JPH11274849A - Vertical multistage antenna - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a vertical multistage antenna which has many antenna elements and is not affected by a reflection from a case or the like. SOLUTION: A conductive arm 10 is vertically erected inside a pole-shaped radome 2 having the hollow inside, and plural antenna elements 12 are provided along with the lengthwise direction of the arm 10. The respective antenna 12 are respectively composed of ground elements 12g and power feeding elements 12h. The ground element 12g is a conical element directly connecting its central part to the arm 10. The power feeding element 12h is a conical element connecting its central part through an insulator 14 to the arm 10. Inside the arm 10, plural feeder lines 18 and 19 are arranged and these feeder lines 18 and 19 are respectively connected to the power feeding points of the power feeding elements 12h. Phase delay elements 24 are respectively arranged between the inner surface of the radome 2 and the respective antenna elements 12. The phase delay element 24 makes the phase of a radio wave radiated from each antenna element common to the phase of a reflected wave of this radio wave on the radome 2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vertical multi-stage antenna for a fixed base station for mobile communication such as a personal handy phone system or a cellular phone.

[0002]

2. Description of the Related Art As an antenna of a fixed base station in a mobile communication system, a vertical diversity antenna is often used in order to prevent a change in reception level due to fading. The vertical diversity antenna has a plurality of antennas arranged in a vertical direction at a certain interval. When each antenna is housed in one case, it looks like a single antenna, so the vertical diversity antenna is advantageous in view.

[0003] As the vertical diversity antenna, for example, there is the following. Two upper and lower antennas are arranged at predetermined intervals along the vertical direction. The upper and lower antennas are each a collinear antenna. The upper antenna and the lower antenna are fed by an upper antenna coaxial cable and a lower antenna coaxial cable, respectively. The coaxial cable for the upper antenna passes through the lower antenna.

[0004]

In the above-mentioned vertical diversity antenna, it is sometimes desirable to arrange three or more stages of collinear antennas in order to improve the gain. However, the collinear antenna has a complicated structure, and it is difficult to adopt a configuration in which three or more collinear antennas are arranged.

As a method of feeding power to the upper and lower collinear antennas, serial feeding may be considered. However, when the upper and lower collinear antennas are accommodated in the above-described case, the reflection at the case is large, the current distribution is disturbed, and the directivity may be significantly deteriorated.

An object of the present invention is to provide a vertical multi-stage antenna capable of having a large number of antenna elements. Another object of the present invention is to provide a vertical multi-stage antenna which is not affected by reflection from a case or the like.

[0007]

According to the present invention, there is provided a column-shaped radome having a hollow interior,
It has a conductive arm which stands upright in the radome, and a plurality of antenna elements provided along the length direction of the arm. Each antenna element includes a ground element and a feed element. The grounding element is a conical element whose center is directly connected to the conductive arm and whose diameter increases from the center toward the tip. The feed element is a conical element whose central part is coupled to the conductive arm via an insulator, and whose diameter increases from the central part toward the distal end. The center part or the tip part of the grounding element and the feeding element are adjacent to each other. A plurality of feed lines are arranged in the conductive arm, and these feed lines are respectively connected to feed points of the respective feed elements. A phase delay element is arranged between the inner surface of the radome and each of the antenna elements.
This phase delay element makes the phase of the radio wave radiated from each of the antenna elements and the phase of the radio wave reflected by the radome the same.

According to the present invention, radio waves are radiated from a plurality of antenna elements each including a ground element and a feed element. Since the conical element is used for the grounding element and the feeding element, its manufacture is easy and a wideband antenna is obtained. Since each feed line passes through the inside of the conductive arm, the conductive arm functions as a shield, and unnecessary radio waves are not emitted from each feed line to each antenna element.

As the phase delay element, a conductor surrounding the periphery of each antenna element can be used. The conductor has about λ / 4 along the length of the conductive arm.
To λ / 2 (λ is the center reception wavelength of each of the antenna elements), and may be arranged at a distance of about λ / 40 to λ / 8 from each of the antenna elements.

Since the phase delay element is provided, the reflected wave from the radome and the radio wave radiated from each antenna element have the same phase, and the impedance of each antenna element does not become abnormally large.

[0011] An even number of the plurality of antenna elements can be provided. An even number of the feed elements of the antenna elements are connected by the feed line shorter than the central reception wavelength of each antenna element by two.

Therefore, it is possible to realize an antenna having a directional characteristic directed downward from the horizontal plane, that is, a beam tilt characteristic directed downward.

[0013]

1 and 2 show a vertical diversity antenna according to an embodiment of the present invention. This vertical diversity antenna is used, for example, for a fixed base station in mobile communication, and has a center reception wavelength λ of, for example, 157 mm (1907 MHz).

This vertical diversity antenna is shown in FIG.
As shown in the figure, the outer case 2 is made of an insulator such as a radome, for example, FRP. The outer case 2 has a hollow inside, for example, in a cylindrical shape, and has a large thickness in order to increase strength. This outer case 2
It is arranged so that its length direction is vertical, and a waterproof cap 4 is provided at the upper end thereof. As the outer case 2, for example, one having an outer diameter of 90 mm is used.

A base 6 is arranged below the outer case 2. A fixing plate 8 provided on the upper part of the outer case 2 from the center of the upper surface of the base 6, that is, from the center of the outer case 2.
Up to a straight line, that is, along the length direction of the outer case 2,
A conductive arm 10, such as a metal pipe, is arranged. The conductive arm 10 has, for example, a diameter of 10
mm (λ / 16).

A plurality, for example, an even number, more specifically, eight antenna elements 12 are attached to the conductive arm 10 along its length. As shown in FIG. 1 in an enlarged manner, each antenna element 12 is
g and a feed element 12h. The ground element 12g and the feed element 12h are both conical elements formed of a conductive material in a conical shape. The grounding element 12g has a central portion (minimum diameter portion) directly attached to the conductive arm 10 with its maximum opening (tip) facing upward. The feeding element 12h has a central portion (minimum diameter portion) attached to the conductive arm 10 via an insulating ring 14 with its maximum opening (tip) facing downward.

The diameter D of the maximum opening of the ground element 12g and the feed element 12h is selected to be, for example, about 11λ / 48 to λ / 4, that is, about λ / 4. The length of the grounding element 12g and the feeding element 12h (the dimension in the length direction of the conductive arm 10)
h is chosen to be approximately λ / 4. Each antenna element 12
In, the central parts of the ground element 12g and the feed element 12h are arranged close to each other. Therefore, as shown in FIG. 1, the distance between the ground element 12g and the maximum opening of the feed element 12h is about λ / 2. Therefore, when power is supplied to the center of the feed element 12h of each antenna element 12, each antenna element 12 functions as a dipole antenna. Note that the maximum openings of the ground element 12g and the feed element 12h may be arranged close to each other.

Although it is conceivable to use cylindrical elements in place of the grounding element 12g and the feed element 12h, a conical element can be easily manufactured by using a diaphragm type or the like, and a wide band can be used. Because it is easy to
A conical element is used as the ground element 12g and the feed element 12h.

As for each antenna element 12, one set is constituted by two adjacent antenna elements 12. Thus, there are a total of four sets in this vertical diversity antenna. The feeding point of the same set of feeding elements 12h, that is, the center portion is connected by a feeding line, for example, a center conductor 18i of the coaxial cable 18. Although not shown, the outer conductor of the coaxial cable 18 is connected to the conductive arm 10. This coaxial cable 18
It is inserted into the conductive arm 10.

The center of the feed element 12h of the lower antenna element 12 of the same set is connected to a feed line inserted into the conductive arm 10, for example, a center conductor 19i of a coaxial cable 19.
It is connected to the. Center conductor 1 of this coaxial cable 19
9i is connected to one center contact of each output terminal 22 provided on the base 6 as shown in FIG. The outer conductor of the coaxial cable 19 is also connected to the output terminal 2.
Two external contacts are also connected to the conductive arm 10. That is, the feed elements 12 h of the same set are electrically fed in parallel by the coaxial cables 18 and 19. Reference numeral 21 denotes a coaxial cable for feeding power to a lower feed element 12h of the set of antenna elements 12 further above the set of antenna elements 12.

The coaxial cable 18 is provided in FIG.
As shown in (1), it is for receiving a radio wave arriving from a direction perpendicular to the conductive arm 10, that is, inclined downward by an angle θ (beam tilt angle) with respect to a horizontal plane. That is, this is because the vertical diversity antenna has a beam tilt characteristic. When it is not desired to receive a radio wave from a far distance, or when it is not desired to transmit a radio wave too far, the vertical tilt antenna may have this beam tilt characteristic.

The distance between the upper feed element 12h and the lower feed element 12h of the same set is d, and the coaxial cable 1
Assuming that the shortening rate η is 8 and the length is L, the phase difference Δφ between the same set of feed elements 12h is expressed by Equation 1.

[0023]

## EQU1 ## Δφ = (2π dsin θ / λ) = 2π− (2π
L / λη)

Accordingly, sin θ is represented by the following equation (2).

[0025]

## EQU2 ## sin θ = (λ / d) [1- (L / λη)]

Thus, by choosing L / λη to be less than 1, ie, choosing L to be less than λη,
The combined directional characteristics of one set of antenna elements 12 can have downward beam tilt characteristics.

The actual impedance of the upper antenna element 12 of the same set is selected to be 2Z0 (Z0 is the design impedance of each antenna 12). The impedance of the coaxial cable 18 connecting the feeding points of the upper and lower antenna elements 12 is selected to be 2Z0. Therefore, the impedance when the upper antenna element 12 is viewed from the feeding point of the lower antenna element 12 is Z0, and matching can be achieved. The coaxial cable 19
Is selected as Z0.

A conductive sleeve 16 is formed at the center of each feed element 12h. These conductive sleeves 1
Numeral 6 has a length of about λ / 4 along the conductive arm 10 and extends from the center of the feed element 12h to the maximum opening. Feeding elements 12h in these conductive sleeves 16
Is connected to the center of the feed element 12h, and the end on the maximum opening side is connected to the conductive arm 10. That is, the conductive sleeve 16 is short-circuited on one side.

The reason why the conductive sleeve 16 is provided is as follows. If the conductive sleeve 16 is not provided, since the feed element 12 and the conductive arm 10 are close to each other, the radiation impedance is reduced, radio waves are radiated between the feed element 12 and the conductive arm 10, and Does not work. Also, a large amount of unnecessary current flows through the conductive arm 10,
The radiation pattern is poor and the gain is greatly reduced.

When the conductive sleeves 16 are provided, they operate as super tops, and the impedance between the feeding element 12h and the conductive arm 10 can be increased, and both can be insulated. Thereby, the feed element 12
h emits radio waves between the same set of grounding elements 12g and operates normally. Further, since the length from the maximum opening of the feed element 12h to the connection to the conductive sleeve 16 is approximately λ / 4, unnecessary current does not flow on the surface of the conductive sleeve 16.

A phase delay element, for example, a resonance ring 24 is provided around each antenna element 12. These resonance rings 24 are provided between the inner surface of the outer case 2 and the respective antenna elements 12.
6 attached. The inner case 26 is made of an insulator, for example, FRP, is formed thinner than the outer case 2, and is disposed along the length direction of the conductive arm 2.

On the inner peripheral surface of the inner case 26, an insulating film 28 is provided. A conductor formed on the insulating film 28, for example, a metal foil such as a copper foil or an aluminum foil is the resonance ring 24. These resonance rings 24
Is formed by etching a copper foil or an aluminum foil formed on one surface of the insulating film 28, and the etched insulating film 28 is wound into a cylindrical shape.
It is attached to the inner surface of the inner case 24. Note that an adhesive tape of copper foil or aluminum foil may be attached to the outer peripheral surface of the inner case 26.

The resonance rings 24 extend from the vicinity of the center of the grounding element 12g and the feeding element 12h of each set of antenna elements 12 by substantially the same length along the length direction of the conductive arm 10. The length W is about λ / 2 to λ /
4. Further, these resonance rings 24 are arranged between the maximum openings of the grounding elements 12g and 12h from about λ / 40 to λ / 8.
Are placed at a distance of

If the resonance ring 24 is not provided, the radio wave radiated from each antenna element 12 is reflected by the outer case 26 and returns to the antenna element 12. As a result, the impedance of the antenna element 12 increases. In particular, when the distance between the maximum opening of each antenna element 12 and the inner surface of the outer case 26 is about λ / 4, the radio waves and reflected waves radiated from each antenna element 12 have opposite phases,
The impedance becomes very high.

When the resonance ring 24 is provided, the phase of the radio wave radiated from each antenna element 12 is
About 90 degrees. Then, the phase is further delayed by 180 degrees by being reflected by the outer case, for a total of 270
Phase lags. Since the radio wave delayed by 270 degrees is further delayed by 90 degrees by the resonance ring 24, in each antenna element 12, the reflected wave and the radiated radio wave have the same phase, and
The impedance decreases.

The length W of the resonance ring 24 and the length of the resonance ring 2
By adjusting the distance from the antenna element 4 to the antenna element 12, the real part of the impedance of each antenna element 12 can be adjusted. By adjusting the length of the sleeve 16, the imaginary part of the impedance can be adjusted.

FIG. 3 shows the frequency characteristics of the gain in the combined maximum radiation direction of one set of antenna elements 12 of the vertical diversity antenna. In these antenna elements 12, 18
3.5 d from 95 MHz to 1920 MHz
Gains of B to 4 dB are obtained. FIG. 4 shows this 1
4 shows the frequency characteristics of the combined standing wave ratio of a set of antenna elements 12. From FIG. 4, the combined standing wave ratio of the antenna element 12 is 1.4 to 1.2, which is a sufficiently practical value.
FIG. 5 shows the combined vertical plane directivity of one set of antenna elements 12 at 1907.5 MHz. From FIG. 5, it can be seen that one set of antenna elements 12 satisfactorily receives radio waves arriving from a direction directed downward by approximately θ with respect to the horizontal plane.
FIG. 6 shows 1907.5 MHz of one set of antenna elements 12.
2 shows the combined horizontal plane directivity at. From FIG. 6, it can be seen that one set of antenna elements 12 is non-directional in a horizontal plane.

In the above embodiment, the feed elements 12h of one set of antenna elements 12 are connected to each other by the coaxial cable 18 which is slightly shorter than λ in order to provide the vertical diversity antenna with tilt characteristics. In the case where characteristics are not provided, the feed element 12 of each antenna element 12 is used.
A power supply coaxial cable may be connected to h. In this case, each coaxial cable is inserted into the conductive arm 10.

In the above embodiment, the present invention is applied to a vertical diversity antenna. However, the present invention can be applied to other vertical antennas. For example, the received signals at each antenna element 12 may be combined by a combiner.

[0040]

As described above, according to the present invention, since each power supply line is inserted into the conductive arm, the characteristics of each antenna element provided along the conductive arm are different from the characteristics of the power supply line. The more leaked current has no effect. Further, since each antenna element has a conical shape, it is easy to manufacture, and the band can be widened. Since the delay element is provided, it is possible to prevent the radiation impedance of each antenna element from increasing due to the reflected wave from the radome. Further, by connecting the feed elements of the two antenna elements with a feed line that is somewhat shorter than the reception wavelength, tilt characteristics can be provided.

[Brief description of the drawings]

FIG. 1 is an enlarged vertical sectional view of a vertical diversity antenna according to a first embodiment of the present invention.

FIG. 2 is a longitudinal sectional view of the vertical diversity antenna of FIG.

FIG. 3 is a gain-frequency characteristic diagram of the antenna of FIG. 1;

FIG. 4 is a diagram illustrating a standing wave ratio vs. frequency characteristic of the antenna of FIG. 1;

FIG. 5 is a directional pattern diagram of a vertical plane of the antenna of FIG. 1;

6 is a directional characteristic diagram of a horizontal plane of the antenna of FIG. 1;

[Explanation of symbols]

 2 Outer Case (Radome) 10 Conductive Arm 12 Antenna Element 12h Feed Element 12g Ground Element 14 Insulator 16 Conductive Sleeve 18 19 Coaxial Cable (Feed Line) 24 Resonant Ring (Conductor)

Claims (4)

[Claims] 1. A column-shaped radome having a hollow interior, a conductive arm vertically set in the radome, and a plurality of the arms provided along a length direction of the arm.
Each of the grounding element and the feeding element is a conical element whose center is directly connected to the conductive arm and whose diameter increases from the center toward the tip end. Is a conical element whose central part is connected to the conductive arm via an insulator, and whose diameter increases from the central part toward the distal end. A plurality of antenna elements adjacent to each other, a plurality of feed lines arranged in the conductive arm and connected to feed points of the respective feed elements, and an inner surface of the radome and the respective antenna elements. A vertical multi-stage antenna, comprising: a radio wave radiated from each of the antenna elements; and a phase delay element that makes the phase of the radio wave reflected by the radome in-phase. 2. The vertical multi-stage antenna according to claim 1, wherein said phase delay element is a conductor surrounding each of said antenna elements. 3. The vertical multi-stage antenna according to claim 2, wherein the conductor has a length of about λ / 4 to λ / 2 (where λ is the center reception of each antenna element) along a length direction of the conductive arm. Wavelength), and is approximately λ
A vertical multi-stage antenna arranged at a distance of / 40 to λ / 8. 4. The vertical multi-stage antenna according to claim 1, wherein an even number of the plurality of antenna elements are provided, and two of the feed elements of the antenna elements are shorter than a center reception wavelength of each of the antenna elements. A vertical multi-stage antenna connected by the feeder.