WO2024116370A1 - Reception directivity control device and reception directivity control method - Google Patents

Abstract

The present invention is provided with: an electro-optical conversion unit that, with respective RF signals obtained by receiving, at respective antenna elements, incoming waves arriving from a desired direction, modulates optical signals respectively given phase slopes that correspond to the RF signals and are of the reverse sign of that of a row direction phase slope produced in accordance with differences in reception location in a row direction and with the desired direction; an optical multiplexing unit for generating multiplexed optical signals by multiplexing with optical signals respectively given phase slopes that correspond to the RF signals and are identical to a column direction phase slope produced in accordance with differences in reception location in a row direction and with the desired direction, and a single sideband component of a modulated optical signal generated by the modulation corresponding to each of the optical signals; an opto-electronic conversion unit for detecting each of the multiplexed optical signals generated by the optical multiplexing unit and generating detected RF signals corresponding respectively to the multiplexed optical signals; and an RF multiplexing unit for compositing the detected RF signals generated by the opto-electronic conversion unit and generating a received signal corresponding to the desired direction.

Description

Reception directivity control device and reception directivity control method

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

In order to achieve faster and larger capacity wireless communication, the use of high frequency bands above the millimeter wave band is being promoted. However, 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, high gain antennas are often used in high frequency bands. High gain antennas have high directivity, so it is necessary to align the direction of the antenna beam with the position of the other station in the wireless communication. If the other station moves, it is also necessary to perform beam steering, which is a means of dynamically controlling the beam direction to match the movement of the other station. Beam steering is not limited to wireless communication, but is also required in applications such as radar, imaging, and wireless power transmission.

Methods of beam steering that have been proposed and are actually in use include mechanically controlling the direction of the antenna, and using movable lenses or reflectors to refract and reflect the radio waves emitted from the antenna. However, these methods involve mechanical structures, which pose problems in terms of durability and ability to follow movement. For this reason, phased array antennas, which do not involve mechanical structures and are suitable for making antennas smaller and lighter, have come into widespread use in recent years.

In a phased array antenna, beam steering is performed, for example, as follows: Multiple antenna elements are arranged on a line or a surface, and variable delay circuits and variable attenuator circuits are connected to the multiple antenna elements. In addition to the variable delay circuits and variable attenuator circuits, digital signal processing and the like are used to control the phase and amplitude of the RF (Radio Frequency) signal supplied to each of the multiple antenna elements, thereby weighting the RF signal. This makes it possible to perform electronic beam steering in a phased array antenna. Note that in fifth-generation mobile communication systems and millimeter-wave wireless LAN (Local Area Network) systems that use millimeter-wave bands, phased array antennas that perform weighting using analog circuits are often used.

As the high frequency bands used expand, higher antenna gains will be required, and it is expected that phased array antennas that weight a larger number of antenna elements will be required. For example, Non-Patent Document 1 discloses a method for constructing a 256-element phased array antenna for use in a fifth generation mobile communication base station in the 28 GHz band. In sixth generation mobile communications, which aims to provide even faster transmission rates, the use of the 300 GHz band, the so-called terahertz band, for example, is being considered. When the radio frequency becomes about 10 times higher than the 28 GHz band, the free space propagation loss becomes 100 times higher. In other words, the free space propagation loss increases by 20 dB. In this case, it is expected that more than 10,000 antenna elements will be required to compensate for the 20 dB increase in free space propagation loss with the antenna gain of the base station.

In order to keep the power supply loss in the antenna element low, for example, it is necessary to make the RF transmission line between the antenna element and the phase shifter circuit as short as possible. Therefore, particularly in high-frequency phased array antennas such as those in the millimeter wave band, the phase shifter circuits are configured to be placed in the vicinity of each antenna element. However, as the radio frequency increases, the antenna element spacing becomes narrower, making it difficult to place a large number of phase shifter circuits, etc., at spacings equal to the antenna element spacing. For example, when the radio frequency is 300 GHz, the free space wavelength is 1 mm, so the spacing between antenna elements is generally set to half the wavelength, or 0.5 mm. In addition, to configure a circuit that forms multiple beams, i.e. a multi-beam forming circuit, it is necessary to place the same number of phase shifters as the number of beams in parallel, making the placement even more difficult.

For example, Non-Patent Document 2 proposes a method that applies optical circuit manufacturing technology that can implement small, low-loss waveguides to convert signals into light and then perform weighting using optical circuits. This method has a high potential for configuring a two-dimensional weighting circuit for a multi-element phased array antenna. However, with this method, the number of components in the weighting circuit increases in accordance with the number of antenna elements. Therefore, measures are needed to suppress the increase in the number of components even if the number of antenna elements increases. For example, the following means have been disclosed as existing technologies for performing weighting using optical circuits.

Patent Document 1 discloses an "optically controlled array antenna device" that uses a wavelength dispersion line to control two-dimensional multi-beams. FIGS. 1 and 2 of Patent Document 1 show the configuration of an optically controlled array antenna according to a first embodiment and the configuration of a second multi-beam forming means according to a second embodiment, respectively. The technology disclosed in Patent Document 1 provides phase tilt in the horizontal and vertical planes by a line using a wavelength-tunable light source and a waveguide with large wavelength dispersion. However, the number of one-dimensional phase shift circuits, i.e., "EL ₁ " to "EL _P " and "AZ ₁ " to "AZ _N " in FIG. 1 of Patent Document 1, which are a group of wavelength dispersion optical fibers, corresponds to the number of antenna elements in the vertical direction and the number of antenna elements in the horizontal direction. Therefore, the technology of Patent Document 1 has a problem that as the number of antenna elements increases, more one-dimensional phase shift circuits are required.

Patent Document 2 discloses a technology for two-dimensional beam control using a wavelength-tunable light source and a wavelength dispersion line. Fig. 2 of Patent Document 2 shows an outline of the configuration of a two-dimensional beam control device equipped with a 5 x 13 array antenna in the vertical x horizontal directions. As shown in Fig. 2, the light of the wavelength-tunable light source #1, indicated by reference numeral 42, is distributed into a number that matches the number of vertical elements (five distributions in the example of Fig. 2). A phase tilt in the vertical plane is given to each of the distributed light of the wavelength-tunable light source #1 by a first wavelength dispersion line array, indicated by reference numeral 52. The light to which the phase tilt has been given is converted into an electric signal train by a photodiode 54, and the converted electric signal train is amplified by an amplifier 56.

Next, the light of the wavelength-tunable light source #2 indicated by reference numeral 84 is distributed to a number equal to the number of vertical elements (distributed to 5 in the example of FIG. 2). The optical modulator 58 modulates each of the distributed lights of the wavelength-tunable light source #2 with the electric 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 to a number equal to the number of horizontal elements (distributed to 13 in the example of FIG. 2). A phase tilt in the horizontal plane is given to each of the distributed optical signal trains by the second wavelength dispersion line train indicated by reference numeral 62. Here, if the wavelength of the wavelength-tunable light source #1 is "λ _V " and the wavelength of the wavelength-tunable light source #2 is "λ _H ", the above configuration makes it possible to control vertical scanning with the wavelength λ _V and control horizontal scanning with the wavelength λ _H.

The operation during reception will be described with reference to Fig. 3 of Patent Document 2. An optical signal is generated by intensity modulating the light from the 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 distributed by an optical fiber splitter 112, and the distributed optical signal is given a delay gradient, i.e., a phase gradient, by a delay waveguide with large chromatic dispersion, indicated 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, indicated by reference numeral 114.

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

In Fig. 3 of Patent Document 2, for ease of understanding, only the configuration of a one-dimensional array is shown. To make this compatible with a two-dimensional array, the device is configured to use two tunable light sources, similar to the configuration shown in Fig. 2, and to input light with a two-dimensional phase gradient to an array of photomixers arranged in two dimensions. If an RF band CW is applied to the optical modulator 46 of a device configured in this way, it becomes possible to control the receiving directivity of the two-dimensional array antenna.

JP 2004-023400 A U.S. Pat. No. 6,337,660

As shown in Fig. 2 of Patent Document 2, the second wavelength dispersion line array, indicated by the reference numeral 62, is composed of lines whose number matches the number of antenna elements in the horizontal direction ("13" in the example shown in Fig. 2), and furthermore, the number of bundles of lines must match the number of antenna elements in the vertical direction ("5" in the example shown in Fig. 2). Therefore, 5 x 13 wavelength dispersion lines are required.

When constructing a larger two-dimensional array antenna, the number of wavelength dispersion lines required increases. This increases the circuit scale, resulting in a problem of increased circuit size, i.e., circuit area and volume. When considering the need to reduce the height of the device configuration and use a printed circuit manufacturing process for mass production, the three-dimensional circuit structure that uses wavelength dispersion lines to provide a phase tilt, as in Patent Documents 1 and 2, is not suitable for mass production.

Therefore, the technologies disclosed in Patent Documents 1 and 2 have the problem that as the scale of the array antenna increases, the number of components and wiring that make up the circuit that forms the beam increases, resulting in a larger circuit size, and furthermore, the circuit structure that forms the beam becomes more complex, making it unsuitable for mass production.

In light of the above circumstances, the present invention aims to provide technology that enables control of the receiving directivity of an array antenna to be implemented using a circuit with a simple structure that is suitable for miniaturization and mass production, even if the size of the array antenna increases.

One aspect of the present invention is a receiving directivity control device that controls the receiving directivity of an array antenna in which an arbitrary straight line in a plane is an axis in the row direction, a straight line perpendicular to the axis in the row direction in the plane is an axis in the column direction, and a plurality of antenna elements are arranged along the axis in the row direction and the axis in the column direction, and the receiving directivity control device controls the receiving directivity of an array antenna in which an arbitrary straight line in a plane is an axis in the row direction and a straight line perpendicular to the axis in the row direction is an axis in the column direction, and the receiving directivity control device controls the receiving directivity of an array antenna in which a plurality of antenna elements are arranged along the axis in the row direction and a plurality of antenna elements are arranged along the axis in the column direction. The receiving directivity control device includes an electro-optical conversion unit that modulates each of optical signals to which a phase gradient corresponding to each of the RF signals is imparted, the phase gradient having an opposite sign to the row-direction phase gradient that occurs depending on the difference in receiving position in the row direction and the desired direction, and the phase gradient control unit modulates each of optical signals to which a phase gradient corresponding to each of the RF signals is imparted, the phase gradient having an opposite sign to the row-direction phase gradient that occurs depending on the difference in receiving position in the row direction and the desired direction, the phase gradient control unit modulating the phase gradient of each of the ... control unit modulating the phase gradient of each of the optical signals to which a phase gradient corresponding to each of the A reception directivity control device that includes: each of the optical signals to which a phase gradient corresponding to each of the RF signals is imparted, the phase gradient being the same as the column-wise phase gradient that occurs depending on the difference in reception position in the column direction and the desired direction; an optical multiplexing unit that multiplexes each of the optical signals with a single sideband component of a modulated optical signal generated by the modulation corresponding to the RF signals to generate a multiplexed optical signal; an opto-electrical conversion unit that detects each of the multiplexed optical signals generated by the optical multiplexing unit and generates a detected RF signal corresponding to each of the multiplexed optical signals; and an RF multiplexing unit that combines each of the detected RF signals generated by the opto-electrical conversion unit to generate a reception signal corresponding to the desired direction.

One aspect of the present invention is a receiving directivity control method for controlling the receiving directivity of an array antenna in which an arbitrary straight line in a plane is defined as a row-direction axis, a straight line perpendicular to the row-direction axis in the plane is defined as a column-direction axis, and a plurality of antenna elements are arranged along the row-direction axis and the column-direction axis, and the receiving directivity of the array antenna is controlled by controlling the receiving directivity of the array antenna in which an incoming wave arriving from a desired direction is received by each of the antenna elements, and each of the RF signals obtained by the reception of the incoming wave from the desired direction has a phase tilt corresponding to each of the RF signals, the phase tilt having an opposite sign to the row-direction phase tilt that occurs depending on the difference in receiving position in the row direction and the desired direction. A reception directivity control method that modulates each of the optical signals to be applied, combines each of the optical signals to which a phase gradient corresponding to each of the RF signals, which is the same as the column-wise phase gradient that occurs depending on the difference in reception position in the column direction and the desired direction, with a single sideband component of the modulated optical signal generated by the modulation corresponding to each of the optical signals to generate a combined optical signal, detects each of the generated combined optical signals to generate a detected RF signal corresponding to each of the combined optical signals, and combines each of the generated detected RF signals to generate a reception signal corresponding to the desired direction.

The present invention makes it possible to implement control of the receiving directivity of an array antenna using a circuit with a simple structure that is suitable for miniaturization and mass production, even if the array antenna becomes large in size.

1 is a block diagram showing a configuration related to a reception directivity control device according to a first embodiment; FIG. 4 is a diagram showing the direction of a beam formed in the first embodiment. 4 is a flowchart showing a flow of processing by the reception directivity control device of the first embodiment. FIG. 11 is a block diagram showing a configuration related to a reception directivity control device according to a second embodiment. FIG. 11 is a block diagram showing a configuration related to a reception directivity control device that forms two beams in a third embodiment. FIG. 13 is a block diagram showing a configuration related to a reception directivity control device that forms four beams in a third embodiment. FIG. 13 is a block diagram showing a configuration related to a reception directivity control device according to a fourth embodiment. FIG. 13 is a block diagram showing an internal configuration of a polarization wavelength demultiplexer included in a reception directivity control device according to a fourth embodiment.

First Embodiment
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings, in which: FIG. 1 is a block diagram showing the internal configuration of a reception directivity control device 1 according to a first embodiment, an array antenna 80 connected to the reception directivity control device 1, and beams 90-1 to 90-4 formed by the array antenna 80.

The reception directivity control device 1 is, for example, a device that is incorporated into a receiving device that demodulates a received signal. The reception directivity control device 1 is used to control the reception directivity of radio waves with sharp directionality that are required, for example, for ultra-high-speed wireless transmission using radio waves in the millimeter wave band or terahertz band, high-definition imaging, radar, etc.

Array antenna 80 is a so-called phased array antenna. Array antenna 80 is an array antenna with a 2x2 configuration, with two elements arranged along the vertical direction and two elements arranged along the horizontal direction, for a total of four antenna elements 80-1-1, 80-1-2, 80-2-1, and 80-2-2. Hereinafter, the vertical direction will also be referred to as the row direction, and the horizontal direction will also be referred to as the column direction. Antenna elements 80-1-1 to 80-2-2 are arranged on a plane, i.e., on the surface of array antenna 80.

More specifically, the line segment connecting antenna element 80-1-1 and antenna element 80-2-1 and the line segment connecting antenna element 80-1-2 and antenna element 80-2-2 are the same length and parallel to the row axis. The line segment connecting antenna element 80-1-1 and antenna element 80-1-2 and the line segment connecting antenna element 80-2-1 and antenna element 80-2-2 are the same length and parallel to the column axis.

Each of the antenna elements 80-1-1 to 80-2-2 receives incoming radio frequency radio waves, i.e., RF radio waves, and is supplied with an electrical RF signal. Hereinafter, the incoming RF radio waves are referred to as incoming waves.

The receiving directivity control device 1 includes an electrical-to-optical conversion unit 11, an optical multiplexing unit 12, an optical-to-electrical conversion unit 13, an RF multiplexing unit 16, a row-direction phase gradient imparting unit 20, a column-direction phase gradient imparting unit 30, a first light source 41, and a second light source 42.

The reception directivity control device 1 controls the directivity so that the incoming wave coming from the direction desired by the user (hereinafter referred to as the desired direction) is received. The reception directivity control device 1 forms one of the beams 90-1, 90-2, 90-3, and 90-4 in the array antenna 80, whose direction coincides with the desired direction. Figures 2(a) and 2(b) are diagrams showing the relationship between the plane of the array antenna 80 and the directions in which the beams 90-1, 90-2, 90-3, and 90-4 are formed. When viewed from the observation direction indicated by the arrow in Figure 2(a) through the plane of the array antenna 80, as shown in Figure 2(b), the beam 90-1 faces in the upper left direction, the beam 90-2 faces in the upper right direction, the beam 90-3 faces in the lower left direction, and the beam 90-4 faces in the lower right direction.

The tilts of beams 90-1 and 90-2 with respect to the horizontal plane, in other words, the vertical components of the tilts of beams 90-1 and 90-2, are the same, and the phase difference caused by this tilt, that is, the phase tilt, is represented by "φ _V ". The tilts of beams 90-2 and 90-4 with respect to the vertical plane, in other words, the horizontal components of the tilts of beams 90-2 and 90-4, are the same, and the phase difference caused by this tilt, that is, the phase tilt, is represented by "φ _H ".

Here, the phase tilt will be described in more detail. For example, suppose that an incoming wave coming from the direction of beam 90-2 is received by two antenna elements 80-1-1 and 80-2-1 in the same column. In this case, due to the tilt of beam 90-2 with respect to the horizontal plane and the difference in the positions of antenna elements 80-1-1 and 80-2-1, a difference occurs in the arrival time required for the incoming wave to reach antenna element 80-1-1 and antenna element 80-2-1. Due to this difference in arrival time, a phase difference _φV occurs in the RF signals obtained from each of antenna elements 80-1-1 and 80-2-1.

As described above, the distance between two antenna elements 80-1-2 and 80-2-2 in the same column is the same as the distance between antenna elements 80-1-1 and 80-2-1. Therefore, even when antenna elements 80-1-2 and 80-2-2 receive an incoming wave coming from the direction of beam 90-2, a phase difference _φV occurs in the RF signal. This phase difference _φV becomes the phase gradient in the row direction of beam 90-2 (hereinafter referred to as row direction phase gradient).

Similarly, when two antenna elements 80-1-1 and 80-1-2 in the same row receive an incoming wave coming from the direction of beam 90-2, a difference occurs in the arrival time required for the incoming wave to reach antenna element 80-1-1 and antenna element 80-1-2. Due to this difference in arrival time, a phase difference _φH occurs in the RF signals obtained from each of antenna elements 80-1-1 and 80-1-2. This is also the case for two antenna elements 80-2-1 and 80-2-2 in the same row. Therefore, this phase difference _φH becomes the phase tilt in the column direction of beam 90-2 (hereinafter referred to as the column-direction phase tilt).

In addition, when three or more antenna elements are arranged at equal intervals in the row direction, the phase difference between the RF signals obtained from two adjacent antenna elements in the row direction for a wave arriving from one direction will be the same. Similarly, when three or more antenna elements are arranged at equal intervals in the column direction, the phase difference between the RF signals obtained from two adjacent antenna elements in the column direction for a wave arriving from one direction will be the same.

The row phase tilt of beams 90-3 and 90-4 is the same and is the opposite of the row phase tilt of beams 90-1 and 90-2. Therefore, the row phase tilt of beams 90-3 and 90-4 is "-φ _V ". The column phase tilt of beams 90-1 and 90-3 is the same and is the opposite of the column phase tilt of beams 90-2 and 90-4. Therefore, the column phase tilt of beams 90-1 and 90-3 is "-φ _H ".

The electro-optical conversion unit 11 includes SSB (Single Side-Band) modulators 11-1-1, 11-1-2, 11-2-1, and 11-2-2, the number of which matches the number of antenna elements 80-1-1 to 80-2-2. Each of the SSB modulators 11-1-1, 11-1-2, 11-2-1, and 11-2-2 is connected to its corresponding antenna element 80-1-1, 80-1-2, 80-2-1, and 80-2-2. Each of the SSB modulators 11-1-1 to 11-2-2 has the same characteristics and is an optical modulator that performs optical modulation according to the same standard, specifications, and method. Each of the SSB modulators 11-1-1 to 11-2-2 modulates the optical signal supplied to it with an RF signal supplied from the antenna elements 80-1-1 to 80-2-2 connected to it, and outputs a single sideband component of the modulated optical signal. Note that the single sideband component includes a USB (Upper Side Band) component and an LSB (Lower Side Band) component, but the following explanation assumes that the SSB modulators 11-1-1 to 11-2-2 output the USB component.

The optical multiplexing unit 12 includes optical multiplexers 12-1-1, 12-1-2, 12-2-1, and 12-2-2, the number of which corresponds to the number of SSB modulators 11-1-1 to 11-2-2. Each of the optical multiplexers 12-1-1, 12-1-2, 12-2-1, and 12-2-2 is connected to the corresponding SSB modulators 11-1-1, 11-1-2, 11-2-1, and 11-2-2. Each of the optical multiplexers 12-1-1 to 12-2-2 generates a multiplexed optical signal by multiplexing the optical signal supplied to it with the optical signal output by the SSB modulators 11-1-1 to 11-2-2 connected to it.

The antenna elements 80-1-1 to 80-2-2, the SSB modulators 11-1-1 to 11-2-2, and the optical multiplexers 12-1-1 to 12-2-2 have two branch numbers, the former of which corresponds to the row number, and the latter of which corresponds to the column number. For example, the antenna element 80-2-1 is located in the second row and first column. In order to reduce RF signal loss, it is desirable to place each of the SSB modulators 11-1-1 to 11-2-2 in the vicinity of the antenna elements 80-1-1 to 80-2-2 to which it is connected. In contrast, the optical multiplexers 12-1-1 to 12-2-2 are shown in correspondence with rows and columns, but they do not need to be arranged three-dimensionally like the antenna elements 80-1-1 to 80-2-2, and can be arranged on a plane.

The photoelectric conversion unit 13 includes four photomixers 13-1, 13-2, 13-3, and 13-4. Each of the photomixers 13-1, 13-2, 13-3, and 13-4 is, for example, a photodiode, and performs square detection on the multiplexed optical signals output by the optical multiplexers 12-1-1, 12-1-2, 12-2-1, and 12-2-2 connected to each of them to generate an electrical RF signal (hereinafter referred to as the detected RF signal).

The RF multiplexer 16 includes an RF multiplexer 17. The RF multiplexer 17 is connected to the photomixers 13-1 to 13-4, and generates an RF signal by combining the detected RF signals output by the photomixers 13-1 to 13-4. This combined RF signal becomes the received signal of the incoming wave arriving from the desired direction.

The first light source 41 and the second light source 42 each generate CW light of the same frequency. However, the amplitude of the second light source 42 is determined according to the modulation depth of the optical modulation by the SSB modulators 11-1-1 to 11-2-2. Hereinafter, the CW light generated by the first light source 41 is referred to as the first optical signal, and the CW light generated by the second light source 42 is referred to as the second optical signal. Note that, in the connection lines within the reception directivity control device 1 in FIG. 1, the dashed connection line indicates the path of the first optical signal, and the dashed connection line indicates the path of the second optical signal, and this is also true in other embodiments described below.

The row direction phase tilt imparting unit 20 comprises a row direction scanning instruction circuit 22, a row direction scanning switching circuit 23, a row direction scanning matrix circuit 24, and distributors 25-1, 25-2. For example, in response to an operation by a user to specify a desired direction, the row direction scanning instruction circuit 22 outputs instruction information indicating the elevation/depression angle, i.e., the vertical angle, of any one of the beams 90-1 to 90-4 having a direction that coincides with the desired direction. Since the vertical direction coincides with the row direction, hereinafter, this instruction information is referred to as "row direction instruction information."

Beams 90-1 to 90-4 formed by the reception directivity control device 1 have two angles in the row direction: the angle that beams 90-1 and 90-2 make with the horizontal plane, and the angle that beams 90-3 and 90-4 make with the horizontal plane. Therefore, for example, the former angle is defined as "upward" and the latter angle is defined as "downward" as row direction instruction information. For example, when beam 90-2 is formed, beam 90-2 corresponds to "upward", so the row direction scanning instruction circuit 22 outputs "upward" as row direction instruction information. On the other hand, when beam 90-4 is formed, beam 90-4 corresponds to "downward", so the row direction scanning instruction circuit 22 outputs "downward" as row direction instruction information.

The row direction scanning switching circuit 23 is connected to the first light source 41 and has two output ports 23-1 and 23-2. The row direction scanning switching circuit 23 captures the first optical signal output by the first light source 41, switches the output destination of the captured first optical signal, and outputs it from one of the output ports 23-1 and 23-2. The row direction scanning switching circuit 23 switches the output destination of the first optical signal according to the elevation/depression angle of any one of the beams 90-1 to 90-4 that matches the desired direction. More specifically, the output port 23-1 is pre-associated with the row direction instruction information "upward" output by the row direction scanning instruction circuit 22, and the output port 23-2 is pre-associated with the row direction instruction information "downward". The row direction scanning switching circuit 23 selects the output port 23-1 or 23-2 that corresponds to the row direction instruction information output by the row direction scanning instruction circuit 22 as the output destination of the first optical signal.

The row direction scanning matrix circuit 24 has two input ports 24-1 and 24-2 and two output ports 24-3 and 24-4. The input port 24-1 is connected to the output port 23-1 of the row direction scanning switching circuit 23. The input port 24-2 is connected to the output port 23-2 of the row direction scanning switching circuit 23. The output port 24-3 is connected to the distributor 25-1. The output port 24-4 is connected to the distributor 25-2.

The row direction scanning matrix circuit 24 imparts a phase tilt to the first optical signal supplied from the input port 24-1 so that the two optical signals output from the output ports 24-3 and 24-4 have a phase tilt that is "-1" times the row direction phase tilt φ _V corresponding to the row direction instruction information "upward". In other words, the row direction scanning matrix circuit 24 imparts a phase tilt so that the first optical signal output from the output port 24-4 becomes an optical signal whose phase leads that of the first optical signal output from the output port 24-3 by φ _V.

The row direction scanning matrix circuit 24 imparts a phase tilt to the first optical signal supplied from the input port 24-2 so that two optical signals output from each of the output ports 24-3 and 24-4 have a phase tilt that is "-1" times the row direction phase tilt -φ _V corresponding to the row direction instruction information "downward." In other words, the row direction scanning matrix circuit 24 imparts a phase tilt so that the first optical signal output from the output port 24-4 becomes an optical signal whose phase lags behind that of the first optical signal output from the output port 24-3 by φ _V.

The distributor 25-1 distributes the first optical signal output by the output port 24-3 of the row-direction scanning matrix circuit 24, and outputs each of the distributed first optical signals to the SSB modulator 11-1-1 and SSB modulator 11-1-2 in the same row while maintaining the phase. The distributor 25-2 distributes the first optical signal output by the output port 24-4 of the row-direction scanning matrix circuit 24, and outputs each of the distributed first optical signals to the SSB modulator 11-2-1 and SSB modulator 11-2-2 in the same row while maintaining the phase.

In other words, the row direction phase gradient imparting unit 20 outputs two combinations of two first optical signals to which a phase gradient of the opposite sign to the row direction phase gradient corresponding to the desired direction has been imparted, the number of sets being equal to the number of rows of the array antenna 80. Hereinafter, the combination of two first optical signals to which a phase gradient of the opposite sign to the row direction phase gradient corresponding to the desired direction output by the row direction phase gradient imparting unit 20 has been referred to as a row optical signal. In other words, using this row optical signal, the row direction phase gradient imparting unit 20 supplies row signals to the combination of SSB modulator 11-1-1 and SSB modulator 11-2-1 in the same column, and the combination of SSB modulator 11-1-2 and SSB modulator 11-2-2 in the same column.

The column-direction phase tilt applying unit 30 comprises a column-direction scanning instruction circuit 32, a column-direction scanning switching circuit 33, a column-direction scanning matrix circuit 34, and distributors 35-1 and 35-2. For example, in response to an operation by a user to specify a desired direction, the column-direction scanning instruction circuit 32 outputs instruction information indicating the azimuth angle, i.e., the horizontal angle, of any one of the beams 90-1 to 90-4 having a direction that coincides with the desired direction. Since the horizontal direction coincides with the column direction, hereinafter, this instruction information is referred to as "column-direction instruction information."

Beams 90-1 to 90-4 formed by the reception directivity control device 1 have two angles in the column direction: the angle that beams 90-2 and 90-4 make with the vertical plane, and the angle that beams 90-1 and 90-3 make with the vertical plane. Therefore, for example, the former angle is defined as "rightward" and the latter angle is defined as "leftward" as column direction instruction information. For example, when beam 90-2 is formed, beam 90-2 corresponds to "rightward", so the column direction scanning instruction circuit 32 outputs "rightward" as column direction instruction information. On the other hand, when beam 90-1 is formed, beam 90-1 corresponds to "leftward", so the column direction scanning instruction circuit 32 outputs "leftward" as column direction instruction information.

The column-direction scanning switching circuit 33 is connected to the second light source 42 and has two output ports 33-1 and 33-2. The column-direction scanning switching circuit 33 captures the second optical signal output by the second light source 42, switches the output destination of the captured second optical signal, and outputs it from one of the output ports 33-1 and 33-2. The column-direction scanning switching circuit 33 switches the output destination of the second optical signal according to the azimuth angle of any one of the beams 90-1 to 90-4 that matches the desired direction. More specifically, the output port 33-1 is previously associated with the column direction instruction information "rightward" output by the column direction scanning instruction circuit 32, and the output port 33-2 is previously associated with the column direction instruction information "leftward". The column-direction scanning switching circuit 33 selects the output port 33-1 or 33-2 that corresponds to the column direction instruction information output by the column direction scanning instruction circuit 32 as the output destination of the second optical signal.

The column-direction scanning matrix circuit 34 has two input ports 34-1 and 34-2 and two output ports 34-3 and 34-4. The input port 34-1 is connected to the output port 33-1 of the column-direction scanning switching circuit 33. The input port 34-2 is connected to the output port 33-2 of the column-direction scanning switching circuit 33. The output port 34-3 is connected to the distributor 35-1. The output port 34-4 is connected to the distributor 35-2.

The column-direction scanning matrix circuit 34 imparts a phase gradient to the second optical signal supplied from the input port 34-1 so that the two optical signals output from the output ports 34-3 and 34-4 have the same phase gradient as the column-direction phase gradient _φH corresponding to the column direction instruction information "rightward". In other words, the column-direction scanning matrix circuit 34 imparts a phase gradient so that the second optical signal output from the output port 34-4 becomes an optical signal whose phase lags behind that of the second optical signal output from the output port 34-3 by _φH .

The column-direction scanning matrix circuit 34 imparts a phase tilt to the second optical signal supplied from the input port 34-2 so that the two optical signals output from the output ports 34-3 and 34-4 have the same phase tilt as the column-direction phase tilt _-φH corresponding to the column direction information "leftward". In other words, the column-direction scanning matrix circuit 34 imparts a phase tilt so that the second optical signal output from the output port 34-4 becomes an optical signal whose phase leads that of the second optical signal output from the output port 34-3 by _φH .

The distributor 35-1 distributes the second optical signal output by the output port 34-3 of the column-direction scanning matrix circuit 34, and outputs each of the distributed second optical signals to the optical multiplexer 12-1-1 and optical multiplexer 12-2-1 in the same column while maintaining the phase. The distributor 35-2 distributes the second optical signal output by the output port 34-4 of the column-direction scanning matrix circuit 34, and outputs each of the distributed second optical signals to the optical multiplexer 12-1-2 and optical multiplexer 12-2-2 in the same column while maintaining the phase.

In other words, the column-directional phase tilt imparting unit 30 outputs two combinations of two second optical signals imparted with the same phase tilt as the column-directional phase tilt corresponding to the desired direction, the number of which corresponds to the number of columns of the array antenna 80. Hereinafter, the combinations of two second optical signals imparted with the same phase tilt as the column-directional phase tilt corresponding to the desired direction output by this column-directional phase tilt imparting unit 30 will also be referred to as column optical signals. In other words, using this column optical signal, the column-directional phase tilt imparting unit 30 supplies column signals to the combination of optical multiplexers 12-1-1 and 12-1-2 in the same row, and the combination of optical multiplexers 12-2-1 and 12-2-2 in the same row.

(Processing by the reception directivity control device 1 of the first embodiment)
3 is a flowchart showing the flow of processing by the reception directivity control device 1 of the first embodiment. Here, it is assumed that the desired direction desired by the user is the direction of beam 90-2. When the user specifies the direction of beam 90-2 as the desired direction in the row direction scanning instruction circuit 22, the row direction scanning instruction circuit 22 outputs row direction instruction information "upward" to the row direction scanning switching circuit 23. When the user specifies the direction of beam 90-2 as the desired direction in the column direction scanning instruction circuit 32, the column direction scanning instruction circuit 32 outputs column direction instruction information "rightward" to the column direction scanning switching circuit 33 (S1).

When the row direction scanning switching circuit 23 receives the row direction instruction information "upward" from the row direction scanning instruction circuit 22, it selects the output port 23-1 corresponding to the row direction instruction information "upward". The row direction scanning switching circuit 23 takes in the first optical signal output by the first light source 41, and outputs the taken in first optical signal from the selected output port 23-1, as shown by the dotted line in the row direction scanning switching circuit 23 in FIG. 1. The row direction scanning matrix circuit 24 takes in the first optical signal from the input port 24-1, and imparts a phase inclination to the taken in first optical signal so that two optical signals output from the output port 24-3 and the output port 24-4 respectively have a phase inclination "-1" times the row direction phase inclination φ _V corresponding to "upward". The row direction scanning matrix circuit 24 outputs the first optical signal to which the phase inclination has been imparted from the output port 24-3 and the output port 24-4.

The distributor 25-1 distributes the first optical signal output by the output port 24-3 into two, and outputs the two distributed first optical signals as CW light to the SSB modulators 11-1-1 and 11-1-2 in the same row. The distributor 25-2 distributes the first optical signal output by the output port 24-4 into two, and outputs the two distributed first optical signals as CW light to the SSB modulators 11-2-1 and 11-2-2 in the same row (S2).

The SSB modulator 11-1-1 takes in the first optical signal output by the distributor 25-1, modulates the taken-in first optical signal with the RF signal supplied from the antenna element 80-1-1, and outputs the USB component of the modulated optical signal. Here, the RF signal that the SSB modulator 11-1-1 acquires from the antenna element 80-1-1 that receives the incoming wave coming from the direction of the beam 90-2 can be expressed as the following equation (1).

In equation (1), ω _RF is the angular frequency of the RF signal. The first optical signal that the SSB modulator 11-1-1 receives from the distributor 25-1 can be expressed by the following equation (2).

In equation (2), ω _C is the angular frequency of the first optical signal generated by the first light source 41. In this case, the modulated optical signal generated by the SSB modulator 11-1-1 through modulation is an intensity-modulated signal, i.e., an amplitude-modulated signal, and is therefore expressed as the following equation (3).

In equation (3), "2A" is the modulation depth. The equation showing the output optical signal output by SSB modulator 11-1-1, i.e., the USB component of the modulated optical signal, is given by the following equation (4) from equation (3).

In contrast, the SSB modulator 11-2-1, which is in a different row but the same column as the SSB modulator 11-1-1, takes in the first optical signal output by the distributor 25-2 and modulates the taken-in first optical signal with an RF signal supplied from the antenna element 80-2-1. Here, the RF signal that the SSB modulator 11-2-1 acquires from the antenna element 80-2-1 that receives the incoming wave arriving from the direction of the beam 90-2 is an RF signal delayed by _φV from the RF signal expressed by equation (1) due to the above-mentioned row-direction phase tilt _φV . Therefore, the RF signal is expressed as the following equation (5).

The first optical signal that the SSB modulator 11-2-1 acquires from the distributor 25-2 is given a phase tilt of "-1" times the row-direction phase tilt φ _V corresponding to "upward" with respect to the first optical signal output by the distributor 25-1. Therefore, the first optical signal that the SSB modulator 11-2-1 receives from the distributor 25-2 is an optical signal whose phase leads that of the first optical signal expressed by formula (2) by φ _V , and is expressed by the following formula (6).

In this case, the output optical signal output by the SSB modulator 11-2-1, i.e., the USB component of the modulated optical signal, is expressed as the following equation (7).

As can be seen from the equation (4) showing the output optical signal of the SSB modulator 11-1-1 and the equation on the right side of the equation (7) showing the output optical signal of the SSB modulator 11-2-1, the output optical signals of the SSB modulators 11-1-1 and 11-2-1 in the same column have the same phase. This is because, in the RF signal and the first optical signal supplied to each of the SSB modulators 11-1-1 and 11-2-1, the two RF signals have a row-direction phase tilt φ _V , and the row optical signal, which is the two first optical signals, has a phase tilt that is "-1" times the row-direction phase tilt φ _V. Therefore, as shown on the left side of the equation (7), the phase difference φ _V is canceled out in the SSB modulator 11-2-1, and the output optical signals of the SSB modulators 11-1-1 and 11-2-1 have the same phase.

Similarly, each of the SSB modulators 11-1-2, 11-2-2 in the same column modulates the first optical signal output by the distributors 25-1, 25-2 connected to each of them with the RF signal output by the antenna elements 80-1-2, 80-2-2 connected to each of them. In this case, the output optical signals output by each of the SSB modulators 11-1-2, 11-2-2, i.e., the USB components of the modulated optical signals, are also in phase (S3).

When the column direction scanning switching circuit 33 receives the column direction instruction information "rightward" from the column direction scanning instruction circuit 32, it selects the output port 33-1 corresponding to the column direction instruction information "rightward". The column direction scanning switching circuit 33 takes in the second optical signal output by the second light source 42, and outputs the taken in second optical signal from the selected output port 33-1, as shown by the dotted line in the column direction scanning switching circuit 33 in FIG. 1. The column direction scanning matrix circuit 34 takes in the second optical signal from the input port 34-1, and imparts a phase inclination to the taken in second optical signal so that two optical signals output from the output port 34-3 and the output port 34-4 have the same phase inclination as the column direction phase inclination φ _H corresponding to "rightward". The column direction scanning matrix circuit 34 outputs the second optical signal to which the phase inclination has been imparted from the output port 34-3 and the output port 34-4.

The distributor 35-1 distributes the second optical signal output by the output port 34-3 into two, and outputs the two distributed second optical signals as CW light to the optical multiplexers 12-1-1 and 12-2-1 in the same row. The distributor 35-2 distributes the second optical signal output by the output port 34-4 into two, and outputs the two distributed second optical signals as CW light to the optical multiplexers 12-1-2 and 12-2-2 in the same row (S4). Note that the processes of S2 and S3 and S4 are performed in parallel.

The optical multiplexer 12-1-1 multiplexes the output optical signal output by the SSB modulator 11-1-1 with the second optical signal output by the distributor 35-1 to generate a multiplexed optical signal. The output optical signal output by the SSB modulator 11-1-1 is expressed by the above formula (4). The second optical signal output by the distributor 35-1 can be expressed by the following formula (8).

In equation (8), "A" is the amplitude value of the second optical signal. As described above, the second light source 42 generates the second optical signal with an amplitude value determined according to the modulation depth of the optical modulation by the SSB modulator 11-1-1. Here, an example is shown in which the second light source 42 generates the second optical signal with an amplitude value that is half the modulation depth "2A" shown in equation (3).

In this case, the multiplexed optical signal output by the optical multiplexer 12-1-1 is expressed by the following equation (9).

Similar to the optical multiplexer 12-1-1, the optical multiplexer 12-2-1 is supplied with the second optical signal output by the distributor 35-1 expressed by equation (8) and the output optical signal output by the SSB modulator 11-2-1 expressed by equation (7). Therefore, the equation of the combined optical signal output by the optical multiplexer 12-2-1 is the same as the above equation (9).

The optical multiplexer 12-1-2 multiplexes the output optical signal output by the SSB modulator 11-1-2 with the second optical signal output by the distributor 35-2 to generate a multiplexed optical signal. The SSB modulator 11-1-2 modulates the first optical signal output by the distributor 25-1 with the RF signal obtained from the antenna element 80-1-2. The first optical signal output by the distributor 25-1 is the same optical signal as the first optical signal supplied to the SSB modulator 11-1-1, and is therefore expressed by equation (2).

The RF signal obtained from antenna element 80-1-2 receiving an incoming wave from the direction of beam 90-2 is a signal whose phase is delayed by _φH from the RF signal obtained from antenna element 80-1-1 receiving an incoming wave from the direction of beam 90-2. The RF signal obtained from antenna element 80-1-1 receiving an incoming wave from the direction of beam 90-2 is an RF signal supplied to SSB modulator 11-1-1, and is expressed by equation (1). Therefore, the RF signal supplied to SSB modulator 11-1-2 is expressed by the following equation (10).

Therefore, the output optical signal output by the SSB modulator 11-1-2 is expressed as the following equation (11).

As can be seen from equations (4) and (11), the phase difference between the output optical signal output by the SSB modulator 11-1-1 and the output optical signal output by the SSB modulator 11-1-2 coincides with the column-wise phase tilt _φH of the beam 90-2.

The second optical signal output by the distributor 35-2 is given a phase tilt that is the same as the column-direction phase tilt _φH corresponding to the "rightward" direction with respect to the second optical signal output by the distributor 35-1. In other words, the second optical signal output by the distributor 35-2 is an optical signal whose phase lags behind that of the second optical signal output by the distributor 35-1 by _φH . Since the second optical signal output by the distributor 35-1 is expressed by equation (8), the second optical signal output by the distributor 35-2 is expressed by the following equation (12).

Therefore, the multiplexed optical signal output by the optical multiplexer 12-1-2 is expressed as the following equation (13) based on equations (11) and (12).

As described above, the output optical signals output by the SSB modulator 11-1-2 and the SSB modulator 11-2-2 have the same phase. Therefore, the output optical signal output by the SSB modulator 11-2-2 is expressed by equation (11). Therefore, the optical multiplexer 12-2-2 is supplied with the second optical signal output by the distributor 35-2 expressed by equation (12) and the output optical signal output by the SSB modulator 11-2-2 shown in equation (11). Therefore, the equation of the combined optical signal output by the optical multiplexer 12-2-2 is the same as the above equation (13) (S5).

The photomixer 13-1 of the photoelectric conversion unit 13 performs square detection on the multiplexed optical signal output by the optical multiplexer 12-1-1, and outputs a detected RF signal. The square detection performed by the photomixer 13-1 can be expressed as the following equation (14) based on equation (9).

The detected RF signal output by photomixer 13-1 is the RF frequency band term in equation (14), and is expressed as the following equation (15).

As described above, the multiplexed optical signal output by the optical multiplexer 12-2-1 is the same as the multiplexed optical signal output by the optical multiplexer 12-1-1. Therefore, the detected RF signal output by the photomixer 13-3 connected to the optical multiplexer 12-2-1 is also expressed as equation (15).

The photomixer 13-2 performs square detection on the multiplexed optical signal output by the optical multiplexer 12-1-2 and outputs a detected RF signal. The square detection performed by the photomixer 13-2 can be expressed as the following equation (16) based on equation (13).

The detected RF signal output by photomixer 13-2 is the RF frequency band term in equation (16), and is expressed as the following equation (17).

As described above, the multiplexed optical signal output by the optical multiplexer 12-2-2 is the same as the multiplexed optical signal output by the optical multiplexer 12-1-2. Therefore, the detected RF signal output by the photomixer 13-4 connected to the optical multiplexer 12-2-2 is also expressed as equation (17) (S6).

As can be seen from equations (15) and (17), the detected RF signals output by photomixers 13-1 to 13-4 are all in phase. The reason they are all in phase is because the combined optical signals have the following relationship:

In the formula (9) showing the multiplexed optical signal output by the optical multiplexer 12-1-1, the second term "Acosω _C t" which is the second optical signal can be regarded as a carrier component with respect to the sideband component of the first term "Acos(ω _C +ω _RF )t". In this case, the multiplexed optical signal output by the optical multiplexer 12-1-2 shown in formula (13) has a form in which the same column-wise phase tilt φ _H exists in both the carrier component and the sideband component, compared to the multiplexed optical signal shown in formula (9). In this way, the column-wise phase tilt applying unit 30 generates two second optical signals having a phase difference equivalent to the phase difference φ _H occurring between the output optical signal of the SSB modulator 11-1-1 and the output optical signal of the SSB modulator 11-1-2, so that the terms of the RF frequency band become the same due to square detection by the photomixers 13-1 and 13-2. This also applies to the relationship between the optical multiplexers 12-2-1 and 12-2-2. Therefore, the RF frequency band terms in the results of square detection by the photomixers 13-3 and 13-4 are also the same.

The output optical signals output by each of the SSB modulators 11-1-1 and 11-2-1 are in phase, and the second optical signal of the same phase output by the distributor 35-1 is multiplexed with the output optical signals of the same phase, so the multiplexed optical signals output by each of the optical multiplexers 12-1-1 and 12-2-1 are in phase. Therefore, the two detected RF signals output by the photomixers 13-1 and 13-3 are also in phase. This is also true for the relationship between the optical multiplexers 12-1-2 and 12-2-2. Therefore, the RF frequency band terms in the results of square detection by the photomixers 13-2 and 13-4 are the same, and as a result, the detected RF signals output by the photomixers 13-1 to 13-4 are all in phase.

The RF combiner 17 of the RF combiner unit 16 combines the detected RF signals output by the photomixers 13-1 to 13-4, resulting in the combination of in-phase components of the detected RF signals output by the photomixers 13-1 to 13-4. The RF combiner 17 outputs the combined RF signal (S7), and the process ends. The RF signal combined by the RF combiner 17 becomes a received signal corresponding to the incoming wave arriving from the direction of the beam 90-2. For example, if a device that performs demodulation processing is connected to the reception directivity control device 1 and takes in the received signal output by the RF combiner 17 and performs demodulation processing, it becomes possible to obtain data superimposed on the received signal.

In addition, when the direction of beam 90-2 is the desired direction, even if there are incoming waves from beams 90-1, 90-3, and 90-4 that do not match the desired direction, the detected RF signals output by photomixers 13-1 to 13-4 for these incoming waves will not be in phase. Therefore, RF combiner 17 will not output a received signal for incoming waves from the directions of beams 90-1, 90-3, and 90-4.

If the user specifies one of the beams 90-1, 90-3, and 90-4 other than beam 90-2 as the desired direction, then, as in the case of beam 90-2 described above, only received signals corresponding to the incoming waves coming from the direction of beams 90-1, 90-3, and 90-4 corresponding to the specified desired direction will be obtained.

(Effects of the First Embodiment)
In the reception directivity control device of the first embodiment described above, the row direction phase gradient imparting unit 20 supplies row optical signals, which are two first optical signals having a phase gradient of "-1" times the row direction phase gradient corresponding to any one of the beams 90-1 to 90-4 having a direction that matches the specified desired direction, to each combination of the combination of the SSB modulators 11-1-1 and 11-2-1 in the same column and the combination of the SSB modulators 11-1-2 and 11-2-2. As a result, the output optical signals output by the two SSB modulators included in each combination have the same phase.

The column-direction phase gradient imparting unit 30 supplies column optical signals, which are two second optical signals having the same phase gradient as the column-direction phase gradient corresponding to any one of the beams 90-1 to 90-4, which has a direction that matches the specified desired direction, to each combination of the optical multiplexers 12-1-1 and 12-1-2 that are in the same row and each combination of the optical multiplexers 12-2-1 and 12-2-2. As a result, the same phase difference exists between the combined optical signals output by the two optical multiplexers included in each combination in both the carrier wave component and the sideband wave component. Therefore, the detected RF signals obtained by the square detection of the photomixers 13-1 to 13-4 are given a two-dimensional phase gradient that reflects the row-direction phase gradient and the column-direction phase gradient, so that they are all in phase. The detected RF signals with the same phase are combined by the RF multiplexer 17, so that only the received signal corresponding to the incoming wave arriving from the desired direction is obtained.

The array antenna 80 connected to the reception directivity control device 1 shown in FIG. 1 is a 2×2 array antenna, and the number of antenna elements is "4", but the number of antenna elements may be increased. When the number of antenna elements is increased, it is necessary to change the configuration so that the number of SSB modulators 11-1-1 to 11-2-2, optical multiplexers 12-1-1 to 12-2-2, and photomixers 13-1 to 13-4 is increased to the same number as the number of antenna elements. The row-direction phase tilt applying unit 20 is changed in configuration so that the number of output ports 24-3, 24-4 is the same as the number of antenna elements in the row direction. The column-direction phase tilt applying unit 30 is changed in configuration so that the number of output ports 34-3, 34-4 is the same as the number of antenna elements in the column direction. Furthermore, the row-direction phase tilt applying unit 20 and the column-direction phase tilt applying unit 30 are changed in configuration to add logic for applying a phase tilt in accordance with the increase in the number of output ports.

However, in the reception directivity control device 1, unlike Patent Documents 1 and 2, the column-direction phase gradient is not directly applied by the wavelength dispersion line, but is applied by the second optical signal to which the same phase gradient as the column-direction phase gradient generated by the column-direction scanning matrix circuit 34 is applied. Therefore, even if the number of antenna elements is increased in the reception directivity control device 1, the above-mentioned configuration change is only made, and the scale of the circuit that applies the phase gradient does not increase significantly as in Patent Documents 1 and 2. In the reception directivity control device 1, the circuit configuration other than the SSB modulators 11-1-1 to 11-2-2 can be configured two-dimensionally, not three-dimensionally as in the technology disclosed in Patent Documents 1 and 2, and even if the number of antenna elements of the array antenna 80 increases, it is only expanded two-dimensionally. Therefore, even if the number of antenna elements is increased, the number of parts and wiring in the reception directivity control device 1 does not increase significantly, and the circuit structure does not become complicated. Therefore, when controlling the reception directivity of the array antenna 80 using the reception directivity control device 1 of the first embodiment, even if the size of the array antenna 80 becomes large, it is possible to implement it using a circuit with a simple structure that is suitable for miniaturization and mass production.

(Another configuration example of the first embodiment)
In the reception directivity control device 1 of the first embodiment described above, four beams 90-1 to 90-4 can be specified as the direction of reception directivity, but more than four directions may be specified. For example, if four row-direction phase inclinations, +2φ _V , φ _V , −φ _V , and −2φ _V , can be set in the row-direction scanning matrix circuit 24, and four column-direction phase inclinations, +2φ _H , φ _H , −φ _H , and −2φ _H , can be set in the column-direction scanning matrix circuit 34, it becomes possible to specify beams in 16 directions.

In this case, the row scanning switching circuit 23 has four output ports corresponding to each of the four row phase gradients, and the row scanning matrix circuit 24 has four input ports corresponding to each of the four row phase gradients. The column scanning switching circuit 33 has four output ports corresponding to each of the four column phase gradients, and the column scanning matrix circuit 34 has four input ports corresponding to each of the four column phase gradients.

In the reception directivity control device 1, for example, four row-direction phase tilts, +2φ _V , φ _V , -φ _V , -2φ _V , can be set in the row-direction scanning matrix circuit 24, and two column-direction phase tilts, φ _H , -φ _H , can be set in the column-direction scanning matrix circuit 34, so that the number of beam directions that can be formed in the row direction and the number of beam directions that can be formed in the column direction may be made different.

Second Embodiment
4 is a block diagram showing the internal configuration of the reception directivity control device 1a of the second embodiment, an array antenna 80 connected to the reception directivity control device 1a, and beams 90a-1 to 90a-4 formed by the array antenna 80. In the second embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and only the different components will be described below.

In the second embodiment, the column-wise phase tilt occurring in the beams 90a-1, 90a-2, 90a-3, and 90a-4 formed by the array antenna 80 is different from the column-wise phase tilt occurring in the beams 90-1, 90-2, 90-3, and 90-4 in the first embodiment. The column-wise phase tilt in the second embodiment is φ _V or -φ _V , not φ _H or -φ _H , and the absolute value of the column-wise phase tilt coincides with the absolute value of the row-wise phase tilt. Therefore, when the phase tilts of the beams 90a-1 to 90a-4 are written in the form of (row-wise phase tilt, column-wise phase tilt), the beam 90a-2 is (φ _V , φ _V ), the beam 90a-1 is (φ _V , -φ _V ), the beam 90a-4 is (-φ _V , φ _V ), and the beam 90a-3 is (-φ _V , -φ _V ).

The receiving directivity control device 1a includes an electro-optical conversion unit 11, an optical multiplexing unit 12, an opto-electrical conversion unit 13, an RF multiplexing unit 16, a phase tilt imparting unit 50, a first light source 41a, and a second light source 42a. The first light source 41a and the second light source 42a each generate CW light of the same frequency but different polarization modes. The first light source 41a generates CW light having a TE (Transverse Magnetic) polarization mode (hereinafter referred to as TE polarization). The second light source 42a generates CW light having a TM (Transverse Electric) polarization mode (hereinafter referred to as TM polarization). However, the amplitude of the second light source 42a is an amplitude determined according to the modulation degree of the optical modulation by the SSB modulators 11-1-1 to 11-2-2. Hereinafter, the CW light generated by the first light source 41a is referred to as the first optical signal, and the CW light generated by the second light source 42a is referred to as the second optical signal.

The phase tilt applying unit 50 includes a row direction scanning instruction circuit 22, a row direction scanning switching circuit 23, a column direction scanning instruction circuit 32, a column direction scanning switching circuit 33a, a scanning matrix circuit 51, polarization multiplexers 52-1 and 52-2, polarization separators 53-1 and 53-2, polarization rotators 54-1 and 54-2, and distributors 25-1, 25-2, 35-1, and 35-2.

The row scanning switching circuit 23 is connected to the first light source 41a, and the column scanning switching circuit 33a is connected to the second light source 42a. The column scanning switching circuit 33a has two output ports 33a-1 and 33a-2. In the column scanning switching circuit 33 of the first embodiment, the output port 33-1 is associated with the column direction instruction information "rightward", and the output port 33-2 is associated with the column direction instruction information "leftward". Conversely, in the column scanning switching circuit 33a, the output port 33a-1 is associated with the column direction instruction information "leftward", and the output port 33a-2 is associated with the column direction instruction information "rightward".

The polarization multiplexer 52-1 is connected to the output port 23-1 of the row scanning switching circuit 23 and the output port 33a-1 of the column scanning switching circuit 33a. The polarization multiplexer 52-1 multiplexes the first optical signal of TE polarization output from the output port 23-1 and the second optical signal of TM polarization output from the output port 33a-1. The polarization multiplexer 52-2 is connected to the output port 23-2 of the row scanning switching circuit 23 and the output port 33a-2 of the column scanning switching circuit 33a. The polarization multiplexer 52-2 multiplexes the first optical signal of TE polarization output from the output port 23-2 and the second optical signal of TM polarization output from the output port 33a-2.

The scanning matrix circuit 51 has two input ports 51-1 and 51-2 and two output ports 51-3 and 51-4. The input port 51-1 is connected to the polarization multiplexer 52-1, and the input port 51-2 is connected to the polarization multiplexer 52-2. The output port 51-3 is connected to the polarization separator 53-1, and the output port 51-4 is connected to the polarization separator 53-2.

The scanning matrix circuit 51 imparts a phase tilt to the optical signal supplied from the input port 51-1 such that two optical signals output from each of the output ports 51-3 and 51-4 have a phase tilt that is "-1" times the phase tilt φ _V. The scanning matrix circuit 51 imparts a phase tilt to the optical signal supplied from the input port 51-2 such that two optical signals output from each of the output ports 51-3 and 51-4 have a phase tilt that is "-1" times the phase tilt -φ _V.

The polarization separator 53-1 is connected to the distributor 25-1 and the polarization rotator 54-1. The polarization separator 53-1 separates the optical signal output by the output port 51-3 of the scanning matrix circuit 51 into a TE polarized optical signal and a TM polarized optical signal. The polarization separator 53-1 outputs the separated TE polarized optical signal, i.e., the first optical signal, to the distributor 25-1, and outputs the separated TM polarized optical signal, i.e., the second optical signal, to the polarization rotator 54-1.

The polarization separator 53-2 is connected to the distributor 25-2 and the polarization rotator 54-2. The polarization separator 53-2 separates the optical signal output by the output port 51-4 of the scanning matrix circuit 51 into a TE-polarized optical signal and a TM-polarized optical signal. The polarization separator 53-2 outputs the separated TE-polarized optical signal, i.e., the first optical signal, to the distributor 25-2, and outputs the separated TM-polarized optical signal, i.e., the second optical signal, to the polarization rotator 54-2.

The polarization rotator 54-1 rotates the polarization of the TM polarized second optical signal output by the polarization separator 53-1 to convert it into a TE polarized second optical signal, and outputs the converted TE polarized second optical signal to the distributor 35-1. The polarization rotator 54-2 rotates the polarization of the TM polarized second optical signal output by the polarization separator 53-2 to convert it into a TE polarized second optical signal, and outputs the converted TE polarized second optical signal to the distributor 35-2.

(Processing by the reception directivity control device 1a of the second embodiment)
The process performed by the reception directivity control device 1a of the second embodiment will be described with reference to the flowchart shown in FIG. 3, which illustrates the flow of the process performed by the reception directivity control device 1 of the first embodiment.

In the following, it is assumed that the desired direction desired by the user is the direction of beam 90a-2. In the first embodiment, the same process of S1 is carried out as when the desired direction is beam 90-2, and as a result, the row direction scanning instruction circuit 22 outputs row direction instruction information "upward" to the row direction scanning switching circuit 23. The column direction scanning instruction circuit 32 outputs column direction instruction information "rightward" to the column direction scanning switching circuit 33a.

The following processing is carried out as the processing of S2 and S4. When the row direction scanning switching circuit 23 receives the row direction instruction information "upward" from the row direction scanning instruction circuit 22, it selects the output port 23-1 corresponding to the row direction instruction information "upward". The row direction scanning switching circuit 23 takes in the first optical signal of TE polarization output by the first light source 41a, and outputs the taken-in first optical signal from the selected output port 23-1, as shown by the dotted line in the row direction scanning switching circuit 23 in FIG. 4.

When the column direction scanning switching circuit 33a receives the column direction instruction information "rightward" from the column direction scanning instruction circuit 32, it selects the output port 33a-2 that corresponds to the column direction instruction information "rightward." The column direction scanning switching circuit 33a takes in the second optical signal of TM polarization output by the second light source 42a, and outputs the taken-in second optical signal from the selected output port 33a-2, as shown by the dotted line in the column direction scanning switching circuit 33a in FIG. 4.

As a result, in the row-direction scanning switching circuit 23, the output port 23-1 outputs the first optical signal, and in the column-direction scanning switching circuit 33a, the output port 33a-1 outputs nothing. Therefore, the polarization multiplexer 52-1 outputs the first optical signal output by the output port 23-1 of the row-direction scanning switching circuit 23 to the input port 51-1 of the scanning matrix circuit 51. In the row-direction scanning switching circuit 23, the output port 23-2 outputs nothing, and in the column-direction scanning switching circuit 33a, the output port 33a-2 outputs the second optical signal. Therefore, the polarization multiplexer 52-2 outputs the second optical signal output by the output port 33a-2 of the column-direction scanning switching circuit 33a to the input port 51-2 of the scanning matrix circuit 51.

The scanning matrix circuit 51 receives a first optical signal from an input port 51-1, and imparts a phase tilt to the received first optical signal so that two optical signals output from the output ports 51-3 and 51-4 have a phase tilt of "-1" times the phase tilt φ _V. The scanning matrix circuit 51 outputs the first optical signal to which a phase tilt of "-1" times the phase tilt φ _V has been imparted from the output ports 51-3 and 51-4. As a result, the first optical signal output from the output port 51-4 becomes an optical signal whose phase leads that of the first optical signal output from the output port 51-3 by φ _V.

The scanning matrix circuit 51 receives a second optical signal from the input port 51-2, and imparts a phase tilt to the received second optical signal so that two optical signals output from the output ports 51-3 and 51-4 have a phase tilt that is "-1" times the phase tilt _-φV , i.e., the same phase tilt as the phase tilt _φV . The scanning matrix circuit 51 outputs the second optical signal to which the phase tilt has been imparted from the output ports 51-3 and 51-4. As a result, the second optical signal output from the output port 51-4 becomes an optical signal whose phase is delayed by _φV from the second optical signal output from the output port 51-3.

The polarization separator 53-1 separates the first optical signal of TE polarization and the second optical signal of TM polarization output by the output port 51-3, outputs the separated first optical signal of TE polarization to the distributor 25-1, and outputs the separated second optical signal of TM polarization to the polarization rotator 54-1. The polarization rotator 54-1 converts the second optical signal of TM polarization output by the polarization separator 53-1 into a second optical signal of TE polarization, and outputs the converted second optical signal of TE polarization to the distributor 35-1.

The polarization separator 53-2 separates the first optical signal of TE polarization and the second optical signal of TM polarization output by the output port 51-4, outputs the separated first optical signal of TE polarization to the distributor 25-2, and outputs the separated second optical signal of TM polarization to the polarization rotator 54-2. The polarization rotator 54-2 converts the second optical signal of TM polarization output by the polarization separator 53-2 into a second optical signal of TE polarization, and outputs the converted second optical signal of TE polarization to the distributor 35-2.

As a result, the first optical signal output by the distributor 25-2 becomes an optical signal whose phase is ahead of the first optical signal output by the distributor 25-1 by φ _V. The second optical signal output by the distributor 35-2 becomes an optical signal whose phase is behind the second optical signal output by the distributor 35-1 by φ _V. The optical signals output by the distributors 25-1, 25-2, 35-1, and 35-2 are all TE polarized, and become optical signals with matching polarization modes.

The processes of S3, S5, S6, and S7 are the same as those of the first embodiment, except that φ _H is replaced with φ _V. As a result, like the first embodiment, only the received signal of the incoming wave coming from the direction of the beam 90a-2 is obtained.

(Effects of the Second Embodiment)
The reception directivity control device 1a of the second embodiment has the effect of reducing the number of components and wiring in addition to the effect of the reception directivity control device 1 of the first embodiment described above. That is, the reception directivity control device 1 of the first embodiment includes the row direction scanning matrix circuit 24 and the column direction scanning matrix circuit 34, but in the second embodiment, a single scanning matrix circuit 51 can realize the processing performed by the row direction scanning matrix circuit 24 and the column direction scanning matrix circuit 34. Although the reception directivity control device 1a of the second embodiment has a constraint that the absolute value of the row direction phase gradient must match the absolute value of the column direction phase gradient, the number of matrix circuits used can be reduced, so that the overall manufacturing cost and size of the reception directivity control device 1a can be reduced compared to the reception directivity control device 1 of the first embodiment.

In the second embodiment, the number of antenna elements of the array antenna 80 may be increased, as in the first embodiment. In this case, it is also possible to make the number of antenna elements in the row direction of the array antenna 80 different from the number of antenna elements in the column direction. However, in this case, the number of output ports 51-3, 51-4 of the scanning matrix circuit 51 must be set to the larger of the number of antenna elements in the row direction and the number of antenna elements in the column direction.

As in the first embodiment, the number of row-direction phase gradients and the number of column-direction phase gradients may be increased. In this case, it is also possible to set the row-direction phase gradients to, for example, four, +2φ _V , φ _V , -φ _V , and -2φ _V , and set the column-direction phase gradients to two, φ _V and -φ _V. However, in this case, the number of input ports 51-1 and 51-2 of the scanning matrix circuit 51 must be set to the number of phase gradients that is greater among the number of row-direction phase gradients and the number of column-direction phase gradients. Therefore, in the reception directivity control device 1a of the second embodiment, a configuration in which the number of antenna elements in the row direction and the number of antenna elements in the column direction are made to match, and the number of row-direction phase gradients and the number of column-direction phase gradients are made to match, is a configuration that can most efficiently utilize the scanning matrix circuit 51.

(Another configuration example of the second embodiment)
In the second embodiment, the polarization modes of the optical signals supplied to the SSB modulators 11-1-1 to 11-2-2 and the optical multiplexers 12-1-1 to 12-2-2 are all TE polarized by converting the TM polarized second optical signals separated by the polarization separators 53-1 and 53-2 into TE polarized second optical signals by the polarization rotators 54-1 and 54-2. Conversely, the polarization modes of the optical signals supplied to the SSB modulators 11-1-1 to 11-2-2 and the optical multiplexers 12-1-1 to 12-2-2 may all be TM polarized. In this case, the reception directivity control device 1a has the following configuration. The polarization rotator 54-1 is inserted between the polarization separator 53-1 and the distributor 25-1, and the polarization rotator 54-2 is inserted between the polarization separator 53-2 and the distributor 25-2. The polarization separator 53-1 and the distributor 35-1 are directly connected, and the polarization separator 53-2 and the distributor 35-2 are directly connected. Each of the polarization separators 53-1 and 53-2 outputs the separated first optical signal of TE polarization to the polarization rotators 54-1 and 54-2 connected to the respective polarization separators, and outputs the separated second optical signal of TM polarization to the distributors 35-1 and 35-2 connected to the respective polarization separators. Each of the polarization rotators 54-1 and 54-2 converts the first optical signal of TE polarization into the first optical signal of TM polarization and outputs it to the distributors 25-1 and 25-2 connected to the respective polarization separators. This makes it possible to make the polarization modes of the optical signals supplied to the SSB modulators 11-1-1 to 11-2-2 and the optical multiplexers 12-1-1 to 12-2-2 all TM polarized.

Third Embodiment
In the reception directivity control device 1 of the first embodiment, the direction of directivity formed by the array antenna 80 is only one direction, and one of the beams 90-1, 90-2, 90-3, and 90-4 is formed. In contrast, in the third embodiment, a description will be given of reception directivity control devices 1b and 1c that can form a plurality of beams in parallel, that is, that can form a multi-beam.

(Configuration Related to the Reception Directivity Control Device 1b of the Third Embodiment)
5 is a block diagram showing the internal configuration of a reception directivity control device 1b capable of forming two beams in parallel, an array antenna 80 connected to the reception directivity control device 1b, and beams 90-1 to 90-4 formed by the array antenna 80. In the third embodiment, the same components as those in the first embodiment are given the same reference numerals. As an example, a case will be described below in which the two beams formed in parallel by the reception directivity control device 1b are beams 90-1 and 90-2.

The receiving directivity control device 1b includes an electrical-to-optical conversion unit 11, an optical multiplexing unit 12, an optical-to-electrical conversion unit 13a, an RF multiplexing unit 16a, a row-direction phase gradient imparting unit 20a, a column-direction phase gradient imparting unit 30a, first light sources 41-1, 41-2, and second light sources 42-1, 42-2. The row-direction phase gradient imparting unit 20a includes a row-direction scanning matrix circuit 24, and distributors 25-1, 25-2. The column-direction phase gradient imparting unit 30a includes a column-direction scanning matrix circuit 34, and distributors 35-1, 35-2.

The first light source 41-1 and the second light source 42-1 are light sources used to form the beam 90-1, and generate CW light of the same frequency. Here, the frequency of the CW light generated by the first light source 41-1 and the second light source 42-1 is "ch1". The first light source 41-2 and the second light source 42-2 are light sources used to form the beam 90-2, and generate CW light of "ch2" which is the same frequency but different from "ch1". However, the amplitude of the second light sources 42-1 and 42-2 is an amplitude determined according to the modulation degree of the optical modulation by the SSB modulators 11-1-1 to 11-2-2. Hereinafter, the CW light generated by the first light sources 41-1 and 41-2 is also referred to as the first optical signal, and the CW light generated by the second light sources 42-1 and 42-2 is also referred to as the second optical signal.

Beams 90-1 and 90-2 are "upward" in the row direction. Therefore, both the first light source 41-1 and the first light source 41-2 are connected to the input port 24-1 of the row scanning matrix circuit 24. Beam 90-1 is "leftward" in the column direction. Therefore, the second light source 42-1 used to form beam 90-1 is connected to the input port 34-2 of the column scanning matrix circuit 34. Beam 90-2 is "rightward" in the column direction. Therefore, the second light source 42-2 used to form beam 90-2 is connected to the input port 34-1 of the column scanning matrix circuit 34.

The photoelectric conversion unit 13a includes four optical splitters 14-1 to 14-4 and eight photomixers 13-1-1 to 13-4-2. The optical splitters 14-1 to 14-4 are connected to the optical multiplexers 12-1-1 to 12-2-2, respectively. Each of the optical splitters 14-1 to 14-4 splits the multiplexed optical signals output by the optical multiplexers 12-1-1 to 12-2-2 connected to it into an optical signal in the frequency band of frequency ch1 and an optical signal in the frequency band of frequency ch2.

Here, the term "frequency band of frequency X" means a certain range of frequency bands around frequency X, and may or may not include frequency X. The letter "X" is a letter that can be replaced with either ch1 or ch2. As described with reference to equations (9) and (13) in the first embodiment, each of the photomixers 13-1-1 to 13-4-2 needs to be appropriately supplied with a combination of the USB component of the modulated optical signal output by the SSB modulators 11-1-1 to 11-2-2 and a second optical signal having a phase difference corresponding to the USB component. For this reason, the frequency band of frequency ch1 and the frequency band of frequency ch2 that can appropriately separate the combination are predetermined for each of the optical splitters 14-1 to 14-4.

To explain in more detail, for example, the optical multiplexer 12-1-2 is supplied with "Acos(ω _C1 +ω _RF )t+φ _H " as an optical signal related to frequency ch1 from the SSB modulator 11-2-1, and is supplied with "Acos(ω _C1 t+φ _H ) " as an optical signal related to frequency ch1 from the column-direction phase gradient imparting unit 30. Here, ω _C1 is an angular frequency corresponding to frequency ch1. As described in the first embodiment, the optical multiplexer 12-1-2 is supplied with "Acos(ω _C2 +ω RF )t-φ _H " and "Acos(ω _C2 +ω _RF )t-φ _H " corresponding to _equations (11) and (12) as optical signals related to frequency ch2. Here, ω _C2 is an angular frequency corresponding to frequency ch2.

Therefore, the optical demultiplexer 14-2 connected to the optical multiplexer 12-1-1 separates the four multiplexed optical signals into a combination of "Acos( _ωC1 + _ωRF )t+ _φH " and "Acos( _ωC1 t+ _φH )" and a combination of "Acos( _ωC2 + _ωRF )t- _φH " and "Acos( _ωC2 t- _φH )." In other words, the frequency band of frequency ch1 is a frequency band that includes "Acos( _ωC1 + _ωRF )t+ _φH " and "Acos( _ωC1 t+ _φH )," and the frequency band of frequency ch2 is a frequency band that includes "Acos( _ωC2 + _ωRF )t- _φH " and "Acos( _ωC2 t- _φH )." In this case, the frequency band of frequency ch2 includes frequency ch2, but the frequency band of frequency ch1 can be determined not to include frequency ch1.

Each of the photomixers 13-1 to 13-4 in the first embodiment has the same configuration as described in the first embodiment, and each of the eight photomixers 13-1-1 to 13-4-2 has the same configuration. The RF multiplexing unit 16a has two RF multiplexers 17-1 and 17-2. Each of the RF multiplexers 17-1 and 17-2 has the same configuration as the RF multiplexer 17 in the first embodiment.

The photomixers 13-1-1, 13-2-1, 13-3-1, and 13-4-1 are each connected on the input side to the output terminals of the optical splitters 14-1 to 14-4 that output optical signals in the frequency band of ch1, and on the output side to the RF multiplexer 17-1. In other words, the photomixers 13-1-1, 13-2-1, 13-3-1, and 13-4-1 are supplied with optical signals in the frequency band of ch1 used to form the beam 90-1.

The photomixers 13-1-2, 13-2-2, 13-3-2, and 13-4-2 are each connected on the input side to the output terminals of the optical splitters 14-1 to 14-4 that output optical signals in the frequency band of ch2, and are each connected on the output side to the RF multiplexer 17-2. In other words, the photomixers 13-1-2, 13-2-2, 13-3-2, and 13-4-2 are supplied with optical signals in the frequency band of ch2 used to form the beam 90-2.

(Processing by the reception directivity control device 1b of the third embodiment)
The processing by the reception directivity control device 1b will be described. In the reception directivity control device 1b, a combination of a first light source 41-1 that generates a first optical signal of frequency ch1, a second light source 42-1 that generates a second optical signal of frequency ch1, a row-direction phase gradient applying unit 20a, a column-direction phase gradient applying unit 30a, an electro-optical conversion unit 11, an optical multiplexing unit 12, optical demultiplexers 14-1 to 14-4, photomixers 13-1-1, 13-2-1, 13-3-1, 13-4-1, and an RF multiplexer 17-1 is defined as a first combination.

In the reception directivity control device 1b, a combination of a first light source 41-2 that generates a first optical signal of frequency ch2, a second light source 42-2 that generates a second optical signal of frequency ch2, a row-direction phase gradient imparting unit 20a, a column-direction phase gradient imparting unit 30a, an electrical-to-optical conversion unit 11, an optical multiplexing unit 12, optical splitters 14-1 to 14-4, photomixers 13-1-2, 13-2-2, 13-3-2, 13-4-2, and an RF multiplexer 17-2 is defined as a second combination.

(In the case of an incoming wave coming from the direction of beam 90-1)
When the array antenna 80 receives an incoming wave coming from the direction of the beam 90-1, the process performed by the first combination is as follows. The row direction scanning matrix circuit 24 imparts a phase inclination of "-1" times the row direction phase inclination φ _V corresponding to "upward" to the first optical signal of frequency ch1 generated by the first light source 41-1. As a result, row optical signals, which are two first optical signals of frequency ch1 having a phase inclination -φ _V , are supplied to the combination of SSB modulators 11-1-1 and 11-2-1 in the same column and the combination of SSB modulators 11-1-2 and 11-2-2 in the same column. In other words, the first optical signal of frequency ch1 supplied to the SSB modulators 11-2-1 and 11-2-2 becomes an optical signal whose phase is ahead of the first optical signal of frequency ch1 supplied to the SSB modulators 11-1-1 and 11-1-2 by φ _V.

The second optical signal of frequency ch1 generated by the second light source 42-1 is given a phase inclination equal to the column-direction phase inclination _-φH corresponding to "leftward" by the column-direction scanning matrix circuit 34. As a result, column optical signals, which are two second optical signals of frequency ch1 having a phase inclination _-φH , are supplied to a combination of optical multiplexers 12-1-1 and 12-1-2 having the same row and a combination of optical multiplexers 12-2-1 and 12-2-2 having the same row. In other words, the second optical signal of frequency ch1 supplied to the optical multiplexers 12-1-2 and 12-2-2 becomes an optical signal whose phase is ahead of the second optical signal of frequency ch1 supplied to the optical multiplexers 12-1-1 and 12-2-1 by _φH .

The multiplexed optical signals output by each of the optical multiplexers 12-1-1 to 12-2-2 include a multiplexed optical signal resulting from the first and second optical signals of frequency ch1, and a multiplexed optical signal resulting from the first and second optical signals of frequency ch2.

Here, as an example, an optical signal propagating through the optical circuit between the SSB modulator 11-1-1 and the optical multiplexer 12-1-1, and between the optical multiplexer 12-1-1 and the optical demultiplexer 14-1 will be described. The first optical signals of frequencies ch1 and ch2 are supplied to the SSB modulator 11-1-1 by the distributor 25-1. The SSB modulator 11-1-1 modulates each of the first optical signals of frequencies ch1 and ch2 with an RF signal supplied from the antenna element 80-1-1. Therefore, an optical signal that is wavelength-multiplexed with the USB component of the modulated optical signal obtained by modulating the first optical signal of frequency ch1 and the USB component of the modulated optical signal obtained by modulating the first optical signal of frequency ch2 propagates through the optical circuit between the SSB modulator 11-1-1 and the optical multiplexer 12-1-1.

The second optical signals of frequencies ch1 and ch2 are supplied to the optical multiplexer 12-1-1 by the distributor 35-1. Therefore, an optical signal in which four types of optical signals are wavelength-multiplexed propagates through the optical line between the optical multiplexer 12-1-1 and the optical demultiplexer 14-1: the USB component of the modulated optical signal obtained by modulating the first optical signal of frequency ch1, the USB component of the modulated optical signal obtained by modulating the first optical signal of frequency ch2, and the second optical signal of frequencies ch1 and ch2.

Each of the optical splitters 14-1 to 14-2 splits the multiplexed optical signals output by the optical multiplexers 12-1-1 to 12-2-2 connected to it into an optical signal in the frequency band of ch1 and an optical signal in the frequency band of ch2. The optical splitters 14-1 to 14-2 output the split optical signals in the frequency band of ch1 to the photomixers 13-1-1, 13-2-1, 13-3-1, and 13-4-1.

In the case of an incoming wave coming from the direction of beam 90-1, the detected RF signals output by photomixers 13-1-1, 13-2-1, 13-3-1, and 13-4-1 after square detection will be in phase. These four in-phase detected RF signals are combined by RF combiner 17-1 to obtain a received signal corresponding to the incoming wave coming from the direction of beam 90-1.

When the array antenna 80 receives an incoming wave coming from the direction of the beam 90-1, the process performed by the second combination is as follows: As in the first combination, the row-direction scanning matrix circuit 24 imparts a phase gradient of "-1" times the row-direction phase gradient φ _V corresponding to "upward" to the first optical signal of frequency ch2 generated by the first light source 41-2. On the other hand, the column-direction scanning matrix circuit 34 imparts a phase gradient identical to the column-direction phase gradient φ _H corresponding to "rightward", which is the opposite to that in the first combination, to the second optical signal of frequency ch2 generated by the second light source 42-2.

The optical splitters 14-1 to 14-2 output the separated optical signals in the frequency band of ch2 to the photomixers 13-1-2, 13-2-2, 13-3-2, and 13-4-2. The second optical signal, which is considered to be a carrier wave component contained in the optical signal in the frequency band of ch2 separated by the optical splitters 14-1 to 14-2, is not given an appropriate phase inclination of φ _H , but -φ _H , by the column direction scanning matrix circuit 34. Therefore, the detected RF signals obtained by the photomixers 13-1-2, 13-2-2, 13-3-2, and 13-4-2 performing square detection on the optical signals in the frequency band of ch2 separated by the optical splitters 14-1 to 14-2 are not in phase. Therefore, the RF combiner 17-2 does not output a received signal corresponding to the incoming wave coming from the direction of the beam 90-1.

(In the case of an incoming wave coming from the direction of beam 90-2)
When the array antenna 80 is receiving an incoming wave coming from the direction of beam 90-2, the processing performed by the above-mentioned second combination is the same as the processing performed in the reception directivity control device 1 of the first embodiment when beam 90-2 is the desired direction. Therefore, in the case of an incoming wave coming from the direction of beam 90-2, the detected RF signals output by the photomixers 13-1-2, 13-2-2, 13-3-2, and 13-4-2 after square detection are in phase. The RF combiner 17-2 combines these four in-phase detected RF signals to obtain a received signal corresponding to the incoming wave coming from the direction of beam 90-2.

When the array antenna 80 receives an incoming wave coming from the direction of the beam 90-2, the process performed by the first combination is as follows: The second optical signal of frequency ch1 generated by the second light source 42-1 is given a phase tilt that is the same as the column-direction phase tilt _-φH corresponding to the "leftward" direction opposite to that in the first combination by the column-direction scanning matrix circuit 34. Therefore, an appropriate phase tilt is not given by the column-direction scanning matrix circuit 34 to the second optical signal regarded as a carrier wave component included in the optical signal of the frequency band of frequency ch1 separated by the optical demultiplexers 14-1 to 14-2.

Therefore, the detected RF signals obtained by photomixers 13-1-1, 13-2-1, 13-3-1, and 13-4-1 performing square detection on the optical signals in the frequency band of frequency ch1 separated by optical splitters 14-1 and 14-2 will not be in phase. As a result, RF combiner 17-1 will not output a received signal corresponding to the incoming wave coming from the direction of beam 90-2.

As a result, in the case where there is an incoming wave coming from the direction of beam 90-1 and an incoming wave coming from the direction of beam 90-2, the reception directivity control device 1b can obtain the received signals of both incoming waves in parallel.

(Configuration Related to the Reception Directivity Control Device 1c of the Third Embodiment)
Fig. 6 is a block diagram showing the internal configuration of a reception directivity control device 1c capable of forming four beams in parallel, an array antenna 80 connected to the reception directivity control device 1c, and beams 90-1 to 90-4 formed by the array antenna 80. In Fig. 6, the same components as those in Fig. 5 are denoted by the same reference numerals.

The receiving directivity control device 1c has the configuration of the receiving directivity control device 1b, and further includes first light sources 41-3 and 41-4 and second light sources 42-3 and 42-4, a photoelectric conversion unit 13b instead of the photoelectric conversion unit 13a, and an RF multiplexing unit 16b instead of the RF multiplexing unit 16a.

The first light source 41-3 and the second light source 42-3 are light sources used to form the beam 90-3, and generate CW light of ch3, which is a CW light of the same frequency but different from the frequencies ch1 and ch2. The first light source 41-4 and the second light source 42-4 are light sources used to form the beam 90-4, and generate CW light of ch4, which is a CW light of the same frequency but different from the frequencies ch1, ch2, and ch3. However, the amplitude of the second light sources 42-3 and 42-4 is determined according to the modulation degree of the optical modulation by the SSB modulators 11-1-1 to 11-2-2, similar to the second light sources 42-1 and 42-2. Hereinafter, the CW light generated by the first light sources 41-3 and 41-4 is also referred to as the first optical signal, and the CW light generated by the second light sources 42-3 and 42-4 is also referred to as the second optical signal.

Beams 90-3 and 90-4 are "downward" in the row direction. Therefore, both the first light source 41-3 and the first light source 41-4 are connected to the input port 24-2 of the row scanning matrix circuit 24. Beam 90-3 is "leftward" in the column direction. Therefore, the second light source 42-3 used to form beam 90-3 is connected to the input port 34-2 of the column scanning matrix circuit 34. Beam 90-4 is "rightward" in the column direction. Therefore, the second light source 42-4 used to form beam 90-4 is connected to the input port 34-1 of the column scanning matrix circuit 34.

The photoelectric conversion unit 13a includes four optical splitters 14a-1 to 14a-4 and 16 photomixers 13-1-1 to 13-4-4. The optical splitters 14a-1 to 14a-4 are connected to the optical multiplexers 12-1-1 to 12-2-2, respectively. Each of the optical splitters 14a-1 to 14a-4 splits the multiplexed optical signals output by the optical multiplexers 12-1-1 to 12-2-2 connected to it into an optical signal in the frequency band of frequency ch1, an optical signal in the frequency band of frequency ch2, an optical signal in the frequency band of frequency ch3, and an optical signal in the frequency band of frequency ch4.

Each of the photomixers 13-1 to 13-4 in the first embodiment has the same configuration as described in the first embodiment, and like the photomixers 13-1-1 to 13-4-1 and 13-1-2 to 13-4-2, each of the photomixers 13-1-3 to 13-4-3 and 13-1-4 to 13-4-4 has the same configuration. The RF multiplexing unit 16b has four RF multiplexers 17-1, 17-2, 17-3 and 17-4. Like the RF multiplexers 17-1 and 17-2, each of the RF multiplexers 17-3 and 17-4 has the same configuration as the RF multiplexer 17 in the first embodiment.

The photomixers 13-1-1, 13-2-1, 13-3-1, and 13-4-1 are each connected on the input side to the output terminals of the optical splitters 14a-1 to 14a-4 that output optical signals in the frequency band of frequency ch1, and connected on the output side to the RF multiplexer 17-1. In other words, the photomixers 13-1-1, 13-2-1, 13-3-1, and 13-4-1 are supplied with optical signals in the frequency band of frequency ch1 used to form beam 90-1.

The photomixers 13-1-2, 13-2-2, 13-3-2, and 13-4-2 are each connected on the input side to an output terminal that outputs an optical signal in the frequency band of frequency ch2 of the optical splitters 14a-1 to 14a-4, and connected on the output side to the RF multiplexer 17-2. In other words, the photomixers 13-1-2, 13-2-2, 13-3-2, and 13-4-2 are supplied with an optical signal in the frequency band of frequency ch2 used to form the beam 90-2.

The photomixers 13-1-3, 13-2-3, 13-3-3, and 13-4-3 are each connected on the input side to output terminals of the optical splitters 14a-1 to 14a-4 that output optical signals in the frequency band of frequency ch3, and connected on the output side to the RF multiplexer 17-3. In other words, the photomixers 13-1-3, 13-2-3, 13-3-3, and 13-4-3 are supplied with optical signals in the frequency band of frequency ch3 used to form beam 90-3.

The photomixers 13-1-4, 13-2-4, 13-3-4, and 13-4-4 are each connected on the input side to the output terminals of the optical splitters 14a-1 to 14a-4 that output optical signals in the frequency band of ch4, and are connected on the output side to the RF multiplexer 17-4. In other words, the photomixers 13-1-4, 13-2-4, 13-3-4, and 13-4-4 are supplied with optical signals in the frequency band of ch3 used to form the beam 90-4.

The reception directivity control device 1c performs the same processing on the incoming waves coming from the direction of beams 90-3 and 90-4 as when the reception directivity control device 1b is used to receive incoming waves coming from the direction of beams 90-1 and 90-2. As a result, the RF combiner 17-1 outputs a reception signal corresponding to the incoming wave coming from the direction of beam 90-1. The RF combiner 17-2 outputs a reception signal corresponding to the incoming wave coming from the direction of beam 90-2. The RF combiner 17-3 outputs a reception signal corresponding to the incoming wave coming from the direction of beam 90-3. The RF combiner 17-4 outputs a reception signal corresponding to the incoming wave coming from the direction of beam 90-4. Therefore, when there are incoming waves coming from the directions of beams 90-1, 90-2, 90-3, and 90-4, it becomes possible to obtain the reception signals of the four incoming waves in parallel.

In the receiving directivity control devices 1b and 1c of the third embodiment, as described above, wavelength-multiplexed optical signals propagate in optical circuits between the SSB modulators 11-1-1 to 11-2-2 and the optical multiplexers 12-1-1 to 12-2-2, and between the optical multiplexers 12-1-1 to 12-2-2 and the optical demultiplexers 14-1, 14-2, and 14a-1 to 14a-4. Therefore, when determining the spacing between the frequency channels of the propagating optical signals (hereinafter referred to as optical frequency channels), it is important to avoid the adverse effects of unnecessary components, i.e., spurious components, that are generated during the optical modulation by the SSB modulators 11-1-1 to 11-2-2, and to make maximum use of the optical frequency bandwidth.

For example, in the case of the reception directivity control device 1c, the modulated optical signal generated by each of the SSB modulators 11-1-1 to 11-2-2 includes four carrier waves and eight sideband waves. The frequency components of the four carrier waves are the same as the frequencies of the CW lights generated by applying a phase inclination to the first optical signal of frequencies ch1, ch2, ch3, and ch4 by the row direction scanning matrix circuit 24. The eight sideband waves are optical signal waves generated by modulating the four CW lights with the RF signals supplied from the antenna elements 80-1-1 to 80-2-2. As described above, the SSB modulators 11-1-1 to 11-2-2 suppress the unnecessary carrier wave components and the LSB components of the sideband waves, and output only the USB components of the sideband waves. Ideally, SSB modulators 11-1-1 to 11-2-2 would completely suppress unwanted components, but in reality, some unwanted components may remain.

If the SSB modulators 11-1-1 to 11-2-2 can sufficiently suppress the unwanted carrier components and the LSB components of the sideband waves, then the spacing of the optical frequency channels can be determined so that the frequency bands including the USB components of the sideband waves do not overlap with each other.

If the SSB modulators 11-1-1 to 11-2-2 cannot sufficiently suppress the carrier wave component but can sufficiently suppress the LSB components of the sideband waves, the spacing of the optical frequency channels must be determined so that the frequency bands including the carrier wave component and the USB components of the sideband waves do not overlap with each other.

If the SSB modulators 11-1-1 to 11-2-2 can adequately suppress only the carrier component, or if they cannot adequately suppress both the carrier component and the LSB component, it is necessary to determine the spacing of the optical frequency channels so that the frequency bands including both sidebands, i.e., the frequency bands including the entire range from the frequency of the LSB component to the frequency of the USB component, do not overlap with each other.

The RF signals supplied by antenna elements 80-1-1 to 80-2-2 may have different bandwidths for each of beams 90-1 to 90-4. In this case, the spacing of the optical frequency channels can be determined according to the bandwidth of the RF signal with the widest bandwidth among the RF signals supplied by antenna elements 80-1-1 to 80-2-2.

The optical frequency channels do not necessarily have to be equally spaced, and the spacing can be varied as appropriate to prevent unwanted components that cannot be sufficiently suppressed from interfering with other USB components, or to minimize the optical frequency bandwidth used.

(Effects of the Third Embodiment)
The reception directivity control devices 1b and 1c of the third embodiment have the effect of forming multiple beams and obtaining reception signals of waves arriving from multiple directions, in addition to the effect of the reception directivity control device 1 of the first embodiment. In the third embodiment, in order to form multiple beams, the first light sources 41-1 to 41-4, the second light sources 42-1 to 42-4, and the RF multiplexers 17-1 to 17-4 are required in a number that matches the number of beams to be formed. The optical splitters 14-1 to 14-4, 14a-1 to 14a-4 are required in a number that matches the number of antenna elements 80-1-1 to 80-2-2. The number of photomixers 13-1-1 to 13-4-4 required is a number that matches the multiplication value obtained by multiplying the number of beams to be formed by the number of antenna elements 80-1-1 to 80-2-2.

Therefore, in the third embodiment, when the number of antenna elements 80-1-1 to 80-2-2 is increased, the number of photomixers 13-1-1 to 13-4-4 required increases by the product of the increase in antenna elements 80-1-1 to 80-2-2 multiplied by the number of beams to be formed. However, the scale of the circuit configuration other than photomixers 13-1-1 to 13-4-4 increases only in direct proportion to the increase in antenna elements 80-1-1 to 80-2-2, as in the first embodiment. Therefore, in the case of the reception directivity control devices 1b and 1c of the third embodiment, when the number of antenna elements 80-1-1 to 80-2-2 is increased, the increase in the number of photomixers 13-1-1 to 13-4-4 increases compared to the first embodiment, but the increase is limited to one circuit element, photomixers 13-1-1 to 13-4-4. Therefore, compared to Patent Document 1 and Patent Document 2, the number of components and wiring is not significantly increased, and the circuit structure is not complicated as in Patent Document 2. Therefore, when controlling the reception directivity in the array antenna 80, the reception directivity control devices 1b and 1c of the third embodiment make it possible to implement a circuit with a simple structure suitable for miniaturization and mass production, even if the size of the array antenna 80 becomes large.

The configuration of the second embodiment may be applied to the reception directivity control devices 1b and 1c of the third embodiment. The reception directivity control devices 1b and 1c to which the configuration of the second embodiment is applied include a scanning matrix circuit 51, polarization multiplexers 52-1 and 52-2, polarization separators 53-1 and 53-2, and polarization rotators 54-1 and 54-2, instead of the row scanning matrix circuit 24 and the column scanning matrix circuit 34. Each of the first light sources 41-1 to 41-4 generates, for example, a first optical signal of TE polarization, and each of the second light sources 42-1 to 42-4 generates, for example, a second optical signal of TM polarization. As a result, although the direction of the formed beam is limited to the direction of the beams 90a-1 to 90a-4 of the second embodiment, the effect of reducing the number of components and wiring in the matrix circuit configuration is achieved.

In the third embodiment of the receiving directivity control device 1b, the optical signal used to form beam 90-1 and the optical signal used to form beam 90-2 may be separated by polarization instead of by frequency. In this case, for example, the receiving directivity control device 1b has the following configuration. That is, the first light source 41-1 and the second light source 42-1 generate a first optical signal of TE polarization, and the first light source 41-2 and the second light source 42-2 generate a second optical signal of TM polarization that has the same frequency as the first optical signal. Instead of the four optical splitters 14-1 to 14-4, four polarization splitters are provided, with the TE polarization output terminals of the polarization splitters connected to the photomixers 13-1-1, 13-2-1, 13-3-1, and 13-3-4, and the TM polarization output terminals of the polarization splitters connected to the photomixers 13-1-2, 13-2-2, 13-3-2, and 13-4-2. By configuring in this way, a received signal corresponding to beam 90-1 and a received signal corresponding to beam 90-2 can be obtained in parallel, just as in the case where frequencies ch1 and ch2 are used.

Fourth Embodiment
In the case of the reception directivity control device 1c of the third embodiment, for example, eight optical signals are wavelength-multiplexed in the optical lines between each of the optical multiplexers 12-1-1 to 12-2-2 and each of the optical demultiplexers 14a-1 to 14a-4. In contrast, in the fourth embodiment, a reception directivity control device 1d that reduces the number of optical signals wavelength-multiplexed in the optical lines by half will be described.

FIG. 7 is a block diagram showing the internal configuration of the reception directivity control device 1d, the array antenna 80 connected to the reception directivity control device 1d, and the beams 90-1 to 90-4 formed by the array antenna 80. Note that in FIG. 7, the same components as in FIG. 6 are given the same reference numerals.

The receiving directivity control device 1d has the same configuration as the receiving directivity control device 1c, except that instead of the first light sources 41-1 to 41-4, the first light sources 41a-1 to 41a-4 are replaced with the first light sources 41-1 to 41-4, instead of the second light sources 42-1 to 42-4, the second light sources 42a-1 to 42a-4 are replaced with the second light sources 42a-1 to 42a-4, and instead of the photoelectric conversion unit 13b, the photoelectric conversion unit 13c is replaced with the photoelectric conversion unit 13b.

The first light source 41a-1 and the second light source 42a-1 are light sources used to form beam 90-1, and generate CW light of the same frequency, ch1, which is TE polarized CW light. The first light source 41a-2 and the second light source 42a-2 are light sources used to form beam 90-2, and generate CW light of the same frequency, ch2, which is TE polarized CW light. The first light source 41a-3 and the second light source 42a-3 are light sources used to form beam 90-3, and generate CW light of the same frequency, ch1, which is TM polarized CW light. The first light source 41a-4 and the second light source 42a-4 are light sources used to form beam 90-4, and generate CW light of the same frequency, ch2, which is TM polarized CW light. However, the amplitude of the second light sources 42a-1 to 42a-4 is determined according to the modulation depth of the optical modulation by the SSB modulators 11-1-1 to 11-2-2.

As described above, in the reception directivity control device 1d of the fourth embodiment, the optical signals used to form the beams 90-1 and 90-2 and the optical signals used to form the beams 90-3 and 90-4 are in different polarization modes. This makes it possible to separate the optical signals used to form the beams 90-1 and 90-2 from the optical signals used to form the beams 90-3 and 90-4 by performing polarization separation. Furthermore, by performing wavelength separation into frequency ch1 and frequency ch2, it is possible to separate the optical signals used to form the beams 90-1 and 90-3 from the optical signals used to form the beams 90-2 and 90-4. Hereinafter, the CW light generated by the first light sources 41a-1 to 41a-4 is also referred to as the first optical signal, and the CW light generated by the second light sources 42a-1 to 42a-4 is also referred to as the second optical signal.

Beams 90-1 and 90-2 are "upward" in the row direction. Therefore, both the first light source 41a-1 and the first light source 41a-2 are connected to the input port 24-1 of the row scanning matrix circuit 24. Beam 90-1 is "leftward" in the column direction. Therefore, the second light source 42a-1 used to form beam 90-1 is connected to the input port 34-2 of the column scanning matrix circuit 34. Beam 90-2 is "rightward" in the column direction. Therefore, the second light source 42a-2 used to form beam 90-2 is connected to the input port 34-1 of the column scanning matrix circuit 34.

Beams 90-3 and 90-4 are "downward" in the row direction. Therefore, both the first light source 41a-3 and the first light source 41a-4 are connected to the input port 24-2 of the row scanning matrix circuit 24. Beam 90-3 is "leftward" in the column direction. Therefore, the second light source 42a-3 used to form beam 90-3 is connected to the input port 34-2 of the column scanning matrix circuit 34. Beam 90-4 is "rightward" in the column direction. Therefore, the second light source 42a-4 used to form beam 90-4 is connected to the input port 34-1 of the column scanning matrix circuit 34.

The photoelectric conversion unit 13c includes four polarization wavelength splitters 15-1 to 15-4 and 16 photomixers 13-1-1 to 13-4-4. The polarization wavelength splitters 15-1 to 15-4 are connected to the optical multiplexers 12-1-1 to 12-2-2, respectively.

The polarization wavelength demultiplexers 15-1 to 15-4 have the same internal configuration, and as an example, the internal configuration of the polarization wavelength demultiplexer 15-1 will be described with reference to FIG. 8. The polarization wavelength demultiplexer 15-1 has a polarization separator 60-1, an optical demultiplexer 14TE-1, and an optical demultiplexer 14TM-1. The polarization separator 60-1 is connected to the optical multiplexer 12-1-1 on the input side, and has two output ports 61-1 and 62-1. The polarization separator 60-1 separates the combined optical signal supplied from the optical multiplexer 12-1-1 into a combined optical signal of TE polarization and a combined optical signal of TM polarization. The polarization separator 60-1 outputs the separated combined optical signal of TE polarization from the output port 61-1, and outputs the separated combined optical signal of TM polarization from the output port 62-1.

The optical splitter 14TE-1 is connected to the output port 61-1 of the polarization splitter 60-1 on the input side, and has two output ports 63-1, 64-1. The optical splitter 14TE-1 splits the TE polarized combined optical signal supplied from the output port 61-1 into an optical signal in the frequency band of ch1 and an optical signal in the frequency band of ch2. The optical splitter 14TE-1 outputs the split optical signal in the frequency band of ch1 from the output port 63-1, and outputs the split optical signal in the frequency band of ch2 from the output port 64-1.

The optical splitter 14TM-1 is connected on the input side to the output port 62-1 of the polarization splitter 60-1, and has two output ports 65-1, 66-1. The optical splitter 14TM-1 splits the TM polarized combined optical signal supplied from the output port 62-1 into an optical signal in the frequency band of ch1 and an optical signal in the frequency band of ch2. The optical splitter 14TM-1 outputs the split optical signal in the frequency band of ch1 from the output port 65-1, and outputs the split optical signal in the frequency band of ch2 from the output port 66-1.

Output port 63-1 connects to photomixer 13-1-1 and supplies an optical signal of frequency ch1 of TE polarization, i.e., the optical signal used to form beam 90-1, to photomixer 13-1-1. Output port 64-1 connects to photomixer 13-1-2 and supplies an optical signal of frequency ch2 of TE polarization, i.e., the optical signal used to form beam 90-2, to photomixer 13-1-2. Output port 65-1 connects to photomixer 13-1-3 and outputs an optical signal of frequency ch1 of TM polarization, i.e., the optical signal used to form beam 90-3, to photomixer 13-1-3. Output port 66-1 connects to photomixer 13-1-4 and outputs an optical signal of frequency ch2 of TM polarization, i.e., the optical signal used to form beam 90-4, to photomixer 13-1-4.

Hereinafter, when referring to the polarization splitters and optical splitters contained within the polarization wavelength splitters 15-2 to 15-4 other than the polarization wavelength splitter 15-1, the branch number "-1" of the symbol will be replaced with the branch number of the corresponding polarization wavelength splitter 15-2 to 15-4. For example, in the case of the polarization wavelength splitter 15-2, it will be shown as polarization splitter 60-2.

The connection configuration of the polarization wavelength splitters 15-2 to 15-4 is the same as that of the polarization wavelength splitter 15-1. Therefore, the output ports 63-2, 64-2, 65-2, and 66-2 of the polarization wavelength splitter 15-2 are connected to the photomixers 13-2-1, 13-2-2, 13-2-3, and 13-2-4, respectively. The output ports 63-3, 64-3, 65-3, and 66-3 of the polarization wavelength splitter 15-3 are connected to the photomixers 13-3-1, 13-3-2, 13-3-3, and 13-3-4, respectively. The output ports 63-4, 64-4, 65-4, and 66-4 of the polarization wavelength splitter 15-4 are connected to the photomixers 13-4-1, 13-4-2, 13-4-3, and 13-4-4, respectively.

Therefore, in the reception directivity control device 1d, similar to the reception directivity control device 1c of the third embodiment, the optical signals used to form beam 90-1 are supplied to photomixers 13-1-1, 13-2-1, 13-3-1, and 13-4-1. The optical signals used to form beam 90-2 are supplied to photomixers 13-1-2, 13-2-2, 13-3-2, and 13-4-2. The optical signals used to form beam 90-3 are supplied to photomixers 13-1-3, 13-2-3, 13-3-3, and 13-4-3. The optical signals used to form beam 90-4 are supplied to photomixers 13-1-4, 13-2-4, 13-3-4, and 13-4-4.

Therefore, RF combiner 17-1 outputs a reception signal corresponding to an incoming wave arriving from the direction of beam 90-1. RF combiner 17-2 outputs a reception signal corresponding to an incoming wave arriving from the direction of beam 90-2. RF combiner 17-3 outputs a reception signal corresponding to an incoming wave arriving from the direction of beam 90-3. RF combiner 17-4 outputs a reception signal corresponding to an incoming wave arriving from the direction of beam 90-4. Therefore, when there are incoming waves arriving from the directions of beams 90-1, 90-2, 90-3, and 90-4, it becomes possible to obtain reception signals of four arriving waves in parallel.

(Effects of the Fourth Embodiment)
The reception directivity control device 1d of the fourth embodiment has the following effects in addition to the effects of the reception directivity control device 1c of the third embodiment. That is, in the reception directivity control device 1d, four types of optical signals are used by combining two different polarizations and two different frequencies as optical signals used to form the beams 90-1 to 90-4. The four types of optical signals can be polarization multiplexed and wavelength multiplexed. Therefore, the row direction scanning matrix circuit 24, the column direction scanning matrix circuit 34, the distributors 25-1, 25-2, 35-1, 35-2, the SSB modulators 11-1-1 to 11-2-2, and the optical multiplexers 12-1-1 to 12-2-2 can process the four types of optical signals independently. The independently processed optical signals are separated into TE polarization and TM polarization by the polarization wavelength demultiplexers 15-1 to 15-4, and further separated into frequency ch1 and frequency ch2. This enables photomixers 13-1-1 to 13-4-4 to individually process the four types of optical signals used to form beams 90-1 to 90-4, and as a result, each of RF combiners 17-1 to 17-4 can individually output the received signals of the incoming waves arriving from the directions of each of beams 90-1 to 90-4.

In terms of the frequencies used, the reception directivity control device 1c uses optical signals of four different frequencies, ch1 to ch4, whereas the reception directivity control device 1d uses optical signals of two different frequencies, ch1 and ch2, making it possible to achieve the same effect as the reception directivity control device 1c. As described above, the reception directivity control device 1c uses four different frequencies, so it is necessary to take care of interference when determining the optical frequency channel. In contrast, the reception directivity control device 1d can use half the frequencies used by the reception directivity control device 1c, which has the effect of making it easier to select the optical frequency channel than the reception directivity control device 1c.

In addition, in the reception directivity control device 1d, the first light source 41a-3 may be removed, a distributor that branches the output of the first light source 41a-1 into two, one output of the distributor is connected to the input port 24-1, a polarization rotator that converts TE polarization to TM polarization is connected to the other output of the distributor, and the output of the polarization rotator is connected to the input port 24-2. In this case, the polarization rotator converts the first optical signal of TE polarization frequency ch1 output by the first light source 41a-1 into a first optical signal of TM polarization frequency ch1 that is the same as the optical signal generated by the first light source 41a-3, and outputs it to the input port 24-2. By applying this configuration to the combination of the first light source 41a-2 and the first light source 41a-4, the combination of the second light source 42a-1 and the second light source 42a-3, and the combination of the second light source 42a-2 and the second light source 42a-4, the number of light sources used can be halved. This makes it possible to reduce the power consumption of the reception directivity control device 1d.

(Other configuration examples of each embodiment)
In the examples shown in the above embodiments, the antenna elements 80-1-1 to 80-2-2 of the array antenna 80 are arranged in a 2×2 configuration along the vertical and horizontal directions. In contrast, the antenna elements 80-1-1 to 80-2-2 of the array antenna 80 may be arranged in the following configuration. That is, an arbitrary straight line on the surface of the array antenna 80 is defined as a row axis, and a straight line perpendicular to the row axis on the surface of the array antenna 80 is defined as a column axis. The antenna elements 80-1-1 to 80-2-2 may be arranged in a 2×2 configuration along the row axis and column axis defined in this way. In other words, on the surface of array antenna 80, a rectangular shape may be assumed with vertices at each of antenna elements 80-1-1, 80-1-2, 80-2-1, and 80-2-2, and antenna elements 80-1-1 to 80-2-2 may be arranged such that, for example, the side connecting antenna element 80-1-1 and antenna element 80-2-1 in the rectangular shape is tilted at an arbitrary angle from the vertical direction.

In each of the above embodiments, an example in which the number of antenna elements in the array antenna 80 is "4" is shown, and in the above first to third embodiments, it has been additionally explained that the number of antenna elements in the array antenna 80 can be increased. Here, the conditions for the number of antenna elements in the array antenna 80 in each embodiment are more specifically shown as follows, for example. If the number of antenna elements in the row direction is M and the number of antenna elements in the column direction is N, and M and N are positive integers and satisfy the condition M×N≧2, any value of M and N may be selected. In this case, either one of M and N may be "1". When three or more antenna elements are arranged in the row direction or column direction, they are arranged so that the intervals between adjacent antenna elements in the row direction are equal, and the intervals between adjacent antenna elements in the column direction are equal. However, the intervals between adjacent antenna elements do not necessarily have to be equal, and the arrangement may be such that some of the antenna elements arranged at equal intervals are removed and thinned out.

In the third embodiment described above, a maximum of four beams 90-1 to 90-4 are formed in parallel, and in the fourth embodiment, an example is shown in which four beams 90-1 to 90-4 are also formed in parallel. In contrast to this, as described in the first and second embodiments, by making the row-direction scanning matrix circuit 24 capable of handling three or more row-direction phase gradients, and by making the column-direction scanning matrix circuit 34 capable of handling three or more column-direction phase gradients, it becomes possible to form more than four beams in parallel in the third and fourth embodiments.

In each of the above embodiments, the SSB modulators 11-1-1 to 11-2-2 are configured to output the USB component of the modulated optical signal, but they may also be configured to output the LSB component, which is the other component of the single sideband wave.

In each of the above embodiments, the SSB modulators 11-1-1 to 11-2-2 output only the USB component of the modulated optical signal, and therefore also function as filters that suppress the carrier component and the LSB component. Therefore, each of the SSB modulators 11-1-1 to 11-2-2 may be replaced with an optical modulator such as an intensity modulator, a phase modulator, or a double sideband modulator, and a filter that suppresses the carrier component and the LSB component may be provided on the output side. In this case, the configuration including the optical modulator and the filter is the electrical-to-optical conversion unit 11.

In each of the above embodiments, the photomixers 13-1 to 13-4, 13-1-1 to 13-4-4 are, for example, photodiodes that perform square-law detection and output a signal in the RF frequency band, i.e., a detected RF signal. Alternatively, instead of the photomixers 13-1 to 13-4, 13-1-1 to 13-4-4, a circuit may be provided that performs detection using a detection means other than square-law detection and outputs a signal in the RF frequency band.

For example, the Butler matrix circuit shown in Reference 1 below is used as the row-direction scanning matrix circuit 24 in the first, third and fourth embodiments, the column-direction scanning matrix circuit 34, and the scanning matrix circuit 51 in the second embodiment.

[Reference 1: Walter Charczenko et al., “Integrated optical Butler matrix for beam forming in phased-array antennas”, OE/LASE '90, Proceedings Volume 1217, Optoelectronic Signal Processing for Phased-Array Antennas II, 1990.]

However, the Butler matrix circuit is just one example, and any matrix circuit may be applied as long as it performs the operations of the row-direction scanning matrix circuit 24, the column-direction scanning matrix circuit 34, and the scanning matrix circuit 51 described above.

In addition, instead of the row-direction scanning matrix circuit 24, the column-direction scanning matrix circuit 34, and the scanning matrix circuit 51, a circuit may be applied that transmits the optical signal of a spatial beam, i.e., the optical signal propagating through space, through a lens and imparts a phase tilt to the optical signal. In addition to optical lenses, the lens may be, for example, a Rotman lens as described in Reference 2 below.

[Reference 2: Z. Zalevsky et al., "A Novel Photonic Rotman-Lens Design for Radar Phased Array Antennas" 2009 IEEE International Conference on Microwaves, Communications, Antennas and Electronics Systems, 9 Nov., 2009.]

In each of the above embodiments, the reception directivity control devices 1, 1a, 1b, 1c, and 1d do not include an array antenna 80, but are configured to be connected to the array antenna 80. However, the reception directivity control devices 1, 1a, 1b, 1c, and 1d may also be configured to include an array antenna 80.

　Although an embodiment of the present invention has been described above in detail with reference to the drawings, the specific configuration is not limited to this embodiment, and includes designs that do not deviate from the gist of the present invention.

It can be used for ultra-high-speed wireless transmission using radio waves in the millimeter wave and terahertz high-frequency bands, high-definition imaging, and receiving radio waves with sharp directionality formed in radar, etc.

1...receiving directivity control device, 11...electrical-optical conversion section, 11-1-1 to 11-2-2...SSB modulator, 12...optical multiplexing section, 12-1-1 to 12-2-2...optical multiplexer, 13...optical-electrical conversion section, 13-1 to 13-4...photomixer, 16...RF multiplexing section, 17...RF multiplexer, 20...row direction phase tilt imparting section, 22...row direction scanning instruction circuit, 23...row direction scanning switching circuit, 24 ...row direction scanning matrix circuit, 25-1, 25-2...distributor, 30...column direction phase tilt applying section, 32...column direction scanning instruction circuit, 33...column direction scanning switching circuit, 34...column direction scanning matrix circuit, 35-1, 35-2...distributor, 41...first light source, 42...second light source, 80...array antenna, 80-1-1 to 80-2-2...antenna elements, 90-1 to 90-4...beam

Claims (8)

1. 1. A reception directivity control device that controls reception directivity of an array antenna in which an arbitrary straight line in a plane is defined as a row-direction axis, a straight line perpendicular to the row-direction axis in the plane is defined as a column-direction axis, and a plurality of antenna elements are arranged along the row-direction axis and the column-direction axis,
   an electro-optical converter that modulates, by each of the RF signals obtained by receiving an incoming wave arriving from a desired direction at each of the antenna elements, each of the optical signals to which a phase gradient corresponding to each of the RF signals is imparted, the phase gradient having an opposite sign to a row-direction phase gradient that occurs in accordance with a difference in receiving position in the row direction and the desired direction;
   an optical multiplexing unit that multiplexes each of the optical signals to which a phase gradient corresponding to each of the RF signals is imparted, the phase gradient being the same as a column-direction phase gradient that occurs in response to a difference in receiving position in the column direction and the desired direction, with a single sideband component of a modulated optical signal generated by the modulation corresponding to each of the optical signals to generate a multiplexed optical signal;
   an opto-electrical conversion unit that detects each of the multiplexed optical signals generated by the optical multiplexing unit and generates a detected RF signal corresponding to each of the multiplexed optical signals;
   an RF combiner that combines the detected RF signals generated by the photoelectric converters to generate a reception signal corresponding to the desired direction;
   A receiving directivity control device comprising:
2. The array antenna includes:
   The antenna element array includes M×N antenna elements arranged in the row direction and N antenna elements arranged in the column direction, under the condition that M×N≧2;
   a first light source that generates a first optical signal;
   a second light source that generates a second optical signal having the same frequency as the first optical signal;
   a row-direction phase gradient imparting unit that generates M row optical signals by imparting, to the first optical signal, phase gradients corresponding to the RF signals and having opposite signs to the row-direction phase gradients;
   a column-wise phase gradient imparting unit that generates N column optical signals by imparting, to the second optical signal, a phase gradient corresponding to each of the RF signals and the same phase gradient as the column-wise phase gradient,
   The electro-optical conversion unit is
   modulating each of the M row optical signals with the RF signal corresponding to the row position of each of the M row optical signals for each of the M RF signals per column to generate M×N single sideband components of modulated optical signals;
   The optical multiplexing unit includes:
   performing multiplexing of each of the N column optical signals with a single sideband component of the modulated optical signal corresponding to the column position for each of the N single sideband components of the modulated optical signals for each row to generate M×N multiplexed optical signals;
   The photoelectric conversion unit is
   Detecting each of the M×N multiplexed optical signals generated by the optical multiplexing unit to generate M×N detected RF signals;
   The RF multiplexing unit includes:
   synthesizing the M×N detected RF signals generated by the photoelectric conversion unit to generate a received signal corresponding to the desired direction;
   The receiving directivity control device according to claim 1 .
3. When the desired directions are multiple,
   The first light source and the second light source are provided for each of the desired directions,
   A combination of the first optical signal and the second optical signal generated by each combination of the first light source and the second light source for each desired direction has a same frequency within each combination, and different combinations are separable,
   The row direction phase gradient imparting unit is
   generating the M row light signals for each of the desired directions;
   The column-direction phase gradient imparting unit is
   generating the N column optical signals for each of the desired directions;
   The electro-optical conversion unit is
   generating single sideband components of the modulated optical signal in a number equal to the number of desired directions x M x N;
   The optical multiplexing unit includes:
   generating the multiplexed optical signals in a number M×N of the desired directions;
   The photoelectric conversion unit is
   Separating the number of the desired directions x M x N of the combined optical signals between the different combinations, and detecting each of the separated M x N combined optical signals for each of the desired directions to generate M x N detected RF signals for each of the desired directions;
   The RF multiplexing unit includes:
   synthesizing the M×N detected RF signals for each desired direction to generate the received signal for each desired direction;
   The receiving directivity control device according to claim 2 .
4. Each combination of the first light source and the second light source for each desired direction is
   generating combinations of the first optical signal and the second optical signal that are separable between the different combinations, the combinations having different frequencies for the desired directions;
   The photoelectric conversion unit is
   Separating the number of desired directions x M x N multiplexed optical signals by frequency to generate the M x N multiplexed optical signals for each desired direction.
   The receiving directivity control device according to claim 3 .
5. Each combination of the first light source and the second light source for each desired direction is
   generating combinations of the first optical signal and the second optical signal that are separable between the different combinations, the combinations having different polarization modes for each desired direction;
   The photoelectric conversion unit is
   Separating the number of desired directions×M×N multiplexed optical signals for each polarization mode to generate the M×N multiplexed optical signals for each desired direction.
   The receiving directivity control device according to claim 3 or 4.
6. The array antenna includes:
   The antenna element array includes M×N antenna elements arranged in the row direction and N antenna elements arranged in the column direction, under the condition that M×N≧2;
   a first light source that generates a first optical signal;
   a second light source that generates a second optical signal having the same frequency as the first optical signal but a different polarization mode;
   a phase gradient imparting unit that generates M row optical signals by imparting, to the first optical signal, phase gradients corresponding to the RF signals and having an opposite sign to the row-directional phase gradient, under a condition that the desired direction in which an absolute value of the row-directional phase gradient and an absolute value of the column-directional phase gradient are equal is specified, and generates N column optical signals by imparting, to the second optical signal, phase gradients corresponding to the RF signals and having the same phase gradient as the column-directional phase gradient, and converts a polarization mode of either the M row optical signals or the N column optical signals to make the polarization modes of the M row optical signals and the N column optical signals equal to each other,
   The electro-optical conversion unit is
   modulating each of the M row optical signals with the RF signal corresponding to the row position of each of the M row optical signals for each of the M RF signals per column to generate M×N single sideband components of modulated optical signals;
   The optical multiplexing unit includes:
   performing multiplexing of each of the N column optical signals with a single sideband component of the modulated optical signal corresponding to the column position for each of the N single sideband components of the modulated optical signals for each row to generate M×N multiplexed optical signals;
   The photoelectric conversion unit is
   Detecting each of the M×N multiplexed optical signals generated by the optical multiplexing unit to generate M×N detected RF signals;
   The RF multiplexing unit includes:
   synthesizing the M×N detected RF signals generated by the photoelectric conversion unit to generate a received signal corresponding to the desired direction;
   The receiving directivity control device according to claim 1 .
7. The photoelectric conversion unit detects the combined optical signal by square detection.
   The receiving directivity control device according to claim 1 .
8. A reception directivity control method for controlling reception directivity of an array antenna in which an arbitrary straight line in a plane is defined as a row-direction axis, a straight line perpendicular to the row-direction axis in the plane is defined as a column-direction axis, and a plurality of antenna elements are arranged along the row-direction axis and the column-direction axis, the method comprising the steps of:
   modulating, by each of the antenna elements receiving an incoming wave arriving from a desired direction, each of optical signals to which a phase gradient corresponding to each of the RF signals and having an opposite sign to a row-direction phase gradient occurring in accordance with a difference in receiving position in the row direction and the desired direction is imparted;
   generating a combined optical signal by multiplexing each of the optical signals to which a phase gradient corresponding to each of the RF signals is imparted, the phase gradient being the same as a column-direction phase gradient that occurs in response to a difference in receiving position in the column direction and the desired direction, with a single sideband component of a modulated optical signal generated by the modulation corresponding to each of the optical signals;
   detecting each of the generated multiplexed optical signals to generate a detected RF signal corresponding to each of the multiplexed optical signals;
   synthesizing the generated detected RF signals to generate a received signal corresponding to the desired direction;
   Receiving directivity control method.

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