JPS6154476A - Clutter suppressing device - Google Patents

Abstract

PURPOSE:To detect accurately a target signal in the ground clutter and the weather clutter by suppressing the ground clutter and weather clutter excellently even in an area where the both are present as to the clutter suppressing device used for a radar. CONSTITUTION:A complex coefficient MTI560 functions move a cutoff area as MTI on a Doppler frequency axis to an optional position. This suppressing device is equipped with delay elements 561 and 562 which delay a signal received by a receiver by RPI (pulse repetition period), complex coefficient multipliers 563-565 which multiply a demodulated signal and delay signals of those delay elements 561 and 562 by complex coefficients ''omega0''-''omega2'', and an adder which adds signals multiplied by those complex coefficients. Therefore, a cutoff area as MTI is formed at the center frequency of the weather clutter, which is then erased.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a clutter suppression device used in a radar device, and more particularly to a device that satisfactorily suppresses both ground clutter and Koup clutter to extract a target signal.

[Technical background of the invention and its problems] - Fig. 6 shows a schematic configuration of a general radar device.

In this radar device, a highly stable oscillator 10 is a circuit that generates a stabilized signal of a predetermined frequency, and the generated signals are supplied to a transmitter PA 2o and a receiver 50, respectively. The transmitter 20 generates a pulse signal having a required repetition period based on this input signal, and supplies this to the antenna 40 via the transmitter/receiver switch 30.

As a result, the same pulse signal is emitted from the antenna 40 as a transmission signal. On the other hand, the reflected wave from the target is received by the same antenna 40, and is supplied to the receiver 50 via the transmitter/receiver switch 30. As described above, this receiver 50 is also supplied with the oscillation signal of the highly stable oscillator IO, and the received signal is mixed with this oscillation signal and demodulated. Further, this receiver 50 has a built-in filter circuit for removing unnecessary signals such as noise, and the signal from which the unnecessary signals have been removed is transmitted to the display 6.
0 and displayed.

By the way, as the above-mentioned filter circuit, MTI (moving target indicator!t) is widely used (this is because the so-called Doppler frequency is "0" in order to remove ground clutter caused mainly by reflection from the ground surface). This is a band-removal filter in which a cutoff band is set at a portion where the filter has a cutoff region, and generally has an output characteristic as shown in FIG.

However, the PRF (pulse repetition frequency) shown in Figure 7
represents the reciprocal of the pulse interval in the transmission pulse signal.

In addition to the ground clutter mentioned above, clutter also includes
There is weather clutter caused by reflections from rain, clouds, etc., but since the Doppler frequency of this weather clutter may not be "0" and cannot be suppressed sufficiently by MTI, conventionally, the target signal and unnecessary signals such as these clutter have been separated. Considering that the Doppler frequency is different in the first place,
For example, as shown in FIG.
(abbreviated as PF) 521 to 52n are connected in parallel and the M
The T power ratio output is further separated into different Doppler frequency bands, and each of these separated signals is sent to a detection circuit 53.
1 to 53n, and from these detected signals, unnecessary signal removal circuits 541 to 54m suppress each unnecessary signal, and then the output synthesis circuit 550 reproduces this to extract the target signal. I'm also trying something like this. Of course, the filtering characteristics of the upper H6Bp y 521 to 52n are respectively set within the MTTb2O3iji overband RMτ, as shown by R1-Rn in FIG. Naori PF521
It is well known that such a filtering operation of ~52n can be achieved by performing FFT (Fast Fourier Transform) on successive received signals at the same distance. Further, as the unnecessary signal removal circuits 541 to 54n°, for example, L
og-C! FAR(Log-008tantFalSe
Altrm Rate) is used.

However, although the clutter suppression device shown in Fig. 8 can be evaluated with a score of 5 because it enables more fine-grained clutter suppression than the previous MTI-based clutter suppression, there are still problems in practical use. There were many.

For example, if the target signal and weather clutter are received in the manner shown in FIG. 10 for the passband Rm'rx of the MTI 510 and the passband R1 of the BPF 521, the target signal that originally passes through the BPF 521 should be output from the output synthesis circuit 550 without any suppression, but in reality weather clutter is also included in the pass band R1 of the BPIF 521. Therefore, even if the spectrum of this weather clutter is Even if these passing signals do not cover the entire band R3, if they are suppressed by the unnecessary signal removal circuit 541 consisting of the above-mentioned Log-OFAR etc., the weak target signal as shown in the figure will be suppressed for the most part. It becomes impossible to collect.
In addition, in radar, since the number of input data (number of received signals) given to BPF is limited, these 5pF
It is difficult to sufficiently suppress the side ropes of 521 to 52n, and therefore, for example, the passband RMτ of the MTI 510 and the set passband Rt of the BPF 522 are
For K, the target signal and weather clutter are the first
In the case of reception as shown in Figure 1, that is, the
Only the spectrum of the target signal is within the set passband R8, and the spectrum of the weather clutter is within the set passband R8.
Even if it is not within 3, B shown in Figure 11
This weather clutter enters from the side ropes of the PF 522, and eventually the target signal is suppressed as described above, making it impossible to collect it.

In the conventional clutter suppression device shown in Figure 8, the filtering characteristics of BPL are optimized to separate the spectrum of weather clutter whose center frequency is not necessarily constant and the spectrum of the target signal. It was extremely difficult to convert.

Another conventional method for suppressing clutter is the so-called NotchBee MT technique, which arbitrarily moves the weather clutter spectrum on the Doppler frequency axis by changing the local frequency in both transmission and reception. However, in this case, if the weather clutter is erased, the ground clutter cannot be erased, resulting in the inconvenience that different types of clutter cannot be erased at the same time. It is an object of the present invention to provide a clutter suppression device that can effectively suppress only the ground clutter and weather clutter and accurately detect the eye Je4 signal existing therein even in an area where ground clutter and weather clutter coexist. .

[Summary of the invention]

In this invention, for weather clutter whose center frequency is not necessarily constant, a cutoff area that can be moved arbitrarily on the Doppler frequency axis is provided to remove a specific Doppler frequency component corresponding to the weather clutter from among the 8 received signals. For example, a variable band rejection filter such as a complex coefficient MTI is prepared, and the center same wave number is at the Doppler frequency "0".
For ground clutter that is fixed at ``, prepare a BPF whose passband is set to at least a frequency band other than the frequency where the Doppler frequency is rOJ, and connect this BPF after the variable band rejection filter described above. Of course, a plurality of filters having different passbands may be provided in parallel as the BPF, and unnecessary signals may be suppressed from the outputs of these filters as described above, and then resynthesized. , Feather Claratan problems can be dealt with flexibly by the variable band rejection filter, and the filtering characteristics of the one or more BPFs can be easily determined. Further, by using such a filter configuration, separation of the spectrum of each type of two-tone spectrum and the spectrum of the target signal, which has been considered difficult in the past, can be easily and satisfactorily achieved.

[Embodiments of the invention]

FIG. 1 shows an embodiment of the double ivy suppression device according to the present invention. However, in FIG. 1, the same circuits as those shown in FIG. 8 are given the same numbers.

Now, in this embodiment device, the complex coefficient hlT operator 560
is an MTI that has the function of moving S Shinshiro as a %MT operator to any position on the Doppler frequency axis.For example, as shown in Fig. 2, the signal demodulated by the receiver C (not shown) is Delay elements 561 and 562 each delay by a PR process (pulse repetition interval), and complex coefficients such as ``H. The complex coefficient multipliers 563,564 and 565 that multiply the complex coefficients, and the adder 5566 that adds the multiplied signals of these complex coefficients, respectively. Therefore, this MT engineer 560 calculates the above-mentioned complex coefficients
”, “bi1”, and “bi,” are each set to 0=1 H−2, it will function as a normal MTI with the response shown in FIG. However, if fd=Doppler frequency, the cutoff range can be moved to the position of Doppler frequency fa, and it will function as an MTI having a response as shown in FIG. By using such a complex coefficient MTI 560, it is possible to form a cutoff region as an MTI at the center frequency of the feather clutter, thereby making it possible to eliminate the feather clutter.

In addition, in the same example device, EP7571-57n is
For example, as shown in FIG. 4, this is a BPF whose bands are set so that the attenuation poles of the respective pass bands that are different and cascaded on the Doppler frequency axis are exactly at the position of the Doppler frequency "0." The characteristics of PF are as follows.
For example, this can be realized by applying FFT (Fast Fourier Transform) without applying quating to the input signal. By implementing such FF'l', the above-mentioned attenuation pole is formed at the position of Doppler same wave number "0" except for FO filters (filters whose passband center frequency is Doppler frequency "0"). become. ' - Of course, this can be achieved using other filter configuration methods, but in any case, forming an attenuation pole in a known frequency portion can be achieved relatively easily. In this way, by forming a reduced-bag pole at the position of the Doppler frequency "0" by the BPFs 571 to 57n, ground clutter in which the center frequency is fixed at the Doppler frequency "0" can be effectively eliminated.

Hereinafter, the clutter suppression mode by the same embodiment device will be explained.

For example, the target signal, feather crack, and ground clutter are each received in the manner shown in FIG. If input to the device, among these signals, feather clutter has its center frequency in the attenuation range of the complex coefficient MT 560 (actually, the attenuation range of the complex coefficient MTI 560 is approximately at the center frequency of the feather clutter). The feather clutter is first removed by the complex coefficient MT process 560. The target signal and ground clutter that have passed through the MEN elementary coefficient MT process 560 are then added to the 13PFs 571 to 57n, but these BP, ? Since 571 to 57n have their attenuation poles at the Doppler frequency "O" as described above, the same B? Ground clutter whose center frequency is at Doppler frequency "0" is also removed by F571 to F57n. In the end, only the target signal passes through the BPF 571, even if it is weak, and only this signal passes through the detection circuit 531, unnecessary signal removal circuit 541, and output synthesis circuit 5.
50, it will be effectively output. Note that the above target signal and feather clutter are based on the assumption that the reception mode illustrated in FIG. In this way, only the target signal can be effectively extracted.

By the way, in the above-mentioned embodiment, a plurality of BPFs with different anchoring bands are provided to form an attenuation pole group of these Bj'F at the position of Doppler frequency "0", but at each B P P' - It is not necessary to form the attenuation pole if sufficient clutter suppression ability is obtained.

The point is that the passbands of these BPFs only need to be at least in a frequency band other than the Doppler frequency "0".

Also, BP is used just to remove the ground clutter.
If F is provided, the same effect as above can be obtained even if only one BPF with a passband as wide as that of the complex coefficient MT is provided under the above conditions. In addition, in the above embodiment, a complex coefficient MT filter is used as the first stage filter, but it has a cutoff band that can be moved arbitrarily on the Doppler frequency axis, and can extract a desired specific Doppler frequency component from the received signal. Any type of filter may be used as long as it is a variable band removal filter that can remove the noise.

〔Effect of the invention〕

As described above, according to the clutter suppressing device according to the present invention, unnecessary signals such as various types of clutter can be effectively suppressed with a simple and easy-to-maintain configuration, and furthermore, only the target signal can be accurately suppressed. It will be possible to collect.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of a clutter suppression device according to the present invention, and FIG. 2 is an example of the configuration of a complex coefficient MTI in the embodiment device shown in FIG. FIG. 3 is a diagram showing an example of the output characteristics of the complex coefficient MTI shown in FIGS. 1 and 2, and FIG. A diagram showing an example, FIG. 5 is a block diagram showing an example of the operating characteristics of the embodiment device shown in FIG. 1, FIG. 6 is a block diagram showing the configuration of a general radar device, and FIG. 7 is a general FIG. 8 is a block diagram showing an example of a conventional clutter suppression device; FIG. 9 is a diagram showing filter characteristics of the device shown in FIG. 8; FIGS. Figure 11. 8 are diagrams showing examples of operating characteristics of the device shown in FIG. 8, respectively. 10... Highly stable oscillator, 20... Transmitter, 30...
・Transmission/reception switch, 40-... antenna, 50... receiver,
60... Display, 510/MTI, 521~52n
, 571-57 n-B P F , 531-53
n = detection circuit, 541-54n... unnecessary signal removal circuit, 550... output synthesis circuit, 560... complex coefficient MTI, 561,562... delay element, 563, 56
4...Complex coefficient multiplier, 566...Adder

Claims (2)

[Claims] (1) A variable band rejection filter that has a cutoff range that can be moved arbitrarily on the Doppler frequency axis and removes a desired specific Doppler frequency component from the received signal, and at least frequencies other than those where the Doppler frequency is "0" a bandpass filter having a passband set in a frequency band and filtering the output of the variable band elimination filter. (2) The bandpass filter is comprised of a plurality of filters each having a different passband.
1) The clutter suppression device described in section 1).