisinθ+
−j straddles εjslnθ” −(
6) + 32e n=1~N In equation (6), the first term is the term expressed as a result of receiving the target signal SlO only, and the second term is the term expressed as the result of receiving the interference signal S2. be. exp shown in the second term
The phase term [-j and ff sin θ2] represents the phase difference due to the time delay when the interference signal S2 arrives at each of the antenna elements 1a to 1c.

Similarly, the phase term shown in the first term represents the phase difference due to the time delay when the target signal S1 arrives at each antenna element. Expressions (5) and (6) are converted to expression (4) -3e
ejλyc4tsthθc[4s+hθ--- for 81 units
2jf], ]3yueJ2t-j'1jlrl9J
[, λt-4Ls+nθx -JllC4ko e i-1~N-1...(7) Furthermore, by substituting equations (2) and (3) into equation (7), the second term [] becomes O, and formula (8) is obtained.

u(1)=[-yut+-,-jyuχ,+]s,
, j4. B Srre θIi! i~N-1...(8) As shown in equation (8), the signal u(1) does not contain any interference signal component, and the notch filter 16 converts the digital signal x(1)~ Interfering signal S2 included in x(N)
It can be seen that the components have been removed. As shown in FIG. 6(a), this reduces the reception gain of the antenna elements 1a to 1c by the interference signal 32. This corresponds to shaping to be 0 with respect to the direction of arrival θ2.

As mentioned above, the output signal u (
1)~u(N)&yo operates to remove the interference signal S2 component, but in one filtering, the interference signal S2
There are many remaining ingredients. Therefore, the notch filter 16
You need to pass it through.

In addition, the notch filter 16 for each filtering
Since the maximum value of the spectral intensity of the output signals u(1) to u(N) of the notch filter 16 also changes, the output signal u(
1) ~u(N) must be transferred to the spectrum calculation means 12. Therefore, the switch 18 performs the following operation.

That is, first, the output signal u (1) of the notch filter 16 ~
u (N) is transferred to the switch 18. FIG. 2 is a detailed block diagram of the switch 18. In FIG. 2, 20 is a counter, and 21 is a switch changeover device. The initial value of the counter 20 is 0, and the signals u(1) to u
(N) is incremented by 1 each time it is input to the switch. The switch switching device 21 is, for example, a counter 20.
until P, the signal u (1) transferred to the switch 18
~u(N) is connected to the switch 19 and the notch filter 16, and when the counter 20 exceeds P, the signal u(11~u(N) is transferred from the notch filter 16.
) is connected to the first FFT processor 4. The signals u(1) to u(N) transferred from the switching 118 to the first FFT processor 4 do not contain the interference signal S2 component due to the effect of the notch filter 16, so the first FFT processor 4 outputs The spectrum V (
The intensity 1v(1)12 of 1) is as shown in Figure 6 (mountain).

As shown in Figure 6), the intensity IV(
1) Only the spectral peak 6 generated by integrating the power of the target signal S1 appears at +2, and the target signal S1 can be detected.

〔Effect of the invention〕

As described above, according to the present invention, the holographic radar is configured to detect the arrival of the interference signal and form a notch in that direction, so that the interference signal can be removed and the target signal can be detected with high accuracy. There is an effect.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a holographic radar according to an embodiment of the present invention, FIG. 2 is a block diagram showing the configuration of the first switching device, and FIG. 3 is a block diagram showing the configuration of the second switching device of the radar. 4 is a block diagram showing the zero data adder of the radar, FIG. 5 is a detailed block diagram showing the structure of the notch filter of the radar, and FIG. 6(a) is a block diagram of the notch filter. A diagram showing reception gain, Fig. 6 (
b) is a diagram showing the switch intensity distribution, FIG. 7 is a diagram showing the configuration of a conventional holographic radar, FIG. 8 is a diagram showing the multi-beam formed by the holographic radar, and FIG.
The figure shows the spectral intensity, FIG. 10 is an enlarged view of the pencil beam, and FIG. 11 is a diagram showing the spectral intensity. 1a to IC...Antenna element, 2a to 2C...Receiver, 3a to 3C...A/D converter, 4...FFT processor, 5...Pencil beam, 6, 7... Peak, 8.9... Side lobe, 10... Main beam, 11... Side lobe, 12... Spectrum calculation means, 13... FFT processor, 14... Detector, 15... - Maximum value detector, 16... Notch filter, 18, 19... Switcher, 20... Counter, 21... Switch switching device, 22... Counter, 23... Swift switching device, 24...Register, 25a-25c...Complex multiplier, 26a-26c
...Complex subtractor, 27...Load calculation means. Note that the same reference numerals in the figures indicate the same or equivalent parts.

Claims (4)

[Claims] (1) A plurality of antenna elements, a plurality of receivers connected to the antenna elements, a plurality of A/D converters connected to the receivers, and a plurality of A/D converters output from the A/D converters. A holographic radar is equipped with FFT calculation means for performing fast Fourier transform on a digital signal, and is configured to digitally process a received signal to remove interference signals contained in the received signal. data addition means; spectrum calculation means for inputting the digital signal to which the zero data has been added and calculating the spectrum of the digital signal; and inputting a plurality of signals output by the spectrum calculation means for calculating the spectrum of the output signal. maximum value detection means for detecting a maximum value; and a specific frequency included in the digital signal that is inserted before the FFT calculation means and output from the A/D converter according to the detection result of the maximum value detection means. a notch filter for removing the component; and a notch filter for outputting the output signal of the notch filter to the notch filter and the zero data addition means for a predetermined number of cycles after the start of processing, and to the FFT calculation means after the elapse of the predetermined number of cycles. In the first cycle after the start of processing, the digital signal output from the A/D converter is input to the zero data addition means, and in the second cycle and thereafter, the output of the first switching means is inputted to the zero data addition means. and second switching means for inputting the zero data adding means to the zero data adding means. (2) The spectrum calculation means is comprised of an FFT calculation means for fast Fourier transforming the digital signal to which the zero data has been added, and a calculation means for calculating the absolute square value of the signal output by the FFT calculation means. A holographic radar according to claim 1, characterized in that: (3) The first switching means includes a counter that counts the number of times the digital signal from the notch filter is input, and a switch switching device that controls switching of the switch based on the count value. A holographic radar according to claim 1 or 2. (4) The second switching means has a counter that counts the number of times the output signal of the A/D converter is input, and a switch switching device that controls switching of the switch based on the count value. A holographic radar according to any one of claims 1 to 3.