JP2007158708A - Microstrip antenna and high frequency sensor employing the microstrip antenna - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a microstrip antenna, wherein a switch with a simple structure is used to obtain excellent performance of controlling a radio wave beam direction. <P>SOLUTION: Grounding points 20A to 20D located at prescribed positions of a plurality of antenna electrodes 12A to 12D on a front side of a board 10 can respectively and selectively be connected to a ground level via the switches provided on a rear side of the board 10 behind the antenna electrodes 12A to 12D. A semiconductor switching element such as a single field effect transistor or bipolar transistor without any special circuit structure for suppressing return of a reflection wave in an OFF state is adopted for each of the switches. The radio wave beam direction can excellently be changed by selecting which switch of which antenna electrode to be turned on. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a microstrip antenna capable of changing the direction of a radio wave beam by controlling the excitation state (current value or phase) of one or more antenna electrodes with a switch, and a high frequency using such a microstrip antenna. It relates to sensors.

  In this type of microstrip antenna disclosed in WO 2005/099039 A1 pamphlet, a plurality of antenna electrodes are arranged on the surface of a dielectric substrate, and the antenna electrodes are, for example, several GHz to several tens GHz. Excited by such a high frequency signal. Then, a switch for individually connecting each specific portion of the antenna electrode (or a specific part of the antenna electrode) to the ground level is provided, and by operating those switches, which antenna electrode is connected to the ground level. By selecting whether to connect to the antenna, the radiation direction of the radio wave beam from this antenna changes.

International publication WO 2005/099039 A1 pamphlet

  Based on general technical common sense, in the above-described microstrip antenna, in order to obtain a practical performance for the direction control of the radio wave beam, as the switch, an isolator in a used frequency band (for example, several GHz to several tens GHz) is used. Switch with high performance (the ability to cut off signals in a specific frequency band in the off state) should be used. As a typical switch having a high isolation performance of such a high frequency signal, a high frequency switch configured as an MMIC (Microwave Monolithic Integrated Circuit) is known. In MMIC type high frequency switches, SPDT switches (Single Pole Double Throw switches) incorporating four switching elements such as FETs are the mainstream. MMIC type high-frequency switches have a structure that prevents reflected waves from returning from the open end of each signal path when each signal path is turned off (for example, connecting 50Ω to the open end and shorting to ground) Built-in, high isolation performance. In addition, in the MMIC type high frequency switch, each signal path is configured by combining a plurality of FETs, and when each signal path is in the ON state, a high frequency current can flow bidirectionally through the signal path. Low transmission loss and excellent propagation characteristics.

  However, MMIC type high frequency switches are expensive. Also, since the MMIC type high frequency switch is large, if it is intended to be mounted on the substrate of the above-described microstrip antenna, it is difficult to make the entire microstrip antenna small.

  Accordingly, it is an object of the present invention to obtain good radio wave beam direction control performance in a microstrip antenna simply by using a switch having a simple structure.

  A microstrip antenna according to the present invention includes an electrically insulating substrate, a plurality of antenna electrodes disposed on one surface of the substrate, a ground electrode provided on the substrate for providing a ground level, and at least one antenna. An electrical conduction path having one end connected to a ground point at a predetermined position of the electrode; and a switch connected between the other end of the electrical conduction path and the ground electrode. The switch has a signal transmission path capable of ON / OFF control connected between the other end of the electrical conduction path and the ground electrode, and a reflection generated at an open end of the signal transmission path when the signal transmission path is OFF. It is a semiconductor switching element that does not have a reflected wave suppression structure for suppressing wave return.

  In the microstrip antenna according to the present invention, as a switch for controlling whether a certain antenna electrode is connected to or disconnected from a ground electrode, a semiconductor switching element having a simple configuration without a special reflected wave suppression structure is used. The direction of the radio wave beam can be variably controlled.

  For example, a single field effect transistor or a single bipolar transistor can be used as the semiconductor switching element as the switch. Specific examples are a single GaAs-metal semiconductor junction field effect transistor, a GaAs high electron mobility transistor, a GaAs-heterojunction bipolar transistor, or a SiGe-heterojunction bipolar transistor.

  In the microstrip antenna of the present invention, the length of the electrical conduction path provided between the antenna electrode and the switch can be set to an integral multiple of a half wavelength on the substrate surface of the high-frequency signal. As a result, the reflected wave that attempts to return from the switch to the antenna electrode when the switch is turned off is suppressed and the isolation performance is improved, so that a better radio beam direction variable control performance can be obtained.

  In the microstrip antenna according to one embodiment, each of the plurality of antenna electrodes on the substrate is a feeding element having a feeding point for applying a high-frequency signal. In the microstrip antenna according to another embodiment, the antenna electrode connected to the switch is a parasitic element having no feeding point for applying a high-frequency signal, and at least one other antenna electrode is It is a feed element having a feed point for applying a high-frequency signal.

  The high-frequency sensor according to the present invention includes the microstrip antenna according to the present invention as a transmitting antenna and a receiving antenna, receives a reflected wave or transmitted wave from an object of a radio wave beam radiated from the transmitting antenna by the receiving antenna, and based on the received signal Sense the object.

  According to the present invention, as a switch for connecting or disconnecting the antenna electrode to or from the ground electrode, a radio wave beam can be obtained simply by using a simple semiconductor switching element that does not have a reflected wave suppression structure, such as a single transistor. Practical performance can be obtained for the direction control.

  FIG. 1 is a plan view of a microstrip antenna according to an embodiment of the present invention, and FIG. 2 is a cross-sectional view of the antenna along the line AA in FIG.

  As shown in FIGS. 1 and 2, the microstrip antenna has a plurality of (for example, four) antenna electrodes 12 each formed of a rectangular metal thin film on the front surface of a substrate 10 made of an electrically insulating dielectric material. It has the sequence of (12A, 12B, 12C, 12D). On the back surface of the substrate 10, a power supply line 14 made of a metal thin film strip is provided. An oscillation circuit 24 that generates a high-frequency signal having a predetermined frequency within a range of several GHz to several tens of GHz is mounted on the back surface of the substrate 10, and an original feeding point having an output terminal of the oscillation circuit 24 in the center of the feeding line 14. 16 is connected. The feed line 14 branches into four branches, and the ends of the branches are respectively fed to feed points 18 (18A, 18B, 18C, 18D) at specific positions of the four antenna electrodes 12 (12A, 12B, 12C, 12D). Connected. The antenna electrode 12 having the feed point 18 that receives the application of the high-frequency signal from the oscillation circuit 24 is hereinafter referred to as a feed element.

  As representatively shown in FIG. 2 only for the two feeding elements 12A and 12C, the connection between each branch of the feeding line 14 and the feeding point 18 of each feeding element 12 is a conduction path (hereinafter referred to as “through”) that passes through the substrate 10. Such a signal transmission path is referred to as a through-hole) 26 (26A, 26C). The length of the signal transmission path from the original feed point 16 in the feed line 14 to the feed point 18 (18A, 18B, 18C, 18D) of the four feed elements 12 (12A, 12B, 12C, 12D) is the same. As a modification, the feed line 14 is arranged on the front surface of the substrate 10 like the feed element 12, and the connection between the original feed point 16 of the feed line 14 and the output terminal of the oscillation circuit 24 is a through hole. It may be done via.

  As shown in FIG. 2, an earth electrode 22 held at the ground level is provided on the back surface of the substrate 10. Further, as representatively shown in FIG. 2 only for the two feeding elements 12A and 12C, four positions on the back surface of the substrate 10 corresponding to the back of the four feeding elements 12 (12A, 12B, 12C, 12D) Four switches 28 (28A, 28C) are respectively mounted. Each switch 28 is a normal single semiconductor switching element such as a FET (field effect transistor) or a bipolar transistor. A typical example thereof is a normal single GaAs-MES-FET (metal semiconductor junction electric field). Effect transistor), GaAs-HEMT (high electron mobility transistor), GaAs-heterojunction bipolar transistor or SiGe-heterojunction bipolar transistor.

  One terminal (for example, a source terminal or an emitter terminal) of a signal transmission path (FET source-drain path or bipolar transistor emitter-collector path) that can be controlled on / off of each switch 28 feeds power to each corresponding power feeding element 12. It is connected to a specific location (hereinafter referred to as a grounding point) 20 (20A, 20B, 20C, 20D) different from the point 18 via the through hole 30 (30A, 30B, 30C, 30D), and the other terminal (for example, The drain terminal or the collector terminal) is connected to the ground electrode 22. Alternatively, the signal transmission path of each switch 28 is in the opposite direction, that is, for example, to the ground point 20 of each feeding element 12 corresponding to the drain terminal or collector terminal, and the source terminal or emitter terminal is grounded. It may be connected to the electrode 22.

  In the microstrip antenna having the above configuration, when all the four switches 28 corresponding to the four feed elements 12 are in the off state, the four feed elements 12 are excited by the high-frequency signals having the same phase. As a result, the direction in which the radio wave beam is emitted is perpendicular to the substrate 10. On the other hand, when some of the four switches 28 are in the on state and the other switches 28 are in the off state, the ground point 20 of the power feeding element 12 corresponding to the switch 28 in the on state is the ground electrode. 22, the high-frequency signal of the power feeding element 12 corresponding to the switch 28 in the on state is shifted by a certain amount in phase with respect to the high-frequency signal of the power feeding element 12 corresponding to the switch 28 in the off state. Or delayed). As a result, the direction in which the radio wave beam is radiated is inclined by a certain angle from the direction perpendicular to the substrate 10 toward the position of the feed element 12 that is relatively delayed in phase. Therefore, the radiation direction of the radio wave beam can be intentionally changed by selecting which switch 28 is turned on and off.

  It is of course possible to use an MMIC type high-frequency switch with high isolation performance for the frequency signal used, such as several GHz to several tens of GHz, as the switch 28. However, according to the research of the inventors, as described later, a normal single semiconductor switching element as described above, which does not have a special reflected wave suppression structure and does not have high isolation performance with respect to a used frequency signal, for example, Even when a single transistor is used as the switch 28, practically sufficient radio beam direction control performance can be obtained.

  FIG. 3 is a plan view of a microstrip antenna according to another embodiment of the present invention, and FIG. 4 is a cross-sectional view of the antenna along the line BB in FIG.

  As shown in FIGS. 3 and 4, this microstrip antenna has a central antenna electrode 42 made of a rectangular metal thin film on the front surface of a substrate 40 made of an electrically insulating dielectric material, A plurality of (for example, four) antenna electrodes 44 (44A, 44B, 44C, and 44D) each made of a rectangular metal thin film disposed around the antenna electrode 42 are provided. On the back surface of the substrate 40, a power supply line 14 made of a metal thin film strip is provided. An oscillation circuit 52 that generates a high-frequency signal having a predetermined frequency within a range of several GHz to several tens of GHz is mounted on the back surface of the substrate 10, and an output terminal of the oscillation circuit 52 is located at a predetermined position of the central antenna electrode 42. The feed point 46 is connected via the through hole 54. The central antenna electrode 42 is a power feeding element that receives application of a high-frequency signal from the oscillation circuit 52. On the other hand, the surrounding four antenna electrodes 44 (44A, 44B, 44C, 44D) do not have a feeding point, that is, do not receive application of a high frequency signal from the oscillation circuit 52, and this is hereinafter referred to as a parasitic element. . In each parasitic element 44, a high frequency is induced by induction from the feeding element 42.

  As shown in FIG. 4, an earth electrode 56 held at the ground level is provided inside the substrate 10 (or may be the back surface). As representatively shown only for the two parasitic elements 44B and 44C in FIG. 4, at four positions on the back surface of the substrate 40 corresponding to the back of the four parasitic elements 44 (44A, 44B, 44C, 44D), Four switches 58 (58A, 58C) are respectively mounted. Each switch 58 is a normal single semiconductor switching element such as an FET or a bipolar transistor. Typical examples thereof include a normal single GaAs-MES-FET (metal semiconductor junction field effect transistor), GaAs, and the like. -HEMT (High Electron Mobility Transistor), GaAs-heterojunction bipolar transistor or SiGe-heterojunction bipolar transistor.

  One terminal (for example, source terminal or emitter terminal) of a signal transmission path (FET source-drain path or bipolar transistor emitter-collector path) which can be controlled on / off of each switch 58 is connected to each parasitic element 44 corresponding thereto. A specific point (hereinafter referred to as a grounding point) 48 (48A, 48B, 48C, 48D) is connected through a through hole 60 (60B, 60C), and the other terminal (for example, drain terminal or collector terminal) is a ground electrode. 56. Alternatively, the signal transmission path of each switch 58 is in the opposite direction, that is, for example, to the ground point 48 of each parasitic element 44 corresponding to the drain terminal or collector terminal, and the source terminal or emitter terminal is It may be connected to the ground electrode 56.

  In the microstrip antenna having the above configuration, there is a phase difference between the high frequency induced in each parasitic element 44 and the high frequency of the feed element 42, and the radiation direction of the radio wave beam is determined by the phase difference. The phase difference between each parasitic element 44 and the feeding element 42 changes depending on whether each switch 58 corresponding to each parasitic element 44 is in an OFF state or an ON state. Radiation direction changes. Therefore, the radiation direction of the radio wave beam can be intentionally changed by selecting which switch 58 is turned on and off.

  It is of course possible to use an MMIC type high-frequency switch having high isolation performance with respect to a used frequency signal such as several GHz to several tens of GHz as the switch 58. However, according to the research of the inventors, as described later, a normal single semiconductor switching element as described above, which does not have a special reflected wave suppression structure and does not have high isolation performance with respect to a used frequency signal, for example, Even when a single transistor is used as the switch 28, practically sufficient radio beam direction control performance can be obtained.

  FIGS. 5A and 5B show a case where the above-described normal single semiconductor switching element is used as a switch for connecting the antenna electrode to the ground electrode in the microstrip antenna according to the two embodiments described above and the MMIC. This shows the difference in the action of the switch when using a type of high-frequency switch.

  FIG. 5A shows a case where a single semiconductor switching element (for example, a single transistor) 74 is used. FIG. 5B shows a case where an MMIC type high frequency switch 76 is used. In the MMIC type high frequency switch 76 shown in FIG. 5B, when the signal transmission path is in an OFF state, the return of the reflected wave from the open end point of the signal transmission path is prevented to improve the isolation performance. The special reflected wave suppression structure is incorporated. Therefore, the reflected wave does not return from the high frequency switch 76 toward the antenna electrode 72 when the high frequency switch 76 is in the OFF state. On the other hand, the single semiconductor switching element 74 shown in FIG. 5A does not have the reflection wave suppressing structure as described above. Therefore, when the single semiconductor switching element 74 is in the OFF state, the high frequency signal that has entered the single semiconductor switching element 74 from the antenna electrode 72 is reflected at the open end of the signal transmission path in the single semiconductor switching element 74, and the reflected wave The phenomenon that 82 returns toward the antenna electrode 72 occurs.

  Further, in the MMIC type high frequency switch 76 shown in FIG. 5B, when the signal transmission path is in an ON state, a high frequency signal current can flow bidirectionally through the signal transmission path. On the other hand, the single transistor switch 74 shown in FIG. 5A can flow current only in one direction in principle when it is in the ON state.

  For this reason, it is expected that, when using a single semiconductor switching element 74, it is difficult to obtain a radio wave beam direction control performance that is practical enough. However, according to the results of tests conducted by the inventors, even when the MMIC type high frequency switch 76 is not bothered to be used, even when the single semiconductor switching element 74 is used, a radio wave beam direction control performance that is practical enough can be obtained. It has been found.

  Incidentally, in the transmission line from the oscillating unit that generates the high frequency signal to the antenna electrode, the transmission line has two or more transmission lines having different line lengths, and the high frequency signal is propagated by the switches connected to both ends of the transmission lines. There is known a phased array antenna capable of variably controlling the direction of a radio wave beam by selecting a transmission path to be selected. In the case of a phased array antenna having such a structure, if a single semiconductor switching element is used for the switch, transmission loss occurs there, the amount of power of the signal propagated to the antenna electrode decreases, and the power of the radio wave beam radiated from the antenna The problem is that the amount is reduced. On the other hand, in the case of the microstrip antenna according to the embodiment of the present invention as described above, a structure in which no switch exists in the transmission line from the oscillation unit to the antenna electrode is employed. Even if the signal propagation performance is not so high, there is no such problem as described above. Therefore, a single semiconductor switching element can be used.

  For the reflected wave 82 from the single semiconductor switching element 74, the length L of the signal transmission path 78 between the antenna electrode 72 and the single semiconductor switching element 74 is set to a high-frequency signal substrate (reference number 10 in FIG. 1). Alternatively, by setting it in the vicinity of an integral multiple of a half wavelength on the surface (reference number 40 in FIG. 3), it is possible to suppress the reflected wave 82 sufficiently small so as not to cause a problem.

  A high-frequency sensor according to an embodiment of the present invention includes a transmission antenna and a reception antenna using a microstrip antenna according to the above-described embodiment of the present invention. A microstrip antenna as a transmission antenna and a microstrip antenna as a reception antenna may be provided separately, or both may be the same microstrip antenna. This high-frequency sensor radiates a radio wave beam in a desired direction from the microstrip antenna according to the present invention, receives a reflected wave or a transmitted wave of the radio wave beam from an object existing in the direction by the microstrip antenna according to the present invention, and receives the received signal. Based on the signal (may be based on the received signal alone or based on the Doppler signal obtained by mixing the received signal and the transmitted signal), the presence / absence or state of the object is sensed.

  As mentioned above, although embodiment of this invention was described, this embodiment is only the illustration for description of this invention, and is not the meaning which limits the scope of the present invention only to this embodiment. The present invention can be implemented in various other modes without departing from the gist thereof. Various variations can be adopted in the arrangement and number of antenna electrodes. For example, the present invention can be applied to various antennas disclosed in International Publication WO 2005/099039 A1.

The top view of the microstrip antenna concerning one embodiment of the present invention. Sectional drawing of the same antenna along the AA line of FIG. The top view of the microstrip antenna concerning another embodiment of the present invention. Sectional drawing of the same antenna along the BB line of FIG. In the microstrip antenna according to the above two embodiments, when a normal single semiconductor switching element is used as a switch for connecting the antenna electrode to the ground electrode (FIG. 5A), and when an MMIC type switch is used. Explanatory drawing which showed the difference of the effect | action of a switch with (FIG. 5B).

Explanation of symbols

10 Substrate 12 (12A, 12B, 12C, 12D) Antenna electrode (feeding element)
14 Feed line 16 Original feed point 18 (18A, 18B, 18C, 18D) Feed point 20 (20A, 20B, 20C, 20D) Ground point 22 Ground electrode 24 Oscillation circuit 26 (26A, 26C) Through hole 28 (28A, 28C) ) Switch 30 (30A, 30B, 30C, 30D) Through hole 40 Substrate 42 Antenna electrode (feeding element)
44 (44A, 44B, 44C, 44D) Antenna electrode (parasitic element)
46 Feed point 54 Through hole 56 Ground electrode 58 (58A, 58C) Switch 60 (60B, 60C) Through hole

Claims (7)

An electrically insulating substrate;
A plurality of antenna electrodes disposed on one surface of the substrate;
An earth electrode for providing a ground level provided on the substrate;
An electrical conduction path having one end connected to a ground point at a predetermined location of at least one antenna electrode;
A switch connected between the other end of the electrical conduction path and the ground electrode;
The switch has a signal transmission path that can be controlled on and off, connected between the other end of the electrical conduction path and the ground electrode, and a reflection that occurs at an open end of the signal transmission path when the signal transmission path is off. A microstrip antenna which is a semiconductor switching element that does not have a reflected wave suppression structure for suppressing wave return. The microstrip antenna according to claim 1.
The microstrip antenna, wherein the switch is a single field effect transistor or a single bipolar transistor. The microstrip antenna according to claim 1.
The microstrip antenna, wherein the switch is a single GaAs-metal semiconductor junction field effect transistor, GaAs high electron mobility transistor, GaAs-heterojunction bipolar transistor, or SiGe-heterojunction bipolar transistor. The microstrip antenna according to claim 1.
A microstrip antenna in which a length of the electric conduction path between the antenna electrode and the switch is set to an integral multiple of a half wavelength of the high-frequency signal on the substrate surface. The microstrip antenna according to claim 1.
The microstrip antenna, wherein each of the plurality of antenna electrodes is a feeding element having a feeding point for applying a high-frequency signal. The microstrip antenna according to claim 1.
The at least one antenna electrode is a parasitic element having no feeding point for applying a high-frequency signal;
A microstrip antenna in which at least one other antenna electrode is a feeding element having a feeding point for applying a high-frequency signal. The microstrip antenna according to claim 1 is provided as a transmission antenna and a reception antenna, a reflected wave or a transmitted wave from an object of a radio wave radiated from the transmission antenna is received by the reception antenna, and the object is sensed based on a received signal. High frequency sensor.

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