JPH02206782A - Holographic radar - Google Patents

Abstract

PURPOSE:To improve accuracy by forming multibeams by a digital multibeam forming means and measuring an angle by a multibeam angle measuring means using the adjacent three beams among these beams. CONSTITUTION:The hologram radar is provided with high-speed Fourier transform means for frequency analysis between respective signal receiving machines 3 and the digital multibeam forming means 5 in order to discriminate the received signals by Doppler frequency differences and is provided with the multibeam angle measuring means 10 using the adjacent three beams behind the digital multibeam forming means 5. The multibeams are formed by the digital multibeam forming means 5 and the target angle is measured by using the above-mentioned three beams by the multibeam angle measuring means 10 connected to the digital multibeam forming means. The measurement angle with the higher accuracy than in the case of using the two beams is possible in this way.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to improving the resolution and angle measurement accuracy of a holographic radar.

[Conventional technology]

Figure 4 shows the applicant's earlier application, Japanese Patent Application No. 1986-1.
It is shown in the specification of No. 8864, and in Figure 2 (tl
is an element antenna, (2) is an antenna array consisting of N element antennas + 11, and (3) is each of the above element antennas (
A receiver (C4) is connected to the receiver (31), which amplifies and detects the high frequency signal received by the element antenna (1), and performs A/D conversion.
An FFT means (5) for frequency-analyzing the time series of the digital complex video signal outputted and discriminating signals with different Doppler frequencies is connected to this FFT means (4), and each FFT means (4) A digital multi-beam forming means (61) is connected to each digital multi-beam forming means (5) for independently forming a multi-beam for each frequency component of
5) is a multi-beam angle measuring means that measures the entire arrival angle of reflected waves from a target using two adjacent beams of the nine multi-beams formed in step 5).

Further, FIG. 5 shows a specific configuration of the multi-beam angle measuring means (6), and (7) shows the multi-beam angle measuring means (
6) an adder/subtractor that calculates the sum and difference of two adjacent beams of the multi-beam input to (81 is the adder/subtractor (7)
) divider that divides the difference output by the sum output.

(9) is an angle converter connected to the divider (8) and converts the output of the divider (8) into an arrival angle of radio waves.

Next, the operation will be explained.

The high frequency signal received by the N element antenna (1) is
N receivers (31) amplify and detect the signal and convert it into a digital complex video signal. Each of the N receivers (31)
time series sn of the digital complex video signal output from 31, / (n=N/2 g...' *
0*..., N/2-L/=0.1.2. ...
, -1) is input to N FFT means (4),
Frequency analysis is performed using point FFT. n represents the number of the corresponding element antenna (1) and receiver (31;
1 represents a time series pulse hit number. FFT means
The time series an,/ input to 41 is the spectrum/l/
8n, k (n=-N/2.

-, O, ., N/2-L k:o, 1.2-, K
-1) Km' is converted.

The outputs Sn subjected to frequency analysis by the N FFT means (4) are input to the same digital multi-beam forming means (51) for each same frequency, and a multi-beam is formed for each frequency component. , N 0 FFT means [4
)'s output Sn, k (n=-N/2,
-0, ..., N/2) is input to the digital multi-beam forming means (51), and the N multi-beams B shown in the formula 1g+21 are input to the digital multi-beam forming means (51),
r, k (r=-N/2. ・-, O,-, N/2-1)
is formed.

In this way, the N multibeams are independently formed for each frequency component by the multibeam forming means (5)K.

With the above configuration, even if multiple targets are close to each other with two beam widths or less than the angular resolution of the multi-beam after formation, the FFT one step ( 4) by reducing the frequency resolution.

Each individual target has a different beam BY,k (r=
: N/2.・", OH"'e N/2 1 v
Each target is separated within "L 1 + 2 m"' -1).

The outputs of the K digital multi-beam forming means (5) are respectively input to the multi-beam angle measuring means (61). ), the operations of the digital multi-beam forming means (5) and the multi-beam angle measuring means (6) K will be explained here. N multi-beams Br, k (r=-N/2..., 0...) formed by the beam forming means (51)
, N/2-1).

It can be expressed as

Here, let the average value of the angles of the two beams be ar.

Eaves = (αr+αr-1)/2 (
5), using the beam spacing Δαr.

αr=ar+Δαr/2l
etαr−1=drunkenness−Δαr/2
(It can be expressed as 71. At this time.

cos ar sin Qr'Δαr/
2 F81cos ar-j middle cos ar
The approximate expression +sin ar a Δar/2 f91 holds true. (81st formula and (9) formula)
By substituting the equation and the equation (41), the sum of the two beams Σr,
To find the difference Δr,k.

Since two adjacent beams Br, and B
r-1, using angles αr and αr-1f, respectively.

, (2cos(gnd 5inarΣar/λ))α
G* (2j 5in(rndsinar Δar/λ
)) becomes at+. That is, in the adder/subtractor (7), the (
n Br, k and Br-1 shown in formula 31 and formula (4)
, and output the sum Σr, the difference Δr, and the sum Σr shown by the 01st formula and the Uth formula. Σr, Δr,
is input to the divider (8).

Fist (2cos(xnd 5inarΔar/λ))! 1
3 is output.

The angle converter (9) uses the relationship between Δr, Σr, and α to calculate the output Δr, Σr,k of the divider (8).
is converted into the arrival angle α of the radio wave.

As described above, by configuring the multi-beam goniometer (6), the arrival angle α of the radio wave can be calculated using the direction angle α of the two beams.
Highly accurate measurement is possible between r and αr-1.

Generally, near the boresight of a monopulse antenna, the relationship between the angle measurement value α and Δr, k /Σr, can be approximated by a straight line with a slope of km, so the signal-to-noise power ratio S
The relationship expressed by equation +13 holds true between NR and the normalized angle measurement error σα/αB (rms value). However, σα/αB is defined by normalizing the angle measurement error by a 3 dB beam width.

σα／αB=1/(km aBV/l碩 α
Jkm: 2.776 αq/αB2
(141Here, if the angular difference in the boresight direction of the two antennas is 2αq, e km is given by the r141 formula.

[Problem to be solved by the invention]

Since the conventional holographic radar is configured as described above, there is a difference between the signal-to-noise power ratio SNR and the normalized angle measurement error σα/αB (rms value).

There is a problem in that even if the relationship of equation +13 holds true and the SNR increases, the standardized angle measurement error Iri does not become much smaller.

This invention was made to solve the above-mentioned problems, and because it uses three adjacent antenna beams, it is easier to use than the monopulse angle measurement method that uses two antenna beams. The purpose is to obtain a holographic radar that can perform angle measurement with higher precision.

[Means to solve the problem]

The holographic radar according to the present invention is provided with fast Fourier transform means for nine-frequency analysis between each receiver and digital multi-beam forming means in order to discriminate received signals based on Doppler frequency differences, and with digital multi-beam forming means. After the means, a multi-beam angle measuring means using three adjacent beams is provided.

[Effect]

In this invention, the digital multi-beam forming means forms a multi-beam, and the multi-beam angle measuring means connected to the digital multi-beam forming means measures three adjacent multi-beams formed by the digital multi-beam forming means. The beam is used to measure the angle of the target.

[Embodiments of the invention]

Embodiments of the present invention will be described below with reference to the drawings.

In Figure 1, (11 is an element antenna, (2) is N
Antenna array consisting of element antennas (1), (3
) is connected to each of the above-mentioned element antennas (1), and a receiver (41 is connected to the above-mentioned receiver (31) and receives FFT means for frequency-analyzing the time series of digital complex video signals output from the machine (3) and discriminating between signals having different Doppler frequencies.

(51 is a digital multi-beam forming means which is connected to this FFT means (41) and forms a multi-beam independently for each frequency component of each FFT means (4); α1 is a digital multi-beam forming means connected to this FFT means (41); connected,
This multi-beam angle measuring means measures the arrival angle of the reflected wave from the target using three adjacent beams of the multi-beam formed by the digital multi-beam forming means +51.

Moreover, FIG. 2 shows a concrete tank F1i of the multi-beam angle measuring means aO, and (9) is the arrival angle of radio waves from three adjacent beams of the multi-beam input to the multi-beam angle measuring means αυ. It is an angle converter that converts to .

Next, the operation will be explained.

It is assumed that the voltage gains G(α) of three adjacent beams can be approximated by a Gaussian pattern as shown in Equation 09.

G(αl= Goexp (-a 2 (α-a*)2
/2) (15 here.

a2= 2.776 / αB2Qf3 and y G
o represents the maximum voltage gain, α8 represents the half width of the beam, and α1 represents the central angle of the three beams.

At this time, each beam output when the arrival angle of the radio wave is α0 is B1=Goexp(-a2(a.-a,)2/2)
(LηB2 = Go exp (-a2(a,
3-a2)2/2)uB,=Qo6z
p (-a2(a, 3-(!3)2/2)
It becomes +19. Here, if Qo=j, then the αη equation ~
Q! Equation 1 is Ih = exp (-a2(ao-α1)2/2)
anB2=exp (-a2(αo-α
2)2/2) alB,=exp (-a
2(a.-(E3)2/2).

becomes. The logarithmic expression of formulas 211 to ① is b1 = 201
OgCeXp(-a2(α.-α1)2/2)]=ka
2(α.to,)2b2==ka2(a.−α2)2α b3”ka2(α.−α5)2(251k>10/1n
It will be 10 m. At this time, 2 points (α1.bl person (α21b2) 1 (α3+b3)
is a point on the parabola b=ka2(a.-a)2,
The α coordinate of the vertex of the parabola is α0.

Here, when the difference between the center angles of adjacent beams is 2α9, α. is α. =α2+α, (b3-bl')/(2b2-(
b, +bS ) 1 is given by.

Now, assuming an antenna α, /α, = Q, 53, the signal-to-noise power ratio SNR and the simplified angle measurement error σα
/αB (rms value) is shown in FIG.

It can be seen from FIG. 3 that the measurement according to the present invention has higher precision than the conventional method.

By configuring the multi-beam goniometer αG as described above, the arrival angle α of the radio wave can be changed to the direction angle αr of the three beams,
, αr+1. It can be measured with high precision based on αr+2.

〔Effect of the invention〕

As described above, according to the present invention, the FFT means connected to each receiver output discriminates a plurality of targets that are close to each other below the angular resolution, and after the discrimination, multi-beams are formed independently for each frequency component. Since the angle can be measured by the multi-beam angle measuring means using three adjacent beams, the angle can be measured with higher precision than when two beams are used.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a holographic radar according to an embodiment of the present invention, and FIG. 2 is a structure 532tg of a multi-beam angle measuring means of this holographic radar. FIG. 3 is a characteristic diagram showing the angle measurement characteristics during operation, and FIG. 4 is a configuration diagram of a conventional holographic radar. FIG. 5 is a block diagram of the multi-beam angle measuring means. In the figures, (1) is an element antenna, (31 is a receiver, (41 is an FFT means, (51 is a digital multi-beam forming means, and α1 is a multi-beam angle measurement means. The same reference numerals in each figure are the same. or a significant portion.

Claims (1)

[Claims] 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, a time series output from each of the receivers. a plurality of fast Fourier transform means for frequency-analyzing each signal; a plurality of digital multi-beam forming means for forming a multi-beam for each frequency component of a spectrum that is an output of the fast Fourier transform means; A holographic radar comprising: multi-beam angle measuring means that receives the multi-beam formed by the forming means and measures the arrival angle of radio waves using three adjacent beams.