JPH07202547A - Antenna beam forming circuit - Google Patents

Abstract

PURPOSE:To supply high frequency electric signals obtained by modulating the amplitude of an optical wave signal by phase distribution control to array antenna elements and to directly perform the control in 1:1 correspondence relations. CONSTITUTION:A superposing means 5 superposes a high frequency electric signal on one or a laser beam 3 distributed into two, and expanding means 61 two-dimensionally expands the beam diameter of this superposed beam to output it as a luminous flux. An intensity distribution modulating means 7 and a phase distribution modulating means 8 modulate the intensity and the phase of this expanded luminous flux by electric modulation signals respectively with respect to face. An expanding means 62 expands the other of the laser beam distributed into two and outputs it as a luminous flux. A synthesizing means 9 synthesizes outputs of modulating means and the output of the expanding means 62, and a photoelectric conversion means 10 outputs the high frequency electric signal by photoelectric conversion.

Description

Detailed Description of the Invention

[0001]

The present invention is used in an antenna beam forming circuit of an array antenna. In particular, the present invention relates to an antenna beam forming circuit of an array antenna that transmits a single beam whose shape and direction are variable.

[0002]

2. Description of the Related Art FIG. 10 is a block diagram of an active array antenna using an antenna beam forming circuit of a first conventional example. The array antenna is an antenna composed of a plurality of antenna elements, and an antenna beam having a desired shape and direction can be formed by feeding each element with a high-frequency signal having an appropriate amplitude and phase. It is known that the electric field distribution in the antenna aperture and the antenna beam pattern have a Fourier transform relationship, and the direction of the beam can be changed by controlling the phase of the signal given to each element.

A conventional antenna beam forming circuit is shown in FIG.
The configuration was as shown in. FIG. 10 shows a configuration when an active array antenna is used as a transmission system. The signal input from the high frequency electric signal input terminal 1 is divided into n pieces by the power distributor 51, and each of the distributed signals is a high frequency signal amplifier (or attenuator) 5
2 _{1 to} 52 _n and high frequency signal phase shifters 53 _{1 to} 53 _n are set to have appropriate amplitudes and phases, and pass through high frequency signal output terminals 2 ₁ to 2 _n, and then power amplifier 54 ₁
Is amplified by through 54 _n, it is fed to the antenna element 55 ₁ to 55 _n. The electromagnetic waves emitted from each of the antenna elements 55 _{1 to} 55 _n form one beam having a certain shape and orientation. Power distributor 51, high frequency signal amplifier (or attenuator) 52 _{1 to} 52 _n , high frequency signal phase shifter 53 _{1 to} 5
The portion 50 composed of 3 _n is called an antenna beam forming circuit because it performs high-frequency signal processing related to antenna beam forming.

In recent years, several research institutes have been conducting researches in which an optical information processing method is applied to an antenna beam forming circuit and beam forming is performed by signal processing in the light wave region. Hereinafter, here, a beam forming circuit that uses an optical signal will be referred to as a light beam forming circuit.

As described above, the electric field distribution in the antenna aperture and the antenna beam pattern have a Fourier transform relationship. The convex lens used for optics has a Fourier transform function, and the one utilizing this function is the light beam forming circuit described below. Research and development of this type of optical beam forming circuit using Fourier optics is underway at several research institutions.

FIG. 11 is a block diagram of an active array antenna using the antenna beam forming circuit of the second conventional example. Figure 11 shows the ATR (Advanced Telec
The optical beam forming circuit researched at ommunications Research Institute International (International Research Institute for Telecommunications) is shown (Technical Report of IEICE, A.P. 91-89, “Optical Control Array Antenna”). Excitation amplitude and phase distribution and radiation characteristics ", Yoshihiko Konishi, Wataru Nakajo, Masayuki Fujise). This circuit draws a beam pattern corresponding to the antenna beam pattern on an image mask and utilizes the Fourier transform action of the lens to obtain a high-frequency excitation distribution given to the antenna aperture plane.

The light emitted from the laser light source 3c is collimated by the collimate lens 15a and passes through the image mask 16 and the Fourier transform lens 17. In the half mirror 9b placed after the Fourier transform lens 17, this luminous flux and the luminous flux emitted from the laser light source 3d and collimated by the collimate lens 15b are combined, and the constituted luminous flux is the optical fiber bundle 18
Of the photodetector array 10a _{1 to} 10a _n , and photoelectric conversion is performed on the photodetector array 10a _{1 to} 10a _n . The image mask 16 is a Fourier transform lens 17
Of the optical fiber bundle 18 is placed on the back focal plane of the Fourier transform lens 17. At this time, a Fourier transform image of the mask pattern (here, a pinhole is used) drawn on the image mask 16 is obtained on the rear focal plane. . Further, the difference between the optical frequencies of the laser light source 3c and the laser light source 3d is controlled to be always constant. The outputs of the photodetector arrays 10a _{1 to} 10a _n that perform coherent detection are weighted in amplitude and phase corresponding to the Fourier transform of the antenna pattern, and their frequencies are the same as those of the two laser light sources 3c and 3d. It is equal to the frequency difference. The output signal of the photodetector (photodetector array 10a _{1 to} 10a _n ) is the power amplifier 54 ₁
Amplified by through 54 _n, the antenna elements 55 ₁ to 55 _n
Emitted more.

FIG. 12 is a block diagram of the antenna beam forming circuit of the third conventional example. FIG. 12 shows the configuration of an optical beam forming circuit which is being researched and developed by Hughes, Inc. of the United States (Proc. Of AIAA '92, pp. 1279-1288, Was.
hinton DC, March 1992., "Phased array antenna beam
forming using optical processor ", LPAnderson, F.Bo
ldissar, DCDChang).

The light beam emitted from the laser light source 3 passes through the spatial filter 19a and the collimator lens 15c into a parallel light beam, which is then split into two paths by the beam splitter 4b. One path is used for the purpose of forming the antenna beam, and the light beam is spatially modulated on the path. The light flux that has passed through the beam splitter 4b strikes the half mirror 11c and enters the reflective spatial light modulator 20. A graphic corresponding to a desired antenna beam pattern is drawn on the reflective spatial light modulator 20, and a light flux whose surface is intensity-modulated is output. This light flux passes through the Fourier transform lens 17, and then reaches the incident surface of the optical fiber bundle 18 placed so as to coincide with the focal plane. The reflective spatial light modulator 20 is placed so as to coincide with the front focal plane of the Fourier transform lens 17.

On the other hand, the light beam reflected by the beam splitter 4b is condensed by the collimate lens 15d and injected into the acousto-optic modulator 5a. The acousto-optic modulator 5a has a high frequency electrical signal input terminal 1 and has a function of shifting the frequency of the light wave signal by an amount corresponding to this frequency. The light emitted from the acousto-optic modulator 5a passes through the spatial filter 19b and passes through the collimate lens 1
After being converted into a parallel light flux by 5e, the optical path is changed to a right angle by the mirror 14c and reaches the half mirror 9c. In the half mirror 9c, it is combined again with the light flux of the other path split by the beam splitter 4b. The combined light flux is received by the lens array 21 and is incident on the optical fiber bundle 18, and the photodetector arrays 10a ₁ to 10
At a _n , photoelectric conversion is performed and a high frequency component is extracted.
The high frequency is amplitude and phase modulated to form the desired beam. This high frequency is generated by the power amplifier 54 ₁
The radiation is emitted from the antenna elements 55 _{1 to} 55 _n via ˜54 _n .

Since the light beam forming circuit uses an optical element, it can be expected that a very small, lightweight and compact circuit can be constructed as compared with the case where the circuit is manufactured in a high frequency band. Further, as described above, the amplitude / phase control of the signal is performed in the light wave region and does not depend on the frequency of the electric signal. The phase shifter in the high frequency band is usually a narrow band,
This means that, in principle, the light beam forming circuit is capable of high-frequency signal processing in a wide band as compared with the conventional beam forming circuit including this as a constituent element.

[0012]

However, in such an antenna beam forming circuit of the prior art, when the light beam forming circuit is used, (1) the Fourier transform image is used as a lens by using the pinhole as a mask pattern. Optical beam forming circuit of a method of performing amplitude and phase control of a high-frequency electric signal necessary for forming an antenna beam in a light wave signal region by combining with a conventional optical method and coherent detection means, or (2 ) Instead of the pinhole mask pattern, a light corresponding to the antenna beam pattern is drawn on the spatial light modulator typified by a liquid crystal panel, and the signal processing required for beam formation in the light wave signal region is performed in the same way. This is a beam forming circuit. In each case, a figure corresponding to the antenna beam pattern is prepared, and its Fourier transform is performed by the lens. Be one carried out have, Fourier optics are applied. The control unit in the two beam forming circuits is the image mask 16 or the spatial light modulator 2.
From the standpoint of giving a high-frequency electric signal having a predetermined amplitude and phase relationship to the antenna element,
The control can be said to be indirect.

In the research of array antennas, excitation distributions of various antenna elements such as Taylor distribution and Chebyshev distribution have long been found for the purpose of obtaining a beam pattern with low side lobes. Even now, many control methods are being researched for weighting signals given to antenna elements forming an array antenna. Although these studies are performed on the premise of signal processing in the high frequency band, they can be applied to the light beam forming circuit as they are in principle. However, since the background of these studies is to directly control the weighting of the signals given to the antenna elements, in order to directly use the results of these studies in the light beam forming circuit, the distribution of the amplitude and phase of the lightwave signal should be considered. It becomes necessary to be able to control directly.

Further, when considering scanning an antenna beam in a beam forming circuit using a pinhole mask, in order to realize this, for example, the mask pattern is changed or the light source is set in the focal plane of the Fourier transform lens. It needs to be moved mechanically. Both require mechanical actuation mechanisms, so there is a limit to rapid beam scanning.
Beam scanning in the array antenna can be realized by changing the phase distribution while keeping the amplitude distribution of the high-frequency electric signal fed to the antenna element, and it is convenient if only the phase distribution can be directly controlled in the light beam forming circuit.

Furthermore, in the experiment of the light beam forming circuit shown in FIG. 11, it has been reported that the amplitude / phase distribution of the high frequency electric signal actually obtained is deviated as compared with the ideal case. The cause is due to the distortion of the optical system. Optical distortion can be compensated by correcting the phase of the optical path. In order to do this in the light beam forming circuit shown in FIG. 12, a mechanism that two-dimensionally controls the phase distribution of the light flux is required. In the light beam forming circuit shown in FIG. 12, a figure corresponding to the antenna beam pattern is drawn on the spatial light modulation element, but applying optical processing called Fourier transform using a lens is common to the circuit shown in FIG. Therefore, it is quite possible that a similar problem will occur. In a light beam forming circuit using Fourier optics, since the relationship between the input image and the amplitude / phase distribution of the signal given to the antenna element is not direct, for example, in order to give the phase correction caused by the distortion of optical components as the input image. Requires tedious calculations.

From the above, if a light beam forming circuit capable of directly controlling the amplitude and phase distribution of the high frequency electric signal given to the antenna element and controlling the amplitude and phase of the light wave signal can be realized, the advantage is great.

The present invention solves the above-mentioned drawbacks by replacing the control of the amplitude and phase distribution of the high frequency electric signal given to the array antenna element with the control of the amplitude and phase distribution of the lightwave signal,
Further, it is an object of the present invention to provide an antenna beam forming circuit which has a one-to-one correspondence with each other and which can be directly controlled.

[0018]

According to the present invention, a high frequency electric signal input terminal (1) to which a transmission signal is inputted as an electric signal.
A superimposing means (5) for superimposing the electric signal from the input terminal (1) on the first lightwave signal (S ₁ ), the output light of the superimposing means (5) and the second lightwave signal (S _2). ) And heterodyne detection are combined, and n output photoelectric conversion elements for photoelectrically converting the output light of the combination means (9) for each of the n different parts of the beam and feeding the antenna elements. And a photoelectric conversion means (10) including a modulation means (7, 8) provided on either the optical path of the first lightwave signal (S ₁ ) or the optical path of the second lightwave signal (S ₂ ). The modulation means (7, 8) includes a first modulation element (7) for performing intensity distribution modulation by a first electrical modulation signal on a surface traversing the optical path, and a surface traversing the output light of the superposing means. The second electrical modulation signal is applied to Characterized in that it comprises an optical circuit and regulating device (8) is connected in cascade.

Further, according to the present invention, the first light wave signal and the second light wave signal can be generated by a common laser light source (3).

Further, according to the present invention, the first light wave signal and the second light wave signal are different laser light sources (3 ₁ ,
3 ₂ ). .

According to the present invention, the first and second modulators are reflection type liquid crystal spatial light modulators, and the two modulators are controlled by the first and second electric modulation signals, respectively. A liquid crystal spatial light modulator controller can be provided.

[0022]

A high-frequency electric signal is superimposed on one of the first light wave signals obtained by dividing the laser beam into two, and the beam diameter of the superimposed light beam is two-dimensionally expanded to form a light beam. The beam diameter of the second lightwave signal is two-dimensionally expanded to form a light beam. The spatial intensity and phase of one of the two light beams are modulated by the first electrical modulation signal and the second electrical modulation signal, respectively. The modulated light flux and the other light flux are combined, Hinterodyne detection is performed, and photoelectric conversion is performed for each of n different parts of the beam, and each is fed to the antenna element. As a result, the control of the amplitude / phase distribution of the high frequency electric signal given to the array antenna element is replaced with the control of the amplitude / phase distribution of the lightwave signal, and the correspondence is one-to-one, and the control can be directly performed.

Here, instead of dividing the laser light source into two to form the first and second light wave signals, two laser beams may be used.

The above description is based on the principle that in the light beam forming circuit, the amplitude and phase of the high frequency signal can be controlled using the light wave signal as a medium. FIG. 9 is a block diagram for explaining the principle of the light beam forming circuit, and shows a system for controlling the amplitude and phase of a high frequency electric signal through a light wave signal. FIG. 9 is for explaining this principle. An EO converter (electro-optical converter) 41 having a high-frequency electric signal input terminal 1, an optical amplitude modulator 42,
Consider a circuit in which the optical phase modulator 43 and the OE converter (optical-electrical converter) 44 having the high-frequency electrical signal output terminal 2 are cascade-connected in this order. As a whole system, a high frequency electric signal is inputted from a high frequency electric signal input terminal 1 and a processed signal is taken out from a high frequency electric signal output terminal 2.

The EO converter 1 converts a high frequency electric signal into a light wave signal, and includes a laser light source 3a and an EO conversion element 41.
and a. EO converter 41 used here
Has a function of outputting a light wave signal whose frequency is shifted by the frequency of the input high frequency electric signal. That is, when the input high-frequency electric signal is cos ω _RF t, the output lightwave signal is cos (ω _RF + ω _OPt ) t. Where ω _RF is the angular frequency of the electrical signal and ω
_OPt represents each frequency of the light wave signal of the laser light source 3a.

The following optical amplitude modulator 42 and optical phase modulator 43 receive the lightwave signal of the preceding stage and output a lightwave signal whose amplitude and phase are modulated based on the input electric signal. When the amount of amplitude modulation is A and the amount of phase modulation is φ, the modulated signal is Acos {(ω _RF + ω _OPt ) t +
can be written as φ}. This lightwave signal is transmitted to the OE conversion unit 44 at the next stage.
Will be input.

The OE conversion section 44 is composed of an OE conversion element 44a and a laser light source 3b for local oscillation light. The OE conversion unit 44 performs coherent detection using cosω _OPt t as local oscillation light. The high frequency electric signal output from the OE converter 44 is Acos (ω _RF t + φ),
This is output from the high frequency electric signal output terminals 2 ₁ to 2 _n .

[0028] That is, in the system shown in FIG. 9, the system for the input of cos .omega _RF t becomes high-frequency electrical signals, the control of the electrical signal and outputs the _{Acos (ω RF t + φ)} . This signal is modulated such that the amplitude component is A and the phase component is φ, and it is shown that the amplitude and phase of the high frequency signal can be controlled by the amplitude and phase modulation processing in the light wave region.

Although the beam forming circuit of the active array antenna for transmission is shown in FIG. 10, each of the amplitude setting circuit and the phase setting circuit therefor has an amplitude setting circuit and a phase via the lightwave signal described in FIG. It can be replaced with a setting circuit.

It has been described above that the electric field distribution at the antenna aperture and the antenna beam pattern have a Fourier transform relationship. Therefore, it can be said that the beam forming circuit feeds each antenna element with a signal having an amplitude and phase component corresponding to the spatial Fourier transform of the desired beam pattern.

[0031]

Embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram of the antenna beam forming circuit according to the first embodiment of the present invention. In FIG. 1, the antenna beam forming circuit is characterized by a high-frequency electric signal input terminal 1 for inputting a high-frequency electric signal to be transmitted, and an electric signal from the high-frequency electric signal input terminal 1 as a first light wave signal. The superimposing means 5 for superimposing with S ₁ , the output light of this superimposing means 5 and the lightwave signal S ₂ as the second lightwave signal.
And a photoelectric converter 10 ₁ as n photoelectric conversion elements for photoelectrically converting the output light of the combining means 9 for each of the n different parts of the beam and feeding each to the antenna element. The photoelectric conversion means 10 including 10 to 10 _n is provided, and the modulation means 7 and 8 are provided in the optical path of the lightwave signal S _1. The modulation means 7 and 8 are provided by the first electrical modulation signal with respect to the plane crossing the optical path. It includes an optical circuit in which a first modulation element for performing intensity distribution modulation and a second modulation element for performing phase distribution modulation by a second electrical modulation signal on a surface traversing the output light of the superposing means 5 are cascade-connected. Especially.

The light wave signal S ₁ and the light wave signal S ₂ are generated by the common laser light source 3.

Further, the first and second modulators are a reflective liquid crystal spatial light intensity modulator 7a and a reflective liquid crystal spatial light phase modulator 7b as reflective liquid crystal spatial light modulators, respectively. A liquid crystal spatial light modulation element controller 13 for controlling the elements by the first and second electrical modulation signals is provided.

That is, specifically, the laser light source 3
A second distribution means 4 for distributing the laser light to the two paths emitted by the laser light source 3, a high frequency electric signal input terminal 1 for inputting a high frequency electric signal of a transmission signal, and a high frequency electric signal input to one of the light beams from the two distribution means. A superimposing means 5 for superimposing the high frequency electric signal from the terminal 1, and a expanding means 6 ₁ for secondarily expanding the beam diameter of the light beam from the superimposing means 5 and outputting it as a constraint.
Intensity distribution modulating means (reflecting liquid crystal light intensity modulating element 7a and liquid crystal spatial light modulating element controller 13) 7 which spatially modulates the spatial intensity distribution of the light flux from the expanding means 6 ₁ by the first electrical modulation signal 7 And a phase distribution modulation means (a reflective liquid crystal spatial light phase modulation element 8a and a liquid crystal spatial light modulation element controller) that planarly modulates the spatial phase distribution of the light flux from the intensity distribution modulation means 7 by the second electrical modulation signal. 13) 8 and a magnifying means 6 ₂ for secondarily magnifying the beam diameter of the other light beam from the two dividing means 4 and outputting it as a luminous flux.
And synthesizing means 9 for combining heterodyne detection of the light beam from the light beam and the enlarging means 6 ₂ from the phase distribution modulation means 8, n-number of photoelectric converter 1 for photoelectrically converting a light beam from combining means 9
0 ₁ to 10 _n and a photoelectric conversion means 10 including high frequency electric signal output terminals 2 ₁ to 2 _n for outputting a high frequency electric signal.

The operation of the antenna beam forming circuit having such a configuration will be described.

In FIG. 1, the antenna beam forming circuit has a high frequency electric signal input terminal 1 for inputting a high frequency electric signal, and high frequency electric signal output terminals 2 ₁ to 2 _n for outputting a high frequency signal to be applied to the array antenna element. It is a network of 1 input and n output.

The light beam forming circuit has a laser light source 3, and the light emitted from the laser light source 3 is input to a two-splitting means 4 for splitting the light into two and split into two optical paths. One light beam is input to the superimposing means 5 for superimposing the high frequency electric signal on the optical signal. A high frequency electric signal to be superimposed on the optical signal is input from the high frequency electric signal input terminal 1. The optical signal output from the superimposing unit 5 that superimposes the high-frequency electrical signal on the optical signal is input to the expanding unit 6 ₁ that expands the light two-dimensionally. The expanding means 6 ₁ expands the beam diameter of the laser beam and emits it again as a light beam. (Here, a light beam having a two-dimensional spread for spatially filtering is called a light beam, and is used in distinction from the term "light beam.") This light beam is two-dimensionally Intensity modulating means 7 for modulating the intensity distribution of the signal and phase distribution modulating means 8 for modulating the phase distribution of the two-dimensional light wave signal cascade-connected thereto.
Is then input, and is output as a light beam having a desired amplitude distribution and phase distribution. The two-dimensional amplitude / phase distribution of this light flux corresponds to the amplitude / phase distribution given to the aperture surface of the antenna. This luminous flux becomes one input of the synthesizing means 9 for synthesizing the light.

[0039] After the other light distribution rays in two by a two dispensing means 4 for two distributing the light, which has been expanded through the expansion means 6 ₂ to spread the light two-dimensionally in two dimensions, the light It becomes the other input of the synthesizing means 9 for synthesizing, and is synthesized with the two-dimensionally amplitude-phase-modulated light flux described above.

The light emitted from the synthesizing means 9 for synthesizing light is input to the photoelectric converting means 10 for photoelectrically converting, which is composed of a two-dimensional array of photoelectric converters 10 ₁ to 10 _n , and the respective photoelectric converters 10 1. _A high-frequency electrical signal is taken out at ₁ to 10 _n . The photoelectric conversion method used here is a so-called heterodyne method, and the light is emitted from the laser light source 3 and divided into two by the two dividing means 4,
Further, the light emitted from the expanding means 6 ₂ which spreads the light two-dimensionally acts as local oscillation light. Since the signal light source and the local oscillation light source are the same light source, the heterodyne detection method is also called a self-heterodyne method. The converted high frequency electric signal reflects the amplitude / phase modulation in the light wave region performed in the intensity distribution modulating means 7 and the phase distribution modulating means 8 as it is.
The high frequency electric signals output from the photoelectric converters 10 ₁ to 10 _n are taken out from the respective high frequency electric signal output terminals 2 ₁ to 2 _n , amplified by the power amplifier, and fed to the antenna element.

Here, an interference system in which the light emitted from the laser light source is divided into two, and the light in the two divided paths is combined again to cause interference is known as a "Mach-Zehnder interferometer". The interference fringes obtained by this interferometer reflect the difference in the two optical paths. It can be said that the configuration of the light beam forming circuit described in FIG. 1 is an application of the Mach-Zehnder interferometer to the light beam forming circuit.

FIG. 2 is a specific block diagram of the antenna beam forming circuit of the first embodiment of the present invention. In FIG. 2, the light beam emitted from the laser light source 3 is divided into two optical paths by the beam splitter 4a. The light beam on one path is for superimposing a high frequency electric signal and performing a desired amplitude and phase modulation process in the light wave region. The light beam on the other path is used as local oscillation light for extracting a high frequency electric signal by heterodyne detection.

First, the former route will be described. The portion composed of the collimate lens 15f, the acousto-optic modulator 5a, and the collimate lens 15g corresponds to the superimposing means 5 for superimposing the high frequency electric signal on the light wave signal. One of the collimated light beams divided by the beam splitter 4a is focused by the collimate lens 15f and added to the acousto-optic modulator 5a. When a high frequency electric signal is input from the high frequency electric signal input terminal 1,
In addition to the light that is transmitted as it is, first-order diffracted light is generated.

Of these, the optical frequency of the first-order diffracted light is shifted from the high frequency electric signal input terminal 1 by the frequency of the high frequency electric signal. The first-order diffracted light is extracted by the collimate lens 15g and is output as collimate light.

This light beam becomes a light beam expanded two-dimensionally by the beam expander 6a. The light flux enters the half mirror 11a, and the transmitted light strikes the reflective liquid crystal spatial light intensity modulation element 7a. The reflected light enters the half mirror 11a again, and the reflected light is further extracted through the analyzer 12. The reflective liquid crystal spatial light intensity modulation element 7a is controlled by the liquid crystal spatial light modulation element controller 13, and the result is reflected in the two-dimensional intensity distribution of the light flux after passing through the analyzer 12. The half mirror 11a and the analyzer 12 placed immediately before the reflective liquid crystal spatial light intensity modulation element 7a are
It is also possible to replace it with a polarization beam splitter, and in this case, there is no light loss due to passing through the half mirror twice.

The light flux transmitted through the analyzer 12 enters another half mirror 11b, and the reflected light enters the reflective liquid crystal spatial light phase modulation element 8a. The reflected light from the reflective liquid crystal spatial light phase modulation element 8a becomes a light beam which is incident on the half mirror 11b again. Handle the transmitted light component as output. The reflective liquid crystal spatial light phase modulation element 8a is also controlled by the liquid crystal spatial light modulation element controller 13, and the phase of the light flux is two-dimensionally modulated. Reflective liquid crystal spatial light phase modulator 8a
Then, compensation for the phase modulation caused by the intensity modulation by the reflective liquid crystal light intensity modulator 7a is also performed.

The luminous flux emitted from the half mirror 11b is
A desired amplitude / phase modulation is performed in the light wave region by the reflective liquid crystal spatial light intensity modulation element 7a and the reflective liquid crystal spatial light phase modulation element 8a. The light flux emitted from the half mirror 11b becomes one of the two input light fluxes of the half mirror 9a.

The other of the light beams split by the beam splitter 4a hits the mirror 14a, and the beam expander 6
After being magnified in b and reflected by the mirror 14b, it becomes the other input light of the half mirror 9a. Here, the light flux from the half mirror 11b is combined (added).

The light fluxes added by the half mirror 9a are incident on the photodetector arrays 10a _{1 to} 10a _n and photoelectrically converted, and then the respective photodetector arrays 10a _{1 are made.}
The high frequency electric signals are taken out from the high frequency electric signal output terminals 21 to _2n of ₁₀ to 10 _n . This high frequency electrical signal
The signal has the same frequency as the high frequency electric signal input from the high frequency electric signal input terminal 1, and the amplitude and phase thereof are directly reflected by the amplitude modulation and the phase modulation performed in the liquid crystal spatial modulation element. Each of the high frequency electric signals is further guided to the power amplifier and radiated from the antenna element.

FIG. 3 is a block diagram of the antenna beam forming circuit of the second embodiment of the present invention.

In the configuration of the first embodiment, of the two optical paths formed by the two dividing means 4 for dividing the light into two, the superposing means 5 for superposing the high frequency electric signal on the optical signal, the amplitude of the luminous flux,
The intensity distribution modulating means 7 and the phase distribution modulating means 8 for modulating the phase are provided on the same light path. Superimposing means 5
Also, a configuration in which the intensity distribution modulating means 7 and the phase distribution modulating means 8 are provided in different optical paths is possible. The second embodiment describes such a configuration.

FIG. 4 is a block diagram of the antenna beam forming circuit of the third embodiment of the present invention. Although the light beam forming circuit using one laser light source has been described with reference to FIGS. 1 to 3, the laser light source may be divided into two. One of the two laser light sources is used for the purpose of superimposing a high frequency electric signal and further performing amplitude phase modulation processing. The other laser light source is used as a local oscillation light source in coherent detection. FIG. 4 shows a configuration diagram of a light beam forming circuit using two light sources.

The laser beam emitted from the laser light source 3 ₁ is directly connected to the superposing means 5 for superposing the high frequency electric signal on the optical signal. The superimposing means 5 superimposes the electric signal on the optical signal. Since the system from the enlarging means 6 ₁ to the combining means 9 via the intensity distribution modulating means 7 and the phase distribution modulating means 8 is the same as that shown in FIG. 1, its explanation is omitted.

The light beam emitted from the other laser light source 3 ₂ enters a magnifying means 6 ₂ which spreads the light two-dimensionally. This luminous flux is emitted from the laser light source 3 ₁ in the synthesizing means 9 for synthesizing light, and is synthesized with the light subjected to the amplitude phase modulation processing.

Light emitted from the synthesizing means 9 is converted into a high frequency electric signal in the photoelectric converters 10 ₁ to 10 _{n for} photoelectric conversion, and is taken out from the high frequency electric signal output terminals 2 ₁ to 2 _n . Each of them is amplified by the power amplifier and radiated from the antenna element.

FIG. 5 is a specific block diagram of the antenna beam forming circuit of the third embodiment of the present invention.

In this structure, one laser light source is used for superimposing a high frequency electric signal and further used for amplitude phase modulation processing in the light wave region, and the other light source is used as a local oscillation light for heterodyne detection for extracting the high frequency electric signal. To do.

In FIG. 5, the light beam emitted from the laser light source 3c is for the former, is directly condensed by the collimate lens 15f, and is input to the acousto-optic modulator 5a. A high-frequency electric signal is input from the high-frequency electric signal input terminal 1 in the acousto-optic modulator 5a, and first-order diffracted light whose frequency is shifted by the frequency of this signal is taken out by the collimate lens 15g.

This light beam is further expanded by the beam expander 6a, and the half mirror 11a, the reflective liquid crystal spatial light intensity modulation element 7a, the half mirror 11a, the analyzer 12, the half mirror 11b, and the reflective liquid crystal spatial light phase modulation. After passing through the element 8a and the half mirror 11b, the half mirror 9
It becomes one input of a. During this period, the light flux undergoes two-dimensional amplitude and phase modulation, which is exactly the same as in FIG.

The light emitted from the other light source 3d is expanded by the beam expander 6b, reflected by the mirror 14b, and becomes the other input light of the half mirror 9a. Here, the light flux from the half mirror 11b is combined (added).

As in the case shown in FIG. 2, the half mirror 9
The luminous fluxes added by a are incident on the photodetector arrays 10a _{1 to} 10a _n arranged two-dimensionally and photoelectrically converted, and the respective photodetector arrays 10a _{1 to} 10a are photoelectrically converted.
_n high frequency electric signal output terminal 2 ₁ high-frequency electric signal from to 2 _n is taken in. This high-frequency electric signal is the sum of the frequencies of the high-frequency electric signal input from the high-frequency electric signal input terminal 1 and the difference between the optical frequencies of the two laser light sources 3c and 3b. In addition, the amplitude and the phase directly reflect the modulation performed in the liquid crystal modulator. Each of these high frequency electrical signals
It is guided to the power amplifier and radiated from the antenna element.

FIG. 6 is a block diagram of the antenna beam forming circuit according to the fourth embodiment of the present invention.

As in the case of the second embodiment, also in the configuration of the third embodiment described above, the superimposing means 5 for superimposing the high frequency electric signal on the lightwave signal is processed by the intensity distribution modulating means 7 for modulating the amplitude and phase of the light beam. It is also possible to consider a configuration in which the phase distribution modulating means 8 is not provided on the same optical path, but is placed between the laser light source 3 ₂ and the expanding means 6 ₂ for expanding the light two-dimensionally.
FIG. 6 shows such a block diagram.

The four types of light beam forming circuits described above are composed of an intensity distribution modulator 7 for spatially modulating the intensity distribution of an optical signal using a spatial light modulator and a two-dimensional optical beam connected in cascade. It is characterized in that the amplitude and phase of the signal are controlled by the phase distribution modulator 8 that modulates the phase distribution of the signal. Known spatial light modulators include those using electro-optic crystals and those utilizing liquid crystals. Here, a spatial light modulator using a nematic liquid crystal will be described.

FIG. 7 is a diagram showing the principle of phase modulation of a light beam by a liquid crystal device. FIG. 8 is a diagram showing the principle of intensity modulation by the liquid crystal device.

First, the phase modulation operation will be described. A liquid crystal device of a type in which liquid crystal molecules are aligned in parallel is used for phase-only modulation. Liquid crystal molecules have a long spheroidal shape, have optical anisotropy, and have different refractive indices in the major axis direction and the minor axis direction. FIG. 7 shows a schematic view of a liquid crystal device constituted by enclosing nematic liquid crystal molecules 32 between two transparent glass electrodes 31. FIG. 7A shows the case where the voltage applied to the two electrodes by the liquid crystal device drive power source 33 is zero, and FIG.
In (c), the voltage of the liquid crystal device drive power supply 33 is increased in order of increasing voltage. It can be seen that the orientation of the liquid crystal molecules (nematic liquid crystal) 32 in the long axis direction becomes perpendicular to the transparent glass electrode 31 as the applied voltage is increased.

Next, the incident light beam 34 is made to enter the transparent glass electrode 31 perpendicularly, and the phase of the transmitted light beam 35 is considered.
The polarization direction of light is the liquid crystal molecule 3 when the power supply voltage is zero.
2 parallel to the major axis direction. When the major axis of the liquid crystal molecule 32 is parallel to the transparent glass electrode 31, the equivalent optical path length is different when the major axis of the liquid crystal molecule 32 is parallel to the transparent glass electrode 31. , The degree of phase modulation of light transmitted through the liquid crystal panel is different. When the orientation of the liquid crystal molecules 32 is intermediate, the degree of phase modulation that the transmitted light receives is also intermediate. If the polarization direction of light is perpendicular to the long axis direction of the liquid crystal molecules 32 when the voltage is zero, the phase does not change even if the voltage is changed.

If the transparent glass electrode 31 is divided into cells and the voltage applied to each of them can be controlled, this becomes an array of variable phase shifters. In the present invention, such an optical modulator (spatial light modulator) is used.

The spatial light phase modulator described above can also be operated as an intensity modulator. In the case of only phase modulation, the voltage applied by the liquid crystal device drive power supply 33 is 0.
A light beam polarized in the same direction as the major axis direction of the liquid crystal molecules 32 in the bolt state was incident. (Hereinafter, the long axis direction of the liquid crystal molecules when the applied voltage is 0 V is defined as the y axis direction, and the axis direction perpendicular to the light flux incident surface is defined as the x axis.) When used as an intensity modulator, Normally, the polarized light of the incident light is used in a state of being inclined by 45 degrees with respect to it. Further, an analyzer 12 is provided at the exit of the liquid crystal device. The orientation of the analyzer 12 is set so that the polarization direction of the transmitted light beam is orthogonal to the polarization direction of the incident light beam. FIG. 8 shows a case where a liquid crystal spatial light modulator is used as the intensity modulator.

Let the electric field of the incident light be cos ωt. Described in the form of space vector,

[0071]

[Equation 1] Can be written as The light after passing through the liquid crystal device is

[0072]

[Equation 2] Becomes Furthermore, the light after passing through the analyzer is

[0073]

[Equation 3] Becomes

As can be seen from the equation (1), the transmitted light is

[0075]

[Equation 4] It can be seen that it is subjected to amplitude modulation.

Further, the transmitted light, together with the above-mentioned amplitude modulation,

[0077]

[Equation 5] It can be seen that the phase modulation is also received at the same time.

Where ω is the optical angular frequency of the laser light,
Since φ _x and φ _y represent phase delays along the respective axes and are functions of the voltage V applied to the liquid crystal device, they are described as arguments.

The spatial modulator for performing only the phase modulation and the spatial light modulator for performing the intensity modulation for the light flux traveling with the two-dimensional spread have been described above. Each element can be regarded as having a two-dimensional array configuration of phase modulators or intensity modulators. When performing intensity modulation, phase modulation is also accompanied with amplitude modulation. However, it is possible to connect elements for performing intensity modulation and elements for performing only phase modulation in cascade, and to compensate the phase modulation accompanying intensity modulation in the element for performing only phase modulation.
In this way, it is possible to directly control the amplitude and phase of the two-dimensional light beam.

[0080]

As described above, according to the present invention, the control of the amplitude / phase distribution of the high frequency electric signal applied to the array antenna element is replaced with the control of the amplitude / phase distribution of the lightwave signal, and the correspondence is one-to-one. There is an excellent effect that control can be performed directly.

[Brief description of drawings]

FIG. 1 is a block configuration diagram of an antenna beam forming circuit according to a first embodiment of the present invention.

FIG. 2 is a specific block configuration diagram of an antenna beam forming circuit according to the first embodiment of the present invention.

FIG. 3 is a block configuration diagram of an antenna beam forming circuit according to a second embodiment of the present invention.

FIG. 4 is a block configuration diagram of an antenna beam forming circuit according to a third embodiment of the present invention.

FIG. 5 is a specific block configuration diagram of an antenna beam forming circuit according to a third embodiment of the present invention.

FIG. 6 is a block configuration diagram of an antenna beam forming circuit according to a fourth embodiment of the present invention.

FIG. 7 is a diagram showing a principle of phase modulation of a light beam by a liquid crystal device of an antenna beam forming circuit.

FIG. 8 is a diagram showing a principle of intensity modulation of a light beam by a liquid crystal device of an antenna beam forming circuit.

FIG. 9 is a block diagram illustrating the principle of a light beam forming circuit.

FIG. 10 is a block configuration diagram of an active array antenna using the antenna beam forming circuit of the first conventional example.

FIG. 11 is a block configuration diagram of an antenna beam forming circuit of a second conventional example.

FIG. 12 is a block configuration diagram of an antenna beam forming circuit of a third conventional example.

[Explanation of symbols]

1 high-frequency electric signal input terminals 2 ₁ to 2 _n high frequency electric signal output terminals 3,3 _1, 3 _2, 3a~3d laser light source 4 two distribution means 4a, 4b beam splitter 5 superposing unit 5a acousto-optic modulator ₆₁ through ₂ Expanding means 6a, 6b Beam expander 7 Intensity distribution modulating means 7a Reflective liquid crystal spatial light intensity modulating element 8 Phase distribution modulating means 8a Reflective liquid crystal spatial light phase modulating element 9 Combining means 9a-9c, 11a-11c Half mirror 10 photoelectric conversion means 10 ₁ to 10 _n photoelectric converter 10a ₁ 10 A _n photodetectors array 12 the analyzer 13 liquid crystal spatial light modulator controller 14a~14c mirror 15a~15g Collie formate lens 16 images the mask 17 the Fourier transform lens 18 optical fiber bundle 19a, 19b Spatial filter 20 Reflective spatial light modulator 21 Array 31 Transparent glass electrode 32 Liquid crystal molecule (nematic liquid crystal) 33 Liquid crystal device driving power supply 34 Incident light flux 35 Transmitted light flux 41 EO converter (electrical light converter) 41a EO converter 42 Optical amplitude modulator 43 Optical phase modulator 44 OE conversion Part (photoelectric conversion part) 44a OE conversion element 50 antenna beam forming circuit 51 power distributor 52 _{1 to} 52 _n high frequency signal amplifier 53 _{1 to} 53 _n high frequency signal phase shifter 54 _{1 to} 54 _n power amplifier 55 _{1 to} 55 _n Antenna element S ₁ , S ₂ Lightwave signal

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical indication H04B 10/22

Claims (4)

[Claims] 1. A high frequency electric signal input terminal (1) to which a transmission signal is inputted as an electric signal, and a superposing means (5) for superposing the electric signal from the input terminal (1) on a first lightwave signal (S ₁ ). ), The combining means (9) for combining the output light of the superimposing means (5) and the second lightwave signal (S ₂ ) to perform heterodyne detection, and the output light of the combining means (9) having different beams. a photoelectric conversion means (10) including n photoelectric conversion elements for photoelectrically converting each of the n parts and feeding the antenna element, and the optical path of the first lightwave signal (S ₁ ) and the second lightwave signal (S ₁ ). Modulating means (7, 8) in any of the optical paths of the lightwave signal (S ₂ ).
The modulation means (7, 8) outputs the output light of the superimposing means and the first modulation element (7) for performing intensity distribution modulation by the first electric modulation signal on the plane crossing the optical path. An antenna beam forming circuit comprising an optical circuit in which a second modulation element (8) for performing phase distribution modulation by a second electrical modulation signal on a transverse plane is cascade-connected. 2. The antenna beam forming circuit according to claim 1, wherein the first lightwave signal and the second lightwave signal are generated by a common laser light source (3). 3. The antenna beam forming circuit according to claim ₁ , wherein the first light wave signal and the second light wave signal are generated by different laser light sources (3 ₁ , 3 ₂ ). 4. The first and second modulators are reflective liquid crystal spatial light modulators, and the liquid crystal spatial light controls the two modulators by the first and second electric modulation signals, respectively. The antenna beam forming circuit according to any one of claims 1 to 3, further comprising a modulator controller.