Transmission directivity control device and transmission directivity control method

Abstract

This transmission directivity control device is provided with: a transmission optical signal generation unit that modulates light with a transmission signal to generate a first optical signal and a second optical signal in different frequency bands; a weighting unit that applies a phase gradient predetermined according to the direction of an arrangement line and the desired transmission direction to the second optical signal to generate phase-graded second optical signals corresponding respectively to antenna elements arranged along the arrangement line; and photoelectric conversion units that are provided corresponding respectively to the antenna elements, and that each combine the corresponding phase-graded second optical signal with the first optical signal, convert the resulting optical signal into an electrical signal, and output the converted electrical signal to the corresponding antenna element. Each of the path differences between the optical paths between adjacent photoelectric conversion units in a row and the wavelength of the light are selected so that a phase difference which occurs in one of the two optical signals combined by each photoelectric conversion unit, and which is caused by the path differences between the optical paths traveled by that one optical signal to reach each photoelectric conversion unit, is absorbed.

Description

Transmission directivity control device and transmission directivity control method

[0001] The present invention relates to a transmission directivity control device and a transmission directivity control method.

[0002] To achieve faster and larger-capacity wireless communications, the use of high-frequency bands, such as millimeter waves, is being promoted. However, the spatial propagation loss of radio waves increases with increasing frequency. For example, free-space propagation loss increases in proportion to the square of the frequency. Therefore, high-gain antennas are often used in high-frequency bands. Because high-gain antennas have high directivity, it is necessary to align the antenna beam direction with the remote station in wireless communications. When the remote station's direction is dynamic, a means for dynamically controlling the beam direction, i.e., beam steering, is essential. Beam steering is required not only for wireless communications but also for other applications, such as radar, imaging, and wireless power transmission.

[0003] As a means of beam steering, various methods have been devised and used, such as mechanically controlling the direction of the antenna and controlling the radio waves emitted from the antenna by refracting or reflecting them with movable lenses or reflectors. However, these methods have problems in terms of durability and tracking ability because they have mechanical moving parts. For this reason, phased array antennas, which do not have mechanical moving parts and are suitable for making antennas smaller and lighter, are becoming more widely used.

[0004] In a phased array antenna, beam steering is performed electronically by controlling the phase and amplitude of the RF (Radio Frequency) signal supplied to each antenna element (hereinafter, this control is also referred to as weighting) using means such as variable delay circuits, variable attenuator circuits, and digital signal processing connected to multiple antenna elements arranged on a line or a surface.

[0005] In fifth-generation mobile communication systems (see, for example, Non-Patent Document 1) that use millimeter-wave bands and millimeter-wave band wireless LAN (Local Area Network) systems, phased array antennas that perform weighting using analog circuits are widely used.

[0006] In many wireless communication systems, the range in which the wireless communication partner station exists varies not within a two-dimensional plane but within a three-dimensional space, so beam steering along two axes, such as azimuth and elevation, is required. Therefore, a phased array antenna requires weighting to perform two-dimensional beam steering using a two-dimensional array antenna in which antenna elements are arranged in a plane.

[0007] Furthermore, as the use of high-frequency bands progresses, even higher antenna gains will be required, and it is expected that phased array antennas that weight a larger number of antenna elements will be required. For example, Non-Patent Document 1 discloses a 256-element phased array antenna used in fifth-generation mobile communication base stations in the 28 GHz band. In the case of the 28 GHz band, if the radio frequency becomes about 10 times higher, the free-space propagation loss will increase by 100 times, or 20 dB. Therefore, it is expected that tens of thousands of antenna elements will be required to compensate for this free-space propagation loss with the antenna gain of the base station. In sixth-generation mobile communications, which aim to provide even higher transmission rates, the use of the 300 GHz band (the so-called terahertz band) is being considered, and it is expected that even more antenna elements will be required than in fifth-generation mobile communications.

[0008] To minimize power loss to antenna elements, each phase shifter circuit must be located near each antenna element. For example, a phase shifter circuit is located directly behind a planar antenna element formed on a printed circuit board and power is supplied via a through hole. However, as radio frequencies increase and antenna element spacing narrows, it becomes difficult to arrange multiple phase shifter circuits two-dimensionally at spacings equivalent to the antenna element spacing. For example, for a radio frequency of 300 GHz, the free-space wavelength is 1 mm, so the antenna element spacing is typically half the wavelength, or 0.5 mm. Furthermore, to configure a circuit that forms multiple beams (a so-called multi-beam forming circuit), the same number of phase shifter circuits as the number of beams must be arranged in parallel, which can easily lead to difficulties in arranging the phase shifter circuits.

[0009] JP 2004-023400 A JP 2007-165956 A

[0010] H. Watanabe, S. Uga, H. Nakamizo, T. Tsutsumi, S. Shinjo, and Y. Kuriyama, “Millimeter-Wave Antenna and RF Front-End Technology for 5th Generation Mobile Communication Base Stations,” IEICE Communications Society Magazine, 2020, Vol. 14, No. 3, pp. 222-231. Dong-Hun KIM, Jiro HIROKAWA, Makoto ANDO, “One-Body 2-D Beam-Switching Butler Matrix with Waveguide Short-Slot 2-Plane Couplers,” IEICE TRANSACTIONS on Electronics, Oct. 2017, Vol. E100-C, No. 10, pp. 884-892. C. Tsokos et al., “Analysis of a Multibeam Optical Beamforming Network Based on Blass Matrix Architecture,” in Journal of Lightwave Technology, Aug. 15, 2018. vol. 36, no. 16, pp. 3354-3372.Y. Liu and J. Klamkin, "Scalable Integrated Photonics Beamforming Circuits," 2020 Asia Communications and Photonics Conference (ACP) and International Conference on Information Photonics and Optical Communications (IPOC), 2020, pp. 1-3.B. Ortega, J. Mora and R. Chulia, "Optical Beamformer for 2-D Phased Array Antenna With Subarray Partitioning Capability," in IEEE Photonics Journal, June 2016, vol. 8, no. 3, pp. 1-9.

[0011] To address the above-mentioned problem of difficulty in arranging phase shifter circuits, etc., there is a method in which a passive circuit that shifts phase by a fixed amount is used and its input terminals are switched, rather than implementing a large number of phase shifter circuits, etc., corresponding to the number of antenna elements. However, in this method, in order to perform two-dimensional beam steering, the circuit structure must be a three-dimensionally assembled structure, as shown in, for example, Non-Patent Document 2. Therefore, implementation in the high frequency band requires a configuration using a waveguide that is three-dimensionally processed from metal with high precision, making mass production difficult. Even if mass production is not performed, it is considered difficult to accommodate multiple elements.

[0012] In response to this, for example, Non-Patent Document 3 proposes a means of applying optical circuit manufacturing technology that can implement small-sized low-loss waveguides to convert signals into light and then perform weighting using an optical circuit. This is thought to increase the possibility of configuring a multi-element, two-dimensional weighting circuit, but the number of components in the weighting circuit increases depending on the number of antenna elements.

[0013] For these reasons, it is highly desirable to avoid using a three-dimensional structure as a means for controlling a two-dimensional array antenna, and to minimize the increase in the number of components while being able to accommodate an increase in the number of antenna elements.

[0014] The following techniques have been disclosed as existing techniques for performing weighting using optical circuits other than those described in Non-Patent Documents 2 and 3: Patent Document 1 discloses a technique relating to a three-dimensional optical circuit that performs two-dimensional beam steering using a wavelength dispersion line; Patent Document 2 discloses a technique for forming multiple beams using wavelength multiplexing, which is considered to be capable of being made two-dimensional and multi-element; Non-Patent Document 4 discloses a technique that can accommodate multi-element configuration without increasing the number of components in the weighting circuit, by using a loop configuration that repeatedly reuses phase shifters while converting the optical wavelength.

[0015] Non-Patent Document 5 discloses a technology for performing one-dimensional (within one plane) beam steering using a planar phase shift circuit by combining a planar phase shift circuit with an FBG (Fiber Bragg Grating) reflection line whose delay time varies depending on the optical wavelength. Furthermore, Non-Patent Document 5 discloses a technology for performing two-dimensional beam steering by using an FBG reflection line to enable beam steering in a plane perpendicular to the plane of the planar phase shift circuit. It is believed that employing this technology will enable two-dimensional beam steering while reducing the number of circuit components.

[0016] However, the technology disclosed in Patent Document 1 requires a matrix circuit with multilayer wiring that is difficult to manufacture, and is therefore unsuitable for mass production using a planar circuit manufacturing process.The technology disclosed in Patent Document 2 has a problem in that the number of components constituting the circuit becomes enormous as the number of antenna elements increases and the circuit becomes two-dimensional.

[0017] The technique disclosed in Non-Patent Document 4 has a problem of complicated wiring due to the use of a loop configuration in which phase shifters are repeatedly reused while converting optical wavelengths. The FBG used in the technique disclosed in Non-Patent Document 5 has a strong frequency band dependency, so when multiplexing multiple wavelengths to accommodate a large number of antenna elements or beams, the number of FBG reflection lines becomes enormous.

[0018] An object of the present invention is to provide a transmission directivity control device and a transmission directivity control method that enable appropriate weighting without complicating the wiring structure even when the scale of the array antenna is large, and that enable control of transmission directivity using a circuit with a simple structure that is suitable for miniaturization and mass production.

[0019] One aspect of the present invention is a system including a plurality of antenna elements arranged along an arrangement line that is arbitrarily determined in a three-dimensional space; a transmission optical signal generation unit that modulates light with a transmission signal to generate a first optical signal and a second optical signal of different frequency bands; a weighting unit that applies a phase gradient to the second optical signal that is predetermined according to the direction of the arrangement line and a desired transmission direction, to generate a second optical signal with a phase gradient corresponding to each of the antenna elements arranged along the arrangement line; and photoelectric conversion units that are provided corresponding to each of the antenna elements and are arranged in a line, and photoelectric conversion units that combine the first optical signal and the second optical signal with a phase tilt corresponding to each of the first optical signals to convert them into electrical signals, and output the converted electrical signals to the antenna elements that correspond to each of the first optical signals, and selects each of the path differences of the optical paths between adjacent photoelectric conversion units in the row and the wavelength of the light so that a phase difference that occurs in one of the two optical signals combined by each of the photoelectric conversion units, which phase difference occurs due to the path difference of the optical path until the one optical signal reaches each of the photoelectric conversion units, is absorbed.

[0020] One aspect of the present invention is a transmission directivity control method for a plurality of antenna elements arranged along an arrangement line arbitrarily determined in a three-dimensional space, the method comprising the steps of: a transmission optical signal generation unit modulating light with a transmission signal to generate a first optical signal and a second optical signal of different frequency bands; a weighting unit applying a phase gradient to the second optical signal that is predetermined according to the direction of the arrangement line and a desired transmission direction, to generate a second optical signal with a phase gradient corresponding to each of the antenna elements arranged along the arrangement line; and a weighting unit provided corresponding to each of the antenna elements and arranged in a row. a step in which each of the photoelectric conversion units arranged in the row combines the corresponding second optical signal with the phase tilt and the first optical signal to convert the combined signal into an electrical signal, and outputs the converted electrical signal to the corresponding antenna element, wherein the method selects each of the path differences of the optical paths between the photoelectric conversion units adjacent in the row and the wavelength of the light so that a phase difference occurring in one of the two optical signals combined by each of the photoelectric conversion units, which phase difference occurs due to a path difference of the optical path until the one optical signal reaches each of the photoelectric conversion units, is absorbed.

[0021] According to the present invention, even if the size of the array antenna is large, it is possible to provide appropriate weighting without complicating the wiring structure, and it is possible to control the transmission directivity using a circuit with a simple structure that is suitable for miniaturization and mass production.

[0022] 1 is a diagram illustrating an example of the configuration of a transmission directivity control device according to a first embodiment. FIG. 2 is a diagram illustrating the internal configuration of a photoelectric conversion unit according to the first embodiment and the connection relationship with antenna elements. FIG. 3 is a flowchart illustrating the operation of the transmission directivity control device according to the first embodiment. FIG. 4 is a diagram illustrating an example of the configuration of a transmission directivity control device according to a second embodiment. FIG. 5 is a diagram illustrating the arrangement of antenna elements according to the second embodiment. FIG. 6 is a flowchart illustrating the operation of the transmission directivity control device according to the second embodiment. FIG. 7 is a diagram illustrating an example of the configuration of a transmission directivity control device according to a third embodiment. FIG. 8 is a diagram illustrating the internal configuration of a transmission optical signal generation unit according to a fourth embodiment, the connection relationship between the transmission optical signal generation unit and a light source, and a wavelength designation unit connected to the light source. FIG. 9 is a diagram illustrating the correspondence relationship between wavelengths and directions, and the correspondence relationship between output terminals assigned within each of a first scanning switching circuit and a second scanning switching circuit and wavelengths according to the fourth embodiment. FIG. 10 is a diagram illustrating an example of the configuration of a transmission directivity control device according to a fifth embodiment. FIG. 11 is a diagram (part 1) illustrating another example of the configuration of the transmission optical signal generation unit shown in the first, second, third, and fifth embodiments, the connection relationship with a light source, and a wavelength designation unit connected to the light source. 10 is a diagram (part 2) showing another example of the configuration of the transmission optical signal generation unit shown in the first, second, third, and fifth embodiments, the connection relationship with the light source, and the wavelength specification unit connected to the light source. 11 is a diagram showing another example of the configuration of the photoelectric conversion unit shown in the first and fifth embodiments, and the connection relationship with the antenna element.

[0023] (First Embodiment) Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Fig. 1 is a block diagram showing an example configuration of a transmission directivity control device 1 according to the first embodiment. The transmission directivity control device 1 includes a wavelength designation unit 10, a light source 11, a transmission optical signal generation unit 12, a weighting unit 13, an operation unit 16, photoelectric conversion units 17-1 to 17-M, and antenna elements 18-1 to 18-M. Here, M is a natural number equal to or greater than 2, and in this specification, a natural number is a positive integer not including 0.

[0024] The wavelength specifying unit 10 receives a user operation and generates and outputs a wavelength specifying signal including a wavelength λ selected by the user. The light source 11 is a wavelength-tunable light source and generates and outputs CW (Continuous Wave) light of the wavelength λ included in the wavelength specifying signal received from the wavelength specifying unit 10. The transmission optical signal generating unit 12 includes an optical modulator 21 and a demultiplexer 22. The optical modulator 21 converts an externally applied electrical transmission signal into a baseband signal, and intensity-modulates the light output by the light source 11 with the baseband signal to generate a modulated optical signal.

[0025] The demultiplexer 22 demultiplexes the modulated optical signal generated by the optical modulator 21 into a carrier optical signal and an upper sideband optical signal. The demultiplexer 22 outputs the demultiplexed carrier optical signal to an optical path 100 connected to the demultiplexer 22, and outputs the demultiplexed upper sideband optical signal to an optical path 200. The optical paths 100, 200, and the optical paths described below are, for example, optical fibers. Note that in FIG. 1 and the following figures, the connecting lines shown by dashed and dotted lines indicate optical paths along which the carrier optical signal is transmitted, and the connecting lines shown by dotted lines indicate optical paths along which the upper sideband optical signal is transmitted.

[0026] The operation unit 16 is capable of selecting a transmission direction and outputs a switching instruction signal corresponding to the selected transmission direction. The weighting unit 13 includes a scanning switching circuit 14 and a scanning matrix circuit 15. The scanning switching circuit 14 is, for example, an optical switch and includes one input terminal 14-S and M output terminals 14-E-1, 14-E-2, ..., 14-E-M. An optical path 200 is connected to the input terminal 14-S. The scanning switching circuit 14 switches the input terminal 14-S to connect to one of the output terminals 14-E-1 to 14-E-M depending on the type of switching instruction signal output by the operation unit 16. In other words, there are M types of transmission directions that can be selected by the operation unit 16, and the operation unit 16 outputs a switching instruction signal corresponding to each of the M types of transmission directions.

[0027] The scanning matrix circuit 15 is a circuit configured to impart a phase gradient using, for example, a delay line, a high-dispersion line, a resonant ring, or the like. For example, a Butler matrix circuit or a Blass matrix circuit may be used as the circuit. The scanning matrix circuit 15 imparts a phase gradient to the supplied optical signal. The scanning matrix circuit 15 includes M input terminals 15-S-1, 15-S-2, ..., 15-S-M and M output terminals 15-E-1, 15-E-2, ..., 15-E-M. Each of the M input terminals 15-S-1 to 15-S-M is connected to each of the output terminals 14-E-1 to 14-E-M of the scanning switching circuit 14.

[0028] In the scanning matrix circuit 15, a tilt phase amount corresponding to the phase tilt to be imparted is predetermined between each of the M input terminals 15-S-1 to 15-S-M and each of the M output terminals 15-E-1 to 15-E-M, and the circuit configuration is predetermined so that the tilt phase amount is imparted.

[0029] In the first embodiment, "j" is an arbitrary natural number between 1 and M. When an optical signal is supplied from any one of the input terminals 15-S-j, the scanning matrix circuit 15 calculates a tilt phase amount φ between the input terminal 15-S-j and each of the M output terminals 15-E-1 to 15-E-M for the supplied optical signal. ｊ The scanning matrix circuit 15 outputs each of the generated M optical signals from M output terminals 15-E-1, 15-E-2, ..., 15-E-M. Note that for the tilt phase amount and other phase amounts, when no unit is indicated, the unit is radian, which is a unit of the radian system, and when indicated in the degree system, the unit "°" is added.

[0030] Here, in the scanning matrix circuit 15, when M=3, the amount of tilt phase φ determined between the input terminal 15-S-j and each of the M output terminals 15-E-1 to 15-E-M is ｊ A specific example of this will be described.

[0031] When an optical signal is supplied to the input terminal 15-S-1, three optical signals to which phases of (0°, 30°, 60°) are added are output from the output terminals 15-E-1, 15-E-2, and 15-E-3, respectively. Therefore, the phase amounts of (0°, 30°, 60°) expressed in radians are the tilt phase amounts φ ｊ In this case, 0° is the tilt phase amount φ １ , 30° is the tilt phase amount φ ２ , 60° is the tilt phase amount φ ３ which provides a phase ramp in 30° increments.

[0032] When an optical signal is supplied to the input terminal 15-S-2, three optical signals to which phases (0°, 60°, 120°) are added are output from the output terminals 15-E-1, 15-E-2, and 15-E-3, respectively. Therefore, the phase amounts of (0°, 60°, 120°) expressed in radians are the tilt phase amounts φ ｊ In this case, 0° is the tilt phase amount φ １ , 60° is the tilt phase amount φ ２ , 120° is the tilt phase amount φ ３ which provides a phase ramp in 60° increments.

[0033] When an optical signal is supplied to the input terminal 15-S-3, three optical signals to which phases of (0°, 90°, 180°) are added are output from the output terminals 15-E-1, 15-E-2, and 15-E-3, respectively. Therefore, the phase amounts of (0°, 90°, 180°) expressed in radians are the tilt phase amounts φ ｊ In this case, 0° is the tilt phase amount φ １ , 90° is the tilt phase amount φ ２ , 180° is the tilt phase amount φ ３ which provides a phase ramp in 90° increments.

[0034] That is, the amount of tilt phase φ ｊ The subscript "j" in the equation corresponds to the "j" indicating the position of the output terminal 15-E-j, and the tilt phase amount φ ｊWhen the input terminals 15-S-1 to 15-SM are different, the phase amount becomes different.

[0035] Each of the photoelectric conversion units 17-1 to 17-M is connected to each of branch optical paths 102-1, 102-2, ..., 102-M branching from M branch points 101-1, 101-2, ..., 101-M in the optical path 100, and to optical paths 200-1, 200-2, ..., 200-M connected to each of output terminals 15-E-1 to 15-E-M of the scanning matrix circuit 15. The branch optical paths 102-1 to 102-M are part of the optical path 100, and the portion of the optical path 100 other than the branch optical paths 102-1 to 102-M is referred to as the main line of the optical path 100.

[0036] Each of the photoelectric conversion units 17-1 to 17-M has the same internal configuration, and the photoelectric conversion unit 17-j has the internal configuration shown in FIG. 2. The photoelectric conversion unit 17-j includes a photodiode (hereinafter referred to as a PD (Photo Diode)) 31-j and a multiplexer 32-j. The multiplexer 32-j is connected to the branched optical path 102-j and the optical path 200-j. The multiplexer 32-j multiplexes the carrier optical signal supplied via the branched optical path 102-j with the upper sideband optical signal supplied via the optical path 200-j. The PD 31-j is connected to the multiplexer 32-j and the antenna element 18-j, and converts the optical signal output by the multiplexer 32-j into an electrical signal to generate an RF signal. Hereinafter, the process performed by the photoelectric conversion unit 17-j to combine two optical signals, convert them into an electrical signal, and generate an RF signal is also referred to as photomixing.

[0037] Antenna elements 18-1 to 18-M are arranged along an arrangement line that is arbitrarily determined in three-dimensional space, forming array antenna 19, which is a so-called one-dimensional array antenna. Note that the arrangement line may be a straight line, or a curved line that forms a curved surface, such as a concave or convex shape, that is generally used in two-dimensional array antennas. Each of antenna elements 18-1 to 18-M radiates an RF signal supplied from photoelectric conversion units 17-1 to 17-M connected thereto as a radio wave. The radio waves radiated from each of antenna elements 18-1 to 18-M form a so-called transmission beam.

[0038] For example, if the placement line is a straight line in the horizontal direction of the paper in Figure 1, the transmission beam radiated from antenna elements 18-1 to 18-M will be directed in any direction between the front direction 80 and the left and right horizontal directions on the plane of the paper in Figure 1, such as the directions indicated by symbols 81 and 82, or the front direction 80, if the direction indicated by symbol 80, which is the vertical upward direction of the paper in Figure 1, is defined as the front direction 80.

[0039] The direction of the transmit beam is determined by the phase gradient imparted by the scanning matrix circuit 15. By changing the phase gradient imparted by the scanning matrix circuit 15, the direction of the transmit beam can be set to any direction between the front direction 80 and the left or right lateral direction. However, the phase gradient is fixedly determined in advance between each of the M input terminals 15-S-1 to 15-S-M and the M output terminals 15-E-1 to 15-E-M according to the direction of the layout line and the transmission direction desired by the user based on the direction of the layout line. Therefore, in the scanning matrix circuit 15, the number of transmit beam directions when the phase gradient is fixedly determined is M, which is the number of input terminals 15-S-1 to 15-S-M of the scanning matrix circuit 15, i.e., the number of antenna elements 18-1 to 18-M.

[0040] The photoelectric conversion units 17-1 to 17-M are arranged in a row along an arrangement line. The photoelectric conversion units 17-1 to 17-M are arranged so that the difference in path length (hereinafter referred to as path difference D) of the optical paths 100 from the output terminal connected to the optical path 100 of the demultiplexer 22 to each of two adjacent photoelectric conversion units 17-1 to 17-M in the row is constant, and this constant path difference D satisfies a connection condition (hereinafter referred to as first connection condition) expressed by the following equation (1):

[0041]

[0042] In equation (1), "λ" is the wavelength λ included in the wavelength specification signal output by the wavelength specification unit 10, i.e., the wavelength λ of the light generated and output by the light source 11. "a" is an arbitrary natural number. In other words, the path difference D may have any value as long as it is a natural number multiple of the wavelength λ of the light output by the light source 11.

[0043] As an example that satisfies the first connection condition, the optical path 100 is wired to the photoelectric conversion units 17-1 to 17-M as follows: The photoelectric conversion units 17-1 to 17-M are arranged in a row along an arrangement line at equal intervals with a path difference D. The main line of the optical path 100 is wired along the row in which the photoelectric conversion units 17-1 to 17-M are lined up. At M branch points 101-1, 101-2, ..., 101-M on the main line of the optical path 100, the distance between adjacent branch points 101-1, 101-2, ..., 101-M is set to the path difference D. Each of the branch points 101-1, 101-2, ..., 101-M is connected to each of the photoelectric conversion units 17-1 to 17-M by branch optical paths 102-1 to 102-M of the same length.

[0044] In this case, as shown in Figure 1, the path difference D of the path length of the optical path 100 that starts from the output terminal to which the optical path 100 of the demultiplexer 22 is connected and reaches each of the photoelectric conversion units 17-1 to 17-M appears as the difference in path length of the optical path 100 that starts from the starting point and reaches each of the branch points 101-1 to 101-M.

[0045] In order to use the phase of the carrier optical signal output from the demultiplexer 22 when it reaches the photoelectric conversion unit 17-1 as a reference, this phase is set to "0." There is a difference in the path length between the branching point 101-1 and the branching point 101-2 between the photoelectric conversion units 17-1 and 17-2, i.e., a difference in the path difference D. Therefore, the optical signal output from the demultiplexer 22 and arriving at the photoelectric conversion unit 17-2 rotates in phase due to the path difference D between the branching point 101-1 and the branching point 101-2, and the phase advances by an amount corresponding to the length of the path difference D. Here, since D = aλ according to equation (1), the optical signal output from the demultiplexer 22 and arriving at the photoelectric conversion unit 17-2 is an optical signal whose phase is advanced by "2aπ" relative to the optical signal output from the demultiplexer 22 and arriving at the photoelectric conversion unit 17-1.

[0046] As described above, the intervals between adjacent branching points 101-1, 101-2, ..., 101-M are equal, so the optical signal output from the demultiplexer 22 and reaching the photoelectric conversion unit 17-j is a signal whose phase is advanced by "2(j-1)aπ" relative to the optical signal output from the demultiplexer 22 and reaching the photoelectric conversion unit 17-1.

[0047] On the other hand, the optical paths 200-1 to 200-M output from the output terminals 15-E-1 to 15-E-M of the scanning matrix circuit 15 and reaching the photoelectric conversion units 17-1 to 17-M are wired so as not to have any path difference. Therefore, the phase difference between the upper sideband optical signals output from the output terminals 15-E-1 to 15-E-M of the scanning matrix circuit 15 and reaching the photoelectric conversion units 17-1 to 17-M is determined by the amount of tilt phase φ given by the scanning matrix circuit 15. ｊ The difference depends on the

[0048] (Processing by the Transmission Directivity Control Device of the First Embodiment) Processing by the transmission directivity control device 1 will be described with reference to Figure 3. A user of the transmission directivity control device 1 determines the wavelength λ, and wires the optical paths 100 to the photoelectric conversion units 17-1 to 17-M so that the path difference D is in accordance with the determined wavelength λ and the first connection condition. Then, when the user performs an operation to select the wavelength λ in the wavelength designation unit 10, the wavelength designation unit 10 outputs a wavelength designation signal including the wavelength λ to the light source 11 in response to the operation.

[0049] The user operates the operation unit 16 to select a desired transmission direction, and in response to this operation, the operation unit 16 outputs a switching instruction signal corresponding to the selected transmission direction to the scanning switching circuit 14. Upon receiving this switching instruction signal, the scanning switching circuit 14 connects, for example, the input terminal 14-S to the output terminal 14-E-j, which is one of the output terminals 14-E-1 to 14-E-M.

[0050] The process of the flowchart shown in FIG. 3 starts. The light source 11 receives the wavelength specification signal output by the wavelength specification unit 10. The light source 11 generates light of wavelength λ included in the received wavelength specification signal and outputs the generated light to the optical modulator 21. The optical modulator 21 intensity-modulates the light using an externally applied transmission signal to generate a modulated optical signal. The optical modulator 21 outputs the generated modulated optical signal to the demultiplexer 22 (Sa1). The demultiplexer 22 demultiplexes the modulated optical signal output by the optical modulator 21 into a carrier optical signal and an upper sideband optical signal. Here, the carrier optical signal is expressed by the following equation (2), and the upper sideband optical signal is expressed by the following equation (3).

[0051]

[0052]

[0053] In equations (2) and (3), ω Ｃ is the angular frequency of the light generated by the light source 11, and t is the time. ＲＦ is the angular frequency of the RF signal, and corresponds to the frequency difference between the carrier optical signal and the upper sideband optical signal. The demultiplexer 22 outputs the carrier optical signal to the optical path 100 and outputs the upper sideband optical signal to the optical path 200 (Sa2).

[0054] The scanning switching circuit 14 receives the upper sideband optical signal output by the demultiplexer 22 from the input terminal 14-S and outputs it from the output terminal 14-E-j (Sa3). The scanning matrix circuit 15 receives the upper sideband optical signal output from the output terminal 14-E-j of the scanning switching circuit 14 from the input terminal 15-S-j. The scanning matrix circuit 15 adjusts the tilt phase amount φ determined between the input terminal 15-S-j and each of the M output terminals 15-E-1 to 15-E-M for the received upper sideband optical signal. ｊ The upper sideband optical signal output from the output terminal 15-E-j of the scanning matrix circuit 15 can be expressed by the following equation (4):

[0055]

[0056] The scanning matrix circuit 15 outputs the generated M upper sideband optical signals from M output terminals 15-E-1 to 15-E-M (Sa4).

[0057] Each of the photoelectric conversion units 17-1 to 17-M is supplied with a carrier optical signal from the demultiplexer 22 via the optical path 100, and with an upper sideband optical signal via the optical paths 200-1 to 200-M. Here, photomixing performed by any photoelectric conversion unit 17-j in the photoelectric conversion units 17-1 to 17-M will be described with reference to FIG.

[0058] As described above, the carrier optical signal supplied to the multiplexer 32-j of the photoelectric conversion unit 17-j via the branched optical path 102-j has a phase lead of "2(j-1)aπ", and is therefore expressed by the following equation (5).

[0059]

[0060] On the other hand, the upper sideband optical signal supplied to multiplexer 32-j via optical path 200-j is expressed by the above-mentioned equation (4). Therefore, multiplexer 32-j multiplexes the carrier optical signal expressed by equation (5) with the upper sideband optical signal expressed by equation (4) to generate a multiplexed optical signal and output it to PD 32-j. The multiplexed optical signal generated by multiplexer 32-j is expressed by the following equation (6).

[0061]

[0062] When PD32-j receives the combined optical signal output by multiplexer 32-j, it converts the combined optical signal into an electrical signal. During this conversion into an electrical signal, PD32-j performs square-law detection on the combined optical signal and generates an electrical signal of a predetermined RF frequency band component that depends on the output frequency characteristics of PD32-j from the result of this square-law detection. The square-law detection by PD32-j can be expressed as the right side of the following equation (7).

[0063]

[0064] The RF signal output by the PD 32-j is an RF signal v expressed by the following equation (8) obtained by extracting the RF frequency band from the calculation result of the right side of equation (7). ＲＦ＿ｊ As shown in equation (8), the RF signal v ＲＦ＿ｊ is cos(ω ＲＦ t-φ ｊ +2jaπ-2aπ).

[0065]

[0066] Each of the photoelectric conversion units 17-1 to 17-M outputs the generated RF signal to the antenna elements 18-1 to 18-M connected thereto. Each of the antenna elements 18-1 to 18-M radiates the RF signal output by the photoelectric conversion unit 17-1 to 17-M connected thereto as a radio wave (Sa5), and the process ends.

[0067] (Effects of the First Embodiment) As described above, in the transmission directivity control device 1 of the first embodiment, when the wavelength of light generated by the light source 11 is λ, the optical path 100 is wired to the photoelectric conversion units 17-1 to 17-M so as to satisfy the first connection condition described above. As a result, the RF signal output from the photoelectric conversion unit 17-j becomes the signal shown in equation (8). The RF signal output from the photoelectric conversion unit 17-(j+1) adjacent to the photoelectric conversion unit 17-j becomes the signal shown in the following equation (9) where "j+1" is substituted for "j" on the right-hand side of equation (8).

[0068]

[0069] As can be seen from a comparison between equations (8) and (9), the phase difference between the RF signals output by the photoelectric conversion unit 17-(j+1) and the photoelectric conversion unit 17-j is "-φ ｊ＋１ +φ ｊ +2aπ". "2aπ" is "a" times 2π, where "a" is a natural number. Therefore, the phase indicated by the phase difference is "-φ ｊ＋１ +φ ｊ ", the phase difference "2aπ" occurring in the carrier optical signal supplied to each of the photoelectric conversion units 17-1 to 17-M is absorbed by the path difference D of the optical path 100 until the carrier optical signal reaches each of the photoelectric conversion units 17-1 to 17-M.

[0070] In the first embodiment described above, the user operates the wavelength specifying unit 10 to select the wavelength λ of light generated by the light source 11. According to the wavelength λ selected by the user, the optical path 100 is wired to the photoelectric conversion units 17-1 to 17-M in advance so as to satisfy the first connection condition. Alternatively, the path difference D is determined in advance, and the optical path 100 is wired to the photoelectric conversion units 17-1 to 17-M. Then, the wavelength λ may be determined so as to satisfy the formula (1), and the user may select the determined wavelength λ in the wavelength specifying unit 10.

[0071] In other words, in the transmission directivity control device 1 of the first embodiment, the path difference D and the wavelength λ of the light generated by the light source 11 are selected so that the phase difference occurring in the carrier optical signal supplied to each of the photoelectric conversion units 17-1 to 17-M is absorbed by the path difference D of the optical path 100 until the carrier optical signal reaches each of the photoelectric conversion units 17-1 to 17-M. This makes it possible to make the phase difference between the carrier optical signal supplied to the adjacent photoelectric conversion unit 17-(j+1) and the photoelectric conversion unit 17-j a natural number multiple of 2π. As a result, as described above, the phase difference between the RF signals output by the adjacent photoelectric conversion unit 17-(j+1) and the photoelectric conversion unit 17-j is "-φ ｊ＋１ +φ ｊ The phase difference of this RF signal indicates the phase gradient applied by the scanning matrix circuit 15, and therefore, by using these RF signals, it becomes possible to propagate the radio waves of the RF signals radiated from the antenna elements 18-1 to 18-M in the transmission direction desired by the user.

[0072] For example, in the configuration of the first embodiment, in order to match the phases of the carrier optical signals reaching each of the photoelectric conversion units 17-1 to 17-M from the demultiplexer 22, it is possible to take measures such as making the optical paths from the output terminal to which the optical path 100 of the demultiplexer 22 is connected to each of the photoelectric conversion units 17-1 to 17-M the same path length. However, when this measure is adopted, the circuit scale required to make the optical paths the same path length becomes enormous as the number of antenna elements 18-1 to 18-M, 18-1-1 to 18-3-3, that is, the number of photoelectric conversion units 17-1 to 17-M, 17-1-1 to 17-3-3, increases. In contrast, in the transmission directivity control device 1 of the first embodiment, the wiring of the optical path 100 to the photoelectric conversion units 17-1 to 17-M is a simple configuration in which a single optical path 100 is branched into M paths and connected to each of the photoelectric conversion units 17-1 to 17-M, thereby achieving the above-mentioned objective. Furthermore, in the transmission directivity control device 1 of the first embodiment, phase shifting of the optical signal is performed using an analog circuit. Therefore, compared to a fully digitally controlled array antenna in which phase shifting is performed entirely using digital signal processing, the number of analog-to-digital converters can be significantly reduced. Therefore, by using the transmission directivity control device 1 of the first embodiment, even if the array antenna 19 is large in size, appropriate weighting is possible without complicating the wiring structure, and transmission directivity can be controlled using a circuit with a simple structure suitable for miniaturization and mass production.

[0073] 4 is a block diagram showing an example of the configuration of a transmission directivity control device 1a according to a second embodiment. In the second embodiment, the same components as those in the first embodiment are described with the same reference numerals. The transmission directivity control device 1a includes a wavelength specifying unit 10, a light source 11, a transmission optical signal generating unit 12, a weighting unit 13a, an operating unit 16a, photoelectric conversion units 17-1-1 to 17-3-3, and antenna elements 18-1-1 to 18-3-3.

[0074] The antenna elements 18-1-1 to 18-3-3 are arranged along a first arrangement line that is arbitrarily determined in three-dimensional space and a second arrangement line that intersects the first arrangement line. Here, the first arrangement line and the second arrangement line may be straight lines or curves that form a curved surface, such as a concave or convex shape, typically used in two-dimensional array antennas. For example, the first arrangement line and the second arrangement line are straight lines that intersect at right angles, with the first arrangement line extending vertically in three-dimensional space and the second arrangement line extending horizontally in three-dimensional space. In this case, the antenna elements 18-1-1 to 18-3-3 are arranged, for example, as shown in FIG. 5 to form an array antenna 19a, which is a so-called two-dimensional array antenna. In other words, the transmission directivity control device 1a of the second embodiment has a configuration in which the shape of the array antenna 19, which is a one-dimensional array antenna in the transmission directivity control device 1 of the first embodiment, is expanded to a two-dimensional shape with M=3.

[0075] Each of the photoelectric conversion units 17-1-1 to 17-3-3 is connected to a corresponding one of the antenna elements 18-1-1 to 18-3-3, and is arranged in a matrix such that the row direction coincides with the direction of the first arrangement lines and the column direction coincides with the direction of the second arrangement lines. In the second embodiment, "i" is a natural number between 1 and 3 indicating the row position, and "j" is a natural number between 1 and 3 indicating the column position. The photoelectric conversion unit 17-i-j arranged in the i-th row and j-th column includes a multiplexer and a PD, similar to the photoelectric conversion unit 17-j of the first embodiment shown in FIG. 2, and performs photomixing on two supplied optical signals. Hereinafter, the multiplexer and PD included in the photoelectric conversion unit 17-i-j will be referred to as multiplexer 32-i-j and PD 31-i-j, respectively.

[0076] The weighting unit 13a includes a first scanning switching circuit 14A, a second scanning switching circuit 14B, a first scanning matrix circuit 15A, and a second scanning matrix circuit 15B. The connection relationship between the first scanning switching circuit 14A and the first scanning matrix circuit 15A and the connection relationship between the second scanning switching circuit 14B and the second scanning matrix circuit 15B are the same as the connection relationship between the scanning switching circuit 14 and the scanning matrix circuit 15 of the first embodiment when M=3. The first scanning switching circuit 14A and the second scanning switching circuit 14B have the same configuration as the configuration of the scanning switching circuit 14 of the first embodiment when M=3.

[0077] The first scanning matrix circuit 15A and the second scanning matrix circuit 15B are circuits corresponding to the configuration of the scanning matrix circuit 15 of the first embodiment when M=3, but the phase gradient to be applied is determined individually for each of the first scanning matrix circuit 15A and the second scanning matrix circuit 15B. That is, a phase gradient is determined for the first scanning matrix circuit 15A according to the direction of the first arrangement line and the transmission direction desired by the user based on the direction of the first arrangement line. A phase gradient is determined for the second scanning matrix circuit 15B according to the direction of the second arrangement line and the transmission direction desired by the user based on the direction of the second arrangement line.

[0078] In the first scanning matrix circuit 15A, the amount of tilt phase predetermined between each of the input terminals 15A-S-1 to 15A-S-3 and each of the output terminals 15A-E-1 to 15A-E-3 will be referred to as φ, where φ is followed by "Vi". Ｖｉ The amount of tilt phase φ Ｖ１ is the amount of phase inclination imparted to the optical signal output from the output terminal 15A-E-1, and the amount of phase inclination φ Ｖ２ is the amount of phase inclination imparted to the optical signal output from the output terminal 15A-E-2, and the amount of phase inclination φ Ｖ３ is the amount of phase inclination given to the optical signal output from the output terminal 15A-E-3. As explained in the first embodiment, (φ Ｖ１ , φ Ｖ２ , φ Ｖ３) will have different values ​​depending on which of the input terminals 15A-S-1, 15A-S-2, and 15A-S-3 the optical signal is supplied to.

[0079] In the second scanning matrix circuit 15B, the amount of tilt phase predetermined between each of the input terminals 15B-S-1 to 15B-S-3 and each of the output terminals 15B-E-1 to 15B-E-3 is hereinafter referred to as φ, where φ is followed by "Hj". Ｈｊ The amount of tilt phase φ Ｈ１ is the amount of phase inclination imparted to the optical signal output from the output terminal 15B-E-1, and the amount of phase inclination φ Ｈ２ is the amount of tilt phase imparted to the optical signal output from the output terminal 15B-E-2, and the amount of tilt phase φ Ｈ３ is the amount of phase inclination given to the optical signal output from the output terminal 15B-E-3. As explained in the first embodiment, (φ Ｈ１ , φ Ｈ２ , φ Ｈ３ ) will have different values ​​depending on which of the input terminals 15B-S-1, 15B-S-2, and 15B-S-3 the optical signal is supplied to.

[0080] (φ Ｖ１ , φ Ｖ２ , φ Ｖ３ There are three combinations of values ​​for (φ Ｈ１ , φ Ｈ２ , φ Ｈ３ ) have three possible combinations of values. Therefore, it is possible to specify 3 × 3 = 9 directions for the transmission beam. Therefore, the user can select one of 9 directions as the transmission direction using the operation unit 16a, and the operation unit 16a outputs a switching instruction signal corresponding to the selected transmission direction to the first scanning switching circuit 14A and the second scanning switching circuit 14B.

[0081] The connection conditions (hereinafter referred to as second connection conditions) between the first scanning matrix circuit 15A, the second scanning matrix circuit 15B, and each of the photoelectric conversion units 17-1-1 to 17-3-3 are represented by the connection relationships shown below.

[0082] The connection relationship of the optical path 100-1 between the output terminal 15A-E-1 of the first scanning matrix circuit 15A and each of the photoelectric conversion units 17-1-1, 17-1-2, and 17-1-3 in the first row is the same as the connection relationship of the optical path 100 between the output terminal to which the optical path 100 of the demultiplexer 22 in the first embodiment is connected and each of the photoelectric conversion units 17-1, 17-2, and 17-3. However, the path difference D in the first embodiment is replaced by a path difference D in the second embodiment. ２ Therefore, the path difference D ２ is expressed as the following equation (10).

[0083]

[0084] The connection relationship of optical path 100-2 between output terminal 15A-E-2 and each of photoelectric conversion units 17-2-1, 17-2-2, and 17-2-3 in the second row, and the connection relationship of optical path 100-3 between output terminal 15A-E-3 and each of photoelectric conversion units 17-3-1, 17-3-2, and 17-3-3 in the third row are the same as the connection relationship of optical path 100-1 between output terminal 15A-E-1 and each of photoelectric conversion units 17-1-1, 17-1-2, and 17-1-3 in the first row.

[0085] The connection relationship of the optical path 200-1 between the output terminal 15B-E-1 of the second scanning matrix circuit 15B and each of the photoelectric conversion units 17-1-1, 17-2-1, and 17-3-1 in the first column is the same as the connection relationship of the optical path 100-1 between the output terminal 15A-E-1 and each of the photoelectric conversion units 17-1-1, 17-1-2, and 17-1-3 in the first row, but the path difference is a path difference D ２ Instead, the path difference D １ The difference is that

[0086]

[0087] In equation (11), "b" is an arbitrary natural number. In other words, the path difference D １ can be any value as long as it is a natural number multiple of the wavelength λ of the light output from the light source 11. Therefore, b may be equal to a, and in this case, the path difference D １ = Path difference D ２ becomes.

[0088] The connection relationship of the optical path 200-2 between the output terminal 15B-E-2 and each of the photoelectric conversion units 17-1-2, 17-2-2, and 17-3-2 in the second column, and the connection relationship of the optical path 200-3 between the output terminal 15B-E-3 and each of the photoelectric conversion units 17-1-3, 17-2-3, and 17-3-3 in the third column are the same as the connection relationship of the optical path 200-1 between the output terminal 15B-E-1 and each of the photoelectric conversion units 17-1-1, 17-2-1, and 17-3-1 in the first column.

[0089] In other words, the second connection condition can be said to be a condition including the following column-direction condition and row-direction condition. That is, the column-direction condition is a condition that starts from each of the output terminals 15A-E-1, 15A-E-2, and 15A-E-3 of the first scanning matrix circuit 15A and reaches each of two adjacent photoelectric conversion units 17-1-1 to 17-3-3 in the photoelectric conversion units 17-1-1 to 17-3-3 for each corresponding row, and is determined by the path difference D ２ is constant, and the path difference D ２ As shown in equation (10), the condition is that λ is an arbitrary natural number a times the wavelength λ of the light generated by the light source 11 .

[0090] The row direction condition is a path difference D of the optical paths 200-1 to 200-3 that start from each of the output terminals 15B-E-1, 15B-E-2, and 15B-E-3 of the second scanning matrix circuit 15B and reach each of two adjacent photoelectric conversion units 17-1-1 to 17-3-3 in the photoelectric conversion units 17-1-1 to 17-3-3 for each corresponding column. １ is constant, and the path difference D １ As shown in equation (11), the condition is that λ is an arbitrary natural number b times the wavelength λ of the light generated by the light source 11.

[0091] As an example that satisfies the second connection condition, optical paths 100-1 to 100-3 and 200-1 to 200-3 are wired to photoelectric conversion units 17-1-1 to 17-3-3 as follows: In the combination of photoelectric conversion units 17-1-1, 17-1-2, and 17-1-3 in the first row, the combination of photoelectric conversion units 17-2-1, 17-2-2, and 17-2-3 in the second row, and the combination of photoelectric conversion units 17-3-1, 17-3-2, and 17-3-3 in the third row, the adjacent intervals in the column direction, i.e., the second arrangement line direction, are all equal to or larger than the path difference D ２ In the combination of photoelectric conversion units 17-1-1, 17-2-1, and 17-3-1 in the first column, the combination of photoelectric conversion units 17-1-2, 17-2-2, and 17-3-2 in the second column, and the combination of photoelectric conversion units 17-1-3, 17-2-3, and 17-3-3 in the third column, the adjacent intervals in the row direction, i.e., the first arrangement line direction, are all equal to or greater than the path difference D １ Arrange them so that

[0092] After arranging the photoelectric conversion units 17-1-1 to 17-3-3 in this manner, the optical paths 100-1 to 100-3 connected to the output terminals 15A-E-1 to 15A-E-3 of the first scanning matrix circuit 15A are wired in the column direction, as in the first embodiment. The distance between adjacent branch points on the main lines of the optical paths 100-1 to 100-3 is equal to the distance between the photoelectric conversion units 17-1-1 to 17-3-3 in the column direction, i.e., the path difference D ２ The branch points of the optical path 100-1 are determined so as to coincide with the optical paths 17-1-1, 17-1-2, and 17-1-3 in the first row, respectively, via branch optical paths of the same length. As with the optical path 100-1, the optical paths 100-2 and 100-3 are also connected to the optical path 17-2-1, 17-2-2, and 17-2-3 in the second row and the optical path 17-3-1, 17-3-2, and 17-3-3 in the third row, respectively.

[0093] Similarly, the optical paths 200-1 to 200-3 connected to the output terminals 15B-E-1 to 15B-E-3 of the second scanning matrix circuit 15B are wired in the row direction. The distance between adjacent branch points on the main lines of the optical paths 200-1 to 200-3 is equal to the distance between the photoelectric conversion units 17-1-1 to 17-3-3 in the row direction, i.e., the path difference D１ The branching points of the optical path 200-1 are determined so as to coincide with the optical paths 17-1-1, 17-2-1, and 17-3-1 in the first column, respectively, via branched optical paths of the same length. As with the optical path 200-1, the optical paths 200-2 and 200-3 are also connected to the optical path 17-1-2, 17-2-2, and 17-3-2 in the second column and the optical path 17-1-3, 17-2-3, and 17-3-3 in the third column, respectively.

[0094] As described above, by arranging the photoelectric conversion units 17-1-1 to 17-3-3 and wiring the optical paths 100-1 to 100-3 and 200-1 to 200-3, as shown in FIG. 4, a path difference D ２ This also applies to the other optical paths 100-1 and 100-2. In addition, the length between the adjacent branch points 201-1-1 and 201-1-2 and the length between the branch points 201-1-2 and 201-1-3 in the optical path 200-1 have a path difference D １ This also applies to the other optical paths 200-2 and 200-3.

[0095] (Processing by the Transmission Directivity Control Device of the Second Embodiment) The processing by the transmission directivity control device 1a of the second embodiment will be described with reference to Fig. 6. The user of the transmission directivity control device 1a determines the wavelength λ, and the path difference D １ , D ２ The optical paths 100-1 to 100-3 and 200-1 to 200-3 are wired to the photoelectric conversion units 17-1-1 to 17-3-3 so that: When a user then performs an operation to select a wavelength λ in the wavelength designation unit 10, the wavelength designation unit 10 outputs a wavelength designation signal including the wavelength λ to the light source 11 in response to the operation.

[0096] The user operates the operation unit 16a to select a desired transmission direction, and in response to this operation, the operation unit 16a outputs a switching instruction signal corresponding to the selected transmission direction to the first scanning switching circuit 14A and the second scanning switching circuit 14B. Upon receiving this switching instruction signal, the first scanning switching circuit 14A connects, for example, the input terminal 14A-S to output terminal 14A-E-i, which is one of output terminals 14A-E-1 to 14A-E-3. Upon receiving this switching instruction signal, the second scanning switching circuit 14B connects, for example, the input terminal 14B-S to output terminal 14B-E-j, which is one of output terminals 14B-E-1 to 14B-E-3.

[0097] 6 starts. The processes in steps Sb1 and Sb2 are the same as those in steps Sa1 and Sa2 of the first embodiment shown in FIG.

[0098] The first scanning switching circuit 14A receives the carrier optical signal output from the demultiplexer 22 through the input terminal 14A-S and outputs it from the output terminal 14A-E-i (Sb3-1). The first scanning matrix circuit 15A receives the carrier optical signal output from the output terminal 14A-E-i of the first scanning switching circuit 14A through the input terminal 15A-S-i. The first scanning matrix circuit 15A calculates the tilt phase amount φ for the received carrier optical signal, which is determined between the input terminal 15A-S-i and each of the output terminals 15A-E-1 to 15A-E-3. Ｖｉ The carrier optical signal output from the demultiplexer 22 is expressed by equation (2), and therefore the carrier optical signal output from the output terminal 15A-E-i of the first scanning matrix circuit 15A is expressed by the following equation (12).

[0099]

[0100] The first scanning matrix circuit 15A outputs the generated optical signals of the three carrier waves from the output terminals 15A-E-1 to 15A-E-3 (Sb4-1).

[0101] The processing of Sb3-2 and Sb4-2 is the same as the processing of Sa3 and Sa4 in the first embodiment shown in FIG. 3, except that M=3 and the amount of tilt phase given by the scanning matrix circuit 15 is φ ｊ From φ Ｈｊ The processing is the same as that performed by the scanning switching circuit 14, but replaced by the second scanning switching circuit 14B, and the processing performed by the scanning matrix circuit 15 is performed by the second scanning matrix circuit 15B.

[0102] In this case, the upper sideband optical signal output by the splitter 22 is expressed by equation (3), and therefore, in the processing of Sb4-2, the upper sideband optical signal output from the output terminal 15B-E-j of the second scanning matrix circuit 15B is expressed by the following equation (13).

[0103]

[0104] The processing of Sb3-1 and Sb4-1 and the processing of Sb3-2 and Sb4-2 are performed in parallel.

[0105] The optical signal of the carrier wave that reaches the photoelectric conversion unit 17-ij in the j-th column has a phase lead of "2(j-1)aπ", and is therefore expressed by the following equation (14).

[0106]

[0107] The upper sideband optical signal that reaches the photoelectric conversion unit 17-ij in the i-th row has a phase lead of "2(i-1)bπ", and is therefore expressed by the following equation (15).

[0108]

[0109] The photoelectric conversion unit 17-i-j photomixes the carrier optical signal represented by equation (14) with the upper sideband optical signal represented by equation (15). That is, the multiplexer 32-i-j included in the photoelectric conversion unit 17-i-j multiplexes the carrier optical signal represented by equation (14) with the upper sideband optical signal represented by equation (15) to generate a multiplexed optical signal. The PD 31-i-j converts the multiplexed optical signal generated by the multiplexer 32-i-j into an electrical signal. During this conversion to an electrical signal, the PD 32-i-j performs square-law detection on the multiplexed optical signal and generates an electrical signal of a predetermined RF frequency band component that depends on the output frequency characteristics of the PD 32-i-j from the result of this square-law detection. The square-law detection by the PD 32-i-j can be expressed as the right side of the following equation (16).

[0110]

[0111] The RF signal output from the photoelectric conversion unit 17-i-j is an RF signal v expressed by the following equation (17), which is obtained by extracting the RF frequency band from the calculation result of the right side of equation (16): ＲＦ＿ｉｊ As shown in equation (17), the RF signal v ＲＦ＿ｉｊ is cos(ω ＲＦ t+(φ Ｖｉ -φ Ｈｊ ) + 2(j-1)aπ + 2(i-1)bπ).

[0112]

[0113] Each of the photoelectric conversion units 17-1-1 to 17-3-3 outputs the generated RF signal to the antenna elements 18-1-1 to 18-3-3 connected thereto. Each of the antenna elements 18-1-1 to 18-3-3 radiates the RF signal output by the photoelectric conversion units 17-1-1 to 17-3-3 connected thereto as a radio wave (Sb5), and the process ends.

[0114] (Effects of the Second Embodiment) As described above, in the transmission directivity control device 1a of the second embodiment, when the wavelength of light generated by the light source 11 is λ, the optical paths 100-1 to 100-3 and 200-1 to 200-3 are wired to the photoelectric conversion units 17-1-1 to 17-3-3 so as to satisfy the second connection condition described above. As a result, the RF signal output from the photoelectric conversion unit 17-i-j becomes the signal shown in equation (17). Here, the RF signal output from the photoelectric conversion unit 17-(i+1)-j adjacent to the photoelectric conversion unit 17-i-j in the row direction becomes the signal shown in the following equation (18) where "i+1" is substituted for "i" on the right-hand side of equation (17).

[0115]

[0116] Furthermore, the RF signal output from the photoelectric conversion unit 17-i-(j+1) adjacent to the photoelectric conversion unit 17-i-j in the column direction is the signal shown in the following equation (19), where "j+1" is substituted for "j" on the right side of equation (17).

[0117]

[0118] As can be seen from a comparison between equations (17) and (18), the phase difference between the RF signals output from the photoelectric conversion unit 17-(i+1)-j and the photoelectric conversion unit 17-i-j is "φ Ｖ（ｉ＋１） -φ Ｖｉ +2bπ". "2bπ" is "b" times 2π, where "b" is a natural number. Therefore, the phase indicated by the phase difference is "φ Ｖ（ｉ＋１） -φ Ｖｉ ", the path difference D of the optical paths 200-1 to 200-3 that the upper sideband optical signal takes to reach each of the photoelectric conversion units 17-1-1 to 17-3-3 for each row is １ This absorbs the phase difference "2bπ" that occurs in the upper sideband optical signals supplied to each of the photoelectric conversion units 17-1-1 to 17-3-3.

[0119] As can be seen from a comparison between equations (17) and (19), the phase difference between the RF signals output from the photoelectric conversion unit 17-i-(j+1) and the photoelectric conversion unit 17-ij is "-φ Ｈ（ｉ＋１） +φ Ｈｉ+2aπ". "2aπ" is "a" times 2π, where "a" is a natural number. Therefore, the phase indicated by the phase difference is "-φ Ｈ（ｉ＋１） +φ Ｈｉ ", the path difference D of the optical paths 100-1 to 100-3 until the carrier optical signal reaches each of the photoelectric conversion units 17-1-1 to 17-3-3 for each column is ２ This absorbs the phase difference "2aπ" that occurs in the carrier optical signal supplied to each of the photoelectric conversion units 17-1-1 to 17-3-3.

[0120] In the second embodiment described above, the user operates the wavelength designation unit 10 to select the wavelength λ of the light generated by the light source 11. In accordance with the wavelength λ selected by the user, the optical paths 100-1 to 100-3 and 200-1 to 200-2 are wired to the photoelectric conversion units 17-1-1 to 17-3-3 in advance so as to satisfy the second connection condition. １ and the path difference D ２ Then, the optical paths 100-1 to 100-3 and 200-1 to 200-2 are wired to the photoelectric conversion units 17-1-1 to 17-3-3. Then, the wavelength λ is determined so as to satisfy the formula (10) and the formula (11), and the user may select the determined wavelength λ in the wavelength designation unit 10.

[0121] In other words, in the transmission directivity control device 1a of the second embodiment, the path difference D of the optical paths 100-1 to 100-3 on which the optical signal of the carrier wave with the phase tilt reaches each of the photoelectric conversion units 17-1-1 to 17-3-3 in the column direction is ２ , the path difference D of the optical paths 200-1 to 200-3 until the phase-inclined upper sideband optical signal reaches each of the row-direction photoelectric conversion units 17-1-1 to 17-3-3 is reduced so that the phase difference occurring in the phase-inclined carrier optical signal supplied to each of the photoelectric conversion units 17-1-1 to 17-3-3 is absorbed. １ The path difference D is set so that the phase difference occurring in the upper sideband optical signal with a phase tilt supplied to each of the photoelectric conversion units 17-1-1 to 17-3-3 is absorbed. ２ and the path difference D １and the wavelength λ generated by the light source 11. As a result, as described above, the phase difference between the RF signals output by the photoelectric conversion unit 17-(i+1)-j and the photoelectric conversion unit 17-i-j adjacent in the row direction is "φ Ｖ（ｉ＋１） -φ Ｖｉ ", and the phase difference between the RF signals output by the photoelectric conversion unit 17-i-(j+1) and the photoelectric conversion unit 17-ij adjacent in the column direction is "-φ Ｈ（ｉ＋１） +φ Ｈｉ The former phase difference "φ Ｖ（ｉ＋１） -φ Ｖｉ " indicates the phase gradient applied by the first scanning matrix circuit 15A, and the latter "-φ Ｈ（ｉ＋１） +φ Ｈｉ " indicates the phase gradient applied by the second scanning matrix circuit 15B. Therefore, by using these RF signals, it becomes possible to propagate the radio waves of the RF signals radiated from the antenna elements 18-1-1 to 18-3-3 in the transmission direction desired by the user.

[0122] The transmission directivity control device 1a of the second embodiment has the following effect in addition to the effect of the transmission directivity control device 1 of the first embodiment described above. That is, the transmission directivity control device 1a can perform large-scale, two-dimensional transmission beam scanning while significantly suppressing an increase in the number of components in the circuit that forms the transmission beam and structural complexity, such as the need for overpasses and three-dimensional wiring, when scanning a two-dimensional transmission beam. In other words, by using the transmission directivity control device 1a, even if the array antenna 19a is large in size, appropriate weighting is possible without complicating the wiring structure, and transmission directivity can be controlled using a circuit with a simple structure that is suitable for miniaturization and mass production.

[0123] Although the second embodiment shows an example in which a 3 × 3 array antenna 19a is configured, the transmission directivity control device 1a of the second embodiment can configure an array antenna of any size N × M. Here, N and M are natural numbers, and one of N and M is at least a natural number equal to or greater than 2.

[0124] (Third Embodiment) Fig. 7 is a block diagram showing an example of the configuration of a transmission directivity control device 1b according to a third embodiment. In the third embodiment, the same components as those in the first and second embodiments will be described with the same reference numerals. Note that the component indicated by reference numeral 400 in Fig. 7 is the same as the component indicated by reference numeral 400 in Fig. 4. Therefore, the transmission directivity control device 1b includes a wavelength designation unit 10, a light source 11, a transmission optical signal generation unit 12, a weighting unit 13b, an operation unit 16a, photoelectric conversion units 17-1-1 to 17-3-3, and antenna elements 18-1-1 to 18-3-3.

[0125] The weighting unit 13b includes a first scanning switching circuit 14A, a second scanning switching circuit 14B, multiplexers 41-1 to 41-3, demultiplexers 42-1 to 42-3, and a scanning matrix circuit 15C. The scanning matrix circuit 15C has the same configuration as the scanning matrix circuit 15 of the first embodiment, except that M=3.

[0126] The multiplexers 41-1 to 41-3 multiplex the supplied carrier optical signal and upper sideband optical signal to generate a multiplexed optical signal. The multiplexer 41-1 is connected on the input side to the output terminal 14A-E-1 of the first scanning switching circuit 14A and the output terminal 14B-E-1 of the second scanning switching circuit 14B, and on the output side to the input terminal 15C-S-1 of the scanning matrix circuit 15C. The multiplexer 41-2 is connected on the input side to the output terminal 14A-E-2 of the first scanning switching circuit 14A and the output terminal 14B-E-2 of the second scanning switching circuit 14B, and on the output side to the input terminal 15C-S-2 of the scanning matrix circuit 15C. The multiplexer 41-3 is connected on the input side to the output terminal 14A-E-3 of the first scanning switching circuit 14A and the output terminal 14B-E-3 of the second scanning switching circuit 14B, and is connected on the output side to the input terminal 15C-S-3 of the scanning matrix circuit 15C.

[0127] The demultiplexers 42-1 to 42-3 demultiplex the supplied optical signal into a carrier optical signal and an upper sideband optical signal. The demultiplexer 42-1 is connected on the input side to the output terminal 15C-E-1 of the scanning matrix circuit 15C, and on the output side to the optical path 100-1 and the optical path 200-1. The demultiplexer 42-2 is connected on the input side to the output terminal 15C-E-2 of the scanning matrix circuit 15C, and on the output side to the optical path 100-2 and the optical path 200-2. The demultiplexer 42-3 is connected on the input side to the output terminal 15C-E-3 of the scanning matrix circuit 15C, and on the output side to the optical path 100-3 and the optical path 200-3. The connection relationship between each of the optical paths 100-1 to 100-3 and 200-1 to 200-3 and each of the photoelectric conversion units 17-1-1 to 17-3-3 is the same as in the second embodiment.

[0128] (Processing by the Transmission Directivity Control Device of the Third Embodiment) In the transmission directivity control device 1a of the third embodiment, the scanning matrix circuit 15C also serves as the first scanning matrix circuit 15A and the second scanning matrix circuit 15B in the transmission directivity control device 1a of the second embodiment. Therefore, in the processing shown in Fig. 6, after the processing of Sb3-1 and Sb3-2, a processing of multiplexing the carrier optical signal and the upper sideband optical signal by the multiplexers 41-1 to 41-3 is added, and the processing of Sb4-1 and Sb4-2 is performed by the scanning matrix circuit 15C.

[0129] In the second embodiment, the amount of tilt phase given by the first scanning matrix circuit 15A is φ Ｖｉ More specifically, when an optical signal is supplied to the input terminal 15A-S-p and output from the output terminal 15A-E-i, the amount of tilt phase imparted to the optical signal is expressed as φ Ｖｐｉ Similarly, the amount of tilt phase given by the second scanning matrix circuit 15B can be expressed as φ Ｈｊ More specifically, when an optical signal is supplied to the input terminal 15B-S-p and output from the output terminal 15B-E-j, the amount of tilt phase imparted to the optical signal is expressed as φ Ｈｐｊ Here, in the third embodiment, p, i, j, and q shown below are any natural numbers between 1 and 3.

[0130] In the second embodiment, even if i=j=q, the first scanning matrix circuit 15A and the second scanning matrix circuit 15B are different circuits, so the tilt phase amount φ Ｖｐｑ and the tilt phase amount φ Ｈｐｑ On the other hand, in the third embodiment, since one scanning matrix circuit 15C is used, when i=j=q, φ Ｖｐｑ =φ Ｈｐｑ The difference is that it becomes

[0131] This difference can be explained as follows in terms of the direction of the transmission beam. For example, in the array antenna 19a of the second embodiment shown in Fig. 5, when viewed from the direction in which the main body of the transmission directivity control device 1a, designated by the reference numeral 90, is located, a transmission beam can be transmitted in a total of nine directions, combining three directions: a direction parallel to the horizontal plane, i.e., a direction tilted at an angle of 0° with respect to the horizontal plane, a direction tilted upward by ψ° from the horizontal plane, and a direction tilted downward by ψ° from the horizontal plane; and three directions: a direction parallel to the vertical plane, i.e., a direction tilted at an angle of 0° with respect to the vertical plane, a direction tilted rightward by ξ° from the vertical plane, and a direction tilted leftward by ξ° from the horizontal plane. In the case of the second embodiment, φ Ｖｐｑ ≠φ Ｈｐｑ Therefore, φ° and ξ° can be different angles. Ｖｐｑ =φ Ｈｐｑ Therefore, φ° and ξ° are the same.

[0132] After the scanning matrix circuit 15C performs the processes of Sb4-1 and Sb4-2, each of the demultiplexers 42-1 to 42-3 receives the optical signal output from the output terminals 15C-E-1 to 15C-E-3 connected thereto and demultiplexes it into a carrier optical signal and an upper sideband optical signal. Each of the demultiplexers 42-1 to 42-3 outputs the demultiplexed carrier optical signal to the optical paths 100-1 to 100-3 connected thereto, and outputs the demultiplexed upper sideband optical signal to the optical paths 200-1 to 200-3 connected thereto. Then, the process of Sb5 is performed, and the process ends.

[0133] (Effects of the Third Embodiment) In addition to the effects of the transmission directivity control device 1a of the second embodiment described above, the transmission directivity control device 1b of the third embodiment has the following effects. While the transmission directivity control device 1a of the second embodiment requires two matrix circuits, the first scanning matrix circuit 15A and the second scanning matrix circuit 15B, the transmission directivity control device 1b of the third embodiment uses a single matrix circuit, the scanning matrix circuit 15C, to impart a phase gradient. Therefore, the transmission directivity control device 1b can be made even more compact than the transmission directivity control device 1a.

[0134] However, as described above, compared to the range of directions of a transmission beam that can be transmitted by the transmission directivity control device 1a, there are restrictions on the range of directions of a transmission beam that can be transmitted by the transmission directivity control device 1b. Also, while the transmission directivity control device 1a can arrange any number of antenna elements 18-i-j in each of the first arrangement line direction and the second arrangement line direction, in the case of the transmission directivity control device 1b, although the configuration of the array antenna 19a can be other than 3 × 3, it is necessary to make the number of antenna elements 18-i-j that can be arranged in the first arrangement line direction and the second arrangement line direction the same.

[0135] In the transmission directivity control device 1a of the second embodiment, the first scanning matrix circuit 15A and the second scanning matrix circuit 15B weight each of the antenna elements 18-1-1 to 18-3-3 arranged along the first arrangement line and each of the antenna elements 18-1-1 to 18-3-3 arranged along the second arrangement line, and electronic beam steering is performed by using the scanning matrix circuit 15C in the transmission directivity control device 1b of the third embodiment. Generally, when weighting is performed collectively on the antenna elements 18-1-1 to 18-3-3 arranged along the first arrangement line and the second arrangement line, the number of elements in the weighting section is proportional to the square of the number of antenna elements. In contrast, when weighting is performed individually on each of the first arrangement line and the second arrangement line, as in the transmission directivity control device 1a of the second embodiment, the number of elements in each of the first scanning matrix circuit 15A and the second scanning matrix circuit 15B is 2 × (number of antenna elements).１／２ Therefore, the transmission directivity control device 1a of the second embodiment can suppress an increase in the number of elements in the weighting unit 13a that occurs with an increase in the number of antenna elements, compared to a general configuration. Furthermore, in the transmission directivity control device 1b of the third embodiment, the scanning matrix circuit 15C serves both the functions of the first scanning matrix circuit 15A and the second scanning matrix circuit 15B, and therefore, can suppress an increase in the number of elements in the weighting unit 13b that occurs with an increase in the number of antenna elements more than the transmission directivity control device 1a of the second embodiment.

[0136] (Fourth Embodiment) The transmission directivity control device 1a of the second embodiment described above has a single-beam configuration that includes one light source 11 and transmits one transmission beam from light of one wavelength λ. In contrast, by configuring the transmission directivity control device 1a as follows, it is possible to configure it as a multi-beam configuration that transmits multiple transmission beams in parallel.

[0137] In the second transmission directivity control device 1a, the light source 11 is replaced with nine light sources 11-1, 11-2, ..., 11-9 having the same configuration as the light source 11. The wavelength designation unit 10 is replaced with nine wavelength designation units 10-1, 10-2, ..., 10-9 having the same configuration as the wavelength designation unit 10. Each of the wavelength designation units 10-1 to 10-9 is connected to each of the light sources 11-1 to 11-9, and each of the light sources 11-1 to 11-9 is assigned a corresponding wavelength λ １ ~λ ９ and the wavelength λ selected by the user １ ~λ ９ and outputs a wavelength designation signal including each of the above.

[0138] Furthermore, the transmission optical signal generation unit 12 is replaced with a transmission optical signal generation unit 12a shown in Fig. 8. The transmission optical signal generation unit 12a includes nine optical modulators 21-1, 21-2, ..., 21-9, a multiplexer 23, and an optical comb filter 24. Each of the optical modulators 21-1 to 21-9 has the same configuration as the optical modulator 21. Each of the optical modulators 21-1 to 21-9 is connected to a corresponding one of the light sources 11-1 to 11-9, and intensity-modulates the light generated and output by the light sources 11-1 to 11-9 connected to it with a different transmission signal 1, transmission signal 2, ..., transmission signal 9 provided to each of the optical modulators.

[0139] The multiplexer 23 has nine input terminals and one output terminal, and each of the nine input terminals is connected to one of the optical modulators 21-1 to 21-9. The multiplexer 23 multiplexes the optical signals supplied from the nine input terminals to generate a multiplexed optical signal, and outputs the generated multiplexed optical signal from the output terminal.

[0140] Optical comb filter 24 has one input terminal and two output terminals 25-1 and 25-2, with the output terminal of multiplexer 23 connected to the input terminal, optical path 100 connected to output terminal 25-1, and optical path 200 connected to output terminal 25-2. Optical comb filter 24 has periodic pass characteristics and separates the nine carrier optical signals and nine upper sideband optical signals contained in the combined optical signal supplied from the input terminal into a carrier group and an upper sideband group, and outputs the combined optical signal of the nine carrier optical signals from output terminal 25-1 and the combined optical signal of the nine upper sideband optical signals from output terminal 25-2.

[0141] As described above, the second transmission directivity control device 1a can transmit a transmission beam in nine directions. If nine different wavelengths of light, each having a frequency difference equal to or greater than the frequency difference between a pair of carrier waves and upper sideband waves, can be assigned to these nine directions, it is possible to prevent the modulated optical signals from interfering with each other even if the light of different wavelengths is intensity-modulated. Therefore, the wavelength λ selected by the user in each of the wavelength designation units 10-1 to 10-9 can be set to １ ~λ ９ must have different wavelengths so as to satisfy the condition that the modulated optical signals do not interfere with each other.

[0142] Furthermore, the wavelength λ selected by the user in each of the wavelength specifying units 10-1 to 10-9 is １ ~λ ９ Each of the wavelengths λ satisfies the relationship shown in the following equation (20): １ , …, λ ｋ , …λ ９ It is necessary to

[0143]

[0144] In formula (20), D１ and D ２ Similarly to the second embodiment, the path difference D １ and the path difference D between the photoelectric conversion units 17-1-1 to 17-3-3 arranged in the column direction. ２ k is any natural number between 1 and 9. １ , ..., a ｋ , ..., a ９ , and b １ , ..., b ｋ , ..., b ９ is any natural number.

[0145] As mentioned above, the wavelength λ １ ~λ ９ are different wavelengths, so a １ ~a ９ Each of the values ​​of b １ ~b ９ Each of the values ​​of a ｋ = b ｋ or a ｋ ≠ b ｋ Therefore, the wavelength λ １ ~λ ９ The wavelength selection condition for selecting is wavelength λ １ ~λ ９ The condition includes the condition that each of the different wavelengths λ is different and the condition that the formula (20) is satisfied. １ ~λ ９ Then, the path difference D is determined to satisfy the equation (20). １ and the path difference D ２ Alternatively, the path difference D １ and the path difference D ２ Then, the wavelength λ is determined so as to satisfy the wavelength selection condition. １ ~λ ９ may be determined.

[0146] The wavelength λ is selected to satisfy the above wavelength selection conditions. １ ~λ ９For example, in the array antenna 19a shown in FIG. 5, when viewed from the direction in which the main body of the transmission directivity control device 1a indicated by reference numeral 90 is located, as shown in FIG. 9(a), １ is in the "upper left direction", and the wavelength λ ２ "left center direction", wavelength λ ３ to the "downward-left direction", and wavelength λ ４ is the "middle-up direction", and the wavelength λ ５ is the "front direction", and the wavelength λ ６ is in the "middle-down direction", and the wavelength λ ７ "upper right direction", wavelength λ ８ "Right center direction", wavelength λ ９ is assigned to the "bottom right direction."

[0147] Furthermore, in the transmission directivity control device 1a of the second embodiment, the first scanning switching circuit 14A and the second scanning switching circuit 14B are replaced with optical switches and configured as a branching filter. In this case, it is no longer necessary for the operation unit 16a to output a switching instruction signal to the first scanning switching circuit 14A and the second scanning switching circuit 14B, and therefore the operation unit 16a is not required in the fourth embodiment.

[0148] The demultiplexers of the first scanning switching circuit 14A and the second scanning switching circuit 14B are set to perform the following demultiplexing: The demultiplexer of the first scanning switching circuit 14A demultiplexes the optical signal supplied from the input terminal 14A-S into a signal having a wavelength λ １ , λ ４ , λ ７ and an optical signal of wavelength λ ２ , λ ５ , λ ８ and an optical signal of wavelength λ ３ , λ ６ , λ ９ Furthermore, the demultiplexer provided in the first scanning switching circuit 14A demultiplexes the optical signals of wavelength λ 1 into three groups, as shown in FIG. １ , λ ４ , λ ７ The optical signal of wavelength λ is output from the output terminal 14A-E-3. ２ , λ ５ , λ ８ The optical signal of wavelength λ is output from the output terminal 14A-E-2. ３ , λ ６ , λ ９The optical signal is output from the output terminal 14A-E-1.

[0149] The demultiplexer of the second scanning switching circuit 14B divides the optical signal supplied from the input terminal 14B-S into two signals of wavelength λ １ , λ ２ , λ ３ and an optical signal of wavelength λ ４ , λ ５ , λ ６ and an optical signal of wavelength λ ７ , λ ８ , λ ９ Furthermore, the demultiplexer provided in the second scanning switching circuit 14B demultiplexes the optical signals of wavelength λ into three groups, as shown in FIG. １ , λ ２ , λ ３ The optical signal of wavelength λ is output from the output terminal 14B-E-1. ４ , λ ５ , λ ６ The optical signal of wavelength λ is output from the output terminal 14B-E-2. ７ , λ ８ , λ ９ The optical signal is output from the output terminal 14B-E-3.

[0150] The phase tilt applied by the first scanning matrix circuit 15A is such that when an optical signal is supplied from input terminal 15A-S-3, the transmitted beam is directed upward; when an optical signal is supplied from input terminal 15A-S-2, the transmitted beam is directed forward; and when an optical signal is supplied from input terminal 15A-S-1, the transmitted beam is directed downward.

[0151] The phase tilt applied by the second scanning matrix circuit 15B is such that when an optical signal is supplied from input terminal 15B-S-1, the transmitted beam is directed to the left; when an optical signal is supplied from input terminal 15B-S-2, the transmitted beam is directed to the front; and when an optical signal is supplied from input terminal 15B-S-3, the transmitted beam is directed to the right.

[0152] With the transmission directivity control device 1a of the second embodiment configured as described above, the process shown in FIG. １ ~λ９ This allows for nine different wavelengths λ １ ~λ ９ Using the above, nine transmission beams in which nine different transmission signals 1 to 9 are superimposed can be transmitted in parallel in the nine directions shown in FIG. 9(a).

[0153] (Effects of the Fourth Embodiment) The transmission directivity control device 1a configured as in the fourth embodiment described above is equipped with nine wavelength designation units 10-1 to 10-9, nine light sources 11-1 to 11-9, a transmission optical signal generation unit 12a, and the first scanning switching circuit 14A and the second scanning switching circuit 14B replaced with demultiplexers, thereby making it possible to perform wavelength multiplexing. １ ~λ ９ is a wavelength that satisfies the wavelength selection conditions described above, and therefore the wavelength λ １ ~λ ９ In each of the above, the phase difference between the upper sideband optical signals supplied to the photoelectric conversion units 17-i-j and 17-(i+1)-j adjacent to each other in the row direction is a natural number multiple of 2π, and the phase difference between the carrier optical signals supplied to the photoelectric conversion units 17-i-j and 17-i-(j+1) adjacent to each other in the column direction is a natural number multiple of 2π. As a result, １ ~λ ９ In each of the above, the phase difference between the RF signals output by the photoelectric conversion unit 17-(i+1)-j and the photoelectric conversion unit 17-ij that are adjacent in the row direction, and the phase difference between the RF signals output by the photoelectric conversion unit 17-i-(j+1) and the photoelectric conversion unit 17-ij that are adjacent in the column direction, are the same as those in the second embodiment. Therefore, the fourth embodiment also has the same effects as the transmission directivity control device 1a of the second embodiment, and further has the effect of being able to perform multi-beam transmission that can transmit nine transmission beams in parallel.

[0154] The technique of configuring the transmission directivity control device 1a of the second embodiment as in the fourth embodiment can be applied to the transmission directivity control device 1 of the first embodiment and the transmission directivity control device 1b of the third embodiment. When this technique is applied to the configuration of the transmission directivity control device 1 of the first embodiment, it becomes possible to transmit M transmission beams in parallel. Furthermore, this technique can also be applied to the transmission directivity control device 1a of the second embodiment and the transmission directivity control device 1b of the third embodiment in which the configuration of the array antenna 19a is other than 3 × 3.

[0155] 10 is a block diagram showing an example of the configuration of a transmission directivity control device 1c according to a fifth embodiment. In the fifth embodiment, the same components as those in the first embodiment are denoted by the same reference numerals. The transmission directivity control device 1c includes a wavelength designation unit 10, a light source 11, a transmission optical signal generation unit 12, a weighting unit 13, photoelectric conversion units 17-1 to 17-M, and antenna elements 18-1 to 18-M.

[0156] The transmission directivity control device 1c of the fifth embodiment differs in configuration from the transmission directivity control device 1 of the first embodiment in the following respects: In the first embodiment, the path difference of the optical path 100 that starts from the output terminal to which the optical path 100 of the demultiplexer 22 is connected and reaches each of two adjacent photoelectric conversion units 17-1 to 17-M in a row in which the photoelectric conversion units 17-1 to 17-M are lined up is a constant path difference D. In contrast, in the fifth embodiment, this path difference is not constant.

[0157] An example of the configuration of the fifth embodiment is shown in Fig. 10. In Fig. 10, for the second to Mth photoelectric conversion units 17-2 to 17-M, as in the first embodiment, the path difference of the optical path 100 from the demultiplexer 22 to each of the adjacent photoelectric conversion units 17-2 to 17-M is set to path difference D. In contrast, the path difference D is not set to the path of the optical path 100 between the photoelectric conversion unit 17-1 and the photoelectric conversion unit 17-2.

[0158] Even in such a case, if the path difference of the optical path 100 between the photoelectric conversion unit 17-1 and the photoelectric conversion unit 17-2 is set to any natural number multiple of the wavelength λ, as in the example shown in Figure 10, the phase difference that occurs due to the path difference in the carrier optical signal supplied to each of the photoelectric conversion units 17-1 to 17-M can be absorbed, as in the first embodiment.

[0159] In order to further generalize the configuration of the transmission directivity control device 1c of the fifth embodiment, let "j" be any natural number between 1 and M, and let m ｊ In the photoelectric conversion units 17-1 to 17-M, the path difference of the optical path 100 between the adjacent photoelectric conversion unit 17-(j-1) and the photoelectric conversion unit 17-j is set to wavelength λ×m ｊ However, when j=1, the photoelectric conversion unit 17-0 does not exist, so m １ = 0. In this case, the RF signal output from the photoelectric conversion unit 17-j is expressed by the following equation (21), and the RF signal output from the photoelectric conversion unit 17-(j+1) is expressed by the following equation (22).

[0160]

[0161]

[0162] The phase difference between the right-hand side of equation (22) and the right-hand side of equation (21) is "-φ ｊ＋１ +φ ｊ +2m ｊ＋１ 10 shows an example in which the path difference of the optical path 100 between the photoelectric conversion unit 17-1 and the photoelectric conversion unit 17-2 is set to twice the path difference D. In this case, the path difference of the optical path 100 between the photoelectric conversion unit 17-1 and the photoelectric conversion unit 17-2 is "2aλ", so m ２ Therefore, the phase difference is "-φ ２ +φ １ +4aπ". For the photoelectric conversion unit 17-2 and onwards, the path difference of the optical path 100 is "aλ", so m ｊ＋１ Therefore, the phase difference is "-φ ｊ＋１ +φ ｊ +2aπ".

[0163] That is, in either case, m ｊ＋１ Since is a natural number, "2m ｊ＋１ π" is a natural number multiple of 2π. Therefore, "-φ ｊ＋１ +φ ｊ +2m ｊ＋１ The phase indicated by "π" is "-φ ｊ＋１ +φ ｊ ", and the phase difference occurring in the carrier optical signal supplied to each of the photoelectric conversion units 17-1 to 17-M is absorbed by the path difference of the optical path 100 until the carrier optical signal reaches each of the photoelectric conversion units 17-1 to 17-M. Therefore, as in the first embodiment, the phase difference between the RF signals output by the adjacent photoelectric conversion units 17-(j+1) and 17-j is adjusted by the phase gradient "-φ ｊ＋１ +φ ｊ " can be set to ".

[0164] (Effects of the Fifth Embodiment) In the fifth embodiment, even if the path difference of the optical paths 100 that start from the output terminal to which the optical paths 100 of the demultiplexer 22 are connected and reach each of two adjacent photoelectric conversion units 17-1 to 17-M is not constant, each path difference is set to an arbitrary natural number multiple of the wavelength λ. As a result, the phase difference between the RF signals output from the adjacent photoelectric conversion units 17-(j+1) and 17-j is adjusted by the phase gradient "-φ" given by the scanning matrix circuit 15. ｊ＋１ +φ ｊ Therefore, by using these RF signals, it is possible to propagate the radio waves of the RF signals radiated from the antenna elements 18-1 to 18-M in the transmission direction desired by the user.

[0165] Therefore, the transmission directivity control device 1c of the fifth embodiment has the same effect as the transmission directivity control device 1 of the first embodiment, and therefore, even if the size of the array antenna 19 is large, it is possible to perform appropriate weighting without complicating the wiring structure, and it is possible to control the transmission directivity using a circuit with a simple structure that is suitable for miniaturization and mass production.

[0166] The technique of making the path difference of the optical path 100 to reach each of two adjacent photoelectric conversion units 17-1 to 17-M of the transmission directivity control device 1c of the fifth embodiment not constant, but making each path difference an arbitrary natural number multiple of the wavelength λ, can also be applied to the second to fourth embodiments in which the array antenna 19 is equipped with an array antenna 19a arranged two-dimensionally, and further, can also be applied to configurations in which the number of antenna elements 18-1-1 to 18-3-3 is increased in the second to fourth embodiments.

[0167] (Effects Common to All Embodiments) In the first to fifth embodiments, phase shifting is achieved by analog processing of optical signals. Therefore, the mechanisms of the transmission directivity control devices 1 to 1c of the first to fifth embodiments can be applied to circuits that electronically, rather than mechanically, perform beam scanning when emitting light in free-space optical wireless communication (so-called FSO (Free Space Optics) communication) and the like, rather than just beam scanning when emitting radio waves. In current FSO communication, the radiation direction is adjusted by a mechanically driven device, which can lead to issues regarding the weight and mass productivity of the device, as well as operational and maintenance issues in terms of operating speed and durability. If the mechanisms of the transmission directivity control devices 1 to 1c of the first to fifth embodiments can be applied to FSO communication, which has such issues, and electronic scanning of optical beams becomes possible, these issues can be resolved.

[0168] (Other Configuration Examples in Each Embodiment) In the first embodiment, there is an allowable range for the phase tilt error of the RF signal fed to the antenna elements 18-1 to 18-M (hereinafter referred to as the feed phase tilt error), and for example, the feed phase tilt error of the antenna element 18-1, which has the shortest path length of the optical path 100 from the output terminal to which the optical path 100 of the demultiplexer 22 is connected, is assumed to be θ°. In this case, the path difference D is determined by the following equation (23):

[0169]

[0170] When the path difference D is determined by equation (23), the RF signal output from the photoelectric conversion unit 17-j is expressed by the following equation (24) instead of equation (8).

[0171]

[0172] Equation (24) can be transformed into equation (25).

[0173]

[0174] The RF signal output by the photoelectric conversion unit 17-(j+1) adjacent to the photoelectric conversion unit 17-j is obtained by substituting "j+1" for "j" in equation (25), and is therefore expressed as the following equation (26).

[0175]

[0176] The phase difference between the right side of the equation (26) and the right side of the equation (25) is "-φ ｊ＋１ +φ ｊ +2aπ±θ°π / 180". "θ°π / 180" is the value when "θ°" is expressed in radians. "2aπ" is "a" times 2π, where "a" is a natural number. Therefore, the phase indicated by the phase difference is "-φ ｊ＋１ +φ ｊ ±θ°π / 180". Therefore, it becomes possible to supply RF signals to antenna elements 18-1 to 18-M within the range of the feed phase tilt error θ° while absorbing the phase difference "2aπ" that occurs in the carrier optical signal supplied to each of photoelectric conversion units 17-1 to 17-M due to the path difference "aλ" of optical path 100 until the carrier optical signal reaches each of photoelectric conversion units 17-1 to 17-M.

[0177] The method of determining the path difference by taking into account the feed phase tilt error θ° can be similarly applied to the fifth embodiment. This method can also be applied to the second to fourth embodiments in which the array antenna 19 includes the array antenna 19a arranged two-dimensionally, and can also be applied to configurations in which the number of antenna elements 18-1-1 to 18-3-3 is increased in the second to fourth embodiments.

[0178] The transmission optical signal generator 12 shown in the first, second, third, and fifth embodiments may be replaced with a transmission optical signal generator 12b shown in FIG. 11 . The transmission optical signal generator 12b includes an SSB (Single Side Band) optical modulator 26 and a demultiplexer 22. The SSB optical modulator 26 SSB-modulates the light having wavelength λ generated by the light source 11 with a transmission signal. Here, the SSB modulation performed by the SSB optical modulator 26 is a modulation that performs intensity modulation while suppressing the lower sideband when intensity-modulating. Therefore, the SSB optical modulator 26 generates a modulated optical signal including a carrier optical signal and an upper sideband optical signal. The demultiplexer 22 demultiplexes the modulated optical signal generated and output by the SSB optical modulator 26 into a carrier optical signal and an upper sideband optical signal, outputs the demultiplexed carrier optical signal to the optical path 100, and outputs the demultiplexed upper sideband optical signal to the optical path 200.

[0179] The transmission optical signal generation unit 12 shown in the first, second, third, and fifth embodiments may be replaced with a transmission optical signal generation unit 12c shown in FIG. 12 . The transmission optical signal generation unit 12c includes a distributor 27 and an SSB optical modulator 26a. The distributor 27 divides the light having a wavelength λ generated and output by the light source 11 into two beams, outputs one of the beams to the optical path 100, and outputs the other beam to the SSB optical modulator 26a. That is, the light having a wavelength λ generated by the light source 11 is output to the optical path 100 as a carrier optical signal. The SSB optical modulator 26a SSB-modulates the light output by the distributor 27 with a transmission signal. Here, the SSB modulation performed by the SSB optical modulator 26a is, for example, a modulation in which the frequency band of the carrier and the lower sideband are suppressed during intensity modulation to perform intensity modulation. Therefore, the SSB optical modulator 26 a generates an upper sideband optical signal as a modulated optical signal, and outputs the generated upper sideband optical signal to the optical path 200 .

[0180] Note that the optical modulators 21-1 to 21-9 of the transmission optical signal generation unit 12a of the fourth embodiment shown in Fig. 8 may be replaced with an SSB optical modulator 26 shown in Fig. 11. Also, the optical comb filter 24 may be removed from the transmission optical signal generation unit 12a of the fourth embodiment shown in Fig. 8, and the optical modulators 21-1 to 21-9 may be replaced with nine distributors 27 and nine SSB optical modulators 26a shown in Fig. 12, providing a multiplexer that multiplexes light that becomes a carrier optical signal output from the nine distributors 27, and a multiplexer that multiplexes upper sideband optical signals output from the nine SSB optical modulators 26a. Furthermore, the transmission optical signal generating unit 12a shown in FIG. 8 may be provided with a splitter that splits the output of the multiplexer 23 into two, and one-input, one-output optical comb filters may be connected to the two outputs of the splitter, with one optical comb filter outputting a carrier combined optical signal and the other optical comb filter outputting an upper sideband combined optical signal.

[0181] In each of the above-described embodiments, the transmission optical signal generators 12, 12a, 12b, and 12c perform intensity modulation to generate a carrier optical signal and an upper sideband optical signal having different frequency bands. However, the transmission optical signal generators 12, 12a, 12b, and 12c are not limited to generating a carrier optical signal and an upper sideband optical signal. They may instead generate a first optical signal and a second optical signal, which are two optical signals having different frequency bands, as in the following example. For example, instead of generating a carrier optical signal and an upper sideband optical signal, the transmission optical signal generators 12, 12a, 12b, and 12c may generate a carrier optical signal and a lower sideband optical signal. Furthermore, instead of generating a carrier optical signal and an upper sideband optical signal, the transmission optical signal generators 12, 12a, 12b, and 12c may generate an upper sideband optical signal and a lower sideband optical signal.

[0182] In each of the above embodiments, a carrier optical signal is transmitted via the optical path 100, and an upper sideband optical signal is transmitted via the optical path 200. Here, the optical signal transmitted via the optical path 100 is referred to as a first optical signal, and the optical signal transmitted via the optical path 200 is referred to as a second optical signal. In this case, the combination of the first optical signal and the second optical signal is not limited to the above-mentioned combination of a carrier optical signal and an upper sideband optical signal, but may be the reverse combination of an upper sideband optical signal and a carrier optical signal, or the above-mentioned combination of a carrier optical signal and a lower sideband optical signal or the reverse combination of that combination, or may be the above-mentioned combination of an upper sideband optical signal and a lower sideband optical signal or the reverse combination of that combination.

[0183] In the photoelectric conversion units 17-1 to 17-M shown in the first and fifth embodiments, the multiplexers 32-1 to 32-M may be replaced with so-called half mirrors. Specifically, the photoelectric conversion unit 17-j is replaced with the photoelectric conversion unit 17a-j shown in FIG. 13. The photoelectric conversion unit 17a-j includes a mirror 33-j, which is a so-called half mirror, instead of the multiplexer 32-j. The mirror 33-j reflects the carrier optical signal supplied via the branched optical path 102-j and causes it to travel in the direction of the PD 31-j, and transmits the upper sideband optical signal supplied via the optical path 200-j and causes it to travel in the direction of the PD 31-j, thereby multiplexing the carrier optical signal and the upper sideband optical signal. Conversely, the mirror 33-j may reflect the upper sideband optical signal and transmit the carrier optical signal. Similarly, the multiplexers 32-1-1 to 32-3-3 provided in the photoelectric conversion units 17-1-1 to 17-3-3 shown in the second to fourth embodiments may be replaced with half mirrors.

[0184] As described above, the configuration in which the photoelectric conversion units 17-1 to 17-M that satisfy the first connection condition described in the first embodiment are arranged at equal intervals, and the configuration in which the photoelectric conversion units 17-1-1 to 17-3-3 that satisfy the second connection condition described in the second embodiment are arranged at equal intervals in the row direction and at equal intervals in the column direction, are merely examples. In the first embodiment, the photoelectric conversion units 17-1 to 17-M may not be arranged at equal intervals, as long as the first connection condition is satisfied. In the second embodiment, the photoelectric conversion units 17-1-1 to 17-3-3 may not be arranged at equal intervals in the row direction or at equal intervals in the column direction, as long as the second connection condition is satisfied. This also applies to the third and fourth embodiments. Furthermore, in the fifth embodiment, the photoelectric conversion units 17-1 to 17-M may be arranged in any manner, and may be arranged at equal intervals, as long as the path differences of the optical paths that start from the output terminal to which the optical path 100 of the demultiplexer 22 is connected and reach each of two adjacent photoelectric conversion units 17-1 to 17-M in the photoelectric conversion units 17-1 to 17-M are not constant. This also applies to the second to fourth embodiments to which the technique of the fifth embodiment is applied.

[0185] In each of the above embodiments, it is desirable that the wiring lengths of the electrical wiring between each of the photoelectric conversion units 17-1 to 17-M, 17-1-1 to 17-3-3 and the antenna elements 18-1 to 18-M, 18-1-1 to 18-3-3 connected to each of them be the same length, but it is sufficient that the wiring lengths are of a length that can be allocated in a general circuit configuration, and they do not have to be strictly the same length.

[0186] In the first embodiment described above, an example is shown in which the photoelectric conversion units 17-1 to 17-M are arranged in a row along the arrangement line that serves as an index for the arrangement of the antenna elements 18-1 to 18-M. In contrast, in the first and fifth embodiments, the row in which the photoelectric conversion units 17-1 to 17-M are arranged does not have to follow the arrangement line. In the second embodiment described above, an example is shown in which the row direction of the photoelectric conversion units 17-1-1 to 17-3-3 coincides with the direction of the first arrangement line, and the column direction coincides with the direction of the second arrangement line. In contrast to this, in the second to fourth embodiments, as long as the row direction corresponds to the first arrangement line and the column direction corresponds to the second arrangement line, the orientation of the photoelectric conversion units 17-1-1 to 17-3-3 arranged in the actual row direction does not have to match the direction of the first arrangement line, and the orientation of the photoelectric conversion units 17-1-1 to 17-3-3 arranged in the actual column direction does not have to match the direction of the second arrangement line.

[0187] In each of the above embodiments, the light sources 11, 11-1 to 11-9 are wavelength-tunable light sources that generate light of a wavelength included in a wavelength specification signal received from the wavelength specification units 10, 10-1 to 10-9. Alternatively, the light sources 11, 11-1 to 11-9 may be light sources that generate and output a single wavelength, rather than wavelength-tunable light sources, and the wavelength specification units 10, 10-1 to 10-9 may not be provided. In this case, a light source that generates a wavelength λ specified by the user is selected and used as the light source 11, and each of the light sources 11-1 to 11-9 is set to the wavelength λ specified by the user. １ ~λ ９ A light source that generates each of the above will be selected and used.

[0188] In each of the above embodiments, the demultiplexers 22, 42-1 to 42-3 and multiplexers 23, 32-j, 41-1 to 41-3 shown in the drawings, as well as the demultiplexers and multiplexers mentioned in the text, may be, for example, AWGs (Arrayed Waveguide Gratings), or may be constructed using optical elements other than AWGs.

[0189] The photoelectric conversion units 17-1 to 17-M, 17-1-1 to 17-3-3, and 17a-j shown in the above embodiments are assumed to generate RF signals, but they may also generate electrical signals of electromagnetic waves in a wider frequency band including RF signals, and radiate electromagnetic waves in a wider frequency band including radio waves from the antenna elements 18-1 to 18-M, and 18-1-1 to 18-3-3.

[0190] In each of the above-described embodiments, the scanning matrix circuits 15, 15A, 15B, and 15C may be configured not to output optical signals to which no tilt phase amount is added.

[0191] Although an embodiment of the present invention has been described above in detail with reference to the drawings, the specific configuration is not limited to this embodiment, and includes designs within the scope of the gist of the present invention.

[0192] The present invention can be applied to the transmission of highly directional electromagnetic waves formed in wireless transmission, imaging, radar, etc. using radio waves in the millimeter wave band or terahertz band.

[0193] 1...Transmission directivity control device, 10...Wavelength designation unit, 11...Light source, 12...Transmission optical signal generation unit, 13...Weighting unit, 14...Scanning switching circuit, 14-S...Input terminal, 14-E-1 to 14-E-M...Output terminal, 15...Scanning matrix circuit, 15-S-1 to 15-S-M...Input terminal, 15-E-1 to 15-E-M...Output terminal, 16...Operation unit, 17-1 to 17-M...Photoelectric conversion unit, 18-1 to 18-M...Antenna element, 80, 81, 82...Direction, 100, 200...Optical path, 101-1 to 101-M...Branch point, 102-1 to 102-M...Branched optical path

Claims

1. A system comprising: a plurality of antenna elements arranged along an arrangement line that is arbitrarily determined in a three-dimensional space; a transmission optical signal generation unit that modulates light with a transmission signal to generate a first optical signal and a second optical signal of different frequency bands; a weighting unit that imparts a phase gradient to the second optical signal that is determined in advance according to the direction of the arrangement line and a desired transmission direction, to generate a second optical signal with a phase gradient that corresponds to each of the antenna elements arranged along the arrangement line; and photoelectric conversion units that are provided corresponding to each of the antenna elements and arranged in a line, each of which combines the second optical signal with the phase gradient and the first optical signal corresponding to each of the antenna elements, converts them into an electrical signal, and outputs the converted electrical signal to the corresponding antenna element, a transmission directivity control device that selects each of the path differences of the optical paths between adjacent photoelectric conversion units in the row and the wavelength of the light so that a phase difference that occurs in one of the two optical signals combined by each of the photoelectric conversion units, the phase difference being caused by a path difference of the optical path until the one optical signal reaches each of the photoelectric conversion units, is absorbed.

2. The arrangement line is a second arrangement line, and a plurality of the antenna elements are arranged along a first arrangement line intersecting the second arrangement line to form an array antenna, the weighting unit imparts a phase gradient to the first optical signal that is predetermined according to a direction of the first arrangement line and the desired transmission direction, to generate a first optical signal with a phase gradient corresponding to each of the antenna elements arranged along the first arrangement line, the photoelectric conversion units are arranged in a matrix shape along a row direction corresponding to the direction of the first arrangement line and a column direction corresponding to the direction of the second arrangement line, and each of the photoelectric conversion units combines the first optical signal with a phase gradient corresponding to each of the photoelectric conversion units and converts it into an electrical signal, instead of combining the second optical signal with a phase gradient corresponding to each of the photoelectric conversion units and the first optical signal and converting it into an electrical signal, and outputs the converted electrical signal to the antenna element corresponding to each of the photoelectric conversion units, 2. The transmission directivity control device according to claim 1, wherein each path difference of the optical paths between adjacent photoelectric conversion units in the column direction, each path difference of the optical paths between adjacent photoelectric conversion units in the row direction, and the wavelength of light are selected so that a phase difference occurring in the first optical signal with a phase tilt is absorbed by a path difference of the optical path until the first optical signal with a phase tilt reaches each of the photoelectric conversion units in the column direction, and so that a phase difference occurring in the second optical signal with a phase tilt is absorbed by a path difference of the optical path until the second optical signal with a phase tilt reaches each of the photoelectric conversion units in the row direction.

3. A transmission directivity control device as described in claim 1 or claim 2, which selects the wavelength of light by predetermining each path difference of the optical path between adjacent photoelectric conversion units so that each path difference of the optical path between adjacent photoelectric conversion units matches one of the multiplication values ​​obtained by multiplying the wavelength of the light by a predetermined value, or selects the wavelength of the light by predetermining the wavelength of the light.

4. The transmission directivity control device according to claim 3, wherein the predetermined value is an arbitrary natural number.

5. A transmission directivity control device as described in claim 3, wherein the predetermined value is a value obtained by adding or subtracting θ° / 360 to any natural number, where θ° is an allowable error in the electrical signal output by the photoelectric conversion unit having the shortest optical path length.

6. A transmission directivity control device according to claim 4, wherein all of the path differences of the optical paths between adjacent photoelectric conversion units are the same, or all or a part of the path differences of the optical paths between adjacent photoelectric conversion units are different.

7. A transmission directivity control device according to claim 5, wherein all of the path differences of the optical paths between adjacent photoelectric conversion units are the same, or all or a part of the path differences of the optical paths between adjacent photoelectric conversion units are different.

8. A method for controlling transmission directivity of a plurality of antenna elements arranged along an arrangement line arbitrarily defined in a three-dimensional space, comprising: a step in which a transmission optical signal generation unit modulates light with a transmission signal to generate a first optical signal and a second optical signal of different frequency bands; a step in which a weighting unit imparts a phase gradient to the second optical signal that is predetermined according to the direction of the arrangement line and a desired transmission direction to generate a second optical signal with a phase gradient corresponding to each of the antenna elements arranged along the arrangement line; and a step in which each of photoelectric conversion units arranged in a line and provided corresponding to each of the antenna elements combines the second optical signal with the phase gradient and the first optical signal corresponding to each of the antenna elements, converts them into an electrical signal, and outputs the converted electrical signal to the corresponding antenna element, A transmission directivity control method comprising: selecting each of the path differences of the optical paths between adjacent photoelectric conversion units in the row and the wavelength of the light so that a phase difference that occurs in one of the two optical signals combined by each of the photoelectric conversion units, the phase difference being caused by a path difference of the optical path until the one optical signal reaches each of the photoelectric conversion units, is absorbed.

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