JP3623714B2 - Broadband antenna and array antenna device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a broadband antenna and an array antenna apparatus suitable for mobile communication on land.
[0002]
[Prior art]
A base station antenna in mobile communication typified by a mobile phone constitutes an array antenna by arranging radiating elements such as a half-wave dipole antenna in a multi-stage array in the vertical direction. For example, with regard to mobile communication, in order to provide services to many subscribers, the service area of 360 degrees is divided into 3 or 6 sectors. Accordingly, the beam width in the horizontal plane is an array antenna having a directivity characteristic of a beam width of about 120 degrees in the case of a service area of 3 sectors and a beam width of about 60 degrees in the case of a service area of 6 sectors. Need to develop.
[0003]
When making an antenna with a relatively narrow beam width, a parasitic element or a reflection element that is slightly longer than the radiating element in the direction opposite to the direction of the beam is applied to a radiating element represented by a dipole antenna such as a so-called Yagi-Uda antenna. A plate is provided, and if necessary, a parasitic element slightly shorter than the radiating element is provided in the direction having the beam, and a desired beam width is obtained by adjusting the interval, length, or shape thereof.
The horizontal radiation beam width of the antenna composed of each radiating element described above, each reflecting plate, and other parasitic elements is composed of each radiating element, each reflecting plate, and other parasitic elements. In the horizontal directivity characteristic of the antenna, the angle range in which the gain decreases by 3 dB with respect to the gain at the front, that is, each radiating element, each reflecting plate, and other parasitic elements This means the full width at half maximum of the directivity of the antenna in the horizontal direction.
[0004]
[Problems to be solved by the invention]
In mobile communication such as a cellular phone, diversity is used to improve communication quality, and it is further classified into space diversity, height diversity, polarization diversity, and the like depending on the method. In particular, polarization diversity enables a stable call by simultaneously receiving vertically polarized waves and horizontally polarized waves.
The base station antenna of such a system requires a polarization diversity antenna that has both a vertical polarization element and a horizontal polarization element and is arranged so that each element can obtain substantially the same directivity characteristics.
[0005]
A half-wave dipole antenna is generally used for the vertical polarization element. As is well known, a half-wave dipole antenna has non-directional characteristics in a plane perpendicular to the dipole axis (in the H plane). Therefore, by combining a reflector with this half-wave dipole antenna for vertical polarization, It is easy to set the radiation beam width in the horizontal plane of the waves to 120 degrees. In FIG. 7, 9a and 9b represent elements of a half-wave dipole antenna, and 6 represents a reflector. As shown in FIG. 7, it is easy to set the radiation beam width to 60 degrees by arranging two 120 degree beam antennas horizontally.
[0006]
However, when a half-wavelength dipole antenna is used as the horizontally polarized antenna, the half-wavelength dipole antenna has an 8-shaped directional characteristic in the plane including the dipole axis (in the E plane). Even if a reflector is combined with a wave half-wave antenna, the beam width in the horizontal plane of horizontal polarization is only about 70 degrees.
As described above, in the conventional technique, when a half-wave dipole antenna is used as a radiating element for horizontally polarized waves, the shape and length of the parasitic element are reduced in order to narrow the beam width in the plane including the dipole axis, that is, in the horizontal plane. On the other hand, when the interval is adjusted, there is a drawback that matching of the input impedance can be achieved only with a narrow bandwidth. An object of the present invention is to provide a technique for matching input impedance over a wide band without changing the beam width.
[0007]
[Means for Solving the Problems]
Of the inventions disclosed in this subject, the outline of typical ones will be briefly described as follows.
Compared to free space wavelength, each coated thin film or linear half-wavelength dipole antenna element is provided on the surface of a thin dielectric, and its width is narrower than the free space wavelength near the ends on both sides. Thus, a metal film having a length of about a quarter of the free space wavelength or a pair of linear parasitic elements is arranged in the same plane as the elements of the half-wave dipole antenna.
[0008]
The radiating element and the parasitic element constituted by the elements of the half-wave dipole antenna have a linear reflecting element or a planar reflecting plate in a direction opposite to the radiating direction.
The radiating element and the parasitic element have a linear reflecting element or a planar reflecting plate in a direction opposite to the reflecting direction, and a parasitic element slightly shorter than the radiating element is disposed in the radiating direction. .
[0009]
[Action]
Both sides of a dipole antenna element approximately 70% longer than the length of one half of the metal film or linear free space wavelength deposited on the surface of a thin dielectric compared to the free space wavelength A metal film or a pair of linear parasitic elements having a width that is narrower than the free space wavelength and about one-fourth of the free space wavelength are placed near the end of the half-wavelength dipole antenna. Place on the same plane. At this time, even when a linear reflecting element or a planar reflecting plate is provided in the direction opposite to the radiation direction, and a parasitic element slightly shorter than the radiation element is arranged in the radiation direction, a wide bandwidth can be obtained without changing the beam width. realizable.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
In all the drawings for explaining the embodiments, parts having the same functions are given the same reference numerals, and their repeated explanation is omitted.
<Example 1>
FIG. 1 is a perspective view showing an embodiment of the present invention, that is, a view of the present invention as viewed obliquely from the front.
[0011]
1 is a thin dielectric plate compared to the free space wavelength, and 2 is a metal film deposited on the surface of the dielectric plate 1, approximately 70% longer than the half of the free space wavelength. The dipole antenna elements 3a, 3b, 3c and 3d are parasitic elements having a narrow width compared to the free space wavelength and a length of about one quarter of the free space wavelength. It is provided on the surface. Reference numeral 4 a denotes a matching line, which is provided on the back side of the dielectric plate 1. Reference numeral 5 denotes an input / output terminal composed of, for example, a coaxial plug, and has an inner conductor connected to the matching line 4a and an outer conductor connected to the element 2 of the dipole antenna. When the dielectric plate 1 is formed using, for example, a thermosetting PPE copper-clad laminate, an unnecessary metal film is removed by a method similar to the printing method, and a dipole antenna element is formed on the front and back surfaces of the dielectric plate 1. 2. The parasitic elements 3a, 3b, 3c, 3d and the matching line 4a are deposited. These manufacturing methods are the same in other embodiments described later.
[0012]
The high frequency energy propagated by the matching line 4a excites the element 2 of the dipole antenna, and a standing wave is generated. A part of the excited energy is also transmitted to the capacitively coupled parasitic elements 3a, 3b, 3c, and 3d, and the parasitic element 3a, 3b, 3c, and 3d has a dipole antenna element 2 on the opposite side. The high-frequency current is reflected at the end, and returns to the element 2 of the dipole antenna. Since the parasitic elements 3a, 3b, 3c, and 3d have a length of about a quarter of the free space wavelength, the phase of the high-frequency current that has been reflected and returned from the end portion is shifted by approximately 180 °. The element 2 of the capacitively coupled dipole antenna is excited again, but the phase is different from the standing wave originally placed on the element 2 of the dipole antenna, so that part of the energy is canceled and returned to the matching line 4a. Less. Therefore, by setting the length of the element 2 of the dipole antenna, the parasitic elements 3a, 3b, 3c, and 3d and the distance between the element 2 of the dipole antenna and the parasitic elements 3a, 3b, 3c, and 3d to appropriate values. The input reflection characteristics are improved over a wide band.
<Example 2>
FIG. 2 is a perspective view showing a second embodiment of the present invention, that is, a view of the present invention as viewed obliquely from the front.
[0013]
2 is a dipole antenna element that is approximately 70% longer than half the free space wavelength, and 3a, 3b, 3c, and 3d are narrower than the free space wavelength. It is a parasitic element having a length of about ¼, and is provided on the same plane as the element 2 of the dipole antenna. 4a is a matching line, and 6 is a reflector. If the reflector 6 is a conductor, a grid or a metal plate (so-called punching metal) with appropriately punched holes may be used. It can be selected as appropriate.
[0014]
A part of the electromagnetic wave radiated from the element 2 of the dipole antenna and the parasitic elements 3a, 3b, 3c, 3d is reflected by the reflecting plate 6, and the element 2 of the dipole antenna and the parasitic elements 3a, 3b, 3c. 3d is combined with the electromagnetic wave radiated in the direction opposite to the reflector 6, and the electromagnetic wave is radiated in the direction opposite to the reflector 6. When the half-wave dipole antenna is used, the half-wave dipole antenna has an 8-shaped directivity characteristic in the plane including the dipole axis (in the E plane), and therefore the element 2 of the dipole antenna and the parasitic element 3a Even if the reflector 6 is combined with 3b, 3c and 3d, the beam width in the horizontal plane is only about 70 degrees. However, when the beam width in the horizontal plane is desired to be narrower than 70 degrees, the distance between the dipole antenna element 2 and the parasitic elements 3a, 3b, 3c, and 3d and the reflector 6 is set to a normal free space wavelength. The width of the beam in the horizontal plane is reduced to about one-eighth of the free space wavelength, so that the beam width in the horizontal plane can be reduced to the dipole antenna element 2 and the parasitic elements 3a and 3b. It is possible to make the distance between 3c, 3d and the reflecting plate 6 slightly smaller than when the length is a quarter of the normal free space wavelength. Even in such a case, by providing the parasitic elements 3a, 3b, 3c, and 3d in the vicinity of the end portions on both sides of the element 2 of the dipole antenna, a wide band can be obtained.
<Example 3>
FIG. 3 is a perspective view showing a third embodiment of the present invention, that is, a view of the present invention as viewed obliquely from the front.
[0015]
The dipole antenna element 2 configured in the second embodiment, the parasitic elements 3a, 3b, 3c, and 3d, and the reflecting plate 6 have a width narrower than the free space wavelength in the radial direction and half the free space wavelength. A parasitic element 7 having a length approximately 70% shorter than that of the dipole antenna and shorter than the element 2 of the dipole antenna is disposed.
Since the parasitic element 7 operates in the same manner as a so-called Yagi-Uda antenna director, the beam width in the horizontal plane can be made narrower than that in the second embodiment. In general, the Yagi-Uda antenna having a large number of parasitic elements has a drawback that the specific bandwidth cannot be widened. However, in this embodiment, by providing the parasitic elements 3a, 3b, 3c, and 3d, the bandwidth can be increased. Is possible.
[0016]
FIG. 4 is a graph showing the relationship between the frequency and the return loss in the element 2 of the dipole antenna of Example 3.
In FIG. 4, the horizontal axis represents the frequency (GHz) and the vertical axis represents the return loss (dB).
As is clear from FIG. 4, in the element 2 of the dipole antenna of this example, the frequency region in which the return loss is 14 dB (voltage standing wave ratio VSWR = 1.5) or less is about 380 MHz, which is 2 GHz. This means that the specific bandwidth is 19%.
<Example 4>
FIG. 5 is a perspective view showing a fourth embodiment of the present invention, that is, a view of the present invention viewed obliquely from the front.
[0017]
The element 2 of the dipole antenna configured in Example 3, the parasitic elements 3a, 3b, 3c, and 3d, and the parasitic element 7 are arranged in four elements in the vertical direction, and are constituted by a series of reflectors 6 as shown in FIG. By arranging as shown, the operating gain is increased, and a high-frequency current with a phase difference and an amplitude difference is supplied to each element 2 of each dipole antenna, so that an in-plane perpendicular to the ground is provided. It is possible to change the directivity characteristic of.
[0018]
FIG. 6 is a perspective view showing another embodiment of the present invention, that is, a view of the present invention viewed obliquely from the front.
The element 2 of the dipole antenna configured in Example 3, the parasitic elements 3a, 3b, 3c, and 3d, and the parasitic element 7 are arranged in the vertical direction, and are composed of a series of reflecting plates 6, and each element In the figure, elements 8a and 8b of a vertically polarized dipole antenna are arranged, and 4b is a matching line for supplying power to the elements 8a and 8b of the vertically polarized dipole antenna.
[0019]
By arranging each element as shown in FIG. 6, the horizontal polarization element and the vertical polarization element are efficiently arranged, and the horizontal radiation beam direction of the vertical polarization and the horizontal polarization is set to 60 degrees. Is possible. Therefore, by using these elements as a polarization diversity antenna of a mobile communication base station, it is possible to transmit and receive radio waves of horizontal polarization and vertical polarization with good balance.
In addition, by supplying a high-frequency current with a phase difference and an amplitude difference to the element 2 of the horizontally polarized dipole antenna and the elements 8a and 8b of the vertically polarized dipole antenna, It is possible to change the directivity in the vertical plane.
[0020]
Although specific description has been given based on the above-described embodiment, the present invention is not limited to the above-described embodiment, and it is needless to say that various modifications can be made without departing from the spirit of the invention.
[0021]
【The invention's effect】
Among the inventions disclosed in the present application, effects obtained by typical ones will be briefly described as follows.
When a half-wave dipole antenna is used as a horizontally polarized radiating element, the antenna of the present invention adjusts the shape, length, and spacing of parasitic elements to narrow the beam width in the horizontal plane. The disadvantage that matching can only be achieved with a narrow bandwidth is that the parasitic elements are placed on both sides of the half-wave dipole antenna element on the same plane as the half-wave dipole antenna element, so that the beam width is hardly changed. It is possible to match the input impedance over a wide band.
[0022]
In the antenna of the present invention, the horizontal polarization element and the vertical polarization element are efficiently arranged, and the horizontal radiation beam direction of the vertical polarization and the horizontal polarization can be set to 60 degrees. Therefore, by using these elements as a polarization diversity antenna of a mobile communication base station, it is possible to transmit and receive radio waves of horizontal polarization and vertical polarization with good balance.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing Example 1 of the present invention.
FIG. 2 is a schematic diagram showing Example 2 of the present invention.
FIG. 3 is a schematic view showing Example 3 of the present invention.
FIG. 4 is a graph showing an actual measurement example of the relationship between the frequency and the return loss in Example 3 of the present invention.
FIG. 5 is a schematic diagram showing Example 4 of the present invention.
FIG. 6 is a schematic view showing another embodiment of the present invention.
FIG. 7 is a schematic diagram for explaining a conventional antenna.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Dielectric board 2, 8a, 8b, 9a, 9b Dipole antenna element 3a, 3b, 3c, 3d, 7 Parasitic element 4a, 4b Matching line 5 Input / output terminal 6 Reflector

Claims (2)

And elements of the dipole antenna arranged on the horizontal ratio and 70% of the length 1 of the length of half the free space wavelength of metals skin membrane, and the corner portions of the upper and lower sides of the ends of the elements of the dipole antenna respectively capacitively coupled, is extended in the longitudinal direction of the element of each dipole antenna, a ratio to the first to fourth passive element and the free space wavelength of the metal skin layer having a first length of a quarter of the free space wavelength Each deposited on the surface of a thin planar dielectric,
A grid or planar reflector is provided in the opposite direction to the radio wave radiation direction.
A wideband antenna, wherein a fifth parasitic element that acts as a director for a radiation wave of the dipole antenna element is disposed in parallel with the dipole antenna element in a radiation direction of the radio wave . A plurality of broadband antennas according to claim 1 are arranged in an array in the vertical direction, each dipole antenna element is provided with a power feeding device that feeds a high-frequency current having a phase difference and an amplitude difference, and each radiation element is excited. An array antenna apparatus characterized by changing a directivity characteristic in a vertical plane.

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