JP3542064B2 - Antenna device - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to, for example, a base station antenna device in mobile communication, and relates to an antenna device having directivity in which a beam width in a horizontal plane is approximately 60 ° by combining two elements of directional radiation beams in phase, and in particular, It is intended to be downsized.
[0002]
[Prior art]
FIG. 12 shows a conventional antenna device of this type. Half-wavelength dipole antennas 21 and 22 which are opposed to the vertically standing reflector 1 on the same side and extend in the vertical direction are arranged at intervals. Each interval D between the reflector 1 and the dipole antennas 21 and 22 is about a quarter wavelength, the horizontal interval S between the dipole antennas 21 and 22 is about a half wavelength, and the vertical interval H is also about a half wavelength. Wavelength.
[0003]
In order to form a beam antenna having a half-value width of 60 ° in the horizontal plane of the antenna device, that is, a so-called 60 ° beam antenna, the width W of the reflector 1 needs to be about 0.97 wavelength as shown in FIG. The diameter Wo of the protective radome 3 to be put on the device needs to be about 0.99 wavelength. FIG. 14 shows the calculated values of the directivity characteristics in the horizontal plane at this time. It can be seen that the beam width (width reduced by half-width 3 dB) is 60 °.
[0004]
In order to further reduce the size of the above-described antenna device, parasitic elements 41 and 42 are arranged in parallel with the dipole antennas 21 and 22 on the opposite side of the reflector 1 as shown in FIGS. There is something. The distance D between the reflector 1 and each of the dipole antennas 21 and 22 is about 波長 wavelength, the horizontal distance S between the dipole antennas 21 and 22 is about 波長 wavelength, the vertical distance H is about 波長 wavelength, and the dipole Each interval G between the antennas 21 and 22 and the parasitic elements 41 and 42 is about a quarter wavelength. The length of the parasitic elements 41 and 42 is about 0.24 wavelength.
[0005]
In order to obtain a 60 ° beam antenna, the width W of the reflector 1 needs to be about 0.83 wavelength, and the diameter of the radome 3 needs to be about 0.89 wavelength as shown in FIG. As for the characteristics, a beam width of 60 ° is obtained as shown in FIG.
[0006]
[Problems to be solved by the invention]
In the wireless zone configuration in the cellular mobile communication system, a sector zone configuration in which a horizontal plane is angularly divided is used in order to increase subscriber capacity and effectively use frequencies. At this time, the number of sectors dividing 360 ° is often a three-sector or six-sector wireless zone configuration. When a 6-sector wireless zone configuration is adopted, six 60 ° beam antenna devices are required to cover 360 °. In order to mount many antenna devices on the roof of a steel tower or a building, miniaturization of the antenna with reduced antenna load and installation space is an important study subject in antenna design.
[0007]
The side lobe level in the directional characteristics of the base station antenna is an important amount that determines the amount of interference between wireless zones. Reducing the sidelobe level allows for repeated use of frequencies between closer zones. Reducing sidelobes is also an important consideration in antenna design.
[0008]
[Means for Solving the Problems]
An antenna device according to the present invention is a device comprising two dipole antennas, respective parasitic elements and a reflector, and particularly, both sides of the reflector are bent and extended toward the dipole antenna to provide side reflectors. , These side reflectors open slightly outward from each other.
[0009]
This configuration makes it possible to reduce side lobes and downsize the antenna device.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 1 shows an embodiment of the present invention. This example is suitable for a mobile communication base station antenna in which two elements of a 120 ° beam antenna are combined in phase to form a 60 ° beam antenna. Two vertically extending dipole antennas 21 and 22 are provided on the same side of the reflector 1 at a distance D from the vertically provided reflector 1, and include the dipole antennas 21 and 22, respectively. Parasitic elements 41 and 42 are provided in parallel to the dipole antennas 21 and 22 in a plane perpendicular to the plane, respectively, at a distance G from the dipole antennas 21 and 22.
[0011]
In this embodiment, on both side ends of the reflector 1, side reflectors 51 and 52 are provided which are inclined at an angle of θ ° outward with respect to a plane perpendicular to the reflector 1. Generally, the reflector 1 and the side reflectors 51 and 52 are integrally formed.
The D is about a quarter wavelength, the horizontal interval S between the dipole antennas 21 and 22 is about a half wavelength, the vertical interval H is about a half wavelength, and the length of the parasitic elements 41 and 42 is longer. The length is about 0.24 wavelength (36 mm).
[0012]
The width W of the reflector 1, the width T of the side reflectors 51, 52, the inclination angle θ of the side reflectors 51, 52, and the respective distances G between the dipole antennas 21, 22 and the corresponding parasitic elements 41, 42 are moments. Each parameter can be determined and optimized using the values calculated by the method.
The moment method is a method of dividing the antenna into minute sections, finding the current flowing in the minute section from the boundary conditions, knowing the current distribution of the antenna, and deriving the electromagnetic field created by the antenna, the input and output impedance of the antenna, etc. is there.
[0013]
Using this moment method, the width W of the reflector 1, the width T of the side reflectors 51, 52, and the inclination angle θ of the side reflectors 51, 52 are changed and simulation is performed to obtain the width W of the reflector 1. , The width T of the side reflector, and the inclination angle θ of the side reflector can be determined. In this embodiment, the width W of the reflector 1 is set to 0.7 wavelength (105 mm), preferably the width of the side reflectors 51 and 52 is set to about 0.13 wavelength (20 mm), and the inclination angle is set to the optimum values. Obtained at a setting of 20 °. The diameter of the radome at this time is about 0.82 wavelength (123 mm).
[0014]
Further, by optimizing the value of each distance G between the dipole antennas 21 and 22 and the corresponding parasitic elements 41 and 42, the size can be further reduced, that is, the width W of the reflector 1 is set to 0.5 to 0.57 wavelength. (75-85 mm), for example, as a value that fits in a radome having a diameter of about 0.67 wavelength (100 mm), for example, when W = 75 mm, G = 26.5 mm (0.177 wavelength) or less, and W = 85 mm At this time, G can be set to 20.5 mm (0.137 wavelength) or less.
[0015]
Hereinafter, it will be described that the above numerical values are optimal.
The measurement was performed at four frequencies (1.920 GHz, 2,000 GHz, 2.080 GHz, 2.160 GHz) in the frequency band of 1.920 GHz to 2.160 GHz.
FIG. 2 is a diagram in which the width T of the side reflector at 2,000 GHz is about 0.13 wavelength (20 mm): the beam width with respect to θ when the wavelength is constant is plotted. From the figure, it is understood that a smaller θ is better in order to obtain a beam width in the horizontal plane of 60 °. However, when the concentration of the beam in the above-mentioned frequency band is measured, when the inclination of the side reflectors 51 and 52 becomes small, the beam becomes too sharp in a high frequency band, and the frequency characteristics tend to be poor. FIG. 5A shows beam widths (dB) at measurement frequencies of 1.920 GHz, 2,000 GHz, 2.080 GHz, and 2.160 GHz when θ is changed with T = 20 mm. When the beam width is 1.920 GHz as a reference, the beam widths of -2.5 dB and -3.5 dB are obtained, and the beam widths of -3 dB at 2,000 GHz, 2.080 GHz and 2.160 GHz fall within this range. When judging whether or not the beam width is high, the beam width becomes too small in a high frequency band and does not fall within this range, that is, the frequency characteristics deteriorate. The frequency characteristics are good when θ = 20 or more. From the above, it is optimal to obtain a beam of about 60 ° at θ = 20 ° at T = 0.13 wavelength (20 mm).
[0016]
FIG. 3 is a plot of the beam width and the side lobe level with respect to T when θ = 20 °: constant at a value of 2,000 GHz. If T = 10 mm or less, the beam width increases, and the side lobe level also increases. When T = 10 mm, the beam width is good and the side lobe level is good at -20 dB or less (generally, the side lobe level should be -20 dB or less). However, if T = 20 mm or less, the frequency characteristics are poor. This means that the beam width (dB) at each measurement frequency when θ is set to 20 ° and T is changed is shown in FIG. 5B, and from each value in FIG. The width increases and the frequency characteristics deteriorate. From the above, it was determined that T = 20 mm was optimal when θ = 20 °. However, the width T is not less than 0.13 wavelength (20 mm), and the beam width is not so narrow from FIG. 3 and the side lobe level is further reduced. Therefore, T may be 0.13 wavelength or more.
[0017]
Regarding the width W of the reflector 1, the beam width increases when the horizontal interval S of the dipole antenna is reduced. Therefore, the horizontal interval S of the antenna is fixed at about a half wavelength, and the size of W is reduced. FIG. 6 is a plot of the beam width in the horizontal plane and the side lobe level with respect to the width W of the reflector 1. Even if the width W of the reflector 1 becomes as small as 0.5 wavelength, the beam width satisfies an almost 60 ° beam. The side lobe level also satisfies approximately -20 dB.
[0018]
In order to further reduce the size of the antenna device so that the radome diameter becomes 100 mm or less, each distance G between the dipole antennas 21 and 22 and the corresponding parasitic elements 41 and 42 is reduced. When the width T of the side reflectors 51 and 52 is about 0.13 wavelength (20 mm) and the inclination angle is 20 °, the width W of the reflector 1 that fits in a radome having a diameter of 100 mm is 0.57 wavelength (85 mm). It is as follows. On the other hand, if the antenna interval S is set to 0.5 wavelength (75 mm) or less, the beam width increases, so that the width W of the reflector 1 is required to be 0.5 to 0.57 wavelength (75 mm to 85 mm). You.
[0019]
As shown in FIG. 7 showing the relationship between the plane of the antenna device and the radome 3, when W = 0.5 wavelength (75 mm) (broken line), the maximum value GM1 of the distance G is about 0.177 wavelength (26.5 mm). , W = 0.57 wavelength (85 mm) (solid line), the maximum value GM2 of G is about 0.137 wavelength (20.5 mm).
8 and 9 show beam widths and side lobe levels for G at 2.000 GHz for W = 0.5 wavelength (75 mm) and W = 0.57 wavelength (85 mm). Are shown below. From these calculated values, the beam width is approximately 60 ° at the maximum G where the radome diameter is less than 100 mm. However, since the beam width does not increase abruptly even if G is reduced, G may be smaller than the maximum value that allows the radome diameter to fall within 100 mm. With respect to the width T of the side reflectors 51 and 52, the beam width increases as T increases, so that T is optimally 0.13 wavelength (20 mm). However, even in the case of more than that, a value almost 60 ° is obtained.
[0020]
The side lobe level also satisfies approximately -20 dB or less even if G is less than the maximum value at a radome diameter of 100 mm.
From the above, the width W of the reflector 1 is about 0.5 to 0.57 wavelength, and the distance G between the dipole antennas 21 and 22 and the parasitic elements 41 and 42 is the maximum value that fits in a radome having a diameter of 100 mm. A smaller value is optimal. As an example, FIG. 10 shows the directivity in the horizontal plane when W = 75 mm (0.5 wavelength), T = 20 mm, G = 26.5 mm (0.177 wavelength), and W = 85 mm (0.57 wavelength). FIG. 11 shows the directivity in the horizontal plane when T = 20 mm and G = 20.5 mm (0.137 wavelength). The horizontal beam width satisfies approximately 60 ° and the side lobe level satisfies approximately −20 dB or less.
[0021]
【The invention's effect】
As described above, according to the present invention, the antenna device having a small radome diameter can be designed by attaching the side reflection plate obliquely to the reflection plate. The radome diameter is about 25 to 33% smaller than the antenna device without the side reflector.
[Brief description of the drawings]
FIG. 1A is a perspective view showing an embodiment of the present invention, and FIG. 1B is a plan view in which a radome is put on the antenna device shown in FIG.
FIG. 2 is a diagram showing a simulation result of a change characteristic of a beam width with respect to θ when T = 20 mm (constant) in the embodiment of FIG. 1;
FIG. 3 is a diagram showing a simulation result of a change in a beam width and a change in a side lobe level with respect to T when θ = 20 ° (constant) in the embodiment of FIG. 1;
FIG. 4 is a diagram showing a directional characteristic in a horizontal plane (at 2,000 GHz) in the optimal design of the embodiment of FIG. 1;
5A is a diagram showing a beam width at each frequency when T is set to 20 mm and θ is changed, and FIG. 5B is a diagram showing a beam width at each frequency when T is changed when θ is changed to 20 °. It is.
FIG. 6 shows changes in the horizontal plane beam width and the side lobe level with respect to the width W of the reflector when θ = 20 ° (constant) and the interval S of the dipole antennas is constant at about a half wavelength in the embodiment of FIG. The figure which shows the simulation result of a characteristic.
FIG. 7 is a plan view showing an embodiment of the present invention adapted to fit in a radome having a diameter of 100 mm.
FIG. 8 shows a horizontal beam width (FIG. A) and a side lobe level with respect to a change in the distance G between the dipole antenna and the parasitic element and the width T of the side reflector when the reflector width W is 0.5 wavelength; The figure which shows each calculation value of FIG. B).
FIG. 9 is a diagram showing calculated values of a horizontal beam width (FIG. A) and side lobe levels (FIG. B) with respect to changes in distances G and T when W is set to 0.57 wavelength.
FIG. 10 is a diagram showing the directional characteristics in the horizontal plane of the antenna device of the present invention when W = 75 mm, T = 20 mm, and G = 26.5 mm.
FIG. 11 is a diagram showing the directional characteristics in the horizontal plane of the antenna device of the present invention when W = 85 mm, T = 20 mm, and G = 20.5 mm.
FIG. 12 is a perspective view showing a conventional antenna device.
FIG. 13 is a plan view in which a radome is attached to the antenna device shown in FIG. 12;
FIG. 14 is a diagram showing a directional characteristic in a horizontal plane of the antenna device of FIG. 12;
FIG. 15 is a perspective view showing another example of the conventional antenna device.
16 is a plan view in which a radome is attached to the antenna device shown in FIG.
FIG. 17 is a diagram showing a directional characteristic in a horizontal plane of the antenna device shown in FIG. 15;

Claims (1)

A reflector on one plane, two dipole antennas parallel to this reflector and spaced apart by a distance D,
A parasitic element parallel to the dipole antenna and located on a plane perpendicular to the reflector including the dipole antenna and separated from the respective dipole antenna by a distance G to the opposite side of the reflector. With
In an antenna device that excites the radiating elements of two dipole antennas with the same phase and the same amplitude,
On both ends of the reflector, about 20 ° tilt outwardly from the vertical direction of the reflector, have a side reflectors having a width greater than or equal to about 0.13 wavelength,
The width W of the reflector is about 0.5 to 0.57 wavelength, and the distance G between the dipole antenna and the parasitic element is about 0.177 to about 0.137 wavelength. Antenna device.

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