JP2007221320A - Variable directivity antenna and information apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a variable directivity antenna capable of being used in a frequency in a wide band and having a size in the same extent as a non-directional antenna, and to provide an information apparatus using the variable directivity antenna. <P>SOLUTION: The variable directivity antenna is constituted so as to have an electric-field distribution changing means composed of a non-directional discone antenna 70 connected to a coaxial line 71, a short-circuit line 74 changing the electric-field distribution of the coaxial line 71 and a switch 75. The variable directivity antenna is constituted so as to further have a TE11-mode reflecting structure 76 on the coaxial line 71 on the reverse side to the direction directed towards the discone antenna 70 from the electric-field distribution changing means. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a directivity variable antenna that switches the directivity of an antenna and an information device that uses the directivity variable antenna.

  With the rapid development of wireless communication technology in recent years, products using wireless communication technology have started to spread widely, and great expectations are placed on expanding the transmission capacity of wireless communication paths. Recently, researches have been actively conducted to increase the transmission capacity by multiplexing signals in multiple dimensions such as time, space, polarization, and code.

  Multiplexing by space is considered to be realized by an adaptive array antenna that consists of a circuit that synthesizes the signal with a plurality of omnidirectional antennas, but the size and spacing of each antenna constituting the adaptive array antenna is large. Therefore, it has become a cause of limiting its application.

  In particular, in order to use an antenna in a mobile communication terminal, it is desired to reduce the size of the antenna as much as possible. Therefore, a directivity variable antenna can usually be made smaller than an adaptive array antenna because its directivity can be changed by a pair of antennas and a feeding circuit, and a small antenna that realizes multiplexing by space Although there are few examples of research on miniaturization of variable directivity antennas, the development of such antennas is expected.

  An example of a conventional directional variable antenna is disclosed in Patent Document 1. FIG. 1 is a diagram in which FIG. 1 of Patent Document 1 is cited. Since the reflective element 11 is configured to mechanically circulate around the radiating element 10 in FIG. 1, the directivity of this antenna can be changed, but in the case of the antenna disclosed in Patent Document 1, Due to the addition of the reflective element 11, the size of the antenna is significantly increased.

  Patent Document 2 discloses an example of an antenna capable of electrically switching directivity. FIG. 2 is a diagram in which FIG. 1 of Patent Document 2 is cited. In FIG. 2, a central driving element 12 and a parasitic element 14 are arranged on a circular ground conductor 13 at positions that radially surround the central driving element 12. An impedance load is provided below the parasitic element 14, and the directivity is switched by switching the impedance. The distance between the central driving element 12 and the parasitic element 14 is about λ / 4, and the whole antenna has a size of 2λ or more.

  An example of a conventional variable directivity antenna is disclosed in Patent Document 3. FIG. 3 is a diagram in which FIG. 1 of Patent Document 3 is cited. In FIG. 3, the feeding antenna element A0 and the parasitic variable reactance elements A1 to A6 are arranged on the circular ground conductor 15 at positions that radially surround the feeding antenna element A0. The distance d between the feeding antenna element and the parasitic variable reactance element has a value of about λ / 4, and the entire antenna has a size of about λ.

  As described above, in the conventional variable directivity antenna, a parasitic element is arranged around the radiator, and the directivity of the antenna is controlled by using electromagnetic mutual coupling between the radiator and the parasitic element. . In the method used in the conventional variable directivity antenna, the equivalent synthetic aperture of the antenna is increased, so that the gain is increased and the directivity of the antenna can be controlled. It is difficult to reduce the size of to the same size as the omnidirectional antenna. Therefore, the present inventors invented a technique for changing the directivity of an antenna without increasing the equivalent synthetic aperture of the antenna, and the invention is disclosed in Patent Document 4.

  Normally, a coaxial line is used for feeding the omnidirectional antenna, but the feeding electric field distribution is uniform in the coaxial line. Further, even if the electric field distribution of the coaxial line is changed by any method, the electric field distribution becomes uniform immediately after propagation through the coaxial line. However, in Patent Document 4, if the electric field distribution of the coaxial line is changed immediately before the feeding portion of the omnidirectional antenna, the antenna radiation mode is combined before the electric field distribution becomes uniform. It is disclosed that it is possible to offset the power supply electric field distribution.

  As described above, the directional variable antennas disclosed in Patent Documents 1 to 3 are larger than the omnidirectional antenna, but the directional variable antenna disclosed in Patent Document 4 is It is about the same size as an omnidirectional antenna. Non-Patent Document 1 describes the details of the antenna implementation disclosed in Patent Document 4, and shows that the directivity can be changed over a wide frequency band with the same size as an omnidirectional antenna.

FIG. 4 is a diagram quoting FIG. 1 of Non-Patent Document 1 that is substantially the same as the antenna disclosed in Patent Document 4, and is a configuration diagram of the antenna whose operation principle has been confirmed by experiments. The antenna shown in FIG. 4A has an antenna directivity by a short-circuit wire 24 provided at a connection portion between the coaxial line 21 and the discone antenna 20 for feeding the discone antenna 20 including the radiator 22 and the ground plane 23. To change. Note that the short-circuit line 24 short-circuits the inner conductor 21A and the outer conductor 21B constituting the coaxial line 21. The figure which looked at the part shown with the broken line from the top is shown in FIG.4 (b). As shown in FIG. 5, the reflection loss frequency characteristics of the antenna shown in FIG. 4 are substantially the same over a wide frequency range regardless of the presence or absence of a short-circuit line.
JP-A-6-350334 Japanese Patent Laid-Open No. 10-154911 JP 2001-24431 A JP 2004-304785 A Sakakibara, Hoshi, Aoi, Sato, “Proposal of antenna directivity control technology using coaxial short-circuit structure”, IEICE Technical Report, AP2003-274. , 2004

  When the antenna shown in FIG. 4 is viewed in detail, it can be seen that the reflection loss is increased by loading a short-circuit wire at some frequencies (around 27 GHz or around 33 GHz). In the example of FIG. 5, the reflection loss without the short-circuit line is slightly higher, so an example in which the reflection loss without the short-circuit line is lower than that in FIG. 5 is shown in FIG.

  The reflection loss when there is no short-circuit line represented by the dotted line in FIG. 6A is −10 dB or less in a wide band. On the other hand, it can be seen that in the case of the reflection loss in the case of the short-circuit line represented by the solid line in FIG. 6A, the reflection loss is large near 27 GHz or 33 GHz. Further, it has been found by the present inventors that the change in the antenna directivity changes at the frequencies near 27 GHz and 33 GHz where the reflection loss increases. FIG. 6B shows the change in directivity with respect to the frequency of the antenna having the reflection loss characteristic of FIG. 6A (ratio of the antenna gain on the side shorted with the coaxial line and the antenna gain on the opposite side). . As can be seen from FIG. 6B, it can be seen that the directivity change amount also changes abruptly in the vicinity of 27 GHz or 33 GHz where the increase in the reflection characteristics is seen in FIG. 6A.

  In the antenna shown in FIG. 4, in addition to the TEM mode having an axially symmetric electric field distribution in the coaxial line, a higher-order mode in which the electric field distribution is not an axis target is generated. Each higher-order mode of the coaxial line has a cutoff frequency determined by the structure of the coaxial line, and electromagnetic waves having a frequency lower than the cutoff frequency cannot propagate through the coaxial line. It can propagate along the coaxial line. In addition, the traveling direction of the higher-order mode generated in the coaxial line is both positive and negative with respect to the axial direction of the coaxial line due to the subjectivity of the field. Both higher-order modes traveling to the opposite coaxial line are generated.

  The higher-order mode when traveling in the antenna direction changes the antenna directivity, but in the higher-order mode traveling to the coaxial line opposite to the antenna, the major problem is that it cannot propagate through the coaxial line below the cutoff frequency. However, at a cutoff frequency or higher, as shown in FIG. 6, a phenomenon such as an increase in reflection loss or a sudden change in directivity change occurs at some frequencies. This phenomenon occurs because a higher-order mode that has traveled to the coaxial line on the opposite side of the antenna shown in FIG. 4 causes reflection at a discontinuous portion of the coaxial line and causes a kind of resonance phenomenon.

  As described above, a small variable directivity antenna as large as an omnidirectional antenna has been proposed, such as the antenna shown in FIG. 4, but the reflection loss increases or the directivity changes at a specific frequency. Since the amount has changed suddenly and the usable frequency band of the directional variable antenna is narrowed, there has been a problem that the directional variable antenna is hindered when used in a wide band.

  The present invention has been made in order to solve the above-described problems, and includes a directional variable antenna that can be used in a wideband frequency and has the same size as an omnidirectional antenna, and the directional variable antenna. The purpose is to provide information equipment to be used.

The directional variable antenna of the present invention includes a non-directional antenna element connected to a coaxial line, electric field distribution changing means for changing the electric field distribution of the coaxial line, and a direction from the electric field distribution changing means toward the antenna element. The coaxial line on the opposite side of the antenna has a configuration including reflection means for reflecting electromagnetic waves of higher-order modes including the TE11 mode.
With this configuration, high-order mode electromagnetic waves traveling in the direction opposite to the direction from the electric field distribution changing means toward the antenna element are reflected by the reflecting means. Therefore, reflection at a partial frequency due to the provision of the electric field distribution changing means. By suppressing the increase in loss, it is possible to realize a directional variable antenna that can be used in a wideband frequency and has the same size as an omnidirectional antenna.

In addition, when the antenna element is fed via the reflecting means in the coaxial line, it is desirable to reduce the loss during feeding as much as possible, so the directivity variable antenna of the present invention is The reflectivity for the TEM mode is equal to or less than the first constant, and the reflectivity for the TE11 mode is equal to or greater than the second constant.
With this configuration, since the antenna element is normally fed in the TEM mode, if the reflectance of the reflecting means for the TEM mode is lowered and the reflectance of the reflecting means for the TE11 mode is kept high, the TEM mode is unnecessary. Reflection can be avoided. Therefore, reflection in the TEM mode is suppressed, and a directional variable antenna that can be used in a wide frequency range and has the same size as that of an omnidirectional antenna can be realized.

Further, in order to form the reflecting means of the directional variable antenna of the present invention in the simplest way on the coaxial line, it seems that there is no impedance change for the TEM mode, but a large impedance change from the higher order mode. The reflection means includes a diameter of an inner conductor constituting the coaxial line, a diameter of an outer conductor constituting the coaxial line, and a dielectric constant between the inner conductor and the outer conductor. The structure is a reflective structure formed by adjusting the structural parameters including.
With this configuration, it is possible to realize a directional variable antenna having a very simple configuration and usable in a wideband frequency and having the same size as an omnidirectional antenna.

In the variable directivity antenna of the present invention, the cutoff frequency of the TE11 mode of the coaxial line forming the reflective structure is higher than the cutoff frequency of the TE11 mode of the coaxial line that is not the reflective structure. Yes.
With this configuration, a very large reflectance can be obtained up to the cutoff frequency of the TE11 mode of the reflective structure even at a frequency at which the TE11 mode can propagate in the coaxial line that is not a reflective structure. In addition, although it seems that there is no impedance change with respect to the TEM mode, a very large reflectance can be obtained up to the cutoff frequency of the TE11 mode of the reflecting structure, so that it has a very simple configuration and a wide bandwidth. It is possible to realize a variable directivity antenna that can be used at a frequency and has the same size as an omnidirectional antenna.

When there is a step in the inner conductor of the coaxial line, an evanescent high-order TM mode is generated, and a parasitic capacitance is generated. Therefore, the variable directivity antenna of the present invention has an inner conductor of the coaxial line that forms the reflective structure. The diameter and the diameter of the inner conductor of the coaxial line that is not the reflective structure are the same.
With this configuration, by making the diameter of the inner conductor the same, generation of unnecessary capacitance at the inner conductor stepped portion can be eliminated, so that the reflectivity for the TEM mode can be kept low in the reflecting structure. Further, if the inner conductor has the same diameter, the processing becomes very easy.

Similarly, even when there is a step in the outer conductor of the coaxial line, an evanescent high-order TM mode is generated and a parasitic capacitance is generated. Therefore, the directional variable antenna of the present invention has the coaxial line that forms the reflective structure. The diameter of the outer conductor and the diameter of the outer conductor of the coaxial line that is not the reflective structure are the same.
With this configuration, the generation of unnecessary capacitance can be eliminated by setting the outer conductor to the same diameter, so that the reflectivity for the TEM mode can be kept low in the reflective structure. Moreover, if the diameter of the outer conductor is the same, processing becomes very easy.

When there is a large change in the dielectric constant between the inner and outer conductors of the coaxial line, some reflection occurs even if the characteristic impedance of the coaxial line is the same and constant before and after the boundary surface. The dielectric constant of the coaxial line that forms the reflective structure and the dielectric constant of the coaxial line that is not the reflective structure are the same.
With this configuration, since the permittivity is the same, the reflectivity for the TEM mode can be kept low in the reflective structure, and the same material is used for the dielectric between the inner conductor and the outer conductor in processing. Can be used and processing becomes very easy.

The above-described reflection structure may be formed close to the electric field distribution changing means, but this is avoided because resonance occurs even at a length of only a few millimeters at a frequency as high as several tens of GHz. As a quantitative guideline, the length between the TE11 mode reflection structure and the electric field distribution changing means is such that the resonance does not occur over the entire operating frequency, that is, half the effective wavelength of the TE11 mode. Since the directional variable antenna of the present invention has only a small value, the length of the reflection structure and the electric field distribution changing means is L, the dielectric constant of the coaxial line is εr, and the coaxial line in the TE11 mode. Is set to satisfy the formula 1, where λ is a wavelength corresponding to a frequency capable of propagating.
With this configuration, it is possible to realize a directional variable antenna that can be used in a wide band frequency and has the same size as an omnidirectional antenna.

When the diameters of the inner conductor and outer conductor of the reflective structure differ greatly from the diameters of the inner conductor and outer conductor of the coaxial line, even if the characteristic impedance for the TEM mode is constant at 50Ω, it is parasitic on the boundary of the reflective structure. Since the reflectivity for the TEM mode is increased due to the influence of the capacitance and the like, at least one of the inner conductor and outer conductor diameters of the coaxial line continuously changes. Thus, the reflection structure is formed.
With this configuration, at least one of the inner conductor and outer conductor diameters continuously changes, and therefore has an intermediate characteristic between the coaxial line and the reflective structure at the boundary where the coaxial line changes to the reflective structure. A transition region is provided and the reflectivity for the TEM mode can be reduced.

The variable directivity antenna of the present invention has a configuration in which the electric field distribution changing means changes the electric field distribution of the coaxial line by short-circuiting a part of the inner conductor and the outer conductor constituting the coaxial line. .
With this configuration, it is possible to change the electric field distribution of a broadband frequency with a very simple configuration.

  The information equipment provided with the directional variable antenna of the present invention can be downsized as much as the omnidirectional antenna, and is particularly useful for a small information terminal.

  As described above, according to the present invention, since the high-order mode electromagnetic wave traveling in the direction opposite to the direction from the electric field distribution changing means toward the antenna element is reflected by the reflecting means, a part of the provision of the electric field distribution changing means is provided. A directional variable antenna that can be used in a wideband frequency and has the same size as an omnidirectional antenna by suppressing an increase in reflection loss at the frequency, and an information device using the directional variable antenna Is to provide.

  Hereinafter, a variable directivity antenna according to an embodiment of the present invention will be described with reference to the drawings.

(First embodiment of the present invention)
FIG. 7 is a schematic diagram of the variable directivity antenna according to the first embodiment of the present invention. FIG. 7A is a cross-sectional view of the variable directivity antenna according to the first embodiment of the present invention. The directional variable antenna shown in FIG. 7 employs a discone antenna 70 composed of a conical radiator 72 and a ground plane 73 as an omnidirectional antenna element connected to a coaxial line 71 for feeding. ing. Of course, the non-directional antenna element according to the present invention is not limited to the discone antenna.

  7 has electric field distribution changing means for changing the electric field distribution of the coaxial line 71. As an example of the electric field distribution changing means, the inner conductor 71A constituting the coaxial line 71 and the outer conductor 71A are arranged. A method of short-circuiting the conductor 71B with the short-circuit line 74 is adopted.

  In FIG. 7A, the electric field distribution changing means includes a short-circuit line 74 and a switch 75 that can electrically turn on / off the short-circuit between the inner conductor 71A and the outer conductor 71B in the middle of the short-circuit line 74. Constructed and shown with dashed lines. Here, as an example, FIG. 7B shows a view of the electric field distribution changing means indicated by a broken line as viewed from above. As shown in FIG. 7B, four short-circuit lines 74 and switches 75 are formed on the surface of the ground plane 73.

  FIG. 8 is a diagram illustrating an example of the switch 75. The switch 75 includes a PIN diode 75D, a capacitor 75C, an inductor 75L, and a resistor 75R that can be electrically controlled on / off using a bias line (not shown) from the outside of the variable directivity antenna. In addition, regarding the terminals 75A, 75B, and 75E shown in FIG. 8, the terminal 75A is connected to the inner conductor 71A, the terminal 75B is connected to the outer conductor 71B, and the terminal 75E is connected to a bias line (not shown).

  The PIN diode 75D is grounded at a high frequency by a capacitor 75C. By changing the value of the DC bias applied to the terminal 75E, the resistance value of the PIN diode 75D is greatly changed, so that it can be operated as a switch.

  If all the switches 75 provided in each of the four short-circuit lines 74 are turned OFF, the electric field distribution of the coaxial line 71 is not disturbed, and the radiation pattern of the directional variable antenna remains omnidirectional. On the other hand, when only one switch 75 is turned ON, the electric field in the coaxial line 71 is disturbed, and the radiation pattern of the variable directivity antenna has directivity. In addition, by switching any one of the four switches 75 to ON, the directionality of the directivity variable antenna can be switched.

  The directivity variable antenna shown in FIG. 7 is close to the electric field distribution changing means constituted by the short-circuit line 74 and the switch 75, and is connected to the coaxial line 71 on the connection side with the non-directional antenna element in the higher-order mode. Reflection means for reflecting electromagnetic waves. More specifically, the reflecting means prevents high-order mode electromagnetic waves generated in the direction opposite to the direction toward the non-directional antenna element in the coaxial line 71 from propagating.

  In the reflecting means, the reflectance for the TEM mode is not more than the first constant and the reflectance for the TE11 mode is not less than the second constant. As a preferable example, the first constant is 10%. The reflectance for the TEM mode is 10% or less, the second constant is 90%, and the reflectance for the TE11 mode is 90% or more.

  Further, for example, as shown in FIG. 7, the reflecting means is formed as a TE11 mode reflecting structure 76 that reflects TE11 mode electromagnetic waves having at least the lowest cutoff frequency. The TE11 mode reflecting structure 76 is realized by adjusting the structural parameters of the feeding coaxial line 71. The structural parameters include, for example, the diameter of the inner conductor 71A constituting the coaxial line 71, the diameter of the outer conductor 71B, and the dielectric constant between the inner conductor 71A and the outer conductor 71B.

  For example, in the directivity variable antenna shown in FIG. 7, the inner conductor 71A and the outer conductor 71B constituting the coaxial line 71 for feeding are circular in cross section, the inner conductor 71A has a diameter of 1.3 mm, and the outer conductor. The diameter of 71B is 4.2 mm, and the dielectric constant between the inner and outer conductors is 2.0. Regarding the TE11 mode reflection structure 76 formed on the feeding coaxial line 71, the inner conductor diameter is 1.3 mm, the outer conductor diameter is 2.9 mm, and the dielectric constant between the inner and outer conductors is 1.0. Yes. The cross sections of the inner conductor 71A and the outer conductor 71B are not limited to a circular shape.

  Here, since the diameter of the inner conductor of the coaxial line 71 for feeding is the same as the diameter of the inner conductor of the TE11 mode reflecting structure 76, the reflection loss is reduced and the processing becomes easy.

  In addition, since the cutoff frequency of the TE11 mode is 25.9 GHz in the coaxial line 71 for power feeding, the cutoff frequency of the TE11 mode in the TE11 mode reflecting structure 76 is set to be as high as 46.8 GHz. In the coaxial line 71 for power feeding, the reflectance of the TE11 mode is approximately 1 at 26 GHz to 46.8 GHz where the TE11 mode can propagate.

Further, in the variable directivity antenna shown in FIG. 7, the TE11 mode wavelength λ is 6 mm or more when the effective dielectric constant εr is 2.0 or 46.8 GHz or less, so that the relationship of Equation 1 is satisfied. Further, the length L between the TE11 mode reflecting structure 76 and the electric field distribution changing means is shortened to 1.5 mm.

  FIG. 9 is a diagram for explaining the reflection loss characteristic of the variable directivity antenna shown in FIG. As shown in FIG. 9 (a), the horizontal axis indicates the frequency, and the vertical axis indicates the reflection loss. The solid line in the figure indicates a case where the switch 75 is turned on at one position and the short line indicates all the dotted lines in the figure. The case where the switch 75 is turned OFF is shown.

  As is clear from FIG. 9 (a), the increase in reflection loss near 27 GHz or at a frequency per 33 GHz as seen in FIGS. 5 and 6 does not occur in this embodiment, and it extends over a wide band. It can be seen that good characteristics with a reflection loss of -10 dB or less are obtained.

  FIG. 9B is a diagram for explaining the change in directivity with respect to the frequency of the directivity variable antenna shown in FIG. As is clear from FIG. 9B, a substantially constant directivity change amount is obtained at 20 GHz or more, and a rapid change in the directivity change amount at a specific frequency as seen in FIG. 6B. You can see that it is gone.

  FIG. 10 is a diagram for explaining the directivity of the directivity variable antenna shown in FIG. In FIG. 10, when the switch at 0 degree is turned on among the four switches 75 shown in FIG. 7 with respect to the conical radiator 72 having an elevation angle of 45 degrees from the ground plane 73, from 0 degree to 360 degrees. The corresponding gain is indicated by a solid line. A dotted line indicates a gain when all the switches are turned off.

  As is apparent from FIG. 10, when all the switches are turned OFF, a constant gain is obtained at any angle, and omnidirectionality is obtained. Further, it is shown that the directivity changes by turning on the switch, and the radiation intensity in the direction opposite to the switch that is turned on becomes stronger.

  As described above, the variable directivity antenna according to the first embodiment of the present invention reflects high-order mode electromagnetic waves that have traveled in a direction opposite to the direction from the electric field distribution changing means toward the antenna element by the reflecting means. Therefore, the increase in reflection loss at some frequencies due to the provision of electric field distribution changing means is suppressed, so that the directivity can be switched over a wide band with the same size as an omnidirectional antenna. Can be done. In addition, since the generation of unnecessary capacitance can be eliminated by setting the diameter of the inner conductor to the same diameter, it is possible to keep the reflectivity for the TEM mode low in the reflective structure. Further, if the inner conductor has the same diameter, the processing becomes very easy.

(Second embodiment of the present invention)
FIG. 11 is a cross-sectional view of a variable directivity antenna according to the second embodiment of the present invention. Of the constituent elements constituting the directivity variable antenna according to the second embodiment of the present invention, the same constituent elements as those constituting the directivity variable antenna according to the first embodiment of the present invention. Are denoted by the same reference numerals, and description thereof is omitted.

  In the variable directivity antenna shown in FIG. 11, the inner conductor 71A has a diameter of 1.3 mm, the outer conductor 71B has a diameter of 4.2 mm, and the dielectric constant between the inner and outer conductors is 2.0. For the TE11 mode reflecting structure 77 formed on the coaxial line 71 for feeding, the inner conductor diameter is 1.8 mm, the outer conductor diameter is 4.2 mm, and the dielectric constant between the inner and outer conductors is 1.0. Yes.

  Here, since the diameter of the outer conductor of the power supply coaxial line 71 is the same as the diameter of the outer conductor of the TE11 mode reflecting structure 77, the reflection loss is reduced and the processing becomes easy.

  In addition, the cutoff frequency of the TE11 mode in the power supply coaxial line 71 is 25.9 GHz, whereas the cutoff frequency of the TE11 mode in the TE11 mode reflection structure 77 is set to be as high as 32.8 GHz. In the feeding coaxial line 71, the reflectance of the TE11 mode is almost 1 at 26 GHz to 32.8 GHz in which the TE11 mode can propagate.

  In the directivity variable antenna shown in FIG. 11, the effective dielectric constant εr is 2.0, and the wavelength λ of the TE11 mode is 8 mm or more at a frequency of 32.8 GHz or less. The length L between the TE11 mode reflecting structure 77 and the electric field distribution changing means is shortened to 1.5 mm so as to satisfy the condition.

  As described above, the variable directivity antenna according to the second embodiment of the present invention can eliminate the generation of unnecessary capacitance by setting the diameter of the outer conductor to the same diameter. It is possible to keep the reflectance with respect to low. Moreover, if the diameter of the outer conductor is the same, processing becomes very easy.

(Third embodiment of the present invention)
FIG. 12 is a sectional view of a variable directivity antenna according to the third embodiment of the present invention. Of the constituent elements constituting the directivity variable antenna according to the third embodiment of the present invention, the same constituent elements as those constituting the directivity variable antenna according to the first embodiment of the present invention. Are denoted by the same reference numerals, and description thereof is omitted.

  In the variable directivity antenna shown in FIG. 12, the inner conductor 71A has a diameter of 1.3 mm, the outer conductor 71B has a diameter of 4.2 mm, and the dielectric constant between the inner and outer conductors is 2.0. The TE11 mode reflection structure 78 formed on the power supply coaxial line 71 has an inner conductor diameter of 0.8 mm, an outer conductor diameter of 2.6 mm, and a dielectric constant between the inner and outer conductors of 2.0. Yes.

  Here, since the dielectric between the inner conductor 71A and the outer conductor 71B is made of the same material (for example, PTFE), the dielectric constant of the feeding coaxial line 71 and the dielectric constant of the TE11 mode reflecting structure 78 are the same. Thus, the reflection loss is reduced and the processing becomes easy.

  In addition, the cutoff frequency of the TE11 mode in the coaxial line 71 for feeding is 25.9 GHz, whereas the cutoff frequency of the TE11 mode in the TE11 mode reflecting structure 78 is set to be as high as 40.8 GHz. In the feeding coaxial line 71, the reflectance of the TE11 mode is almost 1 at 26 GHz to 40.8 GHz in which the TE11 mode can propagate.

  In the variable directivity antenna shown in FIG. 12, the TE11 mode wavelength λ is 7 mm or more when the effective dielectric constant εr is 2.0 or 40.8 GHz or less. The length L between the TE11 mode reflecting structure 78 and the electric field distribution changing means is shortened to 1.5 mm so as to satisfy the condition.

  As described above, in the variable directivity antenna according to the third embodiment of the present invention, the dielectric constant of the feeding coaxial line 71 and the dielectric constant of the TE11 mode reflecting structure 78 are the same. The reflection structure 78 can keep the reflectivity for the TEM mode low, and the same material can be used for processing as long as the dielectric constant is constant.

(Fourth embodiment of the present invention)
FIG. 13 is a cross-sectional view of a variable directivity antenna according to the fourth embodiment of the present invention. Of the constituent elements constituting the directivity variable antenna according to the fourth embodiment of the present invention, the same constituent elements as those constituting the directivity variable antenna according to the first embodiment of the present invention. Are denoted by the same reference numerals, and description thereof is omitted.

  In the variable directivity antenna shown in FIG. 13, the inner conductor 71A has a diameter of 1.3 mm, the outer conductor 71B has a diameter of 4.2 mm, and the dielectric constant between the inner and outer conductors is 2.0. The TE11 mode reflection structure 79 formed on the power supply coaxial line 71 has an inner conductor diameter of 0.6 mm, an outer conductor diameter of 2.0 mm, and a dielectric constant between the inner and outer conductors of 2.0. Yes.

  Here, since the dielectric between the inner conductor 71A and the outer conductor 71B is made of the same material (for example, PTFE), the dielectric constant of the feeding coaxial line 71 and the dielectric constant of the TE11 mode reflection structure 79 are the same. Thus, the reflection loss is reduced and the processing becomes easy.

  Further, as shown in FIG. 13, the diameters of the inner conductor 71A and the outer conductor 71B of the coaxial line 71 are continuously changed, and the coaxial line 71 and the TE11 are changed to a boundary portion where the coaxial line 71 changes to the TE11 mode reflection structure 79. A transition region having intermediate characteristics with the mode reflection structure 79 is provided.

  Further, the cutoff frequency of the TE11 mode in the feeding coaxial line 71 is 25.9 GHz, whereas the cutoff frequency of the TE11 mode in the TE11 mode reflection structure 79 is set to be as high as 54.4 GHz. In the feeding coaxial line 71, the reflectance of the TE11 mode is almost 1 at 26 GHz to 54.4 GHz in which the TE11 mode can propagate.

  Further, in the variable directivity antenna shown in FIG. 13, the effective dielectric constant εr is 2.0 and the wavelength λ of the TE11 mode is 5 mm or more at a frequency of 54.4 GHz or less. The length L between the TE11 mode reflecting structure 79 and the electric field distribution changing means is shortened to 1.5 mm so as to satisfy the condition.

  As described above, the variable directivity antenna according to the fourth embodiment of the present invention has the boundary between the coaxial line 71 and the TE11 mode reflection structure 79 at the boundary where the coaxial line 71 transitions to the TE11 mode reflection structure 79. Since a transition region having intermediate characteristics is provided, the reflectance for the TEM mode can be reduced.

  The present invention has been described above based on the embodiment of the present invention. However, the present invention is limited to requirements such as the shape described in the above-described embodiment of the present invention and the combination with other elements. It is never a thing. With respect to these points, the present invention can be changed within a range that does not detract from the gist of the present invention, and can be appropriately determined according to the application form.

  Note that an information device such as a personal computer or a portable device equipped with a directional variable antenna according to an embodiment of the present invention can be as small as an omnidirectional antenna, and is particularly useful for a small information terminal. is there.

The figure for demonstrating the conventional directivity variable antenna in patent document 1 The figure for demonstrating the conventional directivity variable antenna in patent document 2 The figure for demonstrating the conventional directivity variable antenna in patent document 3 The figure for demonstrating the conventional directivity variable antenna in a nonpatent literature 1. The figure for demonstrating the reflection loss characteristic of the conventional variable directivity antenna The figure which shows the characteristic of the conventional directivity variable antenna Schematic diagram of a variable directivity antenna according to a first embodiment of the present invention The figure which shows an example of the switch of the directivity variable antenna which concerns on the 1st Embodiment of this invention The figure for demonstrating the reflection loss characteristic of the directivity variable antenna which concerns on the 1st Embodiment of this invention The figure for demonstrating the directivity of the directivity variable antenna which concerns on the 1st Embodiment of this invention Sectional drawing of the directivity variable antenna which concerns on the 2nd Embodiment of this invention Sectional drawing of the directivity variable antenna which concerns on the 3rd Embodiment of this invention Sectional drawing of the directivity variable antenna which concerns on the 4th Embodiment of this invention

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Radiation element 11 Reflection element 12 Central drive element 13 Ground conductor 14 Parasitic element 15 Ground conductor 20, 70 Discone antenna 21, 71 Coaxial line 21A, 71A Inner conductor 21B, 71B Outer conductor 22, 72 Radiator 23, 73 Ground plane 24, 74 Short-circuit wire 75 Switch 75C Capacitor 75D PIN diode 75L Inductor 75R Resistor 76, 77, 78, 79 TE11 mode reflection structure

Claims (11)

An omnidirectional antenna element connected to the coaxial line;
Electric field distribution changing means for changing the electric field distribution of the coaxial line;
A variable directivity antenna, comprising: a reflection unit configured to reflect an electromagnetic wave of a higher order mode including a TE11 mode on the coaxial line opposite to a direction from the electric field distribution changing unit toward the antenna element.   2. The variable directivity antenna according to claim 1, wherein the reflection means has a reflectivity for the TEM mode that is equal to or less than a first constant and a reflectivity for the TE11 mode that is equal to or greater than a second constant.   The reflecting means is formed by adjusting structural parameters including a diameter of an inner conductor constituting the coaxial line, a diameter of an outer conductor constituting the coaxial line, and a dielectric constant between the inner conductor and the outer conductor. The variable directivity antenna according to claim 1, wherein the directional variable antenna is a reflective structure.   The directional variable antenna according to claim 3, wherein a cutoff frequency of the TE11 mode of the coaxial line forming the reflective structure is higher than a cutoff frequency of the TE11 mode of the coaxial line that is not the reflective structure.   5. The directivity according to claim 3, wherein the diameter of the inner conductor of the coaxial line forming the reflective structure is the same as the diameter of the inner conductor of the coaxial line that is not the reflective structure. Variable antenna.   5. The directivity according to claim 3, wherein a diameter of the outer conductor of the coaxial line that forms the reflective structure is the same as a diameter of the outer conductor of the coaxial line that is not the reflective structure. Variable antenna.   5. The variable directivity antenna according to claim 3, wherein the dielectric constant of the coaxial line forming the reflective structure is the same as the dielectric constant of the coaxial line that is not the reflective structure. . When the dielectric constant of the coaxial line is εr and the wavelength corresponding to the frequency that can propagate through the coaxial line in the TE11 mode is λ, the length of the reflection structure and the electric field distribution changing means is L, The directional variable antenna according to any one of claims 3 to 7, wherein:

  9. The reflection structure according to claim 3, wherein at least one of the diameters of the inner conductor and the outer conductor of the coaxial line is continuously changed to form the reflection structure. 10. Directional variable antenna.   The electric field distribution changing means changes the electric field distribution of the coaxial line by short-circuiting a part of the inner conductor and the outer conductor constituting the coaxial line. The directional variable antenna according to the above.   An information device comprising the variable directivity antenna according to any one of claims 1 to 10.

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