JP2007104026A - Microstrip antenna and high-frequency sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a microstrip antenna capable of high-accuracy switching the direction of radio wave beam in a predetermined direction. <P>SOLUTION: In the microstrip antenna, a plurality of antenna electrodes 2, 3 and a power feeding line for feeding a high-frequency signal are arranged on the front surface of a substrate 1, and a ground electrode 4 for providing a ground level is provided on the other surface of the substrate 1. In this antenna, a switch 9 for opening and closing connection between the antenna electrodes 2, 3 and the ground electrode 4 via a through hole 5 (connection member), arranged on a predetermined portion and a relay line for adjusting impedance on the portion where the conductive member of the antenna electrodes is arranged, is provided on at least one of the antenna electrodes. By operating this switch 9, the phase of a radio wave beam to be emitted from an antenna electrode connected to the ground electrode 4 is shifted from the phase of a radio wave beam to be emitted from the other antenna electrode not connected to the ground electrode 4, and the direction of the radio wave beam can be switched with high accuracy in a predetermined direction. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a microstrip antenna that radiates microwaves or higher-frequency radio waves, and more particularly to a technique for controlling the direction of an integrated radio wave beam radiated from a plurality of microstrip antennas. The present invention also relates to a high-frequency sensor using a microstrip antenna.

  Conventionally, an antenna electrode and a ground electrode are disposed on the front and back surfaces of a substrate, respectively, and a microwave high-frequency signal is applied between the antenna electrode and the ground electrode to radiate radio waves vertically from the antenna electrode. A strip antenna is known. As techniques for arraying the microstrip antennas and controlling the directing direction of an integrated radio wave beam radiated from a plurality of microstrip antennas, the following is known. For example, in Patent Document 1, a plurality of antenna electrodes are arranged on a surface of a substrate, and a high-frequency switch is switched to change the length of a high-frequency signal feed line to each antenna electrode. Change the direction of the radio beam. That is, by changing the lengths of the feed lines to the plurality of antenna electrodes, a phase difference is generated between the radio waves radiated from the plurality of antenna electrodes, and the integrated radio beam is directed toward the antenna having a delayed phase. Tilt the pointing direction. Further, for example, the one described in Patent Document 2 is configured by arranging a plurality of antenna electrodes having different directions of integrated radio wave beams and switching antenna electrodes to which a high-frequency signal is applied by a high-frequency switch. Change the direction of direct radio beam.

  An object detection device using radio waves radiated from a microstrip antenna is known. In this object detection device, by changing the direction of the integrated radio wave beam from the microstrip antenna as described above, compared to the case where the direction of the integrated radio beam is fixed, The position and state of the object can be detected more accurately. For example, by changing the directivity direction of the integrated radio wave beam radiated from the microstrip antenna to the XY direction and scanning the two-dimensional range, it is possible to grasp the presence and state of an object over the two-dimensional range. Applications of the object detection device are diverse, such as target detection in an automatic tracking missile and user detection in a toilet device. In any application, it is very useful to be able to change the direction of the integrated radio wave beam radiated from the microstrip antenna. For example, in the case of a user detection device in a toilet device, if the position and state of the user are detected more accurately, a toilet cleaning device, a deodorizing device, and the like can be controlled more appropriately. By the way, the camera may be more suitable for the purpose of accurately grasping the state of the user, but it is difficult to use the camera in the toilet device. Therefore, it is very important for an object detection device using radio waves to control the direction of the integrated radio wave beam so that the user can be more accurately grasped. Incidentally, in Japan, a frequency of 10.525 GHz or 24.15 GHz can be used for the purpose of detecting a human body, and a frequency of 76 GHz can be used for the purpose of preventing a vehicle collision.

JP 7-128435 A JP-A-9-214238

  According to the conventional techniques disclosed in Patent Document 1 and Patent Document 2, it is necessary to switch the feed line that propagates the high-frequency signal by switching in order to change the direction of the integrated radio wave beam. For this purpose, it is necessary to use a high-frequency switch having a low transmission loss and having an impedance to a high-frequency signal of a specific frequency to be used adjusted to a predetermined appropriate value and connected to an appropriate position. However, as the frequency increases, the characteristics of the feed line and the high-frequency switch and variations in the connection state (for example, variations in the dielectric constant of the substrate, the performance of the high-frequency switch, the etching accuracy of the feed line pattern, the mounting position of the switch, etc.) The performance is greatly affected. If the connection is poor, the amount of reflection of the high-frequency signal increases at the connection part of the high-frequency switch, the amount of power supplied to the antenna through the high-frequency switch decreases, or the amount of phase changes, causing radio waves to travel in the desired direction. The beam cannot be emitted. In addition, a high-frequency switch with low transmission loss is quite expensive. In particular, a large number of high-frequency switches are required when the direction of the integrated radio wave beam is changed continuously or in multiple stages. However, it is not practical to use many expensive parts for applications such as a user detection device in a toilet device.

  Accordingly, an object of the present invention is to provide a microstrip antenna that switches the directivity direction of a radio wave beam in a predetermined direction with high accuracy.

The microstrip antenna of the present invention includes an insulating substrate, a plurality of antenna electrodes disposed on one surface of the substrate, each having a feeding point for applying a high frequency signal, and disposed on the other surface or inside the substrate. A ground electrode for providing a ground level, and at least one antenna electrode of the plurality of antenna electrodes is disposed in at least one place different from the feeding point for connecting to the ground electrode. A conductive member, a switch for opening and closing a connection between at least one antenna electrode of the plurality of antenna electrodes and the ground electrode, one end connected to the conductive member and the other end to the switch, and the antenna And a relay line that adjusts impedance at a location where the conductive member of the electrode is disposed. The connection member is disposed at a location that falls within a planar area occupied by the at least one antenna electrode when the at least one antenna electrode is viewed in plan, and the antenna electrode and the ground electrode are connected at that location. .
According to this microstrip antenna, when at least one antenna electrode among a plurality of antenna electrodes is connected to the ground electrode by a switch operation, the phase of the radio wave beam radiated from the antenna electrode connected to the ground electrode, and the other Since the phase of the radio wave beam radiated from the antenna electrode not connected to the ground electrode is shifted, it is possible to switch the directivity direction of the integrated radio wave beam radiated from the plurality of antenna electrodes.

  When switching the radio wave beam at a relatively low speed (over 100 mS), use an actuator such as a solenoid as a switch and install the actuator at an appropriate location so that the ground electrode and the conducting member are in contact / non-contact. It ’s fine. When the radio wave beam is switched at a relatively high speed (100 mS or less), a high-frequency switch having a semiconductor structure or a MEMS (hollow) structure may be used. However, if a high-frequency switch having a semiconductor structure or a MEMS (hollow) structure is connected directly to the conducting member without worrying about impedance matching at the location where the conducting member is disposed on the antenna electrode, the impedance matching is shifted and the antenna electrode The phase may change, making it difficult to switch the radio beam in a predetermined direction. Therefore, in the present invention, a relay line for adjusting the impedance at the place where the conductive member is disposed on the antenna electrode is provided. Therefore, when the switch is in an open state (cuts off high-frequency signals), the plurality of antenna electrodes exhibit maximum resonance in the frequency band to be used and maintain a predetermined phase. Therefore, the directivity direction of the radio wave beam can be switched with high accuracy in a predetermined direction. In addition, since there is no need to connect a high-frequency switch to an intermediate path of a feed line that propagates high-frequency signals to a plurality of antenna electrodes, transmission loss of high-frequency signals propagated to the antenna electrodes is small and the efficiency is excellent. In addition, as the performance required for the switch, it is sufficient if the isolation (characteristic for blocking a high-frequency wave signal of a specific frequency) is good, and it is not necessary to have a characteristic for allowing a high-frequency signal to pass well. Since it is not necessary to have an appropriate input impedance, an expensive high-frequency switch is unnecessary.

In a preferred embodiment, the relay line is formed by a coplanar line.
Therefore, the impedance can be adjusted not only by the length of the transmission line through which the high-frequency signal is propagated but also by the width of the transmission line and the gap between the transmission line and the ground electrode. And the transmission loss from an antenna electrode to a switch can be suppressed.

  In a preferred embodiment, the conducting member is a conductive through-hole penetrating a portion of the substrate corresponding to one portion of at least one antenna electrode of the plurality of antenna electrodes, and the plurality of antennas It has one end connected to one place of at least one of the antenna electrodes and the other end connected to the relay line, and can be easily connected to each other with less manufacturing variation.

  In a preferred embodiment, the switch is disposed at a connection location between the relay line and the ground electrode. Since the switch arranged in this way is hidden behind the antenna electrode, it does not adversely affect the radio wave radiation characteristics.

  The present invention also provides a transmitting antenna using the microstrip antenna according to the present invention described above, and the same antenna as the transmitting antenna for receiving a reflected wave or a transmitted wave from a radio wave object output from the transmitting antenna. Alternatively, a high-frequency sensor including a receiving antenna that is different from the transmitting antenna and a processing circuit that receives and processes an electric signal from the receiving antenna is also provided.

  According to the microstrip antenna of the present invention, the directivity direction of the radio wave beam can be accurately switched in a predetermined direction.

  Hereinafter, embodiments of a microstrip antenna according to the present invention will be described with reference to the drawings. FIG. 1 is a perspective view of a general microstrip antenna having a plurality of antenna electrodes.

  In FIG. 1, an A antenna electrode 2 and a B antenna electrode 3 having the same size and the same rectangular shape are arranged on the surface of an insulating substrate 1 with a line-symmetric relationship in terms of shape and position. The ground electrode 4 is disposed on almost the entire back surface. A high-frequency voltage Vf of, for example, 10.525 GHz is applied to the feeding points P and P provided at the same side edge of the A antenna electrode 2 and the B antenna electrode 3 through the feeding line 10. The ground electrode 4 is grounded to provide a ground level. The length of the feed line 10 to the A antenna electrode 2 and the B antenna electrode 3 is the same. In some cases, the feeding points P and P are arranged not at the edges of the antenna electrodes 2 and 3 but at a certain distance from the edges of the antenna electrodes 2 and 3 to the inside. With such a configuration, radio wave beams 7 and 8 having the same electric field intensity are radiated from the A antenna electrode 2 and the B antenna electrode 3 in a directivity direction perpendicular to the substrate 1, respectively.

  FIG. 2 is a plan view showing the radio wave scanning principle of the microstrip antenna of the present invention. FIG. 3 is a cross-sectional view taken along the line AA of FIG.

The microstrip antenna shown in FIGS. 2 and 3 has a substrate 1, an A antenna electrode 2, a B antenna electrode 3, a ground electrode 4, a feed line 10, and a conductive member (hereinafter referred to as “through hole”) 5. The A antenna electrode 2 and the B antenna electrode 3 are in a line-symmetrical relationship in terms of shape and position, and the excitation direction is the same. A high frequency signal is propagated to each antenna electrode 2, 3 via the feed line 10. In addition to this, a certain location 2A of one electrode, for example, the A antenna electrode 2, is connected to the ground electrode 4. That is, a conductive through hole 5 passes through a portion of the substrate 1 corresponding to the one location 2A of the A antenna electrode 2, and this through hole 5 is formed at one end of the A antenna electrode 2 at one end. Coupled to the ground electrode 4 at the other end. Thus, the one location 2A of the A antenna electrode 2 is connected to the ground electrode 4 through the through hole 5. A portion of the antenna electrode connected to the ground electrode 4 in this way (or grounded when desired by a switch or other electric circuit described later) is called a “ground point”. The length of one side of the antenna electrodes 2 and 3 shown in FIG. 2 (in the vertical direction in the figure) is designed to be the same as or slightly smaller than the half wavelength λg / 2 of the high-frequency signal substrate 1. Here, λg is the wavelength of the high-frequency signal propagating through the substrate 1. Further, λ = εr ^1/2 · λg where λ is the wavelength of the radio frequency signal radio wave in vacuum and εr is the dielectric constant of the substrate 1. In the example shown in FIG. 2, the grounding point 2 </ b> A is disposed on the extension line of the feeding point P of the A antenna electrode 2 and in the vicinity of the end face of the A antenna electrode 2. The phase of the radio wave beam emitted from the A antenna electrode 2 advances from the phase of the radio wave beam emitted from the B antenna electrode 3, and as a result, the integrated radio wave beam radiated from the A antenna electrode 2 and the B antenna electrode 3. Is directed toward the B antenna electrode 3 as indicated by an arrow in FIG.

  FIG. 4 is a plan view of the first embodiment of the microstrip antenna of the present invention. 5 is a cross-sectional view taken along the line BB in FIG. FIG. 6 is a plan view of the back surface in which only the portion corresponding to the A antenna electrode 2 of the microstrip antenna shown in FIG. 4 is enlarged.

  The microstrip antenna shown in FIGS. 4 and 5 has a conductive through-hole 5 passing through the portion of the substrate 1 corresponding to the ground point 2A of the A antenna electrode 2 of the microstrip antenna shown in FIGS. The through-hole 5 is coupled to one end of the A antenna electrode 2 at one end, and the relay line 21 for adjusting the impedance at the ground point 2A is coupled to the other end. A switch 9 that opens and closes the connection between the A antenna electrode 2 and the ground electrode 4 is connected to the other end of the relay line 21 to which the through hole 5 is coupled at one end. The grounding point 2 </ b> A is disposed on the extension line of the feeding point P of the A antenna electrode 2 and in the vicinity of the end face of the A antenna electrode 2. In the example shown in FIG. 4, the radio wave emitted from the A antenna electrode 2 by operating the switch 9 connected to the A antenna electrode 2 through the through hole 5 and connecting the A antenna electrode 2 and the ground electrode 4. The phase of the beam advances from the phase of the radio wave beam emitted from the B antenna electrode 3, and as a result, the directivity direction of the radio wave beam radiated from the A antenna electrode 2 and the B antenna electrode 3 is perpendicular to the substrate 1. As shown by an arrow in FIG.

  Here, the role of the relay line 21 for adjusting the impedance at the ground point 2A will be described. FIG. 7 is an enlarged cross-sectional view of only a portion corresponding to the A antenna electrode 2 of the microstrip antenna shown in FIG.

  In the antenna shown in FIG. 7, the portion of the transmission line connected to the A antenna electrode 2 when the switch 9 is in the off state, that is, from the ground point 2A of the A antenna electrode 2 to the inside of the switch 9 on the back surface of the substrate 1. Transmission line length U to the end of the line (more specifically, through hole 5, relay line 21 from through hole 5 on the back surface of substrate 1 to switch 9, and transmission line 22 inside switch 9 The total line length) is λg / 2 × n (n is an integer of 1 or more) (for example, U = λg / 2). The length V of the A antenna electrode 2 is also λg / 2 × n (n is an integer of 1 or more) (for example, V = λg / 2). When the switch 9 is a switch having a transmission line 22 therein, such as a semiconductor switch or a mechanical switch (for example, MEMS) and small in such a way that the loss of the contact at the time of ON can be ignored, the switch 9 is radiated from the antenna. A factor that greatly affects the direction control of the radio wave is a high-frequency characteristic related to the A antenna electrode 2 when the switch 9 is in an OFF state rather than when the switch 9 is in an ON state, such as impedance or phase. If the transmission line path length U when the switch 9 is in the OFF state is an integral multiple of a half wavelength λg / 2 of the high-frequency signal, the impedance Z at the ground point 2A of the A antenna electrode 2 becomes close to infinity. . That is, it is possible to suppress the phase of the A antenna electrode 2 from changing greatly due to the optimal connection of the relay line 21.

  8A and 8B show the change in impedance Z at the ground point 2A of the A antenna electrode 2 and the direction of the radio wave radiated from the antenna, respectively, when the switch 9 is switched on / off in the antenna shown in FIG. .

  The state when the switch 9 is off is shown on the left side of FIGS. 8A and 8B. As shown in FIG. 8A, in the antenna of FIG. 4, when the transmission line length U is an integral multiple of the half wavelength λg / 2 of the high frequency signal, the impedance of the ground point 2A is almost infinite, The direction is perpendicular to the substrate. On the other hand, as shown in FIG. 8B, in the antenna of FIG. 4, when the transmission line length U is not an integral multiple of the half wavelength λg / 2 of the high frequency signal, the impedance of the ground point 2A is lower, The direction is inclined by a certain angle θ1. The state when the switch 9 is on is shown on the right side of FIGS. 8A and 8B. When the switch 9 is on, the radio wave is tilted at a larger angle θ2 in either antenna, but the tilt angle θ2 is not so different between the two antennas. Therefore, when the transmission line length U is an integral multiple of the half wavelength λg / 2 of the high-frequency signal in the antenna of FIG. 4, the change in the radio wave direction obtained by switching the switch 9 on and off is larger.

  The adjustment of the impedance at the ground point 2A can be easily handled by changing the length of the relay line 21. Further, the relay line 21 shown in FIG. 7 is formed in a coplanar line structure, and a wiring material (for example, copper foil) serving as a transmission line is in close contact with the substrate 1. Therefore, transmission loss from the antenna electrode to the switch is small. Then, the width of the transmission line through which the high-frequency signal is propagated is changed, the gap distance between the transmission line and the ground electrode is changed, and a dielectric (for example, resin or ceramic) is fixed to a part of the surface of the transmission line. The impedance can be easily adjusted by post-processing such as.

  9 to 11 are plan views of a second embodiment of the microstrip antenna of the present invention.

  As shown in FIGS. 9 to 11, four antenna electrodes of an A antenna electrode 11, a B antenna electrode 12, a C antenna electrode 13, and a D antenna electrode 14 are arranged on the substrate 1 in a 2 × 2 matrix. . The A antenna electrode 11 and the B antenna electrode 12 are in a line-symmetric relationship with respect to shape and position, and the C antenna electrode 13 and the D antenna electrode 14 are also in a line-symmetric relationship with respect to shape and position. The excitation direction of 14 is the same. The electrode patterns of the A antenna electrode 11 and the B antenna electrode 12 and the patterns of the C antenna electrode 13 and the D antenna electrode 14 are basically the same in shape. The length of the feed line 10 to the A antenna electrode 11, the B antenna electrode 12, the C antenna electrode 13, and the D antenna electrode 14 is the same. The Wilkinson coupler 6 is connected to the feed line 10 portion branched to the A antenna electrode 11 and the B antenna electrode 12 and to the feed line 10 portion branched to the C antenna electrode 13 and the D antenna electrode 14. The grounding point 11A is located at approximately one center of the A antenna electrode 11, the grounding point 12A is disposed at approximately one center of the B antenna electrode 12, and the grounding point 13A and D antenna electrode 14 are disposed at approximately one center of the C antenna electrode 13. A grounding point 14A is arranged at a substantially central location, and through-holes (not shown) pass through each of the grounding points 11A to 14A, and are connected to a grounding electrode (not shown) via a relay line (not shown). A switch 9 (not shown) that opens and closes is connected to each antenna electrode 11-14. When a switch (not shown) connected to the A antenna electrode 11 and the C antenna electrode 13 is operated and the A antenna electrode 11 and the C antenna electrode 13 are connected to a ground electrode (not shown), radiation is performed in a direction perpendicular to the substrate 1. The integrated radio wave beam thus changed, for example, as indicated by a right-pointing arrow in FIG. 6, changes its directing direction from the A and C antenna electrodes 11 and 13 to the B and D antenna electrodes 12 and 14.

  In this embodiment, when a switch (not shown) connected to the A antenna electrode 11 and the B antenna electrode 12 is operated and the A antenna electrode 11 and the B antenna electrode 12 are connected to a ground electrode (not shown), The integrated radio beam radiated in the direction perpendicular to 1 is, for example, as shown by the downward arrow shown in FIG. 7, the directivity direction of the integrated radio beam is A, and the B antenna electrodes 11, 12 to C, D It changes in the direction toward the antenna electrodes 13 and 14.

  Further, in this embodiment, when only the switch (not shown) connected to the A antenna electrode 11 is operated and only the A antenna electrode 11 is connected to the ground electrode (not shown), the radiation is emitted in the direction perpendicular to the substrate 1. The direction of the integrated radio wave beam changes from the A antenna electrode 11 toward the D antenna electrode 14 as indicated by an arrow pointing diagonally downward to the right shown in FIG.

  The above-described microstrip antenna according to the present invention can be applied to a high-frequency sensor for detecting an object. Such a high-frequency sensor receives a transmitting antenna using a microstrip antenna, a receiving antenna for receiving a reflected wave or transmitted wave from a radio wave object output from the transmitting antenna, and an electric signal from the receiving antenna. And a processing circuit for processing. Here, although the receiving antenna can be provided separately from the transmitting antenna, the transmitting antenna can also be used as the receiving antenna, particularly when a reflected wave is received.

  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.

It is a perspective view of a common microstrip antenna provided with a plurality of antenna electrodes. It is a top view which shows the radio wave scanning principle of the microstrip antenna of this invention. It is AA sectional drawing of FIG. It is a top view of 1st Embodiment of the microstrip antenna of this invention. It is BB sectional drawing of FIG. It is the top view of the back surface which expanded only the part corresponding to the A antenna electrode 2 of FIG. It is sectional drawing to which only the part corresponding to the A antenna electrode 2 of FIG. 4 was expanded. 8A and 8B are diagrams showing changes in impedance Z at the ground point 2A of the A antenna electrode 2 due to on / off switching of the switch 9 and directions of radio waves radiated from the antenna in the antenna shown in FIG. It is. It is a top view which shows the method of inclining a radio wave beam rightward in 2nd Embodiment of the microstrip antenna of this invention. In the same embodiment, it is a top view which shows the method of inclining a radio wave beam below. In the same embodiment, it is a top view which shows the method of inclining a radio wave beam to diagonally downward right.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Board | substrate 2, 11 A antenna electrode 3, 12 B antenna electrode 4 Ground electrode 5 Connection member (through hole)
6 Distributor (Wilkinson coupler)
9 switch 10 feed line 13 C antenna electrode 14 D antenna electrode 21 relay line 22 transmission line inside switch

Claims (3)

An insulating substrate;
A plurality of antenna electrodes disposed on one surface of the substrate, each having a feeding point for applying a high-frequency signal;
A ground electrode for providing a ground level, disposed on the other side or inside of the substrate;
A conducting member disposed in at least one location different from the feeding point for connecting at least one antenna electrode of the plurality of antenna electrodes to the ground electrode;
A switch for opening and closing a connection between at least one antenna electrode of the plurality of antenna electrodes and the ground electrode;
One end is connected to the conducting member and the other end is connected to the switch, and the relay line for adjusting the impedance at the place where the conducting member of the antenna electrode is disposed,
A microstrip antenna characterized by comprising:   2. The microstrip antenna according to claim 1, wherein the relay line is formed by a coplanar line. A transmission antenna using a microstrip antenna for outputting a high-frequency radio wave, and the same or the same as the transmission antenna for receiving a reflected wave or a transmitted wave from an object of the radio wave output from the transmission antenna In a high-frequency sensor comprising a receiving antenna that is different from a transmitting antenna, and a processing circuit that receives and processes an electrical signal from the receiving antenna,
The microstrip antenna is
An insulating substrate;
A plurality of antenna electrodes disposed on one surface of the substrate, each having a feeding point for applying a high-frequency signal;
A ground electrode for providing a ground level, disposed on the other side or inside of the substrate;
A conducting member disposed in at least one location different from the feeding point for connecting at least one antenna electrode of the plurality of antenna electrodes to the ground electrode;
A switch for opening and closing a connection between at least one antenna electrode of the plurality of antenna electrodes and the ground electrode;
One end is connected to the conducting member and the other end is connected to the switch, and the relay line for adjusting the impedance at the place where the conducting member of the antenna electrode is disposed,
A high-frequency sensor comprising:

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