Reception directivity control device and reception directivity control method

Abstract

According to the present invention, each of a plurality of antenna elements outputs a wireless signal obtained by receiving radio waves. An electro-optical conversion unit converts light output from a light source into optical signals intensity-modulated with each wireless signal obtained by each of the plurality of antenna elements. A weighting unit performs phase weighting for imparting, to each of the optical signals, a phase inclination that cancels out a phase difference occurring in a first sideband wave of the optical signal in accordance with a difference in position of the plurality of antenna elements and a desired direction that is a desired direction of arrival of the radio waves, and outputs a composite signal obtained by synthesizing the optical signals that have been subjected to the phase weighting. An extraction unit outputs a reception signal obtained by extracting the first sideband wave from the composite signal.

Description

Reception directivity control device and reception directivity control method

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

[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. Therefore, high-gain antennas are often used in high-frequency bands. High-gain antennas necessarily have high directivity. Therefore, it is necessary to align the beam direction with the other station in wireless communications. In other words, when the direction of the other station is dynamic, a means for dynamically controlling the beam direction, i.e., beam steering, is essential. Furthermore, beam steering in antennas is required not only for wireless communications but also for applications such as radar, imaging, and wireless power transmission.

[0003] As a beam steering method, methods that have been devised and used include mechanically controlling the direction of the antenna, and controlling the radio waves emitted from the antenna by refracting or reflecting them with movable lenses or reflectors. In addition to these, phased array antennas are widely used because they have high durability and movement tracking ability as they do not use mechanical moving parts, and are suitable for making antennas smaller and lighter.

[0004] A phased array antenna performs electronic beam steering by controlling (called weighting) the phase and amplitude of the RF (Radio Frequency) signal supplied to each antenna element using means such as variable delay circuits, variable attenuator circuits, and digital signal processing connected to multiple antenna elements arranged on a line or surface.

[0005] 2. Description of the Related Art Phased array antennas that perform weighting using analog circuits are widely used in fifth-generation mobile communication systems and millimeter-wave wireless LAN (Local Area Network) systems that use millimeter-wave bands.

[0006] With the advancement of high-frequency band utilization, even higher antenna gain is required. Therefore, it is expected that phased array antennas that weight a larger number of antenna elements will be required. For example, there is a method for configuring a 256-element phased array antenna for use in fifth-generation mobile communication base stations in the 28 GHz band (see, for example, Non-Patent Document 1). For sixth-generation mobile communications aiming to provide even faster transmission rates, utilization of frequency bands above 100 GHz, the so-called terahertz band (e.g., the 300 GHz 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 (free-space propagation loss increases by 20 dB). Taking this into consideration, it is expected that, for example, more than 10,000 antenna elements will be required to compensate for this with the antenna gain of the base station.

[0007] To minimize power loss to antenna elements, the RF transmission line feeding power from the phase shifter circuit to the antenna element must be as short as possible. Therefore, in high-frequency phased array antennas, particularly those in the millimeter-wave band, phase shifter circuits are typically arranged in close proximity to each antenna element. However, as the radio frequency increases, the spacing between antenna elements becomes narrower. Therefore, it becomes difficult to arrange multiple phase shifter circuits at spacings equivalent to the spacing between antenna elements. For example, when the radio frequency is 300 GHz, the free-space wavelength is 1 mm. Therefore, the spacing between antenna elements is typically half the wavelength, or 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, further increasing the difficulty.

[0008] Therefore, a method has been proposed that applies optical circuit manufacturing technology that can implement low-loss waveguides in a small size, for example, by converting signals into light and then performing weighting using an optical circuit (see, for example, Non-Patent Document 2). 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 depending on the number of antenna elements. Therefore, a method is needed that can accommodate an increase in the number of antenna elements while minimizing the increase in the number of components.

[0009] The following techniques are existing technologies for implementing weighting using optical circuits. One is an optically controlled array antenna device that controls two-dimensional multi-beams by utilizing wavelength dispersion lines (see, for example, Patent Document 1). Figure 1 of Patent Document 1 shows the configuration of an optically controlled array antenna device, and Figure 2 of Patent Document 1 shows the configuration of a multi-beam forming means that is compatible with both transmission and reception. This technology provides phase tilt in the horizontal and vertical planes by using a wavelength-tunable light source and a line that uses a waveguide with large wavelength dispersion. A one-dimensional phase shift circuit ("EL" in Figure 1 of Patent Document 1) １ ~EL Ｐ " and "AZ １ " ~ "AZ Ｎ The number of antenna elements required depends on the number of antenna elements in the vertical direction and the horizontal direction.

[0010] There is also a method of performing two-dimensional beam control using a wavelength-tunable light source and a wavelength dispersion line (see, for example, Patent Document 2). Fig. 2 of Patent Document 2 shows the configuration of a two-dimensional beam control device equipped with an array antenna of 5×13 in the vertical direction and horizontal direction. As shown in Fig. 2 of Patent Document 2, a wavelength-tunable light source #1 (wavelength λ Ｖ The light from wavelength-tunable light source #1 is distributed into a number equal to the number of vertical elements (five distributions in Fig. 2 of Patent Document 2). A phase tilt in the vertical plane is imparted to each of the distributed light beams from wavelength-tunable light source #1 by a first array of wavelength dispersion lines denoted by reference numeral 52. The light to which this phase tilt has been imparted is converted into an electric signal train by a photodiode 54, and the converted electric signal train is amplified by an amplifier 56.

[0011] Next, a wavelength tunable light source #2 (wavelength λ ＨThe light from the wavelength-tunable light source #2 is distributed into a number equal to the number of vertical elements (five distributions in Fig. 2 of Patent Document 2). The optical modulator 58 modulates each of the distributed light from the wavelength-tunable light source #2 with the electrical signal train amplified by the amplifier 56 to generate an optical signal train. Each of the optical signal trains generated by the optical modulator 58 is distributed into a number equal to the number of horizontal elements (13 distributions in Fig. 2 of Patent Document 2). A phase tilt in the horizontal plane is given to each of the distributed optical signal trains by five second wavelength dispersion line arrays denoted by reference numeral 62. By the above operation, λ Ｖ controls vertical scanning, and λ Ｈ Controls horizontal scanning.

[0012] The operation during reception will be described with reference to Fig. 3 of Patent Document 2. An optical signal is generated by intensity-modulating light from a wavelength-tunable light source 98 with a CW (Carrier Wave) at the frequency of a local signal, or so-called LO (Local Signal), by an optical modulator 104. The generated optical signal is split by an optical fiber splitter 112, and the split optical signal is given a delay gradient, i.e., a phase gradient, by a delay waveguide with large chromatic dispersion, denoted by reference numeral 114. A photodiode 116 generates an electrical local signal with a phase gradient from the optical signal obtained from the delay waveguide denoted by reference numeral 114.

[0013] The down-conversion mixer 126 included in the transmit / receive module 94 generates an intermediate frequency (IF) signal by mixing the local oscillator signal having a phase gradient generated by the photodiode 116 with the received RF signal having a phase gradient obtained from the antenna element 96. Here, the local oscillator signal is given a phase gradient according to the beam direction, so the resulting IF signal is in phase in all branches. Therefore, when the IF combiner 106 combines the resulting IF signals, only the received signals in the desired beam direction are combined in phase, resulting in a received signal.

[0014] For ease of understanding, Fig. 3 of Patent Document 2 shows only the configuration of a one-dimensional array. To adapt this to a two-dimensional array, an apparatus is configured using two wavelength-tunable light sources, similar to the configuration shown in Fig. 2, so that light with a two-dimensional phase gradient is input to a two-dimensionally arranged photomixer array. By providing an RF-band CW to the optical modulator 46 of an apparatus configured in this manner, it becomes possible to control the receiving directivity of the two-dimensional array antenna.

[0015] Japanese Patent Application Laid-Open No. 2004-023400 U.S. Patent No. 6,337,660

[0016] 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. C. Tsokos et al., "Analysis of a Multibeam Optical Beamforming Network Based on Blass Matrix Architecture," Journal of Lightwave Technology, vol. 36, no. 16, 15 Aug. 2018, pp. 3354-3372. H. Liu, X. Liu, F. Effenberger, N. Chand, X. Qi, and G. Li, "Optical Implementation of Butler Matrix for Hardware-Efficient Multiuser Beamforming," IEEE Photonics Journal, vol. 10, no. 2, April 2018, doi: 10.1109 / JPHOT.2018.2805875.

[0017] As shown in Fig. 2 of Patent Document 2, the second array of wavelength dispersion lines designated by the reference numeral 62 is composed of lines whose number matches the number of antenna elements in the horizontal direction (13 lines in the example shown in Fig. 2), and furthermore, bundles of these lines must be provided in the same number as the number of antenna elements in the vertical direction (five lines in the example shown in Fig. 2 of Patent Document 2). Therefore, 5 × 13 wavelength dispersion lines are required.

[0018] When constructing a larger-scale two-dimensional array antenna, the number of wavelength dispersion lines required increases. Furthermore, the technology described in Patent Document 2 does not disclose a means for receiving multiple beams. However, when receiving multiple beams, it is considered that a number of multiplexers corresponding to the number of beams is required in the IF signal processing stage. This increases the circuit scale, resulting in a problem of increased circuit size, i.e., circuit area and volume.

[0019] Furthermore, when it is assumed that the device configuration will be made low-profile and that a printed circuit manufacturing process will be used for mass production, there is a problem that the three-dimensional circuit structure that imparts a phase tilt using a wavelength dispersion line as in Patent Documents 1 and 2 is not suitable for mass production.

[0020] As described above, conventional optically controlled array antennas have had the problem that when two-dimensional multi-beam reception directivity control is performed, the antennas are configured to be small and not suitable for implementation using planar circuits.

[0021] Furthermore, after converting an RF signal to an optical signal, in order to perform phase weighting in the optical domain, it is necessary to control the optical phase of only a single sideband component. Therefore, when converting an RF signal received by an antenna element into an optical signal, it is desirable to use an optical SSB (single sideband) modulator. However, SSB modulators require a larger circuit scale than intensity modulators, which have a simpler configuration. Therefore, if an optical modulator is provided for each of the many antenna elements, the circuit scale and size become very large. Furthermore, when the RF frequency is high, it becomes difficult to install the optical modulators at intervals equivalent to the narrowly spaced antenna elements.

[0022] Furthermore, when the number of antenna elements is large, the scale of the circuit (matrix circuit) for performing phase weighting becomes large, which poses a problem of making design and manufacturing difficult.

[0023] In view of the above circumstances, an object of the present invention is to provide a receiving directivity control device and a receiving directivity control method that can reduce the circuit size.

[0024] One aspect of the present invention is a reception directivity control device that includes a plurality of antenna elements that receive radio waves and output radio signals obtained therefrom; an electrical-to-optical converter that converts light output from a light source into optical signals that are intensity-modulated by the radio signals obtained by each of the plurality of antenna elements; a weighting unit that applies phase weighting to each of the optical signals to impart a phase gradient to each of the optical signals that offsets a phase difference that occurs in a first sideband wave of the optical signals depending on differences in the positions of the plurality of antenna elements and a desired direction that is the desired arrival direction of the radio waves, and outputs a combined signal that combines the phase-weighted optical signals; and an extraction unit that outputs a reception signal that is obtained by extracting the first sideband wave from the combined signal.

[0025] One aspect of the present invention is a reception directivity control method including: a receiving step in which a plurality of antenna elements receive radio waves and output radio signals obtained; an electrical-to-optical conversion step in which light output from a light source is converted into optical signals intensity-modulated by the radio signals obtained by each of the plurality of antenna elements; a weighting step in which each of the optical signals is phase-weighted to impart a phase gradient to offset a phase difference that occurs in a first sideband wave of the optical signal depending on differences in the positions of the plurality of antenna elements and a desired direction that is a desired arrival direction of the radio waves, and outputting a composite signal by combining the phase-weighted optical signals; and an extraction step in which the first sideband wave is extracted from the composite signal and outputting a reception signal obtained.

[0026] According to the present invention, it is possible to reduce the circuit size of a receiving directivity control device.

[0027] FIG. 1 is a diagram showing the configuration of a receive directivity control device related to an embodiment of the present invention. FIG. 1 is a diagram showing the configuration of a receive directivity control device according to a first embodiment. FIG. 1 is a diagram showing the configuration of a receive directivity control device according to a first embodiment. FIG. 2 is a diagram showing the configuration of a receive directivity control device according to a second embodiment. FIG. 3 is a diagram showing the configuration of a receive directivity control device according to a third embodiment. FIG. 4 is a diagram showing the configuration of a filter according to a third embodiment. FIG. 5 is a diagram showing the configuration of a receive directivity control device according to a third embodiment. FIG. 6 is a diagram showing the effect of component reduction according to the third embodiment. FIG. 7 is a diagram showing the effect of component reduction according to the third embodiment. FIG. 8 is a diagram showing the configuration of a receive directivity control device according to a fourth embodiment. FIG. 9 is a diagram showing the configuration of a receive directivity control device according to a fifth embodiment. FIG. 10 is a diagram showing the output terminals of a weighting circuit according to the fifth embodiment. FIG. 11 shows an example of beam directions selectable in the receive directivity control device according to the fifth embodiment. FIG. 12 is a diagram showing the configuration of a receive directivity control device according to a sixth embodiment. FIG. 13 is a diagram showing beams that can be generated by the receive directivity control device according to the sixth embodiment.

[0028] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. The embodiment described below is merely an example, and the embodiment to which the present invention is applied is not limited to the following embodiment. The reception directivity control device of this embodiment is used in, for example, a radio signal receiving device.

[0029] [First Embodiment] The first embodiment shows the basic configuration of a receiving directivity control device and the operation of scanning one beam.

[0030] FIG. 1 is a diagram showing the configuration of a receiving directivity control device 9. The receiving directivity control device 9 performs phase weighting in the optical domain. The receiving directivity control device 9 has M (M is an integer of 2 or greater) antenna elements 11, M electro-optical converters 92, a light source 13, and a weighting circuit 14. The mth (m is an integer of 1 to M) antenna element 11 of the M antenna elements 11 will be referred to as antenna element 11-m, and the mth electro-optical converter 92 of the M electro-optical converters 92 will be referred to as electro-optical converter 92-m. The M antenna elements 11 form an array antenna. The weighting circuit 14 has M input terminals 141 and N (N is an integer of 2 or greater) output terminals 142. The mth input terminal 141 of the M input terminals 141 will be referred to as input terminal 141-m, and the nth output terminal 142 of the N output terminals 142 will be referred to as output terminal 142-n. In the following, an example where M=4 and N=4 will be described.

[0031] An overview of the operation of the reception directivity control device 9 is as follows. Radio waves that reach the four antenna elements 11 are output from each antenna element 11 as RF signals. The electro-optical converter 92 converts these RF signals into optical signals. The electro-optical converter 92 is an optical modulator. In this example, an SSB modulator (single side-band modulator) is used as the electro-optical converter 92. The electro-optical converter 92-m converts the received signal from an RF signal to an optical signal by modulating the CW (sinusoidal wave) light output by the light source 13 with the RF signal received by the antenna element 11-m. Each electro-optical converter 92-m inputs the converted optical signal to an input terminal 141-m of the weighting circuit 14.

[0032] The weighting circuit 14 includes a phase shifter. The weighting circuit 14 adjusts the four optical signals input from the input terminals 141-1 to 141-4 to have the same phase using the phase shifter, and then adds them all together. In other words, the four optical signals are combined in phase.

[0033] In FIG. 1, the weighting circuit 14 is a matrix-type circuit using a fixed phase shifter. The weighting circuit 14 outputs a strong received signal from an output terminal 142-n corresponding to the beam arrival direction, and outputs a low-level signal from another output terminal 142-n' (n' ≠ n, n' is an integer between 1 and N). Here, the output terminal 142-n corresponds to the beam direction of direction Dn. A receiver (not shown) is connected to the output terminal 142-n. The receiver performs reception processing (demodulation, etc.) on the received signal output from the output terminal 142-n.

[0034] The weighting circuit 14 performs phase weighting in the optical domain. The RF signals received by each antenna element 11 have a phase difference depending on the direction of arrival of the radio waves. The weighting circuit 14 determines the amount of phase change of the optical signals output from each of the input terminals 141-1 to 141-4 to each of the output terminals 142-1 to 142-4 so that the signal received from direction Dn is output strongly to output terminal 142-n.

[0035] For the sake of explanation, the phase difference between the RF signals output from adjacent antenna elements 11 is defined as φ. In this embodiment, this phase difference is referred to as a phase tilt. Because the RF signals output from antenna elements 11-1 to 11-4 have a phase difference, the optical signals obtained by converting the RF signals by each of electro-optical converters 92-1 to 92-4 also have a phase difference. When the electro-optical converter is an intensity modulator, the optical signal contains three frequency components: LSB (Lower Side Band), USB (Upper Side Band), and carrier wave. The phase difference between the optical signals of adjacent antenna elements 11 is −φ for USB, +φ for LSB, and 0 for carrier wave. In other words, the phase of the RF signal is not reflected in the carrier wave.

[0036] As described above, the phase difference resulting from the direction of arrival of the radio waves is reflected differently for each frequency component. Therefore, by using an SSB modulator as the electro-optical converter 92, only the LSB of the sideband components is extracted as an optical signal, and the weighting circuit 14 performs phase weighting in the optical domain (as described above, the phases of the four optical signals are aligned and combined in phase). This allows for control to select and receive radio waves arriving from a specific direction, i.e., reception directivity control. While FIG. 1 shows a configuration using the LSB, a configuration using USB and performing phase weighting appropriate to the USB may also be used.

[0037] However, an SSB modulator is composed of two intensity modulators, and also includes a phase shifter and a divider to suppress unwanted sideband and carrier components. Therefore, its structure is more complex than that of an intensity modulator, and it also requires many external inputs, such as bias control voltages to be applied to the modulators and control voltages for the phase shifters. Therefore, the circuit scale of an intensity modulator is significantly larger than that of a simpler intensity modulator.

[0038] Therefore, as shown in FIG. 2, instead of using an SSB modulator as the electro-optical conversion section, an intensity modulator may be used and only the necessary sideband components may be extracted by a filter.

[0039] Fig. 2 is a diagram showing an example of the configuration of a reception directivity control device 1 according to the first embodiment. The reception directivity control device 1 shown in Fig. 2 differs from the reception directivity control device 9 shown in Fig. 1 in that it includes an electric-to-optical converter 12 instead of the electric-to-optical converter 92, and in that it includes a filter 15 subsequent to the weighting circuit 14. The electric-to-optical converter 12 connected to the antenna element 11-m is referred to as electric-to-optical converter 12-m. The electric-to-optical converter 12 is an intensity modulator.

[0040] The electro-optical converter 12-m converts the RF signal received by the antenna element 11-m into an intensity-modulated optical signal. This optical signal contains a carrier component and two sideband components, the LSB and USB. If a filter 15 is provided after the output terminal 142 of the weighting circuit 14 and the LSB of the optical signal output from the output terminal 142 is extracted by the filter 15, reception directivity control becomes possible in the same way as the reception directivity control device 9 shown in FIG. 1.

[0041] When a matrix circuit is used as the phase weighting circuit 14, as in the reception directivity control device 9 shown in Fig. 1 and the reception directivity control device 1 shown in Fig. 2, a reception signal is output from the output terminal 142 according to the direction of arrival of the radio wave, as described above. That is, the weighting circuit 14 determines the amount of phase change in the optical signal output from each of the input terminals 141-1 to 141-4 to the output terminal 142-n so that the LSB component (or USB component) of the reception signal is output strongly from the direction Dn. For this reason, it is necessary to switch the direction of reception directivity by using a switching circuit, as shown in Figs. 3 and 4, to switch the output terminal 142-n to which the receiver is connected according to the direction of arrival Dn of the radio wave.

[0042] Fig. 3 is a diagram showing an example of the configuration of the reception directivity control device 2. The reception directivity control device 2 shown in Fig. 3 differs from the reception directivity control device 1 shown in Fig. 2 in that a switching circuit 16 is provided between the weighting circuit 14 and the filter 15. The switching circuit 16 switches which of the outputs from the four output terminals 142 of the weighting circuit 14 is to be output to the filter 15.

[0043] The switching circuit 16 has input terminals 161-1 to 161-4 and an output terminal 162. The input terminal 161-n is connected to the output terminal 142-n of the weighting circuit 14. When the arrival direction of the desired signal is direction Dn, the switching circuit 16 outputs the optical signal input from the input terminal 161-n from the output terminal 162 to the filter 15. The filter 15 extracts the LSB of the optical signal output from the output terminal 162 and outputs it as a received signal.

[0044] In the configuration shown in FIG. 3, the filter 15 that suppresses the USB and carrier wave and extracts the LSB is installed after the switching circuit 16, but as shown in FIG. 4, the filter may be installed between the output terminal 142 of the weighting circuit 14 and the switching circuit 16.

[0045] FIG. 4 is a diagram showing the configuration of the reception directivity control device 3. In the reception directivity control device 3 shown in FIG. 4, the same components as those in the reception directivity control device 2 shown in FIG. 3 are assigned the same reference numerals, and their description will be omitted. The reception directivity control device 3 shown in FIG. 4 differs from the reception directivity control device 2 shown in FIG. 2 in that it does not have filter 15, but instead has four filters 17 between the weighting circuit 14 and the switching circuit 16. The filters 17 between the output terminal 142-n of the weighting circuit 14 and the input terminal 161-n of the switching circuit 16 will be referred to as filters 17-n. The filters 17-n suppress the USB and carrier wave of the received signal output from the output terminal 142-n of the weighting circuit 14, extract the LSB, and output it to the input terminal 161-n of the switching circuit 16.

[0046] Alternatively, as shown in FIG. 5, a filter may be installed immediately after the electro-optical converter 12. FIG. 5 is a diagram showing the configuration of the reception directivity control device 4. In the reception directivity control device 4 shown in FIG. 5, the same components as those in the reception directivity control device 2 shown in FIG. 2 are designated by the same reference numerals, and their description will be omitted. The reception directivity control device 4 shown in FIG. 5 differs from the reception directivity control device 2 shown in FIG. 2 in that it does not include the filter 15, but instead includes a filter 18 between each electro-optical converter 12 and the weighting circuit 14. The filter 18 between the electro-optical converter 12-m and the input terminal 141-m of the weighting circuit 14 will be referred to as filter 18-m. The filter 18-m extracts the LSB of the intensity-modulated optical signal output from the electro-optical converter 12-m and outputs it to the input terminal 141-m of the weighting circuit 14. In this way, the reception directivity control device 4 extracts the LSB of the single sideband wave in the intensity-modulated optical signal before performing phase weighting. The reception directivity control device 4 may have a switching circuit 16 at the subsequent stage of the weighting circuit 14 .

[0047] As described above, there are several positions where filters can be inserted, but the reception directivity control device 3 shown in FIG. 4 and the reception directivity control device 4 shown in FIG. 5 require a larger number of filters than the reception directivity control device 2 shown in FIG. 3.

[0048] Second Embodiment A reception directivity control device according to a second embodiment cancels and suppresses unwanted components remaining in a received signal. The second embodiment will be described, focusing on the differences from the first embodiment.

[0049] FIG. 6 is a diagram showing an example of the configuration of a reception directivity control device 5 according to the second embodiment. The reception directivity control device 5 cancels and suppresses unwanted carrier components remaining in a received signal. The reception directivity control device 5 shown in FIG. 6 differs from the reception directivity control device 2 of the first embodiment shown in FIG. 3 in that it includes an amplitude / phase adjuster 31 and a multiplexer 32. The amplitude / phase adjuster 31 is provided between the light source 13 and the multiplexer 32, and the multiplexer 32 is provided after the filter 15. When it is desired to extract only the desired sideband components using the filter 15 but the filter 15 is unable to sufficiently suppress the unwanted carrier components, the configuration shown in FIG. 6 is used.

[0050] The amplitude and phase adjuster 31 extracts the carrier component from the light source 13, adjusts the amplitude and phase, and then outputs it to the combiner 32. The combiner 32 inversely combines the received signal output by the filter 15 with the carrier component input from the amplitude and phase adjuster 31. In this way, by canceling and suppressing the carrier component contained in the received signal output by the filter 15, it is possible to extract only the desired sideband component as the received signal output by the reception directivity control device 5.

[0051] Fig. 7 is a diagram showing an example of the configuration of the reception directivity control device 6. The reception directivity control device 6 cancels and suppresses unwanted sideband components remaining in the received signal. The reception directivity control device 6 shown in Fig. 7 differs from the reception directivity control device 5 shown in Fig. 6 in that it includes a filter 33. The filter 33 is provided between the electro-optical conversion unit 12 and the amplitude-phase adjuster 31.

[0052] The carrier wave is used in the receiver, but one sideband wave is unnecessary. If the filter 15 cannot sufficiently suppress the unnecessary sideband wave, as shown in FIG. 7 , the filter 33 extracts one sideband wave from the output of one of the electro-optical conversion units 12. For example, suppose the desired sideband wave is the LSB, and the unwanted sideband wave USB remains in the output of the filter 15. In this case, the filter 33 extracts USB from the output of the electro-optical conversion unit 12. The amplitude / phase adjuster 31 adjusts the amplitude and phase of the sideband wave component extracted by the filter 33 and outputs it to the combiner 32. The combiner 32 cancels and suppresses the unwanted sideband wave component (USB in the example of FIG. 7 ) contained in the received signal output by the filter 15 by combining, in antiphase, the sideband wave component whose amplitude and phase has been adjusted by the amplitude / phase adjuster 31 with the received signal output by the filter 15. This allows only the desired sideband wave component to be extracted as the received signal output.

[0053] The filter 33 may extract a sideband wave from the output of any of the four electro-optical converters 12. Alternatively, the RF signal may be extracted and input to a modulator (not shown), and the output of the modulator may be input to the filter 33. Furthermore, if an electro-optical converter 92 of an SSB modulator is provided instead of the electro-optical converter 12, the filter 33 is not necessary.

[0054] [Third Embodiment] A receiving directivity control device of a third embodiment controls the switching of beams in symmetric directions using sideband waves. The third embodiment will be described, focusing on the differences from the above-described embodiments.

[0055] Fig. 8 is a diagram showing an example of the configuration of a reception directivity control device 7 according to the third embodiment. In the reception directivity control device 7 shown in Fig. 8, the same components as those of the reception directivity control device 1 shown in Fig. 2 are assigned the same reference numerals, and their description will be omitted. The reception directivity control device 7 has antenna elements 11-1 to 11-4, electro-optical conversion units 12-1 to 12-4, a light source 13, a weighting circuit 14, a switching circuit 35, and a filter 36.

[0056] The weighting circuit 14 is a matrix circuit. Of the output terminals 142-1 to 142-4 of the weighting circuit 14, the output terminals 142-1 and 142-2 are connected to the switching circuit 35, and the output terminals 142-3 and 142-4 are not connected to the subsequent stage.

[0057] The switching circuit 35 has input terminals 351-1 and 351-2 and an output terminal 352. The input terminal 351-1 is connected to the output terminal 142-1 of the weighting circuit 14, and the input terminal 351-2 is connected to the output terminal 142-2 of the weighting circuit 14. The output terminal 352 is connected to the filter 36. The switching circuit 35 switches between output terminals 142-1 and 142-2 of the weighting circuit 14, and outputs the optical signal output from these terminals to the filter 36 in the subsequent stage.

[0058] The filter 36 is a USB / LSB passband switchable filter that switches between passing either the LSB or USB sideband components of the optical signal input from the switching circuit 35.

[0059] 9 is a diagram showing an example configuration of the filter 36. The filter 36 has a demultiplexer 361 and a switching circuit 362. The demultiplexer 361 demultiplexes the optical signal input from the filter 15 into an LSB and a USB component based on wavelength and outputs the components to the switching circuit 362. The switching circuit 362 inputs the USB component and the LSB component of the optical signal output from the demultiplexer 361 from different input terminals. The switching circuit 362 switches whether to output the signal input from either input terminal to a subsequent stage as a received signal. The number of demultiplexers 361 is N / 2, and the number of switching circuits 362 is N / 2.

[0060] The operation of the receiving directivity control device 7 is as follows: When the direction of arrival of the radio wave is direction D1, the phase gradient (phase difference between the RF signals output from the adjacent antenna elements 11) is φ １ In this case, when radio waves arrive from direction D4, which is a direction symmetrical to direction D1 with respect to the normal of the array antenna formed by four antenna elements 11, the phase tilt is −φ １ is.

[0061] Furthermore, it is assumed that the weighting circuit 14 has a property such that "when the direction of arrival of the radio waves is direction D1, the LSBs are in-phase combined and output at the output terminal 142-1." In this case, when the direction of arrival of the radio waves is direction D4, the USB is in-phase combined and output at the output terminal 142-1 of the weighting circuit 14. The reason for this is that, as described in the first embodiment, when the electro-optical conversion unit 12 is an intensity modulator, the optical signal contains three frequency components: the LSB, the USB, and the carrier wave, and if the phase slope is φ, the phase difference between the optical signals of adjacent antenna elements 11 is −φ for the USB, +φ for the LSB, and 0 for the carrier wave (the phase of the RF signal is not reflected in the carrier wave).

[0062] Furthermore, when the direction of arrival of the radio wave is direction D2, the phase slope is φ ２ When radio waves arrive from direction D3, which is a direction symmetrical to direction D2 with respect to the normal to the array antenna, the phase tilt is −φ ２ If it is assumed that when the radio wave arrives in direction D2, the LSB is combined in phase and output at output terminal 142-2, and when the radio wave arrives in direction D3, the USB is combined in phase and output at output terminal 142-2.

[0063] When using a single sideband (for example, only the LSB) of the electro-optically converted optical signal, it is necessary to switch the four output terminals 142-1 to 142-4 of the weighting circuit in order to scan the receiving beam by switching between the four directions D1 to D4. In contrast, by using the above-mentioned properties, it is possible to provide a filter 36 that selectively passes the LSB and USB, and switch two of the four output terminals 142 of the weighting circuit 14.

[0064] As described above, by utilizing the property of electro-optical conversion that the phase tilt after conversion to an optical signal by the electro-optical converter 12 between both sidebands is inversely positive and negative, switching the sideband (LSB or USB) used doubles the beam scanning direction and halves the required phase shift range and phase amount. Increasing the number of elements in the array antenna increases the size of the weighting circuit 14. For example, when controlling an ultra-large-scale array antenna with tens of thousands of elements, the weighting circuit 14 becomes enormously large. Therefore, reducing the size of the weighting circuit 14 by nearly half offers advantages such as a smaller and lighter circuit, reduced phase error, and improved yield. In other words, the number of output ports of the weighting circuit 14 can be halved to N / 2, thereby reducing the number of components. Furthermore, if the weighting circuit 14 uses a fixed matrix, the number of input ports of the switching circuit 35 can be halved to N / 2, thereby reducing the number of components. If the weighting circuit 14 uses a variable phase shifter, the required variable range of the phase shifter can be halved, and advantages such as faster beam direction switching, smaller scale phase shifter circuitry, and lower voltage are expected. This is particularly effective when the number of antenna elements is large and the matrix is ​​large.

[0065] Figure 10 is a diagram showing the configuration of a reception directivity control device 8 according to the third embodiment. In the reception directivity control device 8 shown in Figure 10, the same components as those in the reception directivity control device 7 shown in Figure 8 are designated by the same reference numerals, and their description will be omitted. The reception directivity control device 8 shown in Figure 10 differs from the reception directivity control device 7 shown in Figure 8 in that it includes sideband branching filters 37-1 and 37-2 and a switching circuit 38 instead of the switching circuit 35 and filter 36.

[0066] Sideband demultiplexer 37-1 is provided subsequent to output terminal 142-1 of weighting circuit 4, and sideband demultiplexer 37-2 is provided subsequent to output terminal 142-2 of weighting circuit 4. Sideband demultiplexer 37-1 separates the optical signal output from output terminal 142-1 into an LSB component in direction D1 and a USB component in direction D4, and outputs the separated components. Sideband demultiplexer 37-2 separates the optical signal output from output terminal 142-2 into an LSB component in direction D2 and a USB component in direction D3, and outputs the separated components.

[0067] Switching circuit 38 has input terminals 381-1 to 381-4 and output terminal 382. Input terminal 381-1 inputs the LSB component of direction D1 from sideband branching filter 37-1, and input terminal 381-2 inputs the USB component of direction D4 from sideband branching filter 37-1. Input terminal 381-3 inputs the LSB component of direction D2 from sideband branching filter 37-1, and input terminal 381-4 inputs the USB component of direction D3 from sideband branching filter 37-1. Switching circuit 38 selects a sideband wave input from one of input terminals 381-1 to 381-4 and outputs it as a received signal to a subsequent stage from output terminal 382.

[0068] The reception directivity control device 8 shown in Fig. 10 can halve the number of matrix circuit ports in the weighting circuit 14, thereby reducing the number of components. The configuration of the reception directivity control device 8 is larger in scale because the number of ports in the switching circuit is the same as that of the reception directivity control device 7 shown in Fig. 8, and the number of filters (sideband branching filters) is increased because it is the number of beams x 2, but this type of configuration method is also possible.

[0069] 11 and 12 show the results of simple calculations of the component reduction effect of this embodiment when a Butler matrix circuit is used as the weighting circuit 14. M is the number of antenna elements in the array antenna, and N is the number of beams. Fig. 11 shows the results of calculations of the number of connections in the Butler matrix circuit, the number of phase shifters in the Butler matrix circuit, the number of intersections in the matrix switching circuit, the number of switches in the sideband switching filter, and the number of sideband branching filters included in the sideband switching filter for a normal system that uses only one sideband, and for the reception directivity control device 7 according to the third embodiment shown in Fig. 8.

[0070] FIG. 12 plots the number of antenna elements M on the horizontal axis and the number of components on the vertical axis for the case where the number of beams N is 10. FIG. 12(a) shows the estimated number of components for a normal system using only one sideband. FIG. 12(b) shows the estimated number of components for the reception directivity control device 7 of the third embodiment shown in FIG. 8. Symbols G11 and G21 indicate the number of connections in the matrix circuit, symbols G12 and G22 indicate the number of phase shifters in the matrix circuit, symbols G13 and G23 indicate the number of intersections in the matrix switching circuit, and symbol G24 indicates the number of selector switches in the USB / LSB switching filter. Referring to FIG. 12(b), it can be seen that the reception directivity control device 7 requires M new selector switches in the sideband switching filter and M new sideband branching filters included in the sideband switching filter, but the number of other components is reduced compared to FIG. 12(a). 12(c) shows the reduction rate of each component count obtained from the calculation results of FIGS. 12(a) and 12(b). Symbol G31 indicates the reduction rate of the number of connections in the matrix circuit, symbol G32 indicates the reduction rate of the number of phase shifters in the matrix circuit, and symbol G33 indicates the reduction rate of the number of intersections in the matrix-type switching circuit.

[0071] As described above, in this embodiment, the property of EO (electrical-optical) conversion, in which the phase slope of the signal after EO conversion between both sidebands is in an inverse relationship between positive and negative, is utilized to switch the sideband in use (LSB or USB), thereby doubling the beam scanning direction and halving the required phase shift range and amount. In the case of a fixed matrix, the number of switching ports can be halved, and in the case of a variable phase shifter matrix, the phase shift range can be halved, which enables faster variable switching, smaller size, and lower voltage for the phase shifter. This is particularly effective when the matrix is ​​large due to the large number of antenna elements.

[0072] [Fourth Embodiment] A receiving directivity control device according to a fourth embodiment performs a multi-beam operation. The fourth embodiment will be described, focusing on the differences from the above-described embodiments.

[0073] Fig. 13 is a diagram showing the configuration of a reception directivity control device 21 according to a fourth embodiment. The reception directivity control device 21 shown in Fig. 13 differs from the reception directivity control device 7 shown in Fig. 8 in that it includes a switching circuit 41 and sideband branching filters 43-1 and 43-2 instead of the switching circuit 35 and filter 36. With respect to the normal to the array antenna formed by the antenna elements 11-1 to 11-4, directions D1 and D4 are line-symmetrical, and directions D2 and D3 are symmetrical. The phase tilt of the arrival direction D1 is φ １ , the phase gradient in the direction D2 is φ ２ , the phase gradient in the direction D3 is −φ ２ , the phase gradient in the direction D4 is −φ １ is.

[0074] The switching circuit 41 has input terminals 411-1 and 411-2 and output terminals 412-1 and 412-2. The input terminal 411-1 is connected to the output terminal 142-1 of the weighting circuit 14, and the input terminal 411-2 is connected to the output terminal 142-2 of the weighting circuit 14. The output terminal 412-1 is connected to the sideband demultiplexer 43-1, and the output terminal 412-2 is connected to the sideband demultiplexer 43-2. ​​In the switching circuit 41, the input terminal 411-1 outputs the optical signal input from the output terminal 142-1 from the output terminal 412-1, and in parallel with this, the input terminal 411-2 outputs the optical signal input from the output terminal 142-2 from the output terminal 412-2.

[0075] Sideband demultiplexer 43-1 demultiplexes the optical signal output from output terminal 412-1 of switching circuit 41 into a first beam signal which is the LSB component of the signal arriving from direction D1, and a fourth beam signal which is the USB component of the signal arriving from direction D4. Sideband demultiplexer 43-2 demultiplexes the optical signal output from output terminal 412-2 of switching circuit 41 into a second beam signal which is the LSB component of the signal arriving from direction D2, and a third beam signal which is the USB component of the signal arriving from direction D3.

[0076] Using Figure 13, we will explain the multi-beam operation in which the reception directivity control device 21 simultaneously receives multiple beams. The reception directivity control device 21 has a configuration similar to that of the reception directivity control device 7 shown in Figure 8, but uses a matrix circuit as the weighting circuit 14. The switching circuit 41 does not extract any one output, but outputs it to the subsequent stage using both output terminals 412-1 and 412-2. The subsequent sideband branching filters 43-1 and 43-2 then separate and output the LSB and USB components of the optical signal output from the switching circuit 41. This makes it possible to simultaneously receive beams in up to four directions.

[0077] Fifth Embodiment A reception directivity control device of this embodiment uses a two-dimensional scanning method and a two-dimensional matrix in the weighting circuit.

[0078] 14 is a diagram showing the reception directivity control device 22 of the fourth embodiment. The reception directivity control device 22 has antenna elements 11-1-1 to 11-1-4, 11-2-1 to 11-2-4, 11-3-1 to 11-3-4, and 11-4-1 to 11-4-4, electro-optical conversion units 12-1-1 to 12-1-4, 12-2-1 to 12-2-4, 12-3-1 to 12-3-4, and 12-4-1 to 12-4-4, a weighting circuit 53, a switching circuit 57, and a filter 59.

[0079] The weighting circuit 53 has a configuration in which matrix circuits 531-1 to 531-4 with a 4×4 matrix are stacked, and matrix circuits 532-1 to 532-4 with a 4×4 matrix are stacked behind them. The matrix circuits 531-1 to 531-4 and the matrix circuits 532-1 to 532-4 are one-dimensional array weighting circuits. For example, the weighting circuit 14 in the first embodiment can be used as the matrix circuits 531-1 to 531-4 and the matrix circuits 532-1 to 532-4. Furthermore, as the matrix circuits 531-1 to 531-4 and the matrix circuits 532-1 to 532-4, not only matrix circuit-type circuits but also weighting circuits configured with variable phase shifters can be used. The antenna elements 11-p-q (p and q are integers between 1 and 4) are connected to the electro-optical converter 12-p-q, and the electro-optical converters 12-p-1 to 12-p-4 are connected to the matrix circuit 531-p. The stack of the matrix circuits 531-1 to 531-4 and the stack of the 4x4 matrix circuits 532-1 to 532-4 are vertically combined. Since the matrix circuits 532-1 to 532-4 each have four output terminals, four output terminals are arranged vertically and four horizontally between the switching circuit 57 and the matrix circuits 532-1 to 532-4 (reference symbol A). The filter 59 is an LSB / USB passband switching filter.

[0080] As described above, the receive directivity control device 22 shown in FIG. 14 uses a two-dimensional weighting circuit 53 in which the weighting circuits 14 for the one-dimensional array antenna shown in FIG. 1 and other figures are stacked three-dimensionally. By configuring the weighting circuit 53 in this way, multiple beams can be scanned in two dimensions (for example, vertical and horizontal directions). For example, this technique is disclosed in FIG. 6(b) of Non-Patent Document 3. The array antenna 51 of the receive directivity control device 22 is a two-dimensional array antenna with 4 vertical elements and 4 horizontal elements, for a total of 16 elements. The weighting circuit 53 has 16 inputs and 16 outputs, and can switch between and receive beams in 4 horizontal and 4 vertical directions, for a total of 16 directions.

[0081] With the above configuration, each matrix circuit 531-p, where p=1 to 4, receives an optical signal from each of the electrical-optical converters 12-p-1 to 12-p-4, performs phase weighting to impart a phase gradient that offsets the phase difference that occurs in the sidebands of the optical signal depending on the difference in the horizontal positions of the antenna elements 11-p-1 to 11-p-4 and the beam direction, and outputs the signal from each of the four output terminals. The optical signal output from the rth (r=1 to 4) output terminal of the matrix circuit 531-p is input to the pth input terminal of the matrix circuit 532-r. Each matrix circuit 532-r, where r=1 to 4, receives the optical signal output from the electrical-optical converters 12-p-1 to 12-p-4 and phase-weighted by the matrix circuit 531-p from its respective pth input terminal. Each matrix circuit 532-r, r=1 to 4, performs phase weighting on the optical signals input from the four input terminals, imparting a phase gradient that offsets the phase difference that occurs in the sideband waves of the optical signals, depending on the difference in the vertical position of the antenna element 11 and the beam direction.

[0082] Even in such a configuration, beams in directions that are point-symmetric with each other with respect to the normal line passing through the center of the array antenna 51 can be generated by switching the sidebands of the optical signal.

[0083] Fig. 15 is a diagram showing the output terminals of the weighting circuit 53. As shown in Fig. 15, the weighting circuit 53 has four output terminals arranged vertically and four horizontally. Fig. 15 shows the arrangement as seen from the front. These 16 output terminals are referred to as output terminals (1,1) to (4,4).

[0084] 16 shows examples of beam directions that can be selected by the reception directivity control device 22. For example, if a received signal in beam direction (1,1) can be received as the LSB of an optical signal at the output terminal (1,1) of the weighting circuit 53, a received signal in beam direction (4,4) can be received as the USB of an optical signal at the output terminal (1,1) of the weighting circuit. This is because the phase tilts of the antenna elements 11 in the beam direction (1,1) and the beam direction (4,4) have opposite positive and negative relationships.

[0085] Furthermore, for example, if the received signal in the beam direction (2,1) can be received as the LSB of an optical signal at the output terminal (2,1) of the weighting circuit 53, the received signal in the beam direction (3,4) can be received as the USB of an optical signal at the output terminal (2,1) of the weighting circuit 53. This is because the phase tilts of the antenna elements 11 in the beam direction (2,1) and the beam direction (3,4) have opposite positive and negative relationships.

[0086] By switching the sidebands in this way, it is possible to scan the beam in all 16 directions using only the upper half of the output terminals arranged in a grid pattern on the output side of the weighting circuit 53.

[0087] Sixth Embodiment The sixth embodiment is a two-dimensional scanning type multi-beam receiving directivity control device configured with a planar circuit using wavelength multiplexing.

[0088] 17 is a diagram showing the configuration of a receiving directivity control device 23 according to the sixth embodiment. The receiving directivity control device 23 performs two-dimensional scanning using a two-dimensional array antenna.

[0089] The reception directivity control device 23 has antenna elements 71-1-1 to 71-J-K, electro-optical converters 72-1-1 to 72-J-K, light sources 73-1 to 73-J, a vertical scanning matrix circuit 74, distributors 75-1 to 75-J, multiplexers 76-1 to 76-K, a horizontal scanning matrix circuit 77, a channel demultiplexer 78, and sideband demultiplexers 79-1 to 79-J. The following description will be given taking the case where J=K=2 as an example.

[0090] Antenna elements 71-1-1, 71-1-2, 71-2-1, and 71-2-2 constitute an array antenna 70. The array antenna 70 is a phased array antenna with a 2x2 configuration that includes two elements arranged along the vertical direction and two elements arranged along the horizontal direction, for a total of four antenna elements 71-1-1, 71-1-2, 71-2-1, and 71-2-2. The vertical direction is also called the row direction, and the horizontal direction is also called the column direction.

[0091] The line segment connecting antenna element 71-1-1 and antenna element 71-2-1 and the line segment connecting antenna element 71-1-2 and antenna element 71-2-2 are the same length and are arranged so as to be parallel to the axis in the row direction. The line segment connecting antenna element 71-1-1 and antenna element 71-1-2 and the line segment connecting antenna element 71-2-1 and antenna element 71-2-2 are the same length and are arranged so as to be parallel to the axis in the column direction. Note that the line segment connecting antenna element 71-1-1 and antenna element 71-2-1 and the line segment connecting antenna element 71-1-1 and antenna element 71-1-2 may be the same length or may be different lengths.

[0092] The array antenna 70 forms first to fourth beams. With respect to the normal of the array antenna 70, the first beam is formed to point in the upper left direction, the second beam is formed to point in the upper right direction, the third beam is formed to point in the lower left direction, and the fourth beam is formed to point in the lower right direction.

[0093] The first and second beams are formed so that the tilts of the first and second beams with respect to the horizontal plane, in other words, the vertical components of the tilts of the first and second beams, are the same. Similarly, the third and fourth beams are formed so that the tilts of the third and fourth beams with respect to the horizontal plane, in other words, the vertical components of the tilts of the third and fourth beams, are the same. The phase tilt, which is the phase difference caused by the vertical component of the tilts of the first and second beams, is referred to as "φ Ｖ ". The first and third beams are formed so that the tilts of the first and third beams with respect to the vertical plane, in other words, the horizontal components of the tilts of the first and third beams, are the same. Similarly, the second and fourth beams are formed so that the tilts of the second and fourth beams with respect to the vertical plane, in other words, the horizontal components of the tilts of the second and fourth beams, are the same. The phase tilt, which is the phase difference caused by the horizontal component of the tilts of the first and third beams, is represented by "φ Ｈ ". Note that "φ Ｖ " and "φ Ｈ " may be different values ​​or may be the same value.

[0094] The first to fourth beams formed by array antenna 70 have two angles: the angle formed by the first and second beams with the horizontal plane, and the angle formed by the third and fourth beams with the horizontal plane. The former angle is referred to as "upward" and the latter angle is referred to as "downward."

[0095] The electrical-to-optical converters 72-1-1, 72-1-2, 72-2-1, and 72-2-2 are intensity modulators. The electrical-to-optical converters 72-j-k (j is an integer between 1 and J, and k is an integer between 1 and K) convert the received signal from an RF signal to an intensity-modulated optical signal by modulating the CW light output from the distributor 75-j with the RF signal received by the antenna element 71-j-k. The electrical-to-optical converters 72-1-1 and 72-2-1 input the converted intensity-modulated optical signals to a multiplexer 76-1, and the electrical-to-optical converters 72-1-2 and 72-2-2 input the converted intensity-modulated optical signals to a multiplexer 76-2.

[0096] The light source 73-1 and the light source 73-2 generate optical signals with carrier waves of different frequencies. Hereinafter, the frequency of the optical signal generated by the light source 73-1 will be referred to as "ch1," and the frequency of the optical signal generated by the light source 73-2 will be referred to as "ch2."

[0097] The vertical scanning matrix circuit 74 has input terminals 741-1 and 741-2 and output terminals 742-1 and 742-2. A light source 73-1 is connected to the input terminal 741-1 of the vertical scanning matrix circuit 74, and a light source 73-2 is connected to the input terminal 741-2. The output terminal 742-1 is connected to a distributor 75-1, and the output terminal 742-2 is connected to a distributor 75-2.

[0098] As a predetermined vertical phase scanning process, the vertical scanning matrix circuit 74 applies a phase gradient to each of the optical signals of different frequencies generated by each of the light sources 73-1 and 73-2, which offsets the vertical phase gradient that occurs depending on the difference in the row position used when each optical signal is modulated by the electro-optical conversion units 72-1-1, 72-1-2, 72-2-1, and 72-2-2 and each desired direction, thereby generating an optical signal with the phase gradient for each frequency.

[0099] When an optical signal of ch1 is supplied from the light source 73-1 to the input terminal 741-1, the vertical scanning matrix circuit 74 outputs the supplied optical signal as is from the output terminal 742-1, and also changes the phase of the optical signal by φ Ｖ When an optical signal of ch2 is supplied from the light source 73-2 to the input terminal 741-2, the vertical scanning matrix circuit 74 outputs the supplied optical signal as is from the output terminal 742-2, and also shifts the phase of the optical signal by φ Ｖ The forwarded optical signal is output from output terminal 742-1.

[0100] The distributor 75-1 distributes the optical signal output from the output terminal 742-1 of the vertical scanning matrix circuit 74 into two signals. The distributor 75-1 outputs each of the distributed optical signals to the electro-optical converters 72-1-1 and 72-1-2 in the first row while maintaining their phases. The distributor 75-2 distributes the optical signal output from the output terminal 742-2 of the vertical scanning matrix circuit 74 into two signals. The distributor 75-2 outputs each of the distributed optical signals to the electro-optical converters 72-2-1 and 72-2-2 in the second row while maintaining their phases.

[0101] The multiplexer 76-1 multiplexes the optical signals output from the electrical-to-optical converters 72-1-1 and 72-2-1 to generate a multiplexed optical signal. The multiplexer 76-2 multiplexes the optical signals output from the electrical-to-optical converters 72-1-2 and 72-2-2 to generate a multiplexed optical signal. In the multiplexers 76-1 and 76-2, the channel ch1 input from the input terminal 741-1 of the vertical scanning matrix circuit 74 is in phase with the LSB upward beam and the USB downward beam. In the multiplexers 76-1 and 76-2, the channel ch2 input from the input terminal 741-2 of the vertical scanning matrix circuit 74 is in phase with the LSB downward beam and the USB upward beam.

[0102] The horizontal scanning matrix circuit 77 has input terminals 771-1 and 771-2 and output terminals 772-1 and 772-2. The input terminal 771-1 is connected to the multiplexer 76-2. The input terminal 771-2 is connected to the multiplexer 76-1.

[0103] The horizontal scanning matrix circuit 77 applies a phase gradient equal to a vertical phase gradient φＶ Instead, the horizontal phase gradient φ Ｈ In other respects, the horizontal scanning matrix circuit 77 has the same configuration as the vertical scanning matrix circuit 74. That is, when an optical signal is supplied from an input terminal 771-1, the horizontal scanning matrix circuit 77 outputs the supplied optical signal from an output terminal 772-1 as is, and also changes the phase of the optical signal to φ Ｈ When an optical signal is supplied from the input terminal 771-2, the horizontal scanning matrix circuit 77 outputs the supplied optical signal from the output terminal 772-2 as is, and also shifts the phase of the optical signal by φ Ｈ The forwarded optical signal is output from output terminal 772-1.

[0104] The channel demultiplexer 78 is connected to the output terminal 772-1 of the horizontal scanning matrix circuit 77. The channel demultiplexer 78 demultiplexes the optical signal input from the output terminal 772-1 into ch1 and ch2 based on wavelength. The channel demultiplexer 78 outputs the optical signal of ch1 to the sideband demultiplexer 79-1 and outputs the optical signal of ch2 to the sideband demultiplexer 79-2.

[0105] The sideband demultiplexer 79-1 demultiplexes the ch1 optical signal input from the channel demultiplexer 78 into an LSB component and a USB component, and outputs the demultiplexed LSB component and USB component. The LSB component output from the sideband demultiplexer 79-1 is a received signal of the second beam, and the USB component output from the sideband demultiplexer 79-1 is a received signal of the third beam. The sideband demultiplexer 79-2 demultiplexes the ch2 optical signal input from the channel demultiplexer 78 into an LSB component and a USB component, and outputs the demultiplexed LSB component and USB component. The LSB component output from the sideband demultiplexer 79-2 is a received signal of the fourth beam, and the USB component output from the sideband demultiplexer 79-2 is a received signal of the fourth beam.

[0106] FIG. 18 is a diagram showing four beams that can be generated by the receiving directivity control device 23 shown in FIG. 17 . When using only the LSB of the optical signal, the output terminals 772-1 and 772-2 of the horizontal scanning matrix circuit 77, which is a phase weighting circuit for horizontal beam scanning, are used, and the optical signals of ch1 and ch2 output from each output terminal are separated by a splitter to simultaneously generate beams in four directions. However, when the LSB and USB of the optical signal are used, only the output terminal 772-1 can be used to output the second beam signal, the third beam signal, the fourth beam signal, and the first beam signal in the four frequency bands of ch1 LSB, ch1 USB, ch2 LSB, and ch2 USB, respectively. In other words, a multi-beam operation can be performed to simultaneously generate beams in four directions. This allows the horizontal scanning matrix circuit 77 to be reduced in size.

[0107] In each of the above embodiments, a matrix circuit is used as a weighting circuit, and a switching circuit is used to select the beam direction from its output terminals, but the reception directivity control device according to this embodiment is not limited to this configuration. For example, the weighting circuit may be configured using multiple variable phase shifters, and the beam direction may be set by changing the phase shift amount of the variable phase shifters.

[0108] Furthermore, when a radio device capable of both transmission and reception is configured by combining a reception directivity control device and a transmission directivity control device, the reception beam direction of the reception directivity control device may be determined by means of a search or the like, or the reception beam direction of the reception directivity control device may be determined using information on the transmission beam direction used in the transmission directivity control device. In this case, even if the weighting value matrix for the transmission beam and the weighting value matrix for the reception beam are the same due to differences in the installation position and installation direction of the transmitting array antenna and the receiving array antenna, or differences in element arrangement and element characteristics, a weighting circuit correction (calibration) function or a function for relating the transmission beam weighting value matrix and the reception beam weighting value matrix that realizes a reception beam direction corresponding to a certain transmission beam direction (for example, a correspondence table between the index of the transmission beam weighting value matrix and the index of the reception beam weighting value matrix) may be provided.

[0109] In conventional optical receive beamformers, RF signals arriving at each receive antenna element are EO converted by an optical modulator, and the resulting optical signal undergoes phase shifting in the optical domain. However, because the phase shifting must be performed on the SSB-modulated signal rather than the intensity-modulated signal, the configuration and control of the EO conversion circuit becomes complex. This is because the received RF signal has a phase that corresponds to the direction of arrival of the radio wave, but the two sideband components generated when EO converted by optical intensity modulation have different phases, so the optical circuit must perform phase shifting on only one of the sidebands. Furthermore, narrow-beam / multi-beam control requires a large number of antenna elements, which increases the amount of phase shifting required. This means that the weighting circuit must be large in size.

[0110] The reception directivity control device of the above-described embodiment utilizes the property that the phases of sidebands generated by electrical-optical conversion have an inverse relationship between positive and negative, and halves the required phase shift range by sideband switching, thereby halving the weighting circuit. For example, a fixed matrix can halve the number of switching ports. Furthermore, a variable phase shifter matrix halves the phase shift range, enabling higher speed, smaller scale, and lower phase shifter voltage. Furthermore, the unwanted sideband replicas branched from the light source and the remaining unwanted sideband components are canceled, thereby suppressing the unwanted sidebands.

[0111] This makes it possible to configure a large number of electro-optical converters, each corresponding to the number of antenna elements, using a small, simple IM modulator that does not require complex bias control. It also makes it possible to halve the size of the weighting circuit and reduce the number of components. It also makes it possible to realize a large-scale THz-band array antenna in which antenna elements are arranged at a narrow pitch.

[0112] As described above, according to this embodiment, multi-element receive beam scanning is possible without significantly increasing the number of circuit components. Furthermore, it is possible to provide a device suitable for mass production and miniaturization by significantly reducing the number of components and wiring in the beam forming circuit. Furthermore, according to this embodiment, an intensity modulator with a simple configuration can be used as the optical modulator that converts the received RF signal into an optical signal. Additionally, according to this embodiment, the circuit for performing phase weighting can be made smaller in size.

[0113] According to the above-described embodiment, the reception directivity control device includes a plurality of antenna elements, an electro-optical converter, a weighting unit, and an extractor. The plurality of antenna elements receive radio waves and output radio signals. The electro-optical converter converts light output from a light source into optical signals intensity-modulated by the radio signals obtained by the plurality of antenna elements. The weighting unit applies phase weighting to each optical signal to impart a phase gradient to offset a phase difference occurring in a first sideband of the optical signal depending on the difference in the positions of the plurality of antenna elements and the desired direction of arrival of the radio waves, and outputs a combined signal by combining the phase-weighted optical signals. The extractor outputs a received signal obtained by extracting the first sideband from the combined signal. The extractor corresponds, for example, to filters 15 and 17 in the embodiments.

[0114] The extractor may extract the first sideband from each of the optical signals converted by the electrical-to-optical converter and output the extracted first sideband to the weighting unit. The extractor corresponds to, for example, the filter 18 in the embodiment. In this case, the weighting unit outputs the combined signal as the received signal.

[0115] The reception directivity control device may further include a multiplexer. The multiplexer reverse-combines the carrier component obtained by adjusting the amplitude and phase of the light output from the light source with the reception signal output from the extractor. For example, the multiplexer corresponds to the amplitude / phase adjuster 31 and the multiplexer 32 in the embodiments. Alternatively, the multiplexer reverse-combines a first sideband extracted from one of the optical signals converted by the electro-optical converter with the reception signal output from the extractor. For example, the multiplexer corresponds to the filter 33, the amplitude / phase adjuster 31, and the multiplexer 32 in the embodiments.

[0116] The extractor may extract the second sideband from the composite signal and output the extracted signal as a received signal of a radio signal arriving from a direction symmetrical to the desired direction with respect to the normal direction of the array antenna formed by a plurality of antenna elements. For example, the extractor corresponds to the filter 36, the sideband branching filters 37-1 and 37-2, the sideband branching filters 43-1 and 43-2, the filter 59, the channel branching filter 78, and the sideband branching filters 79-1 and 79-2 in the embodiment.

[0117] The multiple antenna elements may be arranged at intersections of multiple first lines parallel to a first direction on a plane and multiple second lines parallel to a second direction perpendicular to the first direction. The weighting unit includes multiple first weighting circuits corresponding to the respective first lines and multiple second weighting circuits corresponding to the respective second lines. For example, the first weighting circuits correspond to matrix circuits 531-1 to 531-4 in the embodiment, and the second weighting circuits correspond to matrix circuits 532-1 to 532-4 in the embodiment. Each first weighting circuit applies phase weighting to an optical signal converted from a radio signal received by multiple antenna elements located on the corresponding first line, by applying a phase gradient that offsets a phase difference that occurs in a first sideband of the optical signal depending on the difference in the positions of the antenna elements in the first direction and the desired direction. Each second weighting circuit applies phase weighting to an optical signal that has been converted from radio signals received by a plurality of antenna elements located on a corresponding second straight line and phase-weighted by the first weighting circuit, by applying a phase gradient that offsets a phase difference that occurs in a first sideband wave of the optical signal depending on the difference in the positions of the antenna elements in the second direction and the desired direction.

[0118] The multiple antenna elements may be arranged at intersections of multiple first lines parallel to the first direction and multiple second lines parallel to a second direction perpendicular to the first direction on a plane. The electro-optical converter converts light from the light source, to which an inverse phase has been imparted to a phase difference occurring in the first direction of the first sideband of the optical signal in accordance with the difference in the positions of the antenna elements in the first direction and the desired direction, into an optical signal intensity-modulated by the wireless signal obtained from each of the multiple antenna elements. The weighting unit performs phase weighting on the optical signal converted by the electro-optical converter by imparting a phase gradient to the optical signal converted by the electro-optical converter so as to align the phase difference occurring in the first sideband of the optical signal in accordance with the difference in the positions of the antenna elements in the second direction and the desired direction.

[0119] Although the embodiments of the present invention have been described in detail above with reference to the drawings, the specific configurations are not limited to these embodiments, and include designs within the scope of the present invention that do not deviate from the gist of the present invention.

[0120] 1, 2, 3, 4, 5, 6, 7, 8, 9, 21, 22, 23 Receiving directivity control device 11-1 to 11-4, 11-1-1 to 11-4-4, 71-1-1 to 71-2-2 Antenna element 12-1 to 12-4, 12-1-1 to 12-4-4, 72-1-1 to 72-2-2 Electrical-optical conversion unit 13, 73-1, 73-2 Light source 14, 53 Weighting circuit 15, 17-1 to 17-4, 18-1 to 18-4, 33, 36 Filter 16, 35 Switching circuit 31 Amplitude / phase adjuster 32 Multiplexer 37-1, 37-2, 43-1, 43-2 Sideband branching filter 38, 41 Switching circuit 46 Optical modulator 51 Array antenna 57 Switching circuit 58 Optical modulator 59 Filter 70 Array antenna 74 Vertical scanning matrix circuit 75-1, 75-2 Distributor 76-1, 76-2 Combiner 77 Horizontal scanning matrix circuit 78 Channel demultiplexer 79-1, 79-2 Sideband demultiplexer 92-1 to 92-4 Electrical-optical conversion unit 361 Demultiplexer 362 Switching circuit 531-1 to 531-4, 532-1 to 532-4 Matrix circuit

Claims

1. A receiving directivity control device comprising: a plurality of antenna elements which receive radio waves and output radio signals; an electrical-to-optical converter which converts light output from a light source into an optical signal which is intensity-modulated by each of the radio signals obtained by each of the plurality of antenna elements; a weighting unit which performs phase weighting on each of the optical signals to impart a phase gradient to each of the optical signals in accordance with the difference in the positions of the plurality of antenna elements and the desired direction which is the desired direction of arrival of the radio waves, and outputs a composite signal by combining the phase-weighted optical signals; and an extraction unit which outputs a receiving signal obtained by extracting the first sideband wave from the composite signal.

2. The receiving directivity control device according to claim 1, wherein the extraction unit extracts the first sideband from each of the plurality of optical signals converted by the electrical-to-optical conversion unit and outputs the extracted first sideband to the weighting unit, and the weighting unit outputs the combined signal as the receiving signal.

3. The receiving directivity control device according to claim 1, further comprising a multiplexing section that reverse-combines a carrier component obtained by adjusting the amplitude and phase of the light output from the light source with the receiving signal output from the extraction section.

4. The receiving directivity control device according to claim 1, further comprising a multiplexing section that reverse-combines a first sideband wave extracted from one of the optical signals converted by the electro-optical conversion section into the receiving signal output from the extraction section.

5. The receiving directivity control device according to claim 1, wherein the extraction unit extracts a second sideband wave from the composite signal and outputs it as a receiving signal for a radio signal arriving from a direction symmetrical to the desired direction with respect to a normal direction of an array antenna formed by a plurality of the antenna elements.

6. A reception directivity control device as claimed in claim 5, wherein the multiple antenna elements are arranged at intersections of multiple first lines parallel to a first direction on a plane and multiple second lines parallel to a second direction perpendicular to the first direction, and the weighting unit comprises: multiple first weighting circuits that correspond to each of the first lines and perform phase weighting on the optical signals converted from the radio signals received by the multiple antenna elements located on the corresponding first lines, by imparting a phase gradient that offsets a phase difference occurring in a first sideband wave of the optical signals in accordance with a difference in the positions of the antenna elements in the first direction and the desired direction; and multiple second weighting circuits that correspond to each of the second lines and perform phase weighting on the optical signals converted from the radio signals received by the multiple antenna elements located on the corresponding second lines, by imparting a phase gradient that offsets a phase difference occurring in a first sideband wave of the optical signals in accordance with a difference in the positions of the antenna elements in the second direction and the desired direction.

7. A reception directivity control device as described in claim 5, wherein the multiple antenna elements are arranged at intersections of multiple first straight lines parallel to a first direction on a plane and multiple second straight lines parallel to a second direction perpendicular to the first direction, the electro-optical conversion unit converts light from a light source to which an inverse phase has been imparted to a phase difference occurring in a first direction of a first sideband wave of the optical signal in accordance with a difference in position of the antenna elements in the first direction and the desired direction, into an optical signal that has been intensity modulated by the radio signal obtained from each of the multiple antenna elements, and the weighting unit performs phase weighting on the optical signal converted by the electro-optical conversion unit by imparting a phase gradient to align the phase difference occurring in a first sideband wave of the optical signal in accordance with a difference in position of the antenna elements in the second direction and the desired direction.

8. A reception directivity control method comprising: a receiving step in which a plurality of antenna elements receive radio waves and output radio signals obtained; an electrical-to-optical conversion step in which light output from a light source is converted into an optical signal intensity-modulated by each of the radio signals obtained by each of the plurality of antenna elements; a weighting step in which each of the optical signals is phase-weighted to impart a phase gradient to offset a phase difference occurring in a first sideband wave of the optical signal in accordance with a difference in the positions of the plurality of antenna elements and a desired direction which is the desired direction of arrival of the radio waves, and outputting a composite signal by combining the phase-weighted optical signals; and an extraction step in which the first sideband wave is extracted from the composite signal and outputting a reception signal obtained.

Images