Reception directivity control device and reception directivity control method

Abstract

One aspect of the present invention is a reception directivity control device comprising: a loop circuit which, with respect to an optical signal obtained by converting electromagnetic waves arriving from space into electric signals and performing photoelectric conversion, shifts the frequency to either a high frequency side or a low frequency side in accordance with the number of orbits, and imparts a delay time to the optical signal; and a distribution unit that distributes an initial optical signal, which is an optical signal before being input into the loop circuit, and an optical signal output from the loop circuit, to respective paths connecting to the loop circuit and an output terminal.

Description

[Technical Field]

[0001] The present invention relates to a receiving directivity control device and a receiving 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, millimeter-wave band wireless LAN (Local Area Network) systems, and the like, phased array antennas that perform weighting using analog circuits are widely used.

[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 the antenna element. Therefore, 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 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 at the same spacing as 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] Therefore, it has been proposed to apply optical circuit manufacturing technology that enables compact implementation of low-loss waveguides. For example, Non-Patent Document 2 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 the weighting circuit increases with the number of antenna elements. Therefore, technology is needed to minimize the increase in the number of components while dealing with an increase in the number of antenna elements. In addition, a method to prevent the need for a three-dimensional structure to control a two-dimensional array is strongly desired.

[0009] 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 number of circuit components corresponding to the number of antenna elements.

[0010] The beam forming means using wavelength multiplexing disclosed in Patent Document 2 is also thought to be expandable to a larger number of elements. However, as the number of antenna elements increases, 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.

[0011] In Non-Patent Document 3, an input optical signal is circulated multiple times through a loop circuit, and a predetermined time delay and optical frequency shift are applied to the optical signal with each circumnavigation. This process allows multiple optical signals with different wavelengths and delay times to be output. Therefore, it is possible to feed RF signals with different time delays to each element of a one-dimensional phased array antenna. Non-Patent Document 3 also discloses a method for scanning a transmission 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 makes it possible to increase the size of the array antenna that can be controlled without increasing the size of the beam scanning circuit. However, while the configuration of a transmission directivity control device is disclosed, there is no disclosure regarding reception directivity control. [Prior art documents] [Patent documents]

[0012] [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]

[0013] [Non-Patent Document 1] 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, Vol. 14, No. 3, 2020, pp. 222-231. [Non-patent document 2] 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 3] 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. Summary of the Invention [Problem to be solved by the invention]

[0014] In view of the above circumstances, an object of the present invention is to provide a technology that can achieve reception directivity without increasing the number of components that make up a phase weighting circuit for beam scanning in accordance with the number of antenna elements. [Means for solving the problem]

[0015] One aspect of the present invention is a receiving directivity control device that includes a loop circuit that shifts the frequency of an optical signal obtained by converting an electromagnetic wave arriving from space into an electrical signal and then photoelectrically converting the electrical signal to either the high-frequency side or the low-frequency side 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 before being input to the loop circuit, or an optical signal output from the loop circuit, to paths leading to the loop circuit and an output terminal, respectively.

[0016] One aspect of the present invention is a receiving directivity control method in which a loop circuit converts an electromagnetic wave arriving from space into an electrical signal and then photoelectrically converts the electrical signal to obtain an optical signal, and shifts the frequency to either the higher frequency side or the lower frequency side depending on the number of times the signal has circulated, and imparts a delay time to the optical signal, and a distributor distributes an initial optical signal, which is the optical signal before being input to the loop circuit, or an optical signal output from the loop circuit, to paths leading to the loop circuit and an output terminal, respectively. [Effects of the Invention]

[0017] According to the present invention, it is possible to realize reception directivity without increasing the number of components constituting a phase weighting circuit for beam scanning in accordance with the number of antenna elements. [Brief explanation of the drawings]

[0018] [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 receiving system 100 according to the present invention. [Figure 5] 2 is a diagram illustrating a channel arrangement and passbands of a BPF and an LPF according to the first embodiment. FIG. [Figure 6] 3 is a diagram showing the relationship between the frequency and delay of each signal component of an optical signal in the scanning loop circuit 11. FIG. [Figure 7] FIG. 10 is a diagram illustrating a specific example of a delay circuit. [Figure 8] FIG. 10 is a diagram illustrating a configuration of a modified example of the first embodiment. [Figure 9] FIG. 10 is a diagram illustrating a channel arrangement and passbands of a BPF and an LPF in a modified example of the first embodiment. [Figure 10] 3 is a diagram showing the relationship between the frequency and delay of each signal component of an optical signal in the scanning loop circuit 11. FIG. [Figure 11] FIG. 10 is a diagram illustrating an example of the configuration of a second embodiment of the receiving system 100 according to the present invention. [Figure 12] FIG. 10 is a diagram illustrating a channel arrangement and passbands of a BPF and an LPF according to a second embodiment. [Figure 13] FIG. 2 is a diagram showing the relationship between the frequency and arrival time of a signal on each channel. [Figure 14] FIG. 10 is a diagram illustrating a configuration example of a third embodiment. [Figure 15] FIG. 10 is a diagram illustrating a configuration example of a fourth embodiment. [Figure 16] FIG. 2 is a diagram illustrating the passband characteristics of each filter. DETAILED DESCRIPTION OF THE INVENTION

[0019] 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.

[0020] (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.

[0021] 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.

[0022] 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).

[0023] 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. 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 .

[0024] 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.

[0025] 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.

[0026] 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.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] However, although the above-mentioned transmission technology exists, there is a problem in that the reception technology has not been established.

[0031] (Outline of this embodiment) Three embodiments of the configuration of the present invention will be described below. In the first embodiment, a scanning loop circuit is used to implement time delay and frequency shift of the optical signal, thereby controlling the receiving directivity using a one-dimensional array antenna. In the second embodiment, a two-dimensional array antenna is used to control the receiving directivity. In the third embodiment, multi-beam operation is performed. In the fourth embodiment, scanning is possible not only on one side but also on both sides of the boresight direction. Specific descriptions will be given below. Note that a description of some of the configuration that is the same as that of the conventional transmission system 900 described above will be omitted.

[0032] [First embodiment] FIG. 4 is a diagram showing an example of the configuration of a first embodiment of a receiving system 100 according to the present invention. As shown in FIG. 4, the receiving system 100 includes an array antenna 50 and a receiving directivity control device 10. The array antenna 50 includes a multiplexer 500, antenna elements 511 (Rx1), 521 (Rx2), and 531 (Rx3), optical modulators 512 to 532, a light source 54, and a demultiplexer 55. In the following description, for ease of explanation, the antenna elements 511, 521, and 531 may be referred to as antenna element Rx1, antenna element Rx2, and antenna element Rx3, respectively. Furthermore, signals received by the antenna elements Rx1, Rx2, and Rx3, and optical signals generated by the optical modulator 512 based on the received signals, may be referred to as "Rx1," "Rx2," and "Rx3," respectively.

[0033] The light source 54 generates light of multiple frequencies. Each optical modulator modulates the light from the light source 54 with the output of each antenna element to generate first to third optical signals. The multiplexer 500 multiplexes the first to third optical signals. The reception directivity control device 10 comprises a direction indicating circuit 101, a directional coupler 102, a band pass filter (hereinafter referred to as "BPF") 103, and a scanning loop circuit 11. The output of the reception directivity control device 10 is an optical signal that is output from a reception signal output terminal.

[0034] The scanning loop circuit 11 includes a low-pass filter (hereinafter referred to as "LPF") 104, an RF local oscillator 105, an optical SSB modulator 106, an amplifier 107, and a delay circuit 108. An optical signal is input to the scanning loop circuit 11 from a fourth terminal of a directional coupler 102. The directional coupler 102 distributes the input optical signal to a path that outputs the signal as a received signal via a BPF 103 and a path that is connected to the scanning loop circuit 11, and outputs the distributed signal. The directional coupler 102 is configured using a device that has such a distribution function. The directional coupler 102 is a specific example of a distribution unit. The distribution unit may be implemented using a device other than a directional coupler.

[0035] The optical signal input to the scanning loop circuit 11 is input to the optical SSB modulator 106 via the LPF 104. The optical SSB modulator 106 generates and outputs an upper sideband (USB) by carrier suppressed single sideband modulation. The optical signal output from the optical SSB modulator 106 is amplified by an amplifier 107, and a delay amount is applied to the optical signal by a delay circuit 108. The delay circuit 108 is configured to be able to change the amount of delay applied to the optical signal. The optical signal delayed by the delay circuit 108 is input to a second terminal of the directional coupler 102.

[0036] An RF local oscillator 105 is connected to the optical SSB modulator 106. The RF local oscillator 105 generates an unmodulated RF (radio frequency) signal (hereinafter referred to as the "local RF signal") with a frequency Δf and outputs it to the optical SSB modulator 106. The optical SSB modulator 106 is configured so that the frequency of the optical signal shifts by Δf while the optical signal passes through. The time required for the optical signal to make one circuit around the scanning loop circuit 11 is Δτ, which can be changed by changing the delay time of the delay circuit 108.

[0037] The direction indication circuit 101 controls the time delay amount Δτ in the delay circuit 108 based on the beam direction information input to the reception directivity control device 10. The beam direction information is information relating to the beam direction of the reception beam when the RF signal is received by the array antenna 50. The beam direction information may be information indicating the beam direction itself, or may be identification information (e.g., a beam number) that is set in advance and linked to the beam direction.

[0038] Here, three optical frequency channels are defined. As shown in FIG. 5, they are designated ch1 to ch3 from the high frequency side. The interval between the three channels is Δf. The passbands of BPF 103 and LPF 104 are set as shown in FIG. 5. That is, BPF 103 passes one or more consecutive frequency channels on the high frequency side, including the highest frequency channel, among the frequency channels in the frequency band to be output as the received signal. LPF 104 passes one or more consecutive frequency channels on the low frequency side, including the lowest frequency channel, among the frequency channels in the frequency band to be output as the received signal. It is preferable that the frequency channels passed by BPF 103 and the frequency channels passed by LPF 104 do not overlap. It is also preferable that all frequency channels in the frequency band to be output as the received signal can pass through at least one of BPF 103 and LPF 104.

[0039] The operation of the receive directivity control device 10 will be described below when a received RF signal arrives from the lower left direction in Figure 4 and a beam is received in that direction. The received RF signal arrives at antenna elements Rx3, Rx2, and Rx1 in that order, with a time difference of Δτ between each. Therefore, to operate as a phased array antenna, it is necessary to add a time delay of Δτ to the received signals output from each antenna element so that the arrival time differences between them are aligned, and then add the three received signals together. In the receive directivity control device 10, the process of adding the time delay Δτ is performed using a scanning loop circuit 11.

[0040] The received RF signal radio waves that have reached the antenna elements Rx1 to Rx3 and the respective light beams of ch1 to ch3 generated by the light source 54 are input to the optical modulators 512 to 532. The optical modulators 512 to 532 convert the respective light beams of ch1 to ch3 input from the light source 54 into optical signals of ch1 to ch3, respectively, based on the received RF signal radio waves. The optical modulators 512 to 532 output the optical signals to the multiplexer 500. The multiplexer 500 combines the optical signals of ch1 to ch3 and inputs the combined optical signals to the reception directivity control device 10. The input optical signal is input to the first terminal of the directional coupler 102 and is branched into two components. The relationship between the frequency and delay of each signal component at this point is shown in FIG. 6(A). This point is designated as time 0.

[0041] One component of the optical signal passes from the third terminal of directional coupler 102 through BPF 103, and only the ch1 component (i.e., the received signal component of antenna element Rx1) which is in the passband of BPF 103 is output from the received signal output terminal. The other component (the optical signal input to scanning loop circuit 11) passes from the fourth terminal of directional coupler 102 through LPF 104 and begins to circulate in scanning loop circuit 11. This component of the optical signal is the optical signal of the ch2 and ch3 components (i.e., the received signal components of antenna elements Rx2 and Rx3) which are in the passband of LPF 104, and its frequency is shifted higher by Δf in optical SSB modulator 106.

[0042] Next, the optical signal is amplified by amplifier 107, and a predetermined time delay is given to it by delay circuit 108. The time delay given by delay circuit 108 is set so that the delay given after one loop around scanning loop circuit 11 is Δτ. The optical signal that has circulated around scanning loop circuit 11 is input from the second terminal of directional coupler 102 and branched into two components. The time at this point is Δτ, and the relationship between the frequency and delay of each signal component at this point is shown in Figure 6(B).

[0043] One component passes through the third terminal of directional coupler 102, passes through BPF 103, and is output from the received signal output terminal. The other component passes through the fourth terminal of directional coupler 102 and begins circulating through scanning loop circuit 11 again. As shown in FIG. 6(B), the Rx2 component has a frequency of ch1, so it passes through BPF 103 and is output from the received signal output terminal. On the other hand, the Rx3 component does not pass through BPF 103, but passes through LPF 104 and is input again to optical SSB modulator 106, where it circulates through scanning loop circuit 11. In other words, at this point, the only component remaining as a signal circulating through scanning loop circuit 11 is Rx3.

[0044] The optical signal that has circulated through the scanning loop circuit 11 a second time is input from the second terminal of the directional coupler 102 and split into two components. The time at this point is 2Δτ, and the relationship between the frequency and delay of each signal component at this point is shown in FIG. 6(C). One component passes through the third terminal of the directional coupler 102, then through the BPF 103, and is output from the received signal output terminal. The other component passes through the fourth terminal of the directional coupler 102 and begins circulating through the scanning loop circuit 11 again. As shown in FIG. 6(C), the Rx3 component has a frequency of ch1, so it passes through the BPF 103 and is output from the received signal output terminal. On the other hand, the optical signal input from the fourth terminal of the directional coupler 102 to the LPF 104 (only the Rx3 component, as explained above) does not pass through the LPF 104 and therefore does not circulate through the scanning loop circuit 11.

[0045] After undergoing the above processing, the signal components received by antenna elements Rx1 to Rx3 all have the same frequency, ch1, and a delay of 2Δτ, which are then output from the received signal output terminal. The direction indicator circuit 101 adjusts the time delay of delay circuit 108 to adjust Δτ depending on the angle of arrival of the received RF signal wave and the spacing between the antenna elements. This processing allows the desired receive beam scanning to be performed.

[0046] To perform the above-described operation, it is necessary to match the phase of the optical signal at the reception signal output terminal (the terminal that outputs the output of BPF 103 to the outside of the reception directivity control device 10). For this reason, the delay amount Δτ in delay circuit 108 is configured to be an integer multiple of the wavelength of the light. As a method for configuring a delay line so that the phase rotation amount is an integer multiple of 2π at any optical frequency, for example, the configuration shown in FIG. 7 can be used. 2^M (2 to the Mth power) unit delay lines, each with a delay line length L and a delay time τ0, are connected in series and configured by connecting these sets using a changeover switch whose optical path length is sufficiently shorter than L. In FIG. 7, three sets are connected, and a variable delay line with a delay time τ = 0 to 7τ0 can be configured.

[0047] Here, if the frequency of ch1 is f0 and k is a natural number greater than or equal to 2, then ch(k-1), that is, the wave number in the unit delay line at frequency (f0+kΔf) (the length L of the unit delay line and the wavelength λ of the light of that frequency) g The ratio of (

[0048]

number

[0049] where c g is the speed of light in the unit delay line. This value should be an integer, so for example, f0 and Δf should be set so that the values ​​of the following two equations in Equation 1 are integers.

[0050]

number

[0051]

number

[0052] A specific calculation example is shown below. L=10mm, c g= 0.7c0, f0 = 193.55 THz. The value of Equation 2 is quite large. Therefore, by fine-tuning f0, it is possible to make it an integer. The required value of Δf is determined from the optical frequency bandwidth to be occupied. For example, if you want Δf to be around 100 GHz, you can set the value of Δf to 105 GHz, and the value of Equation 3 will be 48, which can be made an integer. The value of L can also be fine-tuned.

[0053] As described above, the receive directivity control device 10 of the first embodiment is connected to a linear array antenna 50 in which three antenna elements are arranged vertically. In the first embodiment, the number of antenna elements is three, but other numbers may be used. The present invention has the advantage that the number of circuit components can be kept constant regardless of the number of antenna elements. Therefore, it is desirable to implement the configuration of the first embodiment when the number of antenna elements is large.

[0054] [Variations] Next, a modified example of the first embodiment will be described. FIG. 8 is a diagram showing the configuration of the modified example of the first embodiment. Below, only differences from the reception directivity control device 10 of the first embodiment will be described. The RF local oscillator 105 included in the scanning loop circuit 11 generates an RF (radio frequency) unmodulated signal (local RF signal) with a frequency of 3Δf. Therefore, in the optical SSB modulator 106 of the scanning loop circuit 11, the frequency of the optical signal is shifted by 3Δf toward the high-frequency side while it passes through. Here, five optical frequency channels are defined. As shown in FIG. 9, from the high-frequency side (the right side of FIG. 9), they are ch1, ch2a, ch3a, ch2, and ch3. The spacing between the first three channels is Δf, the spacing between ch2a and ch2 is 3Δf, and the spacing between ch3a and ch3 is 6Δf. The passbands of the BPF 103 and the LPF 104 are set as shown in FIG. 9. Although the number of antennas in this modified example is three, channels can be assigned in a similar manner even when the number of antennas is greater than this.

[0055] The operation of the reception directivity control device 10 when a received RF signal wave arrives from the lower left direction of FIG. 8 and a beam is received in that direction will be described.

[0056] The received RF signal radio waves arrive at the antenna elements Rx3, Rx2, and Rx1 in that order, with a time difference of Δτ between each. Therefore, to operate as a phased array antenna, it is necessary to add together the three received signals by applying a time delay of Δτ to the received signals output from each antenna element so that the arrival time differences between them are uniform. In the reception directivity control device 10, the process of applying the time delay Δτ is performed using a scanning loop circuit 11.

[0057] The received RF signal radio waves that have reached the antenna elements Rx1 to Rx3 and the respective light beams of ch1 to ch3 generated by the light source 54 are input to the optical modulators 512 to 532. The optical modulators 512 to 532 convert the respective light beams of ch1 to ch3 input from the light source 54 into optical signals of ch1 to ch3, respectively, based on the received RF signal radio waves. The optical modulators 512 to 532 output the optical signals to the multiplexer 500. The multiplexer 500 combines the optical signals of ch1 to ch3 and inputs the combined optical signals to the reception directivity control device 10. The input optical signal is input to the first terminal of the directional coupler 102 and is branched into two components. The relationship between the frequency and delay of each signal component at this point is shown in FIG. 10(A). This point is designated as time 0.

[0058] One component of the optical signal passes from the third terminal of directional coupler 102 through BPF 103, and only the ch1 component (i.e., the received signal component of antenna element Rx1) within the passband of BPF 103 is output from the received signal output terminal. The other component (the optical signal input to scanning loop circuit 11) passes from the fourth terminal of directional coupler 102 through LPF 104 and begins circulating in scanning loop circuit 11. This component of the optical signal is the optical signal of the ch2 and ch3 components (i.e., the received signal components of antenna elements Rx2 and Rx3) within the passband of LPF 104, and its frequency is shifted higher by 3Δf in optical SSB modulator 106.

[0059] Next, the optical signal is amplified by amplifier 107, and a predetermined time delay is given to it by delay circuit 108. The time delay given by delay circuit 108 is set so that the delay given after one loop around scanning loop circuit 11 is Δτ. The optical signal that has circulated around scanning loop circuit 11 is input from the second terminal of directional coupler 102 and branched into two components. The time at this point is Δτ, and the relationship between the frequency and delay of each signal component at this point is shown in Figure 10(B).

[0060] One component passes through the third terminal of directional coupler 102, passes through BPF 103, and is output from the received signal output terminal. The other component passes through the fourth terminal of directional coupler 102 and begins circulating through scanning loop circuit 11 again. As shown in FIG. 10(B), the Rx2 component has a frequency of ch1, so it passes through BPF 103 and is output from the received signal output terminal. On the other hand, the Rx3 component does not pass through BPF 103, but passes through LPF 104 and is input again to optical SSB modulator 106, where it circulates through scanning loop circuit 11. In other words, at this point, the only component remaining as a signal circulating through scanning loop circuit 11 is Rx3.

[0061] The optical signal that has circulated through the scanning loop circuit 11 for the second time enters the second terminal of the directional coupler 102 and is split into two components. The time at this point is 2Δτ, and the relationship between the frequency and delay of each signal component at this point is shown in FIG. 10(C). One component passes through the third terminal of the directional coupler 102, then through the BPF 103, and is output from the received signal output terminal. The other component passes through the fourth terminal of the directional coupler 102 and begins circulating through the scanning loop circuit 11 again. As shown in FIG. 10(C), the Rx3 component has a frequency of ch1, so it passes through the BPF 103 and is output from the received signal output terminal. On the other hand, the optical signal input from the fourth terminal of the directional coupler 102 to the LPF 104 (only the Rx3 component, as explained above) does not pass through the LPF 104 and therefore does not circulate through the scanning loop circuit 11.

[0062] After undergoing the above-described processing, the frequencies of the signal components received by the antenna elements Rx1 to Rx3 are ch1, ch2a, and ch3a, respectively, with a time delay of 2Δτ, and are input to the demultiplexer 110. The input optical signal is demultiplexed by the demultiplexer 110 and input to the converters 111 to 113, respectively. Each of the converters 111 to 113 converts the optical signal into an electrical signal. Each of the converters 111 to 113 may be configured using, for example, a photomixer. The RF signals output from the converters 111 to 113 are all added together by an adder and output from a received signal output terminal.

[0063] By adopting the above-described configuration, the direction indicating circuit 101 can adjust the time delay amount of the delay circuit 108 to adjust Δτ depending on the arrival angle of the received RF signal radio wave and the spacing between the antenna elements, thereby enabling the desired receiving beam scanning.

[0064] [Second embodiment] FIG. 11 is a diagram showing an example of the configuration of a second embodiment of a receiving system 100 according to the present invention. The following describes the second embodiment of the receiving system 100, focusing mainly on the differences from the first embodiment. Descriptions of configurations that operate in the same way as in the first embodiment may be omitted. The receiving system 100 of the second embodiment includes an array antenna 50. The array antenna 50 of the second embodiment is configured as a two-dimensional array antenna. The two-dimensional array antenna has a two-dimensional array antenna surface 700. The receiving directivity control device 10 of the second embodiment controls the receiving directivity of the two-dimensional array antenna 50 to scan a two-dimensional receiving beam.

[0065] The two-dimensional array antenna surface 700 has nine receiving antenna elements Rx1a, Rx1b, . . . Rx3c arranged in three rows and three columns, as shown in FIG. 11. Each modulator connected to each antenna element of the two-dimensional array antenna uses an RF signal received by the two-dimensional array antenna surface 700 to modulate light of frequencies ch1, ch2, . . . ch9 generated by the light source 54, generating a first optical signal, a second optical signal, . . . . ninth optical signal, respectively. These nine optical signals are multiplexed into a single optical waveguide by the first horizontal scanning multiplexer 500a, the second horizontal scanning multiplexer 500b, the third horizontal scanning multiplexer 500c, and the vertical scanning multiplexer 600. The multiplexed optical signal is then input to a first terminal of the directional coupler 102a of the reception directivity control device 10.

[0066] As shown in Fig. 11, scanning loop circuits 11 are arranged in two stages in series, with vertical scanning loop circuit 11a and horizontal scanning loop circuit 11b, arranged from the side closest to the plane of two-dimensional array antenna 700. As shown in Fig. 12, nine optical frequency channels are defined in reception directivity control device 10, designated ch9, ch8, ..., ch1, respectively, from the lowest frequency side. The passbands of LPF_V104a, BPF_V103a, LPF_H104b, and BPF_H103b are set as shown in Fig. 12. Based on beam direction information input to reception directivity control device 10, direction indicator circuit 101 controls the time delays in horizontal scanning delay circuit 108b and vertical scanning delay circuit 108a.

[0067] The operation of the receiving directivity control device will be described when a received RF signal wave arrives at the two-dimensional array antenna surface 700 from the lower left with respect to the front direction of the two-dimensional array antenna surface 700 (left direction in Figure 11) and the beam is directed in that direction for reception.

[0068] The received RF signal wave has a frequency of Δτ in the vertical plane. V In the horizontal plane, the time difference is Δτ HAssume that the nine received signals arrive at each antenna element with a time difference of 1 / 2 m / s. In this case, to operate the receiving system 100 as a phased array antenna, it is sufficient to add together the nine received signals by applying a time delay to the received signals output from each antenna element so that the arrival time differences are uniform. In the reception directivity control device 10 of this embodiment, the process of applying the required time delay is performed using a vertical scanning loop circuit 11a and a horizontal scanning loop circuit 11b.

[0069] The received RF signal waves that reach each of the antenna elements Rx1a to Rx3c are input to the respective modulators and converted into optical signals of ch1 to ch9. The optical signals of ch1 to ch9 are combined by multiplexers (500a to 500c and 600) and input to the first terminal of directional coupler 102a in vertical scanning loop circuit 11a, where they are branched into two components. Figure 13 shows the relationship between the frequency of each signal component at this point and the relative arrival time (delay) at this terminal. The arrival time of receiving antenna Rx3c, which is the signal component that arrives first at this terminal, and the arrival time of receiving antenna Rx1a, which is the signal component that arrives last at this terminal, are separated by (2ΔτV + 2ΔτH).

[0070] First, an optical signal (frequency: ch9) from the receiving antenna Rx3c is input to the first terminal of the directional coupler 102a of the vertical scanning loop circuit 11a. Since the frequency of this optical signal is ch9, it cannot pass through the BPF_V103a and passes through the LPF_V104a. This optical signal makes one circuit through the vertical scanning loop circuit 11a, and its frequency is changed to Δf in the optical SSB modulator 106a. VThe optical signal is then input to the second terminal of the directional coupler 102a and output from the third and fourth terminals. The output optical signal cannot pass through the BPF_V103a, but passes through the LPF_V104a, circulating in the vertical scanning loop circuit 11a. The frequency of this optical signal then becomes ch3, allowing it to pass through the BPF_V103a and be input to the subsequent horizontal scanning loop circuit 11b. In this way, the optical signal from the receiving antenna Rx3c, which is the signal component output first from the vertical scanning multiplexer 600, has its frequency shifted to ch3 by 2ΔfV in the vertical scanning loop circuit 11a, and is input to the horizontal scanning loop circuit 11b connected downstream with a time delay of 2ΔτV.

[0071] The optical signal from receiving antenna Rx3c makes two circuits in horizontal scanning loop circuit 11b. During this time, the operation of BPF_H 103b and LPF_H 104b, the frequency shift by optical SSB modulator 106b, and the time delay by horizontal scanning delay circuit 108b are all the same as those in vertical scanning loop circuit 11a. As a result, the frequency is shifted higher by 2ΔτH to become ch1, and the time is delayed by (2ΔτV + 2ΔτH), including the delay in vertical scanning loop circuit 11a, before being output from the received signal output terminal.

[0072] To summarize the processing of the signal from receiving antenna Rx3c, the signal from receiving antenna Rx3c makes two rounds through vertical scanning loop circuit 11a and two rounds through horizontal scanning loop circuit 11b, and is finally delayed by (2ΔτV + 2ΔτH) and output from the received signal output terminal at frequency ch1.

[0073] Similarly, the number of times the vertical scanning loop circuit 11a and horizontal scanning loop circuit 11b are turned on is determined by the frequency for processing the signals from the other eight receiving antennas. This determines the amount of time delay that is applied, and the signal is output from the received signal output terminal on frequency channel ch1. In this way, all nine received signal components are output from the received signal output terminal at the same time. As a result, they are combined in phase, enabling operation as a receiving phased array antenna.

[0074] In the second embodiment, the two-dimensional antenna array has nine elements, three elements arranged vertically and three elements arranged horizontally, but the number of antenna elements may be any number. Also, although the scanning direction is horizontal and vertical, other combinations of directions (for example, vertical and horizontal, east-west and north-south, etc.) may also be used.

[0075] [Third embodiment] FIG. 14 is a diagram showing an example configuration of the third embodiment. The receiving system 100 of the third embodiment performs multi-beam receiving operation with two beams. The output of the multiplexer 500 is equally divided by the divider 800 and input to the scanning loop circuits 11 of the two receiving directivity control devices 10. By adjusting the delay time in each scanning loop circuit 11, it is possible to perform scanning of the two receiving beams independently. Although an example configuration with two beams is shown here, three or more beams can be achieved by similarly increasing the number of scanning loop circuits 11 in the receiving directivity control device 10. Furthermore, a configuration for controlling a two-dimensional array antenna 50 as shown in the second embodiment above may also be used, and the number of antenna elements is not limited to this.

[0076] [Fourth embodiment] 15 is a diagram showing an example of the configuration of the fourth embodiment. The receiving system 100 of the fourth embodiment scans a beam in both upward and downward directions. As in the first embodiment, an optical SSB modulator 106 is used to change the optical frequency. In the fourth embodiment, the optical SSB modulator 106 has two RF signal application electrodes 1061 and 1062. Two outputs of an RF directional coupler 142 are connected to the RF signal application electrodes 1061 and 1062, respectively. The output terminal of the RF local oscillator 105 is connected to two input terminals of the RF directional coupler 142 via an RF switch 141, and the local RF signal is input to one of the input terminals of the RF directional coupler 142 depending on the state of the RF switch 141. Depending on the state of the RF switch 141, the phase relationship of the local RF signals applied to the two RF signal application electrodes 1061 and 1062 of the optical SSB modulator 106 can be switched between two states: one where one is delayed by 90° from the other, and one where one is advanced by 90° from the other. In the former state, the optical SSB modulator 106 performs USB modulation, and in the latter state, it performs LSB modulation. This configuration makes it possible to switch the direction of the frequency shift by the optical SSB modulator 106. This switching allows the direction of the received beam to be set over a wider range. Specifically, for example, in the example of FIG. 15, the received beam can be scanned in both the lower left and upper left directions.

[0077] When the beam direction is downward in Figure 15, the optical SSB modulator 106 generates a USB and shifts the frequency to a higher frequency. When the beam direction is upward in the figure, the optical SSB modulator 106 generates a LSB and shifts the frequency to a lower frequency. At this time, the optical signal output from output terminal 3 of directional coupler 102 is passed through HPF@ch1 (122) by first switch 121 when the beam direction is downward in the figure, and is output as a received signal. When the beam direction is upward in the figure, the optical signal output from output terminal 3 of directional coupler 102 is passed through LPF@ch3 (123) by first switch 121, and is output as a received signal.

[0078] Furthermore, when the beam direction is downward in the drawing, the optical signal output from output terminal 4 of directional coupler 102 is output to optical SSB modulator 106 via LPF@ch2,3 (132) by second switch 131. When the beam direction is upward in the drawing, the optical signal output from output terminal 4 of directional coupler 102 is output to optical SSB modulator 106 via HPF@ch1,2 (133) by second switch 131.

[0079] 16 is a diagram showing the passband characteristics of each filter. The direction indication circuit 101 has the function of controlling the amount of time delay in the delay circuit 108 and the paths of the first switch 121, second switch 131, and RF switch 141 based on the beam direction information input to the reception directivity control device 10.

[0080] With this configuration, the fourth embodiment also performs the same optical frequency conversion, time delay, and frequency filtering operations as the first embodiment. Furthermore, in the fourth embodiment, the direction of the received beam can be scanned not only downward in the drawing but also upward.

[0081] Although the above description assumes that the number of antenna elements is three, other numbers may be used. For example, the present invention has the advantage of being able to maintain a constant number of circuit components regardless of the number of antenna elements. Therefore, by implementing the present invention when the number of antenna elements is large, the number of components can be reduced. Furthermore, as in the second embodiment, the antenna array may be arranged two-dimensionally, and scanning loop circuits 11 may be provided in two stages to control beam scanning in the horizontal and vertical directions, respectively. Two-dimensional receive beam scanning may be performed in the up, down, left, and right directions by assigning appropriate optical frequencies to each antenna element and setting the passband of each filter.

[0082] The direction indication circuit 101 is configured using a processor such as a CPU (Central Processing Unit) and a memory. The direction indication circuit 101 may be realized by the processor executing a program. Note that all or part of the functions of the direction indication circuit 101 may be realized using hardware such as an ASIC (Application Specific Integrated Circuit), a PLD (Programmable Logic Device), or an FPGA (Field Programmable Gate Array). The program may be recorded on a computer-readable recording medium. Examples of computer-readable recording media include portable media such as flexible disks, magneto-optical disks, ROMs, CD-ROMs, and semiconductor storage devices (e.g., SSDs: Solid State Drives), as well as storage devices such as hard disks and semiconductor storage devices built into computer systems. The program may be transmitted via a telecommunications line.

[0083] Furthermore, by performing phase shifting using analog circuits, the number of analog-to-digital converters can be significantly reduced compared to fully digitally controlled array antennas in which phase shifting is performed entirely through digital signal processing. Furthermore, because phase shifting is performed through analog processing of optical signals, it can be applied to circuits that electronically, rather than mechanically, perform beam scanning when emitting radio waves, as well as when emitting light in free-space optical communication (FSO communication). In current FSO communications, the radiation direction is adjusted using a mechanically driven device, which raises issues regarding the weight and mass productivity of the device, as well as operational and maintenance issues due to operating speed and durability. However, if electronic scanning of optical beams becomes possible, these issues can be resolved. [Industrial Applicability]

[0084] 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, as well as in high-definition imaging and radar. This technology can be applied to a receiving directivity control device that receives radio waves with dynamic directivity in such phased array antennas. [Explanation of symbols]

[0085] 100...receiving system, 10...receiving directivity control device, 101...direction indication circuit, 102...directional coupler, 103...bandpass filter, 104...lowpass filter, 105...RF local oscillator, 106...optical SSB modulator, 107...amplifier, 108...delay circuit, 11...loop circuit, 50...array antenna, 500a to 500c...horizontal scanning combiner, 600...vertical scanning combiner, 700...two-dimensional array antenna surface

Claims

1. A plurality of antenna elements; a loop circuit that receives electromagnetic waves arriving from space using the antenna element, converts them into electrical signals, and modulates light based on the electrical signals to obtain optical signals, and shifts the frequency of the optical signals to either a higher frequency side or a lower frequency side depending on the number of times the signals have circulated around the same circuit, thereby providing a delay time; a distributor that distributes an initial optical signal, which is an optical signal before being input to the loop circuit, or an optical signal output from the loop circuit, to paths that are connected to the loop circuit and an output terminal; Equipped with the loop circuit has 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, and a delay circuit that delays the optical signal by a predetermined time; further comprising a band-pass filter disposed between the distribution unit and the output terminal, and a low-pass filter disposed between the distribution unit and the optical frequency shifter, A receiving directivity control device, wherein the band passed by the band-pass filter does not overlap with the band passed by the low-pass filter.

2. A receiving directivity control device as described in claim 1, wherein all frequency channels in the frequency band of the output optical signal can pass through at least one of the band-pass filter and the low-pass filter.

3. A plurality of antenna elements receive electromagnetic waves arriving from space and convert them into electrical signals, a loop circuit that modulates light based on the electrical signal, and shifts the frequency of the optical signal to either a higher frequency side or a lower frequency side depending on the number of times the optical signal has circulated around the same circuit, and provides a delay time; a distribution unit that distributes an initial optical signal, which is an optical signal before being input to the loop circuit, or an optical signal output from the loop circuit, to paths that are connected to the loop circuit and an output terminal, respectively; the loop circuit has an optical frequency shifter, a filter, and a delay circuit, the optical frequency shifter shifts the frequency of the input optical signal to a higher or lower frequency by a predetermined amount, the filter passes only optical signals in a predetermined frequency band, and the delay circuit delays the optical signal by a predetermined time; a band-pass filter disposed between the distribution unit and the output terminal passes an optical signal of a predetermined band, and a low-pass filter disposed between the distribution unit and the optical frequency shifter passes an optical signal of a predetermined low band; The band that the band-pass filter passes does not overlap with the band that the low-pass filter passes. Reception directivity control method.

4. A receiving directivity control method as described in Claim 3, wherein all frequency channels in the frequency band of the output optical signal can pass through at least one of the band-pass filter and the low-pass filter.

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