JPS6093978A - Radar equipment - Google Patents

Abstract

PURPOSE:To improve the performance of signal detection without deteriorating the ability of eliminating ground clutter, by supplying an output signal of an MTI (moving target indicator) circuit to a plurality of filters whose central frequency is variable, and by shifting the central frequency of the filters in accordance with a mean frequency of an unrequired signal. CONSTITUTION:An output signal of an MTI circuit 21 is supplied to a plurality of filters 211-22n whose central frequency can be set arbitrarily. The central frequency of these filters 211-22n is shifted in accordance with a mean frequency of an unrequired signal, and thus the number of filters whose output is turned ineffective is reduced to the minimum.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a radar device, and particularly to a filter device for suppressing clutter.

[Technical background of the invention and its points of interest]

FIG. 1 shows a known radar device.

The highly stable oscillator II generates a stabilized signal of a predetermined frequency, which is supplied to the transmitter I2. The transmitter 12 generates a pulse signal having a predetermined repetition period based on the input signal. This pulse signal is supplied to the antenna 14 via the transmitter/receiver switch I3, and is radiated from the antenna I4. (9) The reflected wave from the target is received by the antenna I4 and supplied to the receiver I5 via the duplexer I:I. The receiver 15 is supplied with the output signal of the highly stable oscillator 11, and the received signal is mixed with this signal and demodulated. In addition, this receiver 15
A filter circuit or the like is provided for removing unnecessary signals such as clutter, and the signal from which unnecessary signals have been removed by this filter circuit or the like is supplied to the display device I6 and displayed.

By the way, as a filter for removing ground clutter caused by reflection from the ground surface, a wide < MTI (Moving T
Arget Indlcator) 2
- A circuit is used. This means that the filter is cut off at the Doppler frequency O]Ill! It is a bandpass filter that uses By this lv ('I' circuit,
Ground clutter with an average Doppler frequency of O can be eliminated. However, since the average Doppler frequency of weather clutter caused by reflections from rain, clouds, etc. does not necessarily equal O, sufficient erasing performance may not be obtained.

In order to improve this problem, a filter has been developed that separates noise and weather clutter based on the difference in Doppler frequency. FIG. 2 shows an example. That is, the input signal (demodulated signal: S) is supplied to the MT1 circuit 21, and after removing the signal having a Doppler frequency of 0, it is supplied to filters 22□ to 22n arranged in parallel. These filters 22I to 22n are bandpass filters with responses shown by Fl and IR2 to Rn in FIG. 3, and their passbands are within the passband of the V'I' circuit 21, as shown in FIG. , and are set in a sequentially shifted manner. However, RMT'I is the response of the MTI circuit. Conventionally, such p band-pass filter arrays have been realized by FFT (Fast Fourier Transform) or the like. This FF'
When a bandpass filter array is constructed by r, the filter position and shape are almost uniquely determined by the number of reflected signals from the target, and the number of reflected signals is determined by other requirements for leg performance. There are many. Therefore, it is often difficult to freely select the shape of this filter.

At this time, the configuration shown in FIG. 2 is adopted, and the filter 22. as shown in FIG. jl, 0 (if the clutter spectrum fC exists only in the IP range, the output of the filter 222 is generally turned off. However, when the average Doppler frequency of weather clutter changes, As shown in Figure 5, it is also possible that the clutter spectrum fc exists in the 6 subbands of the filters 22...223.In this case, both outputs of the filters 222 and 223 must be turned off.In this way, the 2 Turning off two filter outputs results in deterioration of signal detection performance because frequency bands that should not be turned off are also turned off.

Similarly, an MTI circuit using a clutter track method is known in which the spectrum of clutter, etc. is shifted in parallel on the frequency axis by changing the frequency of a local oscillation signal in a transmitter/receiver. (There was a drawback that the T circuit made it impossible to eliminate ground clutter.

[Purpose of the invention]

This invention has been made based on the above circumstances, and its purpose is to eliminate (l The present invention aims to provide a surface radar device capable of improving the f-number detection performance.

[Summary of the invention]

This invention supplies the output signal of the IJTI circuit to a plurality of filters whose center frequencies can be set arbitrarily, moves the filters according to the average frequency of unnecessary signals, and minimizes the number of filters whose output is invalid. The idea is to keep it to a few.

[Implementation sequence of the invention]

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

In the situation shown in FIG. 5, the filter 22□.

Both outputs of the 223 were disabled, and the passband of the Iha became narrower. Therefore, as shown in FIG. 6, for example, the center frequency f3c of the passband of the filter 2230 is moved to match the average Doppler frequency fCC of the clutter,
It is sufficient that there is only one filter whose output is invalid. In order to move the center frequency of the band-pass filters arranged in parallel in this way to an arbitrary position, the following means is used.

For example, each of the filters 222 to 224 shown in FIG.
As shown in the figure, the weighting circuits 72o to 724, which are composed of a plurality of delay multipliers 711 to 714 and multipliers, and the adder 73 which combines the output signals of the circuits 728 to 724, Each weighting is a weighting of circuits 72o to 724. -W, UJl, ej27r', A, f-1T (i= o~
4) This can be realized by supplying the value.

Further, as shown in FIG. 8, the input signal is weighted by a circuit 81;
In the case of a cumulative addition type filter circuit, in which the adder 82 is sequentially outputted and a part of the output signal is supplied to the adder 82 via the storage register 83, weighting is performed in substantially the same manner as described above. This can be achieved by doing.

In this way, by not using a circuit configuration that uses FF'T, but by configuring the center frequency of the bandpass filter to be movable arbitrarily, the number of filters that turn off the output can be minimized, and the k4TI circuit Even when it is not possible to eliminate all clutter, the signal detection performance in the clutter can be improved.

〔Effect of the invention〕

As detailed above, the present invention makes it possible to improve signal detection performance under unnecessary signals such as weather clutter where the Doppler frequency is not 0, without reducing the ground clutter elimination ability of the r1VT circuit. Can provide 1 radar reward.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing a general radar device, Fig. 2 is a block diagram showing the clutter suppression section in the receiver of Fig. 1, and Fig. 3 is a diagram showing the characteristics of the clutter suppression section shown in Fig. 2. , FIG. 4 to FIG. 6 are diagrams for explaining in detail the conventional filter and the present invention, and FIG. 7 and FIG. 8 are block diagrams each showing an example of a filter applied to the present invention. I2...Transmitter, I4...Antenna, I5...Receiver, 2I...) JTI, 22+ to 22n...Filter. Applicant's Representative Patent Attorney Takehiko Suzue Figure 4 Figure 5 Figure 6

Claims (1)

[Claims] means for generating a radar transmission signal, means for radiating this signal into space and receiving a reflected signal from a target, means for demodulating the received signal, and detecting a reflected signal from a fixed target from among the demodulated signals. It consists of an MTI removing means and a plurality of band-pass filters to which the output signal of the i, Set the center frequency of the band to 1. (A radar device characterized by comprising: means for matching the average Doppler frequency output from the TI means.