JP6469771B2 - Dipole antenna - Google Patents

Description

  The present invention relates to a dipole antenna.

  As a wireless system, an ultra-wideband wireless system that spreads power over a very wide bandwidth and enables high-speed communication is known. In addition, a dipole antenna may be used as an ultra wide band (UWB) antenna (for example, see Patent Document 1).

JP 2010-178000 A

  By the way, a general antenna is required to have a voltage standing wave ratio (VSWR) value of 2 or less in a specified band. For example, the dipole antenna disclosed in Patent Document 1 has good VSWR characteristics in the specification band.

  However, even with an antenna having good VSWR characteristics, the radiation gain may decrease in some frequency bands of the specification band.

  Accordingly, an object of the present invention is to provide a dipole antenna that can prevent a decrease in radiation gain in a wide band.

  A dipole antenna according to the present invention that solves the above-described problems includes a first connection portion to which the inner conductor of a signal line including an inner conductor and an outer conductor is connected, and first and second extending from the first connection portion in a bifurcated manner. A first radiating element having two radiating portions, a second connecting portion to which the outer conductor is connected, a third radiating portion formed on the first radiating portion side and extending from the second connecting portion, and the second A second radiating element having a fourth radiating portion formed on the radiating portion side and extending from the second connecting portion, and the third radiating portion is arranged on the first radiating portion side as it goes to the tip portion. The first radiating element has a shape in which a first distance between the first radiating element and the second radiating element on the third radiating part side is widened, and the fourth radiating part is located on the second radiating part side as it approaches the tip end part. The second interval between the first radiating element and the second radiating element on the fourth radiating portion side is widened. To have Jo, characterized.

  ADVANTAGE OF THE INVENTION According to this invention, the dipole antenna which can prevent the fall of a radiation gain in a wide band can be provided.

1 is a diagram illustrating a configuration of an antenna 10. FIG. It is a figure which shows the magnitude | size of the surface current of the antenna. It is a figure which shows the radiation characteristic in the yz plane of the antenna. FIG. 3 is a diagram illustrating radiation characteristics in a specification band of the antenna 10. 2 is a diagram illustrating a configuration of an antenna 15. FIG. It is a figure which shows the magnitude | size of the surface current of the antenna. It is a figure which shows the radiation characteristic in the yz plane of the antenna 15. FIG. It is a figure which shows the radiation characteristic in the specification zone | band of the antenna 15.

--- Antenna 10 ---
FIG. 1 is a plan view showing the configuration of the antenna 10. The antenna 10 is a dipole antenna used when transmitting and receiving radio waves of 5 to 6 GHz (specification band), for example, and includes an antenna substrate 20 and radiating elements 21 and 22. In FIG. 1, the x axis, the y axis, and the z axis are illustrated as auxiliary lines representing directions. These x axis, y axis and z axis are orthogonal to each other. In FIG. 1, the x axis is an axis along the short direction of the antenna substrate 20, the y axis is an axis along the longitudinal direction of the antenna substrate 20, and the z axis is the surface of the antenna substrate 20. Is an axis along the vertical direction.

  The antenna substrate 20 is a multilayer printed circuit board, and radiating elements 21 and 22 that transmit and receive radio waves are patterned on the surface. The radiating element 21 is connected to an outer conductor S1 (outer conductor) of a signal line X (cable X) (not shown), and the radiating element 22 is connected to a core S2 (inner conductor) of the signal line X. A gap is formed between the radiating element 21 and the radiating element 22.

  The radiating element 21 is a rectangular metal foil pattern. The radiating element 21 has a symmetrical pattern, and the center line of the radiating element 21 coincides with the center line of the side of the antenna substrate 20 in the short direction. The radiating element 21 is provided with a feeding point P <b> 1 on the center line of the radiating element 21 and inside the side 30. Note that the side 30 is a side of the two short sides of the radiating element 21 on the side of the radiating element 22 (side facing the radiating element 22). The position of the feeding point P1 is determined so that impedance matching between the radiating element 21 and the outer conductor S1 of the signal line X is achieved.

  The radiating element 22 is a bowl-shaped metal foil pattern, and a convex portion 40 is provided near the radiating element 21. The convex portion 40 is a region provided to suppress a rapid change in impedance of the radiating element 22 while improving the directivity of the radio wave radiated from the antenna 10. Here, the convex portion 40 is formed so that the side 35 of the convex portion 40 facing the radiating element 21 and the side 30 are substantially parallel to each other. Further, the radiating element 22 is a left-right symmetric pattern, and the center line of the radiating element 22 coincides with the center line of the side of the antenna substrate 20 in the short direction. The radiating element 22 is provided with a feeding point P2 to which the core line S2 of the signal line X is connected on the center line of the radiating element 22 and inside the side 35. The position of the feeding point P2 is determined so that impedance matching between the radiating element 22 and the core wire S2 can be achieved.

  The shape of the radiating element 22 is determined so that the current flowing through the radiating elements 21 and 22 (current of the antenna 10) resonates in a wide frequency band. Here, the resonance frequency of the current of the antenna 10 is determined based on the inductance according to the position (distance) from the feeding points P1 and P2 and the capacitance according to the distance between the radiating elements 21 and 22. In the radiating elements 21 and 22, the inductance increases as the distance from the feeding points P1 and P2 increases. For this reason, in order for the current of the antenna 10 to resonate in a wide frequency band, it is necessary to reduce the capacitance between the radiating elements 21 and 22 as the distance from the feeding points P1 and P2 increases. That is, the distance between the radiating elements 21 and 22 needs to be increased as the distance from the feeding points P1 and P2 increases.

  Therefore, in the antenna 10, the side 36 extending from the convex portion 40 is gently curved so that the distance between the radiating elements 21 and 22 increases as the distance from the convex portion 40 increases. Similarly, the side 37 extending from the convex portion 40 is gently curved so that the distance between the radiating elements 21 and 22 increases as the distance from the convex portion 40 increases.

--- Simulation result of antenna 10 ---
FIG. 2 is a diagram illustrating the magnitude of a 5 GHz current flowing on the surface of the antenna 10. In FIG. 2, the calculation result of the magnitude of the current of 5 GHz is expressed by a pattern (color and hatching). Therefore, the pattern is the same where the same value of current flows. As is clear from FIG. 2, the pattern greatly changes in a part of the radiating element 21. In FIG. 2, the current values are displayed in 15 levels, and the pattern showing the largest current value to the pattern showing the large current value in the 4th level are hatched. Then, in the 11-step current value not hatched, the current value decreases as the color becomes darker.

  Specifically, the current value is small in the regions 200 and 210, and the current value is large in the region 220 near the center line of the radiating element 21. In addition, although FIG. 2 is a figure which shows the electric current value of 5 GHz, the same tendency is seen also in 5-6 GHz. Thus, even when the shape of the radiating elements 21 and 22 is determined so that the radio waves of the antenna 10 are uniform over a wide frequency range (5 GHz to 6 GHz), the current value of the current flowing on the upper surface of the radiating element 21 The variation of the may become large.

  FIG. 3 is a diagram illustrating the radiation characteristics of the antenna 10 on the yz plane. FIG. 3 shows radiation characteristics when the antenna 10 radiates radio waves having three different frequencies of 5 GHz, 5.5 GHz, and 6 GHz. In the antenna 10, in the frequency band of 5 to 6 GHz, the radiation characteristics at 90 ° and 270 ° are particularly deteriorated compared to other angles. As described above, when the variation of the current values of the radiating elements 21 and 22 is large, the radiation characteristic of the yz plane may be deteriorated.

  FIG. 4 is a diagram showing the radiation gain of the specification band of the antenna 10. As shown in FIG. 4, the antenna 10 has a radiation gain lower than that of other frequency bands in the vicinity of 5.4 GHz in the range of 5 GHz to 6 GHz.

--- Antenna 15 ---
FIG. 5 is a plan view showing the configuration of the antenna 15. The antenna 15 is an improvement of the antenna 10 in order to obtain good radiation characteristics in a wide band.

  The antenna 15 is a dipole antenna used when transmitting and receiving radio waves of 5 GHz to 6 GHz (specification band), for example, and includes an antenna substrate 25 and radiating elements 26 and 27. Also in FIG. 5, the same x-axis, y-axis, and z-axis as in FIG. 1 are shown. The x axis is an axis along the short direction of the antenna substrate 25, the y axis is an axis along the longitudinal direction of the antenna substrate 25, and the z axis is along a direction perpendicular to the surface of the antenna substrate 25. Axis. Further, in the x axis, the direction from the left to the right of the paper surface is the + x direction, in the y axis, the direction from the bottom to the top of the paper surface is the + y direction, and in the z axis, the direction from the back of the paper surface to the front is defined. The direction is + z.

  The antenna substrate 25 is a multilayer printed circuit board, and radiating elements 26 and 27 that transmit and receive radio waves are patterned on the surface.

  The radiating element 26 (first radiating element) is an element to which the core wire S3 (inner conductor) of the signal line Y (not shown) is connected, and is formed of a substantially Y-shaped metal foil. The radiating element 26 includes a connection part 60 and radiating parts 61 to 63 to which the core wire S3 is connected. The radiating elements 26 excluding the radiating portion 63 have a symmetrical pattern, and the center line of the radiating elements 26 coincides with the center line of the side of the antenna substrate 25 in the short direction.

  By the way, in a general dipole antenna, the distance on the pattern from the start point to the end point is long when the feed point is the start point of the two radiating elements and the end point of the pattern farthest from the feed point is the end point. The outer conductor of the signal line is connected to the other element. For example, in the antenna 10, the outer conductor is connected to the radiating element 21. However, in the antenna 15, the core wire S3 is connected to the radiating element 26 to which the outer conductor of the signal line is originally connected. That is, the antenna 15 has a configuration in which the core wire S3 is connected to a general low-frequency radiation element, and an outer conductor is connected to the high-frequency radiation element.

  The connection portion 60 (first connection portion) is a region of the tip portion having a convex shape in the Y-shaped radiating element 26. In order to improve the directivity of the radio wave radiated from the antenna 15 and to suppress a rapid change in the impedance of the radiating element 26, the connection unit 60 has a side 70 to be described later as a long side and a feeding point Q1 inside. It has a rectangular shape to include.

  Further, the connection portion 60 is provided with a feeding point Q1 to which the core wire S3 is connected on the center line of the radiating element 26 and inside the side 70 at the tip of the connection portion 60. The position of the feeding point Q1 is determined so that impedance matching between the radiating element 26 and the core wire S3 is achieved.

  The radiating part 61 (first radiating part) is gently curved in the + x direction of the two parts extending in a bifurcated manner from the connection part 60, and near the side along the y axis in the + x direction of the antenna substrate 25. Extend to. In the radiating portion 61, a side extending from a bifurcated portion 100 (a portion where the radiating portions 61 and 62 are branched) is referred to as a side 71.

  The radiating portion 62 (second radiating portion) is a side along the y-axis in the −x direction of the antenna substrate 25 while being gently curved in the −x direction, out of the two portions extending in a bifurcated shape from the connection portion 60. It extends to near. In the radiating portion 62, a side extending from the bifurcated portion 100 is a side 72.

  The radiating portion 63 (sixth radiating portion) is a pattern extending from the end portion of the radiating portion 61 toward the end portion of the antenna substrate 25 in the + y direction. Specifically, the radiating portion 63 is a pattern that extends from the tip of the side 71 of the radiating element 26 (the tip of the side 71 in the direction opposite to the location 100) to the side opposite to the radiating element 27. In addition, although the connection part 60 and the radiation | emission parts 61-63 are the patterns formed integrally, in FIG. 6, the line which distinguishes the radiation | emission part 61 and the radiation | emission part 63 is drawn for convenience.

  The radiating element 27 (second radiating element) is a radiating element to which the outer conductor S4 (conductor on the outer skin side) of the signal line Y is connected. The radiating element 27 is a substantially concave curved metal foil pattern in which a concave portion corresponding to the connecting portion 60 is formed, and includes a connecting portion 80 and radiating portions 81 to 83. The radiating element 27 excluding the radiating portion 83 has a substantially symmetric pattern, and the center line of the radiating element 27 coincides with the center line of the side of the antenna substrate 25 in the short direction. In addition, although the connection part 80 and the radiation | emission parts 81-83 are integrally formed, the horizontal line (solid line) is drawn from the point D2 between the radiation | emission parts 81 and 83 for convenience. The line from the point D2 is a convenient line for facilitating understanding of the relationship between the radiation portions 81 and 83. For this reason, between the radiation | emission parts 81 and 83, the edge | side 91 may extend and may be distinguished. In such a case, the radiating elements 27 excluding the radiating portion 83 are symmetric.

  The outer conductor S4 of the signal line Y is connected to the connection portion 80 (second connection portion). The connection portion 80 is an area provided to improve the directivity of the radio wave radiated from the antenna 15 and suppress a sudden change in the impedance of the radiating element 27. Here, the radiating element 26 has a side 70 (first side) at the tip of the connecting portion 60 in the radiating element 26 and a side 90 (second side) facing the connecting portion 60 in the connecting portion 80 substantially parallel to each other. The side 90 forming the concave portion 27 is a straight line.

  Further, the connection portion 80 is provided with a feeding point Q2 to which the outer conductor S4 of the signal line Y is connected on the center line of the radiating element 27 and on the inner side of the side 90. The position of the feeding point Q2 is determined so that impedance matching between the radiating element 27 and the outer conductor S4 is achieved.

  The radiation part 81 (third radiation part) is a pattern extending from the connection part 80 toward the radiation part 61 side (+ x direction), and the radiation part 82 (fourth radiation part) is the radiation part 62 side ( This is a pattern extending from the connection portion 80 in the −x direction).

  The radiating portion 81 becomes wider as the interval W (first interval) between the radiating element 26 on the radiating portion 61 side and the radiating element 27 on the radiating portion 81 side approaches the tip end portion (the end portion in the + y direction) of the radiating portion 81. As it goes to the tip, it gets thinner.

  The radiating unit 82 is configured such that the interval (second interval) between the radiating element 26 on the radiating unit 62 side and the radiating element 27 on the radiating unit 82 side becomes wider as it goes toward the distal end (the end in the + y direction) of the radiating unit 82. It becomes thinner as it goes to the tip. In addition, the radiating portions 81 and 82 have a substantially fan shape. The side 73 of the radiating element 26 is bent substantially along a portion (curved portion) of the side 91 corresponding to the arc of the fan-shaped radiating portion 81. Similarly, the side 74 of the radiating element 26 is bent substantially along the side 92 corresponding to the arc of the fan-shaped radiating portion 82. Further, the side 73 extends from one end of the side 70 (the end in the + x direction) toward the long side in the + x direction of the antenna substrate 25, and the side 74 extends from the other end of the side 70 (the end in the −x direction). The antenna substrate 25 extends toward the long side in the −x direction.

  The radiating portion 83 (fifth radiating portion) is a pattern that extends in the + y direction from the distal end portion of the radiating portion 81 and narrows the interval W toward the distal end portion (end portion opposite to the radiating portion 81) of the radiating portion 83. (The radiation part 83 does not contact the radiation part 61). In addition, the width | variety of the front-end | tip part of the radiation | emission part 83 is narrower than the width | variety of the root (end part by the side of the radiation | emission part 81).

  Here, the details of the shape of the antenna 15 will be described. The shape of the antenna 15 is determined so that the current flowing through the radiating elements 26 and 27 (current of the antenna 15) resonates in a wide frequency band (for example, 5 GHz to 6 GHz). The resonance frequency of the current of the antenna 15 is determined based on the inductance according to the distance from the feeding points Q1 and Q2 and the capacitance according to the interval W between the radiating elements 26 and 27. Here, the interval between the sides 73 and 91 is drawn as the interval W between the radiating elements 26 and 27, but the interval between the sides 74 and 92 is also the same.

  The inductance due to the arbitrary position of the radiating elements 26 and 27 increases as the distance from the feeding points Q1 and Q2 increases. For this reason, in order to resonate the current of the antenna 15 in a wide frequency band, it is necessary to reduce the capacitance between the radiating elements 26 and 27 as the distance from the feeding points Q1 and Q2 increases. That is, the distance W between the radiating elements 21 and 22 needs to be increased as the distance from the feeding points Q1 and Q2 increases.

  For example, in this embodiment, when the power supply points Q1 and Q2 to the points C1 and C2 are inductances (effective lengths) corresponding to 6 GHz, the interval W between the points C1 and C2 is a capacitance value corresponding to 6 GHz. Thus, the shape of the radiation portion 81 (the degree of bending of a part of the side 91 (curved portion)) is determined. Similarly, when the points D1 and D2 correspond to an inductance of 5 GHz, the shape of the radiating portion 81 is determined so that the interval W between the points D1 and D2 has a capacitance value corresponding to 5 GHz. As described above, in the antenna 15, a part (curved portion) of the side 91 of the radiating portion 81 is gently curved, and the distance W between the radiating elements 26 and 27 is increased as the distance from the feeding point Q2 increases. Yes. The radiating unit 82 is the same as the radiating unit 81.

  By the way, in order to obtain good frequency characteristics in a band of 5 GHz to 6 GHz, it is preferable to provide a resonance point at a frequency lower than 5 GHz, for example, to stabilize the frequency characteristics at 5 GHz. Therefore, in the antenna 15, the radiating unit 83 is provided so that a resonance point is generated at a frequency lower than 5 GHz (for example, 3 GHz, 4 GHz).

  Specifically, in this embodiment, the radiation extending from the distal end portion of the radiating portion 81 so that a resonance point of 4 GHz is generated by the inductance determined by the points E1 and E2 and the capacitance determined by the interval W between the points E1 and E2. A portion 83 (pattern) is provided. Further, here, the shape of the radiating portion 83 extending from the radiating portion 81 is changed so that a resonance point of 3 GHz is generated by the inductance determined by the points F1 and F2 and the capacitance determined by the interval W between the points F1 and F2. Yes. Specifically, the width of the distal end portion of the radiating portion 83 is made narrower than the width of the root (end portion on the radiating portion 81 side), and the interval W between the points F1 and F2 is adjusted to set the resonance point of 3 GHz. Is generated. In FIG. 5, the lengths up to the points D1, E1, and F1 with respect to the point C1 are equal to the lengths up to the points D2, E2, and F2 with respect to the point C2. .

--- Simulation result of antenna 15 ---
FIG. 6 is a diagram illustrating the magnitude of a 5 GHz current flowing on the surface of the antenna 15. In FIG. 6, as in FIG. 2, the calculation result of the magnitude of the current of 5 GHz is represented by a pattern (color and hatching). Therefore, the pattern is the same where the same value of current flows. Here, as compared with the antenna 10 shown in FIG. 2, the antenna 15 has fewer hatched areas or darker areas as a whole, and less pattern unevenness. That is, as compared with the antenna 10, the antenna 15 has less variation in the value of the current flowing on the surface.

  FIG. 7 is a diagram illustrating the radiation characteristics of the antenna 15 in the yz plane. FIG. 7 shows radiation characteristics when the antenna 15 radiates radio waves having three different frequencies of 5 GHz, 5.5 GHz, and 6 GHz. The intensity of the radio wave from the antenna 15 is slightly reduced at 90 ° and 270 °, but is substantially constant at all angles. Therefore, compared with the radiation characteristic of the antenna 10 shown in FIG. 3, the antenna 15 has particularly improved radiation characteristics of 90 ° and 270 °, and has good radiation characteristics.

  FIG. 8 is a diagram showing the radiation gain and VSWR of the antenna 15. In FIG. 8, the radiation gain of the antenna 10 indicated by the dotted line is added to the radiation gain of the antenna 15 indicated by the solid line. Although the antenna 10 has a reduced radiation gain in the vicinity of 5.4 GHz, the antenna 15 has an improved radiation gain in the band of 5 to 6 GHz. Further, the value of VSWR of the antenna 15 is 2 or less in the band of 5 to 6 GHz.

---- Summary ---
The antenna 15 of this embodiment has been described above. Here, in the antenna 10, in order to increase the distance between the radiating elements 21 and 22 and increase the capacitance formed by the radiating elements 21 and 22, for example, the side 30 is extended, and the sides 36 and 37 and the side 30 are It needs to be separated greatly. However, in such a case, the areas of the radiating elements 21 and 22 are increased. On the other hand, in the antenna 15, radiating portions 81 and 82 are provided in the radiating element 27 corresponding to the radiating portions 61 and 62 that are divided into two forks of the radiating element 26. And the radiation | emission part 81,82 is carrying out the shape where the space | interval of each radiation | emission part 81,82 and the radiation | emission element 26 becomes wide gradually as it goes to a front-end | tip. Such an antenna 15 can have a smaller area than the antenna 10, for example. Furthermore, the antenna 15 can prevent a decrease in radiation gain while obtaining a good VSWR in a wide band.

  Further, a radiating portion 83 is formed from the radiating portion 81 of the antenna 15 to narrow the interval W between the radiating elements 26 and 27. Thereby, for example, a resonance point can be generated at a frequency (for example, 4 GHz) lower than a specification band (for example, 5 to 6 GHz). As a result, the antenna 15 can prevent a decrease in radiation gain in a wide band.

  Moreover, in the radiation | emission part 83, the width | variety of the front-end | tip part is narrower than the width | variety of the edge part by the side of the radiation | emission part 81. FIG. Thereby, for example, a resonance point can be generated at a considerably lower frequency (for example, 3 GHz) than a specification band (for example, 5 to 6 GHz). As a result, for example, as shown in FIG. 8, the antenna 15 can prevent a decrease in radiation gain in a wide band.

  The radiating element 26 is provided with a radiating portion 63 that extends from the end of the radiating portion 61 to the opposite side of the radiating element 27. Thereby, the impedance (the impedance of the pattern corresponding to the radiation parts 81 and 83) of the radiation element 26 can be increased. Therefore, by further forming such a pattern, a good VSWR can be obtained in a wide band.

  Further, in the antenna 15, the side 70 at the tip of the connection part 60 and the side 90 facing the connection part 60 are substantially parallel. For this reason, the antenna 15 can suppress a rapid change in impedance of the radiating elements 26 and 27.

  In this embodiment, the “tip portion” of the predetermined pattern is not only the first part of the predetermined pattern, but also from the first part of the predetermined pattern, for example, near the center of the shape of the predetermined pattern. A wide range including a part may be sufficient.

  In addition, the said Example is for making an understanding of this invention easy, and is not for limiting and interpreting this invention. The present invention can be changed and improved without departing from the gist thereof, and the present invention includes equivalents thereof.

  For example, when it is not necessary to generate a resonance point of 3 GHz with the antenna 15, the radiating unit 83 does not need to extend beyond the point E2.

  For example, the radiating unit 63 is used for adjusting the inductance when generating a resonance point at 4 GHz. However, when it is not necessary to generate a resonance point of 4 GHz, it is not necessary to provide the radiating unit 63.

10, 15 Antenna 20, 25 Antenna substrate 21, 22, 26, 27 Radiating element 30, 35-37, 70-74, 90-92 Side 40 Convex part 60, 80 Connection part 61-63, 80-83 Radiation part 100 Location 200, 210, 220 Region P1, P2, Q1, Q2 Feeding point

Claims (5)

A first radiating element having a first connecting portion to which the inner conductor of a signal line including an inner conductor and an outer conductor is connected, and first and second radiating portions extending in a bifurcated manner from the first connecting portion;
A second connecting portion to which the outer conductor is connected; a third radiating portion formed on the first radiating portion side; and extending from the second connecting portion; and formed on the second radiating portion side; A second radiating element having a fourth radiating portion extending from the portion;
With
The third radiating portion has a shape in which a first interval between the first radiating element on the first radiating portion side and the second radiating element on the third radiating portion side becomes wider toward the distal end portion,
The fourth radiating portion has a shape in which a second interval between the first radiating element on the second radiating portion side and the second radiating element on the fourth radiating portion side becomes wider toward the distal end portion. ,
Dipole antenna characterized by. The dipole antenna according to claim 1,
The second radiating element further includes a fifth radiating portion extending from a tip portion of the third radiating portion and narrowing the first interval in the extending direction;
Dipole antenna characterized by. The dipole antenna according to claim 2,
The fifth radiating portion has a shape in which the width of the tip portion is narrower than the width of the end portion on the third radiating portion side,
Dipole antenna characterized by. The dipole antenna according to any one of claims 1 to 3,
A sixth radiating portion extending from the end of the first radiating portion to the opposite side of the second radiating element;
Dipole antenna characterized by. The dipole antenna according to any one of claims 1 to 4,
A first side facing the second connection part in the first connection part and a second side facing the first connection part in the second connection part are substantially parallel;
Dipole antenna characterized by.