JP4645491B2 - Antenna switching device - Google Patents

Description

  The present invention relates to an antenna switching device that switches a plurality of antennas.

An example of this type of antenna switching device is disclosed in Patent Document 1. According to the configuration disclosed in Patent Document 1, the first antenna unit is operated with the first linear polarization characteristic and the second antenna unit is operated with the second linear polarization characteristic. 1 communication mode and the first antenna unit and the second antenna unit are fed by feeding the first antenna unit and the second antenna unit with a phase difference of approximately 90 degrees by the circularly polarized wave generating means. By switching the second communication mode operated with the circular polarization characteristic by the communication changeover switch, it is sufficient that the polarization is matched with the ground base station and the satellite base station having different polarizations in one terminal. It becomes possible to communicate with gain.
JP 2001-284944 A (FIG. 2)

By the way the antenna can be divided into two types of large divide and send受共for the antenna and the transmitting and receiving another body antenna. Employing a shared transmission / reception antenna has the advantage that it can be installed in a compact manner, while the performance is inferior to that of a separate antenna. On the other hand, when a separate antenna for transmission and reception is adopted, a larger installation place is required as compared with a shared antenna for transmission and reception, but there is an advantage that transmission / reception characteristic performance is good. In recent years, there have been requests from users to place importance on the performance of antennas and to install antennas in a compact manner.

In this case, if the design is focused on the performance of the antenna, it is not compact, and if the compactness is emphasized, the performance is inferior. If both of these requests are accepted, versatility and usability can be further improved. In the configuration disclosed in Patent Document 1, although the feeding circuits for a plurality of antennas can be switched, the above-mentioned problems are not taken into consideration, and thus the problems cannot be solved .

The present invention has been made in view of the above circumstances, and its purpose is to make the antenna easily switchable even when a transmission / reception shared antenna or a separate transmission / reception antenna is used. An object of the present invention is to provide an antenna switching device with improved usability.

According to invention of Claim 1, it acts as follows. When the transmission unit gives a transmission signal to the first port of the circulator, when only the first antenna for transmission and reception is used, the transmission signal is radiated from the first antenna for transmission and reception through the second port of the circulator. When the antenna switching unit switches so as to selectively receive a signal from the first antenna when only the first antenna shared for transmission and reception is used , the receiving unit transmits the received signal from the first antenna to the circulator. It can be received through the third port. When the second antenna for transmission and the third antenna for reception are used as separate antennas, the antenna switching unit includes a third reception antenna provided separately from the second antenna for transmission. switching example to selectively receive signals from the antenna of the receiving unit can receive the signals received through the third antenna for reception. Therefore, since the received signals of the first and third antennas can be switched, the antenna can be easily switched according to the type of antenna to be connected, and versatility can be improved.

The first switch of the antenna switching unit switches so that the signal from the third antenna is received by the receiving unit. The second switching unit of the antenna switching unit switches on and off energization from the third port of the circulator to the receiving unit. For this reason, when the receiving unit is receiving a signal from the third antenna, the energization from the third port of the circulator to the receiving unit can be turned off, and between the third port of the circulator and the receiving unit. Isolation can be further increased. Therefore, the isolation between the transmission unit and the reception unit can be further increased, the reception sensitivity can be further increased, and the communication distance with the communication target can be further increased.

The second switching unit switches the signal from the first antenna to be connected to the terminator through the third port of the circulator when the energization between the third port of the circulator and the receiving unit is turned off. The reflected wave exerted from the port to other ports can be suppressed as much as possible. For example, when a three-port circulator is applied, the reflected wave circulates from the third port to the first port and is given to the output side circuit of the transmission unit. In this case, it is given to the output stage circuit of the transmission unit. Adverse effects can be suppressed as much as possible.

Further, the first antenna has two feeding terminals and is configured to be able to output two types of linearly polarized radio signals of horizontal polarization and vertical polarization, and the polarization plane switching unit is output from the first antenna. Therefore, the polarization plane of the first antenna can be switched according to the application.

  For example, in the case of an RF tag reader / writer system, when communicating with a radio wave signal in the UHF band by a high-gain circularly polarized antenna between the reader / writer and the RF tag, it is necessary to suppress the radio wave output and perform communication. In some cases, the antenna gain can be relatively improved by about 3 dB when a radio wave signal is output. In such a case, it may be desired to increase the communication distance by applying a linearly polarized radio signal. In this case, a linearly polarized radio wave signal is generated by switching the polarization plane, and communication is performed using the linearly polarized radio wave signal, so that the communication distance can be made longer and convenience is improved.

Further, the transmission unit transmits horizontal polarization and vertical polarization test signals to the radio wave transmission object. The receiving unit receives a reflected wave, which is a transmission signal reflected from a radio wave transmission object, as a reception signal. The polarization plane switching unit switches the polarization plane of the radio signal in accordance with the received signal level. For this reason, it is possible to select and transmit a radio signal with a more appropriate plane of polarization, and to perform communication processing by receiving a strong reflected wave.

If the polarization plane switching unit is configured integrally with the first antenna as in the second aspect of the invention, it can be easily matched at the time of manufacturing, and the first antenna and the polarization plane switching unit are matched. Can be improved.

(First embodiment)
Hereinafter, a first embodiment in which the present invention is applied to an antenna switching device used in a reader / writer of an RF tag reader / writer system will be described with reference to FIGS.

FIG. 1 schematically shows an electrical configuration of an RF tag reader / writer system as a block diagram.
As shown in FIG. 1, the RF tag reader / writer system 1 includes a reader / writer 2, two (plural) antennas 3 a and 3 b connected to the reader / writer 2, and an RF tag 4, to which a host controller 5 is connected. Configured.
The reader / writer 2 includes a control unit 6 that performs overall control of the reader / writer 2, a baseband signal processing unit 7, a transmission unit 8, a reception unit 9, and an antenna switching device 10. A function of reading and writing information recorded on the RF tag 4 is provided.

  The control unit 6 is constituted by a microcomputer, for example, and is connected to the baseband signal processing unit 7 and the antenna switching device 10. The control unit 6 generates a data signal to be transmitted to the RF tag 4 and gives it to the baseband signal processing unit 7. The baseband signal processing unit 7 modulates the data signal to generate a predetermined modulation signal and supplies the modulated signal to the transmission unit 8. The transmission unit 8 supplies the supplied modulation signal to the antenna switching device 10 as a high frequency signal having a frequency in the UHF band, for example. The antenna switching device 10 is configured to provide the first antenna 3a with the high-frequency signal given from the transmission unit 8.

FIG. 2 shows an example of the internal configuration of the antenna switching device in detail.
The antenna switching device 10 includes a circulator 11, first and second switchers 12 and 13, and a terminator 14. The circulator 11 is a circulator having a first port 11a to a third port 11c, circulates an input signal for the first port 11a to the second port 11b, and sends an input signal for the second port 11b to the third port 11c. It is configured to circulate and circulate an input signal to the third port 11c to the first port 11a.

  The first port 11 a of the circulator 11 is connected to the transmission output terminal of the transmission unit 8 through the first terminal 10 a of the antenna switching device 10. The second port 11 b of the circulator 11 is connected to the first antenna 3 a through the second terminal 10 b of the antenna switching device 10. The third port 11 c of the circulator 11 is connected to a first terminal 13 a that serves as a movable contact of the second switch 13.

  The first and second switchers 12 and 13 are each constituted by an antenna switch. In addition, these 1st and 2nd switchers 12 and 13 are functioning as the antenna switching part of this invention. A second terminal 13 b serving as a fixed contact of the second switch 13 is connected to the terminator 14. The terminator 14 is constituted by a resistor (for example, a 50Ω resistor) whose resistance value matches the characteristic impedance of the line.

  The third terminal 13 c serving as the fixed contact of the second switch 13 is connected to the third terminal 12 c serving as the fixed contact of the first switch 12. The first terminal 12 a serving as a fixed contact of the first switch 12 is electrically connected to the second antenna 3 b through the fourth terminal 10 d of the antenna switching device 10. The second terminal 12 b serving as the movable contact of the first switch 12 is connected to the receiving unit 9 through the third terminal 10 c of the antenna switching device 10.

  The control unit 6 is connected to each control terminal (not shown) provided in the first and second switchers 12 and 13. The first and second switchers 12 and 13 are configured to be able to switch the electrical continuity connection of the terminals 12 a to 12 c and 13 a to 13 c by switching control by the host controller 5 or the control unit 6. The lines connecting the constituent elements 3a, 3b, 8, 9 and 11 to 14 are all configured by lines having a predetermined characteristic impedance (for example, 50Ω).

  The host controller 5 includes a host-side control unit 5a. The host-side control unit 5a is configured by, for example, a server and a computer, and is connected to the control unit 6 of the reader / writer 2. The host controller 5 is configured to control switching of the antenna switching device 10 through the control unit 6 of the reader / writer 2.

  Here, the structure of the first antenna 3a will be described with reference to FIGS. 3 (a) to 3 (c). FIG. 3A schematically shows a plan view of the first antenna, and FIG. 3B schematically shows a cross-sectional view of the first antenna. FIG. 3C shows an electrical configuration diagram of the first antenna.

  The first antenna 3a is integrally configured with a switching circuit 20 as a polarization plane switching unit, and is configured as a so-called patch antenna that can switch between horizontal polarization and vertical polarization. It is desirable that the switching circuit 20 is configured integrally with the first antenna 3a because it can be stored compactly.

  The first antenna 3a is configured to be connectable to and removable from the reader / writer 2 via a coaxial cable 15. The first antenna 3a includes an element 16 having a metal surface having a first predetermined width of four sides (for example, 25 cm × 25 cm), lines 17 and 18 respectively connected to a part of the element 16, and these lines 17 And an antenna element 19 having a metal surface with a second predetermined width of four sides (for example, 12.5 cm × 12.5 cm) connected to a part thereof. The element 16 is provided as a ground plane (base plate).

  As shown in FIG. 3A, the first antenna 3a includes feeding points 19a and 19b as two feeding terminals. One feeding point 19 a is provided in the vertical center of the horizontal end of the antenna element 19, and the other feeding point 19 b is provided in the horizontal central of the vertical end of the antenna element 19. Yes.

  As shown in FIG. 3B, a switching circuit 20 as a polarization plane switching unit is mounted on the surface (metal surface) of the element 16. The switching circuit 20 is constituted by an antenna switch, for example. Since the switching circuit 20 is mounted on the surface of the element 16, the switching circuit 20 can be installed more compactly.

  The transmitter 8 of the reader / writer 2 is configured to energize / de-energize the DC signal to the switching circuit 20 through the antenna switching device 10 and the coaxial cable 15. The switching circuit 20 supplies a high-frequency signal to any one of the feeding points 19a and 19b according to whether or not a DC signal is given from the transmission unit 8 or according to the level of the level of the given DC signal. These can be switched. Therefore, the reader / writer 2 can be configured without providing a separate control line for the switching circuit 20.

  The first antenna 3a can radiate a horizontally polarized radio wave signal when a high frequency signal is supplied to the feeding point 19a and no high frequency signal is supplied to the feeding point 19b. Conversely, the first antenna 3a can radiate a vertically polarized radio wave signal when a high-frequency signal is supplied to the feeding point 19b and no high-frequency signal is supplied to the feeding point 19a.

  Therefore, when the high-frequency signal is supplied to the first antenna 3a by the switching circuit 20 switching the feeding to the feeding points 19a and 19b, a horizontally polarized wave or a vertically polarized radio signal is sent from the first antenna 3a. Can be radiated. Thereby, the antenna which radiates | emits efficiently a horizontal polarization and a vertical polarization can be comprised simply and easily.

  Such a reader / writer 2 uses, as a radio wave transmission object (data carrier), a radio signal obtained by performing predetermined modulation on a carrier wave in a predetermined frequency band (for example, UHF band or microwave band of several hundred MHz or higher). It is configured to transmit as an interrogation signal toward the RF tag 4 (transponder).

  The RF tag 4 includes a communication control unit 21, an antenna 22 and a memory 23 connected to the communication control unit 21. The RF tag 4 is an information storage medium that can read and write data in the built-in memory 23 from the outside without contact using radio waves. For example, when the RF tag 4 is a passive type, a part of the radio wave signal received from the reader / writer 2 is turned on / off by data (response signal) stored in the memory 23 and reflected by an impedance mismatch, and the reader is passed through the antenna 22. Responds to writer 2. The reader / writer 2 receives this reflected wave by the receiving unit 9 and demodulates it as response data in the baseband signal processing unit 7.

  Further, when the RF tag 4 is, for example, an active type, an internal battery is built in, the inquiry signal received from the reader / writer 2 is demodulated, and a transmission signal generated from the power of the internal battery is stored in the memory 23. It modulates with data (response signal) and responds to the reader / writer 2 through the antenna 22. Similarly, the reader / writer 2 receives this reflected wave at the receiving unit 9 and demodulates it as response data at the baseband signal processing unit 7.

The operation of the above configuration will be described with reference to FIGS. 4 (a), 4 (b), and 5 as well.
The antenna switching device 10 communicates with the RF tag 4 by simultaneously using the first antenna 3a and the second antenna 3b by switching the first and second switching units 12 and 13 through the control unit 6. Alternatively, it is possible to switch between communicating with the RF tag 4 using either the first antenna 3a or the second antenna 3b.

As described above, the control unit 6 can switch and control the first and second switchers 12 and 13 of the antenna switching device 10. For example, when the user wants to use a transmission / reception shared antenna, the transmission / reception shared antenna (corresponding to the first antenna for transmission / reception of the present invention) is connected as the first antenna 3a to the second terminal 10b, and the fourth An antenna is not connected to the terminal 10d.

  After connecting the antenna in this way, the user inputs connection information to the host controller 5. When this connection information is input to the host controller 5, the host controller 5 switches and controls the first and second switchers 12 and 13 through the control unit 6 as shown in FIG. That is, the control unit 6 performs switching control so that the second terminal 12b and the third terminal 12c of the first switch 12 are connected, and at the same time, the first terminal 13a and the third terminal 13c of the second switch 13 are connected. Switching control is performed so as to connect the two.

  Then, the third port 11 c of the circulator 11 is conductively connected to the receiving unit 9 through the first and second switchers 12 and 13. Therefore, the transmission unit 8 can give a high-frequency signal to the first antenna 3a through the circulator 11, and can radiate a radio signal from the first antenna 3a. The receiving unit 9 can receive a signal from the first antenna 3 a through the third port 11 c of the circulator 11. Therefore, the first antenna 3a can be normally used as a transmission / reception shared antenna.

When the user wants to use the transmission antenna and the reception antenna as separate antennas, the transmission antenna (the second antenna for transmission of the present invention) is used as the first antenna 3a with respect to the second terminal 10b. And a reception antenna (corresponding to the third antenna for reception of the present invention) as the second antenna 3b is connected to the fourth terminal 10d.

  In this case, the user connects the second antenna 3b having the same size as the first antenna 3a to the reader / writer 2 as a receiving antenna through the coaxial cable 15, but the first and second antennas 3a and 3b are connected. The distance X (for example, about 20 cm) is set apart. Then, the interaction between the transmission unit 8 and the reception unit 9 can be prevented. Specifically, the dynamic range during reception by the second antenna 3b can be widened, and the characteristics of the second antenna 3b can be fully utilized.

  After the antennas 3 a and 3 b are connected and installed in this manner, the user inputs connection information to the host controller 5. When this information is input to the host controller 5, the host controller 5 switches and controls the first and second switchers 12 and 13 through the controller 6 as shown in FIG. That is, the control unit 6 performs switching control so that the first terminal 12a and the second terminal 12b of the first switch 12 are connected, and at the same time, the first terminal 13a and the second terminal 13b of the second switch 13 are connected. Switching control is performed so as to connect the two.

  Then, the receiving unit 9 is conductively connected to the second antenna 3b through the second terminal 12b and the first terminal 12a of the first switch 12. Further, the third port 11 c of the circulator 11 is connected to the terminator 14 through the first terminal 13 a and the second terminal 13 b of the second switch 13. That is, the transmission unit 8 can transmit a radio wave signal from the first antenna 3a, and the reception unit 9 can receive from the second antenna 3b.

  In this case, even if the second port 11b of the circulator 11 is not matched with the first antenna 3a, the reflected wave from the first antenna 3a is moved from the second port 11b of the circulator 11 to the third port 11c side. Even if it is circulated, the terminator 14 absorbs the reflected wave, so that the reflected wave circulating to the first port 11a side can be suppressed. Thereby, the output side circuit of the transmitter 8 can be protected, and the reliability of the circuit can be improved.

  When the second switch 13 is switched in this way, the first terminal 13a and the third terminal 13c of the second switch 13 are separated from each other, but the first terminal 13a and the third terminal 13c are made of a dielectric. Coupling a little to join.

  However, since the second terminal 12b and the third terminal 12c of the first switching unit 12 are not connected, coupling between the second terminal 12b and the third terminal 12c can be suppressed.

  Therefore, since two (a plurality of) switches 12 and 13 are provided between the third port 11c of the circulator 11 and the receiving unit 9, when separate transmission / reception antennas are used, the circulator 11 can be further improved in isolation between the third port 11c of 11 and the receiver 9, and the isolation characteristics between the transmitter 8 and the receiver 9 can be improved.

FIG. 5 is a flowchart showing a schematic operation at the start of communication between the reader / writer and the RF tag.
As shown in FIG. 5, the control unit 6 of the reader / writer 2 sequentially controls the polarization plane (horizontal polarization plane and vertical polarization plane) at the time of transmission by the first antenna 3a by switching control of the antenna switching device 10. After that, the basic command is transmitted and the response wave from the RF tag 4 is received (steps S2 and S5). At this time, the control unit 6 measures the reception signal level of the response wave of the RF tag (steps S3 and S6). The control unit 6 compares the received signal levels (step S7). As a result, the received signal level of the response wave when the horizontal polarization plane is selected is equal to or higher than the received signal level of the response wave when the vertical polarization plane is selected. Sometimes (step S7, A ≧ B), the horizontal polarization plane is selected and the subsequent command sequence processing is executed (steps S8, S9). Although details of the command sequence processing are not described in detail, processing of the normal reader / writer 2 is performed.

  When the received signal level of the response wave when the vertical polarization plane is selected is lower than the received signal level of the response wave when the vertical polarization plane is selected (step S7, A <B), the control unit 6 Then, the subsequent command sequence processing is executed (steps S10 and S11).

  Therefore, at the start of communication between the reader / writer 2 and the RF tag 4, the reader / writer 2 transmits a test signal of horizontal polarization or vertical polarization to the RF tag 4, and measures the received signal level of the reflected wave reflected. Since the communication process is performed by switching the polarization plane of the radio signal according to the magnitude of the measurement result, a radio signal having a more appropriate polarization plane can be selected and transmitted from the first antenna 3a. Can be received and processed.

  As described above, according to the present embodiment, whether the first and second switchers 12 and 13 receive the signal from the first antenna 3 a via the third port 11 c of the circulator 11. Alternatively, in order to selectively switch whether the receiving unit 9 receives a signal from the second antenna 3b, even when the user uses a transmission / reception shared antenna, the user separates the transmission antenna and the reception antenna. Even when it is used, the antenna can be easily switched according to the convenience of the user. Thereby, versatility and usability can be improved.

  In addition, two first and second switchers 12 and 13 are provided between the third port 11c of the circulator 11 and the receiving unit 9, and both switchers 12 and 12 are used when separate antennas are used. Since the switching state of 13 is kept off, the isolation between the transmission unit 8 and the reception unit 9 can be further increased, reception sensitivity can be further increased, and communication with the RF tag 4 can be achieved. The distance can be made longer.

  In order to obtain higher isolation between the transmission antenna and the reception antenna and improve reception sensitivity, separate antennas for transmission and reception are used. However, it is necessary to install two large circularly polarized antennas, which is not preferable because the installation space becomes large. In the present embodiment, since the radio wave signal is radiated by switching the linear polarization plane, the antenna gain of the RF tag 4 can be improved by about 3 dB, and the communication distance is theoretically increased by about 40%. Can do.

  Further, when the second switch 13 turns off the energization to the receiving unit 9, the second switch 13 switches the third port 11c of the circulator 11 so as to pass to the terminator 14, and therefore the first antenna 3a. It is possible to suppress the reflected wave from the terminator 14. Thereby, the reflected wave given to the transmission part 8 side can be suppressed, and the reliability of the transmission part 8 can be improved more. Since the switching circuit 20 is configured integrally with the first antenna 3a, it can be easily matched at the time of manufacture.

  Further, when the transmission unit 8 and the first antenna 3a are not sufficiently matched, the traveling wave transmitted from the transmission unit 8 is reflected by the first antenna 3a and is affected by the reflected wave. There is a risk that the reliability of the output stage of the transmitter 8 will be significantly reduced. In this embodiment, even if the first antenna 3a for transmission connected from the outside is an antenna for which sufficient matching characteristics cannot be obtained with the transmission unit 8, a problem occurs in the output stage of the transmission unit 8. To improve reliability.

(Reference example)
FIG. 6 shows a reference example . The difference from the first embodiment is that a power divider is provided in place of the polarization plane switching unit for switching the plane direction of linearly polarized waves to radiate circularly polarized radio signals. It is in the place where it was made to do. The same parts as those of the first embodiment are denoted by the same reference numerals, description thereof is omitted, and only different parts will be described below.

FIG. 6 shows an electrical configuration diagram of a first antenna in place of FIG.
As shown in FIG. 6, a first antenna 26 in place of the first antenna 3a is replaced with a switching circuit 20, a power distributor 24 that distributes power to feeding points 19a and 19b, and this power distribution. And a terminator 25 connected to the device 24. The power distributor 24 and the terminator 25 may be provided separately from the first antenna 26 or may be provided in the antenna switching device 10. If the power distributor 24 and the terminator 25 are formed integrally with the first antenna 26, the power distributor 24 and the terminator 25 can be accommodated in a compact manner.

  The power distributor 24 is configured by a so-called 0 ° / 90 ° distributor, and is configured to give 0 ° and 90 ° power to the feeding points 19a and 19b, respectively. Then, a circularly polarized radio signal can be radiated from the first antenna 26. Further, in this case, it is desirable that the electric power of 0 ° and 90 ° is switched to the feeding points 19a and 19b, for example, so that they can be supplied interchangeably. In this case, it becomes possible to switch and radiate radio signals of both circularly polarized waves of right circularly polarized wave or left circularly polarized wave according to the usage.

(Other embodiments)
The present invention is not limited to the above embodiment, and for example, the following modifications or expansions are possible.
Although the embodiment in which the antenna switching device of the present invention is used in the RF tag reader / writer system 1 has been shown, it can be applied to antenna switching devices in various wireless communication systems.
Although the present invention is applied to a communication system using the UHF band, it may be applied to a system in any frequency band as long as the distributed constant circuit is used as an equivalent circuit and has a frequency of, for example, several hundred MHz or more.

Not only the RF tag 4 but also an information storage medium such as an IC card may be applied as a data carrier.
Although it is applied to the circulator 11 having 3 ports, it may be applied to a circulator having 4 or more ports.
Although the embodiment using the two antenna switchers 12 and 13 as the antenna switching device 10 has been shown, it may be configured using one or three or more antenna switchers. In consideration of propagation characteristics and the number of parts, it is preferable to use two first and second antenna switchers 12 and 13.
The switching circuit 20 may be built in the antenna switching device 10 or may be configured separately.

1 is a block diagram showing a schematic electrical configuration of a first embodiment of the present invention. Electrical configuration diagram of antenna switching device FIGS. 1A and 1B are diagrams illustrating an example of an antenna (FIG. 1A is a plan view, FIG. 1B is a side view, and FIG. (A) is a figure which shows the switching state of the antenna switching apparatus when using a transmission / reception shared antenna, (b) is a figure which shows the switching state of the antenna switching apparatus when using a separate transmission / reception antenna. Flow chart schematically showing the operation FIG. 3 (c) equivalent view showing the second embodiment of the present invention.

Explanation of symbols

  In the drawings, 3a and 26 are first antennas, 3b is a second antenna, 6 is a control unit, 8 is a transmission unit, 9 is a reception unit, 10 is an antenna switching device, 11 is a circulator, and 12 is a first switching. (Switching unit), 13 is a second switching unit (antenna switching unit), 20 is a switching circuit (polarization plane switching unit), and 24 is a power distributor.

Claims (2)

A circulator having three or more ports and circulating an input signal for the first port to the second port and circulating an input signal for the second port to the third port , wherein the first port is connected to the transmission unit , both transmission and reception first when the only use the antenna and the first antenna through the second port connection possible, the third antenna and the separate for receiving a second antenna for transmitting a circulator which can be connected to the second antenna for the transmission via the second port when used as an antenna,
When only the first antenna for transmission / reception is used, the reception unit receives the signal received from the first antenna for transmission / reception through the third port of the circulator, and the second unit for transmission is switched . and a said antenna switching unit 3 switches the signal from the antenna to the receiving unit receives the received credit when using a third antenna for the reception antenna separately antenna,
The antenna switching unit is
A first switch comprising a first terminal to a third terminal and configured to be switchable so as to connect the first terminal and the second terminal so that the receiving unit receives a signal from the third antenna. When,
A second switch configured to be able to switch on and off energization from the third port of the circulator to the receiving unit via the second terminal and the third terminal of the first switch;
The second switcher switches the signal from the first antenna to pass from the third port of the circulator to the terminator when the energization from the third port of the circulator to the receiving unit is turned off .
The first antenna has two feed terminals and is configured to output two types of linearly polarized radio signals, horizontal polarization and vertical polarization,
A polarization plane switching unit is provided between the second port of the circulator and the two feeding terminals of the first antenna,
The polarization plane switching unit is configured to be able to switch a polarization plane of a radio wave signal output from the first antenna, and a horizontally polarized wave and a vertical polarization test signal transmitted by the transmission unit are radio wave transmission objects. An antenna switching device characterized in that the polarization plane of the radio signal is switched according to the level of the received signal level reflected by the receiving unit . The antenna switching device according to claim 1, wherein the polarization plane switching unit is configured integrally with the first antenna .

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