JPH0157312B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to improvements in passive radar systems.

Radar emits radio waves in the form of a sharp beam, and the reflected waves from objects in space are collected at the same point (an antenna).
It is a system that measures the direct distance to an object from the round trip time of radio waves by receiving it at the antenna, and its direction from the directivity of the antenna, or obtains the relative speed of the object from the change in the reflected frequency from the emission frequency. .

In recent years, in addition to military use, it has been developed and continues to be improved for various purposes such as navigation for aircraft and ships, and meteorological measurement of clouds and rain.

As is well known, the frequency of radio waves in radar is selected from 10 cm to millimeter range depending on the purpose of use, and its application range is wide ranging from the acoustic range to the optical range.

Pulse radio waves are emitted and received by rotating or swinging the main body of the antenna, which normally serves as transmitter and receiver, or by rotating or swinging its sharp directivity in any direction using electronic switching scanning of a phased array.

Therefore, the received signal of the reflected wave is displayed on a CRT that is linked to the rotation or swinging operation of the antenna.
Check the target object by displaying its coordinates on the screen.

Note that the relative velocity of an object obtained by measuring the reflection frequency follows the Doppler effect.

In military applications, etc., various means have been provided, including changing the frequency to be used to a plurality of frequencies, in order to prevent radio waves of the same or wide band from being emitted to interfere with the measurements of the other party. Passive radar systems are one of the countermeasures.

A passive radar system consists of one transmitting station and one or more receiving stations using a directional antenna. In conventional passive radar systems, if the mutual positions of the transmitting station and each receiving station are determined in advance, the incident azimuth of the reflected wave is determined based on the directivity of the antenna at the receiving station, and the distance is determined in the same way as with normal radar. is obtained from the time required for the radio waves emitted from the transmitting station to be reflected from the target object and arrive at the receiving station, so it is no different from measuring azimuth and distance using the same antenna, but in order to maintain measurement accuracy, the transmitting station Since the timing of the radio waves that are constantly emitted is sent as a synchronized signal to the transmitting station, a separate line with stable propagation is required, and jamming radio waves can be avoided by taking advantage of the differences in the directivity of multiple transmitting stations. The disadvantages are that the location of the station is restricted and the system is expensive.

The present invention aims to provide means to eliminate this drawback.

For this reason, the present invention provides at least one transmitting station that emits radio waves to detect the presence of an object, and at least one receiving station that receives the reflected waves of the radio waves from the target object, at a different location from the receiving station, In a passive radar system that obtains an indication of the position coordinates of the target object, the transmitting station emits pulsed radio waves from a directional antenna that rotates or oscillates on a circumference around a vertical axis. Equipped with a function to insert a pulse train modulated with information corresponding to the launch azimuth and launch angle into pulse radio waves, the receiving station is a directional antenna that rotates or oscillates on a circumference around a vertical axis. It has a function of detecting the incident azimuth of the reflected pulse radio wave from the target object and the launch azimuth and launch angle from the received signal from the reflected pulse radio wave using The present invention is characterized in that the position coordinates of the target object are obtained from the angle, launch angle, incidence azimuth angle, and the positions of the transmitting station and receiving station.

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

FIG. 1 shows the passive mode in one embodiment of the present invention.
Three-dimensional diagram explaining position calculation in radar system,
Figure 2 is a plan view of Figure 1 projected onto a plane;
The figure shows a block diagram of a passive radar system in one embodiment of the present invention.

In Fig. 1, the coordinates of transmitting station A are x _a , y _a , z _a ,
The coordinates of receiving station B are X _b , y _b , z _b and target object T
Let the coordinates of be x, y, and z. In Figure 3, 1 is the transmitting station, 2 is the receiving station, 3 is the target object, 10, 2
0 is a directional antenna whose beam shape is, for example, a pencil beam; 11 and 21 are control units; 12 is a transmitter;
13 is a modulation section, 14 and 24 are antenna drive sections, 1
Reference numerals 5 and 25 designate an azimuth detection section, 22 a reception section, 23 a demodulation section, 26 a storage section, and 27 a display.

In FIGS. 1 and 2, if a radio wave is emitted from the transmitting station A at an azimuth angle θ _a and an elevation angle φ _a and travels straight, and the reflected wave from the target T is received by the receiving station B at an azimuth angle θ _b , then In Figure 2, x _b −x _a = (y−y _a ) tanθ _a − (y−y _b ) tanθ _b y _a − _{y a} = (x−x _b ) cotθ _b − (x−x _a ) cotθ Since the relationship is _a , the coordinates of the target object T are x, y, z
can be obtained using the following formula.

x=( _a cotθ _a −x _b cotθ _b +y _a −y _b ) /(cotθ _a − cotθ _b ) y=(y _a tanθ _a −y _b tanθ _b +x _a −x _b ) /(tanθ _{a −} tanθ _b ) z=l _a tanφ _a + _z aHowever, l _a = [(x-x _a ) ² + (y-y _a ) ² ] ^1/2 , cotθ _a −cotθ _b ≠0, tanθ _a −tanθ _b ≠0 , Furthermore, cotθ _a , cotθ _b , tanθ _a and tanθ _b are not 0 or infinite.

Here, the emission azimuth θ _a and the emission elevation angle φ _a of the emitted radio waves at the transmitting station A were calculated assuming that they were given in advance, but in one embodiment of the present invention, the emission azimuth Obtain θ _a and launch elevation angle φ _a .

In FIG. 3, it is assumed that the control section 11 of the transmitting station 1 organically controls the transmitting section 12, the modulating section 13, the antenna driving section 14, and the azimuth detecting section 15 to emit radio waves from the directional antenna 10. . Transmission section 12
is a conventional pulse transmitter made by Klystron or the like. Antenna drive unit 14 according to instructions from control unit 11
The directional antenna 10 is rotated continuously at a constant angular velocity of 360° about a vertical axis or oscillated back and forth within a set azimuth angle range. Assume that it rotates continuously at a constant angular velocity.

On the other hand, the azimuth angle detection unit 15 attached to the rotation axis of the directional antenna 10 is configured with an angle detection function such as an optical rotary encoder, for example,
The changing azimuth angle of the directional antenna 10 is always sent to the modulator 13. Further, the antenna driving section 14 swings the directional antenna 10 along the vertical axis according to the elevation angle instructed by the control section 11, and the control section 11 always sends the elevation angle of the directional antenna 10 to the modulation section 13. Send.

The modulator 13 transmits, for example, a pulse code modulation (PCM) signal to the transmitter 12 in accordance with the azimuth signal from the azimuth detector 15 and the elevation signal from the controller 11, and transmits pulse radio waves output from the transmitter 12. Modulate.

Therefore, when the reflected wave of the radio wave emitted from the directional antenna 10 to the target object 3 is received by the receiving station 2, the emission azimuth and emission angle of the directional antenna 10 at the transmitting station 1, that is, the The azimuth angle θ _a and the elevation angle φ _a in Fig. 2 are demodulated so that they can be recognized.

However, multiple bits are required to transmit azimuth angle information and elevation angle information by RCM, and during this time, the directional antenna 10 continuously transmits the azimuth angle and elevation angle information.
Since the elevation angle is changed, it is necessary to determine in advance the relationship between multiple bits of launch azimuth angle and launch elevation angle information and the pulses that are emitted at the correct launch azimuth and launch angle.

Therefore, for example, like standard radio wave JJY, multiple bits containing launch azimuth angle information and launch angle information are sent out in advance, and the first pulse immediately after transmission corresponds to the launch azimuth angle information and launch angle information that preceded the launch angle information. Use as reference pulse.

Alternatively, the firing azimuth information, the firing elevation angle information, and pulses for distance measurement may be alternately sent out, and for example, the third pulse among the pulses for distance measurement may be used as the reference pulse.

Note that the directional antenna 10 rotates at a constant angular velocity, so if the firing elevation angle is fixed while it rotates, for example, 360 degrees, then if the emitted pulses are at constant intervals, each pulse will all correspond to an azimuth angle. Therefore, the insertion of azimuth information pulses by PCM is
Needless to say, it's good to have it in just a few places within 360 degrees.

Further, the launch azimuth angle information and launch angle information to be notified in advance may be transmitted by means other than the launch pulse radio waves for distance measurement, for example, by means of communication from the transmitting station to each receiving station. In this way, the receiving station 2 can easily obtain the launch azimuth and launch elevation angle θ _{a and φ a in} FIG. 1 at the transmitting station 1.
can be obtained.

Similarly to the transmitting station 1, the receiving station 2 also has a control unit 2.
1 controls each part. The directional antenna 20 is rotated or swung in the same manner as the antenna 10 by the antenna drive section 24 according to instructions from the control section 21, but for example, n=
15, that is, 15 RPM, and the control units 11 and 21 control the antenna drive unit 14 so that the emission azimuth θ _a and the incident azimuth θ _b of the directional antenna of the transmitting station and the receiving station are 0° when true north. , 24 via the directional antenna 10, 20
control.

Here, the directional antenna of the transmitting station is set to 1 as shown above.
The reason why the emission azimuth angle changes by 6 degrees per second and the incident azimuth angle of the receiving station's directional antenna changes by 90 degrees per second is that both directional antennas are directed toward the target object and the reflection from the target object is reflected. This is to increase the reception probability of waves, and the larger n is, the higher the reception probability becomes.

Furthermore, the reception probability can also be increased by limiting the swing range of the antenna regarding the directivity of the receiving station. Furthermore, n phased array antennas are arranged at equal angles on a circumference centered on the vertical axis, and the incident azimuth θ _b is constantly adjusted by using the difference in electric field strength detected by adjacent antennas. You can ask for it.

Now, the incident azimuth θ _b of the received signal is detected by the azimuth detection section 25 , and the detection signal θ _b is detected by the control section 21
sent to. On the other hand, the reception signal of the reflected radio wave received by the directional antenna 20 is sent from the reception station 22 to the demodulation section 23, and the information on the launch azimuth and launch angle of the transmitting station 1 that the pulse has is obtained and sent to the control section 21. It will be done.

The control unit 21 uses the data of the launch azimuth and launch elevation angle from the demodulation unit 23 and the incident azimuth angle from the azimuth angle detection unit 25 and uses the arithmetic program stored in a part of the storage unit 26 to perform the calculation as shown in FIG. target object T at
The coordinate position (x, y, z) of can be obtained.

In addition, in practical use, cotθ _a , cotθ _b , tanθ _a ,
Each value of tanθ _b becomes zero or infinite and cannot be calculated.
Alternatively, in order to prevent calculation accuracy from decreasing in the vicinity of zero or infinity and from being unable to receive reception due to jamming radio waves, it is desirable to install a plurality of receiving stations 2 at different locations. Further, the control unit 21 displays information obtained through each unit on the screen of the display 27 as a light spot that is linked to the movement of the directional antenna 20.

Thus, according to one embodiment of the present invention, the transmitting station 1
If the coordinate positions of transmitting station 1 and transmitting station 2 can be recognized without directly transmitting a synchronization signal to transmitting station 2, receiving station 2 can determine the emission azimuth and elevation angle of radio waves at transmitting station 1 and the incident azimuth at receiving station 2. By obtaining the angle, an asynchronous passive radar system is obtained that can calculate the coordinate position of the target object.

In the present invention, the rotation or swing of the directional antenna has been explained using a mechanical operation, but instead of this, it is possible to arrange n phased array antennas at equal angles on a circumference centered on a vertical axis. , a transmitting station that electronically switches this to emit pulses containing launch azimuth angle information and launch angle information, and n phased array antennas arranged at equal angles on a circumference centered on the vertical axis. A similar effect can be obtained as a receiving station that can measure the incident azimuth angle based on the proportional relationship by utilizing the property that the electric field strength received in response to the incident radio wave from the azimuth differs for each adjacent phased array antenna. Needless to say, it will happen.

[Brief explanation of drawings]

FIG. 1 is a three-dimensional view explaining position calculation in a passive radar system according to an embodiment of the present invention, FIG. 2 is a plan view of FIG. 1 projected onto a plane, and FIG. 3 is according to an embodiment of the present invention. FIG. 1 is a block diagram of a passive radar system. In the figure, 1 is a transmitting station, 2 is a receiving station, and 3 is a target object.

Claims (1)

[Claims] 1. At least one transmitting station that emits radio waves to detect the presence of an object and a receiving station that receives the reflected waves of the radio waves from the target object are provided at a different location from the transmitting station. , in a passive radar system that obtains an indication of the position coordinates of the target object, the transmitting station emits pulp radio waves from a directional antenna that rotates or oscillates on a circumference around a vertical axis, and Equipped with a function to insert a pulse train modulated with information corresponding to the emission azimuth and emission angle into the emitted pulse radio wave, the receiving station has a directivity that rotates or oscillates on the circumference around the vertical axis. Using an antenna, the incident azimuth of the reflected pulse radio wave from the target object and the emission azimuth from the received signal of the reflected pulse radio wave,
Equipped with a function to detect the emission elevation angle, the emission azimuth angle, emission elevation angle and incident azimuth angle of the pulse radio wave obtained at the receiving station, and the emission station;
A passive radar system characterized in that an indication of the position coordinates of the target object is obtained from the position of a receiving station.