JP2002214330A - Pulse radar apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To rapidly detect a target moving at high speeds, using an LPRF(Low Power Radio Frequency) radar in a sea-clutter environment. SOLUTION: Transmit pulses are transmitted as their pulse hit intervals are varied for each pulse hit. Not a pulse Doppler filter using Fourier Transform but a wavelet conversion which is a time-frequency (hit/Doppler) multiple resolution process is applied to the received signals. Because the hit intervals vary with each transmission of the pulse, even if a target is moving at constant speed the target Doppler frequency held within the sea-clutter range and having ambiguity can be quickly varied up to the outside of the sea-clutter frequency range.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pulse radar apparatus, and more particularly to a technique for detecting a low-altitude flight target earlier in a sea clutter environment.

[0002]

2. Description of the Related Art In ship-mounted pulse radars, STC (Sens
low transmission pulse repetition frequency (LPRF: Low Pu) that enables the reduction of reflected waves from the nearby sea surface by iterative time control (ETI) processing and the like, and enables the acquisition of distance information.
The pulse is transmitted at lse Repetition Frequency). Generally, in a middle-range radar having a detection distance of several tens of km, a frequency of about 2 kHz is used as LPRF. In addition, the speed of the flight target may exceed the speed of sound, and taking the X band as an example, its Doppler frequency is several tens of kilometers.
Hz. Therefore, in such a case, ambiguity of the Doppler frequency occurs.

[0003] On the other hand, the sea clutter, which is a reflected wave from the sea surface, has a width of several tens to several hundreds Hz centering on substantially 0 Hz. Therefore, depending on the flight speed of the target, the target reflected wave may be buried in the sea clutter due to the ambiguity of the transmission pulse repetition frequency. In order to suppress such a phenomenon, in a conventional pulse radar device,
The target Doppler frequency is changed outside the frequency band of the sea clutter by changing the pulse repetition frequency (PRF), and the signal is processed in this state. Hereinafter, this will be described with reference to FIGS. FIG. 3 is a block diagram of a conventional device. 1 is a transmitting antenna, 2 is a transmitter, 3 is a transmitting pulse generator, 4 is a receiving antenna, 5 is a receiver, 6 is a pulse Doppler filter, and 7 is an amplitude detector. is there. FIG. 4 is an explanatory diagram showing signal waveforms in the conventional device.

[0004] As shown in FIG. 4, in the conventional device, after accumulating data in one burst, pulse Doppler filter processing is performed by Fourier transform. That is, the amplitude of each Doppler frequency bin for each burst is obtained by the amplitude detector 7 as the output of the pulse Doppler filter 6. Therefore, this output can be obtained at least 1C
It is for each PI (Coherent Pulse Interval; burst length). CPI is 1 as the pulse hit number (pulse transmission number)
The length of 6 or 32 or an extension of a power of 2 is used as an extension thereof. In the conventional device, since the PRF (or pulse hit interval) is set for each burst, if the Doppler frequency of the target signal overlaps the frequency band of the sea clutter in a predetermined burst, for example, the first CPI (CPI1), A target signal having a Doppler frequency outside the frequency band is obtained at least after the radar output of the next burst (after the lapse of the CPI). As a result, early detection of targets in the sea clutter environment has been difficult.

[0005]

As described above, in the above-mentioned conventional pulse Doppler radar device, although the PRF could be changed, this PRF was kept constant for each burst, so that the target Doppler outside the sea clutter frequency range was used. There is a problem that it takes time to obtain the frequency.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems, and has as its object to obtain a Doppler frequency target signal outside the sea clutter frequency band more quickly.

[0007]

A pulse radar apparatus according to the present invention includes a pulse transmitter for transmitting a pulse at a different transmission interval every time a pulse is transmitted, and a receiving apparatus for receiving a reflected pulse corresponding to the pulse reflected at a target. A wavelet transformer for wavelet transforming the received reflected pulse, and an amplitude detector for detecting the amplitude of an output signal of the wavelet transformer as a radar output.

[0008]

FIG. 1 is a block diagram of a pulse radar device according to an embodiment of the present invention. In the figure,
Reference numeral 8 denotes a transmission stagger pulse generator that controls the change of the CPI of the transmission radar pulse for each pulse hit, and reference numeral 9 denotes a wavelet converter that performs wavelet conversion in the pulse hit direction (pulse transmission direction) for each range bin. A wavelet transformer 9 as a time-frequency multiplexing analysis means performs multiplex analysis on a pulse hit / Doppler frequency axis by applying a wavelet transform to the orthogonal baseband signal output from the receiver 5 for each range bin. . That is, the wavelet transformer 9 functions as a minimum pulse / Doppler resolution window for the quadrature baseband signal as the output of the receiver 5. The transmitter 2 amplifies the transmission radar pulse and converts the frequency into an RF signal.
Amplifies the output from the receiving antenna 4 that has received the reflected pulse with respect to the transmitted pulse reflected at the target, and frequency-converts the output to an orthogonal baseband signal.

FIG. 2 is an explanatory diagram showing signal waveforms in the pulse radar device according to the embodiment of the present invention. As can be seen from this figure, according to the present invention, the pulse hit interval (PRI (Puls
e Repetition Interval)) and send. FIG.
In the example, the pulse hit interval is gradually increased every time a pulse hit occurs. In the reception process, the pulse hit interval is changed for each pulse hit, but the reception signals of the same range bin (sampled for each delay time from the transmission pulse and meaning the distance to the target) are output to the same target. In the pulse hit direction, the wavelet conversion process shown in Expression 1 is performed.

[0010]

(Equation 1) Where a is the scale parameter of the wavelet, b
Is a shift parameter, and ψ is a wavelet function.
P is a variable indicating the PRI of the input data for each PRI. a corresponds to a frequency, and a is referred to as a wavelet transform channel for discretization. Also b
Means the output sample (ie, PRI). FFT that has been known for a long time among wavelet functions
A fast algorithm such as (Fast Fourier Transformation) is the Haar function shown in Expression 2.

[0011]

(Equation 2) The Haar function is a real function and the output is the same complex signal as the input orthogonal baseband signal. Therefore, the amplitude of each channel of the wavelet transform output (that is, the root-mean-square of the real part and the imaginary part) is obtained by Expression 3 using the amplitude detector.

[0012]

(Equation 3) In the pulse radar device according to the present invention, since the transmission pulses are transmitted at non-equidistant intervals in the pulse hit direction, a constant Doppler frequency from a target moving at a high speed and at a constant speed with a return of the frequency is as if the frequency is gradually increasing. Observed as shifted. Therefore, the radar output does not use CPI as the minimum unit in the time direction as shown in FIG.
As shown in FIG. 2, a narrow band filter output by wavelet transform is obtained using PRI as the minimum unit in the time axis direction.
For this reason, even when the target Doppler frequency is buried in the sea clutter frequency band, the Doppler frequency can be moved out of the sea clutter frequency band after several PRIs. As a result, the target can be detected more quickly.

[0013]

As described above, according to the present invention,
The transmission pulse is transmitted with the pulse hit interval changed for each pulse hit, and the receiving side performs narrow band filter processing by the wavelet transform on the signal of the same range bin as if transmitted at a constant pulse hit interval, thereby reducing the frequency. The target Doppler signal buried in the sea clutter by folding back can be moved to the clutter-free area after several PRIs, and the LPRF radar has an excellent effect of being able to detect a high-speed target with ambiguity more quickly. Play.

[Brief description of the drawings]

FIG. 1 is a block diagram of a pulse radar device according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing a signal waveform in the pulse radar device according to the embodiment of the present invention.

FIG. 3 is a block diagram of a conventional pulse radar device.

FIG. 4 is an explanatory diagram showing a signal waveform in a conventional pulse radar device.

[Explanation of symbols]

1 transmitting antenna, 2 transmitter, 3 transmitting pulse generator, 4 receiving antenna, 5 receiver, 6 pulse Doppler filter, 7 amplitude detector, 8 transmitting stagger pulse generator, 9 wavelet converter.

Claims (1)

[Claims] 1. A pulse transmitter that transmits a pulse at a different transmission interval every time a pulse is transmitted, a receiver that receives a reflected pulse corresponding to the pulse reflected at a target, and a wavelet transform of the received reflected pulse A pulse radar device, comprising: a wavelet converter that performs an operation; and an amplitude detector that detects an amplitude of an output signal of the wavelet converter as a radar output.