JP3444079B2 - Collinear array antenna - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a base station antenna mainly used in mobile radio.

[0002]

2. Description of the Related Art A collinear array antenna is mainly used as a vertically polarized high-performance antenna for a base station antenna for mobile radio or the like. A conventional collinear array antenna is disclosed in Japanese Utility Model Laid-Open No. 2-147916.
The cross-sectional structure is as shown in FIG. That is, the annular slits 10 are periodically provided on the outer conductor of the coaxial feed line 101.
2 is provided, and 1 / is provided at both ends sandwiching the annular slit 102.
The four-wavelength sleeve conductors 103 are respectively connected to form a plurality of dipole antenna elements 104, and a plurality of quarter-wavelength impedance conversion circuits 106 are provided between the bottommost dipole antenna element 104 and the input terminal 105 for impedance. We are making adjustments.

[0003]

Generally, a high-performance collinear array antenna used in a base station is required to have a standing wave ratio (SWR) of 1.5 or less in a used frequency band. In the above-mentioned conventional configuration, in order to realize this, a plurality of stages of 1/4 wavelength impedance conversion circuits are provided for impedance matching, which causes a problem that the structure becomes complicated and the total length of the antenna becomes long. there were. As the number of base stations is increased to secure the number of mobile radio channels, the above-mentioned problems of the conventional collinear array antenna have become a big problem as a factor for alienating downsizing and cost reduction of the base station.

The present invention is intended to solve the above problems,
It is an object of the present invention to realize a collinear array antenna having a small size and a simple structure by adopting a configuration capable of obtaining a broadband matching characteristic without using an impedance conversion circuit.

[0005]

In order to solve this problem, a collinear array antenna according to the present invention comprises a coaxial feed line having an input terminal connected to one end thereof, and a plurality of periodically provided outer conductors of the coaxial feed line. At least one of the plurality of annular slits, and a plurality of antenna elements formed by symmetrically arranging a pair of quarter-wave sleeve conductors on both sides of each of the plurality of annular slits. The outer diameter of the outer conductor is made different at the two
While changing the characteristic impedance of the power supply line,
The annular ring closest to one end of the coaxial feed line
Characteristic impedance up to lit is standard impedance
From the circular slit to the other end of the coaxial feed line.
The characteristic impedance at
It is also characterized by lowering .

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION The invention according to claim 1 of the present invention comprises: a coaxial feed line having an input terminal connected to one end; and a plurality of annular slits periodically provided in an outer conductor of the coaxial feed line. , and a plurality of antenna elements configured by arranging symmetrically sleeve conductor of the pair of quarter-wave on both sides of each of the plurality of annular slits, the at least one of the plurality of annular slits as a border Different inner diameter of outer conductor
To change the characteristic impedance of the coaxial feed line.
Causes the reduction, the characteristic impedance from one end of the coaxial feed line to the nearest annular slit in said one end and a standard impedance, the characteristic impedance from the annular slit to the other end of the same <br/> axis feed line The standard
It is characterized by being lower than the impedance .

In the above configuration, the characteristic impedance of the coaxial feed line is set to an optimum value in accordance with the radiation impedance of each antenna element, with the circular slit serving as the feed point of each of the plurality of antenna elements as a boundary. Broadband matching characteristics can be obtained without using an impedance conversion circuit, and a collinear array antenna having a small size and a simple structure can be realized.

Further, the invention according to claim 2 of the present invention is
In claim 1 , the characteristic impedance from the annular slit closest to one end of the coaxial feed line to the other end of the coaxial feed line is set to be constant. With this configuration, the optimum matching condition can be obtained when the radiation impedances of the plurality of antenna elements are substantially the same.

An embodiment of the present invention will be described below with reference to FIGS. 1 to 4. FIG. 1 is a perspective view showing a collinear array antenna of the present invention, and FIG. 2 is a sectional view thereof. In FIGS. 1 and 2, reference numeral 1 denotes a coaxial feed line, which is composed of an outer conductor 1a, an inner conductor 1b, and a dielectric 1c. Reference numeral 2 denotes an input terminal for connecting to an external circuit, which is provided at the lower end 1I of the coaxial feed line 1.
Reference numerals 3a and 3b denote annular slits formed by removing the outer conductor 1a of the coaxial feed line 1 in the circumferential direction, and are provided at predetermined intervals. Reference numeral 4 denotes a sleeve conductor having a quarter wavelength in a frequency band to be used, and two sleeve conductors 4 are vertically symmetrically connected to the outer conductor 1a on both sides of each of the annular slits 3a and 3b so that the dipole antenna element 5a, It constitutes 5b. Further, at the upper end 1J of the coaxial feed line 1, the inner conductor 1b is extended by 1/4 wavelength and exposed upward, and the sleeve conductor 4 is connected downward to the outer conductor 1a so that the uppermost dipole antenna element 5c is formed. Are configured. Reference numeral 6 is a rod-shaped parasitic conductor arranged in parallel with each of the dipole antenna elements 5a to 5c, and each is supported by an arm-shaped spacer 7 attached to the sleeve 4. In the three-element collinear array antenna configured as described above, the inner diameter of the outer conductor 1a of the coaxial feed line 1 is equal to that of the lower annular slit 3
Thick from a to lower end 1I, from annular slit 3a to upper end 1J
It is configured to be thin. That is, the characteristic impedance on the upper end 1J side is set lower than the characteristic impedance on the lower end 1I side with the annular slit 3a as a boundary.

A three-element collinear array antenna intended for use in the 1907 ± 13 MHz band will be described below. Sleeve conductor 4 has an inner diameter of 7.6 mm and an outer diameter of 8 mm
The brass cylinder has a length of 35 mm so that the center of the band has a wavelength of about 1/4. In addition, the parasitic element 6
Is a brass rod having a diameter of 3 mm, and its length is 81 mm so as to be slightly longer than 1/2 wavelength at the center of the band. The length of the parasitic conductor 6 is a factor that determines the radiation pattern in the horizontal plane. When it is longer than ½ wavelength, it operates as a reflector, and when it is shorter, it functions as a waveguide. It should be set accordingly. Here, it was set as the former reflector. The sleeve conductor 4 and the parasitic element 6 were held by a Teflon spacer 7, and the distance between the centers of them was 12 mm. The closer this distance is, the lower the radiation impedance of each of the dipole antenna elements 5a to 5c becomes, and the value is determined so as to be convenient from the viewpoint of impedance matching described later. The inner conductor 1b of the coaxial feed line 1 is a copper wire having an outer diameter of 1.5 mm, and the outer conductor 1a is a copper cylinder having an inner diameter of 5.0 mm from the annular slit 3a to the lower end 1I, and similarly the annular slit 3a.
From the top to 1J is a copper cylinder with an inner diameter of 1.9 mm. Further, the dielectric 1c filled between the outer conductor 1a and the inner conductor 1b
Was used Teflon having a dielectric constant of 2. As a result, the characteristic impedance of the coaxial feed line 1 from the annular slit 3a to the lower end 1I is about 50Ω, and the characteristic impedance from the annular slit 3a to the upper end 1J is about 10Ω. The annular slits 3a and 3b respectively have a width 3 in the circumferential direction of the outer conductor 1a.
It is formed by deleting mm, and the interval between them is set to 111 mm, which is equal to the wavelength of the radio wave propagating in the coaxial feed line 1. In addition, the coaxial feed line 1 from the upper annular slit 3b.
The distance to the upper end 1J was also 111 mm. The annular slits 3a and 3b and the upper end 1J of the outer conductor 1a serve as feed points for the dipole antenna elements 5a to 5c, and their intervals are factors that determine the radiation pattern on the vertical plane. That is, when the distance is longer than the wavelength, the maximum gain direction is tilted upward, and when the distance is shorter than the wavelength, the maximum gain direction is tilted and should be set according to the application. Here, the interval is set equal to the wavelength, and the maximum gain direction is the horizontal direction. The total length of the collinear array antenna having the above configuration was 330 mm.

Input impedance characteristics of the collinear array antenna configured as described above are shown in FIGS.
Will be explained. FIG. 3 is a circuit diagram showing an input equivalent circuit of the collinear array antenna, and FIG. 4 is a standing wave ratio (SW
It is a characteristic view showing a frequency characteristic of (R). As shown in FIG. 3, the input equivalent circuit of the collinear array antenna is one in which the radiation impedances Za to Zc of the individual dipole antenna elements 5 a to 5 c are connected in series via the coaxial feed line 1. Here, the dipole antenna elements 5a-5
Since the distances Lab and Lbc between the feeding points of c (that is, the annular slits 3a and 3b and the upper end 1J of the outer conductor) are set equal to the wavelength, Za to Zc must be added in phase at the center frequency of the band. The impedance Zi seen from the other end 1J side from the lower dipole antenna element 5a
n has a value equal to the sum of Za, Zb and Zc. In order to match the impedance Zin with the standard impedance of the circuit system without using the impedance conversion circuit, it is necessary to make the total sum of Za to Zc equal to the standard impedance value. Here, the standard impedance is 50Ω
However, since the radiation impedance of a normal dipole antenna is as high as about 70Ω, the parasitic conductor 6 is provided at an appropriate position to reduce the value, and each of Za to Zc is reduced to about 17Ω (standard impedance of 50Ω is the number of elements. Three
Divided by). Then, in order to maintain the matching state of the impedance Zin, from the feeding point of the lower dipole antenna element 5a (that is, the annular slit 3a) to the lower end 1I.
The characteristic impedance Z0 of the coaxial feed line 1 up to is set to 50Ω which is equal to the standard impedance.

Next, the SWR characteristic near the band will be described. As shown in FIG. 4, the SWR characteristics near the band of the collinear array antenna are shown by the dipole antennas 5a to 5c.
Characteristic impedance Z of the coaxial feed line 1 connecting between the two
It changes depending on 0 '. Then, it can be seen that as Z0 'becomes lower, the value of SWR in the vicinity of the band decreases and a wide band matching state can be obtained. Since the values of Za to Zc at the center of the band are lower than the standard impedance for the reason described above, the characteristic impedance Z0 ′ of the coaxial feed line 1 connecting them is also lowered accordingly, so that both are appropriately balanced. Thus, a wide band matching characteristic can be obtained. Therefore, in order to obtain this effect, the characteristic impedance Z0 ′ of the coaxial feed line 1 from the feed point of the lower dipole antenna 5a (that is, the annular slit 3a) to the upper end 1J is set to 10Ω, and a wide band matching characteristic is realized. . In the collinear array antenna having the above configuration, the SWR in the required band could be set to 1.5 or less with a small and simple structure that does not use an impedance conversion circuit.

Next, the radiation characteristics of the collinear array antenna having the above configuration will be described with reference to FIG. FIG. 5 is a characteristic diagram showing a radiation pattern at 1907 MHz of the present collinear array antenna. 5, the longitudinal direction of the collinear array antenna is the z direction, the direction in which the parasitic conductor 6 is provided is the x direction, and the direction rotated 90 degrees counterclockwise in the horizontal plane from the x direction is the y direction (see FIG. 1). ). As can be seen from FIG. 5, the radiation pattern in the xy plane (horizontal plane) shows a large gain in the −x direction, that is, the direction opposite to the parasitic conductor 6. This is because the length of the parasitic conductor 6 is set to be longer than 1/2 wavelength.
It shows that the parasitic conductor 6 operates as a reflector. Further, in the radiation patterns in the yz plane and the zx plane (vertical plane), the maximum gain direction indicates the horizontal direction (y-axis or x-axis direction). This is because the feeding point intervals of the dipole antenna elements 5a to 5c are set equal to the wavelength. With the above configuration, it was possible to obtain a high radiation characteristic with a maximum gain of 10 dBi or more with a 3-element collinear array antenna. In this way, an antenna that shows a high gain in a specific direction in the horizontal plane is called a sector antenna, and is useful when limiting the communication area of the base station to a certain direction or when performing angle diversity with a plurality of antennas. It becomes a good antenna.

In the present embodiment, the characteristic impedance of the coaxial feed line 1 is set to the lower annular slit 3a.
, But this is because the radiation impedances Za to Zc of the dipole antenna elements 5a to 5c are set to be substantially constant, and the radiation impedances Za to Z are changed.
When c is different, the characteristic impedance may be further changed with another annular slit as a boundary.

The numerical values and configurations described in the above embodiments are examples, and the present invention is not limited to the details of these numerical values and configurations.

[0016]

As described above, the collinear array antenna of the present invention includes a coaxial feed line having an input terminal connected to one end, and a plurality of annular slits periodically provided on the outer conductor of the coaxial feed line. and a plurality of antenna elements configured by arranging symmetrically sleeve conductor of the pair of quarter-wave on both sides of each of the plurality of annular slits, the outer at least one of the plurality of annular slits as a border Inner diameter of conductor
The characteristic impedance of the coaxial feed line is
Impedance while changing the impedance of the coaxial feed line.
Characteristic in from the end to the annular slit closest to the end
Using the impedance as the standard impedance,
To the other end of the coaxial feed line
It is characterized in that the voltage is lower than the standard impedance .

In the above structure, the characteristic impedance of the coaxial feed line is set to an optimum value in accordance with the radiation impedance of each antenna element with the annular slit, which is the feed point of each of the plurality of antenna elements, as the boundary. Broadband matching characteristics can be obtained without using an impedance conversion circuit, and a collinear array antenna having a small size and a simple structure can be realized.

[Brief description of drawings]

FIG. 1 is a perspective view of a collinear array antenna according to an embodiment of the present invention.

FIG. 2 is a sectional view of the collinear array antenna.

FIG. 3 is a circuit diagram showing an input equivalent circuit of the collinear array antenna.

FIG. 4 is a characteristic diagram showing a standing wave ratio in each frequency band of the collinear array antenna.

FIG. 5 is a characteristic diagram showing a radiation pattern of the collinear array antenna.

FIG. 6 is a sectional view showing a schematic configuration of a conventional collinear array antenna.

[Explanation of symbols]

1 coaxial feed line 1a Outer conductor 1b Inner conductor 1c Dielectric 1I Lower end of coaxial feed line Top of 1J coaxial feed line 2 input terminals 3a, 3b annular slit 4 Sleeve conductor 5a, 5b, 5c Dipole antenna element 6 parasitic conductor 7 Spacer

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-7-202563 (JP, A) JP-A-62-26905 (JP, A) Jikken-hei 6-41377 (JP, Y2) (58) Field (Int.Cl. ⁷ , DB name) H01Q 9/20 H01Q 9/26 H01Q 11/16 H01Q 21/10

Claims (2)

(57) [Claims] 1. A coaxial feed line having an input terminal connected to one end, a plurality of annular slits periodically provided in an outer conductor of the coaxial feed line, and a pair of 1s at both ends of each of the plurality of annular slits. / 4 wavelength sleeve conductors are symmetrically arranged to form a plurality of antenna elements, and the inner diameter of the outer conductor is defined by at least one of the plurality of annular slits.
The characteristic impedance of the coaxial feed line can be changed by making it different.
While changing the dance, one end of the coaxial feed line
To the circular slit closest to the one end.
Impedance as standard impedance, and the ring slit
To the other end of the coaxial feed line
Is lower than the standard impedance described above . 2. The collinear array antenna according to claim 1 , wherein the characteristic impedance from the annular slit closest to one end of the coaxial feed line to the other end of the coaxial feed line is constant.