Transmission directivity control device and transmission directivity control method

Abstract

Provided is a device including: a plurality of antenna elements arranged along an arrangement line defined 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 the second optical signal with a phase slope determined in advance according to the direction of the arrangement line and the desired transmission direction, and generates second optical signals having phase slopes respectively corresponding to the antenna elements arranged along the arrangement line; and photoelectric conversion units that respectively correspond to the antenna elements and synthesize the first optical signal and the second optical signals having phase slopes respectively corresponding thereto, thereby converting the signals into electric signals, and output the converted electric signals to the antenna elements respectively corresponding thereto. In order to cancel out the phase rotation that occurs, in one of the two optical signals synthesized by the photoelectric conversion unit, according to the path length of the optical path until the one optical signal reaches the photoelectric conversion unit, a phase delay is given to the other optical signal.

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 technology disclosed in Non-Patent Document 4 uses a loop configuration in which a phase shifter is repeatedly reused while converting the optical wavelength, which causes a problem of an increase in noise level in proportion to the loop circuit.The FBG used in the technology disclosed in Non-Patent Document 5 has a strong frequency band dependency, so when multiple wavelengths are multiplexed 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 transmission directivity control device comprising: a plurality of antenna elements arranged along an arrangement line that is arbitrarily defined in 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 tilt to the second optical signal that is predetermined depending on the direction of the arrangement line and a desired transmission direction, to generate a second optical signal with a phase tilt that corresponds to each of the antenna elements arranged along the arrangement line; and optoelectric conversion units provided corresponding to each of the antenna elements, each optoelectric conversion unit combining the corresponding second optical signal with the phase tilt and the first optical signal to convert them into an electrical signal and output the converted electrical signal to the corresponding antenna element, wherein the transmission directivity control device imparts a phase delay to one of two optical signals combined by the optoelectric conversion units so as to cancel out a phase rotation that occurs in the other optical signal depending on the path length of the optical path until the one optical signal reaches the optoelectric conversion unit.

[0020] One aspect of the present invention is a transmission directivity control method for a plurality of antenna elements arranged along an arrangement line that is arbitrarily defined in three-dimensional space, the transmission directivity control method including 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 imparting a phase gradient to the second optical signal that is predetermined depending on 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 a photoelectric conversion unit provided corresponding to each of the antenna elements combining the second optical signal with the phase gradient and the first optical signal corresponding thereto, converting the combined second optical signal into an electrical signal, and outputting the converted electrical signal to the corresponding antenna element, wherein the transmission directivity control method imparts a phase delay to one of two optical signals combined by the photoelectric conversion unit so as to cancel out a phase rotation that occurs in the other optical signal depending on the path length of the optical path until the one optical signal reaches the photoelectric conversion unit.

[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 between the photoelectric conversion unit and each of the phase correction units and 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, and the connection relationship with a light source. FIG. 9 is a diagram illustrating the correspondence relationship between wavelengths and directions, and the correspondence relationship between wavelengths and output terminals assigned within each of a first scanning switching circuit and a second scanning switching circuit according to the fourth embodiment. FIG. 10 is a diagram illustrating the internal configuration of a phase correction unit according to the fourth embodiment. FIG. 11 is a diagram illustrating an example of the configuration of a transmission directivity control device according to a fifth embodiment. FIG. 12 is a diagram illustrating an example of the configuration of a transmission directivity control device according to a sixth embodiment. FIG. 13 is a diagram (part 1) illustrating another example of the configuration of a transmission optical signal generation unit shown in the first, second, third, fifth, and sixth embodiments, and the connection relationship with a 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, fifth, and sixth embodiments, and the connection relationship with the light source. 11 is a diagram showing another example of the configuration of the photoelectric conversion unit shown in the first, fifth, and sixth embodiments, and the connection relationship with each of the phase correction unit and 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 an operation unit 10, a light source 11, a transmission optical signal generation unit 12, a weighting unit 13, phase correction units 16-1 to 16-M, photoelectric conversion units 17-1 to 17-M, and antenna elements 18-1 to 18-M, where M is a natural number equal to or greater than 2.

[0024] The light source 11 generates and outputs CW (Continuous Wave) light of a predetermined wavelength. The transmission optical signal generation 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 generates a modulated optical signal by intensity-modulating the light output by the light source 11 with the baseband signal.

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

[0026] The operation unit 10 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 10. In other words, there are M types of transmission directions that can be selected by the operation unit 10, and the operation unit 10 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. Hereinafter, when no unit is indicated for the tilt phase amount, the unit is radian, which is a unit of the radian system, and when the tilt phase amount is indicated in degrees, 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] In other words, 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 phase correctors 16-1 to 16-M is, for example, a phase shifter, and is connected to each of the output terminals 15-E-1 to 15-E-M of the scanning matrix circuit 15. Each of the phase correctors 16-1 to 16-M generates and outputs an optical signal by delaying the phase of the optical signal supplied thereto by a phase amount that is predetermined for that individual optical signal.

[0036] 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 that branch off from M branch points 101-1, 101-2, ..., 101-M in the optical path 100. The branch optical paths 102-1, 102-2, ..., 102-M are parts of the optical path 100, and the part of the optical path 100 other than the branch optical paths 102-1 to 102-M is called the main line of the optical path 100.

[0037] 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 to the phase correction unit 16-j via the optical path. The multiplexer 32-j multiplexes the carrier optical signal supplied via the branched optical path 102-j with the upper sideband optical signal supplied from the phase correction unit 16-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.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] The photoelectric conversion units 17-1 to 17-M are arranged, for example, in a row along an arrangement line, and are arranged so as to satisfy a connection condition (hereinafter referred to as the first connection condition) that the difference in path length of the optical path starting from the output terminal to which the optical path 100 of the splitter 22 is connected and reaching each of two adjacent photoelectric conversion units 17-1 to 17-M in the row is constant.

[0042] 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 at equal intervals. 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 intervals between adjacent branch points 101-1, 101-2, ..., 101-M are set to be the same as the intervals between the photoelectric conversion units 17-1 to 17-M. Each of the branch points 101-1, 101-2, ..., 101-M and each of the photoelectric conversion units 17-1 to 17-M are connected by branch optical paths 102-1 to 102-M of the same length.

[0043] In this case, the difference in the path length of the optical path that starts from the output terminal to which optical path 100 of demultiplexer 22 is connected and reaches each of photoelectric conversion units 17-1 to 17-M will appear as the difference in the path length of the optical path that starts from the starting point and reaches each of branch points 101-1 to 101-M.

[0044] 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°." The photoelectric conversion units 17-1 and 17-2 differ in the path length between branching point 101-1 and branching point 101-2. Therefore, the optical signal output from the demultiplexer 22 and arriving at the photoelectric conversion unit 17-2 undergoes a phase rotation due to the path length between branching point 101-1 and branching point 101-2. The amount of this phase rotation is set to "a°." In other words, 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 "a°" compared to the optical signal output from the demultiplexer 22 and arriving at the photoelectric conversion unit 17-1.

[0045] 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 "(j-1)a°" relative to the optical signal output from the demultiplexer 22 and reaching the photoelectric conversion unit 17-1.

[0046] On the other hand, the optical paths output from the output terminals 15-E-1 to 15-E-M of the scanning matrix circuit 15, passing through the phase correction units 16-1 to 16-M, and reaching the photoelectric conversion units 17-1 to 17-M are wired so that there is no 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

[0047] Therefore, in order to enable the user to transmit an RF signal in the transmission direction desired by the user in the transmission directivity control device 1, it is necessary to cancel the phase rotation occurring in the carrier optical signal supplied to the photoelectric conversion units 17-1 to 17-M. Below, we will explain the procedure for performing this cancellation using the phase correction units 16-1 to 16-M.

[0048] (Processing by the Transmission Directivity Control Device of the First Embodiment) The processing by the transmission directivity control device 1 will be described with reference to FIG. 3. Before the processing of the flowchart shown in FIG. 3 is started, the following is performed. In order to cancel out the phase rotation occurring in the carrier optical signal supplied to the above-described photoelectric conversion units 17-1 to 17-M, a predetermined phase amount is set for each of the M phase correction units 16-1 to 16-M. Specifically, a phase amount of "(j-1)a°" is set in advance for each phase correction unit 16-j. Note that when "a°" is expressed in units of radians, the symbol "α" is used. In other words, the relationship between "a°" and "α" is a° × π / 180 = α.

[0049] A user of the transmission directivity control device 1 operates the operation unit 10 to select a desired transmission direction, and in response to this operation, the operation unit 10 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 generates light 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 (1), and the upper sideband optical signal is expressed by the following equation (2).

[0051]

[0052]

[0053] In equations (1) and (2), 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. ｊ1, as an example, the phase tilt is θ°, that is, the tilt phase amount φ １ is "0°", and the tilt phase amount φ ２ is "θ°", and the tilt phase amount φ Ｍ In general, the tilt phase amount φ ｊ The upper sideband optical signal output from the output terminal 15-E-j of the scanning matrix circuit 15 is expressed by the following equation (3).

[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, respectively (Sa4). Each of the phase correctors 16-1 to 16-M receives the upper sideband optical signal output from the output terminals 15-E-1 to 15-E-M of the scanning matrix circuit 15 connected thereto. Each of the phase correctors 16-1 to 16-M corrects the received upper sideband optical signal by a phase amount that is predetermined for that signal. Specifically, the phase corrector 16-j generates an upper sideband optical signal by applying a phase delay of "(j-1)α" to the upper sideband optical signal output from the output terminal 15-E-j.

[0057] That is, as shown in FIG. 1, the phase of the upper sideband optical signal output by phase corrector 16-1 is "0°", the phase of the upper sideband optical signal output by phase corrector 16-2 is "θ-a°", and the phase of the upper sideband optical signal output by phase corrector 16-M is "(M-1)θ-(M-1)a°". Generalizing this, the phase of the upper sideband optical signal output by phase corrector 16-j is "(j-1)θ-(j-1)a°". The optical signal generated by phase corrector 16-j can be expressed as the following equation (4).

[0058]

[0059] Each of the phase correctors 16-1 to 16-M outputs the upper sideband optical signal that it has generated by delaying the phase to the opto-electrical converters 17-1 to 17-M connected to it (Sa5).

[0060] 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 is supplied with an upper sideband optical signal from the phase correction units 16-1 to 16-M connected to it. 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.

[0061] 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 rotation of “(j−1)α” added to it, and is therefore expressed by the following equation (5).

[0062]

[0063] On the other hand, the upper sideband optical signal supplied to the multiplexer 32-j from the phase corrector 16-j is expressed by the above-mentioned equation (4). Therefore, the 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 outputs it to the PD 32-j. The multiplexed optical signal generated by the multiplexer 32-j is expressed by the following equation (6).

[0064]

[0065] 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).

[0066]

[0067] When the right side of equation (7) is calculated, the phase rotation component of "(j-1)α" of the carrier optical signal shown in equation (5) is cancelled out by the phase delay component of "-(j-1)α" of the upper sideband wave shown in equation (4). Therefore, the RF signal output by PD32-j is an RF signal v shown in the following equation (8) in which the RF frequency band is extracted 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 ) is a signal proportional to

[0068]

[0069] 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 (Sa6), and the process ends.

[0070] (Effects of the First Embodiment) In the transmission directivity control device 1 of the first embodiment, a phase rotation "(j-1)α" occurs in the carrier optical signal output from the demultiplexer 22 according to the path length of the optical path 100 until it reaches each of the photoelectric conversion units 17-1 to 17-M. Therefore, each of the phase correction units 16-1 to 16-M applies a phase delay of "(j-1)α" to the upper sideband optical signal so as to cancel out the phase rotation. As a result, the phase weighted for the antenna element 18-j connected to any one of the photoelectric conversion units 17-1 to 17-M is determined by the tilt phase amount φ ｊ This eliminates the influence of the phase rotation "(j-1)α" due to the position of the photoelectric conversion unit 17-j. This makes it 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.

[0071] In the transmission directivity control device 1 of the first embodiment, phase shifting of optical signals is performed by analog circuits. Therefore, the number of analog-to-digital converters can be significantly reduced compared to a fully digitally controlled array antenna in which phase shifting is performed entirely by digital signal processing. Therefore, by using the transmission directivity control device 1, even if the scale of the array antenna 19 is large, appropriate weighting is possible without complicating the wiring structure, and transmission directivity can be controlled by a circuit with a simple structure suitable for miniaturization and mass production.

[0072] Second Embodiment Fig. 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 an operation unit 10a, a light source 11, a transmission optical signal generation unit 12, a weighting unit 13a, phase correction units 16A-1 to 16A-3, 16B-1 to 16B-3, photoelectric conversion units 17-1-1 to 17-3-3, and antenna elements 18-1-1 to 18-3-3.

[0073] 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.

[0074] 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. For example, the photoelectric conversion units 17-1-1 to 17-3-3 are arranged in a matrix, with the row direction aligned with the first arrangement line and the column direction aligned with the second arrangement line. 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.

[0075] 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.

[0076] 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.

[0077] 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.

[0078] 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.

[0079] (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 10a, and the operation unit 10a 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.

[0080] Each of the phase correction units 16A-1 to 16A-3 and 16B-1 to 16B-3 is, for example, a phase shifter, and generates and outputs an optical signal by delaying the phase of the optical signal supplied thereto by a predetermined phase amount. Each of the phase correction units 16A-1 to 16A-3 is connected to each of the output terminals 15A-E-1 to 15A-E-3 of the first scanning matrix circuit 15A. Each of the phase correction units 16B-1 to 16B-3 is connected to each of the output terminals 15B-E-1 to 15B-E-3 of the second scanning matrix circuit 15B.

[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] When the phase corrector 16A-1 is not inserted, the connection relationship of the optical paths 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 paths between the output terminal to which the optical path 100 of the demultiplexer 22 of the first embodiment is connected and each of the photoelectric conversion units 17-1, 17-2, and 17-3. When the phase corrector 16A-1 is inserted and no phase delay is applied by the phase corrector 16A-1, the phase of the optical signal that is output from the output terminal 15A-E-1 and reaches the photoelectric conversion unit 17-1-1 is set to the reference phase. In this case, the phase of the optical signal output from output terminal 15A-E-1 and reaching photoelectric conversion unit 17-1-2 leads by "α" from the reference phase, and the phase of the optical signal output from output terminal 15A-E-1 and reaching photoelectric conversion unit 17-1-3 leads by "2α" from the reference phase.

[0083] The connection relationship of the optical path between output terminal 15A-E-2 and each of the photoelectric conversion units 17-2-1, 17-2-2, and 17-2-3 in the second row via phase correction unit 16A-2, and the connection relationship of the optical path between output terminal 15A-E-3 and each of the photoelectric conversion units 17-3-1, 17-3-2, and 17-3-3 in the third row via phase correction unit 16A-3 are the same as the connection relationship of the optical path between 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 via phase correction unit 16A-1.

[0084] The connection relationship of the optical path 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 via the phase correction unit 16B-1, and the connection relationship of the optical path 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 via the phase correction unit 16A-1 may be the same or may be different as follows.

[0085] For example, in the photoelectric conversion units 17-1-1 to 17-3-3, the amount of phase rotation occurring in one interval in the column direction, i.e., the second arrangement line direction, may be "α," while the amount of phase rotation occurring in one interval in the row direction, i.e., the first arrangement line direction, may be "β," which is different from "α." When no phase delay is applied by the phase correction unit 16B-1, the phase of the optical signal output from output terminal 15B-E-1 and arriving at photoelectric conversion unit 17-1-1 is taken as the reference phase. In this case, the phase of the optical signal output from output terminal 15B-E-1 and arriving at photoelectric conversion unit 17-2-1 leads "β" from the reference phase, and the phase of the optical signal output from output terminal 15B-E-1 and arriving at photoelectric conversion unit 17-3-1 leads "2β" from the reference phase. The above-mentioned connection relationships are the same when α = β.

[0086] The connection relationship of the optical path between 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 via phase correction unit 16B-2, and the connection relationship of the optical path between 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 via phase correction unit 16B-3 are the same as the connection relationship of the optical path between 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 via phase correction unit 16B-1.

[0087] In other words, the difference in the path length of the optical path from each of the output terminals 15A-E-1, 15A-E-2, and 15A-E-3 of the first scanning matrix circuit 15A to each of two adjacent photoelectric conversion units 17-1-1 to 17-3-3 in the corresponding row of the photoelectric conversion units 17-1-1 to 17-3-3 (hereinafter referred to as the first path difference) is constant, and The second connection condition described above is a condition that the difference in path length of the optical path starting from each of photoelectric conversion units 17-1-1 to 17-3-3 in the corresponding columns, 15B-E-2, 15B-E-3, and reaching each of two adjacent photoelectric conversion units 17-1-1 to 17-3-3 in the corresponding columns (hereinafter referred to as the second path difference) is constant, and the first path difference and the second path difference may be the same or different. In this case, when the first path difference and the second path difference are the same, α=β, and when the first path difference and the second path difference are different, α≠β.

[0088] As an example of satisfying the second connection condition, the photoelectric conversion units 17-1-1 to 17-3-3 may be arranged as follows: 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 are arranged so that the adjacent intervals in the column direction, i.e., the second arrangement line direction, are all the same. 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 are all arranged so that the adjacent spacing in the row direction, i.e., the first arrangement line direction, is the same.

[0089] After arranging the photoelectric conversion units 17-1-1 to 17-3-3 in this manner, as in the first embodiment, optical paths connected to each of the phase correction units 16A-1 to 16A-3 are wired along the column direction, and the branching points of each of the optical paths are determined to match the column-wise spacing of the photoelectric conversion units 17-1-1 to 17-3-3. Each branching point of the optical path connected to the phase correction unit 16A-1 is connected to each of the photoelectric conversion units 17-1-1, 17-1-2, and 17-1-3 in the first row via branched optical paths of the same length. Similarly to the phase correction unit 16A-1, the phase correction units 16A-2 and 16A-3 are connected to the photoelectric conversion units 17-2-1, 17-2-2, and 17-2-3 in the second row and the photoelectric conversion units 17-3-1, 17-3-2, and 17-3-3 in the third row, respectively.

[0090] Similarly, optical paths connected to each of the phase correction units 16B-1 to 16B-3 are wired along the row direction, and the branching points of each of these optical paths are determined to coincide with the row-direction spacing of the photoelectric conversion units 17-1-1 to 17-3-3. Branching optical paths of the same length are used to connect each of the branching points of the optical path connected to the phase correction unit 16B-1 to each of the photoelectric conversion units 17-1-1, 17-2-1, and 17-3-1 in the first column. Similarly to the phase correction unit 16B-1, the phase correction units 16B-2 and 16B-3 are connected to the photoelectric conversion units 17-1-2, 17-2-2, and 17-3-2 in the second column and the photoelectric conversion units 17-1-3, 17-2-3, and 17-3-3 in the third column, respectively. In this case, if the adjacent spacing in the row direction and the adjacent spacing in the column direction are the same, α = β; if they are different, α ≠ β.

[0091] Therefore, in order to enable the user to transmit an RF signal in the transmission direction desired by the user in the transmission directivity control device 1a of the second embodiment, it is necessary to cancel out the phase rotation occurring in the carrier optical signal and the upper sideband optical signal supplied to the photoelectric conversion units 17-1-1 to 17-3-3. The procedure for performing this cancellation using the phase correction units 16A-1 to 16A-3 and 16B-1 to 16B-3 will be described below.

[0092] (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. Before the processing of the flowchart shown in Fig. 6 is started, the following is performed. In order to cancel out the phase rotation occurring in the carrier optical signal and the upper sideband optical signal supplied to the above-described optoelectric conversion units 17-1-1 to 17-3-3, a predetermined phase amount is set for each of the phase correction units 16A-1 to 16A-3 and 16B-1 to 16B-3. Specifically, a phase amount of "(i-1)β" is set in advance for each of the phase correction units 16A-i. A phase amount of "(j-1)α" is set in advance for each of the phase correction units 16B-j.

[0093] A user of the transmission directivity control device 1a operates the operation unit 10a to select a desired transmission direction, and in response to this operation, the operation unit 10a 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.

[0094] 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.

[0095] 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 (1), and therefore the carrier optical signal output from the output terminal 15A-E-i of the first scanning matrix circuit 15A can be expressed by the following equation (9).

[0096]

[0097] The first scanning matrix circuit 15A outputs the generated three carrier optical signals from the output terminals 15A-E-1 to 15A-E-3, respectively (Sb4-1). Each of the phase correctors 16A-1 to 16A-3 receives the carrier optical signal output from the output terminals 15A-E-1 to 15A-E-3 of the first scanning matrix circuit 15A connected thereto. Each of the phase correctors 16A-1 to 16A-3 corrects the received carrier optical signal by a predetermined phase amount. Specifically, the phase corrector 16A-i generates a carrier optical signal with a phase delay of "(i-1)β" relative to the upper sideband optical signal output from the output terminal 15A-E-i. Therefore, the carrier optical signal generated by the phase corrector 16A-i is expressed by the following equation (10):

[0098]

[0099] Each of the phase correctors 16A-1 to 16A-3 outputs the carrier optical signal that it has generated by delaying the phase to the opto-electrical converters 17-1-1 to 17-3-3 connected to it (Sb5-1).

[0100] The processing of Sb3-2, Sb4-2, and Sb5-2 is the same as the processing of Sa3, Sa4, and Sa5 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 performed by the scanning switching circuit 14 is performed by the second scanning switching circuit 14B, the processing performed by the scanning matrix circuit 15 is performed by the second scanning matrix circuit 15B, and the processing performed by each of the phase correction units 16-1 to 16-3 is performed by the phase correction units 16B-1 to 16B-3.

[0101] In this case, the upper sideband optical signal output by the splitter 22 is expressed by equation (2), 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 (11).

[0102]

[0103] In Sb5-2, the upper sideband optical signal output by the phase correction unit 16B-j is an upper sideband optical signal with a phase delay of "(j-1)α" added to equation (11), and is therefore expressed by the following equation (12).

[0104]

[0105] The processes Sb3-1 to Sb5-1 and Sb3-2 to Sb5-2 are performed in parallel.

[0106] In the process of Sb5-1, the carrier optical signal output by the phase correction unit 16A-i undergoes a phase rotation before reaching the jth column photoelectric conversion unit 17-i-j, so a phase of "(j-1)α" is added to the carrier optical signal. Therefore, the carrier optical signal that reaches the jth column photoelectric conversion unit 17-i-j is expressed by the following equation (13).

[0107]

[0108] In the process of Sb5-2, a phase rotation occurs in the upper sideband optical signal output by the phase correction unit 16B-j before it reaches the photoelectric conversion unit 17-i-j in the i-th row, so a phase of "(i-1)β" is added to the upper sideband optical signal. Therefore, the upper sideband optical signal that reaches the photoelectric conversion unit 17-i-j in the i-th row is expressed by the following equation (14).

[0109]

[0110] The photoelectric conversion unit 17-i-j photomixes the carrier optical signal represented by equation (13) with the upper sideband optical signal represented by equation (14). That is, the multiplexer 32-i-j included in the photoelectric conversion unit 17-i-j multiplexes the carrier optical signal represented by equation (13) with the upper sideband optical signal represented by equation (14) 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 the square-law detection. The square-law detection by the PD 32-i-j can be expressed as the right side of the following equation (15).

[0111]

[0112] When the right side of equation (15) is calculated, the component "-(i-1)β+(j-1)α" shown in equation (13) and the component "-(j-1)α+(i-1)β" shown in equation (14) are cancelled out. Therefore, the RF signal output from the photoelectric conversion unit 17-i-j is an RF signal v ＲＦ＿ｉｊ As shown in equation (16), the RF signal v ＲＦ＿ｉｊ is cos(ω ＲＦ t+(φ Ｖｉ -φ Ｈｊ )) to produce a signal proportional to

[0113]

[0114] 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 (Sb6), and the process ends.

[0115] (Effects of the Second Embodiment) In the transmission directivity control device 1a of the second embodiment, the tilt phase amount φ output from the output terminal 15A-E-i of the first scanning matrix circuit 15A is ＶｉIn the optical signal of the carrier wave to which is added a phase rotation "(j-1)α" occurs according to the path length of the optical path until it reaches the photoelectric conversion unit 17-i-j of the jth column, so that the phase correction unit 16B-j imparts a phase delay of "(j-1)α" to the optical signal of the upper sideband wave so as to cancel out the phase rotation. Furthermore, the tilt phase amount φ output from the output terminal 15B-E-j of the second scanning matrix circuit 15B Ｈｊ In the upper sideband optical signal to which is added a phase rotation "(i-1)β" occurs according to the path length of the optical path until it reaches the photoelectric conversion unit 17-i-j in the i-th row, so the phase correction unit 16A-i imparts a phase delay of "(i-1)β" to the carrier optical signal so as to cancel out the phase rotation. As a result, the phase amount weighted for the antenna element 18-i-j connected to any photoelectric conversion unit 17-i-j in the photoelectric conversion units 17-1-1 to 17-3-3 is (φ Ｖｉ -φ Ｈｊ ), and the effects of the phase rotation "(j-1)α" and the phase rotation "(i-1)β" due to the position of the photoelectric conversion unit 17-i-j are removed. This makes it 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.

[0116] 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.

[0117] 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 greater than or equal to 1, and at least one of N and M is a natural number greater than or equal to 2.

[0118] Third Embodiment FIG. 7 is a block diagram showing an example configuration of a transmission directivity control device 1b according to a third embodiment. In the third embodiment, components identical to those in the first and second embodiments are denoted by the same reference numerals. Note that the component designated by reference numeral 400 in FIG. 7 is identical to the component designated by reference numeral 400 in FIG. 4. Therefore, the transmission directivity control device 1b includes an operation unit 10a, a light source 11, a transmission optical signal generation unit 12, a weighting unit 13b, phase correction units 16A-1 to 16A-3, 16B-1 to 16B-3, photoelectric conversion units 17-1-1 to 17-3-3, and antenna elements 18-1-1 to 18-3-3. The connection relationships between the phase correction units 16A-1 to 16A-3, 16B-1 to 16B-3 and the photoelectric conversion units 17-1-1 to 17-3-3 are the same as those in the second embodiment.

[0119] 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.

[0120] 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.

[0121] 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 phase correction units 16A-1 and 16B-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 phase correction units 16A-2 and 16B-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 phase correction units 16A-3 and 16B-3.

[0122] (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.

[0123] 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.

[0124] 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

[0125] 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.

[0126] After the scanning matrix circuit 15C performs the processing 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 phase correction units 16A-1 to 16A-3 connected thereto, and outputs the demultiplexed upper sideband optical signal to the phase correction units 16B-1 to 16B-3 connected thereto.

[0127] Thereafter, the phase correctors 16A-1 to 16A-3 perform the process Sb5-1, and the phase correctors 16B-1 to 16B-3 perform the process Sb5-2, and the process ends.

[0128] (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.

[0129] 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.

[0130] 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.

[0131] (Fourth Embodiment) The transmission directivity control device 1a of the second embodiment described above has a single-beam configuration in which one transmission beam is transmitted from light of one wavelength, and one light source 11. In contrast, by configuring the transmission directivity control device 1a as follows, it is possible to configure it as a multi-beam configuration in which multiple transmission beams are transmitted in parallel.

[0132] The transmission optical signal generation unit 12 included in the second transmission directivity control device 1a is replaced with a transmission optical signal generation unit 12a shown in FIG. 8, and further, the light source 11 is replaced with nine light sources 11-1, 11-2, ..., 11-9. 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.

[0133] 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.

[0134] 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.

[0135] 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 with 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, modulated optical signals can be prevented from interfering with each other even when the light of different wavelengths is intensity-modulated. Therefore, light sources 11-1 to 11-9 are selected that generate light of different wavelengths so as to satisfy the condition that the modulated optical signals do not interfere with each other. Note that if each of light sources 11-1 to 11-9 is a wavelength-tunable light source, a different wavelength is set for each light source 11-1 to 11-9 so as to satisfy the condition that the modulated optical signals do not interfere with each other.

[0136] Here, for 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 the reference symbol 90, is located, wavelength λ1 is predetermined to be the "upper left direction," wavelength λ2 is predetermined to be the "middle left direction," wavelength λ3 is predetermined to be the "lower left direction," wavelength λ4 is predetermined to be the "upper middle direction," wavelength λ5 is predetermined to be the "front direction," wavelength λ6 is predetermined to be the "lower middle direction," wavelength λ7 is predetermined to be the "upper right direction," wavelength λ8 is predetermined to be the "middle right direction," and wavelength λ9 is predetermined to be the "lower right direction," as shown in FIG. 9(a), and light sources 11-1 to 11-9 are configured to output light of wavelengths λ1 to λ9, respectively.

[0137] 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 a demultiplexer is provided. In this case, since it is not necessary to output a switching instruction signal to the first scanning switching circuit 14A and the second scanning switching circuit 14B by operating the operation unit 10a, the operation unit 10a may not be provided, or the operation unit 10a may be used to set the wavelengths of the light sources 11-1 to 11-9 when each of the light sources 11-1 to 11-9 is a wavelength-tunable light source.

[0138] 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 signals supplied from the input terminal 14A-S into three groups: optical signals with wavelengths λ1, λ4, and λ7, optical signals with wavelengths λ2, λ5, and λ8, and optical signals with wavelengths λ3, λ6, and λ9. Furthermore, as shown in FIG. 9B, the demultiplexer included in the first scanning switching circuit 14A outputs the optical signals with wavelengths λ1, λ4, and λ7 from output terminal 14A-E-3, the optical signals with wavelengths λ2, λ5, and λ9 from output terminal 14A-E-2, and the optical signals with wavelengths λ3, λ6, and λ9 from output terminal 14A-E-1.

[0139] The demultiplexer of the second scanning switching circuit 14B demultiplexes the optical signals supplied from the input terminal 14B-S into three groups: optical signals with wavelengths λ1, λ2, and λ3, optical signals with wavelengths λ4, λ5, and λ6, and optical signals with wavelengths λ7, λ8, and λ9. Furthermore, as shown in Fig. 9(c), the demultiplexer provided in the second scanning switching circuit 14B outputs the optical signals with wavelengths λ1, λ2, and λ3 from output terminal 14B-E-1, the optical signals with wavelengths λ4, λ5, and λ6 from output terminal 14B-E-2, and the optical signals with wavelengths λ7, λ8, and λ9 from output terminal 14B-E-3.

[0140] 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.

[0141] 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.

[0142] By configuring the transmission directivity control device 1a of the second embodiment as described above, it becomes possible to perform two-dimensional multi-beam transmission, in which nine wavelengths λ1 to λ9 are used to transmit transmission beams in parallel, in nine different directions, on which different transmission signals 1 to 9 are superimposed. However, when the photoelectric conversion units 17-1-1 to 17-3-3 are arranged at equal intervals in the column direction, the above-mentioned phase rotation amount α is calculated by 360 × (the spacing between adjacent photoelectric conversion units 17-1-1 to 17-3-3 in the column direction) / (the wavelength of the light used) × π / 180. Similarly, when the photoelectric conversion units 17-1-1 to 17-3-3 are arranged at equal intervals in the row direction, the phase rotation amount β is calculated by 360 × (the spacing between adjacent photoelectric conversion units 17-1-1 to 17-3-3 in the row direction) / (the wavelength of the light used) × π / 180. In other words, the phase rotation amounts α and β differ for each wavelength of the light used. Therefore, in order to cancel out the phase rotation amounts α and β for each of the wavelengths λ1 to λ9, for example, instead of the phase correction units 16A-1 to 16A-3 and 16B-1 to 16B-3, phase correction units 16aA-1 to 16aA-3 and 16aB-1 to 16aB-3 having the internal configuration shown below are provided.

[0143] Here, as an example, an arbitrary phase corrector 16aA-i among the phase correctors 16aA-1 to 16aA-3 will be described. Note that "i" is any natural number between 1 and 3. As shown in FIG. 10 , the phase corrector 16a-i includes a demultiplexer 51A-i, nine phase shifters 52A-i-1 to 52A-i-9, and a multiplexer 53A-i. The demultiplexer 51A-i demultiplexes the supplied optical signal into nine optical signals with wavelengths λ1 to λ9, and outputs the optical signals to each of the nine phase shifters 52A-i-1 to 52A-i-9. In each of the nine phase shifters 52A-i-1 to 52A-i-9, a phase amount of "(i-1)β" corresponding to each of the wavelengths λ1 to λ9 supplied thereto is set. Each of the nine phase shifters 52A-i-1 to 52A-i-9 outputs an optical signal that has been phase delayed by a set amount relative to the optical signal supplied thereto. The multiplexer 53A-i multiplexes and outputs the nine optical signals that have been phase delayed by the nine phase shifters 52A-i-1 to 52A-i-9.

[0144] Any phase corrector 16aB-j among phase correctors 16aB-1 to 16aB-3 has the same configuration as phase corrector 16aA-i, but the phase amounts that are set are different. The phase amounts that are set in each of phase shifters 52B-j-1 to 52B-j-9 that are provided inside phase corrector 16aB-j are set to phase amounts of "(j-1)α" that correspond to the wavelengths λ1 to λ9 that are supplied to each of them.

[0145] With the above configuration, the process shown in Fig. 6 is performed for each of the wavelengths λ1 to λ9. In step Sb6 of this process, the phase rotation occurring in the carrier optical signal of each of the wavelengths λ1 to λ9 and the upper sideband optical signal of each of the wavelengths λ1 to λ9 is canceled out. This allows nine transmission beams, each consisting of nine different superimposed transmission signals 1 to 9, to be transmitted in parallel in the nine directions shown in Fig. 9(a).

[0146] (Effects of the Fourth Embodiment) The transmission directivity control device 1a configured as in the above-described fourth embodiment is capable of wavelength multiplexing by including nine light sources 11-1 to 11-9, a transmission optical signal generation unit 12a, a first scanning switching circuit 14A and a second scanning switching circuit 14B replaced with branching filters, and phase correction units 16aA-1 to 16aA-3 and 16aB-1 to 16aB-3. Therefore, in addition to the effects of the transmission directivity control device 1a of the second embodiment, it also has the effect of enabling multi-beam transmission, which can transmit nine transmission beams in parallel.

[0147] 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.

[0148] 11 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 described with the same reference numerals. The transmission directivity control device 1c includes an operation unit 10, a light source 11, a transmission optical signal generation unit 12, a weighting unit 13, phase correction units 16-1 to 16-M, photoelectric conversion units 17-1 to 17-M, and antenna elements 18-1 to 18-M.

[0149] In the first embodiment, the photoelectric conversion units 17-1 to 17-M were arranged to satisfy the first connection condition. That is, the photoelectric conversion units 17-1 to 17-M are arranged so that the difference in the path length 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 is constant. In contrast, the transmission directivity control device 1c of the fifth embodiment differs from the first embodiment in that the photoelectric conversion units 17-1 to 17-M are arranged so that the difference in the path length 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 is not constant.

[0150] As in the first embodiment, if the path lengths of the branched optical paths 102-1 to 102-M are the same, in the fifth embodiment, for example, the photoelectric conversion units 17-1 to 17-M are not arranged at equal intervals, and at M branch points 101-1, 101-2, ..., 101-M, the intervals between adjacent branch points 101-1, 101-2, ..., 101-M become the intervals between the photoelectric conversion units 17-1 to 17-M, resulting in a configuration where the intervals are no longer equal.

[0151] Therefore, the amount of phase rotation occurring in the optical signal supplied to each of the photoelectric conversion units 17-2 to 17-M cannot be expressed by a single formula "(j-1)a°" as in the first embodiment, and each of the optical signals is a different amount of phase rotation. Therefore, the amount of phase rotation occurring in the optical signal supplied to each of the photoelectric conversion units 17-2 to 17-M is expressed by "a １ °", "a ２ °", "a ３ °", "a４ °”, …, “a （Ｍ－１） °". １ °", "a ２ °", "a ３ °", "a ４ °”, …, “a （Ｍ－１） When each of the degrees is expressed in radians, it is expressed as "α １ ", "α ２ ", "α ３ ", "α ４ ", ..., "α （Ｍ－１） " is expressed as ".

[0152] In this case, in each of the phase correcting units 16-1 to 16-M of the transmission directivity control device 1c of the fifth embodiment, "0°", "a １ °", "a ２ °", "a ３ °", "a ４ °”, …, “a （Ｍ－１） 3 is performed after the phase amount of ".degree." is set. The processes Sa1 to Sa4 are the same as those performed by the transmission directivity control device 1 of the first embodiment.

[0153] In the process of Sa5, the following process is performed by the phase correctors 16-1 to 16-M. Hereinafter, in the fifth embodiment, "j" is any natural number between 1 and M. The phase corrector 16-j takes in the upper sideband optical signal output from the output terminal 15-E-j of the scanning matrix circuit 15. The phase corrector 16-j corrects the taken-in upper sideband optical signal by a predetermined phase amount. Specifically, the phase corrector 16-j applies "α （ｊ－１） The optical signal generated by the phase corrector 16-j is expressed by the following equation (17) instead of equation (4).

[0154]

[0155] The phase correctors 16-j output the upper sideband optical signals generated by delaying the phase to the opto-electrical converters 17-j connected to them.

[0156] As the process of Sa6, the following process is performed by the photoelectric conversion units 17-1 to 17-M. That is, the photoelectric conversion unit 17-j photomixes the carrier optical signal supplied from the optical path 100 with the upper sideband optical signal supplied from the phase correction unit 16-j. The carrier optical signal supplied to the multiplexer 32-j of the photoelectric conversion unit 17-j via the branch optical path 102-j is mixed with the signal "α （ｊ－１） " is added, the equation (5) is replaced by the following equation (18).

[0157]

[0158] In contrast, the upper sideband optical signal supplied to the multiplexer 32-j from the phase corrector 16-j is expressed by the above-mentioned equation (17). Therefore, the multiplexer 32-j multiplexes the carrier optical signal expressed by equation (18) with the upper sideband optical signal expressed by equation (17) to generate a multiplexed optical signal, which is output to the PD 32-j. When the PD 32-j takes in the multiplexed optical signal output by the multiplexer 32-j, it converts the multiplexed optical signal into an electrical signal. During this conversion into an electrical signal, the PD 32-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-j from the result of the square-law detection.

[0159] When square-law detection is performed by PD32-j, the carrier optical signal "α （ｊ－１） The phase rotation component of "-α" of the upper sideband wave shown in equation (17) （ｊ－１） Therefore, the RF signal output from the PD 32-j is the RF signal v ＲＦ＿ｊ The photoelectric conversion units 17-j output the generated RF signals to the antenna elements 18-j connected thereto. The antenna elements 18-j radiate the RF signals output by the photoelectric conversion units 17-j as radio waves, and the process ends.

[0160] (Effects of the Fifth Embodiment) The transmission directivity control device 1c of the fifth embodiment can cancel out the phase rotation occurring in the carrier optical signal by imparting a phase delay to the upper sideband optical signal, as in the transmission directivity control device 1 of the first embodiment, even if the difference in the path lengths 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 among the photoelectric conversion units 17-1 to 17-M is not constant. Therefore, 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.

[0161] In the transmission directivity control device 1c of the fifth embodiment, similar to the first embodiment, the phase shift of the optical signal is performed by an analog circuit. Therefore, the number of analog-to-digital converters can be significantly reduced compared to a fully digitally controlled array antenna in which phase shifting is performed entirely by digital signal processing. Therefore, by using the transmission directivity control device 1c, even if the scale of the array antenna 19 is large, it is possible to perform appropriate weighting without complicating the wiring structure, and to control the transmission directivity using a circuit with a simple structure suitable for miniaturization and mass production.

[0162] The method of canceling out phase rotation by the transmission directivity control device 1c of the fifth embodiment 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.

[0163] 12 is a block diagram showing an example of the configuration of a transmission directivity control device 1d according to a sixth embodiment. In the sixth embodiment, the same components as those in the first embodiment are described with the same reference numerals. The transmission directivity control device 1d includes an operation 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.

[0164] The difference between the transmission directivity control device 1d of the sixth embodiment and the transmission directivity control device 1 of the first embodiment is that the transmission directivity control device 1d does not include phase correctors 16-1 to 16-M. Instead, the transmission directivity control device 1d does not include phase correctors 16-1 to 16-M, and the optical paths are wired as follows. As described above, in the first embodiment, there is no path difference between the optical paths output from each of the output terminals 15-E-1 to 15-E-M of the scanning matrix circuit 15, pass through each of the phase correctors 16-1 to 16-M, and reach each of the photoelectric conversion units 17-1 to 17-M. In contrast, in the sixth embodiment, there is a path difference between the optical paths 201-1 to 201-M connecting the output terminals 15-E-1 to 15-E-M of the scanning matrix circuit 15 and the photoelectric conversion units 17-1 to 17-M.

[0165] For example, in the optical path 100, the path length between the branch point 101-1, which has the shortest path length of the optical path from the splitter 22 indicated by the symbol 150, and the branch point 101-M, which has the longest path length of the optical path from the splitter 22, is divided by a subtraction value obtained by subtracting "1" from M, which is the number of output terminals 15-E-1 to 15-E-M of the scanning matrix circuit 15, to calculate a division value.

[0166] Among the optical paths 201-1 to 201-M, the optical paths 201-1 to 201-M that connect to the photoelectric conversion units 17-1 to 17-M, which have a shorter optical path length from the demultiplexer 22, have a longer path length, and the difference in path length between the adjacent optical paths 201-1 to 201-M is set to the calculated division value.

[0167] When the path lengths of optical paths 201-1 to 201-M are as described above, the difference in path length between optical path 201-1, which connects to photoelectric conversion unit 17-1 and has the shortest path length of the optical path from demultiplexer 22, and optical path 201-M, which connects to photoelectric conversion unit 17-M and has the longest path length of the optical path from demultiplexer 22, is the length indicated by symbol 151, and the length indicated by symbol 151 is the same as the length indicated by symbol 150.

[0168] In the sixth embodiment, let "j" be any natural number between 1 and M. A phase rotation corresponding to the path length of the optical path 201-j occurs in the upper sideband optical signal output from the output terminal 15-E-j of the scanning matrix circuit 15.

[0169] Here, for example, it is assumed that the path length of optical path 201-M connecting output terminal 15-E-M and photoelectric conversion unit 17-M is the same as that in the transmission directivity control device 1 of the first embodiment. In this case, the phases of the upper sideband optical signals arriving at each of photoelectric conversion units 17-1 to 17-M, including the amount of tilt phase, are expressed as "0+(M-1)a°," "θ+(M-2)a°," ..., "(j-1)θ+(M-j)a°," ..., "(M-1)θ°," respectively. If this is rewritten using the phase of the upper sideband optical signal arriving at photoelectric conversion unit 17-1 as the reference and assuming that this phase is "0°," then the resulting phases become "0°," "θ-a°," ..., "(j-1)θ-(j-1)a°," ..., "(M-1)θ-(M-1)a°," as shown in FIG. This is the same as the phase of the upper sideband optical signal that reaches each of the photoelectric conversion units 17-1 to 17-M in the first embodiment.

[0170] Therefore, in the photomixing by each of the photoelectric conversion units 17-1 to 17-M, the phase rotation occurring in the carrier optical signal can be canceled out by the phase delay given to the upper sideband optical signal by the difference in path length of each of the optical paths 201-1 to 201-M.

[0171] (Effects of the Sixth Embodiment) The transmission directivity control device 1c of the sixth embodiment has the same effect as the transmission directivity control device 1 of the first embodiment, even if it is configured without the phase correction units 16-1 to 16-M, by changing the path lengths of the optical paths 201-1 to 201-M. The technique for canceling phase rotation by the transmission directivity control device 1d of the sixth embodiment can also be applied to the second to fifth embodiments, 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.

[0172] However, in the case of the fourth embodiment, which transmits multiple beams, the path lengths of the optical paths 201-1 to 201-M must be changed for each wavelength. This method of changing the path length for each wavelength will be described with reference to the configuration of the transmission directivity control device 1d of the sixth embodiment. The connection between the output terminal 15-E-1 of the scanning matrix circuit 15 and the photoelectric conversion unit 17-1 when K wavelengths are used will be described as an example. Here, K is an integer greater than or equal to 2. A demultiplexer that demultiplexes the K wavelengths is connected to the output terminal 15-E-1 of the scanning matrix circuit 15, and a multiplexer that multiplexes the K optical signals is connected to the photoelectric conversion unit 17-1. The demultiplexer and the multiplexer are connected via K optical paths. The path lengths of these K optical paths are determined by applying the method of the sixth embodiment, taking into account the phase rotation that occurs in the wavelengths of the upper sideband optical signals transmitted by each of the K optical paths. This configuration is also applied to the combinations of the output terminals 15-E-2 to 15-E-M and the photoelectric conversion units 17-2 to 17-M, making it possible to use the technique of the sixth embodiment even when transmitting multiple beams.

[0173] 12, the output terminals 15-E-1 to 15-E-M of the scanning matrix circuit 15 are connected to the photoelectric conversion units 17-1 to 17-M, respectively, by linear optical paths 201-1 to 201-M. However, as long as the path lengths of the optical paths 201-1 to 201-M are the same as those described in the sixth embodiment, the optical paths 201-1 to 201-M may be wired in any form other than a straight line.

[0174] (Effects Common to All Embodiments) In the first to sixth embodiments, phase shifting is achieved by analog processing of optical signals. Therefore, the mechanisms of the transmit directivity control devices 1 to 1d of the first to sixth 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 transmit directivity control devices 1 to 1d can be applied to FSO communication, which has these issues, and electronic scanning of optical beams becomes possible, these issues can be resolved.

[0175] (Other Configuration Examples in Each Embodiment) In the first and fifth embodiments, the phase correctors 16-1 to 16-M may not be provided, and the phase delays provided by the phase correctors 16-1 to 16-M may be applied when the scanning matrix circuit 15 imparts a phase gradient. In the second embodiment, the phase correctors 16A-1 to 16A-3 may not be provided, and the phase delays provided by the phase correctors 16A-1 to 16A-3 may be applied when the first scanning matrix circuit 15A imparts a phase gradient, and the phase correctors 16B-1 to 16B-3 may not be provided, and the phase delays provided by the phase correctors 16B-1 to 16B-3 may be applied when the second scanning matrix circuit 15B imparts a phase gradient. In the third embodiment, when α = β, the phase correction units 16A-1 to 16A-3, 16B-1 to 16B-3 may not be provided, and the phase delay provided by the phase correction units 16A-1 to 16A-3, 16B-1 to 16B-3 may be provided by the scanning matrix circuit 15C when applying a phase gradient.

[0176] The transmission optical signal generator 12 shown in the first, second, third, fifth, and sixth embodiments may be replaced with a transmission optical signal generator 12b shown in FIG. 13. 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 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. 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.

[0177] The transmission optical signal generation unit 12 shown in the first, second, third, fifth, and sixth embodiments may be replaced with a transmission optical signal generation unit 12c shown in FIG. 14 . The transmission optical signal generation unit 12c includes a distributor 27 and an SSB optical modulator 26a. The distributor 27 divides the light 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 to the SSB optical modulator 26a. That is, the light 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 that performs intensity modulation by suppressing the frequency band and lower sideband of the carrier when performing 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 .

[0178] 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. 13. 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. 14, 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.

[0179] 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.

[0180] 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.

[0181] In the photoelectric conversion units 17-1 to 17-M shown in the first, fifth, and sixth 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. 15. 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 from the phase correction unit 16-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.

[0182] Similar to the phase shifters provided inside the phase correction units 16-1 to 16-M, 16A-1 to 16A-3, and 16B-1 to 16B-3 shown in the first to fifth embodiments, and the phase shifters 52A-1-1 to 52A-1-9 provided inside the phase correction unit 16aA-1, and the phase correction unit 16aA-1, the phase shifters provided inside the phase correction units 16aA-2, 16aA-3, and 16aB-1 to 16aB-3 may be phase shifters with a predetermined phase amount, or variable phase shifters that can arbitrarily change the set phase amount. When a variable phase shifter is used, it becomes easy to arbitrarily change the wavelength of the light used. The phase amount of the variable phase shifter may be changed by the operation unit 10 or 10a.

[0183] The phase correction units 16-1, 16A-1, 16B-1, 16aA-1, and 16aB-1 shown in the first to fifth embodiments are all configured to provide a phase delay of "0°", and it is possible not to provide the phase correction units 16-1, 16A-1, 16B-1, 16aA-1, and 16aB-1 that provide such a phase delay of "0°".

[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 the column direction, are arranged at equal intervals. In the first embodiment, the photoelectric conversion units 17-1 to 17-M may be arranged at unequal intervals as long as the first connection condition is satisfied. This also applies to the sixth embodiment. In the second embodiment, the photoelectric conversion units 17-1-1 to 17-3-3 may be arranged at unequal intervals 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 difference in the path length of the optical path starting from the output terminal to which the optical path 100 of the demultiplexer 22 is connected and reaching each of two adjacent photoelectric conversion units 17-1 to 17-M among the photoelectric conversion units 17-1 to 17-M is 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, the demultiplexers 22, 42-1 to 42-3, 51A-1 and multiplexers 23, 32-j, 41-1 to 41-3, 53A-1 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.

[0186] In the first and fifth embodiments, assume that there is a difference in the path length of the optical paths connecting each of the output terminals 15-E-1 to 15-E-M of the scanning matrix circuit 15 to each of the photoelectric conversion units 17-1 to 17-M, and that this difference in path length causes a phase rotation in the upper sideband optical signal output from each of the output terminals 15-E-1 to 15-E-M and reaching each of the photoelectric conversion units 17-1 to 17-M. In this case, the output terminal of the demultiplexer 22 that outputs the carrier optical signal is provided with a distributor that distributes the carrier optical signal into M carrier optical signals. Each of the M output terminals of the distributor is provided with a phase correction unit, and each output terminal of the phase correction unit is connected to the corresponding photoelectric conversion unit 17-1 to 17-M via an optical path. With this configuration, the phase correction unit may impart a phase delay to the carrier optical signal that cancels out the phase rotation occurring in the upper sideband optical signal.

[0187] Similarly, in the sixth embodiment, suppose that the optical paths 201-1 to 201-M connecting the output terminals 15-E-1 to 15-E-M of the scanning matrix circuit 15 to the photoelectric conversion units 17-1 to 17-M have a difference in path length sufficient to cancel out the phase rotation occurring in the carrier optical signal, and that this difference in path length causes an extra phase rotation in the upper sideband optical signal output from the output terminals 15-E-1 to 15-E-M and reaching the photoelectric conversion units 17-1 to 17-M. In this case, the output terminal of the demultiplexer 22 that outputs the carrier optical signal is provided with a distributor that distributes the carrier optical signal into M carrier optical signals. Each of the M output terminals of the distributor may be connected to the corresponding photoelectric conversion units 17-1 to 17-M via an optical path, and the path lengths of these M optical paths may be set to cancel out the extra phase rotation occurring in the upper sideband optical signal.

[0188] 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.

[0189] The first embodiment described above shows an example 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, fifth, and sixth embodiments, the row in which the photoelectric conversion units 17-1 to 17-M are arranged does not have to follow the arrangement line. The second embodiment described above shows an example 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.

[0190] 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 said to generate RF signals, but they may also generate electromagnetic wave signals of a wider frequency band including RF signals, and radiate electromagnetic waves of a wider frequency band including radio waves from the antenna elements 18-1 to 18-M, 18-1-1 to 18-3-3.

[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...Operation 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, 16-1 to 16-M...Phase correction 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 transmission directivity control device comprising: a plurality of antenna elements arranged along an arrangement line that is arbitrarily defined in 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 tilt to the second optical signal that is predetermined depending on the direction of the arrangement line and a desired transmission direction, to generate a second optical signal with a phase tilt that corresponds to each of the antenna elements arranged along the arrangement line; and an opto-electrical conversion unit provided corresponding to each of the antenna elements, the opto-electrical conversion unit combining the second optical signal with the phase tilt that corresponds to each of the antenna elements and the first optical signal, converting the combined second optical signal with the phase tilt and the first optical signal into an electrical signal, and outputting the converted electrical signal to the corresponding antenna element, wherein a phase delay is applied to one of the two optical signals combined by the opto-electrical conversion unit so as to cancel out a phase rotation that occurs in the other optical signal depending on the path length of the optical path until the one optical signal reaches the opto-electrical conversion unit.

2. The transmission directivity control device according to claim 1, further comprising: a phase delay being applied to the second optical signal with a phase tilt so as to cancel out the phase rotation occurring in the first optical signal supplied to the photoelectric conversion unit.

3. 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 the 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 the 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, further comprising: a phase delay being imparted to the second optical signal with a phase tilt so as to cancel out the phase rotation occurring in the first optical signal with a phase tilt supplied to each of the photoelectric conversion units in a column direction; and a phase delay being imparted to the first optical signal with a phase tilt so as to cancel out the phase rotation occurring in the second optical signal with a phase tilt supplied to each of the photoelectric conversion units in a row direction.

4. The transmission directivity control device according to claim 2 or 3, further comprising a phase correction section that applies the phase delay between an output terminal of the weighting section and the photoelectric conversion section.

5. The transmission directivity control device according to claim 2 or 3, wherein the length of an optical path connecting an output terminal of said weighting unit and said photoelectric conversion unit is set to the path length at which said phase delay occurs.

6. The transmission directivity control device according to claim 2 or 3, wherein the weighting unit applies the phase gradient so as to cause the phase delay.

7. A transmission directivity control device as described in claim 1, wherein, when i is an arbitrary natural number and a difference between the path length of an optical path taken by the one optical signal to reach the opto-electric conversion unit having the i-th shortest path length and the path length of an optical path taken by the one optical signal to reach the opto-electric conversion unit having the (i+1)th shortest path length is the same for all i, a phase rotation amount caused by the difference is used as a reference phase amount, and a phase delay of (i-1) x the reference phase amount is imparted to the other optical signal supplied to the opto-electric conversion unit having the i-th shortest path length.

8. A transmission directivity control method for 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 tilt 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 tilt that corresponds to each of the antenna elements arranged along the arrangement line; and a step in which each of photoelectric conversion units provided corresponding to each of the antenna elements combines the second optical signal with the phase tilt and the first optical signal corresponding thereto, converts it into an electrical signal, and outputs the converted electrical signal to the corresponding antenna element, wherein a phase delay is imparted to the other optical signal so as to cancel out a phase rotation that occurs in one of the two optical signals combined by the photoelectric conversion unit in accordance with the path length of the optical path until the other optical signal reaches the photoelectric conversion unit.

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