JPS595875B2 - radar device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a radar device equipped with a receiving system that detects only Doppler-shifted components from a received signal, and which is also capable of detecting a fixed target.

Conventionally, the first radar, commonly referred to as MTI, utilizes the Doppler effect to remove fixed targets and detect and instruct only moving targets without impairing its function as a pulse radar.
There is a moving target indicating device shown in the figure.

That is, this device applies an original signal whose frequency is sufficiently stable as a radar from an original oscillator 1 to a transmission signal generator 2 and a transmission side local signal generator 3, respectively, which obtain desired frequency signals by multiplying or the like.

After the output signals of these two generators 2 and 3 are mixed in a mixer 4 to form a signal at a transmission frequency, a modulation pulse is applied from the outside and the signal is passed through an amplifier 5 having means for performing pulse modulation, and is further switched to transmit/receive. The antenna 7 emits the transmitted radio waves through the transmitter 6 as a transmission radio wave.

On the other hand, the received radio waves obtained by reflecting the transmitted radio waves by the target are transmitted to the amplifier 1 via the antenna 1 and the transmitter/receiver switch 6.
0.

A distance gate is applied to the amplifier 10 near the transmission time by a signal from the distance gate circuit 9, so that leakage transmission radio waves can be suppressed.

The signal from the amplifier 10 is led to a mixer 11, where it is converted into a so-called intermediate frequency signal by a local signal from a local signal generator 12 on the receiving side, which operates in the same way as the local signal generator 3 on the transmitting side. The signal is then guided to a clutter removal filter 14 via an amplifier 13.

The clutter removal filter 14, for example, removes the reflected signal of a fixed target (aperture shown) which does not form a so-called line spectrum due to the spread due to clutter fluctuations or the spread due to antenna scanning, as shown in the frequency spectrum of FIG. 2a. By removing the reflected signal from the moving target, only the signal reflected from the moving target as shown in the figure is extracted in the section A of the figure.

Next, the signal from the filter 14 is passed through the narrowband filter bank 1 through an amplifier 15 that compensates for the attenuation caused by the filter.
6 and a detector 1γ, the signal is supplied to the indicating device 18 as an output signal that allows the target's moving speed to be identified.

And more than that. 19 each of both local generators 3
, 12 is required to be sufficiently stable in terms of frequency, and here the frequency relationship between these is treated as so-called coherent, but it does not need to be coherent as long as it is stable.

Generally, radar equipment is calibrated by comparing information on the target's direction and distance (obtained through trigonometry) visually observed with the information on the direction and distance actually measured by the radar equipment. A fixed target is used as the target to be measured.

However, in the above-mentioned moving target indicating device, since the fixed target is of course removed in order to detect the moving target, the fixed target cannot be used during adjustment.

Therefore, if a fixed target is to be used for adjustment, it is necessary to take some kind of measure to cut off the so-called MTI function, even if only temporarily, and installing this function in parallel will complicate the device. At the same time, there is a drawback that the operation becomes complicated.

Further, this applies not only to the above-mentioned adjustment, but also to other cases where signals specific to the radar device are processed.

Therefore, there is an idea to use a moving target in this case, but in reality it is extremely difficult for the following reasons.

That is, it is necessary to prepare a flying object as a moving target, or to install a so-called pseudo signal generator (transponder) at a certain distance away to make it appear as if there is a Doppler signal.

In the case of the latter transponder, a gap (error) occurs between the actual distance due to the delay time of the return pulse generator from the transponder and the distance to the transponder, making it impossible to calibrate the true value of the distance, and making it difficult to stabilize the frequency. There is a drawback that the degree must be very high.

In this case, even if the so-called transponder delay were eliminated, the transponder is installed relatively close to the radar, so it may fall within the recovery time of the device between transmission and reception. In many cases, transponder methods are less practical.

In addition, in order to be able to detect fixed targets with such a system, there is a method of artificially converting the reflected signal from a fixed target into a moving target, for example, one method is to shift the transmitted signal by an amount corresponding to the Doppler frequency. The first to try to adopt the method
I have an idea.

However, in this case, the entire transmitted signal is equivalent to the moving target, and there is a great danger that the transmission signal will directly reach the receiving system 19 beyond the isolation of the transmitting/receiving switch 6 and the suppressing effect of the leakage transmitted radio waves of the distance gate circuit 9 in FIG.

Since the clutter removal filter 14 usually has a narrow band, the signal output from the so-called Doppler filter to the indicating device 18 becomes a continuous signal and cannot be identified.

Such a wrap-around phenomenon is a phenomenon common to radar devices in general, and cannot be easily eliminated.

In addition, in the above system, the repetition frequency of the radar is relatively high, and the distance gate circuit 9 is operated by a control signal from another system, so it suffers from a so-called foldover signal.

A second possibility is that the clutter removal filter 14 may be bypassed.

This idea seems very simple at first glance, but in reality, it is difficult to switch to bypass the clutter removal filter and the so-called Doppler filter because they are combined with high impedance and high gain. As mentioned above, these are narrowband filters, so if they are bypassed, it is necessary to change most of the signal processing methods, resulting in a system that performs signal processing in two series, which is extremely disadvantageous economically. .

Furthermore, a third idea is to shift the frequency of the local oscillator in the receiving system by an amount corresponding to the Doppler frequency, but in this case, it is almost the same as shifting the frequency of the transmitting system according to the first idea. There are disadvantages.

The present invention has been made in view of the above-mentioned points, and an object of the present invention is to provide a radar device capable of obtaining a pulsed Doppler radar which eliminates the various drawbacks of the conventional methods described above and is capable of issuing fixed target detection instructions extremely well. The purpose is to

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

Therefore, in FIG. 3, the parts denoted by the same numbers as in FIG. 1 have the same configuration, and a detailed explanation thereof will be omitted.

That is, the transmission system 8 is constructed in the same manner as in FIG. 1 and operates in the same manner.

The difference from the configuration shown in FIG. 1 is that in the receiving system 19, a gate circuit 20 is newly installed between the local signal generator 12 on the receiving side and the mixer 11, and a second A new local signal generator 21 will be installed.

Furthermore, this newly installed gate circuit 20 includes a distance gate circuit 9.
This point is configured to provide more signals.

Here, the output frequency of the second local signal generator 21 is a frequency obtained by shifting the output frequency of the local signal generator 12, which is the first local signal generator on the receiving side, by an amount equivalent to the Doppler frequency.

That is, when issuing an instruction to detect a specific fixed target located at a predetermined distance known in advance, the receiving system 19 as shown in FIG.
The received signal appearing in the mixer 11, that is, the received signal containing the component A of the transmitted signal leaked to the receiving system 19 and the reflected component B from a specific fixed target, is applied to the mixer 11 as shown in FIG. The component A of the local frequency leaked from the transmitted signal is given as a local signal F1 from the first local signal generator 12 and suppressed as before, and the reflected component B from a specific fixed target is suppressed by a newly established second local signal. Generator 2
1, it is given as a local signal F2 shifted by an amount equivalent to the Doppler frequency, converted to an intermediate frequency signal as if it were a moving target, and then subjected to the same signal processing as conventional methods to be sent to an indicating device. Give instructions.

Here, local signal F1. F2 is switched by applying a gate signal as shown in the figure from the distance gate circuit 9 to the newly installed gate circuit 20.

The timing of applying the local signal F2 is such that signal processing is performed on a specific fixed target as if it were a signal from a moving target, so the spectrum of the signal as shown in Fig. 2 is Just make it a little wider so as not to disrupt the relationship.

Therefore, according to the above-mentioned radar device, the pulse Doppler radar is capable of instructing the detection of a fixed target by substantially one series of signal processing without changing the main configuration of the receiving system 19, that is, in this case, a moving target. An indicating device can be obtained which greatly facilitates the adjustment and calibration of such radar devices, especially in the case of tracking radars or monopulse radars.

Moreover, in such a radar device, the fixed target suppression and removal effect that the radar device inherently has is utilized for leakage components of transmitted signals and reflected components from unnecessary fixed signals, as described above. There is no problem.

Note that the present invention is not limited to the above-described embodiments, and various modifications may be made without departing from the gist of the present invention.

For example, in the above embodiment, the second local signal generator 21 is newly provided in the receiving system 19, and the gate circuit 20, which is also newly installed, uses the distance information from the distance gate circuit 9 to generate the second local signal generator 21. The case has been described in which the local signal is shifted by an amount equivalent to the Doppler frequency, but this is not limitative. As shown in FIG. Then, the output of this is mixed with the output of the first local signal generator 12 by a newly provided mixer 23 and added to the gate circuit 20. The directly applied local signal is output from the mixer 23 using distance information from the distance gate circuit 9 (i.e., a local signal obtained by mixing the output of the first local signal generator 12 with the output of the pseudo Doppler oscillator 22). It may be possible to switch to .

That is, in this case, a means is used to mix a part of the output of the first local signal generator 12 with a frequency shifted by an amount equivalent to the Doppler frequency, and furthermore, frequency modulation is used instead of this. It is also possible to use a method that allows the user to do so.

As described in detail above, according to the present invention, it is possible to provide a radar apparatus that can obtain a pulsed Doppler radar that eliminates various conventional drawbacks and can extremely effectively issue a fixed target detection instruction.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a conventional pulse Doppler moving target indicating device, FIGS. 2a and 2b are diagrams showing frequency spectra of reflected waves from a fixed target and a moving target, respectively, and FIG. 3 is an embodiment of the radar device of the present invention. Configuration diagram showing an example, Figure 4 a, b,
FIG. 5 is a timing diagram illustrating the operation of FIG. 3, and FIG. 5 is a configuration diagram showing another embodiment of the present invention. 8...Transmission system, 19...Reception system, 20
. . . gate circuit, 21 . . . second local signal generator, 22 . . . pseudo Doppler oscillator, 23.
...Mixer.

Claims (1)

[Claims] 1. An antenna that receives a reflected wave from a target due to a radar transmission signal, a transmitter/receiver switch to which the received signal from the antenna is supplied, and an amplifier to which an output signal of the transmitter/receiver switch containing the leakage component of the transmitter signal is supplied. a distance gate circuit that supplies a distance gate signal to the amplifier so as not to amplify leakage components of the transmission signal; a local signal generator that generates a first local signal; and a frequency of the first local signal. means for generating a second local signal having a frequency difference corresponding to a predetermined Doppler frequency; Outputting the first local signal except when receiving a reflected signal from a fixed target at a predetermined distance, and outputting the second local signal using a distance gate signal supplied from the distance gate circuit when receiving the reflected signal. A radar device comprising a gate circuit for switching and extraction, a mixer to which an output signal of the gate circuit and an output signal of the amplifier are supplied, and means to which a signal from the mixer is supplied to detect and indicate a moving target. .