JPS63186174A - Holographic radar - Google Patents

Abstract

PURPOSE:To find the position of a target speedily by finding the position of the target as an angle with a continuous wave signal and ranging the angle of the target with a pulse wave signal. CONSTITUTION:The continuous signal from a continuous wave transmitter 6 is radiated as a radio wave through a transmitting antenna 9. The radio wave reflected by the target is received by N receiving antennas 1 and a carrier frequency is removed by a local oscillation distributing circuit 2. Then a detecting circuit 5 detects the direction where the target is present through a beam generating circuit 3. A controller 10 switches a switch 8 after the target direction is detected to connect a pulse transmitter to the antenna 9, and sends a pulse signal to a certain repetitive period. Then the reflected wave from the target is inputted to a single beam generating circuit 4 through the antenna 1 and circuit 2. The circuit 4 performs ranging to the target in the target direction obtained at the time of the continuous wave transmission to find the direction of the target and the distance to the target efficiently.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a holographic radar that forms multiple beams.

[Conventional technology]

Figure 2 is from "Digital Multibeam Forming Technology for Radar" by A.E., Lupin, L. and Weinbarb.
uvin, L., Weinberg Digital
Multiple Beamforming Tech
``niques for Radar'' E/l5
cON 1978), P, P 152-163; In the figure, 1 is a receiving antenna, 2 is a local oscillator distribution circuit, and 3 is a beam forming circuit.

In a circuit configured in this way, the radio waves reflected by the target are: rice, ..., 1 (K-1), appetizer, rice (K+1).

. . , received by N receiving antennas 1 represented by 4N-1. The received wave by the receiving antenna at tK is 5
k(t)=f(t-rp) ・e x p(j(2π
fd t+φ))−e x p(j′2πfo(L
+ to -d CO3 (2/C))...(1) K-to 0. 1. 2. ..., is represented by N-1. Here f(t) ・e x p (j 2πfot
) is the transmission pulse waveform (where fO is the carrier frequency), rp
is the round trip propagation delay time from the transmitting antenna to the receiving antenna 1 via the target, fd is the Doppler frequency due to the movement of the target, φ is the reflection coefficient of the target and the amount of phase change based on the above τp, and d is the arranged receiving antenna 1 interval, α
is the array speed of one receiving endina 1. From the receiving antenna output shown in equation (1), the local oscillator distribution circuit 2 picks up the carrier frequency fO, then equation (1) becomes 5k(t)-f(t-1) ・e X p (j(2πf
d t+ φ))・e xp(j 2πK −d c
os a /λ)...(2) K=0. 1. 2. ..., given by N-1. Here, λ is the wavelength of the carrier wave.

Here, as an algorithm used when forming a beam by the beam forming circuit 3 from the output shown in equation (2),
For example, D F T (Discrete Fourie
rTransform ), the output of the beam forming circuit 3 is Br=f(t-rp) ・ e x p (j
(2πfd is 10φ))・ΣWk e xp(j
2πK d cos a/λ), exp(-j2π
・Kr/N) ・(3) r=o, 1, 2. -, N
−1. Here, Wk(k・0.1,2...
, N-1> represents a weighting coefficient, and r represents a beam number. Equation (3) is the equation for beam i when the receiving antennas 1 are arranged in one dimension, and when the receiving antennas are arranged in two dimensions, it is expressed by a two-dimensional DFT similar to equation (3). , will be omitted here.

[Problem that the invention seeks to solve]

In the above formula (3), r=Q, 1.2.・, N-1
As shown in Fig. 3, the beam direction α' obtained by
−(41), where θB is λ/N, d
It is.

The N beam directions obtained from equation (4) are given by equation (3)
It can be found when t is set to a certain value.

Therefore, the transmission pulse width is τ, and the maximum detection distance is Rm
If ax, t=τ, 2τ+ 3 “H”・+
2 RmaX/C, respectively, with beam direction α.

, α1°α2. ..., it is necessary to find αN-1.

For this reason, for example, if a DFT algorithm is used, equation (3) must be calculated 2Rmax /rcX (N 1) times.

Instead of DFT, N-point FFT (Fast
Even if the Fourier Transform (Fourier Transform) algorithm is used, it is necessary to repeat 2Rmax/τC times.

In this way, in conventional holographic radar,
Maximum detection distance Rm from the installation point of the holographic radar
There was a problem in that an enormous amount of calculation was required to observe with N multibeams at a distance up to ax.

The present invention was made to solve the above-mentioned problems, and an object of the present invention is to obtain a holographic radar that can quickly locate a target.

[Means for solving problems]

The holographic radar according to the present invention includes a continuous wave transmitter and a pulse transmitter, a switch for selectively outputting the outputs of these transmitters to a transmitting antenna, and a local oscillation distribution system for removing a carrier frequency from each received and received signal. a beam forming circuit that forms a multi-beam from the output of this local distribution circuit, a detection circuit that detects the direction in which a target exists from the output of this beam forming circuit, and the above-mentioned continuous wave transmitter when starting target detection. a controller that controls each of the transmitters and switches so that the output of the pulse transmitter is output as a transmission wave after the direction of existence of the target is detected by the detection circuit; and a receiver for the pulse transmission wave. A single beam forming circuit is provided which receives the signal and forms a single beam from the output of the local distribution circuit in the direction in which the target exists based on the detection result.

[Effect]

In this invention, a continuous wave (CW;
Continuous Have ) is used to find the target position in angles, for example, azimuth angle and elevation angle, and then ranging is performed at a predetermined angle using a pulse wave as a transmission wave.

〔Example〕

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

In Fig. 1, 1 is a receiving antenna, 2 is a local distribution circuit, 3 is a beam forming circuit, 4 is a single beam forming circuit, 5 is a detection circuit, 6 is a CW transmitter, 7 is a pulse transmitter, and 8 is a switch. , 9 is a transmitting antenna, and lO is a controller.

Next, the operation will be explained.

First, the controller 10 switches the CW transmitter 6 to operate, and also switches the switch 8, whereby the CW transmitted by the CW transmitter 6 is input to the transmitting antenna 9, and is radiated from the transmitting antenna 9 as a radio wave. be done. The radio waves reflected by the target are transmitted by bamboo. +1. ..., Ei-ni -1), Kei-ni, God (K+1), ..., Kane (N-1)
It is received by N receiving antennas 1 represented by . - The respective outputs of the receiving antennas 1 are input into a local distribution channel 2 and the carrier frequency is removed.

The output of the local oscillator distribution circuit 2 at this time is 5k(t)
Then, each output of the local oscillator distribution circuit 2 is transmitted to the beam forming circuit 3
The circuit 3 performs the calculation shown in (5). Here, r=0.1゜2,
..., N-1, Wk (K=1.2,3°・
..., N-1) represents a weighting coefficient.

When performing the calculation of equation (5), <t is a certain time to
Set to . By calculating equation (5), a beam can be formed in a direction at an angle αr from the arrangement direction of the receiving antennas 1. Here, αr is Q! r = cos-' (r ・λ/ N d >
−(61r=0.1.2.−, N−1, where λ is the wavelength of the carrier wave and d is the receiving nantenna 1
represents the array interval. The beam forming circuit 3 can use, for example, an FFT algorithm.

If there is a target in the direction of αr, CW is used as the transmitted wave.
Therefore, as long as the signal-to-noise ratio is above a certain level, the target can be detected regardless of the distance. On the other hand, in the conventional method, a pulse is used as a transmission wave, and the time is set in equation (3), and a beam is formed only at a certain distance.

Here, the output B of the beam forming circuit 3. ,B1°B2.・
..., BN-1 is input to the detection circuit 5 and compared with an appropriately set threshold level, and if the signal is above the threshold level, it is possible to determine in which direction the target is present. can be found. The detection circuit 5 detects the direction α6. α7. ..., αN-1
If it is detected that a target exists in either direction, the controller IO turns off the CW transmitter ta6, turns on the pulse transmitter 7, and switches the switch 8 to turn off the pulse transmitter 7 and the transmitting antenna 9. so that they are connected.

The pulses transmitted from the pulse transmitter 7 at a certain repetition period in this way are transmitted to the switch 8. It is radiated back to the target via the transmitting antenna 9. The radio waves reflected by the target are sent to the village,..., total (K-1), rental,
The signal is received by N receiving antennas 1 represented by Gin(K+1), . . . , Kai(N-1). Each output of the receiving antenna 1 is input to a local oscillator distribution circuit 2 to remove the carrier frequency, and then input to a single beam forming circuit 4. At this time, the output of the local oscillator distribution circuit 2 is set to 5k(t), and the direction in which the target exists obtained by the test circuit 5 is, for example, αLl'
αLll ..., αL, the single beam forming circuit 4 is as follows: B r = ΣWk 5k(t) RO -exp(-j (2fc / λ) K d cos
αLr)...(7) r thousand 0.1.2. ...9M, t=τ, 2τ, 3τ, ..., 2R
Perform at max/c respectively. Single beam forming circuit 4
For example, a DFT algorithm can be used.

Here, τ is the transmission pulse width, Rmax is the maximum detection distance,
C represents the speed of light, λ represents the transmission wavelength, d represents the arrangement interval of the receiving antennas 1, and Wk represents the weighting coefficient.

The single beam forming circuit 4 performs ranging to the target in that direction based on the direction in which the target exists, which is obtained during CW transmission.

In the above embodiment, the arrangement of the receiving antennas is one-dimensional, but the same applies to a two-dimensional arrangement.

〔Effect of the invention〕

As described above, according to the present invention, a CW transmitter and a pulse transmitter are used together, and the target position is first determined in terms of angle using the CW as the transmitted wave, and then the position of the target is determined in terms of angle using the pulsed wave as the transmitted wave. Since ranging is performed at a predetermined angle where the detected target exists, there is an effect that the direction of the target and the distance to the target can be efficiently obtained.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the configuration of a holographic radar according to an embodiment of the present invention, FIG. 2 is a diagram showing the configuration of a conventional holographic radar, and FIG. 3 is a diagram showing the configuration of a conventional holographic radar. FIG. 1... Receiving antenna, 2... Local oscillator distribution circuit, 3...
・Beam forming circuit, 4...Single beam forming circuit, 5...
・Detection circuit, 6... CW transmitter, 7... Pulse transmitter, 8... Switch, 9... Transmission antenna, 10
...Controller. Note that the same reference numerals in the figures indicate the same or equivalent parts.

Claims (1)

[Claims] (1) A continuous wave transmitter and a pulse transmitter, a switch that outputs one of the outputs of these transmitters to a transmitting antenna, a plurality of receiving antennas arranged, and each signal received by this receiving antenna. A local oscillation distribution circuit for removing the carrier frequency, and predetermined calculations are performed on each output of this local oscillation distribution circuit,
a beam forming circuit that forms a multi-beam; a detection circuit that compares the output of the beam forming circuit with a predetermined threshold level to detect the direction in which the target is present; a controller that controls each of the transmitters and switches so that the output of the pulse transmitter is output as a transmission wave, and after the direction of existence of the target is detected by the detection circuit, the output of the pulse transmitter is output as a transmission wave; a single beam forming circuit that receives a received signal for the transmitted wave of the aircraft, performs a predetermined calculation on the output of the local oscillator distribution circuit in the direction where the target exists based on the detection result of the detection circuit, and forms a single beam; A holographic radar characterized by comprising: