Antenna device and beamforming method

Abstract

To provide an antenna device and a beamforming method having antenna gain characteristics suitable for ceiling installation.SOLUTION: An antenna device according to this example includes: a Rotman lens 54; a port selection circuit 52 having multiple input ports connected to respective input terminals of the Rotman lens 54 via phase adjustment sections; and multiple antenna elements ANT1 to ANT8 connected to respective output terminals of the Rotman lens 54. Transmission lines 53-1 to 53-8 being the phase adjustment sections are preset with phase adjustment amounts such that phases of signals that have reached a first reference output terminal OUT5 through respective input terminals in first input terminal groups IN1, IN5, IN8, IN10 of the Rotman lens 54 become equal to each other, and the phases of signals that have reached a second reference output terminal OUT4 through respective input terminals in second input terminal groups IN12, IN14, IN17, IN21 of the Rotman lens 54 become equal to each other.SELECTED DRAWING: Figure 10

Description

[Technical field]

[0001] The present invention relates to an antenna device that performs beam forming using a Rotman lens. [Background technology]

[0002] A beamforming antenna is an antenna for controlling the direction of a beam emitted from the antenna to a desired direction. In general, a beamforming antenna is realized using a plurality of antenna elements, a phase control unit that controls the phase of a signal input to each antenna element, and an amplitude control unit that controls the amplitude. The phase control unit and the amplitude control unit may be controlled analogically or digitally, the former being called analog beamforming and the latter being called digital beamforming.

[0003] Fig. 1 shows an example of the configuration of a general analog beamforming antenna device. In the illustrated antenna device, K phase control units 12-1 to 12-K and K amplitude control units 13-1 to 13-K are connected to a power supply path to K transmitting antenna elements 14-1 to 14-K. By appropriately setting the phase and amplitude of signals input to the antenna elements 14-1 to 14-K to desired values ​​by the phase control units 12-1 to 12-K and the amplitude control units 13-1 to 13-K, the intensity of the composite signal of the beam radiated from the antenna elements 14-1 to 14-K is controlled to be strong in a desired direction.

[0004] In FIG. 1, the phase control sections 12-1 to 12-K are inserted in the path after conversion to a high-frequency signal by the mixers 11-1 to 11-K, but this is just one example. There are various configurations of antenna devices, such as a configuration in which a phase control section is inserted in the path of an intermediate frequency signal before being converted to a high-frequency signal, or a configuration in which a phase control section is inserted in the path of a local oscillator signal. An antenna device having a structure as shown in FIG. 1 is disclosed in, for example, Patent Document 1. Note that, although the beamforming antenna on the transmitting side has been described here, if a phase control section or an amplitude control section is inserted in a similar configuration in the receiving path, it is possible to configure a beamforming antenna on the receiving side.

[0005] As a type of beamforming different from the above-mentioned analog beamforming and digital beamforming, there is known a type of beamforming using a Rotman lens, a Butler matrix, etc. Among these, a transmitting antenna device using a beamforming method using a Rotman lens will be described with reference to FIG.

[0006] 2 has M input terminals 24-1 to 24-M and N output terminals 25-1 to 25-N. N antenna elements 26-1 to 26-N are connected to the output terminals 25-1 to 25-N of the Rotman lens 23. The Rotman lens 23 is designed in a shape such that a desired phase difference (phase difference required for beamforming) occurs in each output signal as a signal input to any one of the input terminals 24-1 to 24-M propagates through the lens and reaches each of the output terminals 25-1 to 25-N.

[0007] In beam forming using a conventional Rotman lens, one of the input terminals 24-1 to 24-M is selected by the switches 22-1 to 22-M, and a high frequency signal from the transmission circuit 21 is input to that input terminal. Of the multiple input terminals 24-1 to 24-M, the input terminals other than the selected one are terminated. In addition, in the design of a normal Rotman lens, there may be terminals other than the input / output terminals required for the above operation, and these are also terminated. Such a beam forming circuit using a Rotman lens is disclosed in Patent Document 2, for example.

[0008] Incidentally, when a base station for a wireless LAN (Local Area Network) or a mobile communication device such as a mobile phone is used indoors, the base station having the above-mentioned beamforming antenna is often installed on the ceiling. This is to ensure an efficient radio wave propagation path for communication devices present within the communication area of ​​an indoor floor by reducing the influence of obstruction by people, etc. In this case, the distance from a communication device at a certain height on the floor to the base station changes significantly as the horizontal distance from the point directly below the base station to the communication device increases.

[0009] For example, assume that base station 31 is installed on the ceiling at a height of 3 m from the floor as shown in Fig. 3. In this case, the distance between base station 31 at a height of 3 m from the floor and communication device 32 placed at a height of 1 m from the floor, when the direction of the communication device relative to the direction directly below the base station is represented by an angle θ, is as shown by the solid curve in Fig. 4. In addition, the free space propagation loss of radio waves with a frequency of 28 GHz calculated based on this distance is as shown by the dashed curve in Fig. 4.

[0010] In a typical wireless device, the output power level and the receiving gain are appropriately adjusted in order to secure a necessary signal-to-noise ratio when the free space propagation loss due to the communication distance changes. If the wireless device installed on the ceiling indoors has an antenna gain with angle dependency similar to the free space propagation loss characteristic shown in FIG. 4, the fluctuation of the free space propagation loss due to the transmission direction angle θ can be offset, and the influence on the transmission circuit can be reduced. Therefore, it is desirable that the wireless device installed on the ceiling indoors has an antenna gain with angle dependency as shown in FIG. 4. However, when an array antenna using a planar antenna is used as a general beamforming antenna, the gain generally decreases as the angle θ with respect to the 0 degree direction (front direction) increases, and the desired gain characteristic cannot be obtained. In the above explanation, the transmitting wireless device is taken as an example, but the same applies to the receiving wireless device. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] JP 2016-111605 A [Patent Document 2] Japanese Unexamined Patent Publication No. 54-120558 Summary of the Invention [Problem to be solved by the invention]

[0012] As mentioned above, when a wireless LAN or mobile communication base station is installed indoors, it is desirable to install it on the ceiling. In this case, it is desirable that the angle dependency of the antenna used in the base station has an angle dependency similar to the free space propagation loss from the floor surface to a communication device at a certain height. However, when a general beamforming antenna using a flat antenna is used as the base station antenna, the angle dependency of the antenna gain has a tendency opposite to the desired angle dependency. For this reason, the transmission power adjustment range of the transmitting wireless device and the receiving gain adjustment range of the transmitting wireless device become large, which causes a problem of increasing the load on these.

[0013] The present invention has been made in consideration of the above-mentioned conventional circumstances, and has an object to provide an antenna device and a beamforming method having antenna gain characteristics suitable for installation on a ceiling. [Means for solving the problem]

[0014] In order to achieve the above object, an antenna device according to one aspect of the present invention has the following technical features: That is, an antenna device that performs beamforming using a Rotman lens having multiple input terminals and multiple output terminals includes a port selection circuit having multiple input ports connected to the multiple input terminals via a phase adjustment unit, and an array antenna composed of multiple antenna elements connected to the multiple output terminals, the multiple input terminals include a first input terminal group and a second input terminal group, the multiple output terminals include a first reference output terminal and a second reference output terminal, the phase adjustment unit presets a phase adjustment amount for a signal supplied to each of the multiple input terminals such that the phases of signals arriving at the first reference output terminal through each input terminal in the first input terminal group are equal to each other and the phases of signals arriving at the second reference output terminal through each input terminal in the second input terminal group are equal to each other, and the port selection circuit selects an input port to be used for beamforming from the multiple input ports such that the output is larger for beams in directions with larger angles with respect to the front direction of the array antenna.

[0015] Here, in the above antenna device, the port selection circuit can select all of the plurality of input ports when radiating beams in a front direction of the array antenna.

[0016] Furthermore, in the above antenna device, when a beam is radiated in a direction different from the front direction of the array antenna, the port selection circuit can select an input port connected to an input terminal in the first input terminal group having a larger propagation phase difference with respect to the first reference output terminal, or an input port connected to an input terminal in the second input terminal group having a larger propagation phase difference with respect to the second reference output terminal, the larger the angle of the beam with respect to the front direction of the array antenna.

[0017] In the above antenna device, the port selection circuit can select one or two input ports when radiating a beam in a direction different from the front direction of the array antenna.

[0018] In addition, in the above-mentioned antenna device, the phase adjustment section may include a plurality of transmission lines connecting between the plurality of input ports and the plurality of input terminals, and each of the plurality of transmission lines may have a transmission line length corresponding to the amount of phase adjustment.

[0019] A beamforming method according to another aspect of the present invention has the following technical features: That is, in a beamforming method using a Rotman lens having a plurality of input terminals and a plurality of output terminals, the plurality of input terminals are connected to a plurality of input ports via a phase adjustment unit, the plurality of input terminals include a first input terminal group and a second input terminal group, the plurality of output terminals include a first reference output terminal and a second reference output terminal, the phase adjustment unit presets a phase adjustment amount for a signal supplied to each of the plurality of input terminals such that the phases of signals arriving at the first reference output terminal through each input terminal in the first input terminal group are equal to each other and the phases of signals arriving at the second reference output terminal through each input terminal in the second input terminal group are equal to each other, and the phase adjustment unit selects one, two or all of the plurality of input ports according to the direction of the radiated beam, and inputs a signal to the selected input port. Effect of the Invention

[0020] According to the present invention, it is possible to provide an antenna device and a beamforming method having antenna gain characteristics suitable for installation on a ceiling. [Brief description of the drawings]

[0021] [Figure 1] FIG. 1 is a diagram illustrating an example of the configuration of a conventional analog beamforming antenna device. [Diagram 2] FIG. 1 is a diagram showing an example of the configuration of a beamforming antenna device using a conventional Rotman lens. [Diagram 3] FIG. 1 is a diagram showing a base station installed on an indoor ceiling. [Figure 4] FIG. 1 is a diagram showing free space propagation loss when a base station is installed on an indoor ceiling. [Diagram 5] 1 is a diagram showing an example of the configuration of a main part of an antenna device according to the present invention; [Figure 6] FIG. 6 is a diagram illustrating basic characteristics of the antenna device of FIG. [Figure 7] 6 is a diagram showing the characteristics of a Rotman lens used in the antenna device of FIG. 5. [Figure 8] 6A and 6B are diagrams illustrating an example of use of a Rotman lens used in the antenna device of FIG. 5. [Figure 9] 6A and 6B are diagrams illustrating examples of beam shapes generated by the antenna device of FIG. 5. [Figure 10] 1 is a diagram showing an example of the configuration of a base station equipped with an antenna device according to the present invention; [Figure 11] 11 is a diagram illustrating a configuration example of a port selection circuit of the base station of FIG. 10. [Figure 12] 11A and 11B are diagrams showing a design example of a Rotman lens used in the base station of FIG. 10. [Figure 13] FIG. 13 is a diagram showing an example of a beam shape when the Rotman lens of FIG. 12 is used in the same manner as in the conventional method. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] An embodiment of the present invention will be described with reference to the drawings. FIG. 5 shows an example of the configuration of the main part of an antenna device according to the present invention. The antenna device of this example is mounted on, for example, a ceiling-mounted base station. As shown in FIG. 5, the antenna device of this example includes a Rotman lens 42 having input terminals IN1 to IN8 and output terminals OUT1 to OUT8. Input ports INPort1 to INPort8 are connected to the input terminals IN1 to IN8 of the Rotman lens 42 via transmission lines 41-1 to 41-8, which are an example of a phase adjustment unit. Antenna elements ANT1 to ANT8 constituting an array antenna are connected to the output terminals OUT1 to OUT8 of the Rotman lens 42. The Rotman lens 42 has input terminals 43-1 to 43-L and output terminals 44-1 to 44-L in addition to the input terminals IN1 to IN8 and output terminals OUT1 to OUT8, but these are terminated as they are not used.

[0023] The Rotman lens 42 used in the antenna device of this embodiment is designed in the same manner as a normal Rotman lens. Here, if the Rotman lens 42 is used in the conventional manner without using a phase adjustment unit such as the transmission lines 41-1 to 41-8, the composite beam of the antenna elements ANT1 to ANT8 when one of the input terminals IN1 to IN4 is selected and a signal is inputted will have characteristics as shown in the graph of FIG. 6. In FIG. 6, the horizontal axis represents the angle with respect to the front direction (0 degrees) of the array antenna, and the vertical axis represents the antenna gain in the direction of that angle. Note that the Rotman lens 42 is symmetrical with respect to the X-axis in the figure, so when one of the input terminals IN5 to IN8 is selected and a signal is inputted, the beam characteristics obtained will be the inverted shape of the graph of FIG. 6 with respect to 0 degrees.

[0024] In the following, among the input terminals IN1 to IN8 of the Rotman lens 42, the input terminals IN1 to IN4 located above the X-axis in FIG. 5 are referred to as a first input terminal group, and the input terminals IN5 to IN8 located below are referred to as a second input terminal group. In addition, among the output terminals OUT1 to OUT8 of the Rotman lens 42, the output terminals OUT5 to OUT8 located below the X-axis in FIG. 5 are referred to as a first output terminal group, and the output terminals OUT1 to OUT4 located above are referred to as a second output terminal group. Furthermore, the output terminal OUT5 of the first output terminal group OUT5 to OUT8 is referred to as a first reference output terminal, and the output terminal OUT4 of the second output terminal group OUT1 to OUT4 is referred to as a second reference output terminal. In addition, the input ports INPort1 to INPort4 are referred to as a first input port group, and the input ports INPort5 to INPort8 are referred to as a second input port group. It goes without saying that the above-mentioned assignment of each terminal and port is merely an example, and is not limited thereto.

[0025] The transmission lines 41-1 to 41-4 connecting between the first input port group INPort1 to INPort4 and the first input terminal group IN1 to IN4 have their respective transmission line lengths set so that the propagation phases at the first reference output terminal OUT5 are equal to each other when signals are input to each input port of the first input port group INPort1 to INPort4. Similarly, the transmission lines 41-5 to 41-8 connecting between the second input port group INPort5 to INPort8 and the second input terminal group IN5 to IN8 have their respective transmission line lengths set so that the propagation phases at the second reference output terminal OUT4 are equal to each other when signals are input to each input port of the second input port group INPort5 to INPort8. Furthermore, the transmission line lengths of the transmission lines 41-1 to 41-8 are set so that the propagation phase from each input port of the first input port group INPort1 to INPort4 to the first reference output terminal OUT5 is equal to the propagation phase from each input port of the second input port group INPort5 to INPort8 to the second reference output terminal OUT4. In this way, the transmission lines 41-1 to 41-8 have transmission line lengths according to the desired phase adjustment amount.

[0026] FIG. 7 shows the phases of signals at output terminals OUT1 to OUT8 corresponding to antenna elements ANT1 to ANT8, respectively, when one of input ports INPort1 to INPort8 is selected and a signal is input. In FIG. 7, the horizontal axis represents antenna numbers identifying antenna elements ANT1 to ANT8, and the vertical axis represents the phases of signals at output terminals corresponding to each antenna element. According to the figure, when signals are distributed and input to each input terminal of the first input terminal group IN1 to IN4, the phases of the signals are made to match at the first reference output terminal OUT5. Also, when signals are distributed and input to each input terminal of the second input terminal group IN5 to IN8, the phases of the signals are made to match at the second reference output terminal OUT4. Furthermore, the phases of the signals at the first reference output terminal OUT5 and the second reference output terminal OUT4 are also made to match.

[0027] In the antenna device of this example, in order to form a desired beam shape, all input ports are used, or one or two input ports are selected and used among the input ports INPort1 to INPort8. The operation of the antenna device of this example will be specifically described below.

[0028] First, a case where a communication device is located immediately below the base station will be described. In this case, a signal output from a transmitter (not shown) is distributed into eight by the port selection circuit 52 and input to all of the input ports INPort1 to INPort8. These signals are given a predetermined phase shift by the transmission lines 41-1 to 41-8, and then input to the input terminals IN1 to IN8 of the Rotman lens 42. At this time, the signals input to each input port of the first input port group INPort1 to INPort4 are in phase with each other at the first reference output terminal OUT5 of the Rotman lens 42. Moreover, the signals input to each input port of the second input port group INPort5 to INPort8 are in phase with each other at the second reference output terminal OUT4 of the Rotman lens 42. As a result, as shown by the broken line (ALL) in FIG. 8, signals with relatively high intensity are output from the first reference output terminal OUT4 and the second reference output terminal OUT5. Therefore, among the antenna elements ANT1 to ANT8, the signal strength of antenna elements ANT4 and ANT5 is distributed high, and the output phases of antenna elements ANT4 and ANT5 are almost the same, which results in a beam with a relatively wide radiation angle being output in the front direction of the array antenna (i.e., directly below the antenna device).

[0029] Next, a case where a communication device is located at a position at a slight angle (for example, about 20 degrees to the right in FIG. 3) from directly below the base station will be described. In this case, a signal output from a transmitter (not shown) is divided into two by the port selection circuit 52 and input to the input port INPort2 and the input port INPort3 of the first input port group INPort1 to INPort4. At this time, the signals input to the input port INPort2 and the input port INPort3 become in phase at the first reference output terminal OUT5 of the Rotman lens 42. Also, since only two input terminals, IN2 and IN3, are used, the signal strength at the output terminals OUT1 to OUT8 of the Rotman lens 42 is relatively strong at the output of the first reference output terminal OUT5 as shown by the broken lines (P2, P3) in FIG. 8, and the strength decreases sharply as the output terminal becomes farther from the first reference output terminal OUT5. Also, when a signal is input only to the input port INPort2, the beam obtained by combining the outputs of the antenna elements ANT1 to ANT8 is in a direction with a predetermined tilt angle. The same applies to the input port INPort3. Therefore, when signals are input to both input ports INPort2 and INPort3, a beam is output in a direction with a tilt angle.

[0030] Next, a case will be described in which a communication device is located at a large angle (for example, about 40 degrees to the right in FIG. 3) from directly below the base station. In this case, a signal output from a transmitter (not shown) is split into two by port selection circuit 52 and input to input ports INPort1 and INPort2 of the first input port group INPort1 to INPort4. The operation in this case is similar to when signals are input to input ports INPort2 and INPort3, but because the relationship between the propagation phase and amplitude changes (see broken line (P1, P2) in FIG. 8), the tilt direction and beam shape synthesized by antenna elements ANT1 to ANT8 have different characteristics.

[0031] Next, a case will be described where a communication device is located at an even larger angle (for example, about 50 degrees to the right in FIG. 3) from directly below the base station. In this case, a signal output from a transmitter (not shown) is input only to input port INPort1 by port selection circuit 52. Therefore, the operation is the same as when a normal Rotman lens is used (see broken line (P1) in FIG. 8), and the composite beam radiated from antenna elements ANT1 to ANT8 becomes a beam in a direction with a large tilt angle. In the above description, among the input terminals IN1 to In8 of the Rotman lens 42, the unused input terminals are terminated.

[0032] Figure 9 shows a plot of multiple beam shapes realized by the above-mentioned operation. The dashed-dotted line C in Figure 9 represents the free space propagation loss from the antenna apparatus to the communication device normalized in the 0 degree direction. As shown in Figure 9, the antenna apparatus of this example can cover a wide area almost following the free space propagation loss curve.

[0033] In the above explanation, the first input port group INPort1 to INPort4 is used except when the communication device is located near directly below the antenna device. However, since the Rotman lens is made symmetrical about the X-axis, by using the second input port group INPort5 to INPort8, it is possible to achieve beamforming that is symmetrical with respect to the 0 degree direction (directly below the antenna device).

[0034] In the above explanation, the phase of the signal is adjusted by the transmission line between the input port and the input terminal of the Rotman lens, but it goes without saying that similar characteristics can be obtained by phase shifting using other methods as long as the desired phase shift can be obtained. Also, the number of input and output terminals can be freely determined to a certain extent depending on the design of the Rotman lens. Therefore, the number of terminals of the Rotman lens is not limited to the above example, and similar effects can be obtained using other Rotman lenses.

[0035] FIG. 10 shows a configuration example of a base station equipped with an antenna device according to the present invention. As shown in FIG. 10, the base station of this example is equipped with a Rotman lens 54 having 21 input terminals IN1 to IN21 and eight output terminals OUT1 to OUT8. The Rotman lens 54 has input terminals 55-1 to 55-L and output terminals 56-1 to 56-L in addition to the input terminals IN1 to IN21 and the output terminals OUT1 to OUT8, but these are terminated as they are not used. In this embodiment, eight input terminals, IN1, IN5, IN8, IN10, IN12, IN14, IN17, and IN21, out of the input terminals IN1 to IN21, are used. A port selection circuit 52 having input ports INPort1 to INPort8 is connected to the eight input terminals via transmission lines 53-1 to 53-8, which are an example of a phase adjustment unit. Antenna elements ANT1 to ANT8 constituting an array antenna are connected to the output terminals OUT1 to OUT8 of the Rotman lens 54.

[0036] In the following, among the input terminals IN1, IN5, IN8, IN10, IN12, IN14, IN17, and IN21 of the Rotman lens 54, the input terminals IN1, IN5, IN8, and IN10 on the upper side with respect to the X-axis in FIG. 10 are referred to as a first input terminal group, and the input terminals IN12, IN14, IN17, and IN21 on the lower side are referred to as a second input terminal group. In addition, among the output terminals OUT1 to OUT8 of the Rotman lens 54, the output terminals OUT5 to OUT8 on the lower side with respect to the X-axis in FIG. 10 are referred to as a first output terminal group, and the output terminals OUT1 to OUT4 on the upper side are referred to as a second output terminal group. Furthermore, the output terminal OUT5 of the output terminals OUT5 to OUT8 is referred to as a first reference output terminal, and the output terminal OUT4 of the second output terminal group OUT1 to OUT4 is referred to as a second reference output terminal. In addition, the input ports INPort1 to INPort4 are referred to as a first input port group, and the input ports INPort5 to INPort8 are referred to as a second input port group. It goes without saying that the above-mentioned assignment of terminals and ports is merely an example and is not limited to this.

[0037] The transmission lines 53-1 to 53-4 connecting between the first input port group INPort1 to INPort4 and the first input terminal group IN1, IN5, IN8, IN10 are set in length so that the propagation phases at the first reference output terminal OUT5 are equal when signals are input to each input port of the first input port group INPort1 to INPort4. Similarly, the transmission lines 53-5 to 53-8 connecting between the second input port group INPort5 to INPort8 and the second input terminal group IN12, IN14, IN17, IN21 are set in length so that the propagation phases at the second reference output terminal OUT4 are equal when signals are input to each input port of the second input port group INPort5 to INPort8. Furthermore, the transmission line lengths of the transmission lines 53-1 to 53-8 are set so that the propagation phase from each input port of the first input port group INPort1 to INPort4 to the first reference output terminal OUT5 is equal to the propagation phase from each input port of the second input port group INPort5 to INPort8 to the second reference output terminal OUT4. In this way, the transmission lines 53-1 to 53-8 have transmission line lengths according to the desired phase adjustment amount.

[0038] Here, when one of the first input terminal group IN1, IN5, IN8, IN10 of the Rotman lens 53 is selected and a signal is input, and the Rotman lens 53 is used in the same way as a normal Rotman lens, the composite beam of the radio waves radiated from each of the antenna elements ANT1 to ANT8 will have the characteristics shown in Fig. 6. Since the Rotman lens 53 has a shape symmetrical with respect to the X-axis in the figure, when one of the second input terminal group IN12, IN14, IN17, IN21, which is located symmetrical with the first input terminal group IN1, IN5, IN8, IN10, is selected and a signal is input, the beam characteristics obtained are the inverse of the graph in Fig. 6 with respect to 0 degrees.

[0039] 10, the base station of this example includes a port selection circuit 52 having eight input ports INPort1 to INPort8. The input ports INPort1 to INPort8 of the port selection circuit 52 are connected to input terminals IN1, IN5, IN8, IN10, IN12, IN14, IN17, and IN21 of the Rotman lens 53 via transmission lines 53-1 to 53-8. The port selection circuit 52 controls so that a high-frequency signal from the transmission circuit 51 is input to an input port selected from the input ports INPort1 to INPort8 depending on the direction of the communication device with respect to the base station.

[0040] Specifically, the port selection circuit 52 controls the output of the high-frequency signal from the transmission circuit 51 in seven different states: (1) input to INPort1, (2) input to INPort8, (3) two-way distribution and input to INPort1 and INPort2, (4) two-way distribution and input to INPort2 and INPort3, (5) two-way distribution and input to INPort6 and INPort7, (6) two-way distribution and input to INPort7 and INPort8, and (7) eight-way distribution and input to INPort1 to INPort8. In this case, in the above cases (1), (3), (4), and (7), the beam characteristics obtained by combining the radio waves radiated from each of the antennas ANT1 to ANT8 are as shown in FIG. 9. Since the Rotman lens 52 is symmetrical with respect to the X-axis, in the above cases (2), (5), and (6), the beam characteristics obtained are symmetrical with respect to 0 degrees to the beam characteristics of (1), (4), and (3), respectively. In the above example, there are unused ports in cases other than (7), but these ports are terminated.

[0041] FIG. 11 shows a configuration example of the port selection circuit 52. In the example shown in FIG. 11, the port selection circuit 52 is configured using an SP7T switch 61, SPDT switches 62 to 65, and SP3T switches 66 to 71. The SP7T switch 61 is a switch that selects one of the above (1) to (7) in order to obtain an optimal beam shape according to the position of the communication device that is the communication partner. The SPDT switches 82 to 85 and the SP3T switches 86 to 91 are switches for configuring a path required to generate the beam shape selected by the SP7T switch 61. Note that, although only switches required for functionality are shown in FIG. 11, there is no functional effect even if dummy switches other than the switches shown in the figure are inserted in consideration of the symmetry of the synthesis circuit. In addition, it goes without saying that the port selection circuit 52 is not limited to the configuration shown in FIG. 11, and can be realized with various other configurations.

[0042] Figure 12 shows a design example of a Rotman lens used in the base station in Figure 10. The Rotman lens in Figure 12 is made of a dielectric substrate, with the back surface being completely grounded, and the transmission line formed by a microstrip line. Although Figure 12 only shows the main body of the Rotman lens, in reality wiring is required from the Rotman lens to the antenna and circuit. However, the wiring must be of equal length so as not to affect the phase fed to the antenna or the propagation phase provided by the transmission line.

[0043] In the figure, IN1 to IN21 are input terminals of the Rotman lens, and OUT1 to OUT8 are output terminals of the Rotman lens. Any unused terminals other than those mentioned above are terminated. In this embodiment, of the input terminals IN1 to IN21, only eight terminals IN1, IN5, IN8, IN10, IN12, IN14, IN17, and IN21 are used, so the other input terminals also need to be terminated.

[0044] For reference, Fig. 13 shows an example of the beam shape when only one of the input terminals IN1 to IN21 of the Rotman lens is selected and used in the same way as a conventional Rotman lens. Fig. 13 only shows the beam shape when the upper half of the input terminals IN1 to IN11 in the figure are used out of the input terminals IN1 to IN21 of the Rotman lens in Fig. 12, but because the Rotman lens is made symmetrical from top to bottom, the beam shape obtained when the lower half of the input terminals IN11 to IN21 in the figure are used has characteristics that are the inverse of the graph in Fig. 13 with respect to 0 degrees.

[0045] As described above, the antenna device of this example includes a Rotman lens 54 having a plurality of input terminals and a plurality of output terminals, a port selection circuit 52 having a plurality of input ports connected to the plurality of input terminals via phase adjustment units, and an array antenna composed of a plurality of antenna elements ANT1 to ANT8 connected to the plurality of output terminals. The plurality of input terminals includes a first input terminal group IN1, IN5, IN8, IN10 and a second input terminal group IN12, IN14, IN17, IN21, and the plurality of output terminals includes a first reference output terminal OUT5 and a second reference output terminal OUT4. The transmission lines 53-1 to 53-8, which are phase adjustment units, have preset phase adjustment amounts for signals supplied to each of the multiple input terminals so that the phases of signals arriving at the first reference output terminal OUT5 through each input terminal in the first input terminal group IN1, IN5, IN8, IN10 are equal to each other, and the phases of signals arriving at the second reference output terminal OUT4 through each input terminal in the second input terminal group IN12, IN14, IN17, IN21 are equal to each other. The port selection circuit 52 selects an input port to be used for beamforming from the multiple input ports so that the output is larger for a beam in a direction with a larger angle with respect to the front direction of the array antenna.

[0046] More specifically, when radiating a beam in the front direction of the array antenna, the port selection circuit 52 selects all of the multiple input ports INPort1 to INPort8. When radiating a beam in a direction different from the front direction of the array antenna, the port selection circuit 52 selects one or two input ports (INPort1, INPort1 and INPort2, or INPort2 and INPort3) connected to an input terminal having a larger propagation phase difference with respect to the first reference output terminal OUT5 among the first input terminal group IN1, IN5, IN8, IN10, or one or two input ports (INPort8, INPort7 and INPort8, or INPort6 and INPort7) connected to an input terminal having a larger propagation phase difference with respect to the reference second output terminal OUT4 among the second input terminal group IN12, IN14, IN17, IN21, as the angle of the beam with respect to the front direction of the array antenna increases.

[0047] With this configuration, in a wireless LAN or mobile communication base station installed on an indoor ceiling, the angular dependency of the antenna gain can be made closer to the free space propagation loss characteristics caused by the distance from the base station to the device. In other words, it is possible to obtain antenna gain characteristics suitable for ceiling installation. As a result, when a ceiling-mounted base station communicates with a communication device at a certain height above the floor, it becomes possible to easily adjust the transmission power and reception gain, thereby reducing the burden on the transmission and reception circuits.

[0048] Although the embodiments of the present invention have been described above, these embodiments are merely illustrative and do not limit the technical scope of the present invention. The present invention can take various other embodiments, and various modifications such as omissions and substitutions can be made without departing from the gist of the present invention. These embodiments and modifications are included in the scope and gist of the invention described in this specification, etc., and are included in the scope of the invention described in the claims and their equivalents.

[0049] Furthermore, the present invention can be provided not only as devices such as those described above or as a system composed of these devices, but also as methods executed by these devices, programs for causing a processor to realize the functions of these devices, and storage media for storing such programs in a computer-readable format. [Industrial Applicability]

[0050] The present invention can be used in an antenna device that performs beam forming using a Rotman lens. [Explanation of symbols]

[0051] 11-1 to 11-K: mixers, 12-1 to 12-K: phase control sections, 13-1 to 13-K: amplitude control sections, 14-1 to 14-K: antenna elements, 21: transmission circuit, 22-1 to 22-M: switches, 23: Rotman lenses, 24-1 to 24-M: input terminals, 25-1 to 25-N: output terminals, 26-1 to 26-N: antenna elements, 31: base station, 32: communication device, 41-1 to 41-8: transmission lines, 42: Rotman lenses, 43-1 to 43-L: input terminals (unused), 44-1 to 44-L: output terminals (unused), 51: transmission circuit, 52: port selection circuit, 53-1 to 53-8: transmission lines, 54: Rotman lenses, 55-1 to 55-L: Input terminals (unused), 56-1 to 56-L: Output terminals (unused), 61: SP7T switch, 62 to 65: SPDT switch, 66 to 71: SP3T switch, INPort1 to INPort8: Input ports, IN1 to IN21: Input terminals, OUT1 to OUT8: Output terminals

Claims

1. In an antenna device that performs beamforming using a Rotman lens having a plurality of input terminals and a plurality of output terminals, a port selection circuit having a plurality of input ports connected to the plurality of input terminals via phase adjustment units; an array antenna including a plurality of antenna elements connected to the plurality of output terminals, the plurality of input terminals includes a first group of input terminals and a second group of input terminals; the plurality of output terminals include a first reference output terminal and a second reference output terminal; the phase adjustment unit presets a phase adjustment amount for the signal supplied to each of the plurality of input terminals so that the phases of the signals arriving at the first reference output terminal through each input terminal in the first input terminal group are equal to each other, and the phases of the signals arriving at the second reference output terminal through each input terminal in the second input terminal group are equal to each other, The port selection circuit selects an input port to be used for beamforming from among the multiple input ports so that the output of the beam in a direction with a larger angle relative to the front direction of the array antenna is larger.

2. 2. The antenna device according to claim 1, The antenna device according to claim 1, wherein the port selection circuit selects all of the plurality of input ports when radiating a beam in a front direction of the array antenna.

3. 2. The antenna device according to claim 1, an input port connected to an input terminal of the first input terminal group having a larger propagation phase difference with respect to the first reference output terminal, or an input port connected to an input terminal of the second input terminal group having a larger propagation phase difference with respect to the reference second output terminal, when the port selection circuit selects an input port connected to an input terminal of the first input terminal group having a larger propagation phase difference with respect to the reference second output terminal, the greater the angle of the beam with respect to the front direction of the array antenna, when the array antenna radiates a beam in a direction different from the front direction of the array antenna.

4. 4. The antenna device according to claim 3, The port selection circuit selects one or two input ports when radiating a beam in a direction different from a front direction of the array antenna.

5. 5. The antenna device according to claim 1, the phase adjustment unit includes a plurality of transmission lines connecting the plurality of input ports and the plurality of input terminals; The antenna device according to claim 1, wherein each of the plurality of transmission lines has a transmission line length corresponding to an amount of phase adjustment.

6. A beamforming method using a Rotman lens having a plurality of input terminals and a plurality of output terminals, the plurality of input terminals are connected to a plurality of input ports via phase adjustment units; the plurality of input terminals includes a first group of input terminals and a second group of input terminals; the plurality of output terminals include a first reference output terminal and a second reference output terminal; the phase adjustment unit presets a phase adjustment amount for the signal supplied to each of the plurality of input terminals so that the phases of the signals arriving at the first reference output terminal through each input terminal in the first input terminal group are equal to each other, and the phases of the signals arriving at the second reference output terminal through each input terminal in the second input terminal group are equal to each other, A beamforming method comprising the steps of: selecting one, two, or all of the plurality of input ports according to a direction of a beam to be emitted; and inputting a signal to the selected input port.

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