JPS6018950B2 - radar device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a radar device capable of maintaining good detection performance over a wide range of ranges from short distances to long distances.

Normally, when detecting a target with radar, an appropriate detection method is used depending on the required distance.

In other words, in the case of short-range detection, in addition to the reflected signal from the target, there is also a reflected signal (clutter) from the ground surface (land or sea surface), and the detection of the reflected signal from the target is obstructed by the clutter. Therefore, it is essential to effectively suppress clutter. On the other hand, in the case of long-distance detection, it is only necessary to detect targets in airspace where there is no debris from the ground, and instead it is necessary to increase the reception sensitivity so that targets as far away as possible can be detected.

However, it has generally been difficult to successfully detect a long-range target using a short-range detection method, or conversely, to successfully detect a short-range target using a long-range detection method. The above points will be explained with reference to FIGS. 1 to 5.

FIG. 1 shows an example of a pulse radar system aimed at long-distance detection. This operation will be explained with reference to FIG. Generally, in long-distance detection, the transmission pulse line return cycle is set longer than the radio wave propagation time so that distance information of a long-range target can be uniquely measured (period a in FIG. 3: TL).

Such a transmission pulse line return frequency is set to a low PRF (Pulle
It is called ``Se Repetition Frequency Collection''.

The low PRF transmission signal generated by the transmitter 10 in FIG. , after low noise amplification (high sensitivity reception) in the high frequency amplifier 13, it is mixed with the local oscillation frequency signal from the transmitter 10 in the mixer 14 to become an intermediate frequency,
After being amplified by the intermediate frequency amplifier 15, the moving target display device 1
6 suppresses the clutter and extracts the target signal, and the indicator 17
to be displayed.

FIG. 3b shows the received signal output of the intermediate frequency amplifier 15. A long-range target (delay time tL,) is generally in a clutter-free region, whereas a short-range target (delay time tL, tL2) indicates that it is in a strong clutter region.

The output signal obtained by subjecting this signal to noise suppression processing by the moving target display device 16 is shown in FIG. 3c.

As can be seen from the figure, the clutter suppression performance is insufficient with a low PRF for general head orientation, so it cannot be said that detection of short-range targets is sufficient.

On the other hand, long-range targets can be detected well because there is no clutter. Next, in short-range detection, the transmission pulse repetition frequency is set high in order to obtain high clutter suppression performance. This is called medium PRF or high PRF. FIG. 2 shows a general block diagram.

Although the configuration is almost the same as that in FIG. 1, a distance correlator 18 may be added. This is to prevent the pulse repetition period from becoming shorter as the transmission pulse repetition frequency becomes higher, and therefore from narrowing the range in which distance can be uniquely measured. This is used to determine the distance by taking the correlation.

In FIG. 4, diagram a shows a transmission signal of medium PRF or high PRF.

(The pulse line return period is TM) Figure b shows the received signal as the output signal of the intermediate frequency amplifier. It's on a big level. Furthermore, if the target signal has a delay time exceeding the pulse line return period, an integer multiple of the pulse line return period is subtracted, making the target appear to be closer. Figure c shows an output signal subjected to clutter suppression processing by the moving target display device 16. The reflected signal from a long-range target, which appears to have an apparent delay time of tM, is cluttered due to medium or high PRF. Although this may sound trivial, detection is generally difficult because the reflected signal level from the target is weak at a distance, despite the high clutter suppression performance achieved by medium or high PRF. On the other hand, the reflected signal level from a short-range target whose delay time appears to be tM2 is high, and together with high clutter suppression performance, good detection is possible.

In this diagram c, the distance information detected at tM, tM2 is an apparent value, and a method for obtaining true distance information is to take a correlation using two or more PRFs.

FIG. 5 shows a diagram of the principle of the distance determination method.

This method uses two types of PRF.

FIG. 5a is a transmitted signal of the first PRF, and b is a received signal of the first PRF.

Among the received signals, weak level signals are due to targets located at a far distance, and signals at a strong level are due to targets located at a short distance. Similarly, c is the transmitted signal of the second PRF, and d is the received signal of the second PRF.

When e is correlated with a and b, it appears that both periods (TN1,
This shows that the period expands to the least common multiple (TL') of Tu'
It shows that it can be found as L, TL2.

The above is an explanation of the principle in the time domain, but in reality, in a distance correlator, (t center, tM'',), (t
TL, , TL2 are calculated from the combination of M'2, tM''2), and TL' does not necessarily have to match the TL in FIG. 3.

This invention was made in order to eliminate the drawbacks caused by these conventional methods mainly focusing on either long-range detection or short-range detection.
The present invention provides a radar device that achieves both short-range detection.

An embodiment of the invention shown in FIG. 6 will be described below.

In Fig. 6, as a transmitter, the transmission frequency is f,, f2
A first transmitter 101 and a second transmitter 1 that are different from each other.
02, the first transmitter 101 has a low PRF, and the second transmitter has a plurality of medium PRFs or high PRFs that are sequentially switched at regular intervals.

These transmission signals are combined by a coupler 19 and then radiated into space from the antenna 12 via the transmission/reception switch 11. The reflected signal from the target is collected again by the antenna 12, and after wideband amplification by the high frequency amplifier 13, it is amplified at a demultiplexing number of 20.
frequency. Each received signal is sent to a mixer 14
1.142 becomes an intermediate frequency signal, and intermediate frequency amplifier 1
After amplification at 51 and 152, respectively, the moving target display devices 161 and 162 suppress clutter. The medium PRF or high PRF received signal from the transmitting frequency has two or more PRFs.
Since the signals are switched and received at fixed time intervals, the distance correlator 18 stores the received signals at each time interval and correlates different PRF signals according to the principle shown in FIG. 5 to output true distance information. These signals are alternately displayed on the switching indicator 17 by gate circuits 211 and 212 in synchronization with the transmission period of the transmission frequency. Note that the processing time required for the distance correlator 18 to correlate different PRF signals at fixed time intervals is an allowable error that can be ignored compared to the movement of the target.

These operations will be explained with reference to FIG.

The transmitted signal by the first transmitter 101 has a frequency f. Dea
As shown in the figure, the PRF is low.

Figure b shows the intermediate frequency output of the moving target display device 161, and figure c shows the output of the intermediate frequency detected as a video signal, in which a long-range target is detected in a clutter-free area. Fig. d shows a gate signal synchronized with Fig. a, and the gate 211 passes the signal shown in Fig. C only during the period when the gate is on in Fig. d, to obtain an output as shown in Fig. e. On the other hand, the diagram f shows a transmission frequency PRF or high PRF transmission signal generated by the second transmitter 102, and it is assumed that, for example, two or more PRFs are switched and used in a time division manner for distance correlation. FIG.
Figure h shows the true distance information output processed by the distance correlator 18 based on such a signal obtained for each PRF.

The gate 212 passes this signal only during the ON period of the gate signal in figure i, which is synchronized with figure a, to obtain an output as shown in figure j.

As the input to the indicator 17, the signals that alternately switch from the gates 211 and 212 (Fig. e, Fig. i) are combined to form a waveform as shown in Fig. k.

In FIG. 8, a signal like that shown in FIG. 7 k is sent to the indicator 17 by PP1 (
PlanPositionIndication) The display method is shown in Figure a, where the PPI circular display surface is concentrically divided into two, with the PRF or high PRF reception signal of the transmit frequency on the inside (near range), and the outside (long range). Figure b shows the low PRF received signal of transmission frequency f, and Figure b also shows good clutter suppression performance in airspaces where there is chaff clutter or weather clutter due to rain, clouds, etc., even at short distances. This shows a case where a transmission frequency f2, medium PRF, or high PRF received signal is displayed in a sector-shaped or arbitrary-shaped distance/azimuth area specified so as to obtain the following.

One embodiment of this invention has been described above, but as is clear from this, by using the two transmission formats together and switching over time, good detection performance can be achieved over the entire range from short distances to long distances. can be obtained.

In addition, in the above, distance correlation is performed by time-divisionally switching two or more PRFs at one transmission frequency f21 as a medium PRF or high PRF transmitter, but the present invention is not limited to this. As shown in Figure 2, as a medium PRF or high PRF transmitter, the transmitting frequency is generated by the number of multiple PRFs (f2,..., fn+,) for distance correlation, and transmitted simultaneously, and the received signals are also analyzed. It is also possible to shorten the processing time and improve detection performance by performing parallel processing after dividing the signals into waveforms. In addition, what is shown in FIG. 9 is an example in which RF is generated using the transmitting frequencies f2 and f3 as a medium PRF or high PRF transmitter, and what is shown in FIG. ...・, fn ten,
This is an example of generating nPRF.

As described above, according to the present invention, roughly two types of transmitters are used in combination, these are transmitted simultaneously, and the reception signal suitable for each detection is switched depending on the long-distance area and the short-distance area. Good detection performance can be obtained over the entire distance range.

[Brief explanation of drawings]

Fig. 1 is a block diagram of a conventional low-PRF general pulse radar device, Fig. 2 is a block diagram of a conventional medium-PRF or high-PRF general pulse radar device, and Fig. 3 is a block diagram of a conventional low-PRF general pulse radar device. FIG. 4 is an explanatory diagram of the operation in FIG. 2, FIG. 5 is a principle diagram of the subordinate distance correlation method in FIG. 2, and FIG. 6 is an illustration of an embodiment of the present invention. 7 is an explanatory diagram of the operation of one embodiment of the present invention, FIG. 8 is a diagram illustrating an example of PPI display in one embodiment of the present invention, and FIG. 9 is a diagram illustrating another embodiment of the present invention. As an example, FIG. 10 is a block diagram of a system in which distance correlation is obtained by simultaneous nPRF. FIG. 10 is a block diagram of a method in which distance correlation is obtained by simultaneous nPRF in yet another embodiment of the present invention. In the figure, 101 is a low PRF transmitter, 102 is a medium PR
F or high PRF transmitter, 12 is an antenna, 19 is a combiner, 20 is a demultiplexer, 211 and 212 are gates, 1
7 is an indicator. Note that the same reference numerals in the figures indicate the same or corresponding parts. Figure 1 Figure 4 Figure 2 Figure 3 Figure 8 Figure 5 Figure 9 Figure 6 Figure 10 Figure 7

Claims (1)

[Claims] 1. A first transmitter that generates a transmission signal with a transmission frequency f_1 at a predetermined low pulse repetition frequency;
A second transmitter that generates a plurality of medium or high pulse repetition frequencies by sequentially switching a transmission signal of a transmission frequency f_2 different from 1 at regular intervals, and each transmission signal of the first and second transmitters. An antenna that emits through a coupler and receives a reflected signal from a target object, and a received signal of this antenna is passed through a distributor to suppress clutter from the received signal corresponding to the transmitted signal of the above-mentioned transmission frequency f_1 and obtain distance information. a first reception processing means for extracting distance information from a received signal corresponding to the transmission signal of the transmission frequency f_2, a second reception processing means for suppressing clutter and extracting distance information, and an output of the second reception processing means. a distance correlator that stores signals at regular time intervals and takes correlations between different pulse repetition frequency signals; and a distance correlator that synchronizes with the repetition period of the low pulse repetition frequency and divides this period into two. gate means for passing the output signal of the first reception processing means during the other period, and a sweep for synchronizing the output signal of the gate means with the repetition period of the low pulse repetition frequency. A radar device equipped with an indicator that displays a bright spot superimposed on a signal. 2 a first transmitter that generates a transmission signal with a transmission frequency f_1 at a predetermined low pulse repetition frequency;
1 and a second transmitter that generates each transmission signal of a plurality of transmission frequencies different from each other at different medium or high pulse repetition frequencies, and passing each transmission signal of the first and second transmitters through a combiner. an antenna for receiving reflected signals from a target object; 1 reception processing means and a plurality of reception processing means for suppressing clutter and extracting distance information from the reception signals corresponding to the respective transmission signals of the plurality of transmission frequencies, and from each output signal of the plurality of reception processing means. a distance correlator that takes a correlation between signals of different pulse repetition frequencies; and a distance correlator that synchronizes with the repetition period of the low pulse repetition frequency and divides this period into two, passing the output signal of the distance correlator during one period, and the other gate means for passing the output signal of the first reception processing means during the period; and displaying a bright spot by superimposing the output signal of the gate means on a sweep signal synchronized with the repetition period of the low pulse repetition frequency. A radar device equipped with an indicator.