JPH0456952B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a radio wave detector that detects the direction of arrival of an opponent's radar signal and its frequency components.

Conventional array configuration and its problems In the past, frequency analysis of incoming radio waves and direction finding were generally performed in different receiving systems. As a method for performing this in the same receiving system, a method is known in which radio wave detection is performed by combining an acousto-optic element having multichannels and a two-dimensional photodetector. This type of device is constructed as shown in FIG.
Here, the principle of an acousto-optic element will be briefly explained. Acousto-optic elements consist of a medium that transmits light, such as glass or crystal, and an ultrasonic transducer that is bonded to the surface of the medium and converts high-frequency electrical signals into ultrasonic signals. The operation of an acousto-optic device is to transmit a laser beam through the device and apply an ultrasonic signal in the direction of travel of the laser beam at an angle commonly referred to as the Bragg angle. At this time, a refractive index distribution is generated in the medium due to the ultrasonic waves, which acts as a phase diffraction grating and diffracts the laser beam. This diffraction angle is proportional to the frequency of the ultrasound signal, ie, the frequency of the driving electrical signal, and the intensity of the diffracted light is related to the strength of the ultrasound, ie, the strength of the electrical signal.

The element spacings of the plurality of element antennas arranged on a straight line are all made to be different. Various methods have been considered for this arrangement interval from the viewpoint of detection sensitivity and cost, but for example, the interval between 1b and 1c is set to be relatively prime to the interval between 1a and 1b, for example, 3:4, and then, The interval between 1c and 1d is also the same as the interval between 1b and 1c, 3:4. There is also a method of arranging element antennas by repeating the same relationship one after another in this way. Incoming radio waves 2 from the angle θ direction received by the plurality of element antennas 1a to 1z arranged in this manner are dropped into the drive frequency range of the acousto-optic element as an intermediate frequency by the electric circuit 3, and are transmitted by the electric circuit 4. The power is amplified by each receiving antenna element 1a.
~Multi-transducer 6a on the acousto-optic element 5 arranged in proportion to the arrangement interval with respect to 1z~
6z. On the other hand, the signals applied to each of the multi-transducers have respective delay time differences in arrival radio waves reaching each antenna. The laser beam from the laser beam 7 is made into a parallel beam by the expanding optical system 8, and is then converted into a parallel beam by the acousto-optic element 5.
The beam is irradiated so that it forms a Bragg angle. The light passing through the acousto-optic element 5 is transmitted to each transducer 6a~
It is diffracted by ultrasonic signals emitted from 6z, each having a delay time. In other words, there is a delay time difference, that is, a phase difference, caused by each antenna between these diffracted lights. These diffracted lights 9
When these are caused to interfere with each other by the Fourier transform lens 10, an image is formed on the lens focal plane 11 at a position that is deflected vertically and horizontally from the central axis direction of the surface.

Information in the vertical direction from the central axis direction, that is, in the axial direction corresponding to the direction of propagation of the ultrasonic wave, corresponds to the diffraction angle and therefore has signal frequency information as described above. On the other hand, the left and right directions are caused by the phase difference between the respective diffracted lights, and have information on the delay time difference of the ultrasound signals. This delay time is the difference in arrival time of radio waves to each antenna, and this depends on the array interval of the antennas and the angle of incidence on the antennas (the angle between the direction of arrival of the radio waves and the direction of the array of the antennas). Therefore, a two-dimensional photodetector 12 is placed on the focal plane 11,
By sequentially reading out the output of the two-dimensional photodetector 12 by the signal processor 13, the frequency and direction of the incoming radio waves can be determined. However, in this method, the delay time that occurs between each antenna is determined by the incident angle of the incoming radio wave with respect to the antenna arrangement direction, and this incident angle is determined by the equal phase difference between each antenna element 1a to 1z as shown in FIG. The direction of the incoming radio wave that causes
Although it is known that it exists on the cone 15, it cannot be determined uniquely. Therefore, the direction of the incoming radio waves cannot be determined.

Purpose of the Invention The present invention was made in order to solve the conventional problems as described above, and it is an object of the present invention to provide a radio wave detector that can accurately and instantaneously detect the frequency and direction of incoming radio waves. With the goal.

Structure of the Invention The present invention achieves the above object, and includes a plurality of elements arranged on at least two non-parallel straight lines for receiving incoming radio waves, and arranged such that the intervals between the element antennas are different from each other. For the antenna group and each of the element antenna groups, a reception electric circuit connected to each element antenna of the element antenna group and the output corresponding to each element antenna from the electric circuit are connected, and the antenna interval is It has a plurality of transducers arranged in a proportional relationship with the acousto-optic element provided corresponding to each of the plural element antenna groups, and for irradiating parallel laser light to the acousto-optic element. It consists of a laser light source, an optical system that images the diffracted light, a two-dimensional detector that detects the diffraction system, a signal processor that reads out the output, and a calculator that calculates the direction from the outputs of these two systems. This is a radio wave detector that provides a radio wave detector.

DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of the present invention will be described based on the drawings.

FIG. 3 is an overview diagram of a radio wave detector according to an embodiment of the present invention.
A plurality of element antenna groups 21 arranged so that the antenna spacing, the second and third antenna spacing, and the third and fourth antenna spacing are all different.
a, 21b, ..., 21z and 22a, 22b, ...
..., 22z, and two sets of electrical circuit systems and optical systems connected thereto and having the same characteristics as shown in FIG. Fig. 3 Odor electric circuit 23, 2
3' is a receiver, and element antenna groups 21a to 21z and 22a to 2 receive incoming radio waves (not shown).
2z, and has the role of being amplified and dropping it to a predetermined intermediate frequency. Its output is electrical circuit 24,2
The power is amplified by 4′, respectively, for example, LiNbO ₃ or
Multi-transducer groups 26a, 26b, ..., 26z, 2 arranged on acousto-optic elements 25, 25' made of single crystal such as GaP or TeO ₂
6'a, 26b, . . . , 26'z. On the other hand, the laser beams emitted from the laser light sources 27, 27' are made into parallel beams by the enlarging optical systems 28, 28'.
The light is incident on the acousto-optic elements 25, 25' at a Bragg angle. The laser light that has passed through the acousto-optic elements 25, 25' is transmitted to each transducer group 26a,
26b,..., 26z, 26'a, 26'b,...
..., 26'z and is diffracted by the ultrasonic signal corresponding to the incoming radio wave, and at the same time, these diffracted lights 29, 29' are transmitted to the Fourier transform lens 30,
30' and is imaged onto two-dimensional photodetectors 32, 32' placed at focal planes 31, 31'. The position of this diffracted and interfered light spot indicates the frequency component of the incoming radio wave in the vertical direction of the figure, and the angle of the incoming radio wave in the horizontal direction. The outputs of the two-dimensional photodetectors 32, 32' are sequentially input to signal processors 33, 33'.
A computing unit 34 calculates the true direction of arrival. For example, as shown in FIG. 4, the signal processors 33, 33' output the maximum light intensity at the same frequency as the A/D converter 35 to which the signal from the two-dimensional photodetector 32 or 32' is input. A comparator 36 for detecting the angle to be output, and a counter 3 that sequentially receives this output.
8, a memory 37 for storing data while clarifying the correspondence with frequencies; and a control unit 39 for controlling these.
It consists of When this is used, signals having frequency and angle information from the two-dimensional photodetectors 32, 32' are outputted in time series, converted into digital signals, and then a signal sequence for a certain angle is sent to the comparator 36 as a reference. The signals are compared with each other, and signals exceeding a certain level are stored in the memory 37. Next, a signal train adjacent to the previous signal train of the two-dimensional photodetector, that is, a signal train in a direction slightly different in angle, is input to the comparator 36, which compares the level with the signal previously stored in the memory 37, and selects a larger signal. It is stored in the memory 37 again. This is repeated in sequence, and finally, the angle information having the maximum signal level at a certain frequency is stored in the memory 37.
This finally accumulated signal is processed by the arithmetic unit 3 in FIG.
4 and becomes the data for calculating the true angle.

We will describe the case of detecting radio waves in the vicinity of 10 GHz using a radio wave detector with such a configuration. For each of the element antenna groups 21a to 21z and 22a to 22z, the intervals between adjacent antennas of four half-wavelength dipole antennas are relatively prime, for example, in a relationship of 3:4 and 3:4. Arrange them at intervals of 13.5cm, 18cm, and 24cm as shown in Figure 5a. As the acousto-optic elements 25, 25', four 0.1 mm wide transducers made of ZnO films arranged on a GaP crystal at intervals of 0.9 mm, 1.2 mm, and 1.6 mm as shown in FIG. 5b were used. its center frequency
Set to 1.8GHz. In this case, a bandwidth of 1.3 to 2.3 GHz, that is, 1 GHz can be obtained. The electric circuits 23 and 23' use 8.7G to lower the frequency of the incoming radio waves to the frequency band of the acousto-optic elements 25 and 25'.
Using a local oscillator and mixer (not shown) with a frequency of about Hz, the frequency is reduced to an intermediate frequency, and the electric circuit 24,
At 24', power is amplified to obtain a predetermined diffraction efficiency of the acousto-optic elements 25, 25'. Laser light source 2
7, 27' can use something like a semiconductor laser or a He-Ne laser, and the magnifying optical system 2
8 and 28', the beam is expanded to a beam diameter of 2 to 3 mm and is incident on the acousto-optic element 25. The speed of sound in GaP is approximately 6.5
Km/S, and the time for the ultrasonic wave to cross the light beam (access time) is 0.3 to 0.45 microseconds. The resolution of an acousto-optic element is expressed as the product of frequency bandwidth and access time, and this element, which has a band of 1 GHz, has a resolution of 300 to 450 points. When using a two-dimensional photodetector consisting of 256 x 256 detection elements within the number of resolution points of the element, the upper limit of frequency resolution is that the diffracted light corresponding to a frequency bandwidth of 1 GHz is divided by 256 elements in one axis direction. Therefore, the frequency is approximately 4MHz per element. On the other hand, regarding the azimuth direction, for example, the light/intensity distribution on the two-dimensional photodetector for 10 GHz radio waves arriving from a 45° direction for each element antenna group is as shown in Figure 6 as a result of analysis. . In Figure 6, the vertical axis shows the light intensity on the two-dimensional photodetector, the horizontal axis shows the imaging position of the diffracted light, and shows the light intensity distribution when the direction of the incoming radio wave is changed from 43 degrees to 49 degrees. There is. 44
Comparing the case in the 45 degree direction and the case in the 45 degree direction, the peak positions of the light projected on the two-dimensional photodetector are about 0.1 mm apart, and the intensity of the radio waves in the 44 degree case at the 45 degree peak position is about 80%. corresponds to The dynamic range of sensitivity of two-dimensional photodetectors is usually
Since it is more than 20 dB, it is easy to detect a difference of 10% in light intensity. This shows that with this configuration it is possible to detect the direction of radio wave traffic with a azimuth resolution of about 1 degree.

The principle of determining the true arrival method of radio waves using a radio wave detector configured as described above will be described. The directions of incoming radio waves that can be detected by the element antenna groups arranged orthogonally can be shown as shown in FIG. 7 in the same way as shown in FIG. 2. Element antennas 21a, 21b...21z in the x-axis direction, 22
a, 22b...22z are arranged in the y-axis direction. This arrangement method does not necessarily require that they be actually perpendicular to each other at the origin O as shown in Figure 7, and even if these antenna groups are separated in the z-axis direction or the x and y-axis directions, For radio waves coming from far away, this corresponds to equivalently having both antennas at the origin O. If radio wave 2 comes from the direction of OP,
Element antenna groups 21a arranged in the x-axis direction,...
..., 21z, and the direction in which it is measured is x within a cross section passing through point P and perpendicular to the
The intersection point x _O with the axis and the line segment x _O are on the line connecting the circumference of the circle x whose radius is P and the origin O, and in the configuration shown in Figure 4, the radio waves coming from the direction of OT, that is, from the angle θ _x Detected as . Similarly, in the element antenna groups 22a, ..., 22z arranged in the y-axis direction, the radio waves come from the same angle θ y as the radio waves coming from the line connecting the origin and the circle y centered on the point y _O on the y-axis and passing through the point _P. Detected as radio waves. Using these measurement results θ _x and θ _y , the true direction of the incoming radio wave, that is, the azimuth angle θ in the xy plane and the angle of attack are determined as follows.

In FIG. 7, if the line segment OP has a unit length of 1, the circles x and y can be shown as follows.

<Circle x> y ² + z ² = cos ² θ _x <Circle y> x ² + z ² = cos ² θ The coordinates of _y point Q (x _O , y _O ) are x _O = sinθ _X , y _O = sinθ _y
Then, the angle θ is found as θ=tan ⁻ (x _O /y _O )=tan ⁻ (sin θ _x /sin θ _y ).

Similarly, the angle of attack can be found as = sinz ₁ by finding the value z ₁ of the z coordinate of point P. Using the circle x, this z ₁ can be found from z ² ₁ = cos ² θ _x −sin ² θ _y = sin {(cos ² θ _x −sin ² θ _y ) ^1/2 }.

Note that the intersection of circles x and y exists at point R as well as point P, but if the antennas are arranged on land or on the sea, point R is underground or Since the direction is below the sea surface and is a direction in which radio waves do not actually arrive, the direction of point P can be determined as the true direction of arriving radio waves.

As explained above, using this radio wave detector, it is possible to analyze the frequency and accurately determine the direction of the incoming radio waves.

Furthermore, consider the case where radio waves of a plurality of frequencies arrive simultaneously in the acousto-optic system having the configuration shown in FIG. Radio waves having multiple frequencies are converted into ultrasonic waves having different frequencies within the acousto-optic element, and diffracted light in different directions depending on the frequency is generated. Therefore, on the two-dimensional photodetector, the diffracted light is imaged separately at locations corresponding to each frequency, making it possible to analyze each one. The time used for radio wave analysis is largely determined by the signal readout time of the two-dimensional photodetector. For example, if a 256 x 256 detector array is used and a 10 MHz clock is used, it can be read out in about 7 ms. Therefore, it is possible to perform analysis in approximately 10ms including signal processing time.
It can be seen that it has excellent instantaneous detection. Furthermore, in this method, the light intensity on the two-dimensional photodetector indicates the signal strength of the incoming radio wave, and in addition to frequency information and direction finding information, signal strength information can also be determined at the same time.

In this embodiment, four element antennas are used, but if this number is increased, the azimuth resolution and detection sensitivity will further increase. Further, the arrangement of the element antennas is not particularly limited to orthogonal directions; if the element antennas are not parallel, the direction of the arriving radio waves can be calculated, and if the number of arrangement directions is three, the azimuth accuracy will be further improved.

Effects of the Invention In summary, the present invention provides a plurality of element antenna groups in which a plurality of element antennas are arranged in at least two directions different from each other, and the intervals between the element antennas are different from each other, and each of the element antennas. For each group, a receiving electric circuit connected to each element antenna of the element antenna group and an output corresponding to each element antenna from the electric circuit are connected, and an array relationship having a proportional relationship with the antenna spacing is established. an acousto-optic element having a plurality of transducers arranged in a row and provided corresponding to each of the plurality of element antenna groups, and an optical system that irradiates the acousto-optic element with a laser beam and forms an image of the diffracted light. , a two-dimensional photodetector for detecting the imaged light, and a signal processor for reading and processing the output of the two-dimensional photodetector. The present invention provides a radio wave detector characterized by being equipped with an arithmetic unit that calculates the frequency, intensity, and direction of incoming radio waves instantaneously and at the same time, and its azimuth resolution is extremely high.

[Brief explanation of drawings]

Figure 1 is an overview diagram showing a conventional radio wave detector, Figure 2
3 is an overview diagram showing a radio wave detector according to an embodiment of the present invention; FIG. 4 is a diagram illustrating an example of the signal processing section of the embodiment; Figure 5a shows an example of an element antenna, Figure 5b shows an example of an acousto-optic element, Figure 6 shows the light intensity distribution characteristics of the same example, and Figure 7 shows an example of the same implementation. It is a figure explaining the principle of an example. 21a to 21z, 22a to 22z...element antenna, 23, 23', 24, 24'...electric circuit,
25, 25'... Acousto-optic element, 26a to 26z,
26'a to 26'z...transducer, 27,
27'... Laser light source, 32, 32'... Two-dimensional photodetector, 33, 33'... Signal processor, 34...
Arithmetic unit.

Claims (1)

[Scope of Claims] 1. A plurality of element antenna groups each having a plurality of element antennas in at least two directions different from each other and arranged such that the intervals between the element antennas are different from each other, each of the element antenna groups For each, a receiving electric circuit connected to each element antenna of the element antenna group and an output corresponding to each element antenna from the electric circuit are connected,
It has a plurality of transducers arranged in an array relationship proportional to the antenna spacing, an acousto-optic element provided corresponding to each of the plurality of element antenna groups, and a predetermined angle to the acousto-optic element. an optical system that irradiates laser light from an acousto-optic element and forms an image of the diffracted light with a Fourier transform lens; a two-dimensional photodetector that detects the imaged light;
A radio wave detector, comprising: a signal processor that reads and processes the output of the two-dimensional detector, and further includes an arithmetic unit that calculates a direction from the output of the signal processor for each element antenna group. 2. The radio wave detector according to claim 1, wherein the two-element antenna groups are arranged in two directions perpendicular to each other.