JPH02174302A - Tilt antenna - Google Patents

Abstract

PURPOSE:To apply the antenna to an antenna for mobile communication base station provided with a radiation characteristic over a wide angular range without deteriorating the low side lobe characteristic by grouping radiation elements of a tilt antenna and giving a phase change for each group. CONSTITUTION:Radiation elements 41-44 for a conventional tilt antenna are grouped, the feeding amplitude and phase are adjusted for each group to realize the low side lobe characteristic of the tilt antenna. In this case, in order to satisfy the low side lobe characteristic, the relation among number M of radiation elements in one group, a beam tilt angle thetaT, radiation element interval (s) and a wavelength lambda is selected so as to be thetaT<=sin<-1>(lambda/Ms) is satisfied thereby satisfying the low side lobe characteristic requested for the antenna for mobile communication base station. Thus, number of cables to be replaced for the tilt antenna is decreased, the antenna feeding section is simplified and the simple handling is attained.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention is an array antenna suitable as an antenna for a base station for mobile communication, in which a plurality of radiating elements are arranged at regular intervals in a vertical plane, and each The present invention relates to a tilt antenna that controls the main beam direction of the antenna within a specific angular range below the horizontal plane by adjusting the excitation amplitude and phase of a radiating element. In particular, the present invention relates to a tilt antenna with low sidelobe characteristics in which a plurality of radiating elements are grouped and the feeding phase to the radiating elements is controlled for each group to reduce interference with other base station service zones.

[Conventional technology]

FIG. 6 is an explanatory diagram of the beam tilt of a base station antenna for mobile communication used in a conventional mobile radio, particularly a car telephone, and shows the state in which the base station antenna is used.

In FIG. 6, reference numeral 1 indicates a service zone that one base station 3 has. Reference numeral 2 indicates a service zone of a base station 3 located at a remote location. Reference numeral 4 denotes a base station antenna, which is installed vertically on the base station roof or on a steel tower. The broken line 5 indicates the horizontal direction and is used as the base line of the angle θ indicating the radiation characteristics of the antenna. A broken line 6 indicates an angle from which the outer edge of the service zone 1 or 2 is viewed from the base station antenna 4, and corresponds to the beam tilt angle θ required by the base station antenna 4. A beam 8 indicates the main beam of this base station antenna 4. Also the 6th
The direction indicated by a dashed line 7 in the figure indicates the direction of interference waves to service zones using the same frequency, and the angle from the horizontal direction is given by θ1.

The function required of a base station antenna for mobile communication is to achieve a required electric field level within the service zone of its own base station while preventing radio wave interference from occurring in the service zones of other base stations.

In order to meet this requirement, the directivity characteristics of the mobile communication base station antenna are such that the main beam is tilted below the horizontal plane as shown in FIG. 6, so that the radiated radio waves are effectively confined within the service zone of the base station. This is called beam tilt. Also, the 6th
By lowering the level of the side lobe in the angle range indicated by θ1 in the figure to a sufficiently low level, radio wave interference with other stations' service zones is reduced.

In order to achieve such directivity characteristics, an array antenna with a beam tilt characteristic as shown in FIG. 7 has conventionally been used as a mobile communication base station antenna.

This antenna 4 includes a plurality of radiating elements 9 arranged at regular intervals in a vertical plane, a plurality of phase shifters 10 that determine the feeding phase of each of the radiating elements, and a power that determines the feeding amplitude of each of the radiating elements. It is equipped with a distribution circuit 11, and is denoted by 1.
2 indicates the feeding point of this antenna.

Further, in FIG. 7, the solid line 13 indicates the main beam direction of the radiated wave from each radiating element, and the surface indicated by the dashed-dotted line 14 indicates the wavefront of the radiated wave.

The operation of this conventional array antenna will be explained.

First, in order to direct the main beam of the antenna 4 below the horizontal plane at a beam tilt angle θ, the phase shifter 10 is adjusted respectively, and the wavefront of the radiated wave is set at a beam tilt angle θ with respect to the vertical line.
Tilt only to set.

Furthermore, low sidelobe characteristics are achieved by adjusting the phase shifter 10 and the power distribution circuit 11.

For example, if there are 20 radiating elements 9, the interval between each radiating element is 0.
．． In a vertical ray antenna arranged at 8 wavelength intervals, the radiation characteristics shown in FIG. 9 can be realized by superimposing the feeding amplitude and phase shown in FIG. 8 on the beam tilt angle θ and the phase amount in the direction. In addition, the maximum radiation gain in Fig. 9 is 14
．． It is 5dB. Here, the radiation angle θ in FIG. 9 indicates the amount of change from the beam tilt angle θ7 direction. In FIG. 9, the plus sign direction of the radiation angle θ corresponds to the service zone of the own base station, and the minus sign direction corresponds to the interference zone direction. By adjusting the feeding amplitude and phase as described above, the side lobe level in the interference zone direction can be reduced to about -30 dB, as shown in FIG. 9, and service zones using the same frequency can be brought closer together.

[Problem that the invention seeks to solve]

In this conventional tilt antenna, the method of changing the beam tilt angle θ is to prepare a cable of the necessary length according to each phase amount and replace it in order to simplify the feeding phase adjustment. It is being carried out in

However, in order to change the beam tilt angle according to various changes in the height of the base station, it is necessary to replace all the cables of the phase shifter 10, and as the number of radiating elements 9 increases, this task becomes more difficult. Not only is this extremely complicated, but it also has the disadvantage of increasing the price of the antenna.

In view of the above-mentioned drawbacks, it is an object of the present invention to provide a tilt antenna that can reduce the number of replacement cables of the tilt antenna, simplify the power feeding part of the antenna, reduce the antenna cost, and simplify handling. purpose.

[Means for solving problems]

The present invention has an array structure in which a plurality of radiating elements are arranged in a straight line in a vertical plane at regular intervals, and the amplitude and phase of each radiating element are adjusted so that the radiation side lobe level of this array structure is sufficiently low. In the tilt antenna, the main beam direction of the radiation characteristic of the array antenna is variably controlled over a specific angular range below the horizontal plane. is provided with a phase control means for changing the phase of each of the radiation elements, and a given wavelength is λ, a specific angular range below the horizontal plane of the main beam is θT1T1, and an interval between the anti-radiation elements is S, forming one group. The number of radiating elements is M
It is characterized in that the number of radiating elements in a group is selected so that θT≦sin 1 (λ/M s ).

The radiating element constituting the tilt antenna of the present invention, the means for adjusting the amplitude and phase of this radiating element, and the means for controlling the phase in groups are all bidirectional, and
The tilt antenna of the present invention can be used for both transmission and reception.

[Effect]

The present invention realizes low sidelobe characteristics of the tilt antenna by grouping each radiating element of a conventional tilt antenna and adjusting the feeding amplitude and phase for each group.

At this time, in order to satisfy the low sidelobe characteristic, the relationship between the number M of radiating elements in one group and beam tilt angle θT1 radiating element spacing S1 wavelength λ is set as θT≦5in-1 (λ/
M s ) is selected to satisfy the low sidelobe characteristics required of a base station antenna for mobile communication.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a diagram showing the configuration of a tilt antenna according to an embodiment of the present invention.

The tilt antenna of this embodiment includes a plurality of radiating elements 9, a phase shifter 10 that determines the feeding phase of each radiating element 9, and a power distribution circuit 11 that determines the feeding amplitude of each radiating element 9. Radiating element 9, each phase shifter 10, power distribution circuit 11
Some of them are grouped together, and the grouped antennas 4. It is equipped with phase shifters 15.about.154 for collectively adjusting the positions of the respective radiating elements of .about.4.degree., and power is supplied to these phase shifters 1s, .about.154 from a feeding point 12.

In the tilt antenna shown in FIG. 1, the main beam direction can be adjusted to the angle θ' by a phase shifter 15 that adjusts the phase of the radiating elements 9 for each group. Broken line 17
The surface shown in shows the wavefront according to the angle θ′a, and the solid line 16
The surface shown by represents the actually realized wavefront. In this way, in the method of feeding power by grouping each radiating element 9,
As shown in FIG. 1, there is a phase error of 2δ between the main beam angle θ'7 and the actual radiation wavefront.

It is thought that the presence of this phase error 2δ degrades the low sidelobe characteristics, but in the present invention, this deterioration characteristic is quantified, and the beam tilt angle θa, the number of radiating elements in one group M, and the number of radiating elements By setting the distance S and the wavelength λ in a constant relationship, deterioration of the low sidelobe characteristics is prevented.

First, FIGS. 2(a) to 2(d) show calculation results of sidelobe deterioration in antenna characteristics when radiating elements are grouped.

In calculating this antenna characteristic, it is assumed that the variable range of the beam tilt angle θa is 5° to 12°, and the beam tilt angle 9
It is assumed that the phase of each radiating element 9 is adjusted so that the phases of all the radiating elements 9 are aligned in the ° direction. That is, at beam tilt angles other than 9°, the first
There is a phase error of 2δ associated with the grouping shown in the figure.

FIG. 2 shows how the radiation characteristics change when the number M of radiating elements 9 included in each group is changed when the beam tilt angle θ'7 is 11°. The radiation characteristics of the antenna were calculated by setting the number of radiating elements 9 to 20 and setting the element spacing to 0.8 wavelength.

The number M of radiating elements in each group is a discrete number that is a divisor of 20, and the angular range that should be noted in the radiation characteristics of this antenna is the angular range from the main beam to near the horizontal plane 0°. This may increase the degree of sidelobe level deterioration.

In Fig. 2(a), when the radiating element is divided into two and the number of radiating elements in each group is set to 10, M is 5.
In this case, Fig. 2 (C) shows that when M is 4, the second
Figure (d) shows the case where M is set to 2.

What is remarkable about the side lobe characteristics of the antennas shown in FIGS. 2(a) to d) is that the lobes protrude at the positions indicated by the arrows in each figure, and the positions at which the lobes protrude are as follows: As the number M of radiating elements in a group increases, they approach the main beam.

In other words, as shown in Fig. 2(a), when M = 10, there is a protruding lobe at a position adjacent to the main beam, and the side lobe in the interference angle range with the service zone of other base stations. Significantly deteriorates lobe characteristics. However, when M=5 as shown in FIG. 2), the protruding lobe exists outside the interference angle range, and the problem regarding the zone configuration disappears. On the other hand, the side lobe level in the angular region between the main beam and the protruding lobe, although slightly degraded, maintains a level of about -25 dB, which is a sufficiently low level for practical use.

Next, from the results shown in FIGS. 2(a) to 2(d) above, we will determine the beam tilt angle in order to achieve a large tilt angle while maintaining low sidelobe characteristics when the radiating elements 9 are grouped. The relationship between θT and the number of elements M in the group is determined.

First, in order to examine the cause of the generation of the side lobes shown in FIG. 2, the coordinates for calculating the radiation characteristics of the array antenna are defined as shown in FIG. 3. The length of the antenna is L, the interval between each radiating element is S, and the total number of radiating elements is n. At this time,
Letting the radiation intensity of the antenna be weight (θ), it can be expressed by the following expression when the feeding amplitude and phase of all the radiating elements are the same over all the radiating elements.

Here, λ indicates the wavelength.

Regarding the period of change in the value of the numerator in equation (1), (n
It is given by an angular interval of θ that satisfies πS·sin θ)/λ=π, and represents a fine radiation characteristic change corresponding to each lobe in FIG. On the other hand, the period of the denominator in equation (1) is (π5−
Since the angular interval θ satisfies sin θ)/λ=π, θP= 5irr1(λ/s)
−(2). This is n times the numerator of formula (1). Now, as is often selected for array antennas, S=λ
Then, θ=90°. Further, when S=2λ, θ=30°, which shows a value close to the protruding lobe angle shown in FIG.

The radiation characteristics when the radiating elements 9 of the array antenna are divided into groups of M radiating elements and fed are calculated by the radiation characteristics of the M radiating elements antenna and (1 ) is expressed as the product of the directivity obtained by replacing S with Ms. In this case, the period of the component corresponding to equation (2) can be found by the following equation (3) by replacing S in equation (2) with Ms.

θ, = sin J λ/Ms) (3) In Figure 4,
M and θ, with S as a parameter.

The results of calculating the relationship between . The circles in FIG. 8 are the positions of the protruding lobes in FIGS. 2(a) to 2d). The characteristics of this expression (3) are that θ
P is determined simply by the number of grouped radiating elements, regardless of the total length of the antenna.

As a design method when the maximum value θa of the beam tilt angle is given, it is necessary to position the beam so that θ is 00 or more, and it is necessary to satisfy the following conditional expression.

θ, ≦ sin −5 (λ/Ms>
(4) Number M of radiating elements constituting a group
If the maximum value is adopted in equation (4), the number of variable parts for beam tilt can be minimized. For example, in Fig. 4, when θ = 14° and S = 0.8 λ, (4
), the maximum value of M is found to be M=5.

Furthermore, FIG. 5 shows how the sidelobe level below the horizontal plane and the antenna gain change when the beam tilt angle is varied. Even if the number of feeding divisions is reduced to 4 groups and the number of radiating elements in each group is 5, -1 in the beam tilt angle range of 5° to 12°.
It can be seen that side lobe characteristics of 2 dB or less can be obtained. Further, the variation width of the antenna gain is 1.5 dB or less, which is a value that does not cause any problem.

In the above embodiment, the words "radiating" or "feeding" are used for the operations of the radiating element 9, phase shifter 10, power distribution circuit 11, phase shifter 15, and feeding point 12, but all of these tilt antenna components Being a bidirectional element, the tilt antenna of the present invention can be used not only for transmission but also for transmission.
It is also used for reception.

〔Effect of the invention〕

As described above, the present invention divides the radiating elements of a tilt antenna into groups and gives a phase change to each group, thereby allowing radiation over a wide angular range without deteriorating the low sidelobe characteristics. A tilt antenna suitable for a mobile communication base station antenna with characteristics can be realized.

The structure of this tilt antenna reduces the need for replacement parts such as power supply cables to change the beam tilt angle, which simplifies the configuration and makes the antenna more economical.It also reduces the number of man-hours required for phase adjustment and handling. can be simplified.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the configuration of a tilt antenna according to an embodiment of the present invention. FIG. 2 shows changes in radiation characteristics when radiating elements are grouped. FIG. 3 is a diagram showing an antenna coordinate system for calculating radiation characteristics in this embodiment. FIG. 4 is a diagram showing the relationship between the number of grouped radiating elements and the position of the protruding lobe. FIG. 5 is a diagram showing changes in side lobes and antenna gain when the beam tilt angle is changed. FIG. 6 is an explanatory diagram of beam tilt in a mobile communication base station. FIG. 7 is a diagram showing the configuration of a conventional tilt antenna. FIG. 8 is an example of adjusting the feeding amplitude and phase of a conventional tilt antenna. FIG. 9 is a diagram showing the radiation characteristics of a conventional low sidelobe antenna. ■, 2...Service zone, 3...Wireless base station, 4
... Antenna, 5... Line indicating the horizontal direction, 6...
A line indicating the beam tilt angle, 7...A diagram indicating the direction of interference with service zones using the same frequency. 8...
・Main beam, 9... Radiation element, 10.15... Phase shifter, 11... Power distribution circuit, 12... Antenna feeding point, 13... Radiation wave from the antenna, 14.16・
...wavefront of radiation waves. Patent applicant: Nippon Telegraph and Telephone Corporation Representative: Patent attorney: Naotaka Ide'? F41 angle (deg) (O) 2-division 0-go (M:IO) - hire (deg) (b) 4-division ny%8 (M=5) angle (deg) (C) 5-division 0-4 go (M = 4) Angle (cleg) ((1) In the case of 10x split (M: 2) Shoulder view fan beam tilt angle (deg) Rotation 1st roof +: @a IIL6 + rotation ξM tail beam already tilted Meizu Shoulder 6 Old Shoulder Shoulder Diagram Test Shooting Butcher G (cleg) ?f19 Diagram

Claims (1)

[Claims] 1. An array structure in which a plurality of radiating elements are arranged in a straight line in a vertical plane at regular intervals, and the amplitude of each radiating element is adjusted such that the radiation side lobe level of this array structure is sufficiently low. and a means for adjusting the phase, and in a tilt antenna in which the main beam direction of the radiation characteristic of the array antenna is variably controlled over a specific angular range below the horizontal plane, each of the plurality of radiating elements is divided into a plurality of groups, A phase control means is provided for changing the phase of each of the radiating elements for each group, and the given wavelength is λ, the specific angular range under the horizontal plane of the main beam is θ_T, the interval between each radiating element is s, A tilt antenna characterized in that the number of radiating elements in a group is selected so that θ_T≦sin^−^1 (λ/Ms), where M is the number of radiating elements constituting one group.