Transmission directivity control device, transmission system, and transmission directivity control method

Abstract

One aspect of the present invention is a transmission directivity control device comprising: a loop circuit that shifts the frequency of an inputted optical signal to either a high-frequency side or a low-frequency side in accordance with the number of instances of cycling and imparts a delay time to the optical signal; and a distribution unit that distributes an initial optical signal that is an optical signal being transmitted or an optical signal that is outputted from the loop circuit to the loop circuit or to an array antenna, respectively.

Description

[Technical Field]

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

[0002] The use of high-frequency bands above the millimeter wave band is progressing as a means of achieving faster and larger-capacity wireless communications. The spatial propagation loss of radio waves increases as the frequency increases. For example, free-space propagation loss increases in proportion to the square of the frequency. For this reason, antennas with high gain are often used in these high-frequency bands. High-gain antennas always have high directivity. Therefore, it is necessary to align the beam direction with the other station in wireless communications. If the direction of the other station is dynamic, a means of dynamically controlling the beam direction (i.e., beam steering) must be applied. Beam steering in antennas is required not only for wireless communications but also for applications such as radar, imaging, and wireless power transmission.

[0003] Various methods have been proposed as means of beam steering. Below are some specific examples: A method that mechanically controls the direction of the antenna. A method that controls the radio waves emitted from the antenna by refracting or reflecting them using a movable lens or reflector. A method that uses a phased array antenna. Of these, the method that uses a phased array antenna is the most widely used. This is because phased array antennas have no mechanically moving parts and are highly durable and able to follow movements. They are also suitable for making antennas smaller and lighter.

[0004] In a phased array antenna, multiple antenna elements are arranged on a line or a plane. In a phased array antenna, the phase and amplitude of an RF (Radio Frequency) signal fed to each antenna element are controlled. This control is called weighting. By performing this weighting, beam steering is achieved electronically. The phase and amplitude of the RF signal fed to each antenna element are controlled using means such as a variable delay circuit, a variable attenuator circuit, or digital signal processing.

[0005] In fifth-generation mobile communication systems (Non-Patent Document 1) using millimeter-wave bands and millimeter-wave wireless LAN (Local Area Network) systems, phased array antennas that perform weighting using analog circuits are widely used. In many wireless communication systems, the range in which wireless communication partners exist varies not within a two-dimensional plane but within three-dimensional space. This requires beam steering along two axes, such as azimuth and elevation. Therefore, a phased array antenna requires the use of a two-dimensional array antenna in which antenna elements are arranged in a plane, and weighting for two-dimensional beam steering.

[0006] Furthermore, as the use of high-frequency bands is developed, even higher antenna gains are required. Therefore, it is expected that phased array antennas that weight even more antenna elements will be needed. 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. For sixth-generation mobile communications, which aim to provide even faster transmission rates, the use of the 300 GHz band (the so-called terahertz band) is being considered. If the radio frequency becomes about 10 times higher than the 28 GHz band, the free-space propagation loss will increase by 100 times. In other words, the free-space propagation loss will increase by 20 dB. Taking this into consideration, it is expected that tens of thousands of antenna elements will be required to compensate for this with the antenna gain of a base station, for example.

[0007] To minimize the power loss to the antenna elements, each phase shifter circuit must be located close to each antenna element. Therefore, for example, a phase shifter circuit is placed directly behind a planar antenna element formed on a printed circuit board, and power is supplied via a through-hole. However, as the radio frequency increases, the spacing between antenna elements becomes narrower. This narrowing of the antenna element spacing makes it difficult to arrange multiple phase shifter circuits in two dimensions at spacings equivalent to the antenna element spacing. For example, at a radio frequency of 300 GHz, the free-space wavelength is 1 mm. Therefore, the antenna element spacing is generally set to half the wavelength (i.e., 0.5 mm). Furthermore, to configure a circuit that forms multiple beams (a multi-beam forming circuit), the same number of phase shifters as the number of beams must be arranged in parallel. Therefore, it is easy to imagine that this becomes even more difficult.

[0008] On the other hand, there is a method that uses a passive circuit with a fixed phase shift amount rather than implementing a large number of phase shifter circuits corresponding to the number of antenna elements. In this method, the input terminals of the passive circuit are switched. However, to implement two-dimensional beam steering, as shown in Non-Patent Document 2, the circuit must be assembled three-dimensionally. Therefore, implementation in high frequency bands requires a configuration using a waveguide made of metal processed three-dimensionally with high precision. This makes mass production difficult. Furthermore, even if mass production is not possible, it is thought that it would be difficult to accommodate multiple elements.

[0009] Therefore, it has been proposed to apply optical circuit manufacturing technology that enables compact implementation of low-loss waveguides. For example, Non-Patent Document 3 proposes a method in which signals are converted into light and then weighted using an optical circuit. This is thought to increase the possibility of constructing a multi-element, two-dimensional weighting circuit. However, the number of components in a weighting circuit increases with the number of antenna elements. Therefore, a technology is needed that can accommodate an increase in the number of antenna elements while minimizing the increase in the number of components.

[0010] The following means have been disclosed as existing technologies for implementing weighting using optical circuits. Patent Document 1 discloses a three-dimensional optical circuit that performs two-dimensional beam steering using a wavelength dispersion line. However, this requires a matrix circuit with a multilayer wiring structure, which is difficult to manufacture. As a result, it is not suitable for mass production using a planar circuit manufacturing process.

[0011] Non-Patent Document 5 discloses the combination of a planar phase-shift circuit and an FBG (fiber bragg grating) reflector line. The FBG reflector line has a delay time that varies depending on the optical wavelength. This configuration enables beam steering in a plane perpendicular to the plane achieved by the FBG reflector line, in addition to the one-dimensional (within one plane) beam steering achieved by the planar phase-shift circuit. This beam steering achieves two-dimensional beam steering. This configuration enables two-dimensional beam steering while reducing the number of circuit components. However, Non-Patent Document 5 does not disclose a means for implementing multi-beam steering. Furthermore, FBGs are highly frequency-band dependent. Therefore, when multiple wavelength multiplexing is performed to accommodate a large number of antenna elements and beams, the number of FBG reflectors becomes enormous.

[0012] The beam forming means using wavelength multiplexing disclosed in Patent Document 2 is also thought to be expandable to two dimensions and multiple elements. However, as the number of antenna elements increases and the number of antenna elements becomes two-dimensional, the number of components constituting the circuit becomes enormous. Furthermore, as the number of antenna elements and the number of beams increase, the number of wavelengths multiplexed also increases. This poses a problem in that the required optical frequency bandwidth becomes enormous.

[0013] In Non-Patent Document 4, an input optical signal is circulated multiple times through a loop circuit, imparting a predetermined time delay and optical frequency shift to the optical signal with each circumnavigation. This process allows multiple optical signals with different wavelengths and delay times to be output. Therefore, time-delayed RF signals can be fed to each element of a one-dimensional phased array antenna. Non-Patent Document 4 also discloses a method for scanning a transmitted beam using this process. This method increases the number of optical frequencies used in the circuit in proportion to the number of antenna elements, but it enables the controllable size of the array antenna to be increased without increasing the size of the beam scanning circuit. However, the only operations performed on the signal light input to the loop are a time delay and an optical frequency shift. Therefore, the beam can only be directed in one direction from the normal to the array antenna. For example, it is not possible to scan the beam left or right; it can only scan the beam from the front to the right. [Prior art documents] [Patent documents]

[0014] [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-023400 [Patent Document 2] Japanese Patent Application Laid-Open No. 2007-165956 [Non-patent literature]

[0015] [Non-Patent Document 1] Hikaru Watanabe, Shinsuke Uga, Hideyuki Nakamizo, Tsutsumi, Shintaro Shinjo, and Yu Kuriyama, "Millimeter-Wave Antenna and RF Front-End Technology for 5th Generation Mobile Communication Base Stations," IEICE Communications Society Magazine, Vol. 14, No. 3, 2020, pp. 222-231. [Non-patent document 2] 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, Vol.E100-C, No.10, pp.884-892 [Non-patent document 3] C. Tsokos et al., “Analysis of a Multibeam Optical Beamforming Network Based on Blass Matrix Architecture,” in Journal of Lightwave Technology, vol. 36, no. 16, pp. 3354-3372, 15 Aug.15, 2018. [Non-patent document 4] 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. [Non-patent document 5] B. Ortega, J. Mora and R. Chulia, “Optical Beamformer for 2-D Phased Array Antenna With Subarray Partitioning Capability,” in IEEE Photonics Journal, vol. 8, no. 3, pp. 1-9, June 2016 Summary of the Invention [Problem to be solved by the invention]

[0016] In view of the above circumstances, the present invention aims to provide a technology that can achieve transmission directivity that directs a beam over a wider range without increasing the number of components that make up the phase weighting circuit for beam scanning in accordance with the number of antenna elements. [Means for solving the problem]

[0017] One aspect of the present invention is a transmission directivity control device that includes a loop circuit that shifts the frequency of an input optical signal to either a higher frequency or a lower frequency depending on the number of times the signal has circulated, thereby providing a delay time, and a distribution unit that distributes an initial optical signal, which is an optical signal to be transmitted, or an optical signal output from the loop circuit, to the loop circuit and an array antenna, respectively.

[0018] One aspect of the present invention is a transmission system including the above-described plurality of transmission directivity control devices and a two-dimensional array antenna. The two-dimensional array antenna includes a multiplexer that multiplexes optical signals input from the plurality of transmission directivity control devices, a demultiplexer that outputs the optical signals input from the multiplexer from different predetermined output terminals according to their frequencies, and a plurality of antenna elements that photoelectrically convert the optical signals output from the output terminals of the demultiplexer and radiate them into space. In the two-dimensional array antenna, the antenna elements are arranged in a first direction and a second direction.

[0019] One aspect of the present invention is a transmission directivity control method in which a loop circuit shifts the frequency of an input optical signal to either a higher frequency or a lower frequency depending on the number of times the signal has circulated, the loop circuit imparts a delay time to the input optical signal depending on the number of times the signal has circulated, and distributes an initial optical signal, which is an optical signal to be transmitted, or an optical signal output from the loop circuit, to the loop circuit and an array antenna, respectively. [Effects of the Invention]

[0020] According to the present invention, it is possible to realize transmission directivity that directs a beam over a wider range without increasing the number of components that constitute a phase weighting circuit for beam scanning in accordance with the number of antenna elements. [Brief explanation of the drawings]

[0021] [Figure 1] FIG. 9 is a diagram illustrating an example of the configuration of a conventional transmission system 900. [Figure 2] 10 is a diagram showing the relationship between the frequency and delay time of components of an optical signal that has been processed by a loop circuit and reaches a demultiplexer. FIG. [Figure 3] 10 is a diagram showing the demultiplexing characteristics of a demultiplexer 990. FIG. [Figure 4] 1 is a diagram illustrating an example of the configuration of a first embodiment of a transmission system 100 according to the present invention. [Figure 5] FIG. 10 is a diagram illustrating an example of the relationship between beam direction information, light source frequency, and sidebands. [Figure 6] 10 is a flowchart showing a specific example of control based on beam direction information. [Figure 7] 10 is a flowchart showing a specific example of the flow of processing performed by the transmission directivity control device 10 on an optical signal. [Figure 8] 10 is a diagram showing the relationship between the frequency and delay time of each component of an optical signal that has been processed by loop circuit 11 and reaches demultiplexer 510. FIG. [Figure 9] 10 is a diagram showing the demultiplexing characteristics of a demultiplexer 510. FIG. [Figure 10] 10 is a diagram showing the demultiplexing characteristics of a demultiplexer 510. FIG. [Figure 11] FIG. 10 is a diagram illustrating an example of the configuration of a second embodiment of the transmission system 100 according to the present invention. [Figure 12] 10 is a diagram showing the relationship between the beam direction, the light source frequency, the sidebands for horizontal scanning, the sidebands for vertical scanning, and the passband of the horizontal scanning filter. FIG. [Figure 13] 10 is a diagram showing the demultiplexing characteristics of the vertical scanning demultiplexer 60. FIG. [Figure 14]10 is a diagram showing the demultiplexing characteristics of the first horizontal scanning demultiplexer 510 to the third horizontal scanning demultiplexer 530. FIG. [Figure 15] 10 is a diagram showing the relationship between the frequency and delay time of each component of an optical signal that reaches the vertical scanning demultiplexer 60. FIG. [Figure 16] 10 is a diagram showing the relationship between the frequency and delay time of each component of an optical signal that reaches the vertical scanning demultiplexer 60. FIG. [Figure 17] FIG. 10 is a diagram illustrating an example of the configuration of a third embodiment of the transmission system 100 according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0022] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail with reference to the drawings. It should be noted that the embodiment described below is merely an example, and the embodiments to which the present invention is applied are not limited to the following embodiment.

[0023] (Prior art and its problems) First, the conventional device disclosed in Non-Patent Document 4 will be described. Fig. 1 is a diagram showing an example of the configuration of a conventional transmission system 900. The transmission system 900 includes a transmission directivity control device 90 and an array antenna 99. The transmission directivity control device 90 controls the transmission directivity of the array antenna 99 connected to the transmission system. The array antenna 99 has a linear array. The array antenna 99 has a duplexer 990 and three antenna elements 991 to 993 arranged vertically.

[0024] A transmission signal and beam direction information are input to the transmission system 900. The transmission signal is an electrical signal on which information to be transmitted wirelessly is superimposed. The beam direction information is information regarding the beam direction of a transmission beam transmitted from the array antenna 99. The beam direction information may be information indicating the beam direction itself, or may be identification information (e.g., a beam number) associated with the beam direction and set in advance. The output of the transmission system 900 is an electromagnetic wave radiated into space from the array antenna 99 with directionality toward the beam direction. FIG. 1 illustrates a photomixer p as a specific example of a circuit that converts an optical signal to an RF signal. For example, a circuit may be used that inputs multiple (e.g., two) optical signals with different frequencies to the photomixer p using a photodiode and extracts the difference frequency between the input signals as an RF signal. Note that a device other than a photomixer may be used as the circuit that converts an optical signal to an RF signal.

[0025] 1, the transmission directivity control device 90 includes a direction indicating circuit 901, a light source 902, an optical modulator 903, a directional coupler 904, and a loop circuit 91. The loop circuit 91 includes an optical SSB modulator 905, an RF local oscillator 906, a filter 907, an amplifier 908, and a delay circuit 909. An optical signal is input to the loop circuit 91 from the second output terminal of the directional coupler 904. The output signal of the loop circuit 91 is input to the second input terminal of the directional coupler 904. The optical SSB modulator 905 performs carrier suppressed single sideband modulation (SSB modulation).

[0026] The RF local oscillator 906 generates an unmodulated RF (radio frequency) signal with a frequency Δf and outputs it to the optical SSB modulator 905. The delay circuit 909 imparts a delay to the signal passing through the device. The amount of delay imparted by the delay circuit 909 to the signal is variable. The time required for the signal input to the loop circuit 91 to make one circuit around the loop circuit 91 is Δτ. Δτ can be changed by changing the delay time of the delay circuit 909. The optical SSB modulator 905 shifts the frequency of the input optical signal to a higher frequency by Δf. In other words, the optical SSB modulator 905 has the function of modulating the upper sideband (USB). Therefore, the optical signal input to the loop circuit 91 is delayed by Δτ and its frequency is shifted to a higher frequency by Δf each time it makes one circuit around the loop circuit 91. Three optical frequency channels are defined, designated ch1 to ch3 from the lowest frequency. The spacing between the three channels is Δf.

[0027] The direction indication circuit 901 controls the amount of time delay in the delay circuit 909 of the loop circuit 91 based on the beam direction information input to the transmission directivity control device 90 .

[0028] Next, the operation of the conventional transmission system 900 shown in Figure 1 will be described. Unmodulated light of frequency channel ch1 output from light source 902 and a transmission signal input to transmission directivity control device 90 are input to optical modulator 903. Optical modulator 903 modulates the input unmodulated light with the transmission signal to generate an optical signal. Note that when the application is not for information transmission, optical modulator 903 generates an unmodulated optical signal without performing the modulation process described above. Optical modulator 903 outputs the generated optical signal.

[0029] The optical signal output by the optical modulator 903 is input to a first input terminal (the upper left terminal in FIG. 1 ) of a directional coupler 904. The directional coupler 904 divides the input optical signal into multiple signals (two in FIG. 1 ) and outputs them. One output of the optical signal divided by the directional coupler 904 is output directly from the first output terminal (the upper right terminal in FIG. 1 ) and input to a demultiplexer 990 of the array antenna 99. The other output of the directional coupler 904 is output from the second output terminal (the lower right terminal in FIG. 1 ) and input to the loop circuit 91. The optical signal has its frequency shifted by Δf to the higher frequency side in the optical SSB modulator 905. The optical signal further passes through a filter 907 and an amplifier 908, and is then given a predetermined time delay in a delay circuit 909. The optical signal is then input to a second input terminal (the lower left terminal in FIG. 1 ) of the directional coupler 904, completing its first circuit around the loop circuit 91. This optical signal is further split into two by directional coupler 904. One of the split outputs is input to demultiplexer 990 from the first output terminal, and the other is input back to loop circuit 91 from the second output terminal.

[0030] 2 is a diagram showing the relationship between the frequency and delay time of components of an optical signal that reaches a demultiplexer 990 after being processed by the loop circuit 91. In Fig. 2, reference numeral 951 indicates the passband of the filter 907, reference numeral 952 indicates an optical signal that has made zero trips around the loop circuit 91, reference numeral 953 indicates an optical signal that has made one trip around the loop circuit 91, and reference numeral 954 indicates an optical signal that has made two trips around the loop circuit 91. As the number of trips around the loop circuit 91 increases, the delay time increases by Δτ, the frequency shifts to a higher frequency by Δf, and the channel number increases by one.

[0031] The filter 907 is provided to prevent an infinite loop of the optical signal in the loop circuit 91. The passband of the filter 907 is set to the band of ch2 and the band of ch3, as shown in FIG. 2 . As a result, when the optical signal makes two loops around the loop circuit 91 and its frequency becomes ch3, and then enters the third loop, the optical SSB modulator 905 further shifts the frequency by Δf toward the high frequency side, but the filter 907 does not allow the optical signal to pass through. Therefore, the number of loops of the optical signal around the loop circuit 91 is limited to two. However, the number of loops around the loop circuit 91 does not need to be limited to two, and may be set appropriately depending on, for example, the configuration of the connected array antenna 99.

[0032] The demultiplexing characteristics of demultiplexer 990 are shown in Figure 3. Optical signals of ch1, ch2, and ch3 are output from output terminals 1 to 3 of demultiplexer 990, respectively. The optical signals output from each output terminal of demultiplexer 990 are converted into RF signals by photoelectric conversion circuits (not shown). Each RF signal is input to antenna elements 991 to 993, respectively, and radiated into space from each antenna element.

[0033] As a result of the above operations, the combination of RF signals radiated into space from antenna elements 991 to 993 is a combination of RF signals obtained by converting the signal that has made zero trips around loop circuit 91 to the signal that has made two trips around loop circuit 91, as shown in FIG. 2. Therefore, it is a combination of signals with a sloping time delay of Δτ. Therefore, the beam direction can be changed by changing the amount of time delay in delay circuit 909. Therefore, the configuration shown in FIG. 1 can perform beam scanning as a phased array antenna.

[0034] However, in the above-described configuration, the delay at antenna element 991 is smallest, followed by the delays at antenna elements 992 and 993, which increase in order. Therefore, the direction in which the beam can be scanned is limited to a downward direction (depression angle direction) from the horizontal in FIG. 1. This array antenna 99 is actually a device that can also direct a beam upward (elevation angle direction) in FIG. 1. Therefore, the conventional transmission system 900 shown in FIG. 1 does not fully utilize the performance of the array antenna 99, resulting in a problem of a narrow scannable range.

[0035] (Outline of this embodiment) Three embodiments of the present invention will be described below. The first embodiment is a transmission system 100 having a one-dimensional array antenna 51. The second embodiment is a transmission system 100 having a two-dimensional array antenna 61.

[0036] The third embodiment is a transmission system 100 that enables multi-beam transmission. In any embodiment, transmission directivity that directs beams over a wider range is achieved by combining the frequency of the light source 104 and switching the sidebands output by modulation from the optical SSB modulator 107 in the loop circuit 11. For example, the above-mentioned configuration solves the problem that beam scanning can only be performed in one direction from the front direction of the array antenna. Specific explanations are given below. Note that a description of some of the configuration that is the same as the conventional transmission system 900 described above will be omitted.

[0037] [First embodiment] FIG. 4 is a diagram showing an example of the configuration of a first embodiment of a transmission system 100 according to the present invention. The first embodiment of the transmission system 100 will be described below. The transmission system 100 includes a transmission directivity control device 10 and a linear array antenna 51. The array antenna 51 has a plurality of antenna elements (for example, three antenna elements). The antenna elements are arranged vertically. In the following description, the number of antenna elements in the array antenna 51 is assumed to be three, but other numbers may be used. In the present invention, the number of circuit components can be kept constant regardless of the number of antenna elements. Therefore, the present invention may be applied, for example, when the number of antenna elements is large.

[0038] A transmission signal and beam direction information are input to the transmission system 900. The transmission signal is an electrical signal on which information to be transmitted wirelessly is superimposed. The beam direction information is information regarding the beam direction of a transmission beam transmitted from the array antenna 51. The beam direction information may be information indicating the beam direction itself, or may be identification information (e.g., a beam number) associated with the beam direction and set in advance. The output of the transmission system 100 is an electromagnetic wave emitted into space from the array antenna 51 with directionality toward the beam direction. As in FIG. 1, FIG. 4 also illustrates a photomixer p as a specific example of a circuit that converts an optical signal to an RF signal. For example, a circuit that inputs multiple (e.g., two) optical signals with different frequencies to the photomixer p using a photodiode and extracts the difference frequency as an RF signal may be used. The transmission directivity control device 10 includes a light source frequency indicating circuit 101, a modulation sideband indicating circuit 102, a direction indicating circuit 103, a light source 104, an optical modulator 105, a directional coupler 106, and a loop circuit 11.

[0039] The loop circuit 11 includes an optical SSB modulator 107, an RF local oscillator 108, a switch 109, an RF directional coupler 110, a filter 111, an amplifier 112, and a delay circuit 113. An optical signal is input to the loop circuit 11 from the second output terminal of the directional coupler 106. The directional coupler 106 distributes the input optical signal to the loop circuit 11 and the array antenna 51 and outputs the distributed signal. The directional coupler 106 is configured using a device having such a distribution function. The directional coupler is a specific example of a distribution unit. The distribution unit may be implemented using a device other than a directional coupler.

[0040] The output signal of the loop circuit 11 is input to the second input terminal of the directional coupler 106. The optical SSB modulator 107 is a specific example of an optical frequency shifter. The optical SSB modulator 107 changes (shifts) the frequency of the input optical signal in a predetermined direction, either to a higher frequency or a lower frequency. The direction of the shift is determined according to an instruction from the modulation sideband instruction circuit 102. While one optical signal is looping, this direction remains unchanged and the shift is only in the same direction (to a higher frequency or a lower frequency). The optical frequency shifter (optical SSB modulator 107) in this embodiment is, for example, an optical modulator that performs carrier suppression optical single sideband modulation. More specifically, the optical frequency shifter includes, for example, a first RF signal application electrode and a second RF signal application electrode. The optical frequency shifter is, for example, a Mach-Zehnder optical modulator. The two output terminals of the RF directional coupler 110, which is configured as a 90-degree hybrid circuit, are connected to the first RF signal application electrode and the second RF signal application electrode, respectively. The optical SSB modulator 107 performs carrier-suppressed single-sideband modulation. The carrier-suppressed single-sideband modulation is SSB modulation, and is either upper sideband (USB) or lower sideband (LSB) modulation. The optical frequency shifter may be configured using other devices as long as they can achieve this function.

[0041] The RF local oscillator 108 generates an RF (radio frequency) unmodulated signal (hereinafter referred to as "local RF signal") of a predetermined frequency Δf and outputs it to the switch 109. The switch 109 switches one input (local RF signal) to one of two outputs and outputs it. The two outputs of the switch 109 are connected to a first RF signal application electrode and a second RF signal application electrode of the optical SSB modulator 107, respectively. The delay circuit 113 imparts a delay to the signal passing through the device itself. The amount of delay imparted to the signal by the delay circuit 113 is changeable. The time required for the signal input to the loop circuit 11 to make one circuit around the loop circuit 11 is Δτ. Δτ can be changed by changing the delay time of the delay circuit 113.

[0042] The optical SSB modulator 107 has two RF signal application electrodes (a first RF signal application electrode 1071 and a second RF signal application electrode 1072). As shown in FIG. 4, of the two outputs of the RF directional coupler 110, the first output is connected to the first RF signal application electrode 1071, and the second output is connected to the second RF signal application electrode 1072. The output terminal of the RF local oscillator 108 is connected to two input terminals of the RF directional coupler 110 via a switch 109. Therefore, depending on the state of the switch 109, the local RF signal is input to one of the input terminals of the RF directional coupler 110. With this configuration, the phase relationship of the local RF signals applied to the two RF signal application electrodes (1071 and 1072) of the optical SSB modulator 107 can be switched depending on the state of the switch 109. That is, in the first RF state, depending on the state of the switch 109, the first RF signal application electrode 1071 lags behind the second RF signal application electrode 1072 by 90°. In the second state, the first RF signal application electrode 1071 leads the second RF signal application electrode 1072 by 90°. The optical SSB modulator 107 can perform USB modulation in the first state, and can perform LSB modulation in the second state. As described above, the first embodiment of the present invention can switch the frequency shift direction by including the optical SSB modulator 107 and the switch 109. This switching enables the beam to be scanned in both directions.

[0043] Because the loop circuit 11 is configured in this way, the optical signal input to the loop circuit 11 is delayed in time by Δτ and its frequency is shifted by Δf to a higher or lower frequency each time it makes one circuit. Three optical frequency channels are defined, designated ch1 to ch3 from the lowest frequency side. The interval between the three channels is Δf.

[0044] The light source frequency instruction circuit 101 controls the frequency of the light generated by the light source 104 based on the beam direction information input to the transmission directivity control device 10 .

[0045] The modulation sideband instruction circuit 102 is a specific example of a frequency shift level instruction circuit. The modulation sideband instruction circuit 102 determines whether the frequency shifter (e.g., the optical SSB modulator 107) should shift the frequency to a higher frequency or a lower frequency, and instructs the loop circuit 11. The modulation sideband instruction circuit 102 performs the above processing by instructing the switch 109, but the frequency shift level instruction circuit may be implemented in other ways. The switch 109 controls the path based on beam direction information input to the transmit directivity control device 10. In this way, the switch 109 sets the sideband generated by the optical SSB modulator 107 to USB or LSB. The direction instruction circuit 103 controls the time delay amount in the delay circuit 113 based on the beam direction information input to the transmit directivity control device 10.

[0046] 5 is a diagram showing an example of the relationship between beam direction information, light source frequency, and sideband. The beam direction information is information input to the transmission system 100. The light source frequency is a value set by the light source frequency instruction circuit 101 in accordance with the beam direction information. The sideband is a value set by the modulation sideband instruction circuit 102 in accordance with the beam direction information. The sideband indicates the sideband generated by the optical SSB modulator 107.

[0047] Next, the operation of the transmission system 900 in the first embodiment will be described. It is assumed that the relationship between the scanning direction, the light source frequency, and the sidebands generated by the optical SSB modulator is set as shown in FIG.

[0048] 6 and 7 are flowcharts showing a specific example of the operation of the transmission system 900. FIG. 6 is a flowchart showing a specific example of control based on beam direction information. First, the light source frequency instruction circuit 101, the modulation sideband instruction circuit 102, and the direction instruction circuit 103 acquire beam direction information (step S101). The light source frequency instruction circuit 101 determines the frequency of the light source 104 based on the beam direction information (step S102). The light source frequency instruction circuit 101 instructs the light source 104 on the frequency based on the determination result (step S103). The modulation sideband instruction circuit 102 determines the state of the switch 109 based on the relationship shown in FIG. 5 and the beam direction indicated by the beam direction information (step S104). For example, the modulation sideband instruction circuit 102 selects the phase relationship of the RF signals applied to the RF signal application electrodes 1071 and 1072 of the optical SSB modulator 107 so that modulation of the modulator sideband (USB or LSB) determined according to the beam direction is performed. Then, the modulation sideband instruction circuit 102 determines the state of the switch 109 so that the local RF signal is output to the RF signal application electrode with the selected phase relationship. The modulation sideband instruction circuit 102 instructs the switch 109 on the state based on the determination result (step S105). The direction instruction circuit 103 determines the delay amount of the delay circuit 113 based on the beam direction information (step S106). The direction instruction circuit 103 instructs the delay amount to the delay circuit 113 based on the determination result (step S107).

[0049] (Operation when scanning downwards) FIG. 7 is a flowchart showing a specific example of the flow of processing performed by the transmission directivity control device 10 with respect to an optical signal. Next, a description will be given of the flow of operations performed by the transmission directivity control device 10 when control according to beam direction information is performed by each circuit as described above. First, the operation when scanning downward will be described. First, the light source 104 emits unmodulated light (step S201). The unmodulated light of frequency channel ch1 output from the light source 104 and a transmission signal input to the transmission directivity control device 10 are input to the optical modulator 105. The optical modulator 105 modulates the input unmodulated light with the transmission signal to generate an optical signal (step S202). Note that when the application is not for information transmission, the optical modulator 105 generates an unmodulated optical signal without performing the modulation process described above. The optical modulator 105 outputs the generated optical signal. The optical signal output by the optical modulator 105 is called an "initial optical signal." The initial optical signal is an optical signal that has never circulated through the loop circuit 11, which will be described later.

[0050] The optical signal output by the optical modulator 105 is input to a first input terminal (the upper left terminal in FIG. 4) of the directional coupler 106. The directional coupler 106 divides the input optical signal into multiple parts (two in FIG. 4) and outputs them (step S203). One of the optical signals divided by the directional coupler 106 is output directly from the first output terminal (the upper right terminal in FIG. 4) and input to the demultiplexer 510 of the array antenna 51. The other output of the directional coupler 106 is output from the second output terminal (the lower right terminal in FIG. 4) and input to the loop circuit 11. The optical SSB modulator 107 shifts the frequency of this optical signal to the high-frequency side by Δf (step S204). At this time, the modulation sideband instruction circuit 102 instructs the switch 109 to set the optical SSB modulator 107 to generate a USB. The optical signal is filtered by the filter 111 (step S205). The filter 111 filters out and blocks optical signals of a predetermined frequency.

[0051] By such filtering, optical signals that have not looped through the loop circuit 11 a predetermined number of times or more pass through the filter 111 (step S206-NO), and optical signals that have looped through the loop circuit 11 a predetermined number of times or more are blocked (step S206-YES). The optical signal that has passed through the filter 111 is further amplified by the amplifier 112 (step S207) and then given a predetermined time delay by the delay circuit 113 (step S208). This optical signal is then input to the second input terminal (the terminal at the bottom left in FIG. 4) of the directional coupler 106, completing its first circuit through the loop circuit 11. This optical signal is further split into two by the directional coupler 106 (step S203). One of the split outputs is input to the demultiplexer 510 from the first output terminal, and the other is input again to the loop circuit 11 from the second output terminal.

[0052] Fig. 8 is a diagram showing the relationship between the frequency and delay time of each component of an optical signal that reaches the demultiplexer 510 after being processed by the loop circuit 11. In Fig. 8, reference numeral 911 indicates the passband of the filter 111, reference numeral 912 indicates the optical signal that has made zero trips around the loop circuit 11, reference numeral 913 indicates the optical signal that has made one trip around the loop circuit 11, and reference numeral 914 indicates the optical signal that has made two trips around the loop circuit 11. As the number of trips around the loop circuit 11 increases, the delay time increases by Δτ, the frequency shifts to a higher frequency by Δf, and the channel number increases by one.

[0053] The filter 111 is provided to prevent an infinite loop of the optical signal in the loop circuit 11. The passband of the filter 111 is set to the bands of ch1 to ch3, as shown in FIG. 8 . As a result, when the optical signal enters the third loop after making two loops around the loop circuit 11 and reaching a frequency of ch3, the optical SSB modulator 107 further shifts the frequency to the high frequency side by Δf, but the optical signal cannot pass through the filter 111. Therefore, the number of times the optical signal circulates around the loop circuit 11 is limited to two. However, the number of times the optical signal circulates around the loop circuit 11 does not need to be limited to two, and may be set appropriately depending on, for example, the configuration of the connected array antenna 51.

[0054] The demultiplexing characteristics of demultiplexer 510 are shown in Fig. 9. Optical signals of ch1, ch2, and ch3 are output from output terminals 1 to 3 of demultiplexer 510, respectively. The optical signals output from each output terminal of demultiplexer 510 are converted into RF signals by photoelectric conversion circuits (not shown). Each RF signal is input to antenna elements 511 to 513, respectively, and radiated into space from each antenna element.

[0055] As a result of the above operations, the combination of RF signals radiated into space from antenna elements 511 to 513 is a combination of RF signals obtained by converting the signal that has made zero trips through loop circuit 11 to the signal that has made two trips through loop circuit 11, as shown in Fig. 8. In this case, the RF signal is first radiated into space from antenna element 511, and is a set of RF signals with a sloping time delay of Δτ. Therefore, by changing the amount of time delay in delay circuit 113, the beam direction can be changed from the front to the downward direction in Fig. 4.

[0056] (Operation when scanning upwards) Next, the operation when scanning in the upward direction will be described. Unlike the case of scanning in the downward direction in Figure 4, the frequency of light source 104 is set to ch3. Also, the state of switch 109 is set opposite to that when scanning in the downward direction. As a result, the sideband generated by optical SSB modulator 107 becomes LSB. The relationship between the frequency and delay time of the optical signal components that reach demultiplexer 510 is as shown in Figure 9. As the number of times the signal circulates around loop circuit 11 increases, the delay time increases by Δτ, the frequency shifts to a lower frequency by Δf, and the channel number decreases by one.

[0057] The demultiplexing characteristics of demultiplexer 510 are as shown in Fig. 10. Therefore, the combination of RF signals radiated into space from antenna elements 511 to 513 is a combination of RF signals obtained by converting a signal that has made two trips around loop circuit 11 to a signal that has made zero trips around loop circuit 11, as shown in Fig. 9. In this case, the RF signal from antenna element 513 is first radiated into space, and is a set of RF signals with a sloping time delay of Δτ. Therefore, by changing the amount of time delay in delay circuit 113, the beam direction can be changed from the front to the upward direction in Fig. 4.

[0058] The above operation enables beam scanning both upward and downward from the front of the array antenna 51. Therefore, transmission directivity that directs the beam over a wider range can be achieved.

[0059] [Second embodiment] 11 is a diagram showing a configuration example of a second embodiment of the transmission system 100 according to the present invention. The second embodiment of the transmission system 100 will be described below, focusing mainly on the differences from the first embodiment. Descriptions of configurations that operate in the same way as the first embodiment may be omitted.

[0060] A transmission system 100 of the second embodiment includes a transmission directivity control device 10 and a two-dimensional array antenna 61. The transmission directivity control device 10 of the second embodiment includes two loop circuits 11 arranged in series. Specifically, the transmission directivity control device 10 includes a light source frequency indicating circuit 101, a modulation sideband indicating circuit 102, a direction indicating circuit 103, a filter band indicating circuit 121, a light source 104, an optical modulator 105, a directional coupler 106a, a directional coupler 106b, a horizontal scanning loop circuit 11a, and a vertical scanning loop circuit 11b. The horizontal scanning loop circuit 11a applies a delay for horizontal scanning to the signal. The vertical scanning loop circuit 11b applies a delay for vertical scanning to the signal. The output of the vertical scanning loop circuit 11b, located at the subsequent stage, is connected to each antenna element via a two-stage duplexer. The two-stage demultiplexer includes a vertical scanning demultiplexer 60 and a first horizontal scanning demultiplexer 510 to a third horizontal scanning demultiplexer 530. As in the first embodiment, the circuit that converts an optical signal into an RF signal is not shown in the figure.

[0061] Nine optical frequency channels are defined within the optical circuit. They are called ch1 to ch9 from the low frequency side. The intervals between the nine channels are Δf H The light source frequency instruction circuit 101 controls the frequency of the light generated by the light source 104 based on the beam direction information input to the transmission directivity control device 10.

[0062] The direction indication circuit 103 controls the amount of time delay in the delay circuit 113 (horizontal scanning delay circuit 113a and vertical scanning delay circuit 113b) based on the beam direction information input to the transmission directivity control device 10.

[0063] The filter band instruction circuit 121 switches the pass band of the horizontal scanning filter 111a between two options, "ch1 to ch3" and "ch7 to ch9," based on beam direction information input to the transmission directivity control device 10. The pass band of the vertical scanning filter 111b is set to "ch1 to ch9."

[0064] The modulation sideband instruction circuit 102 controls the paths at the switches 109a and 109b based on the beam direction information input to the transmission directivity control device 10. As a result, the switches 109a and 109b set the sidebands generated by the optical SSB modulators 107a and 107b, respectively, to USB or LSB.

[0065] FIG. 12 is a diagram showing the relationship between the beam direction, light source frequency, horizontal scanning sideband, vertical scanning sideband, and horizontal scanning filter passband. The beam direction indicates the beam direction to be scanned. The light source frequency is a value set by the light source frequency instruction circuit 101. The horizontal scanning sideband is a sideband set in the loop circuit 11a by the modulation sideband instruction circuit 102. The vertical scanning sideband is a sideband set in the loop circuit 11b by the modulation sideband instruction circuit 102. The horizontal scanning filter passband is the horizontal scanning filter passband set by the filter band instruction circuit 122.

[0066] The demultiplexing characteristics of the vertical scanning demultiplexer 60 are set as shown in Fig. 13. The demultiplexing characteristics of the first horizontal scanning demultiplexer 510 to the third horizontal scanning demultiplexer 530 may be set as shown in Figs. 14(A) to 14(C), respectively.

[0067] Next, an example of the operation of the second embodiment of the transmission system 100 shown in Fig. 11 will be described. Note that a description of the same processes as those in the first embodiment will be omitted. The optical signal input to the horizontal scanning loop circuit 11a goes around the loop once for a period of time Δτ H The frequency is delayed by Δf H This frequency shift Δf H The direction of the horizontal scanning loop is determined according to the state of the switch 109a of the horizontal scanning loop. The optical signal output from the horizontal scanning loop circuit 11a and input to the vertical scanning loop circuit 11b goes around the loop once for a period of time Δτ V The frequency is delayed by Δf depending on the state of the switch 109b. V The frequency is shifted to a higher or lower frequency by

[0068] In addition, Δf V is Δf H It can be three times as large as Δf V is Δf H The distance between ch3 and ch4, and the distance between ch6 and ch7 should be set to Δf H As a value exceeding Δf V is Δf H However, in order to use the optical frequency band efficiently, it is appropriate to set the value not to exceed three times the original value.

[0069] where the delay Δτ H is determined by providing a predetermined time delay to the horizontal scanning delay circuit 113a in response to an instruction from the direction indicating circuit 103. H is the quantity that determines the horizontal (azimuth) scanning angle. V is determined by providing a predetermined time delay to the vertical scanning delay circuit 113b in accordance with an instruction from the direction indicating circuit 103. V is a quantity that determines the vertical (elevation) scanning angle.

[0070] As an example, the operation when scanning in the lower left direction will be described. In this embodiment, the direction to the right of the array antenna 61 in the drawing is the front direction. As shown in FIG. 12, the frequency of the light source 104 is ch1, the optical SSB modulator 107a of the horizontal scanning loop circuit 11a generates an upper sideband (USB), and the optical SSB modulator 107b of the vertical scanning loop circuit 11b also generates an upper sideband (USB). The passband of the horizontal scanning filter 111a is set to ch1 to ch3.

[0071] In this case, the optical signal generated by the optical modulator 105 is given a time delay and a frequency shift by the horizontal scanning loop circuit 11a and the vertical scanning loop circuit 11b, and is then input to the vertical scanning demultiplexer 60. The relationship between the frequency and delay time of each component of the optical signal that has undergone such signal processing and reaches the vertical scanning demultiplexer 60 is as shown in Fig. 15.

[0072] In the horizontal scanning loop circuit 11a, the delay time is increased by Δτ H The frequency increases by Δf H In the vertical scanning loop circuit 11b, the delay time is shifted to the high frequency side by Δτ V The frequency increases by Δf V The frequency is shifted to the higher frequency side by

[0073] If these optical signal components are fed to each antenna element through the vertical scanning demultiplexer 60 and the horizontal scanning demultiplexer, the beam will be directed to the lower left. The degree of inclination of the beam from the front can be adjusted by adjusting the delay amounts of the horizontal scanning delay circuit 113a and the vertical scanning delay circuit 113b using the direction indication circuit 103, respectively, to obtain Δτ H and Δτ V These will be adjusted and implemented.

[0074] As an example, the operation when scanning in the upper left direction will be described. As shown in Figure 12, the frequency of the light source 104 is ch7, the optical SSB modulator 107a in the horizontal scanning loop circuit 11a generates an upper sideband (USB), and the optical SSB modulator 107b in the vertical scanning loop circuit 11b generates a lower sideband (LSB). The passband of the horizontal scanning filter 111a is set to ch1 to ch3.

[0075] In this case, the optical signal generated by the optical modulator 105 is given a time delay and a frequency shift by the horizontal scanning loop circuit 11a and the vertical scanning loop circuit 11b, and is then input to the vertical scanning demultiplexer 60. The relationship between the frequency and delay time of each component of the optical signal that has undergone such signal processing and reaches the vertical scanning demultiplexer 60 is as shown in Fig. 16.

[0076] In the horizontal scanning loop circuit 11a, the delay time is increased by Δτ H The frequency increases by Δf H shifts to the high frequency side by Δf V In the vertical scanning loop circuit 11b, the delay time is shifted to the lower frequency side by Δτ VThe frequency increases by Δf H shifts to the high frequency side by Δf V The frequency is shifted to the lower frequency side.

[0077] If these optical signal components are fed to each antenna element through the vertical scanning demultiplexer 60 and the horizontal scanning demultiplexer, the beam will be directed toward the upper left. Even if the beam is scanned toward the upper right or lower right, beam scanning can be achieved using the same mechanism as described above by setting each circuit according to Figure 12.

[0078] In the second embodiment shown here, the two-dimensional array antenna 61 has a configuration of nine elements, with three elements arranged vertically and three elements arranged horizontally. However, any number of antenna elements may be provided in the two-dimensional array antenna 61. Furthermore, although the scanning direction is horizontal and vertical, other combinations of directions (for example, vertical and horizontal, east-west and north-south) may also be used.

[0079] [Third embodiment] 17 is a diagram showing a configuration example of a third embodiment of the transmission system 100 of the present invention. The following describes the third embodiment of the transmission system 100, focusing mainly on the differences from the second embodiment. Descriptions of configurations that operate in the same way as the first or second embodiment may be omitted.

[0080] In the third embodiment, the configuration of the second embodiment is applied to generate multiple beams. With this configuration, in the third embodiment, two different transmission signals can be wirelessly transmitted using beams in different directions. A transmission system 100 of the third embodiment includes a first transmission directivity control device, a second transmission directivity control device, a multiplexer 70, and a two-dimensional array antenna 61. The transmission system 100 of the third embodiment transmits at least two transmission signals (a first transmission signal and a second transmission signal). The first transmission directivity control device and the second transmission directivity control device both have the same configuration as the transmission directivity control device 10 of the second embodiment. The multiplexer 70 combines the output of the first transmission directivity control device and the output of the second transmission directivity control device. The multiplexer 70 outputs the combined optical signal to the vertical scanning demultiplexer 60 of the two-dimensional array antenna 61. The other configurations and operations of the third embodiment are the same as those of the second embodiment, and therefore will not be described again.

[0081] Depending on the beam direction to be scanned, the following values ​​are set so as to satisfy the relationships shown in Fig. 12: light source frequency set by light source frequency instruction circuit 101; sidebands (sidebands generated by optical SSB modulator 107a and optical SSB modulator 107b) set by modulation sideband instruction circuit 102; passband of the horizontal scanning filter set by filter band instruction circuit 121. The demultiplexing characteristics of vertical scanning demultiplexer 60 are set as shown in Fig. 13, and the demultiplexing characteristics of horizontal scanning demultiplexers 510 to 530 are set as shown in Fig. 14.

[0082] In the third embodiment, by adopting such a configuration, it is possible to transmit multiple beams (for example, two beams). By adding a circuit input to the multiplexer 70 in the same manner as in the configuration described here, it is also possible to transmit multiple beams of three or more beams.

[0083] The light source frequency indication circuit 101, modulation sideband indication circuit 102, direction indication circuit 103, and filter band indication circuit 121 in the first to third embodiments may be configured using a processor such as a CPU (Central Processing Unit) and a memory. In this case, the processing performed by these circuits may be implemented by the processor executing a program. Note that all or part of the functions of these circuits may be implemented using hardware such as an ASIC (Application Specific Integrated Circuit), a PLD (Programmable Logic Device), or an FPGA (Field Programmable Gate Array). The above program may be recorded on a computer-readable recording medium. Examples of computer-readable recording media include portable media such as a flexible disk, a magneto-optical disk, a ROM, a CD-ROM, and a semiconductor storage device (e.g., a solid-state drive (SSD)), as well as storage devices such as a hard disk or semiconductor storage device built into a computer system. The above program may be transmitted via a telecommunications line.

[0084] 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. [Industrial Applicability]

[0085] Phased array antennas are important for controlling the transmission directivity of sharply directional radio waves in ultra-high-speed wireless transmission using radio waves in high-frequency bands such as millimeter waves and terahertz waves, high-definition imaging, radar, etc. In such phased array antennas, a transmission directivity control device can be applied, which branches the signal to be transmitted, applies a predetermined phase weighting, and feeds power to the antenna elements. [Explanation of symbols]

[0086] 100...transmission system, 10...transmission directivity control device, 101...light source frequency indication circuit, 102...modulation sideband indication circuit, 103...direction indication circuit, 104...light source, 105...optical modulator, 106...directional coupler, 107...optical SSB modulator, 108...RF local oscillator, 109...switch, 110...RF directional coupler, 111...filter, 112...amplifier, 113...delay circuit, 11...loop circuit, 121...filter band indication circuit, 60...vertical scanning demultiplexer, 510...first horizontal scanning demultiplexer, 520...second horizontal scanning demultiplexer, 530...third horizontal scanning demultiplexer, 60...vertical scanning demultiplexer

Claims

1. a loop circuit that shifts the frequency of an input optical signal to either a higher frequency side or a lower frequency side depending on the number of times the signal has circulated, and provides a delay time; a distributor that distributes an initial optical signal, which is an optical signal to be transmitted, or an optical signal output from the loop circuit to the loop circuit and an array antenna, respectively; Equipped with The loop circuit includes: an optical frequency shifter that changes the frequency of an input optical signal by a predetermined amount to a higher or lower frequency side; a filter that passes only optical signals in a predetermined frequency band; a delay circuit that delays the optical signal by a predetermined time; a direction indicating circuit that determines a delay time in the delay circuit based on beam direction information that is information about the beam direction; a frequency shift level indicating circuit that determines whether the optical frequency shifter should shift the frequency to a higher frequency side or a lower frequency side based on the beam direction information; a light source frequency specifying circuit that determines a frequency of the initial optical signal based on the beam direction information; The array antenna includes a demultiplexer that outputs an input optical signal from different predetermined output terminals according to the frequency, and a plurality of antenna elements that photoelectrically convert the optical signal output from the output terminal of the demultiplexer and radiate the converted signal into space. A transmission directivity control device.

2. a local oscillator for generating a local RF signal having a predetermined frequency; A switch that is a one-input, two-output path changeover switch; a directional coupler for distributing a local oscillator signal, which is configured as a 90-degree hybrid circuit; the optical frequency shifter is an optical modulator that performs carrier suppression type optical single sideband modulation, the optical modulator is an optical modulator including a first RF signal application electrode and a second RF signal application electrode; two output terminals of the local oscillator signal distribution directional coupler are connected to the first RF signal application electrode and the second RF signal application electrode, respectively; an output of the local oscillator is input to the switch, and two output terminals of the switch are respectively connected to two input terminals of the local oscillator signal distribution directional coupler; 2. The transmission directivity control device according to claim 1, wherein the frequency shift high / low indication circuit controls the sideband generated by the optical modulator to be either an upper sideband or a lower sideband by switching the path state of the switch.

3. 3. The transmission directivity control device according to claim 1, wherein the frequency shift height instruction circuit instructs the filter to shift from a relatively low frequency to a relatively high frequency within a frequency band that can be passed through the filter when the direction of the transmission beam is a first direction, and instructs the filter to shift from a relatively high frequency to a relatively low frequency within a frequency band that can be passed through the filter when the direction of the transmission beam is a second direction different from the first direction.

4. the array antenna is a two-dimensional array antenna in which the antenna elements are arranged in a first direction and a second direction, The loop circuit includes a first loop circuit and a second loop circuit, the first loop circuit applies a delay to the optical signal in the first direction; 3. The transmission directivity control device according to claim 1, wherein the second loop circuit applies a delay to the optical signal in the second direction.

5. a plurality of the transmission directivity control devices according to claim 4; a multiplexer that multiplexes optical signals input from the plurality of transmission directivity control devices; a two-dimensional array antenna including a demultiplexer that outputs an optical signal input from the multiplexer from different predetermined output terminals according to the frequency, and a plurality of antenna elements that photoelectrically convert the optical signal output from the output terminal of the demultiplexer and radiate the converted signal into space, the antenna elements being arranged in a first direction and a second direction; A transmission system comprising:

6. The loop circuit shifts the frequency of the input optical signal to either a higher frequency or a lower frequency depending on the number of times the signal has circulated. the loop circuit provides a delay time to the input optical signal according to the number of times it has circulated; an initial optical signal, which is an optical signal to be transmitted, or an optical signal output from the loop circuit is distributed to the loop circuit and the array antenna, respectively; The loop circuit includes: The frequency of the input optical signal is changed by a predetermined amount to the high-frequency side or the low-frequency side by an optical frequency shifter, only optical signals of a predetermined frequency band are passed by a filter, and the optical signal is delayed by a predetermined time by a delay circuit. a direction indicating circuit that determines a delay time in the delay circuit based on beam direction information that is information regarding the beam direction; a frequency shift level indicating circuit that determines whether the optical frequency shifter should shift the frequency to a higher frequency side or a lower frequency side based on the beam direction information; a light source frequency indicating circuit for determining a frequency of the initial optical signal based on the beam direction information; The array antenna outputs an input optical signal from a predetermined different output terminal according to a frequency, and performs photoelectric conversion on the optical signal output from the output terminal, and radiates the converted signal into space from a plurality of antenna elements. Transmission directivity control method.

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