JPH04301584A - Pulse doppler radar equipment - Google Patents

Abstract

PURPOSE:To obtain a pulse Doppler radar equipment enabling attainment of an effect of improvement in a signal-to-noise power ratio(SNR) by coherent integration even when a target being observed is in accelerated movement in the radial direction. CONSTITUTION:A reception signal from a target of observation is converted into a digital complex video signal and stored for each range bin number and pulse hit number in a two-dimensional memory 14. Data trains obtained by dividing data of the two-dimensional memory are subjected to fast Fourier transform in the direction of pulse hit by FFTs 22 respectively. An output signal of each FFT having a phase gradient which is most approximate to the phase gradient of a partial straight line obtained by linear approximation in each partial section of a phase curve of the reception signal from the target of observation being in the accelerated movement supposed beforehand is selected from separate output signals of the FFTs, while such phase compensation as enabling connection of partial straight lines having different phase gradients at a joint of the partial sections is called out of a reference memory, and each of them is subjected to computation of the product and the sum so as to execute coherent integration.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pulse Doppler radar device that uses coherent integration to improve the signal-to-noise ratio (hereinafter referred to as SNR).

0002

2. Description of the Related Art Conventionally, pulse Doppler radar devices of this type have been known, for example, in the literature, G. V. Morris: “
Airborne Pulsed Doppler R
adar ■, Artech House, Inc. (1
988). FIG. 7 is a block diagram of the main parts of a conventional pulse Doppler radar device. In the figure, 1
2 is an antenna, 2 is a transmitting means, 3 is a transmitting/receiving switch, 17 is a receiving means, and 18 is a coherent integrating means. Next, an overview of the operation will be explained. The pulse-shaped transmission radio waves generated by the transmitting means 2 pass through the transmitter/receiver switch 3 and the antenna 1, and are radiated toward the observation target, and the radio waves reflected by the target are received by the antenna 1, and then through the transmitter/receiver switcher 3. Mixer within means 17
5, multiplied by the output of the local oscillator 4, and converted into an intermediate frequency signal. The output of the mixer 5 is amplified by an IF (intermediate frequency) amplifier 6, then divided into two parts and input to phase detectors 7a and 7b, respectively.
Then, the product with the output signal of the coherent oscillator 8 and the product with a signal obtained by delaying the phase of the output signal of the coherent oscillator 8 by 90 degrees by a 90 degree phase shifter 9 are calculated, and the respective phases are detected. The respective phase detector outputs are input to the sample holder 1 as the real part (I) and imaginary part (Q) of the received complex video signal.
After being held by 0a and 10b, the A/D converter 11
a and 11b into a digital complex video signal. The digital complex video signal is stored in a buffer memory 14 within the coherent integration means 18. The digital complex video data of the same range bin number is extracted from the storage means 14 in an amount corresponding to the coherent integral number N, and is subjected to FFT1.
Coherent integration is performed by performing N-point FFT in step 5. An amplitude value is calculated by an amplitude detector 16 based on the output of the FFT 15, and a threshold detector (not shown)
send to The threshold detector determines a target when the amplitude detector 16 output signal exceeds a predetermined threshold level and sends a detection signal to a display (not shown). The display receives the detection signal and displays the target.

Now, if the repetition period of the transmission pulse is Δt and the transmission wavelength is λ, then the center frequency fn is determined by FFT.
N filters are formed, and the bandwidth of each Doppler filter is given by approximately 1/NΔt. fn=n/NΔt,

(1) Here, n=-N/2,...,0,...
, (N/2)-1 FFT assumes the radial velocity of the observation target to be Vn and the N types of the following equation, and performs integration by compensating for the time fluctuation of the phase of the received signal caused by this, that is, the coherence It is equivalent to the rent integral. Vn=λfn/2,

(2) Here, n=-N/2,...,0,...
・,(N/2)−1

0004

[Problems to be Solved by the Invention] In the conventional pulse Doppler radar device configured as described above, the target being observed has a constant velocity (=uniform motion) in the radial direction, or a velocity that can be considered constant. When moving, it is possible to improve the SNR by coherent integration. However, when the observation target accelerates in the radial direction, the Doppler frequency bandwidth expands, so there is a problem that the SNR improvement effect cannot be obtained. This invention was made in order to solve the above-mentioned problems, and even if the target being observed is accelerating in the radial direction within the range bin range, it is possible to obtain a pulse that improves the SNR by coherent integration. The purpose is to obtain a Doppler radar device.

[0005]

[Means for Solving the Problems] In order to achieve the above object, the pulse Doppler radar device of the present invention emits pulsed transmission radio waves toward an observation target, and uses the reflected radio waves as reception signals. This pulse Doppler radar device detects a target by coherently integrating the received signal after converting it into a digital complex video signal, and is equipped with the following elements. (a) storage means for storing received digital complex video signals for each range bin number and pulse hit number; (b) data for dividing the digital complex video data in the storage means;
(c) Fast Fourier transform means (hereinafter referred to as FFT means) that performs fast Fourier transform on each of the divided data in the pulse hit direction; (d) Output of each of the above FFT means; Output switching means for selecting, from the signal, an output signal of the FFT means having a phase gradient closest to a phase gradient of a partial straight line that linearly approximates a phase curve of a received signal of an observation target moving in a predetermined manner for each partial section; (e) a phase compensation amount calculation means that calculates in advance a phase compensation amount such that the above-mentioned partial straight lines having different phase gradients are connected at the seam of the partial sections and stores it in a reference memory; (f) controls the above-mentioned output switching means; selects the specific output signal from the output signals of the respective FFT means, controls the phase compensation amount calculation means to retrieve the phase compensation amounts from the reference memory, and transfers each to the complex product-sum calculation means. (g) complex product-sum calculation means for complex multiplying the output signal of the selected FFT means and the phase compensation amount read from the reference memory and calculating the sum;

[0006]

[Operation] The pulse Doppler radar device of the present invention configured as described above converts the received signal of the observation target into a digital complex video signal, and stores the data in the storage means for each range bin number and pulse hit number. - the data is divided into two parts, each of which is fast Fourier transformed in the pulse hit direction by FFT means. From the output signals of the above-mentioned FFT means, the output of the FFT means has the phase gradient closest to the phase gradient of a partial straight line that linearly approximates the phase curve of the received signal of the observation target that undergoes pre-assumed accelerated motion for each partial section. In addition to selecting a signal, the target being observed is accelerated in the radial direction by recalling the phase compensation amount from the reference memory such that the partial straight lines with different phase gradients are connected at the seams of the partial sections, and calculating the sum of products for each. Even when exercising, the SNR improvement effect can be obtained by coherent integration.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a block diagram of essential parts showing an embodiment of the present invention. In the figure, 14 is a two-dimensional storage means for storing received digital complex video signals for each range bin number m and pulse hit number n, and 21 is a two-dimensional storage means for storing received digital complex video signals in the storage means 14 in the pulse hit direction. T length L
A data dividing means 22 divides the data into sub-interval data (L=8 in the example of FIG. 2), and after weighting each sub-interval data for sidelobe suppression, (not shown), K FFT means each performing fast Fourier transform in the pulse hit direction; 23 is connected to each FFT means 22 to receive an observation target moving in a predetermined manner from the output signal of the FFT means; Output switching means 28 selects the output signal of the FFT means having the phase gradient closest to the phase gradient of the partial straight line that linearly approximates the phase curve of the signal for each partial section; A phase compensation amount calculation means 29 calculates in advance a phase compensation amount that connects at the joint of the partial sections and stores it in a reference memory. Control means 27 selects the output signal, controls the phase compensation amount calculation means 28, reads the phase compensation amounts from the reference memory, and transfers each of them to the complex product-sum calculation means 27. complex product-sum calculation means for calculating the sum by complex multiplication of the output signal of the FFT means and the phase compensation amount read from the reference memory;
Reference numeral 6 denotes an amplitude detector for determining the amplitude value of the output of the complex product-sum calculation means 27.

Next, the operation of the main part of the present invention shown in FIG. 1 will be explained. Duplicate explanation of parts equivalent to the conventional example will be omitted. The received signal converted into a digital complex video signal by the receiving means is stored in the storage means 14 for each range bin number m and pulse hit number n. The shaded area in FIG. 2 exemplifies the range bin number m where the observation target exists. Now, the observation target that makes the assumed motion (in this example, it is assumed to be a uniformly accelerated motion with an initial velocity V0 and an acceleration a) has a range bin number m
Assuming that V exists, the velocity V of the observation target can be expressed by Equation 1. V=V0 +a・t

(1) Here, t=nΔt, n is the pulse hit number, and Δt is the transmission pulse repetition period. The phase φ(t) of the received signal of the observation target that assumes the above-mentioned uniformly accelerated motion can be expressed by the following equation, and an example is shown in FIG.
It becomes the following curve. φ(t)={(2V0 ・t+a・t2 )2
π/λ}+φ0, (2) where t=nΔt
, φ0 is the initial phase, and λ is the wavelength.

The received digital complex video data stored in the storage means 14 described above for each range bin number m and pulse hit number n is divided in the pulse hit direction. In this data division, as illustrated in FIG. 2, the data is overlapped (4 data in the example of FIG. 2), and a data string of data length L (in the example of FIG. Then, it is divided into L=8). After each divided data is weighted for sidelobe suppression (not shown), an L-point FFT is performed by the FFT means 22, respectively. For example, a Taylor window is used as the weight Wl. The output signal of the FFT means which receives the k-th divided data string as input can be expressed by Equation 3, and FIG. 4 shows the temporal change in the phase of the output signal of the FFT means.

0010

[Math 1]

Here, Wl: weight, u(l,k): subinterval data input to the k-th FFT means, (k=1,...K)(l=1,...,L), k: number of the divided data string, (=FFT means number), number of the partial straight line that linearly approximates the phase φ(t) of the received signal for each partial interval α: spectrum number of the output signal of each FFT means ( α=1
,...,L), L: Partial interval data length.

FIG. 5 shows an example of linear approximation of the quadratic curve of the phase φ(t) of the received signal of the observation target having uniformly accelerated motion illustrated in FIG. 3 for each partial section. For approximation,
For example, the least squares method is used to determine the sum of squares of phase errors in each subinterval to be the minimum. When the above quadratic curve is linearly approximated for each subsection, the amount of phase compensation (Fig. 5
In the example, the phase compensation amount P) for the partial straight line with k=3 is calculated in advance and stored in the reference memory. While FIG. 5 describes an example of uniformly accelerated motion as the assumed motion, FIG. 6 adds another example of uniformly accelerated motion. The phase of the received signal φ corresponds to the motion pattern of the observation target.
(t) curve pattern (hereinafter referred to as phase pattern)
is decided on a one-to-one basis, and as shown in Fig. 6, each phase pattern is set to β = 1, 2,
Number them 3,.... And the phase φ(
A number k (=1, 2, . . . ) is assigned to partial straight lines having different phase gradients obtained by linearly approximating each curve of t) for each partial section. A phase compensation amount is calculated in advance for each of the phase pattern number β and the partial straight line number k, and is stored in the reference memory of the phase compensation amount calculation means.

From the above explanation, for an observation target for which uniformly accelerated motion is assumed, the phase φ(t
), consider a phase pattern as shown in FIG. In order to extract the observation target signal having unknown uniformly accelerated motion, coherent integration processing is performed according to the following procedure. Let β be the phase pattern number of the assumed uniformly accelerated motion. First, for each data string obtained by dividing the received signal (=received digital complex video data stored in the storage means 14 for each range bin number m and pulse hit number n) by the data length L, the pulse hit direction is determined. Perform L-point FFT. The control means are
The output switching means 23 is controlled to select an output signal having a phase gradient closest to the phase gradient of the partial straight line number k of the phase pattern number β (α=1 shown in FIG. 4) from the output signal of the FFT number k.
, 2, . The quantities are called from the reference memory and each is transferred to the complex product-sum calculation means 27. Next, in the complex product-sum calculation means 27,
A complex product-sum calculation is performed between the output signal of the selected FFT and the phase compensation amount read from the reference memory of the phase compensation amount calculation means 28. Note that the output signals of the selected FFT means are side-loaded before being input to the complex product-sum calculation means.
Weighting (not shown) is performed to suppress the effects. As described above, the output signal (=
The complex adder output signal) can be expressed by the following equation.

[0014]

[Math 2]

Here, Wk: weight, V(β,k): among the output signals of the FFT means (number k), the signal having the phase gradient closest to the phase gradient of the partial straight line number k of the phase pattern number β. Φ(β,k): Phase compensation amount of partial straight line number k of phase pattern number β, β: Number of phase pattern, (β=1, 2,...)k: FF
The number of the T means (=divided data sequence number), the partial section number of the phase curve of the phase pattern number β (=the number of the partial straight line that linearly approximated the partial section), (k=1, 2, ...K) Equation 4 is the output signal of the product-sum calculation means 27 for the phase pattern β. In the above explanation, we took as an example the case where the observation target moves with uniform acceleration as shown in Equation 1 as the assumed movement, but this is not limited to the movement shown in Equation 1, and the same processing can be applied to any arbitrary movement pattern. By doing this, the effect of improving SNR by coherent integration can be obtained.

[0016]

[Effects of the Invention] According to the present invention as described above, a received signal of an observation target is converted into a digital complex video signal, and the digital complex video data stored in the storage means is divided for each range bin number and pulse hit number. , FFT each
Fast Fourier transform is performed in the pulse hit direction by means of the FFT means, and from the output signal of each FFT means, the phase gradient of a partial straight line is obtained by linearly approximating the phase curve of the received signal of the observation target that is undergoing pre-assumed accelerated motion for each partial section. , selects the output signal of the FFT means with the closest phase gradient, reads from the reference memory the phase compensation amount such that the partial straight lines having different phase gradients are connected at the joint of the partial sections, and calculates the sum of products for each. By performing coherent integration, it is possible to obtain a pulse Doppler radar device that can obtain an SNR improvement effect by coherent integration even if the target being observed is accelerating in the radial direction.

[0017]

[Brief explanation of drawings]

FIG. 1 is a configuration diagram of main parts showing an embodiment of the present invention.

FIG. 2 is a memory map illustrating a method of dividing received digital complex video data to be stored in the storage means of FIG. 1;

FIG. 3 is a diagram showing an example of a phase curve φ(t) of a received signal of an observation target that assumes uniformly accelerated motion.

FIG. 4 is a diagram showing the phase of an FFT output of a received signal of an observation target moving at an assumed uniform velocity.

5 is a diagram illustrating a method of linear approximation of the phase curve φ(t) shown in FIG. 3. FIG.

6 is a diagram including another example of the phase curve φ(t) shown in FIG. 5. FIG.

FIG. 7 is a configuration diagram of main parts of a conventional pulse Doppler radar device.

[Explanation of symbols]

14. Storage means 21 Data division means 22 FFT means 23 Output switching means 25 Complex multiplier 26 Complex adder 27 Complex product-sum calculation means 28 Phase compensation amount calculation means 29 Control means

Claims (1)

[Claims] Claim 1: A pulse that emits a pulsed transmission radio wave toward an observation target, receives the reflected radio wave, converts the received signal into a digital complex video signal, and then performs coherent integration to detect the target. In Doppler radar equipment,
A pulse Doppler radar device having the following elements: (a) storage means for storing received digital complex video signals for each range bin number and pulse hit number; (b) data for dividing the digital complex video data in the storage means;
(c) Fast Fourier transform means (hereinafter referred to as FFT means) that performs fast Fourier transform on each of the divided data in the pulse hit direction; (d) Output of each of the above FFT means; Output switching means for selecting, from the signal, an output signal of the FFT means having a phase gradient closest to a phase gradient of a partial straight line that linearly approximates a phase curve of a received signal of an observation target moving in a predetermined manner for each partial section; (e) a phase compensation amount calculation means that calculates in advance a phase compensation amount such that the above-mentioned partial straight lines having different phase gradients are connected at the seams of the partial sections and stores it in a reference memory; (f) controlling an output switching means; Control means for selecting the above-mentioned specific output signal from the output signals of the respective FFT means, controlling the phase compensation amount calculation means to retrieve the above-mentioned phase compensation amounts from the reference memory, and transferring each of them to the complex product-sum calculation means. , (g) the above selected FF
Complex product-sum calculation means for complex multiplying the output signal of the T means and the phase compensation amount read from the reference memory, respectively, and calculating the sum.