JP2006287766A - Radio wave transmission antenna and object sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress radiation power of harmonics or a fundamental wave by structure of a feeding element in a microstrip antenna. <P>SOLUTION: A point near a part where current amplitude of a wave desired to be suppressed is minimum and in a region where current amplitude which is not desired to be suppressed is close to maximum in the feeding element 22 is grounded. For example, when secondary and tertiary harmonics are desired to be suppressed without suppressing the fundamental wave, when wavelength of the fundamental wave, the secondary harmonics, the tertiary harmonics on a substrate are expressed as λ<SB>g1</SB>, λ<SB>g2</SB>, λ<SB>g3</SB>, points in regions 50A, 50B within a distance range exceeding λ<SB>g1</SB>/6 from a terminal edge in the exciting direction y of the fundamental wave, within a distance range of λ<SB>g2</SB>/2±λ<SB>g2</SB>/6 from a terminal edge in the exciting direction x of the secondary harmonics and further within a distance range of λ<SB>g3</SB>/2±λ<SB>g3</SB>/6 from the terminal edge in the exciting direction y of the tertiary harmonics are grounded. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a radio wave transmission antenna typified by a microstrip antenna that transmits a radio wave of a microwave or higher frequency, and more particularly to a technique for controlling a radio wave transmitted from the antenna.

  The present invention also relates to an object sensor using such a radio wave transmitting antenna.

  2. Description of the Related Art Conventionally, a microscopic antenna that emits radio waves from an antenna electrode by disposing one or more thin film antenna elements on the surface of a dielectric substrate and applying a high-frequency signal such as microwaves from an oscillation circuit to the antenna elements. A strip antenna is known (see, for example, Patent Documents 1 to 4). There is also known a high-frequency sensor for detecting an object by transmitting a radio wave from a microstrip antenna and receiving a radio wave that is reflected when the radio wave hits an object.

  The oscillation circuit generates a high frequency (hereinafter referred to as a fundamental wave) having a desired frequency for exciting the antenna element. At this time, unnecessary harmonics are generated simultaneously with the fundamental wave. In particular, the second and third harmonics have powers that cannot be ignored, so measures to suppress them are necessary. In conventional devices, a filter circuit is provided on the transmission line connecting the oscillation circuit and the antenna, or on the oscillation circuit, and unnecessary second and third harmonics are reflected by the filter circuit, so that harmonics are radiated from the antenna. Is suppressed.

JP 7-128435 A JP-A-9-214238 Japanese Patent Laid-Open No. 9-297174 JP 2003-142919 A

  When the harmonics are suppressed by the filter circuit provided on the oscillation circuit or the transmission line as in the prior art, the transmission loss of the fundamental wave also occurs in the filter circuit, so that there is a problem that the efficiency is lowered. In addition, the harmonics reflected by the filter circuit may scatter in the shield case that covers the oscillation circuit, and if there is a gap between the shield case and the substrate, harmonics may leak from there.

  Accordingly, an object of the present invention is to make it possible to control the radiant power of harmonics with the structure of an antenna element in a radio wave transmitting antenna.

  Furthermore, another object is to make it possible to control the radiation characteristics of radio waves by the structure of the antenna element.

  A radio wave transmitting antenna according to one aspect of the present invention includes a substrate made of a dielectric material, a feed element formed on the substrate, a transmission line for applying an excitation signal to the feed element, and one or more ground points in the feed element. And grounding means for connecting to the ground level. The ground point is arranged in a region where the current amplitude value of the n-th harmonic (n is a predetermined integer equal to or greater than 2) of the excitation signal on the feed element is not the maximum value.

  According to this radio wave transmitting antenna, the radiation power of unnecessary n-order harmonics included in the excitation signal can be reduced by the feed element. That is, by providing a ground point connected to the ground level in a region where the current amplitude value of the n-th harmonic on the feed element is not the maximum value, the radiation power of the n-th harmonic is reduced. Therefore, it is not necessary to provide a filter circuit for reducing the n-th harmonic in the oscillation circuit that generates the excitation signal or on the transmission line that connects the oscillation circuit and the feeding element. If such a filter circuit is not provided, the fundamental wave generated by the oscillation circuit can be efficiently transmitted to the antenna, and the overall size including the radio wave transmission antenna and the oscillation circuit can be reduced. be able to.

In order to effectively reduce the radiant power of the nth harmonic, a grounding point is preferably disposed in a location where the current amplitude value of the nth harmonic in the feed element is the minimum value or in a region near the location. can do. More specifically, preferably, when the wavelength of the n-order harmonic on the substrate is represented by λ _gn , λ _gn / 2-λ from the terminal edge that intersects the excitation direction of the n-order harmonic in the feed element _The grounding point can be arranged within a distance range of _gn / 6 or more and _λgn / 2 + _λgn / 6 or less. Particularly preferably, the ground point can be disposed within a distance range of λ _gn / 2−λ _gn / 12 or more and λ _gn / 2 + λ _gn / 12 or less from the terminal edge.

Usually, the harmonics in question are the second harmonic and the third harmonic. In order to reduce the radiation power of both the secondary and tertiary harmonics, a grounding point should be placed in a region where the current amplitude values of both the secondary and tertiary harmonics in the feed element are not maximum values. Can do. Preferably, the ground point can be arranged in a location where the current amplitude values of both the second harmonic and the third harmonic in the feed element are minimum values or in a region in the vicinity of the location. More specifically, preferably, when the wavelengths of the second and third harmonics of the excitation signal on the substrate are represented by λ _g2 and λ _g3 , respectively, they intersect the excitation direction of the second harmonic in the feed element Λ _g2 / 2−λ _g2 / 6 or more and λ _g2 / 2 + λ _g2 / 6 or less from the terminating edge, and λ _g3 from the terminating edge that intersects the excitation direction of the third harmonic in the feed element A grounding point can be arranged in a region that is within a distance range of not less than / 2−λ _g3 / 6 and not more than λ _g3 / 2 + λ _g3 / 6.

In order to reduce the radiated power of the harmonics while preventing the radiated power of the fundamental wave from being reduced as much as possible, contact is made within the region excluding the place where the current amplitude value of the fundamental wave in the feed element is the minimum value. A point can be placed. Preferably, when expressed wavelength on the substrate of the fundamental wave lambda _g1, from the end edges intersecting the driving direction of the fundamental wave in a region except in lambda _{g1 / 6} or less of the distance range in the feed element, the ground point Can be arranged.

In addition, when the excitation directions of the fundamental wave and the n-th harmonic are different, the excitation direction of the n-th harmonic is crossed instead of or in combination with the above-described region in order to reduce the radiation power of the harmonic. It is also possible to place a ground point in the region near the end edge. More specifically, when the wavelength of the nth-order harmonic on the substrate is represented by λ _gn , λ _gn from the terminal edge that intersects the excitation direction of the n-order harmonic in the feed element. A ground point can be arranged within a distance range of / 6 or less.

  The number of grounding points may be one or more. When a plurality of grounding points are provided, the plurality of grounding points can be arranged at symmetrical positions with respect to the center line of the feed element. Thereby, the influence which a grounding point has on the radiation pattern (directivity) of the fundamental wave radiated from the antenna can be reduced.

  The grounding means can be configured to select whether or not to connect the grounding point to the ground level. For example, it can be configured to open and close a line connecting a ground point and a ground level with a switch. Thereby, it is possible to select whether to suppress the radiation power of the harmonics. By applying this, a specific harmonic can be selectively radiated intentionally.

  The present invention also requires an object sensor using the radio wave transmitting antenna according to the present invention as a transmitting antenna. This object sensor includes a transmission antenna using the above-described radio wave transmission antenna, a reception antenna for receiving a reflected wave reflected from the object by a radio wave emitted from the transmission antenna, and a reception signal from the reception antenna. And a signal processing circuit that detects the presence or movement of the object by processing. The transmitting antenna may be used in combination with the receiving antenna, or a receiving antenna may be provided separately from the transmitting antenna. By using the radio wave transmitting antenna according to the present invention for the transmitting antenna, it is not necessary to provide a filter circuit for reducing harmonics in the oscillation circuit or on the transmission line. When the filter circuit is omitted, the efficiency of the fundamental wave is improved and the size of the object sensor can be reduced.

  A radio wave transmitting antenna according to another aspect of the present invention includes a substrate made of a dielectric material, a feed element formed on the substrate, a transmission line for applying an excitation signal to the feed element, and one or more ground points in the feed element. And grounding means for connecting to the ground level. The grounding point is arranged in a region where the current amplitude value of the fundamental wave of the excitation signal on the feed element is not the maximum value.

  According to the radio wave transmitting antenna, the radiation power of the fundamental wave is reduced by the feed element. To intentionally limit the radiated power of the fundamental wave, for example, when applying multiple excitation signals and radiating only the fundamental wave of a specific excitation signal, or suppressing the fundamental wave and suppressing the second harmonic The present invention can be applied to the case where it is desired to selectively radiate only.

In order to effectively reduce the radiated power of the fundamental wave, it is preferable that the grounding point be disposed in a location where the current amplitude value of the fundamental wave in the feed element is the minimum value or in a region near the location. it can. Specifically, the grounding point can be preferably disposed within a distance range of λ _g1 / 6 or less from a terminal edge that intersects the excitation direction of the fundamental wave in the feed element.

  The grounding means may be configured to select whether or not to connect the ground point to the ground level. Thereby, it is possible to select whether to reduce the fundamental wave.

In a preferred embodiment, a plurality of transmission lines are connected to the feed element, and a plurality of excitation signals are applied to the feed element. Then, a plurality of ground points are provided at a plurality of positions where the fundamental wave radiation power of the plurality of excitation signals can be individually reduced, and each ground point is connected to a ground level at any time via a switch. Can be connected to. By operating the switch, a radio wave is emitted by one excitation signal selected from among a plurality of excitation signals. The excitation directions of the fundamental waves of the plurality of excitation signals can be made different. The excitation direction of the fundamental wave can be selected by operating the switch. By selecting the excitation direction, the vibration direction of the emitted radio wave can be selected. When this antenna is used for an object sensor that uses the Doppler effect, it is possible to select which direction the object has high detection sensitivity by selecting the direction of vibration of the emitted radio wave. .

  According to one aspect of the present invention, the radiation power of harmonics can be controlled by the structure of the feed element.

  Further, according to the present invention, the radiation characteristics of radio waves can be controlled by the structure of the feed element.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a plan view showing one antenna element in a radio wave transmitting antenna according to an embodiment of the present invention, in particular, a microstrip antenna excited by a microwave or a high frequency having a higher frequency. FIG. 2 is a cross-sectional view taken along the line AA in FIG.

There may be various overall structures of the microstrip antenna. For example, the simplest structure in which one antenna element is disposed on a dielectric substrate, or one or more antenna elements (hereinafter referred to as “feeding elements”) connected to a high-frequency signal transmission line on the same dielectric substrate. In addition, a structure in which one or more antenna elements (hereinafter referred to as “parasitic elements”) that are not connected to the transmission line of the high-frequency signal are also arranged, or a large number of power supplies are provided on the same dielectric substrate. There may be a structure in which elements are arranged. In the microstrip antenna having any of these overall structures, the structure of the antenna element (feeding element) shown in FIGS. 1 and 2 can be applied to the feeding element.

  As shown in FIG. 1, a planar antenna element (feeding element) 22 such as a thin film made of a conductive material such as metal is disposed on the front surface of a substrate 20 made of a dielectric material. The planar shape of the feed element 22 is typically a square, for example, and is square in the illustrated example. Here, for convenience of explanation, a direction along one terminal edge of the feed element 22 (lateral direction in the figure) is called an x direction, and a direction orthogonal to the direction (vertical direction in the figure) is called a y direction.

  A feeding point 24 is provided at the center of the feeding element 22 in the x direction and near the lower end edge in the y direction. As shown in FIG. 2, the feeding point 24 is connected to the back side of the substrate 20 via a signal transmission line made of a conductor that penetrates the substrate 20 (hereinafter, a conductor line that penetrates the substrate 20 is referred to as “through hole”) 25. It is connected to the output terminal 31 of the mounted oscillation circuit 30. The oscillation circuit 30 outputs a high-frequency signal, and the high-frequency signal is applied from the output terminal 31 to the feeding point 24 of the feeding element 22 through the through hole 25 as a connection line. The high-frequency signal includes not only a fundamental wave having a predetermined frequency for exciting the feed element 22, but also n times (n is a positive integer of 2 or more, that is, n = 2, 3, 4,... N-order harmonics having a frequency of). Although the powers of these harmonics are both lower than the power of the fundamental wave, the powers of the second and third harmonics are particularly insignificant and need to be suppressed.

The dimension Ly in the y direction of the feed element 22 is a dimension suitable for excitation by the fundamental wave described above, and is typically about ½ of the wavelength λ _g1 of the fundamental wave on the substrate 20. Here, in practice, the y dimension Ly is not designed to be exactly λ _g1 / 2, but slightly shifted from it (for example, about 0.8 × λ _g1 / 2) for various reasons. However, in the description of the present specification, it is referred to as “about λ _g1 / 2” including the actual y dimension slightly deviated from the exact λ _g1 / 2. In the case of the illustrated example, since the feeding element 22 is square, the dimension Lx in the x direction is also approximately λ _g1 / 2. As a specific example, when the frequency of the fundamental wave is about 10 GHz, the y dimension Ly and the x dimension Lx are both about 7.66 mm. Further, the distance L1 from the lower end edge of the feeding point 24 is, for example, about λ _g1 / 4.

  According to the dimensions of the feeding element 22 and the arrangement of the feeding point 24 as described above, the feeding element 22 is normally excited in the y direction (vertical direction in the figure) by the fundamental wave. The direction in which the feed element 22 is excited is hereinafter referred to as “excitation direction”.

Two grounding points 26A and 26B are provided at two positions that are located in the center in the x direction of the feed element 22 and that are different in the y direction. As shown in FIG. 2, the grounding points 26A and 26B provide a ground potential provided on the back side (or inside) of the substrate 20 through through holes 27A and 27B as two connection lines, respectively. Are connected to the ground electrode 28. The position in the y direction of the ground points 26A and 26B on the feed element 22 is expressed as λ _gn , where the wavelength of the n (n = 2, 3 _,. In this case, in the excitation direction of the n-th harmonic (especially the second and third harmonics) of the feed element 22, λ _gn from the terminal edge that intersects the excitation direction (hereinafter referred to as “terminal edge in the excitation direction”). It is selected within a distance range of not less than / 2-λ _gn / 6 and not more than λ _gn / 2 + λ _gn / 6. In other words, the positions of the ground points 26A and 26B are the current amplitudes of the n (n = 2, 3,...) Harmonics (especially the second and third harmonics) on the feed element 22. It can be said that the position is within the region where the value is minimum or in the vicinity of the position, and the current amplitude value of the fundamental wave is not minimum (preferably as large as possible). Alternatively, the position of the grounding points 26A and 26B as described above is such that the voltage amplitude value of the n (n = 2, 3,...) Harmonics (especially the second and third harmonics) on the feeder element 22 is maximum. It is also possible to say that the position is within the vicinity of the position or the position near the position and the voltage amplitude value of the fundamental wave is not the maximum (preferably as small as possible). When the grounding points 26A and 26B are arranged in this way, n (n = 2, 3,...) Harmonics (especially second and third harmonics) while maintaining a large radiation power of the fundamental wave from the feed element 22. ) Radiation power can be reduced.

  In addition, as shown in FIG. 1, the two ground points 26 </ b> A and 26 </ b> B are arranged at symmetrical positions with respect to the center line of the power feeding element 22. In this way, by arranging a plurality of grounding points at symmetrical positions with respect to the center line of the feed element 22, the influence of the grounding points on the radiation pattern (directivity) of the fundamental wave radiated from the antenna (for example, The radiation pattern is not tilted or biased). The number of grounding points is not necessarily two, but may be one or two or more.

  Below, with reference to FIGS. 3-9, the preferable arrangement | positioning of the earthing | grounding point on a feed element and its principle for reducing the radiation power of n order harmonics (especially 2nd order and 3rd order harmonics) are demonstrated. .

  3 and 4 are plan views for explaining the preferred arrangement of the grounding point on the feeding element 22 and the principle thereof for reducing the radiation power of the second harmonic in the embodiment shown in FIG.

  First, the basic principle is that for both the fundamental wave and the n-th harmonic, the smaller the current amplitude value of the wave at the position (grounding point) on the feed element, This means that the radiation power of the wave is more effectively reduced. Since the wave current and voltage distribution on the feed element are approximately 90 degrees out of phase, the basic principle is that the larger the voltage amplitude value of the wave at the ground point, In other words, the radiation power of the wave can be reduced more effectively. Therefore, if the position where the current amplitude value of the wave is minimum (that is, the position where the voltage amplitude value is maximum) is grounded, the radiation power of the wave is most effectively reduced. Further, even when a position in a region near the position where the current amplitude value of the wave is minimum is grounded, the radiation power of the wave can be considerably reduced.

In the embodiment shown in FIG. 1, as shown in FIG. 3, the excitation direction by the fundamental wave of the feed element 22 is the y direction, and the current amplitude value i ₁ of the fundamental wave is represented by y on the feed element 22. Depending on the position of the direction (excitation direction of the fundamental wave), the distribution is as shown in the graph on the left side of the figure. On the other hand, the excitation direction due to the second harmonic is the x direction, and the current amplitude value i ₂ of the second harmonic depends on the position of the feed element 22 in the x direction (excitation direction of the second harmonic). It is distributed as shown in the upper graph.

A region suitable for disposing a ground point connected to the ground potential for the purpose of reducing the second harmonic is a region 40 indicated by hatching. More specifically, the region 40 has a terminal edge (left side or right side) in the excitation direction (x direction) of the second harmonic of the feed element 22 when the wavelength of the second harmonic on the substrate is expressed as _λg2. Λ _g2 / 2−λ _g2 / 6 or more and λ _g2 / 2 + λ _g2 / 6 or less. As can be seen from the distribution of the _second harmonic current amplitude value i ₂ shown in the upper graph, in this region 40, the second harmonic current amplitude value i ₂ is not the maximum and is relatively small. By providing the ground point, the radiation power of the second harmonic can be reduced. Particularly in the region 40, the position of λ _g2 / 2 from the left or right terminal edge (the center in the x direction of the feeding element 22) has a minimum _second harmonic current amplitude value i _2. By providing the ground point, the radiation power of the second harmonic can be reduced most effectively.

However, the region 40 shown in FIG. 3 includes a portion in which not only the second harmonic but also the radiation power of the fundamental wave is reduced by providing a grounding point there. When the wavelength of the fundamental wave on the substrate is expressed as λ _g1 , as shown in FIG. 4, the portion is from the end edge (upper or lower end edge) in the excitation direction (y direction) of the fundamental wave. It is a part of a distance range of λ _g1 / 6 or less, where the current amplitude value i ₁ of the fundamental wave is not maximum but is relatively small. Therefore, the remaining part of the region 42 (the region indicated by hatching in FIG. 4) excluding this portion from the region 40 shown in FIG. This is a preferable region for providing a grounding point for reducing the radiation power.

By the way, when the shape or size of the feed element 22 changes, the excitation direction or current amplitude distribution due to the fundamental wave or the nth-order harmonic changes, and as a result, the preferred arrangement of grounding points for suppressing the nth-order harmonic changes. . For example, in the example shown in FIG. 5, the dimension in the y direction of the feeding element 22 is about λ _g1 / 2 as in the examples shown in FIGS. 1 and 3, but the dimension in the x direction is Unlike the example shown in FIG. 3, it is much shorter than λ _g1 / 2. In the case of the feed element 22 shown in FIG. 5, the excitation direction of the second harmonic is the y direction similarly to that of the fundamental wave, and the current amplitude value i ₂ of the second harmonic is the y direction (secondary harmonic of the feed element 22. Depending on the position of the harmonic excitation direction), the distribution is as shown in the graph on the right side of the figure. Therefore, a region 44 indicated by hatching in FIG. 5, that is, a distance of λ _g2 / 2−λ _g2 / 6 or more and λ _g2 / 2 + λ _g2 / 6 or less in the y direction from the upper or lower terminal edge of the feeding element 22. The range is a region suitable for placing a ground point in order to reduce the radiation power of the second harmonic. Further, in this region 44, the current amplitude value i ₁ of the fundamental wave is close to the maximum or maximum, be arranged grounding point there may remain a large radiant power of the fundamental wave.

  Next, a preferred arrangement of grounding points for reducing the third harmonic in the embodiment shown in FIG. 1 will be described.

  FIGS. 6 and 7 are plan views for explaining a preferred arrangement of the grounding points on the power feeding element 22 for reducing the third harmonic and the principle thereof in the embodiment shown in FIG.

In the case of the embodiment shown in FIG. 1, as shown in FIG. 6, the excitation direction by the third harmonic of the feed element 22 is the y direction, similar to that by the fundamental wave, and the current amplitude value i ₃ of the _third harmonic is Depending on the position in the y direction (excitation direction of the third harmonic) on the feed element 22, the distribution is as shown in the graph on the right side of the figure. Two regions 46A and 46B indicated by hatching are suitable for arranging the ground point for the purpose of reducing the third harmonic. Specifically, each of the regions 46A and 46B has a termination edge (upper side or upper side in the excitation direction (y direction) of the third harmonic of the feed element 22 when the wavelength of the third harmonic on the substrate is expressed as λ _g3. The distance is from λ _g3 / 2−λ _g3 / 6 to λ _g3 / 2 + λ _g3 / 6 from the lower end edge. As can be seen from the third harmonic distribution of the current amplitude value i ₃ of shown on the right side of the graph, the area 46A, the 46B, the third harmonic current amplitude value i ₃ of not the maximum, since a relatively small, there By providing the ground point, the radiation power of the third harmonic can be reduced. This region 46A, among other 46B, left or right position of the lambda _{g3 / 2} from the terminal edge of the (one-third position in the y-direction of the feed element 22), the third harmonic current amplitude value i ₃ of the minimum Therefore, by providing a grounding point here, the radiation power of the third harmonic can be reduced most effectively.

However, the regions 46A and 46B shown in FIG. 6 include a portion in which not only the third harmonic but also the radiation power of the fundamental wave is reduced by providing a ground point there. That portion is as described above, that is, as shown in FIG. 7, λ _g1 / 6 in the y direction from the terminal edge (upper or lower terminal edge) in the excitation direction (y direction) of the fundamental wave. The distance range is the following (that is, λ _g3 / 2 or less). Therefore, as shown in FIG. 7, this portion is removed from the regions 46A and 46B shown in FIG. 6 (from the region indicated by hatching in FIG. 7, ie, from the upper or lower terminal edge). 48A, 48B) is a grounding point for reducing the radiation power of the third harmonic while maintaining the radiation power of the fundamental wave largely while maintaining the radiation power of the fundamental wave large. (Area in the distance range of λ _g3 / 2 and λ _g3 / 2 + λ _g3 / 6) This is a preferable region for providing the film.

  Next, a preferred arrangement of grounding points for reducing both secondary and tertiary harmonics in the embodiment shown in FIG. 1 will be described.

  FIG. 8 is a plan view for explaining the preferred arrangement of the grounding points on the feeding element 22 and the principle thereof for reducing both the secondary and tertiary harmonics in the embodiment shown in FIG.

In FIG. 8, areas 50A and 50B indicated by hatching are arranged with grounding points to reduce the radiation power of both the secondary and tertiary harmonics while maintaining the radiation power of the fundamental wave large. It is an area that can be made to. That is, the regions 50A and 50B are regions where the preferred region 42 shown in FIG. 4 and the preferred regions 48A and 48B shown in FIG. 7 overlap. The preferred region 42 shown in FIG. 4 can reduce the radiation power of the second harmonic while maintaining the radiation power of the fundamental wave large by disposing the ground point there. Further, in the preferable regions 48A and 48B shown in FIG. 7, the ground point is arranged there, so that the radiation power of the third harmonic can be reduced while maintaining the radiation power of the fundamental wave large. Therefore, if the grounding points are arranged in the regions 50A and 50B shown in FIG. 8, which are their common regions, the radiation power of both the second and third harmonics is maintained while keeping the radiation power of the fundamental wave large. Can be effectively reduced. Of the regions 50A and 50B shown in FIG. 8, the regions 52A and 52B shown with finer hatching are more preferable. That is, the regions 52A and 52B have a distance range of λ _g2 / 2 or more and λ _g2 / 2 + λ _g2 / 12 or less from the termination edge (left or right termination edge) in the excitation direction (x direction) of the second harmonic. In the excitation direction (y direction) of the third harmonic, the distance range is λ _g3 / 2−λ _g3 / 12 or more and λ _g3 / 2 + λ _g3 / 12 or less from the termination edge (upper or lower termination edge). This region 52A, the 52B, secondary and tertiary harmonic current amplitude value i ₂ and i ₃ are particularly small, and is particularly large current amplitude value i ₁ of the fundamental wave. In the embodiment shown in FIG. 1, the ground points 26A and 26B are arranged in the regions 52A and 52B. Therefore, the radiation power of both secondary and tertiary harmonics is effectively reduced.

  FIG. 9 is a plan view for explaining another preferred arrangement of the grounding points on the feeding element 22 for reducing the second harmonic in the embodiment shown in FIG.

In accordance with the principles already described, in order to reduce the radiation power of the secondary harmonic is preferably the current amplitude value i ₂ of the second harmonic is arranged a grounding point as small as possible locations. According to this principle, as shown in FIG. 9, near the termination edge (left or right termination edge) in the excitation direction (x direction) of the second harmonic (for example, λ _g2 / 6 or less from the termination edge) A ground point may be arranged in the areas 54A and 54B (of the distance range). When the grounding points are arranged in the regions 54A and 54B, in order to avoid reduction of the radiated power of the fundamental wave, as already described with reference to FIG. 4, the termination edge in the fundamental wave excitation direction (y direction) It is desirable to arrange a grounding point in a portion excluding a distance range of λ _g1 / 6 or less.

  As shown in FIG. 9, the ground point is arranged near the terminal edge in the excitation direction of the harmonic to be reduced, as in the case of the second harmonic in the case of FIG. 9, the excitation direction of the harmonic is the fundamental wave. This is effective when the direction of excitation is different. This is because if the excitation direction is the same, the fundamental wave is also reduced. Therefore, when the excitation direction of the third harmonic is different from the excitation direction of the fundamental wave because the shape and size of the feed element are different from the embodiment shown in FIG. 1, the same principle applies to the third harmonic. Based grounding point arrangement can be adopted.

  For the fourth and higher harmonics, the power is originally so small that it does not become a problem, so it is not usually necessary to take special power reduction measures. However, the radiated power can be further reduced by applying the principle of the present invention to the fourth and higher harmonics.

  FIG. 10 is a plan view showing the entirety of an embodiment of a microstrip antenna having a plurality of feeding elements having a structure according to the principle of the present invention.

  In the microstrip antenna shown in FIG. 10, a plurality of, for example, four feeding elements 62, 64, 66, and 68 are arranged on the same dielectric substrate 60, for example, in a 2 × 2 matrix. The power feeding elements 62, 64, 66, and 68 each have one or more ground points 72, 74, 76, and 78 that are connected to the ground potential. Each of the ground points 72, 74, 76, and 78 has a current amplitude value of the fundamental wave at each of the feed elements 62, 64, 66, and 68 at or near the maximum value and current amplitude values of the second and third harmonics. It is arranged at a position that is at or near the minimum value. Reference numeral 70 indicates a transmission line that supplies a high-frequency signal with the power feeding elements 62, 64, 66, and 68. The transmission line 70 may be disposed on the front surface of the substrate 60 in the same manner as the power feeding elements 62, 64, 66, and 68. Alternatively, the transmission line 70 may be disposed on the back surface or inside the substrate 60 and may be disposed through the through hole. 64, 66, 68 may be connected. Further, when the ground points 72, 74, 76, 78 are arranged in the central part of the feeder elements 62, 64, 66, 68, they are connected to the ground electrode through the through holes. In the case where it is arranged at or near the end edge of the power feeding elements 62, 64, 66, 68, it may be connected to the ground electrode through a through hole, or the microstrip arranged on the surface of the substrate 60 You may connect to a ground electrode through a track | line.

  By the way, FIG. 10 only shows an example of the overall antenna element configuration of the microstrip antenna to which the principle of the present invention is applied. The principle of the present invention can also be applied to microstrip antennas having other types of antenna element configurations. For example, in a microstrip antenna provided with one or more feeding elements and one or more parasitic elements, a configuration according to the principle of the present invention can be applied to each feeding element.

  One of the uses of the radio wave transmitting antenna according to the present invention as described above is an object sensor for detecting the presence or movement of a person or other object. In the object sensor, the radio wave transmitting antenna according to the present invention is used as a transmitting antenna, the radio wave is radiated from the transmitting antenna to the outside, and the reflected wave that is reflected by the object and returned is received by the receiving antenna. Then, the received signal is processed by the signal processing circuit, so that the presence or movement of a person or other object is detected. In such an object sensor, the radio wave transmission antenna according to the present invention can be used not only as a transmission antenna but also as a reception antenna. A single antenna can also serve as a transmission antenna and a reception antenna. A receiving antenna may be provided separately. In the case of an object sensor that detects the movement of an object using the Doppler effect, the signal processing circuit includes a mixer circuit that mixes transmitted and received radio waves, a Doppler circuit that processes a Doppler signal output from the mixer circuit, and the like. . The object sensor using the radio wave transmitting antenna according to the present invention can be easily made small.

  Now, according to the above-described principle, a ground point connected to the ground potential at a location where the current amplitude value of the n-th (n = 2, 3,...) Harmonic in the feed element of the microstrip antenna is relatively small. By providing this, it is possible to selectively reduce the radiation power of the n-order harmonic. However, this principle can be applied not only to the nth harmonic but also to the fundamental wave. That is, by providing a ground point connected to the ground potential at a location where the current amplitude value of the fundamental wave in the feed element is relatively small, the radiated power of the fundamental wave can be selectively reduced.

  By applying this principle, it is possible to select a desired wave from the fundamental wave and the n (n = 2, 3,...) Order harmonics and radiate them as radio waves from the microstrip antenna. One embodiment as such an application will be described below.

  FIG. 11 is a plan view showing a modification of the configuration of the feed element in the second embodiment of the microstrip antenna according to the present invention.

As shown in FIG. 11, the feed element 110 is a rectangular thin film made of a conductor formed on the front surface of a substrate (background in the figure), and its two perpendicular end edges, for example, the lower side and the right side in the figure. Two feed points 112A and 112B are provided in the vicinity of the central part of each of the terminal edges of the high-frequency signal, and high-frequency signal transmission lines 114A and 114B are connected to the feed points 112A and 112B, respectively. Here, although the transmission lines 114A and 114B are microstrip lines formed on the front surface of the substrate in the illustrated example, they may be through holes penetrating the substrate instead. Transmission lines 114A and 114B apply high-frequency signals having the same or different frequencies to feed points 112A and 112B, respectively. The length of the feeding element 110 in the horizontal direction (hereinafter referred to as “x direction”) is a length suitable for excitation by the fundamental wave of the high-frequency signal applied to the right feeding point 112A, that is, the basic length. The wavelength is selected to be about ½ of the wavelength λ _g1A on the wave substrate. Similarly, the length of the feed element 110 in the vertical direction (hereinafter referred to as “y direction”) is a length suitable for excitation with the fundamental wave of the high-frequency signal applied to the lower feed point 112B. That is, it is selected to be about ½ of the wavelength λ _g1B of the fundamental wave on the substrate. Therefore, the excitation direction by the fundamental wave of the high frequency signal applied to the right feeding point 112A is the x direction (lateral direction), whereas the excitation direction by the fundamental wave of the high frequency signal applied to the lower feeding point 112B is The y direction (vertical direction).

Further, the end edges of the feed element 110 in the vicinity of the feed points 112A and 112B are opposite to each other in the excitation direction, for example, near the center portions of the upper and left end edges in the drawing (respective end points). Two ground points 116A and 116B are provided within a distance of λ _g1A / 6 and λ _g1B / 6 from the edge), and the ground points 116A and 116B are respectively connected to through holes (not shown) penetrating the substrate, These through holes can be connected to a ground electrode (not shown) having a ground potential at any time via a switch (not shown) arranged on the back surface of the substrate. When only one of the two ground points 116A and 116B of the power feeding element 110 is connected to the ground electrode by the on / off operation of these switches, the switch is added to the power feed point on the opposite side of the one ground point. Since the radiation power of the fundamental wave of the high-frequency signal is reduced, the excitation by the high-frequency signal is substantially invalidated, and only the excitation by the high-frequency signal applied to the other feeding point is effective.

For example, when the upper grounding point 116B in the figure is connected to the ground electrode, excitation in the y direction by the fundamental wave of the high frequency signal applied to the lower feeding point 112B is substantially invalidated, and the right side Only the excitation in the x direction by the fundamental wave of the high-frequency signal applied to the feeding point 112A is effective. The excitation of the x-direction, the radio wave 120A having a vibration waveform of the electromagnetic field strength in the x-direction is to be radiated from the antenna. On the other hand, when the grounding point 116A on the left side in the figure is connected to the ground electrode, the excitation in the x direction by the high frequency signal at the right feeding point 112A is substantially invalidated, and the lower feeding point 112B is substantially disabled. Only the y-direction excitation by the high-frequency signal is effective. The excitation of the y-direction, radio 120B having a vibration waveform of an electromagnetic field intensity is to be radiated from the antenna in the y-direction. Further, when the frequencies of the high-frequency signals supplied to the feeding points 112A and 112B are different, the frequency of the radio wave radiated from the antenna can be reduced by selectively connecting the grounding points 116A and 116B to the ground electrode by a switch operation. Can be switched.

As described above, the power feeding element 110 is provided with a plurality of power feeding points 112A and 112B that excite the power feeding element 110 in different directions, and ground points 116A and 116B that substantially disable excitation by high-frequency signals at the power feeding points 112A and 112B. And selectively feeding one of the feeding points 112A and 112B by switching the grounding points 116A and 116B can selectively radiate radio waves having different vibration waveform directions or different frequencies. . This method is effective for a vertically polarized antenna.

  FIG. 12 shows one suitable application for the microstrip antenna according to the present invention having the feeding element shown in FIG.

  The application shown in FIG. 12 is an object sensor 132 for detecting the movement of an object 136 such as a person using the Doppler effect of radio waves. The object sensor 132 is attached to, for example, a ceiling surface or a wall surface 130 of a room, and a microstrip antenna (not shown) according to the present invention and a Doppler signal processing circuit (not shown) connected to the microstrip antenna. Built in. The microstrip antenna is used as a transmission antenna for emitting radio waves. A microstrip antenna that is a transmission antenna may be used as a reception antenna, or the reception antenna may be provided separately from the transmission antenna. The microstrip antenna in the object sensor 132 includes the feeding element 110 having the configuration shown in FIG. 11, and the vibration of the radio wave 134 radiated from the microstrip antenna to the outside of the object sensor 132 by changing the excitation direction. The direction of the waveform changes.

  FIG. 13 and FIG. 14 show the difference in detection characteristics caused by changing the excitation direction of the microstrip antenna of the object sensor 132.

  As shown in FIG. 13, when the excitation direction of the microstrip antenna in the object sensor 132 is the horizontal direction in the figure, a radio wave 138 whose vibration waveform is in the horizontal direction is radiated from the object sensor 132. In this case, the detection sensitivity of the object sensor 132 is the best for the movement of the object 136 in the same lateral direction as the vibration waveform direction of the radio wave 138. On the other hand, as shown in FIG. 14, when the excitation direction of the microstrip antenna is the vertical direction in the figure, the radio wave 140 whose vibration waveform direction is the vertical direction is radiated from the object sensor 132. In this case, the detection sensitivity of the object sensor 132 is the best for the movement of the object 136 in the vertical direction. Thus, by switching the excitation direction, it is possible to change the direction component of the movement of the object with good detection sensitivity. Therefore, by using the different excitation directions in combination, for example, alternately switching at high speed, the movement direction of the object 136 is estimated by comparing the levels of Doppler signals detected in the different excitation directions, or It is possible to logically combine determination results as to whether or not an object has been detected in different excitation directions so that it can be detected with high sensitivity regardless of which direction the object 136 moves.

  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. For example, for the purpose of selectively radiating only a specific harmonic (for example, the second harmonic) from the antenna, the radiation power of the specific harmonic is not greatly reduced, but other harmonics (for example, (Third harmonic) A ground point can also be arranged at a position on the feed element that can effectively reduce the radiation power of the fundamental wave. In addition, by providing a switch that opens and closes each line connecting the ground point and the ground electrode to reduce the radiated power of the fundamental wave and nth-order harmonic, the radiation power of which wave can be reduced. It can also be made selectable whether or not.

It is a top view which shows one antenna element in the electromagnetic wave transmission antenna concerning one Embodiment of this invention, especially a microstrip antenna. It is sectional drawing along the AA line of FIG. It is a top view explaining the preferable arrangement | positioning of the grounding point on the electric power feeding element 22 for reducing the radiation power of the 2nd harmonic in the embodiment shown in FIG. 1, and its principle. It is a top view explaining the preferable arrangement | positioning of the grounding point on the electric power feeding element 22 for reducing the radiation power of the 2nd harmonic in the embodiment shown in FIG. 1, and its principle. It is a top view explaining the preferable arrangement | positioning and the principle of the grounding point for reducing the radiation power of the 2nd harmonic on the feed element 22 of the shape different from embodiment shown in FIG. It is a top view explaining the preferable arrangement | positioning and the principle of the earthing | grounding point on the feed element 22 for reducing the radiation power of the 3rd harmonic in the embodiment shown in FIG. It is a top view explaining the preferable arrangement | positioning and the principle of the earthing | grounding point on the feed element 22 for reducing the radiation power of the 3rd harmonic in the embodiment shown in FIG. It is a top view explaining the preferable arrangement | positioning and the principle of the earthing | grounding point on the feed element 22 for reducing the radiation power of the 2nd and 3rd harmonic in the embodiment shown in FIG. It is a top view explaining another preferable arrangement | positioning of the earthing | grounding point on the electric power feeding element 22 for reducing the radiation power of the 2nd harmonic in the embodiment shown in FIG. It is a top view which shows one Embodiment of a microstrip antenna provided with two or more feed elements which have a structure based on the principle of this invention. It is a top view which shows the modification of the structure of the electric power feeding element in 2nd Embodiment of the microstrip antenna according to this invention. It is a side view which shows one of the uses suitable for the microstrip antenna which has a feed element shown in FIG. The top view which shows a detection characteristic when the excitation direction of the object sensor 132 shown in FIG. 12 is a horizontal direction. The top view which shows a detection characteristic when the excitation direction of the object sensor 132 shown in FIG. 13 is a vertical direction.

Explanation of symbols

20, 60 Substrate 22, 62, 63, 64, 66, 110 Feeding element 24 Feeding point 25, 114A, 114B High-frequency signal transmission line 26A, 26B, 72, 73, 74, 76, 116A, 116B Grounding point 27A, 27B Connection line (through hole)
28 Earth electrode 30 Oscillation circuit 40 Preferred region for grounding point to reduce secondary harmonics 42 Preferred region for grounding point to reduce secondary harmonics while avoiding fundamental wave reduction 44 Avoiding fundamental wave reduction Preferred area for grounding point for reducing second harmonic while 46A, 46B Preferred area for grounding point for reducing third harmonic 48A, 48B Connection for reducing third harmonic while avoiding reduction of fundamental wave Preferred area for point 50A, 50B Preferred area for ground point to reduce both secondary and tertiary harmonics while avoiding reduction of fundamental wave 52A, 52B Both secondary and tertiary, avoiding reduction of fundamental wave More preferable region for grounding point for reducing harmonics 54A, 53B Another region preferable for grounding point for reducing second harmonic while avoiding reduction of fundamental wave

Claims (20)

A substrate made of a dielectric material;
A feed element formed on the substrate;
A transmission line for applying an excitation signal to the feed element;
Grounding means for connecting one or more grounding points in the power feeding element to a ground level;
A radio wave transmitting antenna in which the grounding point is disposed in a region where the current amplitude value of the n-th harmonic (n is a predetermined integer equal to or greater than 2) of the excitation signal on the feed element is not the maximum value. The radio wave transmitting antenna according to claim 1, wherein the grounding point is disposed in a location where the current amplitude value of the n-th harmonic in the power feeding element is a minimum value or in a region near the location. When the wavelength of the n-th harmonic on the substrate is represented by λ _gn , λ _gn / 2−λ _gn / 6 or more from the terminal edge intersecting the excitation direction of the n-th harmonic in the feed element, λ The radio wave transmitting antenna according to claim 1, wherein the grounding point is disposed within a distance range of _gn / 2 + _λgn / 6 or less. The radio wave transmitting antenna according to claim 1 , wherein the grounding point is disposed in a region where current amplitude values of both the second harmonic and the third harmonic in the feed element are not maximum values. The radio wave transmitting antenna according to claim 1, wherein the grounding point is disposed in a location where current amplitude values of both the second harmonic and the third harmonic in the power feeding element are minimum values or in a region in the vicinity of the location. When the wavelengths of the second and third harmonics of the excitation signal on the substrate are represented by λ _g2 and λ _g3 , respectively, λ _g2 from the end edge that intersects the excitation direction of the second harmonic in the feed element / 2−λ _g2 / 6 or more and λ _g2 / 2 + λ _g2 / 6 or less, and λ _g3 / 2-λ from a terminal edge that intersects the excitation direction of the third harmonic in the feed element The radio wave transmitting antenna according to claim 1, wherein the grounding point is arranged in an area within a distance range of _g3 / 6 or more and _λg3 / 2 + _λg3 / 6 or less. The radio wave transmitting antenna according to claim 1, wherein the grounding point is disposed in a region excluding a portion where a current amplitude value of a fundamental wave of the excitation signal in the power feeding element is a minimum value. When the wavelength of the fundamental wave of the excitation signal on the substrate is represented by λ _g1 , within a region excluding a distance range of λ _g1 / 6 or less from a terminal edge that intersects the excitation direction of the fundamental wave in the feed element. The radio wave transmitting antenna according to claim 1, wherein the grounding point is disposed. The grounding point is disposed in a region in the vicinity of a terminal edge that intersects the excitation direction of the n-th harmonic when the excitation direction of the fundamental wave of the excitation signal and the n-th harmonic in the feed element are different. 1. The radio wave transmitting antenna according to 1. When the excitation direction of the fundamental wave of the excitation signal and the n-th harmonic in the feed element is different, the wavelength of the n-order harmonic on the substrate is represented by λ _gn , and the n-order harmonic in the feed element Λ _gn from the end edge crossing the wave excitation direction The radio wave transmitting antenna according to claim 1, wherein the grounding point is disposed within a distance range of / 6 or less. The radio wave transmitting antenna according to claim 1, wherein the plurality of grounding points are arranged at symmetrical positions with respect to a center line of the feeding element. 2. The radio wave transmitting antenna according to claim 1, wherein the grounding means can select whether to connect the grounding point to the ground level. The radio transmission antenna according to claim 1 for emitting radio waves to the outside,
A radio wave receiving antenna that is the same as or different from the radio wave transmitting antenna for receiving a reflected wave reflected by an object from the radio wave transmitting antenna;
An object sensor comprising: a signal processing circuit that detects the presence or movement of an object by processing a reception signal from the reception antenna. A substrate made of a dielectric material;
A feed element formed on the substrate;
A transmission line for applying an excitation signal to the feed element;
Grounding means for connecting one or more grounding points in the power feeding element to a ground level;
A radio wave transmitting antenna in which the grounding point is arranged in a region where a current amplitude value of a fundamental wave of the excitation signal on the feeding element is not a maximum value. The radio wave transmitting antenna according to claim 14, wherein the grounding point is disposed in a location where the current amplitude value of the fundamental wave in the power feeding element is a minimum value or in a region near the location. When the wavelength of the fundamental wave on the substrate is represented by λ _g1 , the grounding point is disposed within a distance range of λ _g1 / 6 or less from a terminal edge intersecting the excitation direction of the fundamental wave in the feed element. The radio wave transmitting antenna according to claim 14 . The radio wave transmitting antenna according to claim 14 , wherein the grounding means can select whether or not to connect the grounding point to the ground level. A plurality of the transmission lines that respectively apply a plurality of excitation signals to the feed element;
A plurality of grounding points respectively disposed in a plurality of regions where the current amplitude values of the fundamental waves of the plurality of excitation signals in the power feeding element are not maximum values, respectively;
The radio wave transmitting antenna according to claim 17 , further comprising a plurality of the grounding means respectively connecting the plurality of grounding points to the ground level. The radio wave transmitting antenna according to claim 18, wherein the excitation directions of the fundamental waves of the plurality of excitation signals in the power feeding element are different. The radio wave transmission antenna according to claim 14, for emitting radio waves to the outside,
A radio wave receiving antenna that is the same as or different from the radio wave transmitting antenna for receiving a reflected wave reflected by an object from the radio wave transmitting antenna;
An object sensor comprising: a signal processing circuit that detects the presence or movement of an object by processing a reception signal from the reception antenna.

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