JP2013175895A - Antenna - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an antenna resonating in two frequency bands and sufficiently restraining a directivity deviation in a horizontal plane.SOLUTION: The antenna comprises: a long plate-like dielectric substrate; dipole antennas formed on top and rear surfaces of the dielectric substrate; two long plate-like first frequency band passive elements, each of which is isolated from the dielectric substrate in a direction orthogonal to a dielectric substrate surface and disposed on the top and rear surface sides of the dielectric substrate along a longitudinal direction thereof; and four long plate-like second frequency band passive elements, two pairs of which are isolated from the dielectric substrate and the first frequency band passive element and disposed on the top and rear surface sides of the dielectric substrate along the longitudinal direction thereof between the dielectric substrate and the first frequency band passive element, the adjacent second frequency band passive element being spaced from each other. The first and second frequency band passive elements and the dipole antennas are arranged so that respective electric center points are at the same height, and the adjacent second frequency band passive elements are short-circuited.

Description

  The present invention relates to an antenna, for example, an antenna used for a mobile communication base station and the like.

  Base station antennas used for mobile communications are installed on independent concrete pillars, steel pillars, building rooftops, steel towers, and the like. In order to secure a mobile communication area without holes, it is important to secure an appropriate installation location of the base station antenna. In residential areas, base station antennas are often installed on concrete or steel pillars. Therefore, in a residential area or the like, a rod-shaped omnidirectional antenna in a horizontal plane that can be installed on these independent concrete pillars and iron pillars is often used.

  On the other hand, recent mobile communication secures transmission capacity by providing communication services using a plurality of frequency bands. Therefore, in order to add support for base station antennas already installed on concrete and steel pillars to new frequencies, considering the limitations on installation location and installation space, etc., multiband with the same shape as conventional rod antennas installed It is desirable to realize

The antenna of Patent Document 1 will be described with reference to FIGS. 1, 2, 3, and 4. FIG. 1 is a perspective view and a cross-sectional view of an antenna 900 disclosed in Patent Document 1. FIG. 2 is a front view and a rear view of the antenna 900 of Patent Document 1. FIG. 3 is a graph showing the return loss characteristics of the antenna 900 of Patent Document 1. FIG. 4 is a graph showing the radiation directivity in the horizontal plane of the antenna 900 of Patent Document 1. In the antenna 900 described below, the size and positional relationship of members are finely adjusted for comparison under the same conditions as the antenna of the present invention described later. As shown in FIGS. 1 and 2, the antenna 900 of Patent Document 1 is a dielectric substrate 2 that is a thin rectangular substrate (thickness 0.01λ _2G , λ _2G is a wavelength of 2 GHz) having a relative dielectric constant of about 3.4. It has. Copper foil is bonded to the front and back surfaces of the dielectric substrate 2, and the copper foil is processed by a photo etching method or the like to form a half as a radiating element as described below on the dielectric substrate 2. Wavelength dipole antenna elements 3a and 3b and a feeding circuit (microstrip line 6, parallel two-wire lines 5a and 5b, and ground plane 8) are formed.

The half-wave dipole antenna has a total length of 0.46λ _2G and a width of 0.03λ _2G , and is formed with a length of 0.23λ _2G on the front and back surfaces of the dielectric substrate 2, respectively. Specifically, half-wave dipole antenna, a pair of half-wave dipole antenna elements 3a length respectively 0.23Ramuda _2G, consists 3b, the one half-wave dipole antenna element 3a of the width direction of the dielectric substrate 2 It is arranged along the vertical direction at one edge of the surface of the dielectric substrate 2 so as to be substantially in contact with one end, and the other half-wave dipole antenna element 3b is substantially in contact with one end in the width direction of the dielectric substrate 2. The dielectric substrate 2 is arranged along the vertical direction at one end edge of the back surface of the dielectric substrate 2. The upper end portion of the half-wavelength dipole antenna element 3a and the lower end portion of the half-wavelength dipole antenna element 3b are disposed at positions facing each other, and the facing position is the electrical center point of the half-wavelength dipole antenna.

  The half-wave dipole antenna elements 3a and 3b constituting the half-wave dipole antenna are connected to parallel two-wire lines 5a and 5b formed on the front and back surfaces of the dielectric substrate 2, respectively. Reference numerals 5 a and 5 b are connected to the microstrip line 6 in the vicinity of the center of the width of the dielectric substrate 2. The microstrip line 6 is connected to the power feeding cable 7 via a connector (not shown) serving as an input / output terminal of the antenna 900.

On the other hand, the ground surface 8 of the microstrip line 6 is formed on the back surface of the above-described dielectric substrate 2 in the half portion opposite to the one end edge on the side where the half-wavelength dipole antenna is disposed. The ground plane 8 has its width is 0.06 _2G, are formed so as to further extend upward and downward from upper and lower ends of the half-wave dipole antenna (both end portions of the radiating element).

Furthermore, the antenna 900 of this example includes a pair of first frequency band parasitic elements (non-excited elements) 9a and 9b. These first frequency band parasitic elements 9a and 9b are elements composed of a metal plate having a total length of 0.39λ _2G and a width of 0.03λ _2G , and are near the center position of the lateral width of the dielectric substrate 2 A half-wave dipole antenna at a location separated from the front and back surfaces of the dielectric substrate 2 by 0.05λ _3.5G + 0.01λ _2G (λ _3.5G is a wavelength of 3.5 GHz). 1 each on the front side and the back side of the dielectric substrate 2 so that the electrical center point of the first frequency band parasitic elements 9a and 9b are at the same height. Has been placed. Further, the width direction centers of the first frequency band parasitic elements 9a and 9b and the width direction center of the dielectric substrate 2 are arranged so as to coincide with each other in the x direction described later. The first frequency band parasitic elements 9a and 9b are fixed to the dielectric substrate 2 by an insulator (not shown) such as plastic.

  When the antenna 900 of Patent Document 1 is used outdoors, it is desirable to house it in a cover made of glass reinforced plastic or the like for protection from wind and rain and reduction of wind pressure load. As shown in FIG. 4, the antenna can be accommodated in the dielectric radome 20, and by designing in this way, an antenna structure having a small antenna outer diameter and a small wind pressure load when the antenna is installed can be obtained.

  The xyz axis is shown in the vicinity of the cross-sectional view (c) in FIG. 1, the front view (a), and the back view (b) in FIG. Facing the surface of the dielectric substrate 2 is the x-axis positive direction on the right side, facing the surface of the dielectric substrate 2 is the y-axis positive direction, and the direction perpendicular to the surface of the dielectric substrate 2 is the z-axis positive direction The direction is commonly used below. In FIG. 1 and FIG. 2, the xyz axis is shifted and displayed, but the origin of the axis is a diagonal intersection of the dielectric substrate 2.

  The operation principle of the antenna 900 of Patent Document 1 is as follows. That is, a non-directional radio wave in a horizontal plane is radiated from the half-wave dipole antenna as a radiating element, but the ground plane 8 of the microstrip line 6 in the vicinity acts as a reflector for the half-wave dipole antenna. For this reason, the emission of radio waves in the direction in which the ground plane 8 of the microstrip line 6 exists is weakened and is not omnidirectional in the horizontal plane. However, in the antenna 900 of Patent Document 1, since the first frequency band parasitic elements 9a and 9b are arranged at predetermined positions, radio waves are guided to the first frequency band parasitic elements 9a and 9b. As a result, the radio wave radiation level in the direction of the ground plane 8 of the microstrip line 6 is prevented from being lowered, so that it operates as an omnidirectional antenna in a horizontal plane.

FIG. 3 is a graph showing the return loss (S ₁₁ ) characteristics of the antenna 900 as the vertical axis S parameter [dB] and the horizontal axis as the frequency [GHz]. As shown in FIG. 3, it can be seen that the antenna 900 of Patent Document 1 resonates in the approximately 2 GHz band. FIG. 4A is a graph showing the relationship between the radiation directivity [dB] in the horizontal plane (zx plane) of the antenna 900 and the angle θ in the horizontal plane in the polar coordinate system (display format 1). FIG. 4B is a graph showing the relationship between the radiation directivity [dB] in the horizontal plane (zx plane) of the antenna 900 and the angle θ in the horizontal plane in an orthogonal coordinate system (display format 2). As shown in FIG. 4, the antenna 900 has almost the same radiation directivity in all directions in the horizontal plane (z-x plane) at the measurement frequencies of 1.95 GHz and 2.14 GHz, and the omnidirectional characteristic is Has been obtained. The difference between the maximum value and the minimum value of the radiation directivity in all directions is referred to as a horizontal plane directivity deviation. The lower the horizontal plane directivity deviation value, the closer the antenna radiation directivity approaches to a perfect circle. The lower the directional deviation value in the horizontal plane, the higher the possibility that it can be used as an omnidirectional antenna in the horizontal plane. As shown in FIG. 4, the horizontal plane directivity deviation at the measurement frequencies of 1.95 GHz and 2.14 GHz of the antenna of Patent Document 1 is 3.2 dB, which is a characteristic that satisfies the requirements of the horizontal plane omnidirectional antenna. .

Japanese Patent No. 4155359

  However, the antenna 900 of Patent Document 1 cannot be used as a multiband antenna that radiates radio waves of two or more frequencies as it is. Even if the antenna 900 of Patent Document 1 is improved so that it can be used in a plurality of frequency bands, the directional deviation in the horizontal plane of the improved antenna deteriorates in any frequency band, and the horizontal plane omnidirectional There is a possibility that it cannot be used as a sex antenna. In addition, from the viewpoint of ease of installation with respect to the existing antenna, it is desirable to realize the multi-band base station antenna without changing the antenna diameter. Accordingly, an object of the present invention is to provide an antenna that resonates in two frequency bands and can sufficiently suppress horizontal plane directivity deviation in each band.

  The antenna of the present invention is a long-plate-shaped dielectric substrate, a dipole antenna formed on the front and back surfaces of the dielectric substrate, and formed on the front and back surfaces of the dielectric substrate, and supplies power to the dipole antenna. A feeding circuit to be supplied, two long plate-shaped first frequency band parasitic elements, and four long plate-shaped second frequency band parasitic elements are provided.

  The first frequency band parasitic element is arranged on the front surface side and the back surface side of the dielectric substrate one by one along the longitudinal direction of the dielectric substrate and spaced apart from the dielectric substrate in a direction perpendicular to the dielectric substrate surface. The two second frequency band parasitic elements are adjacent to each other between the dielectric substrate and the first frequency band parasitic element without passing through the dielectric substrate. The second frequency band parasitic elements are separated from each other, separated from the dielectric substrate in a direction perpendicular to the dielectric substrate surface along the longitudinal direction of the dielectric substrate, and orthogonal to the first frequency band parasitic element surface. The first and second frequency band parasitic elements and the dipole antenna are arranged so that their electrical center points are at the same height. The second frequency band parasitic element adjacent to each other without a dielectric substrate Characterized in that each other is short-circuited.

  According to the antenna of the present invention, resonance occurs in two frequency bands, and the horizontal plane directivity deviation in each band can be sufficiently suppressed.

The perspective view and sectional drawing of the antenna of patent document 1. FIG. The front view and back view of the antenna of patent document 1. FIG. The graph which shows the return loss characteristic of the antenna of patent document 1. FIG. The graph which shows the radiation directivity in the horizontal surface of the antenna of patent document 1. FIG. The perspective view and sectional drawing of the antenna of a comparative reference example. The front view and back view of the antenna of a comparative reference example. The graph which shows the return loss characteristic of the antenna of a comparative reference example. The graph which shows the radiation directivity in the horizontal surface of the antenna of a comparative reference example. FIG. 3 is a perspective view and a cross-sectional view of the antenna according to the first embodiment. The front view and back surface figure of the antenna of Example 1. FIG. 3 is a graph showing the return loss characteristics of the antenna of Example 1. 3 is a graph showing the radiation directivity in the horizontal plane of the antenna of Example 1. FIG. FIG. 6 is a front view of the antenna according to the second embodiment. 6 is a graph showing the return loss characteristics of the antenna of Example 2. The graph which shows the radiation directivity in the horizontal surface of the antenna of Example 2. FIG. The figure which shows the surface current measurement position in the antenna of a comparative reference example and Example 2. FIG. The graph which shows the surface current measurement result in the antenna of a comparative reference example and Example 2. FIG. The graph which shows the directivity deviation in a horizontal surface at the time of changing the parameter regarding the distance between 2nd frequency band parasitic elements and a short circuit position. The perspective view and sectional drawing of the antenna of Example 3. FIG. The front view and back surface figure of the antenna of Example 3. 10 is a graph showing the radiation directivity in the horizontal plane of the antenna of Example 3.

  Hereinafter, embodiments of the present invention will be described in detail. In addition, the same number is attached | subjected to the structure part which has the same function, and duplication description is abbreviate | omitted. In addition, the dipole antenna described in the following comparative reference examples and examples may be specifically a half-wave dipole antenna.

<Comparative reference example>
The antenna of the comparative reference example will be described with reference to FIGS. 5, 6, 7, and 8. FIG. 5 is a perspective view and a cross-sectional view of an antenna 800 of this comparative reference example. FIG. 6 is a front view and a back view of the antenna 800 of this comparative reference example. FIG. 7 is a graph showing the return loss characteristics of the antenna 800 of this comparative reference example. FIG. 8 is a graph showing the radiation directivity in the horizontal plane of the antenna 800 of this comparative reference example. The antenna 800 of this comparative reference example includes two long-plate-shaped second frequency band parasitic elements 11 a between the first frequency band parasitic element 9 a of the antenna 900 of Patent Document 1 and the surface of the dielectric substrate 2. , 12a, and two long frequency band parasitic elements 11b and 12b having a long plate shape are disposed between the first frequency band parasitic element 9b and the back surface of the dielectric substrate 2. Specifically, the second frequency band parasitic elements 11 a and 12 a are separated from each other between the surface of the dielectric substrate 2 and the first frequency band parasitic element 9 a, and along the longitudinal direction of the dielectric substrate 2. Thus, it is separated from the dielectric substrate 2 in a direction perpendicular to the surface of the dielectric substrate, and is separated from the first frequency band parasitic element 9a in a direction perpendicular to the first frequency band parasitic element surface. Similarly, the second frequency band parasitic elements 11b and 12b are separated from each other between the back surface of the dielectric substrate 2 and the first frequency band parasitic element 9b, and along the longitudinal direction of the dielectric substrate 2, It is separated from the dielectric substrate 2 in a direction perpendicular to the surface of the dielectric substrate, and is separated from the first frequency band parasitic element 9b in a direction perpendicular to the surface of the first frequency band parasitic element. The electrical center point of the dipole antenna formed on the dielectric substrate 2 and the heights of the electrical center points of the first frequency band parasitic elements 9a and 9b and the second frequency band parasitic elements 11a, 12a, 11b and 12b. It arrange | positions so that height (y direction) may become the same height position. Further, the diagonal intersection of the dielectric substrate 2, the diagonal intersection of the first frequency band parasitic elements 9a and 9b, the midpoint of the inner long end side of the second frequency band parasitic element 11a, and the second frequency band parasitic element 12a. The midpoint of the line connecting the midpoint of the inner long end side, the midpoint of the inner long end side of the second frequency band parasitic element 11b, and the midpoint of the inner long end side of the second frequency band parasitic element 12b Is located on the same axis perpendicular to the dielectric substrate 2 (indicated by a dashed line in FIG. 5).

In another expression, the antenna 800 of this comparative reference example has one long-plate-shaped dielectric substrate 2 and two long-plate-shaped first frequency band parasitics so that the longitudinal directions are approximately the same. Elements 9a, 9b, and four long plate-shaped second frequency band parasitic elements 11a, 12a, 11b, 12b are arranged. On the surface side of the dielectric substrate 2, a first frequency band parasitic element 9a and second frequency band parasitic elements 11a and 12a are arranged. On the back side of the dielectric substrate 2, a first frequency band parasitic element 9b and second frequency band parasitic elements 11b and 12b are arranged. The dielectric substrate and the parasitic element are arranged so that the plate surfaces face each other. The second frequency band parasitic elements 11a and 12a are arranged apart from each other in a plane located between the plane on which the first frequency band parasitic element 9a is disposed and the plane formed by the surface of the dielectric substrate 2. Yes. Similarly, the second frequency band parasitic elements 11b and 12b are separated from each other in a plane located between the plane on which the first frequency band parasitic element 9b is disposed and the plane formed by the back surface of the dielectric substrate 2. Has been placed. The total lengths of the second frequency band parasitic elements 11a, 12a, 11b, and 12b in the longitudinal direction are all 0.44λ _3.5G . Note that the first frequency band parasitic element 9a, the distance between the second frequency band parasitic element 11a, 12a is arranged plane is 0.01λ _2G. Similarly, the first frequency band parasitic element 9b, the distance between the second frequency band parasitic element 11b, 12b are arranged plane is 0.01λ _2G. Since the positional relationship between the dielectric substrate 2 and the first frequency parasitic element 9a is the same as that of the antenna 900 described above, the plane on which the second frequency band parasitic elements 11a and 12a are disposed, and the dielectric substrate 2 The distance from the plane formed by the surface is 0.05λ _3.5G . Similarly, the distance between the plane on which the second frequency band parasitic elements 11b and 12b are arranged and the plane formed by the back surface of the dielectric substrate 2 is 0.05λ _3.5G . The distance between the diagonal intersections of the adjacent second frequency band parasitic elements (11a and 12a, 11b and 12b) (hereinafter referred to as distance) is 0.14λ _3.5G . Further, in this comparative example and examples described later, the first frequency band means the 2 GHz band, and the second frequency band means the 3.5 GHz band.

  It can be seen that the antenna 800 of this comparative reference example formed in this way resonates in approximately 2 GHz band and 3.5 GHz band as shown in the graph showing the return loss characteristics of FIG. Further, from the graph showing the radiation directivity in the horizontal plane (z-x plane) in FIG. 8, in the 1.95 GHz band and the 2.14 GHz band, radiation at substantially the same level in a 360 ° range in the horizontal plane (z-x plane). It turns out that it is directivity. In the 1.95 GHz band and the 2.14 GHz band, the directional deviation in the horizontal plane is as low as about 3 dB. Therefore, it can be seen that the 2 GHz band operates as an omnidirectional antenna in the horizontal plane. On the other hand, it can be seen that the antenna 800 of this comparative reference example deteriorates with a directivity deviation in the horizontal plane of 10 dB in the 3.5 GHz band.

  It should be noted that the dielectric substrate 2 in this comparative reference example and all examples described later, and half-wave dipole antenna elements 3a and 3b, parallel two-line lines 5a and 5b, and microstrip lines formed on the dielectric substrate 2 6, the power feeding cable 7, and the ground plane 8 are present in the same dimensions and in the same positions as the members having the same reference numerals in the antenna 900 of Patent Document 1. This is clear from the fact that common symbols are used in the prior art, comparative reference examples, and examples described later, but the dimensions and arrangement of these members will be described again.

  Copper foil is adhered to the front and back surfaces of the dielectric substrate 2 of this comparative reference example, and the copper foil is processed by a photo etching method or the like to emit radiation as described below on the dielectric substrate 2. Half-wave dipole antenna elements 3a and 3b as elements and a feeding circuit (microstrip line 6, parallel two-wire lines 5a and 5b, and ground plane 8) are formed.

The half-wave dipole antenna has a total length of 0.46λ _2G and a width of 0.03λ _2G , and is formed with a length of 0.23λ _2G on the front and back surfaces of the dielectric substrate 2, respectively. Specifically, half-wave dipole antenna, a pair of half-wave dipole antenna elements 3a length respectively 0.23Ramuda _2G, consists 3b, the one half-wave dipole antenna element 3a of the width direction of the dielectric substrate 2 It is arranged along the vertical direction at one edge of the surface of the dielectric substrate 2 so as to be substantially in contact with one end, and the other half-wave dipole antenna element 3b is substantially in contact with one end in the width direction of the dielectric substrate 2. The dielectric substrate 2 is arranged along the vertical direction at one end edge of the back surface of the dielectric substrate 2. The upper end portion of the half-wavelength dipole antenna element 3a and the lower end portion of the half-wavelength dipole antenna element 3b are disposed at positions facing each other, and the facing position is the electrical center point of the half-wavelength dipole antenna.

  The half-wave dipole antenna elements 3a and 3b constituting the half-wave dipole antenna are connected to parallel two-wire lines 5a and 5b formed on the front and back surfaces of the dielectric substrate 2, respectively. Reference numerals 5 a and 5 b are connected to the microstrip line 6 in the vicinity of the center of the width of the dielectric substrate 2. The microstrip line 6 is connected to the power feeding cable 7 via a connector (not shown) serving as an input / output terminal of the antenna 800.

On the other hand, the ground surface 8 of the microstrip line 6 is formed on the back surface of the above-described dielectric substrate 2 in the half portion opposite to the one end edge on the side where the half-wavelength dipole antenna is disposed. The ground plane 8 has its width is 0.06 _2G, are formed so as to further extend upward and downward from upper and lower ends of the half-wave dipole antenna (both end portions of the radiating element)

  The antenna 100 according to the first embodiment in which the antenna 800 according to the comparative reference example is further improved will be described in detail with reference to FIGS. 9, 10, 11, and 12. FIG. 9 is a perspective view and a sectional view of the antenna 100 of the present embodiment. FIG. 10 is a front view and a back view of the antenna 100 of the present embodiment. FIG. 11 is a graph showing the return loss characteristics of the antenna 100 of this embodiment. FIG. 12 is a graph showing the radiation directivity in the horizontal plane of the antenna 100 of the present embodiment.

The antenna 100 of this embodiment includes a dielectric substrate 2, half-wavelength dipole antenna elements 3a and 3b formed on the dielectric substrate 2, parallel two-wire lines 5a and 5b, a microstrip line 6, a feed cable 7, a dielectric Ground plane 8 formed on body substrate 2, two first frequency parasitic elements 9a, 9b, four second frequency band parasitic elements 11a, 12a, 11b, 12b, and two short-circuit lines 13a and 13b. The positional relationship, arrangement interval, and size of these dielectric substrates and parasitic elements are all the same as those of the above-described prior art antenna 900 and comparative reference example antenna 800. That is, the longitudinal length of the half-wave dipole antenna elements 3a and 3b constituting the half-wave dipole antenna is 0.23λ _2G , and the total length of the half-wave dipole antenna including the front and back surfaces is 0.46λ _2G . The width is 0.03λ _2G . The total length of the first frequency band parasitic elements 9a and 9b in the longitudinal direction is 0.39λ _2G and the width is 0.03λ _2G . The total length of the second frequency band parasitic element in the longitudinal direction is 0.44λ _3.5G , and the width is 0.04λ _3.5G . The distance between adjacent second frequency band parasitic elements (11a and 12a, 11b and 12b) is 0.14λ _3.5G . The distance (h ₁ ) between the plane where the second frequency band parasitic elements 11a, 12a (11b, 12b) are arranged and the plane formed by the front surface (back surface) of the dielectric substrate 2 is 0.05λ _3.5G. It is. The distance (h ₂ ) between the first frequency band parasitic element 9a (9b) and the plane on which the second frequency band parasitic elements 11a, 12a (11b, 12b) are arranged is 0.01λ _2G . The thickness of the dielectric substrate 2 (t) is 0.01λ _2G. The dielectric substrate and the parasitic element are arranged so that the plate surfaces face each other so that the longitudinal directions are approximately the same, and the electrical center point in the longitudinal direction (y direction) of the parasitic element and the dipole antenna is the same height. It has become. Further, the diagonal intersection of the dielectric substrate 2, the diagonal intersection of the first frequency band parasitic elements 9a and 9b, the midpoint of the short circuit 13a, and the midpoint of the short circuit 13b are on the same axis orthogonal to the dielectric substrate 2 (see FIG. 5).

  On the premise of the above, the antenna 100 of the present embodiment further short-circuits the substantially middle points of the inner side edges of the adjacent second frequency band parasitic elements 11a and 12a by the short-circuit line 13a. Similarly, the substantially middle points of the inner side edges of the adjacent second frequency band parasitic elements 11b and 12b are short-circuited by the short-circuit line 13b. The antenna 100 of this embodiment configured as described above resonates in each of the 2 GHz band and the 3.5 GHz band as shown in FIG. 11, and is the same as the antenna 800 of the comparative reference example. Also, as shown in FIG. 12, the directivity deviation in the horizontal plane (z-x plane) in the 3.5 GHz band of the antenna 100 of this example is 6.2 dB, and the antenna 800 of the comparative reference example in the 3.5 GHz band. It can be seen that the improvement is more than 10 dB which is the directivity deviation in the horizontal plane (z-x plane).

  Therefore, according to the antenna 100 of the present embodiment, the antenna diameter is increased by short-circuiting the substantially midpoints of the inner end sides of the adjacent second frequency band parasitic elements (11a and 12a, 11b and 12b). Therefore, it is possible to realize an antenna that is simple in structure and easy to manufacture, resonates in two frequency bands (2 GHz and 3.5 GHz), and suppresses directivity deviation in the horizontal plane.

  The antenna 200 according to the second embodiment, which is a further improvement of the antenna 100 according to the first embodiment, will be described in detail with reference to FIGS. 13, 14, and 15. FIG. 13 is a surface view of the antenna 200 of this embodiment. FIG. 14 is a graph showing the return loss characteristics of the antenna 200 of this embodiment. FIG. 15 is a graph showing the radiation directivity in the horizontal plane of the antenna 200 of the present embodiment.

The antenna 200 according to the present embodiment includes a dielectric substrate 2, half-wave dipole antenna elements 3a and 3b formed on the dielectric substrate 2, parallel two-wire lines 5a and 5b, a microstrip line 6, a feeding cable 7, a dielectric Ground plane 8 formed on body substrate 2, two first frequency parasitic elements 9a, 9b, four second frequency band parasitic elements 11a, 12a, 11b, 12b, and two short-circuit lines 13a and 13b. As shown in FIG. 13, the difference between the antenna 100 of the first embodiment and the antenna 200 of the present embodiment is that the second frequency band parasitic elements are connected to each other from the midpoint of the inner edge of the second frequency band parasitic element. It is only a point that is short-circuited at a position slightly shifted in the y-axis direction. Hereinafter, the distance between the short-circuit position (short-circuit line short-end side midpoint) of the inner side edge of the second frequency band parasitic element and the inner side edge center of the second frequency band parasitic element is referred to as offset_short. The offset_short takes a positive value when it is provided in the y-axis positive direction, and takes a negative value when provided in the y-axis negative direction. In this embodiment, offset_short is + 0.01λ _3.5G .

  The antenna 200 of the present embodiment configured as described above resonates in each of the 2 GHz band and the 3.5 GHz band as shown in FIG. 14, and is the same as the antenna 800 of the comparative reference example and the antenna 100 of the first embodiment. . As shown in FIG. 15, the antenna 200 of this example has a directivity deviation in the horizontal plane (z-x plane) in the 3.5 GHz band of 3.9 dB. The antenna 800 of the comparative reference example and the antenna of the first example It can be seen that this is improved from 10 dB and 6.2 dB which are directivity deviations in the horizontal plane (z-x plane) in the 3.5 GHz band at 100.

  Therefore, according to the antenna 200 of the present embodiment, a short circuit occurs at a position slightly shifted in the y-axis direction from the midpoint of the inner end sides of the adjacent second frequency band parasitic elements (11a and 12a, 11b and 12b). Thus, an antenna that is simple in structure and easy to manufacture, resonates in two frequency bands (2 GHz, 3.5 GHz), and suppresses a directivity deviation in a horizontal plane can be realized without increasing the antenna diameter. .

<Consideration for improvement of directivity deviation in horizontal plane>
Hereinafter, with reference to FIG. 16 and FIG. 17, the reason why the horizontal plane directivity deviation is improved in the second frequency band in the antenna of the present invention will be considered. FIG. 16 is a diagram showing a surface current measurement position in the antenna of the comparative reference example and Example 2. FIG. 17 is a graph showing the results of surface current measurement in the antennas of the comparative reference example and example 2. 16A is a comparative reference example, and FIG. 16B is a surface current measurement position of Example 2. FIG. FIG. 17A shows a comparative reference example, and FIG. 17B shows a surface current measurement result of Example 2. FIG.

  The radiation directivity in the horizontal plane of the second frequency band in the antenna of the present invention is mainly composed of an H-shaped parasitic element that resonates in the second frequency band (adjacent second frequency band parasitic element and a short-circuit line). It is determined by the current flowing on the surface of the member. The reason for the effect of suppressing the directional deviation in the horizontal plane by the H-shaped parasitic element of the second embodiment is described below with respect to the second frequency band parasitic element and the surface of the H-shaped parasitic element of the second embodiment. A description will be given using the current flowing through. As shown by the thick arrows in FIG. 16, the current distribution in the vicinity of the outer edge of the second frequency band parasitic element (the current value has a positive value in the y-axis positive direction) is observed. In the antenna 800 of the comparative reference example and the antenna 100 of the second embodiment, the current distribution at the same position is observed. As shown in FIG. 16, the current distribution on the outer edge of the second frequency band parasitic element 12a is # 1, the current distribution of the outer edge of the second frequency band parasitic element 11a is # 2, the current distribution of the outer edge of the second frequency band parasitic element 12b is # 3, and the current distribution of the second frequency band parasitic element 11b The current distribution on the outer edge will be referred to as # 4.

  In the graph of FIG. 17, the horizontal axis is the observation position Y of the current on the parasitic element for frequency f2 in the y direction (mm, the midpoint of the parasitic element edge is the origin, and the positive y axis direction is a positive value). The vertical axis represents the observed current intensity [A / m]. From FIG. 17A, it can be seen that an extremely strong current flows in # 2 of the comparative reference example as compared with the measurement results at other positions. As the reason, since the ground plane 8 exists in the vicinity of # 2 through the dielectric substrate 2, it can be considered that this functions as a reflector. It can also be seen that the currents at # 3 and # 4 located on the back side of the dielectric substrate are weaker than those at # 1 and # 2 on the front side of the dielectric substrate. In this way, the current flowing on the surface of the four parasitic elements is extremely non-uniform, which may lead to a result that the directivity deviation tends to be large, for example, the radiation directivity in the horizontal plane is strongly emitted in a certain direction. .

  On the other hand, in Example 2, since the H-shaped parasitic element having a structure in which two second frequency band parasitic elements in the same plane are short-circuited is used, the difference in current intensity between the parasitic elements can be reduced. It is expected. As can be seen from FIG. 17 (b), by adopting the configuration of Example 2, the extremely strong current of # 2 is suppressed to about half, and the weak currents of # 3 and # 4 are about twice that of the prior art. Increased to the extent. It is considered that the directivity deviation was reduced by equalizing the surface currents of the four parasitic elements that determine the radiation directivity in the horizontal plane.

<Considerations on shape parameters>
As described above, the H-shaped parasitic element in the antenna of the present invention results in different directivity deviations in the horizontal plane of the antenna depending on the element shape parameter. Specifically, as the shape parameter of the parasitic element that affects the directivity deviation in the horizontal plane, the distance h _{1 of} the H-shaped parasitic element from the dielectric substrate 2, the second frequency band parasitic of the H-shaped parasitic element Examples of the distance between the elements include offset_short which is the distance between the short-circuit position of the inner edge of the second frequency band parasitic element of the H-shaped parasitic element and the midpoint of the inner edge.

Hereinafter, with reference to FIG. 18, a description will be given of the measurement result of the directivity deviation in the horizontal plane when only the shape parameters distance and offset_short are different in the antenna 200 of the second embodiment. FIG. 18 is a graph showing the horizontal plane directivity deviation when the parameters regarding the distance between the second frequency band parasitic elements and the short-circuit position are changed. The vertical axis of the graph in FIG. 18 is the horizontal plane directivity deviation [dB] in the second frequency band (3.5 GHz band). The smaller the directivity deviation, the higher the roundness, and the horizontal plane non-directional antenna. The performance of will improve. The horizontal axis represents distance [mm]. Further, offset_short is displayed as -2, -1, 0, +1, +2 [mm] for each legend. As shown in FIG. 18, any parameter affects the directivity deviation. In particular, the distance 12 [mm] or more 14 [mm] or less in the case of the (≒ 0.140 × λ 0.163 × λ 3.5G inclusive _3.5G), second frequency band parasitic to offset_short 0 Rather than short-circuiting at the center position of the inner edge of the element, offset_short is slightly within the range of −2 mm to +2 mm excluding 0 (≈−0.0233 × λ _{3.5G to} + 0.0233 × λ _3.5G ) It can be seen that the directivity deviation is improved by short-circuiting at the shifted position. Further, when the distance is set to 14 [mm] or more and 16 [mm] or less (≈0.163 × λ _{3.5 G} or more and 0.187 × λ _{3.5 G} or less), the offset_short is set to −2 [mm] (−0 .0233 × λ _3.5G ), +1 [mm] (+ 0.0117 × λ _3.5G ), +2 [mm] (+ 0.0233 × λ _3.5G ) It can be seen that the directivity deviation is improved compared to short-circuiting at the center position.

  In addition, the long dashed line (black circle symbol) in the figure indicates the directivity deviation when the distance is changed in the comparative reference example. Within the range of distance 9.0 [mm] to 15.0 [mm], the condition in which the second frequency band parasitic elements are short-circuited regardless of the value of offset_short is not short-circuited (comparative reference example). It can be seen that the directivity deviation is smaller than that. In the case of distance 16.0 [mm], the second frequency band parasitic elements are short-circuited in many offset_short conditions (-2 [mm], +1 [mm], and +2 [mm]). It can be seen that the directivity deviation is smaller in comparison with the condition that does not cause a short circuit (comparative reference example).

Next, the antenna of the third embodiment, in which a part of the configuration of the second embodiment is omitted, will be described with reference to FIG. 19, FIG. 20, and FIG. FIG. 19 is a perspective view and a cross-sectional view of the antenna 300 of this embodiment. FIG. 20 is a front view and a back view of the antenna 300 of this embodiment. FIG. 21 is a graph showing the radiation directivity in the horizontal plane of the antenna 300 of this example.
As shown in FIG. 21, it can be seen that the directivity deviation in the horizontal plane is suppressed to within 5.5 dB in the frequency band 2.14 GHz to 3.80 GHz.

  Therefore, according to the antenna 300 of the third embodiment, by omitting the first frequency band parasitic element and forming the H-shaped parasitic element by the second frequency band parasitic element and the short-circuit line, the antenna diameter can be reduced. Without increasing the size, it is possible to realize an antenna that is simple in structure and easy to manufacture, resonates in two frequency bands (2 GHz, 3.5 GHz), and suppresses a directivity deviation in a horizontal plane.

Claims (5)

A long-plate-shaped dielectric substrate;
A dipole antenna formed on the front surface and the back surface of the dielectric substrate;
A feeding circuit that is formed on the front surface and the back surface of the dielectric substrate and supplies power to the dipole antenna;
Two long plate-shaped first frequency band parasitic elements;
Four long plate-shaped second frequency band parasitic elements,
The first frequency band parasitic element is provided on the dielectric substrate in a direction perpendicular to the dielectric substrate surface along the longitudinal direction of the dielectric substrate, one on each of the front surface side and the back surface side of the dielectric substrate. And spaced apart,
Two second frequency band parasitic elements are provided between the dielectric substrate and the first frequency band parasitic element, two on each of the front side and the back side of the dielectric substrate. The second frequency band parasitic elements adjacent to each other are separated from each other, separated from the dielectric substrate in a direction perpendicular to the dielectric substrate surface along the longitudinal direction of the dielectric substrate, and the first frequency Arranged in a direction orthogonal to the band parasitic element surface and spaced apart from the first frequency band parasitic element,
The first and second frequency band parasitic elements and the dipole antenna are arranged such that their electrical center points are at the same height,
A second frequency band parasitic element adjacent without passing through the dielectric substrate is short-circuited. The antenna according to claim 1,
An antenna characterized by short-circuiting substantially midpoints of long sides facing each other of the adjacent second frequency band parasitic elements without passing through the dielectric substrate. The antenna according to claim 1,
The first frequency band is 2.0 GHz, the second frequency band is 3.5 GHz,
The length in the longitudinal direction of the dipole antenna is 0.46 times the wavelength of 2.0 GHz,
The overall length in the longitudinal direction of the first frequency band parasitic element is 0.39 times the wavelength of 2.0 GHz,
The total length in the longitudinal direction of the second frequency band parasitic element is 0.44 times the wavelength of 3.5 GHz,
The distance between the dielectric substrate and the second frequency band parasitic element is 0.05 times the wavelength of 3.5 GHz,
The distance between the first frequency band parasitic element and the plane on which the second frequency band parasitic element is disposed is 0.01 times the wavelength of 2 GHz,
When the distance between the center in the width direction of the second frequency band parasitic element adjacent without passing through the dielectric substrate is 0.140 times to 0.163 times the wavelength of 3.5 GHz,
A distance (excluding 0) that is not more than 0.0233 times the wavelength of 3.5 GHz in the longitudinal direction from the midpoint of the long sides facing each other of the adjacent second frequency band parasitic elements without passing through the dielectric substrate An antenna characterized by short-circuiting each other. The antenna according to claim 1,
The first frequency band is 2.0 GHz, the second frequency band is 3.5 GHz,
The length in the longitudinal direction of the dipole antenna is 0.46 times the wavelength of 2.0 GHz,
The overall length in the longitudinal direction of the first frequency band parasitic element is 0.39 times the wavelength of 2.0 GHz,
The total length in the longitudinal direction of the second frequency band parasitic element is 0.44 times the wavelength of 3.5 GHz,
The distance between the dielectric substrate and the second frequency band parasitic element is 0.05 times the wavelength of 3.5 GHz,
The distance between the first frequency band parasitic element and the plane on which the second frequency band parasitic element is disposed is 0.01 times the wavelength of 2 GHz,
When the distance between the center in the width direction of the second frequency band parasitic element adjacent without passing through the dielectric substrate is 0.163 times to 0.187 times the wavelength of 3.5 GHz,
A distance (excluding 0) that is 0.0233 times or less of the wavelength of 3.5 GHz in the longitudinal direction from the midpoint of the long sides of the adjacent second frequency band parasitic elements adjacent to each other without passing through the dielectric substrate vertically above An antenna characterized by short-circuiting distant points or short-circuiting points distant vertically below a distance that is 0.0233 times the wavelength of 3.5 GHz. A long-plate-shaped dielectric substrate;
A dipole antenna formed on the front surface and the back surface of the dielectric substrate;
A feeding circuit that is formed on the front surface and the back surface of the dielectric substrate and supplies power to the dipole antenna;
With four long plate-shaped parasitic elements,
The parasitic elements are arranged on the surface of the dielectric substrate along the longitudinal direction of the dielectric substrate by separating two adjacent parasitic elements from each other on the front side and the back side of the dielectric substrate. Arranged in a direction orthogonal to the dielectric substrate,
The parasitic element and the dipole antenna are arranged so that their electrical center points are at the same height,
An antenna, wherein the adjacent parasitic elements are short-circuited.

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