JPS6352802B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a phased array antenna mounted on a satellite, for example, and more particularly to a phased array antenna that can automatically control the pointing direction of an antenna beam to a desired direction.

In an array antenna such as a phased array antenna in which a large number of antenna elements (radiating elements) are arranged, if each antenna element deviates from a predetermined position, the beam pointing direction changes or side lobes increase.

On the other hand, the distortion of an array antenna due to heat is generally not random, but gradually changes greatly toward the periphery of the array, and this tendency is particularly noticeable in array antennas with a spherical arrangement. Such non-random deformation also causes the pointing direction of the antenna beam to change from the desired direction. The larger the array antenna becomes, that is, the larger the array length and array area, the sharper the beam becomes. Therefore, such a change in the antenna beam direction immediately leads to a disconnection of the communication line. This appears as a position detection error.

By the way, the larger the antenna is, the farther away from the antenna it is necessary to measure the beam axis and directivity of the array antenna. For example, the size of the antenna is 100 wavelengths, and the center wavelength used is
If it is 15 cm, the measurement points must be at least 3 km apart, making measurement extremely difficult.

In such a large array antenna,
There are problems in that it is susceptible to disturbances such as thermal distortion and it is difficult to know the actual beam direction. Therefore, a device is required to monitor the directivity and make corrections.

On the other hand, two methods are conventionally known as methods for measuring the directivity of a large array antenna near the antenna. One is to place one monitor antenna near the array antenna, excite only one antenna element of the array antenna, detect the amplitude and phase of the received output of the monitor antenna, and detect the amplitude and phase of the monitor antenna and the excited antenna of the array antenna. Determine the excitation amplitude and phase of the excited antenna element, taking into account the distance between the antenna element and the element. Then, this measurement is performed sequentially for all antenna elements, the excitation amplitude and phase of all the antenna elements are determined, and the directivity is determined by calculation. Another method is
All antenna elements are excited, a small probe is moved across the entire surface of the array antenna near the front of the array antenna, the amplitude and phase of the received signal are measured with this probe, and the electric field distribution near the front of the array antenna is determined. This method calculates the far electric field and beam axis from the distribution.

However, all of these methods require that the antenna's original transmitting and receiving operations be interrupted while measurements are being made. Therefore, in the case of a satellite array antenna used under constantly changing disturbances, the operation of the antenna will be frequently interrupted, and such a method cannot be adopted. Furthermore, in the latter method, it is necessary to move the probe in a planar or cylindrical shape over a range larger than the size of the array antenna, but such a moving mechanism is more susceptible to disturbance than the antenna. Therefore, accurate measurement cannot be expected, and measurement requires a long time.

The present invention has been made in view of the above points, and it is possible to measure the directivity, that is, the directivity direction of the antenna beam, in a short time without interrupting the original operation of the antenna in the place where the antenna is actually used. The purpose of the present invention is to provide a phased array antenna that can be modified.

The present invention provides a phased array antenna in which an excitation signal is supplied from an excitation signal source to a plurality of arrayed antenna elements via a phase shifter with a variable phase shift amount to excite the antenna elements. a light source that generates a light beam; a light deflector that sequentially irradiates a light beam generated from the light source toward the vicinity of the antenna element; a plurality of optical modulators that modulate light with the excitation signal of the antenna element; an optical demodulator that sequentially demodulates the modulated light by these optical modulators; and distribution from the output signal of the optical demodulator and the excitation signal. a phase detector that detects a phase difference with a reference phase signal, a distance measuring device that optically measures the position of the antenna element, and an output signal of the measuring device and an output signal of the phase detector. excitation phase calculation means for determining the excitation phase of the antenna element; a direction sensor for detecting a desired pointing direction of the antenna beam formed by the antenna element; an output signal of the direction sensor; an output signal of the distance measuring device; and phase shift amount correction means for correcting the phase shift amount of the phase shifter so that the antenna beam is directed in the desired pointing direction based on the excitation phase determined by the excitation phase calculation means. Features.

The principle of this invention will be explained using a phased array antenna mounted on a satellite as an example.

Figure 2 shows the coordinate system x-y-z fixed to the satellite.
This is a schematic diagram of the array surface of a phased array antenna based on . In the same figure,
〓 _i is antenna element #i based on this coordinate system
(i=1 to n), and 〓 ₀ is a unit vector representing the desired direction of the antenna beam based on this coordinate system.

In order to radiate a sharp antenna beam in the direction of 〓 ₀ , the excitation phase φ _i of all antenna elements #i is φ _i + (2π/λ)〓 _i・〓 ₀ = φ ₀ ...(1) ( However, λ is the wavelength of the radio wave, φ ₀ is the constant phase,
It is necessary to satisfy the following condition (≪・” indicates inner product).

However, 〓 ₀ fluctuates or changes from time to time due to changes in the satellite's attitude (for example, it changes from pointing toward Hokkaido to pointing toward Kyushu), so it is not constant. In addition, 〓 _i varies due to thermal deformation of the array surface. Therefore,
By adjusting the phase shifter provided for each antenna element while measuring 〓 ₀ and 〓 _i , φ _i is corrected so that equation (1) holds true.

Here, 〓 ₀ can be known by a direction sensor fixed on the satellite, and 〓 _i can be measured using a ranging device fixed on the satellite. On the other hand, the excitation phase of the antenna element can be determined using an optical deflector, optical modulator, optical demodulator, and phase detector.
If the actual measurement value is φ _i ′, then equation (1) can be established by correcting the excitation phase of the antenna element by φ _i −φ _i ′ using a phase shifter.

Note that when measuring φ _i , it is necessary to consider the phase delay of the light beam due to the distance between the optical deflector and the optical modulator. The phase difference φim indicated by the output of the phase detector is φim=φ _i −k(〓 _i −〓−〓)−c ……(2) (where k is a constant and 〓 is the coordinate system x-y- The position vector of the optical deflector at z, 〓 is the distance vector between the antenna element and the corresponding optical modulator, and c is the phase shift of the reference phase signal from the excitation signal source to the phase detector, the optical modulator, and the optical deflection. This is expressed by the inherent phase difference between both inputs of the phase detector, which is caused by the optical path length difference between the forward and backward paths between the devices and the phase shift of the demodulated output signal from the demodulator to the phase detector. Here, 〓 _i can be measured by a distance measuring device, and 〓
〓, c is a quantity that can be known in advance, so (2)
φ _i can be determined from φ im in the equation. Based on the excitation phase φ _i thus obtained, the desired pointing direction (r ₀ ) obtained by the direction sensor, and the phase of the antenna element (〓 _i ) obtained by the distance measuring device, the phase shifter By correcting the phase shift amount of
If φ _i is corrected to satisfy equation (1), the antenna beam will be directed in the direction of 〓 ₀ .

Examples of the present invention will be described below. FIG. 1 shows the configuration of a phased array antenna according to an embodiment of the present invention. In the figure, the output of a microwave oscillator 1, which is an excitation signal source, is distributed by a divider 2 to an input to a power divider 3 and an input to a phase detector to be described later. The output of the power divider 3 is distributed to a plurality of arrayed antenna elements 6 ₁ to 6n via phase shifters 4 ₁ to 4n whose phase shift amount is variable and power dividers 5 ₁ to 5n. 6 ₁ to 6n are excited. The optical modulators 7 ₁ to 7n use the excitation signals (microwaves) of the antenna elements 6 ₁ to 6n distributed by the power dividers 5 ₁ to 5n,
It modulates the laser light (light beam) from the laser light source 9. Optical reflectors 8 ₁ to 8n, such as corner reflectors, are installed near the antenna elements 6 ₁ to 6n. The laser light from the laser light source 9 is guided to the optical deflector 11 via the optical circulator 10, and the laser light deflected by the optical deflector 11 is sequentially irradiated onto the optical modulators 7 ₁ to 7n.

Further, the modulated laser beams from the optical modulators 7 ₁ to 7n are also guided to the optical demodulator 12 via the optical deflector 11 and the optical circulator 10 . The output of the optical demodulator 12 is guided to a phase detector 13 together with a reference phase signal that is part of the excitation signal distributed by the power divider 2.

The distance measuring device 14 is configured using, for example, a known laser range finder using optical interference method, and optically measures the positions (position vectors) of the antenna elements 6 ₁ to 6n using optical reflectors 8 ₁ to 8n. This is a device that detects the satellite's position, and is fixed at three locations on the satellite, for example, as shown by L ₁ , L ₂ , and L ₃ in FIG. That is, the laser beams from the distance measuring devices 14L ₁ , L ₂ , L ₃ are irradiated toward the optical reflecting object 8 _i (i=1 to n), and the reflected light is received by the distance measuring device 14. Then,
Measure distances r1i, _r2i , and r3i from L ₁ , L ₂ , and L 3 to 8 _i . Here, the coordinate system x-y fixed to the satellite
Let the position vector of the optical reflector 8 _i represented by −z be 〓 _i ′, and the position vectors of L ₁ , L ₂ , and L ₃ be 〓 ₁ ,
If 〓 ₂ and 〓 ₃ , then ｜〓 _i ′−〓 ₁ ｜=r1i ｜〓 _i ′−〓 ₂ ｜=r2i ｜〓 _i ′−〓 ₃ ｜=r3i, so from this simultaneous equation, the optical reflection Thing 8
The position vector of _i 〓 _i ′ can be found. The optical reflector 8 _i is fixed near the antenna element 6 _i , and the optical reflector 8 _i and the antenna element 6 _i
Since the relative position of is known, the position vector P _i of the antenna element 6 _i can be found from 〓 _i ′.

The direction sensor 15 is for detecting the desired pointing direction of the antenna beam based on the coordinate system fixed to the satellite on which the antenna elements 6 ₁ to 6n are mounted, that is, the direction in which the antenna beam should be directed. This direction can be determined by knowing the area (point) on another sphere where the antenna beam should be directed and the attitude and position of the satellite relative to the earth. Attitude of the satellite towards the earth
The position can be determined by the position detection device (directional sensor) installed on most satellites; for example, the position can be measured by receiving beacon waves sent from the ground toward the satellite with a monopulse sensor. . Once the attitude and position of the satellite with respect to the earth are determined in this way, it is possible to determine in which direction the antenna beam should be directed in the coordinate system fixed to the satellite in order to direct the antenna beam to the desired area or point on the earth. Ru. The direction sensor 15 detects the desired pointing direction of the antenna beam in this manner.

The arithmetic and control unit 16 determines the antenna element 6 based on the output signal of the phase detector 13 and the output signal of the distance measuring device 14.
Excitation phase calculation means for determining excitation phases of ₁ to 6n;
Based on the calculated excitation phase, the output signal of the distance measuring device 14, and the output signal of the direction sensor 15, the phase shifter 4 ₁
It constitutes a phase shift amount correction means for correcting a phase shift amount of ~4n.

Next, the operation of this embodiment will be explained.

As shown in equation (1), in order to direct the antenna beam of the phased array antenna in the desired direction, the excitation phase φ _i of the antenna element 6i (i = 1 to n) and the installation of the phased array antenna The position vector of the antenna element 6i with reference to the x-y-z coordinate system fixed at the location where it is located = _i and the unit vector representing the desired pointing direction of the antenna beam =
₀ , and based on that, correction is made to the excitation phase φ _i so that equation (1) holds true.

Here, the excitation phase φ _i of the antenna element 6i is detected as follows. Laser light from the laser light source 9 passes through the optical circulator 10 and is sequentially irradiated onto the optical modulators 7 _i (i=1 to n) by the optical deflector 11. In the optical modulator 7 _i , the power divider 5 _i (i=
The excitation signal of the antenna element 6 _i supplied from the antenna elements 1 to n) is used as a modulation input signal to amplitude-modulate the incident light from the optical deflector 11.
A LiNbO ₃ crystal provided with electrodes can be used. The light modulated by the optical modulator 7 _i exits from the side opposite to the incident light from the optical deflector 11. The optical path of this emitted light is reversed by a mirror or the like, so that it returns to the optical deflector 11, passes through the circulator 10, is guided to the optical demodulator 12, and is demodulated. The demodulated output signal of the optical demodulator 12 is sent to the phase detector 1
3 and is part of the excitation signal distributed by the power divider 2. The phase difference φim with the reference phase signal is detected. This phase difference φim is calculated from the excitation phase φ _i of the antenna element 6 _i (output phase of the power divider 5 _i ) as shown in equation (2), and the position vector of the antenna element 6 _i obtained by the ranging device 14 The distance between _{the optical modulator 7 i and the} optical deflector 11 determined based on i 〓 _i −〓−〓 Phase delay k determined by
) and the inherent phase difference c between both inputs of the phase detector 13.

Further, the distance r1i from the distance measuring device 14 to the optical reflecting object _8i , as described above, is determined by the distance measuring device 14.
r2i, r3i are measured, and based on that, the optical reflector 8 _i is based on the x-y-z coordinate system.
The position vector 〓 _i ′ of is determined, and the position vector 〓 _i of the antenna element 6 _i is determined from _{〓 i} ′.

Furthermore, the direction sensor 15 detects the desired pointing direction of the antenna beam based on the coordinate system x-y-z fixed to the satellite as described above, and the unit vector 〓 ₀ shown in equation (1) is obtained. It will be done.

The phase difference φim obtained by these phase detectors 13
The position vector 〓 _i of the antenna element 6 i obtained by the measuring device 14 and the unit vector 〓 ₀ obtained by the direction sensor 15 are input to the arithmetic _and control device 16 . The arithmetic and control unit 16 calculates the excitation phase φ _i of the antenna element 6 _i from the information of φ im and 〓 _i based on equation (2) (k, 〓, 〓, and c are known). The actual measured value of the excitation phase φ obtained in this way is defined as φ _i '.
On the other hand, since the target excitation position φ _i in equation (1) can be found from 〓 _i and 〓 ₀ , the difference between this and the actual measured value φ _i ′ is φ _i −φ _i ′
is calculated as a correction amount for the movement amount of the phase shifter 4 _i (i=1 to n), and an electric signal is guided to the phase shifter 4 _i according to this correction amount to correct the phase shift amount. As a result of this correction, the excitation position of the antenna element 6 _i is corrected, and the pointing direction of the antenna beam changes. The excitation phase of the antenna element 6 _i after this correction is detected in the same manner, and the same operation is performed thereafter. That is, the excitation phase of the antenna element 6 _i is controlled in a closed loop, and the antenna beam is finally converged to point in a desired direction.

As explained above, according to the present invention, changes in the direction of the antenna beam due to positional fluctuations of the antenna element due to disturbances such as heat are automatically corrected, and the antenna beam can always be directed in a desired direction. Furthermore, this correction can be performed without relaying the original operation of the antenna. Also,
It is extremely effective as an array antenna for communications and radar, as there is no need to provide a specially constructed probe movable stand across the front of the antenna as in the case of nearby electric field measurements.

[Brief explanation of the drawing]

Fig. 1 is a configuration diagram of a phased array antenna according to an embodiment of the present invention, Fig. 2 is a diagram for explaining the principle of the invention, and Fig. 3 is a diagram illustrating the measurement principle of a distance measuring device in the same embodiment. FIG. 3 is a diagram for explaining an example. 1...Microwave oscillator (excitation signal source), 2,
3,5 ₁ to 5n...power divider, _{41 to} 4n...phase shifter, 61 _to 6n...antenna element, _{71 to} 7n...
...Light modulator, 8 ₁ to 8n... Optical reflector, 9...
... Laser light source, 10 ... Optical circulator, 11
. . . Optical deflector, 12 . . . Optical demodulator, 13 . . . Phase detector, 14 . ).

Claims (1)

[Claims] 1. A light source that generates a light beam in a phased array antenna that excites a plurality of arrayed antenna elements by supplying an excitation signal from an excitation signal source through a phase shifter with a variable phase shift amount. an optical deflector that sequentially irradiates a light beam generated from the light source toward the vicinity of the antenna element; a plurality of optical modulators that modulate with excitation signals of antenna elements; an optical demodulator that sequentially demodulates the modulated light by these optical modulators; and an output signal of the optical demodulators that is distributed from the excitation signal source. a phase detector that detects a phase difference with a reference phase signal; a distance measuring device that optically measures the position of the antenna element; and a distance measuring device that optically measures the position of the antenna element. excitation phase calculation means for determining the excitation phase of the element; a direction sensor for detecting a desired pointing direction of the antenna beam formed by the antenna element; an output signal of the direction sensor, an output signal of the distance measuring device, and the excitation It is characterized by comprising a phase shift amount correction means for correcting the phase shift amount of the phase shifter so that the antenna beam is directed in the desired pointing direction based on the excitation phase determined by the phase calculation means. Phased array antenna.