JP2003318635A - Dipole antenna having reflector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a dipole antenna having a reflector for substantially obtaining nondirectivity, even when it has a multi-surface arrangement of 5 surfaces or more, while not changing the basic configuration of a dipole antenna suitable to a four-surface arrangement, as much as possible. <P>SOLUTION: The dipole antenna comprises a power supply circuit (power supply trap 20), a dipole element 10 and a power supply path 30 for connecting the power supply circuit and the dipole element 10. A length of the power supply path 30 is adjusted so as to secure a phase difference between emission from the dipole element 10 and emission from the power supply circuit, and the half width of horizontal plane directivity is made 90° or smaller in the electric field half width. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dipole antenna suitable for transmitting radio waves for broadcasting or communication. In particular, the present invention relates to a 2 or 4 dipole antenna having a horizontal plane directivity suitable for a 5-plane arrangement.

[0002]

2. Description of the Related Art Conventionally, a two-dipole antenna used for transmitting broadcast radio waves has two half-wavelength dipole elements placed at a distance of about 1 / 4λ from a reflector and supplies them in parallel with each other. It is connected in parallel with electric wires and fed from the center. The 4-dipole antenna is a pair of 2-dipole antennas connected to each other by parallel or coaxial feed lines and fed from the center.

[0003]

However, in the above-mentioned conventional dipole antenna, there is a problem that it is difficult to share components between an antenna for four-sided arrangement and an antenna for arrangement of five or more sides. It was

The two-dipole antenna or the four-dipole antenna is an antenna which can obtain almost omnidirectionality when it is attached to a steel tower in a 90 ° arrangement on four sides. That is, if a dipole antenna is attached to each side surface of a steel tower having a square cross section, almost omnidirectionality can be obtained. However, if the overhanging distance from the central portion of the steel tower is long, the directivity in the horizontal plane is greatly reduced, and it becomes impossible to obtain omnidirectionality.

Therefore, conventionally, when attaching a dipole antenna to a steel tower having a wide width, a so-called multifaceted antenna has been used in which the dipole antenna is arranged from 6 to several tens of planes to obtain omnidirectionality. For example, in order to reduce the half-width of horizontal plane directivity in a single dipole antenna, two or three rows of dipole elements are arranged on the same reflector.

However, this is disadvantageous in terms of weight and cost of the antenna. Therefore, it is sufficient to reduce the full width at half maximum of the horizontal plane directivity with only one row of elements, but there is a limit even if the length of the dipole element is increased. In addition, in order to reduce the horizontal plane directivity half-width (90 ° electric field half-width) suitable for four-sided layout, it is necessary to devise an antenna configuration that is different from the four-sided layout. was.

Therefore, a main object of the present invention is to provide a dipole antenna which can obtain substantially omnidirectionality even in a multi-plane arrangement of five or more planes without changing the basic structure of the dipole antenna suitable for the four-plane arrangement as much as possible. Especially.

[0008]

The present invention achieves the above object by adjusting the length of a feeding line connecting a feeding circuit and a dipole element.

That is, the dipole antenna of the present invention is
A dipole antenna comprising a power feeding circuit, a dipole element, and a power feeding line connecting the power feeding circuit and the dipole element, wherein the length of the power feeding line is defined by the radiation from the dipole element and the radiation from the power feeding circuit. It is characterized in that the half-width of the horizontal plane directivity is set to 90 ° or less in the half-width of the electric field by adjusting so that a phase difference is provided between the two.

2 dipole antennas for 4 planes or
A 4-dipole antenna is usually a coaxial feed that feeds a dipole element and a feeding circuit (balance / unbalance conversion circuit), a feed line (parallel feeding line) that connects the dipole element and the balance / unbalance conversion circuit, and a balance / unbalance conversion circuit. It consists of an electric wire. In order to reduce the full width at half maximum of the horizontal plane directivity, generally, the opening in the horizontal plane direction should be large. Therefore, 2
It seems that the element length of the dipole antenna or the 4-dipole antenna and the width of the reflector should be large, but this does not work. This is because the horizontal plane directivity of the antenna is determined not only by the radiation from the radiating element (dipole element) but also by the radiation from the feeding line in the middle, especially from the balanced-unbalanced conversion circuit portion.

In the present invention, the phase difference of radio wave radiation from the main radiation portion is adjusted to increase or decrease the half-width of the horizontal plane directivity. This can be done simply by changing the length of the parallel feed line connecting the dipole element and the balance-unbalance conversion circuit part, and it is not necessary to change the configuration of the part other than the parallel feed line.

More specifically, the length of the feed line is set to 0.
It is preferably 25λ to 0.5λ. This λ is the design center frequency. For example, for the entire UHF band of 440 to 770 MHz, 602 MHz is set as the design center frequency in consideration of the phase change of this band. By selecting such a length of the feed line, adjustment is made so that there is a phase difference between the radiation from the dipole element and the radiation from the feed circuit, and the half-width of horizontal plane directivity is 90 It can be less than or equal to °.

The frequency band used by the dipole antenna of the present invention is suitable for broadcasting / communication in VHF having a frequency band of 90 to 108, 170 to 222 MHz and UHF having a frequency band of 470 to 770 MHz. Of course, the applicable range of the antenna of the present invention is not limited to this frequency band.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below. (Embodiment) FIG. 1 is a partially cutaway plan view of a dipole antenna according to the present invention, FIG. 2 is a front view of the same, and FIG.

<Overall Configuration> This dipole antenna is
Two pairs of dipole elements 10 are arranged on the reflector at a predetermined interval. Each pair of dipole elements 10 is connected to a feed trap 20 (feed circuit) via a feed line 30 arranged in parallel. Meanwhile, a total of a pair of power supply traps
20 is integrated in the power feeding section 50 via the parallel power feeding line on the back surface of the reflection plate 40. The entire dipole elements of these two pairs are covered with a cover 60.

<Dipole Element> Here, a bow-tie type dipole element 10 in which the width is narrowed only in the central portion of a rectangular plate is used. The length of the dipole element 10 (distance in the longitudinal direction of the rectangular plate) is preferably about 0.4 to 0.7λ with respect to the design center frequency λ. The distance of each dipole element 10 from the reflection plate 40 is preferably about 0.1 to 0.3λ. In this example, the dipole element 10 is fixed on the reflection plate 40 via the insulating supporter 11.

<Feed Trap> The feed trap 20 is a portion for supplying electric power to the dipole element 10. Here, a pair of rod-shaped bodies extending vertically from the reflection plate 40 is used. In this rod-shaped body, an inner conductor 22 is coaxially housed in an outer pipe 21.

<Feed Line> The dipole element 10 and the feed trap 20 are connected by a feed line 30. Here, bent plates having three right-angled bent portions are arranged in parallel to connect the dipole element 10 and the power feed trap 20. The feed line 30 projects horizontally from the upper end of the feed trap 20, first bends downward at a right angle, then bends horizontally, then bends upward at a right angle and is connected to the dipole element 10. The bending path at this time is not particularly limited. The length of this feed line 30 is adjusted so as to provide a phase difference between the radiation from the dipole element 10 and the radiation from the feed trap 20, and the half value width of the horizontal plane directivity is 90 ° or less in the electric field half value width. And In this example, the length of the feed line 30
It was set to 0.42λ (λ = 485 MHz).

<Feeding unit> The lower end of the feeding trap 20 described above is connected to the feeding unit 50 located substantially in the center of both feeding traps 20 by connecting the inner conductor 22 to the central conductor 51 on the back surface of the reflection plate 40. . The center conductor 51 is covered with a power feeding section cover 52.

<Operation and Effect> As described above, by adjusting the length of the feed line 30, a phase difference is provided between the radiation from the dipole element 10 and the radiation from the feed trap 20, and the directivity of the horizontal plane is obtained. The full width at half maximum of can be 90 ° or less in full width at half maximum of electric field. Therefore, the dipole element can be used for both 4-sided arrangement and 5-sided arrangement,
Parts can be shared. Further, when the dipole antenna is arranged on five sides, it is not necessary to dispose two or three rows of dipole elements on the same reflector, which is advantageous in terms of weight and cost of the antenna.

(Test Example) An antenna similar to the above dipole antenna was actually used to examine the horizontal plane directivity.
FIG. 4 shows a schematic diagram of the dipole antenna of the present invention with a reflector. Here, the design center frequency λ: 485 MHz, the length of the dipole element 10: 0.58λ, the dipole element 10 and the reflector 40
The distance L to the feed line 30 was set to 0.17λ and the length L of the feed line 30 was changed to examine how the directivity changes. The directivity is represented by the electric field half-width when the direction connecting the center of the dipole element 10 and the feed trap 20 is the vertical direction.

FIG. 5 is a graph showing the relationship between the length of the feed line and the half-width of the electric field. As is clear from this graph, when the length L of the feed line exceeds 0.2λ, the half-value width of the electric field is 90%.
It can be seen that when the length L is around 0.5λ, the half-value width of the electric field is narrowed to nearly 75 °.

The design center frequency λ: 485 MHz, the length of the dipole element: 0.58λ, the distance between the dipole element and the reflecting plate: 0.17λ, and the length L of the feed line is 0.21λ, 0.42λ.
Then, the frequency characteristics of the standing wave ratio in the case of The results are shown in the chart of FIG.

As is clear from this chart, it is understood that the radiation beam is narrowed more when the length L of the feed line is 0.42λ than when it is 0.21λ.

Further, the dipole antenna 100 of the present invention is arranged on each side of a tower 70 having a pentagonal cross section as shown in FIG. 7 (A),
I examined the horizontal plane directivity at that time. Design center frequency λ: 485MHz, dipole element length: 0.58λ, distance between dipole element and reflector: 0.17λ, feed line length L:
0.42λ, distance from the center of the tower to the antenna installation surface d: 0.6
The chart of FIG. 7 shows the horizontal plane directivity when this dipole antenna is arranged on five sides with 3λ.

As is apparent from this chart, it is found that even in the case of the five-sided arrangement, uniform directivity is obtained in almost all directions.

[0027]

As described above, in the dipole antenna of the present invention, the length of the feed line is adjusted so that the radiation from the dipole element and the radiation from the feeding circuit are adjusted to have a horizontal plane. The full width at half maximum of directivity is
It can be 90 ° or less. Therefore, a member of a dipole antenna suitable for four-sided arrangement, such as a dipole element, can be shared with the five-sided dipole antenna.

[Brief description of drawings]

FIG. 1 is a partially cutaway plan view of a 4-dipole antenna of the present invention.

FIG. 2 is a partially cutaway front view of the present invention 4 dipole antenna.

3 is a cross-sectional view taken along the line AA of FIG.

4A is a schematic plan view of a dipole antenna of the present invention with a reflector, and FIG. 4B is a front view of the same.

FIG. 5 is a graph showing the relationship between the length of the feeder line and the half-width of the electric field.

FIG. 6 is a chart showing horizontal plane directivity when the length L of the feed line is 0.21λ and 0.42λ.

FIG. 7A is a layout explanatory view when the antenna of the present invention is arranged on five sides, and FIG. 7B is a chart showing horizontal plane directivity in the case of five-sided arrangement.

[Explanation of symbols] 10 dipole element 11 Insulation support 20 power trap 21 pipes 22 Inner conductor 30 feeder line 40 reflector 50 power supply 51 center conductor 52 Power supply cover 60 cover 70 steel tower 100 dipole antenna

Claims (2)

[Claims] 1. A dipole antenna comprising a feed circuit formed on a reflector, a dipole element, and a feed line connecting the feed circuit and the dipole element, wherein the length of the feed line is: A dipole antenna characterized in that the radiation from the dipole element and the radiation from the feeding circuit are adjusted to have a phase difference, and the half-width of the horizontal plane directivity is 90 ° or less in the half-width of the electric field. 2. The dipole antenna according to claim 1, wherein the length of the feed line is 0.25λ to 0.5λ. However, λ is the design center frequency.